Debugging with gdb
The gnu Source-Level Debugger
Tenth Edition, for gdb version 16.0.50.20241106-git(GDB)

Richard Stallman, Roland Pesch, Stan Shebs, et al.

(Send bugs and comments on gdb to https://www.gnu.org/software/gdb/bugs/.)
Debugging with gdb
TEXinfo 2017-08-23.19

Published by the Free Software Foundation
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
ISBN 978-0-9831592-3-0
Copyright c 1988-2024 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the termsof the GNU Free Documentation License, Version 1.3 or any later version published by
the Free Software Foundation; with the Invariant Sections being “Free Software” and “Free
Software Needs Free Documentation”, with the Front-Cover Texts being “A GNU Manual,”
and with the Back-Cover Texts as in (a) below.
(a) The FSF’s Back-Cover Text is: “You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting
software freedom.”

iTable of Contents
Summary of gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Free Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Free Software Needs Free Documentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Contributors to gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1

A Sample gdb Session. . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2

Getting In and Out of gdb . . . . . . . . . . . . . . . . . . . . 11
2.1

Invoking gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.1 Choosing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.2 Choosing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.3 What gdb Does During Startup . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.1.4 Initialization Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1.4.1 Home directory early initialization files . . . . . . . . . . . . . . . 18
2.1.4.2 System wide initialization files . . . . . . . . . . . . . . . . . . . . . . . 18
2.1.4.3 Home directory initialization file . . . . . . . . . . . . . . . . . . . . . 19
2.1.4.4 Local directory initialization file . . . . . . . . . . . . . . . . . . . . . . 19
2.2 Quitting gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 Shell Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4 Logging Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3

gdb Commands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1
3.2
3.3
3.4
3.5
3.6

4

Command Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Command Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Command Completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Filenames As Command Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Command options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Getting Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Running Programs Under gdb . . . . . . . . . . . . . . . . 33
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9

Compiling for Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Starting your Program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Your Program’s Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Your Program’s Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Your Program’s Working Directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Your Program’s Input and Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Debugging an Already-running Process . . . . . . . . . . . . . . . . . . . . . . . . 41
Killing the Child Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Debugging Multiple Inferiors Connections and Programs . . . . . . . 42
4.9.1 Inferior-Specific Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.10 Debugging Programs with Multiple Threads . . . . . . . . . . . . . . . . . . 47

ii

Debugging with gdb
4.11 Debugging Forks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.12 Setting a Bookmark to Return to Later . . . . . . . . . . . . . . . . . . . . . . . 54
4.12.1 A Non-obvious Benefit of Using Checkpoints . . . . . . . . . . . . . 56

5

Stopping and Continuing . . . . . . . . . . . . . . . . . . . . . . 57
5.1

Breakpoints, Watchpoints, and Catchpoints . . . . . . . . . . . . . . . . . . . . 57
5.1.1 Setting Breakpoints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.1.2 Setting Watchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.1.3 Setting Catchpoints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.1.4 Deleting Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.1.5 Disabling Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.1.6 Break Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.1.7 Breakpoint Command Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.1.8 Dynamic Printf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.1.9 How to save breakpoints to a file . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.1.10 Static Probe Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.1.11 “Cannot insert breakpoints” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.1.12 “Breakpoint address adjusted...” . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2 Continuing and Stepping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.3 Skipping Over Functions and Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.4 Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5.5 Stopping and Starting Multi-thread Programs. . . . . . . . . . . . . . . . . . 92
5.5.1 All-Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.5.2 Non-Stop Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
5.5.3 Background Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.5.4 Thread-Specific Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.5.5 Interrupted System Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
5.5.6 Observer Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

6

Running programs backward . . . . . . . . . . . . . . . . 101

7

Recording Inferior’s Execution
and Replaying It . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

8

Examining the Stack . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.1
8.2
8.3
8.4
8.5
8.6

Stack Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Backtraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Selecting a Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Information About a Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Applying a Command to Several Frames. . . . . . . . . . . . . . . . . . . . . . 120
Management of Frame Filters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

iii

9

Examining Source Files . . . . . . . . . . . . . . . . . . . . . . 125
9.1
9.2

Printing Source Lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Location Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
9.2.1 Linespec Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
9.2.2 Explicit Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
9.2.3 Address Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
9.3 Editing Source Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
9.3.1 Choosing your Editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
9.4 Searching Source Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
9.5 Specifying Source Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
9.6 Source and Machine Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
9.7 Disable Reading Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

10Examining Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

10.1 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
10.2 Ambiguous Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
10.3 Program Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
10.4 Artificial Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
10.5 Output Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
10.6 Examining Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
10.7 Memory Tagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
10.8 Automatic Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
10.9 Print Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
10.10 Pretty Printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
10.10.1 Pretty-Printer Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
10.10.2 Pretty-Printer Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
10.10.3 Pretty-Printer Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
10.11 Value History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
10.12 Convenience Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
10.13 Convenience Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
10.14 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
10.15 Floating Point Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
10.16 Vector Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
10.17 Operating System Auxiliary Information . . . . . . . . . . . . . . . . . . . 181
10.18 Memory Region Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
10.18.1 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
10.18.1.1 Memory Access Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
10.18.1.2 Memory Access Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
10.18.1.3 Data Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
10.18.2 Memory Access Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
10.19 Copy Between Memory and a File . . . . . . . . . . . . . . . . . . . . . . . . . . 185
10.20 How to Produce a Core File from Your Program . . . . . . . . . . . . 186
10.21 Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
10.22 Caching Data of Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
10.23 Search Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.24 Value Sizes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192

iv

Debugging with gdb

11

Debugging Optimized Code . . . . . . . . . . . . . . . . 195

11.1
11.2

Inline Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
Tail Call Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

12

C Preprocessor Macros . . . . . . . . . . . . . . . . . . . . . 199

13

Tracepoints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

13.1 Commands to Set Tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
13.1.1 Create and Delete Tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . 204
13.1.2 Enable and Disable Tracepoints. . . . . . . . . . . . . . . . . . . . . . . . . 206
13.1.3 Tracepoint Passcounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
13.1.4 Tracepoint Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
13.1.5 Trace State Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
13.1.6 Tracepoint Action Lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
13.1.7 Listing Tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
13.1.8 Listing Static Tracepoint Markers. . . . . . . . . . . . . . . . . . . . . . . 211
13.1.9 Starting and Stopping Trace Experiments . . . . . . . . . . . . . . . 212
13.1.10 Tracepoint Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
13.2 Using the Collected Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
13.2.1 tfind n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
13.2.2 tdump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
13.2.3 save tracepoints filename . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
13.3 Convenience Variables for Tracepoints . . . . . . . . . . . . . . . . . . . . . . . 218
13.4 Using Trace Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

14

Debugging Programs That Use Overlays . . 221

14.1
14.2
14.3
14.4

15

How Overlays Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Overlay Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
Automatic Overlay Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
Overlay Sample Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225

Using gdb with Different Languages . . . . . . . 227

15.1 Switching Between Source Languages . . . . . . . . . . . . . . . . . . . . . . . . 227
15.1.1 List of Filename Extensions and Languages . . . . . . . . . . . . . 227
15.1.2 Setting the Working Language . . . . . . . . . . . . . . . . . . . . . . . . . . 228
15.1.3 Having gdb Infer the Source Language . . . . . . . . . . . . . . . . . 228
15.2 Displaying the Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
15.3 Type and Range Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
15.3.1 An Overview of Type Checking . . . . . . . . . . . . . . . . . . . . . . . . . 229
15.3.2 An Overview of Range Checking . . . . . . . . . . . . . . . . . . . . . . . . 230
15.4 Supported Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
15.4.1 C and C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
15.4.1.1 C and C++ Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
15.4.1.2 C and C++ Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
15.4.1.3 C++ Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
15.4.1.4 C and C++ Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235

v
15.4.1.5 C and C++ Type and Range Checks. . . . . . . . . . . . . . . . 235
15.4.1.6 gdb and C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
15.4.1.7 gdb Features for C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
15.4.1.8 Decimal Floating Point format . . . . . . . . . . . . . . . . . . . . . 237
15.4.2 D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
15.4.3 Go . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
15.4.4 Objective-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
15.4.4.1 Method Names in Commands . . . . . . . . . . . . . . . . . . . . . . 238
15.4.4.2 The Print Command With Objective-C . . . . . . . . . . . . 239
15.4.5 OpenCL C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
15.4.5.1 OpenCL C Datatypes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
15.4.5.2 OpenCL C Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
15.4.5.3 OpenCL C Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
15.4.6 Fortran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
15.4.6.1 Fortran Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
15.4.6.2 Fortran Operators and Expressions . . . . . . . . . . . . . . . . 241
15.4.6.3 Fortran Intrinsics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
15.4.6.4 Special Fortran Commands . . . . . . . . . . . . . . . . . . . . . . . . 242
15.4.7 Pascal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
15.4.8 Rust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
15.4.9 Modula-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
15.4.9.1 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
15.4.9.2 Built-in Functions and Procedures . . . . . . . . . . . . . . . . . 245
15.4.9.3 Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
15.4.9.4 Modula-2 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
15.4.9.5 Modula-2 Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
15.4.9.6 Deviations from Standard Modula-2 . . . . . . . . . . . . . . . 249
15.4.9.7 Modula-2 Type and Range Checks . . . . . . . . . . . . . . . . . 249
15.4.9.8 The Scope Operators :: and . . . . . . . . . . . . . . . . . . . . . . 249
15.4.9.9 gdb and Modula-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
15.4.10 Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
15.4.10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
15.4.10.2 Omissions from Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
15.4.10.3 Additions to Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
15.4.10.4 Overloading support for Ada . . . . . . . . . . . . . . . . . . . . . 253
15.4.10.5 Stopping at the Very Beginning . . . . . . . . . . . . . . . . . . . 254
15.4.10.6 Ada Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
15.4.10.7 Extensions for Ada Tasks . . . . . . . . . . . . . . . . . . . . . . . . . 255
15.4.10.8 Tasking Support when Debugging Core Files . . . . . . 258
15.4.10.9 Tasking Support when using the Ravenscar Profile . . 259
15.4.10.10 Ada Source Character Set . . . . . . . . . . . . . . . . . . . . . . . 259
15.4.10.11 Known Peculiarities of Ada Mode . . . . . . . . . . . . . . . 260
15.5 Unsupported Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

16

Examining the Symbol Table . . . . . . . . . . . . . . . 263

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17

Altering Execution . . . . . . . . . . . . . . . . . . . . . . . . . . 277

17.1 Assignment to Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
17.2 Continuing at a Different Address . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
17.3 Giving your Program a Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
17.4 Returning from a Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
17.5 Calling Program Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
17.5.1 Calling functions with no debug info . . . . . . . . . . . . . . . . . . . . 284
17.6 Patching Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
17.7 Compiling and injecting code in gdb . . . . . . . . . . . . . . . . . . . . . . . . 285
17.7.1 Compilation options for the compile command . . . . . . . . . 287
17.7.2 Caveats when using the compile command . . . . . . . . . . . . . 287
17.7.3 Compiler search for the compile command . . . . . . . . . . . . . 289

18

gdb Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

18.1 Commands to Specify Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
18.2 File Caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
18.3 Debugging Information in Separate Files . . . . . . . . . . . . . . . . . . . . . 300
18.4 Debugging information in a special section . . . . . . . . . . . . . . . . . . . 304
18.5 Index Files Speed Up gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
18.5.1 Automatic symbol index cache . . . . . . . . . . . . . . . . . . . . . . . . . . 306
18.5.2 Building the index with GNU gold . . . . . . . . . . . . . . . . . . . . . 306
18.6 Extensions to ‘.debug_names’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
18.7 Errors Reading Symbol Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307
18.8 GDB Data Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

19Specifying a Debugging Target . . . . . . . . . . . . . 311

19.1
19.2
19.3

20

Active Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Commands for Managing Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Choosing Target Byte Order. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314

Debugging Remote Programs . . . . . . . . . . . . . . 315

20.1 Connecting to a Remote Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
20.1.1 Types of Remote Connections . . . . . . . . . . . . . . . . . . . . . . . . . . 315
20.1.2 Host and Target Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
20.1.3 Remote Connection Commands . . . . . . . . . . . . . . . . . . . . . . . . . 317
20.2 Sending files to a remote system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
20.3 Using the gdbserver Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
20.3.1 Running gdbserver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
20.3.1.1 Attaching to a Running Program . . . . . . . . . . . . . . . . . . 321
20.3.1.2 TCP port allocation lifecycle of gdbserver. . . . . . . . . 322
20.3.1.3 Other Command-Line Arguments for gdbserver . . . 322
20.3.2 Connecting to gdbserver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
20.3.3 Monitor Commands for gdbserver . . . . . . . . . . . . . . . . . . . . . 324
20.3.4 Tracepoints support in gdbserver . . . . . . . . . . . . . . . . . . . . . . 325
20.4 Remote Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
20.5 Implementing a Remote Stub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
20.5.1 What the Stub Can Do for You . . . . . . . . . . . . . . . . . . . . . . . . . 334

vii
20.5.220.5.321

What You Must Do for the Stub. . . . . . . . . . . . . . . . . . . . . . . . 334
Putting it All Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336

Configuration-Specific Information . . . . . . . . . 337

21.1 Native . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
21.1.1 BSD libkvm Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
21.1.2 Process Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
21.1.3 Features for Debugging djgpp Programs . . . . . . . . . . . . . . . . 339
21.1.4 Features for Debugging MS Windows PE Executables . . . 342
21.1.4.1 Support for DLLs without Debugging Symbols . . . . . 343
21.1.4.2 DLL Name Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
21.1.4.3 Working with Minimal Symbols . . . . . . . . . . . . . . . . . . . . 344
21.1.5 Commands Specific to gnu Hurd Systems . . . . . . . . . . . . . . 345
21.1.6 Darwin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
21.1.7 FreeBSD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
21.2 Embedded Operating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
21.3 Embedded Processors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
21.3.1 Synopsys ARC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
21.3.2 ARM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
21.3.3 BPF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
21.3.4 M68k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
21.3.5 MicroBlaze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
21.3.6 MIPS Embedded. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
21.3.7 OpenRISC 1000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
21.3.8 PowerPC Embedded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
21.3.9 Atmel AVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
21.3.10 CRIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
21.3.11 Renesas Super-H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
21.4 Architectures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
21.4.1 AArch64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
21.4.1.1 AArch64 SVE.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
21.4.1.2 AArch64 SME. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
21.4.1.3 AArch64 SME2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
21.4.1.4 AArch64 Pointer Authentication. . . . . . . . . . . . . . . . . . . 357
21.4.1.5 AArch64 Memory Tagging Extension. . . . . . . . . . . . . . . 358
21.4.2 x86 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
21.4.2.1 x87 registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
21.4.3 Alpha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
21.4.4 MIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
21.4.5 HPPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
21.4.6 PowerPC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
21.4.7 Nios II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
21.4.8 Sparc64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
21.4.8.1 ADI Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
21.4.9 S12Z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
21.4.10 AMD GPU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
21.4.10.1 AMD GPU Architectures . . . . . . . . . . . . . . . . . . . . . . . . . . 362
21.4.10.2 AMD GPU Device Driver and AMD ROCm Runtime . . 362

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21.4.10.3 AMD GPU Wavefronts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
21.4.10.4 AMD GPU Code Objects. . . . . . . . . . . . . . . . . . . . . . . . . . 363
21.4.10.5 AMD GPU Entity Target
Identifiers and Convenience Variables . . . . . . . . . . . . . . . . . . . . . . 363
21.4.10.6 AMD GPU Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
21.4.10.7 AMD GPU Memory Violation Reporting . . . . . . . . . . 364
21.4.10.8 AMD GPU Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
21.4.10.9 AMD GPU Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

22

Controlling gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

22.1 Prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
22.2 Command Editing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
22.3 Command History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
22.4 Screen Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
22.5 Output Styling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
22.6 Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
22.7 Configuring the Current ABI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
22.8 Automatically loading associated files . . . . . . . . . . . . . . . . . . . . . . . . 376
22.8.1 Automatically loading init file in the current directory . . 378
22.8.2 Automatically loading thread debugging library . . . . . . . . . 378
22.8.3 Security restriction for auto-loading . . . . . . . . . . . . . . . . . . . . . 379
22.8.4 Displaying files tried for auto-load . . . . . . . . . . . . . . . . . . . . . . 381
22.9 Optional Warnings and Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
22.10 Optional Messages about Internal Happenings . . . . . . . . . . . . . . 382
22.11 Other Miscellaneous Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388

23

Extending gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391

23.1 Canned Sequences of Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
23.1.1 User-defined Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
23.1.2 User-defined Command Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . 394
23.1.3 Command Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
23.1.4 Commands for Controlled Output . . . . . . . . . . . . . . . . . . . . . . 397
23.1.5 Controlling auto-loading native gdb scripts . . . . . . . . . . . . . 399
23.2 Command Aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
23.2.1 Default Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
23.3 Extending gdb using Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
23.3.1 Python Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
23.3.2 Python API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
23.3.2.1 Basic Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
23.3.2.2 Threading in GDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
23.3.2.3 Exception Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
23.3.2.4 Values From Inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
23.3.2.5 Types In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
23.3.2.6 Pretty Printing API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
23.3.2.7 Selecting Pretty-Printers . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
23.3.2.8 Writing a Pretty-Printer . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
23.3.2.9 Type Printing API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

ix
23.3.2.10 Filtering Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
23.3.2.11 Decorating Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
23.3.2.12 Writing a Frame Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.3.2.13 Unwinding Frames in Python . . . . . . . . . . . . . . . . . . . . . 439
23.3.2.14 Xmethods In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
23.3.2.15 Xmethod API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
23.3.2.16 Writing an Xmethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
23.3.2.17 Inferiors In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
23.3.2.18 Events In Python. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
23.3.2.19 Threads In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
23.3.2.20 Recordings In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
23.3.2.21 CLI Commands In Python. . . . . . . . . . . . . . . . . . . . . . . . 463
23.3.2.22 gdb/mi Commands In Python . . . . . . . . . . . . . . . . . . . . 467
23.3.2.23 gdb/mi Notifications In Python . . . . . . . . . . . . . . . . . . 469
23.3.2.24 Parameters In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
23.3.2.25 Writing new convenience functions . . . . . . . . . . . . . . . . 473
23.3.2.26 Program Spaces In Python . . . . . . . . . . . . . . . . . . . . . . . 474
23.3.2.27 Objfiles In Python. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
23.3.2.28 Accessing inferior stack frames from Python . . . . . . 479
23.3.2.29 Accessing blocks from Python . . . . . . . . . . . . . . . . . . . . 482
23.3.2.30 Python representation of Symbols . . . . . . . . . . . . . . . . 484
23.3.2.31 Symbol table representation in Python . . . . . . . . . . . . 489
23.3.2.32 Manipulating line tables using Python . . . . . . . . . . . . 490
23.3.2.33 Manipulating breakpoints using Python . . . . . . . . . . . 491
23.3.2.34 Finish Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496
23.3.2.35 Python representation of lazy strings . . . . . . . . . . . . . 497
23.3.2.36 Python representation of architectures . . . . . . . . . . . . 497
23.3.2.37 Registers In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498
23.3.2.38 Connections In Python . . . . . . . . . . . . . . . . . . . . . . . . . . . 499
23.3.2.39 Implementing new TUI windows . . . . . . . . . . . . . . . . . . 501
23.3.2.40 Instruction Disassembly In Python. . . . . . . . . . . . . . . . 502
23.3.2.41 Missing Debug Info In Python . . . . . . . . . . . . . . . . . . . . 511
23.3.3 Python Auto-loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
23.3.4 Python modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
23.3.4.1 gdb.printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
23.3.4.2 gdb.types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
23.3.4.3 gdb.prompt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516
23.3.4.4 gdb.ptwrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
23.4 Extending gdb using Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
23.4.1 Guile Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
23.4.2 Guile Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
23.4.3 Guile API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
23.4.3.1 Basic Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
23.4.3.2 Guile Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
23.4.3.3 GDB Scheme Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . 522
23.4.3.4 Guile Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . 524
23.4.3.5 Values From Inferior In Guile . . . . . . . . . . . . . . . . . . . . . . 525
23.4.3.6 Arithmetic In Guile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531

xDebugging with gdb
23.4.3.7 Types In Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
23.4.3.8 Guile Pretty Printing API . . . . . . . . . . . . . . . . . . . . . . . . . 537
23.4.3.9 Selecting Guile Pretty-Printers . . . . . . . . . . . . . . . . . . . . . 539
23.4.3.10 Writing a Guile Pretty-Printer . . . . . . . . . . . . . . . . . . . . 539
23.4.3.11 Commands In Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
23.4.3.12 Parameters In Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
23.4.3.13 Program Spaces In Guile . . . . . . . . . . . . . . . . . . . . . . . . . 548
23.4.3.14 Objfiles In Guile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
23.4.3.15 Accessing inferior stack frames from Guile. . . . . . . . . 549
23.4.3.16 Accessing blocks from Guile. . . . . . . . . . . . . . . . . . . . . . . 552
23.4.3.17 Guile representation of Symbols. . . . . . . . . . . . . . . . . . . 554
23.4.3.18 Symbol table representation in Guile. . . . . . . . . . . . . . 558
23.4.3.19 Manipulating breakpoints using Guile . . . . . . . . . . . . . 559
23.4.3.20 Guile representation of lazy strings. . . . . . . . . . . . . . . . 563
23.4.3.21 Guile representation of architectures . . . . . . . . . . . . . . 564
23.4.3.22 Disassembly In Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566
23.4.3.23 I/O Ports in Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566
23.4.3.24 Memory Ports in Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
23.4.3.25 Iterators In Guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
23.4.4 Guile Auto-loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
23.4.5 Guile Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
23.4.5.1 Guile Printing Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
23.4.5.2 Guile Types Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
23.5 Auto-loading extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
23.5.1 The objfile-gdb.ext file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
23.5.2 The .debug_gdb_scripts section . . . . . . . . . . . . . . . . . . . . . . 573
23.5.2.1 Script File Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 573
23.5.2.2 Script Text Entries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574
23.5.3 Which flavor to choose? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574
23.6 Multiple Extension Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575
23.6.1 Python comes first . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575

24

Command Interpreters . . . . . . . . . . . . . . . . . . . . . . 577

25

gdb Text User Interface . . . . . . . . . . . . . . . . . . . . . 579

25.1
25.2
25.3
25.4
25.5
25.6

26

TUI Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
TUI Key Bindings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
TUI Single Key Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
TUI Mouse Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
TUI-specific Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
TUI Configuration Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585

Using gdb under gnu Emacs. . . . . . . . . . . . . . . . 587

xi

27

The gdb/mi Interface . . . . . . . . . . . . . . . . . . . . . . . . 589

Function and Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589
Notation and Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589
27.3 gdb/mi General Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589
27.3.1 Context management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
27.3.1.1 Threads and Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 590
27.3.1.2 Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591
27.3.2 Asynchronous command execution and non-stop mode . . 591
27.3.3 Thread groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
27.4 gdb/mi Command Syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
27.4.1 gdb/mi Input Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
27.4.2 gdb/mi Output Syntax. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593
27.5 gdb/mi Compatibility with CLI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595
27.6 gdb/mi Development and Front Ends . . . . . . . . . . . . . . . . . . . . . . . 595
27.7 gdb/mi Output Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
27.7.1 gdb/mi Result Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
27.7.2 gdb/mi Stream Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
27.7.3 gdb/mi Async Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598
27.7.4 gdb/mi Breakpoint Information . . . . . . . . . . . . . . . . . . . . . . . . 602
27.7.5 gdb/mi Frame Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 604
27.7.6 gdb/mi Thread Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605
27.7.7 gdb/mi Ada Exception Information . . . . . . . . . . . . . . . . . . . . 605
27.8 Simple Examples of gdb/mi Interaction . . . . . . . . . . . . . . . . . . . . . 605
27.9 gdb/mi Command Description Format . . . . . . . . . . . . . . . . . . . . . . 606
27.10 gdb/mi Breakpoint Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607
27.11 gdb/mi Catchpoint Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617
27.11.1 Shared Library gdb/mi Catchpoints . . . . . . . . . . . . . . . . . . . 617
27.11.2 Ada Exception gdb/mi Catchpoints . . . . . . . . . . . . . . . . . . . 618
27.11.3 C++ Exception gdb/mi Catchpoints . . . . . . . . . . . . . . . . . . . 620
27.12 gdb/mi Program Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622
27.13 gdb/mi Thread Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624
27.14 gdb/mi Ada Tasking Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 626
27.15 gdb/mi Program Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
27.16 gdb/mi Stack Manipulation Commands . . . . . . . . . . . . . . . . . . . . 634
27.17 gdb/mi Variable Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 640
27.18 gdb/mi Data Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
27.19 gdb/mi Tracepoint Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660
27.20 gdb/mi Symbol Query Commands . . . . . . . . . . . . . . . . . . . . . . . . . 666
27.21 gdb/mi File Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 674
27.22 gdb/mi Target Manipulation Commands . . . . . . . . . . . . . . . . . . . 678
27.23 gdb/mi File Transfer Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 682
27.24 Ada Exceptions gdb/mi Commands . . . . . . . . . . . . . . . . . . . . . . . . 683
27.25 gdb/mi Support Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
27.26 Miscellaneous gdb/mi Commands . . . . . . . . . . . . . . . . . . . . . . . . . . 686

xii

Debugging with gdb

28

gdb Annotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695

28.1
28.2
28.3
28.4
28.5
28.6
28.7

What is an Annotation? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
The Server Prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
Annotation for gdb Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
Invalidation Notices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
Running the Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
Displaying Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 698

29

Debugger Adapter Protocol . . . . . . . . . . . . . . . . 699

30

JIT Compilation Interface . . . . . . . . . . . . . . . . . . 701

30.1 JIT Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 701
30.2 Registering Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
30.3 Unregistering Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
30.4 Custom Debug Info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
30.4.1 Using JIT Debug Info Readers . . . . . . . . . . . . . . . . . . . . . . . . . . 703
30.4.2 Writing JIT Debug Info Readers . . . . . . . . . . . . . . . . . . . . . . . . 703

31

In-Process Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705

31.1 In-Process Agent Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
31.1.1 IPA Protocol Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
31.1.2 IPA Protocol Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707

32

Reporting Bugs in gdb . . . . . . . . . . . . . . . . . . . . . . 709

32.1
32.2

33

Have You Found a Bug? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
How to Report Bugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709

Command Line Editing . . . . . . . . . . . . . . . . . . . . . 713

33.1 Introduction to Line Editing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
33.2 Readline Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
33.2.1 Readline Bare Essentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
33.2.2 Readline Movement Commands . . . . . . . . . . . . . . . . . . . . . . . . . 714
33.2.3 Readline Killing Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
33.2.4 Readline Arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
33.2.5 Searching for Commands in the History . . . . . . . . . . . . . . . . . 715
33.3 Readline Init File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
33.3.1 Readline Init File Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
33.3.2 Conditional Init Constructs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 724
33.3.3 Sample Init File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
33.4 Bindable Readline Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
33.4.1 Commands For Moving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
33.4.2 Commands For Manipulating The History . . . . . . . . . . . . . . 729
33.4.3 Commands For Changing Text . . . . . . . . . . . . . . . . . . . . . . . . . 730
33.4.4 Killing And Yanking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
33.4.5 Specifying Numeric Arguments . . . . . . . . . . . . . . . . . . . . . . . . . 733

xiii
33.4.6 Letting Readline Type For You . . . . . . . . . . . . . . . . . . . . . . . . . 733
33.4.7 Keyboard Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
33.4.8 Some Miscellaneous Commands . . . . . . . . . . . . . . . . . . . . . . . . . 734
33.5 Readline vi Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736

34

Using History Interactively . . . . . . . . . . . . . . . . . 737

34.1 History Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
34.1.1 Event Designators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
34.1.2 Word Designators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738
34.1.3 Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738

Appendix A

In Memoriam . . . . . . . . . . . . . . . . . . . . . 741

Appendix B

Formatting Documentation . . . . . . 743

Appendix C

Installing gdb . . . . . . . . . . . . . . . . . . . . . 745

C.1 Requirements for Building gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
C.2 Invoking the gdb configure Script . . . . . . . . . . . . . . . . . . . . . . . . . . 747
C.3 Compiling gdb in Another Directory . . . . . . . . . . . . . . . . . . . . . . . . . 748
C.4 Specifying Names for Hosts and Targets . . . . . . . . . . . . . . . . . . . . . . 749
C.5 configure Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749
C.6 System-wide configuration and settings . . . . . . . . . . . . . . . . . . . . . . . 753
C.6.1 Installed System-wide Configuration Scripts . . . . . . . . . . . . . 754

Appendix D Maintenance Commands . . . . . . . . . 755
Appendix E

gdb Remote Serial Protocol . . . . . 773

E.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773
E.2 Standard Replies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 774
E.3 Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775
E.4 Stop Reply Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
E.5 General Query Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
E.6 Architecture-Specific Protocol Details . . . . . . . . . . . . . . . . . . . . . . . . 816
E.6.1 ARM-specific Protocol Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
E.6.1.1 ARM Breakpoint Kinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
E.6.1.2 ARM Memory Tag Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
E.6.2 MIPS-specific Protocol Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
E.6.2.1 MIPS Register Packet Format . . . . . . . . . . . . . . . . . . . . . . . 816
E.6.2.2 MIPS Breakpoint Kinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816
E.7 Tracepoint Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
E.7.1 Relocate instruction reply packet . . . . . . . . . . . . . . . . . . . . . . . . 823
E.8 Host I/O Packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823
E.9 Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
E.10 Notification Packets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
E.11 Remote Protocol Support for Non-Stop Mode . . . . . . . . . . . . . . . 828
E.12 Packet Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829

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E.13 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 829
E.14 File-I/O Remote Protocol Extension . . . . . . . . . . . . . . . . . . . . . . . . 830
E.14.1 File-I/O Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
E.14.2 Protocol Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
E.14.3 The F Request Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
E.14.4 The F Reply Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
E.14.5 The ‘Ctrl-C’ Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
E.14.6 Console I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
E.14.7 List of Supported Calls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
open . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834
read. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834
write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834
lseek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
rename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
unlink . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
stat/fstat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
gettimeofday . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
isatty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
E.14.8 Protocol-specific Representation of Datatypes . . . . . . . . . . 838
Integral Datatypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
Pointer Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
Memory Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
struct stat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
struct timeval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
E.14.9 Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
Open Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
mode t Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
Errno Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
Lseek Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
E.14.10 File-I/O Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
E.15 Library List Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
E.16 Library List Format for SVR4 Targets . . . . . . . . . . . . . . . . . . . . . . 842
E.17 Memory Map Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
E.18 Thread List Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
E.19 Traceframe Info Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845
E.20 Branch Trace Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845
E.21 Branch Trace Configuration Format . . . . . . . . . . . . . . . . . . . . . . . . . 846

Appendix F The GDB Agent
Expression Mechanism. . . . . . . . . . . . . . . . . . . . . . . . . 847
F.1
F.2
F.3
F.4
F.5

General Bytecode Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
Bytecode Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
Using Agent Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
Varying Target Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855

xv

Appendix G Target Descriptions . . . . . . . . . . . . . . . 859
G.1 Retrieving Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859
G.2 Target Description Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859
G.2.1 Inclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860
G.2.2 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860
G.2.3 OS ABI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
G.2.4 Compatible Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
G.2.5 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
G.2.6 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
G.2.7 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862
G.3 Predefined Target Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863
G.4 Enum Target Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
G.5 Standard Target Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
G.5.1 AArch64 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
G.5.1.1 AArch64 core registers feature . . . . . . . . . . . . . . . . . . . . . . 865
G.5.1.2 AArch64 floating-point registers feature . . . . . . . . . . . . 865
G.5.1.3 AArch64 SVE registers feature . . . . . . . . . . . . . . . . . . . . . 866
G.5.1.4 AArch64 Pointer Authentication registers feature . . . 867
G.5.1.5 AArch64 TLS registers feature . . . . . . . . . . . . . . . . . . . . . 867
G.5.1.6 AArch64 MTE registers feature . . . . . . . . . . . . . . . . . . . . 868
G.5.1.7 AArch64 SME registers feature . . . . . . . . . . . . . . . . . . . . . 868
G.5.1.8 AArch64 SME2 registers feature . . . . . . . . . . . . . . . . . . . . 868
G.5.2 ARC Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
G.5.3 ARM Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
G.5.3.1 Core register set for non-M-profile . . . . . . . . . . . . . . . . . . 869
G.5.3.2 Core register set for M-profile . . . . . . . . . . . . . . . . . . . . . . 870
G.5.3.3 FPA registers feature (obsolete) . . . . . . . . . . . . . . . . . . . . 870
G.5.3.4 M-profile Vector Extension (MVE) . . . . . . . . . . . . . . . . . 870
G.5.3.5 XScale iwMMXt feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 871
G.5.3.6 Vector Floating-Point (VFP) feature . . . . . . . . . . . . . . . 871
G.5.3.7 NEON architecture feature . . . . . . . . . . . . . . . . . . . . . . . . . 872
G.5.3.8 M-profile Pointer Authentication and
Branch Target Identification feature . . . . . . . . . . . . . . . . . . . . . . . 872
G.5.3.9 M-profile system registers feature . . . . . . . . . . . . . . . . . . . 872
G.5.3.10 M-profile Security Extensions feature . . . . . . . . . . . . . . 872
G.5.3.11 TLS registers feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
G.5.4 i386 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 873
G.5.5 LoongArch Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
G.5.6 MicroBlaze Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
G.5.7 MIPS Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874
G.5.8 M68K Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
G.5.9 NDS32 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
G.5.10 Nios II Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
G.5.11 Openrisc 1000 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
G.5.12 PowerPC Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875
G.5.13 RISC-V Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
G.5.14 RX Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 877
G.5.15 S/390 and System z Features . . . . . . . . . . . . . . . . . . . . . . . . . . 877

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G.5.16G.5.17

Sparc Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878
TMS320C6x Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878

Appendix H Operating System Information . . 879
H.1

Process list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 879

Appendix I

Trace File Format . . . . . . . . . . . . . . . . 881

Appendix J.gdb_index section format . . . . . . . . 883

Appendix K Download debugging
resources with Debuginfod . . . . . . . . . . . . . . . . . . . . 887
K.1

Debuginfod Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 887

Appendix L

Manual pages . . . . . . . . . . . . . . . . . . . . . 889

Appendix M GNU GENERAL
PUBLIC LICENSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899
Appendix N GNU Free Documentation License . . 911
Concept Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 919
Command, Variable, and Function Index . . . . . . . 935

1

Summary of gdb
The purpose of a debugger such as gdb is to allow you to see what is going on “inside”
another program while it executes—or what another program was doing at the moment it
crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you
catch bugs in the act:
• Start your program, specifying anything that might affect its behavior.
• Make your program stop on specified conditions.
• Examine what has happened, when your program has stopped.
• Change things in your program, so you can experiment with correcting the effects of
one bug and go on to learn about another.
You can use gdb to debug programs written in C and C++. For more information, see
Section 15.4 [Supported Languages], page 231. For more information, see Section 15.4.1 [Cand C++], page 231.
Support for D is partial. For information on D, see Section 15.4.2 [D], page 238.
Support for Modula-2 is partial.
[Modula-2], page 244.

For information on Modula-2, see Section 15.4.9

Support for OpenCL C is partial. For information on OpenCL C, see Section 15.4.5[OpenCL C], page 239.
Debugging Pascal programs which use sets, subranges, file variables, or nested functions
does not currently work. gdb does not support entering expressions, printing values, orsimilar features using Pascal syntax.
gdb can be used to debug programs written in Fortran, although it may be necessary
to refer to some variables with a trailing underscore.
gdb can be used to debug programs written in Objective-C, using either the Apple/NeXT or the GNU Objective-C runtime.

Free Software
gdb is free software, protected by the gnu General Public License (GPL). The GPL gives
you the freedom to copy or adapt a licensed program—but every person getting a copy also
gets with it the freedom to modify that copy (which means that they must get access to thesource code), and the freedom to distribute further copies. Typical software companies use
copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve
these freedoms.
Fundamentally, the General Public License is a license which says that you have these
freedoms and that you cannot take these freedoms away from anyone else.

Free Software Needs Free Documentation
The biggest deficiency in the free software community today is not in the software—it is thelack of good free documentation that we can include with the free software. Many of ourmost important programs do not come with free reference manuals and free introductory

2

Debugging with gdb

texts. Documentation is an essential part of any software package; when an important free
software package does not come with a free manual and a free tutorial, that is a major gap.
We have many such gaps today.
Consider Perl, for instance. The tutorial manuals that people normally use are non-free.
How did this come about? Because the authors of those manuals published them withrestrictive terms—no copying, no modification, source files not available—which exclude
them from the free software world.
That wasn’t the first time this sort of thing happened, and it was far from the last.
Many times we have heard a GNU user eagerly describe a manual that he is writing, his
intended contribution to the community, only to learn that he had ruined everything bysigning a publication contract to make it non-free.
Free documentation, like free software, is a matter of freedom, not price. The problem
with the non-free manual is not that publishers charge a price for printed copies—that initself is fine. (The Free Software Foundation sells printed copies of manuals, too.) The
problem is the restrictions on the use of the manual. Free manuals are available in sourcecode form, and give you permission to copy and modify. Non-free manuals do not allow
this.
The criteria of freedom for a free manual are roughly the same as for free software.
Redistribution (including the normal kinds of commercial redistribution) must be permitted,
so that the manual can accompany every copy of the program, both on-line and on paper.
Permission for modification of the technical content is crucial too. When people modify the software, adding or changing features, if they are conscientious they will change
the manual too—so they can provide accurate and clear documentation for the modified
program. A manual that leaves you no choice but to write a new manual to document achanged version of the program is not really available to our community.
Some kinds of limits on the way modification is handled are acceptable. For example,
requirements to preserve the original author’s copyright notice, the distribution terms, orthe list of authors, are ok. It is also no problem to require modified versions to include
notice that they were modified. Even entire sections that may not be deleted or changed
are acceptable, as long as they deal with nontechnical topics (like this one). These kinds ofrestrictions are acceptable because they don’t obstruct the community’s normal use of themanual.
However, it must be possible to modify all the technical content of the manual, and thendistribute the result in all the usual media, through all the usual channels. Otherwise, therestrictions obstruct the use of the manual, it is not free, and we need another manual toreplace it.
Please spread the word about this issue. Our community continues to lose manuals
to proprietary publishing. If we spread the word that free software needs free reference
manuals and free tutorials, perhaps the next person who wants to contribute by writing
documentation will realize, before it is too late, that only free manuals contribute to thefree software community.
If you are writing documentation, please insist on publishing it under the GNU Free
Documentation License or another free documentation license. Remember that this decision requires your approval—you don’t have to let the publisher decide. Some commercial
publishers will use a free license if you insist, but they will not propose the option; it is up

Summary of gdb

3

to you to raise the issue and say firmly that this is what you want. If the publisher you
are dealing with refuses, please try other publishers. If you’re not sure whether a proposed
license is free, write to licensing@gnu.org.
You can encourage commercial publishers to sell more free, copylefted manuals andtutorials by buying them, and particularly by buying copies from the publishers that paid
for their writing or for major improvements. Meanwhile, try to avoid buying non-freedocumentation at all. Check the distribution terms of a manual before you buy it, andinsist that whoever seeks your business must respect your freedom. Check the history of
the book, and try to reward the publishers that have paid or pay the authors to work on it.
The Free Software Foundation maintains a list of free documentation published by otherpublishers, at http://www.fsf.org/doc/other-free-books.html.

Contributors to gdb
Richard Stallman was the original author of gdb, and of many other gnu programs. Manyothers have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it;with regret, we cannot actually acknowledge everyone here. The file ChangeLog in the gdb
distribution approximates a blow-by-blow account.
Changes much prior to version 2.0 are lost in the mists of time.
Plea: Additions to this section are particularly welcome. If you or your friends(or enemies, to be evenhanded) have been unfairly omitted from this list, we
would like to add your names!
So that they may not regard their many labors as thankless, we particularly thank those
who shepherded gdb through major releases: Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0,
5.3, 5.2, 5.1 and 5.0); Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs(release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman
and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1,
4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1,
and 3.0).
Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, andRichard Mlynarik, handled releases through 2.8.
Michael Tiemann is the author of most of the gnu C++ support in gdb, with significant
additional contributions from Per Bothner and Daniel Berlin. James Clark wrote the gnu
C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general
update work leading to release 3.0).
gdb uses the BFD subroutine library to examine multiple object-file formats; BFD wasa joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John
Gilmore.
David Johnson wrote the original COFF support; Pace Willison did the original support
for encapsulated COFF.
Brent Benson of Harris Computer Systems contributed DWARF 2 support.
Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner,
Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete
contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki

4Debugging with gdb

Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff
Law contributed HP PA and SOM support. Keith Packard contributed NS32K support.
Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed HarrisNighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed
SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry
support. Marko Mlinar contributed OpenRISC 1000 support.
Andreas Schwab contributed M68K gnu/Linux support.
Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries.
Jay Fenlason and Roland McGrath ensured that gdb and GAS agree about several
machine instruction sets.
Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remotedebugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remotedebugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively.
Brian Fox is the author of the readline libraries providing command-line editing andcommand history.
Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual.
Fred Fish wrote most of the support for Unix System Vr4. He also enhanced thecommand-completion support to cover C++ overloaded symbols.
Hitachi America (now Renesas America), Ltd. sponsored the support for H8/300,
H8/500, and Super-H processors.
NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D processors.
Toshiba sponsored the support for the TX39 Mips processor.
Matsushita sponsored the support for the MN10200 and MN10300 processors.
Fujitsu sponsored the support for SPARClite and FR30 processors.
Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints.
Michael Snyder added support for tracepoints.
Stu Grossman wrote gdbserver.
Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable
bug fixes and cleanups throughout gdb.
The following people at the Hewlett-Packard Company contributed support for the PARISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP’s implementationof kernel threads, HP’s aC++ compiler, and the Text User Interface (nee Terminal User
Interface): Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish
Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase provided HP-specificinformation in this manual.
DJ Delorie ported gdb to MS-DOS, for the DJGPP project. Robert Hoehne madesignificant contributions to the DJGPP port.

Summary of gdb

5

Cygnus Solutions has sponsored gdb maintenance and much of its development since1991. Cygnus engineers who have worked on gdb fulltime include Mark Alexander, Jim
Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin
Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz,
Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael,
Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank
Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb,
Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine
Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike
Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim
Wilson, and David Zuhn have made contributions both large and small.
Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for Cygnus Solutions, implemented the original gdb/mi interface.
Jim Blandy added support for preprocessor macros, while working for Red Hat.
Andrew Cagney designed gdb’s architecture vector. Many people including Andrew
Cagney, Stephane Carrez, Randolph Chung, Nick Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab,
Jason Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped with the
migration of old architectures to this new framework.
Andrew Cagney completely re-designed and re-implemented gdb’s unwinder framework,
this consisting of a fresh new design featuring frame IDs, independent frame sniffers, andthe sentinel frame. Mark Kettenis implemented the dwarf 2 unwinder, Jeff Johnston the
libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and trad unwinders.
The architecture-specific changes, each involving a complete rewrite of the architecture’s
frame code, were carried out by Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew
Cagney, Stephane Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei Sakamoto, Yoshinori
Sato, Michael Snyder, Corinna Vinschen, and Ulrich Weigand.
Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from Tensilica, Inc.
contributed support for Xtensa processors. Others who have worked on the Xtensa port of
gdb in the past include Steve Tjiang, John Newlin, and Scott Foehner.
Michael Eager and staff of Xilinx, Inc., contributed support for the Xilinx MicroBlaze
architecture.
Initial support for the FreeBSD/mips target and native configuration was developed
by SRI International and the University of Cambridge Computer Laboratory under
DARPA/AFRL contract FA8750-10-C-0237 ("CTSRD"), as part of the DARPA CRASH
research programme.
Initial support for the FreeBSD/riscv target and native configuration was developed by
SRI International and the University of Cambridge Computer Laboratory (Department ofComputer Science and Technology) under DARPA contract HR0011-18-C-0016 ("ECATS"),as part of the DARPA SSITH research programme.
The original port to the OpenRISC 1000 is believed to be due to Alessandro Forin and
Per Bothner. More recent ports have been the work of Jeremy Bennett, Franck Jullien,
Stefan Wallentowitz and Stafford Horne.

6

Debugging with gdb

Weimin Pan, David Faust and Jose E. Marchesi contributed support for the Linux kernel
BPF virtual architecture. This work was sponsored by Oracle.

7

1 A Sample gdb Session
You can use this manual at your leisure to read all about gdb. However, a handful ofcommands are enough to get started using the debugger. This chapter illustrates thosecommands.
In this sample session, we emphasize user input like this: input, to make it easier to pickout from the surrounding output.
One of the preliminary versions of gnu m4 (a generic macro processor) exhibits thefollowing bug: sometimes, when we change its quote strings from the default, the commands
used to capture one macro definition within another stop working. In the following short m4
session, we define a macro foo which expands to 0000; we then use the m4 built-in defn todefine bar as the same thing. However, when we change the open quote string to <QUOTE>
and the close quote string to <UNQUOTE>, the same procedure fails to define a new synonymbaz:$ cd gnu/m4$ ./m4
define(foo,0000)
foo
0000
define(bar,defn(‘foo’))bar
0000
changequote(<QUOTE>,<UNQUOTE>)
define(baz,defn(<QUOTE>foo<UNQUOTE>))baz
Ctrl-dm4: End of input: 0: fatal error: EOF in string

Let us use gdb to try to see what is going on.
$ gdb m4
gdb is free software and you are welcome to distribute copies
of it under certain conditions; type "show copying" to see
the conditions.
There is absolutely no warranty for gdb; type "show warranty"
for details.
gdb 16.0.50.20241106-git, Copyright 1999 Free Software Foundation, Inc...
(gdb)

gdb reads only enough symbol data to know where to find the rest when needed; as a result,the first prompt comes up very quickly. We now tell gdb to use a narrower display widththan usual, so that examples fit in this manual.
(gdb) set width 70

We need to see how the m4 built-in changequote works. Having looked at the source, weknow the relevant subroutine is m4_changequote, so we set a breakpoint there with the
gdb break command.
(gdb) break m4 changequote
Breakpoint 1 at 0x62f4: file builtin.c, line 879.

8

Debugging with gdb

Using the run command, we start m4 running under gdb control; as long as control does
not reach the m4_changequote subroutine, the program runs as usual:(gdb) runStarting program: /work/Editorial/gdb/gnu/m4/m4
define(foo,0000)
foo
0000

To trigger the breakpoint, we call changequote. gdb suspends execution of m4, displaying
information about the context where it stops.
changequote(<QUOTE>,<UNQUOTE>)
Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
at builtin.c:879
879
if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))

Now we use the command n (next) to advance execution to the next line of the current
function.
(gdb) n882
: nil,

set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\set_quotes looks like a promising subroutine. We can go into it by using the command s(step) instead of next. step goes to the next line to be executed in any subroutine, so it
steps into set_quotes.
(gdb) s
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")at input.c:530
530
if (lquote != def_lquote)

The display that shows the subroutine where m4 is now suspended (and its arguments) iscalled a stack frame display. It shows a summary of the stack. We can use the backtracecommand (which can also be spelled bt), to see where we are in the stack as a whole: thebacktrace command displays a stack frame for each active subroutine.
(gdb) bt
#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")at input.c:530#1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
at builtin.c:882#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
at macro.c:71#4 0x79dc in expand_input () at macro.c:40#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195

We step through a few more lines to see what happens. The first two times, we can use ‘s’;the next two times we use n to avoid falling into the xstrdup subroutine.
(gdb) s0x3b5c 532
if (rquote != def_rquote)(gdb) s0x3b80 535
lquote = (lq == nil || *lq == ’\0’) ? \def_lquote : xstrdup(lq);(gdb) n536
rquote = (rq == nil || *rq == ’\0’) ? def_rquote\: xstrdup(rq);(gdb) nChapter 1: A Sample gdb Session538

9

len_lquote = strlen(rquote);

The last line displayed looks a little odd; we can examine the variables lquote and rquote
to see if they are in fact the new left and right quotes we specified. We use the commandp (print) to see their values.
(gdb) p lquote$1 = 0x35d40 "<QUOTE>"(gdb) p rquote$2 = 0x35d50 "<UNQUOTE>"

lquote and rquote are indeed the new left and right quotes. To look at some context, we
can display ten lines of source surrounding the current line with the l (list) command.
(gdb) l533
xfree(rquote);534
535
lquote = (lq == nil || *lq == ’\0’) ? def_lquote\: xstrdup (lq);536rquote = (rq == nil || *rq == ’\0’) ? def_rquote\: xstrdup (rq);537538
len_lquote = strlen(rquote);539
len_rquote = strlen(lquote);
540
}
541
542
void

Let us step past the two lines that set len_lquote and len_rquote, and then examine thevalues of those variables.
(gdb) n539
len_rquote = strlen(lquote);(gdb) n540}(gdb) p len lquote$3 = 9(gdb) p len rquote$4 = 7

That certainly looks wrong, assuming len_lquote and len_rquote are meant to be thelengths of lquote and rquote respectively. We can set them to better values using the pcommand, since it can print the value of any expression—and that expression can include
subroutine calls and assignments.
(gdb) p len lquote=strlen(lquote)$5 = 7(gdb) p len rquote=strlen(rquote)$6 = 9Is that enough to fix the problem of using the new quotes with the m4 built-in defn? We canallow m4 to continue executing with the c (continue) command, and then try the example
that caused trouble initially:(gdb) cContinuing.
define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
0000

10

Debugging with gdb

Success! The new quotes now work just as well as the default ones. The problem seems tohave been just the two typos defining the wrong lengths. We allow m4 exit by giving it an
EOF as input:
Ctrl-dProgram exited normally.

The message ‘Program exited normally.’ is from gdb; it indicates m4 has finished executing. We can end our gdb session with the gdb quit command.
(gdb) quit

11

2 Getting In and Out of gdb
This chapter discusses how to start gdb, and how to get out of it. The essentials are:• type ‘gdb’ to start gdb.
• type quit, exit or Ctrl-d to exit.

2.1 Invoking gdb
Invoke gdb by running the program gdb. Once started, gdb reads commands from theterminal until you tell it to exit.
You can also run gdb with a variety of arguments and options, to specify more of yourdebugging environment at the outset.
The command-line options described here are designed to cover a variety of situations;in some environments, some of these options may effectively be unavailable.
The most usual way to start gdb is with one argument, specifying an executable program:
gdb program

You can also start with both an executable program and a core file specified:
gdb program core

You can, instead, specify a process ID as a second argument or use option -p, if you
want to debug a running process:gdb program 1234
gdb -p 1234

would attach gdb to process 1234. With option -p you can omit the program filename.
Taking advantage of the second command-line argument requires a fairly complete operating system; when you use gdb as a remote debugger attached to a bare board, there
may not be any notion of “process”, and there is often no way to get a core dump. gdb
will warn you if it is unable to attach or to read core dumps.
You can optionally have gdb pass any arguments after the executable file to the inferior
using --args. This option stops option processing.
gdb --args gcc -O2 -c foo.c

This will cause gdb to debug gcc, and to set gcc’s command-line arguments (seeSection 4.3 [Arguments], page 38) to ‘-O2 -c foo.c’.
You can run gdb without printing the front material, which describes gdb’s
non-warranty, by specifying --silent (or -q/--quiet):
gdb --silent

You can further control how gdb starts up by using command-line options. gdb itself canremind you of the options available.
Type
gdb -help

to display all available options and briefly describe their use (‘gdb -h’ is a shorter equivalent).
All options and command line arguments you give are processed in sequential order. The
order makes a difference when the ‘-x’ option is used.

12

Debugging with gdb

2.1.1 Choosing Files
When gdb starts, it reads any arguments other than options as specifying an executable
file and core file (or process ID). This is the same as if the arguments were specified by the‘-se’ and ‘-c’ (or ‘-p’) options respectively. (gdb reads the first argument that does nothave an associated option flag as equivalent to the ‘-se’ option followed by that argument;
and the second argument that does not have an associated option flag, if any, as equivalent
to the ‘-c’/‘-p’ option followed by that argument.) If the second argument begins with adecimal digit, gdb will first attempt to attach to it as a process, and if that fails, attempt
to open it as a corefile. If you have a corefile whose name begins with a digit, you canprevent gdb from treating it as a pid by prefixing it with ./, e.g. ./12345.
If gdb has not been configured to included core file support, such as for most embedded
targets, then it will complain about a second argument and ignore it.
For the ‘-s’, ‘-e’, and ‘-se’ options, and their long form equivalents, the method used
to search the file system for the symbol and/or executable file is the same as that used by
the file command. See Section 18.1 [file], page 291.
Many options have both long and short forms; both are shown in the following list. gdb
also recognizes the long forms if you truncate them, so long as enough of the option ispresent to be unambiguous. (If you prefer, you can flag option arguments with ‘--’ rather
than ‘-’, though we illustrate the more usual convention.)-symbols file-s fileRead symbol table from file file.
-exec file-e fileUse file file as the executable file to execute when appropriate, and for examining
pure data in conjunction with a core dump.
-se file

Read symbol table from file file and use it as the executable file.

-core file-c fileUse file file as a core dump to examine.
-pid number-p number Connect to process ID number, as with the attach command.
-command file-x fileExecute commands from file file. The contents of this file is evaluated exactly
as the source command would. See Section 23.1.3 [Command files], page 395.
-eval-command command-ex command
Execute a single gdb command.
This option may be used multiple times to call multiple commands. It may also
be interleaved with ‘-command’ as required.
gdb -ex ’target sim’ -ex ’load’ \-x setbreakpoints -ex ’run’ a.out-init-command file-ix file Execute commands from file file before loading the inferior (but after loading
gdbinit files). See Section 2.1.3 [Startup], page 16.

Chapter 2: Getting In and Out of gdb

13-init-eval-command command-iex command
Execute a single gdb command before loading the inferior (but after loading
gdbinit files). See Section 2.1.3 [Startup], page 16.
-early-init-command file-eix file Execute commands from file very early in the initialization process, before any
output is produced. See Section 2.1.3 [Startup], page 16.
-early-init-eval-command command-eiex command
Execute a single gdb command very early in the initialization process, before
any output is produced.
-directory directory-d directory
Add directory to the path to search for source and script files.
-r-readnow

Read each symbol file’s entire symbol table immediately, rather than the default,
which is to read it incrementally as it is needed. This makes startup slower,
but makes future operations faster.

--readneverDo not read each symbol file’s symbolic debug information. This makes startup
faster but at the expense of not being able to perform symbolic debugging.
DWARF unwind information is also not read, meaning backtraces may become
incomplete or inaccurate. One use of this is when a user simply wants to do
the following sequence: attach, dump core, detach. Loading the debugging
information in this case is an unnecessary cause of delay.

2.1.2 Choosing Modes
You can run gdb in various alternative modes—for example, in batch mode or quiet mode.
-nx
-n
-nh

-quiet-silent-q

Do not execute commands found in any initialization files (see Section 2.1.4[Initialization Files], page 17).
Do not execute commands found in any home directory initialization file (seeSection 2.1.4 [Home directory initialization file], page 17). The system wideand current directory initialization files are still loaded.

“Quiet”. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.
This can also be enabled using set startup-quietly on. The default isoff. Use show startup-quietly to see the current setting. Place set
startup-quietly on into your early initialization file (see Section 2.1.4[Initialization Files], page 17) to have future gdb sessions startup quietly.

14-batchDebugging with gdb

Run in batch mode. Exit with status 0 after processing all the command files
specified with ‘-x’ (and all commands from initialization files, if not inhibitedwith ‘-n’). Exit with nonzero status if an error occurs in executing the gdb
commands in the command files. Batch mode also disables pagination, sets unlimited terminal width and height see Section 22.4 [Screen Size], page 370, andacts as if set confirm off were in effect (see Section 22.9 [Messages/Warnings],
page 381).
Batch mode may be useful for running gdb as a filter, for example to download
and run a program on another computer; in order to make this more useful, themessage
Program exited normally.

(which is ordinarily issued whenever a program running under gdb control
terminates) is not issued when running in batch mode.
-batch-silent
Run in batch mode exactly like ‘-batch’, but totally silently. All gdb output tostdout is prevented (stderr is unaffected). This is much quieter than ‘-silent’and would be useless for an interactive session.
This is particularly useful when using targets that give ‘Loading section’ messages, for example.
Note that targets that give their output via gdb, as opposed to writing directly
to stdout, will also be made silent.
-return-child-result
The return code from gdb will be the return code from the child process (theprocess being debugged), with the following exceptions:• gdb exits abnormally. E.g., due to an incorrect argument or an internal
error. In this case the exit code is the same as it would have been without‘-return-child-result’.
• The user quits with an explicit value. E.g., ‘quit 1’.
• The child process never runs, or is not allowed to terminate, in which casethe exit code will be -1.
This option is useful in conjunction with ‘-batch’ or ‘-batch-silent’, when
gdb is being used as a remote program loader or simulator interface.
-nowindows-nw“No windows”. If gdb comes with a graphical user interface (GUI) built in,then this option tells gdb to only use the command-line interface. If no GUI isavailable, this option has no effect.
-windows-w

If gdb includes a GUI, then this option requires it to be used if possible.

-cd directory
Run gdb using directory as its working directory, instead of the current directory.

Chapter 2: Getting In and Out of gdb

15-data-directory directory-D directory
Run gdb using directory as its data directory. The data directory is where gdb
searches for its auxiliary files. See Section 18.8 [Data Files], page 308.
-fullname-fgnu Emacs sets this option when it runs gdb as a subprocess. It tells gdb to
output the full file name and line number in a standard, recognizable fashion
each time a stack frame is displayed (which includes each time your program
stops). This recognizable format looks like two ‘\032’ characters, followed by
the file name, line number and character position separated by colons, and a
newline. The Emacs-to-gdb interface program uses the two ‘\032’ characters
as a signal to display the source code for the frame.
-annotate level
This option sets the annotation level inside gdb. Its effect is identical to using‘set annotate level’ (see Chapter 28 [Annotations], page 695). The annotation level controls how much information gdb prints together with its prompt,
values of expressions, source lines, and other types of output. Level 0 is thenormal, level 1 is for use when gdb is run as a subprocess of gnu Emacs, level3 is the maximum annotation suitable for programs that control gdb, and level2 has been deprecated.
The annotation mechanism has largely been superseded by gdb/mi (seeChapter 27 [GDB/MI], page 589).
--argsChange interpretation of command line so that arguments following the executable file are passed as command line arguments to the inferior. This option
stops option processing.

-baud bps
-b bpsSet the line speed (baud rate or bits per second) of any serial interface used by
gdb for remote debugging.
-l timeout
Set the timeout (in seconds) of any communication used by gdb for remotedebugging.
-tty device-t device Run using device for your program’s standard input and output.
-tui

Activate the Text User Interface when starting. The Text User Interface manages several text windows on the terminal, showing source, assembly, registers and gdb command outputs (see Chapter 25 [gdb Text User Interface],
page 579). Do not use this option if you run gdb from Emacs (see Chapter 26[Using gdb under gnu Emacs], page 587).

-interpreter interp
Use the interpreter interp for interface with the controlling program or device.
This option is meant to be set by programs which communicate with gdb using
it as a back end. See Chapter 24 [Command Interpreters], page 577.
‘--interpreter=mi’ (or ‘--interpreter=mi3’) causes gdb to use the gdb/miinterface version 3 (see Chapter 27 [The gdb/mi Interface], page 589) included

16

Debugging with gdb

since gdb version 9.1. gdb/mi version 2 (mi2), included in gdb 6.0 and version
1 (mi1), included in gdb 5.3, are also available. Earlier gdb/mi interfaces are
no longer supported.
-writeOpen the executable and core files for both reading and writing. This is equivalent to the ‘set write on’ command inside gdb (see Section 17.6 [Patching],
page 285).

-statistics
This option causes gdb to print statistics about time and memory usage after
it completes each command and returns to the prompt.
-version

This option causes gdb to print its version number and no-warranty blurb, andexit.

-configuration
This option causes gdb to print details about its build-time configuration parameters, and then exit. These details can be important when reporting gdb
bugs (see Chapter 32 [GDB Bugs], page 709).

2.1.3 What gdb Does During Startup
Here’s the description of what gdb does during session startup:
1. Performs minimal setup required to initialize basic internal state.
2. Reads commands from the early initialization file (if any) in your home directory.
Only a restricted set of commands can be placed into an early initialization file, see
Section 2.1.4 [Initialization Files], page 17, for details.
3. Executes commands and command files specified by the ‘-eiex’ and ‘-eix’ commandline options in their specified order. Only a restricted set of commands can be usedwith ‘-eiex’ and ‘eix’, see Section 2.1.4 [Initialization Files], page 17, for details.
4. Sets up the command interpreter as specified by the command line (see Section 2.1.2[Mode Options], page 13).
5. Reads the system wide initialization file and the files from the system wide initialization
directory, see [System Wide Init Files], page 18.
6. Reads the initialization file (if any) in your home directory and executes all the commands in that file, see [Home Directory Init File], page 18.
7. Executes commands and command files specified by the ‘-iex’ and ‘-ix’ options intheir specified order. Usually you should use the ‘-ex’ and ‘-x’ options instead, but
this way you can apply settings before gdb init files get executed and before inferior
gets loaded.
8. Processes command line options and operands.
9. Reads and executes the commands from the initialization file (if any) in the current working directory as long as ‘set auto-load local-gdbinit’ is set to ‘on’ (seeSection 22.8.1 [Init File in the Current Directory], page 378). This is only done if thecurrent directory is different from your home directory. Thus, you can have more than
one init file, one generic in your home directory, and another, specific to the program
you are debugging, in the directory where you invoke gdb. See [Init File in the Current
Directory during Startup], page 19.

Chapter 2: Getting In and Out of gdb

17

10. If the command line specified a program to debug, or a process to attach to, or a corefile, gdb loads any auto-loaded scripts provided for the program or for its loaded sharedlibraries. See Section 22.8 [Auto-loading], page 376.
If you wish to disable the auto-loading during startup, you must do something like thefollowing:$ gdb -iex "set auto-load python-scripts off" myprogram

Option ‘-ex’ does not work because the auto-loading is then turned off too late.
11. Executes commands and command files specified by the ‘-ex’ and ‘-x’ options in their
specified order. See Section 23.1.3 [Command Files], page 395, for more details about
gdb command files.
12. Reads the command history recorded in the history file. See Section 22.3 [Command
History], page 368, for more details about the command history and the files where
gdb records it.

2.1.4 Initialization Files
During startup (see Section 2.1.3 [Startup], page 16) gdb will execute commands fromseveral initialization files. These initialization files use the same syntax as command files(see Section 23.1.3 [Command Files], page 395) and are processed by gdb in the same way.
To display the list of initialization files loaded by gdb at startup, in the order they will
be loaded, you can use gdb --help.
The early initialization file is loaded very early in gdb’s initialization process, before
the interpreter (see Chapter 24 [Interpreters], page 577) has been initialized, and before
the default target (see Chapter 19 [Targets], page 311) is initialized. Only set or sourcecommands should be placed into an early initialization file, and the only set commands
that can be used are those that control how gdb starts up.
Commands that can be placed into an early initialization file will be documented as suchthroughout this manual. Any command that is not documented as being suitable for an
early initialization file should instead be placed into a general initialization file. Command
files passed to --early-init-command or -eix are also early initialization files, with thesame command restrictions. Only commands that can appear in an early initialization fileshould be passed to --early-init-eval-command or -eiex.
In contrast, the general initialization files are processed later, after gdb has finished its
own internal initialization process, any valid command can be used in these files.
Throughout the rest of this document the term initialization file refers to one of thegeneral initialization files, not the early initialization file. Any discussion of the early initialization file will specifically mention that it is the early initialization file being discussed.
As the system wide and home directory initialization files are processed before mostcommand line options, changes to settings (e.g. ‘set complaints’) can affect subsequent
processing of command line options and operands.
The following sections describe where gdb looks for the early initialization and initialization files, and the order that the files are searched for.

18

Debugging with gdb

2.1.4.1 Home directory early initialization files
gdb initially looks for an early initialization file in the users home directory1 . There are anumber of locations that gdb will search in the home directory, these locations are searched
in order and gdb will load the first file that it finds, and subsequent locations will not bechecked.
On non-macOS hosts the locations searched are:
• The file gdb/gdbearlyinit within the directory pointed to by the environment variable
XDG_CONFIG_HOME, if it is defined.
• The file .config/gdb/gdbearlyinit within the directory pointed to by the environment variable HOME, if it is defined.
• The file .gdbearlyinit within the directory pointed to by the environment variable
HOME, if it is defined.
By contrast, on macOS hosts the locations searched are:
• The file Library/Preferences/gdb/gdbearlyinit within the directory pointed to by
the environment variable HOME, if it is defined.
• The file .gdbearlyinit within the directory pointed to by the environment variable
HOME, if it is defined.
It is possible to prevent the home directory early initialization file from being loaded
using the ‘-nx’ or ‘-nh’ command line options, see Section 2.1.2 [Choosing Modes], page 13.

2.1.4.2 System wide initialization files
There are two locations that are searched for system wide initialization files. Both of theselocations are always checked:
system.gdbinit
This is a single system-wide initialization file. Its location is specified withthe --with-system-gdbinit configure option (see Section C.6 [System-wide
configuration], page 753). It is loaded first when gdb starts, before commandline options have been processed.
system.gdbinit.d
This is the system-wide initialization directory. Its location is specified with the--with-system-gdbinit-dir configure option (see Section C.6 [System-wide
configuration], page 753). Files in this directory are loaded in alphabeticalorder immediately after system.gdbinit (if enabled) when gdb starts, before
command line options have been processed. Files need to have a recognizedscripting language extension (.py/.scm) or be named with a .gdb extension
to be interpreted as regular gdb commands. gdb will not recurse into any
subdirectories of this directory.
It is possible to prevent the system wide initialization files from being loaded using the‘-nx’ command line option, see Section 2.1.2 [Choosing Modes], page 13.
1

On DOS/Windows systems, the home directory is the one pointed to by the HOME environment variable.

Chapter 2: Getting In and Out of gdb

19

2.1.4.3 Home directory initialization file
After loading the system wide initialization files gdb will look for an initialization file in theusers home directory2 . There are a number of locations that gdb will search in the home
directory, these locations are searched in order and gdb will load the first file that it finds,and subsequent locations will not be checked.
On non-Apple hosts the locations searched are:
$XDG_CONFIG_HOME/gdb/gdbinit$HOME/.config/gdb/gdbinit$HOME/.gdbinit
While on Apple hosts the locations searched are:
$HOME/Library/Preferences/gdb/gdbinit$HOME/.gdbinit
It is possible to prevent the home directory initialization file from being loaded using
the ‘-nx’ or ‘-nh’ command line options, see Section 2.1.2 [Choosing Modes], page 13.
The DJGPP port of gdb uses the name gdb.ini instead of .gdbinit or gdbinit, due
to the limitations of file names imposed by DOS filesystems. The Windows port of gdb
uses the standard name, but if it finds a gdb.ini file in your home directory, it warns you
about that and suggests to rename the file to the standard name.

2.1.4.4 Local directory initialization file
gdb will check the current directory for a file called .gdbinit. It is loaded last, after
command line options other than ‘-x’ and ‘-ex’ have been processed. The command line
options ‘-x’ and ‘-ex’ are processed last, after .gdbinit has been loaded, see Section 2.1.1[Choosing Files], page 12.
If the file in the current directory was already loaded as the home directory initialization
file then it will not be loaded a second time.
It is possible to prevent the local directory initialization file from being loaded using the‘-nx’ command line option, see Section 2.1.2 [Choosing Modes], page 13.

2.2 Quitting gdb
quit [expression]
exit [expression]q
To exit gdb, use the quit command (abbreviated q), the exit command, ortype an end-of-file character (usually Ctrl-d). If you do not supply expression,
gdb will terminate normally; otherwise it will terminate using the result ofexpression as the error code.
An interrupt (often Ctrl-c) does not exit from gdb, but rather terminates the actionof any gdb command that is in progress and returns to gdb command level. It is safe totype the interrupt character at any time because gdb does not allow it to take effect until
a time when it is safe.
2

On DOS/Windows systems, the home directory is the one pointed to by the HOME environment variable.

20

Debugging with gdb

If you have been using gdb to control an attached process or device, you can release
it with the detach command (see Section 4.7 [Debugging an Already-running Process],
page 41).

2.3 Shell Commands
If you need to execute occasional shell commands during your debugging session, there isno need to leave or suspend gdb; you can just use the shell command.
shell command-string!command-string
Invoke a shell to execute command-string. Note that no space is needed between! and command-string. On GNU and Unix systems, the environment variable
SHELL, if it exists, determines which shell to run. Otherwise gdb uses thedefault shell (/bin/sh on GNU and Unix systems, cmd.exe on MS-Windows,
COMMAND.COM on MS-DOS, etc.).
You may also invoke shell commands from expressions, using the $_shell convenience
function. See [$ shell convenience function], page 176.
The utility make is often needed in development environments. You do not have to use
the shell command for this purpose in gdb:
make make-args
Execute the make program with the specified arguments. This is equivalent to‘shell make make-args’.
pipe [command] | shell_command| [command] | shell_command
pipe -d delim command delim shell_command| -d delim command delim shell_command
Executes command and sends its output to shell command. Note that no spaceis needed around |. If no command is provided, the last command executed isrepeated.
In case the command contains a |, the option -d delim can be used to specify an alternate delimiter string delim that separates the command from theshell command.
Example:(gdb) p var$1 = {
black = 144,
red = 233,
green = 377,
blue = 610,
white = 987}(gdb) pipe p var|wc
719(gdb) |p var|wc -l
780Chapter 2: Getting In and Out of gdb

21(gdb) p /x var$4 = {
black = 0x90,
red = 0xe9,
green = 0x179,
blue = 0x262,
white = 0x3db}(gdb) ||grep red
red => 0xe9,(gdb) | -d ! echo this contains a | char\n ! sed -e ’s/|/PIPE/’
this contains a PIPE char(gdb) | -d xxx echo this contains a | char!\n xxx sed -e ’s/|/PIPE/’
this contains a PIPE char!
(gdb)

The convenience variables $_shell_exitcode and $_shell_exitsignal can be used to
examine the exit status of the last shell command launched by shell, make, pipe and |.
See Section 10.12 [Convenience Variables], page 171.

2.4 Logging Output
You may want to save the output of gdb commands to a file. There are several commands
to control gdb’s logging.
set logging enabled [on|off]
Enable or disable logging.
set logging file file
Change the name of the current logfile. The default logfile is gdb.txt.
set logging overwrite [on|off]
By default, gdb will append to the logfile. Set overwrite if you want set
logging enabled on to overwrite the logfile instead.
set logging redirect [on|off]
By default, gdb output will go to both the terminal and the logfile. Set
redirect if you want output to go only to the log file.
set logging debugredirect [on|off]
By default, gdb debug output will go to both the terminal and the logfile. Set
debugredirect if you want debug output to go only to the log file.
show logging
Show the current values of the logging settings.
You can also redirect the output of a gdb command to a shell command. See [pipe],
page 20.

23

3 gdb Commands
You can abbreviate a gdb command to the first few letters of the command name, if thatabbreviation is unambiguous; and you can repeat certain gdb commands by typing justRET. You can also use the TAB key to get gdb to fill out the rest of a word in a command(or to show you the alternatives available, if there is more than one possibility).

3.1 Command Syntax
A gdb command is a single line of input. There is no limit on how long it can be. It
starts with a command name, which is followed by arguments whose meaning depends onthe command name. For example, the command step accepts an argument which is thenumber of times to step, as in ‘step 5’. You can also use the step command with noarguments. Some commands do not allow any arguments.
gdb command names may always be truncated if that abbreviation is unambiguous.
Other possible command abbreviations are listed in the documentation for individual commands. In some cases, even ambiguous abbreviations are allowed; for example, s is speciallydefined as equivalent to step even though there are other commands whose names startwith s. You can test abbreviations by using them as arguments to the help command.
A blank line as input to gdb (typing just RET) means to repeat the previous command.
Certain commands (for example, run) will not repeat this way; these are commands whose
unintentional repetition might cause trouble and which you are unlikely to want to repeat.
User-defined commands can disable this feature; see Section 23.1.1 [Define], page 391.
The list and x commands, when you repeat them with RET, construct new arguments
rather than repeating exactly as typed. This permits easy scanning of source or memory.
gdb can also use RET in another way: to partition lengthy output, in a way similar tothe common utility more (see Section 22.4 [Screen Size], page 370). Since it is easy to press
one RET too many in this situation, gdb disables command repetition after any commandthat generates this sort of display.
Any text from a # to the end of the line is a comment; it does nothing. This is usefulmainly in command files (see Section 23.1.3 [Command Files], page 395).
The Ctrl-o binding is useful for repeating a complex sequence of commands. This
command accepts the current line, like RET, and then fetches the next line relative to thecurrent line from the history for editing.

3.2 Command Settings
Many commands change their behavior according to command-specific variables or settings. These settings can be changed with the set subcommands. For example, the printcommand (see Chapter 10 [Examining Data], page 141) prints arrays differently depending
on settings changeable with the commands set print elements NUMBER-OF-ELEMENTS and
set print array-indexes, among others.
You can change these settings to your preference in the gdbinit files loaded at gdb
startup. See Section 2.1.3 [Startup], page 16.
The settings can also be changed interactively during the debugging session. For example, to change the limit of array elements to print, you can do the following:(gdb) set print elements 10

24

Debugging with gdb(gdb) print some_array$1 = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90...}

The above set print elements 10 command changes the number of elements to print
from the default of 200 to 10. If you only intend this limit of 10 to be used for printing
some_array, then you must restore the limit back to 200, with set print elements 200.
Some commands allow overriding settings with command options. For example, theprint command supports a number of options that allow overriding relevant global printsettings as set by set print subcommands. See [print options], page 141. The example
above could be rewritten as:(gdb) print -elements 10 -- some_array$1 = {0, 10, 20, 30, 40, 50, 60, 70, 80, 90...}

Alternatively, you can use the with command to change a setting temporarily, for theduration of a command invocation.
with setting [value] [-- command]w setting [value] [-- command]
Temporarily set setting to value for the duration of command.
setting is any setting you can change with the set subcommands. value is thevalue to assign to setting while running command.
If no command is provided, the last command executed is repeated.
If a command is provided, it must be preceded by a double dash (--) separator.
This is required because some settings accept free-form arguments, such as
expressions or filenames.
For example, the command(gdb) with print array on -- print some_arrayis equivalent to the following 3 commands:(gdb) set print array on(gdb) print some_array(gdb) set print array off

The with command is particularly useful when you want to override a setting
while running user-defined commands, or commands defined in Python or Guile.
See Chapter 23 [Extending GDB], page 391.
(gdb) with print pretty on -- my_complex_command

To change several settings for the same command, you can nest with commands. For example, with language ada -- with print elements 10 temporarily changes the language to Ada and sets a limit of 10 elements to print
for arrays and strings.

3.3 Command Completion
gdb can fill in the rest of a word in a command for you, if there is only one possibility;
it can also show you what the valid possibilities are for the next word in a command, at
any time. This works for gdb commands, gdb subcommands, command options, and thenames of symbols in your program.
Press the TAB key whenever you want gdb to fill out the rest of a word. If there is only
one possibility, gdb fills in the word, and waits for you to finish the command (or press RET
to enter it). For example, if you type

Chapter 3: gdb Commands

25(gdb) info breTAB

gdb fills in the rest of the word ‘breakpoints’, since that is the only info subcommand
beginning with ‘bre’:(gdb) info breakpoints

You can either press RET at this point, to run the info breakpoints command, or backspaceand enter something else, if ‘breakpoints’ does not look like the command you expected. (Ifyou were sure you wanted info breakpoints in the first place, you might as well just type
RET immediately after ‘info bre’, to exploit command abbreviations rather than commandcompletion).
If there is more than one possibility for the next word when you press TAB, gdb sounds abell. You can either supply more characters and try again, or just press TAB a second time;
gdb displays all the possible completions for that word. For example, you might want to
set a breakpoint on a subroutine whose name begins with ‘make_’, but when you type b
make_TAB gdb just sounds the bell. Typing TAB again displays all the function names inyour program that begin with those characters, for example:(gdb) b make_TAB
gdb sounds bell; press TAB again, to see:make_a_section_from_file
make_environ
make_abs_section
make_function_type
make_blockvector
make_pointer_type
make_cleanup
make_reference_type
make_command
make_symbol_completion_list(gdb) b make_

After displaying the available possibilities, gdb copies your partial input (‘b make_’ in theexample) so you can finish the command.
If the command you are trying to complete expects either a keyword or a number tofollow, then ‘NUMBER’ will be shown among the available completions, for example:(gdb) print -elements TABTABNUMBER
unlimited(gdb) print -elements

Here, the option expects a number (e.g., 100), not literal NUMBER. Such metasyntacticalarguments are always presented in uppercase.
If you just want to see the list of alternatives in the first place, you can press M-? rather
than pressing TAB twice. M-? means META ?. You can type this either by holding down akey designated as the META shift on your keyboard (if there is one) while typing ?, or as ESC
followed by ?.
If the number of possible completions is large, gdb will print as much of the list as it
has collected, as well as a message indicating that the list may be truncated.
(gdb) b mTABTAB
main<... the rest of the possible completions ...>*** List may be truncated, max-completions reached. ***(gdb) b m

This behavior can be controlled with the following commands:
set max-completions limit
set max-completions unlimited
Set the maximum number of completion candidates. gdb will stop looking for
more completions once it collects this many candidates. This is useful when26

Debugging with gdb

completing on things like function names as collecting all the possible candidates
can be time consuming. The default value is 200. A value of zero disables tabcompletion. Note that setting either no limit or a very large limit can makecompletion slow.
show max-completionsShow the maximum number of candidates that gdb will collect and show during
completion.
Sometimes the string you need, while logically a “word”, may contain parentheses orother characters that gdb normally excludes from its notion of a word. To permit word
completion to work in this situation, you may enclose words in ’ (single quote marks) in
gdb commands.
A likely situation where you might need this is in typing an expression that involves a
C++ symbol name with template parameters. This is because when completing expressions,
GDB treats the ‘<’ character as word delimiter, assuming that it’s the less-than comparison
operator (see Section 15.4.1.1 [C and C++ Operators], page 231).
For example, when you want to call a C++ template function interactively using theprint or call commands, you may need to distinguish whether you mean the versionof name that was specialized for int, name<int>(), or the version that was specialized for
float, name<float>(). To use the word-completion facilities in this situation, type a single
quote ’ at the beginning of the function name. This alerts gdb that it may need to consider
more information than usual when you press TAB or M-? to request word completion:(gdb) p ’func<M-?
func<int>()
func<float>()(gdb) p ’func<

When setting breakpoints however (see Section 9.2 [Location Specifications], page 126),
you don’t usually need to type a quote before the function name, because gdb understands
that you want to set a breakpoint on a function:(gdb) b func<M-?
func<int>()
func<float>()(gdb) b func<

This is true even in the case of typing the name of C++ overloaded functions (multiple
definitions of the same function, distinguished by argument type). For example, when you
want to set a breakpoint you don’t need to distinguish whether you mean the version ofname that takes an int parameter, name(int), or the version that takes a float parameter,
name(float).
(gdb) b bubble(M-?
bubble(int)bubble(double)(gdb) b bubble(douM-?
bubble(double)

See [quoting names], page 263, for a description of other scenarios that require quoting.
For more information about overloaded functions, see Section 15.4.1.3 [C++ Expressions],
page 234. You can use the command set overload-resolution off to disable overload
resolution; see Section 15.4.1.7 [gdb Features for C++], page 235.

Chapter 3: gdb Commands

27

When completing in an expression which looks up a field in a structure, gdb also tries1
to limit completions to the field names available in the type of the left-hand-side:(gdb) p gdb_stdout.M-?
magic
to_fputs
to_data
to_isatty
to_delete
to_putto_flush
to_readto_rewindto_writeto_write_async_safe

This is because the gdb_stdout is a variable of the type struct ui_file that is defined in
gdb sources as follows:
struct ui_file{
int *magic;
ui_file_flush_ftype *to_flush;
ui_file_write_ftype *to_write;
ui_file_write_async_safe_ftype *to_write_async_safe;
ui_file_fputs_ftype *to_fputs;
ui_file_read_ftype *to_read;
ui_file_delete_ftype *to_delete;
ui_file_isatty_ftype *to_isatty;
ui_file_rewind_ftype *to_rewind;ui_file_put_ftype *to_put;
void *to_data;}

3.4 Filenames As Command Arguments
When passing filenames (or directory names) as arguments to a command, if the filename
argument does not include any whitespace, double quotes, or single quotes, then for allcommands the filename can be written as a simple string, for example:(gdb) file /path/to/some/file

If the filename does include whitespace, double quotes, or single quotes, then gdb has
two approaches for how these filenames should be formatted; which format to use depends
on which command is being used.
Most gdb commands don’t require, or support, quoting and escaping. These commands
treat any text after the command name, that is not a command option (see Section 3.5 [Command Options], page 28), as the filename, even if the filename contains whitespace or quotecharacters. In the following example the user is adding /path/that contains/two spaces/to the auto-load safe-path (see [add-auto-load-safe-path], page 379):(gdb) add-auto-load-safe-path /path/that contains/two spaces/

A small number of commands require that filenames containing whitespace or quotecharacters are either quoted, or have the special characters escaped with a backslash. Commands that support this style are marked as such in the manual, any command not marked
as accepting quoting and escaping of its filename argument, does not accept this filename
argument style.
For example, to load the file /path/with spaces/to/a file with the file command(see Section 18.1 [Commands to Specify Files], page 291), you can escape the whitespacecharacters with a backslash:(gdb) file /path/with\ spaces/to/a\ file1

The completer can be confused by certain kinds of invalid expressions. Also, it only examines the static
type of the expression, not the dynamic type.

28

Debugging with gdb

Alternatively the entire filename can be wrapped in either single or double quotes, inwhich case no backlsashes are needed, for example:(gdb) symbol-file "/path/with spaces/to/a file"(gdb) exec-file ’/path/with spaces/to/a file’

It is possible to include a quote character within a quoted filename by escaping it witha backslash, for example, within a filename surrounded by double quotes, a double quotecharacter should be escaped with a backslash, but a single quote character should not be
escaped. Within a single quoted string a single quote character needs to be escaped, but adouble quote character does not.
A literal backslash character can also be included by escaping it with a backslash.

3.5 Command options
Some commands accept options starting with a leading dash. For example, print -pretty.
Similarly to command names, you can abbreviate a gdb option to the first few letters of
the option name, if that abbreviation is unambiguous, and you can also use the TAB key to
get gdb to fill out the rest of a word in an option (or to show you the alternatives available,
if there is more than one possibility).
Some commands take raw input as argument. For example, the print command processes
arbitrary expressions in any of the languages supported by gdb. With such commands,
because raw input may start with a leading dash that would be confused with an option
or any of its abbreviations, e.g. print -p (short for print -pretty or printing negativep?), if you specify any command option, then you must use a double-dash (--) delimiter toindicate the end of options.
Some options are described as accepting an argument which can be either on or off.
These are known as boolean options. Similarly to boolean settings commands—on and off
are the typical values, but any of 1, yes and enable can also be used as “true” value, andany of 0, no and disable can also be used as “false” value. You can also omit a “true”
value, as it is implied by default.
For example, these are equivalent:(gdb) print -object on -pretty off -element unlimited -- *myptr(gdb) p -o -p 0 -e u -- *myptr

You can discover the set of options some command accepts by completing on - after thecommand name. For example:(gdb) print -TABTAB-address-max-depth-array-memory-tag-violations-array-indexes-nibbles-elements-null-stop-object-pretty-raw-values-repeats-static-members-symbol-union-vtbl

Completion will in some cases guide you with a suggestion of what kind of argument an
option expects. For example:(gdb) print -elements TABTABNUMBER
unlimited

Here, the option expects a number (e.g., 100), not literal NUMBER. Such metasyntacticalarguments are always presented in uppercase.
(For more on using the print command, see Chapter 10 [Examining Data], page 141.)

Chapter 3: gdb Commands

29

3.6 Getting Help
You can always ask gdb itself for information on its commands, using the command help.
helphYou can use help (abbreviated h) with no arguments to display a short list ofnamed classes of commands:(gdb) help
List of classes of commands:
aliases -- User-defined aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without
stopping the programuser-defined -- User-defined commands
Type "help" followed by a class name for a list ofcommands in that class.
Type "help" followed by command name for fulldocumentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

help class
Using one of the general help classes as an argument, you can get a list of
the individual commands in that class. If a command has aliases, the aliases
are given after the command name, separated by commas. If an alias has
default arguments, the full definition of the alias is given after the first line.
For example, here is the help display for the class status:(gdb) help status
Status inquiries.
List of commands:
info, inf, i -- Generic command for showing things
about the program being debugged
info address, iamain -- Describe where symbol SYM is stored.
alias iamain = info address main
info all-registers -- List of all registers and their contents,
for selected stack frame.
...
show, info set -- Generic command for showing things
about the debugger
Type "help" followed by command name for fulldocumentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

30

Debugging with gdb

help commandWith a command name as help argument, gdb displays a short paragraph on
how to use that command. If that command has one or more aliases, gdb
will display a first line with the command name and all its aliases separated bycommas. This first line will be followed by the full definition of all aliases having
default arguments. When asking the help for an alias, the documentation for
the aliased command is shown.
A user-defined alias can optionally be documented using the document command (see Section 23.1.1 [Define], page 391). gdb then considers this alias asdifferent from the aliased command: this alias is not listed in the aliased command help output, and asking help for this alias will show the documentation
provided for the alias instead of the documentation of the aliased command.
apropos [-v] regexp
The apropos command searches through all of the gdb commands and aliases,
and their documentation, for the regular expression specified in args. It prints
out all matches found. The optional flag ‘-v’, which stands for ‘verbose’,
indicates to output the full documentation of the matching commands andhighlight the parts of the documentation matching regexp. For example:
apropos alias

results in:alias -- Define a new command that is an alias of an existing commandaliases -- User-defined aliases of other commands

while
apropos -v cut.*thread apply

results in the below output, where ‘cut for ’thread apply’ is highlighted if
styling is enabled.
taas -- Apply a command to all threads (ignoring errors
and empty output).
Usage: taas COMMAND
shortcut for ’thread apply all -s COMMAND’tfaas -- Apply a command to all frames of all threads(ignoring errors and empty output).
Usage: tfaas COMMAND
shortcut for ’thread apply all -s frame apply all -s COMMAND’complete args
The complete args command lists all the possible completions for the beginning of a command. Use args to specify the beginning of the command you
want completed. For example:
complete i

results in:if
ignoreinfo
inspect

This is intended for use by gnu Emacs.

Chapter 3: gdb Commands

31

In addition to help, you can use the gdb commands info and show to inquire about
the state of your program, or the state of gdb itself. Each command supports many topics
of inquiry; this manual introduces each of them in the appropriate context. The listings
under info and under show in the Command, Variable, and Function Index point to all the
sub-commands. See [Command and Variable Index], page 935.
infoThis command (abbreviated i) is for describing the state of your program. For
example, you can show the arguments passed to a function with info args,
list the registers currently in use with info registers, or list the breakpoints
you have set with info breakpoints. You can get a complete list of the info
sub-commands with help info.

set

You can assign the result of an expression to an environment variable with set.
For example, you can set the gdb prompt to a $-sign with set prompt $.

show

In contrast to info, show is for describing the state of gdb itself. You canchange most of the things you can show, by using the related command set;for example, you can control what number system is used for displays with set
radix, or simply inquire which is currently in use with show radix.
To display all the settable parameters and their current values, you can use
show with no arguments; you may also use info set. Both commands produce
the same display.

Here are several miscellaneous show subcommands, all of which are exceptional in lacking
corresponding set commands:
show version
Show what version of gdb is running. You should include this information in
gdb bug-reports. If multiple versions of gdb are in use at your site, you may
need to determine which version of gdb you are running; as gdb evolves, newcommands are introduced, and old ones may wither away. Also, many systemvendors ship variant versions of gdb, and there are variant versions of gdb in
gnu/Linux distributions as well. The version number is the same as the one
announced when you start gdb.
show copying
info copying
Display information about permission for copying gdb.
show warranty
info warranty
Display the gnu “NO WARRANTY” statement, or a warranty, if your version
of gdb comes with one.
show configuration
Display detailed information about the way gdb was configured when it was
built. This displays the optional arguments passed to the configure script
and also configuration parameters detected automatically by configure. Whenreporting a gdb bug (see Chapter 32 [GDB Bugs], page 709), it is important
to include this information in your report.

33

4 Running Programs Under gdb

When you run a program under gdb, you must first generate debugging information when
you compile it.
You may start gdb with its arguments, if any, in an environment of your choice. If you
are doing native debugging, you may redirect your program’s input and output, debug an
already running process, or kill a child process.

4.1 Compiling for Debugging
In order to debug a program effectively, you need to generate debugging information when
you compile it. This debugging information is stored in the object file; it describes the data
type of each variable or function and the correspondence between source line numbers andaddresses in the executable code.
To request debugging information, specify the ‘-g’ option when you run the compiler.
Programs that are to be shipped to your customers are compiled with optimizations,using the ‘-O’ compiler option. However, some compilers are unable to handle the ‘-g’ and‘-O’ options together. Using those compilers, you cannot generate optimized executables
containing debugging information.
gcc, the gnu C/C++ compiler, supports ‘-g’ with or without ‘-O’, making it possible
to debug optimized code. We recommend that you always use ‘-g’ whenever you compile
a program. You may think your program is correct, but there is no sense in pushing yourluck. For more information, see Chapter 11 [Optimized Code], page 195.
Older versions of the gnu C compiler permitted a variant option ‘-gg’ for debugging
information. gdb no longer supports this format; if your gnu C compiler has this option,
do not use it.
gdb knows about preprocessor macros and can show you their expansion (see Chapter 12[Macros], page 199). Most compilers do not include information about preprocessor macrosin the debugging information if you specify the -g flag alone. Version 3.1 and later of gcc,
the gnu C compiler, provides macro information if you are using the DWARF debugging
format, and specify the option -g3.
See Section “Options for Debugging Your Program or GCC” in Using the gnu Compiler
Collection (GCC), for more information on gcc options affecting debug information.
You will have the best debugging experience if you use the latest version of the DWARF
debugging format that your compiler supports. DWARF is currently the most expressive
and best supported debugging format in gdb.

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Debugging with gdb

4.2 Starting your Programrunr

Use the run command to start your program under gdb. You must first specify
the program name with an argument to gdb (see Chapter 2 [Getting In andOut of gdb], page 11), or by using the file or exec-file command (seeSection 18.1 [Commands to Specify Files], page 291).

If you are running your program in an execution environment that supports processes,
run creates an inferior process and makes that process run your program. In some environments without processes, run jumps to the start of your program. Other targets, like‘remote’, are always running. If you get an error message like this one:The "remote" target does not support "run".
Try "help target" or "continue".

then use continue to run your program. You may need load first (see [load], page 313).
The execution of a program is affected by certain information it receives from its superior.
gdb provides ways to specify this information, which you must do before starting yourprogram. (You can change it after starting your program, but such changes only affect yourprogram the next time you start it.) This information may be divided into four categories:
The arguments.
Specify the arguments to give your program as the arguments of the run command. If a shell is available on your target, the shell is used to pass the arguments, so that you may use normal conventions (such as wildcard expansion orvariable substitution) in describing the arguments. In Unix systems, you cancontrol which shell is used with the SHELL environment variable. If you do not
define SHELL, gdb uses the default shell (/bin/sh). You can disable use of any
shell with the set startup-with-shell command (see below for details).
The environment.
Your program normally inherits its environment from gdb, but you can use
the gdb commands set environment and unset environment to change partsof the environment that affect your program. See Section 4.4 [Your Program’s
Environment], page 38.
The working directory.
You can set your program’s working directory with the command set cwd. If
you do not set any working directory with this command, your program will
inherit gdb’s working directory if native debugging, or the remote server’s working directory if remote debugging. See Section 4.5 [Your Program’s Working
Directory], page 39.
The standard input and output.
Your program normally uses the same device for standard input and standard
output as gdb is using. You can redirect input and output in the run command
line, or you can use the tty command to set a different device for your program.
See Section 4.6 [Your Program’s Input and Output], page 40.

Chapter 4: Running Programs Under gdb

35

Warning: While input and output redirection work, you cannot use pipes topass the output of the program you are debugging to another program; if you
attempt this, gdb is likely to wind up debugging the wrong program.
When you issue the run command, your program begins to execute immediately. See
Chapter 5 [Stopping and Continuing], page 57, for discussion of how to arrange for yourprogram to stop. Once your program has stopped, you may call functions in your program,using the print or call commands. See Chapter 10 [Examining Data], page 141.
If the modification time of your symbol file has changed since the last time gdb read its
symbols, gdb discards its symbol table, and reads it again. When it does this, gdb tries toretain your current breakpoints.
start

The name of the main procedure can vary from language to language. With
C or C++, the main procedure name is always main, but other languages such
as Ada do not require a specific name for their main procedure. The debugger
provides a convenient way to start the execution of the program and to stop at
the beginning of the main procedure, depending on the language used.
The ‘start’ command does the equivalent of setting a temporary breakpointat the beginning of the main procedure and then invoking the ‘run’ command.
Some programs contain an elaboration phase where some startup code is executed before the main procedure is called. This depends on the languages used
to write your program. In C++, for instance, constructors for static and global
objects are executed before main is called. It is therefore possible that the
debugger stops before reaching the main procedure. However, the temporary
breakpoint will remain to halt execution.
Specify the arguments to give to your program as arguments to the ‘start’command. These arguments will be given verbatim to the underlying ‘run’command. Note that the same arguments will be reused if no argument isprovided during subsequent calls to ‘start’ or ‘run’.
It is sometimes necessary to debug the program during elaboration. In thesecases, using the start command would stop the execution of your program
too late, as the program would have already completed the elaboration phase.
Under these circumstances, either insert breakpoints in your elaboration code
before running your program or use the starti command.

startiThe ‘starti’ command does the equivalent of setting a temporary breakpointat the first instruction of a program’s execution and then invoking the ‘run’command. For programs containing an elaboration phase, the starti command
will stop execution at the start of the elaboration phase.

set exec-wrapper wrapper
show exec-wrapper
unset exec-wrapper
When ‘exec-wrapper’ is set, the specified wrapper is used to launch programsfor debugging. gdb starts your program with a shell command of the form exec
wrapper program. Quoting is added to program and its arguments, but not towrapper, so you should add quotes if appropriate for your shell. The wrapper
runs until it executes your program, and then gdb takes control.

36

Debugging with gdb

You can use any program that eventually calls execve with its arguments asa wrapper. Several standard Unix utilities do this, e.g. env and nohup. Any
Unix shell script ending with exec "$@" will also work.
For example, you can use env to pass an environment variable to the debugged
program, without setting the variable in your shell’s environment:(gdb) set exec-wrapper env ’LD_PRELOAD=libtest.so’(gdb) runThis command is available when debugging locally on most targets, excluding
djgpp, Cygwin, and MS Windows.
set startup-with-shell
set startup-with-shell on
set startup-with-shell off
show startup-with-shell
On Unix systems, by default, if a shell is available on your target, gdb) uses it
to start your program. Arguments of the run command are passed to the shell,
which does variable substitution, expands wildcard characters and performs
redirection of I/O. In some circumstances, it may be useful to disable such useof a shell, for example, when debugging the shell itself or diagnosing startup
failures such as:(gdb) runStarting program: ./a.out
During startup program terminated with signal SIGSEGV, Segmentation fault.

which indicates the shell or the wrapper specified with ‘exec-wrapper’ crashed,
not your program. Most often, this is caused by something odd in your shell’s
non-interactive mode initialization file—such as .cshrc for C-shell, $.zshenv
for the Z shell, or the file specified in the BASH_ENV environment variable for
BASH.
set auto-connect-native-target
set auto-connect-native-target on
set auto-connect-native-target off
show auto-connect-native-target
By default, if the current inferior is not connected to any target yet (e.g., withtarget remote), the run command starts your program as a native process
under gdb, on your local machine. If you’re sure you don’t want to debug programs on your local machine, you can tell gdb to not connect to the native target automatically with the set auto-connect-native-target off command.
If on, which is the default, and if the current inferior is not connected to atarget already, the run command automatically connects to the native target,
if one is available.
If off, and if the current inferior is not connected to a target already, the runcommand fails with an error:(gdb) runDon’t know how to run.

Try "help target".

If the current inferior is already connected to a target, gdb always uses it withthe run command.

Chapter 4: Running Programs Under gdb

37

In any case, you can explicitly connect to the native target with the target
native command. For example,(gdb) set auto-connect-native-target off(gdb) runDon’t know how to run. Try "help target".
(gdb) target native(gdb) runStarting program: ./a.out[Inferior 1 (process 10421) exited normally]

In case you connected explicitly to the native target, gdb remains connectedeven if all inferiors exit, ready for the next run command. Use the disconnect
command to disconnect.
Examples of other commands that likewise respect the auto-connect-nativetarget setting: attach, info proc, info os.
set disable-randomization
set disable-randomization on
This option (enabled by default in gdb) will turn off the native randomization of the virtual address space of the started program. This option is usefulfor multiple debugging sessions to make the execution better reproducible andmemory addresses reusable across debugging sessions.
This feature is implemented only on certain targets, including gnu/Linux. On
gnu/Linux you can get the same behavior using(gdb) set exec-wrapper setarch ‘uname -m‘ -R

set disable-randomization off
Leave the behavior of the started executable unchanged. Some bugs rear theirugly heads only when the program is loaded at certain addresses. If your bug
disappears when you run the program under gdb, that might be because gdb
by default disables the address randomization on platforms, such as gnu/Linux,
which do that for stand-alone programs. Use set disable-randomization off
to try to reproduce such elusive bugs.
On targets where it is available, virtual address space randomization protects
the programs against certain kinds of security attacks. In these cases the attacker needs to know the exact location of a concrete executable code. Randomizing its location makes it impossible to inject jumps misusing a code at its
expected addresses.
Prelinking shared libraries provides a startup performance advantage but it
makes addresses in these libraries predictable for privileged processes by having
just unprivileged access at the target system. Reading the shared library binary
gives enough information for assembling the malicious code misusing it. Stilleven a prelinked shared library can get loaded at a new random address justrequiring the regular relocation process during the startup. Shared libraries notalready prelinked are always loaded at a randomly chosen address.
Position independent executables (PIE) contain position independent code similar to the shared libraries and therefore such executables get loaded at a randomly chosen address upon startup. PIE executables always load even already38

Debugging with gdb

prelinked shared libraries at a random address. You can build such executableusing gcc -fPIE -pie.
Heap (malloc storage), stack and custom mmap areas are always placed randomly (as long as the randomization is enabled).
show disable-randomization
Show the current setting of the explicit disable of the native randomization of
the virtual address space of the started program.

4.3 Your Program’s Arguments
The arguments to your program can be specified by the arguments of the run command.
They are passed to a shell, which expands wildcard characters and performs redirection of
I/O, and thence to your program. Your SHELL environment variable (if it exists) specifies
what shell gdb uses. If you do not define SHELL, gdb uses the default shell (/bin/sh onUnix).
On non-Unix systems, the program is usually invoked directly by gdb, which emulates
I/O redirection via the appropriate system calls, and the wildcard characters are expandedby the startup code of the program, not by the shell.
run with no arguments uses the same arguments used by the previous run, or those set
by the set args command.
set args

Specify the arguments to be used the next time your program is run. If set
args has no arguments, run executes your program with no arguments. Onceyou have run your program with arguments, using set args before the next
run is the only way to run it again without arguments.

show args Show the arguments to give your program when it is started.

4.4 Your Program’s Environment
The environment consists of a set of environment variables and their values. Environment
variables conventionally record such things as your user name, your home directory, yourterminal type, and your search path for programs to run. Usually you set up environment
variables with the shell and they are inherited by all the other programs you run. Whendebugging, it can be useful to try running your program with a modified environment
without having to start gdb over again.
path directory
Add directory to the front of the PATH environment variable (the search pathfor executables) that will be passed to your program. The value of PATH usedby gdb does not change. You may specify several directory names, separated
by whitespace or by a system-dependent separator character (‘:’ on Unix, ‘;’
on MS-DOS and MS-Windows). If directory is already in the path, it is moved
to the front, so it is searched sooner.
You can use the string ‘$cwd’ to refer to whatever is the current working directory at the time gdb searches the path. If you use ‘.’ instead, it refers to thedirectory where you executed the path command. gdb replaces ‘.’ in the directory argument (with the current path) before adding directory to the searchpath.

Chapter 4: Running Programs Under gdb

39

show paths
Display the list of search paths for executables (the PATH environment variable).
show environment [varname]Print the value of environment variable varname to be given to your program
when it starts. If you do not supply varname, print the names and values ofall environment variables to be given to your program. You can abbreviate
environment as env.
set environment varname [=value]
Set environment variable varname to value. The value changes for your program (and the shell gdb uses to launch it), not for gdb itself. The value may be
any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The value parameter is optional;
if it is eliminated, the variable is set to a null value.
For example, this command:
set env USER = foo

tells the debugged program, when subsequently run, that its user is named‘foo’. (The spaces around ‘=’ are used for clarity here; they are not actuallyrequired.)
Note that on Unix systems, gdb runs your program via a shell, which also
inherits the environment set with set environment. If necessary, you can avoid
that by using the ‘env’ program as a wrapper instead of using set environment.
See [set exec-wrapper], page 35, for an example doing just that.
Environment variables that are set by the user are also transmitted
to gdbserver to be used when starting the remote inferior.
see[QEnvironmentHexEncoded], page 791.
unset environment varname
Remove variable varname from the environment to be passed to your program.
This is different from ‘set env varname =’; unset environment removes thevariable from the environment, rather than assigning it an empty value.
Environment variables that are unset by the user are also unset on gdbserverwhen starting the remote inferior. see [QEnvironmentUnset], page 791.
Warning: On Unix systems, gdb runs your program using the shell indicated by your
SHELL environment variable if it exists (or /bin/sh if not). If your SHELL variable names
a shell that runs an initialization file when started non-interactively—such as .cshrc for
C-shell, $.zshenv for the Z shell, or the file specified in the BASH_ENV environment variablefor BASH—any variables you set in that file affect your program. You may wish to movesetting of environment variables to files that are only run when you sign on, such as .login
or .profile.

4.5 Your Program’s Working Directory
Each time you start your program with run, the inferior will be initialized with the current
working directory specified by the set cwd command. If no directory has been specified bythis command, then the inferior will inherit gdb’s current working directory as its working

40

Debugging with gdb

directory if native debugging, or it will inherit the remote server’s current working directory
if remote debugging.
set cwd [directory]
Set the inferior’s working directory to directory, which will be glob-expanded
in order to resolve tildes (~). If no argument has been specified, the command
clears the setting and resets it to an empty state. This setting has no effect on
gdb’s working directory, and it only takes effect the next time you start theinferior. The ~ in directory is a short for the home directory, usually pointed
to by the HOME environment variable. On MS-Windows, if HOME is not defined,
gdb uses the concatenation of HOMEDRIVE and HOMEPATH as fallback.
You can also change gdb’s current working directory by using the cd command.
See [cd command], page 40.
show cwd

Show the inferior’s working directory. If no directory has been specified by set
cwd, then the default inferior’s working directory is the same as gdb’s working
directory.

cd [directory]
Set the gdb working directory to directory. If not given, directory uses ’~’.
The gdb working directory serves as a default for the commands that specify
files for gdb to operate on. See Section 18.1 [Commands to Specify Files],page 291. See [set cwd command], page 40.
pwd

Print the gdb working directory.

It is generally impossible to find the current working directory of the process being
debugged (since a program can change its directory during its run). If you work on a system
where gdb supports the info proc command (see Section 21.1.2 [Process Information],
page 337), you can use the info proc command to find out the current working directoryof the debuggee.

4.6 Your Program’s Input and Output
By default, the program you run under gdb does input and output to the same terminalthat gdb uses. gdb switches the terminal to its own terminal modes to interact with you,but it records the terminal modes your program was using and switches back to them when
you continue running your program.
info terminal
Displays information recorded by gdb about the terminal modes your programis using.
You can redirect your program’s input and/or output using shell redirection with the
run command. For example,
run > outfile

starts your program, diverting its output to the file outfile.
Another way to specify where your program should do input and output is with thetty command. This command accepts a file name as argument, and causes this file to beChapter 4: Running Programs Under gdb

41

the default for future run commands. It also resets the controlling terminal for the childprocess, for future run commands. For example,
tty /dev/ttyb

directs that processes started with subsequent run commands default to do input and output
on the terminal /dev/ttyb and have that as their controlling terminal.
An explicit redirection in run overrides the tty command’s effect on the input/output
device, but not its effect on the controlling terminal.
When you use the tty command or redirect input in the run command, only the input
for your program is affected. The input for gdb still comes from your terminal. tty is analias for set inferior-tty.
You can use the show inferior-tty command to tell gdb to display the name of theterminal that will be used for future runs of your program.
set inferior-tty [ tty ]Set the tty for the program being debugged to tty. Omitting tty restores thedefault behavior, which is to use the same terminal as gdb.
show inferior-tty
Show the current tty for the program being debugged.

4.7 Debugging an Already-running Processattach process-id
This command attaches to a running process—one that was started outside
gdb. (info files shows your active targets.) The command takes as argumenta process ID. The usual way to find out the process-id of a Unix process is withthe ps utility, or with the ‘jobs -l’ shell command.
attach does not repeat if you press RET a second time after executing thecommand.
To use attach, your program must be running in an environment which supports processes; for example, attach does not work for programs on bare-board targets that lack an
operating system. You must also have permission to send the process a signal.
When you use attach, the debugger finds the program running in the process first bylooking in the current working directory, then (if the program is not found) by using thesource file search path (see Section 9.5 [Specifying Source Directories], page 131). You canalso use the file command to load the program. See Section 18.1 [Commands to Specify
Files], page 291.
If the debugger can determine that the executable file running in the process it is attaching to does not match the current exec-file loaded by gdb, the option exec-file-mismatch
specifies how to handle the mismatch. gdb tries to compare the files by comparing theirbuild IDs (see [build ID], page 301), if available.
set exec-file-mismatch ‘ask|warn|off’
Whether to detect mismatch between the current executable file loaded by gdb
and the executable file used to start the process. If ‘ask’, the default, display awarning and ask the user whether to load the process executable file; if ‘warn’,just display a warning; if ‘off’, don’t attempt to detect a mismatch. If the user

42

Debugging with gdb

confirms loading the process executable file, then its symbols will be loaded aswell.
show exec-file-mismatch
Show the current value of exec-file-mismatch.
The first thing gdb does after arranging to debug the specified process is to stop it. You
can examine and modify an attached process with all the gdb commands that are ordinarily
available when you start processes with run. You can insert breakpoints; you can step andcontinue; you can modify storage. If you would rather the process continue running, you
may use the continue command after attaching gdb to the process.
detachWhen you have finished debugging the attached process, you can use the detachcommand to release it from gdb control. Detaching the process continues its
execution. After the detach command, that process and gdb become completely independent once more, and you are ready to attach another process
or start one with run. detach does not repeat if you press RET again after
executing the command.

If you exit gdb while you have an attached process, you detach that process. If you use
the run command, you kill that process. By default, gdb asks for confirmation if you try
to do either of these things; you can control whether or not you need to confirm by using
the set confirm command (see Section 22.9 [Optional Warnings and Messages], page 381).

4.8 Killing the Child Process
kill

Kill the child process in which your program is running under gdb.

This command is useful if you wish to debug a core dump instead of a running process.
gdb ignores any core dump file while your program is running.
On some operating systems, a program cannot be executed outside gdb while you havebreakpoints set on it inside gdb. You can use the kill command in this situation to permit
running your program outside the debugger.
The kill command is also useful if you wish to recompile and relink your program,
since on many systems it is impossible to modify an executable file while it is running in aprocess. In this case, when you next type run, gdb notices that the file has changed, andreads the symbol table again (while trying to preserve your current breakpoint settings).

4.9 Debugging Multiple Inferiors Connections and Programs
gdb lets you run and debug multiple programs in a single session. In addition, gdb onsome systems may let you run several programs simultaneously (otherwise you have to exitfrom one before starting another). On some systems gdb may even let you debug several
programs simultaneously on different remote systems. In the most general case, you canhave multiple threads of execution in each of multiple processes, launched from multiple
executables, running on different machines.
gdb represents the state of each program execution with an object called an inferior.
An inferior typically corresponds to a process, but is more general and applies also totargets that do not have processes. Inferiors may be created before a process runs, and mayChapter 4: Running Programs Under gdb

43

be retained after a process exits. Inferiors have unique identifiers that are different fromprocess ids. Usually each inferior will also have its own distinct address space, althoughsome embedded targets may have several inferiors running in different parts of a single
address space. Each inferior may in turn have multiple threads running in it.
The commands info inferiors and info connections, which will be introduced below,
accept a space-separated ID list as their argument specifying one or more elements on
which to operate. A list element can be either a single non-negative number, like ‘5’, or an
ascending range of such numbers, like ‘5-7’. A list can consist of any combination of suchelements, even duplicates or overlapping ranges are valid. E.g. ‘1 4-6 5 4-4’ or ‘1 2 4-7’.
To find out what inferiors exist at any moment, use info inferiors:
info inferiors
Print a list of all inferiors currently being managed by gdb. By default all
inferiors are printed, but the ID list id. . . can be used to limit the display tojust the requested inferiors.
gdb displays for each inferior (in this order):1. the inferior number assigned by gdb
2. the target system’s inferior identifier
3. the target connection the inferior is bound to, including the unique connection number assigned by gdb, and the protocol used by the connection.
4. the name of the executable the inferior is running.
An asterisk ‘*’ preceding the gdb inferior number indicates the current inferior.
For example,(gdb) info inferiors
Num Description* 1
process 3401
2
process 2307

Connection
1 (native)
2 (extended-remote host:10000)

Executable
goodbyehello

To get information about the current inferior, use inferior:inferior

Shows information about the current inferior.
For example,(gdb) inferior[Current inferior is 1 [process 3401] (helloworld)]

To find out what open target connections exist at any moment, use info connections:info connections
Print a list of all open target connections currently being managed by gdb. By
default all connections are printed, but the ID list id. . . can be used to limit
the display to just the requested connections.
gdb displays for each connection (in this order):1. the connection number assigned by gdb.
2. the protocol used by the connection.
3. a textual description of the protocol used by the connection.
An asterisk ‘*’ preceding the connection number indicates the connection of thecurrent inferior.
For example,

44

Debugging with gdb(gdb) info connections
Num What* 1
extended-remote host:10000
2
native3
core

Description
Extended remote serial target in gdb-specific protocol
Native process
Local core dump file

To switch focus between inferiors, use the inferior command:
inferior infno
Make inferior number infno the current inferior. The argument infno is the inferior number assigned by gdb, as shown in the first field of the ‘info inferiors’
display.
The debugger convenience variable ‘$_inferior’ contains the number of the current
inferior. You may find this useful in writing breakpoint conditional expressions, command
scripts, and so forth. See Section 10.12 [Convenience Variables], page 171, for general
information on convenience variables.
You can get multiple executables into a debugging session via the add-inferior andclone-inferior commands. On some systems gdb can add inferiors to the debug session
automatically by following calls to fork and exec. To remove inferiors from the debugging
session use the remove-inferiors command.
add-inferior [ -copies n ] [ -exec executable ] [-no-connection ]Adds n inferiors to be run using executable as the executable; n defaults to 1.
If no executable is specified, the inferiors begins empty, with no program. You
can still assign or change the program assigned to the inferior at any time byusing the file command with the executable name as its argument.
By default, the new inferior begins connected to the same target connection
as the current inferior. For example, if the current inferior was connected to
gdbserver with target remote, then the new inferior will be connected tothe same gdbserver instance. The ‘-no-connection’ option starts the newinferior with no connection yet. You can then for example use the target
remote command to connect to some other gdbserver instance, use run tospawn a local program, etc.
clone-inferior [ -copies n ] [ infno ]Adds n inferiors ready to execute the same program as inferior infno; n defaults
to 1, and infno defaults to the number of the current inferior. This commandcopies the values of the args, inferior-tty and cwd properties from the current
inferior to the new one. It also propagates changes the user made to environment variables using the set environment and unset environment commands.
This is a convenient command when you want to run another instance of theinferior you are debugging.
(gdb) info inferiors
Num Description* 1
process 29964(gdb) clone-inferior
Added inferior 2.
1 inferiors added.
(gdb) info inferiors
Num Description* 1
process 29964

Connection
1 (native)

Executable
helloworld

Connection
1 (native)

Executable
helloworldChapter 4: Running Programs Under gdb

2<null>

45

1 (native)

helloworld

You can now simply switch focus to inferior 2 and run it.
remove-inferiors infno...
Removes the inferior or inferiors infno . . . . It is not possible to remove an
inferior that is running with this command. For those, use the kill or detachcommand first.
To quit debugging one of the running inferiors that is not the current inferior, you
can either detach from it by using the detach inferior command (allowing it to run
independently), or kill it using the kill inferiors command:
detach inferior infno...
Detach from the inferior or inferiors identified by gdb inferior number(s)infno . . . . Note that the inferior’s entry still stays on the list of inferiors shownby info inferiors, but its Description will show ‘<null>’.
kill inferiors infno...
Kill the inferior or inferiors identified by gdb inferior number(s) infno . . . .
Note that the inferior’s entry still stays on the list of inferiors shown by info
inferiors, but its Description will show ‘<null>’.
After the successful completion of a command such as detach, detach inferiors, killor kill inferiors, or after a normal process exit, the inferior is still valid and listed with
info inferiors, ready to be restarted.
To be notified when inferiors are started or exit under gdb’s control use
set print inferior-events:
set print inferior-events
set print inferior-events on
set print inferior-events off
The set print inferior-events command allows you to enable or disable
printing of messages when gdb notices that new inferiors have started or thatinferiors have exited or have been detached. By default, these messages will be
printed.
show print inferior-eventsShow whether messages will be printed when gdb detects that inferiors havestarted, exited or have been detached.
Many commands will work the same with multiple programs as with a single program:e.g., print myglobal will simply display the value of myglobal in the current inferior.
Occasionally, when debugging gdb itself, it may be useful to get more info about therelationship of inferiors, programs, address spaces in a debug session. You can do that withthe maint info program-spaces command.
maint info program-spaces
Print a list of all program spaces currently being managed by gdb.
gdb displays for each program space (in this order):1. the program space number assigned by gdb

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Debugging with gdb

2. the name of the executable loaded into the program space, with e.g., thefile command.
3. the name of the core file loaded into the program space, with e.g., thecore-file command.
An asterisk ‘*’ preceding the gdb program space number indicates the current
program space.
In addition, below each program space line, gdb prints extra information that
isn’t suitable to display in tabular form. For example, the list of inferiors boundto the program space.
(gdb) maint info program-spaces
Id
Executable
Core File
* 1
hello
2
goodbyeBound inferiors: ID 1 (process 21561)

Here we can see that no inferior is running the program hello, while process
21561 is running the program goodbye. On some targets, it is possible thatmultiple inferiors are bound to the same program space. The most common
example is that of debugging both the parent and child processes of a vfork
call. For example,(gdb) maint info program-spaces
Id
Executable
Core File* 1
vfork-test
Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)

Here, both inferior 2 and inferior 1 are running in the same program space asa result of inferior 1 having executed a vfork call.

4.9.1 Inferior-Specific Breakpoints
When debugging multiple inferiors, you can choose whether to set breakpoints for all inferiors, or for a particular inferior.
break locspec inferior inferior-id
break locspec inferior inferior-id if ...
locspec specifies a code location or locations in your program. See Section 9.2[Location Specifications], page 126, for details.
Use the qualifier ‘inferior inferior-id’ with a breakpoint command to specify that you only want gdb to stop when a particular inferior reaches this breakpoint. The inferior-id specifier is one of the inferior identifiers assigned by gdb,
shown in the first column of the ‘info inferiors’ output.
If you do not specify ‘inferior inferior-id’ when you set a breakpoint, thebreakpoint applies to all inferiors of your program.
You can use the inferior qualifier on conditional breakpoints as well; in thiscase, place ‘inferior inferior-id’ before or after the breakpoint condition,
like this:(gdb) break frik.c:13 inferior 2 if bartab > lim

Inferior-specific breakpoints are automatically deleted when the corresponding inferior
is removed from gdb. For example:(gdb) remove-inferiors 2

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Inferior-specific breakpoint 3 deleted - inferior 2 has been removed.

A breakpoint can’t be both inferior-specific and thread-specific (see Section 5.5.4[Thread-Specific Breakpoints], page 96), or task-specific (see Section 15.4.10.7 [Ada Tasks],
page 255); using more than one of the inferior, thread, or task keywords when creatinga breakpoint will give an error.

4.10 Debugging Programs with Multiple Threads
In some operating systems, such as GNU/Linux and Solaris, a single program may have morethan one thread of execution. The precise semantics of threads differ from one operating
system to another, but in general the threads of a single program are akin to multiple
processes—except that they share one address space (that is, they can all examine andmodify the same variables). On the other hand, each thread has its own registers andexecution stack, and perhaps private memory.
gdb provides these facilities for debugging multi-thread programs:• automatic notification of new threads• ‘thread thread-id’, a command to switch among threads• ‘info threads’, a command to inquire about existing threads• ‘thread apply [thread-id-list | all] args’, a command to apply a command to alist of threads• thread-specific breakpoints• ‘set print thread-events’, which controls printing of messages on thread start andexit.
• ‘set libthread-db-search-path path’, which lets the user specify which libthread_db to use if the default choice isn’t compatible with the program.
The gdb thread debugging facility allows you to observe all threads while your program
runs—but whenever gdb takes control, one thread in particular is always the focus of
debugging. This thread is called the current thread. Debugging commands show program
information from the perspective of the current thread.
Whenever gdb detects a new thread in your program, it displays the target system’s
identification for the thread with a message in the form ‘[New systag]’, where systag is athread identifier whose form varies depending on the particular system. For example, on
gnu/Linux, you might see[New Thread 0x41e02940 (LWP 25582)]

when gdb notices a new thread. In contrast, on other systems, the systag is simply something like ‘process 368’, with no further qualifier.
For debugging purposes, gdb associates its own thread number —always a single
integer—with each thread of an inferior. This number is unique between all threads of aninferior, but not unique between threads of different inferiors.
You can refer to a given thread in an inferior using the qualified inferior-num.thread-num
syntax, also known as qualified thread ID, with inferior-num being the inferior number andthread-num being the thread number of the given inferior. For example, thread 2.3 refers
to thread number 3 of inferior 2. If you omit inferior-num (e.g., thread 3), then gdb infers
you’re referring to a thread of the current inferior.

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Until you create a second inferior, gdb does not show the inferior-num part of threadIDs, even though you can always use the full inferior-num.thread-num form to refer tothreads of inferior 1, the initial inferior.
Some commands accept a space-separated thread ID list as argument. A list element
can be:1. A thread ID as shown in the first field of the ‘info threads’ display, with or without
an inferior qualifier. E.g., ‘2.1’ or ‘1’.
2. A range of thread numbers, again with or without an inferior qualifier, as in inf.thr1thr2 or thr1-thr2. E.g., ‘1.2-4’ or ‘2-4’.
3. All threads of an inferior, specified with a star wildcard, with or without an inferior
qualifier, as in inf.* (e.g., ‘1.*’) or *. The former refers to all threads of the given
inferior, and the latter form without an inferior qualifier refers to all threads of thecurrent inferior.
For example, if the current inferior is 1, and inferior 7 has one thread with ID 7.1, thethread list ‘1 2-3 4.5 6.7-9 7.*’ includes threads 1 to 3 of inferior 1, thread 5 of inferior
4, threads 7 to 9 of inferior 6 and all threads of inferior 7. That is, in expanded qualified
form, the same as ‘1.1 1.2 1.3 4.5 6.7 6.8 6.9 7.1’.
In addition to a per-inferior number, each thread is also assigned a unique global number,also known as global thread ID, a single integer. Unlike the thread number component of
the thread ID, no two threads have the same global ID, even when you’re debugging multiple
inferiors.
From gdb’s perspective, a process always has at least one thread. In other words,
gdb assigns a thread number to the program’s “main thread” even if the program is not
multi-threaded.
The debugger convenience variables ‘$_thread’ and ‘$_gthread’ contain, respectively,
the per-inferior thread number and the global thread number of the current thread. You
may find this useful in writing breakpoint conditional expressions, command scripts, and soforth. The convenience variable ‘$_inferior_thread_count’ contains the number of live
threads in the current inferior. See Section 10.12 [Convenience Variables], page 171, forgeneral information on convenience variables.
When running in non-stop mode (see Section 5.5.2 [Non-Stop Mode], page 94), where new
threads can be created, and existing threads exit, at any time, ‘$_inferior_thread_count’
could return a different value each time it is evaluated.
If gdb detects the program is multi-threaded, it augments the usual message about
stopping at a breakpoint with the ID and name of the thread that hit the breakpoint.
Thread 2 "client" hit Breakpoint 1, send_message () at client.c:68

Likewise when the program receives a signal:
Thread 1 "main" received signal SIGINT, Interrupt.

info threads [-gid] [thread-id-list]
Display information about one or more threads. With no arguments displays
information about all threads. You can specify the list of threads that you want
to display using the thread ID list syntax (see [thread ID lists], page 48).
gdb displays for each thread (in this order):1. the per-inferior thread number assigned by gdb

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49

2. the global thread number assigned by gdb, if the ‘-gid’ option was specified
3. the target system’s thread identifier (systag)
4. the thread’s name, if one is known. A thread can either be named by theuser (see thread name, below), or, in some cases, by the program itself.
5. the current stack frame summary for that thread
An asterisk ‘*’ to the left of the gdb thread number indicates the current thread.
For example,(gdb) info threads
Id
Target Id* 1
process 35 thread 13
2
process 35 thread 23
3
process 35 thread 27
at threadtest.c:68

Frame
main (argc=1, argv=0x7ffffff8)
0x34e5 in sigpause ()0x34e5 in sigpause ()If you’re debugging multiple inferiors, gdb displays thread IDs using the qualified
inferior-num.thread-num format. Otherwise, only thread-num is shown.
If you specify the ‘-gid’ option, gdb displays a column indicating each thread’s global
thread ID:(gdb) info threads
Id
GId Target Id
1.1 1
process 35 thread 13
1.2 3
process 35 thread 23
1.3 4
process 35 thread 27* 2.1 2
process 65 thread 1

Frame
main (argc=1, argv=0x7ffffff8)
0x34e5 in sigpause ()0x34e5 in sigpause ()main (argc=1, argv=0x7ffffff8)

On Solaris, you can display more information about user threads with a Solaris-specificcommand:maint info sol-threads
Display info on Solaris user threads.
thread thread-id
Make thread ID thread-id the current thread. The command argument threadid is the gdb thread ID, as shown in the first field of the ‘info threads’ display,with or without an inferior qualifier (e.g., ‘2.1’ or ‘1’).
gdb responds by displaying the system identifier of the thread you selected,
and its current stack frame summary:(gdb) thread 2[Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))]#0 some_function (ignore=0x0) at example.c:8
8
printf ("hello\n");As with the ‘[New ...]’ message, the form of the text after ‘Switching to’depends on your system’s conventions for identifying threads.
thread apply [thread-id-list | all [-ascending]] [flag]... command
The thread apply command allows you to apply the named command to one
or more threads. Specify the threads that you want affected using the thread
ID list syntax (see [thread ID lists], page 48), or specify all to apply to all
threads. To apply a command to all threads in descending order, type thread
apply all command. To apply a command to all threads in ascending order,
type thread apply all -ascending command.

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Debugging with gdb

The flag arguments control what output to produce and how to handle errors
raised when applying command to a thread. flag must start with a - directly
followed by one letter in qcs. If several flags are provided, they must be given
individually, such as -c -q.
By default, gdb displays some thread information before the output producedby command, and an error raised during the execution of a command will abort
thread apply. The following flags can be used to fine-tune this behavior:-c

The flag -c, which stands for ‘continue’, causes any errors in command to be displayed, and the execution of thread apply thencontinues.

-s

The flag -s, which stands for ‘silent’, causes any errors or empty
output produced by a command to be silently ignored. That is, theexecution continues, but the thread information and errors are notprinted.

-q

The flag -q (‘quiet’) disables printing the thread information.

Flags -c and -s cannot be used together.
taas [option]... command
Shortcut for thread apply all -s [option]... command. Applies commandon all threads, ignoring errors and empty output.
The taas command accepts the same options as the thread apply all command. See [thread apply all], page 49.
tfaas [option]... command
Shortcutforthread apply all -s -- frame apply all -s [option]...
command. Applies command on all frames of all threads, ignoring errors andempty output. Note that the flag -s is specified twice: The first -s ensuresthat thread apply only shows the thread information of the threads for whichframe apply produces some output. The second -s is needed to ensure thatframe apply shows the frame information of a frame only if the command
successfully produced some output.
It can for example be used to print a local variable or a function argument
without knowing the thread or frame where this variable or argument is, using:(gdb) tfaas p some_local_var_i_do_not_remember_where_it_is

The tfaas command accepts the same options as the frame apply command.
See Section 8.5 [frame apply], page 120.
thread name [name]
This command assigns a name to the current thread. If no argument is given,
any existing user-specified name is removed. The thread name appears in the‘info threads’ display.
On some systems, such as gnu/Linux, gdb is able to determine the name of
the thread as given by the OS. On these systems, a name specified with ‘thread
name’ will override the system-give name, and removing the user-specified namewill cause gdb to once again display the system-specified name.

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51

thread find [regexp]
Search for and display thread ids whose name or systag matches the supplied
regular expression.
As well as being the complement to the ‘thread name’ command, this commandalso allows you to identify a thread by its target systag. For instance, on
gnu/Linux, the target systag is the LWP id.
(gdb) thread find 26688
Thread 4 has target id ’Thread 0x41e02940 (LWP 26688)’(gdb) info thread 4
Id
Target Id
Frame
4
Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()set print thread-events
set print thread-events on
set print thread-events off
The set print thread-events command allows you to enable or disable printing of messages when gdb notices that new threads have started or that threads
have exited. By default, these messages will be printed if detection of these
events is supported by the target. Note that these messages cannot be disabledon all targets.
show print thread-eventsShow whether messages will be printed when gdb detects that threads havestarted and exited.
See Section 5.5 [Stopping and Starting Multi-thread Programs], page 92, for more information about how gdb behaves when you stop and start programs with multiple threads.
See Section 5.1.2 [Setting Watchpoints], page 66, for information about watchpoints inprograms with multiple threads.
set libthread-db-search-path [path]
If this variable is set, path is a colon-separated list of directories gdb will use
to search for libthread_db. If you omit path, ‘libthread-db-search-path’
will be reset to its default value ($sdir:$pdir on gnu/Linux and Solaris systems). Internally, the default value comes from the LIBTHREAD_DB_SEARCH_
PATH macro.
On gnu/Linux and Solaris systems, gdb uses a “helper” libthread_db library to obtain information about threads in the inferior process. gdb will use‘libthread-db-search-path’ to find libthread_db. gdb also consults first if
inferior specific thread debugging library loading is enabled by ‘set auto-load
libthread-db’ (see Section 22.8.2 [libthread db.so.1 file], page 378).
A special entry ‘$sdir’ for ‘libthread-db-search-path’ refers to the default
system directories that are normally searched for loading shared libraries. The‘$sdir’ entry is the only kind not needing to be enabled by ‘set auto-load
libthread-db’ (see Section 22.8.2 [libthread db.so.1 file], page 378).
A special entry ‘$pdir’ for ‘libthread-db-search-path’ refers to the directoryfrom which libpthread was loaded in the inferior process.
For any libthread_db library gdb finds in above directories, gdb attempts
to initialize it with the current inferior process. If this initialization fails

52

Debugging with gdb(which could happen because of a version mismatch between libthread_db
and libpthread), gdb will unload libthread_db, and continue with the next
directory. If none of libthread_db libraries initialize successfully, gdb will
issue a warning and thread debugging will be disabled.
Setting libthread-db-search-path is currently implemented only on some
platforms.
show libthread-db-search-path
Display current libthread db search path.
set debug libthread-db
show debug libthread-db
Turns on or off display of libthread_db-related events. Use 1 to enable, 0 to
disable.
set debug threads [on|off]show debug threads
When ‘on’ gdb will print additional messages when threads are created anddeleted.

4.11 Debugging Forks
On most systems, gdb has no special support for debugging programs which create additional processes using the fork function. When a program forks, gdb will continue to debug
the parent process and the child process will run unimpeded. If you have set a breakpoint
in any code which the child then executes, the child will get a SIGTRAP signal which (unless
it catches the signal) will cause it to terminate.
However, if you want to debug the child process there is a workaround which isn’t too
painful. Put a call to sleep in the code which the child process executes after the fork. It
may be useful to sleep only if a certain environment variable is set, or a certain file exists,
so that the delay need not occur when you don’t want to run gdb on the child. While thechild is sleeping, use the ps program to get its process ID. Then tell gdb (a new invocationof gdb if you are also debugging the parent process) to attach to the child process (seeSection 4.7 [Attach], page 41). From that point on you can debug the child process just likeany other process which you attached to.
On some systems, gdb provides support for debugging programs that create additional
processes using the fork or vfork functions. On gnu/Linux platforms, this feature is
supported with kernel version 2.5.46 and later.
The fork debugging commands are supported in native mode and when connected to
gdbserver in either target remote mode or target extended-remote mode.
By default, when a program forks, gdb will continue to debug the parent process andthe child process will run unimpeded.
If you want to follow the child process instead of the parent process, use the commandset follow-fork-mode.
set follow-fork-mode mode
Set the debugger response to a program call of fork or vfork. A call to fork
or vfork creates a new process. The mode argument can be:Chapter 4: Running Programs Under gdb

53

parentThe original process is debugged after a fork. The child process
runs unimpeded. This is the default.

child

The new process is debugged after a fork. The parent process runs
unimpeded.

show follow-fork-mode
Display the current debugger response to a fork or vfork call.
On Linux, if you want to debug both the parent and child processes, use the commandset detach-on-fork.
set detach-on-fork mode
Tells gdb whether to detach one of the processes after a fork, or retain debugger
control over them both.
on

The child process (or parent process, depending on the value offollow-fork-mode) will be detached and allowed to run independently. This is the default.

offBoth processes will be held under the control of gdb. One process(child or parent, depending on the value of follow-fork-mode) is
debugged as usual, while the other is held suspended.

show detach-on-fork
Show whether detach-on-fork mode is on/off.
If you choose to set ‘detach-on-fork’ mode off, then gdb will retain control of all forked
processes (including nested forks). You can list the forked processes under the control of
gdb by using the info inferiors command, and switch from one fork to another by using
the inferior command (see Section 4.9 [Debugging Multiple Inferiors Connections andPrograms], page 42).
To quit debugging one of the forked processes, you can either detach from it by using
the detach inferiors command (allowing it to run independently), or kill it using thekill inferiors command. See Section 4.9 [Debugging Multiple Inferiors Connections andPrograms], page 42.
If you ask to debug a child process and a vfork is followed by an exec, gdb executes
the new target up to the first breakpoint in the new target. If you have a breakpoint set on
main in your original program, the breakpoint will also be set on the child process’s main.
On some systems, when a child process is spawned by vfork, you cannot debug the childor parent until an exec call completes.
If you issue a run command to gdb after an exec call executes, the new target restarts.
To restart the parent process, use the file command with the parent executable nameas its argument. By default, after an exec call executes, gdb discards the symbols of theprevious executable image. You can change this behaviour with the set follow-exec-mode
command.
set follow-exec-mode mode
Set debugger response to a program call of exec. An exec call replaces the
program image of a process.

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Debugging with gdb

follow-exec-mode can be:
newgdb creates a new inferior and rebinds the process to this new
inferior. The program the process was running before the exec call
can be restarted afterwards by restarting the original inferior.
For example:(gdb) info inferiors(gdb) info inferior
Id
Description
Executable* 1<null>
prog1(gdb) runprocess 12020 is executing new program: prog2
Program exited normally.
(gdb) info inferiors
Id
Description
Executable
1<null>
prog1* 2<null>
prog2

same

gdb keeps the process bound to the same inferior. The new executable image replaces the previous executable loaded in the inferior. Restarting the inferior after the exec call, with e.g., the runcommand, restarts the executable the process was running after theexec call. This is the default mode.
For example:(gdb) info inferiors
Id
Description
Executable* 1<null>
prog1(gdb) runprocess 12020 is executing new program: prog2
Program exited normally.
(gdb) info inferiors
Id
Description
Executable* 1<null>
prog2

follow-exec-mode is supported in native mode and target extended-remote mode.
You can use the catch command to make gdb stop whenever a fork, vfork, or exec
call is made. See Section 5.1.3 [Setting Catchpoints], page 69.

4.12 Setting a Bookmark to Return to Later
On certain operating systems1 , gdb is able to save a snapshot of a program’s state, calleda checkpoint, and come back to it later.
Returning to a checkpoint effectively undoes everything that has happened in the program since the checkpoint was saved. This includes changes in memory, registers, and even(within some limits) system state. Effectively, it is like going back in time to the moment
when the checkpoint was saved.
Thus, if you’re stepping through a program and you think you’re getting close to thepoint where things go wrong, you can save a checkpoint. Then, if you accidentally go too
far and miss the critical statement, instead of having to restart your program from the
beginning, you can just go back to the checkpoint and start again from there.
1

Currently, only gnu/Linux.

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55

This can be especially useful if it takes a lot of time or steps to reach the point where
you think the bug occurs.
To use the checkpoint/restart method of debugging:checkpoint
Save a snapshot of the debugged program’s current execution state. The
checkpoint command takes no arguments, but each checkpoint is assigned
a small integer id, similar to a breakpoint id.
info checkpoints
List the checkpoints that have been saved in the current debugging session. For
each checkpoint, the following information will be listed:
Checkpoint ID
Process ID
Code Address
Source line, or label
restart checkpoint-id
Restore the program state that was saved as checkpoint number checkpoint-id.
All program variables, registers, stack frames etc. will be returned to the values
that they had when the checkpoint was saved. In essence, gdb will “wind backthe clock” to the point in time when the checkpoint was saved.
Note that breakpoints, gdb variables, command history etc. are not affectedby restoring a checkpoint. In general, a checkpoint only restores things that
reside in the program being debugged, not in the debugger.
delete checkpoint checkpoint-id
Delete the previously-saved checkpoint identified by checkpoint-id.
Returning to a previously saved checkpoint will restore the user state of the program
being debugged, plus a significant subset of the system (OS) state, including file pointers. It
won’t “un-write” data from a file, but it will rewind the file pointer to the previous location,
so that the previously written data can be overwritten. For files opened in read mode, thepointer will also be restored so that the previously read data can be read again.
Of course, characters that have been sent to a printer (or other external device) cannot
be “snatched back”, and characters received from eg. a serial device can be removed frominternal program buffers, but they cannot be “pushed back” into the serial pipeline, readyto be received again. Similarly, the actual contents of files that have been changed cannot
be restored (at this time).
However, within those constraints, you actually can “rewind” your program to a previously saved point in time, and begin debugging it again — and you can change the courseof events so as to debug a different execution path this time.
Finally, there is one bit of internal program state that will be different when you return
to a checkpoint — the program’s process id. Each checkpoint will have a unique process id(or pid), and each will be different from the program’s original pid. If your program has
saved a local copy of its process id, this could potentially pose a problem.

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4.12.1 A Non-obvious Benefit of Using Checkpoints
On some systems such as gnu/Linux, address space randomization is performed on newprocesses for security reasons. This makes it difficult or impossible to set a breakpoint, or
watchpoint, on an absolute address if you have to restart the program, since the absolute
location of a symbol will change from one execution to the next.
A checkpoint, however, is an identical copy of a process. Therefore if you create acheckpoint at (eg.) the start of main, and simply return to that checkpoint instead ofrestarting the process, you can avoid the effects of address randomization and your symbols
will all stay in the same place.

57

5 Stopping and Continuing
The principal purposes of using a debugger are so that you can stop your program before it
terminates; or so that, if your program runs into trouble, you can investigate and find out
why.
Inside gdb, your program may stop for any of several reasons, such as a signal, a breakpoint, or reaching a new line after a gdb command such as step. You may then examineand change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by gdb provide ample explanation of the status of yourprogram—but you can also explicitly request this information at any time.
info program
Display information about the status of your program: whether it is runningor not, what process it is, and why it stopped.

5.1 Breakpoints, Watchpoints, and Catchpoints
A breakpoint makes your program stop whenever a certain point in the program is reached.
For each breakpoint, you can add conditions to control in finer detail whether your program
stops. You can set breakpoints with the break command and its variants (see Section 5.1.1[Setting Breakpoints], page 58), to specify the place where your program should stop byline number, function name or exact address in the program.
On some systems, you can set breakpoints in shared libraries before the executable isrun.
A watchpoint is a special breakpoint that stops your program when the value of an
expression changes. The expression may be a value of a variable, or it could involve valuesof one or more variables combined by operators, such as ‘a + b’. This is sometimes called
data breakpoints. You must use a different command to set watchpoints (see Section 5.1.2[Setting Watchpoints], page 66), but aside from that, you can manage a watchpoint like anyother breakpoint: you enable, disable, and delete both breakpoints and watchpoints using
the same commands.
You can arrange to have values from your program displayed automatically whenever
gdb stops at a breakpoint. See Section 10.8 [Automatic Display], page 155.
A catchpoint is another special breakpoint that stops your program when a certain kindof event occurs, such as the throwing of a C++ exception or the loading of a library. As withwatchpoints, you use a different command to set a catchpoint (see Section 5.1.3 [Setting
Catchpoints], page 69), but aside from that, you can manage a catchpoint like any otherbreakpoint. (To stop when your program receives a signal, use the handle command; see
Section 5.4 [Signals], page 89.)gdb assigns a number to each breakpoint, watchpoint, or catchpoint when you create
it; these numbers are successive integers starting with one. In many of the commands forcontrolling various features of breakpoints you use the breakpoint number to say which
breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled,
it has no effect on your program until you enable it again.
Some gdb commands accept a space-separated list of breakpoints on which to operate.
A list element can be either a single breakpoint number, like ‘5’, or a range of such numbers,

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Debugging with gdb

like ‘5-7’. When a breakpoint list is given to a command, all breakpoints in that list areoperated on.

5.1.1 Setting Breakpoints
Breakpoints are set with the break command (abbreviated b). The debugger conveniencevariable ‘$bpnum’ records the number of the breakpoint you’ve set most recently:(gdb) b main
Breakpoint 1 at 0x11c6: file zeoes.c, line 24.
(gdb) p $bpnum$1 = 1

A breakpoint may be mapped to multiple code locations for example with inlined functions, Ada generics, C++ templates or overloaded function names. gdb then indicates thenumber of code locations in the breakpoint command output:(gdb) b some_func
Breakpoint 2 at 0x1179: some_func. (3 locations)(gdb) p $bpnum$2 = 2(gdb)

When your program stops on a breakpoint, the convenience variables ‘$_hit_bpnum’ and‘$_hit_locno’ are respectively set to the number of the encountered breakpoint and thenumber of the breakpoint’s code location:
Thread 1 "zeoes" hit Breakpoint 2.1, some_func () at zeoes.c:8
8
printf("some func\n");(gdb) p $_hit_bpnum$5 = 2(gdb) p $_hit_locno$6 = 1(gdb)

Note that ‘$_hit_bpnum’ and ‘$bpnum’ are not equivalent: ‘$_hit_bpnum’ is set to thebreakpoint number last hit, while ‘$bpnum’ is set to the breakpoint number last set.
If the encountered breakpoint has only one code location, ‘$_hit_locno’ is set to 1:
Breakpoint 1, main (argc=1, argv=0x7fffffffe018) at zeoes.c:24
24
if (argc > 1)(gdb) p $_hit_bpnum$3 = 1(gdb) p $_hit_locno$4 = 1(gdb)

The ‘$_hit_bpnum’ and ‘$_hit_locno’ variables can typically be used in a breakpointcommand list. (see Section 5.1.7 [Breakpoint Command Lists], page 77). For example, as part of the breakpoint command list, you can disable completely the encountered breakpoint using disable $_hit_bpnum or disable the specific encountered breakpoint location using disable $_hit_bpnum.$_hit_locno. If a breakpoint has only one
location, ‘$_hit_locno’ is set to 1 and the commands disable $_hit_bpnum and disable$_hit_bpnum.$_hit_locno both disable the breakpoint.
You can also define aliases to easily disable the last hit location or last hit breakpoint:(gdb) alias lld = disable $_hit_bpnum.$_hit_locno(gdb) alias lbd = disable $_hit_bpnum

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break locspec
Set a breakpoint at all the code locations in your program that result from resolving the given locspec. locspec can specify a function name, a line number,an address of an instruction, and more. See Section 9.2 [Location Specifications], page 126, for the various forms of locspec. The breakpoint will stop
your program just before it executes the instruction at the address of any ofthe breakpoint’s code locations.
When using source languages that permit overloading of symbols, such as C++,a function name may refer to more than one symbol, and thus more than one
place to break. See Section 10.2 [Ambiguous Expressions], page 146, for a
discussion of that situation.
It is also possible to insert a breakpoint that will stop the program only if
a specific thread (see Section 5.5.4 [Thread-Specific Breakpoints], page 96),
specific inferior (see Section 4.9.1 [Inferior-Specific Breakpoints], page 46), or a
specific task (see Section 15.4.10.7 [Ada Tasks], page 255) hits that breakpoint.
break

When called without any arguments, break sets a breakpoint at the next instruction to be executed in the selected stack frame (see Chapter 8 [Examining
the Stack], page 113). In any selected frame but the innermost, this makes
your program stop as soon as control returns to that frame. This is similar to
the effect of a finish command in the frame inside the selected frame—exceptthat finish does not leave an active breakpoint. If you use break without
an argument in the innermost frame, gdb stops the next time it reaches thecurrent location; this may be useful inside loops.
gdb normally ignores breakpoints when it resumes execution, until at least one
instruction has been executed. If it did not do this, you would be unable to proceed past a breakpoint without first disabling the breakpoint. This rule applies
whether or not the breakpoint already existed when your program stopped.

break ... if cond
Set a breakpoint with condition cond; evaluate the expression cond each time
the breakpoint is reached, and stop only if the value is nonzero—that is, if condevaluates as true. ‘...’ stands for one of the possible arguments describedabove (or no argument) specifying where to break. See Section 5.1.6 [Break
Conditions], page 76, for more information on breakpoint conditions.
The breakpoint may be mapped to multiple locations. If the breakpoint condition cond is invalid at some but not all of the locations, the locations for which
the condition is invalid are disabled. For example, gdb reports below that twoof the three locations are disabled.
(gdb) break func if a == 10
warning: failed to validate condition at location 0x11ce, disabling:
No symbol "a" in current context.
warning: failed to validate condition at location 0x11b6, disabling:
No symbol "a" in current context.
Breakpoint 1 at 0x11b6: func. (3 locations)

Locations that are disabled because of the condition are denoted by an uppercase N in the output of the info breakpoints command:(gdb) info breakpoints

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Debugging with gdb

Num
1

Type
Disp Enb AddressWhat
breakpoint
keep y<MULTIPLE>
stop only if a == 10
1.1
N* 0x00000000000011b6 in ...
1.2
y0x00000000000011c2 in ...
1.3
N* 0x00000000000011ce in ...
(*): Breakpoint condition is invalid at this location.

If the breakpoint condition cond is invalid in the context of all the locations of
the breakpoint, gdb refuses to define the breakpoint. For example, if variable
foo is an undefined variable:(gdb) break func if foo
No symbol "foo" in current context.

break ... -force-condition if cond
There may be cases where the condition cond is invalid at all the current locations, but the user knows that it will be valid at a future location; for example,
because of a library load. In such cases, by using the -force-condition keyword before ‘if’, gdb can be forced to define the breakpoint with the given
condition expression instead of refusing it.
(gdb) break func -force-condition if foo
warning: failed to validate condition at location 1, disabling:
No symbol "foo" in current context.
warning: failed to validate condition at location 2, disabling:
No symbol "foo" in current context.
warning: failed to validate condition at location 3, disabling:
No symbol "foo" in current context.
Breakpoint 1 at 0x1158: test.c:18. (3 locations)This causes all the present locations where the breakpoint would otherwise be
inserted, to be disabled, as seen in the example above. However, if there exist
locations at which the condition is valid, the -force-condition keyword has
no effect.
tbreak args
Set a breakpoint enabled only for one stop. The args are the same as for the
break command, and the breakpoint is set in the same way, but the breakpoint
is automatically deleted after the first time your program stops there. See
Section 5.1.5 [Disabling Breakpoints], page 74.
hbreak args
Set a hardware-assisted breakpoint. The args are the same as for the breakcommand and the breakpoint is set in the same way, but the breakpoint requires hardware support and some target hardware may not have this support.
The main purpose of this is EPROM/ROM code debugging, so you can set
a breakpoint at an instruction without changing the instruction. This can beused with the new trap-generation provided by SPARClite DSU and most x86based targets. These targets will generate traps when a program accesses somedata or instruction address that is assigned to the debug registers. However
the hardware breakpoint registers can take a limited number of breakpoints.
For example, on the DSU, only two data breakpoints can be set at a time, andgdb will reject this command if more than two are used. Delete or disable
unused hardware breakpoints before setting new ones (see Section 5.1.5 [Dis-Chapter 5: Stopping and Continuing

61

abling Breakpoints], page 74). See Section 5.1.6 [Break Conditions], page 76.
For remote targets, you can restrict the number of hardware breakpoints gdb
will use, see [set remote hardware-breakpoint-limit], page 327.
thbreak args
Set a hardware-assisted breakpoint enabled only for one stop. The args are thesame as for the hbreak command and the breakpoint is set in the same way.
However, like the tbreak command, the breakpoint is automatically deleted
after the first time your program stops there. Also, like the hbreak command,the breakpoint requires hardware support and some target hardware may nothave this support. See Section 5.1.5 [Disabling Breakpoints], page 74. See also
Section 5.1.6 [Break Conditions], page 76.
rbreak regex
Set breakpoints on all functions matching the regular expression regex. This
command sets an unconditional breakpoint on all matches, printing a list of all
breakpoints it set. Once these breakpoints are set, they are treated just like thebreakpoints set with the break command. You can delete them, disable them,or make them conditional the same way as any other breakpoint.
In programs using different languages, gdb chooses the syntax to print the listof all breakpoints it sets according to the ‘set language’ value: using ‘set
language auto’ (see Section 15.1.3 [Set Language Automatically], page 228)
means to use the language of the breakpoint’s function, other values mean to use
the manually specified language (see Section 15.1.2 [Set Language Manually],
page 228).
The syntax of the regular expression is the standard one used with tools likegrep. Note that this is different from the syntax used by shells, so for instancefoo* matches all functions that include an fo followed by zero or more os.
There is an implicit .* leading and trailing the regular expression you supply,
so to match only functions that begin with foo, use ^foo.
When debugging C++ programs, rbreak is useful for setting breakpoints on
overloaded functions that are not members of any special classes.
The rbreak command can be used to set breakpoints in all the functions in a
program, like this:(gdb) rbreak .

rbreak file:regex
If rbreak is called with a filename qualification, it limits the search for functions
matching the given regular expression to the specified file. This can be used,
for example, to set breakpoints on every function in a given file:(gdb) rbreak file.c:.

The colon separating the filename qualifier from the regex may optionally besurrounded by spaces.
info breakpoints [list...]info break [list...]Print a table of all breakpoints, watchpoints, tracepoints, and catchpoints set
and not deleted. Optional argument n means print information only about the62

Debugging with gdb

specified breakpoint(s) (or watchpoint(s) or tracepoint(s) or catchpoint(s)). For
each breakpoint, following columns are printed:
Breakpoint Numbers
Type
Breakpoint, watchpoint, tracepoint, or catchpoint.
Disposition
Whether the breakpoint is marked to be disabled or deleted whenhit.
Enabled or Disabled
Enabled breakpoints are marked with ‘y’. ‘n’ marks breakpoints
that are not enabled.
Address

Where the breakpoint is in your program, as a memory address.
For a pending breakpoint whose address is not yet known, thisfield will contain ‘<PENDING>’. Such breakpoint won’t fire until ashared library that has the symbol or line referred by breakpoint isloaded. See below for details. A breakpoint with several locations
will have ‘<MULTIPLE>’ in this field—see below for details.

What

Where the breakpoint is in the source for your program, as a file andline number. For a pending breakpoint, the original string passed
to the breakpoint command will be listed as it cannot be resolved
until the appropriate shared library is loaded in the future.

If a breakpoint is conditional, there are two evaluation modes: “host” and“target”. If mode is “host”, breakpoint condition evaluation is done by gdb on
the host’s side. If it is “target”, then the condition is evaluated by the target.
The info break command shows the condition on the line following the affected
breakpoint, together with its condition evaluation mode in between parentheses.
Breakpoint commands, if any, are listed after that. A pending breakpoint isallowed to have a condition specified for it. The condition is not parsed forvalidity until a shared library is loaded that allows the pending breakpoint toresolve to a valid location.
info break with a breakpoint number n as argument lists only that breakpoint. The convenience variable $_ and the default examining-address for thex command are set to the address of the last breakpoint listed (see Section 10.6
[Examining Memory], page 152).
info break displays a count of the number of times the breakpoint has been
hit. This is especially useful in conjunction with the ignore command. You
can ignore a large number of breakpoint hits, look at the breakpoint info to see
how many times the breakpoint was hit, and then run again, ignoring one lessthan that number. This will get you quickly to the last hit of that breakpoint.
For a breakpoints with an enable count (xref) greater than 1, info break also
displays that count.
gdb allows you to set any number of breakpoints at the same place in your program.
There is nothing silly or meaningless about this. When the breakpoints are conditional,
this is even useful (see Section 5.1.6 [Break Conditions], page 76).

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It is possible that a single logical breakpoint is set at several code locations in yourprogram. See Section 9.2 [Location Specifications], page 126, for examples.
A breakpoint with multiple code locations is displayed in the breakpoint table using
several rows—one header row, followed by one row for each code location. The header
row has ‘<MULTIPLE>’ in the address column. Each code location row contains the actual
address, source file, source line and function of its code location. The number column for acode location is of the form breakpoint-number.location-number.
For example:
Num
1

1.1
1.2

Type
Disp Enb AddressWhat
breakpoint
keep y<MULTIPLE>
stop only if i==1
breakpoint already hit 1 timey0x080486a2 in void foo<int>() at t.cc:8y0x080486ca in void foo<double>() at t.cc:8

You cannot delete the individual locations from a breakpoint. However, each location
can be individually enabled or disabled by passing breakpoint-number.location-number asargument to the enable and disable commands. It’s also possible to enable and disablea range of location-number locations using a breakpoint-number and two location-numbers,
in increasing order, separated by a hyphen, like breakpoint-number.location-number1location-number2, in which case gdb acts on all the locations in the range (inclusive).
Disabling or enabling the parent breakpoint (see Section 5.1.5 [Disabling], page 74) affects
all of the locations that belong to that breakpoint.
Locations that are enabled while their parent breakpoint is disabled won’t trigger abreak, and are denoted by y- in the Enb column. For example:(gdb) info breakpoints
NumType
Disp Enb AddressWhat1
breakpoint
keep n<MULTIPLE>
1.1
y- 0x00000000000011b6 in ...
1.2
y- 0x00000000000011c2 in ...
1.3
n0x00000000000011ce in ...

It’s quite common to have a breakpoint inside a shared library. Shared libraries canbe loaded and unloaded explicitly, and possibly repeatedly, as the program is executed.
To support this use case, gdb updates breakpoint locations whenever any shared libraryis loaded or unloaded. Typically, you would set a breakpoint in a shared library at the
beginning of your debugging session, when the library is not loaded, and when the symbols
from the library are not available. When you try to set breakpoint, gdb will ask you if you
want to set a so called pending breakpoint—breakpoint whose address is not yet resolved.
After the program is run, whenever a new shared library is loaded, gdb reevaluates all the
breakpoints. When a newly loaded shared library contains the symbol or line referred to bysome pending breakpoint, that breakpoint is resolved and becomes an ordinary breakpoint.
When a library is unloaded, all breakpoints that refer to its symbols or source lines become
pending again.
This logic works for breakpoints with multiple locations, too. For example, if you havea breakpoint in a C++ template function, and a newly loaded shared library has an instantiation of that template, a new location is added to the list of locations for the breakpoint.

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Except for having unresolved address, pending breakpoints do not differ from regularbreakpoints. You can set conditions or commands, enable and disable them and perform
other breakpoint operations.
gdb provides some additional commands for controlling what happens when the ‘break’
command cannot resolve the location spec to any code location in your program (seeSection 9.2 [Location Specifications], page 126):
set breakpoint pending auto
This is the default behavior. When gdb cannot resolve the location spec, it
queries you whether a pending breakpoint should be created.
set breakpoint pending on
This indicates that when gdb cannot resolve the location spec, it should createa pending breakpoint without confirmation.
set breakpoint pending off
This indicates that pending breakpoints are not to be created. If gdb cannot
resolve the location spec, it aborts the breakpoint creation with an error. Thissetting does not affect any pending breakpoints previously created.
show breakpoint pending
Show the current behavior setting for creating pending breakpoints.
The settings above only affect the break command and its variants. Once a breakpointis set, it will be automatically updated as shared libraries are loaded and unloaded.
For some targets, gdb can automatically decide if hardware or software breakpoints
should be used, depending on whether the breakpoint address is read-only or read-write.
This applies to breakpoints set with the break command as well as to internal breakpoints
set by commands like next and finish. For breakpoints set with hbreak, gdb will always
use hardware breakpoints.
You can control this automatic behaviour with the following commands:
set breakpoint auto-hw onThis is the default behavior. When gdb sets a breakpoint, it will try to use thetarget memory map to decide if software or hardware breakpoint must be used.
set breakpoint auto-hw off
This indicates gdb should not automatically select breakpoint type. If thetarget provides a memory map, gdb will warn when trying to set software
breakpoint at a read-only address.
gdb normally implements breakpoints by replacing the program code at the breakpoint
address with a special instruction, which, when executed, given control to the debugger.
By default, the program code is so modified only when the program is resumed. As soon as
the program stops, gdb restores the original instructions. This behaviour guards against
leaving breakpoints inserted in the target should gdb abrubptly disconnect. However, withslow remote targets, inserting and removing breakpoint can reduce the performance. Thisbehavior can be controlled with the following commands::

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set breakpoint always-inserted off
All breakpoints, including newly added by the user, are inserted in the target
only when the target is resumed. All breakpoints are removed from the target
when it stops. This is the default mode.
set breakpoint always-inserted on
Causes all breakpoints to be inserted in the target at all times. If the user adds
a new breakpoint, or changes an existing breakpoint, the breakpoints in thetarget are updated immediately. A breakpoint is removed from the target only
when breakpoint itself is deleted.
gdb handles conditional breakpoints by evaluating these conditions when a breakpoint
breaks. If the condition is true, then the process being debugged stops, otherwise the process
is resumed.
If the target supports evaluating conditions on its end, gdb may download the breakpoint, together with its conditions, to it.
This feature can be controlled via the following commands:
set breakpoint condition-evaluation hostThis option commands gdb to evaluate the breakpoint conditions on the host’sside. Unconditional breakpoints are sent to the target which in turn receives
the triggers and reports them back to GDB for condition evaluation. This is
the standard evaluation mode.
set breakpoint condition-evaluation target
This option commands gdb to download breakpoint conditions to the target atthe moment of their insertion. The target is responsible for evaluating the conditional expression and reporting breakpoint stop events back to gdb wheneverthe condition is true. Due to limitations of target-side evaluation, some conditions cannot be evaluated there, e.g., conditions that depend on local data thatis only known to the host. Examples include conditional expressions involving
convenience variables, complex types that cannot be handled by the agent expression parser and expressions that are too long to be sent over to the target,
specially when the target is a remote system. In these cases, the conditions will
be evaluated by gdb.
set breakpoint condition-evaluation auto
This is the default mode. If the target supports evaluating breakpoint conditions on its end, gdb will download breakpoint conditions to the target (limitations mentioned previously apply). If the target does not support breakpointcondition evaluation, then gdb will fallback to evaluating all these conditions
on the host’s side.
gdb itself sometimes sets breakpoints in your program for special purposes, such as
proper handling of longjmp (in C programs). These internal breakpoints are assigned
negative numbers, starting with -1; ‘info breakpoints’ does not display them. You can
see these breakpoints with the gdb maintenance command ‘maint info breakpoints’ (see[maint info breakpoints], page 755).

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5.1.2 Setting Watchpoints
You can use a watchpoint to stop execution whenever the value of an expression changes,
without having to predict a particular place where this may happen. (This is sometimes
called a data breakpoint.) The expression may be as simple as the value of a single variable,or as complex as many variables combined by operators. Examples include:• A reference to the value of a single variable.
• An address cast to an appropriate data type. For example, ‘*(int *)0x12345678’ will
watch a 4-byte region at the specified address (assuming an int occupies 4 bytes).
• An arbitrarily complex expression, such as ‘a*b + c/d’. The expression can use any operators valid in the program’s native language (see Chapter 15 [Languages], page 227).
You can set a watchpoint on an expression even if the expression can not be evaluated yet.
For instance, you can set a watchpoint on ‘*global_ptr’ before ‘global_ptr’ is initialized.
gdb will stop when your program sets ‘global_ptr’ and the expression produces a valid
value. If the expression becomes valid in some other way than changing a variable (e.g. if
the memory pointed to by ‘*global_ptr’ becomes readable as the result of a malloc call),
gdb may not stop until the next time the expression changes.
Depending on your system, watchpoints may be implemented in software or hardware.
gdb does software watchpointing by single-stepping your program and testing the variable’s
value each time, which is hundreds of times slower than normal execution. (But this may
still be worth it, to catch errors where you have no clue what part of your program is the
culprit.)On some systems, such as most PowerPC or x86-based targets, gdb includes support
for hardware watchpoints, which do not slow down the running of your program.
watch [-l|-location] expr [thread thread-id] [mask maskvalue] [task task-id]
Set a watchpoint for an expression. gdb will break when the expression expr
is written into by the program and its value changes. The simplest (and themost popular) use of this command is to watch the value of a single variable:(gdb) watch foo

If the command includes a [thread thread-id] argument, gdb breaks only
when the thread identified by thread-id changes the value of expr. If any otherthreads change the value of expr, gdb will not break. Note that watchpoints
restricted to a single thread in this way only work with Hardware Watchpoints.
Similarly, if the task argument is given, then the watchpoint will be specific to
the indicated Ada task (see Section 15.4.10.7 [Ada Tasks], page 255).
Ordinarily a watchpoint respects the scope of variables in expr (see below).
The -location argument tells gdb to instead watch the memory referred toby expr. In this case, gdb will evaluate expr, take the address of the result, andwatch the memory at that address. The type of the result is used to determine
the size of the watched memory. If the expression’s result does not have anaddress, then gdb will print an error.
The [mask maskvalue] argument allows creation of masked watchpoints, if thecurrent architecture supports this feature (e.g., PowerPC Embedded architecture, see Section 21.3.8 [PowerPC Embedded], page 352.) A masked watchpoint
specifies a mask in addition to an address to watch. The mask specifies that

Chapter 5: Stopping and Continuing

67

some bits of an address (the bits which are reset in the mask) should be ignored
when matching the address accessed by the inferior against the watchpoint address. Thus, a masked watchpoint watches many addresses simultaneously—
those addresses whose unmasked bits are identical to the unmasked bits in thewatchpoint address. The mask argument implies -location. Examples:(gdb) watch foo mask 0xffff00ff(gdb) watch *0xdeadbeef mask 0xffffff00

rwatch [-l|-location] expr [thread thread-id] [mask maskvalue]
Set a watchpoint that will break when the value of expr is read by the program.
awatch [-l|-location] expr [thread thread-id] [mask maskvalue]
Set a watchpoint that will break when expr is either read from or written intoby the program.
info watchpoints [list...]This command prints a list of watchpoints, using the same format as info
break (see Section 5.1.1 [Set Breaks], page 58).
If you watch for a change in a numerically entered address you need to dereference it, as
the address itself is just a constant number which will never change. gdb refuses to create
a watchpoint that watches a never-changing value:(gdb) watch 0x600850
Cannot watch constant value 0x600850.
(gdb) watch *(int *) 0x600850
Watchpoint 1: *(int *) 6293584

gdb sets a hardware watchpoint if possible. Hardware watchpoints execute very quickly,
and the debugger reports a change in value at the exact instruction where the change occurs.
If gdb cannot set a hardware watchpoint, it sets a software watchpoint, which executes more
slowly and reports the change in value at the next statement, not the instruction, after thechange occurs.
You can force gdb to use only software watchpoints with the set can-use-hwwatchpoints 0 command. With this variable set to zero, gdb will never try to use
hardware watchpoints, even if the underlying system supports them.
(Note that
hardware-assisted watchpoints that were set before setting can-use-hw-watchpoints tozero will still use the hardware mechanism of watching expression values.)
set can-use-hw-watchpoints
Set whether or not to use hardware watchpoints.
show can-use-hw-watchpoints
Show the current mode of using hardware watchpoints.
For remote targets, you can restrict the number of hardware watchpoints gdb will use,see [set remote hardware-breakpoint-limit], page 327.
When you issue the watch command, gdb reports
Hardware watchpoint num: expr

if it was able to set a hardware watchpoint.
Currently, the awatch and rwatch commands can only set hardware watchpoints, because accesses to data that don’t change the value of the watched expression cannot be68

Debugging with gdb

detected without examining every instruction as it is being executed, and gdb does not dothat currently. If gdb finds that it is unable to set a hardware breakpoint with the awatch
or rwatch command, it will print a message like this:Expression cannot be implemented with read/access watchpoint.

Sometimes, gdb cannot set a hardware watchpoint because the data type of the watched
expression is wider than what a hardware watchpoint on the target machine can handle.
For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision
floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate
watchpoints.
If you set too many hardware watchpoints, gdb might be unable to insert all of themwhen you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, gdb might not beable to warn you about this when you set the watchpoints, and the warning will be printed
only when the program is resumed:
Hardware watchpoint num: Could not insert watchpoint

If this happens, delete or disable some of the watchpoints.
Watching complex expressions that reference many variables can also exhaust the resources available for hardware-assisted watchpoints. That’s because gdb needs to watch
every variable in the expression with separately allocated resources.
If you call a function interactively using print or call, any watchpoints you have set
will be inactive until gdb reaches another kind of breakpoint or the call completes.
gdb automatically deletes watchpoints that watch local (automatic) variables, or expressions that involve such variables, when they go out of scope, that is, when the execution
leaves the block in which these variables were defined. In particular, when the program
being debugged terminates, all local variables go out of scope, and so only watchpoints
that watch global variables remain set. If you rerun the program, you will need to set all
such watchpoints again. One way of doing that would be to set a code breakpoint at theentry to the main function and when it breaks, set all the watchpoints.
In multi-threaded programs, watchpoints will detect changes to the watched expression
from every thread.
Warning: In multi-threaded programs, software watchpoints have only limited
usefulness. If gdb creates a software watchpoint, it can only watch the valueof an expression in a single thread. If you are confident that the expression can
only change due to the current thread’s activity (and if you are also confident
that no other thread can become current), then you can use software watchpoints as usual. However, gdb may not notice when a non-current thread’s
activity changes the expression. (Hardware watchpoints, in contrast, watch an
expression in all threads.)
See [set remote hardware-watchpoint-limit], page 327.

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5.1.3 Setting Catchpoints
You can use catchpoints to cause the debugger to stop for certain kinds of program events,
such as C++ exceptions or the loading of a shared library. Use the catch command to set
a catchpoint.
catch event
Stop when event occurs. The event can be any of the following:
throw [regexp]
rethrow [regexp]
catch [regexp]
The throwing, re-throwing, or catching of a C++ exception.
If regexp is given, then only exceptions whose type matches theregular expression will be caught.
The convenience variable $_exception is available at an exceptionrelated catchpoint, on some systems. This holds the exception being thrown.
There are currently some limitations to C++ exception handling in
gdb:• The support for these commands is system-dependent.
Currently, only systems using the ‘gnu-v3’ C++ ABI (seeSection 22.7 [ABI], page 375) are supported.
• The regular expression feature and the $_exception convenience variable rely on the presence of some SDT probes inlibstdc++. If these probes are not present, then these features cannot be used. These probes were first available in the
GCC 4.8 release, but whether or not they are available in your
GCC also depends on how it was built.
• The $_exception convenience variable is only valid at the instruction at which an exception-related catchpoint is set.
• When an exception-related catchpoint is hit, gdb stops at alocation in the system library which implements runtime exception support for C++, usually libstdc++. You can use up(see Section 8.3 [Selection], page 117) to get to your code.
• If you call a function interactively, gdb normally returns control to you when the function has finished executing. If the callraises an exception, however, the call may bypass the mechanism that returns control to you and cause your program either
to abort or to simply continue running until it hits a breakpoint, catches a signal that gdb is listening for, or exits. Thisis the case even if you set a catchpoint for the exception; catchpoints on exceptions are disabled within interactive calls. See
Section 17.5 [Calling], page 281, for information on controlling
this with set unwind-on-terminating-exception.
• You cannot raise an exception interactively.
• You cannot install an exception handler interactively.

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exception [name]
An Ada exception being raised. If an exception name is specified
at the end of the command (eg catch exception Program_Error),the debugger will stop only when this specific exception is raised.
Otherwise, the debugger stops execution when any Ada exception
is raised.
When inserting an exception catchpoint on a user-defined exception
whose name is identical to one of the exceptions defined by the language, the fully qualified name must be used as the exception name.
Otherwise, gdb will assume that it should stop on the pre-defined
exception rather than the user-defined one. For instance, assuming an exception called Constraint_Error is defined in package
Pck, then the command to use to catch such exceptions is catch
exception Pck.Constraint_Error.
The convenience variable $_ada_exception holds the address ofthe exception being thrown. This can be useful when setting a
condition for such a catchpoint.
exception unhandled
An exception that was raised but is not handled by the program.
The convenience variable $_ada_exception is set as for catch
exception.
handlers [name]
An Ada exception being handled. If an exception name is specified
at the end of the command (eg catch handlers Program_Error),the debugger will stop only when this specific exception is handled.
Otherwise, the debugger stops execution when any Ada exceptionis handled.
When inserting a handlers catchpoint on a user-defined exception
whose name is identical to one of the exceptions defined by the language, the fully qualified name must be used as the exception name.
Otherwise, gdb will assume that it should stop on the pre-defined
exception rather than the user-defined one. For instance, assuming an exception called Constraint_Error is defined in package
Pck, then the command to use to catch such exceptions handling iscatch handlers Pck.Constraint_Error.
The convenience variable $_ada_exception is set as for catch
exception.
assertA failed Ada assertion. Note that the convenience variable $_ada_
exception is not set by this catchpoint.

exec

A call to exec.

syscallsyscall [name | number | group:groupname | g:groupname] ...
A call to or return from a system call, a.k.a. syscall. A syscall is amechanism for application programs to request a service from theChapter 5: Stopping and Continuing

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operating system (OS) or one of the OS system services. gdb cancatch some or all of the syscalls issued by the debuggee, and show
the related information for each syscall. If no argument is specified,calls to and returns from all system calls will be caught.
name can be any system call name that is valid for the underlying
OS. Just what syscalls are valid depends on the OS. On GNU and
Unix systems, you can find the full list of valid syscall names on/usr/include/asm/unistd.h.
Normally, gdb knows in advance which syscalls are valid for eachOS, so you can use the gdb command-line completion facilities (seeSection 3.3 [command completion], page 24) to list the available
choices.
You may also specify the system call numerically. A syscall’s number is the value passed to the OS’s syscall dispatcher to identify
the requested service. When you specify the syscall by its name,
gdb uses its database of syscalls to convert the name into the corresponding numeric code, but using the number directly may be
useful if gdb’s database does not have the complete list of syscallson your system (e.g., because gdb lags behind the OS upgrades).
You may specify a group of related syscalls to be caught at once using the group: syntax (g: is a shorter equivalent). For instance, onsome platforms gdb allows you to catch all network related syscalls,
by passing the argument group:network to catch syscall. Notethat not all syscall groups are available in every system. You can
use the command completion facilities (see Section 3.3 [commandcompletion], page 24) to list the syscall groups available on yourenvironment.
The example below illustrates how this command works if you don’t
provide arguments to it:(gdb) catch syscall
Catchpoint 1 (syscall)(gdb) rStarting program: /tmp/catch-syscall
Catchpoint 1 (call to syscall ’close’), \0xffffe424 in __kernel_vsyscall ()(gdb) cContinuing.
Catchpoint 1 (returned from syscall ’close’), \0xffffe424 in __kernel_vsyscall ()(gdb)

Here is an example of catching a system call by name:(gdb) catch syscall chroot
Catchpoint 1 (syscall ’chroot’ [61])(gdb) rStarting program: /tmp/catch-syscall
Catchpoint 1 (call to syscall ’chroot’), \72

Debugging with gdb

0xffffe424 in __kernel_vsyscall ()(gdb) cContinuing.
Catchpoint 1 (returned from syscall ’chroot’), \0xffffe424 in __kernel_vsyscall ()(gdb)

An example of specifying a system call numerically. In the casebelow, the syscall number has a corresponding entry in the XML
file, so gdb finds its name and prints it:(gdb) catch syscall 252
Catchpoint 1 (syscall(s) ’exit_group’)(gdb) rStarting program: /tmp/catch-syscall
Catchpoint 1 (call to syscall ’exit_group’), \0xffffe424 in __kernel_vsyscall ()(gdb) cContinuing.
Program exited normally.
(gdb)

Here is an example of catching a syscall group:(gdb) catch syscall group:process
Catchpoint 1 (syscalls ’exit’ [1] ’fork’ [2] ’waitpid’ [7]’execve’ [11] ’wait4’ [114] ’clone’ [120] ’vfork’ [190]’exit_group’ [252] ’waitid’ [284] ’unshare’ [310])(gdb) rStarting program: /tmp/catch-syscall
Catchpoint 1 (call to syscall fork), 0x00007ffff7df4e27 in open64 ()from /lib64/ld-linux-x86-64.so.2(gdb) cContinuing.

However, there can be situations when there is no corresponding
name in XML file for that syscall number. In this case, gdb prints
a warning message saying that it was not able to find the syscall
name, but the catchpoint will be set anyway. See the example
below:(gdb) catch syscall 764
warning: The number ’764’ does not represent a known syscall.
Catchpoint 2 (syscall 764)
(gdb)

If you configure gdb using the ‘--without-expat’ option, it will
not be able to display syscall names. Also, if your architecture does
not have an XML file describing its system calls, you will not beable to see the syscall names. It is important to notice that these
two features are used for accessing the syscall name database. In
either case, you will see a warning like this:(gdb) catch syscall
warning: Could not open "syscalls/i386-linux.xml"
warning: Could not load the syscall XML file ’syscalls/i386-linux.xml’.

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GDB will not be able to display syscall names.
Catchpoint 1 (syscall)(gdb)

Of course, the file name will change depending on your architectureand system.
Still using the example above, you can also try to catch a syscallby its number. In this case, you would see something like:(gdb) catch syscall 252
Catchpoint 1 (syscall(s) 252)

Again, in this case gdb would not be able to display syscall’s names.
fork

A call to fork.

vfork

A call to vfork.

load [regexp]
unload [regexp]
The loading or unloading of a shared library. If regexp is given,
then the catchpoint will stop only if the regular expression matches
one of the affected libraries.
signal [signal... | ‘all’]The delivery of a signal.
With no arguments, this catchpoint will catch any signal that is not
used internally by gdb, specifically, all signals except ‘SIGTRAP’ and‘SIGINT’.
With the argument ‘all’, all signals, including those used by gdb,
will be caught. This argument cannot be used with other signal
names.
Otherwise, the arguments are a list of signal names as given tohandle (see Section 5.4 [Signals], page 89). Only signals specified
in this list will be caught.
One reason that catch signal can be more useful than handle isthat you can attach commands and conditions to the catchpoint.
When a signal is caught by a catchpoint, the signal’s stop andprint settings, as specified by handle, are ignored. However,whether the signal is still delivered to the inferior depends on thepass setting; this can be changed in the catchpoint’s commands.
tcatch event
Set a catchpoint that is enabled only for one stop. The catchpoint is automatically deleted after the first time the event is caught.
Use the info break command to list the current catchpoints.

5.1.4 Deleting Breakpoints
It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done
its job and you no longer want your program to stop there. This is called deleting the
breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.

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With the clear command you can delete breakpoints according to where they are in yourprogram. With the delete command you can delete individual breakpoints, watchpoints,
or catchpoints by specifying their breakpoint numbers.
It is not necessary to delete a breakpoint to proceed past it. gdb automatically ignores
breakpoints on the first instruction to be executed when you continue execution withoutchanging the execution address.
clear

Delete any breakpoints at the next instruction to be executed in the selected
stack frame (see Section 8.3 [Selecting a Frame], page 117). When the innermost
frame is selected, this is a good way to delete a breakpoint where your program
just stopped.

clear locspec
Delete any breakpoint with a code location that corresponds to locspec. See
Section 9.2 [Location Specifications], page 126, for the various forms of locspec.
Which code locations correspond to locspec depends on the form used in thelocation specification locspec:
linenum
filename:linenum-line linenum-source filename -line linenum
If locspec specifies a line number, with or without a file name, thecommand deletes any breakpoint with a code location that is at orwithin the specified line linenum in files that match the specified
filename. If filename is omitted, it defaults to the current source
file.
*address

If locspec specifies an address, the command deletes any breakpointwith a code location that is at the given address.

function-function function
If locspec specifies a function, the command deletes any breakpointwith a code location that is at the entry to any function whose namematches function.
Ambiguity in names of files and functions can be resolved as described in
Section 9.2 [Location Specifications], page 126.
delete [breakpoints] [list...]Delete the breakpoints, watchpoints, tracepoints, or catchpoints of the breakpoint list specified as argument. If no argument is specified, delete all breakpoints, watchpoints, tracepoints, and catchpoints (gdb asks confirmation, unless you have set confirm off). You can abbreviate this command as d.

5.1.5 Disabling Breakpoints
Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to disable
it. This makes the breakpoint inoperative as if it had been deleted, but remembers theinformation on the breakpoint so that you can enable it again later.

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You disable and enable breakpoints, watchpoints, tracepoints, and catchpoints with theenable and disable commands, optionally specifying one or more breakpoint numbers asarguments. Use info break to print a list of all breakpoints, watchpoints, tracepoints, andcatchpoints if you do not know which numbers to use.
Disabling and enabling a breakpoint that has multiple locations affects all of its locations.
A breakpoint, watchpoint, or catchpoint can have any of several different states of enablement:• Enabled. The breakpoint stops your program. A breakpoint set with the break command starts out in this state.
• Disabled. The breakpoint has no effect on your program.
• Enabled once. The breakpoint stops your program, but then becomes disabled.
• Enabled for a count. The breakpoint stops your program for the next N times, thenbecomes disabled.
• Enabled for deletion. The breakpoint stops your program, but immediately after itdoes so it is deleted permanently. A breakpoint set with the tbreak command starts
out in this state.
You can use the following commands to enable or disable breakpoints, watchpoints,
tracepoints, and catchpoints:
disable [breakpoints] [list...]Disable the specified breakpoints—or all breakpoints, if none are listed. A
disabled breakpoint has no effect but is not forgotten. All options such as
ignore-counts, conditions and commands are remembered in case the breakpointis enabled again later. You may abbreviate disable as dis.
enable [breakpoints] [list...]Enable the specified breakpoints (or all defined breakpoints). They become
effective once again in stopping your program.
enable [breakpoints] once list...
Enable the specified breakpoints temporarily. gdb disables any of these breakpoints immediately after stopping your program.
enable [breakpoints] count count list...
Enable the specified breakpoints temporarily. gdb records count with each of
the specified breakpoints, and decrements a breakpoint’s count when it is hit.
When any count reaches 0, gdb disables that breakpoint. If a breakpoint has
an ignore count (see Section 5.1.6 [Break Conditions], page 76), that will bedecremented to 0 before count is affected.
enable [breakpoints] delete list...
Enable the specified breakpoints to work once, then die. gdb deletes any ofthese breakpoints as soon as your program stops there. Breakpoints set by the
tbreak command start out in this state.
Except for a breakpoint set with tbreak (see Section 5.1.1 [Setting Breakpoints],
page 58), breakpoints that you set are initially enabled; subsequently, they become
disabled or enabled only when you use one of the commands above. (The command until

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can set and delete a breakpoint of its own, but it does not change the state of your otherbreakpoints; see Section 5.2 [Continuing and Stepping], page 83.)

5.1.6 Break Conditions
The simplest sort of breakpoint breaks every time your program reaches a specified place.
You can also specify a condition for a breakpoint. A condition is just a Boolean expression inyour programming language (see Section 10.1 [Expressions], page 145). A breakpoint witha condition evaluates the expression each time your program reaches it, and your program
stops only if the condition is true.
This is the converse of using assertions for program validation; in that situation, youwant to stop when the assertion is violated—that is, when the condition is false. In C, if
you want to test an assertion expressed by the condition assert, you should set the condition‘! assert’ on the appropriate breakpoint.
Conditions are also accepted for watchpoints; you may not need them, since a watchpoint
is inspecting the value of an expression anyhow—but it might be simpler, say, to just set a
watchpoint on a variable name, and specify a condition that tests whether the new value isan interesting one.
Break conditions can have side effects, and may even call functions in your program. Thiscan be useful, for example, to activate functions that log program progress, or to use yourown print functions to format special data structures. The effects are completely predictable
unless there is another enabled breakpoint at the same address. (In that case, gdb might
see the other breakpoint first and stop your program without checking the condition ofthis one.) Note that breakpoint commands are usually more convenient and flexible thanbreak conditions for the purpose of performing side effects when a breakpoint is reached(see Section 5.1.7 [Breakpoint Command Lists], page 77).
Breakpoint conditions can also be evaluated on the target’s side if the target supports
it. Instead of evaluating the conditions locally, gdb encodes the expression into an agent
expression (see Appendix F [Agent Expressions], page 847) suitable for execution on thetarget, independently of gdb. Global variables become raw memory locations, locals become
stack accesses, and so forth.
In this case, gdb will only be notified of a breakpoint trigger when its condition evaluates
to true. This mechanism may provide faster response times depending on the performance
characteristics of the target since it does not need to keep gdb informed about every breakpoint trigger, even those with false conditions.
Break conditions can be specified when a breakpoint is set, by using ‘if’ in the arguments
to the break command. See Section 5.1.1 [Setting Breakpoints], page 58. They can also bechanged at any time with the condition command.
You can also use the if keyword with the watch command. The catch command does
not recognize the if keyword; condition is the only way to impose a further condition ona catchpoint.
condition bnum expression
Specify expression as the break condition for breakpoint, watchpoint, or catchpoint number bnum. After you set a condition, breakpoint bnum stops yourprogram only if the value of expression is true (nonzero, in C). When you
use condition, gdb checks expression immediately for syntactic correctness,

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and to determine whether symbols in it have referents in the context of yourbreakpoint. If expression uses symbols not referenced in the context of the
breakpoint, gdb prints an error message:
No symbol "foo" in current context.

gdb does not actually evaluate expression at the time the condition command(or a command that sets a breakpoint with a condition, like break if ...) is
given, however. See Section 10.1 [Expressions], page 145.
condition -force bnum expression
When the -force flag is used, define the condition even if expression is invalid
at all the current locations of breakpoint bnum. This is similar to the -forcecondition option of the break command.
condition bnum
Remove the condition from breakpoint number bnum. It becomes an ordinary
unconditional breakpoint.
A special case of a breakpoint condition is to stop only when the breakpoint has beenreached a certain number of times. This is so useful that there is a special way to do it,
using the ignore count of the breakpoint. Every breakpoint has an ignore count, which isan integer. Most of the time, the ignore count is zero, and therefore has no effect. But if
your program reaches a breakpoint whose ignore count is positive, then instead of stopping,it just decrements the ignore count by one and continues. As a result, if the ignore countvalue is n, the breakpoint does not stop the next n times your program reaches it.
ignore bnum countSet the ignore count of breakpoint number bnum to count. The next counttimes the breakpoint is reached, your program’s execution does not stop; otherthan to decrement the ignore count, gdb takes no action.
To make the breakpoint stop the next time it is reached, specify a count of zero.
When you use continue to resume execution of your program from a breakpoint, you can specify an ignore count directly as an argument to continue,
rather than using ignore. See Section 5.2 [Continuing and Stepping], page 83.
If a breakpoint has a positive ignore count and a condition, the condition is
not checked. Once the ignore count reaches zero, gdb resumes checking thecondition.
You could achieve the effect of the ignore count with a condition such as‘$foo-- <= 0’ using a debugger convenience variable that is decremented eachtime. See Section 10.12 [Convenience Variables], page 171.
Ignore counts apply to breakpoints, watchpoints, tracepoints, and catchpoints.

5.1.7 Breakpoint Command Lists
You can give any breakpoint (or watchpoint or catchpoint) a series of commands to execute
when your program stops due to that breakpoint. For example, you might want to print
the values of certain expressions, or enable other breakpoints.

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commands [list...]... command-list ...
endSpecify a list of commands for the given breakpoints. The commands themselvesappear on the following lines. Type a line containing just end to terminate thecommands.
To remove all commands from a breakpoint, type commands and follow it immediately with end; that is, give no commands.
With no argument, commands refers to the last breakpoint, watchpoint, or catchpoint set (not to the breakpoint most recently encountered). If the most recent
breakpoints were set with a single command, then the commands will apply
to all the breakpoints set by that command. This applies to breakpoints set
by rbreak, and also applies when a single break command creates multiple
breakpoints (see Section 10.2 [Ambiguous Expressions], page 146).
Pressing RET as a means of repeating the last gdb command is disabled within acommand-list.
Inside a command list, you can use the command disable $_hit_bpnum to disable theencountered breakpoint.
If your breakpoint has several code locations, the command disable$_hit_bpnum.$_hit_locno will disable the specific breakpoint code location encountered. If the breakpoint has only one location, this command will disable theencountered breakpoint.
You can use breakpoint commands to start your program up again. Simply use thecontinue command, or step, or any other command that resumes execution.
Any other commands in the command list, after a command that resumes execution, areignored. This is because any time you resume execution (even with a simple next or step),
you may encounter another breakpoint—which could have its own command list, leading
to ambiguities about which list to execute.
If the first command you specify in a command list is silent, the usual message about
stopping at a breakpoint is not printed. This may be desirable for breakpoints that are
to print a specific message and then continue. If none of the remaining commands print
anything, you see no sign that the breakpoint was reached. silent is meaningful only atthe beginning of a breakpoint command list.
The commands echo, output, and printf allow you to print precisely controlled output,
and are often useful in silent breakpoints. See Section 23.1.4 [Commands for Controlled
Output], page 397.
For example, here is how you could use breakpoint commands to print the value of x atentry to foo whenever x is positive.
break foo if x>0
commands
silentprintf "x is %d\n",x
cont
end

One application for breakpoint commands is to compensate for one bug so you can test
for another. Put a breakpoint just after the erroneous line of code, give it a condition

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to detect the case in which something erroneous has been done, and give it commands toassign correct values to any variables that need them. End with the continue command sothat your program does not stop, and start with the silent command so that no output
is produced. Here is an example:
break 403
commands
silentset x = y + 4
cont
end

5.1.8 Dynamic Printf
The dynamic printf command dprintf combines a breakpoint with formatted printing ofyour program’s data to give you the effect of inserting printf calls into your program
on-the-fly, without having to recompile it.
In its most basic form, the output goes to the GDB console. However, you can set
the variable dprintf-style for alternate handling. For instance, you can ask to format
the output by calling your program’s printf function. This has the advantage that thecharacters go to the program’s output device, so they can recorded in redirects to files andso forth.
If you are doing remote debugging with a stub or agent, you can also ask to have theprintf handled by the remote agent. In addition to ensuring that the output goes to theremote program’s device along with any other output the program might produce, you canalso ask that the dprintf remain active even after disconnecting from the remote target.
Using the stub/agent is also more efficient, as it can do everything without needing tocommunicate with gdb.
dprintf locspec,template,expression[,expression...]Whenever execution reaches a code location that results from resolving locspec,
print the values of one or more expressions under the control of the string
template. To print several values, separate them with commas.
set dprintf-style style
Set the dprintf output to be handled in one of several different styles enumerated
below. A change of style affects all existing dynamic printfs immediately. (Ifyou need individual control over the print commands, simply define normal
breakpoints with explicitly-supplied command lists.)
gdb

Handle the output using the gdb printf command. When using
this style, it is possible to use the ‘%V’ format specifier (see [%VFormat Specifier], page 398).

call

Handle the output by calling a function in your program (normallyprintf). When using this style the supported format specifiers
depend entirely on the function being called.
Most of gdb’s format specifiers align with those supported by theprintf function, however, gdb’s ‘%V’ format specifier extension is
not supported by printf. When using ‘call’ style dprintf, careshould be taken to ensure that only format specifiers supported by80

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the output function are used, otherwise the results will be undefined.
agent

Have the remote debugging agent (such as gdbserver) handle theoutput itself. This style is only available for agents that support
running commands on the target. This style does not support the‘%V’ format specifier.

set dprintf-function function
Set the function to call if the dprintf style is call. By default its value isprintf. You may set it to any expression that gdb can evaluate to a function,as per the call command.
set dprintf-channel channel
Set a “channel” for dprintf. If set to a non-empty value, gdb will evaluate it as
an expression and pass the result as a first argument to the dprintf-function,in the manner of fprintf and similar functions. Otherwise, the dprintf format
string will be the first argument, in the manner of printf.
As an example, if you wanted dprintf output to go to a logfile that is a standard
I/O stream assigned to the variable mylog, you could do the following:(gdb) set dprintf-style call(gdb) set dprintf-function fprintf(gdb) set dprintf-channel mylog(gdb) dprintf 25,"at line 25, glob=%d\n",glob
Dprintf 1 at 0x123456: file main.c, line 25.
(gdb) info break1
dprintf
keep y0x00123456 in main at main.c:25
call (void) fprintf (mylog,"at line 25, glob=%d\n",glob)
continue(gdb)
Note that the info break displays the dynamic printf commands as normal
breakpoint commands; you can thus easily see the effect of the variable settings.
set disconnected-dprintf on
set disconnected-dprintf off
Choose whether dprintf commands should continue to run if gdb has disconnected from the target. This only applies if the dprintf-style is agent.
show disconnected-dprintf off
Show the current choice for disconnected dprintf.
gdb does not check the validity of function and channel, relying on you to supply values
that are meaningful for the contexts in which they are being used. For instance, the function
and channel may be the values of local variables, but if that is the case, then all enabled
dynamic prints must be at locations within the scope of those locals. If evaluation fails,
gdb will report an error.

5.1.9 How to save breakpoints to a file
To save breakpoint definitions to a file use the save breakpoints command.

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This command saves all current breakpoint definitions together with their commands and ignore counts, into a file filename suitable for use in a later debugging session. This includes all types of breakpoints (breakpoints, watchpoints,
catchpoints, tracepoints). To read the saved breakpoint definitions, use thesource command (see Section 23.1.3 [Command Files], page 395). Note thatwatchpoints with expressions involving local variables may fail to be recreatedbecause it may not be possible to access the context where the watchpoint isvalid anymore. Because the saved breakpoint definitions are simply a sequenceof gdb commands that recreate the breakpoints, you can edit the file in yourfavorite editing program, and remove the breakpoint definitions you’re not interested in, or that can no longer be recreated.

5.1.10 Static Probe Points
gdb supports SDT probes in the code. SDT stands for Statically Defined Tracing, andthe probes are designed to have a tiny runtime code and data footprint, and no dynamic
relocations.
Currently, the following types of probes are supported on ELF-compatible systems:• SystemTap (http://sourceware.org/systemtap/) SDT probes1 . SystemTap probes
are usable from assembly, C and C++ languages2 .
• DTrace (http://oss.oracle.com/projects/DTrace) USDT probes. DTrace probes
are usable from C and C++ languages.
Some SystemTap probes have an associated semaphore variable; for instance, this happens automatically if you defined your probe using a DTrace-style .d file. If your probe
has a semaphore, gdb will automatically enable it when you specify a breakpoint using
the ‘-probe-stap’ notation. But, if you put a breakpoint at a probe’s location by someother method (e.g., break file:line), then gdb will not automatically set the semaphore.
DTrace probes do not support semaphores.
You can examine the available static static probes using info probes, with optional
arguments:
info probes [type] [provider [name [objfile]]]If given, type is either stap for listing SystemTap probes or dtrace for listing
DTrace probes. If omitted all probes are listed regardless of their types.
If given, provider is a regular expression used to match against provider names
when selecting which probes to list. If omitted, probes by all probes from allproviders are listed.
If given, name is a regular expression to match against probe names whenselecting which probes to list. If omitted, probe names are not considered when
deciding whether to display them.
1

See http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps for more information
on how to add SystemTap SDT probes in your applications.
2
See http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation for a good reference on
how the SDT probes are implemented.

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If given, objfile is a regular expression used to select which object files (executable or shared libraries) to examine. If not given, all object files are considered.
info probes all
List the available static probes, from all types.
Some probe points can be enabled and/or disabled. The effect of enabling or disablinga probe depends on the type of probe being handled. Some DTrace probes can be enabledor disabled, but SystemTap probes cannot be disabled.
You can enable (or disable) one or more probes using the following commands, with
optional arguments:
enable probes [provider [name [objfile]]]If given, provider is a regular expression used to match against provider names
when selecting which probes to enable. If omitted, all probes from all providers
are enabled.
If given, name is a regular expression to match against probe names whenselecting which probes to enable. If omitted, probe names are not consideredwhen deciding whether to enable them.
If given, objfile is a regular expression used to select which object files (executable or shared libraries) to examine. If not given, all object files are considered.
disable probes [provider [name [objfile]]]See the enable probes command above for a description of the optional arguments accepted by this command.
A probe may specify up to twelve arguments. These are available at the point at which
the probe is defined—that is, when the current PC is at the probe’s location. The arguments are available using the convenience variables (see Section 10.12 [Convenience Vars],
page 171) $_probe_arg0. . . $_probe_arg11. In SystemTap probes each probe argument is
an integer of the appropriate size; types are not preserved. In DTrace probes types arepreserved provided that they are recognized as such by gdb; otherwise the value of theprobe argument will be a long integer. The convenience variable $_probe_argc holds thenumber of arguments at the current probe point.
These variables are always available, but attempts to access them at any location otherthan a probe point will cause gdb to give an error message.

5.1.11 “Cannot insert breakpoints”
If you request too many active hardware-assisted breakpoints and watchpoints, you will see
this error message:
Stopped; cannot insert breakpoints.
You may have requested too many hardware breakpoints and watchpoints.

This message is printed when you attempt to resume the program, since only then gdb
knows exactly how many hardware breakpoints and watchpoints it needs to insert.
When this message is printed, you need to disable or remove some of the hardwareassisted breakpoints and watchpoints, and then continue.

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5.1.12 “Breakpoint address adjusted...”Some processor architectures place constraints on the addresses at which breakpoints may
be placed. For architectures thus constrained, gdb will attempt to adjust the breakpoint’s
address to comply with the constraints dictated by the architecture.
One example of such an architecture is the Fujitsu FR-V. The FR-V is a VLIW architecture in which a number of RISC-like instructions may be bundled together for parallel
execution. The FR-V architecture constrains the location of a breakpoint instruction withinsuch a bundle to the instruction with the lowest address. gdb honors this constraint by
adjusting a breakpoint’s address to the first in the bundle.
It is not uncommon for optimized code to have bundles which contain instructions fromdifferent source statements, thus it may happen that a breakpoint’s address will be adjusted
from one source statement to another. Since this adjustment may significantly alter gdb’s
breakpoint related behavior from what the user expects, a warning is printed when the
breakpoint is first set and also when the breakpoint is hit.
A warning like the one below is printed when setting a breakpoint that’s been subject
to address adjustment:
warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.

Such warnings are printed both for user settable and gdb’s internal breakpoints. If you
see one of these warnings, you should verify that a breakpoint set at the adjusted address
will have the desired affect. If not, the breakpoint in question may be removed and otherbreakpoints may be set which will have the desired behavior. E.g., it may be sufficient toplace the breakpoint at a later instruction. A conditional breakpoint may also be useful insome cases to prevent the breakpoint from triggering too often.
gdb will also issue a warning when stopping at one of these adjusted breakpoints:
warning: Breakpoint 1 address previously adjusted from 0x00010414
to 0x00010410.

When this warning is encountered, it may be too late to take remedial action except incases where the breakpoint is hit earlier or more frequently than expected.

5.2 Continuing and Stepping
Continuing means resuming program execution until your program completes normally. In
contrast, stepping means executing just one more “step” of your program, where “step”
may mean either one line of source code, or one machine instruction (depending on whatparticular command you use). Either when continuing or when stepping, your program maystop even sooner, due to a breakpoint or a signal. (If it stops due to a signal, you may want
to use handle, or use ‘signal 0’ to resume execution (see Section 5.4 [Signals], page 89),or you may step into the signal’s handler (see [stepping and signal handlers], page 91).)
continue [ignore-count]c [ignore-count]fg [ignore-count]
Resume program execution, at the address where your program last stopped;
any breakpoints set at that address are bypassed. The optional argument
ignore-count allows you to specify a further number of times to ignore a breakpoint at this location; its effect is like that of ignore (see Section 5.1.6 [Break
Conditions], page 76).

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The argument ignore-count is meaningful only when your program stopped due
to a breakpoint. At other times, the argument to continue is ignored.
The synonyms c and fg (for foreground, as the debugged program is deemed
to be the foreground program) are provided purely for convenience, and haveexactly the same behavior as continue.
To resume execution at a different place, you can use return (see Section 17.4 [Returningfrom a Function], page 280) to go back to the calling function; or jump (see Section 17.2
[Continuing at a Different Address], page 278) to go to an arbitrary location in your program.
A typical technique for using stepping is to set a breakpoint (see Section 5.1 [Breakpoints;
Watchpoints; and Catchpoints], page 57) at the beginning of the function or the sectionof your program where a problem is believed to lie, run your program until it stops atthat breakpoint, and then step through the suspect area, examining the variables that areinteresting, until you see the problem happen.
step

Continue running your program until control reaches a different source line,
then stop it and return control to gdb. This command is abbreviated s.
Warning: If you use the step command while control is withina function that was compiled without debugging information, execution proceeds until control reaches a function that does havedebugging information. Likewise, it will not step into a function
which is compiled without debugging information. To step throughfunctions without debugging information, use the stepi command,
described below.
The step command only stops at the first instruction of a source line. This prevents the multiple stops that could otherwise occur in switch statements, forloops, etc. step continues to stop if a function that has debugging information
is called within the line. In other words, step steps inside any functions called
within the line.
Also, the step command only enters a function if there is line number information for the function. Otherwise it acts like the next command. This avoids
problems when using cc -gl on MIPS machines. Previously, step entered subroutines if there was any debugging information about the routine.

step countContinue running as in step, but do so count times. If a breakpoint is reached,or a signal not related to stepping occurs before count steps, stepping stops
right away.
next [count]
Continue to the next source line in the current (innermost) stack frame. Thisis similar to step, but function calls that appear within the line of code are
executed without stopping. Execution stops when control reaches a different
line of code at the original stack level that was executing when you gave thenext command. This command is abbreviated n.
An argument count is a repeat count, as for step.

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The next command only stops at the first instruction of a source line. This
prevents multiple stops that could otherwise occur in switch statements, forloops, etc.
set step-mode
set step-mode on
The set step-mode on command causes the step command to stop at the first
instruction of a function which contains no debug line information rather thanstepping over it.
This is useful in cases where you may be interested in inspecting the machine
instructions of a function which has no symbolic info and do not want gdb toautomatically skip over this function.
set step-mode off
Causes the step command to step over any functions which contains no debug
information. This is the default.
show step-mode
Show whether gdb will stop in or step over functions without source line debug
information.
finishContinue running until just after function in the selected stack frame returns.
Print the returned value (if any). This command can be abbreviated as fin.
Contrast this with the return command (see Section 17.4 [Returning from a
Function], page 280).

set print finish [on|off]show print finish
By default the finish command will show the value that is returned by thefunction. This can be disabled using set print finish off. When disabled,
the value is still entered into the value history (see Section 10.11 [Value History],
page 170), but not displayed.
untiluContinue running until a source line past the current line, in the current stack
frame, is reached. This command is used to avoid single stepping through a loop
more than once. It is like the next command, except that when until encounters a jump, it automatically continues execution until the program counter isgreater than the address of the jump.
This means that when you reach the end of a loop after single stepping thoughit, until makes your program continue execution until it exits the loop. In contrast, a next command at the end of a loop simply steps back to the beginningof the loop, which forces you to step through the next iteration.
until always stops your program if it attempts to exit the current stack frame.
until may produce somewhat counterintuitive results if the order of machinecode does not match the order of the source lines. For example, in the following
excerpt from a debugging session, the f (frame) command shows that execution
is stopped at line 206; yet when we use until, we get to line 195:(gdb) f

86

Debugging with gdb#0 main (argc=4, argv=0xf7fffae8) at m4.c:206
206
expand_input();(gdb) until195
for ( ; argc > 0; NEXTARG) {This happened because, for execution efficiency, the compiler had generated
code for the loop closure test at the end, rather than the start, of the loop—
even though the test in a C for-loop is written before the body of the loop.
The until command appeared to step back to the beginning of the loop whenit advanced to this expression; however, it has not really gone to an earlier
statement—not in terms of the actual machine code.
until with no argument works by means of single instruction stepping, andhence is slower than until with an argument.
until locspec
u locspec Continue running your program until either it reaches a code location that
results from resolving locspec, or the current stack frame returns. locspec is
any of the forms described in Section 9.2 [Location Specifications], page 126.
This form of the command uses temporary breakpoints, and hence is quicker
than until without an argument. The specified location is actually reachedonly if it is in the current frame. This implies that until can be used toskip over recursive function invocations. For instance in the code below, if thecurrent location is line 96, issuing until 99 will execute the program up toline 99 in the same invocation of factorial, i.e., after the inner invocations havereturned.
94 int factorial (int value)
95 {96
if (value > 1) {97
value *= factorial (value - 1);
98}
99
return (value);100}

advance locspec
Continue running your program until either it reaches a code location that
results from resolving locspec, or the current stack frame returns. locspec is
any of the forms described in Section 9.2 [Location Specifications], page 126.
This command is similar to until, but advance will not skip over recursivefunction calls, and the target code location doesn’t have to be in the same
frame as the current one.
stepi
stepi argsi
Execute one machine instruction, then stop and return to the debugger.
It is often useful to do ‘display/i $pc’ when stepping by machine instructions.
This makes gdb automatically display the next instruction to be executed, eachtime your program stops. See Section 10.8 [Automatic Display], page 155.
An argument is a repeat count, as in step.

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nexti
nexti argni
Execute one machine instruction, but if it is a function call, proceed until thefunction returns.
An argument is a repeat count, as in next.
By default, and if available, gdb makes use of target-assisted range stepping. In otherwords, whenever you use a stepping command (e.g., step, next), gdb tells the target tostep the corresponding range of instruction addresses instead of issuing multiple single-steps.
This speeds up line stepping, particularly for remote targets. Ideally, there should be noreason you would want to turn range stepping off. However, it’s possible that a bug in the
debug info, a bug in the remote stub (for remote targets), or even a bug in gdb could makeline stepping behave incorrectly when target-assisted range stepping is enabled. You can
use the following command to turn off range stepping if necessary:
set range-steppingshow range-stepping
Control whether range stepping is enabled.
If on, and the target supports it, gdb tells the target to step a range of addresses
itself, instead of issuing multiple single-steps. If off, gdb always issues singlesteps, even if range stepping is supported by the target. The default is on.

5.3 Skipping Over Functions and FilesThe program you are debugging may contain some functions which are uninteresting to
debug. The skip command lets you tell gdb to skip a function, all functions in a file or aparticular function in a particular file when stepping.
For example, consider the following C function:
101
102
103
104
105

int func(){
foo(boring());
bar(boring());}

Suppose you wish to step into the functions foo and bar, but you are not interested instepping through boring. If you run step at line 103, you’ll enter boring(), but if you run
next, you’ll step over both foo and boring!
One solution is to step into boring and use the finish command to immediately exit
it. But this can become tedious if boring is called from many places.
A more flexible solution is to execute skip boring. This instructs gdb never to step
into boring. Now when you execute step at line 103, you’ll step over boring and directly
into foo.
Functions may be skipped by providing either a function name, linespec (see Section 9.2[Location Specifications], page 126), regular expression that matches the function’s name,file name or a glob-style pattern that matches the file name.
On Posix systems the form of the regular expression is “Extended Regular Expressions”.
See for example ‘man 7 regex’ on gnu/Linux systems. On non-Posix systems the form of
the regular expression is whatever is provided by the regcomp function of the underlying

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system. See for example ‘man 7 glob’ on gnu/Linux systems for a description of glob-stylepatterns.
skip [options]
The basic form of the skip command takes zero or more options that specify
what to skip. The options argument is any useful combination of the following:-file file-fi file Functions in file will be skipped over when stepping.
-gfile file-glob-pattern-gfi file-glob-pattern
Functions in files matching file-glob-pattern will be skipped overwhen stepping.
(gdb) skip -gfi utils/*.c-function linespec-fu linespec
Functions named by linespec or the function containing the line
named by linespec will be skipped over when stepping. See
Section 9.2 [Location Specifications], page 126.
-rfunction regexp-rfu regexp
Functions whose name matches regexp will be skipped over when
stepping.
This form is useful for complex function names. For example, there
is generally no need to step into C++ std::string constructors ordestructors. Plus with C++ templates it can be hard to write out
the full name of the function, and often it doesn’t matter what the
template arguments are. Specifying the function to be skipped asa regular expression makes this easier.
(gdb) skip -rfu ^std::(allocator|basic_string)<.*>::~?\1 *\(If you want to skip every templated C++ constructor and destructorin the std namespace you can do:(gdb) skip -rfu ^std::([a-zA-z0-9_]+)<.*>::~?\1 *\(If no options are specified, the function you’re currently debugging will beskipped.
skip function [linespec]
After running this command, the function named by linespec or the function
containing the line named by linespec will be skipped over when stepping. See
Section 9.2 [Location Specifications], page 126.
If you do not specify linespec, the function you’re currently debugging will beskipped.
(If you have a function called file that you want to skip, use skip function
file.)

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skip file [filename]
After running this command, any function whose source lives in filename will
be skipped over when stepping.
(gdb) skip file boring.c
File boring.c will be skipped when stepping.

If you do not specify filename, functions whose source lives in the file you’recurrently debugging will be skipped.
Skips can be listed, deleted, disabled, and enabled, much like breakpoints. These are
the commands for managing your list of skips:
info skip [range]
Print details about the specified skip(s). If range is not specified, print a tablewith details about all functions and files marked for skipping. info skip prints
the following information about each skip:
Identifier

A number identifying this skip.

Enabled or Disabled
Enabled skips are marked with ‘y’. Disabled skips are marked with
‘n’.
Glob

If the file name is a ‘glob’ pattern this is ‘y’. Otherwise it is ‘n’.

File

The name or ‘glob’ pattern of the file to be skipped. If no file is
specified this is ‘<none>’.

RE

If the function name is a ‘regular expression’ this is ‘y’. Otherwise it is ‘n’.

Function

The name or regular expression of the function to skip. If no function is specified this is ‘<none>’.

skip delete [range]
Delete the specified skip(s). If range is not specified, delete all skips.
skip enable [range]
Enable the specified skip(s). If range is not specified, enable all skips.
skip disable [range]
Disable the specified skip(s). If range is not specified, disable all skips.
set debug skip [on|off]
Set whether to print the debug output about skipping files and functions.
show debug skip
Show whether the debug output about skipping files and functions is printed.

5.4 Signals
A signal is an asynchronous event that can happen in a program. The operating systemdefines the possible kinds of signals, and gives each kind a name and a number. For example,
in Unix SIGINT is the signal a program gets when you type an interrupt character (often
Ctrl-c); SIGSEGV is the signal a program gets from referencing a place in memory far

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away from all the areas in use; SIGALRM occurs when the alarm clock timer goes off (whichhappens only if your program has requested an alarm).
Some signals, including SIGALRM, are a normal part of the functioning of your program.
Others, such as SIGSEGV, indicate errors; these signals are fatal (they kill your program
immediately) if the program has not specified in advance some other way to handle thesignal. SIGINT does not indicate an error in your program, but it is normally fatal so it can
carry out the purpose of the interrupt: to kill the program.
gdb has the ability to detect any occurrence of a signal in your program. You can tell
gdb in advance what to do for each kind of signal.
Normally, gdb is set up to let the non-erroneous signals like SIGALRM be silently passed
to your program (so as not to interfere with their role in the program’s functioning) but tostop your program immediately whenever an error signal happens. You can change thesesettings with the handle command.
info signals
info handle
Print a table of all the kinds of signals and how gdb has been told to handle
each one. You can use this to see the signal numbers of all the defined types ofsignals.
info signals sig
Similar, but print information only about the specified signal number.
info handle is an alias for info signals.
catch signal [signal... | ‘all’]Set a catchpoint for the indicated signals. See Section 5.1.3 [Set Catchpoints],
page 69, for details about this command.
handle signal [ signal ... ] [keywords...]Change the way gdb handles each signal. Each signal can be the numberof a signal or its name (with or without the ‘SIG’ at the beginning); a listof signal numbers of the form ‘low-high’; or the word ‘all’, meaning all the
known signals, except SIGINT and SIGTRAP, which are used by gdb. Optional
argument keywords, described below, say what changes to make to all of thespecified signals.
The keywords allowed by the handle command can be abbreviated. Their full names
are:nostopgdb should not stop your program when this signal happens. It may still print
a message telling you that the signal has come in.

stop

gdb should stop your program when this signal happens. This implies theprint keyword as well.

print

gdb should print a message when this signal happens.

noprint

gdb should not mention the occurrence of the signal at all. This implies thenostop keyword as well.

Chapter 5: Stopping and Continuing

pass
noignore

nopassignore91

gdb should allow your program to see this signal; your program can handle thesignal, or else it may terminate if the signal is fatal and not handled. pass andnoignore are synonyms.
gdb should not allow your program to see this signal. nopass and ignore aresynonyms.

When a signal stops your program, the signal is not visible to the program until you
continue. Your program sees the signal then, if pass is in effect for the signal in question
at that time. In other words, after gdb reports a signal, you can use the handle commandwith pass or nopass to control whether your program sees that signal when you continue.
The default is set to nostop, noprint, pass for non-erroneous signals such as SIGALRM,
SIGWINCH and SIGCHLD, and to stop, print, pass for the erroneous signals.
You can also use the signal command to prevent your program from seeing a signal, or
cause it to see a signal it normally would not see, or to give it any signal at any time. For
example, if your program stopped due to some sort of memory reference error, you mightstore correct values into the erroneous variables and continue, hoping to see more execution;
but your program would probably terminate immediately as a result of the fatal signal once
it saw the signal. To prevent this, you can continue with ‘signal 0’. See Section 17.3
[Giving your Program a Signal], page 279.
gdb optimizes for stepping the mainline code. If a signal that has handle nostop andhandle pass set arrives while a stepping command (e.g., stepi, step, next) is in progress,
gdb lets the signal handler run and then resumes stepping the mainline code once the signal
handler returns. In other words, gdb steps over the signal handler. This prevents signalsthat you’ve specified as not interesting (with handle nostop) from changing the focus of
debugging unexpectedly. Note that the signal handler itself may still hit a breakpoint, stop
for another signal that has handle stop in effect, or for any other event that normally
results in stopping the stepping command sooner. Also note that gdb still informs you thatthe program received a signal if handle print is set.
If you set handle pass for a signal, and your program sets up a handler for it, thenissuing a stepping command, such as step or stepi, when your program is stopped due tothe signal will step into the signal handler (if the target supports that).
Likewise, if you use the queue-signal command to queue a signal to be delivered tothe current thread when execution of the thread resumes (see Section 17.3 [Giving yourProgram a Signal], page 279), then a stepping command will step into the signal handler.
Here’s an example, using stepi to step to the first instruction of SIGUSR1’s handler:(gdb) handle SIGUSR1
SignalStop
SIGUSR1
Yes(gdb) cContinuing.

Print
Yes

Pass to program Description
Yes
User defined signal 1

Program received signal SIGUSR1, User defined signal 1.
main () sigusr1.c:28
28
p = 0;(gdb) si
sigusr1_handler () at sigusr1.c:9

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9{

The same, but using queue-signal instead of waiting for the program to receive thesignal first:(gdb) n28
p = 0;(gdb) queue-signal SIGUSR1(gdb) si
sigusr1_handler () at sigusr1.c:9
9
{
(gdb)

On some targets, gdb can inspect extra signal information associated with the intercepted signal, before it is actually delivered to the program being debugged. This information is exported by the convenience variable $_siginfo, and consists of data that is passedby the kernel to the signal handler at the time of the receipt of a signal. The data type of
the information itself is target dependent. You can see the data type using the ptype $_siginfo command. On Unix systems, it typically corresponds to the standard siginfo_t
type, as defined in the signal.h system header.
Here’s an example, on a gnu/Linux system, printing the stray referenced address thatraised a segmentation fault.
(gdb) continue
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400766 in main ()69*(int *)p = 0;(gdb) ptype $_siginfo
type = struct {int si_signo;
int si_errno;
int si_code;
union {
int _pad[28];struct {...} _kill;
struct {...} _timer;
struct {...} _rt;struct {...} _sigchld;
struct {...} _sigfault;
struct {...} _sigpoll;} _sifields;}(gdb) ptype $_siginfo._sifields._sigfault
type = struct {void *si_addr;}(gdb) p $_siginfo._sifields._sigfault.si_addr$1 = (void *) 0x7ffff7ff7000

Depending on target support, $_siginfo may also be writable.

5.5 Stopping and Starting Multi-thread Programs
gdb supports debugging programs with multiple threads (see Section 4.10 [Debugging Programs with Multiple Threads], page 47). There are two modes of controlling execution ofyour program within the debugger. In the default mode, referred to as all-stop mode, when
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other threads in the program are also stopped by gdb. On some targets, gdb also supports
non-stop mode, in which other threads can continue to run freely while you examine thestopped thread in the debugger.

5.5.1 All-Stop ModeIn all-stop mode, whenever your program stops under gdb for any reason, all threads ofexecution stop, not just the current thread. This allows you to examine the overall stateof the program, including switching between threads, without worrying that things maychange underfoot.
Conversely, whenever you restart the program, all threads start executing. This is true
even when single-stepping with commands like step or next.
In particular, gdb cannot single-step all threads in lockstep. Since thread schedulingis up to your debugging target’s operating system (not controlled by gdb), other threads
may execute more than one statement while the current thread completes a single step.
Moreover, in general other threads stop in the middle of a statement, rather than at a clean
statement boundary, when the program stops.
You might even find your program stopped in another thread after continuing or evensingle-stepping. This happens whenever some other thread runs into a breakpoint, a signal,or an exception before the first thread completes whatever you requested.
Whenever gdb stops your program, due to a breakpoint or a signal, it automaticallyselects the thread where that breakpoint or signal happened. gdb alerts you to the context
switch with a message such as ‘[Switching to Thread n]’ to identify the thread.
On some OSes, you can modify gdb’s default behavior by locking the OS scheduler toallow only a single thread to run.
set scheduler-locking mode
Set the scheduler locking mode. It applies to normal execution, record mode,and replay mode. mode can be one of the following:
off

There is no locking and any thread may run at any time.

on

Only the current thread may run when the inferior is resumed.
New threads created by the resumed thread are held stopped attheir entry point, before they execute any instruction.

step

Behaves like on when stepping, and off otherwise. Threads otherthan the current never get a chance to run when you step, and they
are completely free to run when you use commands like ‘continue’,‘until’, or ‘finish’.
This mode optimizes for single-stepping; it prevents other threads
from preempting the current thread while you are stepping, so thatthe focus of debugging does not change unexpectedly. However,unless another thread hits a breakpoint during its timeslice, gdb
does not change the current thread away from the thread that you
are debugging.

replayBehaves like on in replay mode, and off in either record mode or
during normal execution. This is the default mode.

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show scheduler-locking
Display the current scheduler locking mode.
By default, when you issue one of the execution commands such as continue, next
or step, gdb allows only threads of the current inferior to run. For example, if gdb is
attached to two inferiors, each with two threads, the continue command resumes only thetwo threads of the current inferior. This is useful, for example, when you debug a programthat forks and you want to hold the parent stopped (so that, for instance, it doesn’t run toexit), while you debug the child. In other situations, you may not be interested in inspecting
the current state of any of the processes gdb is attached to, and you may want to resume
them all until some breakpoint is hit. In the latter case, you can instruct gdb to allow all
threads of all the inferiors to run with the set schedule-multiple command.
set schedule-multiple
Set the mode for allowing threads of multiple processes to be resumed when an
execution command is issued. When on, all threads of all processes are allowed
to run. When off, only the threads of the current process are resumed. The
default is off. The scheduler-locking mode takes precedence when set toon, or while you are stepping and set to step.
show schedule-multiple
Display the current mode for resuming the execution of threads of multiple
processes.

5.5.2 Non-Stop Mode
For some multi-threaded targets, gdb supports an optional mode of operation in which
you can examine stopped program threads in the debugger while other threads continue to
execute freely. This minimizes intrusion when debugging live systems, such as programs
where some threads have real-time constraints or must continue to respond to external
events. This is referred to as non-stop mode.
In non-stop mode, when a thread stops to report a debugging event, only that thread is
stopped; gdb does not stop other threads as well, in contrast to the all-stop mode behavior.
Additionally, execution commands such as continue and step apply by default only tothe current thread in non-stop mode, rather than all threads as in all-stop mode. This
allows you to control threads explicitly in ways that are not possible in all-stop mode — forexample, stepping one thread while allowing others to run freely, stepping one thread while
holding all others stopped, or stepping several threads independently and simultaneously.
To enter non-stop mode, use this sequence of commands before you run or attach toyour program:# If using the CLI, pagination breaks non-stop.
set pagination off# Finally, turn it on!
set non-stop on

You can use these commands to manipulate the non-stop mode setting:
set non-stop on
Enable selection of non-stop mode.

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set non-stop off
Disable selection of non-stop mode.
show non-stop
Show the current non-stop enablement setting.
Note these commands only reflect whether non-stop mode is enabled, not whether thecurrently-executing program is being run in non-stop mode. In particular, the set non-stop
preference is only consulted when gdb starts or connects to the target program, and it isgenerally not possible to switch modes once debugging has started. Furthermore, since not
all targets support non-stop mode, even when you have enabled non-stop mode, gdb may
still fall back to all-stop operation by default.
In non-stop mode, all execution commands apply only to the current thread by default.
That is, continue only continues one thread. To continue all threads, issue continue -aor c -a.
You can use gdb’s background execution commands (see Section 5.5.3 [Background
Execution], page 95) to run some threads in the background while you continue to examineor step others from gdb. The MI execution commands (see Section 27.15 [GDB/MI Program
Execution], page 627) are always executed asynchronously in non-stop mode.
Suspending execution is done with the interrupt command when running in the background, or Ctrl-c during foreground execution. In all-stop mode, this stops the wholeprocess; but in non-stop mode the interrupt applies only to the current thread. To stop thewhole program, use interrupt -a.
Other execution commands do not currently support the -a option.
In non-stop mode, when a thread stops, gdb doesn’t automatically make that thread
current, as it does in all-stop mode. This is because the thread stop notifications are
asynchronous with respect to gdb’s command interpreter, and it would be confusing if gdb
unexpectedly changed to a different thread just as you entered a command to operate on
the previously current thread.

5.5.3 Background Execution
gdb’s execution commands have two variants: the normal foreground (synchronous) behavior, and a background (asynchronous) behavior. In foreground execution, gdb waits for the
program to report that some thread has stopped before prompting for another command.
In background execution, gdb immediately gives a command prompt so that you can issue
other commands while your program runs.
If the target doesn’t support async mode, gdb issues an error message if you attempt
to use the background execution commands.
To specify background execution, add a & to the command. For example, the backgroundform of the continue command is continue&, or just c&. The execution commands that
accept background execution are:run

See Section 4.2 [Starting your Program], page 34.

attachSee Section 4.7 [Debugging an Already-running Process], page 41.

step

See Section 5.2 [Continuing and Stepping], page 83.

stepi

See Section 5.2 [Continuing and Stepping], page 83.

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next

See Section 5.2 [Continuing and Stepping], page 83.

nexti

See Section 5.2 [Continuing and Stepping], page 83.

continue

See Section 5.2 [Continuing and Stepping], page 83.

finishSee Section 5.2 [Continuing and Stepping], page 83.

until

See Section 5.2 [Continuing and Stepping], page 83.

Background execution is especially useful in conjunction with non-stop mode for debugging programs with multiple threads; see Section 5.5.2 [Non-Stop Mode], page 94. However,you can also use these commands in the normal all-stop mode with the restriction that you
cannot issue another execution command until the previous one finishes. Examples of commands that are valid in all-stop mode while the program is running include help and info
break.
You can interrupt your program while it is running in the background by using theinterrupt command.
interrupt
interrupt -a
Suspend execution of the running program. In all-stop mode, interrupt stops
the whole process, but in non-stop mode, it stops only the current thread. To
stop the whole program in non-stop mode, use interrupt -a.

5.5.4 Thread-Specific Breakpoints
When your program has multiple threads (see Section 4.10 [Debugging Programs with
Multiple Threads], page 47), you can choose whether to set breakpoints on all threads, oron a particular thread.
break locspec thread thread-id
break locspec thread thread-id if ...
locspec specifies a code location or locations in your program. See Section 9.2[Location Specifications], page 126, for details.
Use the qualifier ‘thread thread-id’ with a breakpoint command to specify
that you only want gdb to stop the program when a particular thread reaches
this breakpoint. The thread-id specifier is one of the thread identifiers assigned
by gdb, shown in the first column of the ‘info threads’ display.
If you do not specify ‘thread thread-id’ when you set a breakpoint, the breakpoint applies to all threads of your program.
You can use the thread qualifier on conditional breakpoints as well; in thiscase, place ‘thread thread-id’ before or after the breakpoint condition, likethis:(gdb) break frik.c:13 thread 28 if bartab > lim

Thread-specific breakpoints are automatically deleted when gdb detects the corresponding thread is no longer in the thread list. For example:(gdb) cThread-specific breakpoint 3 deleted - thread 28 no longer in the thread list.

There are several ways for a thread to disappear, such as a regular thread exit, but also
when you detach from the process with the detach command (see Section 4.7 [Debugging an

Chapter 5: Stopping and Continuing

97

Already-running Process], page 41), or if gdb loses the remote connection (see Chapter 20[Remote Debugging], page 315), etc. Note that with some targets, gdb is only able todetect a thread has exited when the user explicitly asks for the thread list with the info
threads command.
A breakpoint can’t be both thread-specific and inferior-specific (see Section 4.9.1[Inferior-Specific Breakpoints], page 46), or task-specific (see Section 15.4.10.7 [Ada Tasks],
page 255); using more than one of the thread, inferior, or task keywords when creatinga breakpoint will give an error.

5.5.5 Interrupted System Calls
There is an unfortunate side effect when using gdb to debug multi-threaded programs. If
one thread stops for a breakpoint, or for some other reason, and another thread is blocked
in a system call, then the system call may return prematurely. This is a consequenceof the interaction between multiple threads and the signals that gdb uses to implement
breakpoints and other events that stop execution.
To handle this problem, your program should check the return value of each system calland react appropriately. This is good programming style anyways.
For example, do not write code like this:sleep (10);The call to sleep will return early if a different thread stops at a breakpoint or for someother reason.
Instead, write this:int unslept = 10;
while (unslept > 0)
unslept = sleep (unslept);

A system call is allowed to return early, so the system is still conforming to its specification. But gdb does cause your multi-threaded program to behave differently than it would
without gdb.
Also, gdb uses internal breakpoints in the thread library to monitor certain events suchas thread creation and thread destruction. When such an event happens, a system callin another thread may return prematurely, even though your program does not appear tostop.

5.5.6 Observer ModeIf you want to build on non-stop mode and observe program behavior without any chanceof disruption by gdb, you can set variables to disable all of the debugger’s attempts tomodify state, whether by writing memory, inserting breakpoints, etc. These operate at alow level, intercepting operations from all commands.
When all of these are set to off, then gdb is said to be observer mode. As a convenience,the variable observer can be set to disable these, plus enable non-stop mode.
Note that gdb will not prevent you from making nonsensical combinations of these settings. For instance, if you have enabled may-insert-breakpoints but disabled may-writememory, then breakpoints that work by writing trap instructions into the code stream will
still not be able to be placed.

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set observer on
set observer off
When set to on, this disables all the permission variables below (except for
insert-fast-tracepoints), plus enables non-stop debugging. Setting this tooff switches back to normal debugging, though remaining in non-stop mode.
show observerShow whether observer mode is on or off.
set may-write-registers on
set may-write-registers off
This controls whether gdb will attempt to alter the values of registers, such aswith assignment expressions in print, or the jump command. It defaults to on.
show may-write-registers
Show the current permission to write registers.
set may-write-memory on
set may-write-memory off
This controls whether gdb will attempt to alter the contents of memory, suchas with assignment expressions in print. It defaults to on.
show may-write-memory
Show the current permission to write memory.
set may-insert-breakpoints on
set may-insert-breakpoints off
This controls whether gdb will attempt to insert breakpoints. This affects all
breakpoints, including internal breakpoints defined by gdb. It defaults to on.
show may-insert-breakpoints
Show the current permission to insert breakpoints.
set may-insert-tracepoints on
set may-insert-tracepoints off
This controls whether gdb will attempt to insert (regular) tracepoints at the
beginning of a tracing experiment. It affects only non-fast tracepoints, fast tracepoints being under the control of may-insert-fast-tracepoints. It defaults
to on.
show may-insert-tracepoints
Show the current permission to insert tracepoints.
set may-insert-fast-tracepoints on
set may-insert-fast-tracepoints off
This controls whether gdb will attempt to insert fast tracepoints at the beginning of a tracing experiment. It affects only fast tracepoints, regular (non-fast)
tracepoints being under the control of may-insert-tracepoints. It defaults
to on.
show may-insert-fast-tracepoints
Show the current permission to insert fast tracepoints.

99

set may-interrupt on
set may-interrupt off
This controls whether gdb will attempt to interrupt or stop program execution.
When this variable is off, the interrupt command will have no effect, nor will
Ctrl-c. It defaults to on.
show may-interrupt
Show the current permission to interrupt or stop the program.

101

6 Running programs backward
When you are debugging a program, it is not unusual to realize that you have gone too far,and some event of interest has already happened. If the target environment supports it,
gdb can allow you to “rewind” the program by running it backward.
A target environment that supports reverse execution should be able to “undo” thechanges in machine state that have taken place as the program was executing normally.
Variables, registers etc. should revert to their previous values. Obviously this requires a
great deal of sophistication on the part of the target environment; not all target environments can support reverse execution.
When a program is executed in reverse, the instructions that have most recently been
executed are “un-executed”, in reverse order. The program counter runs backward, following the previous thread of execution in reverse. As each instruction is “un-executed”, thevalues of memory and/or registers that were changed by that instruction are reverted totheir previous states. After executing a piece of source code in reverse, all side effects ofthat code should be “undone”, and all variables should be returned to their prior values1 .
On some platforms, gdb has built-in support for reverse execution, activated with therecord or record btrace commands. See Chapter 7 [Process Record and Replay], page 103.
Some remote targets, typically full system emulators, support reverse execution directly
without requiring any special command.
If you are debugging in a target environment that supports reverse execution, gdb
provides the following commands.
reverse-continue [ignore-count]rc [ignore-count]
Beginning at the point where your program last stopped, start executing inreverse. Reverse execution will stop for breakpoints and synchronous exceptions(signals), just like normal execution. Behavior of asynchronous signals depends
on the target environment.
reverse-step [count]
Run the program backward until control reaches the start of a different source
line; then stop it, and return control to gdb.
Like the step command, reverse-step will only stop at the beginning of asource line. It “un-executes” the previously executed source line. If the previous source line included calls to debuggable functions, reverse-step will
step (backward) into the called function, stopping at the beginning of the laststatement in the called function (typically a return statement).
Also, as with the step command, if non-debuggable functions are called,
reverse-step will run through them backward without stopping.
1

Note that some side effects are easier to undo than others. For instance, memory and registers are
relatively easy, but device I/O is hard. Some targets may be able undo things like device I/O, and some
may not.
The contract between gdb and the reverse executing target requires only that the target do something
reasonable when gdb tells it to execute backwards, and then report the results back to gdb. Whatever
the target reports back to gdb, gdb will report back to the user. gdb assumes that the memory andregisters that the target reports are in a consistent state, but gdb accepts whatever it is given.

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reverse-stepi [count]
Reverse-execute one machine instruction. Note that the instruction to bereverse-executed is not the one pointed to by the program counter, but the
instruction executed prior to that one. For instance, if the last instruction wasa jump, reverse-stepi will take you back from the destination of the jump to
the jump instruction itself.
reverse-next [count]
Run backward to the beginning of the previous line executed in the current(innermost) stack frame. If the line contains function calls, they will be“un-executed” without stopping. Starting from the first line of a function,
reverse-next will take you back to the caller of that function, before thefunction was called, just as the normal next command would take you fromthe last line of a function back to its return to its caller2 .
reverse-nexti [count]
Like nexti, reverse-nexti executes a single instruction in reverse, exceptthat called functions are “un-executed” atomically. That is, if the previously
executed instruction was a return from another function, reverse-nexti willcontinue to execute in reverse until the call to that function (from the current
stack frame) is reached.
reverse-finish
Just as the finish command takes you to the point where the current function
returns, reverse-finish takes you to the point where it was called. Insteadof ending up at the end of the current function invocation, you end up at the
beginning.
set exec-direction
Set the direction of target execution.
set exec-direction reverse
gdb will perform all execution commands in reverse, until the exec-direction
mode is changed to “forward”. Affected commands include step, stepi,
next, nexti, continue, and finish. The return command cannot be usedin reverse mode.
set exec-direction forward
gdb will perform all execution commands in the normal fashion. This is thedefault.

2

Unless the code is too heavily optimized.

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7 Recording Inferior’s Execution and Replaying It
On some platforms, gdb provides a special process record and replay target that can record
a log of the process execution, and replay it later with both forward and reverse executioncommands.
When this target is in use, if the execution log includes the record for the next instruction,
gdb will debug in replay mode. In the replay mode, the inferior does not really executecode instructions. Instead, all the events that normally happen during code execution aretaken from the execution log. While code is not really executed in replay mode, the valuesof registers (including the program counter register) and the memory of the inferior are stillchanged as they normally would. Their contents are taken from the execution log.
If the record for the next instruction is not in the execution log, gdb will debug in record
mode. In this mode, the inferior executes normally, and gdb records the execution log for
future replay.
The process record and replay target supports reverse execution (see Chapter 6 [Reverse
Execution], page 101), even if the platform on which the inferior runs does not. However,
the reverse execution is limited in this case by the range of the instructions recorded in theexecution log. In other words, reverse execution on platforms that don’t support it directly
can only be done in the replay mode.
When debugging in the reverse direction, gdb will work in replay mode as long as theexecution log includes the record for the previous instruction; otherwise, it will work inrecord mode, if the platform supports reverse execution, or stop if not.
Currently, process record and replay is supported on ARM, Aarch64, Moxie, PowerPC,PowerPC64, S/390, and x86 (i386/amd64) running GNU/Linux. Process record and replay
can be used both when native debugging, and when remote debugging via gdbserver.
When recording an inferior, gdb may print auxiliary information during stepping commands and commands displaying the execution history.
For architecture environments that support process record and replay, gdb provides thefollowing commands:
record method
This command starts the process record and replay target. The recording
method can be specified as parameter. Without a parameter the command
uses the full recording method. The following recording methods are available:
full

Full record/replay recording using gdb’s software record and replay implementation. This method allows replaying and reverse
execution.

btrace format
Hardware-supported instruction recording, supported on Intel processors. This method does not record data. Further, the data iscollected in a ring buffer so old data will be overwritten when thebuffer is full. It allows limited reverse execution. Variables andregisters are not available during reverse execution. In remote debugging, recording continues on disconnect. Recorded data can be

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Debugging with gdb

inspected after reconnecting. The recording may be stopped using
record stop.
The recording format can be specified as parameter. Without a parameter the command chooses the recording format. The following
recording formats are available:bts

Use the Branch Trace Store (BTS) recording format.
In this format, the processor stores a from/to record
for each executed branch in the btrace ring buffer.

pt

Use the Intel Processor Trace recording format. In thisformat, the processor stores the execution trace in acompressed form that is afterwards decoded by gdb.
The trace can be recorded with very low overhead. The
compressed trace format also allows small trace buffers
to already contain a big number of instructions compared to BTS.
Decoding the recorded execution trace, on the other
hand, is more expensive than decoding BTS trace. Thisis mostly due to the increased number of instructions toprocess. You should increase the buffer-size with care.

Not all recording formats may be available on all processors.
The process record and replay target can only debug a process that is alreadyrunning. Therefore, you need first to start the process with the run or startcommands, and then start the recording with the record method command.
Displaced stepping (see Appendix D [displaced stepping], page 755) will be
automatically disabled when process record and replay target is started. That’s
because the process record and replay target doesn’t support displaced stepping.
If the inferior is in the non-stop mode (see Section 5.5.2 [Non-Stop Mode],
page 94) or in the asynchronous execution mode (see Section 5.5.3 [Background
Execution], page 95), not all recording methods are available. The full recording method does not support these two modes.
record stop
Stop the process record and replay target. When process record and replay
target stops, the entire execution log will be deleted and the inferior will either
be terminated, or will remain in its final state.
When you stop the process record and replay target in record mode (at theend of the execution log), the inferior will be stopped at the next instructionthat would have been recorded. In other words, if you record for a while andthen stop recording, the inferior process will be left in the same state as if therecording never happened.
On the other hand, if the process record and replay target is stopped while inreplay mode (that is, not at the end of the execution log, but at some earlier
point), the inferior process will become “live” at that earlier state, and it willthen be possible to continue the usual “live” debugging of the process from thatstate.

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When the inferior process exits, or gdb detaches from it, process record andreplay target will automatically stop itself.
record goto
Go to a specific location in the execution log. There are several ways to specify
the location to go to:record goto begin
record goto start
Go to the beginning of the execution log.
record goto end
Go to the end of the execution log.
record goto n
Go to instruction number n in the execution log.
record save filename
Save the execution log to a file filename.
Default filename is
gdb_record.process_id, where process id is the process ID of the inferior.
This command may not be available for all recording methods.
record restore filename
Restore the execution log from a file filename. File must have been createdwith record save.
set record full insn-number-max limit
set record full insn-number-max unlimited
Set the limit of instructions to be recorded for the full recording method.
Default value is 200000.
If limit is a positive number, then gdb will start deleting instructions from thelog once the number of the record instructions becomes greater than limit. For
every new recorded instruction, gdb will delete the earliest recorded instruction to keep the number of recorded instructions at the limit. (Since deleting
recorded instructions loses information, gdb lets you control what happens
when the limit is reached, by means of the stop-at-limit option, described
below.)
If limit is unlimited or zero, gdb will never delete recorded instructions fromthe execution log. The number of recorded instructions is limited only by theavailable memory.
show record full insn-number-max
Show the limit of instructions to be recorded with the full recording method.
set record full stop-at-limit
Control the behavior of the full recording method when the number of recorded
instructions reaches the limit. If ON (the default), gdb will stop when the limit
is reached for the first time and ask you whether you want to stop the inferior orcontinue running it and recording the execution log. If you decide to continue
recording, each new recorded instruction will cause the oldest one to be deleted.
If this option is OFF, gdb will automatically delete the oldest record to makeroom for each new one, without asking.

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show record full stop-at-limit
Show the current setting of stop-at-limit.
set record full memory-query
Control the behavior when gdb is unable to record memory changes caused byan instruction for the full recording method. If ON, gdb will query whether
to stop the inferior in that case.
If this option is OFF (the default), gdb will automatically ignore the effect ofsuch instructions on memory. Later, when gdb replays this execution log, it
will mark the log of this instruction as not accessible, and it will not affect the
replay results.
show record full memory-queryShow the current setting of memory-query.
The btrace record target does not trace data. As a convenience, when replaying, gdb reads read-only memory off the live program directly, assuming thatthe addresses of the read-only areas don’t change. This for example makes it
possible to disassemble code while replaying, but not to print variables. In somecases, being able to inspect variables might be useful. You can use the following
command for that:set record btrace replay-memory-accessControl the behavior of the btrace recording method when accessing memory
during replay. If read-only (the default), gdb will only allow accesses toread-only memory. If read-write, gdb will allow accesses to read-only and toread-write memory. Beware that the accessed memory corresponds to the live
target and not necessarily to the current replay position.
set record btrace cpu identifier
Set the processor to be used for enabling workarounds for processor errata when
decoding the trace.
Processor errata are defects in processor operation, caused by its design or
manufacture. They can cause a trace not to match the specification. This, inturn, may cause trace decode to fail. gdb can detect erroneous trace packets
and correct them, thus avoiding the decoding failures. These corrections are
known as errata workarounds, and are enabled based on the processor on which
the trace was recorded.
By default, gdb attempts to detect the processor automatically, and apply thenecessary workarounds for it. However, you may need to specify the processor
if gdb does not yet support it. This command allows you to do that, and also
allows to disable the workarounds.
The argument identifier identifies the cpu and is of the form: vendor:processor identifier. In addition, there are two special identifiers,
none and auto (default).
The following vendor identifiers and corresponding processor identifiers are currently supported:Chapter 7: Recording Inferior’s Execution and Replaying It

intel

107

family/model[/stepping]On GNU/Linux systems, the processor family, model, and stepping can beobtained from /proc/cpuinfo.
If identifier is auto, enable errata workarounds for the processor on which thetrace was recorded. If identifier is none, errata workarounds are disabled.
For example, when using an old gdb on a new system, decode may fail because
gdb does not support the new processor. It often suffices to specify an older
processor that gdb supports.
(gdb) info record
Active record target: record-btrace
Recording format: Intel Processor Trace.
Buffer size: 16kB.
Failed to configure the Intel Processor Trace decoder: unknown cpu.
(gdb) set record btrace cpu intel:6/158(gdb) info record
Active record target: record-btrace
Recording format: Intel Processor Trace.
Buffer size: 16kB.
Recorded 84872 instructions in 3189 functions (0 gaps) for thread 1 (...).

show record btrace replay-memory-accessShow the current setting of replay-memory-access.
show record btrace cpu
Show the processor to be used for enabling trace decode errata workarounds.
set record btrace bts buffer-size size
set record btrace bts buffer-size unlimited
Set the requested ring buffer size for branch tracing in BTS format. Default is
64KB.
If size is a positive number, then gdb will try to allocate a buffer of at least size
bytes for each new thread that uses the btrace recording method and the BTS
format. The actually obtained buffer size may differ from the requested size.
Use the info record command to see the actual buffer size for each thread thatuses the btrace recording method and the BTS format.
If limit is unlimited or zero, gdb will try to allocate a buffer of 4MB.
Bigger buffers mean longer traces. On the other hand, gdb will also need longer
to process the branch trace data before it can be used.
show record btrace bts buffer-size size
Show the current setting of the requested ring buffer size for branch tracing in
BTS format.
set record btrace pt buffer-size size
set record btrace pt buffer-size unlimited
Set the requested ring buffer size for branch tracing in Intel Processor Traceformat. Default is 16KB.
If size is a positive number, then gdb will try to allocate a buffer of at least
size bytes for each new thread that uses the btrace recording method and the

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Intel Processor Trace format. The actually obtained buffer size may differ fromthe requested size. Use the info record command to see the actual buffer sizefor each thread.
If limit is unlimited or zero, gdb will try to allocate a buffer of 4MB.
Bigger buffers mean longer traces. On the other hand, gdb will also need longer
to process the branch trace data before it can be used.
show record btrace pt buffer-size size
Show the current setting of the requested ring buffer size for branch tracing inIntel Processor Trace format.
set record btrace pt event-tracing
Enable or disable event tracing for branch tracing in Intel Processor Trace format. When enabled, events are recorded during execution as auxiliary information and will be printed during stepping commands and commands displaying
the execution history. Changing this setting has no effect on an active recording.
The default is off.
show record btrace pt event-tracing
Show the current setting of Intel Processor Trace event tracing.
info record
Show various statistics about the recording depending on the recording method:full

For the full recording method, it shows the state of process record
and its in-memory execution log buffer, including:• Whether in record mode or replay mode.
• Lowest recorded instruction number (counting from when thecurrent execution log started recording instructions).
• Highest recorded instruction number.
• Current instruction about to be replayed (if in replay mode).
• Number of instructions contained in the execution log.
• Maximum number of instructions that may be contained in theexecution log.

btraceFor the btrace recording method, it shows:• Recording format.
• Number of instructions that have been recorded.
• Number of blocks of sequential control-flow formed by therecorded instructions.
• Whether in record mode or replay mode.
For the bts recording format, it also shows:• Size of the perf ring buffer.
For the pt recording format, it also shows:• Size of the perf ring buffer.

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109

record delete
When record target runs in replay mode (“in the past”), delete the subsequent
execution log and begin to record a new execution log starting from the current
address. This means you will abandon the previously recorded “future” andbegin recording a new “future”.
record instruction-history
Disassembles instructions from the recorded execution log. By default, ten
instructions are disassembled. This can be changed using the set record
instruction-history-size command. Instructions are printed in execution
order.
It can also print mixed source+disassembly if you specify the the /m or /smodifier, and print the raw instructions in hex as well as in symbolic form byspecifying the /r or /b modifier. The behaviour of the /m, /s, /r, and /b
modifiers are the same as for the disassemble command (see [disassemble],
page 136).
The current position marker is printed for the instruction at the current program
counter value. This instruction can appear multiple times in the trace and thecurrent position marker will be printed every time. To omit the current position
marker, specify the /p modifier.
To better align the printed instructions when the trace contains instructions
from more than one function, the function name may be omitted by specifying
the /f modifier.
Printing auxiliary information is enabled by default and can be omitted withthe /a modifier.
Speculatively executed instructions are prefixed with ‘?’. This feature is notavailable for all recording formats.
There are several ways to specify what part of the execution log to disassemble:
record instruction-history insn
Disassembles ten instructions starting from instruction number
insn.
record instruction-history insn, +/-nDisassembles n instructions around instruction number insn. If n
is preceded with +, disassembles n instructions after instruction
number insn. If n is preceded with -, disassembles n instructions
before instruction number insn.
record instruction-history
Disassembles ten more instructions after the last disassembly.
record instruction-history Disassembles ten more instructions before the last disassembly.
record instruction-history begin, end
Disassembles instructions beginning with instruction number begin until instruction number end. The instruction number end isincluded.

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This command may not be available for all recording methods.
set record instruction-history-size size
set record instruction-history-size unlimited
Define how many instructions to disassemble in the record
instruction-history command. The default value is 10. A size ofunlimited means unlimited instructions.
show record instruction-history-sizeShow how many instructions
instruction-history command.

todisassemble

in

the

recordrecord function-call-history
Prints the execution history at function granularity. For each sequence of instructions that belong to the same function, it prints the name of that function,
the source lines for this instruction sequence (if the /l modifier is specified),
and the instructions numbers that form the sequence (if the /i modifier is specified). The function names are indented to reflect the call stack depth if the /cmodifier is specified. Printing auxiliary information is enabled by default andcan be omitted with the /a modifier. The /l, /i, /a, and /c modifiers can begiven together.
(gdb) list 1, 10
1void foo (void)
2
{
3
}
4
5
void bar (void)
6
{
7
...
8
foo ();
9...
10 }(gdb) record function-call-history /ilc
1 bar
inst 1,4
at foo.c:6,82
foo
inst 5,10
at foo.c:2,3
3 bar
inst 11,13
at foo.c:9,10

By default, ten functions are printed. This can be changed using the set record
function-call-history-size command. Functions are printed in execution
order. There are several ways to specify what to print:
record function-call-history func
Prints ten functions starting from function number func.
record function-call-history func, +/-n
Prints n functions around function number func. If n is precededwith +, prints n functions after function number func. If n is preceded with -, prints n functions before function number func.
record function-call-history
Prints ten more functions after the last ten-function print.
record function-call-history Prints ten more functions before the last ten-function print.

111

record function-call-history begin, end
Prints functions beginning with function number begin until function number end. The function number end is included.
This command may not be available for all recording methods.
set record function-call-history-size size
set record function-call-history-size unlimited
Define how many functions to print in the record function-call-history
command. The default value is 10. A size of unlimited means unlimited
functions.
show record function-call-history-sizeShow how many functions to print in the record function-call-history command.

113

8 Examining the Stack
When your program has stopped, the first thing you need to know is where it stopped andhow it got there.
Each time your program performs a function call, information about the call is generated.
That information includes the location of the call in your program, the arguments of thecall, and the local variables of the function being called. The information is saved in a blockof data called a stack frame. The stack frames are allocated in a region of memory called
the call stack.
When your program stops, the gdb commands for examining the stack allow you to see
all of this information.
One of the stack frames is selected by gdb and many gdb commands refer implicitly
to the selected frame. In particular, whenever you ask gdb for the value of a variable inyour program, the value is found in the selected frame. There are special gdb commands toselect whichever frame you are interested in. See Section 8.3 [Selecting a Frame], page 117.
When your program stops, gdb automatically selects the currently executing frame anddescribes it briefly, similar to the frame command (see Section 8.4 [Information about aFrame], page 119).

8.1 Stack Frames
The call stack is divided up into contiguous pieces called stack frames, or frames for short;each frame is the data associated with one call to one function. The frame contains thearguments given to the function, the function’s local variables, and the address at which
the function is executing.
When your program is started, the stack has only one frame, that of the function main.
This is called the initial frame or the outermost frame. Each time a function is called, a
new frame is made. Each time a function returns, the frame for that function invocation
is eliminated. If a function is recursive, there can be many frames for the same function.
The frame for the function in which execution is actually occurring is called the innermost
frame. This is the most recently created of all the stack frames that still exist.
Inside your program, stack frames are identified by their addresses. A stack frame
consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually thisaddress is kept in a register called the frame pointer register (see Section 10.14 [Registers],
page 179) while execution is going on in that frame.
gdb labels each existing stack frame with a level, a number that is zero for the innermost
frame, one for the frame that called it, and so on upward. These level numbers give you
a way of designating stack frames in gdb commands. The terms frame number and framelevel can be used interchangeably to describe this number.
Some compilers provide a way to compile functions so that they operate without stack
frames. (For example, the gcc option‘-fomit-frame-pointer’

generates functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. gdb has limited facilities for dealing with

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these function invocations. If the innermost function invocation has no stack frame, gdb
nevertheless regards it as though it had a separate frame, which is numbered zero as usual,
allowing correct tracing of the function call chain. However, gdb has no provision forframeless functions elsewhere in the stack.

8.2 Backtraces
A backtrace is a summary of how your program got where it is. It shows one line per frame,
for many frames, starting with the currently executing frame (frame zero), followed by its
caller (frame one), and on up the stack.
To print a backtrace of the entire stack, use the backtrace command, or its alias bt.
This command will print one line per frame for frames in the stack. By default, all stack
frames are printed. You can stop the backtrace at any time by typing the system interrupt
character, normally Ctrl-c.
backtrace [option]... [qualifier]... [count]bt [option]... [qualifier]... [count]
Print the backtrace of the entire stack.
The optional count can be one of the following:nnPrint only the innermost n frames, where n is a positive number.

-n-nPrint only the outermost n frames, where n is a positive number.

Options:-full

Print the values of the local variables also. This can be combinedwith the optional count to limit the number of frames shown.

-no-filters
Do not run Python frame filters on this backtrace.
See
Section 23.3.2.10 [Frame Filter API], page 430, for more
information. Additionally use [disable frame-filter all], page 122,
to turn off all frame filters. This is only relevant when gdb has
been configured with Python support.
-hide

A Python frame filter might decide to “elide” some frames. Normally such elided frames are still printed, but they are indented
relative to the filtered frames that cause them to be elided. The-hide option causes elided frames to not be printed at all.

The backtrace command also supports a number of options that allow overriding relevant global print settings as set by set backtrace and set print
subcommands:-past-main [on|off]
Set whether backtraces should continue past main. Related setting:[set backtrace past-main], page 116.
-past-entry [on|off]
Set whether backtraces should continue past the entry point of aprogram. Related setting: [set backtrace past-entry], page 116.

Chapter 8: Examining the Stack

115-entry-values no|only|preferred|if-needed|both|compact|default
Set printing of function arguments at function entry. Related setting: [set print entry-values], page 161.
-frame-arguments all|scalars|none
Set printing of non-scalar frame arguments. Related setting: [setprint frame-arguments], page 160.
-raw-frame-arguments [on|off]
Set whether to print frame arguments in raw form. Related setting:[set print raw-frame-arguments], page 161.
-frame-info auto|source-line|location|source-andlocation|location-and-address|short-location
Set printing of frame information. Related setting: [set print frameinfo], page 163.
The optional qualifier is maintained for backward compatibility. It can be oneof the following:
full

Equivalent to the -full option.

no-filters
Equivalent to the -no-filters option.
hide

Equivalent to the -hide option.

The names where and info stack (abbreviated info s) are additional aliases forbacktrace.
In a multi-threaded program, gdb by default shows the backtrace only for the current
thread. To display the backtrace for several or all of the threads, use the command thread
apply (see Section 4.10 [Threads], page 47). For example, if you type thread apply all
backtrace, gdb will display the backtrace for all the threads; this is handy when you debug
a core dump of a multi-threaded program.
Each line in the backtrace shows the frame number and the function name. The program
counter value is also shown—unless you use set print address off. The backtrace also
shows the source file name and line number, as well as the arguments to the function. The
program counter value is omitted if it is at the beginning of the code for that line number.
Here is an example of a backtrace. It was made with the command ‘bt 3’, so it shows
the innermost three frames.
#0m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993#1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242#2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
at macro.c:71(More stack frames follow...)

The display for frame zero does not begin with a program counter value, indicating thatyour program has stopped at the beginning of the code for line 993 of builtin.c.
The value of parameter data in frame 1 has been replaced by .... By default, gdb prints
the value of a parameter only if it is a scalar (integer, pointer, enumeration, etc). Seecommand set print frame-arguments in Section 10.9 [Print Settings], page 157, for more

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details on how to configure the way function parameter values are printed. The commandset print frame-info (see Section 10.9 [Print Settings], page 157) controls what frame
information is printed.
If your program was compiled with optimizations, some compilers will optimize away
arguments passed to functions if those arguments are never used after the call. Such optimizations generate code that passes arguments through registers, but doesn’t store thosearguments in the stack frame. gdb has no way of displaying such arguments in stack frames
other than the innermost one. Here’s what such a backtrace might look like:#0m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993#1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242#2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08)
at macro.c:71(More stack frames follow...)

The values of arguments that were not saved in their stack frames are shown as ‘<optimizedout>’.
If you need to display the values of such optimized-out arguments, either deduce thatfrom other variables whose values depend on the one you are interested in, or recompile
without optimizations.
Most programs have a standard user entry point—a place where system libraries andstartup code transition into user code. For C this is main1 . When gdb finds the entry
function in a backtrace it will terminate the backtrace, to avoid tracing into highly systemspecific (and generally uninteresting) code.
If you need to examine the startup code, or limit the number of levels in a backtrace,
you can change this behavior:
set backtrace past-main
set backtrace past-main on
Backtraces will continue past the user entry point.
set backtrace past-main off
Backtraces will stop when they encounter the user entry point. This is thedefault.
show backtrace past-main
Display the current user entry point backtrace policy.
set backtrace past-entry
set backtrace past-entry on
Backtraces will continue past the internal entry point of an application. This
entry point is encoded by the linker when the application is built, and is likely
before the user entry point main (or equivalent) is called.
set backtrace past-entry off
Backtraces will stop when they encounter the internal entry point of an application. This is the default.
1Note that embedded programs (the so-called “free-standing” environment) are not required to have amain function as the entry point. They could even have multiple entry points.

Chapter 8: Examining the Stack

117

show backtrace past-entry
Display the current internal entry point backtrace policy.
set backtrace limit n
set backtrace limit 0
set backtrace limit unlimited
Limit the backtrace to n levels. A value of unlimited or zero means unlimited
levels.
show backtrace limit
Display the current limit on backtrace levels.
You can control how file names are displayed.
set filename-display
set filename-display relative
Display file names relative to the compilation directory. This is the default.
set filename-display basename
Display only basename of a filename.
set filename-display absolute
Display an absolute filename.
show filename-display
Show the current way to display filenames.

8.3 Selecting a Frame
Most commands for examining the stack and other data in your program work on whicheverstack frame is selected at the moment. Here are the commands for selecting a stack frame;
all of them finish by printing a brief description of the stack frame just selected.
frame [ frame-selection-spec ]f [ frame-selection-spec ]The frame command allows different stack frames to be selected. The frameselection-spec can be any of the following:num
level num Select frame level num. Recall that frame zero is the innermost(currently executing) frame, frame one is the frame that called theinnermost one, and so on. The highest level frame is usually the
one for main.
As this is the most common method of navigating the frame stack,the string level can be omitted. For example, the following two
commands are equivalent:(gdb) frame 3(gdb) frame level 3

address stack-address
Select the frame with stack address stack-address. The stackaddress for a frame can be seen in the output of info frame, forexample:(gdb) info frame

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Stack level 1, frame at 0x7fffffffda30:
rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
tail call frame, caller of frame at 0x7fffffffda30
source language c++.
Arglist at unknown address.
Locals at unknown address, Previous frame’s sp is 0x7fffffffda30

The stack-address for this frame is 0x7fffffffda30 as indicatedby the line:
Stack level 1, frame at 0x7fffffffda30:

function function-nameSelect the stack frame for function function-name. If there are
multiple stack frames for function function-name then the innermost stack frame is selected.
view stack-address [ pc-addr ]View a frame that is not part of gdb’s backtrace. The frame viewed
has stack address stack-addr, and optionally, a program counter
address of pc-addr.
This is useful mainly if the chaining of stack frames has been damaged by a bug, making it impossible for gdb to assign numbers
properly to all frames. In addition, this can be useful when yourprogram has multiple stacks and switches between them.
When viewing a frame outside the current backtrace using frame
view then you can always return to the original stack using one ofthe previous stack frame selection instructions, for example framelevel 0.
up nMove n frames up the stack; n defaults to 1. For positive numbers n, thisadvances toward the outermost frame, to higher frame numbers, to frames thathave existed longer.

down nMove n frames down the stack; n defaults to 1. For positive numbers n, thisadvances toward the innermost frame, to lower frame numbers, to frames thatwere created more recently. You may abbreviate down as do.

All of these commands end by printing two lines of output describing the frame. The
first line shows the frame number, the function name, the arguments, and the source fileand line number of execution in that frame. The second line shows the text of that sourceline.
For example:(gdb) up
#1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
at env.c:1010
read_input_file (argv[i]);After such a printout, the list command with no arguments prints ten lines centered on
the point of execution in the frame. You can also edit the program at the point of execution
with your favorite editing program by typing edit. See Section 9.1 [Printing Source Lines],
page 125, for details.

Chapter 8: Examining the Stack

119

select-frame [ frame-selection-spec ]The select-frame command is a variant of frame that does not display the
new frame after selecting it. This command is intended primarily for use in
gdb command scripts, where the output might be unnecessary and distracting.
The frame-selection-spec is as for the frame command described in Section 8.3[Selecting a Frame], page 117.
up-silently ndown-silently n
These two commands are variants of up and down, respectively; they differ inthat they do their work silently, without causing display of the new frame. They
are intended primarily for use in gdb command scripts, where the output might
be unnecessary and distracting.

8.4 Information About a Frame
There are several other commands to print information about the selected stack frame.
frame
fWhen used without any argument, this command does not change which frame
is selected, but prints a brief description of the currently selected stack frame.
It can be abbreviated f. With an argument, this command is used to select astack frame. See Section 8.3 [Selecting a Frame], page 117.

info frame
info fThis command prints a verbose description of the selected stack frame, including:• the address of the frame• the address of the next frame down (called by this frame)• the address of the next frame up (caller of this frame)• the language in which the source code corresponding to this frame is written• the address of the frame’s arguments• the address of the frame’s local variables• the program counter saved in it (the address of execution in the caller
frame)• which registers were saved in the frame
The verbose description is useful when something has gone wrong that has madethe stack format fail to fit the usual conventions.
info frame [ frame-selection-spec ]info f [ frame-selection-spec ]Print a verbose description of the frame selected by frame-selection-spec. The
frame-selection-spec is the same as for the frame command (see Section 8.3[Selecting a Frame], page 117). The selected frame remains unchanged by thiscommand.
info args [-q]Print the arguments of the selected frame, each on a separate line.

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The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no argument have been printed.
info args [-q] [-t type_regexp] [regexp]
Like info args, but only print the arguments selected with the provided regexp(s).
If regexp is provided, print only the arguments whose names match the regularexpression regexp.
If type regexp is provided, print only the arguments whose types, as printed by
the whatis command, match the regular expression type regexp. If type regexp
contains space(s), it should be enclosed in quote characters. If needed, usebackslash to escape the meaning of special characters or quotes.
If both regexp and type regexp are provided, an argument is printed only if its
name matches regexp and its type matches type regexp.
info locals [-q]Print the local variables of the selected frame, each on a separate line. These
are all variables (declared either static or automatic) accessible at the point ofexecution of the selected frame.
The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no local variables have been printed.
info locals [-q] [-t type_regexp] [regexp]
Like info locals, but only print the local variables selected with the provided
regexp(s).
If regexp is provided, print only the local variables whose names match theregular expression regexp.
If type regexp is provided, print only the local variables whose types, as
printed by the whatis command, match the regular expression type regexp.
If type regexp contains space(s), it should be enclosed in quote characters. Ifneeded, use backslash to escape the meaning of special characters or quotes.
If both regexp and type regexp are provided, a local variable is printed only if
its name matches regexp and its type matches type regexp.
The command info locals -q -t type_regexp can usefully be combined withthe commands frame apply and thread apply. For example, your program
might use Resource Acquisition Is Initialization types (RAII) such as lock_something_t: each local variable of type lock_something_t automaticallyplaces a lock that is destroyed when the variable goes out of scope. You canthen list all acquired locks in your program by doing
thread apply all -s frame apply all -s info locals -q -t lock_something_t

or the equivalent shorter formtfaas i lo -q -t lock_something_t

8.5 Applying a Command to Several Frames.
frame apply [all | count | -count | level level...] [option]... command
The frame apply command allows you to apply the named command to one
or more frames.

Chapter 8: Examining the Stack

121

all

Specify all to apply command to all frames.

count

Use count to apply command to the innermost count frames, wherecount is a positive number.

-countUse -count to apply command to the outermost count frames, wherecount is a positive number.

level

Use level to apply command to the set of frames identified by thelevel list. level is a frame level or a range of frame levels as level1level2. The frame level is the number shown in the first field of the‘backtrace’ command output. E.g., ‘2-4 6-8 3’ indicates to applycommand for the frames at levels 2, 3, 4, 6, 7, 8, and then again onframe at level 3.

Note that the frames on which frame apply applies a command are also influenced by the set backtrace settings such as set backtrace past-main andset backtrace limit N. See Section 8.2 [Backtraces], page 114.
The frame apply command also supports a number of options that allow overriding relevant set backtrace settings:-past-main [on|off]
Whether backtraces should continue past main. Related setting:[set backtrace past-main], page 116.
-past-entry [on|off]
Whether backtraces should continue past the entry point of a program. Related setting: [set backtrace past-entry], page 116.
By default, gdb displays some frame information before the output producedby command, and an error raised during the execution of a command will abort
frame apply. The following options can be used to fine-tune these behaviors:-c

The flag -c, which stands for ‘continue’, causes any errors in command to be displayed, and the execution of frame apply then continues.

-s

The flag -s, which stands for ‘silent’, causes any errors or empty
output produced by a command to be silently ignored. That is, theexecution continues, but the frame information and errors are notprinted.

-q

The flag -q (‘quiet’) disables printing the frame information.

The following example shows how the flags -c and -s are working when applying
the command p j to all frames, where variable j can only be successfully printed
in the outermost #1 main frame.

122

Debugging with gdb(gdb) frame apply all p j#0 some_function (i=5) at fun.c:4
No symbol "j" in current context.
(gdb) frame apply all -c p j#0 some_function (i=5) at fun.c:4
No symbol "j" in current context.
#1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11$1 = 5(gdb) frame apply all -s p j#1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11$2 = 5(gdb)

By default, ‘frame apply’, prints the frame location information before thecommand output:(gdb) frame apply all p $sp#0 some_function (i=5) at fun.c:4$4 = (void *) 0xffffd1e0#1 0x565555fb in main (argc=1, argv=0xffffd2c4) at fun.c:11$5 = (void *) 0xffffd1f0(gdb)

If the flag -q is given, no frame information is printed:(gdb) frame apply all -q p $sp$12 = (void *) 0xffffd1e0$13 = (void *) 0xffffd1f0(gdb)

faas command
Shortcut for frame apply all -s command. Applies command on all frames,
ignoring errors and empty output.
It can for example be used to print a local variable or a function argument
without knowing the frame where this variable or argument is, using:(gdb) faas p some_local_var_i_do_not_remember_where_it_is

The faas command accepts the same options as the frame apply command.
See Section 8.5 [frame apply], page 120.
Note that the command tfaas command applies command on all frames of all
threads. See See Section 4.10 [Threads], page 47.

8.6 Management of Frame Filters.
Frame filters are Python based utilities to manage and decorate the output of frames. See
Section 23.3.2.10 [Frame Filter API], page 430, for further information.
Managing frame filters is performed by several commands available within gdb, detailed
here.
info frame-filter
Print a list of installed frame filters from all dictionaries, showing their name,priority and enabled status.
disable frame-filter filter-dictionary filter-name
Disable a frame filter in the dictionary matching filter-dictionary and filtername. The filter-dictionary may be all, global, progspace, or the name ofChapter 8: Examining the Stack123

the object file where the frame filter dictionary resides. When all is specified,
all frame filters across all dictionaries are disabled. The filter-name is the nameof the frame filter and is used when all is not the option for filter-dictionary.
A disabled frame-filter is not deleted, it may be enabled again later.
enable frame-filter filter-dictionary filter-nameEnable a frame filter in the dictionary matching filter-dictionary and filtername. The filter-dictionary may be all, global, progspace or the name ofthe object file where the frame filter dictionary resides. When all is specified,
all frame filters across all dictionaries are enabled. The filter-name is the nameof the frame filter and is used when all is not the option for filter-dictionary.
Example:(gdb) info frame-filter
global frame-filters:
Priority Enabled Name
1000
No
PrimaryFunctionFilter
100
Yes
Reverseprogspace /build/test frame-filters:
Priority Enabled Name
100
Yes
ProgspaceFilter
objfile /build/test frame-filters:
Priority Enabled Name
999
Yes
BuildProgramFilter(gdb) disable frame-filter /build/test BuildProgramFilter(gdb) info frame-filter
global frame-filters:
Priority Enabled Name
1000
No
PrimaryFunctionFilter
100
Yes
Reverseprogspace /build/test frame-filters:
Priority Enabled Name
100
Yes
ProgspaceFilter
objfile /build/test frame-filters:
Priority Enabled Name
999
No
BuildProgramFilter(gdb) enable frame-filter global PrimaryFunctionFilter(gdb) info frame-filter
global frame-filters:
Priority Enabled Name
1000
Yes
PrimaryFunctionFilter
100
Yes
Reverseprogspace /build/test frame-filters:
Priority Enabled Name
100
Yes
ProgspaceFilter
objfile /build/test frame-filters:

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Priority
999

EnabledNo

Name
BuildProgramFilter

set frame-filter priority filter-dictionary filter-name priority
Set the priority of a frame filter in the dictionary matching filter-dictionary,and the frame filter name matching filter-name. The filter-dictionary may beglobal, progspace or the name of the object file where the frame filter dictionary resides. The priority is an integer.
show frame-filter priority filter-dictionary filter-name
Show the priority of a frame filter in the dictionary matching filter-dictionary,and the frame filter name matching filter-name. The filter-dictionary may beglobal, progspace or the name of the object file where the frame filter dictionary resides.
Example:(gdb) info frame-filter
global frame-filters:
Priority Enabled Name
1000
Yes
PrimaryFunctionFilter
100
Yes
Reverseprogspace /build/test frame-filters:
Priority Enabled Name
100
Yes
ProgspaceFilter
objfile /build/test frame-filters:
Priority Enabled Name
999
No
BuildProgramFilter(gdb) set frame-filter priority global Reverse 50(gdb) info frame-filter
global frame-filters:
Priority Enabled Name
1000
Yes
PrimaryFunctionFilter
50
Yes
Reverseprogspace /build/test frame-filters:
Priority Enabled Name
100
Yes
ProgspaceFilter
objfile /build/test frame-filters:
Priority Enabled Name
999
No
BuildProgramFilter

125

9 Examining Source Files
gdb can print parts of your program’s source, since the debugging information recorded in
the program tells gdb what source files were used to build it. When your program stops,
gdb spontaneously prints the line where it stopped. Likewise, when you select a stack frame(see Section 8.3 [Selecting a Frame], page 117), gdb prints the line where execution in thatframe has stopped. You can print other portions of source files by explicit command.
If you use gdb through its gnu Emacs interface, you may prefer to use Emacs facilities
to view source; see Chapter 26 [Using gdb under gnu Emacs], page 587.

9.1 Printing Source Lines
To print lines from a source file, use the list command (abbreviated l). By default, tenlines are printed. There are several ways to specify what part of the file you want to print;
see Section 9.2 [Location Specifications], page 126, for the full list.
Here are the forms of the list command most commonly used:
list linenum
Print lines centered around line number linenum in the current source file.
list function
Print lines centered around the beginning of function function.
list

Print more lines. If the last lines printed were printed with a list command,
this prints lines following the last lines printed; however, if the last line printed
was a solitary line printed as part of displaying a stack frame (see Chapter 8[Examining the Stack], page 113), this prints lines centered around that line. If
no list command has been used and no solitary line was printed, it prints thelines around the function main.

list +

Same as using with no arguments.

list -

Print lines just before the lines last printed.

list .

Print the lines surrounding the point of execution within the currently selected
frame. If the inferior is not running, print lines around the start of the mainfunction instead.

By default, gdb prints ten source lines with any of these forms of the list command.
You can change this using set listsize:
set listsize countset listsize unlimited
Make the list command display count source lines (unless the list argument
explicitly specifies some other number). Setting count to unlimited or 0 means
there’s no limit.
show listsize
Display the number of lines that list prints.
Repeating a list command with RET discards the argument, so it is equivalent to typing
just list. This is more useful than listing the same lines again. An exception is made for126

Debugging with gdb

an argument of ‘-’; that argument is preserved in repetition so that each repetition moves
up in the source file.
In general, the list command expects you to supply zero, one or two location specs.
These location specs are interpreted to resolve to source code lines; there are several waysof writing them (see Section 9.2 [Location Specifications], page 126), but the effect is always
to resolve to some source lines to display.
Here is a complete description of the possible arguments for list:
list locspec
Print lines centered around the line or lines of all the code locations that result
from resolving locspec.
list first,lastPrint lines from first to last. Both arguments are location specs. When a list
command has two location specs, and the source file of the second location spec
is omitted, this refers to the same source file as the first location spec. If either
first or last resolve to more than one source line in the program, then the list
command shows the list of resolved source lines and does not proceed with thesource code listing.
list ,lastPrint lines ending with last.
Likewise, if last resolves to more than one source line in the program, then thelist command prints the list of resolved source lines and does not proceed withthe source code listing.
list first,
Print lines starting with first.
list +

Print lines just after the lines last printed.

list -

Print lines just before the lines last printed.

list

As described in the preceding table.

9.2 Location Specifications
Several gdb commands accept arguments that specify a location or locations of your program’s code. Many times locations are specified using a source line number, but they
can also be specified by a function name, an address, a label, etc. The different forms ofspecifying a location that gdb recognizes are collectively known as forms of location specification, or location spec. This section documents the forms of specifying locations thatgdb recognizes.
When you specify a location, gdb needs to find the place in your program, known ascode location, that corresponds to the given location spec. We call this process of finding
actual code locations corresponding to a location spec location resolution.
A concrete code location in your program is uniquely identifiable by a set of several
attributes: its source line number, the name of its source file, the fully-qualified and prototyped function in which it is defined, and an instruction address. Because each inferior has
its own address space, the inferior number is also a necessary part of these attributes.

Chapter 9: Examining Source Files127

By contrast, location specs you type will many times omit some of these attributes. For
example, it is customary to specify just the source line number to mean a line in the current
source file, or specify just the basename of the file, omitting its directories. In other words,
a location spec is usually incomplete, a kind of blueprint, and gdb needs to complete themissing attributes by using the implied defaults, and by considering the source code andthe debug information available to it. This is what location resolution is about.
The resolution of an incomplete location spec can produce more than a single code
location, if the spec doesn’t allow distinguishing between them. Here are some examples ofsituations that result in a location spec matching multiple code locations in your program:• The location spec specifies a function name, and there are several functions in the
program which have that name. (To distinguish between them, you can specify afully-qualified and prototyped function name, such as A::func(int) instead of justfunc.)• The location spec specifies a source file name, and there are several source files in
the program that share the same name, for example several files with the same basename in different subdirectories. (To distinguish between them, specify enough leading
directories with the file name.)• For a C++ constructor, the gcc compiler generates several instances of the function
body, used in different cases, but their source-level names are identical.
• For a C++ template function, a given line in the function can correspond to any numberof instantiations.
• For an inlined function, a given source line can correspond to several actual code
locations with that function’s inlined code.
Resolution of a location spec can also fail to produce a complete code location, or even
fail to produce any code location. Here are some examples of such situations:• Some parts of the program lack detailed enough debug info, so the resolved code location
lacks some attributes, like source file name and line number, leaving just the instruction
address and perhaps also a function name. Such an incomplete code location is only
usable in contexts that work with addresses and/or function names. Some commands
can only work with complete code locations.
• The location spec specifies a function name, and there are no functions in the programby that name, or they only exist in a yet-unloaded shared library.
• The location spec specifies a source file name, and there are no source files in the
program by that name, or they only exist in a yet-unloaded shared library.
• The location spec specifies both a source file name and a source line number, and eventhough there are source files in the program that match the file name, none of thosefiles has the specified line number.
Locations may be specified using three different formats: linespec locations, explicit
locations, or address locations. The following subsections describe these formats.

9.2.1 Linespec Locations
A linespec is a colon-separated list of source location parameters such as file name, function
name, etc. Here are all the different ways of specifying a linespec:
linenum

Specifies the line number linenum of the current source file.

128-offset+offsetDebugging with gdb

Specifies the line offset lines before or after the current line. For the list
command, the current line is the last one printed; for the breakpoint commands,
this is the line at which execution stopped in the currently selected stack frame(see Section 8.1 [Frames], page 113, for a description of stack frames.) Whenused as the second of the two linespecs in a list command, this specifies theline offset lines up or down from the first linespec.

filename:linenum
Specifies the line linenum in the source file filename. If filename is a relative file
name, then it will match any source file name with the same trailing components. For example, if filename is ‘gcc/expr.c’, then it will match source filename of /build/trunk/gcc/expr.c, but not /build/trunk/libcpp/expr.c
or /build/trunk/gcc/x-expr.c.
function

Specifies the line that begins the body of the function function. For example,
in C, this is the line with the open brace.
By default, in C++ and Ada, function is interpreted as specifying all functions
named function in all scopes. For C++, this means in all namespaces and classes.
For Ada, this means in all packages.
For example, assuming a program with C++ symbols named A::B::func and
B::func, both commands break func and break B::func set a breakpoint on
both symbols.
Commands that accept a linespec let you override this with the -qualified option. For example, break -qualified func sets a breakpoint on a free-function
named func ignoring any C++ class methods and namespace functions calledfunc.
See Section 9.2.2 [Explicit Locations], page 129.

function:label
Specifies the line where label appears in function.
filename:function
Specifies the line that begins the body of the function function in the file
filename. You only need the file name with a function name to avoid ambiguity when there are identically named functions in different source files.
label

Specifies the line at which the label named label appears in the function corresponding to the currently selected stack frame. If there is no current selected
stack frame (for instance, if the inferior is not running), then gdb will notsearch for a label.

-pstap|-probe-stap [objfile:[provider:]]name
The gnu/Linux tool SystemTap provides a way for applications to embed static
probes. See Section 5.1.10 [Static Probe Points], page 81, for more information
on finding and using static probes. This form of linespec specifies the locationof such a static probe.
If objfile is given, only probes coming from that shared library or executablematching objfile as a regular expression are considered. If provider is given,

Chapter 9: Examining Source Files

129

then only probes from that provider are considered. If several probes matchthe spec, gdb will insert a breakpoint at each one of those probes.

9.2.2 Explicit Locations
Explicit locations allow the user to directly specify the source location’s parameters using
option-value pairs.
Explicit locations are useful when several functions, labels, or file names have the same
name (base name for files) in the program’s sources. In these cases, explicit locations point
to the source line you meant more accurately and unambiguously. Also, using explicit
locations might be faster in large programs.
For example, the linespec ‘foo:bar’ may refer to a function bar defined in the file named
foo or the label bar in a function named foo. gdb must search either the file system or
the symbol table to know.
The list of valid explicit location options is summarized in the following table:-source filename
The value specifies the source file name. To differentiate between files withthe same base name, prepend as many directories as is necessary to uniquely
identify the desired file, e.g., foo/bar/baz.c. Otherwise gdb will use the first
file it finds with the given base name. This option requires the use of either-function or -line.
-function function
The value specifies the name of a function. Operations on function locations
unmodified by other options (such as -label or -line) refer to the line thatbegins the body of the function. In C, for example, this is the line with theopen brace.
By default, in C++ and Ada, function is interpreted as specifying all functions
named function in all scopes. For C++, this means in all namespaces and classes.
For Ada, this means in all packages.
For example,
assuming a program with C++ symbols named
A::B::func and B::func,
both commands break -function func
and break -function B::func set a breakpoint on both symbols.
You can use the -qualified flag to override this (see below).
-qualified
This flag makes gdb interpret a function name specified with -function as acomplete fully-qualified name.
For example, assuming a C++ program with symbols named A::B::func and
B::func, the break -qualified -function B::func command sets a breakpoint on B::func, only.
(Note: the -qualified option can precede a linespec as well (see Section 9.2.1[Linespec Locations], page 127), so the particular example above could be simplified as break -qualified B::func.)-label label
The value specifies the name of a label. When the function name is not specified,the label is searched in the function of the currently selected stack frame.

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Debugging with gdb-line number
The value specifies a line offset for the location. The offset may either beabsolute (-line 3) or relative (-line +3), depending on the command. Whenspecified without any other options, the line offset is relative to the current line.
Explicit location options may be abbreviated by omitting any non-unique trailing characters from the option name, e.g., break -s main.c -li 3.

9.2.3 Address Locations
Address locations indicate a specific program address. They have the generalized form
*address.
For line-oriented commands, such as list and edit, this specifies a source line that
contains address. For break and other breakpoint-oriented commands, this can be used
to set breakpoints in parts of your program which do not have debugging information orsource files.
Here address may be any expression valid in the current working language (seeChapter 15 [Languages], page 227) that specifies a code address. In addition, as aconvenience, gdb extends the semantics of expressions used in locations to cover several
situations that frequently occur during debugging. Here are the various forms of address:
expression
Any expression valid in the current working language.
funcaddr

An address of a function or procedure derived from its name. In C, C++,
Objective-C, Fortran, minimal, and assembly, this is simply the function’s namefunction (and actually a special case of a valid expression). In Pascal andModula-2, this is &function. In Ada, this is function’Address (although the
Pascal form also works).
This form specifies the address of the function’s first instruction, before thestack frame and arguments have been set up.

’filename’:funcaddr
Like funcaddr above, but also specifies the name of the source file explicitly.
This is useful if the name of the function does not specify the function unambiguously, e.g., if there are several functions with identical names in different
source files.

9.3 Editing Source Files
To edit the lines in a source file, use the edit command. The editing program of yourchoice is invoked with the current line set to the active line in the program. Alternatively,
there are several ways to specify what part of the file you want to print if you want to see
other parts of the program:edit locspec
Edit the source file of the code location that results from resolving locspec.
Editing starts at the source file and source line locspec resolves to. See
Section 9.2 [Location Specifications], page 126, for all the possible forms of
the locspec argument.

Chapter 9: Examining Source Files131

If locspec resolves to more than one source line in your program, then thecommand prints the list of resolved source lines and does not proceed with theediting.
Here are the forms of the edit command most commonly used:
edit number
Edit the current source file with number as the active line number.
edit function
Edit the file containing function at the beginning of its definition.

9.3.1 Choosing your Editor
You can customize gdb to use any editor you want1 . By default, it is /bin/ex, but you canchange this by setting the environment variable EDITOR before using gdb. For example, toconfigure gdb to use the vi editor, you could use these commands with the sh shell:
EDITOR=/usr/bin/vi
export EDITOR
gdb ...

or in the csh shell,setenv EDITOR /usr/bin/vi
gdb ...

9.4 Searching Source Files
There are two commands for searching through the current source file for a regular expression.
forward-search regexp
search regexp
The command ‘forward-search regexp’ checks each line, starting with theone following the last line listed, for a match for regexp. It lists the line that isfound. You can use the synonym ‘search regexp’ or abbreviate the command
name as fo.
reverse-search regexp
The command ‘reverse-search regexp’ checks each line, starting with the one
before the last line listed and going backward, for a match for regexp. It lists
the line that is found. You can abbreviate this command as rev.

9.5 Specifying Source Directories
Executable programs sometimes do not record the directories of the source files from which
they were compiled, just the names. Even when they do, the directories could be moved
between the compilation and your debugging session. gdb has a list of directories to searchfor source files; this is called the source path. Each time gdb wants a source file, it tries all
1

The only restriction is that your editor (say ex), recognizes the following command-line syntax:
ex +number file
The optional numeric value +number specifies the number of the line in the file where to start editing.

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the directories in the list, in the order they are present in the list, until it finds a file withthe desired name.
For example, suppose an executable references the file /usr/src/foo-1.0/lib/foo.c,does not record a compilation directory, and the source path is /mnt/cross. gdb would
look for the source file in the following locations:
1. /usr/src/foo-1.0/lib/foo.c
2. /mnt/cross/usr/src/foo-1.0/lib/foo.c
3. /mnt/cross/foo.c
If the source file is not present at any of the above locations then an error
is printed.
gdb does not look up the parts of the source file name, such as/mnt/cross/src/foo-1.0/lib/foo.c. Likewise, the subdirectories of the source path are
not searched: if the source path is /mnt/cross, and the binary refers to foo.c, gdb would
not find it under /mnt/cross/usr/src/foo-1.0/lib.
Plain file names, relative file names with leading directories, file names containing dots,
etc. are all treated as described above, except that non-absolute file names are not looked
up literally. If the source path is /mnt/cross, the source file is recorded as ../lib/foo.c,and no compilation directory is recorded, then gdb will search in the following locations:
1. /mnt/cross/../lib/foo.c
2. /mnt/cross/foo.c
The source path will always include two special entries ‘$cdir’ and ‘$cwd’, these refer tothe compilation directory (if one is recorded) and the current working directory respectively.
‘$cdir’ causes gdb to search within the compilation directory, if one is recorded in the
debug information. If no compilation directory is recorded in the debug information then‘$cdir’ is ignored.
‘$cwd’ is not the same as ‘.’—the former tracks the current working directory as itchanges during your gdb session, while the latter is immediately expanded to the current
directory at the time you add an entry to the source path.
If a compilation directory is recorded in the debug information, and gdb has not foundthe source file after the first search using source path, then gdb will combine the compilation
directory and the filename, and then search for the source file again using the source path.
For example, if the executable records the source file as /usr/src/foo-1.0/lib/foo.c,
the compilation directory is recorded as /project/build, and the source path is/mnt/cross:$cdir:$cwd while the current working directory of the gdb session is/home/user, then gdb will search for the source file in the following locations:
1. /usr/src/foo-1.0/lib/foo.c
2. /mnt/cross/usr/src/foo-1.0/lib/foo.c
3. /project/build/usr/src/foo-1.0/lib/foo.c
4. /home/user/usr/src/foo-1.0/lib/foo.c
5. /mnt/cross/project/build/usr/src/foo-1.0/lib/foo.c
6. /project/build/project/build/usr/src/foo-1.0/lib/foo.c
7. /home/user/project/build/usr/src/foo-1.0/lib/foo.c
8. /mnt/cross/foo.c

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133

9. /project/build/foo.c
10. /home/user/foo.c
If the file name in the previous example had been recorded in the executable as a relative
path rather than an absolute path, then the first look up would not have occurred, but allof the remaining steps would be similar.
When searching for source files on MS-DOS and MS-Windows, where absolute paths
start with a drive letter (e.g. C:/project/foo.c), gdb will remove the drive letter fromthe file name before appending it to a search directory from source path; for instanceif the executable references the source file C:/project/foo.c and source path is set to
D:/mnt/cross, then gdb will search in the following locations for the source file:
1. C:/project/foo.c
2. D:/mnt/cross/project/foo.c
3. D:/mnt/cross/foo.c
Note that the executable search path is not used to locate the source files.
Whenever you reset or rearrange the source path, gdb clears out any information it hascached about where source files are found and where each line is in the file.
When you start gdb, its source path includes only ‘$cdir’ and ‘$cwd’, in that order. To
add other directories, use the directory command.
The search path is used to find both program source files and gdb script files (read using
the ‘-command’ option and ‘source’ command).
In addition to the source path, gdb provides a set of commands that manage a list ofsource path substitution rules. A substitution rule specifies how to rewrite source directories
stored in the program’s debug information in case the sources were moved to a different
directory between compilation and debugging. A rule is made of two strings, the first
specifying what needs to be rewritten in the path, and the second specifying how it should
be rewritten. In [set substitute-path], page 134, we name these two parts from and torespectively. gdb does a simple string replacement of from with to at the start of thedirectory part of the source file name, and uses that result instead of the original file nameto look up the sources.
Using the previous example, suppose the foo-1.0 tree has been moved from /usr/src
to /mnt/cross, then you can tell gdb to replace /usr/src in all source path names with/mnt/cross. The first lookup will then be /mnt/cross/foo-1.0/lib/foo.c in place of theoriginal location of /usr/src/foo-1.0/lib/foo.c. To define a source path substitution
rule, use the set substitute-path command (see [set substitute-path], page 134).
To avoid unexpected substitution results, a rule is applied only if the from partof the directory name ends at a directory separator. For instance, a rule substituting/usr/source into /mnt/cross will be applied to /usr/source/foo-1.0 but not to/usr/sourceware/foo-2.0. And because the substitution is applied only at the beginningof the directory name, this rule will not be applied to /root/usr/source/baz.c either.
In many cases, you can achieve the same result using the directory command. However,set substitute-path can be more efficient in the case where the sources are organized in
a complex tree with multiple subdirectories. With the directory command, you need to
add each subdirectory of your project. If you moved the entire tree while preserving its

134

Debugging with gdb

internal organization, then set substitute-path allows you to direct the debugger to all
the sources with one single command.
set substitute-path is also more than just a shortcut command. The source pathis only used if the file at the original location no longer exists. On the other hand, set
substitute-path modifies the debugger behavior to look at the rewritten location instead.
So, if for any reason a source file that is not relevant to your executable is located at theoriginal location, a substitution rule is the only method available to point gdb at the newlocation.
You can configure a default source path substitution rule by configuring gdb with the‘--with-relocated-sources=dir’ option. The dir should be the name of a directory under
gdb’s configured prefix (set with ‘--prefix’ or ‘--exec-prefix’), and directory names indebug information under dir will be adjusted automatically if the installed gdb is moved
to a new location. This is useful if gdb, libraries or executables with debug informationand corresponding source code are being moved together.
directory dirname ...
dir dirname ...
Add directory dirname to the front of the source path. Several directory names
may be given to this command, separated by ‘:’ (‘;’ on MS-DOS and MSWindows, where ‘:’ usually appears as part of absolute file names) or whitespace. You may specify a directory that is already in the source path; thismoves it forward, so gdb searches it sooner.
The special strings ‘$cdir’ (to refer to the compilation directory, if one isrecorded), and ‘$cwd’ (to refer to the current working directory) can also be
included in the list of directories dirname. Though these will already be in thesource path they will be moved forward in the list so gdb searches them sooner.
directory
Reset the source path to its default value (‘$cdir:$cwd’ on Unix systems). Thisrequires confirmation.
set directories path-list
Set the source path to path-list. ‘$cdir:$cwd’ are added if missing.
show directories
Print the source path: show which directories it contains.
set substitute-path from toDefine a source path substitution rule, and add it at the end of the current listof existing substitution rules. If a rule with the same from was already defined,
then the old rule is also deleted.
For example, if the file /foo/bar/baz.c was moved to /mnt/cross/baz.c, thenthe command(gdb) set substitute-path /foo/bar /mnt/crosswill tell gdb to replace ‘/foo/bar’ with ‘/mnt/cross’, which will allow gdb tofind the file baz.c even though it was moved.
In the case when more than one substitution rule have been defined, the rules
are evaluated one by one in the order where they have been defined. The firstone matching, if any, is selected to perform the substitution.

Chapter 9: Examining Source Files135

For instance, if we had entered the following commands:(gdb) set substitute-path /usr/src/include /mnt/include(gdb) set substitute-path /usr/src /mnt/src

gdb would then rewrite /usr/src/include/defs.h into /mnt/include/defs.h
by using the first rule. However, it would use the second rule to rewrite/usr/src/lib/foo.c into /mnt/src/lib/foo.c.
unset substitute-path [path]
If a path is specified, search the current list of substitution rules for a rule thatwould rewrite that path. Delete that rule if found. A warning is emitted by
the debugger if no rule could be found.
If no path is specified, then all substitution rules are deleted.
show substitute-path [path]
If a path is specified, then print the source path substitution rule which would
rewrite that path, if any.
If no path is specified, then print all existing source path substitution rules.
If your source path is cluttered with directories that are no longer of interest, gdb may
sometimes cause confusion by finding the wrong versions of source. You can correct thesituation as follows:
1. Use directory with no argument to reset the source path to its default value.
2. Use directory with suitable arguments to reinstall the directories you want in thesource path. You can add all the directories in one command.

9.6 Source and Machine CodeYou can use the command info line to map source lines to program addresses (and viceversa), and the command disassemble to display a range of addresses as machine instructions. You can use the command set disassemble-next-line to set whether to disassemble next source line when execution stops. When run under gnu Emacs mode, theinfo line command causes the arrow to point to the line specified. Also, info line prints
addresses in symbolic form as well as hex.
info line
info line locspec
Print the starting and ending addresses of the compiled code for the sourcelines of the code locations that result from resolving locspec. See Section 9.2[Location Specifications], page 126, for the various forms of locspec. With nolocspec, information about the current source line is printed.
For example, we can use info line to discover the location of the object code for the
first line of function m4_changequote:(gdb) info line m4_changequote
Line 895 of "builtin.c" starts at pc 0x634c <m4_changequote> and \ends at 0x6350 <m4_changequote+4>.

We can also inquire, using *addr as the form for locspec, what source line covers a particularaddress addr:(gdb) info line *0x63ff

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Line 926 of "builtin.c" starts at pc 0x63e4 <m4_changequote+152> and \ends at 0x6404 <m4_changequote+184>.

After info line, the default address for the x command is changed to the starting
address of the line, so that ‘x/i’ is sufficient to begin examining the machine code (seeSection 10.6 [Examining Memory], page 152). Also, this address is saved as the value of theconvenience variable $_ (see Section 10.12 [Convenience Variables], page 171).
After info line, using info line again without specifying a location will display information about the next source line.
disassemble
disassemble /mdisassemble /sdisassemble /rdisassemble /b
This specialized command dumps a range of memory as machine instructions.
It can also print mixed source+disassembly by specifying the /m or /s modifierand print the raw instructions in hex as well as in symbolic form by specifying
the /r or /b modifier.
Only one of /m and /s can be used, attempting to use both flag will give anerror.
Only one of /r and /b can be used, attempting to use both flag will give anerror.
The default memory range is the function surrounding the program counter ofthe selected frame. A single argument to this command is a program countervalue; gdb dumps the function surrounding this value. When two arguments
are given, they should be separated by a comma, possibly surrounded by whitespace. The arguments specify a range of addresses to dump, in one of two forms:
start,end
the addresses from start (inclusive) to end (exclusive)
start,+length
the addresses from start (inclusive) to start+length (exclusive).
When 2 arguments are specified, the name of the function is also printed (since
there could be several functions in the given range).
The argument(s) can be any expression yielding a numeric value, such as‘0x32c4’, ‘&main+10’ or ‘$pc - 8’.
If the range of memory being disassembled contains current program counter,
the instruction at that location is shown with a => marker.
The following example shows the disassembly of a range of addresses of HP PA-RISC
2.0 code:(gdb) disas 0x32c4, 0x32e4
Dump of assembler code from 0x32c4 to 0x32e4:
0x32c4 <main+204>:
addil 0,dp
0x32c8 <main+208>:
ldw 0x22c(sr0,r1),r26
0x32cc <main+212>:
ldil 0x3000,r31
0x32d0 <main+216>:
ble 0x3f8(sr4,r31)

Chapter 9: Examining Source Files

0x32d4 <main+220>:
0x32d8 <main+224>:
0x32dc <main+228>:
0x32e0 <main+232>:
End of assembler dump.

137

ldo 0(r31),rp
addil -0x800,dp
ldo 0x588(r1),r26
ldil 0x3000,r31

The following two examples are for RISC-V, and demonstrates the difference between
the /r and /b modifiers. First with /b, the bytes of the instruction are printed, in hex, inmemory order:(gdb) disassemble /b 0x00010150,0x0001015c
Dump of assembler code from 0x10150 to 0x1015c:
0x00010150 <call_me+4>:22 dc
0x00010152 <call_me+6>:80 00
0x00010154 <call_me+8>:
23 26 a4 fe
0x00010158 <call_me+12>:
23 24 b4 fe
End of assembler dump.

sw s0,56(sp)addi s0,sp,64
sw a0,-20(s0)sw a1,-24(s0)In contrast, with /r the bytes of the instruction are displayed in the instruction order,
for RISC-V this means that the bytes have been swapped to little-endian order:(gdb) disassemble /r 0x00010150,0x0001015c
Dump of assembler code from 0x10150 to 0x1015c:
0x00010150 <call_me+4>:dc22
0x00010152 <call_me+6>:0080
0x00010154 <call_me+8>:fea42623
0x00010158 <call_me+12>:
feb42423
End of assembler dump.

sw s0,56(sp)addi s0,sp,64
sw a0,-20(s0)sw a1,-24(s0)Here is an example showing mixed source+assembly for Intel x86 with /m or /s, when
the program is stopped just after function prologue in a non-optimized function with noinline code.
(gdb) disas /m main
Dump of assembler code for function main:
5{0x08048330 <+0>:
push
%ebp
0x08048331 <+1>:mov%esp,%ebp
0x08048333 <+3>:
sub$0x8,%esp
0x08048336 <+6>:
and$0xfffffff0,%esp
0x08048339 <+9>:
sub$0x10,%esp
6printf ("Hello.\n");=> 0x0804833c <+12>:
movl$0x8048440,(%esp)
0x08048343 <+19>:
call
0x8048284 <puts@plt>
7
8

return 0;}0x08048348 <+24>:0x0804834d <+29>:
0x0804834e <+30>:

mov
leave
ret

$0x0,%eax

End of assembler dump.

The /m option is deprecated as its output is not useful when there is either inlined codeor re-ordered code. The /s option is the preferred choice. Here is an example for AMD
x86-64 showing the difference between /m output and /s output. This example has one
inline function defined in a header file, and the code is compiled with ‘-O2’ optimization.
Note how the /m output is missing the disassembly of several instructions that are present
in the /s output.

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foo.h:
intfoo (int a){
if (a < 0)return a * 2;
if (a == 0)
return 1;
return a + 10;}

foo.c:#include "foo.h"volatile int x, y;
int
main (){
x = foo (y);return 0;}(gdb) disas /m main
Dump of assembler code for function main:
5 {6

x = foo (y);0x0000000000400400 <+0>: mov
0x0000000000400417 <+23>: mov

7
return 0;
8 }0x000000000040041d <+29>:0x000000000040041f <+31>:0x0000000000400420 <+32>:
0x0000000000400422 <+34>:

xor
retq
add
jmp

0x200c2e(%rip),%eax # 0x601034 <y>%eax,0x200c13(%rip) # 0x601030 <x>%eax,%eax%eax,%eax
0x400417 <main+23>

End of assembler dump.
(gdb) disas /s main
Dump of assembler code for function main:
foo.c:
5 {6
x = foo (y);0x0000000000400400 <+0>: mov
0x200c2e(%rip),%eax # 0x601034 <y>foo.h:
4
if (a < 0)0x0000000000400406 <+6>:0x0000000000400408 <+8>:
67
8

if (a == 0)
return 1;
return a + 10;
0x000000000040040a <+10>:0x000000000040040d <+13>:0x000000000040040f <+15>:0x0000000000400414 <+20>:

foo.c:
6
x = foo (y);

test
js

%eax,%eax
0x400420 <main+32>

lea
0xa(%rax),%edx
test%eax,%eax
mov$0x1,%eax
cmovne %edx,%eax

Chapter 9: Examining Source Files

139

0x0000000000400417 <+23>:

mov%eax,0x200c13(%rip) # 0x601030 <x>

7
return 0;
8 }0x000000000040041d <+29>:0x000000000040041f <+31>:

xor
retq

%eax,%eax

add
jmp%eax,%eax
0x400417 <main+23>

foo.h:
5
return a * 2;0x0000000000400420 <+32>:
0x0000000000400422 <+34>:
End of assembler dump.

Here is another example showing raw instructions in hex for AMD x86-64,(gdb) disas /r 0x400281,+10
Dump of assembler code from 0x400281 to 0x40028b:
0x0000000000400281: 38 36 cmp%dh,(%rsi)
0x0000000000400283: 2d 36 34 2e 73 sub$0x732e3436,%eax
0x0000000000400288: 6f
outsl %ds:(%rsi),(%dx)
0x0000000000400289: 2e 32 00
xor%cs:(%rax),%al
End of assembler dump.

Note that the ‘disassemble’ command’s address arguments are specified using expressions in your programming language (see Section 10.1 [Expressions], page 145), not location
specs (see Section 9.2 [Location Specifications], page 126). So, for example, if you want todisassemble function bar in file foo.c, you must type ‘disassemble ’foo.c’::bar’ andnot ‘disassemble foo.c:bar’.
Some architectures have more than one commonly-used set of instruction mnemonics orother syntax.
For programs that were dynamically linked and use shared libraries, instructions thatcall functions or branch to locations in the shared libraries might show a seemingly bogus
location—it’s actually a location of the relocation table. On some architectures, gdb might
be able to resolve these to actual function names.
set disassembler-options option1[,option2...]This command controls the passing of target specific information to the disassembler. For a list of valid options, please refer to the -M/--disassembleroptions section of the ‘objdump’ manual and/or the output of objdump --help(see Section “objdump” in The GNU Binary Utilities). The default value is theempty string.
If it is necessary to specify more than one disassembler option, then multiple
options can be placed together into a comma separated list. Currently thiscommand is only supported on targets ARC, ARM, MIPS, PowerPC and S/390.
show disassembler-optionsShow the current setting of the disassembler options.
set disassembly-flavor instruction-set
Select the instruction set to use when disassembling the program via thedisassemble or x/i commands.
Currently this command is only defined for the Intel x86 family. You can set
instruction-set to either intel or att. The default is att, the AT&T flavor
used by default by Unix assemblers for x86-based targets.

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Debugging with gdb

show disassembly-flavor
Show the current setting of the disassembly flavor.
set disassemble-next-line
show disassemble-next-line
Control whether or not gdb will disassemble the next source line or instruction
when execution stops. If ON, gdb will display disassembly of the next sourceline when execution of the program being debugged stops. This is in addition
to displaying the source line itself, which gdb always does if possible. If thenext source line cannot be displayed for some reason (e.g., if gdb cannot findthe source file, or there’s no line info in the debug info), gdb will display
disassembly of the next instruction instead of showing the next source line. If
AUTO, gdb will display disassembly of next instruction only if the source line
cannot be displayed. This setting causes gdb to display some feedback when
you step through a function with no line info or whose source file is unavailable.
The default is OFF, which means never display the disassembly of the next line
or instruction.

9.7 Disable Reading Source CodeIn some cases it can be desirable to prevent gdb from accessing source code files. One casewhere this might be desirable is if the source code files are located over a slow network
connection.
The following command can be used to control whether gdb should access source code
files or not:set source open [on|off]show source open
When this option is on, which is the default, gdb will access source code files
when needed, for example to print source lines when gdb stops, or in responseto the list command.
When this option is off, gdb will not access source code files.

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10 Examining Data
The usual way to examine data in your program is with the print command (abbreviated p),
or its synonym inspect. It evaluates and prints the value of an expression of the language
your program is written in (see Chapter 15 [Using gdb with Different Languages], page 227).
It may also print the expression using a Python-based pretty-printer (see Section 10.10[Pretty Printing], page 168).
print [[options] --] expr
print [[options] --] /f expr
expr is an expression (in the source language). By default the value of expr is
printed in a format appropriate to its data type; you can choose a different format by specifying ‘/f’, where f is a letter specifying the format; see Section 10.5
[Output Formats], page 150.
The print command supports a number of options that allow overriding relevant global print settings as set by set print subcommands:-address [on|off]
Set printing of addresses.
page 157.

Related setting: [set print address],-array [on|off]Pretty formatting of arrays. Related setting: [set print array],page 159.
-array-indexes [on|off]
Set printing of array indexes. Related setting: [set print arrayindexes], page 159.
-characters number-of-characters|elements|unlimited
Set limit on string characters to print. The value elements
causes the limit on array elements to print to be used. The value
unlimited causes there to be no limit. Related setting: [set print
characters], page 159.
-elements number-of-elements|unlimited
Set limit on array elements and optionally string characters to print.
See [set print characters], page 159, and the -characters option
above for when this option applies to strings. The value unlimitedcauses there to be no limit. See [set print elements], page 160, fora related CLI command.
-max-depth depth|unlimited
Set the threshold after which nested structures are replaced withellipsis. Related setting: [set print max-depth], page 163.
-nibbles [on|off]
Set whether to print binary values in groups of four bits, known as“nibbles”. See [set print nibbles], page 159.
-memory-tag-violations [on|off]
Set printing of additional information about memory tag violations.
See [set print memory-tag-violations], page 164.

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Debugging with gdb-null-stop [on|off]
Set printing of char arrays to stop at first null char. Related setting:[set print null-stop], page 164.
-object [on|off]
Set printing C++ virtual function tables. Related setting: [set print
object], page 167.
-pretty [on|off]
Set pretty formatting of structures. Related setting: [set printpretty], page 165.
-raw-values [on|off]
Set whether to print values in raw form, bypassing any prettyprinters for that value. Related setting: [set print raw-values],
page 165.
-repeats number-of-repeats|unlimited
Set threshold for repeated print elements. unlimited causes allelements to be individually printed. Related setting: [set print
repeats], page 163.
-static-members [on|off]
Set printing C++ static members. Related setting: [set print staticmembers], page 167.
-symbol [on|off]
Set printing of symbol names when printing pointers. Related setting: [set print symbol], page 158.
-union [on|off]
Set printing of unions interior to structures. Related setting: [setprint union], page 165.
-vtbl [on|off]
Set printing of C++ virtual function tables. Related setting: [setprint vtbl], page 167.
Because the print command accepts arbitrary expressions which may look like
options (including abbreviations), if you specify any command option, then you
must use a double dash (--) to mark the end of option processing.
For example, this prints the value of the -p expression:(gdb) print -p

While this repeats the last value in the value history (see below) with the-pretty option in effect:(gdb) print -p --Here is an example including both on option and an expression:

Chapter 10: Examining Data

143(gdb) print -pretty -- *myptr$1 = {
next = 0x0,
flags = {sweet = 1,
sour = 1},
meat = 0x54 "Pork"}

print [options]print [options] /f
If you omit expr, gdb displays the last value again (from the value history;see Section 10.11 [Value History], page 170). This allows you to conveniently
inspect the same value in an alternative format.
If the architecture supports memory tagging, the print command will display
pointer/memory tag mismatches if what is being printed is a pointer or reference type. See
Section 10.7 [Memory Tagging], page 154.
A more low-level way of examining data is with the x command. It examines data
in memory at a specified address and prints it in a specified format. See Section 10.6
[Examining Memory], page 152.
If you are interested in information about types, or about how the fields of a struct
or a class are declared, use the ptype expr command rather than print. See Chapter 16[Examining the Symbol Table], page 263.
Another way of examining values of expressions and type information is through the
Python extension command explore (available only if the gdb build is configured with--with-python). It offers an interactive way to start at the highest level (or, the mostabstract level) of the data type of an expression (or, the data type itself) and explore all
the way down to leaf scalar values/fields embedded in the higher level data types.
explore arg
arg is either an expression (in the source language), or a type visible in thecurrent context of the program being debugged.
The working of the explore command can be illustrated with an example. If a data
type struct ComplexStruct is defined in your C program as
struct SimpleStruct{
int i;
double d;};struct ComplexStruct{
struct SimpleStruct *ss_p;
int arr[10];};followed by variable declarations as
struct SimpleStruct ss = { 10, 1.11 };struct ComplexStruct cs = { &ss, { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 } };144

Debugging with gdb

then, the value of the variable cs can be explored using the explore command as follows.
(gdb) explore cs
The value of ‘cs’ is a struct/class of type ‘struct ComplexStruct’ withthe following fields:
ss_p = <Enter 0 to explore this field of type ‘struct SimpleStruct *’>arr = <Enter 1 to explore this field of type ‘int [10]’>
Enter the field number of choice:

Since the fields of cs are not scalar values, you are being prompted to chose the field you
want to explore. Let’s say you choose the field ss_p by entering 0. Then, since this field
is a pointer, you will be asked if it is pointing to a single value. From the declaration of
cs above, it is indeed pointing to a single value, hence you enter y. If you enter n, then
you will be asked if it were pointing to an array of values, in which case this field will be
explored as if it were an array.
‘cs.ss_p’ is a pointer to a value of type ‘struct SimpleStruct’
Continue exploring it as a pointer to a single value [y/n]: y
The value of ‘*(cs.ss_p)’ is a struct/class of type ‘struct
SimpleStruct’ with the following fields:
i = 10 .. (Value of type ‘int’)d = 1.1100000000000001 .. (Value of type ‘double’)Press enter to return to parent value:

If the field arr of cs was chosen for exploration by entering 1 earlier, then since it is asarray, you will be prompted to enter the index of the element in the array that you want
to explore.
‘cs.arr’ is an array of ‘int’.
Enter the index of the element you want to explore in ‘cs.arr’: 5‘(cs.arr)[5]’ is a scalar value of type ‘int’.
(cs.arr)[5] = 4
Press enter to return to parent value:

In general, at any stage of exploration, you can go deeper towards the leaf values by
responding to the prompts appropriately, or hit the return key to return to the enclosing
data structure (the higher level data structure).
Similar to exploring values, you can use the explore command to explore types. Insteadof specifying a value (which is typically a variable name or an expression valid in the current
context of the program being debugged), you specify a type name. If you consider thesame example as above, your can explore the type struct ComplexStruct by passing theargument struct ComplexStruct to the explore command.
(gdb) explore struct ComplexStruct

By responding to the prompts appropriately in the subsequent interactive session, you can
explore the type struct ComplexStruct in a manner similar to how the value cs was
explored in the above example.
The explore command also has two sub-commands, explore value and explore type.
The former sub-command is a way to explicitly specify that value exploration of the argu-

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145

ment is being invoked, while the latter is a way to explicitly specify that type explorationof the argument is being invoked.
explore value expr
This sub-command of explore explores the value of the expression expr (if expr
is an expression valid in the current context of the program being debugged).
The behavior of this command is identical to that of the behavior of the explore
command being passed the argument expr.
explore type arg
This sub-command of explore explores the type of arg (if arg is a type visible in the current context of program being debugged), or the type of thevalue/expression arg (if arg is an expression valid in the current context of the
program being debugged). If arg is a type, then the behavior of this commandis identical to that of the explore command being passed the argument arg.
If arg is an expression, then the behavior of this command will be identical tothat of the explore command being passed the type of arg as the argument.

10.1 Expressions
print and many other gdb commands accept an expression and compute its value. Anykind of constant, variable or operator defined by the programming language you are using
is valid in an expression in gdb. This includes conditional expressions, function calls, casts,
and string constants. It also includes preprocessor macros, if you compiled your program
to include this information; see Section 4.1 [Compilation], page 33.
gdb supports array constants in expressions input by the user. The syntax is {element,element. . . }. For example, you can use the command print {1, 2, 3} to create an arrayof three integers. If you pass an array to a function or assign it to a program variable, gdb
copies the array to memory that is malloced in the target program.
Because C is so widespread, most of the expressions shown in examples in this manual
are in C. See Chapter 15 [Using gdb with Different Languages], page 227, for information
on how to use expressions in other languages.
In this section, we discuss operators that you can use in gdb expressions regardless of
your programming language.
Casts are supported in all languages, not just in C, because it is so useful to cast a
number into a pointer in order to examine a structure at that address in memory.
gdb supports these operators, in addition to those common to programming languages:@‘@’ is a binary operator for treating parts of memory as arrays. See Section 10.4
[Artificial Arrays], page 149, for more information.

::‘::’ allows you to specify a variable in terms of the file or function where it isdefined. See Section 10.3 [Program Variables], page 147.

{type} addr
Refers to an object of type type stored at address addr in memory. The address
addr may be any expression whose value is an integer or pointer (but parentheses are required around binary operators, just as in a cast). This construct isallowed regardless of what kind of data is normally supposed to reside at addr.

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10.2 Ambiguous Expressions
Expressions can sometimes contain some ambiguous elements. For instance, some programming languages (notably Ada, C++ and Objective-C) permit a single function name to be
defined several times, for application in different contexts. This is called overloading. Another example involving Ada is generics. A generic package is similar to C++ templates andis typically instantiated several times, resulting in the same function name being defined indifferent contexts.
In some cases and depending on the language, it is possible to adjust the expression toremove the ambiguity. For instance in C++, you can specify the signature of the function
you want to break on, as in break function(types). In Ada, using the fully qualified
name of your function often makes the expression unambiguous as well.
When an ambiguity that needs to be resolved is detected, the debugger has the capability
to display a menu of numbered choices for each possibility, and then waits for the selection
with the prompt ‘>’. The first option is always ‘[0] cancel’, and typing 0 RET aborts thecurrent command. If the command in which the expression was used allows more than one
choice to be selected, the next option in the menu is ‘[1] all’, and typing 1 RET selects all
possible choices.
For example, the following session excerpt shows an attempt to set a breakpoint at theoverloaded symbol String::after. We choose three particular definitions of that function
name:(gdb) b String::after[0] cancel[1] all[2] file:String.cc; line number:867[3] file:String.cc; line number:860[4] file:String.cc; line number:875[5] file:String.cc; line number:853[6] file:String.cc; line number:846[7] file:String.cc; line number:735> 2 4 6
Breakpoint 1 at 0xb26c: file String.cc, line 867.
Breakpoint 2 at 0xb344: file String.cc, line 875.
Breakpoint 3 at 0xafcc: file String.cc, line 846.
Multiple breakpoints were set.
Use the "delete" command to delete unwanted
breakpoints.
(gdb)

set multiple-symbols modeThis option allows you to adjust the debugger behavior when an expression is
ambiguous.
By default, mode is set to all. If the command with which the expression isused allows more than one choice, then gdb automatically selects all possible
choices. For instance, inserting a breakpoint on a function using an ambiguous
name results in a breakpoint inserted on each possible match. However, if a
unique choice must be made, then gdb uses the menu to help you disambiguate
the expression. For instance, printing the address of an overloaded function will
result in the use of the menu.

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147

When mode is set to ask, the debugger always uses the menu when an ambiguity
is detected.
Finally, when mode is set to cancel, the debugger reports an error due to theambiguity and the command is aborted.
show multiple-symbols
Show the current value of the multiple-symbols setting.

10.3 Program Variables
The most common kind of expression to use is the name of a variable in your program.
Variables in expressions are understood in the selected stack frame (see Section 8.3[Selecting a Frame], page 117); they must be either:• global (or file-static)or• visible according to the scope rules of the programming language from the point ofexecution in that frameThis means that in the function
foo (a)int a;{bar (a);{int b = test ();bar (b);}}you can examine and use the variable a whenever your program is executing within thefunction foo, but you can only use or examine the variable b while your program is executing
inside the block where b is declared.
There is an exception: you can refer to a variable or function whose scope is a single
source file even if the current execution point is not in this file. But it is possible to havemore than one such variable or function with the same name (in different source files). If
that happens, referring to that name has unpredictable effects. If you wish, you can specify
a static variable in a particular function or file by using the colon-colon (::) notation:
file::variable
function::variable

Here file or function is the name of the context for the static variable. In the case of filenames, you can use quotes to make sure gdb parses the file name as a single word—for
example, to print a global value of x defined in f2.c:(gdb) p ’f2.c’::x

The :: notation is normally used for referring to static variables, since you typicallydisambiguate uses of local variables in functions by selecting the appropriate frame andusing the simple name of the variable. However, you may also use this notation to refer tolocal variables in frames enclosing the selected frame:void
foo (int a)

148

Debugging with gdb{
if (a < 10)
bar (a);else
process (a);/* Stop here */}intbar (int a){foo (a + 5);}

For example, if there is a breakpoint at the commented line, here is what you might see
when the program stops after executing the call bar(0):(gdb) p a
$1 = 10(gdb) p bar::a$2 = 5(gdb) up 2
#2 0x080483d0 in foo (a=5) at foobar.c:12(gdb) p a$3 = 5(gdb) p bar::a$4 = 0

These uses of ‘::’ are very rarely in conflict with the very similar use of the same notation
in C++. When they are in conflict, the C++ meaning takes precedence; however, this can beoverridden by quoting the file or function name with single quotes.
For example, suppose the program is stopped in a method of a class that has a field
named includefile, and there is also an include file named includefile that defines avariable, some_global.
(gdb) p includefile$1 = 23(gdb) p includefile::some_global
A syntax error in expression, near ‘’.
(gdb) p ’includefile’::some_global$2 = 27

Warning: Occasionally, a local variable may appear to have the wrong value
at certain points in a function—just after entry to a new scope, and just before
exit.
You may see this problem when you are stepping by machine instructions. This isbecause, on most machines, it takes more than one instruction to set up a stack frame(including local variable definitions); if you are stepping by machine instructions, variables
may appear to have the wrong values until the stack frame is completely built. On exit, it
usually also takes more than one machine instruction to destroy a stack frame; after you
begin stepping through that group of instructions, local variable definitions may be gone.
This may also happen when the compiler does significant optimizations. To be sure ofalways seeing accurate values, turn off all optimization when compiling.
Another possible effect of compiler optimizations is to optimize unused variables out ofexistence, or assign variables to registers (as opposed to memory addresses). Dependingon the support for such cases offered by the debug info format used by the compiler, gdb

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149

might not be able to display values for such local variables. If that happens, gdb will print
a message like this:No symbol "foo" in current context.

To solve such problems, either recompile without optimizations, or use a different debug
info format, if the compiler supports several such formats. See Section 4.1 [Compilation],
page 33, for more information on choosing compiler options. See Section 15.4.1 [C andC++], page 231, for more information about debug info formats that are best suited to C++
programs.
If you ask to print an object whose contents are unknown to gdb, e.g., because its
data type is not completely specified by the debug information, gdb will say ‘<incomplete
type>’. See Chapter 16 [Symbols], page 263, for more about this.
If you try to examine or use the value of a (global) variable for which gdb has no type
information, e.g., because the program includes no debug information, gdb displays anerror message. See Chapter 16 [Symbols], page 263, for more about unknown types. If you
cast the variable to its declared type, gdb gets the variable’s value using the cast-to typeas the variable’s type. For example, in a C program:(gdb) p var’var’ has unknown type; cast it to its declared type(gdb) p (float) var$1 = 3.14

If you append @entry string to a function parameter name you get its value at the time
the function got called. If the value is not available an error message is printed. Entry
values are available only with some compilers. Entry values are normally also printed at
the function parameter list according to [set print entry-values], page 161.
Breakpoint 1, d (i=30) at gdb.base/entry-value.c:2929i++;(gdb) next30e (i);(gdb) print i$1 = 31(gdb) print i@entry$2 = 30

Strings are identified as arrays of char values without specified signedness. Arraysof either signed char or unsigned char get printed as arrays of 1 byte sized integers.
-fsigned-char or -funsigned-char gcc options have no effect as gdb defines literal
string type "char" as char without a sign. For program codechar var0[] = "A";signed char var1[] = "A";You get during debugging(gdb) print var0
$1 = "A"(gdb) print var1
$2 = {65 ’A’, 0 ’\0’}10.4 Artificial Arrays
It is often useful to print out several successive objects of the same type in memory; asection of an array, or an array of dynamically determined size for which only a pointerexists in the program.

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You can do this by referring to a contiguous span of memory as an artificial array, using
the binary operator ‘@’. The left operand of ‘@’ should be the first element of the desired
array and be an individual object. The right operand should be the desired length of thearray. The result is an array value whose elements are all of the type of the left argument.
The first element is actually the left argument; the second element comes from bytes ofmemory immediately following those that hold the first element, and so on. Here is an
example. If a program says
int *array = (int *) malloc (len * sizeof (int));

you can print the contents of array withp *array@len

The left operand of ‘@’ must reside in memory. Array values made with ‘@’ in this way
behave just like other arrays in terms of subscripting, and are coerced to pointers whenused in expressions. Artificial arrays most often appear in expressions via the value history(see Section 10.11 [Value History], page 170), after printing one out.
Another way to create an artificial array is to use a cast. This re-interprets a value as if
it were an array. The value need not be in memory:(gdb) p/x (short[2])0x12345678$1 = {0x1234, 0x5678}

As a convenience, if you leave the array length out (as in ‘(type[])value’) gdb calculates the size to fill the value (as ‘sizeof(value)/sizeof(type)’:(gdb) p/x (short[])0x12345678$2 = {0x1234, 0x5678}

Sometimes the artificial array mechanism is not quite enough; in moderately complex
data structures, the elements of interest may not actually be adjacent—for example, if you
are interested in the values of pointers in an array. One useful work-around in this situation
is to use a convenience variable (see Section 10.12 [Convenience Variables], page 171) asa counter in an expression that prints the first interesting value, and then repeat that
expression via RET. For instance, suppose you have an array dtab of pointers to structures,and you are interested in the values of a field fv in each structure. Here is an example ofwhat you might type:
set $i = 0
p dtab[$i++]->fv
RET
RET
...

10.5 Output Formats
By default, gdb prints a value according to its data type. Sometimes this is not what you
want. For example, you might want to print a number in hex, or a pointer in decimal. Or
you might want to view data in memory at a certain address as a character string or as an
instruction. To do these things, specify an output format when you print a value.
The simplest use of output formats is to say how to print a value already computed.
This is done by starting the arguments of the print command with a slash and a format
letter. The format letters supported are:x

Print the binary representation of the value in hexadecimal.

Chapter 10: Examining Data

151dPrint the binary representation of the value in decimal.

uPrint the binary representation of the value as an decimal, as if it were unsigned.

oPrint the binary representation of the value in octal.

tPrint the binary representation of the value in binary. The letter ‘t’ stands for“two”.1aPrint as an address, both absolute in hexadecimal and as an offset from thenearest preceding symbol. You can use this format used to discover where (inwhat function) an unknown address is located:(gdb) p/a 0x54320$3 = 0x54320 <_initialize_vx+396>

The command info symbol 0x54320 yields similar results. See Chapter 16[Symbols], page 263.
cCast the value to an integer (unlike other formats, this does not just reinterpretthe underlying bits) and print it as a character constant. This prints both thenumerical value and its character representation. The character representationis replaced with the octal escape ‘\nnn’ for characters outside the 7-bit ascii
range.
Without this format, gdb displays char, unsigned char, and signed chardata as character constants. Single-byte members of vectors are displayed as
integer data.

fRegard the bits of the value as a floating point number and print using typicalfloating point syntax.

s

Regard as a string, if possible. With this format, pointers to single-byte data aredisplayed as null-terminated strings and arrays of single-byte data are displayed
as fixed-length strings. Other values are displayed in their natural types.
Without this format, gdb displays pointers to and arrays of char,
unsigned char, and signed char as strings. Single-byte members of a vector
are displayed as an integer array.

z

Like ‘x’ formatting, the value is treated as an integer and printed as hexadecimal, but leading zeros are printed to pad the value to the size of the integer
type.

r

Print using the ‘raw’ formatting. By default, gdb will use a Python-based
pretty-printer, if one is available (see Section 10.10 [Pretty Printing], page 168).
This typically results in a higher-level display of the value’s contents. The ‘r’format bypasses any Python pretty-printer which might exist.

For example, to print the program counter in hex (see Section 10.14 [Registers],
page 179), typep/x $pc

Note that no space is required before the slash; this is because command names in gdb
cannot contain a slash.
1‘b’ cannot be used because these format letters are also used with the x command, where ‘b’ stands for“byte”; see Section 10.6 [Examining Memory], page 152.

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To reprint the last value in the value history with a different format, you can use theprint command with just a format and no expression. For example, ‘p/x’ reprints the lastvalue in hex.

10.6 Examining Memory
You can use the command x (for “examine”) to examine memory in any of several formats,
independently of your program’s data types.
x/nfu addr
x addrx
Use the x command to examine memory.
n, f, and u are all optional parameters that specify how much memory to display and how
to format it; addr is an expression giving the address where you want to start displaying
memory. If you use defaults for nfu, you need not type the slash ‘/’. Several commands set
convenient defaults for addr.
n, the repeat count
The repeat count is a decimal integer; the default is 1. It specifies how muchmemory (counting by units u) to display. If a negative number is specified,memory is examined backward from addr.
f, the display format
The display format is one of the formats used by print (‘x’, ‘d’, ‘u’, ‘o’, ‘t’,‘a’, ‘c’, ‘f’, ‘s’), ‘i’ (for machine instructions) and ‘m’ (for displaying memorytags). The default is ‘x’ (hexadecimal) initially. The default changes each time
you use either x or print.
u, the unit size
The unit size is any ofb

Bytes.

h

Halfwords (two bytes).

w

Words (four bytes). This is the initial default.

g

Giant words (eight bytes).

Each time you specify a unit size with x, that size becomes the default unit
the next time you use x. For the ‘i’ format, the unit size is ignored and isnormally not written. For the ‘s’ format, the unit size defaults to ‘b’, unless it
is explicitly given. Use x /hs to display 16-bit char strings and x /ws to display
32-bit strings. The next use of x /s will again display 8-bit strings. Note thatthe results depend on the programming language of the current compilation
unit. If the language is C, the ‘s’ modifier will use the UTF-16 encoding while‘w’ will use UTF-32. The encoding is set by the programming language andcannot be altered.
addr, starting display address
addr is the address where you want gdb to begin displaying memory. The expression need not have a pointer value (though it may); it is always interpretedChapter 10: Examining Data153

as an integer address of a byte of memory. See Section 10.1 [Expressions],
page 145, for more information on expressions. The default for addr is usually just after the last address examined—but several other commands also set
the default address: info breakpoints (to the address of the last breakpoint
listed), info line (to the starting address of a line), and print (if you use it
to display a value from memory).
For example, ‘x/3uh 0x54320’ is a request to display three halfwords (h) of memory,formatted as unsigned decimal integers (‘u’), starting at address 0x54320. ‘x/4xw $sp’
prints the four words (‘w’) of memory above the stack pointer (here, ‘$sp’; see Section 10.14[Registers], page 179) in hexadecimal (‘x’).
You can also specify a negative repeat count to examine memory backward from the given
address. For example, ‘x/-3uh 0x54320’ prints three halfwords (h) at 0x5431a, 0x5431c,
and 0x5431e.
Since the letters indicating unit sizes are all distinct from the letters specifying output
formats, you do not have to remember whether unit size or format comes first; either orderworks. The output specifications ‘4xw’ and ‘4wx’ mean exactly the same thing. (However,the count n must come first; ‘wx4’ does not work.)
Even though the unit size u is ignored for the formats ‘s’ and ‘i’, you might still want touse a count n; for example, ‘3i’ specifies that you want to see three machine instructions,
including any operands. For convenience, especially when used with the display command,the ‘i’ format also prints branch delay slot instructions, if any, beyond the count specified,
which immediately follow the last instruction that is within the count. The commanddisassemble gives an alternative way of inspecting machine instructions; see Section 9.6[Source and Machine Code], page 135.
If a negative repeat count is specified for the formats ‘s’ or ‘i’, the command displays
null-terminated strings or instructions before the given address as many as the absolutevalue of the given number. For the ‘i’ format, we use line number information in the debug
info to accurately locate instruction boundaries while disassembling backward. If line info
is not available, the command stops examining memory with an error message.
All the defaults for the arguments to x are designed to make it easy to continue scanningmemory with minimal specifications each time you use x. For example, after you haveinspected three machine instructions with ‘x/3i addr’, you can inspect the next seven withjust ‘x/7’. If you use RET to repeat the x command, the repeat count n is used again; theother arguments default as for successive uses of x.
When examining machine instructions, the instruction at current program counter isshown with a => marker. For example:(gdb) x/5i $pc-6
0x804837f <main+11>: mov
0x8048381 <main+13>: push
0x8048382 <main+14>: sub=> 0x8048385 <main+17>: movl
0x804838c <main+24>: call%esp,%ebp%ecx$0x4,%esp$0x8048460,(%esp)
0x80482d4 <puts@plt>

If the architecture supports memory tagging, the tags can be displayed by using ‘m’. See
Section 10.7 [Memory Tagging], page 154.

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The information will be displayed once per granule size (the amount of bytes a particularmemory tag covers). For example, AArch64 has a granule size of 16 bytes, so it will display
a tag every 16 bytes.
Due to the way gdb prints information with the x command (not aligned to a particularboundary), the tag information will refer to the initial address displayed on a particular line.
If a memory tag boundary is crossed in the middle of a line displayed by the x command,
it will be displayed on the next line.
The ‘m’ format doesn’t affect any other specified formats that were passed to the xcommand.
The addresses and contents printed by the x command are not saved in the value history
because there is often too much of them and they would get in the way. Instead, gdb
makes these values available for subsequent use in expressions as values of the conveniencevariables $_ and $__. After an x command, the last address examined is available for use
in expressions in the convenience variable $_. The contents of that address, as examined,
are available in the convenience variable $__.
If the x command has a repeat count, the address and contents saved are from the last
memory unit printed; this is not the same as the last address printed if several units wereprinted on the last line of output.
Most targets have an addressable memory unit size of 8 bits. This means that to eachmemory address are associated 8 bits of data. Some targets, however, have other addressable
memory unit sizes. Within gdb and this document, the term addressable memory unit (ormemory unit for short) is used when explicitly referring to a chunk of data of that size.
The word byte is used to refer to a chunk of data of 8 bits, regardless of the addressable
memory unit size of the target. For most systems, addressable memory unit is a synonymof byte.
When you are debugging a program running on a remote target machine (see Chapter 20[Remote Debugging], page 315), you may wish to verify the program’s image in the remotemachine’s memory against the executable file you downloaded to the target. Or, on any
target, you may want to check whether the program has corrupted its own read-only sections.
The compare-sections command is provided for such situations.
compare-sections [section-name|-r]
Compare the data of a loadable section section-name in the executable file of the
program being debugged with the same section in the target machine’s memory,and report any mismatches. With no arguments, compares all loadable sections.
With an argument of -r, compares all loadable read-only sections.
Note: for remote targets, this command can be accelerated if the target supports computing the CRC checksum of a block of memory (see [qCRC packet],page 790).

10.7 Memory Tagging
Memory tagging is a memory protection technology that uses a pair of tags to validate
memory accesses through pointers. The tags are integer values usually comprised of a few
bits, depending on the architecture.

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There are two types of tags that are used in this setup: logical and allocation. A
logical tag is stored in the pointers themselves, usually at the higher bits of the pointers.
An allocation tag is the tag associated with particular ranges of memory in the physicaladdress space, against which the logical tags from pointers are compared.
The pointer tag (logical tag) must match the memory tag (allocation tag) for the memory
access to be valid. If the logical tag does not match the allocation tag, that will raise amemory violation.
Allocation tags cover multiple contiguous bytes of physical memory. This range of bytes
is called a memory tag granule and is architecture-specific. For example, AArch64 has a
tag granule of 16 bytes, meaning each allocation tag spans 16 bytes of memory.
If the underlying architecture supports memory tagging, like AArch64 MTE or SPARC
ADI do, gdb can make use of it to validate pointers against memory allocation tags.
The print (see Chapter 10 [Data], page 141) and x (see Section 10.6 [Memory],
page 152) commands will display tag information when appropriate, and a command prefixof memory-tag gives access to the various memory tagging commands.
The memory-tag commands are the following:
memory-tag print-logical-tag pointer_expression
Print the logical tag stored in pointer expression.
memory-tag with-logical-tag pointer_expression tag_bytes
Print the pointer given by pointer expression, augmented with a logical tag oftag bytes.
memory-tag print-allocation-tag address_expression
Print the allocation tag associated with the memory address given by address expression.
memory-tag setatag starting_address length tag_bytes
Set the allocation tag(s) for memory range [starting address, starting address+ length) to tag bytes.
memory-tag check pointer_expression
Check if the logical tag in the pointer given by pointer expression matches the
allocation tag for the memory referenced by the pointer.
This essentially emulates the hardware validation that is done when tagged
memory is accessed through a pointer, but does not cause a memory fault as it
would during hardware validation.
It can be used to inspect potential memory tagging violations in the running
process, before any faults get triggered.

10.8 Automatic Display
If you find that you want to print the value of an expression frequently (to see how itchanges), you might want to add it to the automatic display list so that gdb prints its
value each time your program stops. Each expression added to the list is given a number to
identify it; to remove an expression from the list, you specify that number. The automatic
display looks like this:
2: foo = 38

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3: bar[5] = (struct hack *) 0x3804

This display shows item numbers, expressions and their current values. As with displays
you request manually using x or print, you can specify the output format you prefer; infact, display decides whether to use print or x depending your format specification—it
uses x if you specify either the ‘i’ or ‘s’ format, or a unit size; otherwise it uses print.
display expr
Add the expression expr to the list of expressions to display each time yourprogram stops. See Section 10.1 [Expressions], page 145.
display does not repeat if you press RET again after using it.
display/fmt expr
For fmt specifying only a display format and not a size or count, add theexpression expr to the auto-display list but arrange to display it each time inthe specified format fmt. See Section 10.5 [Output Formats], page 150.
display/fmt addr
For fmt ‘i’ or ‘s’, or including a unit-size or a number of units, add the expression addr as a memory address to be examined each time your program stops.
Examining means in effect doing ‘x/fmt addr’. See Section 10.6 [Examining
Memory], page 152.
For example, ‘display/i $pc’ can be helpful, to see the machine instruction about tobe executed each time execution stops (‘$pc’ is a common name for the program counter;see Section 10.14 [Registers], page 179).
undisplay dnums...
delete display dnums...
Remove items from the list of expressions to display. Specify the numbers ofthe displays that you want affected with the command argument dnums. It canbe a single display number, one of the numbers shown in the first field of the‘info display’ display; or it could be a range of display numbers, as in 2-4.
undisplay does not repeat if you press RET after using it. (Otherwise you would
just get the error ‘No display number ...’.)
disable display dnums...
Disable the display of item numbers dnums. A disabled display item is notprinted automatically, but is not forgotten. It may be enabled again later.
Specify the numbers of the displays that you want affected with the commandargument dnums. It can be a single display number, one of the numbers shownin the first field of the ‘info display’ display; or it could be a range of display
numbers, as in 2-4.
enable display dnums...
Enable display of item numbers dnums. It becomes effective once again in auto
display of its expression, until you specify otherwise. Specify the numbers ofthe displays that you want affected with the command argument dnums. It canbe a single display number, one of the numbers shown in the first field of the‘info display’ display; or it could be a range of display numbers, as in 2-4.

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Display the current values of the expressions on the list, just as is done whenyour program stops.

info display
Print the list of expressions previously set up to display automatically, each
one with its item number, but without showing the values. This includes disabled expressions, which are marked as such. It also includes expressions which
would not be displayed right now because they refer to automatic variables not
currently available.
If a display expression refers to local variables, then it does not make sense outside thelexical context for which it was set up. Such an expression is disabled when execution entersa context where one of its variables is not defined. For example, if you give the command
display last_char while inside a function with an argument last_char, gdb displays
this argument while your program continues to stop inside that function. When it stops
elsewhere—where there is no variable last_char—the display is disabled automatically.
The next time your program stops where last_char is meaningful, you can enable thedisplay expression once again.

10.9 Print Settings
gdb provides the following ways to control how arrays, structures, and symbols are printed.
These settings are useful for debugging programs in any language:
set print address
set print address on
gdb prints memory addresses showing the location of stack traces, structure
values, pointer values, breakpoints, and so forth, even when it also displays thecontents of those addresses. The default is on. For example, this is what astack frame display looks like with set print address on:(gdb) f#0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
at input.c:530
530
if (lquote != def_lquote)set print address off
Do not print addresses when displaying their contents. For example, this is thesame stack frame displayed with set print address off:(gdb) set print addr off(gdb) f#0 set_quotes (lq="<<", rq=">>") at input.c:530
530
if (lquote != def_lquote)

You can use ‘set print address off’ to eliminate all machine dependent displays from the gdb interface. For example, with print address off, you
should get the same text for backtraces on all machines—whether or not they
involve pointer arguments.
show print addressShow whether or not addresses are to be printed.
When gdb prints a symbolic address, it normally prints the closest earlier symbol plus
an offset. If that symbol does not uniquely identify the address (for example, it is a name158

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whose scope is a single source file), you may need to clarify. One way to do this is with info
line, for example ‘info line *0x4537’. Alternately, you can set gdb to print the source
file and line number when it prints a symbolic address:
set print symbol-filename on
Tell gdb to print the source file name and line number of a symbol in thesymbolic form of an address.
set print symbol-filename off
Do not print source file name and line number of a symbol. This is the default.
show print symbol-filename
Show whether or not gdb will print the source file name and line number of asymbol in the symbolic form of an address.
Another situation where it is helpful to show symbol filenames and line numbers is whendisassembling code; gdb shows you the line number and source file that corresponds to each
instruction.
Also, you may wish to see the symbolic form only if the address being printed is reasonably close to the closest earlier symbol:
set print max-symbolic-offset max-offset
set print max-symbolic-offset unlimited
Tell gdb to only display the symbolic form of an address if the offset between
the closest earlier symbol and the address is less than max-offset. The default
is unlimited, which tells gdb to always print the symbolic form of an address
if any symbol precedes it. Zero is equivalent to unlimited.
show print max-symbolic-offset
Ask how large the maximum offset is that gdb prints in a symbolic address.
If you have a pointer and you are not sure where it points, try ‘set print
symbol-filename on’. Then you can determine the name and source file location of thevariable where it points, using ‘p/a pointer’. This interprets the address in symbolicform. For example, here gdb shows that a variable ptt points at another variable t,defined in hi2.c:(gdb) set print symbol-filename on(gdb) p/a ptt$4 = 0xe008 <t in hi2.c>

Warning: For pointers that point to a local variable, ‘p/a’ does not show thesymbol name and filename of the referent, even with the appropriate set print
options turned on.
You can also enable ‘/a’-like formatting all the time using ‘set print symbol on’:set print symbol on
Tell gdb to print the symbol corresponding to an address, if one exists.
set print symbol off
Tell gdb not to print the symbol corresponding to an address. In this mode,
gdb will still print the symbol corresponding to pointers to functions. This is
the default.

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show print symbol
Show whether gdb will display the symbol corresponding to an address.
Other settings control how different kinds of objects are printed:
set print arrayset print array on
Pretty print arrays. This format is more convenient to read, but uses more
space. The default is off.
set print array off
Return to compressed format for arrays.
show print array
Show whether compressed or pretty format is selected for displaying arrays.
set print array-indexes
set print array-indexes on
Print the index of each element when displaying arrays. May be more convenient
to locate a given element in the array or quickly find the index of a given elementin that printed array. The default is off.
set print array-indexes off
Stop printing element indexes when displaying arrays.
show print array-indexes
Show whether the index of each element is printed when displaying arrays.
set print nibbles
set print nibbles on
Print binary values in groups of four bits, known as nibbles, when using theprint command of gdb with the option ‘/t’. For example, this is what it looks
like with set print nibbles on:(gdb) print val_flags$1 = 1230(gdb) print/t val_flags$2 = 0100 1100 1110

set print nibbles off
Don’t printing binary values in groups. This is the default.
show print nibbles
Show whether to print binary values in groups of four bits.
set print characters number-of-charactersset print characters elements
set print characters unlimited
Set a limit on how many characters of a string gdb will print. If gdb is printing
a large string, it stops printing after it has printed the number of characters set
by the set print characters command. This equally applies to multi-byte
and wide character strings, that is for strings whose character type is wchar_t, char16_t, or char32_t it is the number of actual characters rather thanunderlying bytes the encoding uses that this setting controls. Setting numberof-characters to elements means that the limit on the number of characters to160

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print follows one for array elements; see [set print elements], page 160. Setting
number-of-characters to unlimited means that the number of characters toprint is unlimited. When gdb starts, this limit is set to elements.
show print characters
Display the number of characters of a large string that gdb will print.
set print elements number-of-elements
set print elements unlimited
Set a limit on how many elements of an array gdb will print. If gdb is printing
a large array, it stops printing after it has printed the number of elements set
by the set print elements command. By default this limit also applies to thedisplay of strings; see [set print characters], page 159. When gdb starts, thislimit is set to 200. Setting number-of-elements to unlimited or zero meansthat the number of elements to print is unlimited.
When printing very large arrays, whose size is greater than max-value-size(see [max-value-size], page 192), if the print elements is set such that the sizeof the elements being printed is less than or equal to max-value-size, then gdb
will print the array (up to the print elements limit), and only max-valuesize worth of data will be added into the value history (see Section 10.11 [Value
History], page 170).
show print elements
Display the number of elements of a large array that gdb will print.
set print frame-arguments value
This command allows to control how the values of arguments are printed when
the debugger prints a frame (see Section 8.1 [Frames], page 113). The possible
values are:all

The values of all arguments are printed.

scalars

Print the value of an argument only if it is a scalar. The value ofmore complex arguments such as arrays, structures, unions, etc, isreplaced by .... This is the default. Here is an example where
only scalar arguments are shown:#1 0x08048361 in call_me (i=3, s=..., ss=0xbf8d508c, u=..., e=green)at frame-args.c:23

none

None of the argument values are printed. Instead, the value of eachargument is replaced by .... In this case, the example above now
becomes:#1 0x08048361 in call_me (i=..., s=..., ss=..., u=..., e=...)
at frame-args.c:23

presence

Only the presence of arguments is indicated by .... The ... are
not printed for function without any arguments. None of the argument names and values are printed. In this case, the example
above now becomes:#1

0x08048361 in call_me (...) at frame-args.c:23

By default, only scalar arguments are printed. This command can be used toconfigure the debugger to print the value of all arguments, regardless of theirChapter 10: Examining Data

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type. However, it is often advantageous to not print the value of more complex
parameters. For instance, it reduces the amount of information printed in eachframe, making the backtrace more readable. Also, it improves performance
when displaying Ada frames, because the computation of large arguments cansometimes be CPU-intensive, especially in large applications. Setting print
frame-arguments to scalars (the default), none or presence avoids this computation, thus speeding up the display of each Ada frame.
show print frame-arguments
Show how the value of arguments should be displayed when printing a frame.
set print raw-frame-arguments on
Print frame arguments in raw, non pretty-printed, form.
set print raw-frame-arguments off
Print frame arguments in pretty-printed form, if there is a pretty-printer forthe value (see Section 10.10 [Pretty Printing], page 168), otherwise print thevalue in raw form. This is the default.
show print raw-frame-arguments
Show whether to print frame arguments in raw form.
set print entry-values value
Set printing of frame argument values at function entry. In some cases gdb candetermine the value of function argument which was passed by the function
caller, even if the value was modified inside the called function and therefore isdifferent. With optimized code, the current value could be unavailable, but theentry value may still be known.
The default value is default (see below for its description). Older gdb behaved
as with the setting no. Compilers not supporting this feature will behave in thedefault setting the same way as with the no setting.
This functionality is currently supported only by DWARF 2 debugging format
and the compiler has to produce ‘DW_TAG_call_site’ tags. With gcc, youneed to specify -O -g during compilation, to get this information.
The value parameter can be one of the following:noPrint only actual parameter values, never print values from function
entry point.
#0
#0
#0
#0
#0

only

equal (val=5)
different (val=6)
lost (val=<optimized out>)born (val=10)
invalid (val=<optimized out>)

Print only parameter values from function entry point. The actual
parameter values are never printed.
#0
#0
#0
#0
#0

equal (val@entry=5)
different (val@entry=5)
lost (val@entry=5)
born (val@entry=<optimized out>)
invalid (val@entry=<optimized out>)

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preferred
Print only parameter values from function entry point. If value
from function entry point is not known while the actual value isknown, print the actual value for such parameter.
#0
#0
#0
#0
#0

equal (val@entry=5)
different (val@entry=5)
lost (val@entry=5)
born (val=10)
invalid (val@entry=<optimized out>)

if-needed
Print actual parameter values. If actual parameter value is notknown while value from function entry point is known, print theentry point value for such parameter.
#0
#0
#0
#0
#0

both

Always print both the actual parameter value and its value fromfunction entry point, even if values of one or both are not available
due to compiler optimizations.
#0
#0
#0
#0
#0

compactequal (val=5, val@entry=5)
different (val=6, val@entry=5)
lost (val=<optimized out>, val@entry=5)
born (val=10, val@entry=<optimized out>)
invalid (val=<optimized out>, val@entry=<optimized out>)

Print the actual parameter value if it is known and also its value
from function entry point if it is known. If neither is known, print
for the actual value <optimized out>. If not in MI mode (seeChapter 27 [GDB/MI], page 589) and if both values are known andidentical, print the shortened param=param@entry=VALUE notation.
#0
#0
#0
#0
#0

default

equal (val=5)
different (val=6)
lost (val@entry=5)
born (val=10)
invalid (val=<optimized out>)

equal (val=val@entry=5)
different (val=6, val@entry=5)
lost (val@entry=5)
born (val=10)
invalid (val=<optimized out>)

Always print the actual parameter value. Print also its value fromfunction entry point, but only if it is known. If not in MI mode (seeChapter 27 [GDB/MI], page 589) and if both values are known andidentical, print the shortened param=param@entry=VALUE notation.
#0
#0
#0
#0
#0

equal (val=val@entry=5)
different (val=6, val@entry=5)
lost (val=<optimized out>, val@entry=5)
born (val=10)
invalid (val=<optimized out>)

For analysis messages on possible failures of frame argument values at function
entry resolution see [set debug entry-values], page 196.

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show print entry-values
Show the method being used for printing of frame argument values at function
entry.
set print frame-info value
This command allows to control the information printed when the debugger
prints a frame. See Section 8.1 [Frames], page 113, Section 8.2 [Backtrace],
page 114, for a general explanation about frames and frame information. Notethat some other settings (such as set print frame-arguments and set print
address) are also influencing if and how some frame information is displayed.
In particular, the frame program counter is never printed if set print address
is off.
The possible values for set print frame-info are:short-location
Print the frame level, the program counter (if not at the beginningof the location source line), the function, the function arguments.
location

Same as short-location but also print the source file and sourceline number.

location-and-address
Same as location but print the program counter even if locatedat the beginning of the location source line.
source-line
Print the program counter (if not at the beginning of the location
source line), the line number and the source line.
source-and-location
Print what location and source-line are printing.
auto

The information printed for a frame is decided automatically by
the gdb command that prints a frame. For example, frame prints
the information printed by source-and-location while stepi willswitch between source-line and source-and-location depending on the program counter. The default value is auto.

set print repeats number-of-repeats
set print repeats unlimited
Set the threshold for suppressing display of repeated array elements. Whenthe number of consecutive identical elements of an array exceeds the threshold,gdb prints the string "<repeats n times>", where n is the number of identicalrepetitions, instead of displaying the identical elements themselves. Setting
the threshold to unlimited or zero will cause all elements to be individually
printed. The default threshold is 10.
show print repeats
Display the current threshold for printing repeated identical elements.

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set print max-depth depth
set print max-depth unlimited
Set the threshold after which nested structures are replaced with ellipsis, thiscan make visualising deeply nested structures easier.
For example, given this C code
typedef struct s1 { int a; } s1;
typedef struct s2 { s1 b; } s2;
typedef struct s3 { s2 c; } s3;
typedef struct s4 { s3 d; } s4;
s4 var = { { { { 3 } } } };The following table shows how different values of depth will effect how var isprinted by gdb:
depth setting
unlimited
0
1
2
3
4

Result of ‘p var’
$1 = {d = {c = {b = {a = 3}}}}$1 = {...}$1 = {d = {...}}$1 = {d = {c = {...}}}$1 = {d = {c = {b = {...}}}}$1 = {d = {c = {b = {a = 3}}}}To see the contents of structures that have been hidden the user can either
increase the print max-depth, or they can print the elements of the structurethat are visible, for example(gdb) set print max-depth 2(gdb) p var$1 = {d = {c = {...}}}(gdb) p var.d$2 = {c = {b = {...}}}(gdb) p var.d.c$3 = {b = {a = 3}}

The pattern used to replace nested structures varies based on language, formost languages {...} is used, but Fortran uses (...).
show print max-depth
Display the current threshold after which nested structures are replaces withellipsis.
set print memory-tag-violations
set print memory-tag-violations on
Cause gdb to display additional information about memory tag violations whenprinting pointers and addresses.
set print memory-tag-violations off
Stop printing memory tag violation information.
show print memory-tag-violationsShow whether memory tag violation information is displayed when printing
pointers and addresses.

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set print null-stop
Cause gdb to stop printing the characters of an array when the first nullis encountered. This is useful when large arrays actually contain only shortstrings. The default is off.
show print null-stop
Show whether gdb stops printing an array on the first null character.
set print pretty on
Cause gdb to print structures in an indented format with one member per line,
like this:$1 = {
next = 0x0,
flags = {sweet = 1,
sour = 1},
meat = 0x54 "Pork"}

set print pretty off
Cause gdb to print structures in a compact format, like this:$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \meat = 0x54 "Pork"}

This is the default format.
show print pretty
Show which format gdb is using to print structures.
set print raw-values on
Print values in raw form, without applying the pretty printers for the value.
set print raw-values off
Print values in pretty-printed form, if there is a pretty-printer for the value(see Section 10.10 [Pretty Printing], page 168), otherwise print the value in raw
form.
The default setting is “off”.
show print raw-values
Show whether to print values in raw form.
set print sevenbit-strings on
Print using only seven-bit characters; if this option is set, gdb displays any
eight-bit characters (in strings or character values) using the notation \nnn.
This setting is best if you are working in English (ascii) and you use the highorder bit of characters as a marker or “meta” bit.
set print sevenbit-strings off
Print full eight-bit characters. This allows the use of more international character sets, and is the default.
show print sevenbit-strings
Show whether or not gdb is printing only seven-bit characters.

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set print union on
Tell gdb to print unions which are contained in structures and other unions.
This is the default setting.
set print union off
Tell gdb not to print unions which are contained in structures and other unions.
gdb will print "{...}" instead.
show print union
Ask gdb whether or not it will print unions which are contained in structuresand other unions.
For example, given the declarations
typedef enum {Tree, Bug} Species;
typedef enum {Big_tree, Acorn, Seedling} Tree_forms;
typedef enum {Caterpillar, Cocoon, Butterfly}
Bug_forms;
struct thing {Species it;
union {
Tree_forms tree;
Bug_forms bug;} form;};struct thing foo = {Tree, {Acorn}};with set print union on in effect ‘p foo’ would print$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}

and with set print union off in effect it would print$1 = {it = Tree, form = {...}}

set print union affects programs written in C-like languages and in Pascal.
These settings are of interest when debugging C++ programs:
set print demangle
set print demangle on
Print C++ names in their source form rather than in the encoded (“mangled”)
form passed to the assembler and linker for type-safe linkage. The default ison.
show print demangle
Show whether C++ names are printed in mangled or demangled form.
set print asm-demangle
set print asm-demangle on
Print C++ names in their source form rather than their mangled form, even inassembler code printouts such as instruction disassemblies. The default is off.
show print asm-demangle
Show whether C++ names in assembly listings are printed in mangled or demangled form.

Chapter 10: Examining Data167

set demangle-style style
Choose among several encoding schemes used by different compilers to represent
C++ names. If you omit style, you will see a list of possible formats. The
default value is auto, which lets gdb choose a decoding style by inspecting yourprogram.
show demangle-style
Display the encoding style currently in use for decoding C++ symbols.
set print object
set print object on
When displaying a pointer to an object, identify the actual (derived) type ofthe object rather than the declared type, using the virtual function table. Notethat the virtual function table is required—this feature can only work for objects
that have run-time type identification; a single virtual method in the object’s
declared type is sufficient. Note that this setting is also taken into account whenworking with variable objects via MI (see Chapter 27 [GDB/MI], page 589).
set print object off
Display only the declared type of objects, without reference to the virtual function table. This is the default setting.
show print object
Show whether actual, or declared, object types are displayed.
set print static-members
set print static-members on
Print static members when displaying a C++ object. The default is on.
set print static-members off
Do not print static members when displaying a C++ object.
show print static-members
Show whether C++ static members are printed or not.
set print pascal_static-members
set print pascal_static-members on
Print static members when displaying a Pascal object. The default is on.
set print pascal_static-members off
Do not print static members when displaying a Pascal object.
show print pascal_static-members
Show whether Pascal static members are printed or not.
set print vtbl
set print vtbl on
Pretty print C++ virtual function tables. The default is off. (The vtbl commands do not work on programs compiled with the HP ANSI C++ compiler(aCC).)
set print vtbl off
Do not pretty print C++ virtual function tables.

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show print vtbl
Show whether C++ virtual function tables are pretty printed, or not.

10.10 Pretty Printing
gdb provides a mechanism to allow pretty-printing of values using Python code. It greatly
simplifies the display of complex objects. This mechanism works for both MI and the CLI.

10.10.1 Pretty-Printer Introduction
When gdb prints a value, it first sees if there is a pretty-printer registered for the value.
If there is then gdb invokes the pretty-printer to print the value. Otherwise the value isprinted normally.
Pretty-printers are normally named. This makes them easy to manage. The ‘info
pretty-printer’ command will list all the installed pretty-printers with their names. If apretty-printer can handle multiple data types, then its subprinters are the printers for theindividual data types. Each such subprinter has its own name. The format of the name isprinter-name;subprinter-name.
Pretty-printers are installed by registering them with gdb. Typically they are automatically loaded and registered when the corresponding debug information is loaded, thus
making them available without having to do anything special.
There are three places where a pretty-printer can be registered.
• Pretty-printers registered globally are available when debugging all inferiors.
• Pretty-printers registered with a program space are available only when debugging that
program. See Section 23.3.2.26 [Progspaces In Python], page 474, for more details on
program spaces in Python.
• Pretty-printers registered with an objfile are loaded and unloaded with the corresponding objfile (e.g., shared library). See Section 23.3.2.27 [Objfiles In Python], page 476,
for more details on objfiles in Python.
See Section 23.3.2.7 [Selecting Pretty-Printers], page 426, for further information on how
pretty-printers are selected,
See Section 23.3.2.8 [Writing a Pretty-Printer], page 427, for implementing pretty printers for new types.

10.10.2 Pretty-Printer Example
Here is how a C++ std::string looks without a pretty-printer:(gdb) print s$1 = {
static npos = 4294967295,_M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>},
members of std::basic_string<char, std::char_traits<char>,std::allocator<char> >::_Alloc_hider:_M_p = 0x804a014 "abcd"}

Chapter 10: Examining Data

169}

With a pretty-printer for std::string only the contents are printed:(gdb) print s$2 = "abcd"

10.10.3 Pretty-Printer Commands
info pretty-printer [object-regexp [name-regexp]]
Print the list of installed pretty-printers. This includes disabled pretty-printers,
which are marked as such.
object-regexp is a regular expression matching the objects whose pretty-printers
to list. Objects can be global, the program space’s file (see Section 23.3.2.26[Progspaces In Python], page 474), and the object files within that program
space (see Section 23.3.2.27 [Objfiles In Python], page 476). See Section 23.3.2.7[Selecting Pretty-Printers], page 426, for details on how gdb looks up a printerfrom these three objects.
name-regexp is a regular expression matching the name of the printers to list.
disable pretty-printer [object-regexp [name-regexp]]
Disable pretty-printers matching object-regexp and name-regexp. A disabled
pretty-printer is not forgotten, it may be enabled again later.
enable pretty-printer [object-regexp [name-regexp]]
Enable pretty-printers matching object-regexp and name-regexp.
Example:Suppose we have three pretty-printers installed: one from library1.so named foo thatprints objects of type foo, and another from library2.so named bar that prints two typesof objects, bar1 and bar2.
(gdb) info pretty-printerlibrary1.so:foolibrary2.so:
bar
bar1
bar2
(gdb) info pretty-printer library2
library2.so:
bar
bar1
bar2
(gdb) disable pretty-printer library1
1 printer disabled
2 of 3 printers enabled(gdb) info pretty-printerlibrary1.so:foo [disabled]library2.so:
bar
bar1
bar2

170

Debugging with gdb(gdb) disable pretty-printer library2 bar;bar1
1 printer disabled
1 of 3 printers enabled(gdb) info pretty-printer library2
library2.so:barbar1 [disabled]bar2(gdb) disable pretty-printer library2 bar
1 printer disabled
0 of 3 printers enabled(gdb) info pretty-printerlibrary1.so:foo [disabled]library2.so:bar [disabled]bar1 [disabled]bar2

Note that for bar the entire printer can be disabled, as can each individual subprinter.
Printing values and frame arguments is done by default using the enabled pretty printers.
The print option -raw-values and gdb setting set print raw-values (see [set print
raw-values], page 165) can be used to print values without applying the enabled pretty
printers.
Similarly, the backtrace option -raw-frame-arguments and gdb setting set print
raw-frame-arguments (see [set print raw-frame-arguments], page 161) can be used to ignore the enabled pretty printers when printing frame argument values.

10.11 Value History
Values printed by the print command are saved in the gdb value history. This allows you
to refer to them in other expressions. Values are kept until the symbol table is re-read or
discarded (for example with the file or symbol-file commands). When the symbol tablechanges, the value history is discarded, since the values may contain pointers back to thetypes defined in the symbol table.
The values printed are given history numbers by which you can refer to them. These
are successive integers starting with one. print shows you the history number assigned toa value by printing ‘$num = ’ before the value; here num is the history number.
To refer to any previous value, use ‘$’ followed by the value’s history number. The way
print labels its output is designed to remind you of this. Just $ refers to the most recent
value in the history, and $$ refers to the value before that. $$n refers to the nth value fromthe end; $$2 is the value just prior to $$, $$1 is equivalent to $$, and $$0 is equivalent to$.
For example, suppose you have just printed a pointer to a structure and want to see thecontents of the structure. It suffices to typep *$If you have a chain of structures where the component next points to the next one, you
can print the contents of the next one with this:p *$.nextChapter 10: Examining Data

171

You can print successive links in the chain by repeating this command—which you can doby just typing RET.
Note that the history records values, not expressions. If the value of x is 4 and you typethese commands:
print xset x=5

then the value recorded in the value history by the print command remains 4 even though
the value of x has changed.
show values
Print the last ten values in the value history, with their item numbers. This is
like ‘p $$9’ repeated ten times, except that show values does not change thehistory.
show values nPrint ten history values centered on history item number n.
show values +Print ten history values just after the values last printed. If no more values areavailable, show values + produces no display.
Pressing RET to repeat show values n has exactly the same effect as ‘show values +’.

10.12 Convenience Variables
gdb provides convenience variables that you can use within gdb to hold on to a value
and refer to it later. These variables exist entirely within gdb; they are not part of yourprogram, and setting a convenience variable has no direct effect on further execution of yourprogram. That is why you can use them freely.
Convenience variables are prefixed with ‘$’. Any name preceded by ‘$’ can be used for aconvenience variable, unless it is one of the predefined machine-specific register names (seeSection 10.14 [Registers], page 179). (Value history references, in contrast, are numbers
preceded by ‘$’. See Section 10.11 [Value History], page 170.)
You can save a value in a convenience variable with an assignment expression, just as
you would set a variable in your program. For example:
set $foo = *object_ptr

would save in $foo the value contained in the object pointed to by object_ptr.
Using a convenience variable for the first time creates it, but its value is void until you
assign a new value. You can alter the value with another assignment at any time.
Convenience variables have no fixed types. You can assign a convenience variable any
type of value, including structures and arrays, even if that variable already has a value ofa different type. The convenience variable, when used as an expression, has the type of its
current value.
show convenience
Print a list of convenience variables used so far, and their values, as well as alist of the convenience functions. Abbreviated show conv.

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init-if-undefined $variable = expression
Set a convenience variable if it has not already been set. This is useful for
user-defined commands that keep some state. It is similar, in concept, to using
local static variables with initializers in C (except that convenience variables
are global). It can also be used to allow users to override default values used in
a command script.
If the variable is already defined then the expression is not evaluated so any
side-effects do not occur.
One of the ways to use a convenience variable is as a counter to be incremented or apointer to be advanced. For example, to print a field from successive elements of an arrayof structures:set $i = 0
print bar[$i++]->contents

Repeat that command by typing RET.
Some convenience variables are created automatically by gdb and given values likely to
be useful.
$_

The variable $_ is automatically set by the x command to the last address
examined (see Section 10.6 [Examining Memory], page 152). Other commands
which provide a default address for x to examine also set $_ to that address;
these commands include info line and info breakpoint. The type of $_ isvoid * except when set by the x command, in which case it is a pointer to thetype of $__.

$__The variable $__ is automatically set by the x command to the value found in
the last address examined. Its type is chosen to match the format in which thedata was printed.

$_exitcode
When the program being debugged terminates normally, gdb automaticallysets this variable to the exit code of the program, and resets $_exitsignal tovoid.
$_exitsignal
When the program being debugged dies due to an uncaught signal, gdb automatically sets this variable to that signal’s number, and resets $_exitcode tovoid.
To distinguish between whether the program being debugged has exited (i.e.,$_exitcode is not void) or signalled (i.e., $_exitsignal is not void), theconvenience function $_isvoid can be used (see Section 10.13 [Convenience
Functions], page 174). For example, considering the following source code:#include <signal.h>intmain (int argc, char *argv[]){
raise (SIGALRM);
return 0;}

Chapter 10: Examining Data173

A valid way of telling whether the program being debugged has exited or signalled would be:(gdb) define has_exited_or_signalled
Type commands for definition of ‘‘has_exited_or_signalled’’.
End with a line saying just ‘‘end’’.
>if $_isvoid ($_exitsignal)>echo The program has exited\n>else>echo The program has signalled\n
>end
>end
(gdb) runStarting program:
Program terminated with signal SIGALRM, Alarm clock.
The program no longer exists.
(gdb) has_exited_or_signalled
The program has signalled

As can be seen, gdb correctly informs that the program being debugged has
signalled, since it calls raise and raises a SIGALRM signal. If the program being
debugged had not called raise, then gdb would report a normal exit:(gdb) has_exited_or_signalled
The program has exited$_exception
The variable $_exception is set to the exception object being thrown at an
exception-related catchpoint. See Section 5.1.3 [Set Catchpoints], page 69.
$_ada_exception
The variable $_ada_exception is set to the address of the exception beingcaught or thrown at an Ada exception-related catchpoint. See Section 5.1.3[Set Catchpoints], page 69.
$_probe_argc$_probe_arg0...$_probe_arg11
Arguments to a static probe. See Section 5.1.10 [Static Probe Points], page 81.
$_sdata

The variable $_sdata contains extra collected static tracepoint data. See
Section 13.1.6 [Tracepoint Action Lists], page 208. Note that $_sdata could
be empty, if not inspecting a trace buffer, or if extra static tracepoint data has
not been collected.

$_siginfo
The variable $_siginfo contains extra signal information (see [extra signal
information], page 92). Note that $_siginfo could be empty, if the application
has not yet received any signals. For example, it will be empty before you
execute the run command.
$_tlb

The variable $_tlb is automatically set when debugging applications running
on MS-Windows in native mode or connected to gdbserver that supports theqGetTIBAddr request. See Section E.5 [General Query Packets], page 789. Thisvariable contains the address of the thread information block.

174

Debugging with gdb$_inferior
The number of the current inferior. See Section 4.9 [Debugging Multiple Inferiors Connections and Programs], page 42.
$_thread

The thread number of the current thread. See [thread numbers], page 47.

$_gthreadThe global number of the current thread. See [global thread numbers], page 48.
$_inferior_thread_countThe number of live threads in the current inferior. See Section 4.10 [Threads],
page 47.
$_gdb_major$_gdb_minor
The major and minor version numbers of the running gdb. Development snapshots and pretest versions have their minor version incremented by one; thus,
gdb pretest 9.11.90 will produce the value 12 for $_gdb_minor. These variables
allow you to write scripts that work with different versions of gdb without errors
caused by features unavailable in some of those versions.
$_shell_exitcode$_shell_exitsignal
gdb commands such as shell and | are launching shell commands. Whena launched command terminates, gdb automatically maintains the variables$_shell_exitcode and $_shell_exitsignal according to the exit status of
the last launched command. These variables are set and used similarly to thevariables $_exitcode and $_exitsignal.

10.13 Convenience Functions
gdb also supplies some convenience functions. These have a syntax similar to conveniencevariables. A convenience function can be used in an expression just like an ordinary function;
however, a convenience function is implemented internally to gdb.
These functions do not require gdb to be configured with Python support, which meansthat they are always available.
$_isvoid (expr)
Return one if the expression expr is void. Otherwise it returns zero.
A void expression is an expression where the type of the result is void. For example, you can examine a convenience variable (see Section 10.12 [Convenience
Variables], page 171) to check whether it is void:(gdb) print $_exitcode$1 = void(gdb) print $_isvoid ($_exitcode)$2 = 1(gdb) runStarting program: ./a.out[Inferior 1 (process 29572) exited normally](gdb) print $_exitcode$3 = 0(gdb) print $_isvoid ($_exitcode)

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$4 = 0In the example above, we used $_isvoid to check whether $_exitcode is void
before and after the execution of the program being debugged. Before theexecution there is no exit code to be examined, therefore $_exitcode is void.
After the execution the program being debugged returned zero, therefore $_exitcode is zero, which means that it is not void anymore.
The void expression can also be a call of a function from the program being
debugged. For example, given the following function:void
foo (void){}

The result of calling it inside gdb is void:(gdb) print foo ()$1 = void(gdb) print $_isvoid (foo ())$2 = 1(gdb) set $v = foo ()(gdb) print $v$3 = void(gdb) print $_isvoid ($v)
$4 = 1$_gdb_setting_str (setting)
Return the value of the gdb setting as a string. setting is any setting thatcan be used in a set or show command (see Chapter 22 [Controlling GDB],
page 367).
(gdb) show print frame-arguments
Printing of non-scalar frame arguments is "scalars".
(gdb) p $_gdb_setting_str("print frame-arguments")$1 = "scalars"(gdb) p $_gdb_setting_str("height")$2 = "30"(gdb)$_gdb_setting (setting)
Return the value of the gdb setting. The type of the returned value depends
on the setting.
The value type for boolean and auto boolean settings is int. The boolean
values off and on are converted to the integer values 0 and 1. The value auto
is converted to the value -1.
The value type for integer settings is either unsigned int or int, dependingon the setting.
Some integer settings accept an unlimited value. Depending on the setting,the set command also accepts the value 0 or the value −1 as a synonym forunlimited. For example, set height unlimited is equivalent to set height0.
Some other settings that accept the unlimited value use the value 0 to literally
mean zero. For example, set history size 0 indicates to not record any gdb

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commands in the command history. For such settings, −1 is the synonym forunlimited.
See the documentation of the corresponding set command for the numericalvalue equivalent to unlimited.
The $_gdb_setting function converts the unlimited value to a 0 or a −1 value
according to what the set command uses.
(gdb) p $_gdb_setting_str("height")$1 = "30"(gdb) p $_gdb_setting("height")$2 = 30(gdb) set height unlimited(gdb) p $_gdb_setting_str("height")$3 = "unlimited"(gdb) p $_gdb_setting("height")$4 = 0(gdb) p $_gdb_setting_str("history size")$5 = "unlimited"(gdb) p $_gdb_setting("history size")$6 = -1(gdb) p $_gdb_setting_str("disassemble-next-line")$7 = "auto"(gdb) p $_gdb_setting("disassemble-next-line")$8 = -1(gdb)

Other setting types (enum, filename, optional filename, string, string noescape)are returned as string values.
$_gdb_maint_setting_str (setting)
Like the $_gdb_setting_str function, but works with maintenance set variables.
$_gdb_maint_setting (setting)
Like the $_gdb_setting function, but works with maintenance set variables.
$_shell (command-string)
Invoke a shell to execute command-string. command-string must be a string.
The shell runs on the host machine, the machine gdb is running on. Returns
the command’s exit status. On Unix systems, a command which exits with azero exit status has succeeded, and non-zero exit status indicates failure. Whena command terminates on a fatal signal whose number is N, gdb uses the value
128+N as the exit status, as is standard in Unix shells. Note that N is a hostsignal number, not a target signal number. If you’re native debugging, they
will be the same, but if cross debugging, the host vs target signal numbers
may be completely unrelated. Please consult your host operating system’s
documentation for the mapping between host signal numbers and signal names.
The shell to run is determined in the same way as for the shell command. See
Section 2.3 [Shell Commands], page 20.
(gdb) print $_shell("true")$1 = 0(gdb) print $_shell("false")$2 = 1(gdb) p $_shell("echo hello")

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177

hello
$3 = 0(gdb) p $_shell("foobar")
bash: line 1: foobar: command not found$4 = 127

This may also be useful in breakpoint conditions. For example:(gdb) break function if $_shell("some command") == 0

In this scenario, you’ll want to make sure that the shell command you run in
the breakpoint condition takes the least amount of time possible. For example,
avoid running a command that may block indefinitely, or that sleeps for a while
before exiting. Prefer a command or script which analyzes some state and exits
immediately. This is important because the debugged program stops for the
breakpoint every time, and then gdb evaluates the breakpoint condition. If thecondition is false, the program is re-resumed transparently, without informing
you of the stop. A quick shell command thus avoids significantly slowing down
the debugged program unnecessarily.
Note: unlike the shell command, the $_shell convenience function does notaffect the $_shell_exitcode and $_shell_exitsignal convenience variables.
The following functions require gdb to be configured with Python support.
$_memeq(buf1, buf2, length)
Returns one if the length bytes at the addresses given by buf1 and buf2 areequal. Otherwise it returns zero.
$_regex(str, regex)
Returns one if the string str matches the regular expression regex. Otherwise it
returns zero. The syntax of the regular expression is that specified by Python’s
regular expression support.
$_streq(str1, str2)
Returns one if the strings str1 and str2 are equal. Otherwise it returns zero.
$_strlen(str)
Returns the length of string str.
$_caller_is(name[, number_of_frames])
Returns one if the calling function’s name is equal to name. Otherwise it returns
zero.
If the optional argument number of frames is provided, it is the number offrames up in the stack to look. The default is 1.
Example:(gdb) backtrace#0 bottom_func ()at testsuite/gdb.python/py-caller-is.c:21#1 0x00000000004005a0 in middle_func ()at testsuite/gdb.python/py-caller-is.c:27#2 0x00000000004005ab in top_func ()at testsuite/gdb.python/py-caller-is.c:33#3 0x00000000004005b6 in main ()at testsuite/gdb.python/py-caller-is.c:39(gdb) print $_caller_is ("middle_func")

178

Debugging with gdb$1 = 1(gdb) print $_caller_is ("top_func", 2)$1 = 1$_caller_matches(regexp[, number_of_frames])
Returns one if the calling function’s name matches the regular expression
regexp. Otherwise it returns zero.
If the optional argument number of frames is provided, it is the number offrames up in the stack to look. The default is 1.
$_any_caller_is(name[, number_of_frames])
Returns one if any calling function’s name is equal to name. Otherwise it
returns zero.
If the optional argument number of frames is provided, it is the number offrames up in the stack to look. The default is 1.
This function differs from $_caller_is in that this function checks all stack
frames from the immediate caller to the frame specified by number of frames,
whereas $_caller_is only checks the frame specified by number of frames.
$_any_caller_matches(regexp[, number_of_frames])
Returns one if any calling function’s name matches the regular expression
regexp. Otherwise it returns zero.
If the optional argument number of frames is provided, it is the number offrames up in the stack to look. The default is 1.
This function differs from $_caller_matches in that this function checks
all stack frames from the immediate caller to the frame specified bynumber of frames, whereas $_caller_matches only checks the frame specified
by number of frames.
$_as_string(value)
This convenience function is considered deprecated, and could be removed fromfuture versions of gdb. Use the ‘%V’ format specifier instead (see [%V Format
Specifier], page 398).
Return the string representation of value.
This function is useful to obtain the textual label (enumerator) of an enumeration value. For example, assuming the variable node is of an enumerated type:(gdb) printf "Visiting node of type %s\n", $_as_string(node)
Visiting node of type NODE_INTEGER$_cimag(value)$_creal(value)
Return the imaginary ($_cimag) or real ($_creal) part of the complex number
value.
The type of the imaginary or real part depends on the type of the complex
number, e.g., using $_cimag on a float complex will return an imaginary partof type float.
gdb provides the ability to list and get help on convenience functions.
help function
Print a list of all convenience functions.

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10.14 Registers
You can refer to machine register contents, in expressions, as variables with names startingwith ‘$’. The names of registers are different for each machine; use info registers to see
the names used on your machine.
info registers
Print the names and values of all registers except floating-point and vector
registers (in the selected stack frame).
info all-registers
Print the names and values of all registers, including floating-point and vector
registers (in the selected stack frame).
info registers reggroup ...
Print the name and value of the registers in each of the specified reggroups.
The reggroup can be any of those returned by maint print reggroups (seeAppendix D [Maintenance Commands], page 755).
info registers regname ...
Print the relativized value of each specified register regname. As discussed indetail below, register values are normally relative to the selected stack frame.
The regname may be any register name valid on the machine you are using,with or without the initial ‘$’.
gdb has four “standard” register names that are available (in expressions) on mostmachines—whenever they do not conflict with an architecture’s canonical mnemonics forregisters. The register names $pc and $sp are used for the program counter register andthe stack pointer. $fp is used for a register that contains a pointer to the current stack
frame, and $ps is used for a register that contains the processor status. For example, you
could print the program counter in hex with
p/x $pc

or print the instruction to be executed next with
x/i $pc

or add four to the stack pointer2 with
set $sp += 4

Whenever possible, these four standard register names are available on your machineeven though the machine has different canonical mnemonics, so long as there is no conflict.
The info registers command shows the canonical names. For example, on the SPARC,
info registers displays the processor status register as $psr but you can also refer to it
as $ps; and on x86-based machines $ps is an alias for the eflags register.
gdb always considers the contents of an ordinary register as an integer when the register
is examined in this way. Some machines have special registers which can hold nothing but
floating point; these registers are considered to have floating point values. There is no way
2This is a way of removing one word from the stack, on machines where stacks grow downward in memory(most machines, nowadays). This assumes that the innermost stack frame is selected; setting $sp is notallowed when other stack frames are selected. To pop entire frames off the stack, regardless of machinearchitecture, use return; see Section 17.4 [Returning from a Function], page 280.

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to refer to the contents of an ordinary register as floating point value (although you canprint it as a floating point value with ‘print/f $regname’).
Some registers have distinct “raw” and “virtual” data formats. This means that the data
format in which the register contents are saved by the operating system is not the same
one that your program normally sees. For example, the registers of the 68881 floating point
coprocessor are always saved in “extended” (raw) format, but all C programs expect to workwith “double” (virtual) format. In such cases, gdb normally works with the virtual format
only (the format that makes sense for your program), but the info registers command
prints the data in both formats.
Some machines have special registers whose contents can be interpreted in several different ways. For example, modern x86-based machines have SSE and MMX registers that canhold several values packed together in several different formats. gdb refers to such registers
in struct notation:(gdb) print $xmm1$1 = {
v4_float = {0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044},
v2_double = {9.92129282474342e-303, 2.7585945287983262e-313},
v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",v8_int16 = {0, 0, 14072, 315, 11, 0, 13, 0},v4_int32 = {0, 20657912, 11, 13},v2_int64 = {88725056443645952, 55834574859},
uint128 = 0x0000000d0000000b013b36f800000000}

To set values of such registers, you need to tell gdb which view of the register you wish tochange, as if you were assigning value to a struct member:(gdb) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF

Normally, register values are relative to the selected stack frame (see Section 8.3 [Selecting a Frame], page 117). This means that you get the value that the register would contain
if all stack frames farther in were exited and their saved registers restored. In order to see
the true contents of hardware registers, you must select the innermost frame (with ‘frame0’).
Usually ABIs reserve some registers as not needed to be saved by the callee (a.k.a.:“caller-saved”, “call-clobbered” or “volatile” registers). It may therefore not be possible for
gdb to know the value a register had before the call (in other words, in the outer frame),
if the register value has since been changed by the callee. gdb tries to deduce where
the inner frame saved (“callee-saved”) registers, from the debug info, unwind info, or themachine code generated by your compiler. If some register is not saved, and gdb knows theregister is “caller-saved” (via its own knowledge of the ABI, or because the debug/unwind
info explicitly says the register’s value is undefined), gdb displays ‘<not saved>’ as theregister’s value. With targets that gdb has no knowledge of the register saving convention,
if a register was not saved by the callee, then its value and location in the outer frame areassumed to be the same of the inner frame. This is usually harmless, because if the register
is call-clobbered, the caller either does not care what is in the register after the call, or hascode to restore the value that it does care about. Note, however, that if you change sucha register in the outer frame, you may also be affecting the inner frame. Also, the more
“outer” the frame is you’re looking at, the more likely a call-clobbered register’s value isto be wrong, in the sense that it doesn’t actually represent the value the register had justbefore the call.

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10.15 Floating Point Hardware
Depending on the configuration, gdb may be able to give you more information about thestatus of the floating point hardware.
info float
Display hardware-dependent information about the floating point unit. The
exact contents and layout vary depending on the floating point chip. Currently,‘info float’ is supported on the ARM and x86 machines.

10.16 Vector Unit
Depending on the configuration, gdb may be able to give you more information about thestatus of the vector unit.
info vector
Display information about the vector unit. The exact contents and layout varydepending on the hardware.

10.17 Operating System Auxiliary Information
gdb provides interfaces to useful OS facilities that can help you debug your program.
Some operating systems supply an auxiliary vector to programs at startup. This is akinto the arguments and environment that you specify for a program, but contains a systemdependent variety of binary values that tell system libraries important details about the
hardware, operating system, and process. Each value’s purpose is identified by an integer tag; the meanings are well-known but system-specific. Depending on the configurationand operating system facilities, gdb may be able to show you this information. For remote targets, this functionality may further depend on the remote stub’s support of the‘qXfer:auxv:read’ packet, see [qXfer auxiliary vector read], page 810.
info auxv Display the auxiliary vector of the inferior, which can be either a live process
or a core dump file. gdb prints each tag value numerically, and also shows
names and text descriptions for recognized tags. Some values in the vector are
numbers, some bit masks, and some pointers to strings or other data. gdb
displays each value in the most appropriate form for a recognized tag, and inhexadecimal for an unrecognized tag.
On some targets, gdb can access operating system-specific information and show it toyou. The types of information available will differ depending on the type of operating systemrunning on the target. The mechanism used to fetch the data is described in Appendix H[Operating System Information], page 879. For remote targets, this functionality depends
on the remote stub’s support of the ‘qXfer:osdata:read’ packet, see [qXfer osdata read],page 814.
info os infotype
Display OS information of the requested type.
On gnu/Linux, the following values of infotype are valid:
cpus

Display the list of all CPUs/cores. For each CPU/core, gdb prints
the available fields from /proc/cpuinfo. For each supported archi-

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tecture different fields are available. Two common entries are processor which gives CPU number and bogomips; a system constantthat is calculated during kernel initialization.
files

Display the list of open file descriptors on the target. For eachfile descriptor, gdb prints the identifier of the process owning thedescriptor, the command of the owning process, the value of thedescriptor, and the target of the descriptor.

modules

Display the list of all loaded kernel modules on the target. For
each module, gdb prints the module name, the size of the module
in bytes, the number of times the module is used, the dependenciesof the module, the status of the module, and the address of theloaded module in memory.

msg

Display the list of all System V message queues on the target. For
each message queue, gdb prints the message queue key, the message
queue identifier, the access permissions, the current number of bytes
on the queue, the current number of messages on the queue, theprocesses that last sent and received a message on the queue, theuser and group of the owner and creator of the message queue, thetimes at which a message was last sent and received on the queue,
and the time at which the message queue was last changed.

processes
Display the list of processes on the target. For each process, gdb
prints the process identifier, the name of the user, the commandcorresponding to the process, and the list of processor cores thatthe process is currently running on. (To understand what theseproperties mean, for this and the following info types, please consult
the general gnu/Linux documentation.)procgroups
Display the list of process groups on the target. For each process,gdb prints the identifier of the process group that it belongs to, thecommand corresponding to the process group leader, the process
identifier, and the command line of the process. The list is sorted
first by the process group identifier, then by the process identifier,so that processes belonging to the same process group are grouped
together and the process group leader is listed first.
semaphores
Display the list of all System V semaphore sets on the target.
For each semaphore set, gdb prints the semaphore set key, thesemaphore set identifier, the access permissions, the number ofsemaphores in the set, the user and group of the owner and creatorof the semaphore set, and the times at which the semaphore set
was operated upon and changed.
shm

Display the list of all System V shared-memory regions on the target. For each shared-memory region, gdb prints the region key,Chapter 10: Examining Data183

the shared-memory identifier, the access permissions, the size ofthe region, the process that created the region, the process thatlast attached to or detached from the region, the current number oflive attaches to the region, and the times at which the region waslast attached to, detach from, and changed.

info os

sockets

Display the list of Internet-domain sockets on the target. For eachsocket, gdb prints the address and port of the local and remote
endpoints, the current state of the connection, the creator of thesocket, the IP address family of the socket, and the type of theconnection.

threads

Display the list of threads running on the target. For each thread,gdb prints the identifier of the process that the thread belongs to,the command of the process, the thread identifier, and the processor
core that it is currently running on. The main thread of a process
is not listed.

If infotype is omitted, then list the possible values for infotype and the kind of
OS information available for each infotype. If the target does not return a listof possible types, this command will report an error.

10.18 Memory Region Attributes
Memory region attributes allow you to describe special handling required by regions ofyour target’s memory. gdb uses attributes to determine whether to allow certain typesof memory accesses; whether to use specific width accesses; and whether to cache target
memory. By default the description of memory regions is fetched from the target (if thecurrent target supports this), but the user can override the fetched regions.
Defined memory regions can be individually enabled and disabled. When a memory
region is disabled, gdb uses the default attributes when accessing memory in that region.
Similarly, if no memory regions have been defined, gdb uses the default attributes whenaccessing all memory.
When a memory region is defined, it is given a number to identify it; to enable, disable,or remove a memory region, you specify that number.
mem lower upper attributes...
Define a memory region bounded by lower and upper with attributes
attributes . . . , and add it to the list of regions monitored by gdb. Note thatupper == 0 is a special case: it is treated as the target’s maximum memory
address. (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
mem auto

Discard any user changes to the memory regions and use target-supplied regions,if available, or no regions if the target does not support.

delete mem nums...
Remove memory regions nums . . . from the list of regions monitored by gdb.
disable mem nums...
Disable monitoring of memory regions nums . . . . A disabled memory region is
not forgotten. It may be enabled again later.

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enable mem nums...
Enable monitoring of memory regions nums . . . .
info mem

Print a table of all defined memory regions, with the following columns for eachregion:Memory Region Number
Enabled or Disabled.
Enabled memory regions are marked with ‘y’. Disabled memory
regions are marked with ‘n’.
Lo Address
The address defining the inclusive lower bound of the memory region.
Hi Address
The address defining the exclusive upper bound of the memory
region.
Attributes The list of attributes set for this memory region.

10.18.1 Attributes
10.18.1.1 Memory Access Mode
The access mode attributes set whether gdb may make read or write accesses to a memory
region.
While these attributes prevent gdb from performing invalid memory accesses, they donothing to prevent the target system, I/O DMA, etc. from accessing memory.
ro

Memory is read only.

wo

Memory is write only.

rw

Memory is read/write. This is the default.

10.18.1.2 Memory Access Size
The access size attribute tells gdb to use specific sized accesses in the memory region. Often
memory mapped device registers require specific sized accesses. If no access size attributeis specified, gdb may use accesses of any size.
8

Use 8 bit memory accesses.

16

Use 16 bit memory accesses.

32

Use 32 bit memory accesses.

64

Use 64 bit memory accesses.

10.18.1.3 Data Cache
The data cache attributes set whether gdb will cache target memory. While this generally
improves performance by reducing debug protocol overhead, it can lead to incorrect results
because gdb does not know about volatile variables or memory mapped device registers.
cacheEnable gdb to cache target memory.

nocacheDisable gdb from caching target memory. This is the default.

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185

10.18.2 Memory Access Checking
gdb can be instructed to refuse accesses to memory that is not explicitly described. Thiscan be useful if accessing such regions has undesired effects for a specific target, or to provide
better error checking. The following commands control this behaviour.
set mem inaccessible-by-default [on|off]
If on is specified, make gdb treat memory not explicitly described by the memory ranges as non-existent and refuse accesses to such memory. The checks are
only performed if there’s at least one memory range defined. If off is specified,make gdb treat the memory not explicitly described by the memory ranges asRAM. The default value is on.
show mem inaccessible-by-default
Show the current handling of accesses to unknown memory.

10.19 Copy Between Memory and a File
You can use the commands dump, append, and restore to copy data between target memory
and a file. The dump and append commands write data to a file, and the restore commandreads data from a file back into the inferior’s memory. Files may be in binary, Motorola
S-record, Intel hex, Tektronix Hex, or Verilog Hex format; however, gdb can only append
to binary files, and cannot read from Verilog Hex files.
dump [format] memory filename start_addr end_addr
dump [format] value filename expr
Dump the contents of memory from start addr to end addr, or the value of
expr, to filename in the given format.
The format parameter may be any one of:binaryRaw binary form.

ihexIntel hex format.

srec

Motorola S-record format.

tekhexTektronix Hex format.

verilog

Verilog Hex format.

gdb uses the same definitions of these formats as the gnu binary utilities, like
‘objdump’ and ‘objcopy’. If format is omitted, gdb dumps the data in raw
binary form.
append [binary] memory filename start_addr end_addr
append [binary] value filename expr
Append the contents of memory from start addr to end addr, or the value of
expr, to the file filename, in raw binary form. (gdb can only append data tofiles in raw binary form.)
restore filename [binary] bias start end
Restore the contents of file filename into memory. The restore command can
automatically recognize any known bfd file format, except for raw binary. To

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restore a raw binary file you must specify the optional keyword binary after
the filename.
If bias is non-zero, its value will be added to the addresses contained in the file.
Binary files always start at address zero, so they will be restored at address
bias. Other bfd files have a built-in location; they will be restored at offset bias
from that location.
If start and/or end are non-zero, then only data between file offset start andfile offset end will be restored. These offsets are relative to the addresses in thefile, before the bias argument is applied.

10.20 How to Produce a Core File from Your Program
A core file or core dump is a file that records the memory image of a running process
and its process status (register values etc.). Its primary use is post-mortem debugging of aprogram that crashed while it ran outside a debugger. A program that crashes automatically
produces a core file, unless this feature is disabled by the user. See Section 18.1 [Files],page 291, for information on invoking gdb in the post-mortem debugging mode.
Occasionally, you may wish to produce a core file of the program you are debugging inorder to preserve a snapshot of its state. gdb has a special command for that.
generate-core-file [file]gcore [file]
Produce a core dump of the inferior process. The optional argument file specifies
the file name where to put the core dump. If not specified, the file name defaults
to core.pid, where pid is the inferior process ID.
If supported by the filesystem where the core is written to, gdb generates asparse core dump file.
Note that this command is implemented only for some systems (as of thiswriting, gnu/Linux, FreeBSD, Solaris, and S390).
On gnu/Linux, this command can take into account the value of the file/proc/pid/coredump_filter when generating the core dump (see [set usecoredump-filter], page 186), and by default honors the VM_DONTDUMP flag for
mappings where it is present in the file /proc/pid/smaps (see [set dumpexcluded-mappings], page 187).
set use-coredump-filter on
set use-coredump-filter off
Enable or disable the use of the file /proc/pid/coredump_filter when generating core dump files. This file is used by the Linux kernel to decide whattypes of memory mappings will be dumped or ignored when generating a coredump file. pid is the process ID of a currently running process.
To make use of this feature, you have to write in the /proc/pid/coredump_
filter file a value, in hexadecimal, which is a bit mask representing the memory
mapping types. If a bit is set in the bit mask, then the memory mappings ofthe corresponding types will be dumped; otherwise, they will be ignored. Thisconfiguration is inherited by child processes. For more information about theChapter 10: Examining Data

187

bits that can be set in the /proc/pid/coredump_filter file, please refer to the
manpage of core(5).
By default, this option is on. If this option is turned off, gdb does not readthe coredump_filter file and instead uses the same default value as the Linuxkernel in order to decide which pages will be dumped in the core dump file. Thisvalue is currently 0x33, which means that bits 0 (anonymous private mappings),
1 (anonymous shared mappings), 4 (ELF headers) and 5 (private huge pages)
are active. This will cause these memory mappings to be dumped automatically.
set dump-excluded-mappings on
set dump-excluded-mappings off
If on is specified, gdb will dump memory mappings marked with the VM_
DONTDUMP flag. This flag is represented in the file /proc/pid/smaps with theacronym dd.
The default value is off.

10.21 Character Sets
If the program you are debugging uses a different character set to represent characters andstrings than the one gdb uses itself, gdb can automatically translate between the character
sets for you. The character set gdb uses we call the host character set; the one the inferior
program uses we call the target character set.
For example, if you are running gdb on a gnu/Linux system, which uses the ISO Latin
1 character set, but you are using gdb’s remote protocol (see Chapter 20 [Remote Debugging], page 315) to debug a program running on an IBM mainframe, which uses the ebcdic
character set, then the host character set is Latin-1, and the target character set is ebcdic.
If you give gdb the command set target-charset EBCDIC-US, then gdb translates between ebcdic and Latin 1 as you print character or string values, or use character andstring literals in expressions.
gdb has no way to automatically recognize which character set the inferior program
uses; you must tell it, using the set target-charset command, described below.
Here are the commands for controlling gdb’s character set support:
set target-charset charset
Set the current target character set to charset. To display the list of supported
target character sets, type set target-charset TABTAB.
set host-charset charset
Set the current host character set to charset.
By default, gdb uses a host character set appropriate to the system it is running on; you can override that default using the set host-charset command.
On some systems, gdb cannot automatically determine the appropriate hostcharacter set. In this case, gdb uses ‘UTF-8’.
gdb can only use certain character sets as its host character set. If you type
set host-charset TABTAB, gdb will list the host character sets it supports.

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set charset charset
Set the current host and target character sets to charset. As above, if you typeset charset TABTAB, gdb will list the names of the character sets that can beused for both host and target.
show charset
Show the names of the current host and target character sets.
show host-charset
Show the name of the current host character set.
show target-charset
Show the name of the current target character set.
set target-wide-charset charset
Set the current target’s wide character set to charset. This is the characterset used by the target’s wchar_t type. To display the list of supported wide
character sets, type set target-wide-charset TABTAB.
show target-wide-charset
Show the name of the current target’s wide character set.
Here is an example of gdb’s character set support in action. Assume that the following
source code has been placed in the file charset-test.c:#include <stdio.h>char ascii_hello[]= {72, 101, 108, 108, 111, 44, 32, 119,111, 114, 108, 100, 33, 10, 0};char ibm1047_hello[]= {200, 133, 147, 147, 150, 107, 64, 166,
150, 153, 147, 132, 90, 37, 0};main (){
printf ("Hello, world!\n");}In this program, ascii_hello and ibm1047_hello are arrays containing the string‘Hello, world!’ followed by a newline, encoded in the ascii and ibm1047 character sets.
We compile the program, and invoke the debugger on it:$ gcc -g charset-test.c -o charset-test$ gdb -nw charset-test
GNU gdb 2001-12-19-cvs
Copyright 2001 Free Software Foundation, Inc.
...
(gdb)

We can use the show charset command to see what character sets gdb is currently
using to interpret and display characters and strings:(gdb) show charset
The current host and target character set is ‘ISO-8859-1’.
(gdb)

For the sake of printing this manual, let’s use ascii as our initial character set:(gdb) set charset ASCII

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189(gdb) show charset
The current host and target character set is ‘ASCII’.
(gdb)

Let’s assume that ascii is indeed the correct character set for our host system — inother words, let’s assume that if gdb prints characters using the ascii character set, ourterminal will display them properly. Since our current target character set is also ascii, thecontents of ascii_hello print legibly:(gdb) print ascii_hello$1 = 0x401698 "Hello, world!\n"(gdb) print ascii_hello[0]$2 = 72 ’H’(gdb)

gdb uses the target character set for character and string literals you use in expressions:(gdb) print ’+’$3 = 43 ’+’(gdb)

The ascii character set uses the number 43 to encode the ‘+’ character.
gdb relies on the user to tell it which character set the target program uses. If we print
ibm1047_hello while our target character set is still ascii, we get jibberish:(gdb) print ibm1047_hello$4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%"(gdb) print ibm1047_hello[0]$5 = 200 ’\310’(gdb)

If we invoke the set target-charset followed by TABTAB, gdb tells us the character
sets it supports:(gdb) set target-charset
ASCII
EBCDIC-US
IBM1047(gdb) set target-charset

ISO-8859-1

We can select ibm1047 as our target character set, and examine the program’s strings
again. Now the ascii string is wrong, but gdb translates the contents of ibm1047_hellofrom the target character set, ibm1047, to the host character set, ascii, and they display
correctly:(gdb) set target-charset IBM1047(gdb) show charset
The current host character set is ‘ASCII’.
The current target character set is ‘IBM1047’.
(gdb) print ascii_hello$6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"(gdb) print ascii_hello[0]$7 = 72 ’\110’(gdb) print ibm1047_hello$8 = 0x4016a8 "Hello, world!\n"(gdb) print ibm1047_hello[0]$9 = 200 ’H’(gdb)

As above, gdb uses the target character set for character and string literals you use in
expressions:(gdb) print ’+’$10 = 78 ’+’
(gdb)

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The ibm1047 character set uses the number 78 to encode the ‘+’ character.

10.22 Caching Data of Targets
gdb caches data exchanged between the debugger and a target. Each cache is associatedwith the address space of the inferior. See Section 4.9 [Inferiors Connections and Programs],
page 42, about inferior and address space. Such caching generally improves performance inremote debugging (see Chapter 20 [Remote Debugging], page 315), because it reduces theoverhead of the remote protocol by bundling memory reads and writes into large chunks.
Unfortunately, simply caching everything would lead to incorrect results, since gdb does
not necessarily know anything about volatile values, memory-mapped I/O addresses, etc.
Furthermore, in non-stop mode (see Section 5.5.2 [Non-Stop Mode], page 94) memory canbe changed while a gdb command is executing. Therefore, by default, gdb only caches
data known to be on the stack3 or in the code segment. Other regions of memory can be
explicitly marked as cacheable; see Section 10.18 [Memory Region Attributes], page 183.
set remotecache on
set remotecache off
This option no longer does anything; it exists for compatibility with old scripts.
show remotecacheShow the current state of the obsolete remotecache flag.
set stack-cache on
set stack-cache off
Enable or disable caching of stack accesses. When on, use caching. By default,
this option is on.
show stack-cacheShow the current state of data caching for memory accesses.
set code-cache on
set code-cache off
Enable or disable caching of code segment accesses. When on, use caching. By
default, this option is on. This improves performance of disassembly in remotedebugging.
show code-cacheShow the current state of target memory cache for code segment accesses.
info dcache [line]
Print the information about the performance of data cache of the current inferior’s address space. The information displayed includes the dcache width anddepth, and for each cache line, its number, address, and how many times it wasreferenced. This command is useful for debugging the data cache operation.
If a line number is specified, the contents of that line will be printed in hex.
set dcache size size
Set maximum number of entries in dcache (dcache depth above).
3

In non-stop mode, it is moderately rare for a running thread to modify the stack of a stopped thread ina way that would interfere with a backtrace, and caching of stack reads provides a significant speed upof remote backtraces.

Chapter 10: Examining Data191

set dcache line-size line-size
Set number of bytes each dcache entry caches (dcache width above). Must be
a power of 2.
show dcache size
Show maximum number of dcache entries. See Section 10.22 [Caching Target
Data], page 190.
show dcache line-sizeShow default size of dcache lines.
maint flush dcache
Flush the contents (if any) of the dcache. This maintainer command is usefulwhen debugging the dcache implementation.

10.23 Search Memory
Memory can be searched for a particular sequence of bytes with the find command.
find [/sn] start_addr, +len, val1 [, val2, ...]
find [/sn] start_addr, end_addr, val1 [, val2, ...]
Search memory for the sequence of bytes specified by val1, val2, etc. The search
begins at address start addr and continues for either len bytes or through to
end addr inclusive.
s and n are optional parameters. They may be specified in either order, apart or together.
s, search query size
The size of each search query value.
b

bytes

h

halfwords (two bytes)

w

words (four bytes)

g

giant words (eight bytes)

All values are interpreted in the current language. This means, for example,
that if the current source language is C/C++ then searching for the string “hello”
includes the trailing ’\0’. The null terminator can be removed from searchingby using casts, e.g.: ‘{char[5]}"hello"’.
If the value size is not specified, it is taken from the value’s type in the current
language. This is useful when one wants to specify the search pattern as a
mixture of types. Note that this means, for example, that in the case of C-likelanguages a search for an untyped 0x42 will search for ‘(int) 0x42’ which istypically four bytes.
n, maximum number of finds
The maximum number of matches to print. The default is to print all finds.
You can use strings as search values. Quote them with double-quotes ("). The stringvalue is copied into the search pattern byte by byte, regardless of the endianness of thetarget and the size specification.

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The address of each match found is printed as well as a count of the number of matches
found.
The address of the last value found is stored in convenience variable ‘$_’. A count of thenumber of matches is stored in ‘$numfound’.
For example, if stopped at the printf in this function:
void
hello (){
static char hello[] = "hello-hello";
static struct { char c; short s; int i; }__attribute__ ((packed)) mixed= { ’c’, 0x1234, 0x87654321 };printf ("%s\n", hello);}

you get during debugging:(gdb) find &hello[0], +sizeof(hello), "hello"
0x804956d <hello.1620+6>
1 pattern found(gdb) find &hello[0], +sizeof(hello), ’h’, ’e’, ’l’, ’l’, ’o’
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found.
(gdb) find &hello[0], +sizeof(hello), {char[5]}"hello"
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found.
(gdb) find /b1 &hello[0], +sizeof(hello), ’h’, 0x65, ’l’
0x8049567 <hello.1620>
1 pattern found(gdb) find &mixed, +sizeof(mixed), (char) ’c’, (short) 0x1234, (int) 0x87654321
0x8049560 <mixed.1625>
1 pattern found(gdb) print $numfound$1 = 1(gdb) print $_$2 = (void *) 0x8049560

10.24 Value Sizes
Whenever gdb prints a value memory will be allocated within gdb to hold the contents ofthe value. It is possible in some languages with dynamic typing systems, that an invalid
program may indicate a value that is incorrectly large, this in turn may cause gdb to try
and allocate an overly large amount of memory.
set max-value-size bytes
set max-value-size unlimited
Set the maximum size of memory that gdb will allocate for the contents of avalue to bytes, trying to display a value that requires more memory than thatwill result in an error.
Setting this variable does not effect values that have already been allocatedwithin gdb, only future allocations.
There’s a minimum size that max-value-size can be set to in order that gdb
can still operate correctly, this minimum is currently 16 bytes.

193

The limit applies to the results of some subexpressions as well as to complete
expressions. For example, an expression denoting a simple integer component,such as x.y.z, may fail if the size of x.y is dynamic and exceeds bytes. On theother hand, gdb is sometimes clever; the expression A[i], where A is an arrayvariable with non-constant size, will generally succeed regardless of the bounds
on A, as long as the component size is less than bytes.
The default value of max-value-size is currently 64k.
show max-value-sizeShow the maximum size of memory, in bytes, that gdb will allocate for thecontents of a value.

195

11 Debugging Optimized CodeAlmost all compilers support optimization. With optimization disabled, the compiler generates assembly code that corresponds directly to your source code, in a simplistic way.
As the compiler applies more powerful optimizations, the generated assembly code diverges
from your original source code. With help from debugging information generated by thecompiler, gdb can map from the running program back to constructs from your original
source.
gdb is more accurate with optimization disabled. If you can recompile without optimization, it is easier to follow the progress of your program during debugging. But, there
are many cases where you may need to debug an optimized version.
When you debug a program compiled with ‘-g -O’, remember that the optimizer has
rearranged your code; the debugger shows you what is really there. Do not be too surprised
when the execution path does not exactly match your source file! An extreme example: ifyou define a variable, but never use it, gdb never sees that variable—because the compiler
optimizes it out of existence.
Some things do not work as well with ‘-g -O’ as with just ‘-g’, particularly on machineswith instruction scheduling. If in doubt, recompile with ‘-g’ alone, and if this fixes the
problem, please report it to us as a bug (including a test case!). See Section 10.3 [Variables],page 147, for more information about debugging optimized code.

11.1 Inline Functions
Inlining is an optimization that inserts a copy of the function body directly at each call site,
instead of jumping to a shared routine. gdb displays inlined functions just like non-inlined
functions. They appear in backtraces. You can view their arguments and local variables,
step into them with step, skip them with next, and escape from them with finish. You
can check whether a function was inlined by using the info frame command.
For gdb to support inlined functions, the compiler must record information about inlining in the debug information — gcc using the dwarf 2 format does this, and several other compilers do also. gdb only supports inlined functions when using dwarf 2.
Versions of gcc before 4.1 do not emit two required attributes (‘DW_AT_call_file’ and‘DW_AT_call_line’); gdb does not display inlined function calls with earlier versions ofgcc. It instead displays the arguments and local variables of inlined functions as local
variables in the caller.
The body of an inlined function is directly included at its call site; unlike a non-inlined
function, there are no instructions devoted to the call. gdb still pretends that the call site
and the start of the inlined function are different instructions. Stepping to the call site
shows the call site, and then stepping again shows the first line of the inlined function, eventhough no additional instructions are executed.
This makes source-level debugging much clearer; you can see both the context of the calland then the effect of the call. Only stepping by a single instruction using stepi or nexti
does not do this; single instruction steps always show the inlined body.
There are some ways that gdb does not pretend that inlined function calls are the sameas normal calls:

196

Debugging with gdb• Setting breakpoints at the call site of an inlined function may not work, because thecall site does not contain any code. gdb may incorrectly move the breakpoint to thenext line of the enclosing function, after the call. This limitation will be removed ina future version of gdb; until then, set a breakpoint on an earlier line or inside theinlined function instead.
• gdb cannot locate the return value of inlined calls after using the finish command.
This is a limitation of compiler-generated debugging information; after finish, you
can step to the next line and print a variable where your program stored the return
value.

11.2 Tail Call Frames
Function B can call function C in its very last statement. In unoptimized compilation thecall of C is immediately followed by return instruction at the end of B code. Optimizing
compiler may replace the call and return in function B into one jump to function C instead.
Such use of a jump instruction is called tail call.
During execution of function C, there will be no indication in the function call stack
frames that it was tail-called from B. If function A regularly calls function B which tail-calls
function C, then gdb will see A as the caller of C. However, in some cases gdb can determinethat C was tail-called from B, and it will then create fictitious call frame for that, with thereturn address set up as if B called C normally.
This functionality is currently supported only by DWARF 2 debugging format and thecompiler has to produce ‘DW_TAG_call_site’ tags. With gcc, you need to specify -O -gduring compilation, to get this information.
info frame command (see Section 8.4 [Frame Info], page 119) will indicate the tail callframe kind by text tail call frame such as in this sample gdb output:(gdb) x/i $pc - 20x40066b <b(int, double)+11>: jmp 0x400640 <c(int, double)>(gdb) info frame
Stack level 1, frame at 0x7fffffffda30:
rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
tail call frame, caller of frame at 0x7fffffffda30
source language c++.
Arglist at unknown address.
Locals at unknown address, Previous frame’s sp is 0x7fffffffda30

The detection of all the possible code path executions can find them ambiguous. There is
no execution history stored (possible Chapter 6 [Reverse Execution], page 101, is never used
for this purpose) and the last known caller could have reached the known callee by multiple
different jump sequences. In such case gdb still tries to show at least all the unambiguous
top tail callers and all the unambiguous bottom tail callees, if any.
set debug entry-values
When set to on, enables printing of analysis messages for both frame argument
values at function entry and tail calls. It will show all the possible valid tailcalls code paths it has considered. It will also print the intersection of themwith the final unambiguous (possibly partial or even empty) code path result.

Chapter 11: Debugging Optimized Code197

show debug entry-values
Show the current state of analysis messages printing for both frame argument
values at function entry and tail calls.
The analysis messages for tail calls can for example show why the virtual tail call frame
for function c has not been recognized (due to the indirect reference by variable x):
static void __attribute__((noinline, noclone)) c (void);void (*x) (void) = c;static void __attribute__((noinline, noclone)) a (void) { x++; }static void __attribute__((noinline, noclone)) c (void) { a (); }int main (void) { x (); return 0; }Breakpoint 1, DW_OP_entry_value resolving cannot find
DW_TAG_call_site 0x40039a in maina () at t.c:3
3 static void __attribute__((noinline, noclone)) a (void) { x++; }(gdb) bt
#0 a () at t.c:3#1 0x000000000040039a in main () at t.c:5

Another possibility is an ambiguous virtual tail call frames resolution:
int i;
static void __attribute__((noinline, noclone)) f (void) { i++; }static void __attribute__((noinline, noclone)) e (void) { f (); }static void __attribute__((noinline, noclone)) d (void) { f (); }static void __attribute__((noinline, noclone)) c (void) { d (); }static void __attribute__((noinline, noclone)) b (void){ if (i) c (); else e (); }static void __attribute__((noinline, noclone)) a (void) { b (); }int main (void) { a (); return 0; }tailcall: initial: 0x4004d2(a) 0x4004ce(b) 0x4004b2(c) 0x4004a2(d)tailcall: compare: 0x4004d2(a) 0x4004cc(b) 0x400492(e)tailcall: reduced: 0x4004d2(a) |(gdb) bt
#0 f () at t.c:2#1 0x00000000004004d2 in a () at t.c:8#2 0x0000000000400395 in main () at t.c:9

Frames #0 and #2 are real, #1 is a virtual tail call frame. The code can have possible
execution paths main->a->b->c->d->f or main->a->b->e->f, gdb cannot find which one
from the inferior state.
initial: state shows some random possible calling sequence gdb has found. It thenfinds another possible calling sequence - that one is prefixed by compare:. The nonambiguous intersection of these two is printed as the reduced: calling sequence. Thatone could have many further compare: and reduced: statements as long as there remain
any non-ambiguous sequence entries.
For the frame of function b in both cases there are different possible $pc values (0x4004cc
or 0x4004ce), therefore this frame is also ambiguous. The only non-ambiguous frame is theone for function a, therefore this one is displayed to the user while the ambiguous frames
are omitted.
There can be also reasons why printing of frame argument values at function entry may
fail:
int v;

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static void __attribute__((noinline, noclone)) c (int i) { v++; }static void __attribute__((noinline, noclone)) a (int i);
static void __attribute__((noinline, noclone)) b (int i) { a (i); }static void __attribute__((noinline, noclone)) a (int i){ if (i) b (i - 1); else c (0); }int main (void) { a (5); return 0; }(gdb) bt
#0 c (i=i@entry=0) at t.c:2#1 0x0000000000400428 in a (DW_OP_entry_value resolving has found
function "a" at 0x400420 can call itself via tail calls
i=<optimized out>) at t.c:6#2 0x000000000040036e in main () at t.c:7

gdb cannot find out from the inferior state if and how many times did function a callitself (via function b) as these calls would be tail calls. Such tail calls would modify thei variable, therefore gdb cannot be sure the value it knows would be right - gdb prints<optimized out> instead.

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12 C Preprocessor Macros
Some languages, such as C and C++, provide a way to define and invoke “preprocessor
macros” which expand into strings of tokens. gdb can evaluate expressions containing
macro invocations, show the result of macro expansion, and show a macro’s definition,
including where it was defined.
You may need to compile your program specially to provide gdb with information about
preprocessor macros. Most compilers do not include macros in their debugging information,even when you compile with the -g flag. See Section 4.1 [Compilation], page 33.
A program may define a macro at one point, remove that definition later, and thenprovide a different definition after that. Thus, at different points in the program, a macro
may have different definitions, or have no definition at all. If there is a current stack frame,
gdb uses the macros in scope at that frame’s source code line. Otherwise, gdb uses themacros in scope at the current listing location; see Section 9.1 [List], page 125.
Whenever gdb evaluates an expression, it always expands any macro invocations present
in the expression. gdb also provides the following commands for working with macros
explicitly.
macro expand expression
macro exp expression
Show the results of expanding all preprocessor macro invocations in expression.
Since gdb simply expands macros, but does not parse the result, expressionneed not be a valid expression; it can be any string of tokens.
macro expand-once expression
macro exp1 expression(This command is not yet implemented.) Show the results of expanding those
preprocessor macro invocations that appear explicitly in expression. Macro
invocations appearing in that expansion are left unchanged. This command
allows you to see the effect of a particular macro more clearly, without being
confused by further expansions. Since gdb simply expands macros, but does
not parse the result, expression need not be a valid expression; it can be any
string of tokens.
info macro [-a|-all] [--] macro
Show the current definition or all definitions of the named macro, and describe
the source location or compiler command-line where that definition was established. The optional double dash is to signify the end of argument processing
and the beginning of macro for non C-like macros where the macro may begin
with a hyphen.
info macros locspec
Show all macro definitions that are in effect at the source line of the code
location that results from resolving locspec, and describe the source location orcompiler command-line where those definitions were established.
macro define macro replacement-list
macro define macro(arglist) replacement-list
Introduce a definition for a preprocessor macro named macro, invocations ofwhich are replaced by the tokens given in replacement-list. The first form of200

Debugging with gdb

this command defines an “object-like” macro, which takes no arguments; thesecond form defines a “function-like” macro, which takes the arguments given
in arglist.
A definition introduced by this command is in scope in every expression evaluated in gdb, until it is removed with the macro undef command, described
below. The definition overrides all definitions for macro present in the program
being debugged, as well as any previous user-supplied definition.
macro undef macro
Remove any user-supplied definition for the macro named macro. This command only affects definitions provided with the macro define command, described above; it cannot remove definitions present in the program being debugged.
macro list
List all the macros defined using the macro define command.
Here is a transcript showing the above commands in action. First, we show our source
files:$ cat sample.c#include <stdio.h>#include "sample.h"#define M 42
#define ADD(x) (M + x)
main (){#define N 28
printf ("Hello, world!\n");#undef N
printf ("We’re so creative.\n");#define N 1729
printf ("Goodbye, world!\n");}$ cat sample.h#define Q <$Now, we compile the program using the gnu C compiler, gcc. We pass the -gdwarf-21
and -g3 flags to ensure the compiler includes information about preprocessor macros in the
debugging information.
$ gcc -gdwarf-2 -g3 sample.c -o sample$

Now, we start gdb on our sample program:$ gdb -nw sample
GNU gdb 2002-05-06-cvs
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, ...
(gdb)
1This is the minimum. Recent versions of gcc support -gdwarf-3 and -gdwarf-4; we recommend always
choosing the most recent version of DWARF.

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201

We can expand macros and examine their definitions, even when the program is notrunning. gdb uses the current listing position to decide which macro definitions are inscope:(gdb) list main
3
4
#define M 42
5#define ADD(x) (M + x)
67main ()
8{9#define N 28
10
printf ("Hello, world!\n");11#undef N
12
printf ("We’re so creative.\n");(gdb) info macro ADD
Defined at /home/jimb/gdb/macros/play/sample.c:5#define ADD(x) (M + x)(gdb) info macro Q
Defined at /home/jimb/gdb/macros/play/sample.h:1
included at /home/jimb/gdb/macros/play/sample.c:2#define Q <(gdb) macro expand ADD(1)expands to: (42 + 1)(gdb) macro expand-once ADD(1)expands to: once (M + 1)
(gdb)

In the example above, note that macro expand-once expands only the macro invocation
explicit in the original text — the invocation of ADD — but does not expand the invocationof the macro M, which was introduced by ADD.
Once the program is running, gdb uses the macro definitions in force at the source lineof the current stack frame:(gdb) break main
Breakpoint 1 at 0x8048370: file sample.c, line 10.
(gdb) runStarting program: /home/jimb/gdb/macros/play/sample
Breakpoint 1, main () at sample.c:10
10
printf ("Hello, world!\n");(gdb)

At line 10, the definition of the macro N at line 9 is in force:(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:9#define N 28(gdb) macro expand N Q M
expands to: 28 < 42(gdb) print N Q M$1 = 1(gdb)

As we step over directives that remove N’s definition, and then give it a new definition,
gdb finds the definition (or lack thereof) in force at each point:(gdb) next
Hello, world!
12
printf ("We’re so creative.\n");(gdb) info macro N

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The symbol ‘N’ has no definition as a C/C++ preprocessor macro
at /home/jimb/gdb/macros/play/sample.c:12(gdb) next
We’re so creative.
14
printf ("Goodbye, world!\n");(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:13#define N 1729
(gdb) macro expand N Q M
expands to: 1729 < 42(gdb) print N Q M$2 = 0(gdb)

In addition to source files, macros can be defined on the compilation command line using
the -Dname=value syntax. For macros defined in such a way, gdb displays the location of
their definition as line zero of the source file submitted to the compiler.
(gdb) info macro __STDC__
Defined at /home/jimb/gdb/macros/play/sample.c:0-D__STDC__=1
(gdb)

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13 Tracepoints
In some applications, it is not feasible for the debugger to interrupt the program’s execution
long enough for the developer to learn anything helpful about its behavior. If the program’s
correctness depends on its real-time behavior, delays introduced by a debugger might cause
the program to change its behavior drastically, or perhaps fail, even when the code itself iscorrect. It is useful to be able to observe the program’s behavior without interrupting it.
Using gdb’s trace and collect commands, you can specify locations in the program,called tracepoints, and arbitrary expressions to evaluate when those tracepoints are reached.
Later, using the tfind command, you can examine the values those expressions had when
the program hit the tracepoints. The expressions may also denote objects in memory—
structures or arrays, for example—whose values gdb should record; while visiting a particular tracepoint, you may inspect those objects as if they were in memory at that moment.
However, because gdb records these values without interacting with you, it can do so quickly
and unobtrusively, hopefully not disturbing the program’s behavior.
The tracepoint facility is currently available only for remote targets. See Chapter 19[Targets], page 311. In addition, your remote target must know how to collect trace data.
This functionality is implemented in the remote stub; however, none of the stubs distributedwith gdb support tracepoints as of this writing. The format of the remote packets used to
implement tracepoints are described in Section E.7 [Tracepoint Packets], page 817.
It is also possible to get trace data from a file, in a manner reminiscent of corefiles;
you specify the filename, and use tfind to search through the file. See Section 13.4 [Trace
Files], page 219, for more details.
This chapter describes the tracepoint commands and features.

13.1 Commands to Set Tracepoints
Before running such a trace experiment, an arbitrary number of tracepoints can be set. A
tracepoint is actually a special type of breakpoint (see Section 5.1.1 [Set Breaks], page 58),
so you can manipulate it using standard breakpoint commands. For instance, as withbreakpoints, tracepoint numbers are successive integers starting from one, and many of thecommands associated with tracepoints take the tracepoint number as their argument, toidentify which tracepoint to work on.
For each tracepoint, you can specify, in advance, some arbitrary set of data that you
want the target to collect in the trace buffer when it hits that tracepoint. The collected data
can include registers, local variables, or global data. Later, you can use gdb commands toexamine the values these data had at the time the tracepoint was hit.
Tracepoints do not support every breakpoint feature. Ignore counts on tracepoints haveno effect, and tracepoints cannot run gdb commands when they are hit. Tracepoints may
not be thread-specific either.
Some targets may support fast tracepoints, which are inserted in a different way (suchas with a jump instead of a trap), that is faster but possibly restricted in where they may
be installed.
Regular and fast tracepoints are dynamic tracing facilities, meaning that they can beused to insert tracepoints at (almost) any location in the target. Some targets may also support controlling static tracepoints from gdb. With static tracing, a set of instrumentation

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points, also known as markers, are embedded in the target program, and can be activatedor deactivated by name or address. These are usually placed at locations which facilitate
investigating what the target is actually doing. gdb’s support for static tracing includes
being able to list instrumentation points, and attach them with gdb defined high level tracepoints that expose the whole range of convenience of gdb’s tracepoints support. Namely,
support for collecting registers values and values of global or local (to the instrumentation
point) variables; tracepoint conditions and trace state variables. The act of installing a gdb
static tracepoint on an instrumentation point, or marker, is referred to as probing a static
tracepoint marker.
gdbserver supports tracepoints on some target systems. See Section 20.3 [Tracepoints
support in gdbserver], page 320.
This section describes commands to set tracepoints and associated conditions and actions.

13.1.1 Create and Delete Tracepoints
trace locspec
The trace command is very similar to the break command. Its argument
locspec can be any valid location specification. See Section 9.2 [Location Specifications], page 126. The trace command defines a tracepoint, which is a pointin the target program where the debugger will briefly stop, collect some data,
and then allow the program to continue. Setting a tracepoint or changing its actions takes effect immediately if the remote stub supports the ‘InstallInTrace’feature (see [install tracepoint in tracing], page 807). If remote stub doesn’t support the ‘InstallInTrace’ feature, all these changes don’t take effect until thenext tstart command, and once a trace experiment is running, further changes
will not have any effect until the next trace experiment starts. In addition, gdb
supports pending tracepoints—tracepoints whose address is not yet resolved.
(This is similar to pending breakpoints.) Pending tracepoints are not downloaded to the target and not installed until they are resolved. The resolutionof pending tracepoints requires gdb support—when debugging with the remotetarget, and gdb disconnects from the remote stub (see [disconnected tracing],
page 212), pending tracepoints can not be resolved (and downloaded to theremote stub) while gdb is disconnected.
Here are some examples of using the trace command:(gdb) trace foo.c:121// a source file and line number(gdb) trace +2// 2 lines forward(gdb) trace my function// first source line of function(gdb) trace *my function // EXACT start address of function(gdb) trace *0x2117c4// an address

You can abbreviate trace as tr.
trace locspec if cond
Set a tracepoint with condition cond; evaluate the expression cond each time
the tracepoint is reached, and collect data only if the value is nonzero—that is,Chapter 13: Tracepoints

205

if cond evaluates as true. See Section 13.1.4 [Tracepoint Conditions], page 207,
for more information on tracepoint conditions.
ftrace locspec [ if cond ]The ftrace command sets a fast tracepoint. For targets that support them,
fast tracepoints will use a more efficient but possibly less general technique totrigger data collection, such as a jump instruction instead of a trap, or some
sort of hardware support. It may not be possible to create a fast tracepoint at
the desired location, in which case the command will exit with an explanatory
message.
gdb handles arguments to ftrace exactly as for trace.
On 32-bit x86-architecture systems, fast tracepoints normally need to be placedat an instruction that is 5 bytes or longer, but can be placed at 4-byte instructions if the low 64K of memory of the target program is available to install
trampolines. Some Unix-type systems, such as gnu/Linux, exclude low addresses from the program’s address space; but for instance with the Linuxkernel it is possible to let gdb use this area by doing a sysctl command to set
the mmap_min_addr kernel parameter, as insudo sysctl -w vm.mmap_min_addr=32768
which sets the low address to 32K, which leaves plenty of room for trampolines.
The minimum address should be set to a page boundary.
strace [locspec | -m marker] [ if cond ]The strace command sets a static tracepoint. For targets that support it,setting a static tracepoint probes a static instrumentation point, or marker,
found at the code locations that result from resolving locspec. It may not be
possible to set a static tracepoint at the desired code location, in which casethe command will exit with an explanatory message.
gdb handles arguments to strace exactly as for trace, with the addition thatthe user can also specify -m marker instead of a location spec. This probes
the marker identified by the marker string identifier. This identifier depends
on the static tracepoint backend library your program is using. You can find
all the marker identifiers in the ‘ID’ field of the info static-tracepointmarkers command output. See Section 13.1.8 [Listing Static Tracepoint Markers], page 211. For example, in the following small program using the UST
tracing engine:
main (){
trace_mark(ust, bar33, "str %s", "FOOBAZ");}

the marker id is composed of joining the first two arguments to the trace_mark
call with a slash, which translates to:(gdb) info static-tracepoint-markers
Cnt Enb ID
AddressWhat1n
ust/bar33 0x0000000000400ddc in main at stexample.c:22
Data: "str %s"[etc...]

so you may probe the marker above with:

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Debugging with gdb(gdb) strace -m ust/bar33

Static tracepoints accept an extra collect action — collect $_sdata. This
collects arbitrary user data passed in the probe point call to the tracing library. In the UST example above, you’ll see that the third argument to trace_
mark is a printf-like format string. The user data is then the result of running that formatting string against the following arguments. Note that info
static-tracepoint-markers command output lists that format string in the‘Data:’ field.
You can inspect this data when analyzing the trace buffer, by printing the$ sdata variable like any other variable available to gdb. See Section 13.1.6[Tracepoint Action Lists], page 208.
The convenience variable $tpnum records the tracepoint number of the mostrecently set tracepoint.
delete tracepoint [num]Permanently delete one or more tracepoints. With no argument, the default isto delete all tracepoints. Note that the regular delete command can remove
tracepoints also.
Examples:(gdb) delete trace 1 2 3 // remove three tracepoints(gdb) delete trace// remove all tracepoints

You can abbreviate this command as del tr.

13.1.2 Enable and Disable Tracepoints
These commands are deprecated; they are equivalent to plain disable and enable.
disable tracepoint [num]Disable tracepoint num, or all tracepoints if no argument num is given. A disabled tracepoint will have no effect during a trace experiment, but it is not forgotten. You can re-enable a disabled tracepoint using the enable tracepointcommand. If the command is issued during a trace experiment and the debug
target has support for disabling tracepoints during a trace experiment, then thechange will be effective immediately. Otherwise, it will be applied to the next
trace experiment.
enable tracepoint [num]Enable tracepoint num, or all tracepoints. If this command is issued during a
trace experiment and the debug target supports enabling tracepoints during a
trace experiment, then the enabled tracepoints will become effective immediately. Otherwise, they will become effective the next time a trace experimentis run.

13.1.3 Tracepoint Passcounts
passcount [n [num]]Set the passcount of a tracepoint. The passcount is a way to automaticallystop a trace experiment. If a tracepoint’s passcount is n, then the trace experiment will be automatically stopped on the n’th time that tracepoint is hit. If

Chapter 13: Tracepoints

207

the tracepoint number num is not specified, the passcount command sets thepasscount of the most recently defined tracepoint. If no passcount is given, thetrace experiment will run until stopped explicitly by the user.
Examples:(gdb) passcount 5 2 // Stop on the 5th execution of// tracepoint 2(gdb) passcount 12(gdb) trace foo(gdb) pass 3(gdb) trace bar(gdb) pass 2(gdb) trace baz(gdb) pass 1// Stop on the 12th execution of the// most recently defined tracepoint.

// Stop tracing when foo has been// executed 3 times OR when bar has// been executed 2 times// OR when baz has been executed 1 time.

13.1.4 Tracepoint Conditions
The simplest sort of tracepoint collects data every time your program reaches a specified
place. You can also specify a condition for a tracepoint. A condition is just a Boolean
expression in your programming language (see Section 10.1 [Expressions], page 145). A
tracepoint with a condition evaluates the expression each time your program reaches it,
and data collection happens only if the condition is true.
Tracepoint conditions can be specified when a tracepoint is set, by using ‘if’ in thearguments to the trace command. See Section 13.1.1 [Setting Tracepoints], page 204.
They can also be set or changed at any time with the condition command, just as withbreakpoints.
Unlike breakpoint conditions, gdb does not actually evaluate the conditional expression
itself. Instead, gdb encodes the expression into an agent expression (see Appendix F [Agent
Expressions], page 847) suitable for execution on the target, independently of gdb. Global
variables become raw memory locations, locals become stack accesses, and so forth.
For instance, suppose you have a function that is usually called frequently, but should
not be called after an error has occurred. You could use the following tracepoint command
to collect data about calls of that function that happen while the error code is propagating
through the program; an unconditional tracepoint could end up collecting thousands ofuseless trace frames that you would have to search through.
(gdb) trace normal_operation if errcode > 0

13.1.5 Trace State Variables
A trace state variable is a special type of variable that is created and managed by target-side
code. The syntax is the same as that for GDB’s convenience variables (a string prefixedwith “$”), but they are stored on the target. They must be created explicitly, using atvariable command. They are always 64-bit signed integers.
Trace state variables are remembered by gdb, and downloaded to the target along withtracepoint information when the trace experiment starts. There are no intrinsic limits on
the number of trace state variables, beyond memory limitations of the target.

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Although trace state variables are managed by the target, you can use them in printcommands and expressions as if they were convenience variables; gdb will get the current
value from the target while the trace experiment is running. Trace state variables share thesame namespace as other “$” variables, which means that you cannot have trace state variables with names like $23 or $pc, nor can you have a trace state variable and a conveniencevariable with the same name.
tvariable $name [ = expression ]The tvariable command creates a new trace state variable named $name, andoptionally gives it an initial value of expression. The expression is evaluatedwhen this command is entered; the result will be converted to an integer if
possible, otherwise gdb will report an error. A subsequent tvariable commandspecifying the same name does not create a variable, but instead assigns the
supplied initial value to the existing variable of that name, overwriting any
previous initial value. The default initial value is 0.
info tvariables
List all the trace state variables along with their initial values. Their current
values may also be displayed, if the trace experiment is currently running.
delete tvariable [ $name ... ]Delete the given trace state variables, or all of them if no arguments are specified.

13.1.6 Tracepoint Action Lists
actions [num]This command will prompt for a list of actions to be taken when the tracepoint
is hit. If the tracepoint number num is not specified, this command sets theactions for the one that was most recently defined (so that you can define a
tracepoint and then say actions without bothering about its number). You
specify the actions themselves on the following lines, one action at a time, andterminate the actions list with a line containing just end. So far, the only
defined actions are collect, teval, and while-stepping.
actions is actually equivalent to commands (see Section 5.1.7 [Breakpoint Command Lists], page 77), except that only the defined actions are allowed; anyother gdb command is rejected.
To remove all actions from a tracepoint, type ‘actions num’ and follow it immediately with ‘end’.
(gdb) collect data // collect some data(gdb) while-stepping 5 // single-step 5 times, collect data(gdb) end// signals the end of actions.

In the following example, the action list begins with collect commands indicating the things to be collected when the tracepoint is hit. Then, in order to singlestep and collect additional data following the tracepoint, a while-stepping
command is used, followed by the list of things to be collected after each stepin a sequence of single steps. The while-stepping command is terminated byChapter 13: Tracepoints

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its own separate end command. Lastly, the action list is terminated by an end
command.
(gdb) trace foo(gdb) actions
Enter actions for tracepoint 1, one per line:> collect bar,baz> collect $regs> while-stepping 12> collect $pc, arr[i]
> end
end

collect[/mods] expr1, expr2, ...
Collect values of the given expressions when the tracepoint is hit. This command accepts a comma-separated list of any valid expressions. In addition to
global, static, or local variables, the following special arguments are supported:$regs

Collect all registers.

$args

Collect all function arguments.

$locals

Collect all local variables.

$_retCollect the return address. This is helpful if you want to see moreof a backtrace.
Note: The return address location can not always be reliably determined up front, and the wrong address / registers may end up
collected instead. On some architectures the reliability is higher
for tracepoints at function entry, while on others it’s the opposite.
When this happens, backtracing will stop because the return address is found unavailable (unless another collect rule happened tomatch it).

$_probe_argc
Collects the number of arguments from the static probe at which
the tracepoint is located. See Section 5.1.10 [Static Probe Points],
page 81.
$_probe_argn
n is an integer between 0 and 11. Collects the nth argumentfrom the static probe at which the tracepoint is located. See
Section 5.1.10 [Static Probe Points], page 81.
$_sdata

Collect static tracepoint marker specific data. Only available forstatic tracepoints. See Section 13.1.6 [Tracepoint Action Lists],
page 208. On the UST static tracepoints library backend, an instrumentation point resembles a printf function call. The tracing
library is able to collect user specified data formatted to a character
string using the format provided by the programmer that instrumented the program. Other backends have similar mechanisms.
Here’s an example of a UST marker call:const char master_name[] = "$your_name";
trace_mark(channel1, marker1, "hello %s", master_name)

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In this case, collecting $_sdata collects the string ‘hello$yourname’. When analyzing the trace buffer, you can inspect‘$_sdata’ like any other variable available to gdb.
You can give several consecutive collect commands, each one with a single
argument, or one collect command with several arguments separated by commas; the effect is the same.
The optional mods changes the usual handling of the arguments. s requests
that pointers to chars be handled as strings, in particular collecting the contentsof the memory being pointed at, up to the first zero. The upper bound is bydefault the value of the print characters variable; if s is followed by a decimal
number, that is the upper bound instead. So for instance ‘collect/s25 mystr’collects as many as 25 characters at ‘mystr’.
The command info scope (see Chapter 16 [Symbols], page 263) is particularly
useful for figuring out what data to collect.
teval expr1, expr2, ...
Evaluate the given expressions when the tracepoint is hit. This command accepts a comma-separated list of expressions. The results are discarded, so thisis mainly useful for assigning values to trace state variables (see Section 13.1.5[Trace State Variables], page 207) without adding those values to the trace
buffer, as would be the case if the collect action were used.
while-stepping n
Perform n single-step instruction traces after the tracepoint, collecting new data
after each step. The while-stepping command is followed by the list of what
to collect while stepping (followed by its own end command):> while-stepping 12> collect $regs, myglobal> end>

Note that $pc is not automatically collected by while-stepping; youneed to explicitly collect that register if you need it. You may abbreviate
while-stepping as ws or stepping.
set default-collect expr1, expr2, ...
This variable is a list of expressions to collect at each tracepoint hit. It iseffectively an additional collect action prepended to every tracepoint action
list. The expressions are parsed individually for each tracepoint, so for instancea variable named xyz may be interpreted as a global for one tracepoint, and alocal for another, as appropriate to the tracepoint’s location.
show default-collectShow the list of expressions that are collected by default at each tracepoint hit.

13.1.7 Listing Tracepoints
info tracepoints [num...]
Display information about the tracepoint num. If you don’t specify a tracepoint
number, displays information about all the tracepoints defined so far. The

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format is similar to that used for info breakpoints; in fact, info tracepoints
is the same command, simply restricting itself to tracepoints.
A tracepoint’s listing may include additional information specific to tracing:• its passcount as given by the passcount n command• the state about installed on target of each location(gdb) info trace
Num
Type
Disp Enb AddressWhat1
tracepoint
keep y0x0804ab57 in foo() at main.cxx:7
while-stepping 20
collect globfoo, $regs
endcollect globfoo2
endpass count 1200
2
tracepoint
keep y<MULTIPLE>
collect $eip
2.1
y0x0804859c in func4 at change-loc.h:35
installed on target
2.2
y0xb7ffc480 in func4 at change-loc.h:35
installed on target
2.3
y<PENDING> set_tracepoint3
tracepoint
keep y0x080485b1 in foo at change-loc.c:29
not installed on target(gdb)

This command can be abbreviated info tp.

13.1.8 Listing Static Tracepoint Markers
info static-tracepoint-markers
Display information about all static tracepoint markers defined in the program.
For each marker, the following columns are printed:
Count

An incrementing counter, output to help readability. This is not astable identifier.

ID

The marker ID, as reported by the target.

Enabled or Disabled
Probed markers are tagged with ‘y’. ‘n’ identifies marks that are
not enabled.
Address

Where the marker is in your program, as a memory address.

What

Where the marker is in the source for your program, as a file andline number. If the debug information included in the program does
not allow gdb to locate the source of the marker, this column willbe left blank.

In addition, the following information may be printed for each marker:
Data

User data passed to the tracing library by the marker call. In the
UST backend, this is the format string passed as argument to themarker call.

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Static tracepoints probing the marker
The list of static tracepoints attached to the marker.
(gdb) info static-tracepoint-markers
Cnt ID
Enb AddressWhat1
ust/bar2y0x0000000000400e1a in main at stexample.c:25
Data: number1 %d number2 %d
Probed by static tracepoints: #2
2
ust/bar33 n
0x0000000000400c87 in main at stexample.c:24
Data: str %s(gdb)

13.1.9 Starting and Stopping Trace Experiments
tstartThis command starts the trace experiment, and begins collecting data. It has
the side effect of discarding all the data collected in the trace buffer during theprevious trace experiment. If any arguments are supplied, they are taken as anote and stored with the trace experiment’s state. The notes may be arbitrary
text, and are especially useful with disconnected tracing in a multi-user context;
the notes can explain what the trace is doing, supply user contact information,and so forth.

tstop

This command stops the trace experiment. If any arguments are supplied, they
are recorded with the experiment as a note. This is useful if you are stoppinga trace started by someone else, for instance if the trace is interfering with thesystem’s behavior and needs to be stopped quickly.
Note: a trace experiment and data collection may stop automatically if any
tracepoint’s passcount is reached (see Section 13.1.3 [Tracepoint Passcounts],
page 206), or if the trace buffer becomes full.

tstatusThis command displays the status of the current trace data collection.

Here is an example of the commands we described so far:(gdb) trace gdb c test(gdb) actions
Enter actions for tracepoint #1, one per line.
> collect $regs,$locals,$args> while-stepping 11> collect $regs
> end
> end
(gdb) tstart[time passes ...]
(gdb) tstop

You can choose to continue running the trace experiment even if gdb disconnects fromthe target, voluntarily or involuntarily. For commands such as detach, the debugger will
ask what you want to do with the trace. But for unexpected terminations (gdb crash,
network outage), it would be unfortunate to lose hard-won trace data, so the variable
disconnected-tracing lets you decide whether the trace should continue running without
gdb.

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set disconnected-tracing on
set disconnected-tracing off
Choose whether a tracing run should continue to run if gdb has disconnectedfrom the target. Note that detach or quit will ask you directly what to doabout a running trace no matter what this variable’s setting, so the variable ismainly useful for handling unexpected situations, such as loss of the network.
show disconnected-tracing
Show the current choice for disconnected tracing.
When you reconnect to the target, the trace experiment may or may not still be running;it might have filled the trace buffer in the meantime, or stopped for one of the other reasons.
If it is running, it will continue after reconnection.
Upon reconnection, the target will upload information about the tracepoints in effect.
gdb will then compare that information to the set of tracepoints currently defined, andattempt to match them up, allowing for the possibility that the numbers may have changed
due to creation and deletion in the meantime. If one of the target’s tracepoints does notmatch any in gdb, the debugger will create a new tracepoint, so that you have a number
with which to specify that tracepoint. This matching-up process is necessarily heuristic,
and it may result in useless tracepoints being created; you may simply delete them if they
are of no use.
If your target agent supports a circular trace buffer, then you can run a trace experimentindefinitely without filling the trace buffer; when space runs out, the agent deletes alreadycollected trace frames, oldest first, until there is enough room to continue collecting. Thisis especially useful if your tracepoints are being hit too often, and your trace gets terminated prematurely because the buffer is full. To ask for a circular trace buffer, simply set‘circular-trace-buffer’ to on. You can set this at any time, including during tracing;if the agent can do it, it will change buffer handling on the fly, otherwise it will not takeeffect until the next run.
set circular-trace-buffer on
set circular-trace-buffer off
Choose whether a tracing run should use a linear or circular buffer for trace
data. A linear buffer will not lose any trace data, but may fill up prematurely,
while a circular buffer will discard old trace data, but it will have always room
for the latest tracepoint hits.
show circular-trace-buffer
Show the current choice for the trace buffer. Note that this may not match theagent’s current buffer handling, nor is it guaranteed to match the setting thatmight have been in effect during a past run, for instance if you are looking at
frames from a trace file.
set trace-buffer-size n
set trace-buffer-size unlimited
Request that the target use a trace buffer of n bytes. Not all targets will honor
the request; they may have a compiled-in size for the trace buffer, or some otherlimitation. Set to a value of unlimited or -1 to let the target use whateversize it likes. This is also the default.

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show trace-buffer-sizeShow the current requested size for the trace buffer. Note that this will only
match the actual size if the target supports size-setting, and was able to handle
the requested size. For instance, if the target can only change buffer size between
runs, this variable will not reflect the change until the next run starts. Use
tstatus to get a report of the actual buffer size.
set trace-user text
show trace-user
set trace-notes text
Set the trace run’s notes.
show trace-notes
Show the trace run’s notes.
set trace-stop-notes text
Set the trace run’s stop notes. The handling of the note is as for tstop arguments; the set command is convenient way to fix a stop note that is mistaken
or incomplete.
show trace-stop-notes
Show the trace run’s stop notes.

13.1.10 Tracepoint Restrictions
There are a number of restrictions on the use of tracepoints. As described above, tracepoint
data gathering occurs on the target without interaction from gdb. Thus the full capabilitiesof the debugger are not available during data gathering, and then at data examination time,
you will be limited by only having what was collected. The following items describe somecommon problems, but it is not exhaustive, and you may run into additional difficulties not
mentioned here.
• Tracepoint expressions are intended to gather objects (lvalues). Thus the full flexibilityof GDB’s expression evaluator is not available. You cannot call functions, cast objects
to aggregate types, access convenience variables or modify values (except by assignment
to trace state variables). Some language features may implicitly call functions (forinstance Objective-C fields with accessors), and therefore cannot be collected either.
• Collection of local variables, either individually or in bulk with $locals or $args,
during while-stepping may behave erratically. The stepping action may enter a newscope (for instance by stepping into a function), or the location of the variable may
change (for instance it is loaded into a register). The tracepoint data recorded uses thelocation information for the variables that is correct for the tracepoint location. Whenthe tracepoint is created, it is not possible, in general, to determine where the stepsof a while-stepping sequence will advance the program—particularly if a conditional
branch is stepped.
• Collection of an incompletely-initialized or partially-destroyed object may result insomething that gdb cannot display, or displays in a misleading way.
• When gdb displays a pointer to character it automatically dereferences the pointer toalso display characters of the string being pointed to. However, collecting the pointerduring tracing does not automatically collect the string. You need to explicitly dereference the pointer and provide size information if you want to collect not only theChapter 13: Tracepoints

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pointer, but the memory pointed to. For example, *ptr@50 can be used to collect the
50 element array pointed to by ptr.
• It is not possible to collect a complete stack backtrace at a tracepoint. Instead, you may
collect the registers and a few hundred bytes from the stack pointer with something
like *(unsigned char *)$esp@300 (adjust to use the name of the actual stack pointerregister on your target architecture, and the amount of stack you wish to capture).
Then the backtrace command will show a partial backtrace when using a trace frame.
The number of stack frames that can be examined depends on the sizes of the frames
in the collected stack. Note that if you ask for a block so large that it goes past thebottom of the stack, the target agent may report an error trying to read from an invalid
address.
• If you do not collect registers at a tracepoint, gdb can infer that the value of $pc
must be the same as the address of the tracepoint and use that when you are looking
at a trace frame for that tracepoint. However, this cannot work if the tracepoint has
multiple locations (for instance if it was set in a function that was inlined), or if it has
a while-stepping loop. In those cases gdb will warn you that it can’t infer $pc, anddefault it to zero.

13.2 Using the Collected Data
After the tracepoint experiment ends, you use gdb commands for examining the trace
data. The basic idea is that each tracepoint collects a trace snapshot every time it is
hit and another snapshot every time it single-steps. All these snapshots are consecutively
numbered from zero and go into a buffer, and you can examine them later. The way you
examine them is to focus on a specific trace snapshot. When the remote stub is focused on a
trace snapshot, it will respond to all gdb requests for memory and registers by reading fromthe buffer which belongs to that snapshot, rather than from real memory or registers of the
program being debugged. This means that all gdb commands (print, info registers,
backtrace, etc.) will behave as if we were currently debugging the program state as it waswhen the tracepoint occurred. Any requests for data that are not in the buffer will fail.

13.2.1 tfind n
The basic command for selecting a trace snapshot from the buffer is tfind n, which finds
trace snapshot number n, counting from zero. If no argument n is given, the next snapshot
is selected.
Here are the various forms of using the tfind command.
tfind start
Find the first snapshot in the buffer. This is a synonym for tfind 0 (since 0 is
the number of the first snapshot).
tfind none
Stop debugging trace snapshots, resume live debugging.
tfind end Same as ‘tfind none’.
tfind

No argument means find the next trace snapshot or find the first one if no tracesnapshot is selected.

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Debugging with gdb

tfind -

Find the previous trace snapshot before the current one. This permits retracing
earlier steps.

tfind tracepoint num
Find the next snapshot associated with tracepoint num. Search proceeds forward from the last examined trace snapshot. If no argument num is given, itmeans find the next snapshot collected for the same tracepoint as the current
snapshot.
tfind pc addr
Find the next snapshot associated with the value addr of the program counter.
Search proceeds forward from the last examined trace snapshot. If no argument
addr is given, it means find the next snapshot with the same value of PC as
the current snapshot.
tfind outside addr1, addr2
Find the next snapshot whose PC is outside the given range of addresses (exclusive).
tfind range addr1, addr2
Find the next snapshot whose PC is between addr1 and addr2 (inclusive).
tfind line [file:]nFind the next snapshot associated with the source line n. If the optional argument file is given, refer to line n in that source file. Search proceeds forwardfrom the last examined trace snapshot. If no argument n is given, it means findthe next line other than the one currently being examined; thus saying tfindline repeatedly can appear to have the same effect as stepping from line toline in a live debugging session.
The default arguments for the tfind commands are specifically designed to make it easy
to scan through the trace buffer. For instance, tfind with no argument selects the next
trace snapshot, and tfind - with no argument selects the previous trace snapshot. So, by
giving one tfind command, and then simply hitting RET repeatedly you can examine all
the trace snapshots in order. Or, by saying tfind - and then hitting RET repeatedly you
can examine the snapshots in reverse order. The tfind line command with no argument
selects the snapshot for the next source line executed. The tfind pc command with noargument selects the next snapshot with the same program counter (PC) as the current
frame. The tfind tracepoint command with no argument selects the next trace snapshotcollected by the same tracepoint as the current one.
In addition to letting you scan through the trace buffer manually, these commands makeit easy to construct gdb scripts that scan through the trace buffer and print out whatevercollected data you are interested in. Thus, if we want to examine the PC, FP, and SP
registers from each trace frame in the buffer, we can say this:(gdb) tfind start(gdb) while ($trace frame != -1)> printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \$trace_frame, $pc, $sp, $fp> tfind> end

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Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14

Or, if we want to examine the variable X at each source line in the buffer:(gdb) tfind start(gdb) while ($trace frame != -1)> printf "Frame %d, X == %d\n", $trace_frame, X> tfind line
> end
Frame 0, X = 1
Frame 7, X = 2
Frame 13, X = 255

13.2.2 tdump
This command takes no arguments. It prints all the data collected at the current tracesnapshot.
(gdb) trace 444(gdb) actions
Enter actions for tracepoint #2, one per line:> collect $regs, $locals, $args, gdb_long_test> end(gdb) tstart(gdb) tfind line 444#0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
at gdb_test.c:444
444
printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )(gdb) tdump
Data collected at tracepoint 2, trace frame 1:
d0
0xc4aa0085-995491707
d1
0x18
24
d2
0x80
128
d3
0x33
51
d4
0x71aea3d
119204413
d5
0x22
34
d6
0xe0
224
d7
0x380035 3670069
a0
0x19e24a 1696330
a1
0x3000668
50333288
a2
0x100
256
a3
0x322000 3284992
a40x3000698
50333336a50x1ad3cc 1758156
fp
0x30bf3c 0x30bf3c
sp
0x30bf34 0x30bf34

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ps
0x0
0
pc
0x20b2c8 0x20b2c8
fpcontrol
0x00fpstatus
0x0
0
fpiaddr0x00
p = 0x20e5b4 "gdb-test"
p1 = (void *) 0x11
p2 = (void *) 0x22
p3 = (void *) 0x33
p4 = (void *) 0x44
p5 = (void *) 0x55
p6 = (void *) 0x66
gdb_long_test = 17 ’\021’(gdb)

tdump works by scanning the tracepoint’s current collection actions and printing thevalue of each expression listed. So tdump can fail, if after a run, you change the tracepoint’s
actions to mention variables that were not collected during the run.
Also, for tracepoints with while-stepping loops, tdump uses the collected value of $pc
to distinguish between trace frames that were collected at the tracepoint hit, and framesthat were collected while stepping. This allows it to correctly choose whether to display
the basic list of collections, or the collections from the body of the while-stepping loop.
However, if $pc was not collected, then tdump will always attempt to dump using the basic
collection list, and may fail if a while-stepping frame does not include all the same datathat is collected at the tracepoint hit.

13.2.3 save tracepoints filename
This command saves all current tracepoint definitions together with their actions and passcounts, into a file filename suitable for use in a later debugging session. To read thesaved tracepoint definitions, use the source command (see Section 23.1.3 [Command Files],page 395). The save-tracepoints command is a deprecated alias for save tracepoints

13.3 Convenience Variables for Tracepoints(int) $trace_frame
The current trace snapshot (a.k.a. frame) number, or -1 if no snapshot is selected.
(int) $tracepoint
The tracepoint for the current trace snapshot.
(int) $trace_line
The line number for the current trace snapshot.
(char []) $trace_file
The source file for the current trace snapshot.
(char []) $trace_func
The name of the function containing $tracepoint.
Note: $trace_file is not suitable for use in printf, use output instead.

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Here’s a simple example of using these convenience variables for stepping through all the
trace snapshots and printing some of their data. Note that these are not the same as tracestate variables, which are managed by the target.
(gdb) tfind start(gdb) while $trace frame != -1> output $trace_file> printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint> tfind> end

13.4 Using Trace Files
In some situations, the target running a trace experiment may no longer be available;
perhaps it crashed, or the hardware was needed for a different activity. To handle thesecases, you can arrange to dump the trace data into a file, and later use that file as a sourceof trace data, via the target tfile command.
tsave [ -r ] filename
tsave [-ctf] dirname
Save the trace data to filename. By default, this command assumes that filename refers to the host filesystem, so if necessary gdb will copy raw trace data
up from the target and then save it. If the target supports it, you can also
supply the optional argument -r (“remote”) to direct the target to save thedata directly into filename in its own filesystem, which may be more efficientif the trace buffer is very large. (Note, however, that target tfile can only
read from files accessible to the host.) By default, this command will save trace
frame in tfile format. You can supply the optional argument -ctf to save data
in CTF format. The Common Trace Format (CTF) is proposed as a trace format that can be shared by multiple debugging and tracing tools. Please go to‘http://www.efficios.com/ctf’ to get more information.
target tfile filename
target ctf dirname
Use the file named filename or directory named dirname as a source of trace
data. Commands that examine data work as they do with a live target, but it
is not possible to run any new trace experiments. tstatus will report the stateof the trace run at the moment the data was saved, as well as the current trace
frame you are examining. Both filename and dirname must be on a filesystemaccessible to the host.
The filename and dirname arguments supports escaping and quoting, see
Section 3.4 [Filenames As Command Arguments], page 27.
(gdb) target ctf ctf.ctf(gdb) tfind
Found trace frame 0, tracepoint 2
39++a; /* set tracepoint 1 here */(gdb) tdump
Data collected at tracepoint 2, trace frame 0:
i = 0
a = 0
b = 1 ’\001’

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c = {"123", "456", "789", "123", "456", "789"}
d = {{{a = 1, b = 2}, {a = 3, b = 4}}, {{a = 5, b = 6}, {a = 7, b = 8}}}(gdb) p b
$1 = 1

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14 Debugging Programs That Use Overlays
If your program is too large to fit completely in your target system’s memory, you can sometimes use overlays to work around this problem. gdb provides some support for debugging
programs that use overlays.

14.1 How Overlays Work
Suppose you have a computer whose instruction address space is only 64 kilobytes long, butwhich has much more memory which can be accessed by other means: special instructions,segment registers, or memory management hardware, for example. Suppose further thatyou want to adapt a program which is larger than 64 kilobytes to run on this system.
One solution is to identify modules of your program which are relatively independent,
and need not call each other directly; call these modules overlays. Separate the overlays
from the main program, and place their machine code in the larger memory. Place yourmain program in instruction memory, but leave at least enough space there to hold thelargest overlay as well.
Now, to call a function located in an overlay, you must first copy that overlay’s machinecode from the large memory into the space set aside for it in the instruction memory, andthen jump to its entry point there.
Data
Address Space+-----------+||+-----------+| program|| variables || and heap |+-----------+||+-----------+

Instruction
LargerAddress Space
Address Space+-----------++-----------+||||+-----------++-----------+<-- overlay 1|
main|.----| overlay 1 | load address| program ||+-----------+
|
|
|
|
|
|
|
|
+-----------+<-- overlay 2+-----------+||| load address||| .-| overlay 2 |
|
|
| | |
|
mapped --->+-----------+| | +-----------+
address||| | ||| overlay | <-’ | |||area| <---’ +-----------+<-- overlay 3|| <---. || load address+-----------+‘--| overlay 3 |||||+-----------+||+-----------+||+-----------+A code overlay

The diagram (see [A code overlay], page 221) shows a system with separate data andinstruction address spaces. To map an overlay, the program copies its code from the larger
address space to the instruction address space. Since the overlays shown here all use thesame mapped address, only one may be mapped at a time. For a system with a single
address space for data and instructions, the diagram would be similar, except that the
program variables and heap would share an address space with the main program and theoverlay area.

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An overlay loaded into instruction memory and ready for use is called a mapped overlay;
its mapped address is its address in the instruction memory. An overlay not present (or only
partially present) in instruction memory is called unmapped; its load address is its addressin the larger memory. The mapped address is also called the virtual memory address, orVMA; the load address is also called the load memory address, or LMA.
Unfortunately, overlays are not a completely transparent way to adapt a program tolimited instruction memory. They introduce a new set of global constraints you must keep
in mind as you design your program:• Before calling or returning to a function in an overlay, your program must make surethat overlay is actually mapped. Otherwise, the call or return will transfer control to
the right address, but in the wrong overlay, and your program will probably crash.
• If the process of mapping an overlay is expensive on your system, you will need tochoose your overlays carefully to minimize their effect on your program’s performance.
• The executable file you load onto your system must contain each overlay’s instructions, appearing at the overlay’s load address, not its mapped address. However, eachoverlay’s instructions must be relocated and its symbols defined as if the overlay wereat its mapped address. You can use GNU linker scripts to specify different load andrelocation addresses for pieces of your program; see Section “Overlay Description” inUsing ld: the GNU linker.
• The procedure for loading executable files onto your system must be able to load theircontents into the larger address space as well as the instruction and data spaces.
The overlay system described above is rather simple, and could be improved in manyways:
• If your system has suitable bank switch registers or memory management hardware,
you could use those facilities to make an overlay’s load area contents simply appear attheir mapped address in instruction space. This would probably be faster than copying
the overlay to its mapped area in the usual way.
• If your overlays are small enough, you could set aside more than one overlay area, andhave more than one overlay mapped at a time.
• You can use overlays to manage data, as well as instructions. In general, data overlays
are even less transparent to your design than code overlays: whereas code overlays only
require care when you call or return to functions, data overlays require care every time
you access the data. Also, if you change the contents of a data overlay, you must copy
its contents back out to its load address before you can copy a different data overlay
into the same mapped area.

14.2 Overlay Commands
To use gdb’s overlay support, each overlay in your program must correspond to a separate
section of the executable file. The section’s virtual memory address and load memory
address must be the overlay’s mapped and load addresses. Identifying overlays with sections
allows gdb to determine the appropriate address of a function or variable, depending onwhether the overlay is mapped or not.
gdb’s overlay commands all start with the word overlay; you can abbreviate this as ov
or ovly. The commands are:

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overlay off
Disable gdb’s overlay support. When overlay support is disabled, gdb assumes
that all functions and variables are always present at their mapped addresses.
By default, gdb’s overlay support is disabled.
overlay manual
Enable manual overlay debugging. In this mode, gdb relies on you to tell it
which overlays are mapped, and which are not, using the overlay map-overlay
and overlay unmap-overlay commands described below.
overlay map-overlay overlay
overlay map overlay
Tell gdb that overlay is now mapped; overlay must be the name of the object
file section containing the overlay. When an overlay is mapped, gdb assumes it
can find the overlay’s functions and variables at their mapped addresses. gdb
assumes that any other overlays whose mapped ranges overlap that of overlay
are now unmapped.
overlay unmap-overlay overlay
overlay unmap overlay
Tell gdb that overlay is no longer mapped; overlay must be the name of theobject file section containing the overlay. When an overlay is unmapped, gdb
assumes it can find the overlay’s functions and variables at their load addresses.
overlay auto
Enable automatic overlay debugging. In this mode, gdb consults a data structure the overlay manager maintains in the inferior to see which overlays are
mapped. For details, see Section 14.3 [Automatic Overlay Debugging], page 224.
overlay load-target
overlay load
Re-read the overlay table from the inferior. Normally, gdb re-reads the table
gdb automatically each time the inferior stops, so this command should only
be necessary if you have changed the overlay mapping yourself using gdb. This
command is only useful when using automatic overlay debugging.
overlay list-overlays
overlay list
Display a list of the overlays currently mapped, along with their mapped addresses, load addresses, and sizes.
Normally, when gdb prints a code address, it includes the name of the function theaddress falls in:(gdb) print main
$3 = {int ()} 0x11a0 <main>

When overlay debugging is enabled, gdb recognizes code in unmapped overlays, and prints
the names of unmapped functions with asterisks around them. For example, if foo is afunction in an unmapped overlay, gdb prints it this way:(gdb) overlay list
No sections are mapped.
(gdb) print foo

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Debugging with gdb$5 = {int (int)} 0x100000 <*foo*>

When foo’s overlay is mapped, gdb prints the function’s name normally:(gdb) overlay list
Section .ov.foo.text, loaded at 0x100000 - 0x100034,
mapped at 0x1016 - 0x104a(gdb) print foo$6 = {int (int)} 0x1016 <foo>When overlay debugging is enabled, gdb can find the correct address for functions andvariables in an overlay, whether or not the overlay is mapped. This allows most gdb commands, like break and disassemble, to work normally, even on unmapped code. However,
gdb’s breakpoint support has some limitations:• You can set breakpoints in functions in unmapped overlays, as long as gdb can write
to the overlay at its load address.
• gdb can not set hardware or simulator-based breakpoints in unmapped overlays. However, if you set a breakpoint at the end of your overlay manager (and tell gdb which
overlays are now mapped, if you are using manual overlay management), gdb will re-set
its breakpoints properly.

14.3 Automatic Overlay Debugging
gdb can automatically track which overlays are mapped and which are not, given some
simple co-operation from the overlay manager in the inferior. If you enable automatic
overlay debugging with the overlay auto command (see Section 14.2 [Overlay Commands],
page 222), gdb looks in the inferior’s memory for certain variables describing the current
state of the overlays.
Here are the variables your overlay manager must define to support gdb’s automatic
overlay debugging:_ovly_table:
This variable must be an array of the following structures:
struct{/* The overlay’s mapped address.
unsigned long vma;*//* The size of the overlay, in bytes.
unsigned long size;/* The overlay’s load address.
unsigned long lma;*/*//* Non-zero if the overlay is currently mapped;zero otherwise. */unsigned long mapped;}_novlys:This variable must be a four-byte signed integer, holding the total number of
elements in _ovly_table.

To decide whether a particular overlay is mapped or not, gdb looks for an entry in_ovly_table whose vma and lma members equal the VMA and LMA of the overlay’s section

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in the executable file. When gdb finds a matching entry, it consults the entry’s mapped
member to determine whether the overlay is currently mapped.
In addition, your overlay manager may define a function called _ovly_debug_event. If
this function is defined, gdb will silently set a breakpoint there. If the overlay manager
then calls this function whenever it has changed the overlay table, this will enable gdb toaccurately keep track of which overlays are in program memory, and update any breakpoints
that may be set in overlays. This will allow breakpoints to work even if the overlays are
kept in ROM or other non-writable memory while they are not being executed.

14.4 Overlay Sample Program
When linking a program which uses overlays, you must place the overlays at their load
addresses, while relocating them to run at their mapped addresses. To do this, you must
write a linker script (see Section “Overlay Description” in Using ld: the GNU linker). Unfortunately, since linker scripts are specific to a particular host system, target architecture,and target memory layout, this manual cannot provide portable sample code demonstrating
gdb’s overlay support.
However, the gdb source distribution does contain an overlaid program, with linker
scripts for a few systems, as part of its test suite. The program consists of the following
files from gdb/testsuite/gdb.base:overlays.c
The main program file.
ovlymgr.c
A simple overlay manager, used by overlays.c.
foo.c
bar.c
baz.c
grbx.cd10v.ld
m32r.ld

Overlay modules, loaded and used by overlays.c.
Linker scripts for linking the test program on the d10v-elf and m32r-elf
targets.

You can build the test program using the d10v-elf GCC cross-compiler like this:$ d10v-elf-gcc -g -c overlays.c$ d10v-elf-gcc -g -c ovlymgr.c$ d10v-elf-gcc -g -c foo.c$ d10v-elf-gcc -g -c bar.c$ d10v-elf-gcc -g -c baz.c$ d10v-elf-gcc -g -c grbx.c$ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \baz.o grbx.o -Wl,-Td10v.ld -o overlays

The build process is identical for any other architecture, except that you must substitutethe appropriate compiler and linker script for the target system for d10v-elf-gcc andd10v.ld.

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15 Using gdb with Different Languages
Although programming languages generally have common aspects, they are rarely expressedin the same manner. For instance, in ANSI C, dereferencing a pointer p is accomplishedby *p, but in Modula-2, it is accomplished by p^. Values can also be represented (anddisplayed) differently. Hex numbers in C appear as ‘0x1ae’, while in Modula-2 they appear
as ‘1AEH’.
Language-specific information is built into gdb for some languages, allowing you toexpress operations like the above in your program’s native language, and allowing gdb to
output values in a manner consistent with the syntax of your program’s native language.
The language you use to build expressions is called the working language.

15.1 Switching Between Source Languages
There are two ways to control the working language—either have gdb set it automatically,or select it manually yourself. You can use the set language command for either purpose.
On startup, gdb defaults to setting the language automatically. The working language isused to determine how expressions you type are interpreted, how values are printed, etc.
In addition to the working language, every source file that gdb knows about has its
own working language. For some object file formats, the compiler might indicate which
language a particular source file is in. However, most of the time gdb infers the language
from the name of the file. The language of a source file controls whether C++ names aredemangled—this way backtrace can show each frame appropriately for its own language.
There is no way to set the language of a source file from within gdb, but you can set thelanguage associated with a filename extension. See Section 15.2 [Displaying the Language],
page 228.
This is most commonly a problem when you use a program, such as cfront or f2c, thatgenerates C but is written in another language. In that case, make the program use #line
directives in its C output; that way gdb will know the correct language of the source codeof the original program, and will display that source code, not the generated C code.

15.1.1 List of Filename Extensions and Languages
If a source file name ends in one of the following extensions, then gdb infers that its language
is the one indicated.
.ada
.ads
.adb
.a

Ada source file.

.c

C source file

.C
.cc
.cp
.cpp
.cxx
.c++

C++ source file228

Debugging with gdb.dD source file.m

Objective-C source file.f.F

Fortran source file.mod

Modula-2 source file.s
.S

Assembler source file. This actually behaves almost like C, but gdb does not
skip over function prologues when stepping.

In addition, you may set the language associated with a filename extension.
Section 15.2 [Displaying the Language], page 228.

See

15.1.2 Setting the Working Language
If you allow gdb to set the language automatically, expressions are interpreted the sameway in your debugging session and your program.
If you wish, you may set the language manually. To do this, issue the command ‘set
language lang’, where lang is the name of a language, such as c or modula-2. For a listof the supported languages, type ‘set language’.
Setting the language manually prevents gdb from updating the working language automatically. This can lead to confusion if you try to debug a program when the working
language is not the same as the source language, when an expression is acceptable to bothlanguages—but means different things. For instance, if the current source file were written
in C, and gdb was parsing Modula-2, a command such as:
print a = b + c

might not have the effect you intended. In C, this means to add b and c and place theresult in a. The result printed would be the value of a. In Modula-2, this means to compare
a to the result of b+c, yielding a BOOLEAN value.

15.1.3 Having gdb Infer the Source Language
To have gdb set the working language automatically, use ‘set language local’ or ‘set
language auto’. gdb then infers the working language. That is, when your program stops
in a frame (usually by encountering a breakpoint), gdb sets the working language to thelanguage recorded for the function in that frame. If the language for a frame is unknown(that is, if the function or block corresponding to the frame was defined in a source file that
does not have a recognized extension), the current working language is not changed, andgdb issues a warning.
This may not seem necessary for most programs, which are written entirely in one source
language. However, program modules and libraries written in one source language can beused by a main program written in a different source language. Using ‘set language auto’in this case frees you from having to set the working language manually.

15.2 Displaying the Language
The following commands help you find out which language is the working language, andalso what language source files were written in.

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show language
Display the current working language. This is the language you can use withcommands such as print to build and compute expressions that may involve
variables in your program.
info frame
Display the source language for this frame. This language becomes the working
language if you use an identifier from this frame. See Section 8.4 [Information
about a Frame], page 119, to identify the other information listed here.
info source
Display the source language of this source file. See Chapter 16 [Examining theSymbol Table], page 263, to identify the other information listed here.
In unusual circumstances, you may have source files with extensions not in the standard
list. You can then set the extension associated with a language explicitly:
set extension-language ext language
Tell gdb that source files with extension ext are to be assumed as written in
the source language language.
info extensions
List all the filename extensions and the associated languages.

15.3 Type and Range Checking
Some languages are designed to guard you against making seemingly common errors througha series of compile- and run-time checks. These include checking the type of arguments tofunctions and operators and making sure mathematical overflows are caught at run time.
Checks such as these help to ensure a program’s correctness once it has been compiled
by eliminating type mismatches and providing active checks for range errors when yourprogram is running.
By default gdb checks for these errors according to the rules of the current source
language. Although gdb does not check the statements in your program, it can check
expressions entered directly into gdb for evaluation via the print command, for example.

15.3.1 An Overview of Type Checking
Some languages, such as C and C++, are strongly typed, meaning that the arguments tooperators and functions have to be of the correct type, otherwise an error occurs. Thesechecks prevent type mismatch errors from ever causing any run-time problems. For example,
int klass::my_method(char *b) { returnb ? 1 : 2; }(gdb) print obj.my_method (0)$1 = 2but(gdb) print obj.my_method (0x1234)
Cannot resolve method klass::my_method to any overloaded instance

The second example fails because in C++ the integer constant ‘0x1234’ is not typecompatible with the pointer parameter type.

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Debugging with gdb

For the expressions you use in gdb commands, you can tell gdb to not enforce strict
type checking or to treat any mismatches as errors and abandon the expression; When typechecking is disabled, gdb successfully evaluates expressions like the second example above.
Even if type checking is off, there may be other reasons related to type that prevent gdb
from evaluating an expression. For instance, gdb does not know how to add an int and astruct foo. These particular type errors have nothing to do with the language in use andusually arise from expressions which make little sense to evaluate anyway.
gdb provides some additional commands for controlling type checking:set check type on
set check type off
Set strict type checking on or off. If any type mismatches occur in evaluating an
expression while type checking is on, gdb prints a message and aborts evaluationof the expression.
show check typeShow the current setting of type checking and whether gdb is enforcing strict
type checking rules.

15.3.2 An Overview of Range Checking
In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is
enforced with run-time checks. Such range checking is meant to ensure program correctness
by making sure computations do not overflow, or indices on an array element access do not
exceed the bounds of the array.
For expressions you use in gdb commands, you can tell gdb to treat range errors in oneof three ways: ignore them, always treat them as errors and abandon the expression, or
issue warnings but evaluate the expression anyway.
A range error can result from numerical overflow, from exceeding an array index bound,or when you type a constant that is not a member of any type. Some languages, however,
do not treat overflows as an error. In many implementations of C, mathematical overflow
causes the result to “wrap around” to lower values—for example, if m is the largest integer
value, and s is the smallest, thenm + 1 ⇒ s

This, too, is specific to individual languages, and in some cases specific to individualcompilers or machines. See Section 15.4 [Supported Languages], page 231, for further
details on specific languages.
gdb provides some additional commands for controlling the range checker:
set check range auto
Set range checking on or off based on the current working language. See
Section 15.4 [Supported Languages], page 231, for the default settings for eachlanguage.
set check range on
set check range off
Set range checking on or off, overriding the default setting for the current working language. A warning is issued if the setting does not match the language

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default. If a range error occurs and range checking is on, then a message isprinted and evaluation of the expression is aborted.
set check range warn
Output messages when the gdb range checker detects a range error, but attempt to evaluate the expression anyway. Evaluating the expression may still
be impossible for other reasons, such as accessing memory that the process does
not own (a typical example from many Unix systems).
show check range
Show the current setting of the range checker, and whether or not it is being
set automatically by gdb.

15.4 Supported Languages
gdb supports C, C++, D, Go, Objective-C, Fortran, OpenCL C, Pascal, Rust, assembly,
Modula-2, and Ada. Some gdb features may be used in expressions regardless of the language you use: the gdb @ and :: operators, and the ‘{type}addr’ construct (see Section 10.1
[Expressions], page 145) can be used with the constructs of any supported language.
The following sections detail to what degree each source language is supported by gdb.
These sections are not meant to be language tutorials or references, but serve only as areference guide to what the gdb expression parser accepts, and what input and output
formats should look like for different languages. There are many good books written oneach of these languages; please look to these for a language reference or tutorial.

15.4.1 C and C++
Since C and C++ are so closely related, many features of gdb apply to both languages.
Whenever this is the case, we discuss those languages together.
The C++ debugging facilities are jointly implemented by the C++ compiler and gdb.
Therefore, to debug your C++ code effectively, you must compile your C++ programs witha supported C++ compiler, such as gnu g++, or the HP ANSI C++ compiler (aCC).

15.4.1.1 C and C++ Operators
Operators must be defined on values of specific types. For instance, + is defined on numbers,
but not on structures. Operators are often defined on groups of types.
For the purposes of C and C++, the following definitions hold:• Integral types include int with any of its storage-class specifiers; char; enum; and, for
C++, bool.
• Floating-point types include float, double, and long double (if supported by thetarget platform).
• Pointer types include all types defined as (type *).
• Scalar types include all of the above.
The following operators are supported. They are listed here in order of increasing precedence:,

The comma or sequencing operator. Expressions in a comma-separated list areevaluated from left to right, with the result of the entire expression being thelast expression evaluated.

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Debugging with gdb=

Assignment. The value of an assignment expression is the value assigned. Defined on scalar types.

op=

Used in an expression of the form a op= b, and translated to a = a op b. op=
and = have the same precedence. The operator op is any one of the operators|, ^, &, <<, >>, +, -, *, /, %.

?:The ternary operator. a ? b : c can be thought of as: if a then b else c. The
argument a should be of an integral type.

||

Logical or. Defined on integral types.

&&

Logical and. Defined on integral types.

|

Bitwise or. Defined on integral types.

^

Bitwise exclusive-or. Defined on integral types.

&

Bitwise and. Defined on integral types.

==, !=

Equality and inequality. Defined on scalar types. The value of these expressions
is 0 for false and non-zero for true.

<, >, <=, >=Less than, greater than, less than or equal, greater than or equal. Defined on
scalar types. The value of these expressions is 0 for false and non-zero for true.
<<, >>

left shift, and right shift. Defined on integral types.

@

The gdb “artificial array” operator (see Section 10.1 [Expressions], page 145).

+, -Addition and subtraction. Defined on integral types, floating-point types andpointer types.

*, /, %

Multiplication, division, and modulus. Multiplication and division are definedon integral and floating-point types. Modulus is defined on integral types.

++, --

Increment and decrement. When appearing before a variable, the operation is
performed before the variable is used in an expression; when appearing after it,
the variable’s value is used before the operation takes place.

*

Pointer dereferencing. Defined on pointer types. Same precedence as ++.

&Address operator. Defined on variables. Same precedence as ++.
For debugging C++, gdb implements a use of ‘&’ beyond what is allowed in theC++ language itself: you can use ‘&(&ref)’ to examine the address where a C++
reference variable (declared with ‘&ref’) is stored.

-

Negative. Defined on integral and floating-point types. Same precedence as ++.

!

Logical negation. Defined on integral types. Same precedence as ++.

~Bitwise complement operator. Defined on integral types. Same precedence as
++.

., ->

Structure member, and pointer-to-structure member. For convenience, gdb
regards the two as equivalent, choosing whether to dereference a pointer basedon the stored type information. Defined on struct and union data.

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233.*, ->*

Dereferences of pointers to members.

[]

Array indexing. a[i] is defined as *(a+i). Same precedence as ->.

()Function parameter list. Same precedence as ->.

::C++ scope resolution operator. Defined on struct, union, and class types.

::

Doubled colons also represent the gdb scope operator (see Section 10.1 [Expressions], page 145). Same precedence as ::, above.

If an operator is redefined in the user code, gdb usually attempts to invoke the redefinedversion instead of using the operator’s predefined meaning.

15.4.1.2 C and C++ Constants
gdb allows you to express the constants of C and C++ in the following ways:• Integer constants are a sequence of digits. Octal constants are specified by a leading‘0’ (i.e. zero), and hexadecimal constants by a leading ‘0x’ or ‘0X’. Constants may also
end with a letter ‘l’, specifying that the constant should be treated as a long value.
• Floating point constants are a sequence of digits, followed by a decimal point, followed
by a sequence of digits, and optionally followed by an exponent. An exponent is of
the form: ‘e[[+]|-]nnn’, where nnn is another sequence of digits. The ‘+’ is optional
for positive exponents. A floating-point constant may also end with a letter ‘f’ or ‘F’,
specifying that the constant should be treated as being of the float (as opposed to thedefault double) type; or with a letter ‘l’ or ‘L’, which specifies a long double constant.
• Enumerated constants consist of enumerated identifiers, or their integral equivalents.
• Character constants are a single character surrounded by single quotes (’), or anumber—the ordinal value of the corresponding character (usually its ascii value).
Within quotes, the single character may be represented by a letter or by escapesequences, which are of the form ‘\nnn’, where nnn is the octal representation of
the character’s ordinal value; or of the form ‘\x’, where ‘x’ is a predefined special
character—for example, ‘\n’ for newline.
Wide character constants can be written by prefixing a character constant with ‘L’,
as in C. For example, ‘L’x’’ is the wide form of ‘x’. The target wide character set isused when computing the value of this constant (see Section 10.21 [Character Sets],page 187).
• String constants are a sequence of character constants surrounded by double quotes (").
Any valid character constant (as described above) may appear. Double quotes within
the string must be preceded by a backslash, so for instance ‘"a\"b’c"’ is a string offive characters.
Wide string constants can be written by prefixing a string constant with ‘L’, as in C.
The target wide character set is used when computing the value of this constant (seeSection 10.21 [Character Sets], page 187).
• Pointer constants are an integral value. You can also write pointers to constants using
the C operator ‘&’.
• Array constants are comma-separated lists surrounded by braces ‘{’ and ‘}’; for example, ‘{1,2,3}’ is a three-element array of integers, ‘{{1,2}, {3,4}, {5,6}}’ is a234

Debugging with gdb

three-by-two array, and ‘{&"hi", &"there", &"fred"}’ is a three-element array ofpointers.

15.4.1.3 C++ Expressions
gdb expression handling can interpret most C++ expressions.
Warning: gdb can only debug C++ code if you use the proper compiler andthe proper debug format. Currently, gdb works best when debugging C++ codethat is compiled with the most recent version of gcc possible. The DWARF
debugging format is preferred; gcc defaults to this on most popular platforms.
Other compilers and/or debug formats are likely to work badly or not at allwhen using gdb to debug C++ code. See Section 4.1 [Compilation], page 33.
1. Member function calls are allowed; you can use expressions likecount = aml->GetOriginal(x, y)

2. While a member function is active (in the selected stack frame), your expressions havethe same namespace available as the member function; that is, gdb allows implicit
references to the class instance pointer this following the same rules as C++. using
declarations in the current scope are also respected by gdb.
3. You can call overloaded functions; gdb resolves the function call to the right definition,with some restrictions. gdb does not perform overload resolution involving user-defined
type conversions, calls to constructors, or instantiations of templates that do not exist
in the program. It also cannot handle ellipsis argument lists or default arguments.
It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, andstandard conversions such as those of functions or arrays to pointers; it requires anexact match on the number of function arguments.
Overload resolution is always performed, unless you have specified set
overload-resolution off. See Section 15.4.1.7 [gdb Features for C++], page 235.
You must specify set overload-resolution off in order to use an explicit function
signature to call an overloaded function, as inp ’foo(char,int)’(’x’, 13)

The gdb command-completion facility can simplify this; see Section 3.3 [Command
Completion], page 24.
4. gdb understands variables declared as C++ lvalue or rvalue references; you can use themin expressions just as you do in C++ source—they are automatically dereferenced.
In the parameter list shown when gdb displays a frame, the values of reference variables
are not displayed (unlike other variables); this avoids clutter, since references are often
used for large structures. The address of a reference variable is always shown, unless
you have specified ‘set print address off’.
5. gdb supports the C++ name resolution operator ::—your expressions can use it just as
expressions in your program do. Since one scope may be defined in another, you can use:: repeatedly if necessary, for example in an expression like ‘scope1::scope2::name’.
gdb also allows resolving name scope by reference to source files, in both C and C++
debugging (see Section 10.3 [Program Variables], page 147).
6. gdb performs argument-dependent lookup, following the C++ specification.

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15.4.1.4 C and C++ Defaults
If you allow gdb to set range checking automatically, it defaults to off whenever the working
language changes to C or C++. This happens regardless of whether you or gdb selects theworking language.
If you allow gdb to set the language automatically, it recognizes source files whose names
end with .c, .C, or .cc, etc, and when gdb enters code compiled from one of these files,
it sets the working language to C or C++. See Section 15.1.3 [Having gdb Infer the Source
Language], page 228, for further details.

15.4.1.5 C and C++ Type and Range Checks
By default, when gdb parses C or C++ expressions, strict type checking is used. However,
if you turn type checking off, gdb will allow certain non-standard conversions, such as
promoting integer constants to pointers.
Range checking, if turned on, is done on mathematical operations. Array indices are notchecked, since they are often used to index a pointer that is not itself an array.

15.4.1.6 gdb and C
The set print union and show print union commands apply to the union type. Whenset to ‘on’, any union that is inside a struct or class is also printed. Otherwise, it appears
as ‘{...}’.
The @ operator aids in the debugging of dynamic arrays, formed with pointers and amemory allocation function. See Section 10.1 [Expressions], page 145.

15.4.1.7 gdb Features for C++
Some gdb commands are particularly useful with C++, and some are designed specificallyfor use with C++. Here is a summary:breakpoint menus
When you want a breakpoint in a function whose name is overloaded, gdb
has the capability to display a menu of possible breakpoint locations to help
you specify which function definition you want. See Section 10.2 [Ambiguous
Expressions], page 146.
rbreak regex
Setting breakpoints using regular expressions is helpful for setting breakpoints
on overloaded functions that are not members of any special classes. See
Section 5.1.1 [Setting Breakpoints], page 58.
catch throw
catch rethrow
catch catch
Debug C++ exception handling using these commands. See Section 5.1.3 [Setting Catchpoints], page 69.
ptype typename
Print inheritance relationships as well as other information for type typename.
See Chapter 16 [Examining the Symbol Table], page 263.

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info vtbl expression.
The info vtbl command can be used to display the virtual method tables ofthe object computed by expression. This shows one entry per virtual table;
there may be multiple virtual tables when multiple inheritance is in use.
demangle nameDemangle name. See Chapter 16 [Symbols], page 263, for a more complete
description of the demangle command.
set print demangle
show print demangle
set print asm-demangle
show print asm-demangle
Control whether C++ symbols display in their source form, both when displaying
code as C++ source and when displaying disassemblies. See Section 10.9 [Print
Settings], page 157.
set print object
show print object
Choose whether to print derived (actual) or declared types of objects. See
Section 10.9 [Print Settings], page 157.
set print vtbl
show print vtbl
Control the format for printing virtual function tables. See Section 10.9 [Print
Settings], page 157. (The vtbl commands do not work on programs compiled
with the HP ANSI C++ compiler (aCC).)
set overload-resolution on
Enable overload resolution for C++ expression evaluation. The default is on. For
overloaded functions, gdb evaluates the arguments and searches for a function
whose signature matches the argument types, using the standard C++ conversion rules (see Section 15.4.1.3 [C++ Expressions], page 234, for details). If it
cannot find a match, it emits a message.
set overload-resolution off
Disable overload resolution for C++ expression evaluation. For overloaded functions that are not class member functions, gdb chooses the first function of
the specified name that it finds in the symbol table, whether or not its arguments are of the correct type. For overloaded functions that are class member
functions, gdb searches for a function whose signature exactly matches theargument types.
show overload-resolution
Show the current setting of overload resolution.
Overloaded symbol names
You can specify a particular definition of an overloaded symbol, using the same
notation that is used to declare such symbols in C++: type symbol(types)
rather than just symbol. You can also use the gdb command-line word completion facilities to list the available choices, or to finish the type list for you.
See Section 3.3 [Command Completion], page 24, for details on how to do this.

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Breakpoints in template functions
Similar to how overloaded symbols are handled, gdb will ignore template parameter lists when it encounters a symbol which includes a C++ template. Thispermits setting breakpoints on families of template functions or functions whoseparameters include template types.
The -qualified flag may be used to override this behavior, causing gdb tosearch for a specific function or type.
The gdb command-line word completion facility also understands template parameters and may be used to list available choices or finish template parameter
lists for you. See Section 3.3 [Command Completion], page 24, for details on
how to do this.
Breakpoints in functions with ABI tags
The GNU C++ compiler introduced the notion of ABI “tags”, which correspondto changes in the ABI of a type, function, or variable that would not otherwise
be reflected in a mangled name. See https://developers.redhat.com/blog/
2015/02/05/gcc5-and-the-c11-abi/ for more detail.
The ABI tags are visible in C++ demangled names. For example, a functionthat returns a std::string:
std::string function(int);

when compiled for the C++11 ABI is marked with the cxx11 ABI tag, and gdb
displays the symbol like this:function[abi:cxx11](int)

You can set a breakpoint on such functions simply as if they had no tag. For
example:(gdb) b function(int)
Breakpoint 2 at 0x40060d: file main.cc, line 10.
(gdb) info breakpoints
NumType
Disp Enb AddressWhat1
breakpoint
keep y0x0040060d in function[abi:cxx11](int)at main.cc:10

On the rare occasion you need to disambiguate between different ABI tags, you
can do so by simply including the ABI tag in the function name, like:(gdb) b ambiguous[abi:other_tag](int)

15.4.1.8 Decimal Floating Point format
gdb can examine, set and perform computations with numbers in decimal floating point format, which in the C language correspond to the _Decimal32, _Decimal64 and _Decimal128
types as specified by the extension to support decimal floating-point arithmetic.
There are two encodings in use, depending on the architecture: BID (Binary Integer
Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for PowerPC and S/390.
gdb will use the appropriate encoding for the configured target.
Because of a limitation in libdecnumber, the library used by gdb to manipulate decimal
floating point numbers, it is not possible to convert (using a cast, for example) integers wider
than 32-bit to decimal float.

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In addition, in order to imitate gdb’s behaviour with binary floating point computations,error checking in decimal float operations ignores underflow, overflow and divide by zero
exceptions.
In the PowerPC architecture, gdb provides a set of pseudo-registers to inspect_Decimal128 values stored in floating point registers. See Section 21.4.6 [PowerPC],
page 361, for more details.

15.4.2 D
gdb can be used to debug programs written in D and compiled with GDC, LDC or DMD
compilers. Currently gdb supports only one D specific feature — dynamic arrays.

15.4.3 Go
gdb can be used to debug programs written in Go and compiled with gccgo or 6g compilers.
Here is a summary of the Go-specific features and restrictions:
The current Go package
The name of the current package does not need to be specified when specifying
global variables and functions.
For example, given the program:
package main
var myglob = "Shall we?"func main () {// ...
}
When stopped inside main either of these work:(gdb) p myglob(gdb) p main.myglob
Builtin Go types
The string type is recognized by gdb and is printed as a string.
Builtin Go functions
The gdb expression parser recognizes the unsafe.Sizeof function and handles
it internally.
Restrictions on Go expressions
All Go operators are supported except &^. The Go _ “blank identifier” is notsupported. Automatic dereferencing of pointers is not supported.

15.4.4 Objective-C
This section provides information about some commands and command options that are
useful for debugging Objective-C code. See also Chapter 16 [Symbols], page 263, andChapter 16 [Symbols], page 263, for a few more commands specific to Objective-C support.

15.4.4.1 Method Names in Commands
The following commands have been extended to accept Objective-C method names as line
specifications:• clearChapter 15: Using gdb with Different Languages

239• break• info line
• jump• listA fully qualified Objective-C method name is specified as-[Class methodName]

where the minus sign is used to indicate an instance method and a plus sign (not shown)is used to indicate a class method. The class name Class and method name methodName
are enclosed in brackets, similar to the way messages are specified in Objective-C sourcecode. For example, to set a breakpoint at the create instance method of class Fruit in
the program currently being debugged, enter:break -[Fruit create]

To list ten program lines around the initialize class method, enter:
list +[NSText initialize]

In the current version of gdb, the plus or minus sign is required. In future versions ofgdb, the plus or minus sign will be optional, but you can use it to narrow the search. It isalso possible to specify just a method name:break create

You must specify the complete method name, including any colons. If your program’ssource files contain more than one create method, you’ll be presented with a numbered
list of classes that implement that method. Indicate your choice by number, or type ‘0’ toexit if none apply.
As another example, to clear a breakpoint established at the makeKeyAndOrderFront:
method of the NSWindow class, enter:
clear -[NSWindow makeKeyAndOrderFront:]

15.4.4.2 The Print Command With Objective-C
The print command has also been extended to accept methods. For example:
print -[object hash]will tell gdb to send the hash message to object and print the result. Also, an additionalcommand has been added, print-object or po for short, which is meant to print thedescription of an object. However, this command may only work with certain Objective-C
libraries that have a particular hook function, _NSPrintForDebugger, defined.

15.4.5 OpenCL C
This section provides information about gdbs OpenCL C support.

15.4.5.1 OpenCL C Datatypes
gdb supports the builtin scalar and vector datatypes specified by OpenCL 1.1. In addition
the half- and double-precision floating point data types of the cl_khr_fp16 and cl_khr_
fp64 OpenCL extensions are also known to gdb.

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15.4.5.2 OpenCL C Expressions
gdb supports accesses to vector components including the access as lvalue where possible.
Since OpenCL C is based on C99 most C expressions supported by gdb can be used aswell.

15.4.5.3 OpenCL C Operators
gdb supports the operators specified by OpenCL 1.1 for scalar and vector data types.

15.4.6 Fortrangdb can be used to debug programs written in Fortran. Note, that not all Fortran language
features are available yet.
Some Fortran compilers (gnu Fortran 77 and Fortran 95 compilers among them) append
an underscore to the names of variables and functions. When you debug programs compiled by those compilers, you will need to refer to variables and functions with a trailingunderscore.
Fortran symbols are usually case-insensitive, so gdb by default uses case-insensitive
matching for Fortran symbols. You can change that with the ‘set case-insensitive’command, see Chapter 16 [Symbols], page 263, for the details.

15.4.6.1 Fortran Types
In Fortran the primitive data-types have an associated KIND type parameter, written as‘type*kindparam’, ‘type*kindparam’, or in the gdb-only dialect ‘type_kindparam’. A
concrete example would be ‘Real*4’, ‘Real(kind=4)’, and ‘Real_4’. The kind of a typecan be retrieved by using the intrinsic function KIND, see Section 15.4.6.3 [Fortran Intrinsics],
page 241.
Generally, the actual implementation of the KIND type parameter is compiler specific.
In gdb the kind parameter is implemented in accordance with its use in the gnu gfortrancompiler. Here, the kind parameter for a given type specifies its size in memory — a FortranInteger*4 or Integer(kind=4) would be an integer type occupying 4 bytes of memory.
An exception to this rule is the Complex type for which the kind of the type does not specify
its entire size, but the size of each of the two Real’s it is composed of. A Complex*4 would
thus consist of two Real*4s and occupy 8 bytes of memory.
For every type there is also a default kind associated with it, e.g. Integer in gdb willinternally be an Integer*4 (see the table below for default types). The default types are
the same as in gnu compilers but note, that the gnu default types can actually be changed
by compiler flags such as -fdefault-integer-8 and -fdefault-real-8.
Not every kind parameter is valid for every type and in gdb the following type kinds
are available.
Integer

Integer*1, Integer*2, Integer*4, Integer*8, and Integer = Integer*4.

Logical

Logical*1, Logical*2, Logical*4, Logical*8, and Logical = Logical*4.

Real

Real*4, Real*8, Real*16, and Real = Real*4.

Complex

Complex*4, Complex*8, Complex*16, and Complex = Complex*4.

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15.4.6.2 Fortran Operators and Expressions
Operators must be defined on values of specific types. For instance, + is defined on numbers,
but not on characters or other non- arithmetic types. Operators are often defined on groupsof types.
**

The exponentiation operator. It raises the first operand to the power of thesecond one.

:The range operator. Normally used in the form of array(low:high) to represent
a section of array.

%

The access component operator. Normally used to access elements in derived
types. Also suitable for unions. As unions aren’t part of regular Fortran, thiscan only happen when accessing a register that uses a gdbarch-defined union
type.

::

The scope operator. Normally used to access variables in modules or to set
breakpoints on subroutines nested in modules or in other subroutines (internal
subroutines).

15.4.6.3 Fortran Intrinsics
Fortran provides a large set of intrinsic procedures. gdb implements an incomplete subsetof those procedures and their overloads. Some of these procedures take an optional KIND
parameter, see Section 15.4.6.1 [Fortran Types], page 240.
ABS(a)

Computes the absolute value of its argument a. Currently not supported forComplex arguments.

ALLOCATE(array)
Returns whether array is allocated or not.
ASSOCIATED(pointer [, target])
Returns the association status of the pointer pointer or, if target is present,
whether pointer is associated with the target target.
CEILING(a [, kind])
Computes the least integer greater than or equal to a. The optional parameterkind specifies the kind of the return type Integer(kind).
CMPLX(x [, y [, kind]])Returns a complex number where x is converted to the real component. If y ispresent it is converted to the imaginary component. If y is not present then theimaginary component is set to 0.0 except if x itself is of Complex type. The
optional parameter kind specifies the kind of the return type Complex(kind).
FLOOR(a [, kind])
Computes the greatest integer less than or equal to a. The optional parameterkind specifies the kind of the return type Integer(kind).
KIND(a)Returns the kind value of the argument a, see Section 15.4.6.1 [Fortran Types],
page 240.

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LBOUND(array [, dim [, kind]])Returns the lower bounds of an array, or a single lower bound along the dimdimension if present. The optional parameter kind specifies the kind of the
return type Integer(kind).
LOC(x)

Returns the address of x as an Integer.

MOD(a, p) Computes the remainder of the division of a by p.
MODULO(a, p)
Computes the a modulo p.
RANK(a)Returns the rank of a scalar or array (scalars have rank 0).

SHAPE(a)Returns the shape of a scalar or array (scalars have shape ‘()’).

SIZE(array[, dim [, kind]])Returns the extent of array along a specified dimension dim, or the total numberof elements in array if dim is absent. The optional parameter kind specifies thekind of the return type Integer(kind).
UBOUND(array [, dim [, kind]])Returns the upper bounds of an array, or a single upper bound along the dimdimension if present. The optional parameter kind specifies the kind of the
return type Integer(kind).

15.4.6.4 Special Fortran Commands
gdb has some commands to support Fortran-specific features, such as displaying common
blocks.
info common [common-name]
This command prints the values contained in the Fortran COMMON block whosename is common-name. With no argument, the names of all COMMON blocks
visible at the current program location are printed.
set fortran repack-array-slices [on|off]show fortran repack-array-slices
When taking a slice from an array, a Fortran compiler can choose to either
produce an array descriptor that describes the slice in place, or it may repack
the slice, copying the elements of the slice into a new region of memory.
When this setting is on, then gdb will also repack array slices in some situations.
When this setting is off, then gdb will create array descriptors for slices thatreference the original data in place.
gdb will never repack an array slice if the data for the slice is contiguous within
the original array.
gdb will always repack string slices if the data for the slice is non-contiguous
within the original string as gdb does not support printing non-contiguous
strings.
The default for this setting is off.

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243

15.4.7 Pascal
Debugging Pascal programs which use sets, subranges, file variables, or nested functions
does not currently work. gdb does not support entering expressions, printing values, orsimilar features using Pascal syntax.
The Pascal-specific command set print pascal_static-members controls whether
static members of Pascal objects are displayed. See Section 10.9 [Print Settings], page 157.

15.4.8 Rust
gdb supports the Rust Programming Language (https://www.rust-lang.org/). Typeand value-printing, and expression parsing, are reasonably complete. However, there are a
few peculiarities and holes to be aware of.
• Linespecs (see Section 9.2 [Location Specifications], page 126) are never relative to thecurrent crate. Instead, they act as if there were a global namespace of crates, somewhat
similar to the way extern crate behaves.
That is, if gdb is stopped at a breakpoint in a function in crate ‘A’, module ‘B’, thenbreak B::f will attempt to set a breakpoint in a function named ‘f’ in a crate named‘B’.
As a consequence of this approach, linespecs also cannot refer to items using ‘self::’or ‘super::’.
• Because gdb implements Rust name-lookup semantics in expressions, it will sometimes
prepend the current crate to a name. For example, if gdb is stopped at a breakpointin the crate ‘K’, then print ::x::y will try to find the symbol ‘K::x::y’.
However, since it is useful to be able to refer to other crates when debugging, gdb
provides the extern extension to circumvent this. To use the extension, just put
extern before a path expression to refer to the otherwise unavailable “global” scope.
In the above example, if you wanted to refer to the symbol ‘y’ in the crate ‘x’, you
would use print extern x::y.
• The Rust expression evaluator does not support “statement-like” expressions such as
if or match, or lambda expressions.
• Tuple expressions are not implemented.
• The Rust expression evaluator does not currently implement the Drop trait. Objects
that may be created by the evaluator will never be destroyed.
• gdb does not implement type inference for generics. In order to call generic functions orotherwise refer to generic items, you will have to specify the type parameters manually.
• gdb currently uses the C++ demangler for Rust. In most cases this does not cause any
problems. However, in an expression context, completing a generic function name will
give syntactically invalid results. This happens because Rust requires the ‘::’ operator
between the function name and its generic arguments. For example, gdb might provide
a completion like crate::f<u32>, where the parser would require crate::f::<u32>.
• As of this writing, the Rust compiler (version 1.8) has a few holes in the debugging
information it generates. These holes prevent certain features from being implemented
by gdb:• Method calls cannot be made via traits.

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Debugging with gdb• Operator overloading is not implemented.
• When debugging in a monomorphized function, you cannot use the generic type
names.
• The type Self is not available.
• use statements are not available, so some names may not be available in the crate.

15.4.9 Modula-2
The extensions made to gdb to support Modula-2 only support output from the gnu
Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are notcurrently supported, and attempting to debug executables produced by them is most likely
to give an error as gdb reads in the executable’s symbol table.

15.4.9.1 Operators
Operators must be defined on values of specific types. For instance, + is defined on numbers,
but not on structures. Operators are often defined on groups of types. For the purposes ofModula-2, the following definitions hold:• Integral types consist of INTEGER, CARDINAL, and their subranges.
• Character types consist of CHAR and its subranges.
• Floating-point types consist of REAL.
• Pointer types consist of anything declared as POINTER TO type.
• Scalar types consist of all of the above.
• Set types consist of SET and BITSET types.
• Boolean types consist of BOOLEAN.
The following operators are supported, and appear in order of increasing precedence:,

Function argument or array index separator.

:=

Assignment. The value of var := value is value.

<, >Less than, greater than on integral, floating-point, or enumerated types.

<=, >=

Less than or equal to, greater than or equal to on integral, floating-point andenumerated types, or set inclusion on set types. Same precedence as <.

=, <>, #Equality and two ways of expressing inequality, valid on scalar types. Same
precedence as <. In gdb scripts, only <> is available for inequality, since #conflicts with the script comment character.

IN

Set membership. Defined on set types and the types of their members. Same
precedence as <.

OR

Boolean disjunction. Defined on boolean types.

AND, &

Boolean conjunction. Defined on boolean types.

@

The gdb “artificial array” operator (see Section 10.1 [Expressions], page 145).

+, -Addition and subtraction on integral and floating-point types, or union anddifference on set types.

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245*

Multiplication on integral and floating-point types, or set intersection on set
types.

/

Division on floating-point types, or symmetric set difference on set types. Same
precedence as *.

DIV, MOD

Integer division and remainder. Defined on integral types. Same precedence as*.

-

Negative. Defined on INTEGER and REAL data.

^

Pointer dereferencing. Defined on pointer types.

NOT

Boolean negation. Defined on boolean types. Same precedence as ^.

.

RECORD field selector. Defined on RECORD data. Same precedence as ^.

[]Array indexing. Defined on ARRAY data. Same precedence as ^.

()Procedure argument list. Defined on PROCEDURE objects. Same precedence as
^.

::, .

gdb and Modula-2 scope operators.
Warning: Set expressions and their operations are not yet supported, so gdb
treats the use of the operator IN, or the use of operators +, -, *, /, =, , <>, #,<=, and >= on sets as an error.

15.4.9.2 Built-in Functions and Procedures
Modula-2 also makes available several built-in procedures and functions. In describing these,
the following metavariables are used:arepresents an ARRAY variable.

crepresents a CHAR constant or variable.

irepresents a variable or constant of integral type.

m

represents an identifier that belongs to a set. Generally used in the same function with the metavariable s. The type of s should be SET OF mtype (wheremtype is the type of m).

n

represents a variable or constant of integral or floating-point type.

r

represents a variable or constant of floating-point type.

t

represents a type.

v

represents a variable.

x

represents a variable or constant of one of many types. See the explanation of
the function for details.
All Modula-2 built-in procedures also return a result, described below.

ABS(n)

Returns the absolute value of n.

ADR(n)

Returns the memory address of n.

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CAP(c)

If c is a lower case letter, it returns its upper case equivalent, otherwise it
returns its argument.

CHR(i)

Returns the character whose ordinal value is i.

DEC(v)

Decrements the value in the variable v by one. Returns the new value.

DEC(v,i)Decrements the value in the variable v by i. Returns the new value.

EXCL(m,s)Removes the element m from the set s. Returns the new set.
FLOAT(i)Returns the floating point equivalent of the integer i.

HIGH(a)Returns the index of the last member of a.

INC(v)

Increments the value in the variable v by one. Returns the new value.

INC(v,i)Increments the value in the variable v by i. Returns the new value.

INCL(m,s)
Adds the element m to the set s if it is not already there. Returns the new set.
MAX(t)

Returns the maximum value of the type t.

MIN(t)

Returns the minimum value of the type t.

ODD(i)

Returns boolean TRUE if i is an odd number.

ORD(x)

Returns the ordinal value of its argument. For example, the ordinal value of acharacter is its ascii value (on machines supporting the ascii character set).
The argument x must be of an ordered type, which include integral, characterand enumerated types.

SIZE(x)Returns the size of its argument. The argument x can be a variable or a type.

TRUNC(r)Returns the integral part of r.

TSIZE(x)Returns the size of its argument. The argument x can be a variable or a type.

VAL(t,i)Returns the member of the type t whose ordinal value is i.

Warning: Sets and their operations are not yet supported, so gdb treats theuse of procedures INCL and EXCL as an error.

15.4.9.3 Constants
gdb allows you to express the constants of Modula-2 in the following ways:• Integer constants are simply a sequence of digits. When used in an expression, a constant is interpreted to be type-compatible with the rest of the expression. Hexadecimal
integers are specified by a trailing ‘H’, and octal integers by a trailing ‘B’.
• Floating point constants appear as a sequence of digits, followed by a decimal point
and another sequence of digits. An optional exponent can then be specified, in the form
‘E[+|-]nnn’, where ‘[+|-]nnn’ is the desired exponent. All of the digits of the floating
point constant must be valid decimal (base 10) digits.
• Character constants consist of a single character enclosed by a pair of like quotes, either
single (’) or double ("). They may also be expressed by their ordinal value (their ascii
value, usually) followed by a ‘C’.

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247• String constants consist of a sequence of characters enclosed by a pair of like quotes,
either single (’) or double ("). Escape sequences in the style of C are also allowed.
See Section 15.4.1.2 [C and C++ Constants], page 233, for a brief explanation of escapesequences.
• Enumerated constants consist of an enumerated identifier.
• Boolean constants consist of the identifiers TRUE and FALSE.
• Pointer constants consist of integral values only.
• Set constants are not yet supported.

15.4.9.4 Modula-2 Types
Currently gdb can print the following data types in Modula-2 syntax: array types, record
types, set types, pointer types, procedure types, enumerated types, subrange types and basetypes. You can also print the contents of variables declared using these type. This section
gives a number of simple source code examples together with sample gdb sessions.
The first example contains the following section of code:
VAR
s: SET OF CHAR ;r: [20..40] ;and you can request gdb to interrogate the type and value of r and s.
(gdb) print s{’A’..’C’, ’Z’}
(gdb) ptype s
SET OF CHAR(gdb) print r
21(gdb) ptype r[20..40]

Likewise if your source code declares s as:
VAR
s: SET [’A’..’Z’] ;then you may query the type of s by:(gdb) ptype stype = SET [’A’..’Z’]

Note that at present you cannot interactively manipulate set expressions using the debugger.
The following example shows how you might declare an array in Modula-2 and how you
can interact with gdb to print its type and contents:
VAR
s: ARRAY [-10..10] OF CHAR ;(gdb) ptype s
ARRAY [-10..10] OF CHAR

Note that the array handling is not yet complete and although the type is printed
correctly, expression handling still assumes that all arrays have a lower bound of zero andnot -10 as in the example above.
Here are some more type related Modula-2 examples:
TYPE
colour = (blue, red, yellow, green) ;t = [blue..yellow] ;248

Debugging with gdb

VAR
s: t ;BEGIN
s := blue ;The gdb interaction shows how you can query the data type and value of a variable.
(gdb) print s$1 = blue(gdb) ptype ttype = [blue..yellow]

In this example a Modula-2 array is declared and its contents displayed. Observe that thecontents are written in the same way as their C counterparts.
VAR
s: ARRAY [1..5] OF CARDINAL ;BEGIN
s[1] := 1 ;(gdb) print s$1 = {1, 0, 0, 0, 0}(gdb) ptype stype = ARRAY [1..5] OF CARDINALThe Modula-2 language interface to gdb also understands pointer types as shown in thisexample:VAR
s: POINTER TO ARRAY [1..5] OF CARDINAL ;BEGIN
NEW(s) ;s^[1] := 1 ;and you can request that gdb describes the type of s.
(gdb) ptype stype = POINTER TO ARRAY [1..5] OF CARDINAL

gdb handles compound types as we can see in this example. Here we combine arraytypes, record types, pointer types and subrange types:
TYPE
foo = RECORD
f1: CARDINAL ;f2: CHAR ;f3: myarray ;END ;myarray = ARRAY myrange OF CARDINAL ;myrange = [-2..2] ;VAR
s: POINTER TO ARRAY myrange OF foo ;and you can ask gdb to describe the type of s as shown below.
(gdb) ptype stype = POINTER TO ARRAY [-2..2] OF foo = RECORD
f1 : CARDINAL;
f2 : CHAR;
f3 : ARRAY [-2..2] OF CARDINAL;
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249

15.4.9.5 Modula-2 Defaults
If type and range checking are set automatically by gdb, they both default to on whenever
the working language changes to Modula-2. This happens regardless of whether you or gdb
selected the working language.
If you allow gdb to set the language automatically, then entering code compiled from afile whose name ends with .mod sets the working language to Modula-2. See Section 15.1.3[Having gdb Infer the Source Language], page 228, for further details.

15.4.9.6 Deviations from Standard Modula-2
A few changes have been made to make Modula-2 programs easier to debug. This is done
primarily via loosening its type strictness:• Unlike in standard Modula-2, pointer constants can be formed by integers. This allows
you to modify pointer variables during debugging. (In standard Modula-2, the actual
address contained in a pointer variable is hidden from you; it can only be modified
through direct assignment to another pointer variable or expression that returned apointer.)• C escape sequences can be used in strings and characters to represent non-printablecharacters. gdb prints out strings with these escape sequences embedded. Single nonprintable characters are printed using the ‘CHR(nnn)’ format.
• The assignment operator (:=) returns the value of its right-hand argument.
• All built-in procedures both modify and return their argument.

15.4.9.7 Modula-2 Type and Range Checks
Warning: in this release, gdb does not yet perform type or range checking.
gdb considers two Modula-2 variables type equivalent if:• They are of types that have been declared equivalent via a TYPE t1 = t2 statement• They have been declared on the same line. (Note: This is true of the gnu Modula-2
compiler, but it may not be true of other compilers.)
As long as type checking is enabled, any attempt to combine variables whose types are
not equivalent is an error.
Range checking is done on all mathematical operations, assignment, array index bounds,
and all built-in functions and procedures.

15.4.9.8 The Scope Operators :: and .
There are a few subtle differences between the Modula-2 scope operator (.) and the gdb
scope operator (::). The two have similar syntax:
module . id
scope :: idwhere scope is the name of a module or a procedure, module the name of a module, and
id is any declared identifier within your program, except another module.
Using the :: operator makes gdb search the scope specified by scope for the identifier
id. If it is not found in the specified scope, then gdb searches all scopes enclosing the one
specified by scope.

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Using the . operator makes gdb search the current scope for the identifier specified byid that was imported from the definition module specified by module. With this operator,
it is an error if the identifier id was not imported from definition module module, or if id is
not an identifier in module.

15.4.9.9 gdb and Modula-2
Some gdb commands have little use when debugging Modula-2 programs. Five subcommands of set print and show print apply specifically to C and C++: ‘vtbl’, ‘demangle’,‘asm-demangle’, ‘object’, and ‘union’. The first four apply to C++, and the last to the C
union type, which has no direct analogue in Modula-2.
The @ operator (see Section 10.1 [Expressions], page 145), while available with any
language, is not useful with Modula-2. Its intent is to aid the debugging of dynamic arrays,
which cannot be created in Modula-2 as they can in C or C++. However, because an address
can be specified by an integral constant, the construct ‘{type}adrexp’ is still useful.
In gdb scripts, the Modula-2 inequality operator # is interpreted as the beginning of acomment. Use <> instead.

15.4.10 Ada
The extensions made to gdb for Ada only support output from the gnu Ada (GNAT)
compiler. Other Ada compilers are not currently supported, and attempting to debug
executables produced by them is most likely to be difficult.

15.4.10.1 Introduction
The Ada mode of gdb supports a fairly large subset of Ada expression syntax, with someextensions. The philosophy behind the design of this subset is• That gdb should provide basic literals and access to operations for arithmetic, dereferencing, field selection, indexing, and subprogram calls, leaving more sophisticatedcomputations to subprograms written into the program (which therefore may be calledfrom gdb).
• That type safety and strict adherence to Ada language restrictions are not particularly
important to the gdb user.
• That brevity is important to the gdb user.
Thus, for brevity, the debugger acts as if all names declared in user-written packages
are directly visible, even if they are not visible according to Ada rules, thus making it
unnecessary to fully qualify most names with their packages, regardless of context. Where
this causes ambiguity, gdb asks the user’s intent.
The debugger will start in Ada mode if it detects an Ada main program. As for otherlanguages, it will enter Ada mode when stopped in a program that was translated from an
Ada source file.
While in Ada mode, you may use ‘--’ for comments. This is useful mostly for documenting command files. The standard gdb comment (‘#’) still works at the beginning of aline in Ada mode, but not in the middle (to allow based literals).

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15.4.10.2 Omissions from Ada
Here are the notable omissions from the subset:• Only a subset of the attributes are supported:− ’First, ’Last, and ’Length on array objects (not on types and subtypes).
− ’Min and ’Max.
− ’Pos and ’Val.
− ’Tag.
− ’Range on array objects (not subtypes), but only as the right operand of themembership (in) operator.
− ’Access, ’Unchecked_Access, and ’Unrestricted_Access (a GNAT extension).
− ’Address.
− ’Size is available for objects (not types).
− ’Object_Size is available, but not for indefinite types.
• The names in Characters.Latin_1 are not available.
• Equality tests (‘=’ and ‘/=’) on arrays test for bitwise equality of representations. They
will generally work correctly for strings and arrays whose elements have integer orenumeration types. They may not work correctly for arrays whose element types haveuser-defined equality, for arrays of real values (in particular, IEEE-conformant floating
point, because of negative zeroes and NaNs), and for arrays whose elements containunused bits with indeterminate values.
• The other component-by-component array operations (and, or, xor, not, and relational
tests other than equality) are not implemented.
• There is limited support for array and record aggregates. They are permitted only on
the right sides of assignments, as in these examples:(gdb) set An_Array := (1, 2, 3, 4, 5, 6)(gdb) set An_Array := (1, others => 0)(gdb) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)(gdb) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))(gdb) set A_Record := (1, "Peter", True);(gdb) set A_Record := (Name => "Peter", Id => 1, Alive => True)

Changing a discriminant’s value by assigning an aggregate has an undefined effect ifthat discriminant is used within the record. However, you can first modify discriminantsby directly assigning to them (which normally would not be allowed in Ada), and thenperforming an aggregate assignment. For example, given a variable A_Rec declared tohave a type such as:
type Rec (Len : Small_Integer := 0) is record
Id : Integer;
Vals : IntArray (1 .. Len);end record;

you can assign a value with a different size of Vals with two assignments:(gdb) set A_Rec.Len := 4(gdb) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))

As this example also illustrates, gdb is very loose about the usual rules concerning
aggregates. You may leave out some of the components of an array or record aggregate (such as the Len component in the assignment to A_Rec above); they will retain

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their original values upon assignment. You may freely use dynamic values as indices incomponent associations. You may even use overlapping or redundant component associations, although which component values are assigned in such cases is not defined.
• Calls to dispatching subprograms are not implemented.
• The overloading algorithm is much more limited (i.e., less selective) than that of real
Ada. It makes only limited use of the context in which a subexpression appears toresolve its meaning, and it is much looser in its rules for allowing type matches. As aresult, some function calls will be ambiguous, and the user will be asked to choose theproper resolution.
• The new operator is not implemented.
• Entry calls are not implemented.
• Aside from printing, arithmetic operations on the native VAX floating-point formats
are not supported.
• It is not possible to slice a packed array.
• The names True and False, when not part of a qualified name, are interpreted as if
implicitly prefixed by Standard, regardless of context. Should your program redefine
these names in a package or procedure (at best a dubious practice), you will have to
use fully qualified names to access their new definitions.
• Based real literals are not implemented.

15.4.10.3 Additions to Ada
As it does for other languages, gdb makes certain generic extensions to Ada (see Section 10.1
[Expressions], page 145):• If the expression E is a variable residing in memory (typically a local variable or arrayelement) and N is a positive integer, then E@N displays the values of E and the N -1
adjacent variables following it in memory as an array. In Ada, this operator is generally
not necessary, since its prime use is in displaying parts of an array, and slicing willusually do this in Ada. However, there are occasional uses when debugging programs
in which certain debugging information has been optimized away.
• B::var means “the variable named var that appears in function or file B.” When B isa file name, you must typically surround it in single quotes.
• The expression {type} addr means “the variable of type type that appears at address
addr.”• A name starting with ‘$’ is a convenience variable (see Section 10.12 [Convenience
Vars], page 171) or a machine register (see Section 10.14 [Registers], page 179).
In addition, gdb provides a few other shortcuts and outright additions specific to Ada:
• The assignment statement is allowed as an expression, returning its right-hand operandas its value. Thus, you may enter(gdb) set x := y + 3(gdb) print A(tmp := y + 1)

• The semicolon is allowed as an “operator,” returning as its value the value of its righthand operand. This allows, for example, complex conditional breaks:(gdb) break f(gdb) condition 1 (report(i); k += 1; A(k) > 100)

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253• An extension to based literals can be used to specify the exact byte contents of afloating-point literal. After the base, you can use from zero to two ‘l’ characters,
followed by an ‘f’. The number of ‘l’ characters controls the width of the resulting
real constant: zero means Float is used, one means Long_Float, and two means Long_
Long_Float.
(gdb) print 16f#41b80000#$1 = 23.0• Rather than use catenation and symbolic character names to introduce special characters into strings, one may instead use a special bracket notation, which is also used toprint strings. A sequence of characters of the form ‘["XX"]’ within a string or character
literal denotes the (single) character whose numeric encoding is XX in hexadecimal.
The sequence of characters ‘["""]’ also denotes a single quotation mark in strings. For
example,"One line.["0a"]Next line.["0a"]"contains an ASCII newline character (Ada.Characters.Latin_1.LF) after each period.
• The subtype used as a prefix for the attributes ’Pos, ’Min, and ’Max is optional (andis ignored in any case). For example, it is valid to write(gdb) print ’max(x, y)• When printing arrays, gdb uses positional notation when the array has a lower boundof 1, and uses a modified named notation otherwise. For example, a one-dimensional
array of three integers with a lower bound of 3 might print as(3 => 10, 17, 1)

That is, in contrast to valid Ada, only the first component has a => clause.
• You may abbreviate attributes in expressions with any unique, multi-character subsequence of their names (an exact match gets preference). For example, you may use
a’len, a’gth, or a’lh in place of a’length.
• Since Ada is case-insensitive, the debugger normally maps identifiers you type to lower
case. The GNAT compiler uses upper-case characters for some of its internal identifiers,
which are normally of no interest to users. For the rare occasions when you actually
have to look at them, enclose them in angle brackets to avoid the lower-case mapping.
For example,(gdb) print <JMPBUF_SAVE>[0]• Printing an object of class-wide type or dereferencing an access-to-class-wide value will
display all the components of the object’s specific type (as indicated by its run-timetag). Likewise, component selection on such a value will operate on the specific typeof the object.

15.4.10.4 Overloading support for Ada
The debugger supports limited overloading. Given a subprogram call in which the function
symbol has multiple definitions, it will use the number of actual parameters and some
information about their types to attempt to narrow the set of definitions. It also makes
very limited use of context, preferring procedures to functions in the context of the callcommand, and functions to procedures elsewhere.
If, after narrowing, the set of matching definitions still contains more than one definition,
gdb will display a menu to query which one it should use, for instance:(gdb) print f(1)254

Debugging with gdb

Multiple matches for f[0] cancel[1] foo.f (integer) return boolean at foo.adb:23[2] foo.f (foo.new_integer) return boolean at foo.adb:28>

In this case, just select one menu entry either to cancel expression evaluation (type 0
and press RET) or to continue evaluation with a specific instance (type the corresponding
number and press RET).
Here are a couple of commands to customize gdb’s behavior in this case:set ada print-signatures
Control whether parameter types and return types are displayed in overloads
selection menus. It is on by default. See Section 15.4.10.4 [Overloading support
for Ada], page 253.
show ada print-signatures
Show the current setting for displaying parameter types and return types inoverloads selection menu. See Section 15.4.10.4 [Overloading support for Ada],
page 253.

15.4.10.5 Stopping at the Very Beginning
It is sometimes necessary to debug the program during elaboration, and before reaching themain procedure. As defined in the Ada Reference Manual, the elaboration code is invokedfrom a procedure called adainit. To run your program up to the beginning of elaboration,
simply use the following two commands: tbreak adainit and run.

15.4.10.6 Ada Exceptions
A command is provided to list all Ada exceptions:info exceptions
info exceptions regexp
The info exceptions command allows you to list all Ada exceptions definedwithin the program being debugged, as well as their addresses. With a regularexpression, regexp, as argument, only those exceptions whose names matchregexp are listed.
Below is a small example, showing how the command can be used, first without argument, and next with a regular expression passed as an argument.
(gdb) info exceptions
All defined Ada exceptions:constraint_error: 0x613da0
program_error: 0x613d20
storage_error: 0x613ce0
tasking_error: 0x613ca0
const.aint_global_e: 0x613b00(gdb) info exceptions const.aint
All Ada exceptions matching regular expression "const.aint":
constraint_error: 0x613da0
const.aint_global_e: 0x613b00

It is also possible to ask gdb to stop your program’s execution when an exception israised. For more details, see Section 5.1.3 [Set Catchpoints], page 69.

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15.4.10.7 Extensions for Ada Tasks
Support for Ada tasks is analogous to that for threads (see Section 4.10 [Threads], page 47).
gdb provides the following task-related commands:
info tasks
This command shows a list of current Ada tasks, as in the following example:(gdb) info tasksID
TID P-ID Pri StateName
18088000
0
15 Child Activation Wait main_task
280a4000
1
15 Accept Statementb3
809a800
1
15 Child Activation Wait a* 4
80ae800
3
15 Runnablec

In this listing, the asterisk before the last task indicates it to be the task currently being inspected.
ID

Represents gdb’s internal task number.

TID

The Ada task ID.

P-ID

The parent’s task ID (gdb’s internal task number).

Pri

The base priority of the task.

State

Current state of the task.
Unactivated
The task has been created but has not been activated.
It cannot be executing.
Runnable

The task is not blocked for any reason known to Ada.
(It may be waiting for a mutex, though.) It is conceptually "executing" in normal mode.

Terminated
The task is terminated, in the sense of ARM 9.3 (5).
Any dependents that were waiting on terminate alternatives have been awakened and have terminated themselves.
Child Activation Wait
The task is waiting for created tasks to complete activation.
Accept or Select Term
The task is waiting on an accept or selective wait statement.
Waiting on entry call
The task is waiting on an entry call.
Async Select Wait
The task is waiting to start the abortable part of anasynchronous select statement.

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Delay Sleep
The task is waiting on a select statement with only adelay alternative open.
Child Termination Wait
The task is sleeping having completed a master within
itself, and is waiting for the tasks dependent on thatmaster to become terminated or waiting on a terminate
Phase.
Wait Child in Term Alt
The task is sleeping waiting for tasks on terminate alternatives to finish terminating.
Asynchronous Hold
The task has been held by Ada.Asynchronous_Task_
Control.Hold_Task.
Activating
The task has been created and is being made runnable.
Selective Wait
The task is waiting in a selective wait statement.
Accepting RV with taskno
The task is accepting a rendez-vous with the task
taskno.
Waiting on RV with taskno
The task is waiting for a rendez-vous with the task
taskno.
Name

Name of the task in the program.

info task taskno
This command shows detailed information on the specified task, as in the following example:(gdb) info tasksID
TID P-ID Pri State1
8077880
0 15 Child Activation Wait
* 2
807c468
1 15 Runnable(gdb) info task 2
Ada Task: 0x807c468
Name: "task_1"
Thread: 0
LWP: 0x1fac
Parent: 1 ("main_task")
Base Priority: 15
State: Runnable

task

Name
main_task
task_1This command prints the ID and name of the current task.

Chapter 15: Using gdb with Different Languages(gdb) info tasksID
TID P-ID Pri State1
8077870
0 15 Child Activation Wait
* 2
807c458
1 15 Runnable(gdb) task
[Current task is 2 "some_task"]

257

Name
main_task
some_task

task taskno
This command is like the thread thread-id command (see Section 4.10
[Threads], page 47). It switches the context of debugging from the current
task to the given task.

(gdb) info tasksID
TID P-ID Pri StateName
18077870
0 15 Child Activation Wait main_task* 2807c458
1 15 Runnable
some_task(gdb) task 1[Switching to task 1 "main_task"]#0 0x8067726 in pthread_cond_wait ()(gdb) bt
#0 0x8067726 in pthread_cond_wait ()#1 0x8056714 in system.os_interface.pthread_cond_wait ()#2 0x805cb63 in system.task_primitives.operations.sleep ()#3 0x806153e in system.tasking.stages.activate_tasks ()#4 0x804aacc in un () at un.adb:5

task apply [task-id-list | all] [flag]... command
The task apply command is the Ada tasking analogue of thread apply (seeSection 4.10 [Threads], page 47). It allows you to apply the named command
to one or more tasks. Specify the tasks that you want affected using a list oftask IDs, or specify all to apply to all tasks.
The flag arguments control what output to produce and how to handle errors
raised when applying command to a task. flag must start with a - directly
followed by one letter in qcs. If several flags are provided, they must be given
individually, such as -c -q.
By default, gdb displays some task information before the output produced bycommand, and an error raised during the execution of a command will aborttask apply. The following flags can be used to fine-tune this behavior:-c

The flag -c, which stands for ‘continue’, causes any errors in command to be displayed, and the execution of task apply then continues.

-s

The flag -s, which stands for ‘silent’, causes any errors or empty
output produced by a command to be silently ignored. That is,
the execution continues, but the task information and errors are
not printed.

-q

The flag -q (‘quiet’) disables printing the task information.

Flags -c and -s cannot be used together.

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break locspec task taskno
break locspec task taskno if ...
These commands are like the break ... thread ... command (see Section 5.5[Thread Stops], page 92). See Section 9.2 [Location Specifications], page 126,
for the various forms of locspec.
Use the qualifier ‘task taskno’ with a breakpoint command to specify that you
only want gdb to stop the program when a particular Ada task reaches thisbreakpoint. The taskno is one of the numeric task identifiers assigned by gdb,
shown in the first column of the ‘info tasks’ display.
If you do not specify ‘task taskno’ when you set a breakpoint, the breakpoint
applies to all tasks of your program.
You can use the task qualifier on conditional breakpoints as well; in this case,place ‘task taskno’ before the breakpoint condition (before the if).
For example,(gdb) info tasksID
TID P-ID Pri StateName
1 140022020
015 Child Activation Wait main_task
2 140045060
115 Accept/Select Waitt2
3 140044840
1
15 Runnablet1* 4 140056040
1
15 Runnablet3(gdb) b 15 task 2
Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
(gdb) contContinuing.
task # 1 runningtask # 2 running
Breakpoint 5, test_task_debug () at test_task_debug.adb:15
15
flush;(gdb) info tasksID
TID P-ID Pri StateName
1 140022020
015 Child Activation Wait main_task* 2 140045060
1
15 Runnablet2
3 140044840
1
15 Runnablet1
4 140056040
1
15 Delay Sleept3

15.4.10.8 Tasking Support when Debugging Core Files
When inspecting a core file, as opposed to debugging a live program, tasking support may
be limited or even unavailable, depending on the platform being used. For instance, on
x86-linux, the list of tasks is available, but task switching is not supported.
On certain platforms, the debugger needs to perform some memory writes in order toprovide Ada tasking support. When inspecting a core file, this means that the core file must
be opened with read-write privileges, using the command ‘"set write on"’ (see Section 17.6
[Patching], page 285). Under these circumstances, you should make a backup copy of thecore file before inspecting it with gdb.

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15.4.10.9 Tasking Support when using the Ravenscar Profile
The Ravenscar Profile is a subset of the Ada tasking features, specifically designed forsystems with safety-critical real-time requirements.
set ravenscar task-switching on
Allows task switching when debugging a program that uses the Ravenscar Profile. This is the default.
set ravenscar task-switching off
Turn off task switching when debugging a program that uses the Ravenscar
Profile. This is mostly intended to disable the code that adds support for theRavenscar Profile, in case a bug in either gdb or in the Ravenscar runtime ispreventing gdb from working properly. To be effective, this command should
be run before the program is started.
show ravenscar task-switching
Show whether it is possible to switch from task to task in a program using theRavenscar Profile.
When Ravenscar task-switching is enabled, Ravenscar tasks are announced by gdb as if
they were threads:(gdb) continue[New Ravenscar Thread 0x2b8f0]

Both Ravenscar tasks and the underlying CPU threads will show up in the output of
info threads:(gdb) info threads
Id
Target Id
Frame
1
Thread 1 (CPU#0 [running]) simple () at simple.adb:10
2
Thread 2 (CPU#1 [running]) 0x0000000000003d34 in __gnat_initialize_cpu_devices ()3
Thread 3 (CPU#2 [running]) 0x0000000000003d28 in __gnat_initialize_cpu_devices ()4
Thread 4 (CPU#3 [halted ]) 0x000000000000c6ec in system.task_primitives.operations.idle ()* 5Ravenscar Thread 0x2b8f0
simple () at simple.adb:10
6
Ravenscar Thread 0x2f150
0x000000000000c6ec in system.task_primitives.operations.idle ()One known limitation of the Ravenscar support in gdb is that it isn’t currently possible
to single-step through the runtime initialization sequence. If you need to debug this code,
you should use set ravenscar task-switching off.

15.4.10.10 Ada Source Character Set
The GNAT compiler supports a number of character sets for source files. See Section“Character Set Control” in gnat_ugn. gdb includes support for this as well.
set ada source-charset charset
Set the source character set for Ada. The character set must be supportedby GNAT. Because this setting affects the decoding of symbols coming fromthe debug information in your program, the setting should be set as early as
possible. The default is ISO-8859-1, because that is also GNAT’s default.
show ada source-charset
Show the current source character set for Ada.

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15.4.10.11 Known Peculiarities of Ada Mode
Besides the omissions listed previously (see Section 15.4.10.2 [Omissions from Ada],
page 251), we know of several problems with and limitations of Ada mode in gdb, someof which will be fixed with planned future releases of the debugger and the GNU Ada
compiler.
• Static constants that the compiler chooses not to materialize as objects in storage areinvisible to the debugger.
• Named parameter associations in function argument lists are ignored (the argument
lists are treated as positional).
• Many useful library packages are currently invisible to the debugger.
• Fixed-point arithmetic, conversions, input, and output is carried out using floatingpoint arithmetic, and may give results that only approximate those on the host machine.
• The GNAT compiler never generates the prefix Standard for any of the standard
symbols defined by the Ada language. gdb knows about this: it will strip the prefixfrom names when you use it, and will never look for a name you have so qualified
among local symbols, nor match against symbols in other packages or subprograms. If
you have defined entities anywhere in your program other than parameters and local
variables whose simple names match names in Standard, GNAT’s lack of qualification
here can cause confusion. When this happens, you can usually resolve the confusion
by qualifying the problematic names with package Standard explicitly.
Older versions of the compiler sometimes generate erroneous debugging information,
resulting in the debugger incorrectly printing the value of affected entities. In some cases,
the debugger is able to work around an issue automatically. In other cases, the debugger isable to work around the issue, but the work-around has to be specifically enabled.
set ada trust-PAD-over-XVS on
Configure GDB to strictly follow the GNAT encoding when computing thevalue of Ada entities, particularly when PAD and PAD___XVS types are involved(see ada/exp_dbug.ads in the GCC sources for a complete description of theencoding used by the GNAT compiler). This is the default.
set ada trust-PAD-over-XVS off
This is related to the encoding using by the GNAT compiler. If gdb sometimes
prints the wrong value for certain entities, changing ada trust-PAD-over-XVS
to off activates a work-around which may fix the issue. It is always safe to set
ada trust-PAD-over-XVS to off, but this incurs a slight performance penalty,
so it is recommended to leave this setting to on unless necessary.
Internally, the debugger also relies on the compiler following a number of conventions
known as the ‘GNAT Encoding’, all documented in gcc/ada/exp_dbug.ads in the GCC
sources. This encoding describes how the debugging information should be generated forcertain types. In particular, this convention makes use of descriptive types, which are
artificial types generated purely to help the debugger.
These encodings were defined at a time when the debugging information format used was
not powerful enough to describe some of the more complex types available in Ada. Since
DWARF allows us to express nearly all Ada features, the long-term goal is to slowly replace

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261

these descriptive types by their pure DWARF equivalent. To facilitate that transition, a
new maintenance option is available to force the debugger to ignore those descriptive types.
It allows the user to quickly evaluate how well gdb works without them.
maintenance ada set ignore-descriptive-types [on|off]
Control whether the debugger should ignore descriptive types. The default is
not to ignore descriptives types (off).
maintenance ada show ignore-descriptive-types
Show if descriptive types are ignored by gdb.

15.5 Unsupported Languages
In addition to the other fully-supported programming languages, gdb also provides apseudo-language, called minimal. It does not represent a real programming language, but
provides a set of capabilities close to what the C or assembly languages provide. This should
allow most simple operations to be performed while debugging an application that uses alanguage currently not supported by gdb.
If the language is set to auto, gdb will automatically select this language if the current
frame corresponds to an unsupported language.

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16 Examining the Symbol Table
The commands described in this chapter allow you to inquire about the symbols (namesof variables, functions and types) defined in your program. This information is inherent in
the text of your program and does not change as your program executes. gdb finds it inyour program’s symbol table, in the file indicated when you started gdb (see Section 2.1.1[Choosing Files], page 12), or by one of the file-management commands (see Section 18.1
[Commands to Specify Files], page 291).
Occasionally, you may need to refer to symbols that contain unusual characters, which
gdb ordinarily treats as word delimiters. The most frequent case is in referring to static
variables in other source files (see Section 10.3 [Program Variables], page 147). File names
are recorded in object files as debugging symbols, but gdb would ordinarily parse a typicalfile name, like foo.c, as the three words ‘foo’ ‘.’ ‘c’. To allow gdb to recognize ‘foo.c’ asa single symbol, enclose it in single quotes; for example,
p ’foo.c’::xlooks up the value of x in the scope of the file foo.c.
set case-sensitive on
set case-sensitive off
set case-sensitive auto
Normally, when gdb looks up symbols, it matches their names with case sensitivity determined by the current source language. Occasionally, you may wish
to control that. The command set case-sensitive lets you do that by specifying on for case-sensitive matches or off for case-insensitive ones. If you specify
auto, case sensitivity is reset to the default suitable for the source language.
The default is case-sensitive matches for all languages except for Fortran, forwhich the default is case-insensitive matches.
show case-sensitive
This command shows the current setting of case sensitivity for symbols lookups.
set print type methods
set print type methods on
set print type methods off
Normally, when gdb prints a class, it displays any methods declared in thatclass. You can control this behavior either by passing the appropriate flag
to ptype, or using set print type methods. Specifying on will cause gdb todisplay the methods; this is the default. Specifying off will cause gdb to omit
the methods.
show print type methods
This command shows the current setting of method display when printingclasses.
set print type nested-type-limit limit
set print type nested-type-limit unlimited
Set the limit of displayed nested types that the type printer will show. A limit
of unlimited or -1 will show all nested definitions. By default, the type printerwill not show any nested types defined in classes.

264

Debugging with gdb

show print type nested-type-limit
This command shows the current display limit of nested types when printingclasses.
set print type typedefs
set print type typedefs on
set print type typedefs off
Normally, when gdb prints a class, it displays any typedefs defined in that class.
You can control this behavior either by passing the appropriate flag to ptype,or using set print type typedefs. Specifying on will cause gdb to display thetypedef definitions; this is the default. Specifying off will cause gdb to omit
the typedef definitions. Note that this controls whether the typedef definition
itself is printed, not whether typedef names are substituted when printing othertypes.
show print type typedefs
This command shows the current setting of typedef display when printingclasses.
set print type hex
set print type hex on
set print type hex off
When gdb prints sizes and offsets of struct members, it can use either thedecimal or hexadecimal notation. You can select one or the other either bypassing the appropriate flag to ptype, or by using the set print type hex
command.
show print type hex
This command shows whether the sizes and offsets of struct members are printed
in decimal or hexadecimal notation.
info address symbol
Describe where the data for symbol is stored. For a register variable, this says
which register it is kept in. For a non-register local variable, this prints thestack-frame offset at which the variable is always stored.
Note the contrast with ‘print &symbol’, which does not work at all for a registervariable, and for a stack local variable prints the exact address of the current
instantiation of the variable.
info symbol addr
Print the name of a symbol which is stored at the address addr. If no symbol
is stored exactly at addr, gdb prints the nearest symbol and an offset from it:(gdb) info symbol 0x54320_initialize_vx + 396 in section .text

This is the opposite of the info address command. You can use it to find out
the name of a variable or a function given its address.
For dynamically linked executables, the name of executable or shared library
containing the symbol is also printed:(gdb) info symbol 0x400225_start + 5 in section .text of /tmp/a.out

Chapter 16: Examining the Symbol Table

265(gdb) info symbol 0x2aaaac2811cf__read_nocancel + 6 in section .text of /usr/lib64/libc.so.6

demangle [-l language] [--] nameDemangle name. If language is provided it is the name of the language todemangle name in. Otherwise name is demangled in the current language.
The ‘--’ option specifies the end of options, and is useful when name begins
with a dash.
The parameter demangle-style specifies how to interpret the kind of mangling
used. See Section 10.9 [Print Settings], page 157.
whatis[/flags] [arg]Print the data type of arg, which can be either an expression or a name of adata type. With no argument, print the data type of $, the last value in thevalue history.
If arg is an expression (see Section 10.1 [Expressions], page 145), it is not
actually evaluated, and any side-effecting operations (such as assignments orfunction calls) inside it do not take place.
If arg is a variable or an expression, whatis prints its literal type as it is usedin the source code. If the type was defined using a typedef, whatis will notprint the data type underlying the typedef. If the type of the variable or the
expression is a compound data type, such as struct or class, whatis neverprints their fields or methods. It just prints the struct/class name (a.k.a.
its tag). If you want to see the members of such a compound data type, use
ptype.
If arg is a type name that was defined using typedef, whatis unrolls only one
level of that typedef. Unrolling means that whatis will show the underlying
type used in the typedef declaration of arg. However, if that underlying typeis also a typedef, whatis will not unroll it.
For C code, the type names may also have the form ‘class class-name’,‘struct struct-tag’, ‘union union-tag’ or ‘enum enum-tag’.
flags can be used to modify how the type is displayed. Available flags are:r

Display in “raw” form. Normally, gdb substitutes template parameters and typedefs defined in a class when printing the class’
members. The /r flag disables this.

m

Do not print methods defined in the class.

M

Print methods defined in the class. This is the default, but the flag
exists in case you change the default with set print type methods.

t

Do not print typedefs defined in the class. Note that this controls
whether the typedef definition itself is printed, not whether typedef
names are substituted when printing other types.

T

Print typedefs defined in the class. This is the default, but theflag exists in case you change the default with set print typetypedefs.

266

Debugging with gdb

oPrint the offsets and sizes of fields in a struct, similar to what the
pahole tool does. This option implies the /tm flags.

x

Use hexadecimal notation when printing offsets and sizes of fields
in a struct.

d

Use decimal notation when printing offsets and sizes of fields in a
struct.
For example, given the following declarations:struct tuv{
int a1;char *a2;
int a3;};struct xyz{
int f1;char f2;
void *f3;
struct tuv f4;};
union qwe{struct tuv fff1;
struct xyz fff2;};
struct tyu{
int a1 : 1;
int a2 : 3;
int a3 : 23;
char a4 : 2;
int64_t a5;
int a6 : 5;
int64_t a7 : 3;};

Issuing a ptype /o struct tuv command would print:(gdb) ptype /o struct tuv/* offset|
size *//*
0|
4 *//* XXX 4-byte hole
*/
/*
8
|
8 */
/*
16
|
4 */

type = struct tuv {int a1;char *a2;
int a3;/* total size (bytes):

24 */

}

Notice the format of the first column of comments. There, you
can find two parts separated by the ‘|’ character: the offset, whichindicates where the field is located inside the struct, in bytes, andthe size of the field. Another interesting line is the marker of a hole

Chapter 16: Examining the Symbol Table267

in the struct, indicating that it may be possible to pack the structand make it use less space by reorganizing its fields.
It is also possible to print offsets inside an union:(gdb) ptype /o union qwe/* offset|
size */
/*
24 */
/*
0
|
4 */
/* XXX 4-byte hole
*/
/*
8
|
8 */
/*
16
|
4 */

/*
/*
0
|
/*
4
|
/* XXX 3-byte hole
/*
8
|
/*
16
|
/*
16
|
/* XXX 4-byte hole
/*
24
|
/*
32
|

type = union qwe {struct tuv {int a1;char *a2;
int a3;/* total size (bytes):} fff1;struct xyz {int f1;char f2;

40 */
4 */
1 */
*/
8 */
24 */
4 */
*/
8 */
4 */

24 */

void *f3;
struct tuv {int a1;char *a2;
int a3;/* total size (bytes):} f4;/* total size (bytes):} fff2;/* total size (bytes):

40 */

40 */

}

In this case, since struct tuv and struct xyz occupy the same
space (because we are dealing with an union), the offset is notprinted for them. However, you can still examine the offset of eachof these structures’ fields.
Another useful scenario is printing the offsets of a struct containing
bitfields:(gdb) ptype /o struct tyu/* offset|
size */
/*
0:31
|
4 */
/*
0:28
|
4 */
/*
0: 5
|
4 */
/*
3: 3
|
1 */
/* XXX 3-bit hole*//* XXX 4-byte hole
*/
/*
8
|
8 */
/*
16: 0
|
4 */
/*
16: 5
|
8 */
/* XXX 7-byte padding*/

type = struct tyu {int a1 : 1;
int a2 : 3;
int a3 : 23;
signed char a4 : 2;

int64_t a5;
int a6 : 5;
int64_t a7 : 3;/* total size (bytes):

24 */

24 */

}

Note how the offset information is now extended to also include thefirst bit of the bitfield.

268

Debugging with gdb

ptype[/flags] [arg]ptype accepts the same arguments as whatis, but prints a detailed descriptionof the type, instead of just the name of the type. See Section 10.1 [Expressions],
page 145.
Contrary to whatis, ptype always unrolls any typedefs in its argument declaration, whether the argument is a variable, expression, or a data type. Thismeans that ptype of a variable or an expression will not print literally its typeas present in the source code—use whatis for that. typedefs at the pointeror reference targets are also unrolled. Only typedefs of fields, methods andinner class typedefs of structs, classes and unions are not unrolled evenwith ptype.
For example, for this variable declaration:
typedef double real_t;
struct complex { real_t real; double imag; };typedef struct complex complex_t;
complex_t var;
real_t *real_pointer_var;

the two commands give this output:(gdb) whatis var
type = complex_t(gdb) ptype var
type = struct complex {real_t real;
double imag;}(gdb) whatis complex_ttype = struct complex(gdb) whatis struct complex
type = struct complex(gdb) ptype struct complex
type = struct complex {real_t real;
double imag;}(gdb) whatis real_pointer_var
type = real_t *(gdb) ptype real_pointer_var
type = double *As with whatis, using ptype without an argument refers to the type of $, thelast value in the value history.
Sometimes, programs use opaque data types or incomplete specifications ofcomplex data structure. If the debug information included in the program
does not allow gdb to display a full declaration of the data type, it will say‘<incomplete type>’. For example, given these declarations:struct foo;
struct foo *fooptr;

but no definition for struct foo itself, gdb will say:(gdb) ptype foo$1 = <incomplete type>“Incomplete type” is C terminology for data types that are not completely
specified.

Chapter 16: Examining the Symbol Table

269

Othertimes, information about a variable’s type is completely absent from thedebug information included in the program. This most often happens when the
program or library where the variable is defined includes no debug information
at all. gdb knows the variable exists from inspecting the linker/loader symbol
table (e.g., the ELF dynamic symbol table), but such symbols do not containtype information. Inspecting the type of a (global) variable for which gdb has
no type information shows:(gdb) ptype var
type = <data variable, no debug info>

See Section 10.3 [Variables], page 147, for how to print the values of suchvariables.
info types [-q] [regexp]
Print a brief description of all types whose names match the regular expression
regexp (or all types in your program, if you supply no argument). Each complete
typename is matched as though it were a complete line; thus, ‘i type value’
gives information on all types in your program whose names include the stringvalue, but ‘i type ^value$’ gives information only on types whose complete
name is value.
In programs using different languages, gdb chooses the syntax to print the typedescription according to the ‘set language’ value: using ‘set language auto’(see Section 15.1.3 [Set Language Automatically], page 228) means to use thelanguage of the type, other values mean to use the manually specified language(see Section 15.1.2 [Set Language Manually], page 228).
This command differs from ptype in two ways: first, like whatis, it does notprint a detailed description; second, it lists all source files and line numbers
where a type is defined.
The output from ‘into types’ is proceeded with a header line describing whattypes are being listed. The optional flag ‘-q’, which stands for ‘quiet’, disables
printing this header information.
info type-printers
Versions of gdb that ship with Python scripting enabled may have “type printers” available. When using ptype or whatis, these printers are consulted
when the name of a type is needed. See Section 23.3.2.9 [Type Printing API],
page 429, for more information on writing type printers.
info type-printers displays all the available type printers.
enable type-printer name...
disable type-printer name...
These commands can be used to enable or disable type printers.
info scope locspec
List all the variables local to the lexical scope of the code location that resultsfrom resolving locspec. See Section 9.2 [Location Specifications], page 126, fordetails about supported forms of locspec. For example:(gdb) info scope command line handler
Scope for command_line_handler:
Symbol rl is an argument at stack/frame offset 8, length 4.

270

Debugging with gdb

Symbol linebuffer is in static storage at address 0x150a18, length 4.
Symbol linelength is in static storage at address 0x150a1c, length 4.
Symbol p is a local variable in register $esi, length 4.
Symbol p1 is a local variable in register $ebx, length 4.
Symbol nline is a local variable in register $edx, length 4.
Symbol repeat is a local variable at frame offset -8, length 4.

This command is especially useful for determining what data to collect duringa trace experiment, see Section 13.1.6 [Tracepoint Actions], page 208.
info sourceShow information about the current source file—that is, the source file for thefunction containing the current point of execution:• the name of the source file, and the directory containing it,• the directory it was compiled in,• its length, in lines,• which programming language it is written in,• if the debug information provides it, the program that compiled the file(which may include, e.g., the compiler version and command line arguments),• whether the executable includes debugging information for that file, and if
so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and• whether the debugging information includes information about preprocessor macros.
info sources [-dirname | -basename] [--] [regexp]
With no options ‘info sources’ prints the names of all source files in your program for which there is debugging information. The source files are presented
based on a list of object files (executables and libraries) currently loaded into
gdb. For each object file all of the associated source files are listed.
Each source file will only be printed once for each object file, but a single source
file can be repeated in the output if it is part of multiple object files.
If the optional regexp is provided, then only source files that match the regularexpression will be printed. The matching is case-sensitive, except on operating
systems that have case-insensitive filesystem (e.g., MS-Windows). ‘--’ can beused before regexp to prevent gdb interpreting regexp as a command option(e.g. if regexp starts with ‘-’).
By default, the regexp is used to match anywhere in the filename. If -dirname,only files having a dirname matching regexp are shown. If -basename, only files
having a basename matching regexp are shown.
It is possible that an object file may be printed in the list with no associatedsource files. This can happen when either no source files match regexp, or, theobject file was compiled without debug information and so gdb is unable tofind any source file names.
info functions [-q] [-n]Print the names and data types of all defined functions. Similarly to ‘info
types’, this command groups its output by source files and annotates eachfunction definition with its source line number.

Chapter 16: Examining the Symbol Table

271

In programs using different languages, gdb chooses the syntax to print the function name and type according to the ‘set language’ value: using ‘set language
auto’ (see Section 15.1.3 [Set Language Automatically], page 228) means to use
the language of the function, other values mean to use the manually specified
language (see Section 15.1.2 [Set Language Manually], page 228).
The ‘-n’ flag excludes non-debugging symbols from the results.
A
non-debugging symbol is a symbol that comes from the executable’s symbol
table, not from the debug information (for example, DWARF) associated withthe executable.
The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no functions have been printed.
info functions [-q] [-n] [-t type_regexp] [regexp]
Like ‘info functions’, but only print the names and data types of the functions
selected with the provided regexp(s).
If regexp is provided, print only the functions whose names match the regular expression regexp. Thus, ‘info fun step’ finds all functions whose names
include step; ‘info fun ^step’ finds those whose names start with step. If
a function name contains characters that conflict with the regular expression
language (e.g. ‘operator*()’), they may be quoted with a backslash.
If type regexp is provided, print only the functions whose types, as printed by
the whatis command, match the regular expression type regexp. If type regexp
contains space(s), it should be enclosed in quote characters. If needed, use backslash to escape the meaning of special characters or quotes. Thus, ‘info fun -t’^int (’’ finds the functions that return an integer; ‘info fun -t ’(.*int.*’’finds the functions that have an argument type containing int; ‘info fun -t’^int (’ ^step’ finds the functions whose names start with step and that
return int.
If both regexp and type regexp are provided, a function is printed only if its
name matches regexp and its type matches type regexp.
info variables [-q] [-n]Print the names and data types of all variables that are defined outside offunctions (i.e. excluding local variables). The printed variables are grouped bysource files and annotated with their respective source line numbers.
In programs using different languages, gdb chooses the syntax to print thevariable name and type according to the ‘set language’ value: using ‘set
language auto’ (see Section 15.1.3 [Set Language Automatically], page 228)
means to use the language of the variable, other values mean to use the manuallyspecified language (see Section 15.1.2 [Set Language Manually], page 228).
The ‘-n’ flag excludes non-debugging symbols from the results.
The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no variables have been printed.
info variables [-q] [-n] [-t type_regexp] [regexp]
Like info variables, but only print the variables selected with the provided
regexp(s).

272

Debugging with gdb

If regexp is provided, print only the variables whose names match the regularexpression regexp.
If type regexp is provided, print only the variables whose types, as printed by
the whatis command, match the regular expression type regexp. If type regexp
contains space(s), it should be enclosed in quote characters. If needed, usebackslash to escape the meaning of special characters or quotes.
If both regexp and type regexp are provided, an argument is printed only if its
name matches regexp and its type matches type regexp.
info modules [-q] [regexp]
List all Fortran modules in the program, or all modules matching the optional
regular expression regexp.
The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no modules have been printed.
info module functions [-q] [-m module-regexp] [-t type-regexp] [regexp]
info module variables [-q] [-m module-regexp] [-t type-regexp] [regexp]
List all functions or variables within all Fortran modules. The set of functions
or variables listed can be limited by providing some or all of the optional regularexpressions. If module-regexp is provided, then only Fortran modules matchingmodule-regexp will be searched. Only functions or variables whose type matches
the optional regular expression type-regexp will be listed. And only functions
or variables whose name matches the optional regular expression regexp will belisted.
The optional flag ‘-q’, which stands for ‘quiet’, disables printing header information and messages explaining why no functions or variables have been
printed.
info main Print the name of the starting function of the program. This serves primarily
Fortran programs, which have a user-supplied name for the main subroutine.
info classes
info classes regexp
Display all Objective-C classes in your program, or (with the regexp argument)
all those matching a particular regular expression.
info selectors
info selectors regexp
Display all Objective-C selectors in your program, or (with the regexp argument) all those matching a particular regular expression.
set opaque-type-resolution on
Tell gdb to resolve opaque types. An opaque type is a type declared as apointer to a struct, class, or union—for example, struct MyType *—that
is used in one source file although the full declaration of struct MyType is in
another source file. The default is on.
A change in the setting of this subcommand will not take effect until the nexttime symbols for a file are loaded.

Chapter 16: Examining the Symbol Table273

set opaque-type-resolution off
Tell gdb not to resolve opaque types. In this case, the type is printed as follows:{<no data fields>}

show opaque-type-resolution
Show whether opaque types are resolved or not.
set print symbol-loading
set print symbol-loading fullset print symbol-loading brief
set print symbol-loading off
The set print symbol-loading command allows you to control the printing of
messages when gdb loads symbol information. By default a message is printed
for the executable and one for each shared library, and normally this is what you
want. However, when debugging apps with large numbers of shared libraries
these messages can be annoying. When set to brief a message is printed foreach executable, and when gdb loads a collection of shared libraries at once itwill only print one message regardless of the number of shared libraries. Whenset to off no messages are printed.
show print symbol-loading
Show whether messages will be printed when a gdb command entered from the
keyboard causes symbol information to be loaded.
maint print symbols [-pc address] [filename]maint print symbols [-objfile objfile] [-source source] [--] [filename]maint print psymbols [-objfile objfile] [-pc address] [--] [filename]maint print psymbols [-objfile objfile] [-source source] [--] [filename]maint print msymbols [-objfile objfile] [--] [filename]Write a dump of debugging symbol data into the file filename or the terminal if
filename is unspecified. If -objfile objfile is specified, only dump symbols
for that objfile. If -pc address is specified, only dump symbols for the file withcode at that address. Note that address may be a symbol like main. If -source
source is specified, only dump symbols for that source file.
These commands are used to debug the gdb symbol-reading code. These commands do not modify internal gdb state, therefore ‘maint print symbols’ will
only print symbols for already expanded symbol tables. You can use the command info sources to find out which files these are. If you use ‘maint print
psymbols’ instead, the dump shows information about symbols that gdb only
knows partially—that is, symbols defined in files that gdb has skimmed, but
not yet read completely. Finally, ‘maint print msymbols’ just dumps “minimal
symbols”, e.g., “ELF symbols”.
See Section 18.1 [Commands to Specify Files], page 291, for a discussion of how
gdb reads symbols (in the description of symbol-file).
maint info symtabs [ regexp ]maint info psymtabs [ regexp ]List the struct symtab or struct partial_symtab structures whose names
match regexp. If regexp is not given, list them all. The output includes expres-274

Debugging with gdb

sions which you can copy into a gdb debugging this one to examine a particular
structure in more detail. For example:(gdb) maint info psymtabs dwarf2read{ objfile /home/gnu/build/gdb/gdb((struct objfile *) 0x82e69d0){ psymtab /home/gnu/src/gdb/dwarf2read.c((struct partial_symtab *) 0x8474b10)
readin no
fullname (null)text addresses 0x814d3c8 -- 0x8158074
globals (* (struct partial_symbol **) 0x8507a08 @ 9)
statics (* (struct partial_symbol **) 0x40e95b78 @ 2882)
dependencies (none)}}(gdb) maint info symtabs(gdb)

We see that there is one partial symbol table whose filename contains the string‘dwarf2read’, belonging to the ‘gdb’ executable; and we see that gdb has notread in any symtabs yet at all. If we set a breakpoint on a function, that willcause gdb to read the symtab for the compilation unit containing that function:(gdb) break dwarf2_psymtab_to_symtab
Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,line 1574.
(gdb) maint info symtabs{ objfile /home/gnu/build/gdb/gdb((struct objfile *) 0x82e69d0){ symtab /home/gnu/src/gdb/dwarf2read.c((struct symtab *) 0x86c1f38)
dirname (null)
fullname (null)
blockvector ((struct blockvector *) 0x86c1bd0) (primary)linetable ((struct linetable *) 0x8370fa0)
debugformat DWARF 2
}
}
(gdb)

maint info line-table [ regexp ]List the struct linetable from all struct symtab instances whose namematches regexp. If regexp is not given, list the struct linetable from all
struct symtab. For example:(gdb) maint info line-tableobjfile: /home/gnu/build/a.out ((struct objfile *) 0x6120000e0d40)
compunit_symtab: simple.cpp ((struct compunit_symtab *) 0x6210000ff450)
symtab: /home/gnu/src/simple.cpp ((struct symtab *) 0x6210000ff4d0)
linetable: ((struct linetable *) 0x62100012b760):
INDEX LINEADDRESS
IS-STMT PROLOGUE-END EPILOGUE-BEGIN
030x0000000000401110 Y
1
40x0000000000401114 YYY
2
90x0000000000401120 Y
3
100x0000000000401124 Y
Y
4
10
0x0000000000401129 YY
5
15
0x0000000000401130 Y
6160x0000000000401134 YY
7
16
0x0000000000401139

275

8
9
10
11

21
22
22
END

0x0000000000401140 Y
0x000000000040114f Y
0x0000000000401154
0x000000000040115a YYYYThe ‘IS-STMT’ column indicates if the address is a recommended breakpoint
location to represent a line or a statement. The ‘PROLOGUE-END’ column indicates that a given address is an adequate place to set a breakpoint at the first
instruction following a function prologue. The ‘EPILOGUE-BEGIN’ column indicates that a given address marks the point where a block’s frame is destroyed,
making local variables hard or impossible to find.
set always-read-ctf [on|off]show always-read-ctf
When off, CTF debug info is only read if DWARF debug info is not present.
When on, CTF debug info is read regardless of whether DWARF debug info ispresent. The default value is off.
maint set symbol-cache-size size
Set the size of the symbol cache to size. The default size is intended to begood enough for debugging most applications. This option exists to allow forexperimenting with different sizes.
maint show symbol-cache-sizeShow the size of the symbol cache.
maint print symbol-cache
Print the contents of the symbol cache. This is useful when debugging symbol
cache issues.
maint print symbol-cache-statistics
Print symbol cache usage statistics. This helps determine how well the cache
is being utilized.
maint flush symbol-cachemaint flush-symbol-cache
Flush the contents of the symbol cache, all entries are removed. This commandis useful when debugging the symbol cache. It is also useful when collecting
performance data. The command maint flush-symbol-cache is deprecated infavor of maint flush symbol-cache..
maint set ignore-prologue-end-flag [on|off]
Enable or disable the use of the ‘PROLOGUE-END’ flag from the line-table. When‘off’ (the default), gdb uses the ‘PROLOGUE-END’ flag to place breakpoints past
the end of a function prologue. When ‘on’, gdb ignores the flag and relies on
prologue analyzers to skip function prologues.
maint show ignore-prologue-end-flag
Show whether gdb will ignore the ‘PROLOGUE-END’ flag.

277

17 Altering Execution
Once you think you have found an error in your program, you might want to find out for
certain whether correcting the apparent error would lead to correct results in the rest of therun. You can find the answer by experiment, using the gdb features for altering executionof the program.
For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function.

17.1 Assignment to Variables
To alter the value of a variable, evaluate an assignment expression. See Section 10.1 [Expressions], page 145. For example,
print x=4

stores the value 4 into the variable x, and then prints the value of the assignment expression(which is 4). See Chapter 15 [Using gdb with Different Languages], page 227, for more
information on operators in supported languages.
If you are not interested in seeing the value of the assignment, use the set command
instead of the print command. set is really the same as print except that the expression’svalue is not printed and is not put in the value history (see Section 10.11 [Value History],
page 170). The expression is evaluated only for its effects.
If the beginning of the argument string of the set command appears identical to aset subcommand, use the set variable command instead of just set. This command is
identical to set except for its lack of subcommands. For example, if your program has avariable width, you get an error if you try to set a new value with just ‘set width=13’,
because gdb has the command set width:(gdb) whatis width
type = double(gdb) p width$4 = 13(gdb) set width=47
Invalid syntax in expression.

The invalid expression, of course, is ‘=47’. In order to actually set the program’s variablewidth, use(gdb) set var width=47

Because the set command has many subcommands that can conflict with the names ofprogram variables, it is a good idea to use the set variable command instead of just set.
For example, if your program has a variable g, you run into problems if you try to set a
new value with just ‘set g=4’, because gdb has the command set gnutarget, abbreviatedset g:

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type = double(gdb) p g
$1 = 1(gdb) set g=4(gdb) p g
$2 = 1(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) yStarting program: /home/smith/cc_progs/a.out"/home/smith/cc_progs/a.out": can’t open to read symbols:
Invalid bfd target.
(gdb) show g
The current BFD target is "=4".

The program variable g did not change, and you silently set the gnutarget to an invalid
value. In order to set the variable g, use(gdb) set var g=4

gdb allows more implicit conversions in assignments than C; you can freely store an
integer value into a pointer variable or vice versa, and you can convert any structure to any
other structure that is the same length or shorter.
To store values into arbitrary places in memory, use the ‘{...}’ construct to generate avalue of specified type at a specified address (see Section 10.1 [Expressions], page 145). For
example, {int}0x83040 refers to memory location 0x83040 as an integer (which implies acertain size and representation in memory), andset {int}0x83040 = 4

stores the value 4 into that memory location.

17.2 Continuing at a Different Address
Ordinarily, when you continue your program, you do so at the place where it stopped, withthe continue command. You can instead continue at an address of your own choosing,with the following commands:
jump locspec
j locspec Resume execution at the address of the code location that results from resolving
locspec. See Section 9.2 [Location Specifications], page 126, for a descriptionof the different forms of locspec. If locspec resolves to more than one address,
those outside the current compilation unit are ignored. If considering just theaddresses in the current compilation unit still doesn’t yield a unique address,
the command aborts before jumping. Execution stops again immediately ifthere is a breakpoint there. It is common practice to use the tbreak commandin conjunction with jump. See Section 5.1.1 [Setting Breakpoints], page 58.
The jump command does not change the current stack frame, or the stack
pointer, or the contents of any memory location or any register other than the
program counter. If locspec resolves to an address in a different function fromthe one currently executing, the results may be bizarre if the two functions
expect different patterns of arguments or of local variables. For this reason, thejump command requests confirmation if the jump address is not in the function

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currently executing. However, even bizarre results are predictable if you arewell acquainted with the machine-language code of your program.
On many systems, you can get much the same effect as the jump command by storinga new value into the register $pc. The difference is that this does not start your program
running; it only changes the address of where it will run when you continue. For example,
set $pc = 0x485

makes the next continue command or stepping command execute at address 0x485, rather
than at the address where your program stopped. See Section 5.2 [Continuing and Stepping],
page 83.
However, writing directly to $pc will only change the value of the program-counterregister, while using jump will ensure that any additional auxiliary state is also updated.
For example, on SPARC, jump will update both $pc and $npc registers prior to resuming
execution. When using the approach of writing directly to $pc it is your job to also update
the $npc register.
The most common occasion to use the jump command is to back up—perhaps with more
breakpoints set—over a portion of a program that has already executed, in order to examine
its execution in more detail.

17.3 Giving your Program a Signal
signal signal
Resume execution where your program is stopped, but immediately give it
the signal signal. The signal can be the name or the number of a signal.
For example, on many systems signal 2 and signal SIGINT are both waysof sending an interrupt signal.
Alternatively, if signal is zero, continue execution without giving a signal. Thisis useful when your program stopped on account of a signal and would ordinarily
see the signal when resumed with the continue command; ‘signal 0’ causes it
to resume without a signal.
Note: When resuming a multi-threaded program, signal is delivered to thecurrently selected thread, not the thread that last reported a stop. This includes
the situation where a thread was stopped due to a signal. So if you want tocontinue execution suppressing the signal that stopped a thread, you should
select that same thread before issuing the ‘signal 0’ command. If you issue
the ‘signal 0’ command with another thread as the selected one, gdb detectsthat and asks for confirmation.
Invoking the signal command is not the same as invoking the kill utility fromthe shell. Sending a signal with kill causes gdb to decide what to do withthe signal depending on the signal handling tables (see Section 5.4 [Signals],
page 89). The signal command passes the signal directly to your program.
signal does not repeat when you press RET a second time after executing thecommand.
queue-signal signal
Queue signal to be delivered immediately to the current thread when executionof the thread resumes. The signal can be the name or the number of a signal.

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For example, on many systems signal 2 and signal SIGINT are both ways of
sending an interrupt signal. The handling of the signal must be set to pass
the signal to the program, otherwise gdb will report an error. You can control
the handling of signals from gdb with the handle command (see Section 5.4[Signals], page 89).
Alternatively, if signal is zero, any currently queued signal for the current thread
is discarded and when execution resumes no signal will be delivered. This isuseful when your program stopped on account of a signal and would ordinarily
see the signal when resumed with the continue command.
This command differs from the signal command in that the signal is justqueued, execution is not resumed. And queue-signal cannot be used to passa signal whose handling state has been set to nopass (see Section 5.4 [Signals],
page 89).
See [stepping into signal handlers], page 91, for information on how stepping commands
behave when the thread has a signal queued.

17.4 Returning from a Function
returnreturn expression
You can cancel execution of a function call with the return command. If you
give an expression argument, its value is used as the function’s return value.
When you use return, gdb discards the selected stack frame (and all frames within it).
You can think of this as making the discarded frame return prematurely. If you wish to
specify a value to be returned, give that value as the argument to return.
This pops the selected stack frame (see Section 8.3 [Selecting a Frame], page 117), andany other frames inside of it, leaving its caller as the innermost remaining frame. Thatframe becomes selected. The specified value is stored in the registers used for returning
values of functions.
The return command does not resume execution; it leaves the program stopped in thestate that would exist if the function had just returned. In contrast, the finish command(see Section 5.2 [Continuing and Stepping], page 83) resumes execution until the selected
stack frame returns naturally.
gdb needs to know how the expression argument should be set for the inferior. The
concrete registers assignment depends on the OS ABI and the type being returned by theselected stack frame. For example it is common for OS ABI to return floating point values
in FPU registers while integer values in CPU registers. Still some ABIs return even floating
point values in CPU registers. Larger integer widths (such as long long int) also havespecific placement rules. gdb already knows the OS ABI from its current target so it needs
to find out also the type being returned to make the assignment into the right register(s).
Normally, the selected stack frame has debug info. gdb will always use the debug info
instead of the implicit type of expression when the debug info is available. For example,
if you type return -1, and the function in the current stack frame is declared to return along long int, gdb transparently converts the implicit int value of -1 into a long longint:

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Breakpoint 1, func () at gdb.base/return-nodebug.c:29
29
return 31;(gdb) return -1
Make func return now? (y or n) y
#0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
43
printf ("result=%lld\n", func ());
(gdb)

However, if the selected stack frame does not have a debug info, e.g., if the function wascompiled without debug info, gdb has to find out the type to return from user. Specifying
a different type by mistake may set the value in different inferior registers than the caller
code expects. For example, typing return -1 with its implicit type int would set only
a part of a long long int result for a debug info less function (on 32-bit architectures).
Therefore the user is required to specify the return type by an appropriate cast explicitly:
Breakpoint 2, 0x0040050b in func ()(gdb) return -1
Return value type not available for selected stack frame.
Please use an explicit cast of the value to return.
(gdb) return (long long int) -1
Make selected stack frame return now? (y or n) y
#0 0x00400526 in main ()(gdb)

17.5 Calling Program Functions
print expr
Evaluate the expression expr and display the resulting value. The expression
may include calls to functions in the program being debugged.
call expr Evaluate the expression expr without displaying void returned values.
You can use this variant of the print command if you want to execute a function
from your program that does not return anything (a.k.a. a void function), but
without cluttering the output with void returned values that gdb will otherwise
print. If the result is not void, it is printed and saved in the value history.
It is possible for the function you call via the print or call command to generate asignal (e.g., if there’s a bug in the function, or if you passed it incorrect arguments). What
happens in that case is controlled by the set unwind-on-signal command.
Similarly, with a C++ program it is possible for the function you call via the print orcall command to generate an exception that is not handled due to the constraints of thedummy frame. In this case, any exception that is raised in the frame, but has an out-of-frame
exception handler will not be found. GDB builds a dummy-frame for the inferior function
call, and the unwinder cannot seek for exception handlers outside of this dummy-frame.
What happens in that case is controlled by the set unwind-on-terminating-exceptioncommand.
set unwind-on-signal
Set unwinding of the stack if a signal is received while in a function that gdb
called in the program being debugged. If set to on, gdb unwinds the stack it
created for the call and restores the context to what it was before the call. If
set to off (the default), gdb stops in the frame where the signal was received.

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The command set unwindonsignal is an alias for this command, and is maintained for backward compatibility.
show unwind-on-signal
Show the current setting of stack unwinding in the functions called by gdb.
The command show unwindonsignal is an alias for this command, and is maintained for backward compatibility.
set unwind-on-terminating-exception
Set unwinding of the stack if a C++ exception is raised, but left unhandled while
in a function that gdb called in the program being debugged. If set to on (thedefault), gdb unwinds the stack it created for the call and restores the context
to what it was before the call. If set to off, gdb the exception is delivered tothe default C++ exception handler and the inferior terminated.
show unwind-on-terminating-exception
Show the current setting of stack unwinding in the functions called by gdb.
set unwind-on-timeout
Set unwinding of the stack if a function called from gdb times out. If set tooff (the default), gdb stops in the frame where the timeout occurred. If set
to on, gdb unwinds the stack it created for the call and restores the context towhat it was before the call.
show unwind-on-timeout
Show whether gdb will unwind the stack if a function called from gdb timesout.
set may-call-functions
Set permission to call functions in the program. This controls whether gdb willattempt to call functions in the program, such as with expressions in the printcommand. It defaults to on.
To call a function in the program, gdb has to temporarily modify the stateof the inferior. This has potentially undesired side effects. Also, having gdb
call nested functions is likely to be erroneous and may even crash the program
being debugged. You can avoid such hazards by forbidding gdb from calling
functions in the program being debugged. If calling functions in the program
is forbidden, GDB will throw an error when a command (such as printing an
expression) starts a function call in the program.
show may-call-functionsShow permission to call functions in the program.
When calling a function within a program, it is possible that the program could enter astate from which the called function may never return. If this happens then it is possible
to interrupt the function call by typing the interrupt character (often Ctrl-c).
If a called function is interrupted for any reason, including hitting a breakpoint, or triggering a watchpoint, and the stack is not unwound due to set unwind-on-terminatingexception on, set unwind-on-timeout on, or set unwind-on-signal on (see [stack unwind settings], page 281), then the dummy-frame, created by gdb to facilitate the call toChapter 17: Altering Execution283

the program function, will be visible in the backtrace, for example frame #3 in the following
backtrace:(gdb) backtrace#0 0x00007ffff7b3d1e7 in nanosleep () from /lib64/libc.so.6#1 0x00007ffff7b3d11e in sleep () from /lib64/libc.so.6#2 0x000000000040113f in deadlock () at test.cc:13#3 <function called from gdb>
#4 breakpt () at test.cc:20#5 0x0000000000401151 in main () at test.cc:25

At this point it is possible to examine the state of the inferior just like any other stop.
Depending on why the function was interrupted then it may be possible to resume theinferior (using commands like continue, step, etc). In this case, when the inferior finally
returns to the dummy-frame, gdb will once again halt the inferior.
On targets that support asynchronous execution (see Section 5.5.3 [Background Execution], page 95) gdb can place a timeout on any functions called from gdb. If the timeout
expires and the function call is still ongoing, then gdb will interrupt the program.
If a function called from gdb is interrupted by a timeout, then by default the inferior
is left in the frame where the timeout occurred, this behaviour can be adjusted with ‘set
unwind-on-timeout’ (see [set unwind-on-timeout], page 282).
For targets that don’t support asynchronous execution (see Section 5.5.3 [Background
Execution], page 95) then timeouts for functions called from gdb are not supported, thetimeout settings described below will be treated as unlimited, meaning gdb will wait
indefinitely for function call to complete, unless interrupted by the user using Ctrl-C.
set direct-call-timeout seconds
Set the timeout used when calling functions in the program to seconds, whichshould be an integer greater than zero, or the special value unlimited, whichindicates no timeout should be used. The default for this setting is unlimited.
This setting is used when the user calls a function directly from the commandprompt, for example with a call or print command.
This setting only works for targets that support asynchronous execution (seeSection 5.5.3 [Background Execution], page 95), for any other target the setting
is treated as unlimited.
show direct-call-timeout
Show the timeout used when calling functions in the program with a call or
print command.
It is also possible to call functions within the program from the condition of a conditional
breakpoint (see Section 5.1.6 [Break Conditions], page 76). A different setting controls thetimeout used for function calls made from a breakpoint condition.
set indirect-call-timeout seconds
Set the timeout used when calling functions in the program from a breakpoint
or watchpoint condition to seconds, which should be an integer greater thanzero, or the special value unlimited, which indicates no timeout should be
used. The default for this setting is 30 seconds.

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This setting only works for targets that support asynchronous execution (seeSection 5.5.3 [Background Execution], page 95), for any other target the setting
is treated as unlimited.
If a function called from a breakpoint or watchpoint condition times out, then
gdb will stop at the point where the timeout occurred. The breakpoint condition evaluation will be abandoned.
show indirect-call-timeout
Show the timeout used when calling functions in the program from a breakpoint
or watchpoint condition.

17.5.1 Calling functions with no debug info
Sometimes, a function you wish to call is missing debug information. In such case, gdb
does not know the type of the function, including the types of the function’s parameters.
To avoid calling the inferior function incorrectly, which could result in the called function
functioning erroneously and even crash, gdb refuses to call the function unless you tell it
the type of the function.
For prototyped (i.e. ANSI/ISO style) functions, there are two ways to do that. The
simplest is to cast the call to the function’s declared return type. For example:(gdb) p getenv ("PATH")’getenv’ has unknown return type; cast the call to its declared return type(gdb) p (char *) getenv ("PATH")$1 = 0x7fffffffe7ba "/usr/local/bin:/"...

Casting the return type of a no-debug function is equivalent to casting the function
to a pointer to a prototyped function that has a prototype that matches the types of thepassed-in arguments, and calling that. I.e., the call above is equivalent to:(gdb) p ((char * (*) (const char *)) getenv) ("PATH")

and given this prototyped C or C++ function with float parameters:
float multiply (float v1, float v2) { return v1 * v2; }these calls are equivalent:(gdb) p (float) multiply (2.0f, 3.0f)(gdb) p ((float (*) (float, float)) multiply) (2.0f, 3.0f)

If the function you wish to call is declared as unprototyped (i.e. old K&R style), youmust use the cast-to-function-pointer syntax, so that gdb knows that it needs to apply
default argument promotions (promote float arguments to double). See Section 22.7 [ABI],
page 375. For example, given this unprototyped C function with float parameters, and no
debug info:
float
multiply_noproto (v1, v2)
float v1, v2;{
return v1 * v2;}

you call it like this:(gdb) p ((float (*) ()) multiply_noproto) (2.0f, 3.0f)

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17.6 Patching Programs
By default, gdb opens the file containing your program’s executable code (or the corefile)read-only. This prevents accidental alterations to machine code; but it also prevents you
from intentionally patching your program’s binary.
If you’d like to be able to patch the binary, you can specify that explicitly with the set
write command. For example, you might want to turn on internal debugging flags, or evento make emergency repairs.
set write on
set write off
If you specify ‘set write on’, gdb opens executable and core files for both
reading and writing; if you specify set write off (the default), gdb opens
them read-only.
If you have already loaded a file, you must load it again (using the exec-fileor core-file command) after changing set write, for your new setting to takeeffect.
show write
Display whether executable files and core files are opened for writing as well as
reading.

17.7 Compiling and injecting code in gdb
gdb supports on-demand compilation and code injection into programs running under gdb.
GCC 5.0 or higher built with libcc1.so must be installed for this functionality to beenabled. This functionality is implemented with the following commands.
compile code source-code
compile code -raw -- source-code
Compile source-code with the compiler language found as the current language
in gdb (see Chapter 15 [Languages], page 227). If compilation and injection
is not supported with the current language specified in gdb, or the compiler
does not support this feature, an error message will be printed. If source-code
compiles and links successfully, gdb will load the object-code emitted, andexecute it within the context of the currently selected inferior. It is important
to note that the compiled code is executed immediately. After execution, thecompiled code is removed from gdb and any new types or variables you havedefined will be deleted.
The command allows you to specify source-code in two ways. The simplest
method is to provide a single line of code to the command. E.g.:
compile code printf ("hello world\n");If you specify options on the command line as well as source code, they may
conflict. The ‘--’ delimiter can be used to separate options from actual sourcecode. E.g.:
compile code -r -- printf ("hello world\n");Alternatively you can enter source code as multiple lines of text. To enter
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command. This will start the multiple-line editor and allow you to type as
many lines of source code as required. When you have completed typing, enter‘end’ on its own line to exit the editor.
compile code>printf ("hello\n");>printf ("world\n");>end

Specifying ‘-raw’, prohibits gdb from wrapping the provided source-code ina callable scope. In this case, you must specify the entry point of the codeby defining a function named _gdb_expr_. The ‘-raw’ code cannot accessvariables of the inferior. Using ‘-raw’ option may be needed for example whensource-code requires ‘#include’ lines which may conflict with inferior symbols
otherwise.
compile file filename
compile file -raw filename
Like compile code, but take the source code from filename.
compile file /home/user/example.c

The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
compile print [[options] --] expr
compile print [[options] --] /f expr
Compile and execute expr with the compiler language found as the current
language in gdb (see Chapter 15 [Languages], page 227). By default the valueof expr is printed in a format appropriate to its data type; you can choose a
different format by specifying ‘/f’, where f is a letter specifying the format;
see Section 10.5 [Output Formats], page 150. The compile print command
accepts the same options as the print command; see [print options], page 141.
compile print [[options] --]compile print [[options] --] /f
Alternatively you can enter the expression (source code producing it) as multiplelines of text. To enter this mode, invoke the ‘compile print’ command without
any text following the command. This will start the multiple-line editor.
The process of compiling and injecting the code can be inspected using:set debug compile
Turns on or off display of gdb process of compiling and injecting the code. The
default is off.
show debug compile
Displays the current state of displaying gdb process of compiling and injecting
the code.
set debug compile-cplus-types
Turns on or off the display of C++ type conversion debugging information. The
default is off.

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show debug compile-cplus-types
Displays the current state of displaying debugging information for C++ typeconversion.

17.7.1 Compilation options for the compile command
gdb needs to specify the right compilation options for the code to be injected, in part tomake its ABI compatible with the inferior and in part to make the injected code compatible
with gdb’s injecting process.
The options used, in increasing precedence:target architecture and OS options (gdbarch)
These options depend on target processor type and target operating system,
usually they specify at least 32-bit (-m32) or 64-bit (-m64) compilation option.
compilation options recorded in the target
gcc (since version 4.7) stores the options used for compilation into DW_AT_
producer part of DWARF debugging information according to the gcc option-grecord-gcc-switches. One has to explicitly specify -g during inferior compilation otherwise gcc produces no DWARF. This feature is only relevant for
platforms where -g produces DWARF by default, otherwise one may try to
enforce DWARF by using -gdwarf-4.
compilation options set by set compile-args
You can override compilation options using the following command:set compile-args
Set compilation options used for compiling and injecting code with the compile
commands. These options override any conflicting ones from the target architecture and/or options stored during inferior compilation.
show compile-args
Displays the current state of compilation options override. This does notshow all the options actually used during compilation, use [set debug compile],
page 286, for that.

17.7.2 Caveats when using the compile command
There are a few caveats to keep in mind when using the compile command. As the caveats
are different per language, the table below highlights specific issues on a per language basis.
C code examples and caveats
When the language in gdb is set to ‘C’, the compiler will attempt to compile
the source code with a ‘C’ compiler. The source code provided to the compile
command will have much the same access to variables and types as it normally
would if it were part of the program currently being debugged in gdb.
Below is a sample program that forms the basis of the examples that follow.
This program has been compiled and loaded into gdb, much like any othernormal debugging session.
void function1 (void){
int i = 42;288

Debugging with gdb

printf ("function 1\n");}void function2 (void){
int j = 12;function1 ();}int main(void){
int k = 6;
int *p;function2 ();return 0;}

For the purposes of the examples in this section, the program above has been
compiled, loaded into gdb, stopped at the function main, and gdb is awaiting
input from the user.
To access variables and types for any program in gdb, the program must becompiled and packaged with debug information. The compile command is not
an exception to this rule. Without debug information, you can still use thecompile command, but you will be very limited in what variables and types
you can access.
So with that in mind, the example above has been compiled with debug information enabled. The compile command will have access to all variables andtypes (except those that may have been optimized out). Currently, as gdb has
stopped the program in the main function, the compile command would haveaccess to the variable k. You could invoke the compile command and type somesource code to set the value of k. You can also read it, or do anything withthat variable you would normally do in C. Be aware that changes to inferiorvariables in the compile command are persistent. In the following example:
compile code k = 3;

the variable k is now 3. It will retain that value until something else in theexample program changes it, or another compile command changes it.
Normal scope and access rules apply to source code compiled and injected by
the compile command. In the example, the variables j and k are not accessible
yet, because the program is currently stopped in the main function, where thesevariables are not in scope. Therefore, the following commandcompile code j = 3;

will result in a compilation error message.
Once the program is continued, execution will bring these variables in scope,and they will become accessible; then the code you specify via the compile
command will be able to access them.
You can create variables and types with the compile command as part ofyour source code. Variables and types that are created as part of the compile
command are not visible to the rest of the program for the duration of its run.
This example is valid:
compile code int ff = 5; printf ("ff is %d\n", ff);

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However, if you were to type the following into gdb after that command hascompleted:compile code printf ("ff is %d\n’’, ff);

a compiler error would be raised as the variable ff no longer exists. Object
code generated and injected by the compile command is removed when its
execution ends. Caution is advised when assigning to program variables valuesof variables created by the code submitted to the compile command. This
example is valid:
compile code int ff = 5; k = ff;

The value of the variable ff is assigned to k. The variable k does not require theexistence of ff to maintain the value it has been assigned. However, pointersrequire particular care in assignment. If the source code compiled with thecompile command changed the address of a pointer in the example program,perhaps to a variable created in the compile command, that pointer would
point to an invalid location when the command exits. The following example
would likely cause issues with your debugged program:compile code int ff = 5; p = &ff;

In this example, p would point to ff when the compile command is executing
the source code provided to it. However, as variables in the (example) program
persist with their assigned values, the variable p would point to an invalid
location when the command exists. A general rule should be followed in thatyou should either assign NULL to any assigned pointers, or restore a valid location
to the pointer before the command exits.
Similar caution must be exercised with any structs, unions, and typedefs definedin compile command. Types defined in the compile command will no longer
be available in the next compile command. Therefore, if you cast a variable
to a type defined in the compile command, care must be taken to ensure thatany future need to resolve the type can be achieved.
(gdb) compile code static struct a { int a; } v = { 42 }; argv = &v;(gdb) compile code printf ("%d\n", ((struct a *) argv)->a);gdb command line:1:36: error: dereferencing pointer to incomplete type struct a
Compilation failed.
(gdb) compile code struct a { int a; }; printf ("%d\n", ((struct a *) argv)>a);42

Variables that have been optimized away by the compiler are not accessible tothe code submitted to the compile command. Access to those variables will
generate a compiler error which gdb will print to the console.

17.7.3 Compiler search for the compile command
gdb needs to find gcc for the inferior being debugged which may not be obvious for remotetargets of different architecture than where gdb is running. Environment variable PATH on
gdb host is searched for gcc binary matching the target architecture and operating system.
This search can be overridden by set compile-gcc gdb command below. PATH is takenfrom shell that executed gdb, it is not the value set by gdb command set environment).
See Section 4.4 [Environment], page 38.

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Specifically PATH is searched for binaries matching regular expression arch(-[^-]*)?os-gcc according to the inferior target being debugged. arch is processor name — multiarch
is supported, so for example both i386 and x86_64 targets look for pattern (x86_64|i.86)
and both s390 and s390x targets look for pattern s390x?. os is currently supported only
for pattern linux(-gnu)?.
On Posix hosts the compiler driver gdb needs to find also shared library libcc1.so fromthe compiler. It is searched in default shared library search path (overridable with usualenvironment variable LD_LIBRARY_PATH), unrelated to PATH or set compile-gcc settings.
Contrary to it libcc1plugin.so is found according to the installation of the found compiler— as possibly specified by the set compile-gcc command.
set compile-gcc
Set compilation command used for compiling and injecting code with thecompile commands. If this option is not set (it is set to an empty string), thesearch described above will occur — that is the default.
show compile-gcc
Displays the current compile command gcc driver filename. If set, it is the maincommand gcc, found usually for example under name x86_64-linux-gnu-gcc.

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18 gdb Files
gdb needs to know the file name of the program to be debugged, both in order to read its
symbol table and in order to start your program. To debug a core dump of a previous run,you must also tell gdb the name of the core dump file.

18.1 Commands to Specify Files
You may want to specify executable and core dump file names. The usual way to do this is
at start-up time, using the arguments to gdb’s start-up commands (see Chapter 2 [Getting
In and Out of gdb], page 11).
Occasionally it is necessary to change to a different file during a gdb session. Or you
may run gdb and forget to specify a file you want to use. Or you are debugging a remotetarget via gdbserver (see Section 20.3 [Using the gdbserver Program], page 320). In thesesituations the gdb commands to specify new files are useful.
file filename
Use filename as the program to be debugged. It is read for its symbols and forthe contents of pure memory. It is also the program executed when you use
the run command. If you do not specify a directory and the file is not foundin the gdb working directory, gdb uses the environment variable PATH as a listof directories to search, just as the shell does when looking for a program torun. You can change the value of this variable, for both gdb and your program,using the path command.
The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
You can load unlinked object .o files into gdb using the file command. You
will not be able to “run” an object file, but you can disassemble functions andinspect variables. Also, if the underlying BFD functionality supports it, you
could use gdb -write to patch object files using this technique. Note that gdb
can neither interpret nor modify relocations in this case, so branches and some
initialized variables will appear to go to the wrong place. But this feature is
still handy from time to time.
file

file with no argument makes gdb discard any information it has on both
executable file and the symbol table.

exec-file [ filename ]Specify that the program to be run (but not the symbol table) is found in
filename. gdb searches the environment variable PATH if necessary to locate
your program. Omitting filename means to discard information on the executable file.
The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
symbol-file [ filename [ -o offset ]]Read symbol table information from file filename. PATH is searched when necessary. Use the file command to get both symbol table and program to run
from the same file.

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If an optional offset is specified, it is added to the start address of each sectionin the symbol file. This is useful if the program is relocated at runtime, suchas the Linux kernel with kASLR enabled.
symbol-file with no argument clears out gdb information on your program’s
symbol table.
The symbol-file command causes gdb to forget the contents of some breakpoints and auto-display expressions. This is because they may contain pointersto the internal data recording symbols and data types, which are part of theold symbol table data being discarded inside gdb.
symbol-file does not repeat if you press RET again after executing it once.
The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
When gdb is configured for a particular environment, it understands debugging
information in whatever format is the standard generated for that environment;
you may use either a gnu compiler, or other compilers that adhere to the local
conventions. Best results are usually obtained from gnu compilers; for example,
using gcc you can generate debugging information for optimized code.
For most kinds of object files, with the exception of old SVR3 systems using
COFF, the symbol-file command does not normally read the symbol table infull right away. Instead, it scans the symbol table quickly to find which source
files and which symbols are present. The details are read later, one source fileat a time, as they are needed.
The purpose of this two-stage reading strategy is to make gdb start up faster.
For the most part, it is invisible except for occasional pauses while the symbol
table details for a particular source file are being read. (The set verbose
command can turn these pauses into messages if desired. See Section 22.9
[Optional Warnings and Messages], page 381.)
We have not implemented the two-stage strategy for COFF yet. When thesymbol table is stored in COFF format, symbol-file reads the symbol tabledata in full right away. Note that “stabs-in-COFF” still does the two-stage
strategy, since the debug info is actually in stabs format.
symbol-file [ -readnow ] filename
file [ -readnow ] filename
You can override the gdb two-stage strategy for reading symbol tables by using the ‘-readnow’ option with any of the commands that load symbol table
information, if you want to be sure gdb has the entire symbol table available.
symbol-file [ -readnever ] filename
file [ -readnever ] filename
You can instruct gdb to never read the symbolic information contained infilename by using the ‘-readnever’ option. See [–readnever], page 13.
core-file [filename]core
Specify the whereabouts of a core dump file to be used as the “contents ofmemory”. Traditionally, core files contain only some parts of the address spaceChapter 18: gdb Files

293of the process that generated them; gdb can access the executable file itself forother parts.
core-file with no argument specifies that no core file is to be used.
Note that the core file is ignored when your program is actually running under
gdb. So, if you have been running your program and you wish to debug a core
file instead, you must kill the subprocess in which the program is running. To
do this, use the kill command (see Section 4.8 [Killing the Child Process],
page 42).
add-symbol-file filename [ -readnow | -readnever ] [ -o offset ] [ textaddress ] [-s section address ... ]The add-symbol-file command reads additional symbol table informationfrom the file filename. You would use this command when filename has been
dynamically loaded (by some other means) into the program that is running.
The textaddress parameter gives the memory address at which the file’s text
section has been loaded. You can additionally specify the base address of othersections using an arbitrary number of ‘-s section address’ pairs. If a section
is omitted, gdb will use its default addresses as found in filename. Any address
or textaddress can be given as an expression.
If an optional offset is specified, it is added to the start address of each section,
except those for which the address was specified explicitly.
The symbol table of the file filename is added to the symbol table originally readwith the symbol-file command. You can use the add-symbol-file command
any number of times; the new symbol data thus read is kept in addition to theold.
The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
Changes can be reverted using the command remove-symbol-file.
Although filename is typically a shared library file, an executable file, or someother object file which has been fully relocated for loading into a process, you
can also load symbolic information from relocatable .o files, as long as:• the file’s symbolic information refers only to linker symbols defined in that
file, not to symbols defined by other object files,• every section the file’s symbolic information refers to has actually been
loaded into the inferior, as it appears in the file, and• you can determine the address at which every section was loaded, andprovide these to the add-symbol-file command.
Some embedded operating systems, like Sun Chorus and VxWorks, can load
relocatable files into an already running program; such systems typically makethe requirements above easy to meet. However, it’s important to recognize thatmany native systems use complex link procedures (.linkonce section factoring
and C++ constructor table assembly, for example) that make the requirements
difficult to meet. In general, one cannot assume that using add-symbol-file
to read a relocatable object file’s symbolic information will have the same effectas linking the relocatable object file into the program in the normal way.

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add-symbol-file does not repeat if you press RET after using it.
remove-symbol-file filename
remove-symbol-file -a address
Remove a symbol file added via the add-symbol-file command. The file toremove can be identified by its filename or by an address that lies within theboundaries of this symbol file in memory. Example:(gdb) add-symbol-file /home/user/gdb/mylib.so 0x7ffff7ff9480
add symbol table from file "/home/user/gdb/mylib.so" at.text_addr = 0x7ffff7ff9480(y or n) y
Reading symbols from /home/user/gdb/mylib.so...
(gdb) remove-symbol-file -a 0x7ffff7ff9480
Remove symbol table from file "/home/user/gdb/mylib.so"? (y or n) y
(gdb)

The address can be any expression which evaluates to an address.
remove-symbol-file does not repeat if you press RET after using it.
The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
add-symbol-file-from-memory address
Load symbols from the given address in a dynamically loaded object file whose
image is mapped directly into the inferior’s memory. For example, the Linuxkernel maps a syscall DSO into each process’s address space; this DSO provides
kernel-specific code for some system calls. The argument can be any expression whose evaluation yields the address of the file’s shared object file header.
For this command to work, you must have used symbol-file or exec-filecommands in advance.
section section addr
The section command changes the base address of the named section of theexec file to addr. This can be used if the exec file does not contain section
addresses, (such as in the a.out format), or when the addresses specified in thefile itself are wrong. Each section must be changed separately. The info files
command, described below, lists all the sections and their addresses.
info files
info target
info files and info target are synonymous; both print the current target(see Chapter 19 [Specifying a Debugging Target], page 311), including thenames of the executable and core dump files currently in use by gdb, andthe files from which symbols were loaded. The command help target lists all
possible targets rather than current ones.
maint info sections [-all-objects] [filter-list]
Another command that can give you extra information about program sections
is maint info sections. In addition to the section information displayed byinfo files, this command displays the flags and file offset of each section in
the executable and core dump files.
When ‘-all-objects’ is passed then sections from all loaded object files, including shared libraries, are printed.

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The optional filter-list is a space separated list of filter keywords. Sections thatmatch any one of the filter criteria will be printed. There are two types of filter:
section-nameDisplay information about any section named section-name.
section-flag
Display information for any section with section-flag. The section
flags that gdb currently knows about are:
ALLOC

Section will have space allocated in the process when
loaded. Set for all sections except those containing debug information.

LOAD

Section will be loaded from the file into the child process memory. Set for pre-initialized code and data,clear for .bss sections.

RELOC

Section needs to be relocated before loading.

READONLY

Section cannot be modified by the child process.

CODE

Section contains executable code only.

DATA

Section contains data only (no executable code).

ROM

Section will reside in ROM.

CONSTRUCTOR
Section contains data for constructor/destructor lists.
HAS_CONTENTS
Section is not empty.
NEVER_LOAD
An instruction to the linker to not output the section.
COFF_SHARED_LIBRARY
A notification to the linker that the section contains
COFF shared library information.
IS_COMMON
Section contains common symbols.
maint info target-sections
This command prints gdb’s internal section table. For each target gdb maintains a table containing the allocatable sections from all currently mapped objects, along with information about where the section is mapped.
set trust-readonly-sections on
Tell gdb that readonly sections in your object file really are read-only (i.e.
that their contents will not change). In that case, gdb can fetch values fromthese sections out of the object file, rather than from the target program. For
some targets (notably embedded ones), this can be a significant enhancement
to debugging performance.
The default is off.

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set trust-readonly-sections off
Tell gdb not to trust readonly sections. This means that the contents of thesection might change while the program is running, and must therefore be
fetched from the target when needed.
show trust-readonly-sectionsShow the current setting of trusting readonly sections.
All file-specifying commands allow both absolute and relative file names as arguments.
gdb always converts the file name to an absolute file name and remembers it that way.
gdb supports gnu/Linux, MS-Windows, SunOS, Darwin/Mach-O, SVr4, IBM RS/6000
AIX, FDPIC (FR-V), and DSBT (TIC6X) shared libraries.
On MS-Windows gdb must be linked with the Expat library to support shared libraries.
See [Expat], page 746.
gdb automatically loads symbol definitions from shared libraries when you use the runcommand, or when you examine a core file. (Before you issue the run command, gdb
does not understand references to a function in a shared library, however—unless you aredebugging a core file).
There are times, however, when you may wish to not automatically load symbol definitions from shared libraries, such as when they are particularly large or there are many ofthem.
To control the automatic loading of shared library symbols, use the commands:
set auto-solib-add modeIf mode is on, symbols from all shared object libraries will be loaded automatically when the inferior begins execution, you attach to an independently
started inferior, or when the dynamic linker informs gdb that a new libraryhas been loaded. If mode is off, symbols must be loaded manually, using thesharedlibrary command. The default value is on.
If your program uses lots of shared libraries with debug info that takes large
amounts of memory, you can decrease the gdb memory footprint by preventing it from automatically loading the symbols from shared libraries. To that
end, type set auto-solib-add off before running the inferior, then load eachlibrary whose debug symbols you do need with sharedlibrary regexp, where
regexp is a regular expression that matches the libraries whose symbols you
want to be loaded.
show auto-solib-add
Display the current autoloading mode.
To explicitly load shared library symbols, use the sharedlibrary command:
info share regex
info sharedlibrary regex
Print the names of the shared libraries which are currently loaded that matchregex. If regex is omitted then print all shared libraries that are loaded.
info dll regex
This is an alias of info sharedlibrary.

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sharedlibrary regex
share regex
Load shared object library symbols for files matching a Unix regular expression.
As with files loaded automatically, it only loads shared libraries required by yourprogram for a core file or after typing run. If regex is omitted all shared libraries
required by your program are loaded.
nosharedlibrary
Unload all shared object library symbols. This discards all symbols that havebeen loaded from all shared libraries. Symbols from shared libraries that were
loaded by explicit user requests are not discarded.
Sometimes you may wish that gdb stops and gives you control when any of sharedlibrary events happen. The best way to do this is to use catch load and catch unload(see Section 5.1.3 [Set Catchpoints], page 69).
gdb also supports the set stop-on-solib-events command for this. This commandexists for historical reasons. It is less useful than setting a catchpoint, because it does notallow for conditions or commands as a catchpoint does.
set stop-on-solib-events
This command controls whether gdb should give you control when the dynamic
linker notifies it about some shared library event. The most common event ofinterest is loading or unloading of a new shared library.
show stop-on-solib-eventsShow whether gdb stops and gives you control when shared library events
happen.
Shared libraries are also supported in many cross or remote debugging configurations.
gdb needs to have access to the target’s libraries; this can be accomplished either by
providing copies of the libraries on the host system, or by asking gdb to automatically
retrieve the libraries from the target. If copies of the target libraries are provided, they need
to be the same as the target libraries, although the copies on the target can be stripped aslong as the copies on the host are not.
For remote debugging, you need to tell gdb where the target libraries are, so that it
can load the correct copies—otherwise, it may try to load the host’s libraries. gdb has twovariables to specify the search directories for target libraries.
set sysroot path
Use path as the system root for the program being debugged. Any absoluteshared library paths will be prefixed with path; many runtime loaders store theabsolute paths to the shared library in the target program’s memory. Whenstarting processes remotely, and when attaching to already-running processes(local or remote), their executable filenames will be prefixed with path if reported to gdb as absolute by the operating system. If you use set sysroot
to find executables and shared libraries, they need to be laid out in the same
way that they are on the target, with e.g. a /bin, /lib and /usr/lib hierarchy
under path.
If path starts with the sequence target: and the target system is remote then
gdb will retrieve the target binaries from the remote system. This is only

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supported when using a remote target that supports the remote get command(see Section 20.2 [Sending files to a remote system], page 320). The part of pathfollowing the initial target: (if present) is used as system root prefix on the
remote file system. If path starts with the sequence remote: this is converted
to the sequence target: by set sysroot1 . If you want to specify a local systemroot using a directory that happens to be named target: or remote:, you need
to use some equivalent variant of the name like ./target:.
For targets with an MS-DOS based filesystem, such as MS-Windows, gdb tries
prefixing a few variants of the target absolute file name with path. But first,
on Unix hosts, gdb converts all backslash directory separators into forward
slashes, because the backslash is not a directory separator on Unix:
c:\foo\bar.dll ⇒ c:/foo/bar.dll

Then, gdb attempts prefixing the target file name with path, and looks for the
resulting file name in the host file system:
c:/foo/bar.dll ⇒ /path/to/sysroot/c:/foo/bar.dll

If that does not find the binary, gdb tries removing the ‘:’ character from thedrive spec, both for convenience, and, for the case of the host file system notsupporting file names with colons:c:/foo/bar.dll ⇒ /path/to/sysroot/c/foo/bar.dll

This makes it possible to have a system root that mirrors a target with morethan one drive. E.g., you may want to setup your local copies of the target
system shared libraries like so (note ‘c’ vs ‘z’):/path/to/sysroot/c/sys/bin/foo.dll/path/to/sysroot/c/sys/bin/bar.dll/path/to/sysroot/z/sys/bin/bar.dll

and point the system root at /path/to/sysroot, so that gdb can find thecorrect copies of both c:\sys\bin\foo.dll, and z:\sys\bin\bar.dll.
If that still does not find the binary, gdb tries removing the whole drive specfrom the target file name:c:/foo/bar.dll ⇒ /path/to/sysroot/foo/bar.dll

This last lookup makes it possible to not care about the drive name, if you
don’t want or need to.
The set solib-absolute-prefix command is an alias for set sysroot.
You can set the default system root by using the configure-time‘--with-sysroot’ option. If the system root is inside gdb’s configured binary
prefix (set with ‘--prefix’ or ‘--exec-prefix’), then the default system root
will be updated automatically if the installed gdb is moved to a new location.
show sysroot
Display the current executable and shared library prefix.
set solib-search-path path
If this variable is set, path is a colon-separated list of directories to search forshared libraries. ‘solib-search-path’ is used after ‘sysroot’ fails to locate the1Historically the functionality to retrieve binaries from the remote system was provided by prefixing pathwith remote:Chapter 18: gdb Files

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library, or if the path to the library is relative instead of absolute. If you want
to use ‘solib-search-path’ instead of ‘sysroot’, be sure to set ‘sysroot’
to a nonexistent directory to prevent gdb from finding your host’s libraries.
‘sysroot’ is preferred; setting it to a nonexistent directory may interfere with
automatic loading of shared library symbols.
show solib-search-path
Display the current shared library search path.
set target-file-system-kind kind
Set assumed file system kind for target reported file names.
Shared library file names as reported by the target system may not make sense
as is on the system gdb is running on. For example, when remote debugging
a target that has MS-DOS based file system semantics, from a Unix host, thetarget may be reporting to gdb a list of loaded shared libraries with file names
such as c:\Windows\kernel32.dll. On Unix hosts, there’s no concept of drive
letters, so the ‘c:\’ prefix is not normally understood as indicating an absolute
file name, and neither is the backslash normally considered a directory separator
character. In that case, the native file system would interpret this whole absolute file name as a relative file name with no directory components. This would
make it impossible to point gdb at a copy of the remote target’s shared libraries
on the host using set sysroot, and impractical with set solib-search-path.
Setting target-file-system-kind to dos-based tells gdb to interpret such
file names similarly to how the target would, and to map them to file names
valid on gdb’s native file system semantics. The value of kind can be "auto",in addition to one of the supported file system kinds. In that case, gdb tries
to determine the appropriate file system variant based on the current target’s
operating system (see Section 22.7 [Configuring the Current ABI], page 375).
The supported file system settings are:unix

Instruct gdb to assume the target file system is of Unix kind. Only
file names starting the forward slash (‘/’) character are consideredabsolute, and the directory separator character is also the forward
slash.

dos-based
Instruct gdb to assume the target file system is DOS based. Filenames starting with either a forward slash, or a drive letter followed
by a colon (e.g., ‘c:’), are considered absolute, and both the slash(‘/’) and the backslash (‘\\’) characters are considered directory
separators.
autoInstruct gdb to use the file system kind associated with the target
operating system (see Section 22.7 [Configuring the Current ABI],
page 375). This is the default.

When processing file names provided by the user, gdb frequently needs to comparethem to the file names recorded in the program’s debug info. Normally, gdb compares
just the base names of the files as strings, which is reasonably fast even for very large
programs. (The base name of a file is the last portion of its name, after stripping all the

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leading directories.) This shortcut in comparison is based upon the assumption that files
cannot have more than one base name. This is usually true, but references to files that use
symlinks or similar filesystem facilities violate that assumption. If your program records
files using such facilities, or if you provide file names to gdb using symlinks etc., you can
set basenames-may-differ to true to instruct gdb to completely canonicalize each pairof file names it needs to compare. This will make file-name comparisons accurate, but at a
price of a significant slowdown.
set basenames-may-differ
Set whether a source file may have multiple base names.
show basenames-may-differ
Show whether a source file may have multiple base names.

18.2 File Caching
To speed up file loading, and reduce memory usage, gdb will reuse the bfd objects used to
track open files. See Section “BFD” in The Binary File Descriptor Library. The following
commands allow visibility and control of the caching behavior.
maint info bfds
This prints information about each bfd object that is known to gdb.
maint set bfd-sharing
maint show bfd-sharing
Control whether bfd objects can be shared. When sharing is enabled gdb
reuses already open bfd objects rather than reopening the same file. Turning
sharing off does not cause already shared bfd objects to be unshared, but all
future files that are opened will create a new bfd object. Similarly, re-enabling
sharing does not cause multiple existing bfd objects to be collapsed into a single
shared bfd object.
set debug bfd-cache levelTurns on debugging of the bfd cache, setting the level to level.
show debug bfd-cacheShow the current debugging level of the bfd cache.

18.3 Debugging Information in Separate Files
gdb allows you to put a program’s debugging information in a file separate from the executable itself, in a way that allows gdb to find and load the debugging information automatically. Since debugging information can be very large—sometimes larger than the executablecode itself—some systems distribute debugging information for their executables in separate
files, which users can install only when they need to debug a problem.
gdb supports two ways of specifying the separate debug info file:• The executable contains a debug link that specifies the name of the separate debug
info file. The separate debug file’s name is usually executable.debug, where executable is the name of the corresponding executable file without leading directories(e.g., ls.debug for /usr/bin/ls). In addition, the debug link specifies a 32-bit Cyclic

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Redundancy Check (CRC) checksum for the debug file, which gdb uses to validatethat the executable and the debug file came from the same build.
• The executable contains a build ID, a unique bit string that is also present in thecorresponding debug info file. (This is supported only on some operating systems,
when using the ELF or PE file formats for binary files and the gnu Binutils.) For moredetails about this feature, see the description of the --build-id command-line option
in Section “Command Line Options” in The GNU Linker. The debug info file’s nameis not specified explicitly by the build ID, but can be computed from the build ID, see
below.
Depending on the way the debug info file is specified, gdb uses two different methods oflooking for the debug file:• For the “debug link” method, gdb looks up the named file in the directory of theexecutable file, then in a subdirectory of that directory named .debug, and finally undereach one of the global debug directories, in a subdirectory whose name is identical to
the leading directories of the executable’s absolute file name. (On MS-Windows/MSDOS, the drive letter of the executable’s leading directories is converted to a oneletter subdirectory, i.e. d:/usr/bin/ is converted to /d/usr/bin/, because Windows
filesystems disallow colons in file names.)• For the “build ID” method, gdb looks in the .build-id subdirectory of each one of the
global debug directories for a file named nn/nnnnnnnn.debug, where nn are the first 2
hex characters of the build ID bit string, and nnnnnnnn are the rest of the bit string.
(Real build ID strings are 32 or more hex characters, not 10.) gdb can automaticallyquery debuginfod servers using build IDs in order to download separate debug files
that cannot be found locally. For more information see Appendix K [Debuginfod],
page 887.
So, for example, suppose you ask gdb to debug /usr/bin/ls, which has a debug linkthat specifies the file ls.debug, and a build ID whose value in hex is abcdef1234. If thelist of the global debug directories includes /usr/lib/debug, then gdb will look for thefollowing debug information files, in the indicated order:− /usr/lib/debug/.build-id/ab/cdef1234.debug− /usr/bin/ls.debug− /usr/bin/.debug/ls.debug− /usr/lib/debug/usr/bin/ls.debug.
If the debug file still has not been found and debuginfod (see Appendix K [Debuginfod],
page 887) is enabled, gdb will attempt to download the file from debuginfod servers.
Global debugging info directories default to what is set by gdb configure option --withseparate-debug-dir and augmented by the colon-separated list of directories provided via
gdb configure option --additional-debug-dirs. During gdb run you can also set the
global debugging info directories, and view the list gdb is currently using.
set debug-file-directory directories
Set the directories which gdb searches for separate debugging information files
to directory. Multiple path components can be set concatenating them by apath separator.

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show debug-file-directoryShow the directories gdb searches for separate debugging information files.
A debug link is a special section of the executable file named .gnu_debuglink. The
section must contain:• A filename, with any leading directory components removed, followed by a zero byte,• zero to three bytes of padding, as needed to reach the next four-byte boundary within
the section, and• a four-byte CRC checksum, stored in the same endianness used for the executable fileitself. The checksum is computed on the debugging information file’s full contents by
the function given below, passing zero as the crc argument.
Any executable file format can carry a debug link, as long as it can contain a section
named .gnu_debuglink with the contents described above.
The build ID is a special section in the executable file (and in other ELF binary files that
gdb may consider). This section is often named .note.gnu.build-id, but that name is
not mandatory. It contains unique identification for the built files—the ID remains the sameacross multiple builds of the same build tree. The default algorithm SHA1 produces 160
bits (40 hexadecimal characters) of the content for the build ID string. The same section
with an identical value is present in the original built binary with symbols, in its strippedvariant, and in the separate debugging information file.
The debugging information file itself should be an ordinary executable, containing a fullset of linker symbols, sections, and debugging information. The sections of the debugging
information file should have the same names, addresses, and sizes as the original file, butthey need not contain any data—much like a .bss section in an ordinary executable.
The gnu binary utilities (Binutils) package includes the ‘objcopy’ utility that can produce the separated executable / debugging information file pairs using the following commands:
objcopy --only-keep-debug foo foo.debug
strip -g foo

These commands remove the debugging information from the executable file foo and place
it in the file foo.debug. You can use the first, second or both methods to link the two files:• The debug link method needs the following additional command to also leave behinda debug link in foo:objcopy --add-gnu-debuglink=foo.debug foo

Ulrich Drepper’s elfutils package, starting with version 0.53, contains a version of
the strip command such that the command strip foo -f foo.debug has the samefunctionality as the two objcopy commands and the ln -s command above, together.
• Build ID gets embedded into the main executable using ld --build-id or the gcc
counterpart gcc -Wl,--build-id. Build ID support plus compatibility fixes for debug
files separation are present in gnu binary utilities (Binutils) package since version 2.18.
The CRC used in .gnu_debuglink is the CRC-32 defined in IEEE 802.3 using thepolynomial:
x32 + x26 + x23 + x22 + x16 + x12 + x11+ x10 + x8 + x7 + x5 + x4 + x2 + x + 1

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The function is computed byte at a time, taking the least significant bit of each byte
first. The initial pattern 0xffffffff is used, to ensure leading zeros affect the CRC andthe final result is inverted to ensure trailing zeros also affect the CRC.
Note: This is the same CRC polynomial as used in handling the Remote Serial Protocol
qCRC packet (see [qCRC packet], page 790). However in the case of the Remote Serial
Protocol, the CRC is computed most significant bit first, and the result is not inverted, so
trailing zeros have no effect on the CRC value.
To complete the description, we show below the code of the function which produces the
CRC used in .gnu_debuglink. Inverting the initially supplied crc argument means that an
initial call to this function passing in zero will start computing the CRC using 0xffffffff.
unsigned longgnu_debuglink_crc32 (unsigned long crc,
unsigned char *buf, size_t len){static const unsigned long crc32_table[256] ={0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,

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0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,0x2d02ef8d};
unsigned char *end;
crc = ~crc & 0xffffffff;
for (end = buf + len; buf < end; ++buf)
crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
return ~crc & 0xffffffff;}

This computation does not apply to the “build ID” method.

18.4 Debugging information in a special section
Some systems ship pre-built executables and libraries that have a special ‘.gnu_debugdata’
section. This feature is called MiniDebugInfo. This section holds an LZMA-compressed
object and is used to supply extra symbols for backtraces.
The intent of this section is to provide extra minimal debugging information for use
in simple backtraces. It is not intended to be a replacement for full separate debugging
information (see Section 18.3 [Separate Debug Files], page 300). The example below shows
the intended use; however, gdb does not currently put restrictions on what sort of debugging
information might be included in the section.
gdb has support for this extension. If the section exists, then it is used provided thatno other source of debugging information can be found, and that gdb was configured with
LZMA support.
This section can be easily created using objcopy and other standard utilities:# Extract the dynamic symbols from the main binary, there is no need
# to also have these in the normal symbol table.
nm -D binary --format=posix --defined-only \| awk ’{ print $1 }’ | sort > dynsyms# Extract all the text (i.e. function) symbols from the debuginfo.
# (Note that we actually also accept "D" symbols, for the benefit# of platforms like PowerPC64 that use function descriptors.)
nm binary --format=posix --defined-only \| awk ’{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 }’ \| sort > funcsyms# Keep all the function symbols not already in the dynamic symbol# table.
comm -13 dynsyms funcsyms > keep_symbols# Separate full debug info into debug binary.

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objcopy --only-keep-debug binary debug# Copy the full debuginfo, keeping only a minimal set of symbols and# removing some unnecessary sections.
objcopy -S --remove-section .gdb_index --remove-section .comment \--keep-symbols=keep_symbols debug mini_debuginfo# Drop the full debug info from the original binary.
strip --strip-all -R .comment binary# Inject the compressed data into the .gnu_debugdata section of the# original binary.
xz mini_debuginfo
objcopy --add-section .gnu_debugdata=mini_debuginfo.xz binary

18.5 Index Files Speed Up gdb
When gdb finds a symbol file, it scans the symbols in the file in order to construct aninternal symbol table. This lets most gdb operations work quickly—at the cost of a delay
early on. For large programs, this delay can be quite lengthy, so gdb provides a way tobuild an index, which speeds up startup.
For convenience, gdb comes with a program, gdb-add-index, which can be used to add
the index to a symbol file. It takes the symbol file as its only argument:$ gdb-add-index symfile

See [gdb-add-index], page 897.
It is also possible to do the work manually. Here is what gdb-add-index does behindthe curtains.
The index is stored as a section in the symbol file. gdb can write the index to a file,then you can put it into the symbol file using objcopy.
To create an index file, use the save gdb-index command:save gdb-index [-dwarf-5] directory
Create index files for all symbol files currently known by gdb. For each known
symbol-file, this command by default creates it produces a single file symbolfile.gdb-index. If you invoke this command with the -dwarf-5 option, it produces 2 files: symbol-file.debug_names and symbol-file.debug_str. The
files are created in the given directory.
The directory argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
Once you have created an index file you can merge it into your symbol file, here named
symfile, using objcopy:$ objcopy --add-section .gdb_index=symfile.gdb-index \--set-section-flags .gdb_index=readonly symfile symfile

Or for -dwarf-5:$ objcopy --dump-section .debug_str=symfile.debug_str.new symfile$ cat symfile.debug_str >>symfile.debug_str.new$ objcopy --add-section .debug_names=symfile.gdb-index \--set-section-flags .debug_names=readonly \--update-section .debug_str=symfile.debug_str.new symfile symfile306

Debugging with gdb

gdb will normally ignore older versions of .gdb_index sections that have been deprecated. Usually they are deprecated because they are missing a new feature or have
performance issues. To tell gdb to use a deprecated index section anyway specify set
use-deprecated-index-sections on. The default is off. This can speed up startup,
but may result in some functionality being lost. See Appendix J [Index Section Format],page 883.
Warning: Setting use-deprecated-index-sections to on must be done before gdb
reads the file. The following will not work:$ gdb -ex "set use-deprecated-index-sections on" <program>Instead you must do, for example,$ gdb -iex "set use-deprecated-index-sections on" <program>Indices only work when using DWARF debugging information, not stabs.

18.5.1 Automatic symbol index cache
It is possible for gdb to automatically save a copy of this index in a cache on disk andretrieve it from there when loading the same binary in the future. This feature can beturned on with set index-cache enabled on. The following commands can be used to
tweak the behavior of the index cache.
set index-cache enabled on
set index-cache enabled off
Enable or disable the use of the symbol index cache.
set index-cache directory directory
show index-cache directorySet/show the directory where index files will be saved.
The default value for this directory depends on the host platform. On most
systems, the index is cached in the gdb subdirectory of the directory pointed
to by the XDG_CACHE_HOME environment variable, if it is defined, else in the.cache/gdb subdirectory of your home directory. However, on some systems,
the default may differ according to local convention.
There is no limit on the disk space used by index cache. It is perfectly safe todelete the content of that directory to free up disk space.
show index-cache stats
Print the number of cache hits and misses since the launch of gdb.

18.5.2 Building the index with GNU gold
The GNU gold linker can write the index at link time into the resulting ELF file, by passing
the --gdb-index flag to gold.
This is especially helpful if you intend to build a program and immediately run it under
gdb. You may find that it is faster overall for the linker to write the index while it has
the relevant information in memory anyways, rather than re-reloading the data from disk
with gdb-add-index, or debugging the program without an index at all, especially for large
programs.

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18.6 Extensions to ‘.debug_names’
The DWARF specification documents an optional index section called ‘.debug_names’. gdb
can both read and create this section. However, in order to work with gdb, some extensions
were necessary.
gdb uses the augmentation string ‘GDB2’. Earlier versions used the string ‘GDB’, butthese versions of the index are no longer supported.
gdb does not use the specified hash table. Therefore, because this hash table is optional,
gdb also does not write it.
gdb also generates and uses some extra index attributes:
DW_IDX_GNU_internalThis has the value ‘0x2000’. It is a flag that, when set, indicates that theassociated entry has static linkage.
DW_IDX_GNU_main
This has the value ‘0x2002’. It is a flag that, when set, indicates that theassociated entry is the program’s main.
DW_IDX_GNU_language
This has the value ‘0x2003’. It is ‘DW_LANG_’ constant, indicating the languageof the associated entry.
DW_IDX_GNU_linkage_name
This has the value ‘0x2004’. It is a flag that, when set, indicates that theassociated entry is a linkage name, and not a source name.

18.7 Errors Reading Symbol Files
While reading a symbol file, gdb occasionally encounters problems, such as symbol types
it does not recognize, or known bugs in compiler output. By default, gdb does not notify
you of such problems, since they are relatively common and primarily of interest to people debugging compilers. If you are interested in seeing information about ill-constructed
symbol tables, you can either ask gdb to print only one message about each such type ofproblem, no matter how many times the problem occurs; or you can ask gdb to print moremessages, to see how many times the problems occur, with the set complaints command(see Section 22.9 [Optional Warnings and Messages], page 381).
The messages currently printed, and their meanings, include:
inner block not inside outer block in symbol
The symbol information shows where symbol scopes begin and end (such as at
the start of a function or a block of statements). This error indicates that an
inner scope block is not fully contained in its outer scope blocks.
gdb circumvents the problem by treating the inner block as if it had the same
scope as the outer block. In the error message, symbol may be shown as “(don’tknow)” if the outer block is not a function.
block at address out of order
The symbol information for symbol scope blocks should occur in order of increasing addresses. This error indicates that it does not do so.

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gdb does not circumvent this problem, and has trouble locating symbols inthe source file whose symbols it is reading. (You can often determine whatsource file is affected by specifying set verbose on. See Section 22.9 [Optional
Warnings and Messages], page 381.)
bad block start address patched
The symbol information for a symbol scope block has a start address smaller
than the address of the preceding source line. This is known to occur in the
SunOS 4.1.1 (and earlier) C compiler.
gdb circumvents the problem by treating the symbol scope block as startingon the previous source line.
bad string table offset in symbol n
Symbol number n contains a pointer into the string table which is larger than
the size of the string table.
gdb circumvents the problem by considering the symbol to have the name foo,
which may cause other problems if many symbols end up with this name.
unknown symbol type 0xnn
The symbol information contains new data types that gdb does not yet know
how to read. 0xnn is the symbol type of the uncomprehended information, in
hexadecimal.
gdb circumvents the error by ignoring this symbol information. This usually
allows you to debug your program, though certain symbols are not accessible. If
you encounter such a problem and feel like debugging it, you can debug gdb withitself, breakpoint on complain, then go up to the function read_dbx_symtab
and examine *bufp to see the symbol.
stub type has NULL namegdb could not find the full definition for a struct or class.
const/volatile indicator missing (ok if using g++ v1.x), got...
The symbol information for a C++ member function is missing some informationthat recent versions of the compiler should have output for it.
info mismatch between compiler and debugger
gdb could not parse a type specification output by the compiler.

18.8 GDB Data Files
gdb will sometimes read an auxiliary data file. These files are kept in a directory known as
the data directory.
You can set the data directory’s name, and view the name gdb is currently using.
set data-directory directory
Set the directory which gdb searches for auxiliary data files to directory.
show data-directoryShow the directory gdb searches for auxiliary data files.
You can set the default data directory by using the configure-time ‘--with-gdb-datadir’
option. If the data directory is inside gdb’s configured binary prefix (set with ‘--prefix’Chapter 18: gdb Files309

or ‘--exec-prefix’), then the default data directory will be updated automatically if theinstalled gdb is moved to a new location.
The data directory may also be specified with the --data-directory command line
option. See Section 2.1.2 [Mode Options], page 13.

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19 Specifying a Debugging Target
A target is the execution environment occupied by your program.
Often, gdb runs in the same host environment as your program; in that case, the debugging target is specified as a side effect when you use the file or core commands.
When you need more flexibility—for example, running gdb on a physically separate host,or controlling a standalone system over a serial port or a realtime system over a TCP/IP
connection—you can use the target command to specify one of the target types configured
for gdb (see Section 19.2 [Commands for Managing Targets], page 311).
It is possible to build gdb for several different target architectures. When gdb is built
like that, you can choose one of the available architectures with the set architecturecommand.
set architecture arch
This command sets the current target architecture to arch. The value of arch
can be "auto", in addition to one of the supported architectures.
show architectureShow the current target architecture.
set processor
processor
These are alias commands for, respectively, set architecture and showarchitecture.

19.1 Active Targets
There are multiple classes of targets such as: processes, executable files or recording sessions.
Core files belong to the process class, making core file and process mutually exclusive.
Otherwise, gdb can work concurrently on multiple active targets, one in each class. This
allows you to (for example) start a process and inspect its activity, while still having access tothe executable file after the process finishes. Or if you start process recording (see Chapter 6[Reverse Execution], page 101) and reverse-step there, you are presented a virtual layerof the recording target, while the process target remains stopped at the chronologically lastpoint of the process execution.
Use the core-file and exec-file commands to select a new core file or executabletarget (see Section 18.1 [Commands to Specify Files], page 291). To specify as a target aprocess that is already running, use the attach command (see Section 4.7 [Debugging an
Already-running Process], page 41).

19.2 Commands for Managing Targets
target type parameters
Connects the gdb host environment to a target machine or process. A target
is typically a protocol for talking to debugging facilities. You use the argument
type to specify the type or protocol of the target machine.
Further parameters are interpreted by the target protocol, but typically include
things like device names or host names to connect with, process numbers, andbaud rates.

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The target command does not repeat if you press RET again after executing
the command.
help target
Displays the names of all targets available. To display targets currently selected,
use either info target or info files (see Section 18.1 [Commands to Specify
Files], page 291).
help target name
Describe a particular target, including any parameters necessary to select it.
set gnutarget args
gdb uses its own library BFD to read your files. gdb knows whether it isreading an executable, a core, or a .o file; however, you can specify the fileformat with the set gnutarget command. Unlike most target commands,
with gnutarget the target refers to a program, not a machine.
Warning: To specify a file format with set gnutarget, you must
know the actual BFD name.
See Section 18.1 [Commands to Specify Files], page 291.
show gnutarget
Use the show gnutarget command to display what file format gnutarget is set
to read. If you have not set gnutarget, gdb will determine the file format foreach file automatically, and show gnutarget displays ‘The current BFD target
is "auto"’.
Here are some common targets (available, or not, depending on the GDB configuration):target exec program
An executable file. ‘target exec program’ is the same as ‘exec-file program’.
The program argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
target core filename
A core dump file.
filename’.

‘target core filename’ is the same as ‘core-file

The filename argument supports escaping and quoting, see Section 3.4 [Filenames As Command Arguments], page 27.
target remote medium
A remote system connected to gdb via a serial line or network connection. This
command tells gdb to use its own remote protocol over medium for debugging.
See Chapter 20 [Remote Debugging], page 315.
For example, if you have a board connected to /dev/ttya on the machinerunning gdb, you could say:target remote /dev/ttyatarget remote supports the load command. This is only useful if you havesome other way of getting the stub to the target system, and you can put it
somewhere in memory where it won’t get clobbered by the download.

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313

target sim [simargs] ...
Builtin CPU simulator. gdb includes simulators for most architectures. In
general,target sim
load
run

works; however, you cannot assume that a specific memory map, device drivers,or even basic I/O is available, although some simulators do provide these. For
info about any processor-specific simulator details, see the appropriate section
in Section 21.3 [Embedded Processors], page 348.
target native
Setup for local/native process debugging. Useful to make the run command
spawn native processes (likewise attach, etc.) even when set auto-connectnative-target is off (see [set auto-connect-native-target], page 36).
Different targets are available on different configurations of gdb; your configuration may
have more or fewer targets.
Many remote targets require you to download the executable’s code once you’ve successfully established a connection. You may wish to control various aspects of this process.
set hashThis command controls whether a hash mark ‘#’ is displayed while downloading
a file to the remote monitor. If on, a hash mark is displayed after each S-record
is successfully downloaded to the monitor.

show hash Show the current status of displaying the hash mark.
set debug monitor
Enable or disable display of communications messages between gdb and theremote monitor.
show debug monitor
Show the current status of displaying communications between gdb and theremote monitor.
load filename offset
Depending on what remote debugging facilities are configured into gdb, theload command may be available. Where it exists, it is meant to make filename(an executable) available for debugging on the remote system—by downloading,or dynamic linking, for example. load also records the filename symbol tablein gdb, like the add-symbol-file command.
If your gdb does not have a load command, attempting to execute it gets theerror message “You can’t do that when your target is ...”
The file is loaded at whatever address is specified in the executable. For some
object file formats, you can specify the load address when you link the program;for other formats, like a.out, the object file format specifies a fixed address.
It is also possible to tell gdb to load the executable file at a specific offset
described by the optional argument offset. When offset is provided, filename
must also be provided.

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Depending on the remote side capabilities, gdb may be able to load programs
into flash memory.
load does not repeat if you press RET again after using it.
flash-erase
Erases all known flash memory regions on the target.

19.3 Choosing Target Byte Order
Some types of processors, such as the MIPS, PowerPC, and Renesas SH, offer the ability
to run either big-endian or little-endian byte orders. Usually the executable or symbol will
include a bit to designate the endian-ness, and you will not need to worry about which touse. However, you may still find it useful to adjust gdb’s idea of processor endian-nessmanually.
set endian big
Instruct gdb to assume the target is big-endian.
set endian little
Instruct gdb to assume the target is little-endian.
set endian auto
Instruct gdb to use the byte order associated with the executable.
show endian
Display gdb’s current idea of the target byte order.
If the set endian auto mode is in effect and no executable has been selected, then theendianness used is the last one chosen either by one of the set endian big and set endian
little commands or by inferring from the last executable used. If no endianness has beenpreviously chosen, then the default for this mode is inferred from the target gdb has been
built for, and is little if the name of the target CPU has an el suffix and big otherwise.
Note that these commands merely adjust interpretation of symbolic data on the host,and that they have absolutely no effect on the target system.

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20 Debugging Remote Programs
If you are trying to debug a program running on a machine that cannot run gdb in theusual way, it is often useful to use remote debugging. For example, you might use remotedebugging on an operating system kernel, or on a small system which does not have ageneral purpose operating system powerful enough to run a full-featured debugger.
Some configurations of gdb have special serial or TCP/IP interfaces to make this workwith particular debugging targets. In addition, gdb comes with a generic serial protocol(specific to gdb, but not specific to any particular target system) which you can use if you
write the remote stubs—the code that runs on the remote system to communicate with
gdb.
Other remote targets may be available in your configuration of gdb; use help target
to list them.

20.1 Connecting to a Remote Target
This section describes how to connect to a remote target, including the types of connections
and their differences, how to set up executable and symbol files on the host and target, andthe commands used for connecting to and disconnecting from the remote target.

20.1.1 Types of Remote Connections
gdb supports two types of remote connections, target remote mode and target
extended-remote mode. Note that many remote targets support only target remotemode. There are several major differences between the two types of connections,
enumerated here:
Result of detach or program exit
With target remote mode: When the debugged program exits or you detachfrom it, gdb disconnects from the target. When using gdbserver, gdbserver
will exit.
With target extended-remote mode: When the debugged program exits or you
detach from it, gdb remains connected to the target, even though no programis running. You can rerun the program, attach to a running program, or use
monitor commands specific to the target.
When using gdbserver in this case, it does not exit unless it was invoked using
the --once option. If the --once option was not used, you can ask gdbserver toexit using the monitor exit command (see [Monitor Commands for gdbserver],page 324).
Specifying the program to debug
For both connection types you use the file command to specify the programon the host system. If you are using gdbserver there are some differences in
how to specify the location of the program on the target.
With target remote mode: You must either specify the program to debug on
the gdbserver command line or use the --attach option (see [Attaching to a
Running Program], page 321).

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With target extended-remote mode: You may specify the program to debugon the gdbserver command line, or you can load the program or attach to it
using gdb commands after connecting to gdbserver.
You can start gdbserver without supplying an initial command to run or process ID to attach. To do this, use the --multi command line option. Then
you can connect using target extended-remote and start the program you
want to debug (see below for details on using the run command in this scenario). Note that the conditions under which gdbserver terminates dependon how gdb connects to it (target remote or target extended-remote). The--multi option to gdbserver has no influence on that.
The run commandWith target remote mode: The run command is not supported. Once a connection has been established, you can use all the usual gdb commands to examineand change data. The remote program is already running, so you can use
commands like step and continue.
With target extended-remote mode: The run command is supported. The runcommand uses the value set by set remote exec-file (see [set remote execfile], page 328) to select the program to run. Command line arguments aresupported, except for wildcard expansion and I/O redirection (see Section 4.3[Arguments], page 38).
If you specify the program to debug on the command line, then the run command is not required to start execution, and you can resume using commands
like step and continue as with target remote mode.
Attaching With target remote mode: The gdb command attach is not supported. To
attach to a running program using gdbserver, you must use the --attach
option (see [Running gdbserver], page 321).
With target extended-remote mode: To attach to a running program, you may
use the attach command after the connection has been established. If you areusing gdbserver, you may also invoke gdbserver using the --attach option(see [Running gdbserver], page 321).
Some remote targets allow gdb to determine the executable file running in theprocess the debugger is attaching to. In such a case, gdb uses the value of
exec-file-mismatch to handle a possible mismatch between the executable
file name running in the process and the name of the current exec-file loaded
by gdb (see [set exec-file-mismatch], page 41).

20.1.2 Host and Target Files
gdb, running on the host, needs access to symbol and debugging information for yourprogram running on the target. This requires access to an unstripped copy of your program,and possibly any associated symbol files. Note that this section applies equally to bothtarget remote mode and target extended-remote mode.
Some remote targets (see [qXfer executable filename read], page 811, and see Section E.8[Host I/O Packets], page 823) allow gdb to access program files over the same connectionused to communicate with gdb. With such a target, if the remote program is unstripped,
the only command you need is target remote (or target extended-remote).

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If the remote program is stripped, or the target does not support remote program fileaccess, start up gdb using the name of the local unstripped copy of your program as thefirst argument, or use the file command. Use set sysroot to specify the location (onthe host) of target libraries (unless your gdb was compiled with the correct sysroot using--with-sysroot). Alternatively, you may use set solib-search-path to specify how gdb
locates target libraries.
The symbol file and target libraries must exactly match the executable and libraries on
the target, with one exception: the files on the host system should not be stripped, even if
the files on the target system are. Mismatched or missing files will lead to confusing results
during debugging. On gnu/Linux targets, mismatched or missing files may also prevent
gdbserver from debugging multi-threaded programs.

20.1.3 Remote Connection Commands
gdb can communicate with the target over a serial line, a local Unix domain socket, or overan IP network using TCP or UDP. In each case, gdb uses the same protocol for debugging your program; only the medium carrying the debugging packets varies. The target
remote and target extended-remote commands establish a connection to the target. Bothcommands accept the same arguments, which indicate the medium to use:target remote serial-device
target extended-remote serial-device
Use serial-device to communicate with the target. For example, to use a serialline connected to the device named /dev/ttyb:
target remote /dev/ttyb

If you’re using a serial line, you may want to give gdb the ‘--baud’ option, or
use the set serial baud command (see Section 20.4 [Remote Configuration],
page 326) before the target command.

target remote local-socket
target extended-remote local-socket
Use local-socket to communicate with the target. For example, to use a local
Unix domain socket bound to the file system entry /tmp/gdb-socket0:
target remote /tmp/gdb-socket0

Note that this command has the same form as the command to connect toa serial line. gdb will automatically determine which kind of file you havespecified and will make the appropriate kind of connection. This feature is notavailable if the host system does not support Unix domain sockets.

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target remote host:porttarget remote [host]:porttarget remote tcp:host:porttarget remote tcp:[host]:porttarget remote tcp4:host:porttarget remote tcp6:host:porttarget remote tcp6:[host]:porttarget extended-remote host:porttarget extended-remote [host]:porttarget extended-remote tcp:host:porttarget extended-remote tcp:[host]:porttarget extended-remote tcp4:host:porttarget extended-remote tcp6:host:porttarget extended-remote tcp6:[host]:port
Debug using a TCP connection to port on host. The host may be either a hostname, a numeric IPv4 address, or a numeric IPv6 address (with or without thesquare brackets to separate the address from the port); port must be a decimal
number. The host could be the target machine itself, if it is directly connectedto the net, or it might be a terminal server which in turn has a serial line to
the target.
For example, to connect to port 2828 on a terminal server named manyfarms:
target remote manyfarms:2828

To connect to port 2828 on a terminal server whose address is
2001:0db8:85a3:0000:0000:8a2e:0370:7334, you can either use the square
bracket syntax:
target remote [2001:0db8:85a3:0000:0000:8a2e:0370:7334]:2828

or explicitly specify the IPv6 protocol:
target remote tcp6:2001:0db8:85a3:0000:0000:8a2e:0370:7334:2828

This last example may be confusing to the reader, because there is no visible
separation between the hostname and the port number. Therefore, we recommend the user to provide IPv6 addresses using square brackets for clarity.
However, it is important to mention that for gdb there is no ambiguity: thenumber after the last colon is considered to be the port number.
If your remote target is actually running on the same machine as your debugger
session (e.g. a simulator for your target running on the same host), you can omit
the hostname. For example, to connect to port 1234 on your local machine:target remote :1234

Note that the colon is still required here.

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target remote udp:host:porttarget remote udp:[host]:porttarget remote udp4:host:porttarget remote udp6:[host]:porttarget extended-remote udp:host:porttarget extended-remote udp:host:porttarget extended-remote udp:[host]:porttarget extended-remote udp4:host:porttarget extended-remote udp6:host:porttarget extended-remote udp6:[host]:port
Debug using UDP packets to port on host. For example, to connect to UDP
port 2828 on a terminal server named manyfarms:
target remote udp:manyfarms:2828

When using a UDP connection for remote debugging, you should keep in mind
that the ‘U’ stands for “Unreliable”. UDP can silently drop packets on busy or
unreliable networks, which will cause havoc with your debugging session.
target remote | commandtarget extended-remote | command
Run command in the background and communicate with it using a pipe. The
command is a shell command, to be parsed and expanded by the system’s command shell, /bin/sh; it should expect remote protocol packets on its standard
input, and send replies on its standard output. You could use this to run astand-alone simulator that speaks the remote debugging protocol, to make net
connections using programs like ssh, or for other similar tricks.
If command closes its standard output (perhaps by exiting), gdb will try tosend it a SIGTERM signal. (If the program has already exited, this will have noeffect.)Whenever gdb is waiting for the remote program, if you type the interrupt character(often Ctrl-c), gdb attempts to stop the program. This may or may not succeed, dependingin part on the hardware and the serial drivers the remote system uses. If you type theinterrupt character once again, gdb displays this prompt:
Interrupted while waiting for the program.
Give up (and stop debugging it)? (y or n)

In target remote mode, if you type y, gdb abandons the remote debugging session. (Ifyou decide you want to try again later, you can use target remote again to connect once
more.) If you type n, gdb goes back to waiting.
In target extended-remote mode, typing n will leave gdb connected to the target.
detachWhen you have finished debugging the remote program, you can use the detachcommand to release it from gdb control. Detaching from the target normally resumes its execution, but the results will depend on your particular remote stub.
After the detach command in target remote mode, gdb is free to connect toanother target. In target extended-remote mode, gdb is still connected tothe target.

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disconnect
The disconnect command closes the connection to the target, and the target
is generally not resumed. It will wait for gdb (this instance or another one)to connect and continue debugging. After the disconnect command, gdb isagain free to connect to another target.
monitor cmd
This command allows you to send arbitrary commands directly to the remotemonitor. Since gdb doesn’t care about the commands it sends like this, thiscommand is the way to extend gdb—you can add new commands that only
the external monitor will understand and implement.

20.2 Sending files to a remote system
Some remote targets offer the ability to transfer files over the same connection used tocommunicate with gdb. This is convenient for targets accessible through other means, e.g.
gnu/Linux systems running gdbserver over a network interface. For other targets, e.g.
embedded devices with only a single serial port, this may be the only way to upload or
download files.
Not all remote targets support these commands.
remote put hostfile targetfile
Copy file hostfile from the host system (the machine running gdb) to targetfile
on the target system.
remote get targetfile hostfile
Copy file targetfile from the target system to hostfile on the host system.
remote delete targetfile
Delete targetfile from the target system.

20.3 Using the gdbserver Program
gdbserver is a control program for Unix-like systems, which allows you to connect yourprogram with a remote gdb via target remote or target extended-remote—but without
linking in the usual debugging stub.
gdbserver is not a complete replacement for the debugging stubs, because it requires
essentially the same operating-system facilities that gdb itself does. In fact, a system thatcan run gdbserver to connect to a remote gdb could also run gdb locally! gdbserver issometimes useful nevertheless, because it is a much smaller program than gdb itself. It isalso easier to port than all of gdb, so you may be able to get started more quickly on a
new system by using gdbserver. Finally, if you develop code for real-time systems, you
may find that the tradeoffs involved in real-time operation make it more convenient to do
as much development work as possible on another system, for example by cross-compiling.
You can use gdbserver to make a similar choice for debugging.
gdb and gdbserver communicate via either a serial line or a TCP connection, using thestandard gdb remote serial protocol.
Warning: gdbserver does not have any built-in security. Do not run
gdbserver connected to any public network; a gdb connection to gdbserver

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provides access to the target system with the same privileges as the user
running gdbserver.

20.3.1 Running gdbserver
Run gdbserver on the target system. You need a copy of the program you want to debug,
including any libraries it requires. gdbserver does not need your program’s symbol table,
so you can strip the program if necessary to save space. gdb on the host system does all
the symbol handling.
To use the server, you must tell it how to communicate with gdb; the name of yourprogram; and the arguments for your program. The usual syntax is:target> gdbserver comm program [ args ... ]comm is either a device name (to use a serial line), or a TCP hostname and portnumber,or - or stdio to use stdin/stdout of gdbserver. For example, to debug Emacs with theargument ‘foo.txt’ and communicate with gdb over the serial port /dev/com1:
target> gdbserver /dev/com1 emacs foo.txt

gdbserver waits passively for the host gdb to communicate with it.
To use a TCP connection instead of a serial line:
target> gdbserver host:2345 emacs foo.txt

The only difference from the previous example is the first argument, specifying that you
are communicating with the host gdb via TCP. The ‘host:2345’ argument means that
gdbserver is to expect a TCP connection from machine ‘host’ to local TCP port 2345.
(Currently, the ‘host’ part is ignored.) You can choose any number you want for the port
number as long as it does not conflict with any TCP ports already in use on the target
system (for example, 23 is reserved for telnet).1 You must use the same port number withthe host gdb target remote command.
The stdio connection is useful when starting gdbserver with ssh:(gdb) target remote | ssh -T hostname gdbserver - hello

The ‘-T’ option to ssh is provided because we don’t need a remote pty, and we don’t
want escape-character handling. Ssh does this by default when a command is provided, theflag is provided to make it explicit. You could elide it if you want to.
Programs started with stdio-connected gdbserver have /dev/null for stdin, andstdout,stderr are sent back to gdb for display through a pipe connected to gdbserver.
Both stdout and stderr use the same pipe.

20.3.1.1 Attaching to a Running Program
On some targets, gdbserver can also attach to running programs. This is accomplished
via the --attach argument. The syntax is:target> gdbserver --attach comm pid

pid is the process ID of a currently running process. It isn’t necessary to point gdbserver
at a binary for the running process.
In target extended-remote mode, you can also attach using the gdb attach command(see [Attaching in Types of Remote Connections], page 316).
1

If you choose a port number that conflicts with another service, gdbserver prints an error message andexits.

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You can debug processes by name instead of process ID if your target has the pidof
utility:target> gdbserver --attach comm ‘pidof program‘In case more than one copy of program is running, or program has multiple threads,
most versions of pidof support the -s option to only return the first process ID.

20.3.1.2 TCP port allocation lifecycle of gdbserverThis section applies only when gdbserver is run to listen on a TCP port.
gdbserver normally terminates after all of its debugged processes have terminated intarget remote mode. On the other hand, for target extended-remote, gdbserver stays
running even with no processes left. gdb normally terminates the spawned debugged process on its exit, which normally also terminates gdbserver in the target remote mode.
Therefore, when the connection drops unexpectedly, and gdb cannot ask gdbserver to killits debugged processes, gdbserver stays running even in the target remote mode.
When gdbserver stays running, gdb can connect to it again later. Such reconnecting
is useful for features like [disconnected tracing], page 212. For completeness, at most one
gdb can be connected at a time.
By default, gdbserver keeps the listening TCP port open, so that subsequent connections are possible. However, if you start gdbserver with the --once option, it will stop
listening for any further connection attempts after connecting to the first gdb session. Thismeans no further connections to gdbserver will be possible after the first one. It also means
gdbserver will terminate after the first connection with remote gdb has closed, even for
unexpectedly closed connections and even in the target extended-remote mode. The--once option allows reusing the same port number for connecting to multiple instancesof gdbserver running on the same host, since each instance closes its port after the firstconnection.

20.3.1.3 Other Command-Line Arguments for gdbserver
You can use the --multi option to start gdbserver without specifying a program to debug
or a process to attach to. Then you can attach in target extended-remote mode andrun or attach to a program. For more information, see [–multi Option in Types of Remote
Connnections], page 316.
The --debug[=option1,option2,...] option tells gdbserver to display extra diagnostic information about the debugging process. The options (option1, option2, etc) control
for which areas of gdbserver additional information will be displayed, possible values are:all

This enables all available diagnostic output.

threads

This enables diagnostic output related to threading. Currently other generaldiagnostic output is included in this category, but this could change in future
releases of gdbserver.

event-loop
This enables event-loop specific diagnostic output.
remoteThis enables diagnostic output related to the transfer of remote protocol packets
too and from the debugger.

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If no options are passed to --debug then this is treated as equivalent to --debug=threads.
This could change in future releases of gdbserver. The options passed to --debug areprocessed left to right, and individual options can be prefixed with the - (minus) characterto disable diagnostic output from this area, so it is possible to use:target> gdbserver --debug=all,-event-loop

In order to enable all diagnostic output except that for the event-loop.
The --debug-file=filename option tells gdbserver to write any debug output to thegiven filename. These options are intended for gdbserver development and for bug reports
to the developers.
The --debug-format=option1[,option2,...] option tells gdbserver to include additional information in each output. Possible options are:none

Turn off all extra information in debugging output.

allTurn on all extra information in debugging output.

timestamps
Include a timestamp in each line of debugging output.
Options are processed in order. Thus, for example, if none appears last then no additional
information is added to debugging output.
The --wrapper option specifies a wrapper to launch programs for debugging. The option
should be followed by the name of the wrapper, then any command-line arguments to passto the wrapper, then -- indicating the end of the wrapper arguments.
gdbserver runs the specified wrapper program with a combined command line including
the wrapper arguments, then the name of the program to debug, then any arguments to theprogram. The wrapper runs until it executes your program, and then gdb gains control.
You can use any program that eventually calls execve with its arguments as a wrapper.
Several standard Unix utilities do this, e.g. env and nohup. Any Unix shell script ending
with exec "$@" will also work.
For example, you can use env to pass an environment variable to the debugged program,without setting the variable in gdbserver’s environment:$ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog

The --selftest option runs the self tests in gdbserver:$ gdbserver --selftest
Ran 2 unit tests, 0 failed

These tests are disabled in release.

20.3.2 Connecting to gdbserver
The basic procedure for connecting to the remote target is:• Run gdb on the host system.
• Make sure you have the necessary symbol files (see [Host and target files], page 316).
Load symbols for your application using the file command before you connect. Use
set sysroot to locate target libraries (unless your gdb was compiled with the correct
sysroot using --with-sysroot).

324

Debugging with gdb• Connect to your target (see Section 20.1 [Connecting to a Remote Target], page 315).
For TCP connections, you must start up gdbserver prior to using the target command. Otherwise you may get an error whose text depends on the host system, butwhich usually looks something like ‘Connection refused’. Don’t use the load command in gdb when using target remote mode, since the program is already on thetarget.

20.3.3 Monitor Commands for gdbserver
During a gdb session using gdbserver, you can use the monitor command to send special
requests to gdbserver. Here are the available commands.
monitor help
List the available monitor commands.
monitor set debug off
Disable all internal logging from gdbserver.
monitor set debug on
Enable some general logging from within gdbserver. Currently this is equivalent
to monitor set debug threads on, but this might change in future releases of
gdbserver.
monitor set debug threads offmonitor set debug threads on
Disable or enable specific logging messages associated with thread handling in
gdbserver. Currently this category also includes additional output not specifically related to thread handling, this could change in future releases of gdbserver.
monitor set debug remote offmonitor set debug remote on
Disable or enable specific logging messages associated with the remote protocol(see Appendix E [Remote Protocol], page 773).
monitor set debug event-loop offmonitor set debug event-loop on
Disable or enable specific logging messages associated with gdbserver’s eventloop.
monitor set debug-file filename
monitor set debug-fileSend any debug output to the given file, or to stderr.
monitor set debug-format option1[,option2,...]
Specify additional text to add to debugging messages. Possible options are:none

Turn off all extra information in debugging output.

allTurn on all extra information in debugging output.

timestamps
Include a timestamp in each line of debugging output.

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Options are processed in order. Thus, for example, if none appears last thenno additional information is added to debugging output.
monitor set libthread-db-search-path [PATH]
When this command is issued, path is a colon-separated list of directories
to search for libthread_db (see Section 4.10 [set libthread-db-search-path],
page 47). If you omit path, ‘libthread-db-search-path’ will be reset to its
default value.
The special entry ‘$pdir’ for ‘libthread-db-search-path’ is not supported in
gdbserver.
monitor exit
Tell gdbserver to exit immediately. This command should be followed bydisconnect to close the debugging session. gdbserver will detach from any
attached processes and kill any processes it created. Use monitor exit to terminate gdbserver at the end of a multi-process mode debug session.

20.3.4 Tracepoints support in gdbserver
On some targets, gdbserver supports tracepoints, fast tracepoints and static tracepoints.
For fast or static tracepoints to work, a special library called the in-process agent (IPA),
must be loaded in the inferior process. This library is built and distributed as an integral part of gdbserver. In addition, support for static tracepoints requires building thein-process agent library with static tracepoints support. At present, the UST (LTTng
Userspace Tracer, http://lttng.org/ust) tracing engine is supported. This support is
automatically available if UST development headers are found in the standard include pathwhen gdbserver is built, or if gdbserver was explicitly configured using --with-ust to
point at such headers. You can explicitly disable the support using --with-ust=no.
There are several ways to load the in-process agent in your program:Specifying it as dependency at link time
You can link your program dynamically with the in-process agent library. On
most systems, this is accomplished by adding -linproctrace to the link command.
Using the system’s preloading mechanisms
You can force loading the in-process agent at startup time by using your system’s support for preloading shared libraries. Many Unixes support the conceptof preloading user defined libraries. In most cases, you do that by specifying
LD_PRELOAD=libinproctrace.so in the environment. See also the descriptionof gdbserver’s --wrapper command line option.
Using gdb to force loading the agent at run time
On some systems, you can force the inferior to load a shared library, by callinga dynamic loader function in the inferior that takes care of dynamically looking
up and loading a shared library. On most Unix systems, the function is dlopen.
You’ll use the call command for that. For example:(gdb) call dlopen ("libinproctrace.so", ...)

Note that on most Unix systems, for the dlopen function to be available, theprogram needs to be linked with -ldl.

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On systems that have a userspace dynamic loader, like most Unix systems, when you
connect to gdbserver using target remote, you’ll find that the program is stopped at
the dynamic loader’s entry point, and no shared library has been loaded in the program’s
address space yet, including the in-process agent. In that case, before being able to use anyof the fast or static tracepoints features, you need to let the loader run and load the sharedlibraries. The simplest way to do that is to run the program to the main procedure. E.g.,
if debugging a C or C++ program, start gdbserver like so:$ gdbserver :9999 myprogram

Start GDB and connect to gdbserver like so, and run to main:$ gdb myprogram(gdb) target remote myhost:9999
0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2(gdb) b main(gdb) continue

The in-process tracing agent library should now be loaded into the process; you canconfirm it with the info sharedlibrary command, which will list libinproctrace.so as
loaded in the process. You are now ready to install fast tracepoints, list static tracepoint
markers, probe static tracepoints markers, and start tracing.

20.4 Remote Configuration
This section documents the configuration options available when debugging remote programs. For the options related to the File I/O extensions of the remote protocol, see[system], page 837.
set remoteaddresssize bits
Set the maximum size of address in a memory packet to the specified numberof bits. gdb will mask off the address bits above that number, when it passes
addresses to the remote target. The default value is the number of bits in thetarget’s address.
show remoteaddresssize
Show the current value of remote address size in bits.
set serial baud n
Set the baud rate for the remote serial I/O to n baud. The value is used to set
the speed of the serial port used for debugging remote targets.
show serial baudShow the current speed of the remote connection.
set serial parity parity
Set the parity for the remote serial I/O. Supported values of parity are: even,none, and odd. The default is none.
show serial parity
Show the current parity of the serial port.
set remotebreak
If set to on, gdb sends a BREAK signal to the remote when you type Ctrl-c
to interrupt the program running on the remote. If set to off, gdb sends theChapter 20: Debugging Remote Programs

327‘Ctrl-C’ character instead. The default is off, since most remote systems expect
to see ‘Ctrl-C’ as the interrupt signal.
show remotebreakShow whether gdb sends BREAK or ‘Ctrl-C’ to interrupt the remote program.
set remoteflow on
set remoteflow off
Enable or disable hardware flow control (RTS/CTS) on the serial port used tocommunicate to the remote target.
show remoteflow
Show the current setting of hardware flow control.
set remotelogbase base
Set the base (a.k.a. radix) of logging serial protocol communications to base.
Supported values of base are: ascii, octal, and hex. The default is ascii.
show remotelogbase
Show the current setting of the radix for logging remote serial protocol.
set remotelogfile file
Record remote serial communications on the named file. The default is not torecord at all.
show remotelogfile
Show the current setting of the file name on which to record the serial communications.
set remotetimeout num
Set the timeout limit to wait for the remote target to respond to num seconds.
The default is 2 seconds.
show remotetimeout
Show the current number of seconds to wait for the remote target responses.
set remote hardware-watchpoint-limit limit
set remote hardware-breakpoint-limit limit
Restrict gdb to using limit remote hardware watchpoints or breakpoints. The
limit can be set to 0 to disable hardware watchpoints or breakpoints, andunlimited for unlimited watchpoints or breakpoints.
show remote hardware-watchpoint-limit
show remote hardware-breakpoint-limit
Show the current limit for the number of hardware watchpoints or breakpoints
that gdb can use.
set remote hardware-watchpoint-length-limit limit
Restrict gdb to using limit bytes for the maximum length of a remote hardware
watchpoint. A limit of 0 disables hardware watchpoints and unlimited allows
watchpoints of any length.
show remote hardware-watchpoint-length-limit
Show the current limit (in bytes) of the maximum length of a remote hardware
watchpoint.

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set remote exec-file filename
show remote exec-file
Select the file used for run with target extended-remote. This should be set
to a filename valid on the target system. If it is not set, the target will use adefault filename (e.g. the last program run).
set remote interrupt-sequence
Allow the user to select one of ‘Ctrl-C’, a BREAK or ‘BREAK-g’ as the sequence
to the remote target in order to interrupt the execution. ‘Ctrl-C’ is a default.
Some system prefers BREAK which is high level of serial line for some certain
time. Linux kernel prefers ‘BREAK-g’, a.k.a Magic SysRq g. It is BREAK signal
followed by character g.
show remote interrupt-sequence
Show which of ‘Ctrl-C’, BREAK or BREAK-g is sent by gdb to interrupt the
remote program. BREAK-g is BREAK signal followed by g and also known as
Magic SysRq g.
set remote interrupt-on-connect
Specify whether interrupt-sequence is sent to remote target when gdb connects
to it. This is mostly needed when you debug Linux kernel. Linux kernel expects
BREAK followed by g which is known as Magic SysRq g in order to connect gdb.
show remote interrupt-on-connect
Show whether interrupt-sequence is sent to remote target when gdb connects
to it.
set tcp auto-retry on
Enable auto-retry for remote TCP connections. This is useful if the remotedebugging agent is launched in parallel with gdb; there is a race condition
because the agent may not become ready to accept the connection before gdb
attempts to connect. When auto-retry is enabled, if the initial attempt toconnect fails, gdb reattempts to establish the connection using the timeout
specified by set tcp connect-timeout.
set tcp auto-retry off
Do not auto-retry failed TCP connections.
show tcp auto-retry
Show the current auto-retry setting.
set tcp connect-timeout seconds
set tcp connect-timeout unlimited
Set the timeout for establishing a TCP connection to the remote target toseconds. The timeout affects both polling to retry failed connections (enabled
by set tcp auto-retry on) and waiting for connections that are merely slow
to complete, and represents an approximate cumulative value. If seconds is
unlimited, there is no timeout and gdb will keep attempting to establish aconnection forever, unless interrupted with Ctrl-c. The default is 15 seconds.
show tcp connect-timeout
Show the current connection timeout setting.

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The gdb remote protocol autodetects the packets supported by your debugging stub. If
you need to override the autodetection, you can use these commands to enable or disable
individual packets. Each packet can be set to ‘on’ (the remote target supports this packet),‘off’ (the remote target does not support this packet), or ‘auto’ (detect remote target
support for this packet). They all default to ‘auto’. For more information about eachpacket, see Appendix E [Remote Protocol], page 773.
During normal use, you should not have to use any of these commands. If you do, that
may be a bug in your remote debugging stub, or a bug in gdb. You may want to report
the problem to the gdb developers.
For each packet name, the command to enable or disable the packet is set remote
name-packet. If you configure a packet, the configuration will apply for all future remotetargets if no target is selected. In case there is a target selected, only the configuration of
the current target is changed. All other existing remote targets’ features are not affected.
The command to print the current configuration of a packet is show remote name-packet.
It displays the current remote target’s configuration. If no remote target is selected, thedefault configuration for future connections is shown. The available settings are:Command Name

Remote Packet

Related Features

fetch-registerpinfo registers

set-registerP

setbinary-download

Xload, set

read-aux-vector

qXfer:auxv:read

info auxv

symbol-lookup

qSymbol

Detectingthreads

attachvAttachattachverbose-resume

vCont

Stepping or resuming multiple threads

run

vRun

run

software-breakpoint

Z0

break

hardware-breakpoint

Z1

hbreakwrite-watchpoint

Z2

watch

read-watchpoint

Z3

rwatchaccess-watchpoint

Z4

awatchmultiple

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pid-to-exec-file

qXfer:exec-file:read

attach, runtarget-features

qXfer:features:read

set architecture

library-info

qXfer:libraries:read

info
sharedlibrarymemory-map

qXfer:memory-map:read

info mem

read-sdata-object

qXfer:sdata:read

print $_sdata

read-siginfo-object

qXfer:siginfo:read

print $_siginfo

write-siginfo-object

qXfer:siginfo:write

set $_siginfo

threads

qXfer:threads:read

info threads

get-thread-localstorage-address

qGetTLSAddr

Displaying__thread variables

get-threadinformation-blockaddress

qGetTIBAddr

Display
MSWindows
ThreadInformation Block.

search-memory

qSearch:memoryfindsupported-packets

qSupported

Remotemunications
parameters

catch-syscalls

QCatchSyscalls

catch syscall

pass-signals

QPassSignals

handle signal

program-signals

QProgramSignals

handle signal

hostio-close-packet

vFile:close

remote get, remoteputhostio-open-packet

vFile:open

remote get, remoteputhostio-pread-packet

vFile:pread

remote get, remote
put

com-

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hostio-pwrite-packet

vFile:pwrite

remote get, remoteputhostio-unlink-packet

vFile:unlink

remote delete

hostio-readlinkpacket
hostio-fstat-packet

vFile:readlink

Host I/O

vFile:fstat

Host I/O

hostio-stat-packet

vFile:stat

Host I/O

hostio-setfs-packet

vFile:setfs

Host I/O

noack-packet

QStartNoAckMode

Packet acknowledgment

osdataqXfer:osdata:read

info osquery-attachedqAttached

Querying
process
state.

trace-buffer-size

QTBuffer:size

set trace-buffersize

trace-status

qTStatus

tstatustraceframe-info

qXfer:traceframe-info:read
Traceframe info

install-in-trace

InstallInTrace

Install tracepoint in
tracingdisable-randomization

QDisableRandomization

set
disable-randomization

startup-with-shell

QStartupWithShell

set startup-withshellenvironment-hexencodedenvironment-unset

QEnvironmentHexEncoded

set environment

QEnvironmentUnset

unset environment

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environment-reset

QEnvironmentReset

Reset theinferior
environment(i.e., unset
user-setvariables)

set-working-dir

QSetWorkingDir

set cwd

conditional-breakpoints-Z0 and Z1
packetSupport fortarget-side
breakpointcondition
evaluation

multiprocess-extensions multiprocessextensions

Debug multiple processes and remote
process PID awarenessswbreak-feature

swbreak stop reason

break

hwbreak-feature

hwbreak stop reason

hbreakfork-event-featurefork stop reasonfork

vfork-event-feature

vfork stop reason

vfork

exec-event-featureexec stop reason

exec

thread-events

QThreadEvents

Tracking thread lifetime.

thread-options

QThreadOptions

Set thread event reporting options.

no-resumed-stop-reply

no resumed thread left
stop reply

Tracking thread lifetime.

The number of bytes per memory-read or memory-write packet for a remote target
can be configured using the commands set remote memory-read-packet-size andset remote memory-write-packet-size. If set to ‘0’ (zero) the default packet size will
be used. The actual limit is further reduced depending on the target. Specify ‘fixed’
to disable the target-dependent restriction and ‘limit’ to enable it. Similar to theenabling and disabling of remote packets, the command applies to the currently selected
target (if available). If no remote target is selected, it applies to all future remoteconnections. The configuration of the selected target can be displayed using the commands

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show remote memory-read-packet-size and show remote memory-write-packet-size.
If no remote target is selected, the default configuration for future connections is shown.

20.5 Implementing a Remote Stub
The stub files provided with gdb implement the target side of the communication protocol,and the gdb side is implemented in the gdb source file remote.c. Normally, you can simply
allow these subroutines to communicate, and ignore the details. (If you’re implementing
your own stub file, you can still ignore the details: start with one of the existing stub files.
sparc-stub.c is the best organized, and therefore the easiest to read.)To debug a program running on another machine (the debugging target machine), youmust first arrange for all the usual prerequisites for the program to run by itself. For
example, for a C program, you need:
1. A startup routine to set up the C runtime environment; these usually have a name like
crt0. The startup routine may be supplied by your hardware supplier, or you may
have to write your own.
2. A C subroutine library to support your program’s subroutine calls, notably managing
input and output.
3. A way of getting your program to the other machine—for example, a download program. These are often supplied by the hardware manufacturer, but you may have towrite your own from hardware documentation.
The next step is to arrange for your program to use a serial port to communicate withthe machine where gdb is running (the host machine). In general terms, the scheme looks
like this:On the host,
gdb already understands how to use this protocol; when everything else is
set up, you can simply use the ‘target remote’ command (see Chapter 19[Specifying a Debugging Target], page 311).
On the target,
you must link with your program a few special-purpose subroutines that implement the gdb remote serial protocol. The file containing these subroutines iscalled a debugging stub.
On certain remote targets, you can use an auxiliary program gdbserver insteadof linking a stub into your program. See Section 20.3 [Using the gdbserver
Program], page 320, for details.
The debugging stub is specific to the architecture of the remote machine; for example,
use sparc-stub.c to debug programs on sparc boards.
These working remote stubs are distributed with gdb:
i386-stub.c
For Intel 386 and compatible architectures.
m68k-stub.c
For Motorola 680x0 architectures.

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sh-stub.c
For Renesas SH architectures.
sparc-stub.c
For sparc architectures.
sparcl-stub.c
For Fujitsu sparclite architectures.
The README file in the gdb distribution may list other recently added stubs.

20.5.1 What the Stub Can Do for You
The debugging stub for your architecture supplies these three subroutines:
set_debug_traps
This routine arranges for handle_exception to run when your program stops.
You must call this subroutine explicitly in your program’s startup code.
handle_exception
This is the central workhorse, but your program never calls it explicitly—the
setup code arranges for handle_exception to run when a trap is triggered.
handle_exception takes control when your program stops during execution(for example, on a breakpoint), and mediates communications with gdb on
the host machine. This is where the communications protocol is implemented;
handle_exception acts as the gdb representative on the target machine. It
begins by sending summary information on the state of your program, then continues to execute, retrieving and transmitting any information gdb needs, until
you execute a gdb command that makes your program resume; at that point,
handle_exception returns control to your own code on the target machine.
breakpoint
Use this auxiliary subroutine to make your program contain a breakpoint. Depending on the particular situation, this may be the only way for gdb to get
control. For instance, if your target machine has some sort of interrupt button,
you won’t need to call this; pressing the interrupt button transfers control tohandle_exception—in effect, to gdb. On some machines, simply receiving
characters on the serial port may also trigger a trap; again, in that situation,
you don’t need to call breakpoint from your own program—simply running‘target remote’ from the host gdb session gets control.
Call breakpoint if none of these is true, or if you simply want to make certain
your program stops at a predetermined point for the start of your debugging
session.

20.5.2 What You Must Do for the Stub
The debugging stubs that come with gdb are set up for a particular chip architecture, butthey have no information about the rest of your debugging target machine.
First of all you need to tell the stub how to communicate with the serial port.

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int getDebugChar()Write this subroutine to read a single character from the serial port. It may be
identical to getchar for your target system; a different name is used to allow
you to distinguish the two if you wish.
void putDebugChar(int)Write this subroutine to write a single character to the serial port. It may be
identical to putchar for your target system; a different name is used to allow
you to distinguish the two if you wish.
If you want gdb to be able to stop your program while it is running, you need to use
an interrupt-driven serial driver, and arrange for it to stop when it receives a ^C (‘\003’,
the control-C character). That is the character which gdb uses to tell the remote system
to stop.
Getting the debugging target to return the proper status to gdb probably requires
changes to the standard stub; one quick and dirty way is to just execute a breakpoint
instruction (the “dirty” part is that gdb reports a SIGTRAP instead of a SIGINT).
Other routines you need to supply are:void exceptionHandler (int exception_number, void *exception_address)
Write this function to install exception address in the exception handling tables. You need to do this because the stub does not have any way of knowing
what the exception handling tables on your target system are like (for example, the processor’s table might be in rom, containing entries which point to atable in ram). The exception number specifies the exception which should bechanged; its meaning is architecture-dependent (for example, different numbers
might represent divide by zero, misaligned access, etc). When this exception
occurs, control should be transferred directly to exception address, and theprocessor state (stack, registers, and so on) should be just as it is when a processor exception occurs. So if you want to use a jump instruction to reach
exception address, it should be a simple jump, not a jump to subroutine.
For the 386, exception address should be installed as an interrupt gate so thatinterrupts are masked while the handler runs. The gate should be at privilege
level 0 (the most privileged level). The sparc and 68k stubs are able to maskinterrupts themselves without help from exceptionHandler.
void flush_i_cache()On sparc and sparclite only, write this subroutine to flush the instruction
cache, if any, on your target machine. If there is no instruction cache, thissubroutine may be a no-op.
On target machines that have instruction caches, gdb requires this function to
make certain that the state of your program is stable.
You must also make sure this library routine is available:
void *memset(void *, int, int)
This is the standard library function memset that sets an area of memory to a
known value. If you have one of the free versions of libc.a, memset can be foundthere; otherwise, you must either obtain it from your hardware manufacturer,
or write your own.

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If you do not use the GNU C compiler, you may need other standard library subroutines
as well; this varies from one stub to another, but in general the stubs are likely to use anyof the common library subroutines which gcc generates as inline code.

20.5.3 Putting it All Together
In summary, when your program is ready to debug, you must follow these steps.
1. Make sure you have defined the supporting low-level routines (see Section 20.5.2 [WhatYou Must Do for the Stub], page 334):
getDebugChar, putDebugChar,flush_i_cache, memset, exceptionHandler.
2. Insert these lines in your program’s startup code, before the main procedure is called:
set_debug_traps();breakpoint();

On some machines, when a breakpoint trap is raised, the hardware automatically makes
the PC point to the instruction after the breakpoint. If your machine doesn’t do that,you may need to adjust handle_exception to arrange for it to return to the instruction
after the breakpoint on this first invocation, so that your program doesn’t keep hitting
the initial breakpoint instead of making progress.
3. For the 680x0 stub only, you need to provide a variable called exceptionHook. Normally you just use:
void (*exceptionHook)() = 0;

but if before calling set_debug_traps, you set it to point to a function in your program,that function is called when gdb continues after stopping on a trap (for example, bus
error). The function indicated by exceptionHook is called with one parameter: an int
which is the exception number.
4. Compile and link together: your program, the gdb debugging stub for your target
architecture, and the supporting subroutines.
5. Make sure you have a serial connection between your target machine and the gdb host,and identify the serial port on the host.
6. Download your program to your target machine (or get it there by whatever means the
manufacturer provides), and start it.
7. Start gdb on the host, and connect to the target (see Section 20.1 [Connecting to a
Remote Target], page 315).

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21 Configuration-Specific Information
While nearly all gdb commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available incertain configurations.
There are three major categories of configurations: native configurations, where the hostand target are the same, embedded operating system configurations, which are usually thesame for several different processor architectures, and bare embedded processors, which arequite different from each other.

21.1 Native
This section describes details specific to particular native configurations.

21.1.1 BSD libkvm Interface
BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory interface thatprovides a uniform interface for accessing kernel virtual memory images, including live
systems and crash dumps. gdb uses this interface to allow you to debug live kernels andkernel crash dumps on many native BSD configurations. This is implemented as a special
kvm debugging target. For debugging a live system, load the currently running kernel into
gdb and connect to the kvm target:(gdb) target kvm

For debugging crash dumps, provide the file name of the crash dump as an argument:(gdb) target kvm /var/crash/bsd.0

Once connected to the kvm target, the following commands are available:
kvm pcb

Set current context from the Process Control Block (PCB) address.

kvm proc

Set current context from proc address. This command isn’t available on modern
FreeBSD systems.

21.1.2 Process Information
Some operating systems provide interfaces to fetch additional information about running
processes beyond memory and per-thread register state. If gdb is configured for an operating system with a supported interface, the command info proc is available to report
information about the process running your program, or about any process running on yoursystem.
One supported interface is a facility called ‘/proc’ that can be used to examine the imageof a running process using file-system subroutines. This facility is supported on gnu/Linuxand Solaris systems.
On FreeBSD and NetBSD systems, system control nodes are used to query process
information.
In addition, some systems may provide additional process information in core files. Notethat a core file may include a subset of the information available from a live process. Process
information is currently available from cores created on gnu/Linux and FreeBSD systems.

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info proc
info proc process-id
Summarize available information about a process. If a process ID is specified byprocess-id, display information about that process; otherwise display information about the program being debugged. The summary includes the debugged
process ID, the command line used to invoke it, its current working directory,
and its executable file’s absolute file name.
On some systems, process-id can be of the form ‘[pid]/tid’ which specifies
a certain thread ID within a process. If the optional pid part is missing, itmeans a thread from the process being debugged (the leading ‘/’ still needs tobe present, or else gdb will interpret the number as a process ID rather than athread ID).
info proc cmdline
Show the original command line of the process. This command is supported on
gnu/Linux, FreeBSD and NetBSD.
info proc cwd
Show the current working directory of the process. This command is supported
on gnu/Linux, FreeBSD and NetBSD.
info proc exe
Show the name of executable of the process. This command is supported on
gnu/Linux, FreeBSD and NetBSD.
info proc files
Show the file descriptors open by the process. For each open file descriptor, gdb
shows its number, type (file, directory, character device, socket), file pointeroffset, and the name of the resource open on the descriptor. The resource namecan be a file name (for files, directories, and devices) or a protocol followedby socket address (for network connections). This command is supported on
FreeBSD.
This example shows the open file descriptors for a process using a tty for standard input and output as well as two network sockets:(gdb) info proc files 22136
process 22136
Open files:
FD
Type
text
file
ctty
chr
cwd
dir
root
dir
0
chr
1
chr
2
chr
3 socket
4 socket

OffsetFlags
Name- r-------- /usr/bin/ssh- rw------- /dev/pts/20- r-------- /usr/home/john- r-------- /0x32933a4 rw------- /dev/pts/20
0x32933a4 rw------- /dev/pts/20
0x32933a4 rw------- /dev/pts/20
0x0 rw----n-- tcp4 10.0.1.2:53014 -> 10.0.1.10:22
0x0 rw------- unix stream:/tmp/ssh-FIt89oAzOn5f/agent.2456

info proc mappings
Report the memory address space ranges accessible in a process. On Solaris,
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339

whether the process has read, write, or execute access rights to each range. On
gnu/Linux, FreeBSD and NetBSD systems, each memory range includes theobject file which is mapped to that range.
info proc statinfo proc status
Show additional process-related information, including the user ID and group
ID; virtual memory usage; the signals that are pending, blocked, and ignored;
its TTY; its consumption of system and user time; its stack size; its ‘nice’ value;etc. These commands are supported on gnu/Linux, FreeBSD and NetBSD.
For gnu/Linux systems, see the ‘proc’ man page for more information (typeman 5 proc from your shell prompt).
For FreeBSD and NetBSD systems, info proc stat is an alias for info proc
status.
info proc all
Show all the information about the process described under all of the above
info proc subcommands.
set procfs-trace
This command enables and disables tracing of procfs API calls.
show procfs-trace
Show the current state of procfs API call tracing.
set procfs-file file
Tell gdb to write procfs API trace to the named file. gdb appends the trace
info to the previous contents of the file. The default is to display the trace on
the standard output.
show procfs-file
Show the file to which procfs API trace is written.
proc-trace-entry
proc-trace-exit
proc-untrace-entry
proc-untrace-exit
These commands enable and disable tracing of entries into and exits from thesyscall interface.

21.1.3 Features for Debugging djgpp Programs
djgpp is a port of the gnu development tools to MS-DOS and MS-Windows. djgpp
programs are 32-bit protected-mode programs that use the DPMI (DOS Protected-ModeInterface) API to run on top of real-mode DOS systems and their emulations.
gdb supports native debugging of djgpp programs, and defines a few commands specificto the djgpp port. This subsection describes those commands.
info dos

This is a prefix of djgpp-specific commands which print information about thetarget system and important OS structures.

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info dos sysinfoThis command displays assorted information about the underlying platform:
the CPU type and features, the OS version and flavor, the DPMI version, andthe available conventional and DPMI memory.
info dos gdt
info dos ldt
info dos idt
These 3 commands display entries from, respectively, Global, Local, and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor tables are data
structures which store a descriptor for each segment that is currently in use.
The segment’s selector is an index into a descriptor table; the table entry forthat index holds the descriptor’s base address and limit, and its attributes andaccess rights.
A typical djgpp program uses 3 segments: a code segment, a data segment(used for both data and the stack), and a DOS segment (which allows access to
DOS/BIOS data structures and absolute addresses in conventional memory).
However, the DPMI host will usually define additional segments in order tosupport the DPMI environment.
These commands allow to display entries from the descriptor tables. Without
an argument, all entries from the specified table are displayed. An argument,
which should be an integer expression, means display a single entry whose index
is given by the argument. For example, here’s a convenient way to display
information about the debugged program’s data segment:(gdb) info dos ldt $ds
0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)

This comes in handy when you want to see whether a pointer is outside thedata segment’s limit (i.e. garbled).
info dos pde
info dos pte
These two commands display entries from, respectively, the Page Directory and
the Page Tables. Page Directories and Page Tables are data structures which
control how virtual memory addresses are mapped into physical addresses. A
Page Table includes an entry for every page of memory that is mapped into theprogram’s address space; there may be several Page Tables, each one holding
up to 4096 entries. A Page Directory has up to 4096 entries, one each for every
Page Table that is currently in use.
Without an argument, info dos pde displays the entire Page Directory, andinfo dos pte displays all the entries in all of the Page Tables. An argument,
an integer expression, given to the info dos pde command means display onlythat entry from the Page Directory table. An argument given to the info dos
pte command means display entries from a single Page Table, the one pointed
to by the specified entry in the Page Directory.
These commands are useful when your program uses DMA (Direct Memory
Access), which needs physical addresses to program the DMA controller.
These commands are supported only with some DPMI servers.

Chapter 21: Configuration-Specific Information341

info dos address-pte addr
This command displays the Page Table entry for a specified linear address. The
argument addr is a linear address which should already have the appropriate
segment’s base address added to it, because this command accepts addresses
which may belong to any segment. For example, here’s how to display the Page
Table entry for the page where a variable i is stored:(gdb) info dos address-pte __djgpp_base_address + (char *)&iPage Table entry for address 0x11a00d30:
Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30

This says that i is stored at offset 0xd30 from the page whose physical baseaddress is 0x02698000, and shows all the attributes of that page.
Note that you must cast the addresses of variables to a char *, since otherwise
the value of __djgpp_base_address, the base address of all variables and functions in a djgpp program, will be added using the rules of C pointer arithmetic:
if i is declared an int, gdb will add 4 times the value of __djgpp_base_address
to the address of i.
Here’s another example, it displays the Page Table entry for the transfer buffer:(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)
Page Table entry for address 0x29110:
Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110(The + 3 offset is because the transfer buffer’s address is the 3rd member of the_go32_info_block structure.) The output clearly shows that this DPMI server
maps the addresses in conventional memory 1:1, i.e. the physical (0x00029000+ 0x110) and linear (0x29110) addresses are identical.
This command is supported only with some DPMI servers.
In addition to native debugging, the DJGPP port supports remote debugging via a serial
data link. The following commands are specific to remote serial debugging in the DJGPP
port of gdb.
set com1base addr
This command sets the base I/O port address of the COM1 serial port.
set com1irq irq
This command sets the Interrupt Request (IRQ) line to use for the COM1 serial
port.
There are similar commands ‘set com2base’, ‘set com3irq’, etc. for setting theport address and the IRQ lines for the other 3 COM ports.
The related commands ‘show com1base’, ‘show com1irq’ etc. display the current settings of the base address and the IRQ lines used by the COM ports.
info serial
This command prints the status of the 4 DOS serial ports. For each port,
it prints whether it’s active or not, its I/O base address and IRQ number,whether it uses a 16550-style FIFO, its baudrate, and the counts of various
errors encountered so far.

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21.1.4 Features for Debugging MS Windows PE Executables
gdb supports native debugging of MS Windows programs, including DLLs with and without
symbolic debugging information.
MS-Windows programs that call SetConsoleMode to switch off the special meaning ofthe ‘Ctrl-C’ keystroke cannot be interrupted by typing C-c. For this reason, gdb on MSWindows supports C-BREAK as an alternative interrupt key sequence, which can be used tointerrupt the debuggee even if it ignores C-c.
There are various additional Cygwin-specific commands, described in this section. Working with DLLs that have no debugging symbols is described in Section 21.1.4.1 [Non-debug
DLL Symbols], page 343.
info w32

This is a prefix of MS Windows-specific commands which print information
about the target system and important OS structures.

info w32 selector
This command displays information returned by the Win32 API
GetThreadSelectorEntry function. It takes an optional argument that isevaluated to a long value to give the information about this given selector.
Without argument, this command displays information about the six segment
registers.
info w32 thread-information-block
This command displays thread specific information stored in the Thread Information Block (readable on the X86 CPU family using $fs selector for 32-bit
programs and $gs for 64-bit programs).
signal-event id
This command signals an event with user-provided id. Used to resume crashingprocess when attached to it using MS-Windows JIT debugging (AeDebug).
To use it, create or edit the following keys in HKLM\SOFTWARE\Microsoft\Windows
NT\CurrentVersion\AeDebug and/or HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows
NT\CurrentVersion\AeDebug (for x86 64 versions):− Debugger (REG SZ) — a command to launch the debugger. Suggested
command is: fully-qualified-path-to-gdb.exe -ex "attach %ld" -ex"signal-event %ld" -ex "continue".
The first %ld will be replaced by the process ID of the crashing process, thesecond %ld will be replaced by the ID of the event that blocks the crashingprocess, waiting for gdb to attach.
− Auto (REG SZ) — either 1 or 0. 1 will make the system run debugger
specified by the Debugger key automatically, 0 will cause a dialog box with
“OK” and “Cancel” buttons to appear, which allows the user to either
terminate the crashing process (OK) or debug it (Cancel).
set cygwin-exceptions modeIf mode is on, gdb will break on exceptions that happen inside the Cygwin DLL.
If mode is off, gdb will delay recognition of exceptions, and may ignore some
exceptions which seem to be caused by internal Cygwin DLL “bookkeeping”.
This option is meant primarily for debugging the Cygwin DLL itself; the default
value is off to avoid annoying gdb users with false SIGSEGV signals.

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show cygwin-exceptions
Displays whether gdb will break on exceptions that happen inside the Cygwin
DLL itself.
set new-console modeIf mode is on the debuggee will be started in a new console on next start. If
mode is off, the debuggee will be started in the same console as the debugger.
show new-console
Displays whether a new console is used when the debuggee is started.
set new-group modeThis boolean value controls whether the debuggee should start a new group or
stay in the same group as the debugger. This affects the way the Windows OS
handles ‘Ctrl-C’.
show new-group
Displays current value of new-group boolean.
set debugevents
This boolean value adds debug output concerning kernel events related to the
debuggee seen by the debugger. This includes events that signal thread andprocess creation and exit, DLL loading and unloading, console interrupts, anddebugging messages produced by the Windows OutputDebugString API call.
set debugexec
This boolean value adds debug output concerning execute events (such as resume thread) seen by the debugger.
set debugexceptions
This boolean value adds debug output concerning exceptions in the debuggee
seen by the debugger.
set debugmemory
This boolean value adds debug output concerning debuggee memory reads andwrites by the debugger.
set shell This boolean values specifies whether the debuggee is called via a shell or directly (default value is on).
show shell
Displays if the debuggee will be started with a shell.

21.1.4.1 Support for DLLs without Debugging Symbols
Very often on windows, some of the DLLs that your program relies on do not include
symbolic debugging information (for example, kernel32.dll). When gdb doesn’t recognize
any debugging symbols in a DLL, it relies on the minimal amount of symbolic information
contained in the DLL’s export table. This section describes working with such symbols,
known internally to gdb as “minimal symbols”.
Note that before the debugged program has started execution, no DLLs will have been
loaded. The easiest way around this problem is simply to start the program — either by
setting a breakpoint or letting the program run once to completion.

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21.1.4.2 DLL Name Prefixes
In keeping with the naming conventions used by the Microsoft debugging tools, DLL
export symbols are made available with a prefix based on the DLL name, for instance
KERNEL32!CreateFileA. The plain name is also entered into the symbol table, so
CreateFileA is often sufficient. In some cases there will be name clashes within a program(particularly if the executable itself includes full debugging symbols) necessitating the useof the fully qualified name when referring to the contents of the DLL. Use single-quotes
around the name to avoid the exclamation mark (“!”) being interpreted as a language
operator.
Note that the internal name of the DLL may be all upper-case, even though the filename of the DLL is lower-case, or vice-versa. Since symbols within gdb are case-sensitive
this may cause some confusion. If in doubt, try the info functions and info variables
commands or even maint print msymbols (see Chapter 16 [Symbols], page 263). Here’s an
example:(gdb) info function CreateFileAAll functions matching regular expression "CreateFileA":
Non-debugging symbols:
0x77e885f4 CreateFileA
0x77e885f4 KERNEL32!CreateFileA(gdb) info function !
All functions matching regular expression "!":
Non-debugging symbols:
0x6100114c cygwin1!__assert
0x61004034 cygwin1!_dll_crt0@0
0x61004240 cygwin1!dll_crt0(per_process *)[etc...]

21.1.4.3 Working with Minimal Symbols
Symbols extracted from a DLL’s export table do not contain very much type information.
All that gdb can do is guess whether a symbol refers to a function or variable dependingon the linker section that contains the symbol. Also note that the actual contents of thememory contained in a DLL are not available unless the program is running. This meansthat you cannot examine the contents of a variable or disassemble a function within a DLL
without a running program.
Variables are generally treated as pointers and dereferenced automatically. For thisreason, it is often necessary to prefix a variable name with the address-of operator (“&”)
and provide explicit type information in the command. Here’s an example of the type ofproblem:(gdb) print ’cygwin1!__argv’’cygwin1!__argv’ has unknown type; cast it to its declared type(gdb) x ’cygwin1!__argv’’cygwin1!__argv’ has unknown type; cast it to its declared typeAnd two possible solutions:(gdb) print ((char **)’cygwin1!__argv’)[0]$2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"(gdb) x/2x &’cygwin1!__argv’
0x610c0aa8 <cygwin1!__argv>:
0x10021608
0x00000000

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345(gdb) x/x 0x10021608
0x10021608:
0x0022fd98(gdb) x/s 0x0022fd98
0x22fd98:"/cygdrive/c/mydirectory/myprogram"

Setting a break point within a DLL is possible even before the program starts execution. However, under these circumstances, gdb can’t examine the initial instructions of thefunction in order to skip the function’s frame set-up code. You can work around this byusing “*&” to set the breakpoint at a raw memory address:(gdb) break *&’python22!PyOS_Readline’
Breakpoint 1 at 0x1e04eff0

The author of these extensions is not entirely convinced that setting a break point withina shared DLL like kernel32.dll is completely safe.

21.1.5 Commands Specific to gnu Hurd Systems
This subsection describes gdb commands specific to the gnu Hurd native debugging.
set signals
set sigs This command toggles the state of inferior signal interception by gdb. Machexceptions, such as breakpoint traps, are not affected by this command. sigs
is a shorthand alias for signals.
show signals
show sigs Show the current state of intercepting inferior’s signals.
set signal-thread
set sigthreadThis command tells gdb which thread is the libc signal thread. That thread
is run when a signal is delivered to a running process. set sigthread is theshorthand alias of set signal-thread.
show signal-thread
show sigthread
These two commands show which thread will run when the inferior is delivereda signal.
set stopped
This commands tells gdb that the inferior process is stopped, as with the
SIGSTOP signal. The stopped process can be continued by delivering a signal
to it.
show stopped
This command shows whether gdb thinks the debuggee is stopped.
set exceptions
Use this command to turn off trapping of exceptions in the inferior. When
exception trapping is off, neither breakpoints nor single-stepping will work. To
restore the default, set exception trapping on.
show exceptionsShow the current state of trapping exceptions in the inferior.

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set task pause
This command toggles task suspension when gdb has control. Setting it to on
takes effect immediately, and the task is suspended whenever gdb gets control.
Setting it to off will take effect the next time the inferior is continued. If thisoption is set to off, you can use set thread default pause on or set threadpause on (see below) to pause individual threads.
show task pause
Show the current state of task suspension.
set task detach-suspend-countThis command sets the suspend count the task will be left with when gdb
detaches from it.
show task detach-suspend-countShow the suspend count the task will be left with when detaching.
set task exception-port
set task excp
This command sets the task exception port to which gdb will forward exceptions. The argument should be the value of the send rights of the task. settask excp is a shorthand alias.
set noninvasive
This command switches gdb to a mode that is the least invasive as far as
interfering with the inferior is concerned. This is the same as using set task
pause, set exceptions, and set signals to values opposite to the defaults.
info send-rights
info receive-rights
info port-rights
info port-sets
info dead-names
info ports
info psets
These commands display information about, respectively, send rights, receive
rights, port rights, port sets, and dead names of a task. There are also shorthand aliases: info ports for info port-rights and info psets for info
port-sets.
set thread pause
This command toggles current thread suspension when gdb has control. Setting
it to on takes effect immediately, and the current thread is suspended whenever
gdb gets control. Setting it to off will take effect the next time the inferior iscontinued. Normally, this command has no effect, since when gdb has control,
the whole task is suspended. However, if you used set task pause off (seeabove), this command comes in handy to suspend only the current thread.
show thread pause
This command shows the state of current thread suspension.
set thread run
This command sets whether the current thread is allowed to run.

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show thread run
Show whether the current thread is allowed to run.
set thread detach-suspend-countThis command sets the suspend count gdb will leave on a thread when detaching. This number is relative to the suspend count found by gdb when it
notices the thread; use set thread takeover-suspend-count to force it to an
absolute value.
show thread detach-suspend-countShow the suspend count gdb will leave on the thread when detaching.
set thread exception-port
set thread excp
Set the thread exception port to which to forward exceptions. This overrides
the port set by set task exception-port (see above). set thread excp is theshorthand alias.
set thread takeover-suspend-countNormally, gdb’s thread suspend counts are relative to the value gdb finds
when it notices each thread. This command changes the suspend counts to beabsolute instead.
set thread default
show thread default
Each of the above set thread commands has a set thread default counterpart (e.g., set thread default pause, set thread default exception-port,etc.). The thread default variety of commands sets the default thread properties for all threads; you can then change the properties of individual threads
with the non-default commands.

21.1.6 Darwin
gdb provides the following commands specific to the Darwin target:
set debug darwin num
When set to a non zero value, enables debugging messages specific to the Darwin
support. Higher values produce more verbose output.
show debug darwin
Show the current state of Darwin messages.
set debug mach-o num
When set to a non zero value, enables debugging messages while gdb is reading
Darwin object files. (Mach-O is the file format used on Darwin for object
and executable files.) Higher values produce more verbose output. This is acommand to diagnose problems internal to gdb and should not be needed innormal usage.
show debug mach-oShow the current state of Mach-O file messages.

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set mach-exceptions on
set mach-exceptions off
On Darwin, faults are first reported as a Mach exception and are then mapped
to a Posix signal. Use this command to turn on trapping of Mach exceptionsin the inferior. This might be sometimes useful to better understand the causeof a fault. The default is off.
show mach-exceptionsShow the current state of exceptions trapping.

21.1.7 FreeBSD
When the ABI of a system call is changed in the FreeBSD kernel, this is implemented byleaving a compatibility system call using the old ABI at the existing number and allocatinga new system call number for the version using the new ABI. As a convenience, when asystem call is caught by name (see [catch syscall], page 70), compatibility system calls arealso caught.
For example, FreeBSD 12 introduced a new variant of the kevent system call and catching the kevent system call by name catches both variants:(gdb) catch syscall kevent
Catchpoint 1 (syscalls ’freebsd11_kevent’ [363] ’kevent’ [560])(gdb)

21.2 Embedded Operating Systems
This section describes configurations involving the debugging of embedded operating systems that are available for several different architectures.
gdb includes the ability to debug programs running on various real-time operating systems.

21.3 Embedded Processors
This section goes into details specific to particular embedded configurations.
Whenever a specific embedded processor has a simulator, gdb allows to send an arbitrary
command to the simulator.
sim command
Send an arbitrary command string to the simulator. Consult the documentation
for the specific simulator in use for information about acceptable commands.

21.3.1 Synopsys ARC
gdb provides the following ARC-specific commands:
set debug arc
Control the level of ARC specific debug messages. Use 0 for no messages (thedefault), 1 for debug messages, and 2 for even more debug messages.
show debug arc
Show the level of ARC specific debugging in operation.
maint print arc arc-instruction address
Print internal disassembler information about instruction at a given address.

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21.3.2 ARM
gdb provides the following ARM-specific commands:
set arm disassembler
This commands selects from a list of disassembly styles. The "std" style is thestandard style.
show arm disassembler
Show the current disassembly style.
set arm apcs32
This command toggles ARM operation mode between 32-bit and 26-bit.
show arm apcs32
Display the current usage of the ARM 32-bit mode.
set arm fpu fputypeThis command sets the ARM floating-point unit (FPU) type. The argument
fputype can be one of these:
auto

Determine the FPU type by querying the OS ABI.

softfpa

Software FPU, with mixed-endian doubles on little-endian ARM
processors.

fpa

GCC-compiled FPA co-processor.

softvfp

Software FPU with pure-endian doubles.

vfp

VFP co-processor.

show arm fpu
Show the current type of the FPU.
set arm abi
This command forces gdb to use the specified ABI.
show arm abi
Show the currently used ABI.
set arm fallback-mode (arm|thumb|auto)
gdb uses the symbol table, when available, to determine whether instructions
are ARM or Thumb. This command controls gdb’s default behavior when thesymbol table is not available. The default is ‘auto’, which causes gdb to use
the current execution mode (from the T bit in the CPSR register).
show arm fallback-mode
Show the current fallback instruction mode.
set arm force-mode (arm|thumb|auto)
This command overrides use of the symbol table to determine whether instructions are ARM or Thumb. The default is ‘auto’, which causes gdb to use thesymbol table and then the setting of ‘set arm fallback-mode’.
show arm force-mode
Show the current forced instruction mode.

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set arm unwind-secure-framesThis command enables unwinding from Non-secure to Secure mode on Cortex-M
with Security extension. This can trigger security exceptions when unwinding
the exception stack. It is enabled by default.
show arm unwind-secure-frames
Show whether unwinding from Non-secure to Secure mode is enabled.
set debug arm
Toggle whether to display ARM-specific debugging messages from the ARM
target support subsystem.
show debug arm
Show whether ARM-specific debugging messages are enabled.
target sim [simargs] ...
The gdb ARM simulator accepts the following optional arguments.
--swi-support=type
Tell the simulator which SWI interfaces to support. The argument
type may be a comma separated list of the following values. The
default value is all.
none
demon
angel
redbootall

21.3.3 BPF
target sim [simargs] ...
The gdb BPF simulator accepts the following optional arguments.
--skb-data-offset=offset
Tell the simulator the offset, measured in bytes, of the skb_data
field in the kernel struct sk_buff structure. This offset is used bysome BPF specific-purpose load/store instructions. Defaults to 0.

21.3.4 M68k
The Motorola m68k configuration includes ColdFire support.

21.3.5 MicroBlaze
The MicroBlaze is a soft-core processor supported on various Xilinx FPGAs, such as Spartan or Virtex series. Boards with these processors usually have JTAG ports which connect
to a host system running the Xilinx Embedded Development Kit (EDK) or Software Development Kit (SDK). This host system is used to download the configuration bitstream
to the target FPGA. The Xilinx Microprocessor Debugger (XMD) program communicateswith the target board using the JTAG interface and presents a gdbserver interface to theChapter 21: Configuration-Specific Information

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board. By default xmd uses port 1234. (While it is possible to change this default port, it
requires the use of undocumented xmd commands. Contact Xilinx support if you need to
do this.)Use these GDB commands to connect to the MicroBlaze target processor.
target remote :1234
Use this command to connect to the target if you are running gdb on the same
system as xmd.
target remote xmd-host:1234
Use this command to connect to the target if it is connected to xmd running ona different system named xmd-host.
load

Use this command to download a program to the MicroBlaze target.

set debug microblaze n
Enable MicroBlaze-specific debugging messages if non-zero.
show debug microblaze nShow MicroBlaze-specific debugging level.

21.3.6 MIPS Embedded
gdb supports these special commands for MIPS targets:set mipsfpu double
set mipsfpu single
set mipsfpu none
set mipsfpu autoshow mipsfpu
If your target board does not support the MIPS floating point coprocessor, you
should use the command ‘set mipsfpu none’ (if you need this, you may wish to
put the command in your gdb init file). This tells gdb how to find the return
value of functions which return floating point values. It also allows gdb to avoid
saving the floating point registers when calling functions on the board. If you
are using a floating point coprocessor with only single precision floating point
support, as on the r4650 processor, use the command ‘set mipsfpu single’.
The default double precision floating point coprocessor may be selected using‘set mipsfpu double’.
In previous versions the only choices were double precision or no floating point,so ‘set mipsfpu on’ will select double precision and ‘set mipsfpu off’ will select no floating point.
As usual, you can inquire about the mipsfpu variable with ‘show mipsfpu’.

21.3.7 OpenRISC 1000
The OpenRISC 1000 provides a free RISC instruction set architecture. It is mainly provided
as a soft-core which can run on Xilinx, Altera and other FPGA’s.
gdb for OpenRISC supports the below commands when connecting to a target:

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target sim
Runs the builtin CPU simulator which can run very basic programs but does
not support most hardware functions like MMU. For more complex use cases theuser is advised to run an external target, and connect using ‘target remote’.
Example: target sim
set debug or1k
Toggle whether to display OpenRISC-specific debugging messages from the
OpenRISC target support subsystem.
show debug or1kShow whether OpenRISC-specific debugging messages are enabled.

21.3.8 PowerPC Embedded
gdb supports using the DVC (Data Value Compare) register to implement in hardware
simple hardware watchpoint conditions of the form:(gdb) watch address|variable \if address|variable == constant expression

The DVC register will be automatically used when gdb detects such pattern in acondition expression, and the created watchpoint uses one debug register (either theexact-watchpoints option is on and the variable is scalar, or the variable has a length of
one byte). This feature is available in native gdb running on a Linux kernel version 2.6.34
or newer.
When running on PowerPC embedded processors, gdb automatically uses ranged hardware watchpoints, unless the exact-watchpoints option is on, in which case watchpoints
using only one debug register are created when watching variables of scalar types.
You can create an artificial array to watch an arbitrary memory region using one of thefollowing commands (see Section 10.1 [Expressions], page 145):(gdb) watch *((char *) address)@length(gdb) watch {char[length]} address

PowerPC embedded processors support masked watchpoints. See the discussion about
the mask argument in Section 5.1.2 [Set Watchpoints], page 66.
PowerPC embedded processors support hardware accelerated ranged breakpoints. A
ranged breakpoint stops execution of the inferior whenever it executes an instruction at
any address within the range it was set at. To set a ranged breakpoint in gdb, use thebreak-range command.
gdb provides the following PowerPC-specific commands:
break-range start-locspec, end-locspec
Set a breakpoint for an address range given by start-locspec and end-locspec,
which are location specs. See Section 9.2 [Location Specifications], page 126, fora list of all the possible forms of location specs. gdb resolves both start-locspec
and end-locspec, and uses the addresses of the resolved code locations as startand end addresses of the range to break at. The breakpoint will stop executionof the inferior whenever it executes an instruction at any address between thestart and end addresses, inclusive. If either start-locspec or end-locspec resolve
to multiple code locations in the program, then the command aborts with anerror without creating a breakpoint.

Chapter 21: Configuration-Specific Information353

set powerpc soft-float
show powerpc soft-float
Force gdb to use (or not use) a software floating point calling convention. Bydefault, gdb selects the calling convention based on the selected architecture
and the provided executable file.
set powerpc vector-abi
show powerpc vector-abi
Force gdb to use the specified calling convention for vector arguments andreturn values. The valid options are ‘auto’; ‘generic’, to avoid vector registers
even if they are present; ‘altivec’, to use AltiVec registers; and ‘spe’ to use
SPE registers. By default, gdb selects the calling convention based on theselected architecture and the provided executable file.
set powerpc exact-watchpoints
show powerpc exact-watchpoints
Allow gdb to use only one debug register when watching a variable of scalar
type, thus assuming that the variable is accessed through the address of its firstbyte.

21.3.9 Atmel AVR
When configured for debugging the Atmel AVR, gdb supports the following AVR-specificcommands:
info io_registers
This command displays information about the AVR I/O registers. For eachregister, gdb prints its number and value.

21.3.10 CRIS
When configured for debugging CRIS, gdb provides the following CRIS-specific commands:
set cris-version ver
Set the current CRIS version to ver, either ‘10’ or ‘32’. The CRIS version affects
register names and sizes. This command is useful in case autodetection of the
CRIS version fails.
show cris-version
Show the current CRIS version.
set cris-dwarf2-cfi
Set the usage of DWARF-2 CFI for CRIS debugging. The default is ‘on’.
Change to ‘off’ when using gcc-cris whose version is below R59.
show cris-dwarf2-cfi
Show the current state of using DWARF-2 CFI.
set cris-mode mode
Set the current CRIS mode to mode. It should only be changed when debugging
in guru mode, in which case it should be set to ‘guru’ (the default is ‘normal’).
show cris-mode
Show the current CRIS mode.

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21.3.11 Renesas Super-H
For the Renesas Super-H processor, gdb provides these commands:
set sh calling-convention convention
Set the calling-convention used when calling functions from gdb. Allowed values are ‘gcc’, which is the default setting, and ‘renesas’. With the ‘gcc’ setting,functions are called using the gcc calling convention. If the DWARF-2 information of the called function specifies that the function follows the Renesas
calling convention, the function is called using the Renesas calling convention.
If the calling convention is set to ‘renesas’, the Renesas calling convention isalways used, regardless of the DWARF-2 information. This can be used tooverride the default of ‘gcc’ if debug information is missing, or the compiler
does not emit the DWARF-2 calling convention entry for a function.
show sh calling-convention
Show the current calling convention setting.

21.4 Architectures
This section describes characteristics of architectures that affect all uses of gdb with thearchitecture, both native and cross.

21.4.1 AArch64
When gdb is debugging the AArch64 architecture, it provides the following special commands:
set debug aarch64
This command determines whether AArch64 architecture-specific debugging
messages are to be displayed.
show debug aarch64
Show whether AArch64 debugging messages are displayed.

21.4.1.1 AArch64 SVE.
When gdb is debugging the AArch64 architecture, if the Scalable Vector Extension (SVE)
is present, then gdb will provide the vector registers $z0 through $z31, vector predicate
registers $p0 through $p15, and the $ffr register. In addition, the pseudo register $vg will
be provided. This is the vector granule for the current thread and represents the numberof 64-bit chunks in an SVE z register.
If the vector length changes, then the $vg register will be updated, but the lengths ofthe z and p registers will not change. This is a known limitation of gdb and does not affectthe execution of the target process.
For SVE, the following definitions are used throughout gdb’s source code and in thisdocument:• vl: The vector length, in bytes. It defines the size of each Z register.
• vq: The number of 128 bit units in vl. This is mostly used internally by gdb and theLinux Kernel.
• vg: The number of 64 bit units in vl. This is mostly used internally by gdb and theLinux Kernel.

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21.4.1.2 AArch64 SME.
The Scalable Matrix Extension (SME (https: / / community . arm . com /arm-community-blogs / b / architectures-and-processors-blog / posts /scalable-matrix-extension-armv9-a-architecture))isanAArch64
architecture extension that expands on the concept of the Scalable Vector Extension (SVE (https: / / developer . arm . com / documentation / 101726 / 4-0 /Learn-about-the-Scalable-Vector-Extension--SVE-/What-is-the-Scalable-Vector-Extension-))by providing a 2-dimensional register ZA, which is a square matrix of variable size, just likeSVE provides a group of vector registers of variable size.
Similarly to SVE, where the size of each Z register is directly related to the vector length(vl for short), the SME ZA matrix register’s size is directly related to the streaming vector
length (svl for short). See [vl], page 354. See [svl], page 355.
The ZA register state can be either active or inactive, if it is not in use.
SME also introduces a new execution mode called streaming SVE mode (streaming modefor short). When streaming mode is enabled, the program supports execution of SVE2
instructions and the SVE registers will have vector length svl. When streaming mode isdisabled, the SVE registers have vector length vl.
For more information about SME and SVE, please refer to official architecture documentation (https://developer.arm.com/documentation/ddi0487/latest).
The following definitions are used throughout gdb’s source code and in this document:• svl: The streaming vector length, in bytes. It defines the size of each dimension of the
2-dimensional square ZA matrix. The total size of ZA is therefore svl by svl.
When streaming mode is enabled, it defines the size of the SVE registers as well.
• svq: The number of 128 bit units in svl, also known as streaming vector granule. Thisis mostly used internally by gdb and the Linux Kernel.
• svg: The number of 64 bit units in svl. This is mostly used internally by gdb and theLinux Kernel.
When gdb is debugging the AArch64 architecture, if the Scalable Matrix Extension(SME) is present, then gdb will make the ZA register available. gdb will also make the SVG
register and SVCR pseudo-register available.
The ZA register is a 2-dimensional square svl by svl matrix of bytes. To simplify the
representation and access to the ZA register in gdb, it is defined as a vector of svlxsvl bytes.
If the user wants to index the ZA register as a matrix, it is possible to reference ZA as
ZA[i][j], where i is the row number and j is the column number.
The SVG register always contains the streaming vector granule (svg) for the current
thread. From the value of register SVG we can easily derive the svl value.
The SVCR pseudo-register (streaming vector control register) is a status register that
holds two state bits: sm in bit 0 and za in bit 1.
If the sm bit is 1, it means the current thread is in streaming mode, and the SVE registers
will use svl for their sizes. If the sm bit is 0, the current thread is not in streaming mode,and the SVE registers will use vl for their sizes. See [vl], page 354.
If the za bit is 1, it means the ZA register is being used and has meaningful contents. If
the za bit is 0, the ZA register is unavailable and its contents are undefined.

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For convenience and simplicity, if the za bit is 0, the ZA register and all of its pseudoregisters will read as zero.
If svl changes during the execution of a program, then the ZA register size and the bitsin the SVCR pseudo-register will be updated to reflect it.
It is possible for users to change svl during the execution of a program by modifying the
SVG register value.
Whenever the SVG register is modified with a new value, the following will be observed:• The za and sm bits will be cleared in the SVCR pseudo-register.
• The ZA register will have a new size and its state will be cleared, forcing its contents
and the contents of all of its pseudo-registers back to zero.
• If the sm bit was 1, the SVE registers will be reset to having their sizes based on vl as
opposed to svl. If the sm bit was 0 prior to modifying the SVG register, there will be
no observable effect on the SVE registers.
The possible values for the SVG register are 2, 4, 8, 16, 32. These numbers correspondto streaming vector length (svl) values of 16 bytes, 32 bytes, 64 bytes, 128 bytes and 256
bytes respectively.
The minimum size of the ZA register is 16 x 16 (256) bytes, and the maximum size is
256 x 256 (65536) bytes. In streaming mode, with bit sm set, the size of the ZA register isthe size of all the SVE Z registers combined.
The ZA register can also be accessed using tiles and tile slices.
Tile pseudo-registers are square, 2-dimensional sub-arrays of elements within the ZA
register.
The tile pseudo-registers
number><qualifier>.

have

the

following

namingpattern:

ZA<tileThere is a total of 31 ZA tile pseudo-registers. They are ZA0B, ZA0H through ZA1H, ZA0S
through ZA3S, ZA0D through ZA7D and ZA0Q through ZA15Q.
Tile slice pseudo-registers are vectors of horizontally or vertically contiguous elements
within the ZA register.
The tile slice pseudo-registers have the following naming pattern:number><direction><qualifier> <slice number>.

ZA<tileThere are up to 16 tiles (0 ~ 15), the direction can be either v (vertical) or h (horizontal),
the qualifiers can be b (byte), h (halfword), s (word), d (doubleword) and q (quadword)
and there are up to 256 slices (0 ~ 255) depending on the value of svl. The number of slices
is the same as the value of svl.
The number of available tile slice pseudo-registers can be large. For a minimum svl of
16 bytes, there are 5 (number of qualifiers) x 2 (number of directions) x 16 (svl) pseudoregisters. For the maximum svl of 256 bytes, there are 5 x 2 x 256 pseudo-registers.
When listing all the available registers, users will see the currently-available ZA pseudoregisters. Pseudo-registers that don’t exist for a given svl value will not be displayed.
For more information on SME and its terminology, please refer to the Arm Architecture
Reference Manual Supplement (https://developer.arm.com/documentation/ddi0616/aa/), The Scalable Matrix Extension (SME), for Armv9-A.

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Some features are still under development and rely on ACLE (https://github.com/
ARM-software/acle/releases/latest) and ABI (https://github.com/ARM-software/
abi-aa/blob/main/aapcs64/aapcs64.rst) definitions, so there are known limitations tothe current SME support in gdb.
One such example is calling functions in the program being debugged by gdb. Suchcalls are not SME-aware and thus don’t take into account the SVCR pseudo-register bits nor
the ZA register contents. See Section 17.5 [Calling], page 281.
The lazy saving scheme (https://github.com/ARM-software/abi-aa/blob/main/
aapcs64/aapcs64.rst#the-za-lazy-saving-scheme) involving the TPIDR2 register is not
yet supported by gdb, though the TPIDR2 register is known and supported by gdb.
Lastly, an important limitation for gdbserver is its inability to communicate svl changes
to gdb. This means gdbserver, even though it is capable of adjusting its internal caches toreflect a change in the value of svl mid-execution, will operate with a potentially different svl
value compared to gdb. This can lead to gdb showing incorrect values for the ZA registerand incorrect values for SVE registers (when in streaming mode).
This is the same limitation we have for the SVE registers, and there are plans to address
this limitation going forward.

21.4.1.3 AArch64 SME2.
The Scalable Matrix Extension 2 is an AArch64 architecture extension that further expands
the SME extension with the following:• The ability to address the ZA array through groups of one-dimensional ZA array vectors,
as opposed to ZA tiles with 2 dimensions.
• Instructions to operate on groups of SVE Z registers and ZA array vectors.
• A new 512 bit ZT0 lookup table register, for data decompression.
When gdb is debugging the AArch64 architecture, if the Scalable Matrix Extension 2(SME2) is present, then gdb will make the ZT0 register available.
The ZT0 register is only considered active when the ZA register state is active, therefore
when the za bit of the SVCR is 1.
When the za bit of SVCR is 0, that means the ZA register state is not active, which means
the ZT0 register state is also not active.
When ZT0 is not active, it is comprised of zeroes, just like ZA.
Similarly to the ZA register, if the ZT0 state is not active and the user attempts to modify
its value such that any of its bytes is non-zero, then gdb will initialize the ZA register state
as well, which means the SVCR za bit gets set to 1.
For more information about SME2, please refer to the official architecture documentation(https://developer.arm.com/documentation/ddi0487/latest).

21.4.1.4 AArch64 Pointer Authentication.
When gdb is debugging the AArch64 architecture, and the program is using the v8.3-Afeature Pointer Authentication (PAC), then whenever the link register $lr is pointing to
an PAC function its value will be masked. When GDB prints a backtrace, any addresses
that required unmasking will be postfixed with the marker [PAC]. When using the MI, thisis printed as part of the addr_flags field.

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21.4.1.5 AArch64 Memory Tagging Extension.
When gdb is debugging the AArch64 architecture, the program is using the v8.5-A feature Memory Tagging Extension (MTE) and there is support in the kernel for MTE, gdb
will make memory tagging functionality available for inspection and editing of logical andallocation tags. See Section 10.7 [Memory Tagging], page 154.
To aid debugging, gdb will output additional information when SIGSEGV signals are
generated as a result of memory tag failures.
If the tag violation is synchronous, the following will be shown:
Program received signal SIGSEGV, Segmentation fault
Memory tag violation while accessing address 0x0500fffff7ff8000
Allocation tag 0x1
Logical tag 0x5.

If the tag violation is asynchronous, the fault address is not available. In this case gdb
will show the following:
Program received signal SIGSEGV, Segmentation fault
Memory tag violation
Fault address unavailable.

A special register, tag_ctl, is made available through the org.gnu.gdb.aarch64.mte
feature. This register exposes some options that can be controlled at runtime and emulates
the prctl option PR_SET_TAGGED_ADDR_CTRL. For further information, see the documentation in the Linux kernel.
gdb supports dumping memory tag data to core files through the gcore command andreading memory tag data from core files generated by the gcore command or the Linuxkernel.
When a process uses memory-mapped pages protected by memory tags (for example,
AArch64 MTE), this additional information will be recorded in the core file in the event ofa crash or if gdb generates a core file from the current process state.
The memory tag data will be used so developers can display the memory tags froma particular memory region (using the ‘m’ modifier to the x command, using the printcommand or using the various memory-tag subcommands.
In the case of a crash, gdb will attempt to retrieve the memory tag information automatically from the core file, and will show one of the above messages depending on whether
the synchronous or asynchronous mode is selected. See Section 10.7 [Memory Tagging],
page 154. See Section 10.6 [Memory], page 152.

21.4.2 x86
set struct-convention mode
Set the convention used by the inferior to return structs and unions fromfunctions to mode. Possible values of mode are "pcc", "reg", and "default"(the default). "default" or "pcc" means that structs are returned on thestack, while "reg" means that a struct or a union whose size is 1, 2, 4, or 8
bytes will be returned in a register.
show struct-convention
Show the current setting of the convention to return structs from functions.

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21.4.2.1 x87 registers
gdb provides access to the x87 state through the following registers:• $st0 to st7: ST(0) to ST(7) floating-point registers• $fctrl: control word register (FCW)• $fstat: status word register (FSW)• $ftag: tag word (FTW)• $fiseg: last instruction pointer segment• $fioff: last instruction pointer• $foseg: last data pointer segment• $fooff: last data pointer• $fop: last opcode

21.4.3 Alpha
See the following section.

21.4.4 MIPS
Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires
gdb to search backward in the object code to find the beginning of a function.
To improve response time (especially for embedded applications, where gdb may be
restricted to a slow serial line for this search) you may want to limit the size of this search,using one of these commands:
set heuristic-fence-post limit
Restrict gdb to examining at most limit bytes in its search for the beginningof a function. A value of 0 (the default) means there is no limit. However,except for 0, the larger the limit the more bytes heuristic-fence-post mustsearch and therefore the longer it takes to run. You should only need to use
this command when debugging a stripped executable.
show heuristic-fence-post
Display the current limit.
These commands are available only when gdb is configured for debugging programs on
Alpha or MIPS processors.
Several MIPS-specific commands are available when debugging MIPS programs:
set mips abi arg
Tell gdb which MIPS ABI is used by the inferior. Possible values of arg are:‘auto’
‘o32’
‘o64’
‘n32’
‘n64’

The default ABI associated with the current binary (this is thedefault).

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show mips abi
Show the MIPS ABI used by gdb to debug the inferior.
set mips compression arg
Tell gdb which MIPS compressed ISA (Instruction Set Architecture) encoding
is used by the inferior. gdb uses this for code disassembly and other internalinterpretation purposes. This setting is only referred to when no executable has
been associated with the debugging session or the executable does not provide
information about the encoding it uses. Otherwise this setting is automatically
updated from information provided by the executable.
Possible values of arg are ‘mips16’ and ‘micromips’. The default compressed
ISA encoding is ‘mips16’, as executables containing MIPS16 code frequently are
not identified as such.
This setting is “sticky”; that is, it retains its value across debugging sessions
until reset either explicitly with this command or implicitly from an executable.
The compiler and/or assembler typically add symbol table annotations to identify functions compiled for the MIPS16 or microMIPS ISAs. If these functionscope annotations are present, gdb uses them in preference to the global compressed ISA encoding setting.
show mips compression
Show the MIPS compressed ISA encoding used by gdb to debug the inferior.
set mipsfpu
show mipsfpu
See Section 21.3.6 [MIPS Embedded], page 351.
set mips mask-address arg
This command determines whether the most-significant 32 bits of 64-bit MIPS
addresses are masked off. The argument arg can be ‘on’, ‘off’, or ‘auto’. The
latter is the default setting, which lets gdb determine the correct value.
show mips mask-addressShow whether the upper 32 bits of MIPS addresses are masked off or not.
set remote-mips64-transfers-32bit-regs
This command controls compatibility with 64-bit MIPS targets that transfer
data in 32-bit quantities. If you have an old MIPS 64 target that transfers 32
bits for some registers, like sr and fsr, and 64 bits for other registers, set thisoption to ‘on’.
show remote-mips64-transfers-32bit-regs
Show the current setting of compatibility with older MIPS 64 targets.
set debug mips
This command turns on and off debugging messages for the MIPS-specific target
code in gdb.
show debug mips
Show the current setting of MIPS debugging messages.

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21.4.5 HPPA
When gdb is debugging the HP PA architecture, it provides the following special commands:
set debug hppa
This command determines whether HPPA architecture-specific debugging messages are to be displayed.
show debug hppa
Show whether HPPA debugging messages are displayed.
maint print unwind addressThis command displays the contents of the unwind table entry at the given
address.

21.4.6 PowerPC
When gdb is debugging the PowerPC architecture, it provides a set of pseudo-registers toenable inspection of 128-bit wide Decimal Floating Point numbers stored in the floating
point registers. These values must be stored in two consecutive registers, always startingat an even register like f0 or f2.
The pseudo-registers go from $dl0 through $dl15, and are formed by joining theeven/odd register pairs f0 and f1 for $dl0, f2 and f3 for $dl1 and so on.
For POWER7 processors, gdb provides a set of pseudo-registers, the 64-bit wide Extended Floating Point Registers (‘f32’ through ‘f63’).

21.4.7 Nios II
When gdb is debugging the Nios II architecture, it provides the following special commands:
set debug nios2This command turns on and off debugging messages for the Nios II target codein gdb.
show debug nios2Show the current setting of Nios II debugging messages.

21.4.8 Sparc64
21.4.8.1 ADI Support
The M7 processor supports an Application Data Integrity (ADI) feature that detects invalid
data accesses. When software allocates memory and enables ADI on the allocated memory,
it chooses a 4-bit version number, sets the version in the upper 4 bits of the 64-bit pointerto that data, and stores the 4-bit version in every cacheline of that data. Hardware saves
the latter in spare bits in the cache and memory hierarchy. On each load and store, theprocessor compares the upper 4 VA (virtual address) bits to the cacheline’s version. If there
is a mismatch, the processor generates a version mismatch trap which can be either precise
or disrupting. The trap is an error condition which the kernel delivers to the process as a
SIGSEGV signal.
Note that only 64-bit applications can use ADI and need to be built with ADI-enabled.

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Values of the ADI version tags, which are in granularity of a cacheline (64 bytes), canbe viewed or modified.
adi (examine | x) [ / n ] addr
The adi examine command displays the value of one ADI version tag per cacheline.
n is a decimal integer specifying the number in bytes; the default is 1. It specifies
how much ADI version information, at the ratio of 1:ADI block size, to display.
addr is the address in user address space where you want gdb to begin displaying the ADI version tags.
Below is an example of displaying ADI versions of variable "shmaddr".
(gdb) adi x/100 shmaddr
0xfff800010002c000:0 0

adi (assign | a) [ / n ] addr = tag
The adi assign command is used to assign new ADI version tag to an address.
n is a decimal integer specifying the number in bytes; the default is 1. It specifies
how much ADI version information, at the ratio of 1:ADI block size, to modify.
addr is the address in user address space where you want gdb to begin modifying the ADI version tags.
tag is the new ADI version tag.
For example, do the following to modify then verify ADI versions of variable"shmaddr":(gdb) adi a/100 shmaddr = 7(gdb) adi x/100 shmaddr
0xfff800010002c000:
7 721.4.9 S12Z
When gdb is debugging the S12Z architecture, it provides the following special command:
maint info bdccsr
This command displays the current value of the microprocessor’s BDCCSR
register.

21.4.10 AMD GPU
gdb supports debugging programs offloaded to AMD GPU devices using the AMD ROCm
(https://docs.amd.com/) platform. gdb presents host threads alongside GPU wavefronts,
allowing debugging both the host and device parts of the program simultaneously.

21.4.10.1 AMD GPU Architectures
The list of AMD GPU architectures supported by gdb depends on the version of the AMD
Debugger API library used. See its documentation (https://docs.amd.com/bundle/
ROCDebugger_User_and_API) for more details.

21.4.10.2 AMD GPU Device Driver and AMD ROCm Runtime
gdb requires a compatible AMD GPU device driver to be installed. A warning message isdisplayed if either the device driver version or the version of the debug support it implements

Chapter 21: Configuration-Specific Information363

is unsupported. gdb will continue to function except no AMD GPU debugging will bepossible.
gdb requires each agent to have compatible firmware installed by the device driver. A
warning message is displayed if unsupported firmware is detected. gdb will continue tofunction except no AMD GPU debugging will be possible on the agent.
gdb requires a compatible AMD ROCm runtime to be loaded in order to detect AMD
GPU code objects and wavefronts. A warning message is displayed if an unsupported AMD
ROCm runtime is detected, or there is an error or restriction that prevents debugging. gdb
will continue to function except no AMD GPU debugging will be possible.

21.4.10.3 AMD GPU Wavefronts
An AMD GPU wavefront is represented in gdb as a thread.
Note that some AMD GPU architectures may have restrictions on providing information
about AMD GPU wavefronts created when gdb is not attached (see [AMD GPU Attaching
Restrictions], page 366).
When scheduler-locking is in effect (see [set scheduler-locking], page 93), new wavefronts
created by the resumed thread (either CPU thread or GPU wavefront) are held in the halt
state.

21.4.10.4 AMD GPU Code Objects
The ‘info sharedlibrary’ command will show the AMD GPU code objects as file or memory URIs, together with the host’s shared libraries. For example:(gdb) info sharedlibrary
From
To
Syms Read
Shared Object Library
0x1111 0x2222 Yes (*)/lib64/ld-linux-x86-64.so.2...
0x3333 0x4444 Yes (*)/opt/rocm-4.5.0/.../libamd_comgr.so
0x5555 0x6666 Yes (*)/lib/x86_64-linux-gnu/libtinfo.so.50x7777 0x8888 Yes
file:///tmp/a.out#offset=6477&size=10832
0x9999 0xaaaa Yes (*)
memory://95557/mem#offset=0x1234&size=100(*): Shared library is missing debugging information.
(gdb)

For a ‘file’ URI, the path portion is the file on disk containing the code object. The
offset parameter is a 0-based offset in this file, to the start of the code object. If omitted,
it defaults to 0. The size parameter is the size of the code object in bytes. If omitted, it
defaults to the size of the file.
For a ‘memory’ URI, the path portion is the process id of the process owning the memory
containing the code object. The offset parameter is the memory address where the code
object is found, and the size parameter is its size in bytes.
AMD GPU code objects are loaded into each AMD GPU device separately. The ‘info
sharedlibrary’ command may therefore show the same code object loaded multiple times.
As a consequence, setting a breakpoint in AMD GPU code will result in multiple breakpoint
locations if there are multiple AMD GPU devices.

21.4.10.5 AMD GPU Entity Target Identifiers and Convenience
Variables
The AMD GPU entities have the following target identifier formats:364

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Thread Target ID
The AMD GPU thread target identifier (systag) string has the following format:
AMDGPU Wave agent-id:queue-id:dispatch-id:wave-id (work-group-x,work-groupy,work-group-z)/work-group-thread-index

21.4.10.6 AMD GPU Signals
For AMD GPU wavefronts, gdb maps target conditions to stop signals in the following way:
SIGILL

Execution of an illegal instruction.

SIGTRAP

Execution of a S_TRAP instruction other than:• S_TRAP 1 which is used by gdb to insert breakpoints.
• S_TRAP 2 which raises SIGABRT.

SIGABRT

Execution of a S_TRAP 2 instruction.

SIGFPE

Execution of a floating point or integer instruction detects a condition that is
enabled to raise a signal. The conditions include:• Floating point operation is invalid.
• Floating point operation had subnormal input that was rounded to zero.
• Floating point operation performed a division by zero.
• Floating point operation produced an overflow result. The result was
rounded to infinity.
• Floating point operation produced an underflow result. A subnormal result
was rounded to zero.
• Floating point operation produced an inexact result.
• Integer operation performed a division by zero.
By default, these conditions are not enabled to raise signals. The ‘set $mode’command can be used to change the AMD GPU wavefront’s register that has bits
controlling which conditions are enabled to raise signals. The ‘print $trapsts’command can be used to inspect which conditions have been detected even if
they are not enabled to raise a signal.

SIGBUS

Execution of an instruction that accessed global memory using an address thatis outside the virtual address range.

SIGSEGV

Execution of an instruction that accessed a global memory page that is either
not mapped or accessed with incompatible permissions.

If a single instruction raises more than one signal, they will be reported one at a timeeach time the wavefront is continued.

21.4.10.7 AMD GPU Memory Violation Reporting
A wavefront can report memory violation events. However, the program location at which
they are reported may be after the machine instruction that caused them. This can resultin the reported source statement being incorrect. The following commands can be used tocontrol this behavior:Chapter 21: Configuration-Specific Information

365

set amdgpu precise-memory mode
Controls how AMD GPU devices detect memory violations, where mode can be:off

The program location may not be immediately after the instructionthat caused the memory violation. This is the default.

on

Requests that the program location will be immediately after the
instruction that caused a memory violation. Enabling this mode
may make the AMD GPU device execution significantly slower as it
has to wait for each memory operation to complete before executing
the next instruction.

The amdgpu precise-memory parameter is per-inferior. When an inferior forks
or execs, or the user uses the clone-inferior command, and an inferior iscreated as a result, the newly created inferior inherits the parameter value ofthe original inferior.
show amdgpu precise-memory
Displays the currently requested AMD GPU precise memory setting.

21.4.10.8 AMD GPU Logging
The ‘set debug amd-dbgapi’ command can be used to enable diagnostic messages in the‘amd-dbgapi’ target. The ‘show debug amd-dbgapi’ command displays the current setting.
See [set debug amd-dbgapi], page 383.
The ‘set debug amd-dbgapi-lib log-level level’ command can be used to enable diagnostic messages from the ‘amd-dbgapi’ library (which gdb uses under the hood). The‘show debug amd-dbgapi-lib log-level’ command displays the current ‘amd-dbgapi’ library log level. See [set debug amd-dbgapi-lib], page 383.

21.4.10.9 AMD GPU Restrictions
1. When in non-stop mode, wavefronts may not hit breakpoints inserted while not stopped,
nor see memory updates made while not stopped, until the wavefront is next stopped.
Memory updated by non-stopped wavefronts may not be visible until the wavefront isnext stopped.
2. The HIP runtime performs deferred code object loading by default. AMD GPU code
objects are not loaded until the first kernel is launched. Before then, all breakpoints
have to be set as pending breakpoints.
If source line positions are used that only correspond to source lines in unloaded code
objects, then gdb may not set pending breakpoints, and instead set breakpoints on
the next following source line that maps to host code. This can result in unexpected
breakpoint hits being reported. When the code object containing the source lines isloaded, the incorrect breakpoints will be removed and replaced by the correct ones.
This problem can be avoided by only setting breakpoints in unloaded code objects
using symbol or function names.
Setting the HIP_ENABLE_DEFERRED_LOADING environment variable to 0 can be used todisable deferred code object loading by the HIP runtime. This ensures all code objects
will be loaded when the inferior reaches the beginning of the main function.

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3. If no CPU thread is running, then ‘Ctrl-C’ is not able to stop AMD GPU threads. Thiscan happen for example if you enable scheduler-locking after the whole program
stopped, and then resume an AMD GPU thread. The only way to unblock the situation
is to kill the gdb process.
4.
By default, for some architectures, the AMD GPU device driver causes all AMD GPU
wavefronts created when gdb is not attached to be unable to report the dispatch
associated with the wavefront, or the wavefront’s work-group position. The ‘info
threads’ command will display this missing information with a ‘?’.
This does not affect wavefronts created while gdb is attached which are always capableof reporting this information.
If the HSA_ENABLE_DEBUG environment variable is set to ‘1’ when the AMD ROCm
runtime is initialized, then this information will be available for all architectures evenfor wavefronts created when gdb was not attached.

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22 Controlling gdb
You can alter the way gdb interacts with you by using the set command. For commands
controlling how gdb displays data, see Section 10.9 [Print Settings], page 157. Other settings
are described here.

22.1 Prompt
gdb indicates its readiness to read a command by printing a string called the prompt.
This string is normally ‘(gdb)’. You can change the prompt string with the set prompt
command. For instance, when debugging gdb with gdb, it is useful to change the prompt
in one of the gdb sessions so that you can always tell which one you are talking to.
Note: set prompt does not add a space for you after the prompt you set. This allows
you to set a prompt which ends in a space or a prompt that does not.
set prompt newprompt
Directs gdb to use newprompt as its prompt string henceforth.
show prompt
Prints a line of the form: ‘Gdb’s prompt is: your-prompt’Versions of gdb that ship with Python scripting enabled have prompt extensions. The
commands for interacting with these extensions are:set extended-prompt prompt
Set an extended prompt that allows for substitutions. See Section 23.3.4.3[gdb.prompt], page 516, for a list of escape sequences that can be used for
substitution. Any escape sequences specified as part of the prompt string are
replaced with the corresponding strings each time the prompt is displayed.
For example:
set extended-prompt Current working directory: \w (gdb)

Note that when an extended-prompt is set, it takes control of the prompt hook
hook. See [prompt hook], page 408, for further information.
show extended-prompt
Prints the extended prompt. Any escape sequences specified as part of theprompt string with set extended-prompt, are replaced with the corresponding
strings each time the prompt is displayed.

22.2 Command Editing
gdb reads its input commands via the Readline interface. This gnu library provides consistent behavior for programs which provide a command line interface to the user. Advantages
are gnu Emacs-style or vi-style inline editing of commands, csh-like history substitution,
and a storage and recall of command history across debugging sessions.
You may control the behavior of command line editing in gdb with the command set.
set editing
set editing on
Enable command line editing (enabled by default).

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set editing off
Disable command line editing.
show editing
Show whether command line editing is enabled.
See Chapter 33 [Command Line Editing], page 713, for more details about the Readline
interface. Users unfamiliar with gnu Emacs or vi are encouraged to read that chapter.
gdb sets the Readline application name to ‘gdb’. This is useful for conditions in.inputrc.
gdb defines a bindable Readline command, operate-and-get-next. This is bound to
C-o by default. This command accepts the current line for execution and fetches the nextline relative to the current line from the history for editing. Any argument is ignored.

22.3 Command History
gdb can keep track of the commands you type during your debugging sessions, so thatyou can be certain of precisely what happened. Use these commands to manage the gdb
command history facility.
gdb uses the gnu History library, a part of the Readline package, to provide the history
facility. See Chapter 34 [Using History Interactively], page 737, for the detailed descriptionof the History library.
To issue a command to gdb without affecting certain aspects of the state which is seenby users, prefix it with ‘server ’ (see Section 28.2 [Server Prefix], page 696). This meansthat this command will not affect the command history, nor will it affect gdb’s notion ofwhich command to repeat if RET is pressed on a line by itself.
The server prefix does not affect the recording of values into the value history; to print
a value without recording it into the value history, use the output command instead of theprint command.
Here is the description of gdb commands related to command history.
set history filename [fname]Set the name of the gdb command history file to fname. This is the file where
gdb reads an initial command history list, and where it writes the command
history from this session when it exits. You can access this list through history
expansion or through the history command editing characters listed below.
This file defaults to the value of the environment variable GDBHISTFILE, or to./.gdb_history (./_gdb_history on MS-DOS) if this variable is not set.
The GDBHISTFILE environment variable is read after processing any gdb initialization files (see Section 2.1.3 [Startup], page 16) and after processing any
commands passed using command line options (for example, -ex).
If the fname argument is not given, or if the GDBHISTFILE is the empty string
then gdb will neither try to load an existing history file, nor will it try to savethe history on exit.
set history save
set history save on
Record command history in a file, whose name may be specified with the set
history filename command. By default, this option is disabled. The com-

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mand history will be recorded when gdb exits. If set history filename is set
to the empty string then history saving is disabled, even when set history
save is on.
set history save off
Don’t record the command history into the file specified by set history
filename when gdb exits.
set history size size
set history size unlimited
Set the number of commands which gdb keeps in its history list. This defaults
to the value of the environment variable GDBHISTSIZE, or to 256 if this variable
is not set. Non-numeric values of GDBHISTSIZE are ignored. If size is unlimited
or if GDBHISTSIZE is either a negative number or the empty string, then thenumber of commands gdb keeps in the history list is unlimited.
The GDBHISTSIZE environment variable is read after processing any gdb initialization files (see Section 2.1.3 [Startup], page 16) and after processing any
commands passed using command line options (for example, -ex).
set history remove-duplicates countset history remove-duplicates unlimited
Control the removal of duplicate history entries in the command history list.
If count is non-zero, gdb will look back at the last count history entries andremove the first entry that is a duplicate of the current entry being added to thecommand history list. If count is unlimited then this lookbehind is unbounded.
If count is 0, then removal of duplicate history entries is disabled.
Only history entries added during the current session are considered for removal.
This option is set to 0 by default.
History expansion assigns special meaning to the character !. See Section 34.1.1 [Event
Designators], page 737, for more details.
Since ! is also the logical not operator in C, history expansion is off by default. If you
decide to enable history expansion with the set history expansion on command, you may
sometimes need to follow ! (when it is used as logical not, in an expression) with a spaceor a tab to prevent it from being expanded. The readline history facilities do not attempt
substitution on the strings != and !(, even when history expansion is enabled.
The commands to control history expansion are:set history expansion on
set history expansion
Enable history expansion. History expansion is off by default.
set history expansion off
Disable history expansion.

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show history
show history filename
show history saveshow history sizeshow history expansion
These commands display the state of the gdb history parameters.
history by itself displays all four states.

show

show commands
Display the last ten commands in the command history.
show commands n
Print ten commands centered on command number n.
show commands +Print ten commands just after the commands last printed.

22.4 Screen Size
Certain commands to gdb may produce large amounts of information output to the screen.
To help you read all of it, gdb pauses and asks you for input at the end of each pageof output. Type RET when you want to see one more page of output, q to discard theremaining output, or c to continue without paging for the rest of the current command.
Also, the screen width setting determines when to wrap lines of output. Depending on what
is being printed, gdb tries to break the line at a readable place, rather than simply letting
it overflow onto the following line.
Normally gdb knows the size of the screen from the terminal driver software. For
example, on Unix gdb uses the termcap data base together with the value of the TERM
environment variable and the stty rows and stty cols settings. If this is not correct, you
can override it with the set height and set width commands:
set height lpp
set height unlimited
show height
set width cpl
set width unlimited
show width
These set commands specify a screen height of lpp lines and a screen width of
cpl characters. The associated show commands display the current settings.
If you specify a height of either unlimited or zero lines, gdb does not pause
during output no matter how long the output is. This is useful if output is toa file or to an editor buffer.
Likewise, you can specify ‘set width unlimited’ or ‘set width 0’ to prevent
gdb from wrapping its output.
set pagination on
set pagination off
Turn the output pagination on or off; the default is on. Turning pagination off
is the alternative to set height unlimited. Note that running gdb with theChapter 22: Controlling gdb

371--batch option (see Section 2.1.2 [Mode Options], page 13) also automaticallydisables pagination.
show pagination
Show the current pagination mode.

22.5 Output Styling
gdb can style its output on a capable terminal. This is enabled by default on most systems,
but disabled by default when in batch mode (see Section 2.1.2 [Mode Options], page 13).
Various style settings are available; and styles can also be disabled entirely.
set style enabled ‘on|off’
Enable or disable all styling. The default is host-dependent, with most hosts
defaulting to ‘on’.
If the NO_COLOR environment variable is set to a non-empty value, then gdb
will change this to ‘off’ at startup.
show style enabledShow the current state of styling.
set style sources ‘on|off’
Enable or disable source code styling. This affects whether source code, such as
the output of the list command, is styled. The default is ‘on’. Note that source
styling only works if styling in general is enabled, and if a source highlighting
library is available to gdb.
There are two ways that highlighting can be done. First, if gdb was linked
with the GNU Source Highlight library, then it is used. Otherwise, if gdb was
configured with Python scripting support, and if the Python Pygments package
is available, then it will be used.
show style sources
Show the current state of source code styling.
set style tui-current-position ‘on|off’
Enable or disable styling of the source and assembly code highlighted by the
TUI’s current position indicator. The default is ‘off’. See Chapter 25 [gdbText User Interface], page 579.
show style tui-current-position
Show whether the source and assembly code highlighted by the TUI’s current
position indicator is styled.
set style disassembler enabled ‘on|off’
Enable or disable disassembler styling. This affects whether disassembler output, such as the output of the disassemble command, is styled. Disassembler
styling only works if styling in general is enabled (with set style enabled on),and if a source highlighting library is available to gdb.
The two source highlighting libraries that gdb could use to style disassembler
output are; gdb’s builtin disassembler, or the Python Pygments package.

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gdb’s first choice will be to use the builtin disassembler for styling, this usually provides better results, being able to style different types of instruction
operands differently. However, the builtin disassembler is not able to style allarchitectures.
For architectures that the builtin disassembler is unable to style, gdb will fallback to use the Python Pygments package where possible. In order to use thePython Pygments package, gdb must be built with Python support, and the
Pygments package must be installed.
If neither of these options are available then gdb will produce unstyled disassembler output, even when this setting is ‘on’.
To discover if the current architecture supports styling using the builtin disassembler library see [maint show libopcodes-styling enabled], page 769.
show style disassembler enabledShow the current state of disassembler styling.
Subcommands of set style control specific forms of styling. These subcommands allfollow the same pattern: each style-able object can be styled with a foreground color, abackground color, and an intensity.
For example, the style of file names can be controlled using the set style filenamegroup of commands:
set style filename background color
Set the background to color. Valid colors are ‘none’ (meaning the terminal’s default color), ‘black’, ‘red’, ‘green’, ‘yellow’, ‘blue’, ‘magenta’, ‘cyan’,
and‘white’.
set style filename foreground color
Set the foreground to color. Valid colors are ‘none’ (meaning the terminal’s
default color), ‘black’, ‘red’, ‘green’, ‘yellow’, ‘blue’, ‘magenta’, ‘cyan’,
and‘white’.
set style filename intensity value
Set the intensity to value. Valid intensities are ‘normal’ (the default), ‘bold’,and ‘dim’.
The show style command and its subcommands are styling a style name in their output
using its own style. So, use show style to see the complete list of styles, their characteristics
and the visual aspect of each style.
The style-able objects are:filename

Control the styling of file names and URLs. By default, this style’s foregroundcolor is green.

functionControl the styling of function names. These are managed with the set stylefunction family of commands. By default, this style’s foreground color isyellow.
This style is also used for symbol names in styled disassembler output if gdb isusing its builtin disassembler library for styling (see [set style disassembler
enabled], page 371).

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line-number
Control the styling of line numbers. By default, this style’s intensity is dim.
variable

Control the styling of variable names. These are managed with the set stylevariable family of commands. By default, this style’s foreground color is cyan.

address

Control the styling of addresses. These are managed with the set styleaddress family of commands. By default, this style’s foreground color is blue.
This style is also used for addresses in styled disassembler output if gdb isusing its builtin disassembler library for styling (see [set style disassembler
enabled], page 371).

versionControl the styling of gdb’s version number text. By default, this style’s foreground color is magenta and it has bold intensity. The version number isdisplayed in two places, the output of show version, and when gdb starts up.
In order to control how gdb styles the version number at startup, add the set
style version family of commands to the early initialization command file(see Section 2.1.4 [Initialization Files], page 17).

title

Control the styling of titles. These are managed with the set style title
family of commands. By default, this style’s intensity is bold. Commands areusing the title style to improve the readability of large output. For example, thecommands apropos and help are using the title style for the command names.

highlight
Control the styling of highlightings. These are managed with the set stylehighlight family of commands. By default, this style’s foreground color isred. Commands are using the highlight style to draw the user attention tosome specific parts of their output. For example, the command apropos -v
REGEXP uses the highlight style to mark the documentation parts matchingregexp.
metadata

Control the styling of data annotations added by gdb to data it displays. By
default, this style’s intensity is dim. Metadata annotations include the ‘repeatsn times’ annotation for suppressed display of repeated array elements (seeSection 10.9 [Print Settings], page 157), ‘<unavailable>’ and ‘<error descr>’
annotations for errors and ‘<optimized-out>’ annotations for optimized-out
values in displaying stack frame information in backtraces (see Section 8.2[Backtrace], page 114), etc.

tui-border
Control the styling of the TUI border. Note that, unlike other styling options,only the color of the border can be controlled via set style. This was done
for compatibility reasons, as TUI controls to set the border’s intensity predated
the addition of general styling to gdb. See Section 25.6 [TUI Configuration],
page 585.
tui-active-border
Control the styling of the active TUI border; that is, the TUI window that has
the focus.

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disassembler comment
Control the styling of comments in the disassembler output. These are managedwith the set style disassembler comment family of commands. This style isonly used when gdb is styling using its builtin disassembler library (see [setstyle disassembler enabled], page 371). By default, this style’s intensity isdim, and its foreground color is white.
disassembler immediate
Control the styling of numeric operands in the disassembler output. These aremanaged with the set style disassembler immediate family of commands.
This style is not used for instruction operands that represent addresses, in thatcase the ‘disassembler address’ style is used. This style is only used when
gdb is styling using its builtin disassembler library. By default, this style’s
foreground color is blue.
disassembler address
Control the styling of address operands in the disassembler output. This is analias for the ‘address’ style.
disassembler symbol
Control the styling of symbol names in the disassembler output. This is an alias
for the ‘function’ style.
disassembler mnemonic
Control the styling of instruction mnemonics in the disassembler output. These
are managed with the set style disassembler mnemonic family of commands.
This style is also used for assembler directives, e.g. .byte, .word, etc. This
style is only used when gdb is styling using its builtin disassembler library. Bydefault, this style’s foreground color is green.
disassembler register
Control the styling of register operands in the disassembler output. These aremanaged with the set style disassembler register family of commands.
This style is only used when gdb is styling using its builtin disassembler library.
By default, this style’s foreground color is red.

22.6 Numbers
You can always enter numbers in octal, decimal, or hexadecimal in gdb by the usual
conventions: octal numbers begin with ‘0’, decimal numbers end with ‘.’, and hexadecimal
numbers begin with ‘0x’. Numbers that neither begin with ‘0’ or ‘0x’, nor end with a ‘.’
are, by default, entered in base 10; likewise, the default display for numbers—when no
particular format is specified—is base 10. You can change the default base for both input
and output with the commands described below.
set input-radix base
Set the default base for numeric input. Supported choices for base are decimal
8, 10, or 16. The base must itself be specified either unambiguously or using
the current input radix; for example, any of
set input-radix 012
set input-radix 10.

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set input-radix 0xa

sets the input base to decimal. On the other hand, ‘set input-radix 10’ leaves
the input radix unchanged, no matter what it was, since ‘10’, being without any
leading or trailing signs of its base, is interpreted in the current radix. Thus,
if the current radix is 16, ‘10’ is interpreted in hex, i.e. as 16 decimal, which
doesn’t change the radix.
set output-radix base
Set the default base for numeric display. Supported choices for base are decimal
8, 10, or 16. The base must itself be specified either unambiguously or using
the current input radix.
show input-radix
Display the current default base for numeric input.
show output-radix
Display the current default base for numeric display.
set radix [base]show radix
These commands set and show the default base for both input and output
of numbers. set radix sets the radix of input and output to the same base;without an argument, it resets the radix back to its default value of 10.

22.7 Configuring the Current ABI
gdb can determine the ABI (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands tomanage gdb’s view of the current ABI.
One gdb configuration can debug binaries for multiple operating system targets, either
via remote debugging or native emulation. gdb will autodetect the OS ABI (Operating
System ABI) in use, but you can override its conclusion using the set osabi command. One
example where this is useful is in debugging of binaries which use an alternate C library (e.g.
uClibc for gnu/Linux) which does not have the same identifying marks that the standard
C library for your platform provides.
When gdb is debugging the AArch64 architecture, it provides a “Newlib” OS ABI. Thisis useful for handling setjmp and longjmp when debugging binaries that use the newlib
C library. The “Newlib” OS ABI can be selected by set osabi Newlib.
show osabi
Show the OS ABI currently in use.
set osabi With no argument, show the list of registered available OS ABI’s.
set osabi abi
Set the current OS ABI to abi.
Generally, the way that an argument of type float is passed to a function depends onwhether the function is prototyped. For a prototyped (i.e. ANSI/ISO style) function, float
arguments are passed unchanged, according to the architecture’s convention for float. For

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unprototyped (i.e. K&R style) functions, float arguments are first promoted to type double
and then passed.
Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If gdb calls a function that is not marked as prototyped, it consults
set coerce-float-to-double.
set coerce-float-to-double
set coerce-float-to-double on
Arguments of type float will be promoted to double when passed to an unprototyped function. This is the default setting.
set coerce-float-to-double off
Arguments of type float will be passed directly to unprototyped functions.
show coerce-float-to-double
Show the current setting of promoting float to double.
gdb needs to know the ABI used for your program’s C++ objects. The correct C++ ABI
depends on which C++ compiler was used to build your application. gdb only fully supports
programs with a single C++ ABI; if your program contains code using multiple C++ ABI’sor if gdb can not identify your program’s ABI correctly, you can tell gdb which ABI to use.
Currently supported ABI’s include “gnu-v2”, for g++ versions before 3.0, “gnu-v3”, for g++
versions 3.0 and later, and “hpaCC” for the HP ANSI C++ compiler. Other C++ compilers
may use the “gnu-v2” or “gnu-v3” ABI’s as well. The default setting is “auto”.
show cp-abi
Show the C++ ABI currently in use.
set cp-abi
With no argument, show the list of supported C++ ABI’s.
set cp-abi abi
set cp-abi auto
Set the current C++ ABI to abi, or return to automatic detection.

22.8 Automatically loading associated files
gdb sometimes reads files with commands and settings automatically, without being explicitly told so by the user. We call this feature auto-loading. While auto-loading is usefulfor automatically adapting gdb to the needs of your project, it can sometimes produce unexpected results or introduce security risks (e.g., if the file comes from untrusted sources).
There are various kinds of files gdb can automatically load. In addition to these files,
gdb supports auto-loading code written in various extension languages. See Section 23.5
[Auto-loading extensions], page 571.
Note that loading of these associated files (including the local .gdbinit file) requires
accordingly configured auto-load safe-path (see Section 22.8.3 [Auto-loading safe path],
page 379).
For these reasons, gdb includes commands and options to let you control when to autoload files and which files should be auto-loaded.

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set auto-load off
Globally disable loading of all auto-loaded files. You may want to use thiscommand with the ‘-iex’ option (see [Option -init-eval-command], page 16)
such as:$ gdb -iex "set auto-load off" untrusted-executable corefile

Be aware that system init file (see Section C.6 [System-wide configuration],
page 753) and init files from your home directory (see [Home Directory Init
File], page 18) still get read (as they come from generally trusted directories).
To prevent gdb from auto-loading even those init files, use the -nx option (seeSection 2.1.2 [Mode Options], page 13), in addition to set auto-load no.
show auto-loadShow whether auto-loading of each specific ‘auto-load’ file(s) is enabled or
disabled.
(gdb) show auto-load
gdb-scripts: Auto-loading of canned sequences of commands scripts is on.
libthread-db: Auto-loading of inferior specific libthread_db is on.
local-gdbinit: Auto-loading of .gdbinit script from current directoryis on.
python-scripts: Auto-loading of Python scripts is on.
safe-path: List of directories from which it is safe to auto-load files
is $debugdir:$datadir/auto-load.
scripts-directory: List of directories from which to load auto-loaded scripts
is $debugdir:$datadir/auto-load.

info auto-loadPrint whether each specific ‘auto-load’ file(s) have been auto-loaded or not.
(gdb) info auto-load
gdb-scripts:
Loaded Script
Yes/home/user/gdb/gdb-gdb.gdb
libthread-db: No auto-loaded libthread-db.
local-gdbinit: Local .gdbinit file "/home/user/gdb/.gdbinit" has been
loaded.
python-scripts:
Loaded Script
Yes/home/user/gdb/gdb-gdb.py

These are gdb control commands for the auto-loading:See [set auto-load off], page 377.
See [show auto-load], page 377.
See [info auto-load], page 377.
See [set auto-load gdb-scripts], page 399.
See [show auto-load gdb-scripts], page 399.
See [info auto-load gdb-scripts], page 399.
See [set auto-load python-scripts], page 513.
See [show auto-load python-scripts], page 513.
See [info auto-load python-scripts], page 513.
See [set auto-load guile-scripts], page 570.
See [show auto-load guile-scripts], page 570.
See [info auto-load guile-scripts], page 570.

Disable auto-loading globally.
Show setting of all kinds of files.
Show state of all kinds of files.
Control for gdb command scripts.
Show setting of gdb command scripts.
Show state of gdb command scripts.
Control for gdb Python scripts.
Show setting of gdb Python scripts.
Show state of gdb Python scripts.
Control for gdb Guile scripts.
Show setting of gdb Guile scripts.
Show state of gdb Guile scripts.

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See [set auto-load scripts-directory], page 572.
See [show auto-load scripts-directory],
page 573.
See[add-auto-load-scripts-directory],
page 573.
See [set auto-load local-gdbinit], page 378.
See [show auto-load local-gdbinit], page 378.
See [info auto-load local-gdbinit], page 378.
See [set auto-load libthread-db], page 379.
See [show auto-load libthread-db], page 379.
See [info auto-load libthread-db], page 379.
See [set auto-load safe-path], page 379.
See [show auto-load safe-path], page 379.
See [add-auto-load-safe-path], page 379.

Debugging with gdb

Control for gdb auto-loaded scripts
location.
Show gdb auto-loaded scripts location.
Add directory for auto-loaded scripts location list.
Control for init file in the current directory.
Show setting of init file in the current
directory.
Show state of init file in the current
directory.
Control for thread debugging library.
Show setting of thread debugging library.
Show state of thread debugging library.
Control directories trusted for automatic
loading.
Show directories trusted for automatic
loading.
Add directory trusted for automatic
loading.

22.8.1 Automatically loading init file in the current directory
By default, gdb reads and executes the canned sequences of commands from init file (if any)in the current working directory, see [Init File in the Current Directory during Startup],
page 19.
Note that loading of this local .gdbinit file also requires accordingly configured
auto-load safe-path (see Section 22.8.3 [Auto-loading safe path], page 379).
set auto-load local-gdbinit [on|off]
Enable or disable the auto-loading of canned sequences of commands (seeSection 23.1 [Sequences], page 391) found in init file in the current directory.
show auto-load local-gdbinitShow whether auto-loading of canned sequences of commands from init file inthe current directory is enabled or disabled.
info auto-load local-gdbinit
Print whether canned sequences of commands from init file in the current directory have been auto-loaded.

22.8.2 Automatically loading thread debugging libraryThis feature is currently present only on gnu/Linux native hosts.
gdb reads in some cases thread debugging library from places specific to the inferior(see [set libthread-db-search-path], page 51).
The special ‘libthread-db-search-path’ entry ‘$sdir’ is processed without checking
this ‘set auto-load libthread-db’ switch as system libraries have to be trusted in general.

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In all other cases of ‘libthread-db-search-path’ entries gdb checks first if ‘set auto-load
libthread-db’ is enabled before trying to open such thread debugging library.
Note that loading of this debugging library also requires accordingly configured
auto-load safe-path (see Section 22.8.3 [Auto-loading safe path], page 379).
set auto-load libthread-db [on|off]
Enable or disable the auto-loading of inferior specific thread debugging library.
show auto-load libthread-db
Show whether auto-loading of inferior specific thread debugging library is enabled or disabled.
info auto-load libthread-db
Print the list of all loaded inferior specific thread debugging libraries and foreach such library print list of inferior pids using it.

22.8.3 Security restriction for auto-loading
As the files of inferior can come from untrusted source (such as submitted by an applicationuser) gdb does not always load any files automatically. gdb provides the ‘set auto-load
safe-path’ setting to list directories trusted for loading files not explicitly requested byuser. Each directory can also be a shell wildcard pattern.
If the path is not set properly you will see a warning and the file will not get loaded:$ ./gdb -q ./gdb
Reading symbols from /home/user/gdb/gdb...
warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been
declined by your ‘auto-load safe-path’ set
to "$debugdir:$datadir/auto-load".
warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been
declined by your ‘auto-load safe-path’ set
to "$debugdir:$datadir/auto-load".

To instruct gdb to go ahead and use the init files anyway, invoke gdb like this:$ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb

The list of trusted directories is controlled by the following commands:
set auto-load safe-path [directories]
Set the list of directories (and their subdirectories) trusted for automatic loading and execution of scripts. You can also enter a specific trusted file. Eachdirectory can also be a shell wildcard pattern; wildcards do not match directory
separator - see FNM_PATHNAME for system function fnmatch (see Section “Wildcard Matching” in GNU C Library Reference Manual). If you omit directories,‘auto-load safe-path’ will be reset to its default value as specified during gdb
compilation.
The list of directories uses path separator (‘:’ on GNU and Unix systems, ‘;’
on MS-Windows and MS-DOS) to separate directories, similarly to the PATH
environment variable.
show auto-load safe-path
Show the list of directories trusted for automatic loading and execution of
scripts.

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add-auto-load-safe-path
Add an entry (or list of entries) to the list of directories trusted for automatic
loading and execution of scripts. Multiple entries may be delimited by the hostplatform path separator in use.
This variable defaults to what --with-auto-load-dir has been configured to (see [withauto-load-dir], page 572). $debugdir and $datadir substitution applies the same as for[set auto-load scripts-directory], page 572. The default set auto-load safe-path value
can be also overridden by gdb configuration option --with-auto-load-safe-path.
Setting this variable to / disables this security protection, corresponding gdb configuration option is --without-auto-load-safe-path. This variable is supposed to be set tothe system directories writable by the system superuser only. Users can add their source
directories in init files in their home directories (see [Home Directory Init File], page 18).
See also deprecated init file in the current directory (see [Init File in the Current Directoryduring Startup], page 19).
To force gdb to load the files it declined to load in the previous example, you could use
one of the following ways:~/.gdbinit: ‘add-auto-load-safe-path ~/src/gdb’
Specify this trusted directory (or a file) as additional component of the list. You
have to specify also any existing directories displayed by by ‘show auto-load
safe-path’ (such as ‘/usr:/bin’ in this example).
gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" ...
Specify this directory as in the previous case but just for a single gdb session.
gdb -iex "set auto-load safe-path /" ...
Disable auto-loading safety for a single gdb session. This assumes all the files
you debug during this gdb session will come from trusted sources.
./configure --without-auto-load-safe-path
During compilation of gdb you may disable any auto-loading safety. This
assumes all the files you will ever debug with this gdb come from trusted
sources.
On the other hand you can also explicitly forbid automatic files loading which also
suppresses any such warning messages:
gdb -iex "set auto-load no" ...
You can use gdb command-line option for a single gdb session.
~/.gdbinit: ‘set auto-load no’
Disable auto-loading globally for the user (see [Home Directory Init File],
page 18). While it is improbable, you could also use system init file instead(see Section C.6 [System-wide configuration], page 753).
This setting applies to the file names as entered by user. If no entry matches gdb
tries as a last resort to also resolve all the file names into their canonical form (typicallyresolving symbolic links) and compare the entries again. gdb already canonicalizes most of
the filenames on its own before starting the comparison so a canonical form of directories
is recommended to be entered.

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22.8.4 Displaying files tried for auto-load
For better visibility of all the file locations where you can place scripts to be auto-loadedwith inferior — or to protect yourself against accidental execution of untrusted scripts —gdb provides a feature for printing all the files attempted to be loaded. Both existing andnon-existing files may be printed.
For example the list of directories from which it is safe to auto-load files (seeSection 22.8.3 [Auto-loading safe path], page 379) applies also to canonicalized filenames
which may not be too obvious while setting it up.
(gdb) set debug auto-load on(gdb) file ~/src/t/trueauto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb"
for objfile "/tmp/true".
auto-load: Updating directories of "/usr:/opt".
auto-load: Using directory "/usr".
auto-load: Using directory "/opt".
warning: File "/tmp/true-gdb.gdb" auto-loading has been declinedby your ‘auto-load safe-path’ set to "/usr:/opt".

set debug auto-load [on|off]
Set whether to print the filenames attempted to be auto-loaded.
show debug auto-loadShow whether printing of the filenames attempted to be auto-loaded is turnedon or off.

22.9 Optional Warnings and Messages
By default, gdb is silent about its inner workings. If you are running on a slow machine,
you may want to use the set verbose command. This makes gdb tell you when it does alengthy internal operation, so you will not think it has crashed.
Currently, the messages controlled by set verbose are those which announce that thesymbol table for a source file is being read; see symbol-file in Section 18.1 [Commands toSpecify Files], page 291.
set verbose on
Enables gdb output of certain informational messages.
set verbose off
Disables gdb output of certain informational messages.
show verbose
Displays whether set verbose is on or off.
By default, if gdb encounters bugs in the symbol table of an object file, it is silent; but if
you are debugging a compiler, you may find this information useful (see Section 18.7 [Errors
Reading Symbol Files], page 307).
set complaints limit
Permits gdb to output limit complaints about each type of unusual symbols
before becoming silent about the problem. Set limit to zero to suppress all complaints; set it to a large number to prevent complaints from being suppressed.

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show complaints
Displays how many symbol complaints gdb is permitted to produce.
By default, gdb is cautious, and asks what sometimes seems to be a lot of stupid
questions to confirm certain commands. For example, if you try to run a program which isalready running:(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n)

If you are willing to unflinchingly face the consequences of your own commands, you candisable this “feature”:
set confirm off
Disables confirmation requests. Note that running gdb with the --batch option (see Section 2.1.2 [Mode Options], page 13) also automatically disables
confirmation requests.
set confirm on
Enables confirmation requests (the default).
show confirm
Displays state of confirmation requests.
If you need to debug user-defined commands or sourced files you may find it useful toenable command tracing. In this mode each command will be printed as it is executed, prefixed with one or more ‘+’ symbols, the quantity denoting the call depth of each command.
set trace-commands on
Enable command tracing.
set trace-commands off
Disable command tracing.
show trace-commands
Display the current state of command tracing.

22.10 Optional Messages about Internal Happenings
gdb has commands that enable optional debugging messages from various gdb subsystems;
normally these commands are of interest to gdb maintainers, or when reporting a bug. Thissection documents those commands.
set exec-done-display
Turns on or off the notification of asynchronous commands’ completion. Whenon, gdb will print a message when an asynchronous command finishes its execution. The default is off.
show exec-done-display
Displays the current setting of asynchronous command completion notification.
set debug aarch64
Turns on or off display of debugging messages related to ARM AArch64. The
default is off.

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show debug aarch64
Displays the current state of displaying debugging messages related to ARM
AArch64.
set debug arch
Turns on or off display of gdbarch debugging info. The default is offshow debug arch
Displays the current state of displaying gdbarch debugging info.
set debug aix-thread
Display debugging messages about inner workings of the AIX thread module.
show debug aix-thread
Show the current state of AIX thread debugging info display.
set debug amd-dbgapi-lib
show debug amd-dbgapi-lib
The set debug amd-dbgapi-lib log-level level command can be used toenable diagnostic messages from the ‘amd-dbgapi’ library, where level can be:off

no logging is enablederror

fatal errors are reported

warningfatal errors and warnings are reported

info

fatal errors, warnings, and info messages are reported

verboseall messages are reported

The show debug amd-dbgapi-lib log-level command displays the current
amd-dbgapi library log level.
set debug amd-dbgapi
show debug amd-dbgapi
The ‘set debug amd-dbgapi’ command can be used to enable diagnostic messages in the ‘amd-dbgapi’ target. The ‘show debug amd-dbgapi’ command displays the current setting. See [set debug amd-dbgapi], page 383.
set debug check-physname
Check the results of the “physname” computation. When reading DWARF
debugging information for C++, gdb attempts to compute each entity’s name.
gdb can do this computation in two different ways, depending on exactly what
information is present. When enabled, this setting causes gdb to compute thenames both ways and display any discrepancies.
show debug check-physname
Show the current state of “physname” checking.
set debug coff-pe-readControl display of debugging messages related to reading of COFF/PE exported
symbols. The default is off.
show debug coff-pe-read
Displays the current state of displaying debugging messages related to readingof COFF/PE exported symbols.

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set debug dwarf-die
Dump DWARF DIEs after they are read in. The value is the number of nestinglevels to print. A value of zero turns off the display.
show debug dwarf-die
Show the current state of DWARF DIE debugging.
set debug dwarf-line
Turns on or off display of debugging messages related to reading DWARF line
tables. The default is 0 (off). A value of 1 provides basic information. A value
greater than 1 provides more verbose information.
show debug dwarf-line
Show the current state of DWARF line table debugging.
set debug dwarf-readTurns on or off display of debugging messages related to reading DWARF debug
info. The default is 0 (off). A value of 1 provides basic information. A value
greater than 1 provides more verbose information.
show debug dwarf-readShow the current state of DWARF reader debugging.
set debug displaced
Turns on or off display of gdb debugging info for the displaced stepping support.
The default is off.
show debug displaced
Displays the current state of displaying gdb debugging info related to displaced
stepping.
set debug event
Turns on or off display of gdb event debugging info. The default is off.
show debug event
Displays the current state of displaying gdb event debugging info.
set debug event-loop
Controls output of debugging info about the event loop. The possible values
are ‘off’, ‘all’ (shows all debugging info) and ‘all-except-ui’ (shows all
debugging info except those about UI-related events).
show debug event-loop
Shows the current state of displaying debugging info about the event loop.
set debug expression
Turns on or off display of debugging info about gdb expression parsing. The
default is off.
show debug expression
Displays the current state of displaying debugging info about gdb expression
parsing.
set debug fbsd-lwp
Turns on or off debugging messages from the FreeBSD LWP debug support.

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show debug fbsd-lwp
Show the current state of FreeBSD LWP debugging messages.
set debug fbsd-nat
Turns on or off debugging messages from the FreeBSD native target.
show debug fbsd-nat
Show the current state of FreeBSD native target debugging messages.
set debug fortran-array-slicing
Turns on or off display of gdb Fortran array slicing debugging info. The default
is off.
show debug fortran-array-slicing
Displays the current state of displaying gdb Fortran array slicing debugging
info.
set debug frame
Turns on or off display of gdb frame debugging info. The default is off.
show debug frame
Displays the current state of displaying gdb frame debugging info.
set debug gnu-nat
Turn on or off debugging messages from the gnu/Hurd debug support.
show debug gnu-nat
Show the current state of gnu/Hurd debugging messages.
set debug infrun
Turns on or off display of gdb debugging info for running the inferior. The
default is off. infrun.c contains GDB’s runtime state machine used for implementing operations such as single-stepping the inferior.
show debug infrun
Displays the current state of gdb inferior debugging.
set debug infcall
Turns on or off display of debugging info related to inferior function calls madeby gdb.
show debug infcall
Displays the current state of gdb inferior function call debugging.
set debug jit
Turn on or off debugging messages from JIT debug support.
show debug jit
Displays the current state of gdb JIT debugging.
set debug linux-nat [on|off]Turn on or off debugging messages from the Linux native target debug support.
show debug linux-nat
Show the current state of Linux native target debugging messages.

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set debug linux-namespaces
Turn on or off debugging messages from the Linux namespaces debug support.
show debug linux-namespaces
Show the current state of Linux namespaces debugging messages.
set debug mach-oControl display of debugging messages related to Mach-O symbols processing.
The default is off.
show debug mach-o
Displays the current state of displaying debugging messages related to readingof COFF/PE exported symbols.
set debug notification
Turn on or off debugging messages about remote async notification. The default
is off.
show debug notification
Displays the current state of remote async notification debugging messages.
set debug observer
Turns on or off display of gdb observer debugging. This includes info such as
the notification of observable events.
show debug observer
Displays the current state of observer debugging.
set debug overload
Turns on or off display of gdb C++ overload debugging info. This includes info
such as ranking of functions, etc. The default is off.
show debug overload
Displays the current state of displaying gdb C++ overload debugging info.
set debug parser
Turns on or off the display of expression parser debugging output. Internally,
this sets the yydebug variable in the expression parser. See Section “Tracing
Your Parser” in Bison, for details. The default is off.
show debug parser
Show the current state of expression parser debugging.
set debug remote
Turns on or off display of reports on all packets sent back and forth across theserial line to the remote machine. The info is printed on the gdb standard
output stream. The default is off.
show debug remote
Displays the state of display of remote packets.
set debug remote-packet-max-chars
Sets the maximum number of characters to display for each remote packet whenset debug remote is on. This is useful to prevent gdb from displaying lengthy
remote packets and polluting the console.

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The default value is 512, which means gdb will truncate each remote packet
after 512 bytes.
Setting this option to unlimited will disable truncation and will output thefull length of the remote packets.
show debug remote-packet-max-chars
Displays the number of bytes to output for remote packet debugging.
set debug separate-debug-fileTurns on or off display of debug output about separate debug file search.
show debug separate-debug-file
Displays the state of separate debug file search debug output.
set debug serial
Turns on or off display of gdb serial debugging info. The default is off.
show debug serial
Displays the current state of displaying gdb serial debugging info.
set debug solib
Turns on or off display of debugging messages related to shared libraries. The
default is off.
show debug solib
Show the current state of solib debugging messages.
set debug symbol-lookup
Turns on or off display of debugging messages related to symbol lookup. The
default is 0 (off). A value of 1 provides basic information. A value greater than
1 provides more verbose information.
show debug symbol-lookup
Show the current state of symbol lookup debugging messages.
set debug symfile
Turns on or off display of debugging messages related to symbol file functions.
The default is off. See Section 18.1 [Files], page 291.
show debug symfile
Show the current state of symbol file debugging messages.
set debug symtab-create
Turns on or off display of debugging messages related to symbol table creation.
The default is 0 (off). A value of 1 provides basic information. A value greaterthan 1 provides more verbose information.
show debug symtab-create
Show the current state of symbol table creation debugging.
set debug target
Turns on or off display of gdb target debugging info. This info includes what
is going on at the target level of GDB, as it happens. The default is 0. Set it
to 1 to track events, and to 2 to also track the value of large memory transfers.

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show debug target
Displays the current state of displaying gdb target debugging info.
set debug timestamp
Turns on or off display of timestamps with gdb debugging info. When enabled,
seconds and microseconds are displayed before each debugging message.
show debug timestamp
Displays the current state of displaying timestamps with gdb debugging info.
set debug varobj
Turns on or off display of gdb variable object debugging info. The default isoff.
show debug varobj
Displays the current state of displaying gdb variable object debugging info.
set debug xml
Turn on or off debugging messages for built-in XML parsers.
show debug xml
Displays the current state of XML debugging messages.
set debug breakpoints
Turns on or off display of gdb debugging info for breakpoint insertion andremoval. The default is off.
show debug breakpoints
Displays the current state of displaying gdb debugging info for breakpoint
insertion and removal.

22.11 Other Miscellaneous Settings
set interactive-mode
If on, forces gdb to assume that GDB was started in a terminal. In practice,
this means that gdb should wait for the user to answer queries generated bycommands entered at the command prompt. If off, forces gdb to operate in
the opposite mode, and it uses the default answers to all queries. If auto (thedefault), gdb tries to determine whether its standard input is a terminal, andworks in interactive-mode if it is, non-interactively otherwise.
In the vast majority of cases, the debugger should be able to guess correctly
which mode should be used. But this setting can be useful in certain specificcases, such as running a MinGW gdb inside a cygwin window.
show interactive-mode
Displays whether the debugger is operating in interactive mode or not.
set suppress-cli-notifications
If on, command-line-interface (CLI) notifications that are printed by gdb aresuppressed. If off, the notifications are printed as usual. The default value isoff. CLI notifications occur when you change the selected context or when the
program being debugged stops, as detailed below.

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User-selected context changes:
When you change the selected context (i.e. the current inferior,thread and/or the frame), gdb prints information about the newcontext. For example, the default behavior is below:(gdb) inferior 1[Switching to inferior 1 [process 634] (/tmp/test)][Switching to thread 1 (process 634)]#0 main () at test.c:3
3
return 0;(gdb)

When the notifications are suppressed, the new context is notprinted:(gdb) set suppress-cli-notifications on(gdb) inferior 1(gdb)

The program being debugged stops:
When the program you are debugging stops (e.g. because of hitting
a breakpoint, completing source-stepping, an interrupt, etc.), gdb
prints information about the stop event. For example, below is abreakpoint hit:(gdb) break test.c:3
Breakpoint 2 at 0x555555555155: file test.c, line 3.
(gdb) continue
Continuing.
Breakpoint 2, main () at test.c:3
3
return 0;(gdb)

When the notifications are suppressed, the output becomes:(gdb) break test.c:3
Breakpoint 2 at 0x555555555155: file test.c, line 3.
(gdb) set suppress-cli-notifications on(gdb) continue
Continuing.
(gdb)

Suppressing CLI notifications may be useful in scripts to obtain areduced output from a list of commands.
show suppress-cli-notifications
Displays whether printing CLI notifications is suppressed or not.

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23 Extending gdb
gdb provides several mechanisms for extension. gdb also provides the ability to automatically load extensions when it reads a file for debugging. This allows the user to automaticallycustomize gdb for the program being debugged.
To facilitate the use of extension languages, gdb is capable of evaluating the contents ofa file. When doing so, gdb can recognize which extension language is being used by looking
at the filename extension. Files with an unrecognized filename extension are always treatedas a gdb Command Files. See Section 23.1.3 [Command files], page 395.
You can control how gdb evaluates these files with the following setting:set script-extension off
All scripts are always evaluated as gdb Command Files.
set script-extension soft
The debugger determines the scripting language based on filename extension.
If this scripting language is supported, gdb evaluates the script using that
language. Otherwise, it evaluates the file as a gdb Command File.
set script-extension strict
The debugger determines the scripting language based on filename extension,and evaluates the script using that language. If the language is not supported,
then the evaluation fails.
show script-extension
Display the current value of the script-extension option.

23.1 Canned Sequences of Commands
Aside from breakpoint commands (see Section 5.1.7 [Breakpoint Command Lists], page 77),gdb provides two ways to store sequences of commands for execution as a unit: user-definedcommands and command files.

23.1.1 User-defined Commands
A user-defined command is a sequence of gdb commands to which you assign a new nameas a command. This is done with the define command.
User commands may accept an unlimited number of arguments separated by whitespace.
Arguments are accessed within the user command via $arg0...$argN. The arguments are
text substitutions, so they may reference variables, use complex expressions, or even perform
inferior functions calls. Note, however, that this textual substitution means that working
with certain arguments is difficult. For example, there is no way for the user to passan argument containing a space; and while stringifying an argument can be done using an
expression like "$arg1", this will fail if the argument contains a quote. For more complicatedand robust commands, we recommend writing them in Python; see Section 23.3.2.21 [CLI
Commands In Python], page 463.
A trivial example:
define adderprint $arg0 + $arg1 + $arg2
end

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To execute the command use:
adder 1 2 3This defines the command adder, which prints the sum of its three arguments.
In addition, $argc may be used to find out how many arguments have been passed.
define adderif $argc == 2print $arg0 + $arg1
end
if $argc == 3
print $arg0 + $arg1 + $arg2
end
end

Combining with the eval command (see [eval], page 398) makes it easier to process avariable number of arguments:
define adder
set $i = 0
set $sum = 0
while $i < $argc
eval "set $sum = $sum + $arg%d", $i
set $i = $i + 1
endprint $sum
enddefine commandname
Define a command named commandname. If there is already a command bythat name, you are asked to confirm that you want to redefine it. The argumentcommandname may be a bare command name consisting of letters, numbers,
dashes, dots, and underscores. It may also start with any predefined or userdefined prefix command. For example, ‘define target my-target’ creates auser-defined ‘target my-target’ command.
The definition of the command is made up of other gdb command lines, which
are given following the define command. The end of these commands is marked
by a line containing end.
document commandname
Document the user-defined command commandname, so that it can be accessed by help. The command commandname must already be defined. This
command reads lines of documentation just as define reads the lines of thecommand definition, ending with end. After the document command is finished, help on command commandname displays the documentation you havewritten.
You may use the document command again to change the documentation of acommand. Redefining the command with define does not change the documentation.
It is also possible to document user-defined aliases. The alias documentation
will then be used by the help and apropos commands instead of the documentation of the aliased command. Documenting a user-defined alias is particularly useful when defining an alias as a set of nested with commands (seeSection 23.2.1 [Command aliases default args], page 400).

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define-prefix commandname
Define or mark the command commandname as a user-defined prefix command. Once marked, commandname can be used as prefix command by thedefine command. Note that define-prefix can be used with a not yet defined commandname. In such a case, commandname is defined as an empty
user-defined command. In case you redefine a command that was marked as auser-defined prefix command, the subcommands of the redefined command are
kept (and gdb indicates so to the user).
Example:(gdb) define-prefix abc(gdb) define-prefix abc def(gdb) define abc def
Type commands for definition of "abc def".
End with a line saying just "end".
>echo command initial def\n>end(gdb) define abc def ghi
Type commands for definition of "abc def ghi".
End with a line saying just "end".
>echo command ghi\n>end(gdb) define abc def
Keeping subcommands of prefix command "def".
Redefine command "def"? (y or n) yType commands for definition of "abc def".
End with a line saying just "end".
>echo command def\n>end(gdb) abc def ghi
command ghi(gdb) abc def
command def(gdb)

dont-repeat
Used inside a user-defined command, this tells gdb that this command should
not be repeated when the user hits RET (see Section 3.1 [Command Syntax],
page 23).

help user-defined
List all user-defined commands and all python commands defined in class COMMAND USER. The first line of the documentation or docstring is included (if
any).

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show user
show user commandname
Display the gdb commands used to define commandname (but not its documentation). If no commandname is given, display the definitions for all user-definedcommands. This does not work for user-defined python commands.
show max-user-call-depth
set max-user-call-depth
The value of max-user-call-depth controls how many recursion levels areallowed in user-defined commands before gdb suspects an infinite recursion andaborts the command. This does not apply to user-defined python commands.
In addition to the above commands, user-defined commands frequently use control flowcommands, described in Section 23.1.3 [Command Files], page 395.
When user-defined commands are executed, the commands of the definition are notprinted. An error in any command stops execution of the user-defined command.
If used interactively, commands that would ask for confirmation proceed without asking
when used inside a user-defined command. Many gdb commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.

23.1.2 User-defined Command Hooks
You may define hooks, which are a special kind of user-defined command. Whenever you
run the command ‘foo’, if the user-defined command ‘hook-foo’ exists, it is executed (withno arguments) before that command.
A hook may also be defined which is run after the command you executed. Whenever you
run the command ‘foo’, if the user-defined command ‘hookpost-foo’ exists, it is executed(with no arguments) after that command. Post-execution hooks may exist simultaneouslywith pre-execution hooks, for the same command.
It is valid for a hook to call the command which it hooks. If this occurs, the hook is not
re-executed, thereby avoiding infinite recursion.
In addition, a pseudo-command, ‘stop’ exists. Defining (‘hook-stop’) makes the associated commands execute every time execution stops in your program: before breakpointcommands are run, displays are printed, or the stack frame is printed.
For example, to ignore SIGALRM signals while single-stepping, but treat them normallyduring normal execution, you could define:define hook-stop
handle SIGALRM nopass
end
define hook-run
handle SIGALRM passend
define hook-continue
handle SIGALRM passend

As a further example, to hook at the beginning and end of the echo command, and to
add extra text to the beginning and end of the message, you could define:define hook-echo

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echo <<<--end
define hookpost-echo
echo --->>>\nend(gdb) echo Hello World<<<---Hello World--->>>(gdb)

You can define a hook for any single-word command in gdb, but not for commandaliases; you should define a hook for the basic command name, e.g. backtrace rather thanbt. You can hook a multi-word command by adding hook- or hookpost- to the last wordof the command, e.g. ‘define target hook-remote’ to add a hook to ‘target remote’.
If an error occurs during the execution of your hook, execution of gdb commands stops
and gdb issues a prompt (before the command that you actually typed had a chance torun).
If you try to define a hook which does not match any known command, you get a warningfrom the define command.

23.1.3 Command Files
A command file for gdb is a text file made of lines that are gdb commands. Comments(lines starting with #) may also be included. An empty line in a command file does nothing;
it does not mean to repeat the last command, as it would from the terminal.
You can request the execution of a command file with the source command. Note thatthe source command is also used to evaluate scripts that are not Command Files. The
exact behavior can be configured using the script-extension setting. See Chapter 23[Extending GDB], page 391.
source [-s] [-v] filename
Execute the command file filename.
The lines in a command file are generally executed sequentially, unless the order of
execution is changed by one of the flow-control commands described below. The commands
are not printed as they are executed. An error in any command terminates execution of
the command file and control is returned to the console.
gdb first searches for filename in the current directory. If the file is not found there, andfilename does not specify a directory, then gdb also looks for the file on the source search
path (specified with the ‘directory’ command); except that $cdir is not searched because
the compilation directory is not relevant to scripts.
If -s is specified, then gdb searches for filename on the search path even if filename specifies a directory. The search is done by appending filename to each element of the search path.
So, for example, if filename is mylib/myscript and the search path contains /home/user
then gdb will look for the script /home/user/mylib/myscript. The search is also done iffilename is an absolute path. For example, if filename is /tmp/myscript and the search
path contains /home/user then gdb will look for the script /home/user/tmp/myscript.
For DOS-like systems, if filename contains a drive specification, it is stripped before con-

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catenation. For example, if filename is d:myscript and the search path contains c:/tmpthen gdb will look for the script c:/tmp/myscript.
If -v, for verbose mode, is given then gdb displays each command as it is executed. The
option must be given before filename, and is interpreted as part of the filename anywhere
else.
Commands that would ask for confirmation if used interactively proceed without asking
when used in a command file. Many gdb commands that normally print messages to say
what they are doing omit the messages when called from command files.
gdb also accepts command input from standard input. In this mode, normal output
goes to standard output and error output goes to standard error. Errors in a command
file supplied on standard input do not terminate execution of the command file—execution
continues with the next command.
gdb < cmds > log 2>&1

(The syntax above will vary depending on the shell used.) This example will executecommands from the file cmds. All output and errors would be directed to log.
Since commands stored on command files tend to be more general than commands typed
interactively, they frequently need to deal with complicated situations, such as different or
unexpected values of variables and symbols, changes in how the program being debugged
is built, etc. gdb provides a set of flow-control commands to deal with these complexities.
Using these commands, you can write complex scripts that loop over data structures, executecommands conditionally, etc.
if
else

while

This command allows to include in your script conditionally executed commands. The if command takes a single argument, which is an expression toevaluate. It is followed by a series of commands that are executed only if theexpression is true (its value is nonzero). There can then optionally be an elseline, followed by a series of commands that are only executed if the expression
was false. The end of the list is marked by a line containing end.
This command allows to write loops. Its syntax is similar to if: the commandtakes a single argument, which is an expression to evaluate, and must be followed by the commands to execute, one per line, terminated by an end. These
commands are called the body of the loop. The commands in the body of whileare executed repeatedly as long as the expression evaluates to true.

loop_breakThis command exits the while loop in whose body it is included. Execution of
the script continues after that whiles end line.
loop_continue
This command skips the execution of the rest of the body of commands in thewhile loop in whose body it is included. Execution branches to the beginningof the while loop, where it evaluates the controlling expression.
end

Terminate the block of commands that are the body of if, else, or while
flow-control commands.

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23.1.4 Commands for Controlled Output
During the execution of a command file or a user-defined command, normal gdb output
is suppressed; the only output that appears is what is explicitly printed by the commandsin the definition. This section describes three commands useful for generating exactly theoutput you want.
echo text Print text. Nonprinting characters can be included in text using C escape sequences, such as ‘\n’ to print a newline. No newline is printed unless you specify
one. In addition to the standard C escape sequences, a backslash followed by aspace stands for a space. This is useful for displaying a string with spaces at the
beginning or the end, since leading and trailing spaces are otherwise trimmed
from all arguments. To print ‘ and foo = ’, use the command ‘echo \ and foo= \ ’.
A backslash at the end of text can be used, as in C, to continue the command
onto subsequent lines. For example,
echo This is some text\n\which is continued\n\onto several lines.\n

produces the same output asecho This is some text\necho which is continued\necho onto several lines.\noutput expression
Print the value of expression and nothing but that value: no newlines, no ‘$nn
= ’. The value is not entered in the value history either. See Section 10.1
[Expressions], page 145, for more information on expressions.
output/fmt expression
Print the value of expression in format fmt. You can use the same formats as
for print. See Section 10.5 [Output Formats], page 150, for more information.
printf template, expressions...
Print the values of one or more expressions under the control of the string
template. To print several values, make expressions be a comma-separated
list of individual expressions, which may be either numbers or pointers. Theirvalues are printed as specified by template, exactly as a C program would doby executing the code below:
printf (template, expressions...);As in C printf, ordinary characters in template are printed verbatim, whileconversion specification introduced by the ‘%’ character cause subsequent expressions to be evaluated, their values converted and formatted according totype and style information encoded in the conversion specifications, and thenprinted.
For example, you can print two values in hex like this:printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo

printf supports all the standard C conversion specifications, including the flags
and modifiers between the ‘%’ character and the conversion letter, with thefollowing exceptions:398

Debugging with gdb• The argument-ordering modifiers, such as ‘2$’, are not supported.
• The modifier ‘*’ is not supported for specifying precision or width.
• The ‘’’ flag (for separation of digits into groups according to LC_NUMERIC’)
is not supported.
• The type modifiers ‘hh’, ‘j’, ‘t’, and ‘z’ are not supported.
• The conversion letter ‘n’ (as in ‘%n’) is not supported.
• The conversion letters ‘a’ and ‘A’ are not supported.
Note that the ‘ll’ type modifier is supported only if the underlying C implementation used to build gdb supports the long long int type, and the ‘L’ typemodifier is supported only if long double type is available.
As in C, printf supports simple backslash-escape sequences, such as \n, ‘\t’,‘\\’, ‘\"’, ‘\a’, and ‘\f’, that consist of backslash followed by a single character.
Octal and hexadecimal escape sequences are not supported.
Additionally, printf supports conversion specifications for DFP (Decimal
Floating Point) types using the following length modifiers together with afloating point specifier. letters:• ‘H’ for printing Decimal32 types.
• ‘D’ for printing Decimal64 types.
• ‘DD’ for printing Decimal128 types.
If the underlying C implementation used to build gdb has support for the threelength modifiers for DFP types, other modifiers such as width and precision
will also be available for gdb to use.
In case there is no such C support, no additional modifiers will be available andthe value will be printed in the standard way.
Here’s an example of printing DFP types using the above conversion letters:
printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl

Additionally, printf supports a special ‘%V’ output format. This format prints
the string representation of an expression just as gdb would produce with thestandard print command (see Chapter 10 [Examining Data], page 141):(gdb) print array$1 = {0, 1, 2, 3, 4, 5}(gdb) printf "Array is: %V\n", array
Array is: {0, 1, 2, 3, 4, 5}

It is possible to include print options with the ‘%V’ format by placing them in‘[...]’ immediately after the ‘%V’, like this:(gdb) printf "Array is: %V[-array-indexes on]\n", array
Array is: {[0] = 0, [1] = 1, [2] = 2, [3] = 3, [4] = 4, [5] = 5}

If you need to print a literal ‘[’ directly after a ‘%V’, then just include an empty
print options list:(gdb) printf "Array is: %V[][Hello]\n", array
Array is: {0, 1, 2, 3, 4, 5}[Hello]

eval template, expressions...
Convert the values of one or more expressions under the control of the string
template to a command line, and call it.

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23.1.5 Controlling auto-loading native gdb scripts
When a new object file is read (for example, due to the file command, or because theinferior has loaded a shared library), gdb will look for the command file objfile-gdb.gdb.
See Section 23.5 [Auto-loading extensions], page 571.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be
printed.
set auto-load gdb-scripts [on|off]
Enable or disable the auto-loading of canned sequences of commands scripts.
show auto-load gdb-scripts
Show whether auto-loading of canned sequences of commands scripts is enabledor disabled.
info auto-load gdb-scripts [regexp]
Print the list of all canned sequences of commands scripts that gdb auto-loaded.
If regexp is supplied only canned sequences of commands scripts with matching names
are printed.

23.2 Command Aliases
Aliases allow you to define alternate spellings for existing commands. For example, if a new
gdb command defined in Python (see Section 23.3 [Python], page 401) has a long name, it
is handy to have an abbreviated version of it that involves less typing.
gdb itself uses aliases. For example ‘s’ is an alias of the ‘step’ command even though
it is otherwise an ambiguous abbreviation of other commands like ‘set’ and ‘show’.
Aliases are also used to provide shortened or more common versions of multi-word commands. For example, gdb provides the ‘tty’ alias of the ‘set inferior-tty’ command.
You can define a new alias with the ‘alias’ command.
alias [-a] [--] alias = command [default-args]
alias specifies the name of the new alias. Each word of alias must consist of letters,
numbers, dashes and underscores.
command specifies the name of an existing command that is being aliased.
command can also be the name of an existing alias. In this case, command cannot be
an alias that has default arguments.
The ‘-a’ option specifies that the new alias is an abbreviation of the command. Abbreviations are not used in command completion.
The ‘--’ option specifies the end of options, and is useful when alias begins with a dash.
You can specify default-args for your alias. These default-args will be automatically
added before the alias arguments typed explicitly on the command line.
For example, the below defines an alias btfullall that shows all local variables and allframe arguments:(gdb) alias btfullall = backtrace -full -frame-arguments all

For more information about default-args, see Section 23.2.1 [Default Arguments],
page 400.

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Here is a simple example showing how to make an abbreviation of a command so that
there is less to type. Suppose you were tired of typing ‘disas’, the current shortest unambiguous abbreviation of the ‘disassemble’ command and you wanted an even shorter
version named ‘di’. The following will accomplish this.
(gdb) alias -a di = disas

Note that aliases are different from user-defined commands. With a user-defined command, you also need to write documentation for it with the ‘document’ command. An alias
automatically picks up the documentation of the existing command.
Here is an example where we make ‘elms’ an abbreviation of ‘elements’ in the ‘set
print elements’ command. This is to show that you can make an abbreviation of any partof a command.
(gdb) alias -a set print elms = set print elements(gdb) alias -a show print elms = show print elements(gdb) set p elms 200(gdb) show p elms
Limit on string chars or array elements to print is 200.

Note that if you are defining an alias of a ‘set’ command, and you want to have an alias
for the corresponding ‘show’ command, then you need to define the latter separately.
Unambiguously abbreviated commands are allowed in command and alias, just as they
are normally.
(gdb) alias -a set pr elms = set p ele

Finally, here is an example showing the creation of a one word alias for a more complex
command. This creates alias ‘spe’ of the command ‘set print elements’.
(gdb) alias spe = set print elements(gdb) spe 20

23.2.1 Default Arguments
You can tell gdb to always prepend some default arguments to the list of arguments provided
explicitly by the user when using a user-defined alias.
If you repeatedly use the same arguments or options for a command, you can define analias for this command and tell gdb to automatically prepend these arguments or options
to the list of arguments you type explicitly when using the alias1 .
For example, if you often use the command thread apply all specifying to work on thethreads in ascending order and to continue in case it encounters an error, you can tell gdb
to automatically preprend the -ascending and -c options by using:(gdb) alias thread apply asc-all = thread apply all -ascending -c

Once you have defined this alias with its default args, any time you type the thread
apply asc-all followed by some arguments, gdb will execute thread apply all-ascending -c some arguments.
To have even less to type, you can also define a one word alias:(gdb) alias t_a_c = thread apply all -ascending -c

As usual, unambiguous abbreviations can be used for alias and default-args.
1

gdb could easily accept default arguments for pre-defined commands and aliases, but it was deemed thiswould be confusing, and so is not allowed.

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The different aliases of a command do not share their default args. For example, youdefine a new alias bt_ALL showing all possible information and another alias bt_SMALL
showing very limited information using:(gdb) alias bt_ALL = backtrace -entry-values both -frame-arg all \-past-main -past-entry -full(gdb) alias bt_SMALL = backtrace -entry-values no -frame-arg none \-past-main off -past-entry off(For more on using the alias command, see Section 23.2 [Aliases], page 399.)
Default args are not limited to the arguments and options of command, but can specify
nested commands if command accepts such a nested command as argument. For example,
the below defines faalocalsoftype that lists the frames having locals of a certain type,
together with the matching local vars:(gdb) alias faalocalsoftype = frame apply all info locals -q -t(gdb) faalocalsoftype int#1 0x55554f5e in sleeper_or_burner (v=0xdf50) at sleepers.c:86
i = 0
ret = 21845

This is also very useful to define an alias for a set of nested with commands to have aparticular combination of temporary settings. For example, the below defines the alias pp10
that pretty prints an expression argument, with a maximum of 10 elements if the expression
is a string or an array:(gdb) alias pp10 = with print pretty -- with print elements 10 -- print

This defines the alias pp10 as being a sequence of 3 commands. The first part withprint pretty -- temporarily activates the setting set print pretty, then launches thecommand that follows the separator --. The command following the first part is also
a with command that temporarily changes the setting set print elements to 10, thenlaunches the command that follows the second separator --. The third part print is thecommand the pp10 alias will launch, using the temporary values of the settings and thearguments explicitly given by the user. For more information about the with commandusage, see Section 3.2 [Command Settings], page 23.
By default, asking the help for an alias shows the documentation of the aliased command.
When the alias is a set of nested commands, help of an alias shows the documentation of
the first command. This help is not particularly useful for an alias such as pp10. For suchan alias, it is useful to give a specific documentation using the document command (seeSection 23.1.1 [Define], page 391).

23.3 Extending gdb using Python
You can extend gdb using the Python programming language (http://www.python.org/). This feature is available only if gdb was configured using --with-python.
Python scripts used by gdb should be installed in data-directory/python, where datadirectory is the data directory as determined at gdb startup (see Section 18.8 [Data Files],page 308). This directory, known as the python directory, is automatically added to the
Python Search Path in order to allow the Python interpreter to locate all scripts installedat this location.
Additionally, gdb commands and convenience functions which are written in
Python and are located in the data-directory/python/gdb/command or data-

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directory/python/gdb/function directories are automatically imported when gdb
starts.

23.3.1 Python Commands
gdb provides two commands for accessing the Python interpreter, and one related setting:python-interactive [command]pi [command]
Without an argument, the python-interactive command can be used to start
an interactive Python prompt. To return to gdb, type the EOF character (e.g.,
Ctrl-D on an empty prompt).
Alternatively, a single-line Python command can be given as an argument andevaluated. If the command is an expression, the result will be printed; otherwise, nothing will be printed. For example:(gdb) python-interactive 2 + 3
5python [command]py [command]
The python command can be used to evaluate Python code.
If given an argument, the python command will evaluate the argument as a
Python command. For example:(gdb) python print 23
23

If you do not provide an argument to python, it will act as a multi-line command, like define. In this case, the Python script is made up of subsequentcommand lines, given after the python command. This command list is terminated using a line containing end. For example:(gdb) python>print 23>end
23

set python print-stack
By default, gdb will print only the message component of a Python exception
when an error occurs in a Python script. This can be controlled using set
python print-stack: if full, then full Python stack printing is enabled; ifnone, then Python stack and message printing is disabled; if message, thedefault, only the message component of the error is printed.
set python ignore-environment [on|off]
By default this option is ‘off’, and, when gdb initializes its internal Pythoninterpreter, the Python interpreter will check the environment for variables thatwill effect how it behaves, for example PYTHONHOME, and PYTHONPATH2 .
If this option is set to ‘on’ before Python is initialized then Python will ignore
all such environment variables. As Python is initialized early during gdb’s
startup process, then this option must be placed into the early initialization file(see Section 2.1.4 [Initialization Files], page 17) to have the desired effect.
2

See the ENVIRONMENT VARIABLES section of man 1 python for a comprehensive list.

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This option is equivalent to passing -E to the real python executable.
set python dont-write-bytecode [auto|on|off]
When this option is ‘off’, then, once gdb has initialized the Python interpreter,
the interpreter will byte-compile any Python modules that it imports and write
the byte code to disk in .pyc files.
If this option is set to ‘on’ before Python is initialized then Python will nolonger write the byte code to disk. As Python is initialized early during gdb’s
startup process, then this option must be placed into the early initialization file(see Section 2.1.4 [Initialization Files], page 17) to have the desired effect.
By default this option is set to ‘auto’.
In this mode, provided thepython ignore-environment setting is ‘off’, the environment variable
PYTHONDONTWRITEBYTECODE is examined to see if it should write out byte-codeor not. PYTHONDONTWRITEBYTECODE is considered to be off/disabled either
when set to the empty string or when the environment variable doesn’t exist.
All other settings, including those which don’t seem to make sense, indicatethat it’s on/enabled.
This option is equivalent to passing -B to the real python executable.
It is also possible to execute a Python script from the gdb interpreter:
source script-name
The script name must end with ‘.py’ and gdb must be configured to recognize
the script language based on filename extension using the script-extension
setting. See Chapter 23 [Extending GDB], page 391.
The following commands are intended to help debug gdb itself:
set debug py-breakpoint on|off
show debug py-breakpoint
When ‘on’, gdb prints debug messages related to the Python breakpoint API.
This is ‘off’ by default.
set debug py-unwind on|off
show debug py-unwind
When ‘on’, gdb prints debug messages related to the Python unwinder API.
This is ‘off’ by default.

23.3.2 Python API
You can get quick online help for gdb’s Python API by issuing the command
python help (gdb).
Functions and methods which have two or more optional arguments allow them to be
specified using keyword syntax. This allows passing some optional arguments while skipping
others. Example: gdb.some_function (’foo’, bar = 1, baz = 2).

23.3.2.1 Basic Python
At startup, gdb overrides Python’s sys.stdout and sys.stderr to print using gdb’s
output-paging streams. A Python program which outputs to one of these streams may

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have its output interrupted by the user (see Section 22.4 [Screen Size], page 370). In thissituation, a Python KeyboardInterrupt exception is thrown.
Some care must be taken when writing Python code to run in gdb. Two things worth
noting in particular:• gdb installs handlers for SIGCHLD and SIGINT. Python code must not override these,or even change the options using sigaction. If your program changes the handling ofthese signals, gdb will most likely stop working correctly. Note that it is unfortunately
common for GUI toolkits to install a SIGCHLD handler. When creating a new Python
thread, you can use gdb.block_signals or gdb.Thread to handle this correctly; see
Section 23.3.2.2 [Threading in GDB], page 409.
• gdb takes care to mark its internal file descriptors as close-on-exec. However, thiscannot be done in a thread-safe way on all platforms. Your Python programs should
be aware of this and should both create new file descriptors with the close-on-exec flag
set and arrange to close unneeded file descriptors before starting a child process.
gdb introduces a new Python module, named gdb. All methods and classes added by
gdb are placed in this module. gdb automatically imports the gdb module for use in all
scripts evaluated by the python command.
Some types of the gdb module come with a textual representation (accessible throughthe repr or str functions). These are offered for debugging purposes only, expect them tochange over time.
[Variable]
A string containing the python directory (see Section 23.3 [Python], page 401).

gdb.PYTHONDIR

gdb.execute (command [, from tty [, to string]])[Function]
Evaluate command, a string, as a gdb CLI command. If a GDB exception happens
while command runs, it is translated as described in Section 23.3.2.3 [Exception
Handling], page 410.
The from tty flag specifies whether gdb ought to consider this command as having
originated from the user invoking it interactively. It must be a boolean value. If
omitted, it defaults to False.
By default, any output produced by command is sent to gdb’s standard output (andto the log output if logging is turned on). If the to string parameter is True, thenoutput will be collected by gdb.execute and returned as a string. The default isFalse, in which case the return value is None. If to string is True, the gdb virtual
terminal will be temporarily set to unlimited width and height, and its pagination
will be disabled; see Section 22.4 [Screen Size], page 370.

gdb.breakpoints ()[Function]
Return a sequence holding all of gdb’s breakpoints. See Section 23.3.2.33 [Breakpoints In Python], page 491, for more information. In gdb version 7.11 and earlier,this function returned None if there were no breakpoints. This peculiarity was subsequently fixed, and now gdb.breakpoints returns an empty sequence in this case.

gdb.rbreak (regex [, minsyms [, throttle, [, symtabs ]]])

[Function]
Return a Python list holding a collection of newly set gdb.Breakpoint objects matching function names defined by the regex pattern. If the minsyms keyword is True, allChapter 23: Extending gdb

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system functions (those not explicitly defined in the inferior) will also be included in
the match. The throttle keyword takes an integer that defines the maximum numberof pattern matches for functions matched by the regex pattern. If the number ofmatches exceeds the integer value of throttle, a RuntimeError will be raised and nobreakpoints will be created. If throttle is not defined then there is no imposed limit on
the maximum number of matches and breakpoints to be created. The symtabs keyword takes a Python iterable that yields a collection of gdb.Symtab objects and will
restrict the search to those functions only contained within the gdb.Symtab objects.

gdb.parameter (parameter)[Function]
Return the value of a gdb parameter given by its name, a string; the parametername string may contain spaces if the parameter has a multi-part name. For example,‘print object’ is a valid parameter name.
If the named parameter does not exist, this function throws a gdb.error (seeSection 23.3.2.3 [Exception Handling], page 410). Otherwise, the parameter’s value
is converted to a Python value of the appropriate type, and returned.

gdb.set_parameter (name, value)[Function]
Sets the gdb parameter name to value. As with gdb.parameter, the parameter namestring may contain spaces if the parameter has a multi-part name.

gdb.with_parameter (name, value)[Function]
Create a Python context manager (for use with the Python with statement) that
temporarily sets the gdb parameter name to value. On exit from the context, theprevious value will be restored.
This uses gdb.parameter in its implementation, so it can throw the same exceptions
as that function.
For example, it’s sometimes useful to evaluate some Python code with a particular
gdb language:
with gdb.with_parameter(’language’, ’pascal’):... language-specific operations

gdb.history (number)[Function]
Return a value from gdb’s value history (see Section 10.11 [Value History], page 170).
The number argument indicates which history element to return. If number is negative, then gdb will take its absolute value and count backward from the last element(i.e., the most recent element) to find the value to return. If number is zero, then
gdb will return the most recent element. If the element specified by number doesn’t
exist in the value history, a gdb.error exception will be raised.
If no exception is raised, the return value is always an instance of gdb.Value (seeSection 23.3.2.4 [Values From Inferior], page 411).

gdb.add_history (value)[Function]
Takes value, an instance of gdb.Value (see Section 23.3.2.4 [Values From Inferior],
page 411), and appends the value this object represents to gdb’s value history (seeSection 10.11 [Value History], page 170), and return an integer, its history number.
If value is not a gdb.Value, it is is converted using the gdb.Value constructor. If
value can’t be converted to a gdb.Value then a TypeError is raised.

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When a command implemented in Python prints a single gdb.Value as its result,then placing the value into the history will allow the user convenient access to thosevalues via CLI history facilities.

gdb.history_count ()[Function]
Return an integer indicating the number of values in gdb’s value history (seeSection 10.11 [Value History], page 170).

gdb.convenience_variable (name)[Function]
Return the value of the convenience variable (see Section 10.12 [Convenience Vars],
page 171) named name. name must be a string. The name should not include the‘$’ that is used to mark a convenience variable in an expression. If the conveniencevariable does not exist, then None is returned.

gdb.set_convenience_variable (name, value)[Function]
Set the value of the convenience variable (see Section 10.12 [Convenience Vars],
page 171) named name. name must be a string. The name should not include
the ‘$’ that is used to mark a convenience variable in an expression. If value is None,then the convenience variable is removed. Otherwise, if value is not a gdb.Value(see Section 23.3.2.4 [Values From Inferior], page 411), it is is converted using the
gdb.Value constructor.

gdb.parse_and_eval (expression [, global context])[Function]
Parse expression, which must be a string, as an expression in the current language,
evaluate it, and return the result as a gdb.Value.

global context, if provided, is a boolean indicating whether the parsing should bedone in the global context. The default is ‘False’, meaning that the current frameor current static context should be used.
This function can be useful when implementing a new command (see Section 23.3.2.21[CLI Commands In Python], page 463, see Section 23.3.2.22 [GDB/MI Commands
In Python], page 467), as it provides a way to parse the command’s argument as an
expression. It is also useful simply to compute values.

gdb.find_pc_line (pc)

[Function]
Return the gdb.Symtab_and_line object corresponding to the pc value. See
Section 23.3.2.31 [Symbol Tables In Python], page 489. If an invalid value of pc
is passed as an argument, then the symtab and line attributes of the returned
gdb.Symtab_and_line object will be None and 0 respectively. This is identicalto gdb.current_progspace().find_pc_line(pc) and is included for historicalcompatibility.

gdb.write (string [, stream])[Function]
Print a string to gdb’s paginated output stream. The optional stream determines
the stream to print to. The default stream is gdb’s standard output stream. Possible
stream values are:gdb.STDOUT
gdb’s standard output stream.

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gdb.STDERR
gdb’s standard error stream.
gdb.STDLOG
gdb’s log stream (see Section 2.4 [Logging Output], page 21).
Writing to sys.stdout or sys.stderr will automatically call this function and willautomatically direct the output to the relevant stream.

gdb.flush ([, stream])[Function]
Flush the buffer of a gdb paginated stream so that the contents are displayed immediately. gdb will flush the contents of a stream automatically when it encounters
a newline in the buffer. The optional stream determines the stream to flush. The
default stream is gdb’s standard output stream. Possible stream values are:gdb.STDOUT
gdb’s standard output stream.
gdb.STDERR
gdb’s standard error stream.
gdb.STDLOG
gdb’s log stream (see Section 2.4 [Logging Output], page 21).

Flushing sys.stdout or sys.stderr will automatically call this function for the
relevant stream.

gdb.target_charset ()[Function]
Return the name of the current target character set (see Section 10.21 [Character
Sets], page 187). This differs from gdb.parameter(’target-charset’) in that ‘auto’is never returned.

gdb.target_wide_charset ()[Function]
Return the name of the current target wide character set (see Section 10.21 [Character
Sets], page 187). This differs from gdb.parameter(’target-wide-charset’) in that
‘auto’ is never returned.

gdb.host_charset ()[Function]
Return a string, the name of the current host character set (see Section 10.21 [Character Sets], page 187). This differs from gdb.parameter(’host-charset’) in that
‘auto’ is never returned.

gdb.solib_name (address)[Function]
Return the name of the shared library holding the given address as a string, orNone. This is identical to gdb.current_progspace().solib_name(address) and isincluded for historical compatibility.

gdb.decode_line ([expression])[Function]
Return locations of the line specified by expression, or of the current line if no argument was given. This function returns a Python tuple containing two elements. The
first element contains a string holding any unparsed section of expression (or None if
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another tuple that contains all the locations that match the expression represented
as gdb.Symtab_and_line objects (see Section 23.3.2.31 [Symbol Tables In Python],page 489). If expression is provided, it is decoded the way that gdb’s inbuilt breakor edit commands do (see Section 9.2 [Location Specifications], page 126).

gdb.prompt_hook (current prompt)[Function]
If prompt hook is callable, gdb will call the method assigned to this operation before
a prompt is displayed by gdb.

The parameter current_prompt contains the current gdb prompt. This method must
return a Python string, or None. If a string is returned, the gdb prompt will be set
to that string. If None is returned, gdb will continue to use the current prompt.
Some prompts cannot be substituted in gdb. Secondary prompts such as those usedby readline for command input, and annotation related prompts are prohibited frombeing changed.

gdb.architecture_names ()[Function]
Return a list containing all of the architecture names that the current build of gdb
supports. Each architecture name is a string. The names returned in this list are thesame names as are returned from gdb.Architecture.name (see [Architecture.name],
page 497).
[Function]
Return a list of gdb.TargetConnection objects, one for each currently active connection (see Section 23.3.2.38 [Connections In Python], page 499). The connection
objects are in no particular order in the returned list.

gdb.connections

gdb.format_address (address [, progspace, architecture])[Function]
Return a string in the format ‘addr <symbol+offset>’, where addr is address formatted in hexadecimal, symbol is the symbol whose address is the nearest to address
and below it in memory, and offset is the offset from symbol to address in decimal.
If no suitable symbol was found, then the <symbol+offset> part is not included in the
returned string, instead the returned string will just contain the address formatted
as hexadecimal. How far gdb looks back for a suitable symbol can be controlled withset print max-symbolic-offset (see Section 10.9 [Print Settings], page 157).

Additionally, the returned string can include file name and line number information
when set print symbol-filename on (see Section 10.9 [Print Settings], page 157),in this case the format of the returned string is ‘addr <symbol+offset> atfilename:line-number’.
The progspace is the gdb.Progspace in which symbol is looked up, and architecture isused when formatting addr, e.g. in order to determine the size of an address in bytes.
If neither progspace or architecture are passed, then by default gdb will use theprogram space and architecture of the currently selected inferior, thus, the following
two calls are equivalent:
gdb.format_address(address)
gdb.format_address(address,
gdb.selected_inferior().progspace,
gdb.selected_inferior().architecture())

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It is not valid to only pass one of progspace or architecture, either they must both beprovided, or neither must be provided (and the defaults will be used).
This method uses the same mechanism for formatting address, symbol, and offset
information as core gdb does in commands such as disassemble.
Here are some examples of the possible string formats:
0x00001042
0x00001042 <symbol+16>0x00001042 <symbol+16 at file.c:123>

gdb.current_language ()[Function]
Return the name of the current language as a string. Unlike gdb.parameter(’language’),this function will never return ‘auto’. If a gdb.Frame object is available (seeSection 23.3.2.28 [Frames In Python], page 479), the language method might bepreferable in some cases, as that is not affected by the user’s language setting.

23.3.2.2 Threading in GDB
gdb is not thread-safe. If your Python program uses multiple threads, you must be careful
to only call gdb-specific functions in the gdb thread. gdb provides some functions to help
with this.

gdb.block_signals ()[Function]
As mentioned earlier (see Section 23.3.2.1 [Basic Python], page 403), certain signals
must be delivered to the gdb main thread. The block_signals function returns
a context manager that will block these signals on entry. This can be used whenstarting a new thread to ensure that the signals are blocked there, like:with gdb.block_signals():
start_new_thread()[class]This is a subclass of Python’s threading.Thread class. It overrides the start method
to call block_signals, making this an easy-to-use drop-in replacement for creating
threads that will work well in gdb.

gdb.Thread

gdb.interrupt ()[Function]
This causes gdb to react as if the user had typed a control-C character at the terminal.
That is, if the inferior is running, it is interrupted; if a gdb command is executing, it
is stopped; and if a Python command is running, KeyboardInterrupt will be raised.
Unlike most Python APIs in gdb, interrupt is thread-safe.

gdb.post_event (event)[Function]
Put event, a callable object taking no arguments, into gdb’s internal event queue.
This callable will be invoked at some later point, during gdb’s event processing.
Events posted using post_event will be run in the order in which they were posted;
however, there is no way to know when they will be processed relative to other events
inside gdb.
Unlike most Python APIs in gdb, post_event is thread-safe. For example:(gdb) python>import threading

410

Debugging with gdb>>class Writer():> def __init__(self, message):>
self.message = message;> def __call__(self):>
gdb.write(self.message)>>class MyThread1 (threading.Thread):> def run (self):>
gdb.post_event(Writer("Hello "))>>class MyThread2 (threading.Thread):> def run (self):>
gdb.post_event(Writer("World\n"))>>MyThread1().start()>MyThread2().start()>end(gdb) Hello World

23.3.2.3 Exception Handling
When executing the python command, Python exceptions uncaught within the Python
code are translated to calls to gdb error-reporting mechanism. If the command that called
python does not handle the error, gdb will terminate it and print an error message. Exactly what will be printed depends on set python print-stack (see Section 23.3.1 [Python
Commands], page 402). Example:(gdb) python print foo
Traceback (most recent call last):
File "<string>", line 1, in <module>
NameError: name ’foo’ is not defined

gdb errors that happen in gdb commands invoked by Python code are converted to
Python exceptions. The type of the Python exception depends on the error.
gdb.error
This is the base class for most exceptions generated by gdb. It is derived from
RuntimeError, for compatibility with earlier versions of gdb.
If an error occurring in gdb does not fit into some more specific category, thenthe generated exception will have this type.
gdb.MemoryError
This is a subclass of gdb.error which is thrown when an operation tried toaccess invalid memory in the inferior.
KeyboardInterrupt
User interrupt (via C-c or by typing q at a pagination prompt) is translated toa Python KeyboardInterrupt exception.
In all cases, your exception handler will see the gdb error message as its value and
the Python call stack backtrace at the Python statement closest to where the gdb error
occurred as the traceback.
When implementing gdb commands in Python via gdb.Command, or functions via
gdb.Function, it is useful to be able to throw an exception that doesn’t cause a traceback

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to be printed. For example, the user may have invoked the command incorrectly. gdb
provides a special exception class that can be used for this purpose.
gdb.GdbError
When thrown from a command or function, this exception will cause the command or function to fail, but the Python stack will not be displayed. gdb does
not throw this exception itself, but rather recognizes it when thrown from user
Python code. Example:(gdb) python>class HelloWorld (gdb.Command):> """Greet the whole world."""> def __init__ (self):>
super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)> def invoke (self, args, from_tty):>
argv = gdb.string_to_argv (args)>
if len (argv) != 0:>
raise gdb.GdbError ("hello-world takes no arguments")>
print ("Hello, World!")>HelloWorld ()>end(gdb) hello-world 42
hello-world takes no arguments

23.3.2.4 Values From Inferior
gdb provides values it obtains from the inferior program in an object of type gdb.Value.
gdb uses this object for its internal bookkeeping of the inferior’s values, and for fetchingvalues when necessary.
Inferior values that are simple scalars can be used directly in Python expressions thatare valid for the value’s data type. Here’s an example for an integer or floating-point value
some_val:
bar = some_val + 2

As result of this, bar will also be a gdb.Value object whose values are of the same type as
those of some_val. Valid Python operations can also be performed on gdb.Value objects
representing a struct or class object. For such cases, the overloaded operator (if present),
is used to perform the operation. For example, if val1 and val2 are gdb.Value objects
representing instances of a class which overloads the + operator, then one can use the +operator in their Python script as follows:
val3 = val1 + val2

The result of the operation val3 is also a gdb.Value object corresponding to the value
returned by the overloaded + operator. In general, overloaded operators are invoked for thefollowing operations: + (binary addition), - (binary subtraction), * (multiplication), /, %,<<, >>, |, &, ^.
Inferior values that are structures or instances of some class can be accessed using the
Python dictionary syntax. For example, if some_val is a gdb.Value instance holding a
structure, you can access its foo element with:bar = some_val[’foo’]

Again, bar will also be a gdb.Value object. Structure elements can also be accessed byusing gdb.Field objects as subscripts (see Section 23.3.2.5 [Types In Python], page 418,
for more information on gdb.Field objects). For example, if foo_field is a gdb.Field

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object corresponding to element foo of the above structure, then bar can also be accessed
as follows:bar = some_val[foo_field]

If a gdb.Value has array or pointer type, an integer index can be used to access elements.
result = some_array[23]A gdb.Value that represents a function can be executed via inferior function call. Anyarguments provided to the call must match the function’s prototype, and must be provided
in the order specified by that prototype.
For example, some_val is a gdb.Value instance representing a function that takes two
integers as arguments. To execute this function, call it like so:result = some_val (10,20)

Any values returned from a function call will be stored as a gdb.Value.
The following attributes are provided:[Variable]
If this object is addressable, this read-only attribute holds a gdb.Value object representing the address. Otherwise, this attribute holds None.

Value.address[Variable]
This read-only boolean attribute is true if the compiler optimized out this value, thus
it is not available for fetching from the inferior.

Value.is_optimized_out[Variable]
The type of this gdb.Value. The value of this attribute is a gdb.Type object (seeSection 23.3.2.5 [Types In Python], page 418).

Value.type[Variable]
The dynamic type of this gdb.Value. This uses the object’s virtual table and the C++
run-time type information (RTTI) to determine the dynamic type of the value. If thisvalue is of class type, it will return the class in which the value is embedded, if any. If
this value is of pointer or reference to a class type, it will compute the dynamic typeof the referenced object, and return a pointer or reference to that type, respectively.
In all other cases, it will return the value’s static type.

Value.dynamic_type

Note that this feature will only work when debugging a C++ program that includes
RTTI for the object in question. Otherwise, it will just return the static type of thevalue as in ptype foo (see Chapter 16 [Symbols], page 263).
[Variable]
The value of this read-only boolean attribute is True if this gdb.Value has not yet
been fetched from the inferior. gdb does not fetch values until necessary, for efficiency.
For example:

Value.is_lazymyval = gdb.parse_and_eval (’somevar’)

The value of somevar is not fetched at this time. It will be fetched when the value isneeded, or when the fetch_lazy method is invoked.

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The value of this attribute is a bytes object containing the bytes that make up thisValue’s complete value in little endian order. If the complete contents of this value
are not available then accessing this attribute will raise an exception.
This attribute can also be assigned to. The new value should be a buffer object (e.g.
a bytes object), the length of the new buffer must exactly match the length of thisValue’s type. The bytes values in the new buffer should be in little endian order.
As with Value.assign (see [Value.assign], page 414), if this value cannot be assigned
to, then an exception will be thrown.

Value.bytes

The following methods are provided:

Value.__init__ (val)[Function]
Many Python values can be converted directly to a gdb.Value via this object initializer. Specifically:
Python boolean
A Python boolean is converted to the boolean type from the current
language.
Python integer
A Python integer is converted to the C long type for the current architecture.
Python long
A Python long is converted to the C long long type for the current
architecture.
Python float
A Python float is converted to the C double type for the current architecture.
Python string
A Python string is converted to a target string in the current target
language using the current target encoding. If a character cannot be
represented in the current target encoding, then an exception is thrown.
gdb.Value
If val is a gdb.Value, then a copy of the value is made.
gdb.LazyString
If val is a gdb.LazyString (see Section 23.3.2.35 [Lazy Strings In
Python], page 497), then the lazy string’s value method is called, andits result is used.

Value.__init__ (val, type)[Function]
This second form of the gdb.Value constructor returns a gdb.Value of type typewhere the value contents are taken from the Python buffer object specified by val.
The number of bytes in the Python buffer object must be greater than or equal to
the size of type.
If type is None then this version of __init__ behaves as though type was not passed
at all.

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Value.assign (rhs)[Function]
Assign rhs to this value, and return None. If this value cannot be assigned to, or if
the assignment is invalid for some reason (for example a type-checking failure), an
exception will be thrown.

Value.cast (type)[Function]
Return a new instance of gdb.Value that is the result of casting this instance to thetype described by type, which must be a gdb.Type object. If the cast cannot be
performed for some reason, this method throws an exception.

Value.dereference ()[Function]
For pointer data types, this method returns a new gdb.Value object whose contents
is the object pointed to by the pointer. For example, if foo is a C pointer to an int,
declared in your C program as
int *foo;then you can use the corresponding gdb.Value to access what foo points to like this:bar = foo.dereference ()The result bar will be a gdb.Value object holding the value pointed to by foo.
A similar function Value.referenced_value exists which also returns gdb.Value objects corresponding to the values pointed to by pointer values (and additionally, values
referenced by reference values). However, the behavior of Value.dereference differsfrom Value.referenced_value by the fact that the behavior of Value.dereferenceis identical to applying the C unary operator * on a given value. For example, consider
a reference to a pointer ptrref, declared in your C++ program as
typedef int *intptr;...
int val = 10;
intptr ptr = &val;
intptr &ptrref = ptr;

Though ptrref is a reference value, one can apply the method Value.dereference tothe gdb.Value object corresponding to it and obtain a gdb.Value which is identicalto that corresponding to val. However, if you apply the method Value.referenced_
value, the result would be a gdb.Value object identical to that corresponding toptr.
py_ptrref = gdb.parse_and_eval ("ptrref")py_val = py_ptrref.dereference ()py_ptr = py_ptrref.referenced_value ()The gdb.Value object py_val is identical to that corresponding to val, and py_
ptr is identical to that corresponding to ptr. In general, Value.dereference can beapplied whenever the C unary operator * can be applied to the corresponding C value.
For those cases where applying both Value.dereference and Value.referenced_
value is allowed, the results obtained need not be identical (as we have seen in theabove example). The results are however identical when applied on gdb.Value objects
corresponding to pointers (gdb.Value objects with type code TYPE_CODE_PTR) in a
C/C++ program.

Value.referenced_value ()[Function]
For pointer or reference data types, this method returns a new gdb.Value object
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types, Value.dereference and Value.referenced_value produce identical results.
The difference between these methods is that Value.dereference cannot get thevalues referenced by reference values. For example, consider a reference to an int,
declared in your C++ program as
int val = 10;
int &ref = val;then applying Value.dereference to the gdb.Value object corresponding to ref will
result in an error, while applying Value.referenced_value will result in a gdb.Value
object identical to that corresponding to val.
py_ref = gdb.parse_and_eval ("ref")er_ref = py_ref.dereference ()py_val = py_ref.referenced_value ()# Results in error# Returns the referenced value

The gdb.Value object py_val is identical to that corresponding to val.

Value.reference_value ()[Function]
Return a gdb.Value object which is a reference to the value encapsulated by thisinstance.

Value.const_value ()[Function]
Return a gdb.Value object which is a const version of the value encapsulated by thisinstance.

Value.dynamic_cast (type)[Function]
Like Value.cast, but works as if the C++ dynamic_cast operator were used. Consult
a C++ reference for details.

Value.reinterpret_cast (type)[Function]
Like Value.cast, but works as if the C++ reinterpret_cast operator were used.
Consult a C++ reference for details.

Value.format_string (...)[Function]
Convert a gdb.Value to a string, similarly to what the print command does. Invokedwith no arguments, this is equivalent to calling the str function on the gdb.Value.
The representation of the same value may change across different versions of gdb, so
you shouldn’t, for instance, parse the strings returned by this method.
All the arguments are keyword only. If an argument is not specified, the current
global default setting is used.
raw

True if pretty-printers (see Section 10.10 [Pretty Printing], page 168)
should not be used to format the value. False if enabled pretty-printers
matching the type represented by the gdb.Value should be used to formatit.

pretty_arrays
True if arrays should be pretty printed to be more convenient to read,
False if they shouldn’t (see set print array in Section 10.9 [Print Settings], page 157).
pretty_structs
True if structs should be pretty printed to be more convenient to read,
False if they shouldn’t (see set print pretty in Section 10.9 [Print
Settings], page 157).

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array_indexes
True if array indexes should be included in the string representationof arrays, False if they shouldn’t (see set print array-indexes in
Section 10.9 [Print Settings], page 157).
symbols

True if the string representation of a pointer should include the corresponding symbol name (if one exists), False if it shouldn’t (see set
print symbol in Section 10.9 [Print Settings], page 157).

unionsTrue if unions which are contained in other structures or unions should be
expanded, False if they shouldn’t (see set print union in Section 10.9
[Print Settings], page 157).

address

True if the string representation of a pointer should include the address,
False if it shouldn’t (see set print address in Section 10.9 [Print Settings], page 157).

nibblesTrue if binary values should be displayed in groups of four bits, known as
nibbles. False if it shouldn’t (see Section 10.9 [Print Settings], page 157).

deref_refs
True if C++ references should be resolved to the value they refer to,
False (the default) if they shouldn’t. Note that, unlike for the printcommand, references are not automatically expanded when using theformat_string method or the str function. There is no global printsetting to change the default behaviour.
actual_objects
True if the representation of a pointer to an object should identify theactual (derived) type of the object rather than the declared type, using
the virtual function table. False if the declared type should be used.
(See set print object in Section 10.9 [Print Settings], page 157).
static_members
True if static members should be included in the string representation ofa C++ object, False if they shouldn’t (see set print static-members in
Section 10.9 [Print Settings], page 157).
max_characters
Number of string characters to print, 0 to follow max_elements, or
UINT_MAX to print an unlimited number of characters (see set print
characters in Section 10.9 [Print Settings], page 157).
max_elements
Number of array elements to print, or 0 to print an unlimited numberof elements (see set print elements in Section 10.9 [Print Settings],
page 157).
max_depth
The maximum depth to print for nested structs and unions, or -1 toprint an unlimited number of elements (see set print max-depth in
Section 10.9 [Print Settings], page 157).

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repeat_threshold
Set the threshold for suppressing display of repeated array elements, or
0 to represent all elements, even if repeated. (See set print repeats in
Section 10.9 [Print Settings], page 157).
formatA string containing a single character representing the format to use forthe returned string. For instance, ’x’ is equivalent to using the gdb command print with the /x option and formats the value as a hexadecimal
number.

styling

True if gdb should apply styling to the returned string. When stylingis applied, the returned string might contain ANSI terminal escape sequences. Escape sequences will only be included if styling is turned on,
see Section 22.5 [Output Styling], page 371. Additionally, gdb only styles
some value contents, so not every output string will contain escape sequences.
When False, which is the default, no output styling is applied.

summary

True when just a summary should be printed. In this mode, scalar values
are printed in their entirety, but aggregates such as structures or unions
are omitted. This mode is used by set print frame-arguments scalars(see Section 10.9 [Print Settings], page 157).

Value.to_array ()[Function]
If this value is array-like (see [Type.is array like], page 420), then this method converts it to an array, which is returned. If this value is already an array, it is simply
returned. Otherwise, an exception is throw.

Value.string ([encoding[, errors[, length]]])[Function]
If this gdb.Value represents a string, then this method converts the contents to a
Python string. Otherwise, this method will throw an exception.
Values are interpreted as strings according to the rules of the current language. If
the optional length argument is given, the string will be converted to that length,
and will include any embedded zeroes that the string may contain. Otherwise, for
languages where the string is zero-terminated, the entire string will be converted.
For example, in C-like languages, a value is a string if it is a pointer to or an array ofcharacters or ints of type wchar_t, char16_t, or char32_t.
If the optional encoding argument is given, it must be a string naming the encodingof the string in the gdb.Value, such as "ascii", "iso-8859-6" or "utf-8". It accepts the same encodings as the corresponding argument to Python’s string.decode
method, and the Python codec machinery will be used to convert the string. If encoding is not given, or if encoding is the empty string, then either the target-charset(see Section 10.21 [Character Sets], page 187) will be used, or a language-specificencoding will be used, if the current language is able to supply one.
The optional errors argument is the same as the corresponding argument to Python’s
string.decode method.
If the optional length argument is given, the string will be fetched and converted to
the given length.

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Value.lazy_string ([encoding [, length]])[Function]
If this gdb.Value represents a string, then this method converts the contents to a
gdb.LazyString (see Section 23.3.2.35 [Lazy Strings In Python], page 497). Otherwise, this method will throw an exception.
If the optional encoding argument is given, it must be a string naming the encodingof the gdb.LazyString. Some examples are: ‘ascii’, ‘iso-8859-6’ or ‘utf-8’. If theencoding argument is an encoding that gdb does recognize, gdb will raise an error.
When a lazy string is printed, the gdb encoding machinery is used to convert thestring during printing. If the optional encoding argument is not provided, or is anempty string, gdb will automatically select the encoding most suitable for the string
type. For further information on encoding in gdb please see Section 10.21 [Character
Sets], page 187.
If the optional length argument is given, the string will be fetched and encoded to
the length of characters specified. If the length argument is not provided, the string
will be fetched and encoded until a null of appropriate width is found.

Value.fetch_lazy ()[Function]
If the gdb.Value object is currently a lazy value (gdb.Value.is_lazy is True), thenthe value is fetched from the inferior. Any errors that occur in the process will produce
a Python exception.
If the gdb.Value object is not a lazy value, this method has no effect.
This method does not return a value.

23.3.2.5 Types In Python
gdb represents types from the inferior using the class gdb.Type.
The following type-related functions are available in the gdb module:

gdb.lookup_type (name [, block])[Function]

This function looks up a type by its name, which must be a string.
If block is given, then name is looked up in that scope. Otherwise, it is searched for
globally.
Ordinarily, this function will return an instance of gdb.Type. If the named typecannot be found, it will throw an exception.
Integer types can be found without looking them up by name. See Section 23.3.2.36[Architectures In Python], page 497, for the integer_type method.
If the type is a structure or class type, or an enum type, the fields of that type can beaccessed using the Python dictionary syntax. For example, if some_type is a gdb.Type
instance holding a structure type, you can access its foo field with:bar = some_type[’foo’]

bar will be a gdb.Field object; see below under the description of the Type.fields
method for a description of the gdb.Field class.
An instance of Type has the following attributes:

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The alignment of this type, in bytes. Type alignment comes from the debugging
information; if it was not specified, then gdb will use the relevant ABI to try to
determine the alignment. In some cases, even this is not possible, and zero will be
returned.

Type.alignof[Variable]
The type code for this type. The type code will be one of the TYPE_CODE_ constants
defined below.

Type.code[Variable]
A boolean indicating whether this type is dynamic. In some situations, such as Rust
enum types or Ada variant records, the concrete type of a value may vary depending
on its contents. That is, the declared type of a variable, or the type returned by
gdb.lookup_type may be dynamic; while the type of the variable’s value will be aconcrete instance of that dynamic type.

Type.dynamic

For example, consider this code:
int n;
int array[n];Here, at least conceptually (whether your compiler actually does this is a separate
issue), examining gdb.lookup_symbol("array", ...).type could yield a gdb.Type
which reports a size of None. This is the dynamic type.
However, examining gdb.parse_and_eval("array").type would yield a concrete
type, whose length would be known.

Type.name[Variable]

The name of this type. If this type has no name, then None is returned.
[Variable]
The size of this type, in target char units. Usually, a target’s char type will be an
8-bit byte. However, on some unusual platforms, this type may have a different size.
A dynamic type may not have a fixed size; in this case, this attribute’s value will be
None.

Type.sizeof[Variable]
The tag name for this type. The tag name is the name after struct, union, or enumin C and C++; not all languages have this concept. If this type has no tag name, thenNone is returned.

Type.tag[Variable]
The gdb.Objfile that this type was defined in, or None if there is no associatedobjfile.

Type.objfile[Variable]
This property is True if the type is a scalar type, otherwise, this property is False.
Examples of non-scalar types include structures, unions, and classes.

Type.is_scalar

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For scalar types (those for which Type.is_scalar is True), this property is True if
the type is signed, otherwise this property is False.
Attempting to read this property for a non-scalar type (a type for which Type.is_scalar is False), will raise a ValueError.

Type.is_signed

Type.is_array_like[Variable]

A boolean indicating whether this type is array-like.
Some languages have array-like objects that are represented internally as structures.
For example, this is true for a Rust slice type, or for an Ada unconstrained array.
gdb may know about these types. This determination is done based on the language
from which the type originated.
[Variable]
A boolean indicating whether this type is string-like. Like Type.is_array_like, thisis determined based on the originating language of the type.

Type.is_string_like

The following methods are provided:

Type.fields ()[Function]
Return the fields of this type. The behavior depends on the type code:• For structure and union types, this method returns the fields.
• Enum types have one field per enum constant.
• Function and method types have one field per parameter. The base types of C++
classes are also represented as fields.
• Array types have one field representing the array’s range.
• If the type does not fit into one of these categories, a TypeError is raised.
Each field is a gdb.Field object, with some pre-defined attributes:
bitposThis attribute is not available for enum or static (as in C++) fields. The
value is the position, counting in bits, from the start of the containing
type. Note that, in a dynamic type, the position of a field may not be
constant. In this case, the value will be None. Also, a dynamic type may
have fields that do not appear in a corresponding concrete type.

enumvalThis attribute is only available for enum fields, and its value is the enumeration member’s integer representation.

name

The name of the field, or None for anonymous fields.

artificial
This is True if the field is artificial, usually meaning that it was provided
by the compiler and not the user. This attribute is always provided, andis False if the field is not artificial.
is_base_classThis is True if the field represents a base class of a C++ structure. This
attribute is always provided, and is False if the field is not a base classof the type that is the argument of fields, or if that type was not a C++
class.

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bitsize

If the field is packed, or is a bitfield, then this will have a non-zero value,
which is the size of the field in bits. Otherwise, this will be zero; in thiscase the field’s size is given by its type.

type

The type of the field. This is usually an instance of Type, but it can beNone in some situations.

parent_type
The type which contains this field. This is an instance of gdb.Type.

Type.array (n1 [, n2])

[Function]
Return a new gdb.Type object which represents an array of this type. If one argument
is given, it is the inclusive upper bound of the array; in this case the lower bound iszero. If two arguments are given, the first argument is the lower bound of the array,and the second argument is the upper bound of the array. An array’s length mustnot be negative, but the bounds can be.

Type.vector (n1 [, n2])

[Function]
Return a new gdb.Type object which represents a vector of this type. If one argument
is given, it is the inclusive upper bound of the vector; in this case the lower bound iszero. If two arguments are given, the first argument is the lower bound of the vector,
and the second argument is the upper bound of the vector. A vector’s length mustnot be negative, but the bounds can be.
The difference between an array and a vector is that arrays behave like in C: whenused in expressions they decay to a pointer to the first element whereas vectors aretreated as first class values.

Type.const ()[Function]
Return a new gdb.Type object which represents a const-qualified variant of this type.

Type.volatile ()[Function]
Return a new gdb.Type object which represents a volatile-qualified variant of thistype.

Type.unqualified ()[Function]
Return a new gdb.Type object which represents an unqualified variant of this type.
That is, the result is neither const nor volatile.

Type.range ()[Function]
Return a Python Tuple object that contains two elements: the low bound of theargument type and the high bound of that type. If the type does not have a range,
gdb will raise a gdb.error exception (see Section 23.3.2.3 [Exception Handling],
page 410).

Type.reference ()[Function]

Return a new gdb.Type object which represents a reference to this type.

Type.pointer ()Return a new gdb.Type object which represents a pointer to this type.

[Function]

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Type.strip_typedefs ()[Function]
Return a new gdb.Type that represents the real type, after removing all layers of
typedefs.

Type.target ()[Function]
Return a new gdb.Type object which represents the target type of this type.
For a pointer type, the target type is the type of the pointed-to object. For an array
type (meaning C-like arrays), the target type is the type of the elements of the array.
For a function or method type, the target type is the type of the return value. For acomplex type, the target type is the type of the elements. For a typedef, the target
type is the aliased type.
If the type does not have a target, this method will throw an exception.

Type.template_argument (n [, block])[Function]
If this gdb.Type is an instantiation of a template, this will return a new gdb.Value or
gdb.Type which represents the value of the nth template argument (indexed startingat 0).
If this gdb.Type is not a template type, or if the type has fewer than n templatearguments, this will throw an exception. Ordinarily, only C++ code will have templatetypes.
If block is given, then name is looked up in that scope. Otherwise, it is searched for
globally.

Type.optimized_out ()[Function]
Return gdb.Value instance of this type whose value is optimized out. This allows aframe decorator to indicate that the value of an argument or a local variable is notknown.

Each type has a code, which indicates what category this type falls into. The available
type categories are represented by constants defined in the gdb module:
gdb.TYPE_CODE_PTR
The type is a pointer.
gdb.TYPE_CODE_ARRAY
The type is an array.
gdb.TYPE_CODE_STRUCTThe type is a structure.
gdb.TYPE_CODE_UNION
The type is a union.
gdb.TYPE_CODE_ENUM
The type is an enum.
gdb.TYPE_CODE_FLAGS
A bit flags type, used for things such as status registers.
gdb.TYPE_CODE_FUNC
The type is a function.

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gdb.TYPE_CODE_INT
The type is an integer type.
gdb.TYPE_CODE_FLT
A floating point type.
gdb.TYPE_CODE_VOID
The special type void.
gdb.TYPE_CODE_SETA Pascal set type.
gdb.TYPE_CODE_RANGE
A range type, that is, an integer type with bounds.
gdb.TYPE_CODE_STRING
A string type. Note that this is only used for certain languages with languagedefined string types; C strings are not represented this way.
gdb.TYPE_CODE_BITSTRING
A string of bits. It is deprecated.
gdb.TYPE_CODE_ERROR
An unknown or erroneous type.
gdb.TYPE_CODE_METHOD
A method type, as found in C++.
gdb.TYPE_CODE_METHODPTR
A pointer-to-member-function.
gdb.TYPE_CODE_MEMBERPTR
A pointer-to-member.
gdb.TYPE_CODE_REF
A reference type.
gdb.TYPE_CODE_RVALUE_REF
A C++11 rvalue reference type.
gdb.TYPE_CODE_CHAR
A character type.
gdb.TYPE_CODE_BOOL
A boolean type.
gdb.TYPE_CODE_COMPLEX
A complex float type.
gdb.TYPE_CODE_TYPEDEF
A typedef to some other type.
gdb.TYPE_CODE_NAMESPACEA C++ namespace.
gdb.TYPE_CODE_DECFLOAT
A decimal floating point type.

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gdb.TYPE_CODE_INTERNAL_FUNCTION
A function internal to gdb. This is the type used to represent convenience
functions.
gdb.TYPE_CODE_XMETHOD
A method internal to gdb. This is the type used to represent xmethods (seeSection 23.3.2.16 [Writing an Xmethod], page 446).
gdb.TYPE_CODE_FIXED_POINT
A fixed-point number.
gdb.TYPE_CODE_NAMESPACE
A Fortran namelist.
Further support for types is provided in the gdb.types Python module (seeSection 23.3.4.2 [gdb.types], page 514).

23.3.2.6 Pretty Printing API
A pretty-printer is just an object that holds a value and implements a specific interface,defined here. An example output is provided (see Section 10.10 [Pretty Printing], page 168).
Because gdb did not document extensibility for pretty-printers, by default gdb willassume that only the basic pretty-printer methods may be available. The basic methods
are marked as such, below.
To allow extensibility, gdb provides the gdb.ValuePrinter base class. This class does
not provide any attributes or behavior, but instead serves as a tag that can be recognized by
gdb. For such printers, gdb reserves all attributes starting with a lower-case letter. Thatis, in the future, gdb may add a new method or attribute to the pretty-printer protocol, andgdb.ValuePrinter-based printers are expected to handle this gracefully. A simple way to
do this would be to use a leading underscore (or two, following the Python name-mangling
scheme) to any attributes local to the implementation.

pretty_printer.children (self)[Function]
gdb will call this method on a pretty-printer to compute the children of the prettyprinter’s value.
This method must return an object conforming to the Python iterator protocol. Each
item returned by the iterator must be a tuple holding two elements. The first element
is the “name” of the child; the second element is the child’s value. The value can be
any Python object which is convertible to a gdb value.
This is a basic method, and is optional. If it does not exist, gdb will act as though
the value has no children.

For efficiency, the children method should lazily compute its results. This will let
gdb read as few elements as necessary, for example when various print settings (seeSection 10.9 [Print Settings], page 157) or -var-list-children (see Section 27.17[GDB/MI Variable Objects], page 640) limit the number of elements to be displayed.
Children may be hidden from display based on the value of ‘set print max-depth’(see Section 10.9 [Print Settings], page 157).

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pretty_printer.display_hint (self)[Function]
The CLI may call this method and use its result to change the formatting of a value.
The result will also be supplied to an MI consumer as a ‘displayhint’ attribute of
the variable being printed.
This is a basic method, and is optional. If it does exist, this method must return astring or the special value None.
Some display hints are predefined by gdb:
‘array’Indicate that the object being printed is “array-like”. The CLI uses this torespect parameters such as set print elements and set print array.

‘map’

Indicate that the object being printed is “map-like”, and that the childrenof this value can be assumed to alternate between keys and values.

‘string’

Indicate that the object being printed is “string-like”. If the printer’s to_string method returns a Python string of some kind, then gdb will call
its internal language-specific string-printing function to format the string.
For the CLI this means adding quotation marks, possibly escaping somecharacters, respecting set print elements, and the like.

The special value None causes gdb to apply the default display rules.

pretty_printer.to_string (self)[Function]
gdb will call this method to display the string representation of the value passed tothe object’s constructor.
This is a basic method, and is optional.
When printing from the CLI, if the to_string method exists, then gdb will prepend
its result to the values returned by children. Exactly how this formatting is done
is dependent on the display hint, and may change as more hints are added. Also,
depending on the print settings (see Section 10.9 [Print Settings], page 157), the
CLI may print just the result of to_string in a stack trace, omitting the result ofchildren.
If this method returns a string, it is printed verbatim.
Otherwise, if this method returns an instance of gdb.Value, then gdb prints thisvalue. This may result in a call to another pretty-printer.
If instead the method returns a Python value which is convertible to a gdb.Value,then gdb performs the conversion and prints the resulting value. Again, this may result in a call to another pretty-printer. Python scalars (integers, floats, and booleans)and strings are convertible to gdb.Value; other types are not.
Finally, if this method returns None then no further operations are performed in thismethod and nothing is printed.
If the result is not one of these types, an exception is raised.

pretty_printer.num_children ()[Function]
This is not a basic method, so gdb will only ever call it for objects derived from
gdb.ValuePrinter.
If available, this method should return the number of children. None may be returned
if the number can’t readily be computed.

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pretty_printer.child (n)[Function]
This is not a basic method, so gdb will only ever call it for objects derived from
gdb.ValuePrinter.
If available, this method should return the child item (that is, a tuple holding thename and value of this child) indicated by n. Indices start at zero.

gdb provides a function which can be used to look up the default pretty-printer for a
gdb.Value:

gdb.default_visualizer (value)[Function]
This function takes a gdb.Value object as an argument. If a pretty-printer for thisvalue exists, then it is returned. If no such printer exists, then this returns None.

Normally, a pretty-printer can respect the user’s print settings (including temporarily
applied settings, such as ‘/x’) simply by calling Value.format_string (see Section 23.3.2.4[Values From Inferior], page 411). However, these settings can also be queried directly:

gdb.print_options ()[Function]
Return a dictionary whose keys are the valid keywords that can be given to
Value.format_string, and whose values are the user’s settings. During a print orother operation, the values will reflect any flags that are temporarily in effect.
(gdb) python print (gdb.print_options ()[’max_elements’])
200

23.3.2.7 Selecting Pretty-Printers
gdb provides several ways to register a pretty-printer: globally, per program space, and per
objfile. When choosing how to register your pretty-printer, a good rule is to register it withthe smallest scope possible: that is prefer a specific objfile first, then a program space, andonly register a printer globally as a last resort.
[Variable]
The Python list gdb.pretty_printers contains an array of functions or callable
objects that have been registered via addition as a pretty-printer. Printers in this list
are called global printers, they’re available when debugging all inferiors.

gdb.pretty_printers

Each gdb.Progspace contains a pretty_printers attribute. Each gdb.Objfile also
contains a pretty_printers attribute.
Each function on these lists is passed a single gdb.Value argument and should returna pretty-printer object conforming to the interface definition above (see Section 23.3.2.6[Pretty Printing API], page 424). If a function cannot create a pretty-printer for the value,
it should return None.
gdb first checks the pretty_printers attribute of each gdb.Objfile in the current program space and iteratively calls each enabled lookup routine in the list for that gdb.Objfile
until it receives a pretty-printer object. If no pretty-printer is found in the objfile lists, gdb
then searches the pretty-printer list of the current program space, calling each enabled function until an object is returned. After these lists have been exhausted, it tries the global
gdb.pretty_printers list, again calling each enabled function until an object is returned.

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The order in which the objfiles are searched is not specified. For a given list, functions
are always invoked from the head of the list, and iterated over sequentially until the end of
the list, or a printer object is returned.
For various reasons a pretty-printer may not work. For example, the underlying data
structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that gdb provides support
for enabling and disabling individual printers. For example, if print frame-arguments is
on, a backtrace can become highly illegible if any argument is printed with a broken printer.
Pretty-printers are enabled and disabled by attaching an enabled attribute to the registered function or callable object. If this attribute is present and its value is False, theprinter is disabled, otherwise the printer is enabled.

23.3.2.8 Writing a Pretty-PrinterA pretty-printer consists of two parts: a lookup function to detect if the type is supported,and the printer itself.
Here is an example showing how a std::string printer might be written. See
Section 23.3.2.6 [Pretty Printing API], page 424, for details on the API this class must
provide. Note that this example uses the gdb.ValuePrinter base class, and is careful touse a leading underscore for its local state.
class StdStringPrinter(gdb.ValuePrinter):"Print a std::string"def __init__(self, val):
self.__val = val
def to_string(self):
return self.__val[’_M_dataplus’][’_M_p’]def display_hint(self):
return ’string’And here is an example showing how a lookup function for the printer example above
might be written.
def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag is None:
return Noneregex = re.compile("^std::basic_string<char,.*>$")
if regex.match(lookup_tag):
return StdStringPrinter(val)return None

The example lookup function extracts the value’s type, and attempts to match it to a
type that it can pretty-print. If it is a type the printer can pretty-print, it will return aprinter object. If not, it returns None.
We recommend that you put your core pretty-printers into a Python package. If yourpretty-printers are for use with a library, we further recommend embedding a version number
into the package name. This practice will enable gdb to load multiple versions of yourpretty-printers at the same time, because they will have different names.
You should write auto-loaded code (see Section 23.3.3 [Python Auto-loading], page 513)
such that it can be evaluated multiple times without changing its meaning. An ideal auto-

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load file will consist solely of imports of your printer modules, followed by a call to a register
pretty-printers with the current objfile.
Taken as a whole, this approach will scale nicely to multiple inferiors, each potentiallyusing a different library version. Embedding a version number in the Python package namewill ensure that gdb is able to load both sets of printers simultaneously. Then, because thesearch for pretty-printers is done by objfile, and because your auto-loaded code took careto register your library’s printers with a specific objfile, gdb will find the correct printers
for the specific version of the library used by each inferior.
To continue the std::string example (see Section 23.3.2.6 [Pretty Printing API],
page 424), this code might appear in gdb.libstdcxx.v6:
def register_printers(objfile):
objfile.pretty_printers.append(str_lookup_function)

And then the corresponding contents of the auto-load file would be:
import gdb.libstdcxx.v6
gdb.libstdcxx.v6.register_printers(gdb.current_objfile())

The previous example illustrates a basic pretty-printer. There are a few things that canbe improved on. The printer doesn’t have a name, making it hard to identify in a list of
installed printers. The lookup function has a name, but lookup functions can have arbitrary,even identical, names.
Second, the printer only handles one type, whereas a library typically has several types.
One could install a lookup function for each desired type in the library, but one could also
have a single lookup function recognize several types. The latter is the conventional way
this is handled. If a pretty-printer can handle multiple data types, then its subprinters are
the printers for the individual data types.
The gdb.printing module provides a formal way of solving these problems (seeSection 23.3.4.1 [gdb.printing], page 514). Here is another example that handles multiple
types.
These are the types we are going to pretty-print:
struct foo { int a, b; };struct bar { struct foo x, y; };Here are the printers:
class fooPrinter(gdb.ValuePrinter):"""Print a foo object."""def __init__(self, val):
self.__val = val
def to_string(self):
return ("a=<" + str(self.__val["a"]) +"> b=<" + str(self.__val["b"]) + ">")
class barPrinter(gdb.ValuePrinter):"""Print a bar object."""def __init__(self, val):
self.__val = val
def to_string(self):
return ("x=<" + str(self.__val["x"]) +Chapter 23: Extending gdb

429"> y=<" + str(self.__val["y"]) + ">")

This example doesn’t need a lookup function, that is handled by the gdb.printing
module. Instead a function is provided to build up the object that handles the lookup.
import gdb.printing
def build_pretty_printer():
pp = gdb.printing.RegexpCollectionPrettyPrinter("my_library")
pp.add_printer(’foo’, ’^foo$’, fooPrinter)
pp.add_printer(’bar’, ’^bar$’, barPrinter)
return pp

And here is the autoload support:
import gdb.printing
import my_library
gdb.printing.register_pretty_printer(gdb.current_objfile(),my_library.build_pretty_printer())

Finally, when this printer is loaded into gdb, here is the corresponding output of ‘info
pretty-printer’:(gdb) info pretty-printermy_library.so:
my_libraryfoobar

23.3.2.9 Type Printing API
gdb provides a way for Python code to customize type display. This is mainly useful for
substituting canonical typedef names for types.
A type printer is just a Python object conforming to a certain protocol. A simple baseclass implementing the protocol is provided; see Section 23.3.4.2 [gdb.types], page 514. A
type printer must supply at least:[Instance Variable of type_printer]A boolean which is True if the printer is enabled, and False otherwise. This is manipulated by the enable type-printer and disable type-printer commands.

enabledname[Instance Variable of type_printer]
The name of the type printer. This must be a string. This is used by the enabletype-printer and disable type-printer commands.

instantiate (self)[Method on type_printer]
This is called by gdb at the start of type-printing. It is only called if the type printeris enabled. This method must return a new object that supplies a recognize method,
as described below.

When displaying a type, say via the ptype command, gdb will compute a list of
type recognizers. This is done by iterating first over the per-objfile type printers (seeSection 23.3.2.27 [Objfiles In Python], page 476), followed by the per-progspace type printers (see Section 23.3.2.26 [Progspaces In Python], page 474), and finally the global type
printers.

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gdb will call the instantiate method of each enabled type printer. If this method
returns None, then the result is ignored; otherwise, it is appended to the list of recognizers.
Then, when gdb is going to display a type name, it iterates over the list of recognizers.
For each one, it calls the recognition function, stopping if the function returns a non-Nonevalue. The recognition function is defined as:recognize (self, type)[Method on type_recognizer]
If type is not recognized, return None. Otherwise, return a string which is to beprinted as the name of type. The type argument will be an instance of gdb.Type (seeSection 23.3.2.5 [Types In Python], page 418).

gdb uses this two-pass approach so that type printers can efficiently cache information
without holding on to it too long. For example, it can be convenient to look up type
information in a type printer and hold it for a recognizer’s lifetime; if a single pass weredone then type printers would have to make use of the event system in order to avoid
holding information that could become stale as the inferior changed.

23.3.2.10 Filtering Frames
Frame filters are Python objects that manipulate the visibility of a frame or frames when abacktrace (see Section 8.2 [Backtrace], page 114) is printed by gdb.
Only commands that print a backtrace, or, in the case of gdb/mi commands (seeChapter 27 [GDB/MI], page 589), those that return a collection of frames are affected.
The commands that work with frame filters are:backtrace (see [The backtrace command], page 114), -stack-list-frames (see [The-stack-list-frames command], page 637), -stack-list-variables (see [The -stack-listvariables command], page 639), -stack-list-arguments see [The -stack-list-argumentscommand], page 635) and -stack-list-locals (see [The -stack-list-locals command],page 639).
A frame filter works by taking an iterator as an argument, applying actions to thecontents of that iterator, and returning another iterator (or, possibly, the same iterator it
was provided in the case where the filter does not perform any operations). Typically, frame
filters utilize tools such as the Python’s itertools module to work with and create new
iterators from the source iterator. Regardless of how a filter chooses to apply actions, it
must not alter the underlying gdb frame or frames, or attempt to alter the call-stack within
gdb. This preserves data integrity within gdb. Frame filters are executed on a priority
basis and care should be taken that some frame filters may have been executed before, andthat some frame filters will be executed after.
An important consideration when designing frame filters, and well worth reflecting upon,is that frame filters should avoid unwinding the call stack if possible. Some stacks can runvery deep, into the tens of thousands in some cases. To search every frame when a frame
filter executes may be too expensive at that step. The frame filter cannot know how many
frames it has to iterate over, and it may have to iterate through them all. This ends up
duplicating effort as gdb performs this iteration when it prints the frames. If the filter candefer unwinding frames until frame decorators are executed, after the last filter has executed,
it should. See Section 23.3.2.11 [Frame Decorator API], page 432, for more information on
decorators. Also, there are examples for both frame decorators and filters in later chapters.
See Section 23.3.2.12 [Writing a Frame Filter], page 435, for more information.

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The Python dictionary gdb.frame_filters contains key/object pairings that comprise a frame filter. Frame filters in this dictionary are called global frame filters, andthey are available when debugging all inferiors. These frame filters must register withthe dictionary directly. In addition to the global dictionary, there are other dictionaries that are loaded with different inferiors via auto-loading (see Section 23.3.3 [Python
Auto-loading], page 513). The two other areas where frame filter dictionaries can befound are: gdb.Progspace which contains a frame_filters dictionary attribute, and each
gdb.Objfile object which also contains a frame_filters dictionary attribute.
When a command is executed from gdb that is compatible with frame filters, gdb
combines the global, gdb.Progspace and all gdb.Objfile dictionaries currently loaded.
All of the gdb.Objfile dictionaries are combined, as several frames, and thus several object
files, might be in use. gdb then prunes any frame filter whose enabled attribute is False.
This pruned list is then sorted according to the priority attribute in each filter.
Once the dictionaries are combined, pruned and sorted, gdb creates an iterator which
wraps each frame in the call stack in a FrameDecorator object, and calls each filter in order.
The output from the previous filter will always be the input to the next filter, and so on.
Frame filters have a mandatory interface which each frame filter must implement, defined
here:

FrameFilter.filter (iterator)[Function]
gdb will call this method on a frame filter when it has reached the order in the priority
list for that filter.
For example, if there are four frame filters:
Name

Priority

Filter1
Filter2
Filter3
Filter4

5
10
100
1

The order that the frame filters will be called is:
Filter3 -> Filter2 -> Filter1 -> Filter4

Note that the output from Filter3 is passed to the input of Filter2, and so on.
This filter method is passed a Python iterator. This iterator contains a sequence offrame decorators that wrap each gdb.Frame, or a frame decorator that wraps anotherframe decorator. The first filter that is executed in the sequence of frame filters will
receive an iterator entirely comprised of default FrameDecorator objects. However,after each frame filter is executed, the previous frame filter may have wrapped someor all of the frame decorators with their own frame decorator. As frame decorators
must also conform to a mandatory interface, these decorators can be assumed to act
in a uniform manner (see Section 23.3.2.11 [Frame Decorator API], page 432).
This method must return an object conforming to the Python iterator protocol. Each
item in the iterator must be an object conforming to the frame decorator interface.
If a frame filter does not wish to perform any operations on this iterator, it should
return that iterator untouched.
This method is not optional. If it does not exist, gdb will raise and print an error.

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The name attribute must be Python string which contains the name of the filter displayed by gdb (see Section 8.6 [Frame Filter Management], page 122). This attribute
may contain any combination of letters or numbers. Care should be taken to ensurethat it is unique. This attribute is mandatory.

FrameFilter.name[Variable]
The enabled attribute must be Python boolean. This attribute indicates to gdb
whether the frame filter is enabled, and should be considered when frame filters are
executed. If enabled is True, then the frame filter will be executed when any ofthe backtrace commands detailed earlier in this chapter are executed. If enabled isFalse, then the frame filter will not be executed. This attribute is mandatory.

FrameFilter.enabled[Variable]
The priority attribute must be Python integer. This attribute controls the orderof execution in relation to other frame filters. There are no imposed limits on therange of priority other than it must be a valid integer. The higher the priority
attribute, the sooner the frame filter will be executed in relation to other frame filters.
Although priority can be negative, it is recommended practice to assume zero is
the lowest priority that a frame filter can be assigned. Frame filters that have thesame priority are executed in unsorted order in that priority slot. This attribute is
mandatory. 100 is a good default priority.

FrameFilter.priority

23.3.2.11 Decorating Frames
Frame decorators are sister objects to frame filters (see Section 23.3.2.10 [Frame Filter
API], page 430). Frame decorators are applied by a frame filter and can only be used inconjunction with frame filters.
The purpose of a frame decorator is to customize the printed content of each gdb.Framein commands where frame filters are executed. This concept is called decorating a frame.
Frame decorators decorate a gdb.Frame with Python code contained within each API call.
This separates the actual data contained in a gdb.Frame from the decorated data produced by a frame decorator. This abstraction is necessary to maintain integrity of the datacontained in each gdb.Frame.
Frame decorators have a mandatory interface, defined below.
gdb already contains a frame decorator called FrameDecorator. This contains substantial amounts of boilerplate code to decorate the content of a gdb.Frame. It is recommended
that other frame decorators inherit and extend this object, and only to override the methods
needed.
FrameDecorator is defined in the Python module gdb.FrameDecorator, so your code
can import it like:from gdb.FrameDecorator import FrameDecorator

FrameDecorator.elided (self)[Function]
The elided method groups frames together in a hierarchical system. An example
would be an interpreter, where multiple low-level frames make up a single call in
the interpreted language. In this example, the frame filter would elide the low-level

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frames and present a single high-level frame, representing the call in the interpreted
language, to the user.
The elided function must return an iterable and this iterable must contain the framesthat are being elided wrapped in a suitable frame decorator. If no frames are being
elided this function may return an empty iterable, or None. Elided frames are indented
from normal frames in a CLI backtrace, or in the case of gdb/mi, are placed in thechildren field of the eliding frame.
It is the frame filter’s task to also filter out the elided frames from the source iterator.
This will avoid printing the frame twice.

FrameDecorator.function (self)[Function]
This method returns the name of the function in the frame that is to be printed.
This method must return a Python string describing the function, or None.
If this function returns None, gdb will not print any data for this field.

FrameDecorator.address (self)[Function]

This method returns the address of the frame that is to be printed.
This method must return a Python numeric integer type of sufficient size to describe
the address of the frame, or None.
If this function returns a None, gdb will not print any data for this field.

FrameDecorator.filename (self)[Function]
This method returns the filename and path associated with this frame.
This method must return a Python string containing the filename and the path tothe object file backing the frame, or None.
If this function returns a None, gdb will not print any data for this field.

FrameDecorator.line (self):[Function]
This method returns the line number associated with the current position within thefunction addressed by this frame.
This method must return a Python integer type, or None.
If this function returns a None, gdb will not print any data for this field.

FrameDecorator.frame_args (self)[Function]
This method must return an iterable, or None. Returning an empty iterable, or Nonemeans frame arguments will not be printed for this frame. This iterable must containobjects that implement two methods, described here.
This object must implement a symbol method which takes a single self parameterand must return a gdb.Symbol (see Section 23.3.2.30 [Symbols In Python], page 484),
or a Python string. The object must also implement a value method which takes
a single self parameter and must return a gdb.Value (see Section 23.3.2.4 [Values
From Inferior], page 411), a Python value, or None. If the value method returns
None, and the argument method returns a gdb.Symbol, gdb will look-up and print
the value of the gdb.Symbol automatically.
A brief example:
class SymValueWrapper():

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def __init__(self, symbol, value):self.sym = symbol
self.val = value
def value(self):
return self.val
def symbol(self):
return self.sym
class SomeFrameDecorator()...
...
def frame_args(self):args = []try:block = self.inferior_frame.block()
except:return None
# Iterate over all symbols in a block. Only add# symbols that are arguments.
for sym in block:
if not sym.is_argument:
continueargs.append(SymValueWrapper(sym,None))# Add example synthetic argument.
args.append(SymValueWrapper(‘‘foo’’, 42))
return args

FrameDecorator.frame_locals (self)[Function]
This method must return an iterable or None. Returning an empty iterable, or Nonemeans frame local arguments will not be printed for this frame.
The object interface, the description of the various strategies for reading frame locals,
and the example are largely similar to those described in the frame_args function,(see [The frame filter frame args function], page 433). Below is a modified example:
class SomeFrameDecorator()...
...
def frame_locals(self):vars = []try:block = self.inferior_frame.block()
except:return None
# Iterate over all symbols in a block. Add all# symbols, except arguments.
for sym in block:
if sym.is_argument:
continuevars.append(SymValueWrapper(sym,None))# Add an example of a synthetic local variable.

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vars.append(SymValueWrapper(‘‘bar’’, 99))
return vars

FrameDecorator.inferior_frame (self):[Function]
This method must return the underlying gdb.Frame that this frame decorator isdecorating. gdb requires the underlying frame for internal frame information todetermine how to print certain values when printing a frame.

23.3.2.12 Writing a Frame Filter
There are three basic elements that a frame filter must implement: it must correctly implement the documented interface (see Section 23.3.2.10 [Frame Filter API], page 430), it mustregister itself with gdb, and finally, it must decide if it is to work on the data provided by
gdb. In all cases, whether it works on the iterator or not, each frame filter must return an
iterator. A bare-bones frame filter follows the pattern in the following example.
import gdb
class FrameFilter():
def __init__(self):# Frame filter attribute creation.
## ’name’ is the name of the filter that GDB will display.
## ’priority’ is the priority of the filter relative to other# filters.
## ’enabled’ is a boolean that indicates whether this filter is# enabled and should be executed.
self.name = "Foo"self.priority = 100
self.enabled = True
# Register this frame filter with the global frame_filters# dictionary.
gdb.frame_filters[self.name] = self
def filter(self, frame_iter):# Just return the iterator.
return frame_iter

The frame filter in the example above implements the three requirements for all frame
filters. It implements the API, self registers, and makes a decision on the iterator (in thiscase, it just returns the iterator untouched).
The first step is attribute creation and assignment, and as shown in the comments thefilter assigns the following attributes: name, priority and whether the filter should beenabled with the enabled attribute.
The second step is registering the frame filter with the dictionary or dictionaries thatthe frame filter has interest in. As shown in the comments, this filter just registers itself
with the global dictionary gdb.frame_filters. As noted earlier, gdb.frame_filters is adictionary that is initialized in the gdb module when gdb starts. What dictionary a filter
registers with is an important consideration. Generally, if a filter is specific to a set of code,436

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it should be registered either in the objfile or progspace dictionaries as they are specificto the program currently loaded in gdb. The global dictionary is always present in gdb
and is never unloaded. Any filters registered with the global dictionary will exist until gdb
exits. To avoid filters that may conflict, it is generally better to register frame filters against
the dictionaries that more closely align with the usage of the filter currently in question.
See Section 23.3.3 [Python Auto-loading], page 513, for further information on auto-loading
Python scripts.
gdb takes a hands-off approach to frame filter registration, therefore it is the frame
filter’s responsibility to ensure registration has occurred, and that any exceptions are handled appropriately. In particular, you may wish to handle exceptions relating to Python
dictionary key uniqueness. It is mandatory that the dictionary key is the same as frame
filter’s name attribute. When a user manages frame filters (see Section 8.6 [Frame Filter Management], page 122), the names gdb will display are those contained in the nameattribute.
The final step of this example is the implementation of the filter method. As shownin the example comments, we define the filter method and note that the method musttake an iterator, and also must return an iterator. In this bare-bones example, the frame
filter is not very useful as it just returns the iterator untouched. However this is a valid
operation for frame filters that have the enabled attribute set, but decide not to operate
on any frames.
In the next example, the frame filter operates on all frames and utilizes a frame decorator
to perform some work on the frames. See Section 23.3.2.11 [Frame Decorator API], page 432,
for further information on the frame decorator interface.
This example works on inlined frames. It highlights frames which are inlined by tagging them with an “[inlined]” tag. By applying a frame decorator to all frames with the
Python itertools imap method, the example defers actions to the frame decorator. Framedecorators are only processed when gdb prints the backtrace.
This introduces a new decision making topic: whether to perform decision making operations at the filtering step, or at the printing step. In this example’s approach, it does
not perform any filtering decisions at the filtering step beyond mapping a frame decorator
to each frame. This allows the actual decision making to be performed when each frame isprinted. This is an important consideration, and well worth reflecting upon when designinga frame filter. An issue that frame filters should avoid is unwinding the stack if possible.
Some stacks can run very deep, into the tens of thousands in some cases. To search every
frame to determine if it is inlined ahead of time may be too expensive at the filtering step.
The frame filter cannot know how many frames it has to iterate over, and it would haveto iterate through them all. This ends up duplicating effort as gdb performs this iteration
when it prints the frames.
In this example decision making can be deferred to the printing step. As each frame isprinted, the frame decorator can examine each frame in turn when gdb iterates. From aperformance viewpoint, this is the most appropriate decision to make as it avoids duplicating
the effort that the printing step would undertake anyway. Also, if there are many frame
filters unwinding the stack during filtering, it can substantially delay the printing of the
backtrace which will result in large memory usage, and a poor user experience.
class InlineFilter():Chapter 23: Extending gdb

437

def __init__(self):
self.name = "InlinedFrameFilter"
self.priority = 100
self.enabled = True
gdb.frame_filters[self.name] = self
def filter(self, frame_iter):frame_iter = itertools.imap(InlinedFrameDecorator,
frame_iter)
return frame_iter

This frame filter is somewhat similar to the earlier example, except that the filter
method applies a frame decorator object called InlinedFrameDecorator to each elementin the iterator. The imap Python method is light-weight. It does not proactively iterateover the iterator, but rather creates a new iterator which wraps the existing one.
Below is the frame decorator for this example.
class InlinedFrameDecorator(FrameDecorator):
def __init__(self, fobj):
super(InlinedFrameDecorator, self).__init__(fobj)
def function(self):frame = self.inferior_frame()name = str(frame.name())
if frame.type() == gdb.INLINE_FRAME:
name = name + " [inlined]"
return name

This frame decorator only defines and overrides the function method. It lets the supplied FrameDecorator, which is shipped with gdb, perform the other work associated withprinting this frame.
The combination of these two objects create this output from a backtrace:
#0
#1
#2

0x004004e0 in bar () at inline.c:110x00400566 in max [inlined] (b=6, a=12) at inline.c:210x00400566 in main () at inline.c:31

So in the case of this example, a frame decorator is applied to all frames, regardless ofwhether they may be inlined or not. As gdb iterates over the iterator produced by theframe filters, gdb executes each frame decorator which then makes a decision on what toprint in the function callback. Using a strategy like this is a way to defer decisions on theframe content to printing time.

Eliding Frames
It might be that the above example is not desirable for representing inlined frames, and ahierarchical approach may be preferred. If we want to hierarchically represent frames, theelided frame decorator interface might be preferable.
This example approaches the issue with the elided method. This example is quite long,
but very simplistic. It is out-of-scope for this section to write a complete example thatcomprehensively covers all approaches of finding and printing inlined frames. However, thisexample illustrates the approach an author might use.

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This example comprises of three sections.
class InlineFrameFilter():
def __init__(self):
self.name = "InlinedFrameFilter"
self.priority = 100
self.enabled = True
gdb.frame_filters[self.name] = self
def filter(self, frame_iter):return ElidingInlineIterator(frame_iter)

This frame filter is very similar to the other examples. The only difference is this frame
filter is wrapping the iterator provided to it (frame_iter) with a custom iterator called
ElidingInlineIterator. This again defers actions to when gdb prints the backtrace, as
the iterator is not traversed until printing.
The iterator for this example is as follows. It is in this section of the example where
decisions are made on the content of the backtrace.
class ElidingInlineIterator:
def __init__(self, ii):
self.input_iterator = ii
def __iter__(self):
return self
def next(self):frame = next(self.input_iterator)
if frame.inferior_frame().type() != gdb.INLINE_FRAME:
return frametry:eliding_frame = next(self.input_iterator)
except StopIteration:
return frame
return ElidingFrameDecorator(eliding_frame, [frame])

This iterator implements the Python iterator protocol. When the next function is called(when gdb prints each frame), the iterator checks if this frame decorator, frame, is wrapping
an inlined frame. If it is not, it returns the existing frame decorator untouched. If it iswrapping an inlined frame, it assumes that the inlined frame was contained within thenext oldest frame, eliding_frame, which it fetches. It then creates and returns a frame
decorator, ElidingFrameDecorator, which contains both the elided frame, and the eliding
frame.
class ElidingInlineDecorator(FrameDecorator):
def __init__(self, frame, elided_frames):
super(ElidingInlineDecorator, self).__init__(frame)
self.frame = frame
self.elided_frames = elided_frames
def elided(self):
return iter(self.elided_frames)

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439This frame decorator overrides one function and returns the inlined frame in the elided
method. As before it lets FrameDecorator do the rest of the work involved in printing thisframe. This produces the following output.
#0#2

0x004004e0 in bar () at inline.c:110x00400529 in main () at inline.c:25#1 0x00400529 in max (b=6, a=12) at inline.c:15

In that output, max which has been inlined into main is printed hierarchically. Anotherapproach would be to combine the function method, and the elided method to both print
a marker in the inlined frame, and also show the hierarchical relationship.

23.3.2.13 Unwinding Frames in Python
In gdb terminology “unwinding” is the process of finding the previous frame (that is,caller’s) from the current one. An unwinder has three methods. The first one checks if it
can handle given frame (“sniff” it). For the frames it can sniff an unwinder provides two
additional methods: it can return frame’s ID, and it can fetch registers from the previous
frame. A running gdb maintains a list of the unwinders and calls each unwinder’s sniffer
in turn until it finds the one that recognizes the current frame. There is an API to register
an unwinder.
The unwinders that come with gdb handle standard frames. However, mixed language
applications (for example, an application running Java Virtual Machine) sometimes use
frame layouts that cannot be handled by the gdb unwinders. You can write Python codethat can handle such custom frames.
You implement a frame unwinder in Python as a class with which has two attributes,name and enabled, with obvious meanings, and a single method __call__, which examines
a given frame and returns an object (an instance of gdb.UnwindInfo class) describing it.
If an unwinder does not recognize a frame, it should return None. The code in gdb thatenables writing unwinders in Python uses this object to return frame’s ID and previous
frame registers when gdb core asks for them.
An unwinder should do as little work as possible. Some otherwise innocuous operations
can cause problems (even crashes, as this code is not well-hardened yet). For example,
making an inferior call from an unwinder is unadvisable, as an inferior call will reset gdb’s
stack unwinding process, potentially causing re-entrant unwinding.

Unwinder Input
An object passed to an unwinder (a gdb.PendingFrame instance) provides a method toread frame’s registers:

PendingFrame.read_register (register)[Function]
This method returns the contents of register in the frame as a gdb.Value object. Fora description of the acceptable values of register see [Frame.read register], page 482.
If register does not name a register for the current architecture, this method willthrow an exception.

Note that this method will always return a gdb.Value for a valid register name. This
does not mean that the value will be valid. For example, you may request a registerthat an earlier unwinder could not unwind—the value will be unavailable. Instead,the gdb.Value returned from this method will be lazy; that is, its underlying bits

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will not be fetched until it is first used. So, attempting to use such a value will cause
an exception at the point of use.
The type of the returned gdb.Value depends on the register and the architecture. It
is common for registers to have a scalar type, like long long; but many other types
are possible, such as pointer, pointer-to-function, floating point or vector types.
It also provides a factory method to create a gdb.UnwindInfo instance to be returned
to gdb:PendingFrame.create_unwind_info (frame id)[Function]
Returns a new gdb.UnwindInfo instance identified by given frame id. The frame id
is used internally by gdb to identify the frames within the current thread’s stack.
The attributes of frame id determine what type of frame is created within gdb:
sp, pcThe frame is identified by the given stack address and PC. The stackaddress must be chosen so that it is constant throughout the lifetime of
the frame, so a typical choice is the value of the stack pointer at the startof the function—in the DWARF standard, this would be the “Call Frame
Address”.
This is the most common case by far. The other cases are documented
for completeness but are only useful in specialized situations.

sp, pc, special
The frame is identified by the stack address, the PC, and a “special”
address. The special address is used on architectures that can have framesthat do not change the stack, but which are still distinct, for example theIA-64, which has a second stack for registers. Both sp and special must
be constant throughout the lifetime of the frame.
sp

The frame is identified by the stack address only. Any other stack framewith a matching sp will be considered to match this frame. Inside gdb,
this is called a “wild frame”. You will never need this.

Each attribute value should either be an instance of gdb.Value or an integer.
A helper class is provided in the gdb.unwinder module that can be used to represent
a frame-id (see [gdb.unwinder.FrameId], page 442).

PendingFrame.architecture ()[Function]
Return the gdb.Architecture (see Section 23.3.2.36 [Architectures In Python],page 497) for this gdb.PendingFrame. This represents the architecture of theparticular frame being unwound.

PendingFrame.level ()[Function]
Return an integer, the stack frame level for this frame. See Section 8.1 [Stack Frames],
page 113.

PendingFrame.name ()[Function]
Returns the function name of this pending frame, or None if it can’t be obtained.

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441

PendingFrame.is_valid ()[Function]
Returns true if the gdb.PendingFrame object is valid, false if not. A pending frame
object becomes invalid when the call to the unwinder, for which the pending frame
was created, returns.
All gdb.PendingFrame methods, except this one, will raise an exception if the pending
frame object is invalid at the time the method is called.

PendingFrame.pc ()[Function]

Returns the pending frame’s resume address.

PendingFrame.block ()[Function]
Return the pending frame’s code block (see Section 23.3.2.29 [Blocks In Python],page 482). If the frame does not have a block – for example, if there is no debugging
information for the code in question – then this will raise a RuntimeError exception.

PendingFrame.function ()[Function]
Return the symbol for the function corresponding to this pending frame. See
Section 23.3.2.30 [Symbols In Python], page 484.

PendingFrame.find_sal ()[Function]
Return the pending frame’s symtab and line object (see Section 23.3.2.31 [Symbol
Tables In Python], page 489).

PendingFrame.language ()[Function]

Return the language of this frame, as a string, or None.

Unwinder Output: UnwindInfo
Use PendingFrame.create_unwind_info method described above to create a
gdb.UnwindInfo instance. Use the following method to specify caller registers that havebeen saved in this frame:

gdb.UnwindInfo.add_saved_register (register, value)[Function]
register identifies the register, for a description of the acceptable values see[Frame.read register], page 482. value is a register value (a gdb.Value object).

The gdb.unwinder Module
gdb comes with a gdb.unwinder module which contains the following classes:[class]The Unwinder class is a base class from which user created unwinders can derive,
though it is not required that unwinders derive from this class, so long as any user
created unwinder has the required name and enabled attributes.

gdb.unwinder.Unwinder[Function]
The name is a string used to reference this unwinder within some gdb commands (see [Managing Registered Unwinders], page 443).

gdb.unwinder.Unwinder.__init__(name)gdb.unwinder.name
A read-only attribute which is a string, the name of this unwinder.

[Variable]

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A modifiable attribute containing a boolean; when True, the unwinder is enabled, and will be used by gdb. When False, the unwinder has been disabled,
and will not be used.

gdb.unwinder.enabled[class]This is a class suitable for being used as the frame-id when calling
gdb.PendingFrame.create_unwind_info. It is not required to use this class,any class with the required attribute (see [gdb.PendingFrame.create unwind info],
page 440) will be accepted, but in most cases this class will be sufficient.

gdb.unwinder.FrameId

gdb.unwinder.FrameId has the following method:

gdb.unwinder.FrameId.__init__(sp, pc, special = None)[Function]
The sp and pc arguments are required and should be either a gdb.Value object,or an integer.
The special argument is optional; if specified, it should be a gdb.Value object,or an integer.

gdb.unwinder.FrameId has the following read-only attributes:

gdb.unwinder.sp[Variable]

The sp value passed to the constructor.

gdb.unwinder.pc[Variable]

The pc value passed to the constructor.
[Variable]
The special value passed to the constructor, or None if no such value was passed.

gdb.unwinder.special

Registering an Unwinder
Object files and program spaces can have unwinders registered with them. In addition, you
can register unwinders globally.
The gdb.unwinders module provides the function to register an unwinder:

gdb.unwinder.register_unwinder (locus, unwinder, replace=False)[Function]
locus specifies to which unwinder list to prepend the unwinder. It can be either an
object file (see Section 23.3.2.27 [Objfiles In Python], page 476), a program space(see Section 23.3.2.26 [Progspaces In Python], page 474), or None, in which case theunwinder is registered globally. The newly added unwinder will be called before anyother unwinder from the same locus. Two unwinders in the same locus cannot havethe same name. An attempt to add an unwinder with an already existing name raises
an exception unless replace is True, in which case the old unwinder is deleted and the
new unwinder is registered in its place.
gdb first calls the unwinders from all the object files in no particular order, then theunwinders from the current program space, then the globally registered unwinders,and finally the unwinders builtin to gdb.

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443

Unwinder Skeleton Code
Here is an example of how to structure a user created unwinder:from gdb.unwinder import Unwinder, FrameId
class MyUnwinder(Unwinder):def __init__(self):
super().__init___("MyUnwinder_Name")
def __call__(self, pending_frame):
if not <we recognize frame>:
return None
# Create a FrameID. Usually the frame is identified by a
# stack pointer and the function address.
sp = ... compute a stack address ...
pc = ... compute function address ...
unwind_info = pending_frame.create_unwind_info(FrameId(sp, pc))
# Find the values of the registers in the caller’s frame and# save them in the result:
unwind_info.add_saved_register(<register-number>, <register-value>)....
# Return the result:
return unwind_info
gdb.unwinder.register_unwinder(<locus>, MyUnwinder(), <replace>)

Managing Registered Unwinders
gdb defines 3 commands to manage registered unwinders. These are:info unwinder [ locus [ name-regexp ] ]Lists all registered unwinders. Arguments locus and name-regexp are both
optional and can be used to filter which unwinders are listed.
The locus argument should be either global, progspace, or the name of an
object file. Only unwinders registered for the specified locus will be listed.
The name-regexp is a regular expression used to match against unwinder names.
When trying to match against unwinder names that include a string enclose
name-regexp in quotes.
disable unwinder [ locus [ name-regexp ] ]The locus and name-regexp are interpreted as in info unwinder above, butinstead of listing the matching unwinders, all of the matching unwinders are
disabled. The enabled field of each matching unwinder is set to False.
enable unwinder [ locus [ name-regexp ] ]The locus and name-regexp are interpreted as in info unwinder above, butinstead of listing the matching unwinders, all of the matching unwinders areenabled. The enabled field of each matching unwinder is set to True.

23.3.2.14 Xmethods In Python
Xmethods are additional methods or replacements for existing methods of a C++ class.
This feature is useful for those cases where a method defined in C++ source code could be444

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inlined or optimized out by the compiler, making it unavailable to gdb. For such cases,
one can define an xmethod to serve as a replacement for the method defined in the C++
source code. gdb will then invoke the xmethod, instead of the C++ method, to evaluate
expressions. One can also use xmethods when debugging with core files. Moreover, when
debugging live programs, invoking an xmethod need not involve running the inferior (which
can potentially perturb its state). Hence, even if the C++ method is available, it is better
to use its replacement xmethod if one is defined.
The xmethods feature in Python is available via the concepts of an xmethod matcher
and an xmethod worker. To implement an xmethod, one has to implement a matcher anda corresponding worker for it (more than one worker can be implemented, each catering toa different overloaded instance of the method). Internally, gdb invokes the match methodof a matcher to match the class type and method name. On a match, the match method
returns a list of matching worker objects. Each worker object typically corresponds toan overloaded instance of the xmethod. They implement a get_arg_types method which
returns a sequence of types corresponding to the arguments the xmethod requires. gdb uses
this sequence of types to perform overload resolution and picks a winning xmethod worker.
A winner is also selected from among the methods gdb finds in the C++ source code. Next,
the winning xmethod worker and the winning C++ method are compared to select an overall
winner. In case of a tie between a xmethod worker and a C++ method, the xmethod worker
is selected as the winner. That is, if a winning xmethod worker is found to be equivalent
to the winning C++ method, then the xmethod worker is treated as a replacement for theC++ method. gdb uses the overall winner to invoke the method. If the winning xmethod
worker is the overall winner, then the corresponding xmethod is invoked via the __call__method of the worker object.
If one wants to implement an xmethod as a replacement for an existing C++ method,then they have to implement an equivalent xmethod which has exactly the same name andtakes arguments of exactly the same type as the C++ method. If the user wants to invoke
the C++ method even though a replacement xmethod is available for that method, thenthey can disable the xmethod.
See Section 23.3.2.15 [Xmethod API], page 444, for API to implement xmethods inPython. See Section 23.3.2.16 [Writing an Xmethod], page 446, for implementing xmethods
in Python.

23.3.2.15 Xmethod API
The gdb Python API provides classes, interfaces and functions to implement, register andmanipulate xmethods. See Section 23.3.2.14 [Xmethods In Python], page 443.
An xmethod matcher should be an instance of a class derived from XMethodMatcher
defined in the module gdb.xmethod, or an object with similar interface and attributes. An
instance of XMethodMatcher has the following attributes:[Variable]

name
The name of the matcher.

enabled
A boolean value indicating whether the matcher is enabled or disabled.

[Variable]

Chapter 23: Extending gdb

445[Variable]
A list of named methods managed by the matcher. Each object in the list is an
instance of the class XMethod defined in the module gdb.xmethod, or any object withthe following attributes:

methods

nameName of the xmethod which should be unique for each xmethod managed
by the matcher.

enabled

A boolean value indicating whether the xmethod is enabled or disabled.

The class XMethod is a convenience class with same attributes as above along withthe following constructor:

XMethod.__init__ (self, name)[Function]

Constructs an enabled xmethod with name name.
The XMethodMatcher class has the following methods:

XMethodMatcher.__init__ (self, name)[Function]
Constructs an enabled xmethod matcher with name name. The methods attribute is
initialized to None.

XMethodMatcher.match (self, class type, method name)[Function]
Derived classes should override this method. It should return a xmethod worker object(or a sequence of xmethod worker objects) matching the class type and method name.
class type is a gdb.Type object, and method name is a string value. If the matcher
manages named methods as listed in its methods attribute, then only those worker
objects whose corresponding entries in the methods list are enabled should be returned.

An xmethod worker should be an instance of a class derived from XMethodWorker definedin the module gdb.xmethod, or support the following interface:

XMethodWorker.get_arg_types (self)[Function]
This method returns a sequence of gdb.Type objects corresponding to the argumentsthat the xmethod takes. It can return an empty sequence or None if the xmethod
does not take any arguments. If the xmethod takes a single argument, then a single
gdb.Type object corresponding to it can be returned.

XMethodWorker.get_result_type (self, *args)[Function]
This method returns a gdb.Type object representing the type of the result of invoking
this xmethod. The args argument is the same tuple of arguments that would be passed
to the __call__ method of this worker.

XMethodWorker.__call__ (self, *args)[Function]
This is the method which does the work of the xmethod. The args arguments is thetuple of arguments to the xmethod. Each element in this tuple is a gdb.Value object.
The first element is always the this pointer value.

For gdb to lookup xmethods, the xmethod matchers should be registered using thefollowing function defined in the module gdb.xmethod:

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register_xmethod_matcher (locus, matcher, replace=False)[Function]
The matcher is registered with locus, replacing an existing matcher with the same
name as matcher if replace is True. locus can be a gdb.Objfile object (seeSection 23.3.2.27 [Objfiles In Python], page 476), or a gdb.Progspace object (seeSection 23.3.2.26 [Progspaces In Python], page 474), or None. If it is None, thenmatcher is registered globally.

23.3.2.16 Writing an Xmethod
Implementing xmethods in Python will require implementing xmethod matchers andxmethod workers (see Section 23.3.2.14 [Xmethods In Python], page 443). Consider thefollowing C++ class:class MyClass{
public:
MyClass (int a) : a_(a) { }int geta (void) { return a_; }int operator+ (int b);
private:int a_;};
int
MyClass::operator+ (int b){
return a_ + b;}

Let us define two xmethods for the class MyClass, one replacing the method geta, andanother adding an overloaded flavor of operator+ which takes a MyClass argument (theC++ code above already has an overloaded operator+ which takes an int argument). The
xmethod matcher can be defined as follows:class MyClass_geta(gdb.xmethod.XMethod):
def __init__(self):
gdb.xmethod.XMethod.__init__(self, ’geta’)def get_worker(self, method_name):
if method_name == ’geta’:return MyClassWorker_geta()

class MyClass_sum(gdb.xmethod.XMethod):
def __init__(self):
gdb.xmethod.XMethod.__init__(self, ’sum’)
def get_worker(self, method_name):
if method_name == ’operator+’:return MyClassWorker_plus()class MyClassMatcher(gdb.xmethod.XMethodMatcher):def __init__(self):
gdb.xmethod.XMethodMatcher.__init__(self, ’MyClassMatcher’)# List of methods ’managed’ by this matcherChapter 23: Extending gdb

447

self.methods = [MyClass_geta(), MyClass_sum()]
def match(self, class_type, method_name):
if class_type.tag != ’MyClass’:return None
workers = []for method in self.methods:
if method.enabled:
worker = method.get_worker(method_name)
if worker:
workers.append(worker)
return workers

Notice that the match method of MyClassMatcher returns a worker object of type
MyClassWorker_geta for the geta method, and a worker object of type MyClassWorker_
plus for the operator+ method. This is done indirectly via helper classes derived fromgdb.xmethod.XMethod. One does not need to use the methods attribute in a matcher
as it is optional. However, if a matcher manages more than one xmethod, it is a goodpractice to list the xmethods in the methods attribute of the matcher. This will thenfacilitate enabling and disabling individual xmethods via the enable/disable commands.
Notice also that a worker object is returned only if the corresponding entry in the methods
attribute of the matcher is enabled.
The implementation of the worker classes returned by the matcher setup above is asfollows:class MyClassWorker_geta(gdb.xmethod.XMethodWorker):def get_arg_types(self):
return Nonedef get_result_type(self, obj):
return gdb.lookup_type(’int’)
def __call__(self, obj):
return obj[’a_’]class MyClassWorker_plus(gdb.xmethod.XMethodWorker):def get_arg_types(self):
return gdb.lookup_type(’MyClass’)def get_result_type(self, obj):
return gdb.lookup_type(’int’)
def __call__(self, obj, other):return obj[’a_’] + other[’a_’]

For gdb to actually lookup a xmethod, it has to be registered with it. The matcher
defined above is registered with gdb globally as follows:
gdb.xmethod.register_xmethod_matcher(None, MyClassMatcher())

If an object obj of type MyClass is initialized in C++ code as follows:
MyClass obj(5);then, after loading the Python script defining the xmethod matchers and workers into gdb,
invoking the method geta or using the operator + on obj will invoke the xmethods defined
above:

448

Debugging with gdb(gdb) p obj.geta()$1 = 5(gdb) p obj + obj$2 = 10Consider another example with a C++ template class:
template <class T>class MyTemplate{
public:MyTemplate () : dsize_(10), data_ (new T [10]) { }~MyTemplate () { delete [] data_; }int footprint (void){
return sizeof (T) * dsize_ + sizeof (MyTemplate<T>);}
private:int dsize_;
T *data_;};

Let us implement an xmethod for the above class which serves as a replacement for thefootprint method. The full code listing of the xmethod workers and xmethod matchers is
as follows:class MyTemplateWorker_footprint(gdb.xmethod.XMethodWorker):def __init__(self, class_type):
self.class_type = class_type
def get_arg_types(self):
return Nonedef get_result_type(self):
return gdb.lookup_type(’int’)
def __call__(self, obj):
return (self.class_type.sizeof +obj[’dsize_’] *self.class_type.template_argument(0).sizeof)

class MyTemplateMatcher_footprint(gdb.xmethod.XMethodMatcher):def __init__(self):
gdb.xmethod.XMethodMatcher.__init__(self, ’MyTemplateMatcher’)def match(self, class_type, method_name):if (re.match(’MyTemplate<[ \t\n]*[_a-zA-Z][ _a-zA-Z0-9]*>’,
class_type.tag) andmethod_name == ’footprint’):
return MyTemplateWorker_footprint(class_type)

Notice that, in this example, we have not used the methods attribute of the matcher
as the matcher manages only one xmethod. The user can enable/disable this xmethod byenabling/disabling the matcher itself.

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23.3.2.17 Inferiors In Python
Programs which are being run under gdb are called inferiors (see Section 4.9 [Inferiors
Connections and Programs], page 42). Python scripts can access information about andmanipulate inferiors controlled by gdb via objects of the gdb.Inferior class.
The following inferior-related functions are available in the gdb module:

gdb.inferiors ()[Function]

Return a tuple containing all inferior objects.

gdb.selected_inferior ()[Function]

Return an object representing the current inferior.
A gdb.Inferior object has the following attributes:[Variable]
ID of inferior, as assigned by gdb. You can use this to make Python breakpoints
inferior-specific, for example (see [The Breakpoint.inferior attribute], page 494).

Inferior.num[Variable]
The gdb.TargetConnection for this inferior (see Section 23.3.2.38 [Connections In
Python], page 499), or None if this inferior has no connection.

Inferior.connection[Variable]
ID of inferior’s connection as assigned by gdb, or None if the inferior is notconnected to a target. See Section 4.9 [Inferiors Connections and Programs],
page 42. This is equivalent to gdb.Inferior.connection.num in the case where
gdb.Inferior.connection is not None.

Inferior.connection_num

Inferior.pid[Variable]

Process ID of the inferior, as assigned by the underlying operating system.
[Variable]
Boolean signaling whether the inferior was created using ‘attach’, or started by gdb
itself.

Inferior.was_attached[Variable]
A string holding the name of this inferior’s “main” function, if it can be determined.
If the name of main is not known, this is None.

Inferior.main_name[Variable]
The inferior’s program space. See Section 23.3.2.26 [Progspaces In Python], page 474.

Inferior.progspace[Variable]
The inferior’s command line arguments, if known. This corresponds to the set args
and show args commands. See Section 4.3 [Arguments], page 38.
When accessed, the value is a string holding all the arguments. The contents arequoted as they would be when passed to the shell. If there are no arguments, thevalue is None.
Either a string or a sequence of strings can be assigned to this attribute. When astring is assigned, it is assumed to have any necessary quoting for the shell; when asequence is assigned, the quoting is applied by gdb.

Inferior.arguments

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A gdb.Inferior object has the following methods:

Inferior.is_valid ()[Function]
Returns True if the gdb.Inferior object is valid, False if not. A gdb.Inferior
object will become invalid if the inferior no longer exists within gdb. All othergdb.Inferior methods will throw an exception if it is invalid at the time the method
is called.

Inferior.threads ()[Function]
This method returns a tuple holding all the threads which are valid when it is called.
If there are no valid threads, the method will return an empty tuple.

Inferior.architecture ()[Function]
Return the gdb.Architecture (see Section 23.3.2.36 [Architectures In Python],page 497) for this inferior. This represents the architecture of the inferior as a whole.
Some platforms can have multiple architectures in a single address space, so thismay not match the architecture of a particular frame (see Section 23.3.2.28 [Frames
In Python], page 479).

Inferior.read_memory (address, length)[Function]
Read length addressable memory units from the inferior, starting at address. Returns
a memoryview object, which behaves much like an array or a string. It can be modified
and given to the Inferior.write_memory function.

Inferior.write_memory (address, buffer [, length])[Function]
Write the contents of buffer to the inferior, starting at address. The buffer parametermust be a Python object which supports the buffer protocol, i.e., a string, an arrayor the object returned from Inferior.read_memory. If given, length determines thenumber of addressable memory units from buffer to be written.

Inferior.search_memory (address, length, pattern)[Function]
Search a region of the inferior memory starting at address with the given length using
the search pattern supplied in pattern. The pattern parameter must be a Python
object which supports the buffer protocol, i.e., a string, an array or the object returned
from gdb.read_memory. Returns a Python Long containing the address where thepattern was found, or None if the pattern could not be found.

Inferior.thread_from_handle (handle)[Function]
Return the thread object corresponding to handle, a thread library specific data
structure such as pthread_t for pthreads library implementations.

The function Inferior.thread_from_thread_handle provides the same functionality, but use of Inferior.thread_from_thread_handle is deprecated.
The environment that will be passed to the inferior can be changed from Python byusing the following methods. These methods only take effect when the inferior is started –they will not affect an inferior that is already executing.

Inferior.clear_env ()[Function]
Clear the current environment variables that will be passed to this inferior.

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Inferior.set_env (name, value)[Function]
Set the environment variable name to have the indicated value. Both parametersmust be strings.

Inferior.unset_env (name)[Function]

Unset the environment variable name. name must be a string.
One may add arbitrary attributes to gdb.Inferior objects in the usual Python way.
This is useful if, for example, one needs to do some extra record keeping associated with
the inferior.
When selecting a name for a new attribute, avoid starting the new attribute name witha lower case letter; future attributes added by gdb will start with a lower case letter.
Additionally, avoid starting attribute names with two underscore characters, as these could
clash with Python builtin attribute names.
In this contrived example we record the time when an inferior last stopped:(gdb) python
import datetime
def thread_stopped(event):
if event.inferior_thread is not None:
thread = event.inferior_threadelse:
thread = gdb.selected_thread()inferior = thread.inferior
inferior._last_stop_time = datetime.datetime.today()gdb.events.stop.connect(thread_stopped)(gdb) file /tmp/hello
Reading symbols from /tmp/hello...
(gdb) start
Temporary breakpoint 1 at 0x401198: file /tmp/hello.c, line 18.
Starting program: /tmp/hello
Temporary breakpoint 1, main () at /tmp/hello.c:18
18
printf ("Hello World\n");(gdb) python print(gdb.selected_inferior()._last_stop_time)2024-01-04 14:48:41.347036

23.3.2.18 Events In Python
gdb provides a general event facility so that Python code can be notified of various statechanges, particularly changes that occur in the inferior.
An event is just an object that describes some state change. The type of the object andits attributes will vary depending on the details of the change. All the existing events aredescribed below.
In order to be notified of an event, you must register an event handler with an event registry. An event registry is an object in the gdb.events module which dispatches particular
events. A registry provides methods to register and unregister event handlers:

EventRegistry.connect (object)[Function]
Add the given callable object to the registry. This object will be called when an event
corresponding to this registry occurs.

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EventRegistry.disconnect (object)[Function]
Remove the given object from the registry. Once removed, the object will no longer
receive notifications of events.

Here is an example:
def exit_handler (event):
print ("event type: exit")
if hasattr (event, ’exit_code’):print ("exit code: %d" % (event.exit_code))
else:
print ("exit code not available")
gdb.events.exited.connect (exit_handler)

In the above example we connect our handler exit_handler to the registry
events.exited. Once connected, exit_handler gets called when the inferior exits. The
argument event in this example is of type gdb.ExitedEvent. As you can see in theexample the ExitedEvent object has an attribute which indicates the exit code of theinferior.
Some events can be thread specific when gdb is running in non-stop mode. When
represented in Python, these events all extend gdb.ThreadEvent. This event is a baseclass and is never emitted directly; instead, events which are emitted by this or othermodules might extend this event. Examples of these events are gdb.BreakpointEvent andgdb.ContinueEvent. gdb.ThreadEvent holds the following attributes:[Variable]
In non-stop mode this attribute will be set to the specific thread which was involvedin the emitted event. Otherwise, it will be set to None.

ThreadEvent.inferior_thread

The following is a listing of the event registries that are available and details of the events
they emit:
events.cont
Emits gdb.ContinueEvent, which extends gdb.ThreadEvent. This event indicates that the inferior has been continued after a stop. For inherited attributerefer to gdb.ThreadEvent above.
events.exited
Emits events.ExitedEvent, which indicates that the inferior has exited.
events.ExitedEvent has two attributes:[Variable]
An integer representing the exit code, if available, which the inferior has
returned. (The exit code could be unavailable if, for example, gdb detaches from the inferior.) If the exit code is unavailable, the attribute
does not exist.

ExitedEvent.exit_code

ExitedEvent.inferior
A reference to the inferior which triggered the exited event.
events.stop
Emits gdb.StopEvent, which extends gdb.ThreadEvent.

[Variable]

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Indicates that the inferior has stopped. All events emitted by this registry
extend gdb.StopEvent. As a child of gdb.ThreadEvent, gdb.StopEvent will
indicate the stopped thread when gdb is running in non-stop mode. Refer to
gdb.ThreadEvent above for more details.
gdb.StopEvent has the following additional attributes:[Variable]
A dictionary holding any details relevant to the stop. The exact keys andvalues depend on the type of stop, but are identical to the corresponding
MI output (see Section 27.7.3 [GDB/MI Async Records], page 598).
A dictionary was used for this (rather than adding attributes directly tothe event object) so that the MI keys could be used unchanged.
When a StopEvent results from a finish command, it will also hold thereturn value from the function, if that is available. This will be an entry
named ‘return-value’ in the details dictionary. The value of this entry
will be a gdb.Value object.

StopEvent.details

Emits gdb.SignalEvent, which extends gdb.StopEvent.
This event indicates that the inferior or one of its threads has received a signal.
gdb.SignalEvent has the following attributes:[Variable]
A string representing the signal received by the inferior. A list of possible
signal values can be obtained by running the command info signals in
the gdb command prompt.

SignalEvent.stop_signal

Also emits gdb.BreakpointEvent, which extends gdb.StopEvent.
gdb.BreakpointEvent event indicates that one or more breakpoints have been
hit, and has the following attributes:[Variable]
A sequence containing references to all the breakpoints (typegdb.Breakpoint) that were hit. See Section 23.3.2.33 [Breakpoints In
Python], page 491, for details of the gdb.Breakpoint object.

BreakpointEvent.breakpoints[Variable]
A reference to the first breakpoint that was hit. This attribute is maintained for backward compatibility and is now deprecated in favor of the
gdb.BreakpointEvent.breakpoints attribute.

BreakpointEvent.breakpoint

events.new_objfile
Emits gdb.NewObjFileEvent which indicates that a new object file has been
loaded by gdb. gdb.NewObjFileEvent has one attribute:[Variable]
A reference to the object file (gdb.Objfile) which has been loaded.
See Section 23.3.2.27 [Objfiles In Python], page 476, for details of the
gdb.Objfile object.

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events.free_objfile
Emits gdb.FreeObjFileEvent which indicates that an object file is about tobe removed from gdb. One reason this can happen is when the inferior calls
dlclose. gdb.FreeObjFileEvent has one attribute:[Variable]
A reference to the object file (gdb.Objfile) which will be unloaded.
See Section 23.3.2.27 [Objfiles In Python], page 476, for details of the
gdb.Objfile object.

FreeObjFileEvent.objfile

events.clear_objfiles
Emits gdb.ClearObjFilesEvent which indicates that the list of object files fora program space has been reset. gdb.ClearObjFilesEvent has one attribute:[Variable]
A reference to the program space (gdb.Progspace) whose objfile list has
been cleared. See Section 23.3.2.26 [Progspaces In Python], page 474.

ClearObjFilesEvent.progspace

events.inferior_call
Emits events just before and after a function in the inferior iscalled by gdb.
Before an inferior call, this emits an event of typegdb.InferiorCallPreEvent, and after an inferior call, this emits an event oftype gdb.InferiorCallPostEvent.
gdb.InferiorCallPreEvent
Indicates that a function in the inferior is about to be called.

InferiorCallPreEvent.ptid[Variable]

The thread in which the call will be run.

InferiorCallPreEvent.address[Variable]

The location of the function to be called.
gdb.InferiorCallPostEvent
Indicates that a function in the inferior has just been called.

InferiorCallPostEvent.ptid[Variable]

The thread in which the call was run.

InferiorCallPostEvent.address[Variable]

The location of the function that was called.
events.memory_changed
Emits gdb.MemoryChangedEvent which indicates that the memory of the inferior has been modified by the gdb user, for instance via a command likeset *addr = value. The event has the following attributes:

MemoryChangedEvent.address[Variable]

The start address of the changed region.

MemoryChangedEvent.length
Length in bytes of the changed region.

[Variable]

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events.register_changed
Emits gdb.RegisterChangedEvent which indicates that a register in the inferior has been modified by the gdb user.
[Variable]
A gdb.Frame object representing the frame in which the register was
modified.

RegisterChangedEvent.frame

RegisterChangedEvent.regnum[Variable]

Denotes which register was modified.
events.breakpoint_createdThis is emitted when a new breakpoint has been created. The argument thatis passed is the new gdb.Breakpoint object.
events.breakpoint_modified
This is emitted when a breakpoint has been modified in some way. The argument that is passed is the new gdb.Breakpoint object.
events.breakpoint_deletedThis is emitted when a breakpoint has been deleted. The argument thatis passed is the gdb.Breakpoint object. When this event is emitted, thegdb.Breakpoint object will already be in its invalid state; that is, the is_valid method will return False.
events.before_prompt
This event carries no payload. It is emitted each time gdb presents a prompt
to the user.
events.new_inferiorThis is emitted when a new inferior is created. Note that the inferior is notnecessarily running; in fact, it may not even have an associated executable.
The event is of type gdb.NewInferiorEvent. This has a single attribute:

NewInferiorEvent.inferior[Variable]

The new inferior, a gdb.Inferior object.
events.inferior_deletedThis is emitted when an inferior has been deleted. Note that this is not thesame as process exit; it is notified when the inferior itself is removed, say via
remove-inferiors.
The event is of type gdb.InferiorDeletedEvent. This has a single attribute:

InferiorDeletedEvent.inferior[Variable]

The inferior that is being removed, a gdb.Inferior object.
events.new_threadThis is emitted when gdb notices a new thread. The event is of typegdb.NewThreadEvent, which extends gdb.ThreadEvent. This has a single
attribute:

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NewThreadEvent.inferior_thread[Variable]

The new thread.
events.thread_exited
This is emitted when gdb notices a thread has exited. The event is of typegdb.ThreadExitedEvent which extends gdb.ThreadEvent. This has a single
attribute:

ThreadExitedEvent.inferior_thread[Variable]

The exiting thread.
events.gdb_exiting
This is emitted when gdb exits. This event is not emitted if gdb exits as aresult of an internal error, or after an unexpected signal. The event is of typegdb.GdbExitingEvent, which has a single attribute:

GdbExitingEvent.exit_code[Variable]

An integer, the value of the exit code gdb will return.
events.connection_removed
This is emitted when gdb removes a connection (see Section 23.3.2.38 [Connections In Python], page 499). The event is of type gdb.ConnectionEvent. This
has a single read-only attribute:

ConnectionEvent.connection[Variable]

The gdb.TargetConnection that is being removed.
events.executable_changed
Emits
gdb.ExecutableChangedEventwhichindicates
that
thegdb.Progspace.executable_filename has changed.
This event is emitted when either the value of gdb.Progspace.executable_
filename has changed to name a different file, or the executable file named
by gdb.Progspace.executable_filename has changed on disk, and gdb has
therefore reloaded it.
[Variable]
The gdb.Progspace in which the current executable has changed.
The file name of the updated executable will be visible in
Section23.3.2.26
gdb.Progspace.executable_filename(see[Progspaces In Python], page 474).

ExecutableChangedEvent.progspace[Variable]
This attribute will be True if the value of gdb.Progspace.executable_
filename didn’t change, but the file it names changed on disk instead,and gdb reloaded it.
When this attribute is False, the value in gdb.Progspace.executable_
filename was changed to name a different file.

ExecutableChangedEvent.reload

Remember that gdb tracks the executable file and the symbol fileseparately, these are visible as gdb.Progspace.executable_filename andChapter 23: Extending gdb

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gdb.Progspace.filename respectively. When using the file command, gdb
updates both of these fields, but the executable file is updated first, so when
this event is emitted, the executable filename will have changed, but thesymbol filename might still hold its previous value.
events.new_progspace
This is emitted when gdb adds a new program space (see Section 23.3.2.26[Program Spaces In Python], page 474).
The event is of typegdb.NewProgspaceEvent, and has a single read-only attribute:

NewProgspaceEvent.progspace[Variable]

The gdb.Progspace that was added to gdb.
No NewProgspaceEvent is emitted for the very first program space, which is
assigned to the first inferior. This first program space is created within gdb
before any Python scripts are sourced.
events.free_progspace
This is emitted when gdb removes a program space (see Section 23.3.2.26 [Program Spaces In Python], page 474), for example as a result of the removeinferiors command (see [remove-inferiors], page 45). The event is of typegdb.FreeProgspaceEvent, and has a single read-only attribute:

FreeProgspaceEvent.progspace[Variable]

The gdb.Progspace that is about to be removed from gdb.
events.tui_enabledThis is emitted when the TUI is enabled or disabled. The event is of typegdb.TuiEnabledEvent, which has a single read-only attribute:[Variable]
If the TUI has just been enabled, this is True; otherwise it is False.

TuiStatusEvent.enabled

23.3.2.19 Threads In Python
Python scripts can access information about, and manipulate inferior threads controlled bygdb, via objects of the gdb.InferiorThread class.
The following thread-related functions are available in the gdb module:

gdb.selected_thread ()[Function]
This function returns the thread object for the selected thread. If there is no selected
thread, this will return None.

To get the list of threads for an inferior, use the Inferior.threads() method. See
Section 23.3.2.17 [Inferiors In Python], page 449.
A gdb.InferiorThread object has the following attributes:[Variable]
The name of the thread. If the user specified a name using thread name, then thisreturns that name. Otherwise, if an OS-supplied name is available, then it is returned.
Otherwise, this returns None.
This attribute can be assigned to. The new value must be a string object, which sets
the new name, or None, which removes any user-specified thread name.

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InferiorThread.num[Variable]

The per-inferior number of the thread, as assigned by GDB.
[Variable]
The global ID of the thread, as assigned by GDB. You can use this to make Python
breakpoints thread-specific, for example (see [The Breakpoint.thread attribute],
page 494).

InferiorThread.global_num[Variable]
ID of the thread, as assigned by the operating system. This attribute is a tuple containing three integers. The first is the Process ID (PID); the second is the Lightweight
Process ID (LWPID), and the third is the Thread ID (TID). Either the LWPID or
TID may be 0, which indicates that the operating system does not use that identifier.

InferiorThread.ptid[Variable]
This read-only attribute contains a string representing InferiorThread.ptid. Thisis the string that gdb uses in the ‘Target Id’ column in the info threads output(see [‘info threads’], page 48).

InferiorThread.ptid_string[Variable]
The inferior this thread belongs to. This attribute is represented as a gdb.Inferior
object. This attribute is not writable.

InferiorThread.inferior[Variable]
A string containing target specific thread state information. The format of this string
varies by target. If there is no additional state information for this thread, then this
attribute contains None.
For example, on a gnu/Linux system, a thread that is in the process of exiting
will return the string ‘Exiting’. For remote targets the details string will be obtained with the ‘qThreadExtraInfo’ remote packet, if the target supports it (see[‘qThreadExtraInfo’], page 809).
gdb displays the details string as part of the ‘Target Id’ column, in the info
threads output (see [‘info threads’], page 48).

InferiorThread.details

A gdb.InferiorThread object has the following methods:

InferiorThread.is_valid ()[Function]
Returns True if the gdb.InferiorThread object is valid, False if not.
A
gdb.InferiorThread object will become invalid if the thread exits, or the inferior
that the thread belongs is deleted. All other gdb.InferiorThread methods willthrow an exception if it is invalid at the time the method is called.

InferiorThread.switch ()[Function]
This changes gdb’s currently selected thread to the one represented by this object.

InferiorThread.is_stopped ()[Function]

Return a Boolean indicating whether the thread is stopped.

InferiorThread.is_running ()Return a Boolean indicating whether the thread is running.

[Function]

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InferiorThread.is_exited ()459[Function]

Return a Boolean indicating whether the thread is exited.

InferiorThread.handle ()[Function]
Return the thread object’s handle, represented as a Python bytes object. A
gdb.Value representation of the handle may be constructed via gdb.Value(bufobj,type) where bufobj is the Python bytes representation of the handle and type is a
gdb.Type for the handle type.

One may add arbitrary attributes to gdb.InferiorThread objects in the usual Python
way. This is useful if, for example, one needs to do some extra record keeping associatedwith the thread.
See [choosing attribute names], page 451, for guidance on selecting a suitable name for
new attributes.
In this contrived example we record the time when a thread last stopped:(gdb) python
import datetime
def thread_stopped(event):
if event.inferior_thread is not None:
thread = event.inferior_threadelse:
thread = gdb.selected_thread()thread._last_stop_time = datetime.datetime.today()gdb.events.stop.connect(thread_stopped)(gdb) file /tmp/hello
Reading symbols from /tmp/hello...
(gdb) start
Temporary breakpoint 1 at 0x401198: file /tmp/hello.c, line 18.
Starting program: /tmp/hello
Temporary breakpoint 1, main () at /tmp/hello.c:18
18
printf ("Hello World\n");(gdb) python print(gdb.selected_thread()._last_stop_time)2024-01-04 14:48:41.347036

23.3.2.20 Recordings In Python
The following recordings-related functions (see Chapter 7 [Process Record and Replay],
page 103) are available in the gdb module:

gdb.start_recording ([method], [format])[Function]
Start a recording using the given method and format. If no format is given, thedefault format for the recording method is used. If no method is given, the default
method will be used. Returns a gdb.Record object on success. Throw an exception
on failure.
The following strings can be passed as method:• "full"• "btrace": Possible values for format: "pt", "bts" or leave out for default format.

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gdb.current_recording ()[Function]
Access a currently running recording. Return a gdb.Record object on success. Return
None if no recording is currently active.

gdb.stop_recording ()[Function]
Stop the current recording. Throw an exception if no recording is currently active.
All record objects become invalid after this call.

A gdb.Record object has the following attributes:

Record.method[Variable]

A string with the current recording method, e.g. full or btrace.

Record.format[Variable]

A string with the current recording format, e.g. bt, pts or None.
[Variable]
A method specific instruction object representing the first instruction in this recording.

Record.begin[Variable]
A method specific instruction object representing the current instruction, that is not
actually part of the recording.

Record.end[Variable]
The instruction representing the current replay position. If there is no replay active,
this will be None.

Record.replay_position

Record.instruction_history[Variable]

A list with all recorded instructions.

Record.function_call_history[Variable]

A list with all recorded function call segments.
A gdb.Record object has the following methods:

Record.goto (instruction)[Function]

Move the replay position to the given instruction.

Record.clear ()[Function]
Clear the trace data of the current recording. This forces re-decoding of the trace forsuccessive commands.

The common gdb.Instruction class that recording method specific instruction objects
inherit from, has the following attributes:

Instruction.pc[Variable]

An integer representing this instruction’s address.

Instruction.data
A memoryview object holding the raw instruction data.

[Variable]

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Instruction.decoded

461[Variable]

A human readable string with the disassembled instruction.

Instruction.size[Variable]

The size of the instruction in bytes.
Additionally gdb.RecordInstruction has the following attributes:[Variable]
An integer identifying this instruction. number corresponds to the numbers seen
in record instruction-history (see Chapter 7 [Process Record and Replay],
page 103).

RecordInstruction.number[Variable]
A gdb.Symtab_and_line object representing the associated symtab and line of this
instruction. May be None if no debug information is available.

RecordInstruction.sal

RecordInstruction.is_speculative[Variable]

A boolean indicating whether the instruction was executed speculatively.
If an error occurred during recording or decoding a recording, this error is represented
by a gdb.RecordGap object in the instruction list. It has the following attributes:[Variable]
An integer identifying this gap. number corresponds to the numbers seen in record
instruction-history (see Chapter 7 [Process Record and Replay], page 103).

RecordGap.number[Variable]
A numerical representation of the reason for the gap. The value is specific to thecurrent recording method.

RecordGap.error_code

RecordGap.error_string[Variable]

A human readable string with the reason for the gap.
Some gdb features write auxiliary information into the execution history. This information is represented by a gdb.RecordAuxiliary object in the instruction list. It has thefollowing attributes:[Variable]
An integer identifying this auxiliary. number corresponds to the numbers seen
in record instruction-history (see Chapter 7 [Process Record and Replay],
page 103).

RecordAuxiliary.number

RecordAuxiliary.data[Variable]

A string representation of the auxiliary data.
A gdb.RecordFunctionSegment object has the following attributes:[Variable]
An integer identifying this function segment. number corresponds to the numbers
seen in record function-call-history (see Chapter 7 [Process Record and Replay],
page 103).

RecordFunctionSegment.number

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A gdb.Symbol object representing the associated symbol. May be None if no debug
information is available.

RecordFunctionSegment.symbol[Variable]
An integer representing the function call’s stack level. May be None if the function
call is a gap.

RecordFunctionSegment.level[Variable]
A list of gdb.RecordInstruction or gdb.RecordGap objects associated with thisfunction call.

RecordFunctionSegment.instructions[Variable]
A gdb.RecordFunctionSegment object representing the caller’s function segment. If
the call has not been recorded, this will be the function segment to which control
returns. If neither the call nor the return have been recorded, this will be None.

RecordFunctionSegment.up[Variable]
A gdb.RecordFunctionSegment object representing the previous segment of thisfunction call. May be None.

RecordFunctionSegment.prev[Variable]
A gdb.RecordFunctionSegment object representing the next segment of this function
call. May be None.

RecordFunctionSegment.next

The following example demonstrates the usage of these objects and functions to create afunction that will rewind a record to the last time a function in a different file was executed.
This would typically be used to track the execution of user provided callback functions ina library which typically are not visible in a back trace.
def bringback ():rec = gdb.current_recording ()if not rec:returninsn = rec.instruction_history
if len (insn) == 0:
returntry:
position = insn.index (rec.replay_position)
except:position = -1
try:filename = insn[position].sal.symtab.fullname ()except:filename = Nonefor i in reversed (insn[:position]):try:
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continuerec.goto (i)returnAnother possible application is to write a function that counts the number of code
executions in a given line range. This line range can contain parts of functions or span
across several functions and is not limited to be contiguous.
def countrange (filename, linerange):
count = 0
def filter_only (file_name):for call in gdb.current_recording ().function_call_history:try:
if file_name in call.symbol.symtab.fullname ():yield call
except:pass
for c in filter_only (filename):
for i in c.instructions:try:
if i.sal.line in linerange:
count += 1
break;
except:pass
return count23.3.2.21 CLI Commands In Python
You can implement new gdb CLI commands in Python. A CLI command is implemented
using an instance of the gdb.Command class, most commonly using a subclass.

Command.__init__ (name, command class [, completer class [,prefix]])[Function]

The object initializer for Command registers the new command with gdb. This initializer is normally invoked from the subclass’ own __init__ method.
name is the name of the command. If name consists of multiple words, then the initialwords are looked for as prefix commands. In this case, if one of the prefix commands
does not exist, an exception is raised.
There is no support for multi-line commands.
command class should be one of the ‘COMMAND_’ constants defined below. This argument tells gdb how to categorize the new command in the help system.
completer class is an optional argument. If given, it should be one of the ‘COMPLETE_’
constants defined below. This argument tells gdb how to perform completion for thiscommand. If not given, gdb will attempt to complete using the object’s complete
method (see below); if no such method is found, an error will occur when completionis attempted.
prefix is an optional argument. If True, then the new command is a prefix command;
sub-commands of this command may be registered.

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The help text for the new command is taken from the Python documentation string
for the command’s class, if there is one. If no documentation string is provided, thedefault value “This command is not documented.” is used.

Command.dont_repeat ()[Function]
By default, a gdb command is repeated when the user enters a blank line at thecommand prompt. A command can suppress this behavior by invoking the dont_
repeat method at some point in its invoke method (normally this is done early in caseof exception). This is similar to the user command dont-repeat, see Section 23.1.1[Define], page 391.

Command.invoke (argument, from tty)

[Function]

This method is called by gdb when this command is invoked.
argument is a string. It is the argument to the command, after leading and trailingwhitespace has been stripped.
from tty is a boolean argument. When true, this means that the command wasentered by the user at the terminal; when false it means that the command camefrom elsewhere.
If this method throws an exception, it is turned into a gdb error call. Otherwise,
the return value is ignored.
To break argument up into an argv-like string use gdb.string_to_argv. This function behaves identically to gdb’s internal argument lexer buildargv. It is recommended to use this for consistency. Arguments are separated by spaces and may bequoted. Example:
print gdb.string_to_argv ("1 2\ \\\"3 ’4 \"5’ \"6 ’7\"")[’1’, ’2 "3’, ’4 "5’, "6 ’7"]

Command.complete (text, word)[Function]
This method is called by gdb when the user attempts completion on this command.
All forms of completion are handled by this method, that is, the TAB and M-? key
bindings (see Section 3.3 [Completion], page 24), and the complete command (seeSection 3.6 [Help], page 29).

The arguments text and word are both strings; text holds the complete commandline up to the cursor’s location, while word holds the last word of the command line;
this is computed using a word-breaking heuristic.
The complete method can return several values:• If the return value is a sequence, the contents of the sequence are used as thecompletions. It is up to complete to ensure that the contents actually do complete the word. A zero-length sequence is allowed, it means that there were
no completions available. Only string elements of the sequence are used; otherelements in the sequence are ignored.
• If the return value is one of the ‘COMPLETE_’ constants defined below, then thecorresponding gdb-internal completion function is invoked, and its result is used.
• All other results are treated as though there were no available completions.

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When a new command is registered, it must be declared as a member of some generalclass of commands. This is used to classify top-level commands in the on-line help system;
note that prefix commands are not listed under their own category but rather that of their
top-level command. The available classifications are represented by constants defined in the
gdb module:
gdb.COMMAND_NONE
The command does not belong to any particular class. A command in thiscategory will not be displayed in any of the help categories.
gdb.COMMAND_RUNNING
The command is related to running the inferior. For example, start, step,and continue are in this category. Type help running at the gdb prompt tosee a list of commands in this category.
gdb.COMMAND_DATA
The command is related to data or variables. For example, call, find, andprint are in this category. Type help data at the gdb prompt to see a list ofcommands in this category.
gdb.COMMAND_STACK
The command has to do with manipulation of the stack. For example,
backtrace, frame, and return are in this category. Type help stack at thegdb prompt to see a list of commands in this category.
gdb.COMMAND_FILESThis class is used for file-related commands. For example, file, list andsection are in this category. Type help files at the gdb prompt to see a listof commands in this category.
gdb.COMMAND_SUPPORTThis should be used for “support facilities”, generally meaning things that are
useful to the user when interacting with gdb, but not related to the state of
the inferior. For example, help, make, and shell are in this category. Typehelp support at the gdb prompt to see a list of commands in this category.
gdb.COMMAND_STATUS
The command is an ‘info’-related command, that is, related to the state of
gdb itself. For example, info, macro, and show are in this category. Typehelp status at the gdb prompt to see a list of commands in this category.
gdb.COMMAND_BREAKPOINTSThe command has to do with breakpoints. For example, break, clear, anddelete are in this category. Type help breakpoints at the gdb prompt to see
a list of commands in this category.
gdb.COMMAND_TRACEPOINTSThe command has to do with tracepoints. For example, trace, actions, andtfind are in this category. Type help tracepoints at the gdb prompt to see
a list of commands in this category.

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gdb.COMMAND_TUIThe command has to do with the text user interface (see Chapter 25 [TUI],
page 579). Type help tui at the gdb prompt to see a list of commands in thiscategory.
gdb.COMMAND_USER
The command is a general purpose command for the user, and typically does
not fit in one of the other categories. Type help user-defined at the gdb
prompt to see a list of commands in this category, as well as the list of gdb
macros (see Section 23.1 [Sequences], page 391).
gdb.COMMAND_OBSCURE
The command is only used in unusual circumstances, or is not of general interest
to users. For example, checkpoint, fork, and stop are in this category. Typehelp obscure at the gdb prompt to see a list of commands in this category.
gdb.COMMAND_MAINTENANCE
The command is only useful to gdb maintainers. The maintenance andflushregs commands are in this category. Type help internals at the gdb
prompt to see a list of commands in this category.
A new command can use a predefined completion function, either by specifying it via anargument at initialization, or by returning it from the complete method. These predefinedcompletion constants are all defined in the gdb module:
gdb.COMPLETE_NONE
This constant means that no completion should be done.
gdb.COMPLETE_FILENAME
This constant means that filename completion should be performed.
gdb.COMPLETE_LOCATIONThis constant means that location completion should be done. See Section 9.2[Location Specifications], page 126.
gdb.COMPLETE_COMMAND
This constant means that completion should examine gdb command names.
gdb.COMPLETE_SYMBOLThis constant means that completion should be done using symbol names as
the source.
gdb.COMPLETE_EXPRESSION
This constant means that completion should be done on expressions. Often
this means completing on symbol names, but some language parsers also havesupport for completing on field names.
The following code snippet shows how a trivial CLI command can be implemented in
Python:class HelloWorld (gdb.Command):"""Greet the whole world."""def __init__ (self):
super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER)

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def invoke (self, arg, from_tty):
print ("Hello, World!")
HelloWorld ()The last line instantiates the class, and is necessary to trigger the registration of thecommand with gdb. Depending on how the Python code is read into gdb, you may needto import the gdb module explicitly.

23.3.2.22 gdb/mi Commands In Python
It is possible to add gdb/mi (see Chapter 27 [GDB/MI], page 589) commands implemented
in Python. A gdb/mi command is implemented using an instance of the gdb.MICommandclass, most commonly using a subclass.

MICommand.__init__ (name)[Function]
The object initializer for MICommand registers the new command with gdb. Thisinitializer is normally invoked from the subclass’ own __init__ method.

name is the name of the command. It must be a valid name of a gdb/mi command,and in particular must start with a hyphen (-). Reusing the name of a built-in
gdb/mi is not allowed, and a RuntimeError will be raised. Using the name of an
gdb/mi command previously defined in Python is allowed, the previous command
will be replaced with the new command.

MICommand.invoke (arguments)[Function]

This method is called by gdb when the new MI command is invoked.
arguments is a list of strings. Note, that --thread and --frame arguments arehandled by gdb itself therefore they do not show up in arguments.
If this method raises an exception, then it is turned into a gdb/mi ^error response.
Only gdb.GdbError exceptions (or its sub-classes) should be used for reporting errors
to users, any other exception type is treated as a failure of the invoke method, andthe exception will be printed to the error stream according to the set python printstack setting (see [set python print-stack], page 402).
If this method returns None, then the gdb/mi command will return a ^done responsewith no additional values.
Otherwise, the return value must be a dictionary, which is converted to a gdb/miresult-record (see Section 27.4.2 [GDB/MI Output Syntax], page 593). The keys ofthis dictionary must be strings, and are used as variable names in the result-record,these strings must comply with the naming rules detailed below. The values of this
dictionary are recursively handled as follows:• If the value is Python sequence or iterator, it is converted to gdb/mi list withelements converted recursively.
• If the value is Python dictionary, it is converted to gdb/mi tuple. Keys in that
dictionary must be strings, which comply with the variable naming rules detailed
below. Values are converted recursively.
• Otherwise, value is first converted to a Python string using str () and thenconverted to gdb/mi const.

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The strings used for variable names in the gdb/mi output must follow the following
rules; the string must be at least one character long, the first character must be in theset [a-zA-Z], while every subsequent character must be in the set [-_a-zA-Z0-9].
An instance of MICommand has the following attributes:[Variable]
A string, the name of this gdb/mi command, as was passed to the __init__ method.
This attribute is read-only.

MICommand.name[Variable]
A boolean value indicating if this command is installed ready for a user to call fromthe command line. Commands are automatically installed when they are instantiated,
after which this attribute will be True.
If later, a new command is created with the same name, then the original command
will become uninstalled, and this attribute will be False.
This attribute is read-write, setting this attribute to False will uninstall the command, removing it from the set of available commands. Setting this attribute toTrue will install the command for use. If there is already a Python command withthis name installed, the currently installed command will be uninstalled, and thiscommand installed in its stead.

MICommand.installed

The following code snippet shows how some trivial MI commands can be implemented
in Python:class MIEcho(gdb.MICommand):"""Echo arguments passed to the command."""def __init__(self, name, mode):
self._mode = mode
super(MIEcho, self).__init__(name)def invoke(self, argv):
if self._mode == ’dict’:return { ’dict’: { ’argv’ : argv } }elif self._mode == ’list’:return { ’list’: argv }else:
return { ’string’: ", ".join(argv) }MIEcho("-echo-dict", "dict")
MIEcho("-echo-list", "list")
MIEcho("-echo-string", "string")

The last three lines instantiate the class three times, creating three new gdb/micommands -echo-dict, -echo-list, and -echo-string. Each time a subclass of
gdb.MICommand is instantiated, the new command is automatically registered with gdb.
Depending on how the Python code is read into gdb, you may need to import the gdb
module explicitly.
The following example shows a gdb session in which the above commands have been
added:(gdb)

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(gdb)

Conversely, it is possible to execute gdb/mi commands from Python, with the results being a Python object and not a specially-formatted string. This is done with the
gdb.execute_mi function.

gdb.execute_mi (command [, arg ]. . . )[Function]
Invoke a gdb/mi command. command is the name of the command, a string. The
arguments, arg, are passed to the command. Each argument must also be a string.
This function returns a Python dictionary whose contents reflect the corresponding
GDB/MI command’s output. Refer to the documentation for these commands fordetails. Lists are represented as Python lists, and tuples are represented as Python
dictionaries.
If the command fails, it will raise a Python exception.

Here is how this works using the commands from the example above:(gdb) python print(gdb.execute_mi("-echo-dict", "abc", "def", "ghi")){’dict’: {’argv’: [’abc’, ’def’, ’ghi’]}}(gdb) python print(gdb.execute_mi("-echo-list", "abc", "def", "ghi")){’list’: [’abc’, ’def’, ’ghi’]}(gdb) python print(gdb.execute_mi("-echo-string", "abc", "def", "ghi")){’string’: ’abc, def, ghi’}23.3.2.23 gdb/mi Notifications In Python
It is possible to emit gdb/mi notifications from Python. Use the gdb.notify_mi function
to do that.

gdb.notify_mi (name [, data])[Function]
Emit a gdb/mi asynchronous notification. name is the name of the notification,
consisting of alphanumeric characters and a hyphen (-). data is any additional data
to be emitted with the notification, passed as a Python dictionary. This argument is
optional. The dictionary is converted to a gdb/mi result records (see Section 27.4.2[GDB/MI Output Syntax], page 593) the same way as result of Python MI command(see Section 23.3.2.22 [GDB/MI Commands In Python], page 467).
If data is None then no additional values are emitted.

While using existing notification names (see Section 27.7.3 [GDB/MI Async Records],
page 598) with gdb.notify_mi is allowed, users are encouraged to prefix user-defined notification with a hyphen (-) to avoid possible conflict. gdb will never introduce notification
starting with hyphen.
Here is how to emit =-connection-removed whenever a connection to remote GDB
server is closed (see Section 23.3.2.38 [Connections In Python], page 499):
def notify_connection_removed(event):

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data = {"id": event.connection.num, "type": event.connection.type}gdb.notify_mi("-connection-removed", data)

gdb.events.connection_removed.connect(notify_connection_removed)Then, each time a connection is closed, there will be a notification on MI channel:=-connection-removed,id="1",type="remote"23.3.2.24 Parameters In Python
You can implement new gdb parameters using Python. A new parameter is implemented
as an instance of the gdb.Parameter class.
Parameters are exposed to the user via the set and show commands. See Section 3.6[Help], page 29.
There are many parameters that already exist and can be set in gdb. Two examples are:set follow fork and set charset. Setting these parameters influences certain behavior in
gdb. Similarly, you can define parameters that can be used to influence behavior in custom
Python scripts and commands.

Parameter.__init__ (name, command class, parameter class [,enum sequence])[Function]

The object initializer for Parameter registers the new parameter with gdb. Thisinitializer is normally invoked from the subclass’ own __init__ method.
name is the name of the new parameter. If name consists of multiple words, thenthe initial words are looked for as prefix parameters. An example of this can beillustrated with the set print set of parameters. If name is print foo, then print
will be searched as the prefix parameter. In this case the parameter can subsequently
be accessed in gdb as set print foo.
If name consists of multiple words, and no prefix parameter group can be found, an
exception is raised.
command class should be one of the ‘COMMAND_’ constants (see Section 23.3.2.21 [CLI
Commands In Python], page 463). This argument tells gdb how to categorize thenew parameter in the help system.
parameter class should be one of the ‘PARAM_’ constants defined below. This argument
tells gdb the type of the new parameter; this information is used for input validationand completion.
If parameter class is PARAM_ENUM, then enum sequence must be a sequence of strings.
These strings represent the possible values for the parameter.
If parameter class is not PARAM_ENUM, then the presence of a fourth argument willcause an exception to be thrown.
The help text for the new parameter includes the Python documentation string fromthe parameter’s class, if there is one. If there is no documentation string, a default
value is used. The documentation string is included in the output of the parameters
help set and help show commands, and should be written taking this into account.

Chapter 23: Extending gdb

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If this attribute exists, and is a string, then its value is used as the first part of thehelp text for this parameter’s set command. The second part of the help text istaken from the documentation string for the parameter’s class, if there is one.
The value of set_doc should give a brief summary specific to the set action, this text
is only displayed when the user runs the help set command for this parameter. The
class documentation should be used to give a fuller description of what the parameter
does, this text is displayed for both the help set and help show commands.
The set_doc value is examined when Parameter.__init__ is invoked; subsequentchanges have no effect.

Parameter.set_doc[Variable]
If this attribute exists, and is a string, then its value is used as the first part of thehelp text for this parameter’s show command. The second part of the help text istaken from the documentation string for the parameter’s class, if there is one.
The value of show_doc should give a brief summary specific to the show action, thistext is only displayed when the user runs the help show command for this parameter.
The class documentation should be used to give a fuller description of what the parameter does, this text is displayed for both the help set and help show commands.
The show_doc value is examined when Parameter.__init__ is invoked; subsequentchanges have no effect.

Parameter.show_doc[Variable]
The value attribute holds the underlying value of the parameter. It can be read andassigned to just as any other attribute. gdb does validation when assignments are
made.

Parameter.value

There are two methods that may be implemented in any Parameter class. These are:Parameter.get_set_string (self)[Function]
If this method exists, gdb will call it when a parameter’s value has been changed
via the set API (for example, set foo off). The value attribute has already been
populated with the new value and may be used in output. This method must returna string. If the returned string is not empty, gdb will present it to the user.
If this method raises the gdb.GdbError exception (see Section 23.3.2.3 [Exception
Handling], page 410), then gdb will print the exception’s string and the set command
will fail. Note, however, that the value attribute will not be reset in this case. So,
if your parameter must validate values, it should store the old value internally andreset the exposed value, like so:class ExampleParam (gdb.Parameter):def __init__ (self, name):
super (ExampleParam, self).__init__ (name,gdb.COMMAND_DATA,
gdb.PARAM_BOOLEAN)
self.value = True
self.saved_value = Truedef validate(self):
return False
def get_set_string (self):

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if not self.validate():self.value = self.saved_value
raise gdb.GdbError(’Failed to validate’)self.saved_value = self.value
return ""Parameter.get_show_string (self, svalue)[Function]
gdb will call this method when a parameter’s show API has been invoked (for example, show foo). The argument svalue receives the string representation of thecurrent value. This method must return a string.

When a new parameter is defined, its type must be specified. The available types are
represented by constants defined in the gdb module:
gdb.PARAM_BOOLEAN
The value is a plain boolean. The Python boolean values, True and False are
the only valid values.
gdb.PARAM_AUTO_BOOLEAN
The value has three possible states: true, false, and ‘auto’. In Python, true andfalse are represented using boolean constants, and ‘auto’ is represented using
None.
gdb.PARAM_UINTEGER
The value is an unsigned integer. The value of None should be interpreted tomean “unlimited” (literal ’unlimited’ can also be used to set that value), andthe value of 0 is reserved and should not be used.
gdb.PARAM_INTEGER
The value is a signed integer. The value of None should be interpreted to mean
“unlimited” (literal ’unlimited’ can also be used to set that value), and thevalue of 0 is reserved and should not be used.
gdb.PARAM_STRING
The value is a string. When the user modifies the string, any escape sequences,such as ‘\t’, ‘\f’, and octal escapes, are translated into corresponding charactersand encoded into the current host charset.
gdb.PARAM_STRING_NOESCAPE
The value is a string. When the user modifies the string, escapes are passed
through untranslated.
gdb.PARAM_OPTIONAL_FILENAME
The value is a either a filename (a string), or None.
gdb.PARAM_FILENAME
The value is a filename. This is just like PARAM_STRING_NOESCAPE, but uses filenames for completion.
gdb.PARAM_ZINTEGER
The value is a signed integer. This is like PARAM_INTEGER, except that 0 isallowed and the value of None is not supported.

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gdb.PARAM_ZUINTEGER
The value is an unsigned integer. This is like PARAM_UINTEGER, except that 0
is allowed and the value of None is not supported.
gdb.PARAM_ZUINTEGER_UNLIMITEDThe value is a signed integer. This is like PARAM_INTEGER including that thevalue of None should be interpreted to mean “unlimited” (literal ’unlimited’
can also be used to set that value), except that 0 is allowed, and the value
cannot be negative, except the special value -1 is returned for the setting of“unlimited”.
gdb.PARAM_ENUM
The value is a string, which must be one of a collection string constants provided
when the parameter is created.

23.3.2.25 Writing new convenience functions
You can implement new convenience functions (see Section 10.12 [Convenience Vars],
page 171) in Python. A convenience function is an instance of a subclass of the class
gdb.Function.

Function.__init__ (name)[Function]
The initializer for Function registers the new function with gdb. The argumentname is the name of the function, a string. The function will be visible to the user
as a convenience variable of type internal function, whose name is the same as thegiven name.
The documentation for the new function is taken from the documentation string forthe new class.

Function.invoke (*args)[Function]
When a convenience function is evaluated, its arguments are converted to instances of
gdb.Value, and then the function’s invoke method is called. Note that gdb does notpredetermine the arity of convenience functions. Instead, all available arguments are
passed to invoke, following the standard Python calling convention. In particular, aconvenience function can have default values for parameters without ill effect.

The return value of this method is used as its value in the enclosing expression. If an
ordinary Python value is returned, it is converted to a gdb.Value following the usual
rules.
The following code snippet shows how a trivial convenience function can be implemented
in Python:class Greet (gdb.Function):"""Return string to greet someone.
Takes a name as argument."""def __init__ (self):
super (Greet, self).__init__ ("greet")def invoke (self, name):
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Greet ()The last line instantiates the class, and is necessary to trigger the registration of thefunction with gdb. Depending on how the Python code is read into gdb, you may need toimport the gdb module explicitly.
Now you can use the function in an expression:(gdb) print $greet("Bob")$1 = "Hello, Bob!"

23.3.2.26 Program Spaces In Python
A program space, or progspace, represents a symbolic view of an address space. It consistsof all of the objfiles of the program. See Section 23.3.2.27 [Objfiles In Python], page 476. See
Section 4.9 [Inferiors Connections and Programs], page 42, for more details about program
spaces.
The following progspace-related functions are available in the gdb module:

gdb.current_progspace ()[Function]
This function returns the program space of the currently selected inferior. See
Section 4.9 [Inferiors Connections and Programs], page 42. This is identical to
gdb.selected_inferior().progspace (see Section 23.3.2.17 [Inferiors In Python],page 449) and is included for historical compatibility.

gdb.progspaces ()[Function]

Return a sequence of all the progspaces currently known to gdb.
Each progspace is represented by an instance of the gdb.Progspace class.
[Variable]
The file name, as a string, of the main symbol file (from which debug symbols havebeen loaded) for the progspace, e.g. the argument to the symbol-file or file commands.
If there is no main symbol table currently loaded, then this attribute will be None.

Progspace.filename[Variable]
The gdb.Objfile representing the main symbol file (from which debug symbols havebeen loaded) for the gdb.Progspace. This is the symbol file set by the symbol-fileor file commands.
This will be the gdb.Objfile representing Progspace.filename when
Progspace.filename is not None.
If there is no main symbol table currently loaded, then this attribute will be None.
If the Progspace is invalid, i.e., when Progspace.is_valid() returns False, thenattempting to access this attribute will raise a RuntimeError exception.

Progspace.symbol_file[Variable]
The file name, as a string, of the executable file in use by this program space. The
executable file is the file that gdb will invoke in order to start an inferior when usinga native target. The file name within this attribute is updated by the exec-file andfile commands.

Progspace.executable_filename

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If no executable is currently set within this Progspace then this attribute contains
None.
If the Progspace is invalid, i.e., when Progspace.is_valid() returns False, thenattempting to access this attribute will raise a RuntimeError exception.
[Variable]
The pretty_printers attribute is a list of functions. It is used to look up prettyprinters. A Value is passed to each function in order; if the function returns None,then the search continues. Otherwise, the return value should be an object which isused to format the value. See Section 23.3.2.6 [Pretty Printing API], page 424, formore information.

Progspace.pretty_printers[Variable]
The type_printers attribute is a list of type printer objects. See Section 23.3.2.9[Type Printing API], page 429, for more information.

Progspace.type_printers[Variable]
The frame_filters attribute is a dictionary of frame filter objects.
See
Section 23.3.2.10 [Frame Filter API], page 430, for more information.

Progspace.frame_filters[Variable]
The missing_debug_handlers attribute is a list of the missing debug handler objects for this program space. See Section 23.3.2.41 [Missing Debug Info In Python],page 511, for more information.

Progspace.missing_debug_handlers

A program space has the following methods:

Progspace.block_for_pc (pc)

[Function]
Return the innermost gdb.Block containing the given pc value. If the block cannot
be found for the pc value specified, the function will return None.

Progspace.find_pc_line (pc)

[Function]
Return the gdb.Symtab_and_line object corresponding to the pc value. See
Section 23.3.2.31 [Symbol Tables In Python], page 489. If an invalid value of pc
is passed as an argument, then the symtab and line attributes of the returned
gdb.Symtab_and_line object will be None and 0 respectively.

Progspace.is_valid ()[Function]
Returns True if the gdb.Progspace object is valid, False if not. A gdb.Progspace
object can become invalid if the program space file it refers to is not referenced byany inferior. All other gdb.Progspace methods will throw an exception if it is invalid
at the time the method is called.

Progspace.objfiles ()[Function]
Return a sequence of all the objfiles referenced by this program space. See
Section 23.3.2.27 [Objfiles In Python], page 476.

Progspace.solib_name (address)[Function]
Return the name of the shared library holding the given address as a string, or None.

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Progspace.objfile_for_address (address)[Function]
Return the gdb.Objfile holding the given address, or None if no objfile covers it.

One may add arbitrary attributes to gdb.Progspace objects in the usual Python way.
This is useful if, for example, one needs to do some extra record keeping associated withthe program space.
See [choosing attribute names], page 451, for guidance on selecting a suitable name for
new attributes.
In this contrived example, we want to perform some processing when an objfile witha certain symbol is loaded, but we only want to do this once because it is expensive. To
achieve this we record the results with the program space because we can’t predict when
the desired objfile will be loaded.
(gdb) python
def clear_objfiles_handler(event):
event.progspace.expensive_computation = Nonedef expensive(symbol):"""A mock routine to perform an "expensive" computation on symbol."""print ("Computing the answer to the ultimate question ...")
return 42
def new_objfile_handler(event):
objfile = event.new_objfile
progspace = objfile.progspace
if not hasattr(progspace, ’expensive_computation’) or \progspace.expensive_computation is None:# We use ’main’ for the symbol to keep the example simple.
# Note: There’s no current way to constrain the lookup# to one objfile.
symbol = gdb.lookup_global_symbol(’main’)
if symbol is not None:progspace.expensive_computation = expensive(symbol)
gdb.events.clear_objfiles.connect(clear_objfiles_handler)
gdb.events.new_objfile.connect(new_objfile_handler)end(gdb) file /tmp/hello
Reading symbols from /tmp/hello...
Computing the answer to the ultimate question ...
(gdb) python print(gdb.current_progspace().expensive_computation)42(gdb) runStarting program: /tmp/hello
Hello.
[Inferior 1 (process 4242) exited normally]

23.3.2.27 Objfiles In Python
gdb loads symbols for an inferior from various symbol-containing files (see Section 18.1
[Files], page 291). These include the primary executable file, any shared libraries used by
the inferior, and any separate debug info files (see Section 18.3 [Separate Debug Files],page 300). gdb calls these symbol-containing files objfiles.
The following objfile-related functions are available in the gdb module:

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gdb.current_objfile ()[Function]
When auto-loading a Python script (see Section 23.3.3 [Python Auto-loading],
page 513), gdb sets the “current objfile” to the corresponding objfile. This function
returns the current objfile. If there is no current objfile, this function returns None.

gdb.objfiles ()[Function]
Return a sequence of objfiles referenced by the current program space.
See Section 23.3.2.27 [Objfiles In Python], page 476, and Section 23.3.2.26[Progspaces In Python], page 474.
This is identical to gdb.selected_
inferior().progspace.objfiles() and is included for historical compatibility.

gdb.lookup_objfile (name [, by build id])

[Function]
Look up name, a file name or build ID, in the list of objfiles for the current program
space (see Section 23.3.2.26 [Progspaces In Python], page 474). If the objfile is notfound throw the Python ValueError exception.
If name is a relative file name, then it will match any source file name with the same
trailing components. For example, if name is ‘gcc/expr.c’, then it will match source
file name of /build/trunk/gcc/expr.c, but not /build/trunk/libcpp/expr.c or/build/trunk/gcc/x-expr.c.
If by build id is provided and is True then name is the build ID of the objfile. Otherwise, name is a file name. This is supported only on some operating systems, notably
those which use the ELF format for binary files and the gnu Binutils. For more details about this feature, see the description of the --build-id command-line option
in Section “Command Line Options” in The GNU Linker.

Each objfile is represented by an instance of the gdb.Objfile class.

Objfile.filename[Variable]

The file name of the objfile as a string, with symbolic links resolved.
The value is None if the objfile is no longer valid. See the gdb.Objfile.is_valid
method, described below.

Objfile.username[Variable]

The file name of the objfile as specified by the user as a string.
The value is None if the objfile is no longer valid. See the gdb.Objfile.is_valid
method, described below.
[Variable]
An objfile often comes from an ordinary file, but in some cases it may be constructedfrom the contents of memory. This attribute is True for file-backed objfiles, and False
for other kinds.

Objfile.is_file[Variable]
For separate debug info objfiles this is the corresponding gdb.Objfile object thatdebug info is being provided for. Otherwise this is None. Separate debug info objfiles are added with the gdb.Objfile.add_separate_debug_file method, described
below.

Objfile.owner

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The build ID of the objfile as a string. If the objfile does not have a build ID thenthe value is None.
This is supported only on some operating systems, notably those which use the ELF
format for binary files and the gnu Binutils. For more details about this feature, see
the description of the --build-id command-line option in Section “Command Line
Options” in The GNU Linker.

Objfile.build_id[Variable]
The containing program space of the objfile as a gdb.Progspace object. See
Section 23.3.2.26 [Progspaces In Python], page 474.

Objfile.progspace[Variable]
The pretty_printers attribute is a list of functions. It is used to look up prettyprinters. A Value is passed to each function in order; if the function returns None,then the search continues. Otherwise, the return value should be an object which isused to format the value. See Section 23.3.2.6 [Pretty Printing API], page 424, formore information.

Objfile.pretty_printers[Variable]
The type_printers attribute is a list of type printer objects. See Section 23.3.2.9[Type Printing API], page 429, for more information.

Objfile.type_printers[Variable]
The frame_filters attribute is a dictionary of frame filter objects.
See
Section 23.3.2.10 [Frame Filter API], page 430, for more information.

Objfile.frame_filters

One may add arbitrary attributes to gdb.Objfile objects in the usual Python way.
This is useful if, for example, one needs to do some extra record keeping associated withthe objfile.
See [choosing attribute names], page 451, for guidance on selecting a suitable name for
new attributes.
In this contrived example we record the time when gdb loaded the objfile.
(gdb) python
import datetime
def new_objfile_handler(event):# Set the time_loaded attribute of the new objfile.
event.new_objfile.time_loaded = datetime.datetime.today()gdb.events.new_objfile.connect(new_objfile_handler)end(gdb) file ./hello
Reading symbols from ./hello...
(gdb) python print(gdb.objfiles()[0].time_loaded)
2014-10-09 11:41:36.770345

A gdb.Objfile object has the following methods:

Objfile.is_valid ()[Function]
Returns True if the gdb.Objfile object is valid, False if not. A gdb.Objfile object
can become invalid if the object file it refers to is not loaded in gdb any longer. Allother gdb.Objfile methods will throw an exception if it is invalid at the time themethod is called.

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Objfile.add_separate_debug_file (file)[Function]
Add file to the list of files that gdb will search for debug information for the objfile.
This is useful when the debug info has been removed from the program and stored
in a separate file. gdb has built-in support for finding separate debug info files (seeSection 18.3 [Separate Debug Files], page 300), but if the file doesn’t live in one of
the standard places that gdb searches then this function can be used to add a debug
info file from a different place.

Objfile.lookup_global_symbol (name [, domain])[Function]
Search for a global symbol named name in this objfile. Optionally, the search scope
can be restricted with the domain argument. The domain argument must be a domain
constant defined in the gdb module and described in Section 23.3.2.30 [Symbols In
Python], page 484. This function is similar to gdb.lookup_global_symbol, exceptthat the search is limited to this objfile.
The result is a gdb.Symbol object or None if the symbol is not found.

Objfile.lookup_static_symbol (name [, domain])[Function]
Like Objfile.lookup_global_symbol, but searches for a global symbol with static
linkage named name in this objfile.

23.3.2.28 Accessing inferior stack frames from Python
When the debugged program stops, gdb is able to analyze its call stack (see Section 8.1[Stack frames], page 113). The gdb.Frame class represents a frame in the stack. A
gdb.Frame object is only valid while its corresponding frame exists in the inferior’s stack.
If you try to use an invalid frame object, gdb will throw a gdb.error exception (seeSection 23.3.2.3 [Exception Handling], page 410).
Two gdb.Frame objects can be compared for equality with the == operator, like:(gdb) python print gdb.newest_frame() == gdb.selected_frame ()True

The following frame-related functions are available in the gdb module:

gdb.selected_frame ()[Function]
Return the selected frame object. (see Section 8.3 [Selecting a Frame], page 117).

gdb.newest_frame ()[Function]

Return the newest frame object for the selected thread.

gdb.frame_stop_reason_string (reason)[Function]
Return a string explaining the reason why gdb stopped unwinding frames, as expressed by the given reason code (an integer, see the unwind_stop_reason method
further down in this section).
[Function]
gdb internally keeps a cache of the frames that have been unwound. This function
invalidates this cache.
This function should not generally be called by ordinary Python code. It is documented for the sake of completeness.

gdb.invalidate_cached_frames

A gdb.Frame object has the following methods:

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Frame.is_valid ()[Function]
Returns true if the gdb.Frame object is valid, false if not. A frame object can become
invalid if the frame it refers to doesn’t exist anymore in the inferior. All gdb.Frame
methods will throw an exception if it is invalid at the time the method is called.

Frame.name ()[Function]

Returns the function name of the frame, or None if it can’t be obtained.

Frame.architecture ()[Function]
Returns the gdb.Architecture object corresponding to the frame’s architecture. See
Section 23.3.2.36 [Architectures In Python], page 497.

Frame.type ()[Function]

Returns the type of the frame. The value can be one of:
gdb.NORMAL_FRAME
An ordinary stack frame.
gdb.DUMMY_FRAME
A fake stack frame that was created by gdb when performing an inferior
function call.
gdb.INLINE_FRAME
A frame representing an inlined function. The function was inlined into
a gdb.NORMAL_FRAME that is older than this one.
gdb.TAILCALL_FRAME
A frame representing a tail call. See Section 11.2 [Tail Call Frames],
page 196.
gdb.SIGTRAMP_FRAME
A signal trampoline frame. This is the frame created by the OS when it
calls into a signal handler.
gdb.ARCH_FRAME
A fake stack frame representing a cross-architecture call.
gdb.SENTINEL_FRAME
This is like gdb.NORMAL_FRAME, but it is only used for the newest frame.

Frame.unwind_stop_reason ()[Function]
Return an integer representing the reason why it’s not possible to find more frames
toward the outermost frame. Use gdb.frame_stop_reason_string to convert thevalue returned by this function to a string. The value can be one of:
gdb.FRAME_UNWIND_NO_REASON
No particular reason (older frames should be available).
gdb.FRAME_UNWIND_NULL_ID
The previous frame’s analyzer returns an invalid result. This is no longer
used by gdb, and is kept only for backward compatibility.
gdb.FRAME_UNWIND_OUTERMOSTThis frame is the outermost.

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gdb.FRAME_UNWIND_UNAVAILABLE
Cannot unwind further, because that would require knowing the valuesof registers or memory that have not been collected.
gdb.FRAME_UNWIND_INNER_ID
This frame ID looks like it ought to belong to a NEXT frame, but we
got it for a PREV frame. Normally, this is a sign of unwinder failure. It
could also indicate stack corruption.
gdb.FRAME_UNWIND_SAME_ID
This frame has the same ID as the previous one. That means that unwinding further would almost certainly give us another frame with exactly thesame ID, so break the chain. Normally, this is a sign of unwinder failure.
It could also indicate stack corruption.
gdb.FRAME_UNWIND_NO_SAVED_PC
The frame unwinder did not find any saved PC, but we needed one tounwind further.
gdb.FRAME_UNWIND_MEMORY_ERROR
The frame unwinder caused an error while trying to access memory.
gdb.FRAME_UNWIND_FIRST_ERROR
Any stop reason greater or equal to this value indicates some kind oferror. This special value facilitates writing code that tests for errors in
unwinding in a way that will work correctly even if the list of the othervalues is modified in future gdb versions. Using it, you could write:
reason = gdb.selected_frame().unwind_stop_reason ()reason_str = gdb.frame_stop_reason_string (reason)
if reason >= gdb.FRAME_UNWIND_FIRST_ERROR:
print ("An error occurred: %s" % reason_str)

Frame.pc ()[Function]

Returns the frame’s resume address.

Frame.block ()[Function]
Return the frame’s code block. See Section 23.3.2.29 [Blocks In Python], page 482. If
the frame does not have a block – for example, if there is no debugging information
for the code in question – then this will throw an exception.

Frame.function ()[Function]
Return the symbol for the function corresponding to this frame. See Section 23.3.2.30[Symbols In Python], page 484.

Frame.older ()[Function]
Return the frame that called this frame. If this is the oldest frame, return None.

Frame.newer ()[Function]
Return the frame called by this frame. If this is the newest frame, return None.

Frame.find_sal ()[Function]
Return the frame’s symtab and line object. See Section 23.3.2.31 [Symbol Tables In
Python], page 489.

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Frame.read_register (register)[Function]
Return the value of register in this frame. Returns a Gdb.Value object. Throws
an exception if register does not exist. The register argument must be one of thefollowing:
1. A string that is the name of a valid register (e.g., ’sp’ or ’rax’).
2. A gdb.RegisterDescriptor object (see Section 23.3.2.37 [Registers In Python],page 498).
3. A gdb internal, platform specific number. Using these numbers is supported forhistoric reasons, but is not recommended as future changes to gdb could change
the mapping between numbers and the registers they represent, breaking any
Python code that uses the platform-specific numbers. The numbers are usuallyfound in the corresponding platform-tdep.h file in the gdb source tree.

Using a string to access registers will be slightly slower than the other two methods
as gdb must look up the mapping between name and internal register number. If
performance is critical consider looking up and caching a gdb.RegisterDescriptor
object.

Frame.read_var (variable [, block])[Function]
Return the value of variable in this frame. If the optional argument block is provided,search for the variable from that block; otherwise start at the frame’s current block(which is determined by the frame’s current program counter). The variable argument
must be a string or a gdb.Symbol object; block must be a gdb.Block object.

Frame.select ()[Function]
Set this frame to be the selected frame. See Chapter 8 [Examining the Stack],
page 113.

Frame.static_link ()[Function]
In some languages (e.g., Ada, but also a GNU C extension), a nested function canaccess the variables in the outer scope. This is done via a “static link”, which is areference from the nested frame to the appropriate outer frame.
This method returns this frame’s static link frame, if one exists. If there is no staticlink, this method returns None.

Frame.level ()[Function]
Return an integer, the stack frame level for this frame. See Section 8.1 [Stack Frames],
page 113.

Frame.language ()[Function]

Return a string, the source language for this frame.

23.3.2.29 Accessing blocks from Python
In gdb, symbols are stored in blocks. A block corresponds roughly to a scope in the sourcecode. Blocks are organized hierarchically, and are represented individually in Python as agdb.Block. Blocks rely on debugging information being available.
A frame has a block. Please see Section 23.3.2.28 [Frames In Python], page 479, for amore in-depth discussion of frames.

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The outermost block is known as the global block. The global block typically holds
public global variables and functions.
The block nested just inside the global block is the static block. The static block typicallyholds file-scoped variables and functions.
gdb provides a method to get a block’s superblock, but there is currently no way to
examine the sub-blocks of a block, or to iterate over all the blocks in a symbol table (seeSection 23.3.2.31 [Symbol Tables In Python], page 489).
Here is a short example that should help explain blocks:/* This is in the global block.
int global;*//* This is in the static block.
static int file_scope;*//* ’function’ is in the global block, and ’argument’ isin a block nested inside of ’function’. */int function (int argument){/* ’local’ is in a block inside ’function’. It may or may
not be in the same block as ’argument’. */int local;{/* ’inner’ is in a block whose superblock is the one holding’local’. */int inner;/* If this call is expanded by the compiler, you may see
a nested block here whose function is ’inline_function’and whose superblock is the one holding ’inner’. */inline_function ();}}A gdb.Block is iterable. The iterator returns the symbols (see Section 23.3.2.30 [Symbols
In Python], page 484) local to the block. Python programs should not assume that a
specific block object will always contain a given symbol, since changes in gdb features andinfrastructure may cause symbols move across blocks in a symbol table. You can also use
Python’s dictionary syntax to access variables in this block, e.g.:
symbol = some_block[’variable’]# symbol is of type gdb.Symbol

The following block-related functions are available in the gdb module:

gdb.block_for_pc (pc)

[Function]
Return the innermost gdb.Block containing the given pc value. If the block cannot
be found for the pc value specified, the function will return None. This is identical to gdb.current_progspace().block_for_pc(pc) and is included for historicalcompatibility.

A gdb.Block object has the following methods:

Block.is_valid ()[Function]
Returns True if the gdb.Block object is valid, False if not. A block object canbecome invalid if the block it refers to doesn’t exist anymore in the inferior. All other484

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gdb.Block methods will throw an exception if it is invalid at the time the method iscalled. The block’s validity is also checked during iteration over symbols of the block.
A gdb.Block object has the following attributes:

Block.start[Variable]

The start address of the block. This attribute is not writable.
[Variable]
One past the last address that appears in the block. This attribute is not writable.

Block.end[Variable]
The name of the block represented as a gdb.Symbol. If the block is not named, thenthis attribute holds None. This attribute is not writable.
For ordinary function blocks, the superblock is the static block. However, you shouldnote that it is possible for a function block to have a superblock that is not the static
block – for instance this happens for an inlined function.

Block.function[Variable]
The block containing this block. If this parent block does not exist, this attributeholds None. This attribute is not writable.

Block.superblock

Block.global_block[Variable]

The global block associated with this block. This attribute is not writable.

Block.static_block[Variable]

The static block associated with this block. This attribute is not writable.
[Variable]
True if the gdb.Block object is a global block, False if not. This attribute is notwritable.

Block.is_global[Variable]
True if the gdb.Block object is a static block, False if not. This attribute is notwritable.

Block.is_static

23.3.2.30 Python representation of Symbols
gdb represents every variable, function and type as an entry in a symbol table. See
Chapter 16 [Examining the Symbol Table], page 263. Similarly, Python represents thesesymbols in gdb with the gdb.Symbol object.
The following symbol-related functions are available in the gdb module:

gdb.lookup_symbol (name [, block [, domain]])[Function]
This function searches for a symbol by name. The search scope can be restricted tothe parameters defined in the optional domain and block arguments.
name is the name of the symbol. It must be a string. The optional block argument
restricts the search to symbols visible in that block. The block argument must be a
gdb.Block object. If omitted, the block for the current frame is used. The optional
domain argument restricts the search to the domain type. The domain argument

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must be a domain constant defined in the gdb module and described later in thischapter.
The result is a tuple of two elements. The first element is a gdb.Symbol object orNone if the symbol is not found. If the symbol is found, the second element is True if
the symbol is a field of a method’s object (e.g., this in C++), otherwise it is False.
If the symbol is not found, the second element is False.

gdb.lookup_global_symbol (name [, domain])[Function]
This function searches for a global symbol by name. The search scope can be restricted
to by the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument
restricts the search to the domain type. The domain argument must be a domain
constant defined in the gdb module and described later in this chapter.
The result is a gdb.Symbol object or None if the symbol is not found.

gdb.lookup_static_symbol (name [, domain])[Function]
This function searches for a global symbol with static linkage by name. The searchscope can be restricted to by the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument
restricts the search to the domain type. The domain argument must be a domain
constant defined in the gdb module and described later in this chapter.
The result is a gdb.Symbol object or None if the symbol is not found.
Note that this function will not find function-scoped static variables. To look upsuch variables, iterate over the variables of the function’s gdb.Block and check thatblock.addr_class is gdb.SYMBOL_LOC_STATIC.
There can be multiple global symbols with static linkage with the same name. Thisfunction will only return the first matching symbol that it finds. Which symbol
is found depends on where gdb is currently stopped, as gdb will first search formatching symbols in the current object file, and then search all other object files. If
the application is not yet running then gdb will search all object files in the order
they appear in the debug information.

gdb.lookup_static_symbols (name [, domain])[Function]
Similar to gdb.lookup_static_symbol, this function searches for global symbols withstatic linkage by name, and optionally restricted by the domain argument. However,this function returns a list of all matching symbols found, not just the first one.
name is the name of the symbol. It must be a string. The optional domain argument
restricts the search to the domain type. The domain argument must be a domain
constant defined in the gdb module and described later in this chapter.
The result is a list of gdb.Symbol objects which could be empty if no matching
symbols were found.
Note that this function will not find function-scoped static variables. To look upsuch variables, iterate over the variables of the function’s gdb.Block and check thatblock.addr_class is gdb.SYMBOL_LOC_STATIC.

A gdb.Symbol object has the following attributes:

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The type of the symbol or None if no type is recorded. This attribute is represented asa gdb.Type object. See Section 23.3.2.5 [Types In Python], page 418. This attributeis not writable.

Symbol.type[Variable]
The symbol table in which the symbol appears. This attribute is represented as a
gdb.Symtab object. See Section 23.3.2.31 [Symbol Tables In Python], page 489. This
attribute is not writable.

Symbol.symtab[Variable]
The line number in the source code at which the symbol was defined. This is an
integer.

Symbol.line

Symbol.name[Variable]

The name of the symbol as a string. This attribute is not writable.
[Variable]
The name of the symbol, as used by the linker (i.e., may be mangled). This attributeis not writable.

Symbol.linkage_name[Variable]
The name of the symbol in a form suitable for output. This is either name or linkage_
name, depending on whether the user asked gdb to display demangled or manglednames.

Symbol.print_name[Variable]
The address class of the symbol. This classifies how to find the value of a symbol.
Each address class is a constant defined in the gdb module and described later in thischapter.

Symbol.addr_class[Variable]
This is True if evaluating this symbol’s value requires a frame (see Section 23.3.2.28[Frames In Python], page 479) and False otherwise. Typically, local variables will
require a frame, but other symbols will not.

Symbol.needs_frame

Symbol.is_argument[Variable]

True if the symbol is an argument of a function.

Symbol.is_constant[Variable]

True if the symbol is a constant.

Symbol.is_function[Variable]

True if the symbol is a function or a method.
[Variable]
True if the symbol is a variable, as opposed to something like a function or type.
Note that this also returns False for arguments.

Symbol.is_variable

A gdb.Symbol object has the following methods:

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Symbol.is_valid ()[Function]
Returns True if the gdb.Symbol object is valid, False if not. A gdb.Symbol object
can become invalid if the symbol it refers to does not exist in gdb any longer. Allother gdb.Symbol methods will throw an exception if it is invalid at the time themethod is called.

Symbol.value ([frame])[Function]
Compute the value of the symbol, as a gdb.Value. For functions, this computes theaddress of the function, cast to the appropriate type. If the symbol requires a framein order to compute its value, then frame must be given. If frame is not given, or ifframe is invalid, then this method will throw an exception.

The available domain categories in gdb.Symbol are represented as constants in the gdb
module:gdb.SYMBOL_UNDEF_DOMAIN
This is used when a domain has not been discovered or none of the following
domains apply. This usually indicates an error either in the symbol information
or in gdb’s handling of symbols.
gdb.SYMBOL_VAR_DOMAIN
This domain contains variables.
gdb.SYMBOL_FUNCTION_DOMAIN
This domain contains functions.
gdb.SYMBOL_TYPE_DOMAIN
This domain contains types. In a C-like language, types using a tag (the nameappearing after a struct, union, or enum keyword) will not appear here; inother languages, all types are in this domain.
gdb.SYMBOL_STRUCT_DOMAIN
This domain holds struct, union and enum tag names. This domain is onlyused for C-like languages. For example, in this code:
struct type_one { int x; };typedef struct type_one type_two;

Here type_one will be in SYMBOL_STRUCT_DOMAIN, but type_two will be in
SYMBOL_TYPE_DOMAIN.
gdb.SYMBOL_LABEL_DOMAIN
This domain contains names of labels (for gotos).
gdb.SYMBOL_MODULE_DOMAIN
This domain contains names of Fortran module types.
gdb.SYMBOL_COMMON_BLOCK_DOMAIN
This domain contains names of Fortran common blocks.
When searching for a symbol, the desired domain constant can be passed verbatim to
the lookup function. For example:
symbol = gdb.lookup_symbol ("name", domain=gdb.SYMBOL_VAR_DOMAIN)

For more complex searches, there is a corresponding set of constants, each named after
one of the preceding constants, but with the ‘SEARCH’ prefix replacing the ‘SYMBOL’ prefix;

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for example, SEARCH_LABEL_DOMAIN. These may be or’d together to form a search constant,e.g.:symbol = gdb.lookup_symbol ("name",domain=gdb.SEARCH_VAR_DOMAIN | gdb.SEARCH_TYPE_DOMAIN)

The available address class categories in gdb.Symbol are represented as constants in the
gdb module:
gdb.SYMBOL_LOC_UNDEF
If this is returned by address class, it indicates an error either in the symbol
information or in gdb’s handling of symbols.
gdb.SYMBOL_LOC_CONST
Value is constant int.
gdb.SYMBOL_LOC_STATIC
Value is at a fixed address.
gdb.SYMBOL_LOC_REGISTER
Value is in a register.
gdb.SYMBOL_LOC_ARG
Value is an argument. This value is at the offset stored within the symbol inside
the frame’s argument list.
gdb.SYMBOL_LOC_REF_ARG
Value address is stored in the frame’s argument list. Just like LOC_ARG exceptthat the value’s address is stored at the offset, not the value itself.
gdb.SYMBOL_LOC_REGPARM_ADDRValue is a specified register. Just like LOC_REGISTER except the register holds
the address of the argument instead of the argument itself.
gdb.SYMBOL_LOC_LOCAL
Value is a local variable.
gdb.SYMBOL_LOC_TYPEDEF
Value not used. Symbols in the domain SYMBOL_STRUCT_DOMAIN all have thisclass.
gdb.SYMBOL_LOC_LABEL
Value is a label.
gdb.SYMBOL_LOC_BLOCK
Value is a block.
gdb.SYMBOL_LOC_CONST_BYTES
Value is a byte-sequence.
gdb.SYMBOL_LOC_UNRESOLVED
Value is at a fixed address, but the address of the variable has to be determinedfrom the minimal symbol table whenever the variable is referenced.
gdb.SYMBOL_LOC_OPTIMIZED_OUT
The value does not actually exist in the program.

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gdb.SYMBOL_LOC_COMPUTED
The value’s address is a computed location.
gdb.SYMBOL_LOC_COMMON_BLOCK
The value’s address is a symbol. This is only used for Fortran common blocks.

23.3.2.31 Symbol table representation in Python
Access to symbol table data maintained by gdb on the inferior is exposed to Python via two
objects: gdb.Symtab_and_line and gdb.Symtab. Symbol table and line data for a frame
is returned from the find_sal method in gdb.Frame object. See Section 23.3.2.28 [Frames
In Python], page 479.
For more information on gdb’s symbol table management, see Chapter 16 [Examining
the Symbol Table], page 263, for more information.
A gdb.Symtab_and_line object has the following attributes:[Variable]
The symbol table object (gdb.Symtab) for this frame. This attribute is not writable.

Symtab_and_line.symtab[Variable]
Indicates the start of the address range occupied by code for the current source line.
This attribute is not writable.

Symtab_and_line.pc[Variable]
Indicates the end of the address range occupied by code for the current source line.
This attribute is not writable.

Symtab_and_line.last[Variable]
Indicates the current line number for this object. This attribute is not writable.

Symtab_and_line.line

A gdb.Symtab_and_line object has the following methods:

Symtab_and_line.is_valid ()[Function]
Returns True if the gdb.Symtab_and_line object is valid, False if not. A
gdb.Symtab_and_line object can become invalid if the Symbol table and line object
it refers to does not exist in gdb any longer. All other gdb.Symtab_and_line
methods will throw an exception if it is invalid at the time the method is called.

A gdb.Symtab object has the following attributes:

Symtab.filename[Variable]

The symbol table’s source filename. This attribute is not writable.
[Variable]
The symbol table’s backing object file. See Section 23.3.2.27 [Objfiles In Python],page 476. This attribute is not writable.

Symtab.objfile[Variable]
The name and possibly version number of the program that compiled the code in
the symbol table. The contents of this string is up to the compiler. If no producer
information is available then None is returned. This attribute is not writable.

Symtab.producer

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A gdb.Symtab object has the following methods:

Symtab.is_valid ()[Function]
Returns True if the gdb.Symtab object is valid, False if not. A gdb.Symtab object
can become invalid if the symbol table it refers to does not exist in gdb any longer.
All other gdb.Symtab methods will throw an exception if it is invalid at the time themethod is called.

Symtab.fullname ()[Function]

Return the symbol table’s source absolute file name.

Symtab.global_block ()[Function]
Return the global block of the underlying symbol table. See Section 23.3.2.29 [Blocks
In Python], page 482.

Symtab.static_block ()[Function]
Return the static block of the underlying symbol table. See Section 23.3.2.29 [Blocks
In Python], page 482.

Symtab.linetable ()[Function]
Return the line table associated with the symbol table. See Section 23.3.2.32 [LineTables In Python], page 490.

23.3.2.32 Manipulating line tables using Python
Python code can request and inspect line table information from a symbol table that is
loaded in gdb. A line table is a mapping of source lines to their executable locations
in memory. To acquire the line table information for a particular symbol table, use thelinetable function (see Section 23.3.2.31 [Symbol Tables In Python], page 489).
A gdb.LineTable is iterable. The iterator returns LineTableEntry objects that correspond to the source line and address for each line table entry. LineTableEntry objects
have the following attributes:[Variable]
The source line number for this line table entry. This number corresponds to theactual line of source. This attribute is not writable.

LineTableEntry.line[Variable]
The address that is associated with the line table entry where the executable code forthat source line resides in memory. This attribute is not writable.

LineTableEntry.pc

As there can be multiple addresses for a single source line, you may receive multiple
LineTableEntry objects with matching line attributes, but with different pc attributes.
The iterator is sorted in ascending pc order. Here is a small example illustrating iteratingover a line table.
symtab = gdb.selected_frame().find_sal().symtab
linetable = symtab.linetable()for line in linetable:
print ("Line: "+str(line.line)+" Address: "+hex(line.pc))

This will have the following output:
Line: 33 Address: 0x4005c8L

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Line: 37 Address: 0x4005caL
Line: 39 Address: 0x4005d2L
Line: 40 Address: 0x4005f8L
Line: 42 Address: 0x4005ffL
Line: 44 Address: 0x400608L
Line: 42 Address: 0x40060cL
Line: 45 Address: 0x400615L

In addition to being able to iterate over a LineTable, it also has the following directaccess methods:

LineTable.line (line)[Function]
Return a Python Tuple of LineTableEntry objects for any entries in the line table
for the given line, which specifies the source code line. If there are no entries for thatsource code line, the Python None is returned.

LineTable.has_line (line)[Function]
Return a Python Boolean indicating whether there is an entry in the line table forthis source line. Return True if an entry is found, or False if not.

LineTable.source_lines ()[Function]
Return a Python List of the source line numbers in the symbol table. Only lines
with executable code locations are returned. The contents of the List will just be
the source line entries represented as Python Long values.

23.3.2.33 Manipulating breakpoints using Python
Python code can manipulate breakpoints via the gdb.Breakpoint class.
A breakpoint can be created using one of the two forms of the gdb.Breakpoint constructor. The first one accepts a string like one would pass to the break (see Section 5.1.1[Setting Breakpoints], page 58) and watch (see Section 5.1.2 [Setting Watchpoints], page 66)
commands, and can be used to create both breakpoints and watchpoints. The second accepts separate Python arguments similar to Section 9.2.2 [Explicit Locations], page 129,and can only be used to create breakpoints.

Breakpoint.__init__ (spec [, type ][, wp class ][, internal ][,temporary ][, qualified ])[Function]

Create a new breakpoint according to spec, which is a string naming the location ofa breakpoint, or an expression that defines a watchpoint. The string should describe
a location in a format recognized by the break command (see Section 5.1.1 [Setting
Breakpoints], page 58) or, in the case of a watchpoint, by the watch command (seeSection 5.1.2 [Setting Watchpoints], page 66).
The optional type argument specifies the type of the breakpoint to create, as defined
below.
The optional wp class argument defines the class of watchpoint to create, if type is
gdb.BP_WATCHPOINT. If wp class is omitted, it defaults to gdb.WP_WRITE.
The optional internal argument allows the breakpoint to become invisible to the user.
The breakpoint will neither be reported when created, nor will it be listed in the
output from info breakpoints (but will be listed with the maint info breakpoints
command).

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The optional temporary argument makes the breakpoint a temporary breakpoint.
Temporary breakpoints are deleted after they have been hit. Any further access to
the Python breakpoint after it has been hit will result in a runtime error (as thatbreakpoint has now been automatically deleted).
The optional qualified argument is a boolean that allows interpreting the function
passed in spec as a fully-qualified name. It is equivalent to break’s -qualified
flag (see Section 9.2.1 [Linespec Locations], page 127, and Section 9.2.2 [Explicit
Locations], page 129).

Breakpoint.__init__ ([ source ][, function ][, label ][, line ], ][internal ][, temporary ][, qualified ])[Function]

This second form of creating a new breakpoint specifies the explicit location (seeSection 9.2.2 [Explicit Locations], page 129) using keywords. The new breakpoint
will be created in the specified source file source, at the specified function, label and
line.
internal, temporary and qualified have the same usage as explained previously.
The available types are represented by constants defined in the gdb module:
gdb.BP_BREAKPOINT
Normal code breakpoint.
gdb.BP_HARDWARE_BREAKPOINT
Hardware assisted code breakpoint.
gdb.BP_WATCHPOINT
Watchpoint breakpoint.
gdb.BP_HARDWARE_WATCHPOINT
Hardware assisted watchpoint.
gdb.BP_READ_WATCHPOINT
Hardware assisted read watchpoint.
gdb.BP_ACCESS_WATCHPOINT
Hardware assisted access watchpoint.
gdb.BP_CATCHPOINT
Catchpoint. Currently, this type can’t be used when creating gdb.Breakpoint
objects, but will be present in gdb.Breakpoint objects reported from
gdb.BreakpointEvents (see Section 23.3.2.18 [Events In Python], page 451).
The available watchpoint types are represented by constants defined in the gdb module:
gdb.WP_READ
Read only watchpoint.
gdb.WP_WRITE
Write only watchpoint.
gdb.WP_ACCESS
Read/Write watchpoint.

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Breakpoint.stop (self)[Function]
The gdb.Breakpoint class can be sub-classed and, in particular, you may choose
to implement the stop method. If this method is defined in a sub-class of
gdb.Breakpoint, it will be called when the inferior reaches any location of abreakpoint which instantiates that sub-class. If the method returns True, the inferior
will be stopped at the location of the breakpoint, otherwise the inferior will continue.
If there are multiple breakpoints at the same location with a stop method, each one
will be called regardless of the return status of the previous. This ensures that allstop methods have a chance to execute at that location. In this scenario if one of themethods returns True but the others return False, the inferior will still be stopped.
You should not alter the execution state of the inferior (i.e., step, next, etc.), alter thecurrent frame context (i.e., change the current active frame), or alter, add or delete
any breakpoint. As a general rule, you should not alter any data within gdb or theinferior at this time.
Example stop implementation:
class MyBreakpoint (gdb.Breakpoint):
def stop (self):
inf_val = gdb.parse_and_eval("foo")
if inf_val == 3:
return True
return False

Breakpoint.is_valid ()[Function]
Return True if this Breakpoint object is valid, False otherwise. A Breakpoint
object can become invalid if the user deletes the breakpoint. In this case, the object
still exists, but the underlying breakpoint does not. In the cases of watchpoint scope,
the watchpoint remains valid even if execution of the inferior leaves the scope of thatwatchpoint.

Breakpoint.delete ()[Function]
Permanently deletes the gdb breakpoint.
This also invalidates the Python
Breakpoint object. Any further access to this object’s attributes or methods willraise an error.

[Variable]
This attribute is True if the breakpoint is enabled, and False otherwise. This attribute is writable. You can use it to enable or disable the breakpoint.

Breakpoint.enabled[Variable]
This attribute is True if the breakpoint is silent, and False otherwise. This attributeis writable.

Breakpoint.silent

Note that a breakpoint can also be silent if it has commands and the first commandis silent. This is not reported by the silent attribute.
[Variable]
This attribute is True if the breakpoint is pending, and False otherwise. See
Section 5.1.1 [Set Breaks], page 58. This attribute is read-only.

Breakpoint.pending

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If the breakpoint is thread-specific (see Section 5.5.4 [Thread-Specific Breakpoints],
page 96), this attribute holds the thread’s global id. If the breakpoint is not threadspecific, this attribute is None. This attribute is writable.
Only one of Breakpoint.thread or Breakpoint.inferior can be set to a valid id
at any time, that is, a breakpoint can be thread specific, or inferior specific, but not
both.

Breakpoint.thread[Variable]
If the breakpoint is inferior-specific (see Section 4.9.1 [Inferior-Specific Breakpoints],
page 46), this attribute holds the inferior’s id. If the breakpoint is not inferior-specific,
this attribute is None.
This attribute can be written for breakpoints of type gdb.BP_BREAKPOINT and
gdb.BP_HARDWARE_BREAKPOINT.

Breakpoint.inferior[Variable]
If the breakpoint is Ada task-specific, this attribute holds the Ada task id. If the
breakpoint is not task-specific (or the underlying language is not Ada), this attribute
is None. This attribute is writable.

Breakpoint.task[Variable]
This attribute holds the ignore count for the breakpoint, an integer. This attributeis writable.

Breakpoint.ignore_count[Variable]
This attribute holds the breakpoint’s number — the identifier used by the user tomanipulate the breakpoint. This attribute is not writable.

Breakpoint.number[Variable]
This attribute holds the breakpoint’s type — the identifier used to determine theactual breakpoint type or use-case. This attribute is not writable.

Breakpoint.type[Variable]
This attribute tells whether the breakpoint is visible to the user when set, or whenthe ‘info breakpoints’ command is run. This attribute is not writable.

Breakpoint.visible[Variable]
This attribute indicates whether the breakpoint was created as a temporary breakpoint. Temporary breakpoints are automatically deleted after that breakpoint has
been hit. Access to this attribute, and all other attributes and functions other than
the is_valid function, will result in an error after the breakpoint has been hit (as it
has been automatically deleted). This attribute is not writable.

Breakpoint.temporary[Variable]
This attribute holds the hit count for the breakpoint, an integer. This attribute is
writable, but currently it can only be set to zero.

Breakpoint.hit_count[Variable]
This attribute holds the location of the breakpoint, as specified by the user. It is astring. If the breakpoint does not have a location (that is, it is a watchpoint) the
attribute’s value is None. This attribute is not writable.

Breakpoint.location

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Get the most current list of breakpoint locations that are inserted for this breakpoint,with elements of type gdb.BreakpointLocation (described below). This functionality matches that of the info breakpoint command (see Section 5.1.1 [Set Breaks],
page 58), in that it only retrieves the most current list of locations, thus the list itself
when returned is not updated behind the scenes. This attribute is not writable.

Breakpoint.locations[Variable]
This attribute holds a breakpoint expression, as specified by the user. It is a string.
If the breakpoint does not have an expression (the breakpoint is not a watchpoint)
the attribute’s value is None. This attribute is not writable.

Breakpoint.expression[Variable]
This attribute holds the condition of the breakpoint, as specified by the user. It isa string. If there is no condition, this attribute’s value is None. This attribute is
writable.

Breakpoint.condition[Variable]
This attribute holds the commands attached to the breakpoint. If there are commands, this attribute’s value is a string holding all the commands, separated by
newlines. If there are no commands, this attribute is None. This attribute is writable.

Breakpoint.commands

Breakpoint Locations
A breakpoint location is one of the actual places where a breakpoint has been set, represented in the Python API by the gdb.BreakpointLocation type. This type is neverinstantiated by the user directly, but is retrieved from Breakpoint.locations which returns a list of breakpoint locations where it is currently set. Breakpoint locations canbecome invalid if new symbol files are loaded or dynamically loaded libraries are closed.
Accessing the attributes of an invalidated breakpoint location will throw a RuntimeError
exception. Access the Breakpoint.locations attribute again to retrieve the new and valid
breakpoints location list.
[Variable]
This attribute returns the source file path and line number where this location wasset. The type of the attribute is a tuple of string and long. If the breakpoint location
doesn’t have a source location, it returns None, which is the case for watchpoints
and catchpoints. This will throw a RuntimeError exception if the location has been
invalidated. This attribute is not writable.

BreakpointLocation.source[Variable]
This attribute returns the address where this location was set. This attribute isof type long. This will throw a RuntimeError exception if the location has been
invalidated. This attribute is not writable.

BreakpointLocation.address[Variable]
This attribute holds the value for whether or not this location is enabled. This
attribute is writable (boolean). This will throw a RuntimeError exception if thelocation has been invalidated.

BreakpointLocation.enabled

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This attribute holds a reference to the gdb.Breakpoint owner object, from which
this gdb.BreakpointLocation was retrieved from. This will throw a RuntimeError
exception if the location has been invalidated. This attribute is not writable.

BreakpointLocation.owner[Variable]
This attribute gets the name of the function where this location was set. If no function
could be found this attribute returns None. This will throw a RuntimeError exception
if the location has been invalidated. This attribute is not writable.

BreakpointLocation.function[Variable]
This attribute gets the full name of where this location was set. If no full name could
be found, this attribute returns None. This will throw a RuntimeError exception if
the location has been invalidated. This attribute is not writable.

BreakpointLocation.fullname[Variable]
This attribute gets the thread groups it was set in. It returns a List of the threadgroup ID’s. This will throw a RuntimeError exception if the location has been invalidated. This attribute is not writable.

BreakpointLocation.thread_groups

23.3.2.34 Finish Breakpoints
A finish breakpoint is a temporary breakpoint set at the return address of a frame, basedon the finish command. gdb.FinishBreakpoint extends gdb.Breakpoint. The underlying breakpoint will be disabled and deleted when the execution will run out of the breakpoint scope (i.e. Breakpoint.stop or FinishBreakpoint.out_of_scope triggered). Finish
breakpoints are thread specific and must be create with the right thread selected.

FinishBreakpoint.__init__ ([frame] [, internal])[Function]
Create a finish breakpoint at the return address of the gdb.Frame object frame.
If frame is not provided, this defaults to the newest frame. The optional internalargument allows the breakpoint to become invisible to the user. See Section 23.3.2.33[Breakpoints In Python], page 491, for further details about this argument.

FinishBreakpoint.out_of_scope (self)[Function]
In some circumstances (e.g. longjmp, C++ exceptions, gdb return command, . . . ), afunction may not properly terminate, and thus never hit the finish breakpoint. When
gdb notices such a situation, the out_of_scope callback will be triggered.
You may want to sub-class gdb.FinishBreakpoint and override this method:class MyFinishBreakpoint (gdb.FinishBreakpoint)
def stop (self):
print ("normal finish")return Truedef out_of_scope ():print ("abnormal finish")[Variable]
When gdb is stopped at a finish breakpoint and the frame used to build the
gdb.FinishBreakpoint object had debug symbols, this attribute will contain a
gdb.Value object corresponding to the return value of the function. The value will

FinishBreakpoint.return_value

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be None if the function return type is void or if the return value was not computable.
This attribute is not writable.

23.3.2.35 Python representation of lazy strings
A lazy string is a string whose contents is not retrieved or encoded until it is needed.
A gdb.LazyString is represented in gdb as an address that points to a region of memory, an encoding that will be used to encode that region of memory, and a length to delimit
the region of memory that represents the string. The difference between a gdb.LazyString
and a string wrapped within a gdb.Value is that a gdb.LazyString will be treated differently by gdb when printing. A gdb.LazyString is retrieved and encoded during printing,while a gdb.Value wrapping a string is immediately retrieved and encoded on creation.
A gdb.LazyString object has the following functions:

LazyString.value ()[Function]
Convert the gdb.LazyString to a gdb.Value. This value will point to the string
in memory, but will lose all the delayed retrieval, encoding and handling that gdb
applies to a gdb.LazyString.

[Variable]
This attribute holds the address of the string. This attribute is not writable.

LazyString.address[Variable]
This attribute holds the length of the string in characters. If the length is -1, thenthe string will be fetched and encoded up to the first null of appropriate width. This
attribute is not writable.

LazyString.length[Variable]
This attribute holds the encoding that will be applied to the string when the string
is printed by gdb. If the encoding is not set, or contains an empty string, then gdb
will select the most appropriate encoding when the string is printed. This attributeis not writable.

LazyString.encoding[Variable]
This attribute holds the type that is represented by the lazy string’s type. For a lazystring this is a pointer or array type. To resolve this to the lazy string’s character
type, use the type’s target method. See Section 23.3.2.5 [Types In Python], page 418.
This attribute is not writable.

LazyString.type

23.3.2.36 Python representation of architectures
gdb uses architecture specific parameters and artifacts in a number of its various computations. An architecture is represented by an instance of the gdb.Architecture class.
A gdb.Architecture class has the following methods:

Architecture.name ()[Function]

Return the name (string value) of the architecture.

Architecture.disassemble (start pc [, end pc [, count]])[Function]
Return a list of disassembled instructions starting from the memory address start pc.
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the returned list. If both the optional arguments end pc and count are specified,then a list of at most count disassembled instructions whose start address falls in theclosed memory address interval from start pc to end pc are returned. If end pc is
not specified, but count is specified, then count number of instructions starting fromthe address start pc are returned. If count is not specified but end pc is specified,then all instructions whose start address falls in the closed memory address intervalfrom start pc to end pc are returned. If neither end pc nor count are specified, thena single instruction at start pc is returned. For all of these cases, each element of the
returned list is a Python dict with the following string keys:
addr

The value corresponding to this key is a Python long integer capturing
the memory address of the instruction.

asm

The value corresponding to this key is a string value which represents the
instruction with assembly language mnemonics. The assembly language
flavor used is the same as that specified by the current CLI variabledisassembly-flavor. See Section 9.6 [Machine Code], page 135.

lengthThe value corresponding to this key is the length (integer value) of the
instruction in bytes.

Architecture.integer_type (size [, signed])[Function]
This function looks up an integer type by its size, and optionally whether or not it issigned.
size is the size, in bits, of the desired integer type. Only certain sizes are currently
supported: 0, 8, 16, 24, 32, 64, and 128.
If signed is not specified, it defaults to True. If signed is False, the returned typewill be unsigned.
If the indicated type cannot be found, this function will throw a ValueError exception.

Architecture.registers ([ reggroup ])[Function]
Return a gdb.RegisterDescriptorIterator (see Section 23.3.2.37 [Registers In
Python], page 498) for all of the registers in reggroup, a string that is the nameof a register group. If reggroup is omitted, or is the empty string, then the registergroup ‘all’ is assumed.

Architecture.register_groups ()[Function]
Return a gdb.RegisterGroupsIterator (see Section 23.3.2.37 [Registers In Python],page 498) for all of the register groups available for the gdb.Architecture.

23.3.2.37 Registers In Python
Python code can request from a gdb.Architecture information about the set of registers available (see [Architecture.registers], page 498). The register information is returned as a gdb.RegisterDescriptorIterator, which is an iterator that in turn returns
gdb.RegisterDescriptor objects.
A gdb.RegisterDescriptor does not provide the value of a register (see [Frame.read_register], page 482, for reading a register’s value), instead the RegisterDescriptor is a
way to discover which registers are available for a particular architecture.

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A gdb.RegisterDescriptor has the following read-only properties:

RegisterDescriptor.name[Variable]

The name of this register.
It is also possible to lookup a register descriptor based on its name using the following
gdb.RegisterDescriptorIterator function:

RegisterDescriptorIterator.find (name)[Function]
Takes name as an argument, which must be a string, and returns a
gdb.RegisterDescriptor for the register with that name, or None if there is no
register with that name.

Python code can also request from a gdb.Architecture information about the set ofregister groups available on a given architecture (see [Architecture.register_groups],
page 498).
Every register can be a member of zero or more register groups. Some register groups areused internally within gdb to control things like which registers must be saved when calling
into the program being debugged (see Section 17.5 [Calling Program Functions], page 281).
Other register groups exist to allow users to easily see related sets of registers in commands
like info registers (see [info registers reggroup], page 179).
The register groups information is returned as a gdb.RegisterGroupsIterator, which
is an iterator that in turn returns gdb.RegisterGroup objects.
A gdb.RegisterGroup object has the following read-only properties:

RegisterGroup.name[Variable]

A string that is the name of this register group.

23.3.2.38 Connections In Python
gdb lets you run and debug multiple programs in a single session. Each program being
debugged has a connection, the connection describes how gdb controls the program being
debugged. Examples of different connection types are ‘native’ and ‘remote’. See Section 4.9[Inferiors Connections and Programs], page 42.
Connections in gdb are represented as instances of gdb.TargetConnection, or as one ofits sub-classes. To get a list of all connections use gdb.connections (see [gdb.connections],
page 408).
To get the connection for a single gdb.Inferior read its gdb.Inferior.connection
attribute (see [gdb.Inferior.connection], page 449).
Currently there is only a single sub-class of gdb.TargetConnection,
gdb.RemoteTargetConnection, however, additional sub-classes may be added infuture releases of gdb. As a result you should avoid writing code like:conn = gdb.selected_inferior().connection
if type(conn) is gdb.RemoteTargetConnection:
print("This is a remote target connection")as this may fail when more connection types are added. Instead, you should write:
conn = gdb.selected_inferior().connection
if isinstance(conn, gdb.RemoteTargetConnection):
print("This is a remote target connection")

A gdb.TargetConnection has the following method:

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TargetConnection.is_valid ()[Function]
Return True if the gdb.TargetConnection object is valid, False if not. A
gdb.TargetConnection will become invalid if the connection no longer exists within
gdb, this might happen when no inferiors are using the connection, but could bedelayed until the user replaces the current target.
Reading any of the gdb.TargetConnection properties will throw an exception if theconnection is invalid.

A gdb.TargetConnection has the following read-only properties:[Variable]
An integer assigned by gdb to uniquely identify this connection. This is the samevalue as displayed in the ‘Num’ column of the info connections command output(see Section 4.9 [info connections], page 42).

TargetConnection.num[Variable]
A string that describes what type of connection this is. This string will be one ofthe valid names that can be passed to the target command (see Section 19.2 [target
command], page 311).

TargetConnection.type[Variable]
A string that gives a short description of this target type. This is the same string thatis displayed in the ‘Description’ column of the info connection command output(see Section 4.9 [info connections], page 42).

TargetConnection.description[Variable]
An optional string that gives additional information about this connection. This
attribute can be None if there are no additional details for this connection.
An example of a connection type that might have additional details is the ‘remote’connection, in this case the details string can contain the ‘hostname:port’ that wasused to connect to the remote target.

TargetConnection.details

The gdb.RemoteTargetConnection class is a sub-class of gdb.TargetConnection,and is used to represent ‘remote’ and ‘extended-remote’ connections. In addition to
the attributes and methods available from the gdb.TargetConnection base class, a
gdb.RemoteTargetConnection has the following method:

RemoteTargetConnection.send_packet (packet)[Function]
This method sends packet to the remote target and returns the response. The packet
should either be a bytes object, or a Unicode string.
If packet is a Unicode string, then the string is encoded to a bytes object using theascii codec. If the string can’t be encoded then an UnicodeError is raised.
If packet is not a bytes object, or a Unicode string, then a TypeError is raised. If
packet is empty then a ValueError is raised.
The response is returned as a bytes object. If it is known that the response can be
represented as a string then this can be decoded from the buffer. For example, if it
is known that the response is an ascii string:
remote_connection.send_packet("some_packet").decode("ascii")

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The prefix, suffix, and checksum (as required by the remote serial protocol) are automatically added to the outgoing packet, and removed from the incoming packet
before the contents of the reply are returned.
This is equivalent to the maintenance packet command (see [maint packet],page 759).

23.3.2.39 Implementing new TUI windows
New TUI (see Chapter 25 [TUI], page 579) windows can be implemented in Python.

gdb.register_window_type (name, factory)[Function]
Because TUI windows are created and destroyed depending on the layout the user
chooses, new window types are implemented by registering a factory function with
gdb.
name is the name of the new window. It’s an error to try to replace one of thebuilt-in windows, but other window types can be replaced. The name should matchthe regular expression [a-zA-Z][-_.a-zA-Z0-9]*, it is an error to try and create awindow with an invalid name.
function is a factory function that is called to create the TUI window. This is calledwith a single argument of type gdb.TuiWindow, described below. It should return an
object that implements the TUI window protocol, also described below.

As mentioned above, when a factory function is called, it is passed an object of typegdb.TuiWindow. This object has these methods and attributes:

TuiWindow.is_valid ()[Function]
This method returns True when this window is valid. When the user changes the TUI
layout, windows no longer visible in the new layout will be destroyed. At this point,
the gdb.TuiWindow will no longer be valid, and methods (and attributes) other thanis_valid will throw an exception.
When the TUI is disabled using tui disable (see Section 25.5 [tui disable], page 582)
the window is hidden rather than destroyed, but is_valid will still return False andother methods (and attributes) will still throw an exception.

TuiWindow.width[Variable]

This attribute holds the width of the window. It is not writable.

TuiWindow.height[Variable]

This attribute holds the height of the window. It is not writable.
[Variable]
This attribute holds the window’s title, a string. This is normally displayed above
the window. This attribute can be modified.

TuiWindow.title

TuiWindow.erase ()[Function]

Remove all the contents of the window.

TuiWindow.write (string [, full window])[Function]
Write string to the window. string can contain ANSI terminal escape styling sequences; gdb will translate these as appropriate for the terminal.

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If the full window parameter is True, then string contains the full contents of thewindow. This is similar to calling erase before write, but avoids the flickering.
The factory function that you supply should return an object conforming to the TUI
window protocol. These are the methods that can be called on this object, which is referred
to below as the “window object”. The methods documented below are optional; if the object
does not implement one of these methods, gdb will not attempt to call it. Additional new
methods may be added to the window protocol in the future. gdb guarantees that they will
begin with a lower-case letter, so you can start implementation methods with upper-caseletters or underscore to avoid any future conflicts.

Window.close ()[Function]
When the TUI window is closed, the gdb.TuiWindow object will be put into an invalid
state. At this time, gdb will call close method on the window object.
After this method is called, gdb will discard any references it holds on this window
object, and will no longer call methods on this object.

Window.render ()[Function]
In some situations, a TUI window can change size. For example, this can happen if
the user resizes the terminal, or changes the layout. When this happens, gdb willcall the render method on the window object.
If your window is intended to update in response to changes in the inferior, you willprobably also want to register event listeners and send output to the gdb.TuiWindow.

Window.hscroll (num)[Function]
This is a request to scroll the window horizontally. num is the amount by whichto scroll, with negative numbers meaning to scroll right. In the TUI model, it isthe viewport that moves, not the contents. A positive argument should cause theviewport to move right, and so the content should appear to move to the left.

Window.vscroll (num)[Function]
This is a request to scroll the window vertically. num is the amount by which toscroll, with negative numbers meaning to scroll backward. In the TUI model, it isthe viewport that moves, not the contents. A positive argument should cause theviewport to move down, and so the content should appear to move up.

Window.click (x, y, button)[Function]
This is called on a mouse click in this window. x and y are the mouse coordinates
inside the window (0-based, from the top left corner), and button specifies whichmouse button was used, whose values can be 1 (left), 2 (middle), or 3 (right).
When TUI mouse events are disabled by turning off the tui mouse-events setting(see [set tui mouse-events], page 586), then click will not be called.

23.3.2.40 Instruction Disassembly In Python
gdb’s builtin disassembler can be extended, or even replaced, using the Python API. The
disassembler related features are contained within the gdb.disassembler module:

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503[class]Disassembly is driven by instances of this class. Each time gdb needs to disassemble
an instruction, an instance of this class is created and passed to a registered disassembler. The disassembler is then responsible for disassembling an instruction andreturning a result.
Instances of this type are usually created within gdb, however, it is possible to createa copy of an instance of this type, see the description of __init__ for more details.
This class has the following properties and methods:

gdb.disassembler.DisassembleInfo[Variable]
A read-only integer containing the address at which gdb wishes to disassemble
a single instruction.

DisassembleInfo.address[Variable]
The gdb.Architecture (see Section 23.3.2.36 [Architectures In Python],page 497) for which gdb is currently disassembling, this property is read-only.

DisassembleInfo.architecture[Variable]
The gdb.Progspace (see Section 23.3.2.26 [Program Spaces In Python],page 474) for which gdb is currently disassembling, this property is read-only.

DisassembleInfo.progspace

DisassembleInfo.is_valid ()[Function]
Returns True if the DisassembleInfo object is valid, False if not. A
DisassembleInfo object will become invalid once the disassembly callfor which the DisassembleInfo was created, has returned. Calling other
DisassembleInfo methods, or accessing DisassembleInfo properties, willraise a RuntimeError exception if it is invalid.

DisassembleInfo.__init__ (info)[Function]
This can be used to create a new DisassembleInfo object that is a copy of
info. The copy will have the same address, architecture, and progspacevalues as info, and will become invalid at the same time as info.
This method exists so that sub-classes of DisassembleInfo can be created,these sub-classes must be initialized as copies of an existing DisassembleInfo
object, but sub-classes might choose to override the read_memory method, andso control what gdb sees when reading from memory (see [builtin disassemble],
page 510).

DisassembleInfo.read_memory (length, offset)[Function]
This method allows the disassembler to read the bytes of the instruction
to be disassembled. The method reads length bytes, starting at offset from
DisassembleInfo.address.
It is important that the disassembler read the instruction bytes using thismethod, rather than reading inferior memory directly, as in some cases gdb
disassembles from an internal buffer rather than directly from inferior memory,
calling this method handles this detail.
Returns a buffer object, which behaves much like an array or a string, justas Inferior.read_memory does (see [Inferior.read memory], page 450). The
length of the returned buffer will always be exactly length.

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If gdb is unable to read the required memory then a gdb.MemoryError exception is raised (see Section 23.3.2.3 [Exception Handling], page 410).
This method can be overridden by a sub-class in order to control what gdb sees
when reading from memory (see [builtin disassemble], page 510). When overriding this method it is important to understand how builtin_disassemble
makes use of this method.
While disassembling a single instruction there could be multiple calls to thismethod, and the same bytes might be read multiple times. Any single callmight only read a subset of the total instruction bytes.
If an implementation of read_memory is unable to read the requested memory
contents, for example, if there’s a request to read from an invalid memory
address, then a gdb.MemoryError should be raised.
Raising a MemoryError inside read_memory does not automatically mean aMemoryError will be raised by builtin_disassemble. It is possible the gdb’s
builtin disassembler is probing to see how many bytes are available. When
read_memory raises the MemoryError the builtin disassembler might be able
to perform a complete disassembly with the bytes it has available, in this casebuiltin_disassemble will not itself raise a MemoryError.
Any other exception type raised in read_memory will propagate back and be
re-raised by builtin_disassemble.

DisassembleInfo.text_part (style, string)[Function]
Create a new DisassemblerTextPart representing a piece of a disassembled
instruction. string should be a non-empty string, and style should be an appropriate style constant (see [Disassembler Style Constants], page 507).
Disassembler parts are used when creating a DisassemblerResult in orderto represent the styling within an instruction (see [DisassemblerResult Class],
page 505).

DisassembleInfo.address_part (address)[Function]
Create a new DisassemblerAddressPart. address is the value of the absoluteaddress this part represents. A DisassemblerAddressPart is displayed as an
absolute address and an associated symbol, the address and symbol are styled
appropriately.

[class]This is a base class from which all user implemented disassemblers must inherit.

gdb.disassembler.Disassembler

Disassembler.__init__ (name)[Function]
The constructor takes name, a string, which should be a short name for thisdisassembler.

Disassembler.__call__ (info)[Function]
The __call__ method must be overridden by sub-classes to perform disassembly. Calling __call__ on this base class will raise a NotImplementedError
exception.

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The info argument is an instance of DisassembleInfo, and describes the instruction that gdb wants disassembling.
If this function returns None, this indicates to gdb that this sub-class doesn’twish to disassemble the requested instruction. gdb will then use its builtin
disassembler to perform the disassembly.
Alternatively, this function can return a DisassemblerResult that represents
the disassembled instruction, this type is described in more detail below.
The __call__ method can raise a gdb.MemoryError exception (seeSection 23.3.2.3 [Exception Handling], page 410) to indicate to gdb that there
was a problem accessing the required memory, this will then be displayed by
gdb within the disassembler output.
Ideally, the only three outcomes from invoking __call__ would be a returnof None, a successful disassembly returned in a DisassemblerResult, or a
MemoryError indicating that there was a problem reading memory.
However, as an implementation of __call__ could fail due to other reasons,e.g. some external resource required to perform disassembly is temporarily unavailable, then, if __call__ raises a GdbError, the exception will be converted
to a string and printed at the end of the disassembly output, the disassembly
request will then stop.
Any other exception type raised by the __call__ method is considered anerror in the user code, the exception will be printed to the error stream according to the set python print-stack setting (see [set python print-stack],
page 402).
[class]This class represents the result of disassembling a single instruction.
Aninstance of this class will be returned from builtin_disassemble (see[builtin disassemble], page 510), and an instance of this class should be returned
from Disassembler.__call__ (see [Disassembler Class], page 504) if an instruction
was successfully disassembled.

gdb.disassembler.DisassemblerResult

It is not possible to sub-class the DisassemblerResult class.
The DisassemblerResult class has the following properties and methods:

DisassemblerResult.__init__ (length, string, parts)[Function]
Initialize an instance of this class, length is the length of the disassembled
instruction in bytes, which must be greater than zero.
Only one of string or parts should be used to initialize a new
DisassemblerResult; the other one should be passed the value None.
Alternatively, the arguments can be passed by name, and the unused argument
can be ignored.

The string argument, if not None, is a non-empty string that represents theentire disassembled instruction. Building a result object using the string argument does not allow for any styling information to be included in the result.
gdb will style the result as a single DisassemblerTextPart with STYLE_TEXT
style (see [Disassembler Styling Parts], page 506).

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The parts argument, if not None, is a non-empty sequence of DisassemblerPart
objects. Each part represents a small part of the disassembled instruction alongwith associated styling information. A result object built using parts can bedisplayed by gdb with full styling information (see [set style disassembler
enabled], page 371).
[Variable]
A read-only property containing the length of the disassembled instruction inbytes, this will always be greater than zero.

DisassemblerResult.length[Variable]
A read-only property containing a non-empty string representing the disassembled instruction. The string is a representation of the disassembled instruction
without any styling information. To see how the instruction will be styled use
the parts property.

DisassemblerResult.string

If this instance was initialized using separate DisassemblerPart objects,
the string property will still be valid. The string value is created byconcatenating the DisassemblerPart.string values of each component part(see [Disassembler Styling Parts], page 506).
[Variable]
A read-only property containing a non-empty sequence of DisassemblerPart
objects. Each DisassemblerPart object contains a small part of the instruction
along with information about how that part should be styled. gdb uses thisinformation to create styled disassembler output (see [set style disassembler
enabled], page 371).

DisassemblerResult.parts

If this instance was initialized using a single string rather than with asequence of DisassemblerPart objects, the parts property will still be valid.
In this case the parts property will hold a sequence containing a single
DisassemblerTextPart object, the string of which will represent the entire
instruction, and the style of which will be STYLE_TEXT.
[class]This is a parent class from which the different part sub-classes inherit. Only instancesof the sub-classes detailed below will be returned by the Python API.

gdb.disassembler.DisassemblerPart

It is not possible to directly create instances of either this parent class, or any of the
sub-classes listed below. Instances of the sub-classes listed below are created by calling
builtin_disassemble (see [builtin disassemble], page 510) and are returned within
the DisassemblerResult object, or can be created by calling the text_part andaddress_part methods on the DisassembleInfo class (see [DisassembleInfo Class],
page 502).
The DisassemblerPart class has a single property:[Variable]
A read-only property that contains a non-empty string representing this part ofthe disassembled instruction. The string within this property doesn’t include
any styling information.

DisassemblerPart.stringChapter 23: Extending gdb

507[class]The DisassemblerTextPart class represents a piece of the disassembled instruction
and the associated style for that piece. Instances of this class can’t be created directly,
instead call DisassembleInfo.text_part to create a new instance of this class (see[DisassembleInfo Class], page 502).

gdb.disassembler.DisassemblerTextPart

As well as the properties of its parent class, the DisassemblerTextPart has thefollowing additional property:[Variable]
A read-only property that contains one of the defined style constants. gdb
will use this style when styling this part of the disassembled instruction (see[Disassembler Style Constants], page 507).

DisassemblerTextPart.style[class]The DisassemblerAddressPart class represents an absolute address within
a disassembled instruction.
Using a DisassemblerAddressPart instead of aDisassemblerTextPart with STYLE_ADDRESS is preferred, gdb will display theaddress as both an absolute address, and will look up a suitable symbol to display
next to the address. Using DisassemblerAddressPart also ensures that user
settings such as set print max-symbolic-offset are respected.

gdb.disassembler.DisassemblerAddressPart

Here is an example of an x86-64 instruction:call

0x401136 <foo>In this instruction the 0x401136 <foo> was generated from a single
DisassemblerAddressPart. The 0x401136 will be styled with STYLE_ADDRESS, andfoo will be styled with STYLE_SYMBOL. The < and > will be styled as STYLE_TEXT.
If the inclusion of the symbol name is not required then a DisassemblerTextPart
with style STYLE_ADDRESS can be used instead.
Instances of this class can’t be created directly, instead call DisassembleInfo.address_
part to create a new instance of this class (see [DisassembleInfo Class], page 502).
As well as the properties of its parent class, the DisassemblerAddressPart has thefollowing additional property:[Variable]
A read-only property that contains the address passed to this object’s __init__
method.

DisassemblerAddressPart.address

The following table lists all of the disassembler styles that are available. gdb maps
these style constants onto its style settings (see Section 22.5 [Output Styling], page 371). In
some cases, several style constants produce the same style settings, and thus will produce
the same visual effect on the screen. This could change in future releases of gdb, so careshould be taken to select the correct style constant to ensure correct output styling in future
releases of gdb.
gdb.disassembler.STYLE_TEXT
This is the default style used by gdb when styling disassembler output. This
style should be used for any parts of the instruction that don’t fit any of theother styles listed below. gdb styles text with this style using its default style.

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gdb.disassembler.STYLE_MNEMONIC
This style is used for styling the primary instruction mnemonic, which usuallyappears at, or near, the start of the disassembled instruction string.
gdb styles text with this style using the disassembler mnemonic style setting.
gdb.disassembler.STYLE_SUB_MNEMONIC
This style is used for styling any sub-mnemonics within a disassembled instruction. A sub-mnemonic is any text within the instruction that controls thefunction of the instruction, but which is disjoint from the primary mnemonic(which will have styled STYLE_MNEMONIC).
As an example, consider this AArch64 instruction:
add w16, w7, w1, lsl #1

The add is the primary instruction mnemonic, and would be given style STYLE_MNEMONIC, while lsl is the sub-mnemonic, and would be given the style STYLE_
SUB_MNEMONIC.
gdb styles text with this style using the disassembler mnemonic style setting.
gdb.disassembler.STYLE_ASSEMBLER_DIRECTIVE
Sometimes a series of bytes doesn’t decode to a valid instruction. In this casethe disassembler may choose to represent the result of disassembling using an
assembler directive, for example:.word 0x1234

In this case, the .word would be give the STYLE_ASSEMBLER_DIRECTIVE style.
An assembler directive is similar to a mnemonic in many ways but is somethingthat is not part of the architecture’s instruction set.
gdb styles text with this style using the disassembler mnemonic style setting.
gdb.disassembler.STYLE_REGISTER
This style is used for styling any text that represents a register name, or register
number, within a disassembled instruction.
gdb styles text with this style using the disassembler register style setting.
gdb.disassembler.STYLE_ADDRESSThis style is used for styling numerical values that represent absolute addresses
within the disassembled instruction.
When creating a DisassemblerTextPart with this style, you should consider
if a DisassemblerAddressPart would be more appropriate. See [Disassembler
Styling Parts], page 506, for a description of what each part offers.
gdb styles text with this style using the disassembler address style setting.
gdb.disassembler.STYLE_ADDRESS_OFFSETThis style is used for styling numerical values that represent offsets to addresses
within the disassembled instruction. A value is considered an address offset
when the instruction itself is going to access memory, and the value is being
used to offset which address is accessed.
For example, an architecture might have an instruction that loads from memory using an address within a register. If that instruction also allowed for anChapter 23: Extending gdb

509

immediate offset to be encoded into the instruction, this would be an addressoffset. Similarly, a branch instruction might jump to an address in a registerplus an address offset that is encoded into the instruction.
gdb styles text with this style using the disassembler immediate style setting.
gdb.disassembler.STYLE_IMMEDIATEUse STYLE_IMMEDIATE for any numerical values within a disassembled instruction when those values are not addresses, address offsets, or register numbers(The styles STYLE_ADDRESS, STYLE_ADDRESS_OFFSET, or STYLE_REGISTER canbe used in those cases).
gdb styles text with this style using the disassembler immediate style setting.
gdb.disassembler.STYLE_SYMBOLThis style is used for styling the textual name of a symbol that is included
within a disassembled instruction. A symbol name is often included next toan absolute address within a disassembled instruction to make it easier for theuser to understand what the address is referring too. For example:
call

0x401136 <foo>

Here foo is the name of a symbol, and should be given the STYLE_SYMBOL style.
Adding symbols next to absolute addresses like this is handled automaticallyby the DisassemblerAddressPart class (see [Disassembler Styling Parts],
page 506).
gdb styles text with this style using the disassembler symbol style setting.
gdb.disassembler.STYLE_COMMENT_START
This style is used to start a line comment in the disassembly output. Unlike
other styles, which only apply to the single DisassemblerTextPiece to which
they are applied, the comment style is sticky, and overrides the style of any
further pieces within this instruction.
This means that, after a STYLE_COMMENT_START piece has been seen, gdb will
apply the comment style until the end of the line, ignoring the specific style
within a piece.
gdb styles text with this style using the disassembler comment style setting.
The following functions are also contained in the gdb.disassembler module:

register_disassembler (disassembler, architecture)[Function]
The disassembler must be a sub-class of gdb.disassembler.Disassembler or None.
The optional architecture is either a string, or the value None. If it is a string,then it should be the name of an architecture known to gdb, as returned either
from gdb.Architecture.name (see [gdb.Architecture.name], page 497), or fromgdb.architecture_names (see [gdb.architecture names], page 408).
The disassembler will be installed for the architecture named by architecture, or if
architecture is None, then disassembler will be installed as a global disassembler for
use by all architectures.
gdb only records a single disassembler for each architecture, and a single global
disassembler. Calling register_disassembler for an architecture, or for the global

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disassembler, will replace any existing disassembler registered for that architecture
value. The previous disassembler is returned.
If disassembler is None then any disassembler currently registered for architecture isderegistered and returned.
When gdb is looking for a disassembler to use, gdb first looks for an architecture
specific disassembler. If none has been registered then gdb looks for a global disassembler (one registered with architecture set to None). Only one disassembler is called
to perform disassembly, so, if there is both an architecture specific disassembler, anda global disassembler registered, it is the architecture specific disassembler that will
be used.
gdb tracks the architecture specific, and global disassemblers separately, so it doesn’t
matter in which order disassemblers are created or registered; an architecture specificdisassembler, if present, will always be used in preference to a global disassembler.
You can use the maint info python-disassemblers command (see [maint info
python-disassemblers], page 756) to see which disassemblers have been registered.

builtin_disassemble (info)[Function]
This function calls back into gdb’s builtin disassembler to disassemble the instruction
identified by info, an instance, or sub-class, of DisassembleInfo.
When the builtin disassembler needs to read memory the read_memory method on
info will be called. By sub-classing DisassembleInfo and overriding the read_memory
method, it is possible to intercept calls to read_memory from the builtin disassembler,
and to modify the values returned.
It is important to understand that, even when DisassembleInfo.read_memory raises
a gdb.MemoryError, it is the internal disassembler itself that reports the memory error
to gdb. The reason for this is that the disassembler might probe memory to see if abyte is readable or not; if the byte can’t be read then the disassembler may choose notto report an error, but instead to disassemble the bytes that it does have available.
If the builtin disassembler is successful then an instance of DisassemblerResult
is returned from builtin_disassemble, alternatively, if something goes wrong, an
exception will be raised.
A MemoryError will be raised if builtin_disassemble is unable to read some memorythat is required in order to perform disassembly correctly.
Any exception that is not a MemoryError, that is raised in a call to read_memory,
will pass through builtin_disassemble, and be visible to the caller.
Finally, there are a few cases where gdb’s builtin disassembler can fail for reasonsthat are not covered by MemoryError. In these cases, a GdbError will be raised. The
contents of the exception will be a string describing the problem the disassembler
encountered.

Here is an example that registers a global disassembler. The new disassembler invokes
the builtin disassembler, and then adds a comment, ## Comment, to each line of disassembly
output:class ExampleDisassembler(gdb.disassembler.Disassembler):
def __init__(self):
super().__init__("ExampleDisassembler")Chapter 23: Extending gdb

511

def __call__(self, info):
result = gdb.disassembler.builtin_disassemble(info)
length = result.length
text = result.string + "\t## Comment"
return gdb.disassembler.DisassemblerResult(length, text)
gdb.disassembler.register_disassembler(ExampleDisassembler())

The following example creates a sub-class of DisassembleInfo in order to intercept theread_memory calls, within read_memory any bytes read from memory have the two 4-bit
nibbles swapped around. This isn’t a very useful adjustment, but serves as an example.
class MyInfo(gdb.disassembler.DisassembleInfo):
def __init__(self, info):super().__init__(info)
def read_memory(self, length, offset):
buffer = super().read_memory(length, offset)
result = bytearray()for b in buffer:v = int.from_bytes(b, ’little’)v = (v << 4) & 0xf0 | (v >> 4)
result.append(v)return memoryview(result)class NibbleSwapDisassembler(gdb.disassembler.Disassembler):
def __init__(self):
super().__init__("NibbleSwapDisassembler")
def __call__(self, info):
info = MyInfo(info)
return gdb.disassembler.builtin_disassemble(info)
gdb.disassembler.register_disassembler(NibbleSwapDisassembler())

23.3.2.41 Missing Debug Info In Python
When gdb encounters a new objfile (see Section 23.3.2.27 [Objfiles In Python], page 476),
e.g. the primary executable, or any shared libraries used by the inferior, gdb will attempt
to load the corresponding debug information for that objfile. The debug information might
be found within the objfile itself, or within a separate objfile which gdb will automaticallylocate and load.
Sometimes though, gdb might not find any debug information for an objfile, in this casethe debugging experience will be restricted.
If gdb fails to locate any debug information for a particular objfile, there is an opportunity for a Python extension to step in. A Python extension can potentially locate themissing debug information using some platform- or project-specific steps, and inform gdb
of its location. Or a Python extension might provide some platform- or project-specificadvice to the user about how to obtain the missing debug information.
A missing debug information Python extension consists of a handler object which has thename and enabled attributes, and implements the __call__ method. When gdb encounters
an objfile for which it is unable to find any debug information, it invokes the __call__method. Full details of how handlers are written can be found below.

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The gdb.missing_debug Module
gdb comes with a gdb.missing_debug module which contains the following class and global
function:[class]MissingDebugHandler is a base class from which user-created handlers can derive,
though it is not required that handlers derive from this class, so long as any user
created handler has the name and enabled attributes, and implements the __call__method.

gdb.missing_debug.MissingDebugHandler

MissingDebugHandler.__init__ (name)[Function]
The name is a string used to reference this missing debug handler within some
gdb commands. Valid names consist of the characters [-_a-zA-Z0-9], creatinga handler with an invalid name raises a ValueError exception.

MissingDebugHandler.__call__ (objfile)[Function]
Sub-classes must override the __call__ method. The objfile argument will be
a gdb.Objfile, this is the objfile for which gdb was unable to find any debug
information.
The return value from the __call__ method indicates what gdb should donext. The possible return values are:• NoneThis indicates that this handler could not help with objfile, gdb should
call any other registered handlers.
• TrueThis indicates that this handler has installed the debug information into
a location where gdb would normally expect to find it when looking forseparate debug information files (see Section 18.3 [Separate Debug Files],page 300). gdb will repeat the normal lookup process, which should now
find the separate debug file.
If gdb still doesn’t find the separate debug information file after this second attempt, then the Python missing debug information handlers are notinvoked a second time, this prevents a badly behaved handler causing gdb
to get stuck in a loop. gdb will continue without any debug informationfor objfile.
• FalseThis indicates that this handler has done everything that it intends to dowith objfile, but no separate debug information can be found. gdb will
not call any other registered handlers for objfile. gdb will continue without
debugging information for objfile.
• A string
The returned string should contain a filename. gdb will not call any further
registered handlers, and will instead load the debug information from thefile identified by the returned filename.

Invoking the __call__ method
NotImplementedError exception.

from

this

base

class

will

raise

a

Chapter 23: Extending gdb

513[Variable]
A read-only attribute which is a string, the name of this handler passed to the__init__ method.

MissingDebugHandler.name[Variable]
A modifiable attribute containing a boolean; when True, the handler is enabled,
and will be used by gdb. When False, the handler has been disabled, and will
not be used.

MissingDebugHandler.enabled

gdb.missing_debug.register_handler (locus, handler,
replace=False)[Function]

Register a new missing debug handler with gdb.
handler is an instance of a sub-class of MissingDebugHandler, or at least an instanceof an object that has the same attributes and methods as MissingDebugHandler.
locus specifies to which handler list to prepend handler. It can be either a
gdb.Progspace (see Section 23.3.2.26 [Progspaces In Python], page 474) or None, inwhich case the handler is registered globally. The newly registered handler will becalled before any other handler from the same locus. Two handlers in the same locus
cannot have the same name, an attempt to add a handler with an already existing
name raises an exception unless replace is True, in which case the old handler isdeleted and the new handler is prepended to the selected handler list.
gdb first calls the handlers for the current program space, and then the globally
registered handlers. As soon as a handler returns a value other than None, no further
handlers are called for this objfile.

23.3.3 Python Auto-loading
When a new object file is read (for example, due to the file command, or because theinferior has loaded a shared library), gdb will look for Python support scripts in several
ways: objfile-gdb.py and .debug_gdb_scripts section. See Section 23.5 [Auto-loading
extensions], page 571.
The auto-loading feature is useful for supplying application-specific debugging commands
and scripts.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be
printed.
set auto-load python-scripts [on|off]
Enable or disable the auto-loading of Python scripts.
show auto-load python-scripts
Show whether auto-loading of Python scripts is enabled or disabled.
info auto-load python-scripts [regexp]
Print the list of all Python scripts that gdb auto-loaded.
Also printed is the list of Python scripts that were mentioned in the .debug_
gdb_scripts section and were either not found (see Section 23.5.2 [dotdebug gdb scripts section], page 573) or were not auto-loaded due to auto-load
safe-path rejection (see Section 22.8 [Auto-loading], page 376). This is useful
because their names are not printed when gdb tries to load them and fails.

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There may be many of them, and printing an error message for each one isproblematic.
If regexp is supplied only Python scripts with matching names are printed.
Example:(gdb) info auto-load python-scripts
Loaded ScriptYes
py-section-script.py
full name: /tmp/py-section-script.py
No
my-foo-pretty-printers.py

When reading an auto-loaded file or script, gdb sets the current objfile. This is available via the gdb.current_objfile function (see Section 23.3.2.27 [Objfiles In Python],page 476). This can be useful for registering objfile-specific pretty-printers and frame-filters.

23.3.4 Python modules
gdb comes with several modules to assist writing Python code.

23.3.4.1 gdb.printing
This module provides a collection of utilities for working with pretty-printers.
PrettyPrinter (name, subprinters=None)
This class specifies the API that makes ‘info pretty-printer’, ‘enablepretty-printer’ and ‘disable pretty-printer’ work.
Pretty-printersshould generally inherit from this class.
SubPrettyPrinter (name)
For printers that handle multiple types, this class specifies the corresponding
API for the subprinters.
RegexpCollectionPrettyPrinter (name)Utility class for handling multiple printers, all recognized via regular expressions. See Section 23.3.2.8 [Writing a Pretty-Printer], page 427, for an example.
FlagEnumerationPrinter (name)A pretty-printer which handles printing of enum values. Unlike gdb’s builtin enum printing, this printer attempts to work properly when there is someoverlap between the enumeration constants. The argument name is the nameof the printer and also the name of the enum type to look up.
register_pretty_printer (obj, printer, replace=False)
Register printer with the pretty-printer list of obj. If replace is True then any
existing copy of the printer is replaced. Otherwise a RuntimeError exception
is raised if a printer with the same name already exists.

23.3.4.2 gdb.types
This module provides a collection of utilities for working with gdb.Type objects.
get_basic_type (type)
Return type with const and volatile qualifiers stripped, and with typedefs andC++ references converted to the underlying type.

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C++ example:
typedef const int const_int;
const_int foo (3);const_int& foo_ref (foo);
int main () { return 0; }Then in gdb:(gdb) start(gdb) python import gdb.types(gdb) python foo_ref = gdb.parse_and_eval("foo_ref")(gdb) python print gdb.types.get_basic_type(foo_ref.type)
int

has_field (type, field)
Return True if type, assumed to be a type with fields (e.g., a structure orunion), has field field.
make_enum_dict (enum_type)
Return a Python dictionary type produced from enum type.
deep_items (type)
Returns a Python iterator similar to the standard gdb.Type.iteritems
method, except that the iterator returned by deep_items will recursively
traverse anonymous struct or union fields. For example:
struct A{
int a;
union {
int b0;
int b1;};};

Then in gdb:(gdb) python import gdb.types(gdb) python struct_a = gdb.lookup_type("struct A")(gdb) python print struct_a.keys (){[’a’, ’’]}
(gdb) python print [k for k,v in gdb.types.deep_items(struct_a)]{[’a’, ’b0’, ’b1’]}

get_type_recognizers ()Return a list of the enabled type recognizers for the current context. Thisis called by gdb during the type-printing process (see Section 23.3.2.9 [TypePrinting API], page 429).
apply_type_recognizers (recognizers, type_obj)
Apply the type recognizers, recognizers, to the type object type obj. If any
recognizer returns a string, return that string. Otherwise, return None. Thisis called by gdb during the type-printing process (see Section 23.3.2.9 [TypePrinting API], page 429).
register_type_printer (locus, printer)
This is a convenience function to register a type printer printer. The printermust implement the type printer protocol. The locus argument is either
a gdb.Objfile, in which case the printer is registered with that objfile; a516

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gdb.Progspace, in which case the printer is registered with that progspace; orNone, in which case the printer is registered globally.
TypePrinterThis is a base class that implements the type printer protocol. Type printers areencouraged, but not required, to derive from this class. It defines a constructor:__init__ (self, name)[Method on TypePrinter]
Initialize the type printer with the given name. The new printer starts
in the enabled state.

23.3.4.3 gdb.prompt
This module provides a method for prompt value-substitution.
substitute_prompt (string)
Return string with escape sequences substituted by values. Some escape sequences take arguments. You can specify arguments inside “{}” immediately
following the escape sequence.
The escape sequences you can pass to this function are:\\Substitute a backslash.

\e

Substitute an ESC character.

\f

Substitute the selected frame; an argument names a frame parameter.

\n

Substitute a newline.

\p

Substitute a parameter’s value; the argument names the parameter.

\r

Substitute a carriage return.

\t

Substitute the selected thread; an argument names a thread parameter.

\v

Substitute the version of GDB.

\w

Substitute the current working directory.

\[

Begin a sequence of non-printing characters. These sequences are
typically used with the ESC character, and are not counted in thestring length. Example: “\[\e[0;34m\](gdb)\[\e[0m\]” will returna blue-colored “(gdb)” prompt where the length is five.

\]End a sequence of non-printing characters.

For example:
substitute_prompt ("frame: \f, args: \p{print frame-arguments}")

will return the string:"frame: main, args: scalars"Chapter 23: Extending gdb

517

23.3.4.4 gdb.ptwrite
This module provides additional functionality for recording programs that make use of the
PTWRITE instruction. PTWRITE is a x86 instruction that allows to write values into the Intel
Processor Trace (see Chapter 7 [Process Record and Replay], page 103). The gcc intrinsics
for it are:void _ptwrite32 (unsigned int a)void _ptwrite64 (unsigned __int64 a)

If an inferior uses the instruction, gdb by default inserts the raw payload value as
auxiliary information into the execution history. Auxiliary information is by default printed
during record instruction-history, record function-call-history, and all stepping
commands, and is accessible in Python as a RecordAuxiliary object (see Section 23.3.2.20[Recordings In Python], page 459).
Sample program:#include <immintrin.h>void
ptwrite64 (unsigned long long value){_ptwrite64 (value);}int
main (void){
ptwrite64 (0x42);
return 0; /* break here.
}*/

gdb output after recording the sample program in pt format:(gdb) record instruction-history 12,14
120x0040074c <ptwrite64+16>:
13[0x42]
14
0x00400751 <ptwrite64+21>:(gdb) record function-call-history
1
main
2
ptwrite64[0x42]
3main

ptwrite %rbx
mov -0x8(%rbp),%rbx

The gdb.ptwrite module allows customizing the default output of PTWRITE auxiliary
information. A custom Python function can be registered as the PTWRITE filter function.
This function will be called with the PTWRITE payload and PC as arguments during trace
decoding. The function can return a string, which will be printed by gdb during the
aforementioned commands, or None, resulting in no output. To register such a filter function,
the user needs to provide a filter factory function, which returns a new filter function object
to be called by gdb.

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register_filter_factory (filter factory)[Function]
Used to register the PTWRITE filter factory. This filter factory can be any callable
object that accepts one argument, the current thread as a gdb.InferiorThread. It
can return None or a callable. This callable is the PTWRITE filter function for the
specified thread. If None is returned by the factory function, the default auxiliary
information will be printed.

get_filter ()Return the currently active PTWRITE filter function.

An example:(gdb) python-interactive>>> class my_filter():...
def __init__(self):...
self.var = 0...
def __call__(self, payload, ip):...
self.var += 1...
return f"counter: {self.var}, ip: {ip:#x}"...
>>> def my_filter_factory(thread):...
if thread.global_num == 1:...
return my_filter()
...
else:
...
return None...
>>> import gdb.ptwrite>>> gdb.ptwrite.register_filter_factory(my_filter_factory)>>>(gdb) record function-call-history 59,64
59
pthread_create@GLIBC_2.2.5
60
job()
61
task(void*)
62
ptwrite64(unsigned long)[counter: 1, ip: 0x401156]
63
task(void*)64
ptwrite32(unsigned int)
[counter: 2, ip: 0x40116c](gdb) info threads* 1
Thread 0x7ffff7fd8740 (LWP 25796) "ptw_threads" task ()at bin/ptwrite/ptw_threads.c:45
2
Thread 0x7ffff6eb8700 (LWP 25797) "ptw_threads" task ()at bin/ptwrite/ptw_threads.c:45(gdb) thread 2[Switching to thread 2 (Thread 0x7ffff6eb8700 (LWP 25797))]#0 task (arg=0x0) at ptwrite_threads.c:45
45
return NULL;[Function]

Chapter 23: Extending gdb

519(gdb) record function-call-history 10,14
10
start_thread11
task(void*)
12
ptwrite64(unsigned long)[0x42]
13
task(void*)
14
ptwrite32(unsigned int)
[0x43]

This gdb feature is dependent on hardware and operating system support and requires
the Intel Processor Trace decoder library in version 2.0.0 or newer.

23.4 Extending gdb using Guile
You can extend gdb using the Guile implementation of the Scheme programming language(http: / / www . gnu . org / software / guile / ). This feature is available only if gdb was
configured using --with-guile.

23.4.1 Guile Introduction
Guile is an implementation of the Scheme programming language and is the GNU project’s
official extension language.
Guile support in gdb follows the Python support in gdb reasonably closely, so concepts
there should carry over. However, some things are done differently where it makes sense.
gdb requires Guile version 3.0, 2.2, or 2.0.
Guile scripts used by gdb should be installed in data-directory/guile, where datadirectory is the data directory as determined at gdb startup (see Section 18.8 [Data Files],page 308). This directory, known as the guile directory, is automatically added to the Guile
Search Path in order to allow the Guile interpreter to locate all scripts installed at thislocation.

23.4.2 Guile Commands
gdb provides two commands for accessing the Guile interpreter:
guile-repl
gr
The guile-repl command can be used to start an interactive Guile prompt or
repl. To return to gdb, type ,q or the EOF character (e.g., Ctrl-D on an empty
prompt). These commands do not take any arguments.
guile [scheme-expression]
gu [scheme-expression]
The guile command can be used to evaluate a Scheme expression.
If given an argument, gdb will pass the argument to the Guile interpreter forevaluation.
(gdb) guile (display (+ 20 3)) (newline)23

The result of the Scheme expression is displayed using normal Guile rules.
(gdb) guile (+ 20 3)
23

If you do not provide an argument to guile, it will act as a multi-line command,
like define. In this case, the Guile script is made up of subsequent command

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Debugging with gdb

lines, given after the guile command. This command list is terminated using
a line containing end. For example:(gdb) guile>(display 23)>(newline)>end
23

It is also possible to execute a Guile script from the gdb interpreter:
source script-name
The script name must end with ‘.scm’ and gdb must be configured to recognize
the script language based on filename extension using the script-extension
setting. See Chapter 23 [Extending GDB], page 391.
guile (load "script-name")
This method uses the load Guile function. It takes a string argument that is
the name of the script to load. See the Guile documentation for a descriptionof this function. (see Section “Loading” in GNU Guile Reference Manual).

23.4.3 Guile API
You can get quick online help for gdb’s Guile API by issuing the command help guile,
or by issuing the command ,help from an interactive Guile session. Furthermore, most
Guile procedures provided by gdb have doc strings which can be obtained with ,describe
procedure-name or ,d procedure-name from the Guile interactive prompt.

23.4.3.1 Basic Guile
At startup, gdb overrides Guile’s current-output-port and current-error-port to print
using gdb’s output-paging streams. A Guile program which outputs to one of these streams
may have its output interrupted by the user (see Section 22.4 [Screen Size], page 370). In
this situation, a Guile signal exception is thrown with value SIGINT.
Guile’s history mechanism uses the same naming as gdb’s, namely the user of dollarvariables (e.g., $1, $2, etc.). The results of evaluations in Guile and in GDB are counted
separately, $1 in Guile is not the same value as $1 in gdb.
gdb is not thread-safe. If your Guile program uses multiple threads, you must be careful
to only call gdb-specific functions in the gdb thread.
Some care must be taken when writing Guile code to run in gdb. Two things are worth
noting in particular:• gdb installs handlers for SIGCHLD and SIGINT. Guile code must not override these, oreven change the options using sigaction. If your program changes the handling ofthese signals, gdb will most likely stop working correctly. Note that it is unfortunately
common for GUI toolkits to install a SIGCHLD handler.
• gdb takes care to mark its internal file descriptors as close-on-exec. However, thiscannot be done in a thread-safe way on all platforms. Your Guile programs should beaware of this and should both create new file descriptors with the close-on-exec flag set
and arrange to close unneeded file descriptors before starting a child process.
gdb introduces a new Guile module, named gdb. All methods and classes added by gdb
are placed in this module. gdb does not automatically import the gdb module, scripts

Chapter 23: Extending gdb

521

must do this themselves. There are various options for how to import a module, so gdb
leaves the choice of how the gdb module is imported to the user. To simplify interactiveuse, it is recommended to add one of the following to your ~/.gdbinit.
guile (use-modules (gdb))
guile (use-modules ((gdb) #:renamer (symbol-prefix-proc ’gdb:)))Which one to choose depends on your preference. The second one adds gdb: as a prefix
to all module functions and variables.
The rest of this manual assumes the gdb module has been imported without any prefix.
See the Guile documentation for use-modules for more information (see Section “Using
Guile Modules” in GNU Guile Reference Manual).
Example:(gdb) guile (value-type (make-value 1))
ERROR: Unbound variable: value-type
Error while executing Scheme code.
(gdb) guile (use-modules (gdb))(gdb) guile (value-type (make-value 1))
int
(gdb)

The (gdb) module provides these basic Guile functions.

execute command [#:from-tty boolean][#:to-string boolean][Scheme Procedure]

Evaluate command, a string, as a gdb CLI command. If a gdb exception happens
while command runs, it is translated as described in Section 23.4.3.4 [Guile Exception
Handling], page 524.
from-tty specifies whether gdb ought to consider this command as having originatedfrom the user invoking it interactively. It must be a boolean value. If omitted, it
defaults to #f.
By default, any output produced by command is sent to gdb’s standard output (andto the log output if logging is turned on). If the to-string parameter is #t, then output
will be collected by execute and returned as a string. The default is #f, in whichcase the return value is unspecified. If to-string is #t, the gdb virtual terminal will
be temporarily set to unlimited width and height, and its pagination will be disabled;
see Section 22.4 [Screen Size], page 370.

history-ref number[Scheme Procedure]
Return a value from gdb’s value history (see Section 10.11 [Value History], page 170).
The number argument indicates which history element to return. If number is negative, then gdb will take its absolute value and count backward from the last element(i.e., the most recent element) to find the value to return. If number is zero, then
gdb will return the most recent element. If the element specified by number doesn’t
exist in the value history, a gdb:error exception will be raised.
If no exception is raised, the return value is always an instance of <gdb:value> (seeSection 23.4.3.5 [Values From Inferior In Guile], page 525).
Note: gdb’s value history is independent of Guile’s. $1 in gdb’s value history contains
the result of evaluating an expression from gdb’s command line and $1 from Guile’s
history contains the result of evaluating an expression from Guile’s command line.

522

Debugging with gdb

history-append! value[Scheme Procedure]
Append value, an instance of <gdb:value>, to gdb’s value history. Return its index
in the history.
Putting into history values returned by Guile extensions will allow the user convenient
access to those values via CLI history facilities.

parse-and-eval expression[Scheme Procedure]
Parse expression as an expression in the current language, evaluate it, and return the
result as a <gdb:value>. The expression must be a string.

This function can be useful when implementing a new command (see Section 23.4.3.11[Commands In Guile], page 541), as it provides a way to parse the command’s arguments as an expression. It is also is useful when computing values. For example, it is
the only way to get the value of a convenience variable (see Section 10.12 [Convenience
Vars], page 171) as a <gdb:value>.

23.4.3.2 Guile Configuration
gdb provides these Scheme functions to access various configuration parameters.
[Scheme Procedure]
Return a string containing gdb’s data directory. This directory contains gdb’s ancillary files.

data-directory[Scheme Procedure]
Return a string containing gdb’s Guile data directory. This directory contains the
Guile modules provided by gdb.

guile-data-directory

gdb-version[Scheme Procedure]

Return a string containing the gdb version.
[Scheme Procedure]
Return a string containing the host configuration. This is the string passed to --hostwhen gdb was configured.

host-config[Scheme Procedure]
Return a string containing the target configuration. This is the string passed to--target when gdb was configured.

target-config

23.4.3.3 GDB Scheme Data Types
The values exposed by gdb to Guile are known as gdb objects. There are several kinds of
gdb object, and each is disjoint from all other types known to Guile.

gdb-object-kind object[Scheme Procedure]
Return the kind of the gdb object, e.g., <gdb:breakpoint>, as a symbol.

gdb defines the following object types:<gdb:arch>
See Section 23.4.3.21 [Architectures In Guile], page 564.

Chapter 23: Extending gdb<gdb:block>See Section 23.4.3.16 [Blocks In Guile], page 552.
<gdb:block-symbols-iterator>
See Section 23.4.3.16 [Blocks In Guile], page 552.
<gdb:breakpoint>
See Section 23.4.3.19 [Breakpoints In Guile], page 559.
<gdb:command>
See Section 23.4.3.11 [Commands In Guile], page 541.
<gdb:exception>See Section 23.4.3.4 [Guile Exception Handling], page 524.
<gdb:frame>
See Section 23.4.3.15 [Frames In Guile], page 549.
<gdb:iterator>
See Section 23.4.3.25 [Iterators In Guile], page 568.
<gdb:lazy-string>See Section 23.4.3.20 [Lazy Strings In Guile], page 563.
<gdb:objfile>
See Section 23.4.3.14 [Objfiles In Guile], page 549.
<gdb:parameter>
See Section 23.4.3.12 [Parameters In Guile], page 545.
<gdb:pretty-printer>
See Section 23.4.3.8 [Guile Pretty Printing API], page 537.
<gdb:pretty-printer-worker>
See Section 23.4.3.8 [Guile Pretty Printing API], page 537.
<gdb:progspace>
See Section 23.4.3.13 [Progspaces In Guile], page 548.
<gdb:symbol>
See Section 23.4.3.17 [Symbols In Guile], page 554.
<gdb:symtab>
See Section 23.4.3.18 [Symbol Tables In Guile], page 558.
<gdb:sal>See Section 23.4.3.18 [Symbol Tables In Guile], page 558.
<gdb:type>See Section 23.4.3.7 [Types In Guile], page 532.
<gdb:field>
See Section 23.4.3.7 [Types In Guile], page 532.
<gdb:value>
See Section 23.4.3.5 [Values From Inferior In Guile], page 525.

523

524

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The following gdb objects are managed internally so that the Scheme function eq? may
be applied to them.
<gdb:arch><gdb:block><gdb:breakpoint><gdb:frame><gdb:objfile><gdb:progspace><gdb:symbol><gdb:symtab><gdb:type>23.4.3.4 Guile Exception Handling
When executing the guile command, Guile exceptions uncaught within the Guile code
are translated to calls to the gdb error-reporting mechanism. If the command that called
guile does not handle the error, gdb will terminate it and report the error according to
the setting of the guile print-stack parameter.
The guile print-stack parameter has three settings:
none

Nothing is printed.

message

An error message is printed containing the Guile exception name, the associatedvalue, and the Guile call stack backtrace at the point where the exception was
raised. Example:(gdb) guile (display foo)
ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.

full

In addition to an error message a full backtrace is printed.
(gdb) set guile print-stack full(gdb) guile (display foo)
Guile Backtrace:
In ice-9/boot-9.scm:
157: 10 [catch #t #<catch-closure 2c76e20> ...]In unknown file:?: 9 [apply-smob/1 #<catch-closure 2c76e20>]
In ice-9/boot-9.scm:
157: 8 [catch #t #<catch-closure 2c76d20> ...]In unknown file:?: 7 [apply-smob/1 #<catch-closure 2c76d20>]?: 6 [call-with-input-string "(display foo)" ...]
In ice-9/boot-9.scm:
2320: 5 [save-module-excursion #<procedure 2c2dc30 ... ()>]
In ice-9/eval-string.scm:
44: 4 [read-and-eval #<input: string 27cb410> #:lang ...]
37: 3 [lp (display foo)]
In ice-9/eval.scm:
387: 2 [eval # ()]393: 1 [eval #<memoized foo> ()]In unknown file:?: 0 [memoize-variable-access! #<memoized foo> ...]

Chapter 23: Extending gdb

525

ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.

gdb errors that happen in gdb commands invoked by Guile code are converted to Guile
exceptions. The type of the Guile exception depends on the error.
Guile procedures provided by gdb can throw the standard Guile exceptions likewrong-type-arg and out-of-range.
User interrupt (via C-c or by typing q at a pagination prompt) is translated to a Guilesignal exception with value SIGINT.
gdb Guile procedures can also throw these exceptions:
gdb:error
This exception is a catch-all for errors generated from within gdb.
gdb:invalid-object
This exception is thrown when accessing Guile objects that wrap underlying
gdb objects have become invalid. For example, a <gdb:breakpoint> object
becomes invalid if the user deletes it from the command line. The object still
exists in Guile, but the object it represents is gone. Further operations on thisbreakpoint will throw this exception.
gdb:memory-error
This exception is thrown when an operation tried to access invalid memory in
the inferior.
gdb:pp-type-error
This exception is thrown when a Guile pretty-printer passes a bad object to
gdb.
The following exception-related procedures are provided by the (gdb) module.

make-exception key args

[Scheme Procedure]
Return a <gdb:exception> object given by its key and args, which are the standard
Guile parameters of an exception. See the Guile documentation for more information(see Section “Exceptions” in GNU Guile Reference Manual).

exception? object[Scheme Procedure]
Return #t if object is a <gdb:exception> object. Otherwise return #f.

exception-key exception[Scheme Procedure]

Return the args field of a <gdb:exception> object.

exception-args exception[Scheme Procedure]

Return the args field of a <gdb:exception> object.

23.4.3.5 Values From Inferior In Guile
gdb provides values it obtains from the inferior program in an object of type <gdb:value>.
gdb uses this object for its internal bookkeeping of the inferior’s values, and for fetchingvalues when necessary.

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gdb does not memoize <gdb:value> objects. make-value always returns a fresh object.
(gdb) guile (eq? (make-value 1) (make-value 1))$1 = #f(gdb) guile (equal? (make-value 1) (make-value 1))$1 = #t

A <gdb:value> that represents a function can be executed via inferior function call withvalue-call. Any arguments provided to the call must match the function’s prototype, andmust be provided in the order specified by that prototype.
For example, some-val is a <gdb:value> instance representing a function that takes
two integers as arguments. To execute this function, call it like so:(define result (value-call some-val 10 20))

Any values returned from a function call are <gdb:value> objects.
Note: Unlike Python scripting in gdb, inferior values that are simple scalars cannot be
used directly in Scheme expressions that are valid for the value’s data type. For example,(+ (parse-and-eval "int_variable") 2) does not work. And inferior values that are
structures or instances of some class cannot be accessed using any special syntax, instead
value-field must be used.
The following value-related procedures are provided by the (gdb) module.

value? object[Scheme Procedure]
Return #t if object is a <gdb:value> object. Otherwise return #f.

make-value value [#:type type][Scheme Procedure]
Many Scheme values can be converted directly to a <gdb:value> with this procedure.
If type is specified, the result is a value of this type, and if value can’t be represented
with this type an exception is thrown. Otherwise the type of the result is determinedfrom value as described below.
See Section 23.4.3.21 [Architectures In Guile], page 564, for a list of the builtin types
for an architecture.
Here’s how Scheme values are converted when type argument to make-value is not
specified:
Scheme boolean
A Scheme boolean is converted the boolean type for the current language.
Scheme integer
A Scheme integer is converted to the first of a C int, unsigned int, long,unsigned long, long long or unsigned long long type for the current
architecture that can represent the value.
If the Scheme integer cannot be represented as a target integer an out-ofrange exception is thrown.

Scheme realA Scheme real is converted to the C double type for the current architecture.
Scheme string
A Scheme string is converted to a string in the current target language using the current target encoding. Characters that cannot be represented inChapter 23: Extending gdb527

the current target encoding are replaced with the corresponding escape sequence. This is Guile’s SCM_FAILED_CONVERSION_ESCAPE_SEQUENCE conversion strategy (see Section “Strings” in GNU Guile Reference Manual).
Passing type is not supported in this case, if it is provided a wrong-typearg exception is thrown.
<gdb:lazy-string>If value is a <gdb:lazy-string> object (see Section 23.4.3.20 [LazyStrings In Guile], page 563), then the lazy-string->value procedure
is called, and its result is used.
Passing type is not supported in this case, if it is provided a wrong-typearg exception is thrown.
Scheme bytevector
If value is a Scheme bytevector and type is provided, value must be thesame size, in bytes, of values of type type, and the result is essentiallycreated by using memcpy.
If value is a Scheme bytevector and type is not provided, the result is anarray of type uint8 of the same length.

value-optimized-out? value[Scheme Procedure]
Return #t if the compiler optimized out value, thus it is not available for fetchingfrom the inferior. Otherwise return #f.

value-address value[Scheme Procedure]If value is addressable, returns a <gdb:value> object representing the address. Otherwise, #f is returned.

value-type value[Scheme Procedure]
Return the type of value as a <gdb:type> object (see Section 23.4.3.7 [Types In
Guile], page 532).

value-dynamic-type value[Scheme Procedure]
Return the dynamic type of value. This uses C++ run-time type information (RTTI)
to determine the dynamic type of the value. If the value is of class type, it will returnthe class in which the value is embedded, if any. If the value is of pointer or reference
to a class type, it will compute the dynamic type of the referenced object, and return
a pointer or reference to that type, respectively. In all other cases, it will return thevalue’s static type.
Note that this feature will only work when debugging a C++ program that includes
RTTI for the object in question. Otherwise, it will just return the static type of thevalue as in ptype foo. See Chapter 16 [Symbols], page 263.

value-cast value type

[Scheme Procedure]
Return a new instance of <gdb:value> that is the result of casting value to thetype described by type, which must be a <gdb:type> object. If the cast cannot be
performed for some reason, this method throws an exception.

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Debugging with gdb

value-dynamic-cast value type

[Scheme Procedure]
Like value-cast, but works as if the C++ dynamic_cast operator were used. Consult
a C++ reference for details.

value-reinterpret-cast value type

[Scheme Procedure]
Like value-cast, but works as if the C++ reinterpret_cast operator were used.
Consult a C++ reference for details.

value-dereference value[Scheme Procedure]
For pointer data types, this method returns a new <gdb:value> object whose contents
is the object pointed to by value. For example, if foo is a C pointer to an int, declaredin your C program as
int *foo;then you can use the corresponding <gdb:value> to access what foo points to likethis:(define bar (value-dereference foo))

The result bar will be a <gdb:value> object holding the value pointed to by foo.
A similar function value-referenced-value exists which also returns <gdb:value>
objects corresponding to the values pointed to by pointer values (and additionally,values referenced by reference values). However, the behavior of value-dereference
differs from value-referenced-value by the fact that the behavior ofvalue-dereference is identical to applying the C unary operator * on a given
value. For example, consider a reference to a pointer ptrref, declared in your C++
program as
typedef int *intptr;...
int val = 10;
intptr ptr = &val;
intptr &ptrref = ptr;

Though ptrref is a reference value, one can apply the method value-dereference
to the <gdb:value> object corresponding to it and obtain a <gdb:value> which
is identical to that corresponding to val. However, if you apply the method
value-referenced-value, the result would be a <gdb:value> object identical tothat corresponding to ptr.
(define scm-ptrref (parse-and-eval "ptrref"))(define scm-val (value-dereference scm-ptrref))(define scm-ptr (value-referenced-value scm-ptrref))

The <gdb:value> object scm-val is identical to that corresponding to val, andscm-ptr is identical to that corresponding to ptr. In general, value-dereference
can be applied whenever the C unary operator * can be applied to thecorresponding C value. For those cases where applying both value-dereference
and value-referenced-value is allowed, the results obtained need not be identical(as we have seen in the above example). The results are however identical whenapplied on <gdb:value> objects corresponding to pointers (<gdb:value> objects
with type code TYPE_CODE_PTR) in a C/C++ program.

value-referenced-value value[Scheme Procedure]
For pointer or reference data types, this method returns a new <gdb:value> object
corresponding to the value referenced by the pointer/reference value. For pointer dataChapter 23: Extending gdb

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types, value-dereference and value-referenced-value produce identical results.
The difference between these methods is that value-dereference cannot get thevalues referenced by reference values. For example, consider a reference to an int,
declared in your C++ program as
int val = 10;
int &ref = val;then applying value-dereference to the <gdb:value> object corresponding to refwill result in an error, while applying value-referenced-value will result in a
<gdb:value> object identical to that corresponding to val.
(define scm-ref (parse-and-eval "ref"))(define err-ref (value-dereference scm-ref));; error(define scm-val (value-referenced-value scm-ref)) ;; okThe <gdb:value> object scm-val is identical to that corresponding to val.

value-reference-value value[Scheme Procedure]
Return a new <gdb:value> object which is a reference to the value encapsulated by<gdb:value> object value.

value-rvalue-reference-value value[Scheme Procedure]
Return a new <gdb:value> object which is an rvalue reference to the value encapsulated by <gdb:value> object value.

value-const-value value[Scheme Procedure]
Return a new <gdb:value> object which is a ‘const’ version of <gdb:value> object
value.

value-field value field-name[Scheme Procedure]

Return field field-name from <gdb:value> object value.

value-subscript value index[Scheme Procedure]
Return the value of array value at index index. The value argument must be a
subscriptable <gdb:value> object.

value-call value arg-list[Scheme Procedure]
Perform an inferior function call, taking value as a pointer to the function to call.
Each element of list arg-list must be a <gdb:value> object or an object that can beconverted to a value. The result is the value returned by the function.

value->bool value[Scheme Procedure]
Return the Scheme boolean representing <gdb:value> value. The value must be“integer like”. Pointers are ok.
[Scheme Procedure]
Return the Scheme integer representing <gdb:value> value. The value must be “integer like”. Pointers are ok.

value->integer[Scheme Procedure]
Return the Scheme real number representing <gdb:value> value. The value must be
a number.

value->real530

Debugging with gdb[Scheme Procedure]
Return a Scheme bytevector with the raw contents of <gdb:value> value. No transformation, endian or otherwise, is performed.

value->bytevector

value->string value [#:encoding encoding][#:errors errors] [#:length length][Scheme Procedure]If value> represents a string, then this method converts the contents to a Guile string.
Otherwise, this method will throw an exception.
Values are interpreted as strings according to the rules of the current language. If
the optional length argument is given, the string will be converted to that length,
and will include any embedded zeroes that the string may contain. Otherwise, for
languages where the string is zero-terminated, the entire string will be converted.
For example, in C-like languages, a value is a string if it is a pointer to or an array ofcharacters or ints of type wchar_t, char16_t, or char32_t.
If the optional encoding argument is given, it must be a string naming the encoding of
the string in the <gdb:value>, such as "ascii", "iso-8859-6" or "utf-8". It accepts
the same encodings as the corresponding argument to Guile’s scm_from_stringn
function, and the Guile codec machinery will be used to convert the string. If encoding
is not given, or if encoding is the empty string, then either the target-charset (seeSection 10.21 [Character Sets], page 187) will be used, or a language-specific encoding
will be used, if the current language is able to supply one.
The optional errors argument is one of #f, error or substitute. error andsubstitute must be symbols. If errors is not specified, or if its value is #f, thenthe default conversion strategy is used, which is set with the Scheme function
set-port-conversion-strategy!. If the value is ’error then an exception isthrown if there is any conversion error. If the value is ’substitute then any
conversion error is replaced with question marks. See Section “Strings” in GNU
Guile Reference Manual.
If the optional length argument is given, the string will be fetched and converted
to the given length. The length must be a Scheme integer and not a <gdb:value>
integer.

value->lazy-string value [#:encoding encoding][#:length length][Scheme Procedure]

If this <gdb:value> represents a string, then this method converts value to a
<gdb:lazy-string (see Section 23.4.3.20 [Lazy Strings In Guile], page 563).
Otherwise, this method will throw an exception.
If the optional encoding argument is given, it must be a string naming the encodingof the <gdb:lazy-string. Some examples are: "ascii", "iso-8859-6" or "utf-8".
If the encoding argument is an encoding that gdb does not recognize, gdb will raise
an error.
When a lazy string is printed, the gdb encoding machinery is used to convert thestring during printing. If the optional encoding argument is not provided, or is anempty string, gdb will automatically select the encoding most suitable for the string
type. For further information on encoding in gdb please see Section 10.21 [Character
Sets], page 187.

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If the optional length argument is given, the string will be fetched and encoded to thelength of characters specified. If the length argument is not provided, the string will
be fetched and encoded until a null of appropriate width is found. The length must
be a Scheme integer and not a <gdb:value> integer.

value-lazy? value[Scheme Procedure]
Return #t if value has not yet been fetched from the inferior. Otherwise return #f.
gdb does not fetch values until necessary, for efficiency. For example:(define myval (parse-and-eval "somevar"))

The value of somevar is not fetched at this time. It will be fetched when the value isneeded, or when the fetch-lazy procedure is invoked.

make-lazy-value type address[Scheme Procedure]
Return a <gdb:value> that will be lazily fetched from the target. The object oftype <gdb:type> whose value to fetch is specified by its type and its target memory
address, which is a Scheme integer.

value-fetch-lazy! value[Scheme Procedure]If value is a lazy value ((value-lazy? value) is #t), then the value is fetched fromthe inferior. Any errors that occur in the process will produce a Guile exception.
If value is not a lazy value, this method has no effect.
The result of this function is unspecified.

value-print value[Scheme Procedure]
Return the string representation (print form) of <gdb:value> value.

23.4.3.6 Arithmetic In Guile
The (gdb) module provides several functions for performing arithmetic on <gdb:value>
objects. The arithmetic is performed as if it were done by the target, and therefore hastarget semantics which are not necessarily those of Scheme. For example operations workwith a fixed precision, not the arbitrary precision of Scheme.
Wherever a function takes an integer or pointer as an operand, gdb will convert appropriate Scheme values to perform the operation.

value-add a b[Scheme Procedure]value-sub a b[Scheme Procedure]value-mul a b[Scheme Procedure]value-div a b[Scheme Procedure]value-rem a b[Scheme Procedure]value-mod a b[Scheme Procedure]value-pow a b[Scheme Procedure]value-not a[Scheme Procedure]value-neg a[Scheme Procedure]

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value-pos a[Scheme Procedure]value-abs a[Scheme Procedure]value-lsh a b[Scheme Procedure]value-rsh a b[Scheme Procedure]value-min a b[Scheme Procedure]value-max a b[Scheme Procedure]value-lognot a[Scheme Procedure]value-logand a b[Scheme Procedure]value-logior a b[Scheme Procedure]value-logxor a b[Scheme Procedure]value=? a b[Scheme Procedure]value<? a b[Scheme Procedure]value<=? a b[Scheme Procedure]value>? a b[Scheme Procedure]value>=? a b[Scheme Procedure]

Scheme does not provide a not-equal function, and thus Guile support in gdb does noteither.

23.4.3.7 Types In Guile
gdb represents types from the inferior in objects of type <gdb:type>.
The following type-related procedures are provided by the (gdb) module.

type? object[Scheme Procedure]
Return #t if object is an object of type <gdb:type>. Otherwise return #f.

lookup-type name [#:block block][Scheme Procedure]This function looks up a type by its name, which must be a string.
If block is given, it is an object of type <gdb:block>, and name is looked up in that
scope. Otherwise, it is searched for globally.
Ordinarily, this function will return an instance of <gdb:type>. If the named typecannot be found, it will throw an exception.

type-code type

[Scheme Procedure]
Return the type code of type. The type code will be one of the TYPE_CODE_ constants
defined below.

type-tag type

[Scheme Procedure]
Return the tag name of type. The tag name is the name after struct, union, or enumin C and C++; not all languages have this concept. If this type has no tag name, then#f is returned.

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type-name type

[Scheme Procedure]
Return the name of type. If this type has no name, then #f is returned.

type-print-name type

[Scheme Procedure]
Return the print name of type. This returns something even for anonymous types.
For example, for an anonymous C struct "struct {...}" is returned.

type-sizeof type

[Scheme Procedure]
Return the size of this type, in target char units. Usually, a target’s char type will
be an 8-bit byte. However, on some unusual platforms, this type may have a differentsize.

type-strip-typedefs type

[Scheme Procedure]
Return a new <gdb:type> that represents the real type of type, after removing alllayers of typedefs.

type-array type n1 [n2][Scheme Procedure]
Return a new <gdb:type> object which represents an array of this type. If one
argument is given, it is the inclusive upper bound of the array; in this case the lower
bound is zero. If two arguments are given, the first argument is the lower boundof the array, and the second argument is the upper bound of the array. An array’s
length must not be negative, but the bounds can be.

type-vector type n1 [n2][Scheme Procedure]
Return a new <gdb:type> object which represents a vector of this type. If one
argument is given, it is the inclusive upper bound of the vector; in this case the lower
bound is zero. If two arguments are given, the first argument is the lower bound of
the vector, and the second argument is the upper bound of the vector. A vector’s
length must not be negative, but the bounds can be.
The difference between an array and a vector is that arrays behave like in C: whenused in expressions they decay to a pointer to the first element whereas vectors aretreated as first class values.

type-pointer type

[Scheme Procedure]
Return a new <gdb:type> object which represents a pointer to type.

type-range type

[Scheme Procedure]
Return a list of two elements: the low bound and high bound of type. If type does
not have a range, an exception is thrown.

type-reference type

[Scheme Procedure]
Return a new <gdb:type> object which represents a reference to type.

type-target type

[Scheme Procedure]
Return a new <gdb:type> object which represents the target type of type.
For a pointer type, the target type is the type of the pointed-to object. For an array
type (meaning C-like arrays), the target type is the type of the elements of the array.
For a function or method type, the target type is the type of the return value. For acomplex type, the target type is the type of the elements. For a typedef, the target
type is the aliased type.
If the type does not have a target, this method will throw an exception.

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type-const type

[Scheme Procedure]
Return a new <gdb:type> object which represents a const-qualified variant of type.

type-volatile type

[Scheme Procedure]
Return a new <gdb:type> object which represents a volatile-qualified variant oftype.

type-unqualified type

[Scheme Procedure]
Return a new <gdb:type> object which represents an unqualified variant of type.
That is, the result is neither const nor volatile.

type-num-fields[Scheme Procedure]

Return the number of fields of <gdb:type> type.

type-fields type

[Scheme Procedure]
Return the fields of type as a list. For structure and union types, fields has theusual meaning. Range types have two fields, the minimum and maximum values.
Enum types have one field per enum constant. Function and method types have one
field per parameter. The base types of C++ classes are also represented as fields. If
the type has no fields, or does not fit into one of these categories, an empty list will
be returned. See [Fields of a type in Guile], page 536.

make-field-iterator type

[Scheme Procedure]
Return the fields of type as a <gdb:iterator> object. See Section 23.4.3.25 [Iterators
In Guile], page 568.

type-field type field-name[Scheme Procedure]
Return field named field-name in type. The result is an object of type <gdb:field>.
See [Fields of a type in Guile], page 536. If the type does not have fields, or field-nameis not a field of type, an exception is thrown.
For example, if some-type is a <gdb:type> instance holding a structure type, you
can access its foo field with:(define bar (type-field some-type "foo"))bar will be a <gdb:field> object.

type-has-field? type name

[Scheme Procedure]
Return #t if <gdb:type> type has field named name. Otherwise return #f.

Each type has a code, which indicates what category this type falls into. The available
type categories are represented by constants defined in the (gdb) module:
TYPE_CODE_PTR
The type is a pointer.
TYPE_CODE_ARRAY
The type is an array.
TYPE_CODE_STRUCTThe type is a structure.
TYPE_CODE_UNION
The type is a union.

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TYPE_CODE_ENUM
The type is an enum.
TYPE_CODE_FLAGS
A bit flags type, used for things such as status registers.
TYPE_CODE_FUNC
The type is a function.
TYPE_CODE_INT
The type is an integer type.
TYPE_CODE_FLT
A floating point type.
TYPE_CODE_VOID
The special type void.
TYPE_CODE_SETA Pascal set type.
TYPE_CODE_RANGE
A range type, that is, an integer type with bounds.
TYPE_CODE_STRING
A string type. Note that this is only used for certain languages with languagedefined string types; C strings are not represented this way.
TYPE_CODE_BITSTRING
A string of bits. It is deprecated.
TYPE_CODE_ERROR
An unknown or erroneous type.
TYPE_CODE_METHOD
A method type, as found in C++.
TYPE_CODE_METHODPTR
A pointer-to-member-function.
TYPE_CODE_MEMBERPTR
A pointer-to-member.
TYPE_CODE_REF
A reference type.
TYPE_CODE_RVALUE_REF
A C++11 rvalue reference type.
TYPE_CODE_CHAR
A character type.
TYPE_CODE_BOOL
A boolean type.
TYPE_CODE_COMPLEX
A complex float type.

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TYPE_CODE_TYPEDEF
A typedef to some other type.
TYPE_CODE_NAMESPACEA C++ namespace.
TYPE_CODE_DECFLOAT
A decimal floating point type.
TYPE_CODE_INTERNAL_FUNCTION
A function internal to gdb. This is the type used to represent convenience
functions (see Section 10.13 [Convenience Funs], page 174).
gdb.TYPE_CODE_XMETHOD
A method internal to gdb. This is the type used to represent xmethods (seeSection 23.3.2.16 [Writing an Xmethod], page 446).
gdb.TYPE_CODE_FIXED_POINT
A fixed-point number.
gdb.TYPE_CODE_NAMESPACE
A Fortran namelist.
Further support for types is provided in the (gdb types) Guile module (seeSection 23.4.5.2 [Guile Types Module], page 571).
Each field is represented as an object of type <gdb:field>.
The following field-related procedures are provided by the (gdb) module:

field? object[Scheme Procedure]
Return #t if object is an object of type <gdb:field>. Otherwise return #f.

field-name field[Scheme Procedure]

Return the name of the field, or #f for anonymous fields.

field-type field[Scheme Procedure]
Return the type of the field. This is usually an instance of <gdb:type>, but it canbe #f in some situations.

field-enumval field[Scheme Procedure]

Return the enum value represented by <gdb:field> field.

field-bitpos field[Scheme Procedure]
Return the bit position of <gdb:field> field. This attribute is not available forstatic fields (as in C++).

field-bitsize field[Scheme Procedure]
If the field is packed, or is a bitfield, return the size of <gdb:field> field in bits.
Otherwise, zero is returned; in which case the field’s size is given by its type.

field-artificial? field[Scheme Procedure]
Return #t if the field is artificial, usually meaning that it was provided by the compiler
and not the user. Otherwise return #f.

field-base-class? field[Scheme Procedure]
Return #t if the field represents a base class of a C++ structure. Otherwise return #f.

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23.4.3.8 Guile Pretty Printing API
An example output is provided (see Section 10.10 [Pretty Printing], page 168).
A pretty-printer is represented by an object of type <gdb:pretty-printer>. Pretty-printerobjects are created with make-pretty-printer.
The following pretty-printer-related procedures are provided by the (gdb) module:

make-pretty-printer name lookup-function[Scheme Procedure]
Return a <gdb:pretty-printer> object named name.
lookup-function is a function of one parameter: the value to be printed. If the value
is handled by this pretty-printer, then lookup-function returns an object of type<gdb:pretty-printer-worker> to perform the actual pretty-printing. Otherwise lookupfunction returns #f.

pretty-printer? object[Scheme Procedure]
Return #t if object is a <gdb:pretty-printer> object. Otherwise return #f.

pretty-printer-enabled? pretty-printer[Scheme Procedure]

Return #t if pretty-printer is enabled. Otherwise return #f.

set-pretty-printer-enabled! pretty-printer flag

[Scheme Procedure]
Set the enabled flag of pretty-printer to flag. The value returned is unspecified.
[Scheme Procedure]pretty-printers
Return the list of global pretty-printers.

set-pretty-printers! pretty-printers[Scheme Procedure]
Set the list of global pretty-printers to pretty-printers. The value returned is unspecified.

make-pretty-printer-worker display-hint to-stringchildren[Scheme Procedure]

Return an object of type <gdb:pretty-printer-worker>.
This function takes three parameters:‘display-hint’
display-hint provides a hint to gdb or gdb front end via MI to change theformatting of the value being printed. The value must be a string or #f(meaning there is no hint). Several values for display-hint are predefinedby gdb:‘array’Indicate that the object being printed is “array-like”. The
CLI uses this to respect parameters such as set print
elements and set print array.

‘map’

Indicate that the object being printed is “map-like”, and thatthe children of this value can be assumed to alternate between
keys and values.

‘string’

Indicate that the object being printed is “string-like”. If theprinter’s to-string function returns a Guile string of some

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kind, then gdb will call its internal language-specific stringprinting function to format the string. For the CLI this means
adding quotation marks, possibly escaping some characters,
respecting set print elements, and the like.
‘to-string’
to-string is either a function of one parameter, the <gdb:pretty-printerworker> object, or #f.
When printing from the CLI, if the to-string method exists, then gdb
will prepend its result to the values returned by children. Exactly how
this formatting is done is dependent on the display hint, and may change
as more hints are added. Also, depending on the print settings (seeSection 10.9 [Print Settings], page 157), the CLI may print just the resultof to-string in a stack trace, omitting the result of children.
If this method returns a string, it is printed verbatim.
Otherwise, if this method returns an instance of <gdb:value>, then gdb
prints this value. This may result in a call to another pretty-printer.
If instead the method returns a Guile value which is convertible to a
<gdb:value>, then gdb performs the conversion and prints the resulting value. Again, this may result in a call to another pretty-printer.
Guile scalars (integers, floats, and booleans) and strings are convertible
to <gdb:value>; other types are not.
Finally, if this method returns #f then no further operations are performed in this method and nothing is printed.
If the result is not one of these types, an exception is raised.
to-string may also be #f in which case it is left to children to print thevalue.
‘children’
children is either a function of one parameter, the <gdb:pretty-printerworker> object, or #f.
gdb will call this function on a pretty-printer to compute the children of
the pretty-printer’s value.
This function must return a <gdb:iterator> object. Each item returnedby the iterator must be a tuple holding two elements. The first element
is the “name” of the child; the second element is the child’s value. The
value can be any Guile object which is convertible to a gdb value.
If children is #f, gdb will act as though the value has no children.
Children may be hidden from display based on the value of ‘set printmax-depth’ (see Section 10.9 [Print Settings], page 157).
gdb provides a function which can be used to look up the default pretty-printer for a<gdb:value>:default-visualizer value[Scheme Procedure]This function takes a <gdb:value> object as an argument. If a pretty-printer for thisvalue exists, then it is returned. If no such printer exists, then this returns #f.

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23.4.3.9 Selecting Guile Pretty-Printers
There are three sets of pretty-printers that gdb searches:• Per-objfile list of pretty-printers (see Section 23.4.3.14 [Objfiles In Guile], page 549).
• Per-progspace list of pretty-printers (see Section 23.4.3.13 [Progspaces In Guile],
page 548).
• The global list of pretty-printers (see Section 23.4.3.8 [Guile Pretty Printing API],
page 537). These printers are available when debugging any inferior.
Pretty-printer lookup is done by passing the value to be printed to the lookup function ofeach enabled object in turn. Lookup stops when a lookup function returns a non-#f value orwhen the list is exhausted. Lookup functions must return either a <gdb:pretty-printerworker> object or #f. Otherwise an exception is thrown.
gdb first checks the result of objfile-pretty-printers of each <gdb:objfile> in thecurrent program space and iteratively calls each enabled lookup function in the list for that
<gdb:objfile> until a non-#f object is returned. If no pretty-printer is found in the objfile
lists, gdb then searches the result of progspace-pretty-printers of the current program
space, calling each enabled function until a non-#f object is returned. After these lists havebeen exhausted, it tries the global pretty-printers list, obtained with pretty-printers,
again calling each enabled function until a non-#f object is returned.
The order in which the objfiles are searched is not specified. For a given list, functions
are always invoked from the head of the list, and iterated over sequentially until the end of
the list, or a <gdb:pretty-printer-worker> object is returned.
For various reasons a pretty-printer may not work. For example, the underlying data
structure may have changed and the pretty-printer is out of date.
The consequences of a broken pretty-printer are severe enough that gdb provides support
for enabling and disabling individual printers. For example, if print frame-arguments is
on, a backtrace can become highly illegible if any argument is printed with a broken printer.
Pretty-printers are enabled and disabled from Scheme by calling set-pretty-printerenabled!. See Section 23.4.3.8 [Guile Pretty Printing API], page 537.

23.4.3.10 Writing a Guile Pretty-PrinterA pretty-printer consists of two basic parts: a lookup function to determine if the type is
supported, and the printer itself.
Here is an example showing how a std::string printer might be written. See
Section 23.4.3.8 [Guile Pretty Printing API], page 537, for details.
(define (make-my-string-printer value)"Print a my::string string"(make-pretty-printer-worker"string"(lambda (printer)(value-field value "_data"))#f))

And here is an example showing how a lookup function for the printer example above
might be written.
(define (str-lookup-function pretty-printer value)(let ((tag (type-tag (value-type value))))540

Debugging with gdb(and tag(string-prefix? "std::string<" tag)(make-my-string-printer value))))Then to register this printer in the global printer list:(append-pretty-printer!
(make-pretty-printer "my-string" str-lookup-function))

The example lookup function extracts the value’s type, and attempts to match it to a
type that it can pretty-print. If it is a type the printer can pretty-print, it will return a<gdb:pretty-printer-worker> object. If not, it returns #f.
We recommend that you put your core pretty-printers into a Guile package. If yourpretty-printers are for use with a library, we further recommend embedding a version number
into the package name. This practice will enable gdb to load multiple versions of yourpretty-printers at the same time, because they will have different names.
You should write auto-loaded code (see Section 23.4.4 [Guile Auto-loading], page 570)
such that it can be evaluated multiple times without changing its meaning. An ideal autoload file will consist solely of imports of your printer modules, followed by a call to a register
pretty-printers with the current objfile.
Taken as a whole, this approach will scale nicely to multiple inferiors, each potentiallyusing a different library version. Embedding a version number in the Guile package namewill ensure that gdb is able to load both sets of printers simultaneously. Then, because thesearch for pretty-printers is done by objfile, and because your auto-loaded code took careto register your library’s printers with a specific objfile, gdb will find the correct printers
for the specific version of the library used by each inferior.
To continue the my::string example, this code might appear in (my-project mylibrary v1):
(use-modules (gdb))(define (register-printers objfile)(append-objfile-pretty-printer!
(make-pretty-printer "my-string" str-lookup-function)))And then the corresponding contents of the auto-load file would be:(use-modules (gdb) (my-project my-library v1))
(register-printers (current-objfile))

The previous example illustrates a basic pretty-printer. There are a few things that canbe improved on. The printer only handles one type, whereas a library typically has several
types. One could install a lookup function for each desired type in the library, but one could
also have a single lookup function recognize several types. The latter is the conventional
way this is handled. If a pretty-printer can handle multiple data types, then its subprinters
are the printers for the individual data types.
The (gdb printing) module provides a formal way of solving this problem (seeSection 23.4.5.1 [Guile Printing Module], page 570). Here is another example that handles
multiple types.
These are the types we are going to pretty-print:
struct foo { int a, b; };struct bar { struct foo x, y; };Here are the printers:(define (make-foo-printer value)Chapter 23: Extending gdb

541"Print a foo object"(make-pretty-printer-worker"foo"(lambda (printer)(format #f "a=<~a> b=<~a>"(value-field value "a") (value-field value "a")))#f))(define (make-bar-printer value)"Print a bar object"(make-pretty-printer-worker"foo"(lambda (printer)(format #f "x=<~a> y=<~a>"(value-field value "x") (value-field value "y")))#f))This example doesn’t need a lookup function, that is handled by the (gdb printing)module. Instead a function is provided to build up the object that handles the lookup.
(use-modules (gdb printing))(define (build-pretty-printer)(let ((pp (make-pretty-printer-collection "my-library")))(pp-collection-add-tag-printer "foo" make-foo-printer)(pp-collection-add-tag-printer "bar" make-bar-printer)pp))

And here is the autoload support:(use-modules (gdb) (my-library))(append-objfile-pretty-printer! (current-objfile) (build-pretty-printer))

Finally, when this printer is loaded into gdb, here is the corresponding output of ‘info
pretty-printer’:(gdb) info pretty-printermy_library.so:
my-libraryfoobar

23.4.3.11 Commands In Guile
You can implement new gdb CLI commands in Guile. A CLI command object is createdwith the make-command Guile function, and added to gdb with the register-command!
Guile function. This two-step approach is taken to separate out the side-effect of adding
the command to gdb from make-command.
There is no support for multi-line commands, that is commands that consist of multiplelines and are terminated with end.

make-command name [#:invoke invoke][Scheme Procedure][#:command-class command-class] [#:completer-class completer][#:prefix? prefix] [#:doc doc-string]
The argument name is the name of the command. If name consists of multiple words,
then the initial words are looked for as prefix commands. In this case, if one of theprefix commands does not exist, an exception is raised.
The result is the <gdb:command> object representing the command. The commandis not usable until it has been registered with gdb with register-command!.

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The rest of the arguments are optional.
The argument invoke is a procedure of three arguments: self, args and from-tty. The
argument self is the <gdb:command> object representing the command. The argument
args is a string representing the arguments passed to the command, after leading andtrailing whitespace has been stripped. The argument from-tty is a boolean flag andspecifies whether the command should consider itself to have been originated fromthe user invoking it interactively. If this function throws an exception, it is turned
into a gdb error call. Otherwise, the return value is ignored.
The argument command-class is one of the ‘COMMAND_’ constants defined below. This
argument tells gdb how to categorize the new command in the help system. The
default is COMMAND_NONE.
The argument completer is either #f, one of the ‘COMPLETE_’ constants defined below,
or a procedure, also defined below. This argument tells gdb how to perform completion for this command. If not provided or if the value is #f, then no completion is
performed on the command.
The argument prefix is a boolean flag indicating whether the new command is a prefixcommand; sub-commands of this command may be registered.
The argument doc-string is help text for the new command. If no documentation
string is provided, the default value “This command is not documented.” is used.

register-command! command[Scheme Procedure]
Add command, a <gdb:command> object, to gdb’s list of commands. It is an error toregister a command more than once. The result is unspecified.

command? object[Scheme Procedure]
Return #t if object is a <gdb:command> object. Otherwise return #f.

[Scheme Procedure]
By default, a gdb command is repeated when the user enters a blank line at the command prompt. A command can suppress this behavior by invoking the dont-repeat
function. This is similar to the user command dont-repeat, see Section 23.1.1 [Define], page 391.

dont-repeat

string->argv string[Scheme Procedure]
Convert a string to a list of strings split up according to gdb’s argv parsing rules. It
is recommended to use this for consistency. Arguments are separated by spaces andmay be quoted. Example:
scheme@(guile-user)> (string->argv "1 2\\ \\\"3 ’4 \"5’ \"6 ’7\"")$1 = ("1" "2 \"3" "4 \"5" "6 ’7")

throw-user-error message . args

[Scheme Procedure]
Throw a gdb:user-error exception. The argument message is the error message asa format string, like the fmt argument to the format Scheme function. See Section“Formatted Output” in GNU Guile Reference Manual. The argument args is a listof the optional arguments of message.
This is used when the command detects a user error of some kind, say a bad commandargument.
(gdb) guile (use-modules (gdb))

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543(gdb) guile(register-command! (make-command "test-user-error"#:command-class COMMAND_OBSCURE#:invoke (lambda (self arg from-tty)(throw-user-error "Bad argument ~a" arg))))end(gdb) test-user-error ugh
ERROR: Bad argument ugh

self text word[completer]
If the completer option to make-command is a procedure, it takes three arguments:
self which is the <gdb:command> object, and text and word which are both strings.
The argument text holds the complete command line up to the cursor’s location. The
argument word holds the last word of the command line; this is computed using aword-breaking heuristic.
All forms of completion are handled by this function, that is, the TAB and M-? key
bindings (see Section 3.3 [Completion], page 24), and the complete command (seeSection 3.6 [Help], page 29).
This procedure can return several kinds of values:• If the return value is a list, the contents of the list are used as the completions.
It is up to completer to ensure that the contents actually do complete the word.
An empty list is allowed, it means that there were no completions available. Only
string elements of the list are used; other elements in the list are ignored.
• If the return value is a <gdb:iterator> object, it is iterated over to obtain thecompletions. It is up to completer-procedure to ensure that the results actually
do complete the word. Only string elements of the result are used; other elementsin the sequence are ignored.
• All other results are treated as though there were no available completions.

When a new command is registered, it will have been declared as a member of some
general class of commands. This is used to classify top-level commands in the on-line help
system; note that prefix commands are not listed under their own category but rather
that of their top-level command. The available classifications are represented by constants
defined in the gdb module:
COMMAND_NONE
The command does not belong to any particular class. A command in thiscategory will not be displayed in any of the help categories. This is the default.
COMMAND_RUNNING
The command is related to running the inferior. For example, start, step,and continue are in this category. Type help running at the gdb prompt tosee a list of commands in this category.
COMMAND_DATA
The command is related to data or variables. For example, call, find, andprint are in this category. Type help data at the gdb prompt to see a list ofcommands in this category.

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COMMAND_STACK
The command has to do with manipulation of the stack. For example,
backtrace, frame, and return are in this category. Type help stack at thegdb prompt to see a list of commands in this category.
COMMAND_FILESThis class is used for file-related commands. For example, file, list andsection are in this category. Type help files at the gdb prompt to see a listof commands in this category.
COMMAND_SUPPORTThis should be used for “support facilities”, generally meaning things that are
useful to the user when interacting with gdb, but not related to the state of
the inferior. For example, help, make, and shell are in this category. Typehelp support at the gdb prompt to see a list of commands in this category.
COMMAND_STATUS
The command is an ‘info’-related command, that is, related to the state of
gdb itself. For example, info, macro, and show are in this category. Typehelp status at the gdb prompt to see a list of commands in this category.
COMMAND_BREAKPOINTSThe command has to do with breakpoints. For example, break, clear, anddelete are in this category. Type help breakpoints at the gdb prompt to see
a list of commands in this category.
COMMAND_TRACEPOINTSThe command has to do with tracepoints. For example, trace, actions, andtfind are in this category. Type help tracepoints at the gdb prompt to see
a list of commands in this category.
COMMAND_USER
The command is a general purpose command for the user, and typically does
not fit in one of the other categories. Type help user-defined at the gdb
prompt to see a list of commands in this category, as well as the list of gdb
macros (see Section 23.1 [Sequences], page 391).
COMMAND_OBSCURE
The command is only used in unusual circumstances, or is not of general interest
to users. For example, checkpoint, fork, and stop are in this category. Typehelp obscure at the gdb prompt to see a list of commands in this category.
COMMAND_MAINTENANCE
The command is only useful to gdb maintainers. The maintenance andflushregs commands are in this category. Type help internals at the gdb
prompt to see a list of commands in this category.
A new command can use a predefined completion function, either by specifying it via
an argument at initialization, or by returning it from the completer procedure. These
predefined completion constants are all defined in the gdb module:
COMPLETE_NONE
This constant means that no completion should be done.

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COMPLETE_FILENAME
This constant means that filename completion should be performed.
COMPLETE_LOCATIONThis constant means that location completion should be done. See Section 9.2[Location Specifications], page 126.
COMPLETE_COMMAND
This constant means that completion should examine gdb command names.
COMPLETE_SYMBOLThis constant means that completion should be done using symbol names as
the source.
COMPLETE_EXPRESSION
This constant means that completion should be done on expressions. Often
this means completing on symbol names, but some language parsers also havesupport for completing on field names.
The following code snippet shows how a trivial CLI command can be implemented in
Guile:(gdb) guile(register-command! (make-command "hello-world"#:command-class COMMAND_USER#:doc "Greet the whole world."#:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
end(gdb) hello-world
Hello, World!

23.4.3.12 Parameters In Guile
You can implement new gdb parameters using Guile3 .
There are many parameters that already exist and can be set in gdb. Two examples are:set follow-fork and set charset. Setting these parameters influences certain behavior
in gdb. Similarly, you can define parameters that can be used to influence behavior incustom Guile scripts and commands.
A new parameter is defined with the make-parameter Guile function, and added to gdb
with the register-parameter! Guile function. This two-step approach is taken to separate
out the side-effect of adding the parameter to gdb from make-parameter.
Parameters are exposed to the user via the set and show commands. See Section 3.6[Help], page 29.

make-parameter name [#:command-class command-class][Scheme Procedure][#:parameter-type parameter-type] [#:enum-list enum-list][#:set-func set-func] [#:show-func show-func] [#:doc doc][#:set-doc set-doc] [#:show-doc show-doc] [#:initial-value initial-value]
The argument name is the name of the new parameter. If name consists of multiple
words, then the initial words are looked for as prefix parameters. An example of3

Note that gdb parameters must not be confused with Guiles parameter objects (see Section “Parameters”
in GNU Guile Reference Manual).

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this can be illustrated with the set print set of parameters. If name is print foo,then print will be searched as the prefix parameter. In this case the parametercan subsequently be accessed in gdb as set print foo. If name consists of multiple
words, and no prefix parameter group can be found, an exception is raised.
The result is the <gdb:parameter> object representing the parameter. The parameter
is not usable until it has been registered with gdb with register-parameter!.
The rest of the arguments are optional.
The argument command-class should be one of the ‘COMMAND_’ constants (seeSection 23.4.3.11 [Commands In Guile], page 541). This argument tells gdb how tocategorize the new parameter in the help system. The default is COMMAND_NONE.
The argument parameter-type should be one of the ‘PARAM_’ constants defined below.
This argument tells gdb the type of the new parameter; this information is used for
input validation and completion. The default is PARAM_BOOLEAN.
If parameter-type is PARAM_ENUM, then enum-list must be a list of strings. These
strings represent the possible values for the parameter.
If parameter-type is not PARAM_ENUM, then the presence of enum-list will cause an
exception to be thrown.
The argument set-func is a function of one argument: self which is the<gdb:parameter> object representing the parameter. gdb will call this function
when a parameter’s value has been changed via the set API (for example, set
foo off). The value of the parameter has already been set to the new value. Thisfunction must return a string to be displayed to the user. gdb will add a trailing
newline if the string is non-empty. gdb generally doesn’t print anything when aparameter is set, thus typically this function should return ‘""’. A non-empty string
result should typically be used for displaying warnings and errors.
The argument show-func is a function of two arguments: self which is the<gdb:parameter> object representing the parameter, and svalue which is the string
representation of the current value. gdb will call this function when a parameter’sshow API has been invoked (for example, show foo). This function must return astring, and will be displayed to the user. gdb will add a trailing newline.
The argument doc is the help text for the new parameter. If there is no documentation
string, a default value is used.
The argument set-doc is the help text for this parameter’s set command.
The argument show-doc is the help text for this parameter’s show command.
The argument initial-value specifies the initial value of the parameter. If it is afunction, it takes one parameter, the <gdb:parameter> object and its result is usedas the initial value of the parameter. The initial value must be valid for the parameter
type, otherwise an exception is thrown.

register-parameter! parameter[Scheme Procedure]
Add parameter, a <gdb:parameter> object, to gdb’s list of parameters. It is an error
to register a parameter more than once. The result is unspecified.

parameter? object[Scheme Procedure]
Return #t if object is a <gdb:parameter> object. Otherwise return #f.

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parameter-value parameter[Scheme Procedure]
Return the value of parameter which may either be a <gdb:parameter> object or astring naming the parameter.

set-parameter-value! parameter new-value[Scheme Procedure]
Assign parameter the value of new-value. The argument parameter must be an objectof type <gdb:parameter>. gdb does validation when assignments are made.

When a new parameter is defined, its type must be specified. The available types are
represented by constants defined in the gdb module:
PARAM_BOOLEAN
The value is a plain boolean. The Guile boolean values, #t and #f are the only
valid values.
PARAM_AUTO_BOOLEAN
The value has three possible states: true, false, and ‘auto’. In Guile, true andfalse are represented using boolean constants, and ‘auto’ is represented using#:auto.
PARAM_UINTEGER
The value is an unsigned integer. The value of #:unlimited should be interpreted to mean “unlimited”, and the value of ‘0’ is reserved and should not be
used.
PARAM_ZINTEGER
The value is an integer.
PARAM_ZUINTEGER
The value is an unsigned integer.
PARAM_ZUINTEGER_UNLIMITEDThe value is an integer in the range ‘[0, INT_MAX]’. The value of #:unlimitedmeans “unlimited”, the value of ‘-1’ is reserved and should not be used, andother negative numbers are not allowed.
PARAM_STRING
The value is a string. When the user modifies the string, any escape sequences,such as ‘\t’, ‘\f’, and octal escapes, are translated into corresponding charactersand encoded into the current host charset.
PARAM_STRING_NOESCAPE
The value is a string. When the user modifies the string, escapes are passed
through untranslated.
PARAM_OPTIONAL_FILENAME
The value is a either a filename (a string), or #f.
PARAM_FILENAME
The value is a filename. This is just like PARAM_STRING_NOESCAPE, but uses filenames for completion.
PARAM_ENUM
The value is a string, which must be one of a collection of string constants
provided when the parameter is created.

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23.4.3.13 Program Spaces In Guile
A program space, or progspace, represents a symbolic view of an address space. It consistsof all of the objfiles of the program. See Section 23.4.3.14 [Objfiles In Guile], page 549. See
Section 4.9 [Inferiors Connections and Programs], page 42, for more details about program
spaces.
Each progspace is represented by an instance of the <gdb:progspace> smob.
Section 23.4.3.3 [GDB Scheme Data Types], page 522.

See

The following progspace-related functions are available in the (gdb) module:

progspace? object[Scheme Procedure]
Return #t if object is a <gdb:progspace> object. Otherwise return #f.

progspace-valid? progspace[Scheme Procedure]
Return #t if progspace is valid, #f if not. A <gdb:progspace> object can become
invalid if the program it refers to is not loaded in gdb any longer.

[Scheme Procedure]This function returns the program space of the currently selected inferior. There is always a current progspace, this never returns #f. See Section 4.9 [Inferiors Connections
and Programs], page 42.

current-progspace

progspaces[Scheme Procedure]

Return a list of all the progspaces currently known to gdb.

progspace-filename progspace[Scheme Procedure]
Return the absolute file name of progspace as a string. This is the name of the filepassed as the argument to the file or symbol-file commands. If the program spacedoes not have an associated file name, then #f is returned. This occurs, for example,
when gdb is started without a program to debug.
A gdb:invalid-object-error exception is thrown if progspace is invalid.

progspace-objfiles progspace[Scheme Procedure]
Return the list of objfiles of progspace. The order of objfiles in the result is arbitrary.
Each element is an object of type <gdb:objfile>. See Section 23.4.3.14 [Objfiles In
Guile], page 549.

A gdb:invalid-object-error exception is thrown if progspace is invalid.

progspace-pretty-printers progspace[Scheme Procedure]
Return the list of pretty-printers of progspace. Each element is an object of type<gdb:pretty-printer>. See Section 23.4.3.8 [Guile Pretty Printing API], page 537,
for more information.

set-progspace-pretty-printers! progspace printer-list[Scheme Procedure]
Set the list of registered <gdb:pretty-printer> objects for progspace to printer-list.
See Section 23.4.3.8 [Guile Pretty Printing API], page 537, for more information.

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23.4.3.14 Objfiles In Guile
gdb loads symbols for an inferior from various symbol-containing files (see Section 18.1
[Files], page 291). These include the primary executable file, any shared libraries used by
the inferior, and any separate debug info files (see Section 18.3 [Separate Debug Files],page 300). gdb calls these symbol-containing files objfiles.
Each objfile is represented as an object of type <gdb:objfile>.
The following objfile-related procedures are provided by the (gdb) module:

objfile? object[Scheme Procedure]
Return #t if object is a <gdb:objfile> object. Otherwise return #f.

objfile-valid? objfile[Scheme Procedure]
Return #t if objfile is valid, #f if not. A <gdb:objfile> object can become invalid if
the object file it refers to is not loaded in gdb any longer. All other <gdb:objfile>procedures will throw an exception if it is invalid at the time the procedure is called.

objfile-filename objfile[Scheme Procedure]
Return the file name of objfile as a string, with symbolic links resolved.

objfile-progspace objfile[Scheme Procedure]
Return the <gdb:progspace> that this object file lives in. See Section 23.4.3.13[Progspaces In Guile], page 548, for more on progspaces.

objfile-pretty-printers objfile[Scheme Procedure]
Return the list of registered <gdb:pretty-printer> objects for objfile. See
Section 23.4.3.8 [Guile Pretty Printing API], page 537, for more information.

set-objfile-pretty-printers! objfile printer-list[Scheme Procedure]
Set the list of registered <gdb:pretty-printer> objects for objfile to printer-list.
The printer-list must be a list of <gdb:pretty-printer> objects. See Section 23.4.3.8[Guile Pretty Printing API], page 537, for more information.
[Scheme Procedure]
When auto-loading a Guile script (see Section 23.4.4 [Guile Auto-loading], page 570),
gdb sets the “current objfile” to the corresponding objfile. This function returns thecurrent objfile. If there is no current objfile, this function returns #f.

current-objfile

objfiles[Scheme Procedure]

Return a list of all the objfiles in the current program space.

23.4.3.15 Accessing inferior stack frames from Guile.
When the debugged program stops, gdb is able to analyze its call stack (see Section 8.1[Stack frames], page 113). The <gdb:frame> class represents a frame in the stack. A<gdb:frame> object is only valid while its corresponding frame exists in the inferior’s stack.
If you try to use an invalid frame object, gdb will throw a gdb:invalid-object exception(see Section 23.4.3.4 [Guile Exception Handling], page 524).
Two <gdb:frame> objects can be compared for equality with the equal? function, like:(gdb) guile (equal? (newest-frame) (selected-frame))#t

The following frame-related procedures are provided by the (gdb) module:

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frame? object[Scheme Procedure]
Return #t if object is a <gdb:frame> object. Otherwise return #f.

frame-valid? frame[Scheme Procedure]
Returns #t if frame is valid, #f if not. A frame object can become invalid if the frame
it refers to doesn’t exist anymore in the inferior. All <gdb:frame> procedures willthrow an exception if the frame is invalid at the time the procedure is called.

frame-name frame[Scheme Procedure]

Return the function name of frame, or #f if it can’t be obtained.

frame-arch frame[Scheme Procedure]
Return the <gdb:architecture> object corresponding to frame’s architecture. See
Section 23.4.3.21 [Architectures In Guile], page 564.

frame-type frame[Scheme Procedure]

Return the type of frame. The value can be one of:
NORMAL_FRAME
An ordinary stack frame.
DUMMY_FRAME
A fake stack frame that was created by gdb when performing an inferior
function call.
INLINE_FRAME
A frame representing an inlined function. The function was inlined into
a NORMAL_FRAME that is older than this one.
TAILCALL_FRAME
A frame representing a tail call. See Section 11.2 [Tail Call Frames],
page 196.
SIGTRAMP_FRAME
A signal trampoline frame. This is the frame created by the OS when it
calls into a signal handler.
ARCH_FRAME
A fake stack frame representing a cross-architecture call.
SENTINEL_FRAME
This is like NORMAL_FRAME, but it is only used for the newest frame.

frame-unwind-stop-reason frame[Scheme Procedure]
Return an integer representing the reason why it’s not possible to find more frames
toward the outermost frame. Use unwind-stop-reason-string to convert the value
returned by this function to a string. The value can be one of:
FRAME_UNWIND_NO_REASON
No particular reason (older frames should be available).
FRAME_UNWIND_NULL_ID
The previous frame’s analyzer returns an invalid result.

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FRAME_UNWIND_OUTERMOSTThis frame is the outermost.
FRAME_UNWIND_UNAVAILABLE
Cannot unwind further, because that would require knowing the valuesof registers or memory that have not been collected.
FRAME_UNWIND_INNER_ID
This frame ID looks like it ought to belong to a NEXT frame, but we
got it for a PREV frame. Normally, this is a sign of unwinder failure. It
could also indicate stack corruption.
FRAME_UNWIND_SAME_ID
This frame has the same ID as the previous one. That means that unwinding further would almost certainly give us another frame with exactly thesame ID, so break the chain. Normally, this is a sign of unwinder failure.
It could also indicate stack corruption.
FRAME_UNWIND_NO_SAVED_PC
The frame unwinder did not find any saved PC, but we needed one tounwind further.
FRAME_UNWIND_MEMORY_ERROR
The frame unwinder caused an error while trying to access memory.
FRAME_UNWIND_FIRST_ERROR
Any stop reason greater or equal to this value indicates some kind oferror. This special value facilitates writing code that tests for errors in
unwinding in a way that will work correctly even if the list of the othervalues is modified in future gdb versions. Using it, you could write:(define reason (frame-unwind-stop-readon (selected-frame)))(define reason-str (unwind-stop-reason-string reason))(if (>= reason FRAME_UNWIND_FIRST_ERROR)(format #t "An error occurred: ~s\n" reason-str))

frame-pc frame[Scheme Procedure]

Return the frame’s resume address.

frame-block frame[Scheme Procedure]
Return the frame’s code block as a <gdb:block> object. See Section 23.4.3.16 [Blocks
In Guile], page 552.

frame-function frame[Scheme Procedure]
Return the symbol for the function corresponding to this frame as a <gdb:symbol>
object, or #f if there isn’t one. See Section 23.4.3.17 [Symbols In Guile], page 554.

frame-older frame[Scheme Procedure]

Return the frame that called frame.

frame-newer frame
Return the frame called by frame.

[Scheme Procedure]

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frame-sal frame[Scheme Procedure]
Return the frame’s <gdb:sal> (symtab and line) object. See Section 23.4.3.18 [Symbol Tables In Guile], page 558.

frame-read-register frame register[Scheme Procedure]
Return the value of register in frame. register should be a string, like ‘pc’.

frame-read-var frame variable [#:block block][Scheme Procedure]
Return the value of variable in frame. If the optional argument block is provided,search for the variable from that block; otherwise start at the frame’s current block(which is determined by the frame’s current program counter). The variable mustbe given as a string or a <gdb:symbol> object, and block must be a <gdb:block>object.

frame-select frame[Scheme Procedure]
Set frame to be the selected frame. See Chapter 8 [Examining the Stack], page 113.
[Scheme Procedure]
Return the selected frame object. See Section 8.3 [Selecting a Frame], page 117.

selected-frame[Scheme Procedure]

newest-frame
Return the newest frame object for the selected thread.

unwind-stop-reason-string reason[Scheme Procedure]
Return a string explaining the reason why gdb stopped unwinding frames, as expressed by the given reason code (an integer, see the frame-unwind-stop-reason
procedure above in this section).

23.4.3.16 Accessing blocks from Guile.
In gdb, symbols are stored in blocks. A block corresponds roughly to a scope in the sourcecode. Blocks are organized hierarchically, and are represented individually in Guile as an
object of type <gdb:block>. Blocks rely on debugging information being available.
A frame has a block. Please see Section 23.4.3.15 [Frames In Guile], page 549, for a morein-depth discussion of frames.
The outermost block is known as the global block. The global block typically holds
public global variables and functions.
The block nested just inside the global block is the static block. The static block typicallyholds file-scoped variables and functions.
gdb provides a method to get a block’s superblock, but there is currently no way to
examine the sub-blocks of a block, or to iterate over all the blocks in a symbol table (seeSection 23.4.3.18 [Symbol Tables In Guile], page 558).
Here is a short example that should help explain blocks:/* This is in the global block.
int global;*//* This is in the static block.
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in a block nested inside of ’function’. */int function (int argument){/* ’local’ is in a block inside ’function’. It may or may
not be in the same block as ’argument’. */int local;{/* ’inner’ is in a block whose superblock is the one holding’local’. */int inner;/* If this call is expanded by the compiler, you may see
a nested block here whose function is ’inline_function’and whose superblock is the one holding ’inner’. */inline_function ();}}The following block-related procedures are provided by the (gdb) module:

block? object[Scheme Procedure]
Return #t if object is a <gdb:block> object. Otherwise return #f.

block-valid? block[Scheme Procedure]
Returns #t if <gdb:block> block is valid, #f if not. A block object can become invalid
if the block it refers to doesn’t exist anymore in the inferior. All other <gdb:block>methods will throw an exception if it is invalid at the time the procedure is called.
The block’s validity is also checked during iteration over symbols of the block.

block-start block[Scheme Procedure]

Return the start address of <gdb:block> block.

block-end block[Scheme Procedure]

Return the end address of <gdb:block> block.

block-function block[Scheme Procedure]
Return the name of <gdb:block> block represented as a <gdb:symbol> object. If theblock is not named, then #f is returned.
For ordinary function blocks, the superblock is the static block. However, you shouldnote that it is possible for a function block to have a superblock that is not the static
block – for instance this happens for an inlined function.

block-superblock block[Scheme Procedure]
Return the block containing <gdb:block> block. If the parent block does not exist,
then #f is returned.

block-global-block block[Scheme Procedure]

Return the global block associated with <gdb:block> block.

block-static-block block[Scheme Procedure]

Return the static block associated with <gdb:block> block.

block-global? block[Scheme Procedure]
Return #t if <gdb:block> block is a global block. Otherwise return #f.

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block-static? block[Scheme Procedure]
Return #t if <gdb:block> block is a static block. Otherwise return #f.
[Scheme Procedure]
Return a list of all symbols (as <gdb:symbol> objects) in <gdb:block> block.

block-symbols

make-block-symbols-iterator block[Scheme Procedure]
Return an object of type <gdb:iterator> that will iterate over all symbols of theblock. Guile programs should not assume that a specific block object will always
contain a given symbol, since changes in gdb features and infrastructure may cause
symbols move across blocks in a symbol table. See Section 23.4.3.25 [Iterators In
Guile], page 568.
[Scheme Procedure]
Return #t if the object is a <gdb:block-symbols-progress> object. This object would
be obtained from the progress element of the <gdb:iterator> object returned by
make-block-symbols-iterator.

block-symbols-progress?

lookup-block pc[Scheme Procedure]
Return the innermost <gdb:block> containing the given pc value. If the block cannot
be found for the pc value specified, the function will return #f.

23.4.3.17 Guile representation of Symbols.
gdb represents every variable, function and type as an entry in a symbol table. See
Chapter 16 [Examining the Symbol Table], page 263. Guile represents these symbols in
gdb with the <gdb:symbol> object.
The following symbol-related procedures are provided by the (gdb) module:

symbol? object[Scheme Procedure]
Return #t if object is an object of type <gdb:symbol>. Otherwise return #f.

symbol-valid? symbol[Scheme Procedure]
Return #t if the <gdb:symbol> object is valid, #f if not. A <gdb:symbol> object
can become invalid if the symbol it refers to does not exist in gdb any longer. Allother <gdb:symbol> procedures will throw an exception if it is invalid at the time theprocedure is called.

symbol-type symbol[Scheme Procedure]
Return the type of symbol or #f if no type is recorded. The result is an object oftype <gdb:type>. See Section 23.4.3.7 [Types In Guile], page 532.

symbol-symtab symbol[Scheme Procedure]
Return the symbol table in which symbol appears. The result is an object of type<gdb:symtab>. See Section 23.4.3.18 [Symbol Tables In Guile], page 558.

symbol-line symbol[Scheme Procedure]
Return the line number in the source code at which symbol was defined. This is an
integer.

symbol-name symbol
Return the name of symbol as a string.

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symbol-linkage-name symbol[Scheme Procedure]
Return the name of symbol, as used by the linker (i.e., may be mangled).

symbol-print-name symbol[Scheme Procedure]
Return the name of symbol in a form suitable for output. This is either name or
linkage_name, depending on whether the user asked gdb to display demangled or
mangled names.

symbol-addr-class symbol[Scheme Procedure]
Return the address class of the symbol. This classifies how to find the value of asymbol. Each address class is a constant defined in the (gdb) module and describedlater in this chapter.

symbol-needs-frame? symbol[Scheme Procedure]
Return #t if evaluating symbol’s value requires a frame (see Section 23.4.3.15 [Frames
In Guile], page 549) and #f otherwise. Typically, local variables will require a frame,
but other symbols will not.

symbol-argument? symbol[Scheme Procedure]
Return #t if symbol is an argument of a function. Otherwise return #f.

symbol-constant? symbol[Scheme Procedure]

Return #t if symbol is a constant. Otherwise return #f.

symbol-function? symbol[Scheme Procedure]
Return #t if symbol is a function or a method. Otherwise return #f.

symbol-variable? symbol[Scheme Procedure]

Return #t if symbol is a variable. Otherwise return #f.

symbol-value symbol [#:frame frame][Scheme Procedure]
Compute the value of symbol, as a <gdb:value>. For functions, this computes theaddress of the function, cast to the appropriate type. If the symbol requires a framein order to compute its value, then frame must be given. If frame is not given, or ifframe is invalid, then an exception is thrown.

lookup-symbol name [#:block block] [#:domain domain][Scheme Procedure]This function searches for a symbol by name. The search scope can be restricted tothe parameters defined in the optional domain and block arguments.
name is the name of the symbol. It must be a string. The optional block argument
restricts the search to symbols visible in that block. The block argument must be a
<gdb:block> object. If omitted, the block for the current frame is used. The optional
domain argument restricts the search to the domain type. The domain argument must
be a domain constant defined in the (gdb) module and described later in this chapter.

The result is a list of two elements. The first element is a <gdb:symbol> object or#f if the symbol is not found. If the symbol is found, the second element is #t if thesymbol is a field of a method’s object (e.g., this in C++), otherwise it is #f. If thesymbol is not found, the second element is #f.

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lookup-global-symbol name [#:domain domain][Scheme Procedure]This function searches for a global symbol by name. The search scope can be restrictedby the domain argument.
name is the name of the symbol. It must be a string. The optional domain argument
restricts the search to the domain type. The domain argument must be a domain
constant defined in the (gdb) module and described later in this chapter.
The result is a <gdb:symbol> object or #f if the symbol is not found.

The available domain categories in <gdb:symbol> are represented as constants in the(gdb) module:
SYMBOL_UNDEF_DOMAIN
This is used when a domain has not been discovered or none of the following
domains apply. This usually indicates an error either in the symbol information
or in gdb’s handling of symbols.
SYMBOL_VAR_DOMAIN
This domain contains variables, function names, typedef names and enum typevalues.
SYMBOL_FUNCTION_DOMAIN
This domain contains functions.
SYMBOL_TYPE_DOMAIN
This domain contains types. In a C-like language, types using a tag (the nameappearing after a struct, union, or enum keyword) will not appear here; inother languages, all types are in this domain.
SYMBOL_STRUCT_DOMAIN
This domain holds struct, union and enum tag names. This domain is onlyused for C-like languages. For example, in this code:
struct type_one { int x; };typedef struct type_one type_two;

Here type_one will be in SYMBOL_STRUCT_DOMAIN, but type_two will be in
SYMBOL_TYPE_DOMAIN.
SYMBOL_LABEL_DOMAIN
This domain contains names of labels (for gotos).
SYMBOL_VARIABLES_DOMAIN
This domain holds a subset of the SYMBOLS_VAR_DOMAIN; it contains everything
minus functions and types.
SYMBOL_FUNCTIONS_DOMAIN
This domain contains all functions.
SYMBOL_TYPES_DOMAIN
This domain contains all types.
The available address class categories in <gdb:symbol> are represented as constants in
the gdb module:
When searching for a symbol, the desired domain constant can be passed verbatim to
the lookup function.

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For more complex searches, there is a corresponding set of constants, each named after
one of the preceding constants, but with the ‘SEARCH’ prefix replacing the ‘SYMBOL’ prefix;
for example, SEARCH_LABEL_DOMAIN. These may be or’d together to form a search constant.
SYMBOL_LOC_UNDEF
If this is returned by address class, it indicates an error either in the symbol
information or in gdb’s handling of symbols.
SYMBOL_LOC_CONST
Value is constant int.
SYMBOL_LOC_STATIC
Value is at a fixed address.
SYMBOL_LOC_REGISTER
Value is in a register.
SYMBOL_LOC_ARG
Value is an argument. This value is at the offset stored within the symbol inside
the frame’s argument list.
SYMBOL_LOC_REF_ARG
Value address is stored in the frame’s argument list. Just like LOC_ARG exceptthat the value’s address is stored at the offset, not the value itself.
SYMBOL_LOC_REGPARM_ADDRValue is a specified register. Just like LOC_REGISTER except the register holds
the address of the argument instead of the argument itself.
SYMBOL_LOC_LOCAL
Value is a local variable.
SYMBOL_LOC_TYPEDEF
Value not used. Symbols in the domain SYMBOL_STRUCT_DOMAIN all have thisclass.
SYMBOL_LOC_BLOCK
Value is a block.
SYMBOL_LOC_CONST_BYTES
Value is a byte-sequence.
SYMBOL_LOC_UNRESOLVED
Value is at a fixed address, but the address of the variable has to be determinedfrom the minimal symbol table whenever the variable is referenced.
SYMBOL_LOC_OPTIMIZED_OUT
The value does not actually exist in the program.
SYMBOL_LOC_COMPUTED
The value’s address is a computed location.

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23.4.3.18 Symbol table representation in Guile.
Access to symbol table data maintained by gdb on the inferior is exposed to Guile via two
objects: <gdb:sal> (symtab-and-line) and <gdb:symtab>. Symbol table and line data for aframe is returned from the frame-find-sal <gdb:frame> procedure. See Section 23.4.3.15[Frames In Guile], page 549.
For more information on gdb’s symbol table management, see Chapter 16 [Examining
the Symbol Table], page 263.
The following symtab-related procedures are provided by the (gdb) module:

symtab? object[Scheme Procedure]
Return #t if object is an object of type <gdb:symtab>. Otherwise return #f.

symtab-valid? symtab[Scheme Procedure]
Return #t if the <gdb:symtab> object is valid, #f if not. A <gdb:symtab> object
becomes invalid when the symbol table it refers to no longer exists in gdb. All other<gdb:symtab> procedures will throw an exception if it is invalid at the time theprocedure is called.

symtab-filename symtab[Scheme Procedure]

Return the symbol table’s source filename.

symtab-fullname symtab[Scheme Procedure]

Return the symbol table’s source absolute file name.

symtab-objfile symtab[Scheme Procedure]
Return the symbol table’s backing object file. See Section 23.4.3.14 [Objfiles In Guile],
page 549.

symtab-global-block symtab[Scheme Procedure]
Return the global block of the underlying symbol table. See Section 23.4.3.16 [Blocks
In Guile], page 552.

symtab-static-block symtab[Scheme Procedure]
Return the static block of the underlying symbol table. See Section 23.4.3.16 [Blocks
In Guile], page 552.

The following symtab-and-line-related procedures are provided by the (gdb) module:sal? object[Scheme Procedure]
Return #t if object is an object of type <gdb:sal>. Otherwise return #f.

sal-valid? sal[Scheme Procedure]
Return #t if sal is valid, #f if not. A <gdb:sal> object becomes invalid when the Symbol table object it refers to no longer exists in gdb. All other <gdb:sal> procedures
will throw an exception if it is invalid at the time the procedure is called.

sal-symtab sal[Scheme Procedure]

Return the symbol table object (<gdb:symtab>) for sal.

sal-line sal
Return the line number for sal.

[Scheme Procedure]Chapter 23: Extending gdb

sal-pc sal

559[Scheme Procedure]

Return the start of the address range occupied by code for sal.

sal-last sal[Scheme Procedure]

Return the end of the address range occupied by code for sal.

find-pc-line pc[Scheme Procedure]
Return the <gdb:sal> object corresponding to the pc value. If an invalid value of
pc is passed as an argument, then the symtab and line attributes of the returned<gdb:sal> object will be #f and 0 respectively.

23.4.3.19 Manipulating breakpoints using Guile
Breakpoints in Guile are represented by objects of type <gdb:breakpoint>. New breakpoints can be created with the make-breakpoint Guile function, and then added to gdb
with the register-breakpoint! Guile function. This two-step approach is taken to separate out the side-effect of adding the breakpoint to gdb from make-breakpoint.
Support is also provided to view and manipulate breakpoints created outside of Guile.
The following breakpoint-related procedures are provided by the (gdb) module:

make-breakpoint location [#:type type][Scheme Procedure][#:wp-class wp-class] [#:internal internal] [#:temporary temporary]
Create a new breakpoint at location, a string naming the location of the breakpoint, oran expression that defines a watchpoint. The contents can be any location recognizedby the break command, or in the case of a watchpoint, by the watch command.
The breakpoint is initially marked as ‘invalid’. The breakpoint is not usable until it
has been registered with gdb with register-breakpoint!, at which point it becomes‘valid’. The result is the <gdb:breakpoint> object representing the breakpoint.
The optional type denotes the breakpoint to create. This argument can be either
BP_BREAKPOINT or BP_WATCHPOINT, and defaults to BP_BREAKPOINT.
The optional wp-class argument defines the class of watchpoint to create, if type is
BP_WATCHPOINT. If a watchpoint class is not provided, it is assumed to be a WP_WRITE
class.
The optional internal argument allows the breakpoint to become invisible to the user.
The breakpoint will neither be reported when registered, nor will it be listed in the
output from info breakpoints (but will be listed with the maint info breakpoints
command). If an internal flag is not provided, the breakpoint is visible (non-internal).
The optional temporary argument makes the breakpoint a temporary breakpoint.
Temporary breakpoints are deleted after they have been hit, after which the
Guile breakpoint is no longer usable (although it may be re-registered withregister-breakpoint!).
When a watchpoint is created, gdb will try to create a hardware assisted watchpoint.
If successful, the type of the watchpoint is changed from BP_WATCHPOINT to BP_
HARDWARE_WATCHPOINT for WP_WRITE, BP_READ_WATCHPOINT for WP_READ, and BP_
ACCESS_WATCHPOINT for WP_ACCESS. If not successful, the type of the watchpoint isleft as WP_WATCHPOINT.

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The available types are represented by constants defined in the gdb module:
BP_BREAKPOINT
Normal code breakpoint.
BP_WATCHPOINT
Watchpoint breakpoint.
BP_HARDWARE_WATCHPOINT
Hardware assisted watchpoint. This value cannot be specified when creating the breakpoint.
BP_READ_WATCHPOINT
Hardware assisted read watchpoint. This value cannot be specified whencreating the breakpoint.
BP_ACCESS_WATCHPOINT
Hardware assisted access watchpoint. This value cannot be specified whencreating the breakpoint.
BP_CATCHPOINT
Catchpoint. This value cannot be specified when creating the breakpoint.
The available watchpoint types are represented by constants defined in the (gdb)
module:WP_READ

Read only watchpoint.

WP_WRITE

Write only watchpoint.

WP_ACCESS
Read/Write watchpoint.

register-breakpoint! breakpoint[Scheme Procedure]
Add breakpoint, a <gdb:breakpoint> object, to gdb’s list of breakpoints. The breakpoint must have been created with make-breakpoint. One cannot register breakpoints that have been created outside of Guile. Once a breakpoint is registered it
becomes ‘valid’. It is an error to register an already registered breakpoint. The
result is unspecified.

delete-breakpoint! breakpoint[Scheme Procedure]
Remove breakpoint from gdb’s list of breakpoints. This also invalidates the Guile
breakpoint object. Any further attempt to access the object will throw an exception.
If breakpoint was created from Guile with make-breakpoint it may be re-registeredwith gdb, in which case the breakpoint becomes valid again.
[Scheme Procedure]
Return a list of all breakpoints. Each element of the list is a <gdb:breakpoint>
object.

breakpoints

breakpoint? object[Scheme Procedure]
Return #t if object is a <gdb:breakpoint> object, and #f otherwise.

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breakpoint-valid? breakpoint[Scheme Procedure]
Return #t if breakpoint is valid, #f otherwise.
Breakpoints created withmake-breakpoint are marked as invalid until they are registered with gdb withregister-breakpoint!. A <gdb:breakpoint> object can become invalid if theuser deletes the breakpoint. In this case, the object still exists, but the underlying
breakpoint does not. In the cases of watchpoint scope, the watchpoint remains valid
even if execution of the inferior leaves the scope of that watchpoint.

breakpoint-number breakpoint[Scheme Procedure]
Return the breakpoint’s number — the identifier used by the user to manipulate thebreakpoint.

breakpoint-temporary? breakpoint[Scheme Procedure]
Return #t if the breakpoint was created as a temporary breakpoint. Temporary breakpoints are automatically deleted after they’ve been hit. Calling this procedure, and allother procedures other than breakpoint-valid? and register-breakpoint!, will
result in an error after the breakpoint has been hit (since it has been automaticallydeleted).

breakpoint-type breakpoint[Scheme Procedure]
Return the breakpoint’s type — the identifier used to determine the actual breakpointtype or use-case.

breakpoint-visible? breakpoint[Scheme Procedure]
Return #t if the breakpoint is visible to the user when hit, or when the ‘info
breakpoints’ command is run. Otherwise return #f.

breakpoint-location breakpoint[Scheme Procedure]
Return the location of the breakpoint, as specified by the user. It is a string. If the
breakpoint does not have a location (that is, it is a watchpoint) return #f.

breakpoint-expression breakpoint[Scheme Procedure]
Return the breakpoint expression, as specified by the user. It is a string. If the
breakpoint does not have an expression (the breakpoint is not a watchpoint) return#f.

breakpoint-enabled? breakpoint[Scheme Procedure]

Return #t if the breakpoint is enabled, and #f otherwise.

set-breakpoint-enabled! breakpoint flag

[Scheme Procedure]
Set the enabled state of breakpoint to flag. If flag is #f it is disabled, otherwise it isenabled.

breakpoint-silent? breakpoint[Scheme Procedure]

Return #t if the breakpoint is silent, and #f otherwise.
Note that a breakpoint can also be silent if it has commands and the first commandis silent. This is not reported by the silent attribute.

set-breakpoint-silent! breakpoint flag

[Scheme Procedure]
Set the silent state of breakpoint to flag. If flag is #f the breakpoint is made silent,otherwise it is made non-silent (or noisy).

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breakpoint-ignore-count breakpoint[Scheme Procedure]

Return the ignore count for breakpoint.

set-breakpoint-ignore-count! breakpoint count[Scheme Procedure]

Set the ignore count for breakpoint to count.

breakpoint-hit-count breakpoint[Scheme Procedure]

Return hit count of breakpoint.

set-breakpoint-hit-count! breakpoint count[Scheme Procedure]
Set the hit count of breakpoint to count. At present, count must be zero.

breakpoint-thread breakpoint[Scheme Procedure]
Return the global-thread-id for thread-specific breakpoint breakpoint. Return #f if
breakpoint is not thread-specific.

set-breakpoint-thread! breakpoint global-thread-id|#f[Scheme Procedure]
Set the thread-id for breakpoint to global-thread-id If set to #f, the breakpoint is nolonger thread-specific.

breakpoint-task breakpoint[Scheme Procedure]
If the breakpoint is Ada task-specific, return the Ada task id. If the breakpoint is nottask-specific (or the underlying language is not Ada), return #f.

set-breakpoint-task! breakpoint task

[Scheme Procedure]
Set the Ada task of breakpoint to task. If set to #f, the breakpoint is no longer
task-specific.

breakpoint-condition breakpoint[Scheme Procedure]
Return the condition of breakpoint, as specified by the user. It is a string. If there isno condition, return #f.

set-breakpoint-condition! breakpoint condition[Scheme Procedure]
Set the condition of breakpoint to condition, which must be a string. If set to #f thenthe breakpoint becomes unconditional.

breakpoint-stop breakpoint[Scheme Procedure]
Return the stop predicate of breakpoint. See set-breakpoint-stop! below in thissection.

set-breakpoint-stop! breakpoint procedure|#f[Scheme Procedure]
Set the stop predicate of breakpoint. The predicate procedure takes one argument:
the <gdb:breakpoint> object. If this predicate is set to a procedure then it is invokedwhenever the inferior reaches this breakpoint. If it returns #t, or any non-#f value,then the inferior is stopped, otherwise the inferior will continue.
If there are multiple breakpoints at the same location with a stop predicate, each
one will be called regardless of the return status of the previous. This ensures thatall stop predicates have a chance to execute at that location. In this scenario if oneof the methods returns #t but the others return #f, the inferior will still be stopped.
You should not alter the execution state of the inferior (i.e., step, next, etc.), alter thecurrent frame context (i.e., change the current active frame), or alter, add or delete

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any breakpoint. As a general rule, you should not alter any data within gdb or theinferior at this time.
Example stop implementation:(define (my-stop? bkpt)(let ((int-val (parse-and-eval "foo")))(value=? int-val 3)))(define bkpt (make-breakpoint "main.c:42"))(register-breakpoint! bkpt)(set-breakpoint-stop! bkpt my-stop?)

breakpoint-commands breakpoint[Scheme Procedure]
Return the commands attached to breakpoint as a string, or #f if there are none.

23.4.3.20 Guile representation of lazy strings.
A lazy string is a string whose contents is not retrieved or encoded until it is needed.
A <gdb:lazy-string> is represented in gdb as an address that points to aregion of memory, an encoding that will be used to encode that region of memory,and a length to delimit the region of memory that represents the string.
The
difference between a <gdb:lazy-string> and a string wrapped within a <gdb:value>is that a <gdb:lazy-string> will be treated differently by gdb when printing. A<gdb:lazy-string> is retrieved and encoded during printing, while a <gdb:value>
wrapping a string is immediately retrieved and encoded on creation.
The following lazy-string-related procedures are provided by the (gdb) module:

lazy-string? object[Scheme Procedure]
Return #t if object is an object of type <gdb:lazy-string>. Otherwise return #f.

lazy-string-address lazy-sring[Scheme Procedure]

Return the address of lazy-string.

lazy-string-length lazy-string[Scheme Procedure]
Return the length of lazy-string in characters. If the length is -1, then the string will
be fetched and encoded up to the first null of appropriate width.

lazy-string-encoding lazy-string[Scheme Procedure]
Return the encoding that will be applied to lazy-string when the string is printed by
gdb. If the encoding is not set, or contains an empty string, then gdb will select themost appropriate encoding when the string is printed.

lazy-string-type lazy-string[Scheme Procedure]
Return the type that is represented by lazy-string’s type. For a lazy string thisis a pointer or array type. To resolve this to the lazy string’s character type, use
type-target-type. See Section 23.4.3.7 [Types In Guile], page 532.

lazy-string->value lazy-string[Scheme Procedure]
Convert the <gdb:lazy-string> to a <gdb:value>. This value will point to thestring in memory, but will lose all the delayed retrieval, encoding and handling that
gdb applies to a <gdb:lazy-string>.

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23.4.3.21 Guile representation of architectures
gdb uses architecture specific parameters and artifacts in a number of its various computations. An architecture is represented by an instance of the <gdb:arch> class.
The following architecture-related procedures are provided by the (gdb) module:

arch? object[Scheme Procedure]
Return #t if object is an object of type <gdb:arch>. Otherwise return #f.

current-arch[Scheme Procedure]

Return the current architecture as a <gdb:arch> object.

arch-name arch

[Scheme Procedure]

Return the name (string value) of <gdb:arch> arch.

arch-charset arch

[Scheme Procedure]

Return name of target character set of <gdb:arch> arch.

arch-wide-charset[Scheme Procedure]

Return name of target wide character set of <gdb:arch> arch.
Each architecture provides a set of predefined types, obtained by the following functions.

arch-void-type arch

[Scheme Procedure]
Return the <gdb:type> object for a void type of architecture arch.

arch-char-type arch

[Scheme Procedure]
Return the <gdb:type> object for a char type of architecture arch.

arch-short-type arch

[Scheme Procedure]
Return the <gdb:type> object for a short type of architecture arch.

arch-int-type arch

[Scheme Procedure]
Return the <gdb:type> object for an int type of architecture arch.

arch-long-type arch

[Scheme Procedure]
Return the <gdb:type> object for a long type of architecture arch.

arch-schar-type arch

[Scheme Procedure]
Return the <gdb:type> object for a signed char type of architecture arch.

arch-uchar-type arch

[Scheme Procedure]
Return the <gdb:type> object for an unsigned char type of architecture arch.

arch-ushort-type arch

[Scheme Procedure]
Return the <gdb:type> object for an unsigned short type of architecture arch.

arch-uint-type arch

[Scheme Procedure]
Return the <gdb:type> object for an unsigned int type of architecture arch.

arch-ulong-type arch

[Scheme Procedure]
Return the <gdb:type> object for an unsigned long type of architecture arch.

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arch-float-type arch

[Scheme Procedure]
Return the <gdb:type> object for a float type of architecture arch.

arch-double-type arch

[Scheme Procedure]
Return the <gdb:type> object for a double type of architecture arch.

arch-longdouble-type arch

[Scheme Procedure]
Return the <gdb:type> object for a long double type of architecture arch.

arch-bool-type arch

[Scheme Procedure]
Return the <gdb:type> object for a bool type of architecture arch.

arch-longlong-type arch

[Scheme Procedure]
Return the <gdb:type> object for a long long type of architecture arch.

arch-ulonglong-type arch

[Scheme Procedure]
Return the <gdb:type> object for an unsigned long long type of architecture arch.

arch-int8-type arch

[Scheme Procedure]
Return the <gdb:type> object for an int8 type of architecture arch.

arch-uint8-type arch

[Scheme Procedure]
Return the <gdb:type> object for a uint8 type of architecture arch.

arch-int16-type arch

[Scheme Procedure]
Return the <gdb:type> object for an int16 type of architecture arch.

arch-uint16-type arch

[Scheme Procedure]
Return the <gdb:type> object for a uint16 type of architecture arch.

arch-int32-type arch

[Scheme Procedure]
Return the <gdb:type> object for an int32 type of architecture arch.

arch-uint32-type arch

[Scheme Procedure]
Return the <gdb:type> object for a uint32 type of architecture arch.

arch-int64-type arch

[Scheme Procedure]
Return the <gdb:type> object for an int64 type of architecture arch.

arch-uint64-type arch

[Scheme Procedure]
Return the <gdb:type> object for a uint64 type of architecture arch.

Example:(gdb) guile (type-name (arch-uchar-type (current-arch)))"unsigned char"

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23.4.3.22 Disassembly In Guile
The disassembler can be invoked from Scheme code. Furthermore, the disassembler cantake a Guile port as input, allowing one to disassemble from any source, and not just target
memory.

arch-disassemble arch start-pc [#:port port][#:offset offset] [#:size size] [#:count count][Scheme Procedure]

Return a list of disassembled instructions starting from the memory address start-pc.
The optional argument port specifies the input port to read bytes from. If port is #f
then bytes are read from target memory.
The optional argument offset specifies the address offset of the first byte in port.
This is useful, for example, when port specifies a ‘bytevector’ and you want the
bytevector to be disassembled as if it came from that address. The start-pc passed
to the reader for port is offset by the same amount.
Example:(gdb) guile (use-modules (rnrs io ports))(gdb) guile (define pc (value->integer (parse-and-eval "$pc")))(gdb) guile (define mem (open-memory #:start pc))(gdb) guile (define bv (get-bytevector-n mem 10))(gdb) guile (define bv-port (open-bytevector-input-port bv))(gdb) guile (define arch (current-arch))(gdb) guile (arch-disassemble arch pc #:port bv-port #:offset pc)(((address . 4195516) (asm . "mov$0x4005c8,%edi") (length . 5)))The optional arguments size and count determine the number of instructions in the
returned list. If either size or count is specified as zero, then no instructions are
disassembled and an empty list is returned. If both the optional arguments sizeand count are specified, then a list of at most count disassembled instructions whose
start address falls in the closed memory address interval from start-pc to (start-pc+ size - 1) are returned. If size is not specified, but count is specified, then countnumber of instructions starting from the address start-pc are returned. If count is
not specified but size is specified, then all instructions whose start address falls in theclosed memory address interval from start-pc to (start-pc + size - 1) are returned. Ifneither size nor count are specified, then a single instruction at start-pc is returned.
Each element of the returned list is an alist (associative list) with the following keys:
address

The value corresponding to this key is a Guile integer of the memory
address of the instruction.

asm

The value corresponding to this key is a string value which represents the
instruction with assembly language mnemonics. The assembly language
flavor used is the same as that specified by the current CLI variabledisassembly-flavor. See Section 9.6 [Machine Code], page 135.

lengthThe value corresponding to this key is the length of the instruction inbytes.

23.4.3.23 I/O Ports in Guile
input-port
Return gdb’s input port as a Guile port object.

[Scheme Procedure]Chapter 23: Extending gdb

output-port

567[Scheme Procedure]

Return gdb’s output port as a Guile port object.

error-port[Scheme Procedure]

Return gdb’s error port as a Guile port object.

stdio-port? object[Scheme Procedure]

Return #t if object is a gdb stdio port. Otherwise return #f.

23.4.3.24 Memory Ports in Guile
gdb provides a port interface to target memory. This allows Guile code to read/write target
memory using Guile’s port and bytevector functionality. The main routine is open-memory
which returns a port object. One can then read/write memory using that object.

open-memory [#:mode mode] [#:start address] [#:size size][Scheme Procedure]
Return a port object that can be used for reading and writing memory. The port
will be open according to mode, which is the standard mode argument to Guile port
open routines, except that the ‘"a"’ and ‘"l"’ modes are not supported. See Section“File Ports” in GNU Guile Reference Manual. The ‘"b"’ (binary) character may bepresent, but is ignored: memory ports are binary only. If ‘"0"’ is appended then theport is marked as unbuffered. The default is ‘"r"’, read-only and buffered.
The chunk of memory that can be accessed can be bounded. If both start and size areunspecified, all of memory can be accessed. If only start is specified, all of memory
from that point on can be accessed. If only size if specified, all memory in the range[0,size) can be accessed. If both are specified, all memory in the rane [start,start+size)
can be accessed.
[Scheme Procedure]
Return #t if object is an object of type <gdb:memory-port>. Otherwise return #f.

memory-port?

memory-port-range memory-port[Scheme Procedure]
Return the range of <gdb:memory-port> memory-port as a list of two elements:(start end). The range is start to end inclusive.

memory-port-read-buffer-size memory-port[Scheme Procedure]
Return the size of the read buffer of <gdb:memory-port> memory-port.
This procedure is deprecated and will be removed in gdb 11. It returns 0 when using
Guile 2.2 or later.

set-memory-port-read-buffer-size! memory-port size

[Scheme Procedure]
Set the size of the read buffer of <gdb:memory-port> memory-port to size. The result
is unspecified.
This procedure is deprecated and will be removed in gdb 11. When gdb is builtwith Guile 2.2 or later, you can call setvbuf instead (see Section “Buffering” in GNU
Guile Reference Manual).

memory-port-write-buffer-size memory-port[Scheme Procedure]
Return the size of the write buffer of <gdb:memory-port> memory-port.
This procedure is deprecated and will be removed in gdb 11. It returns 0 when gdb
is built with Guile 2.2 or later.

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set-memory-port-write-buffer-size! memory-port size

[Scheme Procedure]
Set the size of the write buffer of <gdb:memory-port> memory-port to size. The
result is unspecified.
This procedure is deprecated and will be removed in gdb 11. When gdb is built with
Guile 2.2 or later, you can call setvbuf instead.

A memory port is closed like any other port, with close-port.
Combined with Guile’s bytevectors, memory ports provide a lot of utility. For example,
to fill a buffer of 10 integers in memory, one can do something like the following.
;; In the program: int buffer[10];(use-modules (rnrs bytevectors))(use-modules (rnrs io ports))(define addr (parse-and-eval "buffer"))(define n 10)(define byte-size (* n 4))(define mem-port (open-memory #:mode "r+" #:start(value->integer addr) #:size byte-size))(define byte-vec (make-bytevector byte-size))(do ((i 0 (+ i 1)))((>= i n))(bytevector-s32-native-set! byte-vec (* i 4) (* i 42)))(put-bytevector mem-port byte-vec)(close-port mem-port)

23.4.3.25 Iterators In Guile
A simple iterator facility is provided to allow, for example, iterating over the set of program
symbols without having to first construct a list of all of them. A useful contribution would
be to add support for SRFI 41 and SRFI 45.

make-iterator object progress next!

[Scheme Procedure]
A <gdb:iterator> object is constructed with the make-iterator procedure. It takes
three arguments: the object to be iterated over, an object to record the progress of
the iteration, and a procedure to return the next element in the iteration, or an
implementation chosen value to denote the end of iteration.
By convention, end of iteration is marked with (end-of-iteration), and may betested with the end-of-iteration? predicate. The result of (end-of-iteration)is chosen so that it is not otherwise used by the (gdb) module. If you are using<gdb:iterator> in your own code it is your responsibility to maintain this invariant.
A trivial example for illustration’s sake:(use-modules (gdb iterator))(define my-list (list 1 2 3))(define iter
(make-iterator my-list my-list(lambda (iter)(let ((l (iterator-progress iter)))(if (eq? l ’())
(end-of-iteration)(begin(set-iterator-progress! iter (cdr l))(car l)))))))

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Here is a slightly more realistic example, which computes a list of all the functions in
my-global-block.
(use-modules (gdb iterator))(define this-sal (find-pc-line (frame-pc (selected-frame))))(define this-symtab (sal-symtab this-sal))(define this-global-block (symtab-global-block this-symtab))(define syms-iter (make-block-symbols-iterator this-global-block))(define functions (iterator-filter symbol-function? syms-iter))iterator? object[Scheme Procedure]
Return #t if object is a <gdb:iterator> object. Otherwise return #f.

iterator-object iterator[Scheme Procedure]
Return the first argument that was passed to make-iterator. This is the object
being iterated over.

iterator-progress iterator[Scheme Procedure]

Return the object tracking iteration progress.

set-iterator-progress! iterator new-value[Scheme Procedure]

Set the object tracking iteration progress.

iterator-next! iterator[Scheme Procedure]
Invoke the procedure that was the third argument to make-iterator, passing it one
argument, the <gdb:iterator> object. The result is either the next element in theiteration, or an end marker as implemented by the next! procedure. By convention
the end marker is the result of (end-of-iteration).

end-of-iteration[Scheme Procedure]

Return the Scheme object that denotes end of iteration.

end-of-iteration? object[Scheme Procedure]
Return #t if object is the end of iteration marker. Otherwise return #f.

These functions are provided by the (gdb iterator) module to assist in using iterators.

make-list-iterator list

[Scheme Procedure]

Return a <gdb:iterator> object that will iterate over list.

iterator->list iterator[Scheme Procedure]

Return the elements pointed to by iterator as a list.

iterator-map proc iterator[Scheme Procedure]
Return the list of objects obtained by applying proc to the object pointed to by
iterator and to each subsequent object.

iterator-for-each proc iterator[Scheme Procedure]
Apply proc to each element pointed to by iterator. The result is unspecified.

iterator-filter pred iterator[Scheme Procedure]
Return the list of elements pointed to by iterator that satisfy pred.

iterator-until pred iterator[Scheme Procedure]
Run iterator until the result of (pred element) is true and return that as the result.
Otherwise return #f.

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23.4.4 Guile Auto-loading
When a new object file is read (for example, due to the file command, or because theinferior has loaded a shared library), gdb will look for Guile support scripts in two ways:
objfile-gdb.scm and the .debug_gdb_scripts section. See Section 23.5 [Auto-loading
extensions], page 571.
The auto-loading feature is useful for supplying application-specific debugging commands
and scripts.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be
printed.
set auto-load guile-scripts [on|off]
Enable or disable the auto-loading of Guile scripts.
show auto-load guile-scripts
Show whether auto-loading of Guile scripts is enabled or disabled.
info auto-load guile-scripts [regexp]
Print the list of all Guile scripts that gdb auto-loaded.
Also printed is the list of Guile scripts that were mentioned in the .debug_
gdb_scripts section and were not found. This is useful because their names
are not printed when gdb tries to load them and fails. There may be many ofthem, and printing an error message for each one is problematic.
If regexp is supplied only Guile scripts with matching names are printed.
Example:(gdb) info auto-load guile-scripts
Loaded ScriptYes
scm-section-script.scm
full name: /tmp/scm-section-script.scm
No
my-foo-pretty-printers.scm

When reading an auto-loaded file, gdb sets the current objfile. This is available via thecurrent-objfile procedure (see Section 23.4.3.14 [Objfiles In Guile], page 549). This canbe useful for registering objfile-specific pretty-printers.

23.4.5 Guile Modules
gdb comes with several modules to assist writing Guile code.

23.4.5.1 Guile Printing ModuleThis module provides a collection of utilities for working with pretty-printers.
Usage:(use-modules (gdb printing))

prepend-pretty-printer! object printer[Scheme Procedure]
Add printer to the front of the list of pretty-printers for object. The object must
either be a <gdb:objfile> object, or #f in which case printer is added to the global
list of printers.

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append-pretty-printer! object printer[Scheme Procedure]
Add printer to the end of the list of pretty-printers for object. The object must either
be a <gdb:objfile> object, or #f in which case printer is added to the global list of
printers.

23.4.5.2 Guile Types ModuleThis module provides a collection of utilities for working with <gdb:type> objects.
Usage:(use-modules (gdb types))

get-basic-type type

[Scheme Procedure]
Return type with const and volatile qualifiers stripped, and with typedefs and C++
references converted to the underlying type.
C++ example:
typedef const int const_int;
const_int foo (3);const_int& foo_ref (foo);
int main () { return 0; }Then in gdb:(gdb) start(gdb) guile (use-modules (gdb) (gdb types))(gdb) guile (define foo-ref (parse-and-eval "foo_ref"))(gdb) guile (get-basic-type (value-type foo-ref))#<gdb:type int>

type-has-field-deep? type field[Scheme Procedure]
Return #t if type, assumed to be a type with fields (e.g., a structure or union), has
field field. Otherwise return #f. This searches baseclasses, whereas type-has-field?
does not.

make-enum-hashtable enum-type[Scheme Procedure]
Return a Guile hash table produced from enum-type. Elements in the hash table arereferenced with hashq-ref.

23.5 Auto-loading extensions
gdb provides two mechanisms for automatically loading extensions when a new object fileis read (for example, due to the file command, or because the inferior has loaded a sharedlibrary): objfile-gdb.ext (see Section 23.5.1 [The objfile-gdb.ext file], page 572) andthe .debug_gdb_scripts section of modern file formats like ELF (see Section 23.5.2 [The.debug_gdb_scripts section], page 573). For a discussion of the differences between these
two approaches see Section 23.5.3 [Which flavor to choose?], page 574.
The auto-loading feature is useful for supplying application-specific debugging commands
and features.
Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be
printed. See the ‘auto-loading’ section of each extension language for more information.
For gdb command files see Section 23.1.5 [Auto-loading sequences], page 399. For Python
files see Section 23.3.3 [Python Auto-loading], page 513.

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Note that loading of this script file also requires accordingly configured auto-load safepath (see Section 22.8.3 [Auto-loading safe path], page 379).

23.5.1 The objfile-gdb.ext file
When a new object file is read, gdb looks for a file named objfile-gdb.ext (we call it
script-name below), where objfile is the object file’s name and where ext is the file extension
for the extension language:
objfile-gdb.gdb
GDB’s own command language
objfile-gdb.py
Pythonobjfile-gdb.scm
Guilescript-name is formed by ensuring that the file name of objfile is absolute, following
all symlinks, and resolving . and .. components, and appending the -gdb.ext suffix. If
this file exists and is readable, gdb will evaluate it as a script in the specified extension
language.
If this file does not exist, then gdb will look for script-name file in all of the directories
as specified below. (On MS-Windows/MS-DOS, the drive letter of the executable’s leading directories is converted to a one-letter subdirectory, i.e. d:/usr/bin/ is converted to/d/usr/bin/, because Windows filesystems disallow colons in file names.)
Note that loading of these files requires an accordingly configured auto-load safe-path(see Section 22.8.3 [Auto-loading safe path], page 379).
For object files using .exe suffix gdb tries to load first the scripts normally according
to its .exe filename. But if no scripts are found gdb also tries script filenames matching
the object file without its .exe suffix. This .exe stripping is case insensitive and it is
attempted on any platform. This makes the script filenames compatible between Unix and
MS-Windows hosts.
set auto-load scripts-directory [directories]
Control gdb auto-loaded scripts location. Multiple directory entries may bedelimited by the host platform path separator in use (‘:’ on Unix, ‘;’ on MSWindows and MS-DOS).
Each entry here needs to be covered also by the security setting set auto-load
safe-path (see [set auto-load safe-path], page 379).
This variable defaults to $debugdir:$datadir/auto-load. The default set
auto-load safe-path value can be also overridden by gdb configuration option--with-auto-load-dir.
Any reference to $debugdir will get replaced by debug-file-directory value (seeSection 18.3 [Separate Debug Files], page 300) and any reference to $datadir
will get replaced by data-directory which is determined at gdb startup (seeSection 18.8 [Data Files], page 308). $debugdir and $datadir must be placed
as a directory component — either alone or delimited by / or \ directory separators, depending on the host platform.

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The list of directories uses path separator (‘:’ on GNU and Unix systems, ‘;’
on MS-Windows and MS-DOS) to separate directories, similarly to the PATH
environment variable.
show auto-load scripts-directoryShow gdb auto-loaded scripts location.
add-auto-load-scripts-directory [directories...]
Add an entry (or list of entries) to the list of auto-loaded scripts locations.
Multiple entries may be delimited by the host platform path separator in use.
gdb does not track which files it has already auto-loaded this way. gdb will load theassociated script every time the corresponding objfile is opened. So your -gdb.ext fileshould be careful to avoid errors if it is evaluated more than once.

23.5.2 The .debug_gdb_scripts section
For systems using file formats like ELF and COFF, when gdb loads a new object file it will
look for a special section named .debug_gdb_scripts. If this section exists, its contents is
a list of null-terminated entries specifying scripts to load. Each entry begins with a non-null
prefix byte that specifies the kind of entry, typically the extension language and whether
the script is in a file or inlined in .debug_gdb_scripts.
The following entries are supported:
SECTION_SCRIPT_ID_PYTHON_FILE = 1
SECTION_SCRIPT_ID_SCHEME_FILE = 3
SECTION_SCRIPT_ID_PYTHON_TEXT = 4
SECTION_SCRIPT_ID_SCHEME_TEXT = 6

23.5.2.1 Script File Entries
If the entry specifies a file, gdb will look for the file first in the current directory and thenalong the source search path (see Section 9.5 [Specifying Source Directories], page 131),
except that $cdir is not searched, since the compilation directory is not relevant to scripts.
File entries can be placed in section .debug_gdb_scripts with, for example, this GCC
macro for Python scripts.
/* Note: The "MS" section flags are to remove duplicates. */#define DEFINE_GDB_PY_SCRIPT(script_name) \asm("\.pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\.byte 1 /* Python */\n\.asciz \"" script_name "\"\n\.popsection \n\");
For Guile scripts, replace .byte 1 with .byte 3. Then one can reference the macro in aheader or source file like this:DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py")
The script name may include directories if desired.
Note that loading of this script file also requires accordingly configured auto-load safepath (see Section 22.8.3 [Auto-loading safe path], page 379).

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If the macro invocation is put in a header, any application or library using this header
will get a reference to the specified script, and with the use of "MS" attributes on the section,
the linker will remove duplicates.

23.5.2.2 Script Text Entries
Script text entries allow to put the executable script in the entry itself instead of loading
it from a file. The first line of the entry, everything after the prefix byte and up to thefirst newline (0xa) character, is the script name, and must not contain any kind of spacecharacter, e.g., spaces or tabs. The rest of the entry, up to the trailing null byte, is the
script to execute in the specified language. The name needs to be unique among all script
names, as gdb executes each script only once based on its name.
Here is an example from file py-section-script.c in the gdb testsuite.
#include "symcat.h"#include "gdb/section-scripts.h"asm(".pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n"".byte " XSTRING (SECTION_SCRIPT_ID_PYTHON_TEXT) "\n"".ascii \"gdb.inlined-script\\n\"\n"".ascii \"class test_cmd (gdb.Command):\\n\"\n"".ascii \" def __init__ (self):\\n\"\n"".ascii \"super (test_cmd, self).__init__ (""\\\"test-cmd\\\", gdb.COMMAND_OBSCURE)\\n\"\n"".ascii \" def invoke (self, arg, from_tty):\\n\"\n"".ascii \"print (\\\"test-cmd output, arg = %s\\\" % arg)\\n\"\n"".ascii \"test_cmd ()\\n\"\n"".byte 0\n"".popsection\n");Loading of inlined scripts requires a properly configured auto-load safe-path (seeSection 22.8.3 [Auto-loading safe path], page 379). The path to specify in auto-load
safe-path is the path of the file containing the .debug_gdb_scripts section.

23.5.3 Which flavor to choose?
Given the multiple ways of auto-loading extensions, it might not always be clear which one
to choose. This section provides some guidance.
Benefits of the -gdb.ext way:
• Can be used with file formats that don’t support multiple sections.
• Ease of finding scripts for public libraries.
Scripts specified in the .debug_gdb_scripts section are searched for in the source
search path. For publicly installed libraries, e.g., libstdc++, there typically isn’t asource directory in which to find the script.
• Doesn’t require source code additions.
Benefits of the .debug_gdb_scripts way:

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Scripts for libraries done the -gdb.ext way require an objfile to trigger their loading.
When an application is statically linked the only objfile available is the executable, and
it is cumbersome to attach all the scripts from all the input libraries to the executable’s-gdb.ext script.
• Works with classes that are entirely inlined.
Some classes can be entirely inlined, and thus there may not be an associated sharedlibrary to attach a -gdb.ext script to.
• Scripts needn’t be copied out of the source tree.
In some circumstances, apps can be built out of large collections of internal libraries,
and the build infrastructure necessary to install the -gdb.ext scripts in a place where
gdb can find them is cumbersome. It may be easier to specify the scripts in the.debug_gdb_scripts section as relative paths, and add a path to the top of the source
tree to the source search path.

23.6 Multiple Extension Languages
The Guile and Python extension languages do not share any state, and generally do notinterfere with each other. There are some things to be aware of, however.

23.6.1 Python comes first
Python was gdb’s first extension language, and to avoid breaking existing behaviour Python
comes first. This is generally solved by the “first one wins” principle. gdb maintains a listof enabled extension languages, and when it makes a call to an extension language, (sayto pretty-print a value), it tries each in turn until an extension language indicates it has
performed the request (e.g., has returned the pretty-printed form of a value). This extends
to errors while performing such requests: If an error happens while, for example, trying topretty-print an object then the error is reported and any following extension languages are
not tried.

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24 Command Interpreters
gdb supports multiple command interpreters, and some command infrastructure to allow
users or user interface writers to switch between interpreters or run commands in otherinterpreters.
gdb currently supports two command interpreters, the console interpreter (sometimes
called the command-line interpreter or cli) and the machine interface interpreter (orgdb/mi). This manual describes both of these interfaces in great detail.
By default, gdb will start with the console interpreter. However, the user may choose tostart gdb with another interpreter by specifying the -i or --interpreter startup options.
Defined interpreters include:
consoleThe traditional console or command-line interpreter. This is the most often
used interpreter with gdb. With no interpreter specified at runtime, gdb will
use this interpreter.

dap

When gdb has been built with Python support, it also supports the Debugger
Adapter Protocol. This protocol can be used by a debugger GUI or an IDE tocommunicate with gdb. This protocol is documented at https://microsoft.
github.io/debug-adapter-protocol/. See Chapter 29 [Debugger Adapter
Protocol], page 699, for information about gdb extensions to the protocol.

mi

The newest gdb/mi interface (currently mi3). Used primarily by programs
wishing to use gdb as a backend for a debugger GUI or an IDE. For more
information, see Chapter 27 [The gdb/mi Interface], page 589.

mi3

The gdb/mi interface introduced in gdb 9.1.

mi2

The gdb/mi interface introduced in gdb 6.0.

You may execute commands in any interpreter from the current interpreter using
the appropriate command. If you are running the console interpreter, simply use theinterpreter-exec command:interpreter-exec mi "-data-list-register-names"

gdb/mi has a similar command, although it is only available in versions of gdb which
support gdb/mi version 2 (or greater).
Note that interpreter-exec only changes the interpreter for the duration of the specified command. It does not change the interpreter permanently.
Although you may only choose a single interpreter at startup, it is possible to run an
independent interpreter on a specified input/output device (usually a tty).
For example, consider a debugger GUI or IDE that wants to provide a gdb console view.
It may do so by embedding a terminal emulator widget in its GUI, starting gdb in the
traditional command-line mode with stdin/stdout/stderr redirected to that terminal, andthen creating an MI interpreter running on a specified input/output device. The console
interpreter created by gdb at startup handles commands the user types in the terminal
widget, while the GUI controls and synchronizes state with gdb using the separate MIinterpreter.
To start a new secondary user interface running MI, use the new-ui command:
new-ui interpreter tty

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The interpreter parameter specifies the interpreter to run. This accepts the same values
as the interpreter-exec command. For example, ‘console’, ‘mi’, ‘mi2’, etc. The tty
parameter specifies the name of the bidirectional file the interpreter uses for input/output,
usually the name of a pseudoterminal slave on Unix systems. For example:(gdb) new-ui mi /dev/pts/9

runs an MI interpreter on /dev/pts/9.

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25 gdb Text User Interface
The gdb Text User Interface (TUI) is a terminal interface which uses the curses libraryto show the source file, the assembly output, the program registers and gdb commands inseparate text windows. The TUI mode is supported only on platforms where a suitableversion of the curses library is available.
The TUI mode is enabled by default when you invoke gdb as ‘gdb -tui’. You can also
switch in and out of TUI mode while gdb runs by using various TUI commands and key
bindings, such as tui enable or C-x C-a. See Section 25.5 [TUI Commands], page 582, andSection 25.2 [TUI Key Bindings], page 580.

25.1 TUI Overview
In TUI mode, gdb can display several text windows:
commandThis window is the gdb command window with the gdb prompt and the gdb
output. The gdb input is still managed using readline.

sourceThe source window shows the source file of the program. The current line andactive breakpoints are displayed in this window.

assembly

The assembly window shows the disassembly output of the program.

registerThis window shows the processor registers. Registers are highlighted when theirvalues change.

The source and assembly windows show the current program position by highlighting thecurrent line and marking it with a ‘>’ marker. By default, source and assembly code stylingis disabled for the highlighted text, but you can enable it with the set style tui-currentposition on command. See Section 22.5 [Output Styling], page 371.
Breakpoints are indicated with two markers. The first marker indicates the breakpoint
type:
B

Breakpoint which was hit at least once.

b

Breakpoint which was never hit.

H

Hardware breakpoint which was hit at least once.

hHardware breakpoint which was never hit.
The second marker indicates whether the breakpoint is enabled or not:+Breakpoint is enabled.

-

Breakpoint is disabled.

The source, assembly and register windows are updated when the current thread changes,
when the frame changes, or when the program counter changes.
These windows are not all visible at the same time. The command window is always
visible. The others can be arranged in several layouts:• source only,• assembly only,

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These are the standard layouts, but other layouts can be defined.
A status line above the command window shows the following information:
targetIndicates the current gdb target. (see Chapter 19 [Specifying a Debugging
Target], page 311).

process

Gives the current process or thread number. When no process is being debugged, this field is set to No process.

focus

Shows the name of the TUI window that has the focus.

function

Gives the current function name for the selected frame. The name is demangled
if demangling is turned on (see Section 10.9 [Print Settings], page 157). When
there is no symbol corresponding to the current program counter, the string ??
is displayed.

line

Indicates the current line number for the selected frame. When the current line
number is not known, the string ?? is displayed.

pc

Indicates the current program counter address.

25.2 TUI Key Bindings
The TUI installs several key bindings in the readline keymaps (see Chapter 33 [Command
Line Editing], page 713). The following key bindings are installed for both TUI mode andthe gdb standard mode.
C-x C-a
C-x a
C-x A

Enter or leave the TUI mode. When leaving the TUI mode, the curses window
management stops and gdb operates using its standard mode, writing on theterminal directly. When reentering the TUI mode, control is given back to thecurses windows. The screen is then refreshed.
This key binding uses the bindable Readline function tui-switch-mode.

C-x 1

Use a TUI layout with only one window. The layout will either be ‘source’ or‘assembly’. When the TUI mode is not active, it will switch to the TUI mode.
Think of this key binding as the Emacs C-x 1 binding.
This key binding uses the bindable Readline function tui-delete-otherwindows.

C-x 2

Use a TUI layout with at least two windows. When the current layout alreadyhas two windows, the next layout with two windows is used. When a new layout
is chosen, one window will always be common to the previous layout and thenew one.
Think of it as the Emacs C-x 2 binding.
This key binding uses the bindable Readline function tui-change-windows.

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C-x o

Change the active window. The TUI associates several key bindings (likescrolling and arrow keys) with the active window. This command gives thefocus to the next TUI window.
Think of it as the Emacs C-x o binding.
This key binding uses the bindable Readline function tui-other-window.

C-x s

Switch in and out of the TUI SingleKey mode that binds single keys to gdb
commands (see Section 25.3 [TUI Single Key Mode], page 581).
This key binding uses the bindable Readline function next-keymap.

The following key bindings only work in the TUI mode:
PgUp

Scroll the active window one page up.

PgDn

Scroll the active window one page down.

Up

Scroll the active window one line up.

Down

Scroll the active window one line down.

Left

Scroll the active window one column left.

Right

Scroll the active window one column right.

C-L

Refresh the screen.

Because the arrow keys scroll the active window in the TUI mode, they are not available
for their normal use by readline unless the command window has the focus. When anotherwindow is active, you must use other readline key bindings such as C-p, C-n, C-b and C-f
to control the command window.

25.3 TUI Single Key Mode
The TUI also provides a SingleKey mode, which binds several frequently used gdb commands to single keys. Type C-x s to switch into this mode, where the following key bindings
are used:ccontinueCreverse-continue

d

down

f

finishFreverse-finish

n

next

N

reverse-nextonexti. The shortcut letter ‘o’ stands for “step Over”.

O

reverse-nextiqexit the SingleKey mode.

r

run

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s

step

S

reverse-stepi

stepi. The shortcut letter ‘i’ stands for “step Into”.

I

reverse-stepi

u

up

v

info locals

w

where

Other keys temporarily switch to the gdb command prompt. The key that was pressed
is inserted in the editing buffer so that it is possible to type most gdb commands without
interaction with the TUI SingleKey mode. Once the command is entered the TUI SingleKey
mode is restored. The only way to permanently leave this mode is by typing q or C-x s.
If gdb was built with Readline 8.0 or later, the TUI SingleKey keymap will be named‘SingleKey’. This can be used in .inputrc to add additional bindings to this keymap.

25.4 TUI Mouse Support
If the curses library supports the mouse, the TUI supports mouse actions.
The mouse wheel scrolls the appropriate window under the mouse cursor.
The TUI itself does not directly support copying/pasting with the mouse. However, on
Unix terminals, you can typically press and hold the SHIFT key on your keyboard to temporarily bypass gdb’s TUI and access the terminal’s native mouse copy/paste functionality(commonly, click-drag-release or double-click to select text, middle-click to paste). This
copy/paste works with the terminal’s selection buffer, as opposed to the TUI’s buffer. Alternatively, to disable mouse support in the TUI entirely and give the terminal control overmouse clicks, turn off the tui mouse-events setting (see [set tui mouse-events], page 586).
Python extensions can react to mouse clicks (see [Window.click], page 502).

25.5 TUI-specific Commands
The TUI has specific commands to control the text windows. These commands are always
available, even when gdb is not in the TUI mode. When gdb is in the standard mode,
most of these commands will automatically switch to the TUI mode.
Note that if gdb’s stdout is not connected to a terminal, or gdb has been started withthe machine interface interpreter (see Chapter 27 [The gdb/mi Interface], page 589), mostof these commands will fail with an error, because it would not be possible or desirable toenable curses window management.
tui enable
Activate TUI mode. The last active TUI window layout will be used if TUImode has previously been used in the current debugging session, otherwise adefault layout is used.
tui disable
Disable TUI mode, returning to the console interpreter.

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info win

583

List the names and sizes of all currently displayed windows.

tui new-layout name window weight [window weight...]Create a new TUI layout. The new layout will be named name, and can beaccessed using the layout command (see below).
Each window parameter is either the name of a window to display, or a window
description. The windows will be displayed from top to bottom in the order
listed.
The names of the windows are the same as the ones given to the focus command(see below); additionally, the status window can be specified. Note that,
because it is of fixed height, the weight assigned to the status window is of noimportance. It is conventional to use ‘0’ here.
A window description looks a bit like an invocation of tui new-layout, and isof the form {[-horizontal]window weight [window weight. . . ]}.
This specifies a sub-layout. If -horizontal is given, the windows in this description will be arranged side-by-side, rather than top-to-bottom.
Each weight is an integer. It is the weight of this window relative to all theother windows in the layout. These numbers are used to calculate how muchof the screen is given to each window.
For example:(gdb) tui new-layout example src 1 regs 1 status 0 cmd 1
Here, the new layout is called ‘example’. It shows the source and register
windows, followed by the status window, and then finally the command window.
The non-status windows all have the same weight, so the terminal will be split
into three roughly equal sections.
Here is a more complex example, showing a horizontal layout:(gdb) tui new-layout example {-horizontal src 1 asm 1} 2 status 0 cmd 1
This will result in side-by-side source and assembly windows; with the status
and command window being beneath these, filling the entire width of the terminal. Because they have weight 2, the source and assembly windows will betwice the height of the command window.
tui layout namelayout name
Changes which TUI windows are displayed. The name parameter controls which
layout is shown. It can be either one of the built-in layout names, or the nameof a layout defined by the user using tui new-layout.
The built-in layouts are as follows:
next

Display the next layout.

prev

Display the previous layout.

src

Display the source and command windows.

asm

Display the assembly and command windows.

split

Display the source, assembly, and command windows.

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regs

When in src layout display the register, source, and command windows. When in asm or split layout display the register, assembler,and command windows.

tui focus namefocus name
Changes which TUI window is currently active for scrolling. The name parameter can be any of the following:
nextMake the next window active for scrolling.

prev

Make the previous window active for scrolling.

src

Make the source window active for scrolling.

asm

Make the assembly window active for scrolling.

regs

Make the register window active for scrolling.

cmd

Make the command window active for scrolling.

tui refresh
refreshRefresh the screen. This is similar to typing C-L.
tui reg group
Changes the register group displayed in the tui register window to group. If theregister window is not currently displayed this command will cause the register
window to be displayed. The list of register groups, as well as their order istarget specific. The following groups are available on most targets:

updatenext

Repeatedly selecting this group will cause the display to cycle
through all of the available register groups.

prev

Repeatedly selecting this group will cause the display to cycle
through all of the available register groups in the reverse order to
next.

general

Display the general registers.

float

Display the floating point registers.

system

Display the system registers.

vector

Display the vector registers.

all

Display all registers.

Update the source window and the current execution point.

tui window height name +counttui window height name -countwinheight name +countwinheight name -count
Change the height of the window name by count lines. Positive counts increase
the height, while negative counts decrease it. The name parameter can be
the name of any currently visible window. The names of the currently visible
windows can be discovered using info win (see [info win], page 582).

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The set of currently visible windows must always fill the terminal, and so, it is
only possible to resize on window if there are other visible windows that caneither give or receive the extra terminal space.
tui window width name +counttui window width name -countwinwidth name +countwinwidth name -count
Change the width of the window name by count columns. Positive counts
increase the width, while negative counts decrease it. The name parameter canbe the name of any currently visible window. The names of the currently visible
windows can be discovered using info win (see [info win], page 582).
The set of currently visible windows must always fill the terminal, and so, it is
only possible to resize on window if there are other visible windows that caneither give or receive the extra terminal space.

25.6 TUI Configuration Variables
Several configuration variables control the appearance of TUI windows.
set tui border-kind kind
Select the border appearance for the source, assembly and register windows.
The possible values are the following:
space

Use a space character to draw the border.

ascii

Use ascii characters ‘+’, ‘-’ and ‘|’ to draw the border.

acs

Use the Alternate Character Set to draw the border. The border isdrawn using character line graphics if the terminal supports them.

set tui border-mode mode
set tui active-border-mode mode
Select the display attributes for the borders of the inactive windows or theactive window. The mode can be one of the following:normal

Use normal attributes to display the border.

standout

Use standout mode.

reverseUse reverse video mode.

half

Use half bright mode.

half-standout
Use half bright and standout mode.
bold

Use extra bright or bold mode.

bold-standout
Use extra bright or bold and standout mode.
set tui tab-width nchars
Set the width of tab stops to be nchars characters. This setting affects thedisplay of TAB characters in the source and assembly windows.

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set tui compact-source [on|off]
Set whether the TUI source window is displayed in “compact” form. The
default display uses more space for line numbers; the compact display uses only
as much space as is needed for the line numbers in the current file.
set tui mouse-events [on|off]
When on (default), mouse clicks control the TUI (see Section 25.4 [TUI Mouse
Support], page 582). When off, mouse clicks are handled by the terminal,
enabling terminal-native text selection.
set debug tui [on|off]Turn on or off display of gdb internal debug messages relating to the TUI.
show debug tui
Show the current status of displaying gdb internal debug messages relating to
the TUI.
Note that the colors of the TUI borders can be controlled using the appropriate set
style commands. See Section 22.5 [Output Styling], page 371.

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26 Using gdb under gnu Emacs
A special interface allows you to use gnu Emacs to view (and edit) the source files for the
program you are debugging with gdb.
To use this interface, use the command M-x gdb in Emacs. Give the executable file youwant to debug as an argument. This command starts gdb as a subprocess of Emacs, with
input and output through a newly created Emacs buffer.
Running gdb under Emacs can be just like running gdb normally except for two things:• All “terminal” input and output goes through an Emacs buffer, called the GUD buffer.
This applies both to gdb commands and their output, and to the input and output
done by the program you are debugging.
This is useful because it means that you can copy the text of previous commands andinput them again; you can even use parts of the output in this way.
All the facilities of Emacs’ Shell mode are available for interacting with your program.
In particular, you can send signals the usual way—for example, C-c C-c for an interrupt, C-c C-z for a stop.
• gdb displays source code through Emacs.
Each time gdb displays a stack frame, Emacs automatically finds the source file forthat frame and puts an arrow (‘=>’) at the left margin of the current line. Emacs uses a
separate buffer for source display, and splits the screen to show both your gdb session
and the source.
Explicit gdb list or search commands still produce output as usual, but you probably
have no reason to use them from Emacs.
We call this text command mode. Emacs 22.1, and later, also uses a graphical mode, enabled by default, which provides further buffers that can control the execution and describe
the state of your program. See Section “GDB Graphical Interface” in The gnu Emacs
Manual.
If you specify an absolute file name when prompted for the M-x gdb argument, thenEmacs sets your current working directory to where your program resides. If you only
specify the file name, then Emacs sets your current working directory to the directory
associated with the previous buffer. In this case, gdb may find your program by searching
your environment’s PATH variable, but on some operating systems it might not find thesource. So, although the gdb input and output session proceeds normally, the auxiliary
buffer does not display the current source and line of execution.
The initial working directory of gdb is printed on the top line of the GUD buffer andthis serves as a default for the commands that specify files for gdb to operate on. See
Section 18.1 [Commands to Specify Files], page 291.
By default, M-x gdb calls the program called gdb. If you need to call gdb by a different
name (for example, if you keep several configurations around, with different names) you cancustomize the Emacs variable gud-gdb-command-name to run the one you want.
In the GUD buffer, you can use these special Emacs commands in addition to thestandard Shell mode commands:
C-h m

Describe the features of Emacs’ GUD Mode.

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C-c C-s

Execute to another source line, like the gdb step command; also update thedisplay window to show the current file and location.

C-c C-nExecute to next source line in this function, skipping all function calls, like thegdb next command. Then update the display window to show the current fileand location.

C-c C-i

Execute one instruction, like the gdb stepi command; update display window
accordingly.

C-c C-f

Execute until exit from the selected stack frame, like the gdb finish command.

C-c C-rContinue execution of your program, like the gdb continue command.

C-c <Go up the number of frames indicated by the numeric argument (see Section“Numeric Arguments” in The gnu Emacs Manual), like the gdb up command.

C-c >Go down the number of frames indicated by the numeric argument, like thegdb down command.

In any source file, the Emacs command C-x SPC (gud-break) tells gdb to set a breakpoint on the source line point is on.
In text command mode, if you type M-x speedbar, Emacs displays a separate frame
which shows a backtrace when the GUD buffer is current. Move point to any frame in thestack and type RET to make it become the current frame and display the associated sourcein the source buffer. Alternatively, click Mouse-2 to make the selected frame become thecurrent one. In graphical mode, the speedbar displays watch expressions.
If you accidentally delete the source-display buffer, an easy way to get it back is to typethe command f in the gdb buffer, to request a frame display; when you run under Emacs,
this recreates the source buffer if necessary to show you the context of the current frame.
The source files displayed in Emacs are in ordinary Emacs buffers which are visiting thesource files in the usual way. You can edit the files with these buffers if you wish; but keep
in mind that gdb communicates with Emacs in terms of line numbers. If you add or deletelines from the text, the line numbers that gdb knows cease to correspond properly with thecode.
A more detailed description of Emacs’ interaction with gdb is given in the Emacs manual(see Section “Debuggers” in The gnu Emacs Manual).

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27 The gdb/mi Interface
Function and Purpose
gdb/mi is a line based machine oriented text interface to gdb and is activated by specifying
using the --interpreter command line option (see Section 2.1.2 [Mode Options], page 13).
It is specifically intended to support the development of systems which use the debugger asjust one small component of a larger system.
This chapter is a specification of the gdb/mi interface. It is written in the form of areference manual.
Note that gdb/mi is still under construction, so some of the features described below
are incomplete and subject to change (see Section 27.6 [gdb/mi Development and Front
Ends], page 595).

Notation and Terminology
This chapter uses the following notation:• | separates two alternatives.
• [ something ] indicates that something is optional: it may or may not be given.
• ( group )* means that group inside the parentheses may repeat zero or more times.
• ( group )+ means that group inside the parentheses may repeat one or more times.
• ( group ) means that group inside the parentheses occurs exactly once.
• "string" means a literal string.

27.3 gdb/mi General Design
Interaction of a gdb/mi frontend with gdb involves three parts—commands sent to gdb,
responses to those commands and notifications. Each command results in exactly one
response, indicating either successful completion of the command, or an error. For thecommands that do not resume the target, the response contains the requested information.
For the commands that resume the target, the response only indicates whether the target
was successfully resumed. Notifications is the mechanism for reporting changes in the stateof the target, or in gdb state, that cannot conveniently be associated with a command andreported as part of that command response.
The important examples of notifications are:• Exec notifications. These are used to report changes in target state—when a target isresumed, or stopped. It would not be feasible to include this information in responseof resuming commands, because one resume commands can result in multiple eventsin different threads. Also, quite some time may pass before any event happens in
the target, while a frontend needs to know whether the resuming command itself was
successfully executed.
• Console output, and status notifications. Console output notifications are used toreport output of CLI commands, as well as diagnostics for other commands. Status
notifications are used to report the progress of a long-running operation. Naturally,

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including this information in command response would mean no output is produced
until the command is finished, which is undesirable.
• General notifications. Commands may have various side effects on the gdb or target
state beyond their official purpose. For example, a command may change the selected
thread. Although such changes can be included in command response, using notification
allows for more orthogonal frontend design.
There’s no guarantee that whenever an MI command reports an error, gdb or the target
are in any specific state, and especially, the state is not reverted to the state before theMI command was processed. Therefore, whenever an MI command results in an error, werecommend that the frontend refreshes all the information shown in the user interface.

27.3.1 Context management
27.3.1.1 Threads and Frames
In most cases when gdb accesses the target, this access is done in context of a specific thread
and frame (see Section 8.1 [Frames], page 113). Often, even when accessing global data, thetarget requires that a thread be specified. The CLI interface maintains the selected thread
and frame, and supplies them to target on each command. This is convenient, because acommand line user would not want to specify that information explicitly on each command,and because user interacts with gdb via a single terminal, so no confusion is possible as towhat thread and frame are the current ones.
In the case of MI, the concept of selected thread and frame is less useful. First, afrontend can easily remember this information itself. Second, a graphical frontend can havemore than one window, each one used for debugging a different thread, and the frontend
might want to access additional threads for internal purposes. This increases the risk thatby relying on implicitly selected thread, the frontend may be operating on a wrong one.
Therefore, each MI command should explicitly specify which thread and frame to operate
on. To make it possible, each MI command accepts the ‘--thread’ and ‘--frame’ options,the value to each is gdb global identifier for thread and frame to operate on.
Usually, each top-level window in a frontend allows the user to select a thread and aframe, and remembers the user selection for further operations. However, in some cases
gdb may suggest that the current thread or frame be changed. For example, when stopping on a breakpoint it is reasonable to switch to the thread where breakpoint is hit. For
another example, if the user issues the CLI ‘thread’ or ‘frame’ commands via the frontend,
it is desirable to change the frontend’s selection to the one specified by user. gdb communicates the suggestion to change current thread and frame using the ‘=thread-selected’
notification.
Note that historically, MI shares the selected thread with CLI, so frontends used the-thread-select to execute commands in the right context. However, getting this to work
right is cumbersome. The simplest way is for frontend to emit -thread-select command
before every command. This doubles the number of commands that need to be sent. The
alternative approach is to suppress -thread-select if the selected thread in gdb is supposed to be identical to the thread the frontend wants to operate on. However, getting thisoptimization right can be tricky. In particular, if the frontend sends several commands to
gdb, and one of the commands changes the selected thread, then the behaviour of subsequent commands will change. So, a frontend should either wait for response from such

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problematic commands, or explicitly add -thread-select for all subsequent commands.
No frontend is known to do this exactly right, so it is suggested to just always pass the‘--thread’ and ‘--frame’ options.

27.3.1.2 Language
The execution of several commands depends on which language is selected. By default, thecurrent language (see [show language], page 229) is used. But for commands known to be
language-sensitive, it is recommended to use the ‘--language’ option. This option takes
one argument, which is the name of the language to use while executing the command. For
instance:-data-evaluate-expression --language c "sizeof (void*)"^done,value="4"(gdb)

The valid language names are the same names accepted by the ‘set language’ command(see Section 15.1.2 [Manually], page 228), excluding ‘auto’, ‘local’ or ‘unknown’.

27.3.2 Asynchronous command execution and non-stop mode
On some targets, gdb is capable of processing MI commands even while the target isrunning. This is called asynchronous command execution (see Section 5.5.3 [Background
Execution], page 95). The frontend may specify a preference for asynchronous execution
using the -gdb-set mi-async 1 command, which should be emitted before either runningthe executable or attaching to the target. After the frontend has started the executable orattached to the target, it can find if asynchronous execution is enabled using the -listtarget-features command.
-gdb-set mi-async [on|off]
Set whether MI is in asynchronous mode.
When off, which is the default, MI execution commands (e.g., -execcontinue) are foreground commands, and gdb waits for the program to stop
before processing further commands.
When on, MI execution commands are background execution commands (e.g.,-exec-continue becomes the equivalent of the c& CLI command), and so gdb
is capable of processing MI commands even while the target is running.
-gdb-show mi-async
Show whether MI asynchronous mode is enabled.
Note: In gdb version 7.7 and earlier, this option was called target-async instead of
mi-async, and it had the effect of both putting MI in asynchronous mode and making CLI
background commands possible. CLI background commands are now always possible “outof the box” if the target supports them. The old spelling is kept as a deprecated alias forbackwards compatibility.
Even if gdb can accept a command while target is running, many commands that accessthe target do not work when the target is running. Therefore, asynchronous commandexecution is most useful when combined with non-stop mode (see Section 5.5.2 [Non-StopMode], page 94). Then, it is possible to examine the state of one thread, while other threads
are running.

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When a given thread is running, MI commands that try to access the target in thecontext of that thread may not work, or may work only on some targets. In particular,commands that try to operate on thread’s stack will not work, on any target. Commands
that read memory, or modify breakpoints, may work or not work, depending on the target.
Note that even commands that operate on global state, such as print, set, and breakpointcommands, still access the target in the context of a specific thread, so frontend should try
to find a stopped thread and perform the operation on that thread (using the ‘--thread’
option).
Which commands will work in the context of a running thread is highly target dependent.
However, the two commands -exec-interrupt, to stop a thread, and -thread-info, tofind the state of a thread, will always work.

27.3.3 Thread groups
gdb may be used to debug several processes at the same time. On some platforms, gdb
may support debugging of several hardware systems, each one having several cores withseveral different processes running on each core. This section describes the MI mechanism
to support such debugging scenarios.
The key observation is that regardless of the structure of the target, MI can have a global
list of threads, because most commands that accept the ‘--thread’ option do not need toknow what process that thread belongs to. Therefore, it is not necessary to introduce neither
additional ‘--process’ option, nor an notion of the current process in the MI interface. The
only strictly new feature that is required is the ability to find how the threads are grouped
into processes.
To allow the user to discover such grouping, and to support arbitrary hierarchy of machines/cores/processes, MI introduces the concept of a thread group. Thread group is acollection of threads and other thread groups. A thread group always has a string identifier,a type, and may have additional attributes specific to the type. A new command, -listthread-groups, returns the list of top-level thread groups, which correspond to processes
that gdb is debugging at the moment. By passing an identifier of a thread group to the-list-thread-groups command, it is possible to obtain the members of specific threadgroup.
To allow the user to easily discover processes, and other objects, he wishes to debug, a concept of available thread group is introduced. Available thread group is anthread group that gdb is not debugging, but that can be attached to, using the -targetattach command. The list of available top-level thread groups can be obtained using‘-list-thread-groups --available’. In general, the content of a thread group may be
only retrieved only after attaching to that thread group.
Thread groups are related to inferiors (see Section 4.9 [Inferiors Connections and Programs], page 42). Each inferior corresponds to a thread group of a special type ‘process’,and some additional operations are permitted on such thread groups.

27.4 gdb/mi Command Syntax

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27.4.1 gdb/mi Input Syntax
command 7→
cli-command | mi-command
cli-command 7→[ token ] cli-command nl, where cli-command is any existing gdb CLI command.
mi-command 7→[ token ] "-" operation ( " " option )* [ " --" ] ( " " parameter )* nl
token 7→"any sequence of digits"

option 7→ "-" parameter [ " " parameter ]parameter 7→
non-blank-sequence | c-string
operation 7→
any of the operations described in this chapter
non-blank-sequence 7→
anything, provided it doesn’t contain special characters such as "-", nl, """ andof course " "c-string 7→""" seven-bit-iso-c-string-content """nl 7→

CR | CR-LF

Notes:• The CLI commands are still handled by the mi interpreter; their output is described
below.
• The token, when present, is passed back when the command finishes.
• Some mi commands accept optional arguments as part of the parameter list. Each
option is identified by a leading ‘-’ (dash) and may be followed by an optional argument
parameter. Options occur first in the parameter list and can be delimited from normal
parameters using ‘--’ (this is useful when some parameters begin with a dash).
Pragmatics:• We want easy access to the existing CLI syntax (for debugging).
• We want it to be easy to spot a mi operation.

27.4.2 gdb/mi Output Syntax
The output from gdb/mi consists of zero or more out-of-band records followed, optionally,
by a single result record. This result record is for the most recent command. The sequenceof output records is terminated by ‘(gdb)’.
If an input command was prefixed with a token then the corresponding output for thatcommand will also be prefixed by that same token.
output 7→ ( out-of-band-record )* [ result-record ] "(gdb)" nl594

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result-record 7→[ token ] "^" result-class ( "," result )* nl
out-of-band-record 7→
async-record | stream-record
async-record 7→
exec-async-output | status-async-output | notify-async-output
exec-async-output 7→[ token ] "*" async-output nl
status-async-output 7→[ token ] "+" async-output nl
notify-async-output 7→[ token ] "=" async-output nl
async-output 7→
async-class ( "," result )*result-class 7→"done" | "running" | "connected" | "error" | "exit"
async-class 7→"stopped" | others (where others will be added depending on the needs—thisis still in development).
result 7→

variable "=" value

variable 7→
stringvalue 7→

const | tuple | list

const 7→c-string

tuple 7→"{}" | "{" result ( "," result )* "}"list 7→"[]" | "[" value ( "," value )* "]" | "[" result ( "," result )* "]"stream-record 7→
console-stream-output | target-stream-output | log-stream-output
console-stream-output 7→"~" c-string nl
target-stream-output 7→"@" c-string nl
log-stream-output 7→"&" c-string nl
nl 7→

CR | CR-LF

token 7→any sequence of digits.

Notes:• All output sequences end in a single line containing a period.

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595• The token is from the corresponding request. Note that for all async output, while
the token is allowed by the grammar and may be output by future versions of gdb for
select async output messages, it is generally omitted. Frontends should treat all async
output as reporting general changes in the state of the target and there should be noneed to associate async output to any prior command.
• status-async-output contains on-going status information about the progress of a slow
operation. It can be discarded. All status output is prefixed by ‘+’.
• exec-async-output contains asynchronous state change on the target (stopped, started,
disappeared). All async output is prefixed by ‘*’.
• notify-async-output contains supplementary information that the client should handle(e.g., a new breakpoint information). All notify output is prefixed by ‘=’.
• console-stream-output is output that should be displayed as is in the console. It is the
textual response to a CLI command. All the console output is prefixed by ‘~’.
• target-stream-output is the output produced by the target program. All the target
output is prefixed by ‘@’.
• log-stream-output is output text coming from gdb’s internals, for instance messages
that should be displayed as part of an error log. All the log output is prefixed by ‘&’.
• New gdb/mi commands should only output lists containing values.
See Section 27.7.2 [gdb/mi Stream Records], page 597, for more details about the various
output records.

27.5 gdb/mi Compatibility with CLI
For the developers convenience CLI commands can be entered directly, but there may besome unexpected behaviour. For example, commands that query the user will behave as if
the user replied yes, breakpoint command lists are not executed and some CLI commands,
such as if, when and define, prompt for further input with ‘>’, which is not valid MI
output.
This feature may be removed at some stage in the future and it is recommended thatfront ends use the -interpreter-exec command (see [-interpreter-exec], page 691).

27.6 gdb/mi Development and Front Ends
The application which takes the MI output and presents the state of the program being
debugged to the user is called a front end.
Since gdb/mi is used by a variety of front ends to gdb, changes to the MI interface may
break existing usage. This section describes how the protocol changes and how to request
previous version of the protocol when it does.
Some changes in MI need not break a carefully designed front end, and for these the MI
version will remain unchanged. The following is a list of changes that may occur within one
level, so front ends should parse MI output in a way that can handle them:• New MI commands may be added.
• New fields may be added to the output of any MI command.
• The range of values for fields with specified values, e.g., in_scope (see [-var-update],
page 648) may be extended.

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If the changes are likely to break front ends, the MI version level will be increased by one.
The new versions of the MI protocol are not compatible with the old versions. Old versionsof MI remain available, allowing front ends to keep using them until they are modified touse the latest MI version.
Since --interpreter=mi always points to the latest MI version, it is recommended thatfront ends request a specific version of MI when launching gdb (e.g. --interpreter=mi2)
to make sure they get an interpreter with the MI version they expect.
The following table gives a summary of the released versions of the MI interface: theversion number, the version of GDB in which it first appeared and the breaking changes
compared to the previous version.
MI
version1

GDB
Breaking changes
version
None
5.1

2

6.0

• The
-environment-pwd,-environment-directoryand-environment-path commands now returns values using the MI
output syntax, rather than CLI output syntax.
• -var-list-children’s children result field is now a list, rather
than a tuple.
• -var-update’s changelist result field is now a list, rather thana tuple.

3

9.1• The output of information about multi-location breakpoints haschanged in the responses to the -break-insert and -breakinfo commands, as well as in the =breakpoint-created and=breakpoint-modified events. The multiple locations are now
placed in a locations field, whose value is a list.

4

13.1

• The syntax of the "script" field in breakpoint output haschanged in the responses to the -break-insert and -breakinfo commands, as well as the =breakpoint-created and=breakpoint-modified events. The previous output was syntactically invalid. The new output is a list.

If your front end cannot yet migrate to a more recent version of the MI protocol, you
can nevertheless selectively enable specific features available in those recent MI versions,using the following commands:-fix-multi-location-breakpoint-output
Use the output for multi-location breakpoints which was introduced by MI 3,even when using MI versions below 3. This command has no effect when using
MI version 3 or later.

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597-fix-breakpoint-script-output
Use the output for the breakpoint "script" field which was introduced by MI 4,even when using MI versions below 4. This command has no effect when using
MI version 4 or later.
The best way to avoid unexpected changes in MI that might break your front
end is to make your project known to gdb developers and follow development on
gdb@sourceware.org and gdb-patches@sourceware.org.

27.7 gdb/mi Output Records
27.7.1 gdb/mi Result Records
In addition to a number of out-of-band notifications, the response to a gdb/mi commandincludes one of the following result indications:"^done" [ "," results ]The synchronous operation was successful, results are the return values.
"^running"This result record is equivalent to ‘^done’. Historically, it was output insteadof ‘^done’ if the command has resumed the target. This behaviour is maintained for backward compatibility, but all frontends should treat ‘^done’ and‘^running’ identically and rely on the ‘*running’ output record to determine
which threads are resumed.
"^connected"
gdb has connected to a remote target.
"^error" "," "msg=" c-string [ "," "code=" c-string ]The operation failed. The msg=c-string variable contains the corresponding
error message.
If present, the code=c-string variable provides an error code on which consumers can rely on to detect the corresponding error condition. At present,
only one error code is defined:‘"undefined-command"’Indicates that the command causing the error does not exist.
"^exit"gdb has terminated.

27.7.2 gdb/mi Stream Records
gdb internally maintains a number of output streams: the console, the target, and the log.
The output intended for each of these streams is funneled through the gdb/mi interface
using stream records.
Each stream record begins with a unique prefix character which identifies its stream (seeSection 27.4.2 [gdb/mi Output Syntax], page 593). In addition to the prefix, each stream
record contains a string-output. This is either raw text (with an implicit new line) or aquoted C string (which does not contain an implicit newline).

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Debugging with gdb"~" string-output
The console output stream contains text that should be displayed in the CLI
console window. It contains the textual responses to CLI commands.
"@" string-output
The target output stream contains any textual output from the running target.
This is only present when GDB’s event loop is truly asynchronous, which iscurrently only the case for remote targets.
"&" string-output
The log stream contains debugging messages being produced by gdb’s internals.

27.7.3 gdb/mi Async Records
Async records are used to notify the gdb/mi client of additional changes that have occurred.
Those changes can either be a consequence of gdb/mi commands (e.g., a breakpoint modified) or a result of target activity (e.g., target stopped).
The following is the list of possible async records:*running,thread-id="thread"
The target is now running. The thread field can be the global thread ID of thethread that is now running, and it can be ‘all’ if all threads are running. The
frontend should assume that no interaction with a running thread is possible
after this notification is produced. The frontend should not assume that thisnotification is output only once for any command. gdb may emit this notification several times, either for different threads, because it cannot resume all
threads together, or even for a single thread, if the thread must be steppedthough some code before letting it run freely.
*stopped,reason="reason",thread-id="id",stoppedthreads="stopped",core="core"
The target has stopped. The reason field can have one of the following values:
breakpoint-hit
A breakpoint was reached.
watchpoint-trigger
A watchpoint was triggered.
read-watchpoint-trigger
A read watchpoint was triggered.
access-watchpoint-trigger
An access watchpoint was triggered.
function-finishedAn -exec-finish or similar CLI command was accomplished.
location-reachedAn -exec-until or similar CLI command was accomplished.
watchpoint-scope
A watchpoint has gone out of scope.

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end-stepping-range
An -exec-next, -exec-next-instruction, -exec-step, -exec-stepinstruction or similar CLI command was accomplished.
exited-signalled
The inferior exited because of a signal.
exitedThe inferior exited.

exited-normally
The inferior exited normally.
signal-received
A signal was received by the inferior.
solib-event
The inferior has stopped due to a library being loaded or unloaded.
This can happen when stop-on-solib-events (see Section 18.1
[Files], page 291) is set or when a catch load or catch unload
catchpoint is in use (see Section 5.1.3 [Set Catchpoints], page 69).
fork

The inferior has forked. This is reported when catch fork (seeSection 5.1.3 [Set Catchpoints], page 69) has been used.

vfork

The inferior has vforked. This is reported in when catch vfork(see Section 5.1.3 [Set Catchpoints], page 69) has been used.

syscall-entry
The inferior entered a system call. This is reported when catch
syscall (see Section 5.1.3 [Set Catchpoints], page 69) has beenused.
syscall-return
The inferior returned from a system call. This is reported whencatch syscall (see Section 5.1.3 [Set Catchpoints], page 69) has
been used.
exec

The inferior called exec. This is reported when catch exec (seeSection 5.1.3 [Set Catchpoints], page 69) has been used.

no-history
There isn’t enough history recorded to continue reverse execution.
The id field identifies the global thread ID of the thread that directly caused
the stop – for example by hitting a breakpoint. Depending on whether allstop mode is in effect (see Section 5.5.1 [All-Stop Mode], page 93), gdb may
either stop all threads, or only the thread that directly triggered the stop. If all
threads are stopped, the stopped field will have the value of "all". Otherwise,
the value of the stopped field will be a list of thread identifiers. Presently, thislist will always include a single thread, but frontend should be prepared to see
several threads in the list. The core field reports the processor core on which
the stop event has happened. This field may be absent if such information is
not available.

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Debugging with gdb=thread-group-added,id="id"=thread-group-removed,id="id"A thread group was either added or removed. The id field contains the gdb
identifier of the thread group. When a thread group is added, it generally might
not be associated with a running process. When a thread group is removed, its
id becomes invalid and cannot be used in any way.
=thread-group-started,id="id",pid="pid"A thread group became associated with a running program, either because theprogram was just started or the thread group was attached to a program. The
id field contains the gdb identifier of the thread group. The pid field contains
process identifier, specific to the operating system.
=thread-group-exited,id="id"[,exit-code="code"]A thread group is no longer associated with a running program, either because
the program has exited, or because it was detached from. The id field contains
the gdb identifier of the thread group. The code field is the exit code of theinferior; it exists only when the inferior exited with some code.
=thread-created,id="id",group-id="gid"=thread-exited,id="id",group-id="gid"A thread either was created, or has exited. The id field contains the global gdb
identifier of the thread. The gid field identifies the thread group this thread
belongs to.
=thread-selected,id="id"[,frame="frame"]
Informs that the selected thread or frame were changed. This notification is not
emitted as result of the -thread-select or -stack-select-frame commands,
but is emitted whenever an MI command that is not documented to change
the selected thread and frame actually changes them. In particular, invoking,directly or indirectly (via user-defined command), the CLI thread or frame
commands, will generate this notification. Changing the thread or frame fromanother user interface (see Chapter 24 [Interpreters], page 577) will also generate
this notification.
The frame field is only present if the newly selected thread is stopped. See
Section 27.7.5 [GDB/MI Frame Information], page 604, for the format of its
value.
We suggest that in response to this notification, front ends highlight the selected
thread and cause subsequent commands to apply to that thread.
=library-loaded,...
Reports that a new library file was loaded by the program. This notification has
5 fields—id, target-name, host-name, symbols-loaded and ranges. The id field
is an opaque identifier of the library. For remote debugging case, target-nameand host-name fields give the name of the library file on the target, and on thehost respectively. For native debugging, both those fields have the same value.
The symbols-loaded field is emitted only for backward compatibility and should
not be relied on to convey any useful information. The thread-group field, if
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loaded. If the field is absent, it means the library was loaded in the context
of all present thread groups. The ranges field specifies the ranges of addresses
belonging to this library.
=library-unloaded,...
Reports that a library was unloaded by the program. This notification has
3 fields—id, target-name and host-name with the same meaning as for the=library-loaded notification. The thread-group field, if present, specifies theid of the thread group in whose context the library was unloaded. If the field isabsent, it means the library was unloaded in the context of all present threadgroups.
=traceframe-changed,num=tfnum,tracepoint=tpnum=traceframe-changed,end
Reports that the trace frame was changed and its new number is tfnum. The
number of the tracepoint associated with this trace frame is tpnum.
=tsv-created,name=name,initial=initial
Reports that the new trace state variable name is created with initial value
initial.
=tsv-deleted,name=name=tsv-deleted
Reports that the trace state variable name is deleted or all trace state variables
are deleted.
=tsv-modified,name=name,initial=initial[,current=current]
Reports that the trace state variable name is modified with the initial value
initial. The current value current of trace state variable is optional and isreported if the current value of trace state variable is known.
=breakpoint-created,bkpt={...}=breakpoint-modified,bkpt={...}=breakpoint-deleted,id=number
Reports that a breakpoint was created, modified, or deleted, respectively. Only
user-visible breakpoints are reported to the MI user.
The bkpt argument is of the same form as returned by the various breakpointcommands; See Section 27.10 [GDB/MI Breakpoint Commands], page 607. The
number is the ordinal number of the breakpoint.
Note that if a breakpoint is emitted in the result record of a command, then it
will not also be emitted in an async record.
=record-started,thread-group="id",method="method"[,format="format"]=record-stopped,thread-group="id"Execution log recording was either started or stopped on an inferior. The id isthe gdb identifier of the thread group corresponding to the affected inferior.
The method field indicates the method used to record execution. If the method
in use supports multiple recording formats, format will be present and contain the currently used format. See Chapter 7 [Process Record and Replay],
page 103, for existing method and format values.

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Debugging with gdb=cmd-param-changed,param=param,value=value
Reports that a parameter of the command set param is changed to value. In
the multi-word set command, the param is the whole parameter list to set
command. For example, In command set check type on, param is check typeand value is on.
=memory-changed,thread-group=id,addr=addr,len=len[,type="code"]
Reports that bytes from addr to data + len were written in an inferior. The
id is the identifier of the thread group corresponding to the affected inferior.
The optional type="code" part is reported if the memory written to holds
executable code.

27.7.4 gdb/mi Breakpoint Information
When gdb reports information about a breakpoint, a tracepoint, a watchpoint, or a catchpoint, it uses a tuple with the following fields:
number

The breakpoint number.

type

The type of the breakpoint. For ordinary breakpoints this will be ‘breakpoint’,but many values are possible.

catch-type
If the type of the breakpoint is ‘catchpoint’, then this indicates the exact typeof catchpoint.
dispThis is the breakpoint disposition—either ‘del’, meaning that the breakpoint
will be deleted at the next stop, or ‘keep’, meaning that the breakpoint will
not be deleted.

enabledThis indicates whether the breakpoint is enabled, in which case the value is ‘y’,or disabled, in which case the value is ‘n’. Note that this is not the same as thefield enable.

addr

The address of the breakpoint. This may be a hexadecimal number, giving
the address; or the string ‘<PENDING>’, for a pending breakpoint; or the string‘<MULTIPLE>’, for a breakpoint with multiple locations. This field will not bepresent if no address can be determined. For example, a watchpoint does nothave an address.

addr_flags
Optional field containing any flags related to the address. These flags arearchitecture-dependent; see Section 21.4 [Architectures], page 354, for their
meaning for a particular CPU.
func

If known, the function in which the breakpoint appears. If not known, this field
is not present.

filename

The name of the source file which contains this function, if known. If not known,
this field is not present.

fullname

The full file name of the source file which contains this function, if known. If
not known, this field is not present.

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line

The line number at which this breakpoint appears, if known. If not known, thisfield is not present.

at

If the source file is not known, this field may be provided. If provided, thisholds the address of the breakpoint, possibly followed by a symbol name.

pending

If this breakpoint is pending, this field is present and holds the text used to set
the breakpoint, as entered by the user.

evaluated-by
Where this breakpoint’s condition is evaluated, either ‘host’ or ‘target’.
threadIf this is a thread-specific breakpoint, then this identifies the thread in which
the breakpoint can trigger.

inferior

If this is an inferior-specific breakpoint, this this identifies the inferior in which
the breakpoint can trigger.

task

If this breakpoint is restricted to a particular Ada task, then this field will holdthe task identifier.

cond

If the breakpoint is conditional, this is the condition expression.

ignore

The ignore count of the breakpoint.

enable

The enable count of the breakpoint.

traceframe-usage
FIXME.
static-tracepoint-marker-string-id
For a static tracepoint, the name of the static tracepoint marker.
mask

For a masked watchpoint, this is the mask.

pass

A tracepoint’s pass count.

original-location
The location of the breakpoint as originally specified by the user. This field is
optional.
times

The number of times the breakpoint has been hit.

installed
This field is only given for tracepoints. This is either ‘y’, meaning that thetracepoint is installed, or ‘n’, meaning that it is not.
what

Some extra data, the exact contents of which are type-dependent.

locationsThis field is present if the breakpoint has multiple locations. It is also exceptionally present if the breakpoint is enabled and has a single, disabled location.
The value is a list of locations. The format of a location is described below.
A location in a multi-location breakpoint is represented as a tuple with the following
fields:number

The location number as a dotted pair, like ‘1.2’. The first digit is the numberof the parent breakpoint. The second digit is the number of the location withinthat breakpoint.

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Debugging with gdb

enabled

There are three possible values, with the following meanings:yThe location is enabled.

n

The location is disabled by the user.

N

The location is disabled because the breakpoint condition is invalid
at this location.

The address of this location as an hexadecimal number.

addr
addr_flags

Optional field containing any flags related to the address. These flags arearchitecture-dependent; see Section 21.4 [Architectures], page 354, for their
meaning for a particular CPU.
func

If known, the function in which the location appears. If not known, this field
is not present.

file

The name of the source file which contains this location, if known. If not known,
this field is not present.

fullname

The full file name of the source file which contains this location, if known. If
not known, this field is not present.

line

The line number at which this location appears, if known. If not known, thisfield is not present.

thread-groups
The thread groups this location is in.
For example, here is what the output of -break-insert (see Section 27.10 [GDB/MI
Breakpoint Commands], page 607) might be:-> -break-insert main<- ^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x08048564",func="main",file="myprog.c",fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"],
times="0"}<- (gdb)

27.7.5 gdb/mi Frame Information
Response from many MI commands includes an information about stack frame. This information is a tuple that may have the following fields:
level

The level of the stack frame. The innermost frame has the level of zero. This
field is always present.

func

The name of the function corresponding to the frame. This field may be absent
if gdb is unable to determine the function name.

addr

The code address for the frame. This field is always present.

addr_flags
Optional field containing any flags related to the address. These flags arearchitecture-dependent; see Section 21.4 [Architectures], page 354, for their
meaning for a particular CPU.

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file

The name of the source files that correspond to the frame’s code address. This
field may be absent.

line

The source line corresponding to the frames’ code address. This field may beabsent.

from

The name of the binary file (either executable or shared library) the corresponds
to the frame’s code address. This field may be absent.

27.7.6 gdb/mi Thread Information
Whenever gdb has to report an information about a thread, it uses a tuple with the following
fields. The fields are always present unless stated otherwise.
id

The global numeric id assigned to the thread by gdb.

target-id
The target-specific string identifying the thread.
details

Additional information about the thread provided by the target. It is supposed
to be human-readable and not interpreted by the frontend. This field is optional.

name

The name of the thread. If the user specified a name using the thread namecommand, then this name is given. Otherwise, if gdb can extract the threadname from the target, then that name is given. If gdb cannot find the thread
name, then this field is omitted.

state

The execution state of the thread, either ‘stopped’ or ‘running’, depending onwhether the thread is presently running.

frame

The stack frame currently executing in the thread. This field is only present
if the thread is stopped. Its format is documented in Section 27.7.5 [GDB/MI
Frame Information], page 604.

core

The value of this field is an integer number of the processor core the thread waslast seen on. This field is optional.

27.7.7 gdb/mi Ada Exception Information
Whenever a *stopped record is emitted because the program stopped after hitting an
exception catchpoint (see Section 5.1.3 [Set Catchpoints], page 69), gdb provides the nameof the exception that was raised via the exception-name field. Also, for exceptions that wereraised with an exception message, gdb provides that message via the exception-message
field.

27.8 Simple Examples of gdb/mi Interaction
This subsection presents several simple examples of interaction using the gdb/mi interface.
In these examples, ‘->’ means that the following line is passed to gdb/mi as input, while‘<-’ means the output received from gdb/mi.
Note the line breaks shown in the examples are here only for readability, they don’t
appear in the real output.

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Setting a Breakpoint
Setting a breakpoint generates synchronous output which contains detailed information of
the breakpoint.
-> -break-insert main<- ^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x08048564",func="main",file="myprog.c",fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"],
times="0"}<- (gdb)

Program Execution
Program execution generates asynchronous records and MI gives the reason that execution
stopped.
-> -exec-run<- ^running<- (gdb)<- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",frame={addr="0x08048564",func="main",
args=[{name="argc",value="1"},{name="argv",value="0xbfc4d4d4"}],
file="myprog.c",fullname="/home/nickrob/myprog.c",line="68",
arch="i386:x86_64"}<- (gdb)-> -exec-continue<- ^running<- (gdb)<- *stopped,reason="exited-normally"<- (gdb)

Quitting gdb
Quitting gdb just prints the result class ‘^exit’.
-> (gdb)<- -gdb-exit<- ^exit

Please note that ‘^exit’ is printed immediately, but it might take some time for gdb
to actually exit. During that time, gdb performs necessary cleanups, including killing
programs being debugged or disconnecting from debug hardware, so the frontend should
wait till gdb exits and should only forcibly kill gdb if it fails to exit in reasonable time.

A Bad Command
Here’s what happens if you pass a non-existent command:-> -rubbish<- ^error,msg="Undefined MI command: rubbish"<- (gdb)

27.9 gdb/mi Command Description Format
The remaining sections describe blocks of commands. Each block of commands is laid out
in a fashion similar to this section.

Motivation
The motivation for this collection of commands.

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Introduction
A brief introduction to this collection of commands as a whole.

Commands
For each command in the block, the following is described:

Synopsis-command args...

Resultgdb Command
The corresponding gdb CLI command(s), if any.

ExampleExample(s) formatted for readability. Some of the described commands have not been
implemented yet and these are labeled N.A. (not available).

27.10 gdb/mi Breakpoint Commands
This section documents gdb/mi commands for manipulating breakpoints.

The -break-after Command
Synopsis-break-after number count

The breakpoint number number is not in effect until it has been hit count times. To see
how this is reflected in the output of the ‘-break-list’ command, see the description ofthe ‘-break-list’ command below.

gdb Command
The corresponding gdb command is ‘ignore’.

Example(gdb)-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],
times="0"}(gdb)-break-after 1 3
~
^done
(gdb)
-break-list^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},608

Debugging with gdb{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],times="0",ignore="3"}]}(gdb)

The -break-commands Command
Synopsis-break-commands number [ command1 ... commandN ]Specifies the CLI commands that should be executed when breakpoint number is hit.
The parameters command1 to commandN are the commands. If no command is specified,
any previously-set commands are cleared. See Section 5.1.7 [Break Commands], page 77.
Typical use of this functionality is tracing a program, that is, printing of values of somevariables whenever breakpoint is hit and then continuing.

gdb Command
The corresponding gdb command is ‘commands’.

Example(gdb)-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],
times="0"}(gdb)-break-commands 1 "print v" "continue"
^done
(gdb)

The -break-condition Command
Synopsis-break-condition [ --force ] number [ expr ]Breakpoint number will stop the program only if the condition in expr is true. The condition becomes part of the ‘-break-list’ output (see the description of the ‘-break-list’command below). If the ‘--force’ flag is passed, the condition is forcibly defined evenwhen it is invalid for all locations of breakpoint number. If the expr argument is omitted,
breakpoint number becomes unconditional.

gdb Command
The corresponding gdb command is ‘condition’.

Example(gdb)-break-condition 1 1

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^done
(gdb)
-break-list^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",line="5",cond="1",thread-groups=["i1"],times="0",ignore="3"}]}(gdb)

The -break-delete Command
Synopsis-break-delete ( breakpoint )+Delete the breakpoint(s) whose number(s) are specified in the argument list. This is
obviously reflected in the breakpoint list.

gdb Command
The corresponding gdb command is ‘delete’.

Example(gdb)-break-delete 1
^done
(gdb)
-break-list^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[]}(gdb)

The -break-disable Command
Synopsis-break-disable ( breakpoint )+Disable the named breakpoint(s). The field ‘enabled’ in the break list is now set to ‘n’
for the named breakpoint(s).

gdb Command
The corresponding gdb command is ‘disable’.

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Debugging with gdb

Example(gdb)-break-disable 2
^done
(gdb)
-break-list^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n",addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],times="0"}]}(gdb)

The -break-enable Command
Synopsis-break-enable ( breakpoint )+Enable (previously disabled) breakpoint(s).

gdb Command
The corresponding gdb command is ‘enable’.

Example(gdb)-break-enable 2
^done
(gdb)
-break-list^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y",addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],times="0"}]}(gdb)

The -break-info Command
Synopsis-break-info breakpoint

Get information about a single breakpoint.
The result is a table of breakpoints. See Section 27.7.4 [GDB/MI Breakpoint Information], page 602, for details on the format of each breakpoint in the table.

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gdb Command
The corresponding gdb command is ‘info break breakpoint’.

ExampleN.A.

The -break-insert Command
Synopsis-break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ] [ --qualified ][ -c condition ] [ --force-condition ] [ -i ignore-count ][ -p thread-id ] [ -g thread-group-id ] [ locspec ]If specified, locspec, can be one of:linespec location
A linespec location. See Section 9.2.1 [Linespec Locations], page 127.
explicit location
An explicit location. gdb/mi explicit locations are analogous to the CLI’s explicit locations using the option names listed below. See Section 9.2.2 [Explicit
Locations], page 129.
‘--source filename’The source file name of the location. This option requires the useof either ‘--function’ or ‘--line’.
‘--function function’
The name of a function or method.
‘--label label’
The name of a label.
‘--line lineoffset’
An absolute or relative line offset from the start of the location.
address location
An address location, *address. See Section 9.2.3 [Address Locations], page 130.
The possible optional parameters of this command are:‘-t’

Insert a temporary breakpoint.

‘-h’Insert a hardware breakpoint.

‘-f’

If locspec cannot be resolved (for example if it refers to unknown files or functions), create a pending breakpoint. Without this flag, gdb will report an error,
and won’t create a breakpoint, if locspec cannot be parsed.

‘-d’Create a disabled breakpoint.

‘-a’Create a tracepoint. See Chapter 13 [Tracepoints], page 203. When this parameter is used together with ‘-h’, a fast tracepoint is created.

‘-c condition’
Make the breakpoint conditional on condition.

612

Debugging with gdb‘--force-condition’
Forcibly define the breakpoint even if the condition is invalid at all of the
breakpoint locations.
‘-i ignore-count’
Initialize the ignore-count.
‘-p thread-id’
Restrict the breakpoint to the thread with the specified global thread-id.
thread-id must be a valid thread-id at the time the breakpoint is requested.
Breakpoints created with a thread-id will automatically be deleted when thecorresponding thread exits.
‘-g thread-group-id’
Restrict the breakpoint to the thread group with the specified thread-group-id.
‘--qualified’This option makes gdb interpret a function name specified as a complete fullyqualified name.

ResultSee Section 27.7.4 [GDB/MI Breakpoint Information], page 602, for details on the formatof the resulting breakpoint.
Note: this format is open to change.

gdb Command
The corresponding gdb commands are ‘break’, ‘tbreak’, ‘hbreak’, and ‘thbreak’.

Example(gdb)-break-insert main
^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",fullname="/home/foo/recursive2.c,line="4",thread-groups=["i1"],
times="0"}(gdb)-break-insert -t foo^done,bkpt={number="2",addr="0x00010774",file="recursive2.c",fullname="/home/foo/recursive2.c,line="11",thread-groups=["i1"],
times="0"}(gdb)-break-list^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x0001072c", func="main",file="recursive2.c",fullname="/home/foo/recursive2.c,"line="4",thread-groups=["i1"],
times="0"},bkpt={number="2",type="breakpoint",disp="del",enabled="y",Chapter 27: The gdb/mi Interface613

addr="0x00010774",func="foo",file="recursive2.c",fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"],
times="0"}]}(gdb)

The -dprintf-insert Command
Synopsis-dprintf-insert [ -t ] [ -f ] [ -d ] [ --qualified ][ -c condition ] [--force-condition] [ -i ignore-count ][ -p thread-id ] [ locspec ] format[ argument... ]Insert a new dynamic print breakpoint at the given location. See Section 5.1.8 [Dynamic
Printf], page 79. format is the format to use, and any remaining arguments are passed as
expressions to substitute.
If supplied, locspec and --qualified may be specified the same way as for the -breakinsert command. See [-break-insert], page 611.
The possible optional parameters of this command are:‘-t’

Insert a temporary breakpoint.

‘-f’

If locspec cannot be parsed (for example, if it refers to unknown files or functions), create a pending breakpoint. Without this flag, gdb will report an error,
and won’t create a breakpoint, if locspec cannot be parsed.

‘-d’Create a disabled breakpoint.

‘-c condition’
Make the breakpoint conditional on condition.
‘--force-condition’
Forcibly define the breakpoint even if the condition is invalid at all of the
breakpoint locations.
‘-i ignore-count’
Set the ignore count of the breakpoint (see Section 5.1.6 [Conditions], page 76)
to ignore-count.
‘-p thread-id’
Restrict the breakpoint to the thread with the specified global thread-id.

ResultSee Section 27.7.4 [GDB/MI Breakpoint Information], page 602, for details on the formatof the resulting breakpoint.

gdb Command
The corresponding gdb command is ‘dprintf’.

Example(gdb)
4-dprintf-insert foo "At foo entry\n"4^done,bkpt={number="1",type="dprintf",disp="keep",enabled="y",614

Debugging with gdb

addr="0x000000000040061b",func="foo",file="mi-dprintf.c",fullname="mi-dprintf.c",line="25",thread-groups=["i1"],
times="0",script=["printf \"At foo entry\\n\"","continue"],original-location="foo"}(gdb)
5-dprintf-insert 26 "arg=%d, g=%d\n" arg g5^done,bkpt={number="2",type="dprintf",disp="keep",enabled="y",addr="0x000000000040062a",func="foo",file="mi-dprintf.c",fullname="mi-dprintf.c",line="26",thread-groups=["i1"],
times="0",script=["printf \"arg=%d, g=%d\\n\", arg, g","continue"],original-location="mi-dprintf.c:26"}(gdb)

The -break-list Command
Synopsis-break-list

Displays the list of inserted breakpoints, showing the following fields:‘Number’number of the breakpoint‘Type’

type of the breakpoint: ‘breakpoint’ or ‘watchpoint’‘Disposition’should the breakpoint be deleted or disabled when it is hit: ‘keep’ or ‘nokeep’‘Enabled’is the breakpoint enabled or no: ‘y’ or ‘n’‘Address’

memory location at which the breakpoint is set‘What’

logical location of the breakpoint, expressed by function name, file name, line
number‘Thread-groups’
list of thread groups to which this breakpoint applies‘Times’number of times the breakpoint has been hit

If there are no breakpoints, watchpoints,
BreakpointTable body field is an empty list.

tracepoints,

or catchpoints,

gdb Command
The corresponding gdb command is ‘info break’.

Example(gdb)-break-list^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x000100d0",func="main",file="hello.c",line="5",thread-groups=["i1"],theChapter 27: The gdb/mi Interface

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times="0"},bkpt={number="2",type="breakpoint",disp="keep",enabled="y",addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",line="13",thread-groups=["i1"],times="0"}]}(gdb)

Here’s an example of the result when there are no breakpoints:(gdb)-break-list^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[]}(gdb)

The -break-passcount Command
Synopsis-break-passcount tracepoint-number passcountSet the passcount for tracepoint tracepoint-number to passcount. If the breakpointreferred to by tracepoint-number is not a tracepoint, error is emitted. This corresponds to
CLI command ‘passcount’.

The -break-watch Command
Synopsis-break-watch [ -a | -r ]Create a watchpoint. With the ‘-a’ option it will create an access watchpoint, i.e., awatchpoint that triggers either on a read from or on a write to the memory location. Withthe ‘-r’ option, the watchpoint created is a read watchpoint, i.e., it will trigger only whenthe memory location is accessed for reading. Without either of the options, the watchpoint
created is a regular watchpoint, i.e., it will trigger when the memory location is accessed
for writing. See Section 5.1.2 [Setting Watchpoints], page 66.
Note that ‘-break-list’ will report a single list of watchpoints and breakpoints inserted.

gdb Command
The corresponding gdb commands are ‘watch’, ‘awatch’, and ‘rwatch’.

ExampleSetting a watchpoint on a variable in the main function:(gdb)-break-watch x^done,wpt={number="2",exp="x"}(gdb)-exec-continue^running
(gdb)

616

Debugging with gdb*stopped,reason="watchpoint-trigger",wpt={number="2",exp="x"},value={old="-268439212",new="55"},
frame={func="main",args=[],file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="5",arch="i386:x86_64"}(gdb)

Setting a watchpoint on a variable local to a function. gdb will stop the program
execution twice: first for the variable changing value, then for the watchpoint going out of
scope.
(gdb)-break-watch C^done,wpt={number="5",exp="C"}(gdb)-exec-continue^running(gdb)*stopped,reason="watchpoint-trigger",
wpt={number="5",exp="C"},value={old="-276895068",new="3"},frame={func="callee4",args=[],file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13",arch="i386:x86_64"}(gdb)-exec-continue^running(gdb)*stopped,reason="watchpoint-scope",wpnum="5",frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18",
arch="i386:x86_64"}(gdb)

Listing breakpoints and watchpoints, at different points in the program execution. Notethat once the watchpoint goes out of scope, it is deleted.
(gdb)-break-watch C^done,wpt={number="2",exp="C"}(gdb)-break-list^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",thread-groups=["i1"],
times="1"},bkpt={number="2",type="watchpoint",disp="keep",enabled="y",addr="",what="C",thread-groups=["i1"],times="0"}]}(gdb)-exec-continue^running

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(gdb)
*stopped,reason="watchpoint-trigger",wpt={number="2",exp="C"},value={old="-276895068",new="3"},frame={func="callee4",args=[],file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13",arch="i386:x86_64"}(gdb)-break-list^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",thread-groups=["i1"],
times="1"},bkpt={number="2",type="watchpoint",disp="keep",enabled="y",addr="",what="C",thread-groups=["i1"],times="-5"}]}(gdb)-exec-continue^running^done,reason="watchpoint-scope",wpnum="2",frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18",
arch="i386:x86_64"}(gdb)-break-list^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},{width="14",alignment="-1",col_name="type",colhdr="Type"},{width="4",alignment="-1",col_name="disp",colhdr="Disp"},{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},{width="10",alignment="-1",col_name="addr",colhdr="Address"},{width="40",alignment="2",col_name="what",colhdr="What"}],body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",thread-groups=["i1"],times="1"}]}(gdb)

27.11 gdb/mi Catchpoint Commands
This section documents gdb/mi commands for manipulating catchpoints.

27.11.1 Shared Library gdb/mi Catchpoints
The -catch-load Command

618

Debugging with gdb

Synopsis-catch-load [ -t ] [ -d ] regexp

Add a catchpoint for library load events. If the ‘-t’ option is used, the catchpoint is atemporary one (see Section 5.1.1 [Setting Breakpoints], page 58). If the ‘-d’ option is used,the catchpoint is created in a disabled state. The ‘regexp’ argument is a regular expression
used to match the name of the loaded library.

gdb Command
The corresponding gdb command is ‘catch load’.

Example-catch-load -t foo.so^done,bkpt={number="1",type="catchpoint",disp="del",enabled="y",what="load of library matching foo.so",catch-type="load",times="0"}(gdb)

The -catch-unload Command
Synopsis-catch-unload [ -t ] [ -d ] regexp

Add a catchpoint for library unload events. If the ‘-t’ option is used, the catchpoint is atemporary one (see Section 5.1.1 [Setting Breakpoints], page 58). If the ‘-d’ option is used,the catchpoint is created in a disabled state. The ‘regexp’ argument is a regular expression
used to match the name of the unloaded library.

gdb Command
The corresponding gdb command is ‘catch unload’.

Example-catch-unload -d bar.so^done,bkpt={number="2",type="catchpoint",disp="keep",enabled="n",what="load of library matching bar.so",catch-type="unload",times="0"}(gdb)

27.11.2 Ada Exception gdb/mi Catchpoints
The following gdb/mi commands can be used to create catchpoints that stop the execution
when Ada exceptions are being raised.

The -catch-assert Command
Synopsis-catch-assert [ -c condition] [ -d ] [ -t ]Add a catchpoint for failed Ada assertions.
The possible optional parameters for this command are:‘-c condition’
Make the catchpoint conditional on condition.

Chapter 27: The gdb/mi Interface‘-d’Create a disabled catchpoint.

‘-t’Create a temporary catchpoint.

619

gdb Command
The corresponding gdb command is ‘catch assert’.

Example-catch-assert^done,bkptno="5",bkpt={number="5",type="breakpoint",disp="keep",enabled="y",addr="0x0000000000404888",what="failed Ada assertions",
thread-groups=["i1"],times="0",original-location="__gnat_debug_raise_assert_failure"}(gdb)

The -catch-exception Command
Synopsis-catch-exception [ -c condition] [ -d ] [ -e exception-name ][ -t ] [ -u ]Add a catchpoint stopping when Ada exceptions are raised. By default, the commandstops the program when any Ada exception gets raised. But it is also possible, by using
some of the optional parameters described below, to create more selective catchpoints.
The possible optional parameters for this command are:‘-c condition’
Make the catchpoint conditional on condition.
‘-d’Create a disabled catchpoint.

‘-e exception-name’
Only stop when exception-name is raised. This option cannot be used combinedwith ‘-u’.
‘-t’

Create a temporary catchpoint.

‘-u’

Stop only when an unhandled exception gets raised. This option cannot be
used combined with ‘-e’.

gdb Command
The corresponding gdb commands are ‘catch exception’ and ‘catch exception
unhandled’.

Example-catch-exception -e Program_Error^done,bkptno="4",bkpt={number="4",type="breakpoint",disp="keep",enabled="y",addr="0x0000000000404874",
what="‘Program_Error’ Ada exception", thread-groups=["i1"],
times="0",original-location="__gnat_debug_raise_exception"}(gdb)

The -catch-handlers Command

620

Debugging with gdb

Synopsis-catch-handlers [ -c condition] [ -d ] [ -e exception-name ][ -t ]

Add a catchpoint stopping when Ada exceptions are handled. By default, the commandstops the program when any Ada exception gets handled. But it is also possible, by using
some of the optional parameters described below, to create more selective catchpoints.
The possible optional parameters for this command are:‘-c condition’
Make the catchpoint conditional on condition.
‘-d’Create a disabled catchpoint.

‘-e exception-name’
Only stop when exception-name is handled.
‘-t’

Create a temporary catchpoint.

gdb Command
The corresponding gdb command is ‘catch handlers’.

Example-catch-handlers -e Constraint_Error^done,bkptno="4",bkpt={number="4",type="breakpoint",disp="keep",enabled="y",addr="0x0000000000402f68",
what="‘Constraint_Error’ Ada exception handlers",thread-groups=["i1"],
times="0",original-location="__gnat_begin_handler"}(gdb)

27.11.3 C++ Exception gdb/mi Catchpoints
The following gdb/mi commands can be used to create catchpoints that stop the execution
when C++ exceptions are being throw, rethrown, or caught.

The -catch-throw Command
Synopsis-catch-throw [ -t ] [ -r regexp]

Stop when the debuggee throws a C++ exception. If regexp is given, then only exceptions
whose type matches the regular expression will be caught.
If ‘-t’ is given, then the catchpoint is enabled only for one stop, the catchpoint is
automatically deleted after stopping once for the event.

gdb Command
The corresponding gdb commands are ‘catch throw’ and ‘tcatch throw’ (see Section 5.1.3[Set Catchpoints], page 69).

Example-catch-throw -r exception_type^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y",Chapter 27: The gdb/mi Interface

621

what="exception throw",catch-type="throw",
thread-groups=["i1"],
regexp="exception_type",times="0"}(gdb)-exec-run^running
(gdb)
~"\n"
~"Catchpoint 1 (exception thrown), 0x00007ffff7ae00ed
in __cxa_throw () from /lib64/libstdc++.so.6\n"*stopped,bkptno="1",reason="breakpoint-hit",disp="keep",frame={addr="0x00007ffff7ae00ed",func="__cxa_throw",args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"},
thread-id="1",stopped-threads="all",core="6"(gdb)

The -catch-rethrow Command
Synopsis-catch-rethrow [ -t ] [ -r regexp]

Stop when a C++ exception is re-thrown. If regexp is given, then only exceptions whosetype matches the regular expression will be caught.
If ‘-t’ is given, then the catchpoint is enabled only for one stop, the catchpoint is
automatically deleted after the first event is caught.

gdb Command
The corresponding gdb commands are ‘catch rethrow’ and ‘tcatch rethrow’ (seeSection 5.1.3 [Set Catchpoints], page 69).

Example-catch-rethrow -r exception_type^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y",what="exception rethrow",catch-type="rethrow",
thread-groups=["i1"],
regexp="exception_type",times="0"}(gdb)-exec-run^running
(gdb)
~"\n"
~"Catchpoint 1 (exception rethrown), 0x00007ffff7ae00ed
in __cxa_rethrow () from /lib64/libstdc++.so.6\n"*stopped,bkptno="1",reason="breakpoint-hit",disp="keep",frame={addr="0x00007ffff7ae00ed",func="__cxa_rethrow",args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"},
thread-id="1",stopped-threads="all",core="6"(gdb)

The -catch-catch Command
Synopsis-catch-catch [ -t ] [ -r regexp]

622

Debugging with gdb

Stop when the debuggee catches a C++ exception. If regexp is given, then only exceptions
whose type matches the regular expression will be caught.
If ‘-t’ is given, then the catchpoint is enabled only for one stop, the catchpoint is
automatically deleted after the first event is caught.

gdb Command
The corresponding gdb commands are ‘catch catch’ and ‘tcatch catch’ (see Section 5.1.3[Set Catchpoints], page 69).

Example-catch-catch -r exception_type^done,bkpt={number="1",type="catchpoint",disp="keep",enabled="y",what="exception catch",catch-type="catch",thread-groups=["i1"],
regexp="exception_type",times="0"}(gdb)-exec-run^running
(gdb)
~"\n"
~"Catchpoint 1 (exception caught), 0x00007ffff7ae00ed
in __cxa_begin_catch () from /lib64/libstdc++.so.6\n"*stopped,bkptno="1",reason="breakpoint-hit",disp="keep",frame={addr="0x00007ffff7ae00ed",func="__cxa_begin_catch",
args=[],from="/lib64/libstdc++.so.6",arch="i386:x86-64"},
thread-id="1",stopped-threads="all",core="6"(gdb)

27.12 gdb/mi Program Context
The -exec-arguments Command
Synopsis-exec-arguments args

Set the inferior program arguments, to be used in the next ‘-exec-run’.

gdb Command
The corresponding gdb command is ‘set args’.

Example(gdb)-exec-arguments -v word
^done
(gdb)

The -environment-cd Command
Synopsis-environment-cd pathdir

Set gdb’s working directory.

Chapter 27: The gdb/mi Interface623

gdb Command
The corresponding gdb command is ‘cd’.

Example(gdb)-environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
^done
(gdb)

The -environment-directory Command
Synopsis-environment-directory [ -r ] [ pathdir ]+Add directories pathdir to beginning of search path for source files. If the ‘-r’ option isused, the search path is reset to the default search path. If directories pathdir are suppliedin addition to the ‘-r’ option, the search path is first reset and then addition occurs asnormal. Multiple directories may be specified, separated by blanks. Specifying multiple
directories in a single command results in the directories added to the beginning of thesearch path in the same order they were presented in the command. If blanks are needed aspart of a directory name, double-quotes should be used around the name. In the command
output, the path will show up separated by the system directory-separator character. The
directory-separator character must not be used in any directory name. If no directories are
specified, the current search path is displayed.

gdb Command
The corresponding gdb command is ‘dir’.

Example(gdb)-environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"(gdb)-environment-directory ""^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"(gdb)-environment-directory -r /home/jjohnstn/src/gdb /usr/src^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"(gdb)-environment-directory -r^done,source-path="$cdir:$cwd"(gdb)

The -environment-path Command
Synopsis-environment-path [ -r ] [ pathdir ]+Add directories pathdir to beginning of search path for object files. If the ‘-r’ option
is used, the search path is reset to the original search path that existed at gdb start-up.
If directories pathdir are supplied in addition to the ‘-r’ option, the search path is first624

Debugging with gdb

reset and then addition occurs as normal. Multiple directories may be specified, separated
by blanks. Specifying multiple directories in a single command results in the directories
added to the beginning of the search path in the same order they were presented in thecommand. If blanks are needed as part of a directory name, double-quotes should be usedaround the name. In the command output, the path will show up separated by the system
directory-separator character. The directory-separator character must not be used in any
directory name. If no directories are specified, the current path is displayed.

gdb Command
The corresponding gdb command is ‘path’.

Example(gdb)-environment-path^done,path="/usr/bin"(gdb)-environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"(gdb)-environment-path -r /usr/local/bin^done,path="/usr/local/bin:/usr/bin"(gdb)

The -environment-pwd Command
Synopsis-environment-pwd

Show the current working directory.

gdb Command
The corresponding gdb command is ‘pwd’.

Example(gdb)-environment-pwd^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"(gdb)

27.13 gdb/mi Thread Commands
The -thread-info Command
Synopsis-thread-info [ thread-id ]Reports information about either a specific thread, if the thread-id parameter is present,or about all threads. thread-id is the thread’s global thread ID. When printing information
about all threads, also reports the global ID of the current thread.

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gdb Command
The ‘info thread’ command prints the same information about all threads.

Result
The result contains the following attributes:‘threads’

A list of threads. The format of the elements of the list is described in
Section 27.7.6 [GDB/MI Thread Information], page 605.

‘current-thread-id’
The global id of the currently selected thread. This field is omitted if there
is no selected thread (for example, when the selected inferior is not running,
and therefore has no threads) or if a thread-id argument was passed to thecommand.

Example-thread-info^done,threads=[{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]},state="running"},{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
frame={level="0",addr="0x0804891f",func="foo",
args=[{name="i",value="10"}],file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"},
state="running"}],current-thread-id="1"(gdb)

The -thread-list-ids Command
Synopsis-thread-list-ids

Produces a list of the currently known global gdb thread ids. At the end of the list it
also prints the total number of such threads.
This command is retained for historical reasons, the -thread-info command should be
used instead.

gdb Command
Part of ‘info threads’ supplies the same information.

Example(gdb)-thread-list-ids^done,thread-ids={thread-id="3",thread-id="2",thread-id="1"},current-thread-id="1",number-of-threads="3"(gdb)

The -thread-select Command

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Synopsis-thread-select thread-id

Make thread with global thread number thread-id the current thread. It prints thenumber of the new current thread, and the topmost frame for that thread.
This command is deprecated in favor of explicitly using the ‘--thread’ option to eachcommand.

gdb Command
The corresponding gdb command is ‘thread’.

Example(gdb)-exec-next^running(gdb)*stopped,reason="end-stepping-range",thread-id="2",line="187",
file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"(gdb)-thread-list-ids^done,
thread-ids={thread-id="3",thread-id="2",thread-id="1"},number-of-threads="3"(gdb)-thread-select 3^done,new-thread-id="3",
frame={level="0",func="vprintf",
args=[{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""},{name="arg",value="0x2"}],file="vprintf.c",line="31",arch="i386:x86_64"}(gdb)

27.14 gdb/mi Ada Tasking Commands
The -ada-task-info Command
Synopsis-ada-task-info [ task-id ]Reports information about either a specific Ada task, if the task-id parameter is present,or about all Ada tasks.

gdb Command
The ‘info tasks’ command prints the same information about all Ada tasks (seeSection 15.4.10.7 [Ada Tasks], page 255).

Result
The result is a table of Ada tasks. The following columns are defined for each Ada task:‘current’This field exists only for the current thread. It has the value ‘*’.

‘id’

The identifier that gdb uses to refer to the Ada task.

‘task-id’

The identifier that the target uses to refer to the Ada task.

Chapter 27: The gdb/mi Interface

627‘thread-id’
The global thread identifier of the thread corresponding to the Ada task.
This field should always exist, as Ada tasks are always implemented on top ofa thread. But if gdb cannot find this corresponding thread for any reason, thefield is omitted.
‘parent-id’
This field exists only when the task was created by another task. In this case,it provides the ID of the parent task.
‘priority’
The base priority of the task.
‘state’The current state of the task. For a detailed description of the possible states,
see Section 15.4.10.7 [Ada Tasks], page 255.

‘name’The name of the task.

Example-ada-task-info^done,tasks={nr_rows="3",nr_cols="8",hdr=[{width="1",alignment="-1",col_name="current",colhdr=""},{width="3",alignment="1",col_name="id",colhdr="ID"},{width="9",alignment="1",col_name="task-id",colhdr="TID"},{width="4",alignment="1",col_name="thread-id",colhdr=""},{width="4",alignment="1",col_name="parent-id",colhdr="P-ID"},{width="3",alignment="1",col_name="priority",colhdr="Pri"},{width="22",alignment="-1",col_name="state",colhdr="State"},{width="1",alignment="2",col_name="name",colhdr="Name"}],body=[{current="*",id="1",task-id="
644010",thread-id="1",priority="48",state="Child Termination Wait",name="main_task"}]}(gdb)

27.15 gdb/mi Program Execution
These are the asynchronous commands which generate the out-of-band record ‘*stopped’.
Currently gdb only really executes asynchronously with remote targets and this interaction
is mimicked in other cases.

The -exec-continue Command
Synopsis-exec-continue [--reverse] [--all|--thread-group N]

Resumes the execution of the inferior program, which will continue to execute until itreaches a debugger stop event. If the ‘--reverse’ option is specified, execution resumes inreverse until it reaches a stop event. Stop events may include• breakpoints, watchpoints, tracepoints, or catchpoints• signals or exceptions• the end of the process (or its beginning under ‘--reverse’)• the end or beginning of a replay log if one is being used.

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Debugging with gdb

In all-stop mode (see Section 5.5.1 [All-Stop Mode], page 93), may resume only one
thread, or all threads, depending on the value of the ‘scheduler-locking’ variable. If‘--all’ is specified, all threads (in all inferiors) will be resumed. The ‘--all’ option is
ignored in all-stop mode. If the ‘--thread-group’ options is specified, then all threads inthat thread group are resumed.

gdb Command
The corresponding gdb corresponding is ‘continue’.

Example-exec-continue^running(gdb)@Hello world*stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame={
func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",line="13",arch="i386:x86_64"}(gdb)

For a ‘breakpoint-hit’ stopped reason, when the breakpoint encountered has multiple
locations, the field ‘bkptno’ is followed by the field ‘locno’.
-exec-continue^running(gdb)@Hello world*stopped,reason="breakpoint-hit",disp="keep",bkptno="2",locno="3",frame={
func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",line="13",arch="i386:x86_64"}(gdb)

The -exec-finish Command
Synopsis-exec-finish [--reverse]

Resumes the execution of the inferior program until the current function is exited. Displays the results returned by the function. If the ‘--reverse’ option is specified, resumes
the reverse execution of the inferior program until the point where current function was
called.

gdb Command
The corresponding gdb command is ‘finish’.

ExampleFunction returning void.
-exec-finish^running(gdb)@hello from foo*stopped,reason="function-finished",frame={func="main",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",line="7",arch="i386:x86_64"}(gdb)Chapter 27: The gdb/mi Interface

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Function returning other than void. The name of the internal gdb variable storing theresult is printed, together with the value itself.
-exec-finish^running(gdb)*stopped,reason="function-finished",frame={addr="0x000107b0",func="foo",
args=[{name="a",value="1"],{name="b",value="9"}},file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},gdb-result-var="$1",return-value="0"(gdb)

The -exec-interrupt Command
Synopsis-exec-interrupt [--all|--thread-group N]

Interrupts the background execution of the target. Note how the token associated withthe stop message is the one for the execution command that has been interrupted. The
token for the interrupt itself only appears in the ‘^done’ output. If the user is trying tointerrupt a non-running program, an error message will be printed.
Note that when asynchronous execution is enabled, this command is asynchronous justlike other execution commands. That is, first the ‘^done’ response will be printed, and thetarget stop will be reported after that using the ‘*stopped’ notification.
In non-stop mode, only the context thread is interrupted by default. All threads (inall inferiors) will be interrupted if the ‘--all’ option is specified. If the ‘--thread-group’option is specified, all threads in that group will be interrupted.

gdb Command
The corresponding gdb command is ‘interrupt’.

Example(gdb)
111-exec-continue
111^running(gdb)
222-exec-interrupt
222^done(gdb)
111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
frame={addr="0x00010140",func="foo",args=[],file="try.c",fullname="/home/foo/bar/try.c",line="13",arch="i386:x86_64"}
(gdb)
(gdb)
-exec-interrupt^error,msg="mi_cmd_exec_interrupt: Inferior not executing."(gdb)

The -exec-jump Command

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Debugging with gdb

Synopsis-exec-jump locspec

Resumes execution of the inferior program at the address to which locspec resolves. See
Section 9.2 [Location Specifications], page 126, for a description of the different forms oflocspec.

gdb Command
The corresponding gdb command is ‘jump’.

Example-exec-jump foo.c:10*running,thread-id="all"^running

The -exec-next Command
Synopsis-exec-next [--reverse]

Resumes execution of the inferior program, stopping when the beginning of the next
source line is reached.
If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program,
stopping at the beginning of the previous source line. If you issue this command on thefirst line of a function, it will take you back to the caller of that function, to the source line
where the function was called.

gdb Command
The corresponding gdb command is ‘next’.

Example-exec-next^running(gdb)*stopped,reason="end-stepping-range",line="8",file="hello.c"(gdb)

The -exec-next-instruction Command
Synopsis-exec-next-instruction [--reverse]

Executes one machine instruction. If the instruction is a function call, continues until
the function returns. If the program stops at an instruction in the middle of a source line,
the address will be printed as well.
If the ‘--reverse’ option is specified, resumes reverse execution of the inferior program,
stopping at the previous instruction. If the previously executed instruction was a returnfrom another function, it will continue to execute in reverse until the call to that function(from the current stack frame) is reached.

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gdb Command
The corresponding gdb command is ‘nexti’.

Example(gdb)-exec-next-instruction^running(gdb)*stopped,reason="end-stepping-range",
addr="0x000100d4",line="5",file="hello.c"(gdb)

The -exec-return Command
Synopsis-exec-return

Makes current function return immediately. Doesn’t execute the inferior. Displays the
new current frame.

gdb Command
The corresponding gdb command is ‘return’.

Example(gdb)
200-break-insert callee4
200^done,bkpt={number="1",addr="0x00010734",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"}(gdb)000-exec-run
000^running(gdb)
000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
frame={func="callee4",args=[],file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8",arch="i386:x86_64"}(gdb)
205-break-delete
205^done(gdb)
111-exec-return
111^done,frame={level="0",func="callee3",
args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18",
arch="i386:x86_64"}(gdb)

The -exec-run Command

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Synopsis-exec-run [ --all | --thread-group N ] [ --start ]Starts execution of the inferior from the beginning. The inferior executes until either abreakpoint is encountered or the program exits. In the latter case the output will include
an exit code, if the program has exited exceptionally.
When neither the ‘--all’ nor the ‘--thread-group’ option is specified, the current
inferior is started. If the ‘--thread-group’ option is specified, it should refer to a threadgroup of type ‘process’, and that thread group will be started. If the ‘--all’ option is
specified, then all inferiors will be started.
Using the ‘--start’ option instructs the debugger to stop the execution at the start ofthe inferior’s main subprogram, following the same behavior as the start command (seeSection 4.2 [Starting], page 34).

gdb Command
The corresponding gdb command is ‘run’.

Examples(gdb)-break-insert main
^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"}(gdb)-exec-run^running(gdb)*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
frame={func="main",args=[],file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4",arch="i386:x86_64"}(gdb)

Program exited normally:(gdb)-exec-run^running(gdb)
x = 55*stopped,reason="exited-normally"(gdb)

Program exited exceptionally:(gdb)-exec-run^running(gdb)
x = 55*stopped,reason="exited",exit-code="01"(gdb)

Another way the program can terminate is if it receives a signal such as SIGINT. In thiscase, gdb/mi displays this:(gdb)*stopped,reason="exited-signalled",signal-name="SIGINT",
signal-meaning="Interrupt"

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The -exec-step Command
Synopsis-exec-step [--reverse]

Resumes execution of the inferior program, stopping when the beginning of the next
source line is reached, if the next source line is not a function call. If it is, stop at the first
instruction of the called function. If the ‘--reverse’ option is specified, resumes reverse
execution of the inferior program, stopping at the beginning of the previously executed
source line.

gdb Command
The corresponding gdb command is ‘step’.

ExampleStepping into a function:-exec-step^running(gdb)*stopped,reason="end-stepping-range",frame={func="foo",args=[{name="a",value="10"},{name="b",value="0"}],file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11",arch="i386:x86_64"}(gdb)

Regular stepping:-exec-step^running(gdb)*stopped,reason="end-stepping-range",line="14",file="recursive2.c"(gdb)

The -exec-step-instruction Command
Synopsis-exec-step-instruction [--reverse]

Resumes the inferior which executes one machine instruction. If the ‘--reverse’ option
is specified, resumes reverse execution of the inferior program, stopping at the previously
executed instruction. The output, once gdb has stopped, will vary depending on whether
we have stopped in the middle of a source line or not. In the former case, the address at
which the program stopped will be printed as well.

gdb Command
The corresponding gdb command is ‘stepi’.

Example(gdb)-exec-step-instruction^running
(gdb)

634

Debugging with gdb*stopped,reason="end-stepping-range",frame={func="foo",args=[],file="try.c",fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"}(gdb)-exec-step-instruction^running(gdb)*stopped,reason="end-stepping-range",frame={addr="0x000100f4",func="foo",args=[],file="try.c",fullname="/home/foo/bar/try.c",line="10",arch="i386:x86_64"}(gdb)

The -exec-until Command
Synopsis-exec-until [ locspec ]Executes the inferior until it reaches the address to which locspec resolves. If there is noargument, the inferior executes until it reaches a source line greater than the current one.
The reason for stopping in this case will be ‘location-reached’.

gdb Command
The corresponding gdb command is ‘until’.

Example(gdb)-exec-until recursive2.c:6^running(gdb)
x = 55*stopped,reason="location-reached",frame={func="main",args=[],file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6",arch="i386:x86_64"}(gdb)

27.16 gdb/mi Stack Manipulation Commands
The -enable-frame-filters Command-enable-frame-filters

gdb allows Python-based frame filters to affect the output of the MI commands relating
to stack traces. As there is no way to implement this in a fully backward-compatible way,a front end must request that this functionality be enabled.
Once enabled, this feature cannot be disabled.
Note that if Python support has not been compiled into gdb, this command will still
succeed (and do nothing).

The -stack-info-frame Command
Synopsis-stack-info-frame

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635

Get info on the selected frame.

gdb Command
The corresponding gdb command is ‘info frame’ or ‘frame’ (without arguments).

Example(gdb)-stack-info-frame^done,frame={level="1",addr="0x0001076c",func="callee3",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17",arch="i386:x86_64"}(gdb)

The -stack-info-depth Command
Synopsis-stack-info-depth [ max-depth ]Return the depth of the stack. If the integer argument max-depth is specified, do notcount beyond max-depth frames.

gdb Command
There’s no equivalent gdb command.

ExampleFor a stack with frame levels 0 through 11:(gdb)-stack-info-depth^done,depth="12"(gdb)-stack-info-depth 4^done,depth="4"(gdb)-stack-info-depth 12^done,depth="12"(gdb)-stack-info-depth 11^done,depth="11"(gdb)-stack-info-depth 13^done,depth="12"(gdb)

The -stack-list-arguments Command
Synopsis-stack-list-arguments [ --no-frame-filters ] [ --skip-unavailable ] print-values[ low-frame high-frame ]Display a list of the arguments for the frames between low-frame and high-frame (inclusive). If low-frame and high-frame are not provided, list the arguments for the whole callstack. If the two arguments are equal, show the single frame at the corresponding level.

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Debugging with gdb

It is an error if low-frame is larger than the actual number of frames. On the other hand,
high-frame may be larger than the actual number of frames, in which case only existing
frames will be returned.
If print-values is 0 or --no-values, print only the names of the variables; if it is 1 or--all-values, print also their values; and if it is 2 or --simple-values, print the name,type and value for simple data types, and the name and type for arrays, structures andunions. If the option --no-frame-filters is supplied, then Python frame filters will not
be executed.
If the --skip-unavailable option is specified, arguments that are not available are notlisted. Partially available arguments are still displayed, however.
Use of this command to obtain arguments in a single frame is deprecated in favor of the‘-stack-list-variables’ command.

gdb Command
gdb does not have an equivalent command. gdbtk has a ‘gdb_get_args’ command which
partially overlaps with the functionality of ‘-stack-list-arguments’.

Example(gdb)-stack-list-frames^done,
stack=[
frame={level="0",addr="0x00010734",func="callee4",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8",arch="i386:x86_64"},
frame={level="1",addr="0x0001076c",func="callee3",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17",arch="i386:x86_64"},
frame={level="2",addr="0x0001078c",func="callee2",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22",arch="i386:x86_64"},
frame={level="3",addr="0x000107b4",func="callee1",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27",
arch="i386:x86_64"},
frame={level="4",addr="0x000107e0",func="main",file="../../../devo/gdb/testsuite/gdb.mi/basics.c",fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32",arch="i386:x86_64"}](gdb)-stack-list-arguments 0^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",args=[name="strarg"]},frame={level="2",args=[name="intarg",name="strarg"]},frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]},frame={level="4",args=[]}](gdb)-stack-list-arguments 1

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637^done,
stack-args=[
frame={level="0",args=[]},
frame={level="1",
args=[{name="strarg",value="0x11940 \"A string argument.\""}]},
frame={level="2",args=[{name="intarg",value="2"},{name="strarg",value="0x11940 \"A string argument.\""}]},{frame={level="3",args=[{name="intarg",value="2"},{name="strarg",value="0x11940 \"A string argument.\""},{name="fltarg",value="3.5"}]},
frame={level="4",args=[]}](gdb)-stack-list-arguments 0 2 2^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}](gdb)-stack-list-arguments 1 2 2^done,stack-args=[frame={level="2",
args=[{name="intarg",value="2"},{name="strarg",value="0x11940 \"A string argument.\""}]}](gdb)

The -stack-list-frames Command
Synopsis-stack-list-frames [ --no-frame-filters low-frame high-frame ]List the frames currently on the stack. For each frame it displays the following info:‘level’The frame number, 0 being the topmost frame, i.e., the innermost function.

‘addr’

The $pc value for that frame.

‘func’

Function name.

‘file’

File name of the source file where the function lives.

‘fullname’
The full file name of the source file where the function lives.
‘line’

Line number corresponding to the $pc.

‘from’The shared library where this function is defined. This is only given if theframe’s function is not known.

‘arch’

Frame’s architecture.

If invoked without arguments, this command prints a backtrace for the whole stack. If
given two integer arguments, it shows the frames whose levels are between the two arguments(inclusive). If the two arguments are equal, it shows the single frame at the corresponding
level. It is an error if low-frame is larger than the actual number of frames. On theother hand, high-frame may be larger than the actual number of frames, in which caseonly existing frames will be returned. If the option --no-frame-filters is supplied, thenPython frame filters will not be executed.

gdb Command
The corresponding gdb commands are ‘backtrace’ and ‘where’.

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ExampleFull stack backtrace:(gdb)-stack-list-frames^done,stack=[frame={level="0",addr="0x0001076c",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11",arch="i386:x86_64"},
frame={level="1",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="2",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="4",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="5",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="6",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="7",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="8",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="9",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="10",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="11",addr="0x00010738",func="main",file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4",arch="i386:x86_64"}](gdb)

Show frames between low frame and high frame:(gdb)-stack-list-frames 3 5^done,stack=[frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="4",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"},
frame={level="5",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"}](gdb)

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Show a single frame:(gdb)-stack-list-frames 3 3^done,stack=[frame={level="3",addr="0x000107a4",func="foo",
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14",arch="i386:x86_64"}](gdb)

The -stack-list-locals Command
Synopsis-stack-list-locals [ --no-frame-filters ] [ --skip-unavailable ] print-values

Display the local variable names for the selected frame. If print-values is 0 or --novalues, print only the names of the variables; if it is 1 or --all-values, print also theirvalues; and if it is 2 or --simple-values, print the name, type and value for simple datatypes, and the name and type for arrays, structures and unions. In this last case, a frontend
can immediately display the value of simple data types and create variable objects for otherdata types when the user wishes to explore their values in more detail. If the option --noframe-filters is supplied, then Python frame filters will not be executed.
If the --skip-unavailable option is specified, local variables that are not available are
not listed. Partially available local variables are still displayed, however.
This command is deprecated in favor of the ‘-stack-list-variables’ command.

gdb Command‘info locals’ in gdb, ‘gdb_get_locals’ in gdbtk.

Example(gdb)-stack-list-locals 0^done,locals=[name="A",name="B",name="C"](gdb)-stack-list-locals --all-values^done,locals=[{name="A",value="1"},{name="B",value="2"},{name="C",value="{1, 2, 3}"}]-stack-list-locals --simple-values^done,locals=[{name="A",type="int",value="1"},{name="B",type="int",value="2"},{name="C",type="int [3]"}](gdb)

The -stack-list-variables Command
Synopsis-stack-list-variables [ --no-frame-filters ] [ --skip-unavailable ] print-values

Display the names of local variables and function arguments for the selected frame. If
print-values is 0 or --no-values, print only the names of the variables; if it is 1 or --allvalues, print also their values; and if it is 2 or --simple-values, print the name, type andvalue for simple data types, and the name and type for arrays, structures and unions. If theoption --no-frame-filters is supplied, then Python frame filters will not be executed.

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Debugging with gdb

If the --skip-unavailable option is specified, local variables and arguments that are notavailable are not listed. Partially available arguments and local variables are still displayed,
however.

Example(gdb)-stack-list-variables --thread 1 --frame 0 --all-values^done,variables=[{name="x",value="11"},{name="s",value="{a = 1, b = 2}"}](gdb)

The -stack-select-frame Command
Synopsis-stack-select-frame framenum

Change the selected frame. Select a different frame framenum on the stack.
This command in deprecated in favor of passing the ‘--frame’ option to every command.

gdb Command
The corresponding gdb commands are ‘frame’, ‘up’, ‘down’, ‘select-frame’, ‘up-silent’,and ‘down-silent’.

Example(gdb)-stack-select-frame 2
^done
(gdb)

27.17 gdb/mi Variable Objects
Introduction to Variable Objects
Variable objects are "object-oriented" MI interface for examining and changing values of
expressions. Unlike some other MI interfaces that work with expressions, variable objects
are specifically designed for simple and efficient presentation in the frontend. A variableobject is identified by string name. When a variable object is created, the frontend specifies
the expression for that variable object. The expression can be a simple variable, or it canbe an arbitrary complex expression, and can even involve CPU registers. After creating avariable object, the frontend can invoke other variable object operations—for example toobtain or change the value of a variable object, or to change display format.
Variable objects have hierarchical tree structure. Any variable object that corresponds to
a composite type, such as structure in C, has a number of child variable objects, for example
corresponding to each element of a structure. A child variable object can itself have children,
recursively. Recursion ends when we reach leaf variable objects, which always have built-in
types. Child variable objects are created only by explicit request, so if a frontend is notinterested in the children of a particular variable object, no child will be created.
For a leaf variable object it is possible to obtain its value as a string, or set the value
from a string. String value can be also obtained for a non-leaf variable object, but it’s

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generally a string that only indicates the type of the object, and does not list its contents.
Assignment to a non-leaf variable object is not allowed.
A frontend does not need to read the values of all variable objects each time the program
stops. Instead, MI provides an update command that lists all variable objects whose values
has changed since the last update operation. This considerably reduces the amount of datathat must be transferred to the frontend. As noted above, children variable objects are
created on demand, and only leaf variable objects have a real value. As result, gdb will
read target memory only for leaf variables that frontend has created.
The automatic update is not always desirable. For example, a frontend might wantto keep a value of some expression for future reference, and never update it. For anotherexample, fetching memory is relatively slow for embedded targets, so a frontend might want
to disable automatic update for the variables that are either not visible on the screen, or“closed”. This is possible using so called “frozen variable objects”. Such variable objects
are never implicitly updated.
Variable objects can be either fixed or floating. For the fixed variable object, the expression is parsed when the variable object is created, including associating identifiers tospecific variables. The meaning of expression never changes. For a floating variable object
the values of variables whose names appear in the expressions are re-evaluated every timein the context of the current frame. Consider this example:
void do_work(...){
struct work_state state;if (...)
do_work(...);}

If a fixed variable object for the state variable is created in this function, and we enter
the recursive call, the variable object will report the value of state in the top-level do_work
invocation. On the other hand, a floating variable object will report the value of state in
the current frame.
If an expression specified when creating a fixed variable object refers to a local variable,
the variable object becomes bound to the thread and frame in which the variable object
is created. When such variable object is updated, gdb makes sure that the thread/frame
combination the variable object is bound to still exists, and re-evaluates the variable object
in context of that thread/frame.
The following is the complete set of gdb/mi operations defined to access this functionality:
Operation

Description-enable-pretty-printing-var-create-var-delete-var-set-format-var-show-format-var-info-num-children-var-list-children

enable Python-based pretty-printing
create a variable object
delete the variable object and/or its children
set the display format of this variableshow the display format of this variable
tells how many children this object has
return a list of the object’s children

642

Debugging with gdb-var-info-type-var-info-expression-var-info-path-expression-var-show-attributes-var-evaluate-expression-var-assign-var-update-var-set-frozen-var-set-update-range

show the type of this variable object
print parent-relative expression that this variable object represents
print full expression that this variable object
represents
is this variable editable? does it exist here?
get the value of this variable
set the value of this variable
update the variable and its children
set frozenness attributeset range of children to display on update

In the next subsection we describe each operation in detail and suggest how it can beused.

Description And Use of Operations on Variable Objects
The -enable-pretty-printing Command-enable-pretty-printing

gdb allows Python-based visualizers to affect the output of the MI variable objectcommands. However, because there was no way to implement this in a fully backwardcompatible way, a front end must request that this functionality be enabled.
Once enabled, this feature cannot be disabled.
Note that if Python support has not been compiled into gdb, this command will still
succeed (and do nothing).

The -var-create Command
Synopsis-var-create {name | "-"}
{frame-addr | "*" | "@"} expression

This operation creates a variable object, which allows the monitoring of a variable, theresult of an expression, a memory cell or a CPU register.
The name parameter is the string by which the object can be referenced. It must
be unique. If ‘-’ is specified, the varobj system will generate a string “varNNNNNN”
automatically. It will be unique provided that one does not specify name of that format.
The command fails if a duplicate name is found.
The frame under which the expression should be evaluated can be specified by frameaddr. A ‘*’ indicates that the current frame should be used. A ‘@’ indicates that a floating
variable object must be created.
expression is any expression valid on the current language set (must not begin with a‘*’), or one of the following:• ‘*addr’, where addr is the address of a memory cell
• ‘*addr-addr’ — a memory address range (TBD)• ‘$regname’ — a CPU register name

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A varobj’s contents may be provided by a Python-based pretty-printer. In this case thevarobj is known as a dynamic varobj. Dynamic varobjs have slightly different semantics insome cases. If the -enable-pretty-printing command is not sent, then gdb will nevercreate a dynamic varobj. This ensures backward compatibility for existing clients.

ResultThis operation returns attributes of the newly-created varobj. These are:‘name’The name of the varobj.

‘numchild’
The number of children of the varobj. This number is not necessarily reliable
for a dynamic varobj. Instead, you must examine the ‘has_more’ attribute.
‘value’The varobj’s scalar value. For a varobj whose type is some sort of aggregate(e.g., a struct), this value will not be interesting. For a dynamic varobj,
this value comes directly from the Python pretty-printer object’s to_string
method.

‘type’The varobj’s type. This is a string representation of the type, as would beprinted by the gdb CLI. If ‘print object’ (see Section 10.9 [Print Settings],
page 157) is set to on, the actual (derived) type of the object is shown rather
than the declared one.

‘thread-id’
If a variable object is bound to a specific thread, then this is the thread’s global
identifier.
‘has_more’
For a dynamic varobj, this indicates whether there appear to be any children
available. For a non-dynamic varobj, this will be 0.
‘dynamic’This attribute will be present and have the value ‘1’ if the varobj is a dynamic
varobj. If the varobj is not a dynamic varobj, then this attribute will not bepresent.

‘displayhint’
A dynamic varobj can supply a display hint to the front end. The value comes
directly from the Python pretty-printer object’s display_hint method. See
Section 23.3.2.6 [Pretty Printing API], page 424.
Typical output will look like this:
name="name",numchild="N",type="type",thread-id="M",has_more="has_more"

The -var-delete Command
Synopsis-var-delete [ -c ] name

Deletes a previously created variable object and all of its children. With the ‘-c’ option,
just deletes the children.
Returns an error if the object name is not found.

644

Debugging with gdb

The -var-set-format Command
Synopsis-var-set-format name format-spec

Sets the output format for the value of the object name to be format-spec.
The syntax for the format-spec is as follows:format-spec 7→{binary | decimal | hexadecimal | octal | natural | zero-hexadecimal}

The natural format is the default format chosen automatically based on the variable
type (like decimal for an int, hex for pointers, etc.).
The zero-hexadecimal format has a representation similar to hexadecimal but withpadding zeroes to the left of the value. For example, a 32-bit hexadecimal value of 0x1234
would be represented as 0x00001234 in the zero-hexadecimal format.
For a variable with children, the format is set only on the variable itself, and the children
are not affected.

The -var-show-format Command
Synopsis-var-show-format nameReturns the format used to display the value of the object name.
format 7→
format-spec

The -var-info-num-children Command
Synopsis-var-info-num-children nameReturns the number of children of a variable object name:numchild=nNote that this number is not completely reliable for a dynamic varobj. It will return thecurrent number of children, but more children may be available.

The -var-list-children Command
Synopsis-var-list-children [print-values] name [from to]Return a list of the children of the specified variable object and create variable objects
for them, if they do not already exist. With a single argument or if print-values has avalue of 0 or --no-values, print only the names of the variables; if print-values is 1 or--all-values, also print their values; and if it is 2 or --simple-values print the nameand value for simple data types and just the name for arrays, structures and unions.
from and to, if specified, indicate the range of children to report. If from or to is lessthan zero, the range is reset and all children will be reported. Otherwise, children startingat from (zero-based) and up to and excluding to will be reported.

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If a child range is requested, it will only affect the current call to -var-list-children,
but not future calls to -var-update. For this, you must instead use -var-set-updaterange. The intent of this approach is to enable a front end to implement any update
approach it likes; for example, scrolling a view may cause the front end to request morechildren with -var-list-children, and then the front end could call -var-set-updaterange with a different range to ensure that future updates are restricted to just the visible
items.
For each child the following results are returned:
nameName of the variable object created for this child.

exp

The expression to be shown to the user by the front end to designate this child.
For example this may be the name of a structure member.
For a dynamic varobj, this value cannot be used to form an expression. Thereis no way to do this at all with a dynamic varobj.
For C/C++ structures there are several pseudo children returned to designate
access qualifiers. For these pseudo children exp is ‘public’, ‘private’, or‘protected’. In this case the type and value are not present.
A dynamic varobj will not report the access qualifying pseudo-children, regardless of the language. This information is not available at all with a dynamic
varobj.

numchild

Number of children this child has. For a dynamic varobj, this will be 0.

type

The type of the child. If ‘print object’ (see Section 10.9 [Print Settings],
page 157) is set to on, the actual (derived) type of the object is shown rather
than the declared one.

value

If values were requested, this is the value.

thread-id

If this variable object is associated with a thread, this is the thread’s global
thread id. Otherwise this result is not present.

frozenIf the variable object is frozen, this variable will be present with a value of 1.

displayhint
A dynamic varobj can supply a display hint to the front end. The value comes
directly from the Python pretty-printer object’s display_hint method. See
Section 23.3.2.6 [Pretty Printing API], page 424.
dynamic

This attribute will be present and have the value ‘1’ if the varobj is a dynamic
varobj. If the varobj is not a dynamic varobj, then this attribute will not bepresent.

The result may have its own attributes:‘displayhint’
A dynamic varobj can supply a display hint to the front end. The value comes
directly from the Python pretty-printer object’s display_hint method. See
Section 23.3.2.6 [Pretty Printing API], page 424.
‘has_more’
This is an integer attribute which is nonzero if there are children remaining
after the end of the selected range.

646

Debugging with gdb

Example(gdb)-var-list-children n^done,numchild=n,children=[child={name=name,exp=exp,
numchild=n,type=type},(repeats N times)](gdb)-var-list-children --all-values n^done,numchild=n,children=[child={name=name,exp=exp,
numchild=n,value=value,type=type},(repeats N times)]

The -var-info-type Command
Synopsis-var-info-type nameReturns the type of the specified variable name. The type is returned as a string in thesame format as it is output by the gdb CLI:
type=typename

The -var-info-expression Command
Synopsis-var-info-expression nameReturns a string that is suitable for presenting this variable object in user interface. The
string is generally not valid expression in the current language, and cannot be evaluated.
For example, if a is an array, and variable object A was created for a, then we’ll get this
output:(gdb) -var-info-expression A.1^done,lang="C",exp="1"

Here, the value of lang is the language name, which can be found in Section 15.4 [Supported
Languages], page 231.
Note that the output of the -var-list-children command also includes those expressions, so the -var-info-expression command is of limited use.

The -var-info-path-expression Command
Synopsis-var-info-path-expression nameReturns an expression that can be evaluated in the current context and will yield thesame value that a variable object has. Compare this with the -var-info-expressioncommand, which result can be used only for UI presentation. Typical use of the -varinfo-path-expression command is creating a watchpoint from a variable object.
This command is currently not valid for children of a dynamic varobj, and will give anerror when invoked on one.
For example, suppose C is a C++ class, derived from class Base, and that the Base class
has a member called m_size. Assume a variable c is has the type of C and a variable object
C was created for variable c. Then, we’ll get this output:(gdb) -var-info-path-expression C.Base.public.m_size^done,path_expr=((Base)c).m_size)Chapter 27: The gdb/mi Interface

647

The -var-show-attributes Command
Synopsis-var-show-attributes name

List attributes of the specified variable object name:status=attr [ ( ,attr )* ]where attr is { { editable | noneditable } | TBD }.

The -var-evaluate-expression Command
Synopsis-var-evaluate-expression [-f format-spec] nameEvaluates the expression that is represented by the specified variable object and returns
its value as a string. The format of the string can be specified with the ‘-f’ option. The
possible values of this option are the same as for -var-set-format (see [-var-set-format],page 644). If the ‘-f’ option is not specified, the current display format will be used. The
current display format can be changed using the -var-set-format command.
value=value

Note that one must invoke -var-list-children for a variable before the value of a childvariable can be evaluated.

The -var-assign Command
Synopsis-var-assign name expression

Assigns the value of expression to the variable object specified by name. The object
must be ‘editable’. If the variable’s value is altered by the assign, the variable will show
up in any subsequent -var-update list.

Example(gdb)-var-assign var1 3^done,value="3"(gdb)-var-update *^done,changelist=[{name="var1",in_scope="true",type_changed="false"}](gdb)

The -var-update Command
Synopsis-var-update [print-values] {name | "*"}

Reevaluate the expressions corresponding to the variable object name and all its direct
and indirect children, and return the list of variable objects whose values have changed;
name must be a root variable object. Here, “changed” means that the result of -varevaluate-expression before and after the -var-update is different. If ‘*’ is used as thevariable object names, all existing variable objects are updated, except for frozen ones (see648

Debugging with gdb[-var-set-frozen], page 649). The option print-values determines whether both names andvalues, or just names are printed. The possible values of this option are the same as for-var-list-children (see [-var-list-children], page 644). It is recommended to use the‘--all-values’ option, to reduce the number of MI commands needed on each program
stop.
With the ‘*’ parameter, if a variable object is bound to a currently running thread, it
will not be updated, without any diagnostic.
If -var-set-update-range was previously used on a varobj, then only the selected rangeof children will be reported.
-var-update reports all the changed varobjs in a tuple named ‘changelist’.
Each item in the change list is itself a tuple holding:‘name’The name of the varobj.

‘value’If values were requested for this update, then this field will be present and willhold the value of the varobj.

‘in_scope’This field is a string which may take one of three values:"true"The variable object’s current value is valid.

"false"The variable object does not currently hold a valid value but it may
hold one in the future if its associated expression comes back into
scope.

"invalid"
The variable object no longer holds a valid value. This can occur when the executable file being debugged has changed, either
through recompilation or by using the gdb file command. The
front end should normally choose to delete these variable objects.
In the future new values may be added to this list so the front should be
prepared for this possibility. See Section 27.6 [gdb/mi Development and Front
Ends], page 595.
‘type_changed’
This is only present if the varobj is still valid. If the type changed, then thiswill be the string ‘true’; otherwise it will be ‘false’.
When a varobj’s type changes, its children are also likely to have become incorrect. Therefore, the varobj’s children are automatically deleted when this
attribute is ‘true’. Also, the varobj’s update range, when set using the -varset-update-range command, is unset.
‘new_type’
If the varobj’s type changed, then this field will be present and will hold the
new type.
‘new_num_children’
For a dynamic varobj, if the number of children changed, or if the type changed,
this will be the new number of children.

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The ‘numchild’ field in other varobj responses is generally not valid for a dynamic varobj – it will show the number of children that gdb knows about, but
because dynamic varobjs lazily instantiate their children, this will not reflect
the number of children which may be available.
The ‘new_num_children’ attribute only reports changes to the number of children known by gdb. This is the only way to detect whether an update has
removed children (which necessarily can only happen at the end of the update
range).
‘displayhint’
The display hint, if any.
‘has_more’
This is an integer value, which will be 1 if there are more children available
outside the varobj’s update range.
‘dynamic’This attribute will be present and have the value ‘1’ if the varobj is a dynamic
varobj. If the varobj is not a dynamic varobj, then this attribute will not bepresent.

‘new_children’
If new children were added to a dynamic varobj within the selected update range(as set by -var-set-update-range), then they will be listed in this attribute.

Example(gdb)-var-assign var1 3^done,value="3"(gdb)-var-update --all-values var1
^done,changelist=[{name="var1",value="3",in_scope="true",
type_changed="false"}](gdb)

The -var-set-frozen Command
Synopsis-var-set-frozen name flag

Set the frozenness flag on the variable object name. The flag parameter should be either‘1’ to make the variable frozen or ‘0’ to make it unfrozen. If a variable object is frozen, thenneither itself, nor any of its children, are implicitly updated by -var-update of a parent
variable or by -var-update *. Only -var-update of the variable itself will update its value
and values of its children. After a variable object is unfrozen, it is implicitly updated by
all subsequent -var-update operations. Unfreezing a variable does not update it, only
subsequent -var-update does.

Example(gdb)-var-set-frozen V 1
^done
(gdb)

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Debugging with gdb

The -var-set-update-range command
Synopsis-var-set-update-range name from to

Set the range of children to be returned by future invocations of -var-update.
from and to indicate the range of children to report. If from or to is less than zero,
the range is reset and all children will be reported. Otherwise, children starting at from(zero-based) and up to and excluding to will be reported.

Example(gdb)-var-set-update-range V 1 2^done

The -var-set-visualizer command
Synopsis-var-set-visualizer name visualizer

Set a visualizer for the variable object name.
visualizer is the visualizer to use. The special value ‘None’ means to disable any visualizer
in use.
If not ‘None’, visualizer must be a Python expression. This expression must evaluate toa callable object which accepts a single argument. gdb will call this object with the valueof the varobj name as an argument (this is done so that the same Python pretty-printing
code can be used for both the CLI and MI). When called, this object must return an object
which conforms to the pretty-printing interface (see Section 23.3.2.6 [Pretty Printing API],
page 424).
The pre-defined function gdb.default_visualizer may be used to select a visualizer
by following the built-in process (see Section 23.3.2.7 [Selecting Pretty-Printers], page 426).
This is done automatically when a varobj is created, and so ordinarily is not needed.
This feature is only available if Python support is enabled. The MI command -listfeatures (see Section 27.25 [GDB/MI Support Commands], page 684) can be used to checkthis.

ExampleResetting the visualizer:(gdb)-var-set-visualizer V None
^done

Reselecting the default (type-based) visualizer:(gdb)-var-set-visualizer V gdb.default_visualizer^done

Suppose SomeClass is a visualizer class. A lambda expression can be used to instantiate
this class for a varobj:(gdb)Chapter 27: The gdb/mi Interface

651-var-set-visualizer V "lambda val: SomeClass()"^done

27.18 gdb/mi Data Manipulation
This section describes the gdb/mi commands that manipulate data: examine memory andregisters, evaluate expressions, etc.
For details about what an addressable memory unit is, see [addressable memory unit],
page 154.

The -data-disassemble Command
Synopsis-data-disassemble( -s start-addr -e end-addr| -a addr| -f filename -l linenum [ -n lines ] )[ --opcodes opcodes-mode ][ --source ][ -- mode ]Where:‘start-addr’is the beginning address (or $pc)
‘end-addr’is the end address‘addr’

is an address anywhere within (or the name of) the function to disassemble.
If an address is specified, the whole function surrounding that address will bedisassembled. If a name is specified, the whole function with that name will bedisassembled.

‘filename’is the name of the file to disassemble‘linenum’is the line number to disassemble around‘lines’is the number of disassembly lines to be produced. If it is -1, the whole function
will be disassembled, in case no end-addr is specified. If end-addr is specified
as a non-zero value, and lines is lower than the number of disassembly lines
between start-addr and end-addr, only lines lines are displayed; if lines is higher
than the number of lines between start-addr and end-addr, only the lines up to
end-addr are displayed.

‘opcodes-mode’
can only be used with mode 0, and should be one of the following:‘none’

no opcode information will be included in the result.

‘bytes’opcodes will be included in the result, the opcodes will be formatted
as for disassemble /b.

‘display’

opcodes will be included in the result, the opcodes will be formatted
as for disassemble /r.

652‘mode’

Debugging with gdb

the use of mode is deprecated in favour of using the --opcodes and --source
options. When no mode is given, mode 0 will be assumed. However, the modeis still available for backward compatibility. The mode should be one of:‘0’disassembly only, this is the default mode if no mode is specified.

‘1’

mixed source and disassembly (deprecated), it is not possible torecreate this mode using --opcodes and --source options.

‘2’disassembly with raw opcodes, this mode is equivalent to using mode
0 and passing --opcodes bytes to the command.

‘3’

mixed source and disassembly with raw opcodes (deprecated), it is
not possible to recreate this mode using --opcodes and --source
options.

‘4’

mixed source and disassembly, this mode is equivalent to using
mode 0 and passing --source to the command.

‘5’

mixed source and disassembly with raw opcodes, this mode is equivalent to using mode 0 and passing --opcodes bytes and --source
to the command.

Modes 1 and 3 are deprecated. The output is “source centric” which hasn’t
proved useful in practice. See Section 9.6 [Machine Code], page 135, for a
discussion of the difference between /m and /s output of the disassemble
command.
The --source can only be used with mode 0. Passing this option will include the sourcecode in the disassembly result as if mode 4 or 5 had been used.

Result
The result of the -data-disassemble command will be a list named ‘asm_insns’, thecontents of this list depend on the options used with the -data-disassemble command.
For modes 0 and 2, and when the --source option is not used, the ‘asm_insns’ list
contains tuples with the following fields:
address

The address at which this instruction was disassembled.

func-name
The name of the function this instruction is within.
offset

The decimal offset in bytes from the start of ‘func-name’.

inst

The text disassembly for this ‘address’.

opcodesThis field is only present for modes 2, 3 and 5, or when the --opcodes option‘bytes’ or ‘display’ is used. This contains the raw opcode bytes for the ‘inst’
field.
When the ‘--opcodes’ option is not passed to -data-disassemble, or the‘bytes’ value is passed to ‘--opcodes’, then the bytes are formatted as a seriesof single bytes, in hex, in ascending address order, with a single space between
each byte. This format is equivalent to the ‘/b’ option being used with thedisassemble command (see [disassemble], page 136).

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When ‘--opcodes’ is passed the value ‘display’ then the bytes are formatted in
the natural instruction display order. This means multiple bytes can be grouped
together, and the bytes might be byte-swapped. This format is equivalent tothe ‘/r’ option being used with the disassemble command.
For modes 1, 3, 4 and 5, or when the --source option is used, the ‘asm_insns’ list
contains tuples named ‘src_and_asm_line’, each of which has the following fields:
line

The line number within ‘file’.

file

The file name from the compilation unit. This might be an absolute file nameor a relative file name depending on the compile command used.

fullname

Absolute file name of ‘file’. It is converted to a canonical form using the source
file search path (see Section 9.5 [Specifying Source Directories], page 131) andafter resolving all the symbolic links.
If the source file is not found this field will contain the path as present in the
debug information.

line_asm_insn
This is a list of tuples containing the disassembly for ‘line’ in ‘file’. The
fields of each tuple are the same as for -data-disassemble in mode 0 and 2,
so ‘address’, ‘func-name’, ‘offset’, ‘inst’, and optionally ‘opcodes’.
Note that whatever included in the ‘inst’ field, is not manipulated directly by gdb/mi,i.e., it is not possible to adjust its format.

gdb Command
The corresponding gdb command is ‘disassemble’.

ExampleDisassemble from the current value of $pc to $pc + 20:(gdb)-data-disassemble -s $pc -e "$pc + 20" -- 0
^done,
asm_insns=[{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},{address="0x000107c8",func-name="main",offset="12",inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"},{address="0x000107cc",func-name="main",offset="16",inst="sethi %hi(0x11800), %o2"},{address="0x000107d0",func-name="main",offset="20",
inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}](gdb)

Disassemble the whole main function. Line 32 is part of main.
-data-disassemble -f basics.c -l 32 -- 0
^done,asm_insns=[{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},{address="0x000107c0",func-name="main",offset="4",654

Debugging with gdb

inst="mov2, %o0"},{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"},[...]{address="0x0001081c",func-name="main",offset="96",inst="ret "},{address="0x00010820",func-name="main",offset="100",inst="restore "}](gdb)

Disassemble 3 instructions from the start of main:(gdb)-data-disassemble -f basics.c -l 32 -n 3 -- 0
^done,asm_insns=[{address="0x000107bc",func-name="main",offset="0",
inst="save %sp, -112, %sp"},{address="0x000107c0",func-name="main",offset="4",
inst="mov 2, %o0"},{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}](gdb)

Disassemble 3 instructions from the start of main in mixed mode:(gdb)-data-disassemble -f basics.c -l 32 -n 3 -- 1
^done,asm_insns=[
src_and_asm_line={line="31",
file="../../../src/gdb/testsuite/gdb.mi/basics.c",fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c",line_asm_insn=[{address="0x000107bc",
func-name="main",offset="0",inst="save %sp, -112, %sp"}]},
src_and_asm_line={line="32",file="../../../src/gdb/testsuite/gdb.mi/basics.c",fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c",line_asm_insn=[{address="0x000107c0",
func-name="main",offset="4",inst="mov 2, %o0"},{address="0x000107c4",func-name="main",offset="8",
inst="sethi %hi(0x11800), %o2"}]}](gdb)

The -data-evaluate-expression Command
Synopsis-data-evaluate-expression expr

Evaluate expr as an expression. The expression could contain an inferior function call.
The function call will execute synchronously. If the expression contains spaces, it must be
enclosed in double quotes.

gdb Command
The corresponding gdb commands are ‘print’, ‘output’, and ‘call’. In gdbtk only, there’s
a corresponding ‘gdb_eval’ command.

ExampleIn the following example, the numbers that precede the commands are the tokens describedin Section 27.4 [gdb/mi Command Syntax], page 592. Notice how gdb/mi returns the same
tokens in its output.
211-data-evaluate-expression AChapter 27: The gdb/mi Interface

655

211^done,value="1"(gdb)
311-data-evaluate-expression &A
311^done,value="0xefffeb7c"(gdb)
411-data-evaluate-expression A+3
411^done,value="4"(gdb)
511-data-evaluate-expression "A + 3"
511^done,value="4"(gdb)

The -data-list-changed-registers Command
Synopsis-data-list-changed-registers

Display a list of the registers that have changed.

gdb Command
gdb doesn’t have a direct analog for this command; gdbtk has the corresponding command‘gdb_changed_register_list’.

ExampleOn a PPC MBX board:(gdb)-exec-continue^running(gdb)*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame={
func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",line="5",arch="powerpc"}(gdb)-data-list-changed-registers^done,changed-registers=["0","1","2","4","5","6","7","8","9","10","11","13","14","15","16","17","18","19","20","21","22","23","24","25","26","27","28","30","31","64","65","66","67","69"](gdb)

The -data-list-register-names Command
Synopsis-data-list-register-names [ ( regno )+ ]Show a list of register names for the current target. If no arguments are given, it shows alist of the names of all the registers. If integer numbers are given as arguments, it will print
a list of the names of the registers corresponding to the arguments. To ensure consistency
between a register name and its number, the output list may include empty register names.

gdb Command
gdb does not have a command which corresponds to ‘-data-list-register-names’. In
gdbtk there is a corresponding command ‘gdb_regnames’.

656

Debugging with gdb

ExampleFor the PPC MBX board:(gdb)-data-list-register-names^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7","r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18","r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29","r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9","f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20","f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31","", "pc","ps","cr","lr","ctr","xer"](gdb)-data-list-register-names 1 2 3^done,register-names=["r1","r2","r3"](gdb)

The -data-list-register-values Command
Synopsis-data-list-register-values[ --skip-unavailable ] fmt [ ( regno )*]Display the registers’ contents. The format according to which the registers’ contents areto be returned is given by fmt, followed by an optional list of numbers specifying the registers
to display. A missing list of numbers indicates that the contents of all the registers must be
returned. The --skip-unavailable option indicates that only the available registers areto be returned.
Allowed formats for fmt are:x

Hexadecimal

o

Octal

t

Binaryd

Decimalr

RawN

Naturalgdb Command
The corresponding gdb commands are ‘info reg’, ‘info all-reg’, and (in gdbtk)‘gdb_fetch_registers’.

ExampleFor a PPC MBX board (note: line breaks are for readability only, they don’t appear in theactual output):(gdb)-data-list-register-values r 64 65^done,register-values=[{number="64",value="0xfe00a300"},{number="65",value="0x00029002"}](gdb)-data-list-register-values xChapter 27: The gdb/mi Interface

657^done,register-values=[{number="0",value="0xfe0043c8"},{number="1",value="0x3fff88"},{number="2",value="0xfffffffe"},{number="3",value="0x0"},{number="4",value="0xa"},{number="5",value="0x3fff68"},{number="6",value="0x3fff58"},{number="7",value="0xfe011e98"},{number="8",value="0x2"},{number="9",value="0xfa202820"},{number="10",value="0xfa202808"},{number="11",value="0x1"},{number="12",value="0x0"},{number="13",value="0x4544"},{number="14",value="0xffdfffff"},{number="15",value="0xffffffff"},{number="16",value="0xfffffeff"},{number="17",value="0xefffffed"},{number="18",value="0xfffffffe"},{number="19",value="0xffffffff"},{number="20",value="0xffffffff"},{number="21",value="0xffffffff"},{number="22",value="0xfffffff7"},{number="23",value="0xffffffff"},{number="24",value="0xffffffff"},{number="25",value="0xffffffff"},{number="26",value="0xfffffffb"},{number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"},{number="29",value="0x0"},{number="30",value="0xfe010000"},{number="31",value="0x0"},{number="32",value="0x0"},{number="33",value="0x0"},{number="34",value="0x0"},{number="35",value="0x0"},{number="36",value="0x0"},{number="37",value="0x0"},{number="38",value="0x0"},{number="39",value="0x0"},{number="40",value="0x0"},{number="41",value="0x0"},{number="42",value="0x0"},{number="43",value="0x0"},{number="44",value="0x0"},{number="45",value="0x0"},{number="46",value="0x0"},{number="47",value="0x0"},{number="48",value="0x0"},{number="49",value="0x0"},{number="50",value="0x0"},{number="51",value="0x0"},{number="52",value="0x0"},{number="53",value="0x0"},{number="54",value="0x0"},{number="55",value="0x0"},{number="56",value="0x0"},{number="57",value="0x0"},{number="58",value="0x0"},{number="59",value="0x0"},{number="60",value="0x0"},{number="61",value="0x0"},{number="62",value="0x0"},{number="63",value="0x0"},{number="64",value="0xfe00a300"},{number="65",value="0x29002"},{number="66",value="0x202f04b5"},{number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"},{number="69",value="0x20002b03"}](gdb)

The -data-read-memory Command
This command is deprecated, use -data-read-memory-bytes instead.

Synopsis-data-read-memory [ -o byte-offset ]address word-format word-size
nr-rows nr-cols [ aschar ]where:‘address’An expression specifying the address of the first memory word to be read.
Complex expressions containing embedded white space should be quoted using
the C convention.

‘word-format’
The format to be used to print the memory words. The notation is the same
as for gdb’s print command (see Section 10.5 [Output Formats], page 150).

658

Debugging with gdb‘word-size’
The size of each memory word in bytes.
‘nr-rows’

The number of rows in the output table.

‘nr-cols’

The number of columns in the output table.

‘aschar’If present, indicates that each row should include an ascii dump. The valueof aschar is used as a padding character when a byte is not a member of theprintable ascii character set (printable ascii characters are those whose code
is between 32 and 126, inclusively).

‘byte-offset’
An offset to add to the address before fetching memory.
This command displays memory contents as a table of nr-rows by nr-cols words, eachword being word-size bytes. In total, nr-rows * nr-cols * word-size bytes are read (returned as ‘total-bytes’). Should less than the requested number of bytes be returned by
the target, the missing words are identified using ‘N/A’. The number of bytes read from thetarget is returned in ‘nr-bytes’ and the starting address used to read memory in ‘addr’.
The address of the next/previous row or page is available in ‘next-row’ and ‘prev-row’,‘next-page’ and ‘prev-page’.

gdb Command
The corresponding gdb command is ‘x’. gdbtk has ‘gdb_get_mem’ memory read command.

ExampleRead six bytes of memory starting at bytes+6 but then offset by -6 bytes. Format as threerows of two columns. One byte per word. Display each word in hex.
(gdb)
9-data-read-memory -o -6 -- bytes+6 x 1 3 2
9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
prev-page="0x0000138a",memory=[{addr="0x00001390",data=["0x00","0x01"]},{addr="0x00001392",data=["0x02","0x03"]},{addr="0x00001394",data=["0x04","0x05"]}](gdb)

Read two bytes of memory starting at address shorts + 64 and display as a single word
formatted in decimal.
(gdb)
5-data-read-memory shorts+64 d 2 1 1
5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
next-row="0x00001512",prev-row="0x0000150e",
next-page="0x00001512",prev-page="0x0000150e",memory=[{addr="0x00001510",data=["128"]}](gdb)

Read thirty two bytes of memory starting at bytes+16 and format as eight rows of fourcolumns. Include a string encoding with ‘x’ used as the non-printable character.
(gdb)
4-data-read-memory bytes+16 x 1 8 4 x
4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",Chapter 27: The gdb/mi Interface659

next-row="0x000013c0",prev-row="0x0000139c",
next-page="0x000013c0",prev-page="0x00001380",memory=[{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"},{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"},{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"},{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"},{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"},{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&’"},{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"},{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"}](gdb)

The -data-read-memory-bytes Command
Synopsis-data-read-memory-bytes [ -o offset ]address countwhere:‘address’An expression specifying the address of the first addressable memory unit to beread. Complex expressions containing embedded white space should be quoted
using the C convention.

‘count’

The number of addressable memory units to read. This should be an integer
literal.

‘offset’

The offset relative to address at which to start reading. This should be an
integer literal. This option is provided so that a frontend is not required to firstevaluate address and then perform address arithmetic itself.

This command attempts to read all accessible memory regions in the specified range.
First, all regions marked as unreadable in the memory map (if one is defined) will be skipped.
See Section 10.18 [Memory Region Attributes], page 183. Second, gdb will attempt to readthe remaining regions. For each one, if reading full region results in an errors, gdb will try
to read a subset of the region.
In general, every single memory unit in the region may be readable or not, and the only
way to read every readable unit is to try a read at every address, which is not practical.
Therefore, gdb will attempt to read all accessible memory units at either beginning or theend of the region, using a binary division scheme. This heuristic works well for reading
across a memory map boundary. Note that if a region has a readable range that is neither
at the beginning or the end, gdb will not read it.
The result record (see Section 27.7.1 [GDB/MI Result Records], page 597) that is outputof the command includes a field named ‘memory’ whose content is a list of tuples. Each tuple
represent a successfully read memory block and has the following fields:
begin

The start address of the memory block, as hexadecimal literal.

end

The end address of the memory block, as hexadecimal literal.

offsetThe offset of the memory block, as hexadecimal literal, relative to the start
address passed to -data-read-memory-bytes.

contents

The contents of the memory block, in hex.

660

Debugging with gdb

gdb Command
The corresponding gdb command is ‘x’.

Example(gdb)-data-read-memory-bytes &a 10^done,memory=[{begin="0xbffff154",offset="0x00000000",end="0xbffff15e",
contents="01000000020000000300"}](gdb)

The -data-write-memory-bytes Command
Synopsis-data-write-memory-bytes address contents-data-write-memory-bytes address contents [count]where:‘address’An expression specifying the address of the first addressable memory unit tobe written. Complex expressions containing embedded white space should bequoted using the C convention.

‘contents’
The hex-encoded data to write. It is an error if contents does not represent an
integral number of addressable memory units.
‘count’Optional argument indicating the number of addressable memory units to be
written. If count is greater than contents’ length, gdb will repeatedly write
contents until it fills count memory units.

gdb Command
There’s no corresponding gdb command.

Example(gdb)-data-write-memory-bytes &a "aabbccdd"
^done
(gdb)
(gdb)
-data-write-memory-bytes &a "aabbccdd" 16e
^done
(gdb)

27.19 gdb/mi Tracepoint Commands
The commands defined in this section implement MI support for tracepoints. For detailed
introduction, see Chapter 13 [Tracepoints], page 203.

The -trace-find CommandChapter 27: The gdb/mi Interface

661

Synopsis-trace-find mode [parameters...]Find a trace frame using criteria defined by mode and parameters. The following tablelists permissible modes and their parameters. For details of operation, see Section 13.2.1[tfind], page 215.
‘none’

No parameters are required. Stops examining trace frames.

‘frame-number’
An integer is required as parameter. Selects tracepoint frame with that index.
‘tracepoint-number’
An integer is required as parameter. Finds next trace frame that corresponds
to tracepoint with the specified number.
‘pc’

An address is required as parameter. Finds next trace frame that corresponds
to any tracepoint at the specified address.

‘pc-inside-range’
Two addresses are required as parameters. Finds next trace frame that corresponds to a tracepoint at an address inside the specified range. Both bounds
are considered to be inside the range.
‘pc-outside-range’
Two addresses are required as parameters. Finds next trace frame that corresponds to a tracepoint at an address outside the specified range. Both bounds
are considered to be inside the range.
‘line’

Location specification is required as parameter. See Section 9.2 [Location Specifications], page 126. Finds next trace frame that corresponds to a tracepointat the specified location.

If ‘none’ was passed as mode, the response does not have fields. Otherwise, the response
may have the following fields:‘found’This field has either ‘0’ or ‘1’ as the value, depending on whether a matching
tracepoint was found.

‘traceframe’
The index of the found traceframe. This field is present iff the ‘found’ field has
value of ‘1’.
‘tracepoint’
The index of the found tracepoint. This field is present iff the ‘found’ field has
value of ‘1’.
‘frame’The information about the frame corresponding to the found trace frame. This
field is present only if a trace frame was found. See Section 27.7.5 [GDB/MI
Frame Information], page 604, for description of this field.

gdb Command
The corresponding gdb command is ‘tfind’.

The -trace-define-variable Command

662

Debugging with gdb

Synopsis-trace-define-variable name [ value ]Create trace variable name if it does not exist. If value is specified, sets the initial valueof the specified trace variable to that value. Note that the name should start with the ‘$’character.

gdb Command
The corresponding gdb command is ‘tvariable’.

The -trace-frame-collected Command
Synopsis-trace-frame-collected[--var-print-values var_pval][--comp-print-values comp_pval][--registers-format regformat][--memory-contents]

This command returns the set of collected objects, register names, trace state variablenames, memory ranges and computed expressions that have been collected at a particular
trace frame. The optional parameters to the command affect the output format in different
ways. See the output description table below for more details.
The reported names can be used in the normal manner to create varobjs and inspect theobjects themselves. The items returned by this command are categorized so that it is clear
which is a variable, which is a register, which is a trace state variable, which is a memory
range and which is a computed expression.
For instance, if the actions werecollect myVar, myArray[myIndex], myObj.field, myPtr->field, myCount + 2
collect *(int*)0xaf02bef0@40

the object collected in its entirety would be myVar. The object myArray would be partiallycollected, because only the element at index myIndex would be collected. The remaining
objects would be computed expressions.
An example output would be:(gdb)-trace-frame-collected^done,
explicit-variables=[{name="myVar",value="1"}],computed-expressions=[{name="myArray[myIndex]",value="0"},{name="myObj.field",value="0"},{name="myPtr->field",value="1"},{name="myCount + 2",value="3"},{name="$tvar1 + 1",value="43970027"}],
registers=[{number="0",value="0x7fe2c6e79ec8"},{number="1",value="0x0"},{number="2",value="0x4"},...
{number="125",value="0x0"}],tvars=[{name="$tvar1",current="43970026"}],
memory=[{address="0x0000000000602264",length="4"},{address="0x0000000000615bc0",length="4"}](gdb)

Chapter 27: The gdb/mi Interface

663

Where:
explicit-variables
The set of objects that have been collected in their entirety (as opposed tocollecting just a few elements of an array or a few struct members). For eachobject, its name and value are printed. The --var-print-values option affects
how or whether the value field is output. If var pval is 0, then print only thenames; if it is 1, print also their values; and if it is 2, print the name, type andvalue for simple data types, and the name and type for arrays, structures andunions.
computed-expressions
The set of computed expressions that have been collected at the current trace
frame. The --comp-print-values option affects this set like the --var-printvalues option affects the explicit-variables set. See above.
registers
The registers that have been collected at the current trace frame. For each register collected, the name and current value are returned. The value is formatted
according to the --registers-format option. See the -data-list-registervalues command for a list of the allowed formats. The default is ‘x’.
tvars

The trace state variables that have been collected at the current trace frame.
For each trace state variable collected, the name and current value are returned.

memoryThe set of memory ranges that have been collected at the current trace frame.
Its content is a list of tuples. Each tuple represents a collected memory range
and has the following fields:
address

The start address of the memory range, as hexadecimal literal.

lengthThe length of the memory range, as decimal literal.

contents

The contents of the memory block, in hex. This field is only present
if the --memory-contents option is specified.

gdb Command
There is no corresponding gdb command.

ExampleThe -trace-list-variables Command
Synopsis-trace-list-variables

Return a table of all defined trace variables. Each element of the table has the following
fields:‘name’The name of the trace variable. This field is always present.

‘initial’

The initial value. This is a 64-bit signed integer. This field is always present.

664

Debugging with gdb‘current’

The value the trace variable has at the moment. This is a 64-bit signed integer.
This field is absent iff current value is not defined, for example if the trace wasnever run, or is presently running.

gdb Command
The corresponding gdb command is ‘tvariables’.

Example(gdb)-trace-list-variables^done,trace-variables={nr_rows="1",nr_cols="3",
hdr=[{width="15",alignment="-1",col_name="name",colhdr="Name"},{width="11",alignment="-1",col_name="initial",colhdr="Initial"},{width="11",alignment="-1",col_name="current",colhdr="Current"}],body=[variable={name="$trace_timestamp",initial="0"}variable={name="$foo",initial="10",current="15"}]}(gdb)

The -trace-save Command
Synopsis-trace-save [ -r ] [ -ctf ] filename

Saves the collected trace data to filename. Without the ‘-r’ option, the data is downloaded from the target and saved in a local file. With the ‘-r’ option the target is asked toperform the save.
By default, this command will save the trace in the tfile format. You can supply the
optional ‘-ctf’ argument to save it the CTF format. See Section 13.4 [Trace Files], page 219,
for more information about CTF.

gdb Command
The corresponding gdb command is ‘tsave’.

The -trace-start Command
Synopsis-trace-start

Starts a tracing experiment. The result of this command does not have any fields.

gdb Command
The corresponding gdb command is ‘tstart’.

The -trace-status Command
Synopsis-trace-status

Obtains the status of a tracing experiment. The result may include the following fields:

Chapter 27: The gdb/mi Interface

665‘supported’
May have a value of either ‘0’, when no tracing operations are supported, ‘1’,
when all tracing operations are supported, or ‘file’ when examining trace
file. In the latter case, examining of trace frame is possible but new tracing
experiment cannot be started. This field is always present.
‘running’

May have a value of either ‘0’ or ‘1’ depending on whether tracing experimentis in progress on target. This field is present if ‘supported’ field is not ‘0’.

‘stop-reason’
Report the reason why the tracing was stopped last time. This field may beabsent iff tracing was never stopped on target yet. The value of ‘request’ means
the tracing was stopped as result of the -trace-stop command. The value of‘overflow’ means the tracing buffer is full. The value of ‘disconnection’means tracing was automatically stopped when gdb has disconnected. The
value of ‘passcount’ means tracing was stopped when a tracepoint was passed amaximal number of times for that tracepoint. This field is present if ‘supported’
field is not ‘0’.
‘stopping-tracepoint’
The number of tracepoint whose passcount as exceeded. This field is present
iff the ‘stop-reason’ field has the value of ‘passcount’.
‘frames’‘frames-created’
The ‘frames’ field is a count of the total number of trace frames in the trace
buffer, while ‘frames-created’ is the total created during the run, includingones that were discarded, such as when a circular trace buffer filled up. Bothfields are optional.
‘buffer-size’‘buffer-free’
These fields tell the current size of the tracing buffer and the remaining space.
These fields are optional.
‘circular’
The value of the circular trace buffer flag. 1 means that the trace buffer iscircular and old trace frames will be discarded if necessary to make room, 0means that the trace buffer is linear and may fill up.
‘disconnected’
The value of the disconnected tracing flag. 1 means that tracing will continue
after gdb disconnects, 0 means that the trace run will stop.
‘trace-file’
The filename of the trace file being examined. This field is optional, and only
present when examining a trace file.

gdb Command
The corresponding gdb command is ‘tstatus’.

The -trace-stop Command

666

Debugging with gdb

Synopsis-trace-stop

Stops a tracing experiment. The result of this command has the same fields as -tracestatus, except that the ‘supported’ and ‘running’ fields are not output.

gdb Command
The corresponding gdb command is ‘tstop’.

27.20 gdb/mi Symbol Query Commands
The -symbol-info-functions Command
Synopsis-symbol-info-functions [--include-nondebug][--type type_regexp][--name name_regexp][--max-results limit]

Return a list containing the names and types for all global functions taken from the debug
information. The functions are grouped by source file, and shown with the line number onwhich each function is defined.

The --include-nondebug option causes the output to include code symbols from thesymbol table.

The options --type and --name allow the symbols returned to be filtered based on either
the name of the function, or the type signature of the function.

The option --max-results restricts the command to return no more than limit results.
If exactly limit results are returned then there might be additional results available if ahigher limit is used.

gdb Command
The corresponding gdb command is ‘info functions’.

Chapter 27: The gdb/mi Interface

Example(gdb)-symbol-info-functions^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="36", name="f4", type="void (int *)",
description="void f4(int *);"},{line="42", name="main", type="int ()",
description="int main();"},{line="30", name="f1", type="my_int_t (int, int)",
description="static my_int_t f1(int, int);"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="33", name="f2", type="float (another_float_t)",
description="float f2(another_float_t);"},{line="39", name="f3", type="int (another_int_t)",
description="int f3(another_int_t);"},{line="27", name="f1", type="another_float_t (int)",
description="static another_float_t f1(int);"}]}]}(gdb)-symbol-info-functions --name f1^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="30", name="f1", type="my_int_t (int, int)",
description="static my_int_t f1(int, int);"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="27", name="f1", type="another_float_t (int)",
description="static another_float_t f1(int);"}]}]}(gdb)-symbol-info-functions --type void
^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="36", name="f4", type="void (int *)",
description="void f4(int *);"}]}]}

667

668

Debugging with gdb(gdb)-symbol-info-functions --include-nondebug^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="36", name="f4", type="void (int *)",
description="void f4(int *);"},{line="42", name="main", type="int ()",
description="int main();"},{line="30", name="f1", type="my_int_t (int, int)",
description="static my_int_t f1(int, int);"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="33", name="f2", type="float (another_float_t)",
description="float f2(another_float_t);"},{line="39", name="f3", type="int (another_int_t)",
description="int f3(another_int_t);"},{line="27", name="f1", type="another_float_t (int)",
description="static another_float_t f1(int);"}]}],
nondebug=[{address="0x0000000000400398",name="_init"},{address="0x00000000004003b0",name="_start"},...
]}

The -symbol-info-module-functions Command
Synopsis-symbol-info-module-functions [--module module_regexp][--name name_regexp][--type type_regexp]

Return a list containing the names of all known functions within all know Fortran modules.
The functions are grouped by source file and containing module, and shown with the line
number on which each function is defined.

The option --module only returns results for modules matching module regexp. The
option --name only returns functions whose name matches name regexp, and --type only
returns functions whose type matches type regexp.

gdb Command
The corresponding gdb command is ‘info module functions’.

Chapter 27: The gdb/mi Interface

669

Example(gdb)-symbol-info-module-functions^done,symbols=[{module="mod1",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="21",name="mod1::check_all",type="void (void)",
description="void mod1::check_all(void);"}]}]},{module="mod2",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="30",name="mod2::check_var_i",type="void (void)",
description="void mod2::check_var_i(void);"}]}]},{module="mod3",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="21",name="mod3::check_all",type="void (void)",
description="void mod3::check_all(void);"},{line="27",name="mod3::check_mod2",type="void (void)",
description="void mod3::check_mod2(void);"}]}]},{module="modmany",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="35",name="modmany::check_some",type="void (void)",
description="void modmany::check_some(void);"}]}]},{module="moduse",files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="44",name="moduse::check_all",type="void (void)",
description="void moduse::check_all(void);"},{line="49",name="moduse::check_var_x",type="void (void)",
description="void moduse::check_var_x(void);"}]}]}]The -symbol-info-module-variables Command
Synopsis-symbol-info-module-variables [--module module_regexp][--name name_regexp][--type type_regexp]

Return a list containing the names of all known variables within all know Fortran modules.
The variables are grouped by source file and containing module, and shown with the line
number on which each variable is defined.
The option --module only returns results for modules matching module regexp. The
option --name only returns variables whose name matches name regexp, and --type only
returns variables whose type matches type regexp.

gdb Command
The corresponding gdb command is ‘info module variables’.

670

Debugging with gdb

Example(gdb)-symbol-info-module-variables^done,symbols=[{module="mod1",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="18",name="mod1::var_const",type="integer(kind=4)",
description="integer(kind=4) mod1::var_const;"},{line="17",name="mod1::var_i",type="integer(kind=4)",
description="integer(kind=4) mod1::var_i;"}]}]},{module="mod2",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="28",name="mod2::var_i",type="integer(kind=4)",
description="integer(kind=4) mod2::var_i;"}]}]},{module="mod3",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="18",name="mod3::mod1",type="integer(kind=4)",
description="integer(kind=4) mod3::mod1;"},{line="17",name="mod3::mod2",type="integer(kind=4)",
description="integer(kind=4) mod3::mod2;"},{line="19",name="mod3::var_i",type="integer(kind=4)",
description="integer(kind=4) mod3::var_i;"}]}]},{module="modmany",
files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="33",name="modmany::var_a",type="integer(kind=4)",
description="integer(kind=4) modmany::var_a;"},{line="33",name="modmany::var_b",type="integer(kind=4)",
description="integer(kind=4) modmany::var_b;"},{line="33",name="modmany::var_c",type="integer(kind=4)",
description="integer(kind=4) modmany::var_c;"},{line="33",name="modmany::var_i",type="integer(kind=4)",
description="integer(kind=4) modmany::var_i;"}]}]},{module="moduse",files=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="42",name="moduse::var_x",type="integer(kind=4)",
description="integer(kind=4) moduse::var_x;"},{line="42",name="moduse::var_y",type="integer(kind=4)",
description="integer(kind=4) moduse::var_y;"}]}]}]The -symbol-info-modules Command
Synopsis-symbol-info-modules [--name name_regexp][--max-results limit]

Return a list containing the names of all known Fortran modules. The modules are groupedby source file, and shown with the line number on which each modules is defined.
The option --name allows the modules returned to be filtered based the name of themodule.

Chapter 27: The gdb/mi Interface

671

The option --max-results restricts the command to return no more than limit results.
If exactly limit results are returned then there might be additional results available if ahigher limit is used.

gdb Command
The corresponding gdb command is ‘info modules’.

Example(gdb)-symbol-info-modules^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="16",name="mod1"},{line="22",name="mod2"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="16",name="mod3"},{line="22",name="modmany"},{line="26",name="moduse"}]}]}(gdb)-symbol-info-modules --name mod[123]^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules-2.f90",
symbols=[{line="16",name="mod1"},{line="22",name="mod2"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
fullname="/project/gdb/testsuite/gdb.mi/mi-fortran-modules.f90",
symbols=[{line="16",name="mod3"}]}]}The -symbol-info-types Command
Synopsis-symbol-info-types [--name name_regexp][--max-results limit]

Return a list of all defined types. The types are grouped by source file, and shown with theline number on which each user defined type is defined. Some base types are not defined in
the source code but are added to the debug information by the compiler, for example int,
float, etc.; these types do not have an associated line number.
The option --name allows the list of types returned to be filtered by name.
The option --max-results restricts the command to return no more than limit results.
If exactly limit results are returned then there might be additional results available if ahigher limit is used.

gdb Command
The corresponding gdb command is ‘info types’.

672

Debugging with gdb

Example(gdb)-symbol-info-types^done,symbols={debug=[{filename="gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{name="float"},{name="int"},{line="27",name="typedef int my_int_t;"}]},{filename="gdb.mi/mi-sym-info-2.c",fullname="/project/gdb.mi/mi-sym-info-2.c",symbols=[{line="24",name="typedef float another_float_t;"},{line="23",name="typedef int another_int_t;"},{name="float"},{name="int"}]}]}(gdb)-symbol-info-types --name _int_^done,symbols={debug=[{filename="gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="27",name="typedef int my_int_t;"}]},{filename="gdb.mi/mi-sym-info-2.c",fullname="/project/gdb.mi/mi-sym-info-2.c",symbols=[{line="23",name="typedef int another_int_t;"}]}]}The -symbol-info-variables Command
Synopsis-symbol-info-variables [--include-nondebug][--type type_regexp][--name name_regexp][--max-results limit]

Return a list containing the names and types for all global variables taken from the debug
information. The variables are grouped by source file, and shown with the line number onwhich each variable is defined.
The --include-nondebug option causes the output to include data symbols from thesymbol table.
The options --type and --name allow the symbols returned to be filtered based on either
the name of the variable, or the type of the variable.
The option --max-results restricts the command to return no more than limit results.
If exactly limit results are returned then there might be additional results available if ahigher limit is used.

gdb Command
The corresponding gdb command is ‘info variables’.

Chapter 27: The gdb/mi Interface

Example(gdb)-symbol-info-variables^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"},{line="24",name="global_i1",type="int",
description="static int global_i1;"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="21",name="global_f2",type="int",
description="int global_f2;"},{line="20",name="global_i2",type="int",
description="int global_i2;"},{line="19",name="global_f1",type="float",
description="static float global_f1;"},{line="18",name="global_i1",type="int",
description="static int global_i1;"}]}]}(gdb)-symbol-info-variables --name f1^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="19",name="global_f1",type="float",
description="static float global_f1;"}]}]}(gdb)-symbol-info-variables --type float^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="19",name="global_f1",type="float",
description="static float global_f1;"}]}]}

673

674

Debugging with gdb(gdb)-symbol-info-variables --include-nondebug^done,symbols={debug=[{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-1.c",symbols=[{line="25",name="global_f1",type="float",
description="static float global_f1;"},{line="24",name="global_i1",type="int",
description="static int global_i1;"}]},{filename="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",fullname="/project/gdb/testsuite/gdb.mi/mi-sym-info-2.c",symbols=[{line="21",name="global_f2",type="int",
description="int global_f2;"},{line="20",name="global_i2",type="int",
description="int global_i2;"},{line="19",name="global_f1",type="float",
description="static float global_f1;"},{line="18",name="global_i1",type="int",
description="static int global_i1;"}]}],
nondebug=[{address="0x00000000004005d0",name="_IO_stdin_used"},{address="0x00000000004005d8",name="__dso_handle"}...
]}

The -symbol-list-lines Command
Synopsis-symbol-list-lines filename

Print the list of lines that contain code and their associated program addresses for the
given source filename. The entries are sorted in ascending PC order.

gdb Command
There is no corresponding gdb command.

Example(gdb)-symbol-list-lines basics.c^done,lines=[{pc="0x08048554",line="7"},{pc="0x0804855a",line="8"}](gdb)

27.21 gdb/mi File Commands
This section describes the GDB/MI commands to specify executable file names and to readin and obtain symbol table information.

The -file-exec-and-symbols Command
Synopsis-file-exec-and-symbols fileSpecify the executable file to be debugged. This file is the one from which the symbol
table is also read. If no file is specified, the command clears the executable and symbolChapter 27: The gdb/mi Interface

675

information. If breakpoints are set when using this command with no arguments, gdb willproduce error messages. Otherwise, no output is produced, except a completion notification.

gdb Command
The corresponding gdb command is ‘file’.

Example(gdb)-file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)

The -file-exec-file Command
Synopsis-file-exec-file fileSpecify the executable file to be debugged. Unlike ‘-file-exec-and-symbols’, thesymbol table is not read from this file. If used without argument, gdb clears the information
about the executable file. No output is produced, except a completion notification.

gdb Command
The corresponding gdb command is ‘exec-file’.

Example(gdb)-file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)

The -file-list-exec-source-file Command
Synopsis-file-list-exec-source-file

List the line number, the current source file, and the absolute path to the current source
file for the current executable. The macro information field has a value of ‘1’ or ‘0’ dependingon whether or not the file includes preprocessor macro information.

gdb Command
The gdb equivalent is ‘info source’

Example(gdb)
123-file-list-exec-source-file123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"(gdb)

The -file-list-exec-source-files Command

676

Debugging with gdb

Synopsis-file-list-exec-source-files [ --group-by-objfile ][ --dirname | --basename ][ -- ][ regexp ]This command returns information about the source files gdb knows about, it will output
both the filename and fullname (absolute file name) of a source file, though the fullname
can be elided if this information is not known to gdb.
With no arguments this command returns a list of source files. Each source file isrepresented by a tuple with the fields; file, fullname, and debug-fully-read. The file is thedisplay name for the file, while fullname is the absolute name of the file. The fullname
field can be elided if the absolute name of the source file can’t be computed. The field
debug-fully-read will be a string, either true or false. When true, this indicates the fulldebug information for the compilation unit describing this file has been read in. Whenfalse, the full debug information has not yet been read in. While reading in the full debug
information it is possible that gdb could become aware of additional source files.
The optional regexp can be used to filter the list of source files returned. The regexp
will be matched against the full source file name. The matching is case-sensitive, except
on operating systems that have case-insensitive filesystem (e.g., MS-Windows). ‘--’ can beused before regexp to prevent gdb interpreting regexp as a command option (e.g. if regexp
starts with ‘-’).
If --dirname is provided, then regexp is matched only against the directory name ofeach source file. If --basename is provided, then regexp is matched against the basenameof each source file. Only one of --dirname or --basename may be given, and if either isgiven then regexp is required.
If --group-by-objfile is used then the format of the results is changed. The results
will now be a list of tuples, with each tuple representing an object file (executable or sharedlibrary) loaded into gdb. The fields of these tuples are; filename, debug-info, and sources.
The filename is the absolute name of the object file, debug-info is a string with one of thefollowing values:noneThis object file has no debug information.

partially-readThis object file has debug information, but it is not fully read in yet. When it
is read in later, GDB might become aware of additional source files.
fully-readThis object file has debug information, and this information is fully read into
GDB. The list of source files is complete.
The sources is a list or tuples, with each tuple describing a single source file with thesame fields as described previously. The sources list can be empty for object files that haveno debug information.

gdb Command
The gdb equivalent is ‘info sources’. gdbtk has an analogous command ‘gdb_listfiles’.

Chapter 27: The gdb/mi Interface

Example(gdb)-file-list-exec-source-files^done,files=[{file="foo.c",fullname="/home/foo.c",debug-fully-read="true"},{file="/home/bar.c",fullname="/home/bar.c",debug-fully-read="true"},{file="gdb_could_not_find_fullpath.c",debug-fully-read="true"}](gdb)-file-list-exec-source-files^done,files=[{file="test.c",fullname="/tmp/info-sources/test.c",debug-fully-read="true"},{file="/usr/include/stdc-predef.h",fullname="/usr/include/stdc-predef.h",debug-fully-read="true"},{file="header.h",fullname="/tmp/info-sources/header.h",debug-fully-read="true"},{file="helper.c",fullname="/tmp/info-sources/helper.c",debug-fully-read="true"}](gdb)-file-list-exec-source-files -- \\.c^done,files=[{file="test.c",fullname="/tmp/info-sources/test.c",debug-fully-read="true"},{file="helper.c",fullname="/tmp/info-sources/helper.c",debug-fully-read="true"}](gdb)-file-list-exec-source-files --group-by-objfile^done,files=[{filename="/tmp/info-sources/test.x",
debug-info="fully-read",sources=[{file="test.c",fullname="/tmp/info-sources/test.c",debug-fully-read="true"},{file="/usr/include/stdc-predef.h",fullname="/usr/include/stdc-predef.h",debug-fully-read="true"},{file="header.h",fullname="/tmp/info-sources/header.h",debug-fully-read="true"}]},{filename="/lib64/ld-linux-x86-64.so.2",
debug-info="none",sources=[]},{filename="system-supplied DSO at 0x7ffff7fcf000",
debug-info="none",sources=[]},{filename="/tmp/info-sources/libhelper.so",
debug-info="fully-read",sources=[{file="helper.c",fullname="/tmp/info-sources/helper.c",debug-fully-read="true"},{file="/usr/include/stdc-predef.h",fullname="/usr/include/stdc-predef.h",debug-fully-read="true"},{file="header.h",fullname="/tmp/info-sources/header.h",debug-fully-read="true"}]},

677

678

Debugging with gdb{filename="/lib64/libc.so.6",
debug-info="none",sources=[]}]The -file-list-shared-libraries Command
Synopsis-file-list-shared-libraries [ regexp ]List the shared libraries in the program. With a regular expression regexp, only thoselibraries whose names match regexp are listed.

gdb Command
The corresponding gdb command is ‘info shared’. The fields have a similar meaning to the=library-loaded notification. The ranges field specifies the multiple segments belonging
to this library. Each range has the following fields:‘from’

The address defining the inclusive lower bound of the segment.

‘to’

The address defining the exclusive upper bound of the segment.

Example(gdb)-file-list-exec-source-files^done,shared-libraries=[{id="/lib/libfoo.so",target-name="/lib/libfoo.so",host-name="/lib/libfoo.so",symbols-loaded="1",threadgroup="i1",ranges=[{from="0x72815989",to="0x728162c0"}]},{id="/lib/libbar.so",target-name="/lib/libbar.so",host-name="/lib/libbar.so",symbols-loaded="1",threadgroup="i1",ranges=[{from="0x76ee48c0",to="0x76ee9160"}]}](gdb)

The -file-symbol-file Command
Synopsis-file-symbol-file file

Read symbol table info from the specified file argument. When used without arguments,
clears gdb’s symbol table info. No output is produced, except for a completion notification.

gdb Command
The corresponding gdb command is ‘symbol-file’.

Example(gdb)-file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
^done
(gdb)

27.22 gdb/mi Target Manipulation Commands
The -target-attach CommandChapter 27: The gdb/mi Interface

679

Synopsis-target-attach pid | gid | file

Attach to a process pid or a file file outside of gdb, or a thread group gid. If attaching toa thread group, the id previously returned by ‘-list-thread-groups --available’ must
be used.

gdb Command
The corresponding gdb command is ‘attach’.

Example(gdb)-target-attach 34=thread-created,id="1"*stopped,thread-id="1",frame={addr="0xb7f7e410",func="bar",args=[]}
^done
(gdb)

The -target-detach Command
Synopsis-target-detach [ pid | gid ]Detach from the remote target which normally resumes its execution. If either pid or gid
is specified, detaches from either the specified process, or specified thread group. There’s
no output.

gdb Command
The corresponding gdb command is ‘detach’.

Example(gdb)-target-detach
^done
(gdb)

The -target-disconnect Command
Synopsis-target-disconnect

Disconnect from the remote target. There’s no output and the target is generally notresumed.

gdb Command
The corresponding gdb command is ‘disconnect’.

Example(gdb)-target-disconnect
^done
(gdb)

680

Debugging with gdb

The -target-download Command
Synopsis-target-download

Loads the executable onto the remote target. It prints out an update message every halfsecond, which includes the fields:‘section’

The name of the section.

‘section-sent’
The size of what has been sent so far for that section.
‘section-size’
The size of the section.
‘total-sent’
The total size of what was sent so far (the current and the previous sections).
‘total-size’
The size of the overall executable to download.
Each message is sent as status record (see Section 27.4.2 [gdb/mi Output Syntax], page 593).
In addition, it prints the name and size of the sections, as they are downloaded. Thesemessages include the following fields:‘section’

The name of the section.

‘section-size’
The size of the section.
‘total-size’
The size of the overall executable to download.
At the end, a summary is printed.

gdb Command
The corresponding gdb command is ‘load’.

ExampleNote: each status message appears on a single line. Here the messages have been broken
down so that they can fit onto a page.
(gdb)-target-download+download,{section=".text",section-size="6668",total-size="9880"}+download,{section=".text",section-sent="512",section-size="6668",
total-sent="512",total-size="9880"}+download,{section=".text",section-sent="1024",section-size="6668",
total-sent="1024",total-size="9880"}+download,{section=".text",section-sent="1536",section-size="6668",
total-sent="1536",total-size="9880"}+download,{section=".text",section-sent="2048",section-size="6668",
total-sent="2048",total-size="9880"}+download,{section=".text",section-sent="2560",section-size="6668",
total-sent="2560",total-size="9880"}

Chapter 27: The gdb/mi Interface

681+download,{section=".text",section-sent="3072",section-size="6668",
total-sent="3072",total-size="9880"}+download,{section=".text",section-sent="3584",section-size="6668",
total-sent="3584",total-size="9880"}+download,{section=".text",section-sent="4096",section-size="6668",
total-sent="4096",total-size="9880"}+download,{section=".text",section-sent="4608",section-size="6668",
total-sent="4608",total-size="9880"}+download,{section=".text",section-sent="5120",section-size="6668",
total-sent="5120",total-size="9880"}+download,{section=".text",section-sent="5632",section-size="6668",
total-sent="5632",total-size="9880"}+download,{section=".text",section-sent="6144",section-size="6668",
total-sent="6144",total-size="9880"}+download,{section=".text",section-sent="6656",section-size="6668",
total-sent="6656",total-size="9880"}+download,{section=".init",section-size="28",total-size="9880"}+download,{section=".fini",section-size="28",total-size="9880"}+download,{section=".data",section-size="3156",total-size="9880"}+download,{section=".data",section-sent="512",section-size="3156",
total-sent="7236",total-size="9880"}+download,{section=".data",section-sent="1024",section-size="3156",
total-sent="7748",total-size="9880"}+download,{section=".data",section-sent="1536",section-size="3156",
total-sent="8260",total-size="9880"}+download,{section=".data",section-sent="2048",section-size="3156",
total-sent="8772",total-size="9880"}+download,{section=".data",section-sent="2560",section-size="3156",
total-sent="9284",total-size="9880"}+download,{section=".data",section-sent="3072",section-size="3156",
total-sent="9796",total-size="9880"}^done,address="0x10004",load-size="9880",transfer-rate="6586",
write-rate="429"(gdb)

gdb CommandNo equivalent.

ExampleN.A.

The -target-flash-erase Command
Synopsis-target-flash-erase

Erases all known flash memory regions on the target.
The corresponding gdb command is ‘flash-erase’.
The output is a list of flash regions that have been erased, with starting addresses andmemory region sizes.
(gdb)-target-flash-erase^done,erased-regions={address="0x0",size="0x40000"}
(gdb)

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The -target-select Command
Synopsis-target-select type parameters ...

Connect gdb to the remote target. This command takes two args:‘type’The type of target, for instance ‘remote’, etc.

‘parameters’
Device names, host names and the like. See Section 19.2 [Commands for Managing Targets], page 311, for more details.
The output is a connection notification, followed by the address at which the target
program is, in the following form:^connected,addr="address",func="function name",
args=[arg list]

gdb Command
The corresponding gdb command is ‘target’.

Example(gdb)-target-select remote /dev/ttya^connected,addr="0xfe00a300",func="??",args=[](gdb)

27.23 gdb/mi File Transfer Commands
The -target-file-put Command
Synopsis-target-file-put hostfile targetfile

Copy file hostfile from the host system (the machine running gdb) to targetfile on thetarget system.

gdb Command
The corresponding gdb command is ‘remote put’.

Example(gdb)-target-file-put localfile remotefile
^done
(gdb)

The -target-file-get Command
Synopsis-target-file-get targetfile hostfile

Copy file targetfile from the target system to hostfile on the host system.

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683

gdb Command
The corresponding gdb command is ‘remote get’.

Example(gdb)-target-file-get remotefile localfile
^done
(gdb)

The -target-file-delete Command
Synopsis-target-file-delete targetfile

Delete targetfile from the target system.

gdb Command
The corresponding gdb command is ‘remote delete’.

Example(gdb)-target-file-delete remotefile
^done
(gdb)

27.24 Ada Exceptions gdb/mi Commands
The -info-ada-exceptions Command
Synopsis-info-ada-exceptions [ regexp]

List all Ada exceptions defined within the program being debugged. With a regularexpression regexp, only those exceptions whose names match regexp are listed.

gdb Command
The corresponding gdb command is ‘info exceptions’.

Result
The result is a table of Ada exceptions. The following columns are defined for each exception:‘name’The name of the exception.

‘address’

The address of the exception.

Example-info-ada-exceptions aint
^done,ada-exceptions={nr_rows="2",nr_cols="2",
hdr=[{width="1",alignment="-1",col_name="name",colhdr="Name"},{width="1",alignment="-1",col_name="address",colhdr="Address"}],684

Debugging with gdb

body=[{name="constraint_error",address="0x0000000000613da0"},{name="const.aint_global_e",address="0x0000000000613b00"}]}Catching Ada Exceptions
The commands describing how to ask gdb to stop when a program raises an exception are
described at Section 27.11.2 [Ada Exception GDB/MI Catchpoint Commands], page 618.

27.25 gdb/mi Support Commands
Since new commands and features get regularly added to gdb/mi, some commands are available to help front-ends query the debugger about support for these capabilities. Similarly,
it is also possible to query gdb about target support of certain features.

The -info-gdb-mi-command Command
Synopsis-info-gdb-mi-command cmd_name

Query support for the gdb/mi command named cmd name.
Note that the dash (-) starting all gdb/mi commands is technically not part of thecommand name (see Section 27.4.1 [GDB/MI Input Syntax], page 593), and thus should beomitted in cmd name. However, for ease of use, this command also accepts the form withthe leading dash.

gdb Command
There is no corresponding gdb command.

Result
The result is a tuple. There is currently only one field:‘exists’This field is equal to "true" if the gdb/mi command exists, "false" otherwise.

ExampleHere is an example where the gdb/mi command does not exist:-info-gdb-mi-command unsupported-command^done,command={exists="false"}

And here is an example where the gdb/mi command is known to the debugger:-info-gdb-mi-command symbol-list-lines^done,command={exists="true"}

The -list-features Command
Returns a list of particular features of the MI protocol that this version of gdb implements.
A feature can be a command, or a new field in an output of some command, or even an
important bugfix. While a frontend can sometimes detect presence of a feature at runtime,
it is easier to perform detection at debugger startup.
The command returns a list of strings, with each string naming an available feature.
Each returned string is just a name, it does not have any internal structure. The list of
possible feature names is given below.

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Example output:(gdb) -list-features^done,result=["feature1","feature2"]

The current list of features is:‘frozen-varobjs’
Indicates support for the -var-set-frozen command, as well as possible presence of the frozen field in the output of -varobj-create.
‘pending-breakpoints’
Indicates support for the -f option to the -break-insert command.
‘python’

Indicates Python scripting support, Python-based pretty-printing commands,
and possible presence of the ‘display_hint’ field in the output of -var-listchildren‘thread-info’
Indicates support for the -thread-info command.
‘data-read-memory-bytes’
Indicates support for the -data-read-memory-bytes and the -data-writememory-bytes commands.
‘breakpoint-notifications’
Indicates that changes to breakpoints and breakpoints created via the CLI will
be announced via async records.
‘ada-task-info’
Indicates support for the -ada-task-info command.
‘language-option’
Indicates that all gdb/mi commands accept the --language option (seeSection 27.3.1 [Context management], page 590).
‘info-gdb-mi-command’
Indicates support for the -info-gdb-mi-command command.
‘undefined-command-error-code’
Indicates support for the "undefined-command" error code in error result
records, produced when trying to execute an undefined gdb/mi command (seeSection 27.7.1 [GDB/MI Result Records], page 597).
‘exec-run-start-option’
Indicates that the -exec-run command supports the --start option (seeSection 27.15 [GDB/MI Program Execution], page 627).
‘data-disassemble-a-option’
Indicates that the -data-disassemble command supports the -a option (seeSection 27.18 [GDB/MI Data Manipulation], page 651).
‘simple-values-ref-types’
Indicates that the --simple-values argument to the -stack-listarguments,-stack-list-locals,-stack-list-variables,and-var-list-children commands takes reference types into account: that is, avalue is considered simple if it is neither an array, structure, or union, nor areference to an array, structure, or union.

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Debugging with gdb

The -list-target-features Command
Returns a list of particular features that are supported by the target. Those features affectthe permitted MI commands, but unlike the features reported by the -list-featurescommand, the features depend on which target GDB is using at the moment. Whenever atarget can change, due to commands such as -target-select, -target-attach or -execrun, the list of target features may change, and the frontend should obtain it again. Example
output:(gdb) -list-target-features^done,result=["async"]

The current list of features is:‘async’Indicates that the target is capable of asynchronous command execution, whichmeans that gdb will accept further commands while the target is running.

‘reverse’

Indicates that the target is capable of reverse execution. See Chapter 6 [Reverse
Execution], page 101, for more information.

27.26 Miscellaneous gdb/mi Commands
The -gdb-exit Command
Synopsis-gdb-exit

Exit gdb immediately.

gdb Command
Approximately corresponds to ‘quit’.

Example(gdb)-gdb-exit^exit

The -gdb-set Command
Synopsis-gdb-set

Set an internal gdb variable.

gdb Command
The corresponding gdb command is ‘set’.

Example(gdb)-gdb-set $foo=3
^done
(gdb)

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687

The -gdb-show Command
Synopsis-gdb-show

Show the current value of a gdb variable.

gdb Command
The corresponding gdb command is ‘show’.

Example(gdb)-gdb-show annotate^done,value="0"(gdb)

The -gdb-version Command
Synopsis-gdb-version

Show version information for gdb. Used mostly in testing.

gdb Command
The gdb equivalent is ‘show version’. gdb by default shows this information when you
start an interactive session.

Example(gdb)-gdb-version~GNU gdb 5.2.1~Copyright 2000 Free Software Foundation, Inc.
~GDB is free software, covered by the GNU General Public License, and~you are welcome to change it and/or distribute copies of it under~ certain conditions.
~Type "show copying" to see the conditions.
~There is absolutely no warranty for GDB. Type "show warranty" for~ details.
~This GDB was configured as"--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
^done
(gdb)

The -list-thread-groups Command
Synopsis-list-thread-groups [ --available ] [ --recurse 1 ] [ group ... ]Lists thread groups (see Section 27.3.3 [Thread groups], page 592). When a single threadgroup is passed as the argument, lists the children of that group. When several threadgroup are passed, lists information about those thread groups. Without any parameters,
lists information about all top-level thread groups.

688

Debugging with gdb

Normally, thread groups that are being debugged are reported. With the ‘--available’
option, gdb reports thread groups available on the target.
The output of this command may have either a ‘threads’ result or a ‘groups’ result.
The ‘thread’ result has a list of tuples as value, with each tuple describing a thread (seeSection 27.7.6 [GDB/MI Thread Information], page 605). The ‘groups’ result has a listof tuples as value, each tuple describing a thread group. If top-level groups are requested(that is, no parameter is passed), or when several groups are passed, the output always has
a ‘groups’ result. The format of the ‘group’ result is described below.
To reduce the number of roundtrips it’s possible to list thread groups together with
their children, by passing the ‘--recurse’ option and the recursion depth. Presently, only
recursion depth of 1 is permitted. If this option is present, then every reported thread groupwill also include its children, either as ‘group’ or ‘threads’ field.
In general, any combination of option and parameters is permitted, with the following
caveats:• When a single thread group is passed, the output will typically be the ‘threads’ result.
Because threads may not contain anything, the ‘recurse’ option will be ignored.
• When the ‘--available’ option is passed, limited information may be available. In
particular, the list of threads of a process might be inaccessible. Further, specifying
specific thread groups might not give any performance advantage over listing all threadgroups. The frontend should assume that ‘-list-thread-groups --available’ isalways an expensive operation and cache the results.
The ‘groups’ result is a list of tuples, where each tuple may have the following fields:
id

Identifier of the thread group. This field is always present. The identifier is an
opaque string; frontends should not try to convert it to an integer, even though
it might look like one.

type

The type of the thread group. At present, only ‘process’ is a valid type.

pid

The target-specific process identifier. This field is only present for thread groupsof type ‘process’ and only if the process exists.

exit-code
The exit code of this group’s last exited thread, formatted in octal. This field
is only present for thread groups of type ‘process’ and only if the process is
not running.
num_children
The number of children this thread group has. This field may be absent for anavailable thread group.
threads

This field has a list of tuples as value, each tuple describing a thread. It may
be present if the ‘--recurse’ option is specified, and it’s actually possible toobtain the threads.

coresThis field is a list of integers, each identifying a core that one thread of the groupis running on. This field may be absent if such information is not available.

Chapter 27: The gdb/mi Interface

689

executable
The name of the executable file that corresponds to this thread group. The
field is only present for thread groups of type ‘process’, and only if there is acorresponding executable file.

Example(gdb)-list-thread-groups^done,groups=[{id="17",type="process",pid="yyy",num_children="2"}]-list-thread-groups 17^done,threads=[{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
frame={level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]},state="running"},{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
frame={level="0",addr="0x0804891f",func="foo",args=[{name="i",value="10"}],file="/tmp/a.c",fullname="/tmp/a.c",line="158",arch="i386:x86_64"},state="running"}]]-list-thread-groups --available^done,groups=[{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]}]-list-thread-groups --available --recurse 1^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]},{id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},..]-list-thread-groups --available --recurse 1 17 18^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
threads=[{id="1",target-id="Thread 0xb7e14b90",cores=[1]},{id="2",target-id="Thread 0xb7e14b90",cores=[2]}]},...]The -info-os Command
Synopsis-info-os [ type ]If no argument is supplied, the command returns a table of available operating-systemspecific information types. If one of these types is supplied as an argument type, then thecommand returns a table of data of that type.
The types of information available depend on the target operating system.

gdb Command
The corresponding gdb command is ‘info os’.

ExampleWhen run on a gnu/Linux system, the output will look something like this:(gdb)-info-os^done,OSDataTable={nr_rows="10",nr_cols="3",
hdr=[{width="10",alignment="-1",col_name="col0",colhdr="Type"},{width="10",alignment="-1",col_name="col1",colhdr="Description"},{width="10",alignment="-1",col_name="col2",colhdr="Title"}],body=[item={col0="cpus",col1="Listing of all cpus/cores on the system",
col2="CPUs"},
item={col0="files",col1="Listing of all file descriptors",
col2="File descriptors"},
item={col0="modules",col1="Listing of all loaded kernel modules",col2="Kernel modules"},

690

Debugging with gdb

item={col0="msg",col1="Listing of all message queues",
col2="Message queues"},
item={col0="processes",col1="Listing of all processes",col2="Processes"},
item={col0="procgroups",col1="Listing of all process groups",
col2="Process groups"},
item={col0="semaphores",col1="Listing of all semaphores",col2="Semaphores"},
item={col0="shm",col1="Listing of all shared-memory regions",
col2="Shared-memory regions"},
item={col0="sockets",col1="Listing of all internet-domain sockets",
col2="Sockets"},
item={col0="threads",col1="Listing of all threads",
col2="Threads"}](gdb)-info-os processes^done,OSDataTable={nr_rows="190",nr_cols="4",
hdr=[{width="10",alignment="-1",col_name="col0",colhdr="pid"},{width="10",alignment="-1",col_name="col1",colhdr="user"},{width="10",alignment="-1",col_name="col2",colhdr="command"},{width="10",alignment="-1",col_name="col3",colhdr="cores"}],body=[item={col0="1",col1="root",col2="/sbin/init",col3="0"},item={col0="2",col1="root",col2="[kthreadd]",col3="1"},
item={col0="3",col1="root",col2="[ksoftirqd/0]",col3="0"},...
item={col0="26446",col1="stan",col2="bash",col3="0"},item={col0="28152",col1="stan",col2="bash",col3="1"}]}(gdb)(Note that the MI output here includes a "Title" column that does not appear incommand-line info os; this column is useful for MI clients that want to enumerate thetypes of data, such as in a popup menu, but is needless clutter on the command line, andinfo os omits it.)

The -add-inferior Command
Synopsis-add-inferior [ --no-connection ]Creates a new inferior (see Section 4.9 [Inferiors Connections and Programs], page 42).
The created inferior is not associated with any executable. Such association may be established with the ‘-file-exec-and-symbols’ command (see Section 27.21 [GDB/MI File
Commands], page 674).
By default, the new inferior begins connected to the same target connection as thecurrent inferior. For example, if the current inferior was connected to gdbserver withtarget remote, then the new inferior will be connected to the same gdbserver instance.
The ‘--no-connection’ option starts the new inferior with no connection yet. You can thenfor example use the -target-select remote command to connect to some other gdbserver
instance, use -exec-run to spawn a local program, etc.
The command response always has a field, inferior, whose value is the identifier of thethread group corresponding to the new inferior.
An additional section field, connection, is optional. This field will only exist if the newinferior has a target connection. If this field exists, then its value will be a tuple containing
the following fields:

Chapter 27: The gdb/mi Interface‘number’The number of the connection used for the new inferior.

‘name’The name of the connection type used for the new inferior.

691

gdb Command
The corresponding gdb command is ‘add-inferior’ (see [‘add-inferior’], page 44).

Example(gdb)-add-inferior^done,inferior="i3"

The -remove-inferior Command
Synopsis-remove-inferior inferior-id

Removes an inferior (see Section 4.9 [Inferiors Connections and Programs], page 42).
Only inferiors that have exited can be removed. The inferior-id is the inferior to be removed,and should be the same id string as returned by the ‘-add-inferior’ command.
When an inferior is successfully removed a =thread-group-removed notification (seeSection 27.7.3 [GDB/MI Async Records], page 598) is emitted, the id field of which contains
the inferior-id for the removed inferior.

gdb Command
The corresponding gdb command is ‘remove-inferiors’ (see [‘remove-inferiors’],
page 45).

Example(gdb)-remove-inferior i3=thread-group-removed,id="i3"^done

The -interpreter-exec Command
Synopsis-interpreter-exec interpreter command

Execute the specified command in the given interpreter.

gdb Command
The corresponding gdb command is ‘interpreter-exec’.

Example(gdb)-interpreter-exec console "break main"&"During symbol reading, couldn’t parse type; debugger out of date?.\n"&"During symbol reading, bad structure-type format.\n"~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
^done
(gdb)

692

Debugging with gdb

The -inferior-tty-set Command
Synopsis-inferior-tty-set /dev/pts/1

Set terminal for future runs of the program being debugged.

gdb Command
The corresponding gdb command is ‘set inferior-tty’ /dev/pts/1.

Example(gdb)-inferior-tty-set /dev/pts/1
^done
(gdb)

The -inferior-tty-show Command
Synopsis-inferior-tty-show

Show terminal for future runs of program being debugged.

gdb Command
The corresponding gdb command is ‘show inferior-tty’.

Example(gdb)-inferior-tty-set /dev/pts/1
^done
(gdb)
-inferior-tty-show^done,inferior_tty_terminal="/dev/pts/1"(gdb)

The -enable-timings Command
Synopsis-enable-timings [yes | no]

Toggle the printing of the wallclock, user and system times for an MI command as afield in its output. This command is to help frontend developers optimize the performanceof their code. No argument is equivalent to ‘yes’.

gdb CommandNo equivalent.

Example(gdb)-enable-timings
^done
(gdb)

Chapter 27: The gdb/mi Interface

693-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",addr="0x080484ed",func="main",file="myprog.c",fullname="/home/nickrob/myprog.c",line="73",thread-groups=["i1"],
times="0"},time={wallclock="0.05185",user="0.00800",system="0.00000"}(gdb)-enable-timings no
^done
(gdb)
-exec-run^running(gdb)*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",frame={addr="0x080484ed",func="main",args=[{name="argc",value="1"},{name="argv",value="0xbfb60364"}],file="myprog.c",fullname="/home/nickrob/myprog.c",line="73",arch="i386:x86_64"}(gdb)

The -complete Command
Synopsis-complete command

Show a list of completions for partially typed CLI command.
This command is intended for gdb/mi frontends that cannot use two separate CLI andMI channels — for example: because of lack of PTYs like on Windows or because gdb isused remotely via a SSH connection.

Result
The result consists of two or three fields:‘completion’This field contains the completed command. If command has no known completions, this field is omitted.
‘matches’

This field contains a (possibly empty) array of matches. It is always present.

‘max_completions_reached’
This field contains 1 if number of known completions is above max-completions
limit (see Section 3.3 [Completion], page 24), otherwise it contains 0. It is always
present.

gdb Command
The corresponding gdb command is ‘complete’.

Example(gdb)-complete br^done,completion="break",matches=["break","break-range"],
max_completions_reached="0"(gdb)-complete "b ma"

694

Debugging with gdb^done,completion="b ma",matches=["b madvise","b main"],max_completions_reached="0"(gdb)-complete "b push_b"^done,completion="b push_back(",
matches=["b A::push_back(void*)","b std::string::push_back(char)","b std::vector<int, std::allocator<int> >::push_back(int&&)"],
max_completions_reached="0"(gdb)-complete "nonexist"^done,matches=[],max_completions_reached="0"
(gdb)

695

28 gdb Annotations
This chapter describes annotations in gdb. Annotations were designed to interface gdb tographical user interfaces or other similar programs which want to interact with gdb at a
relatively high level.
The annotation mechanism has largely been superseded by gdb/mi (see Chapter 27[GDB/MI], page 589).

28.1 What is an Annotation?
Annotations start with a newline character, two ‘control-z’ characters, and the nameof the annotation. If there is no additional information associated with this annotation,
the name of the annotation is followed immediately by a newline. If there is additional
information, the name of the annotation is followed by a space, the additional information,
and a newline. The additional information cannot contain newline characters.
Any output not beginning with a newline and two ‘control-z’ characters denotes literal
output from gdb. Currently there is no need for gdb to output a newline followed by two‘control-z’ characters, but if there was such a need, the annotations could be extended
with an ‘escape’ annotation which means those three characters as output.
The annotation level, which is specified using the --annotate command line option (seeSection 2.1.2 [Mode Options], page 13), controls how much information gdb prints together
with its prompt, values of expressions, source lines, and other types of output. Level 0 is forno annotations, level 1 is for use when gdb is run as a subprocess of gnu Emacs, level 3 isthe maximum annotation suitable for programs that control gdb, and level 2 annotations
have been made obsolete (see Section “Limitations of the Annotation Interface” in GDB’s
Obsolete Annotations).
set annotate level
The gdb command set annotate sets the level of annotations to the specified
level.
show annotate
Show the current annotation level.
This chapter describes level 3 annotations.
A simple example of starting up gdb with annotations is:$ gdb --annotate=3
GNU gdb 6.0
Copyright 2003 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License,and you are welcome to change it and/or distribute copies of it
under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty"
for details.
This GDB was configured as "i386-pc-linux-gnu"^Z^Zpre-prompt(gdb)^Z^Zprompt
quit

696

Debugging with gdb^Z^Zpost-prompt$

Here ‘quit’ is input to gdb; the rest is output from gdb. The three lines beginning‘^Z^Z’ (where ‘^Z’ denotes a ‘control-z’ character) are annotations; the rest is output
from gdb.

28.2 The Server Prefix
If you prefix a command with ‘server ’ then it will not affect the command history, norwill it affect gdb’s notion of which command to repeat if RET is pressed on a line by itself.
This means that commands can be run behind a user’s back by a front-end in a transparent
manner.
The server prefix does not affect the recording of values into the value history; to print
a value without recording it into the value history, use the output command instead of theprint command.
Using this prefix also disables confirmation requests (see [confirmation requests],
page 382).

28.3 Annotation for gdb Input
When gdb prompts for input, it annotates this fact so it is possible to know when to send
output, when the output from a given command is over, etc.
Different kinds of input each have a different input type. Each input type has three
annotations: a pre- annotation, which denotes the beginning of any prompt which is being
output, a plain annotation, which denotes the end of the prompt, and then a post- annotation which denotes the end of any echo which may (or may not) be associated with the
input. For example, the prompt input type features the following annotations:^Z^Zpre-prompt^Z^Zprompt^Z^Zpost-prompt

The input types arepromptWhen gdb is prompting for a command (the main gdb prompt).

commands

When gdb prompts for a set of commands, like in the commands command.
The annotations are repeated for each command which is input.

overload-choice
When gdb wants the user to select between various overloaded functions.
query

When gdb wants the user to confirm a potentially dangerous operation.

prompt-for-continue
When gdb is asking the user to press return to continue. Note: Don’t expect
this to work well; instead use set height 0 to disable prompting. This isbecause the counting of lines is buggy in the presence of annotations.

Chapter 28: gdb Annotations

697

28.4 Errors^Z^Zquit

This annotation occurs right before gdb responds to an interrupt.
^Z^Zerror

This annotation occurs right before gdb responds to an error.
Quit and error annotations indicate that any annotations which gdb was in the middleof may end abruptly. For example, if a value-history-begin annotation is followed by aerror, one cannot expect to receive the matching value-history-end. One cannot expect
not to receive it either, however; an error annotation does not necessarily mean that gdb
is immediately returning all the way to the top level.
A quit or error annotation may be preceded by^Z^Zerror-begin

Any output between that and the quit or error annotation is the error message.
Warning messages are not yet annotated.

28.5 Invalidation Notices
The following annotations say that certain pieces of state may have changed.
^Z^Zframes-invalid
The frames (for example, output from the backtrace command) may havechanged.
^Z^Zbreakpoints-invalid
The breakpoints may have changed. For example, the user just added or deleted
a breakpoint.

28.6 Running the Program
When the program starts executing due to a gdb command such as step or continue,^Z^Zstartingis output. When the program stops,^Z^Zstopped

is output. Before the stopped annotation, a variety of annotations describe how the
program stopped.
^Z^Zexited exit-status
The program exited, and exit-status is the exit status (zero for successful exit,
otherwise nonzero).
^Z^Zsignalled
The program exited with a signal. After the ^Z^Zsignalled, the annotation
continues:
intro-text^Z^Zsignal-namename^Z^Zsignal-name-end
middle-text^Z^Zsignal-string

698

Debugging with gdb

string^Z^Zsignal-string-end
end-text

where name is the name of the signal, such as SIGILL or SIGSEGV, and string is
the explanation of the signal, such as Illegal Instruction or Segmentation
fault. The arguments intro-text, middle-text, and end-text are for the user’s
benefit and have no particular format.
^Z^Zsignal
The syntax of this annotation is just like signalled, but gdb is just sayingthat the program received the signal, not that it was terminated with it.
^Z^Zbreakpoint number
The program hit breakpoint number number.
^Z^Zwatchpoint number
The program hit watchpoint number number.

28.7 Displaying Source
The following annotation is used instead of displaying source code:^Z^Zsource filename:line:character:middle:addr

where filename is an absolute file name indicating which source file, line is the line
number within that file (where 1 is the first line in the file), character is the character
position within the file (where 0 is the first character in the file) (for most debug formats
this will necessarily point to the beginning of a line), middle is ‘middle’ if addr is in the
middle of the line, or ‘beg’ if addr is at the beginning of the line, and addr is the addressin the target program associated with the source which is being displayed. The addr is in
the form ‘0x’ followed by one or more lowercase hex digits (note that this does not dependon the language).

699

29 Debugger Adapter Protocol
The Debugger Adapter Protocol is a generic API that is used by some IDEs tocommunicate with debuggers. It is documented at https: / / microsoft . github . io /debug-adapter-protocol/.
Generally, gdb implements the Debugger Adapter Protocol as written. However, insome cases, extensions are either needed or even expected.
gdb defines some parameters that can be passed to the launch request:args

If provided, this should be an array of strings. These strings are provided ascommand-line arguments to the inferior, as if by set args. See Section 4.3[Arguments], page 38.

cwd

If provided, this should be a string. gdb will change its working directory tothis directory, as if by the cd command (see Section 4.5 [Working Directory],
page 39). The launched program will inherit this as its working directory. Notethat change of directory happens before the program parameter is processed.
This will affect the result if program is a relative filename.

env

If provided, this should be an object. Each key of the object will be used as thename of an environment variable; each value must be a string and will be thevalue of that variable. The environment of the inferior will be set to exactly as
passed in. See Section 4.4 [Environment], page 38.

programIf provided, this is a string that specifies the program to use. This corresponds
to the file command. See Section 18.1 [Files], page 291.

stopAtBeginningOfMainSubprogram
If provided, this must be a boolean. When ‘True’, gdb will set a temporary
breakpoint at the program’s main procedure, using the same approach as thestart command. See Section 4.2 [Starting], page 34.
stopOnEntry
If provided, this must be a boolean. When ‘True’, gdb will set a temporary
breakpoint at the program’s first instruction, using the same approach as thestarti command. See Section 4.2 [Starting], page 34.
gdb defines some parameters that can be passed to the attach request. Either pid ortarget must be specified, but if both are specified then target will be ignored.
pid

The process ID to which gdb should attach. See Section 4.7 [Attach], page 41.

programIf provided, this is a string that specifies the program to use. This corresponds
to the file command. See Section 18.1 [Files], page 291. In some cases, gdb
can automatically determine which program is running. However, for many
remote targets, this is not the case, and so this should be supplied.

target

The target to which gdb should connect. This is a string and is passed to thetarget remote command. See Section 20.1 [Connecting], page 315.

In response to the disassemble request, DAP allows the client to return the bytes ofeach instruction in an implementation-defined format. gdb implements this by sending astring with the bytes encoded in hex, like "55a2b900".

700

Debugging with gdb

When the repl context is used for the evaluate request, gdb evaluates the provided
expression as a CLI command.
Evaluation in general can cause the inferior to continue execution. For example, evaluating the continue command could do this, as could evaluating an expression that involves
an inferior function call.
repl evaluation can also cause gdb to appear to stop responding to requests, for example
if a CLI script does a lengthy computation.
Evaluations like this can be interrupted using the DAP cancel request. (In fact, cancel
should work for any request, but it is unlikely to be useful for most of them.)
gdb provides a couple of logging settings that can be used in DAP mode. These can be
set on the command line using the -iex option (see Section 2.1.1 [File Options], page 12).
set debug dap-log-file [filename]Enable DAP logging. Logs are written to filename. If no filename is given,
logging is stopped.
set debug dap-log-level levelSet the DAP logging level. The default is ‘1’, which logs the DAP protocol,
whatever debug messages the developers thought were useful, and unexpected
exceptions. Level ‘2’ can be used to log all exceptions, including ones that areconsidered to be expected. For example, a failure to parse an expression would
be considered a normal exception and not normally be logged.

701

30 JIT Compilation Interface
This chapter documents gdb’s just-in-time (JIT) compilation interface. A JIT compiler
is a program or library that generates native executable code at runtime and executes it,
usually in order to achieve good performance while maintaining platform independence.
Programs that use JIT compilation are normally difficult to debug because portions of
their code are generated at runtime, instead of being loaded from object files, which iswhere gdb normally finds the program’s symbols and debug information. In order to debug
programs that use JIT compilation, gdb has an interface that allows the program to registerin-memory symbol files with gdb at runtime.
If you are using gdb to debug a program that uses this interface, then it should worktransparently so long as you have not stripped the binary. If you are developing a JIT
compiler, then the interface is documented in the rest of this chapter. At this time, theonly known client of this interface is the LLVM JIT.
Broadly speaking, the JIT interface mirrors the dynamic loader interface. The JIT compiler communicates with gdb by writing data into a global variable and calling a function
at a well-known symbol. When gdb attaches, it reads a linked list of symbol files from theglobal variable to find existing code, and puts a breakpoint in the function so that it canfind out about additional code.

30.1 JIT Declarations
These are the relevant struct declarations that a C program should include to implement
the interface:
typedef enum{
JIT_NOACTION = 0,
JIT_REGISTER_FN,
JIT_UNREGISTER_FN} jit_actions_t;
struct jit_code_entry{
struct jit_code_entry *next_entry;
struct jit_code_entry *prev_entry;
const char *symfile_addr;
uint64_t symfile_size;};
struct jit_descriptor{
uint32_t version;/* This type should be jit_actions_t, but we use uint32_t
to be explicit about the bitwidth. */uint32_t action_flag;
struct jit_code_entry *relevant_entry;
struct jit_code_entry *first_entry;};/* GDB puts a breakpoint in this function. */void __attribute__((noinline)) __jit_debug_register_code() { };702

Debugging with gdb/* Make sure to specify the version statically, because thedebugger may check the version before we can set it. */struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };If the JIT is multi-threaded, then it is important that the JIT synchronize any modifications to this global data properly, which can easily be done by putting a global mutex
around modifications to these structures.

30.2 Registering CodeTo register code with gdb, the JIT should follow this protocol:• Generate an object file in memory with symbols and other desired debug information.
The file must include the virtual addresses of the sections.
• Create a code entry for the file, which gives the start and size of the symbol file.
• Add it to the linked list in the JIT descriptor.
• Point the relevant entry field of the descriptor at the entry.
• Set action_flag to JIT_REGISTER and call __jit_debug_register_code.
When gdb is attached and the breakpoint fires, gdb uses the relevant_entry pointerso it doesn’t have to walk the list looking for new code. However, the linked list must still
be maintained in order to allow gdb to attach to a running process and still find the symbol
files.

30.3 Unregistering CodeIf code is freed, then the JIT should use the following protocol:• Remove the code entry corresponding to the code from the linked list.
• Point the relevant_entry field of the descriptor at the code entry.
• Set action_flag to JIT_UNREGISTER and call __jit_debug_register_code.
If the JIT frees or recompiles code without unregistering it, then gdb and the JIT willleak the memory used for the associated symbol files.

30.4 Custom Debug Info
Generating debug information in platform-native file formats (like ELF or COFF) may
be an overkill for JIT compilers; especially if all the debug info is used for is displaying
a meaningful backtrace. The issue can be resolved by having the JIT writers decide on a
debug info format and also provide a reader that parses the debug info generated by the JIT
compiler. This section gives a brief overview on writing such a parser. More specific details
can be found in the source file gdb/jit-reader.in, which is also installed as a header at
includedir/gdb/jit-reader.h for easy inclusion.
The reader is implemented as a shared object (so this functionality is not available
on platforms which don’t allow loading shared objects at runtime). Two gdb commands,
jit-reader-load and jit-reader-unload are provided, to be used to load and unload thereaders from a preconfigured directory. Once loaded, the shared object is used the parsethe debug information emitted by the JIT compiler.

Chapter 30: JIT Compilation Interface703

30.4.1 Using JIT Debug Info Readers
Readers can be loaded and unloaded using the jit-reader-load and jit-reader-unload
commands.
jit-reader-load reader
Load the JIT reader named reader, which is a shared object specified as either
an absolute or a relative file name. In the latter case, gdb will try to load thereader from a pre-configured directory, usually libdir/gdb/ on a UNIX system(here libdir is the system library directory, often /usr/local/lib).
Only one reader can be active at a time; trying to load a second reader when
one is already loaded will result in gdb reporting an error. A new JIT reader
can be loaded by first unloading the current one using jit-reader-unload andthen invoking jit-reader-load.
jit-reader-unload
Unload the currently loaded JIT reader.

30.4.2 Writing JIT Debug Info Readers
As mentioned, a reader is essentially a shared object conforming to a certain ABI. This ABI
is described in jit-reader.h.
jit-reader.h defines the structures, macros and functions required to write a reader.
It is installed (along with gdb), in includedir/gdb where includedir is the system include
directory.
Readers need to be released under a GPL compatible license. A reader can be declared as
released under such a license by placing the macro GDB_DECLARE_GPL_COMPATIBLE_READER
in a source file.
The entry point for readers is the symbol gdb_init_reader, which is expected to be afunction with the prototype
extern struct gdb_reader_funcs *gdb_init_reader (void);

struct gdb_reader_funcs contains a set of pointers to callback functions. These functions are executed to read the debug info generated by the JIT compiler (read), to unwind
stack frames (unwind) and to create canonical frame IDs (get_frame_id). It also has acallback that is called when the reader is being unloaded (destroy). The struct looks likethis
struct gdb_reader_funcs{/* Must be set to GDB_READER_INTERFACE_VERSION.
int reader_version;/* For use by the reader.
void *priv_data;*/*/

gdb_read_debug_info *read;
gdb_unwind_frame *unwind;gdb_get_frame_id *get_frame_id;
gdb_destroy_reader *destroy;};

The callbacks are provided with another set of callbacks by gdb to do their job. For
read, these callbacks are passed in a struct gdb_symbol_callbacks and for unwind and704

Debugging with gdb

get_frame_id, in a struct gdb_unwind_callbacks. struct gdb_symbol_callbacks has
callbacks to create new object files and new symbol tables inside those object files. struct
gdb_unwind_callbacks has callbacks to read registers off the current frame and to writeout the values of the registers in the previous frame. Both have a callback (target_read)to read bytes off the target’s address space.

705

31 In-Process Agent
The traditional debugging model is conceptually low-speed, but works fine, because mostbugs can be reproduced in debugging-mode execution. However, as multi-core or many-coreprocessors are becoming mainstream, and multi-threaded programs become more and more
popular, there should be more and more bugs that only manifest themselves at normal-mode
execution, for example, thread races, because debugger’s interference with the program’s
timing may conceal the bugs. On the other hand, in some applications, it is not feasible forthe debugger to interrupt the program’s execution long enough for the developer to learn
anything helpful about its behavior. If the program’s correctness depends on its real-time
behavior, delays introduced by a debugger might cause the program to fail, even when thecode itself is correct. It is useful to be able to observe the program’s behavior without
interrupting it.
Therefore, traditional debugging model is too intrusive to reproduce some bugs. In
order to reduce the interference with the program, we can reduce the number of operations
performed by debugger. The In-Process Agent, a shared library, is running within the sameprocess with inferior, and is able to perform some debugging operations itself. As a result,debugger is only involved when necessary, and performance of debugging can be improved
accordingly. Note that interference with program can be reduced but can’t be removed
completely, because the in-process agent will still stop or slow down the program.
The in-process agent can interpret and execute Agent Expressions (see Appendix F[Agent Expressions], page 847) during performing debugging operations. The agent expressions can be used for different purposes, such as collecting data in tracepoints, and condition
evaluation in breakpoints.
You can control whether the in-process agent is used as an aid for debugging with thefollowing commands:
set agent on
Causes the in-process agent to perform some operations on behalf of the debugger. Just which operations requested by the user will be done by the in-process
agent depends on the its capabilities. For example, if you request to evaluate
breakpoint conditions in the in-process agent, and the in-process agent has suchcapability as well, then breakpoint conditions will be evaluated in the in-process
agent.
set agent off
Disables execution of debugging operations by the in-process agent. All of theoperations will be performed by gdb.
show agent
Display the current setting of execution of debugging operations by the inprocess agent.

31.1 In-Process Agent Protocol
The in-process agent is able to communicate with both gdb and GDBserver (see Chapter 31[In-Process Agent], page 705). This section documents the protocol used for communications
between gdb or GDBserver and the IPA. In general, gdb or GDBserver sends commands

706

Debugging with gdb(see Section 31.1.2 [IPA Protocol Commands], page 707) and data to in-process agent, andthen in-process agent replies back with the return result of the command, or some otherinformation. The data sent to in-process agent is composed of primitive data types, suchas 4-byte or 8-byte type, and composite types, which are called objects (see Section 31.1.1[IPA Protocol Objects], page 706).

31.1.1 IPA Protocol Objects
The commands sent to and results received from agent may contain some complex datatypes called objects.
The in-process agent is running on the same machine with gdb or GDBserver, so it
doesn’t have to handle as much differences between two ends as remote protocol (seeAppendix E [Remote Protocol], page 773) tries to handle. However, there are still somedifferences of two ends in two processes:
1. word size. On some 64-bit machines, gdb or GDBserver can be compiled as a 64-bit
executable, while in-process agent is a 32-bit one.
2. ABI. Some machines may have multiple types of ABI, gdb or GDBserver is compiled
with one, and in-process agent is compiled with the other one.
Here are the IPA Protocol Objects:
1. agent expression object. It represents an agent expression (see Appendix F [Agent
Expressions], page 847).
2. tracepoint action object. It represents a tracepoint action (see Section 13.1.6 [Tracepoint Action Lists], page 208) to collect registers, memory, static trace data and toevaluate expression.
3. tracepoint object. It represents a tracepoint (see Chapter 13 [Tracepoints], page 203).
The following table describes important attributes of each IPA protocol object:
Nameagent expression object
lengthbyte code
tracepoint action for collecting memory
’M’
addr

Size

Description

4
lengthlength of bytes code
contents of byte code

1
8

type of tracepoint action
if basereg is ‘-1’, addr is the address of thelowest byte to collect, otherwise addr is theoffset of basereg for memory collecting.
length of memory for collecting
the register number containing the starting
memory address for collecting.

lenbasereg

8
4

tracepoint action for collecting registers’R’

1

type of tracepoint action

Chapter 31: In-Process Agent

tracepoint action for collecting static trace data
’L’tracepoint action for expression evaluation’X’agent expression
tracepoint object
numberaddress
type
enabledstep countpass countnumactions
hit counttrace frame usage
compiled cond
orig size
conditionactions707

1

type of tracepoint action

1
length oftype of tracepoint action[agent expression object], page 706,

4
8
4
1
8
8
4
8
8
8
8
4 if conditionis
NULL
otherwise
length of [agent
expression
object],page 706,
variablenumber of tracepoint
address of tracepoint inserted ontype of tracepoint
enable or disable of tracepoint
step
pass
number of tracepoint actions
hit counttrace frame usage
compiled condition
orig size
zero if condition is NULL, otherwise is[agent expression object], page 706,

numactions number of [tracepoint action
object], page 706,

31.1.2 IPA Protocol Commands
The spaces in each command are delimiters to ease reading this commands specification.
They don’t exist in real commands.
‘FastTrace:tracepoint_object gdb_jump_pad_head’
Installs a new fast tracepoint described by tracepoint object (see [tracepoint
object], page 706). The gdb jump pad head, 8-byte long, is the head of jumppad, which is used to jump to data collection routine in IPA finally.
Replies:‘OK target_address gdb_jump_pad_head fjump_size fjump’
target address is address of tracepoint in the inferior. The
gdb jump pad head is updated head of jumppad.
Both oftarget address and gdb jump pad head are 8-byte long. The
fjump contains a sequence of instructions jump to jumppad entry.
The fjump size, 4-byte long, is the size of fjump.
‘close’Closes the in-process agent. This command is sent when gdb or GDBserver isabout to kill inferiors.

708

Debugging with gdb‘qTfSTM’

See [qTfSTM], page 822.

‘qTsSTM’

See [qTsSTM], page 822.

‘qTSTMat’See [qTSTMat], page 822.

‘probe_marker_at:address’
Asks in-process agent to probe the marker at address.
Replies:‘unprobe_marker_at:address’
Asks in-process agent to unprobe the marker at address.

709

32 Reporting Bugs in gdb
Your bug reports play an essential role in making gdb reliable.
Reporting a bug may help you by bringing a solution to your problem, or it may not.
But in any case the principal function of a bug report is to help the entire community bymaking the next version of gdb work better. Bug reports are your contribution to themaintenance of gdb.
In order for a bug report to serve its purpose, you must include the information thatenables us to fix the bug.

32.1 Have You Found a Bug?
If you are not sure whether you have found a bug, here are some guidelines:• If the debugger gets a fatal signal, for any input whatever, that is a gdb bug. Reliabledebuggers never crash.
• If gdb produces an error message for valid input, that is a bug. (Note that if you’re
cross debugging, the problem may also be somewhere in the connection to the target.)• If gdb does not produce an error message for invalid input, that is a bug. However,
you should note that your idea of “invalid input” might be our idea of “an extension”
or “support for traditional practice”.
• If you are an experienced user of debugging tools, your suggestions for improvement of
gdb are welcome in any case.

32.2 How to Report Bugs
A number of companies and individuals offer support for gnu products. If you obtained
gdb from a support organization, we recommend you contact that organization first.
You can find contact information for many support companies and individuals in the file
etc/SERVICE in the gnu Emacs distribution.
In any event, we also recommend that you submit bug reports for gdb tohttps://www.gnu.org/software/gdb/bugs/.
The fundamental principle of reporting bugs usefully is this: report all the facts. If you
are not sure whether to state a fact or leave it out, state it!
Often people omit facts because they think they know what causes the problem andassume that some details do not matter. Thus, you might assume that the name of thevariable you use in an example does not matter. Well, probably it does not, but one cannot
be sure. Perhaps the bug is a stray memory reference which happens to fetch from thelocation where that name is stored in memory; perhaps, if the name were different, thecontents of that location would fool the debugger into doing the right thing despite the bug.
Play it safe and give a specific, complete example. That is the easiest thing for you to do,
and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may
be that the bug has been reported previously, but neither you nor we can know that unless
your bug report is complete and self-contained.

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Sometimes people give a few sketchy facts and ask, “Does this ring a bell?” Those bug
reports are useless, and we urge everyone to refuse to respond to them except to chide thesender to report bugs properly.
To enable us to fix the bug, you should include all these things:• The version of gdb. gdb announces it if you start with no arguments; you can also
print it at any time using show version.
Without this, we will not know whether there is any point in looking for the bug in thecurrent version of gdb.
• The type of machine you are using, and the operating system name and version number.
• The details of the gdb build-time configuration. gdb shows these details if you invoke itwith the --configuration command-line option, or if you type show configuration
at gdb’s prompt.
• What compiler (and its version) was used to compile gdb—e.g. “gcc–2.8.1”.
• What compiler (and its version) was used to compile the program you are debugging—e.g. “gcc–2.8.1”, or “HP92453-01 A.10.32.03 HP C Compiler”. For gcc, you can say
gcc --version to get this information; for other compilers, see the documentation for
those compilers.
• The command arguments you gave the compiler to compile your example and observe
the bug. For example, did you use ‘-O’? To guarantee you will not omit somethingimportant, list them all. A copy of the Makefile (or the output from make) is sufficient.
If we were to try to guess the arguments, we would probably guess wrong and then wemight not encounter the bug.
• A complete input script, and all necessary source files, that will reproduce the bug.
• A description of what behavior you observe that you believe is incorrect. For example,“It gets a fatal signal.”
Of course, if the bug is that gdb gets a fatal signal, then we will certainly notice it.
But if the bug is incorrect output, we might not notice unless it is glaringly wrong.
You might as well not give us a chance to make a mistake.
Even if the problem you experience is a fatal signal, you should still say so explicitly.
Suppose something strange is going on, such as, your copy of gdb is out of synch, oryou have encountered a bug in the C library on your system. (This has happened!)
Your copy might crash and ours would not. If you told us to expect a crash, then whenours fails to crash, we would know that the bug was not happening for us. If you had
not told us to expect a crash, then we would not be able to draw any conclusion fromour observations.
To collect all this information, you can use a session recording program such as script,
which is available on many Unix systems. Just run your gdb session inside script andthen include the typescript file with your bug report.
Another way to record a gdb session is to run gdb inside Emacs and then save theentire buffer to a file.
• If you wish to suggest changes to the gdb source, send us context diffs. If you evendiscuss something in the gdb source, refer to it by context, not by line number.
The line numbers in our development sources will not match those in your sources.
Your line numbers would convey no useful information to us.

711

Here are some things that are not necessary:• A description of the envelope of the bug.
Often people who encounter a bug spend a lot of time investigating which changes tothe input file will make the bug go away and which changes will not affect it.
This is often time consuming and not very useful, because the way we will find the
bug is by running a single example under the debugger with breakpoints, not by purededuction from a series of examples. We recommend that you save your time forsomething else.
Of course, if you can find a simpler example to report instead of the original one, thatis a convenience for us. Errors in the output will be easier to spot, running under the
debugger will take less time, and so on.
However, simplification is not vital; if you do not want to do this, report the bug
anyway and send us the entire test case you used.
• A patch for the bug.
A patch for the bug does help us if it is a good one. But do not omit the necessary
information, such as the test case, on the assumption that a patch is all we need. We
might see problems with your patch and decide to fix the problem another way, or wemight not understand it at all.
Sometimes with a program as complicated as gdb it is very hard to construct anexample that will make the program follow a certain path through the code. If you do
not send us the example, we will not be able to construct one, so we will not be able
to verify that the bug is fixed.
And if we cannot understand what bug you are trying to fix, or why your patch should
be an improvement, we will not install it. A test case will help us to understand.
• A guess about what the bug is or what it depends on.
Such guesses are usually wrong. Even we cannot guess right about such things without
first using the debugger to find the facts.

713

33 Command Line Editing
This chapter describes the basic features of the gnu command line editing interface.

33.1 Introduction to Line Editing
The following paragraphs describe the notation used to represent keystrokes.
The text C-k is read as ‘Control-K’ and describes the character produced when the kkey is pressed while the Control key is depressed.
The text M-k is read as ‘Meta-K’ and describes the character produced when the Meta
key (if you have one) is depressed, and the k key is pressed. The Meta key is labeled ALT
on many keyboards. On keyboards with two keys labeled ALT (usually to either side of thespace bar), the ALT on the left side is generally set to work as a Meta key. The ALT key on
the right may also be configured to work as a Meta key or may be configured as some othermodifier, such as a Compose key for typing accented characters.
If you do not have a Meta or ALT key, or another key working as a Meta key, the identical
keystroke can be generated by typing ESC first, and then typing k. Either process is known
as metafying the k key.
The text M-C-k is read as ‘Meta-Control-k’ and describes the character produced bymetafying C-k.
In addition, several keys have their own names. Specifically, DEL, ESC, LFD, SPC, RET,and TAB all stand for themselves when seen in this text, or in an init file (see Section 33.3
[Readline Init File], page 716). If your keyboard lacks a LFD key, typing C-j will produce
the desired character. The RET key may be labeled Return or Enter on some keyboards.

33.2 Readline Interaction
Often during an interactive session you type in a long line of text, only to notice that thefirst word on the line is misspelled. The Readline library gives you a set of commands for
manipulating the text as you type it in, allowing you to just fix your typo, and not forcing
you to retype the majority of the line. Using these editing commands, you move the cursor
to the place that needs correction, and delete or insert the text of the corrections. Then,
when you are satisfied with the line, you simply press RET. You do not have to be at the endof the line to press RET; the entire line is accepted regardless of the location of the cursor
within the line.

33.2.1 Readline Bare Essentials
In order to enter characters into the line, simply type them. The typed character appears
where the cursor was, and then the cursor moves one space to the right. If you mistype acharacter, you can use your erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and not notice the error until you have typed
several other characters. In that case, you can type C-b to move the cursor to the left, andthen correct your mistake. Afterwards, you can move the cursor to the right with C-f.
When you add text in the middle of a line, you will notice that characters to the rightof the cursor are ‘pushed over’ to make room for the text that you have inserted. Likewise,
when you delete text behind the cursor, characters to the right of the cursor are ‘pulled

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back’ to fill in the blank space created by the removal of the text. A list of the bare essentials
for editing the text of an input line follows.
C-b

Move back one character.

C-fMove forward one character.

DEL or Backspace
Delete the character to the left of the cursor.
C-d

Delete the character underneath the cursor.

Printing characters
Insert the character into the line at the cursor.
C-_ or C-x C-u
Undo the last editing command. You can undo all the way back to an empty
line.
(Depending on your configuration, the Backspace key be set to delete the character to theleft of the cursor and the DEL key set to delete the character underneath the cursor, likeC-d, rather than the character to the left of the cursor.)

33.2.2 Readline Movement Commands
The above table describes the most basic keystrokes that you need in order to do editing of
the input line. For your convenience, many other commands have been added in addition
to C-b, C-f, C-d, and DEL. Here are some commands for moving more rapidly about the
line.
C-a

Move to the start of the line.

C-e

Move to the end of the line.

M-f

Move forward a word, where a word is composed of letters and digits.

M-bMove backward a word.

C-l

Clear the screen, reprinting the current line at the top.

Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose
convention that control keystrokes operate on characters while meta keystrokes operate onwords.

33.2.3 Readline Killing Commands
Killing text means to delete the text from the line, but to save it away for later use, usually
by yanking (re-inserting) it back into the line. (‘Cut’ and ‘paste’ are more recent jargon for‘kill’ and ‘yank’.)
If the description for a command says that it ‘kills’ text, then you can be sure that you
can get the text back in a different (or the same) place later.
When you use a kill command, the text is saved in a kill-ring. Any number of consecutive
kills save all of the killed text together, so that when you yank it back, you get it all. The
kill ring is not line specific; the text that you killed on a previously typed line is available
to be yanked back later, when you are typing another line.

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Here is the list of commands for killing text.
C-k

Kill the text from the current cursor position to the end of the line.

M-dKill from the cursor to the end of the current word, or, if between words, to theend of the next word. Word boundaries are the same as those used by M-f.

M-DEL

Kill from the cursor the start of the current word, or, if between words, to thestart of the previous word. Word boundaries are the same as those used by
M-b.

C-w

Kill from the cursor to the previous whitespace. This is different than M-DEL
because the word boundaries differ.

Here is how to yank the text back into the line. Yanking means to copy the mostrecently-killed text from the kill buffer.
C-yYank the most recently killed text back into the buffer at the cursor.

M-yRotate the kill-ring, and yank the new top. You can only do this if the priorcommand is C-y or M-y.

33.2.4 Readline Arguments
You can pass numeric arguments to Readline commands. Sometimes the argument acts
as a repeat count, other times it is the sign of the argument that is significant. If you
pass a negative argument to a command which normally acts in a forward direction, thatcommand will act in a backward direction. For example, to kill text back to the start ofthe line, you might type ‘M-- C-k’.
The general way to pass numeric arguments to a command is to type meta digits before
the command. If the first ‘digit’ typed is a minus sign (‘-’), then the sign of the argument
will be negative. Once you have typed one meta digit to get the argument started, you
can type the remainder of the digits, and then the command. For example, to give the C-dcommand an argument of 10, you could type ‘M-1 0 C-d’, which will delete the next ten
characters on the input line.

33.2.5 Searching for Commands in the History
Readline provides commands for searching through the command history for lines containing
a specified string. There are two search modes: incremental and non-incremental.
Incremental searches begin before the user has finished typing the search string. As eachcharacter of the search string is typed, Readline displays the next entry from the history
matching the string typed so far. An incremental search requires only as many characters asneeded to find the desired history entry. To search backward in the history for a particularstring, type C-r. Typing C-s searches forward through the history. The characters present
in the value of the isearch-terminators variable are used to terminate an incremental
search. If that variable has not been assigned a value, the ESC and C-J characters willterminate an incremental search. C-g will abort an incremental search and restore theoriginal line. When the search is terminated, the history entry containing the search string
becomes the current line.
To find other matching entries in the history list, type C-r or C-s as appropriate. This
will search backward or forward in the history for the next entry matching the search string

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typed so far. Any other key sequence bound to a Readline command will terminate thesearch and execute that command. For instance, a RET will terminate the search and accept
the line, thereby executing the command from the history list. A movement command willterminate the search, make the last line found the current line, and begin editing.
Readline remembers the last incremental search string. If two C-rs are typed without
any intervening characters defining a new search string, any remembered search string is
used.
Non-incremental searches read the entire search string before starting to search formatching history lines. The search string may be typed by the user or be part of thecontents of the current line.

33.3 Readline Init File
Although the Readline library comes with a set of Emacs-like keybindings installed bydefault, it is possible to use a different set of keybindings. Any user can customize programs
that use Readline by putting commands in an inputrc file, conventionally in his home
directory. The name of this file is taken from the value of the environment variable INPUTRC.
If that variable is unset, the default is ~/.inputrc. If that file does not exist or cannot be
read, the ultimate default is /etc/inputrc.
When a program which uses the Readline library starts up, the init file is read, and the
key bindings are set.
In addition, the C-x C-r command re-reads this init file, thus incorporating any changes
that you might have made to it.

33.3.1 Readline Init File Syntax
There are only a few basic constructs allowed in the Readline init file. Blank lines are
ignored. Lines beginning with a ‘#’ are comments. Lines beginning with a ‘$’ indicate
conditional constructs (see Section 33.3.2 [Conditional Init Constructs], page 724). Otherlines denote variable settings and key bindings.
Variable Settings
You can modify the run-time behavior of Readline by altering the values ofvariables in Readline using the set command within the init file. The syntax
is simple:
set variable value
Here, for example, is how to change from the default Emacs-like key binding touse vi line editing commands:
set editing-mode vi
Variable names and values, where appropriate, are recognized without regard
to case. Unrecognized variable names are ignored.
Boolean variables (those that can be set to on or off) are set to on if the value isnull or empty, on (case-insensitive), or 1. Any other value results in the variablebeing set to off.
A great deal of run-time behavior is changeable with the following variables.

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bell-styleControls what happens when Readline wants to ring the terminal bell. If set to ‘none’, Readline never rings the bell. If set to‘visible’, Readline uses a visible bell if one is available. If set to‘audible’ (the default), Readline attempts to ring the terminal’s
bell.
bind-tty-special-chars
If set to ‘on’ (the default), Readline attempts to bind the control
characters treated specially by the kernel’s terminal driver to their
Readline equivalents.
blink-matching-paren
If set to ‘on’, Readline attempts to briefly move the cursor to an
opening parenthesis when a closing parenthesis is inserted. The
default is ‘off’.
colored-completion-prefix
If set to ‘on’, when listing completions, Readline displays the common prefix of the set of possible completions using a different color.
The color definitions are taken from the value of the LS_COLORS
environment variable. The default is ‘off’.
colored-stats
If set to ‘on’, Readline displays possible completions using different
colors to indicate their file type. The color definitions are takenfrom the value of the LS_COLORS environment variable. The default
is ‘off’.
comment-begin
The string to insert at the beginning of the line when theinsert-comment command is executed. The default value is "#".
completion-display-width
The number of screen columns used to display possible matches
when performing completion. The value is ignored if it is less than
0 or greater than the terminal screen width. A value of 0 will cause
matches to be displayed one per line. The default value is -1.
completion-ignore-case
If set to ‘on’, Readline performs filename matching and completionin a case-insensitive fashion. The default value is ‘off’.
completion-map-case
If set to ‘on’, and completion-ignore-case is enabled, Readline treats
hyphens (‘-’) and underscores (‘_’) as equivalent when performing
case-insensitive filename matching and completion. The default
value is ‘off’.
completion-prefix-display-length
The length in characters of the common prefix of a list of possible
completions that is displayed without modification. When set to a

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value greater than zero, common prefixes longer than this value are
replaced with an ellipsis when displaying possible completions.
completion-query-items
The number of possible completions that determines when the user
is asked whether the list of possibilities should be displayed. If
the number of possible completions is greater than or equal to thisvalue, Readline will ask whether or not the user wishes to view
them; otherwise, they are simply listed. This variable must be set
to an integer value greater than or equal to 0. A negative valuemeans Readline should never ask. The default limit is 100.
convert-meta
If set to ‘on’, Readline will convert characters with the eighth bit set
to an ascii key sequence by stripping the eighth bit and prefixing
an ESC character, converting them to a meta-prefixed key sequence.
The default value is ‘on’, but will be set to ‘off’ if the locale is one
that contains eight-bit characters.
disable-completion
If set to ‘On’, Readline will inhibit word completion. Completion
characters will be inserted into the line as if they had been mapped
to self-insert. The default is ‘off’.
echo-control-characters
When set to ‘on’, on operating systems that indicate they support
it, readline echoes a character corresponding to a signal generated
from the keyboard. The default is ‘on’.
editing-mode
The editing-mode variable controls which default set of key bindings is used. By default, Readline starts up in Emacs editing mode,
where the keystrokes are most similar to Emacs. This variable canbe set to either ‘emacs’ or ‘vi’.
emacs-mode-string
If the show-mode-in-prompt variable is enabled, this string is displayed immediately before the last line of the primary prompt whenemacs editing mode is active. The value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash
escape sequences is available. Use the ‘\1’ and ‘\2’ escapes to begin
and end sequences of non-printing characters, which can be used
to embed a terminal control sequence into the mode string. The
default is ‘@’.
enable-bracketed-paste
When set to ‘On’, Readline will configure the terminal in a way thatwill enable it to insert each paste into the editing buffer as a single
string of characters, instead of treating each character as if it had
been read from the keyboard. This can prevent pasted charactersfrom being interpreted as editing commands. The default is ‘On’.

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enable-keypad
When set to ‘on’, Readline will try to enable the application keypadwhen it is called. Some systems need this to enable the arrow keys.
The default is ‘off’.
enable-meta-key
When set to ‘on’, Readline will try to enable any meta modifier
key the terminal claims to support when it is called. On many
terminals, the meta key is used to send eight-bit characters. The
default is ‘on’.
expand-tilde
If set to ‘on’, tilde expansion is performed when Readline attempts
word completion. The default is ‘off’.
history-preserve-point
If set to ‘on’, the history code attempts to place the point (thecurrent cursor position) at the same location on each history line
retrieved with previous-history or next-history. The default
is ‘off’.
history-size
Set the maximum number of history entries saved in the history
list. If set to zero, any existing history entries are deleted and no
new entries are saved. If set to a value less than zero, the numberof history entries is not limited. By default, the number of history
entries is not limited. If an attempt is made to set history-size toa non-numeric value, the maximum number of history entries will
be set to 500.
horizontal-scroll-mode
This variable can be set to either ‘on’ or ‘off’. Setting it to ‘on’means that the text of the lines being edited will scroll horizontallyon a single screen line when they are longer than the width of thescreen, instead of wrapping onto a new screen line. This variable isautomatically set to ‘on’ for terminals of height 1. By default, thisvariable is set to ‘off’.
input-meta
If set to ‘on’, Readline will enable eight-bit input (it will not clear
the eighth bit in the characters it reads), regardless of what theterminal claims it can support. The default value is ‘off’, but
Readline will set it to ‘on’ if the locale contains eight-bit characters.
The name meta-flag is a synonym for this variable.
isearch-terminators
The string of characters that should terminate an incremental
search without subsequently executing the character as a command(see Section 33.2.5 [Searching], page 715). If this variable has notbeen given a value, the characters ESC and C-J will terminate anincremental search.

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keymap

Sets Readline’s idea of the current keymap for key binding
commands. Built-in keymap names are emacs, emacs-standard,
emacs-meta, emacs-ctlx, vi, vi-move, vi-command, andvi-insert. vi is equivalent to vi-command (vi-move is also asynonym); emacs is equivalent to emacs-standard. Applications
may add additional names. The default value is emacs. The valueof the editing-mode variable also affects the default keymap.

keyseq-timeout
Specifies the duration Readline will wait for a character when reading an ambiguous key sequence (one that can form a complete key
sequence using the input read so far, or can take additional input
to complete a longer key sequence). If no input is received within
the timeout, Readline will use the shorter but complete key sequence. Readline uses this value to determine whether or not input
is available on the current input source (rl_instream by default).
The value is specified in milliseconds, so a value of 1000 means that
Readline will wait one second for additional input. If this variable isset to a value less than or equal to zero, or to a non-numeric value,
Readline will wait until another key is pressed to decide which key
sequence to complete. The default value is 500.
mark-directories
If set to ‘on’, completed directory names have a slash appended.
The default is ‘on’.
mark-modified-lines
This variable, when set to ‘on’, causes Readline to display an asterisk (‘*’) at the start of history lines which have been modified.
This variable is ‘off’ by default.
mark-symlinked-directories
If set to ‘on’, completed names which are symbolic links todirectories have a slash appended (subject to the value of
mark-directories). The default is ‘off’.
match-hidden-files
This variable, when set to ‘on’, causes Readline to match files whosenames begin with a ‘.’ (hidden files) when performing filename
completion. If set to ‘off’, the leading ‘.’ must be supplied by
the user in the filename to be completed. This variable is ‘on’ by
default.
menu-complete-display-prefix
If set to ‘on’, menu completion displays the common prefix of thelist of possible completions (which may be empty) before cycling
through the list. The default is ‘off’.
output-meta
If set to ‘on’, Readline will display characters with the eighth bit
set directly rather than as a meta-prefixed escape sequence. The

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default is ‘off’, but Readline will set it to ‘on’ if the locale contains
eight-bit characters.
page-completions
If set to ‘on’, Readline uses an internal more-like pager to display
a screenful of possible completions at a time. This variable is ‘on’by default.
print-completions-horizontally
If set to ‘on’, Readline will display completions with matches sorted
horizontally in alphabetical order, rather than down the screen.
The default is ‘off’.
revert-all-at-newline
If set to ‘on’, Readline will undo all changes to history lines before
returning when accept-line is executed. By default, history lines
may be modified and retain individual undo lists across calls toreadline. The default is ‘off’.
show-all-if-ambiguous
This alters the default behavior of the completion functions. If set
to ‘on’, words which have more than one possible completion cause
the matches to be listed immediately instead of ringing the bell.
The default value is ‘off’.
show-all-if-unmodified
This alters the default behavior of the completion functions in a
fashion similar to show-all-if-ambiguous. If set to ‘on’, words whichhave more than one possible completion without any possible partial completion (the possible completions don’t share a common
prefix) cause the matches to be listed immediately instead of ringing the bell. The default value is ‘off’.
show-mode-in-prompt
If set to ‘on’, add a string to the beginning of the prompt indicating
the editing mode: emacs, vi command, or vi insertion. The mode
strings are user-settable (e.g., emacs-mode-string). The default
value is ‘off’.
skip-completed-text
If set to ‘on’, this alters the default completion behavior when inserting a single match into the line. It’s only active when performing completion in the middle of a word. If enabled, readline does
not insert characters from the completion that match characters
after point in the word being completed, so portions of the word
following the cursor are not duplicated. For instance, if this is enabled, attempting completion when the cursor is after the ‘e’ in‘Makefile’ will result in ‘Makefile’ rather than ‘Makefilefile’,
assuming there is a single possible completion. The default valueis ‘off’.

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Debugging with gdb

vi-cmd-mode-string
If the show-mode-in-prompt variable is enabled, this string is displayed immediately before the last line of the primary prompt whenvi editing mode is active and in command mode. The value is expanded like a key binding, so the standard set of meta- and control
prefixes and backslash escape sequences is available. Use the ‘\1’and ‘\2’ escapes to begin and end sequences of non-printing characters, which can be used to embed a terminal control sequence into
the mode string. The default is ‘(cmd)’.
vi-ins-mode-string
If the show-mode-in-prompt variable is enabled, this string is displayed immediately before the last line of the primary prompt whenvi editing mode is active and in insertion mode. The value is expanded like a key binding, so the standard set of meta- and control
prefixes and backslash escape sequences is available. Use the ‘\1’and ‘\2’ escapes to begin and end sequences of non-printing characters, which can be used to embed a terminal control sequence into
the mode string. The default is ‘(ins)’.
visible-stats
If set to ‘on’, a character denoting a file’s type is appended to thefilename when listing possible completions. The default is ‘off’.
Key Bindings
The syntax for controlling key bindings in the init file is simple. First you
need to find the name of the command that you want to change. The following
sections contain tables of the command name, the default keybinding, if any,
and a short description of what the command does.
Once you know the name of the command, simply place on a line in the init
file the name of the key you wish to bind the command to, a colon, and then
the name of the command. There can be no space between the key name andthe colon – that will be interpreted as part of the key name. The name of
the key can be expressed in different ways, depending on what you find most
comfortable.
In addition to command names, readline allows keys to be bound to a stringthat is inserted when the key is pressed (a macro).
keyname: function-name or macro
keyname is the name of a key spelled out in English. For example:
Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: "> output"
In the example above, C-u is bound to the function
universal-argument, M-DEL is bound to the function
backward-kill-word, and C-o is bound to run the macro
expressed on the right hand side (that is, to insert the text ‘>
output’ into the line).

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A number of symbolic character names are recognized while
processing this key binding syntax: DEL, ESC, ESCAPE, LFD,NEWLINE, RET, RETURN, RUBOUT, SPACE, SPC, and TAB.
"keyseq": function-name or macro
keyseq differs from keyname above in that strings denoting an entire key sequence can be specified, by placing the key sequence indouble quotes. Some gnu Emacs style key escapes can be used, as
in the following example, but the special character names are notrecognized.
"\C-u": universal-argument"\C-x\C-r": re-read-init-file"\e[11~": "Function Key 1"
In the above example, C-u is again bound to the function
universal-argument (just as it was in the first example), ‘C-x
C-r’ is bound to the function re-read-init-file, and ‘ESC [ 1 1~’ is bound to insert the text ‘Function Key 1’.
The following gnu Emacs style escape sequences are available when specifying
key sequences:\C-

control prefix\M-meta prefix\ean escape character\\backslash\"", a double quotation mark\’’, a single quote or apostrophe

In addition to the gnu Emacs style escape sequences, a second set of backslash
escapes is available:\aalert (bell)\bbackspace\ddelete\fform feed\nnewline\r

carriage return\thorizontal tab\vvertical tab\nnn

the eight-bit character whose value is the octal value nnn (one tothree digits)\xHH

the eight-bit character whose value is the hexadecimal value HH(one or two hex digits)

724

Debugging with gdb

When entering the text of a macro, single or double quotes must be used toindicate a macro definition. Unquoted text is assumed to be a function name. In
the macro body, the backslash escapes described above are expanded. Backslash
will quote any other character in the macro text, including ‘"’ and ‘’’. For
example, the following binding will make ‘C-x \’ insert a single ‘\’ into the line:"\C-x\\": "\\"

33.3.2 Conditional Init Constructs
Readline implements a facility similar in spirit to the conditional compilation features of
the C preprocessor which allows key bindings and variable settings to be performed as theresult of tests. There are four parser directives used.
$if

The $if construct allows bindings to be made based on the editing mode, theterminal being used, or the application using Readline. The text of the test,
after any comparison operator, extends to the end of the line; unless otherwise
noted, no characters are required to isolate it.
mode

The mode= form of the $if directive is used to test whether Readline is in emacs or vi mode. This may be used in conjunction
with the ‘set keymap’ command, for instance, to set bindings in
the emacs-standard and emacs-ctlx keymaps only if Readline isstarting out in emacs mode.

term

The term= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal’s
function keys. The word on the right side of the ‘=’ is tested against
both the full name of the terminal and the portion of the terminal
name before the first ‘-’. This allows sun to match both sun andsun-cmd, for instance.

versionThe version test may be used to perform comparisons against
specific Readline versions. The version expands to the current
Readline version. The set of comparison operators includes ‘=’ (and‘==’), ‘!=’, ‘<=’, ‘>=’, ‘<’, and ‘>’. The version number supplied on
the right side of the operator consists of a major version number,an optional decimal point, and an optional minor version (e.g.,‘7.1’). If the minor version is omitted, it is assumed to be ‘0’. The
operator may be separated from the string version and from theversion number argument by whitespace. The following example
sets a variable if the Readline version being used is 7.0 or newer:$if version >= 7.0
set show-mode-in-prompt on$endifapplication
The application construct is used to include application-specific settings. Each program using the Readline library sets the application
name, and you can test for a particular value. This could be used tobind key sequences to functions useful for a specific program. For

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725

instance, the following command adds a key sequence that quotes
the current or previous word in Bash:$if Bash# Quote the current or previous word"\C-xq": "\eb\"\ef\""$endifvariable

The variable construct provides simple equality tests for Readline
variables and values. The permitted comparison operators are ‘=’,‘==’, and ‘!=’. The variable name must be separated from thecomparison operator by whitespace; the operator may be separated
from the value on the right hand side by whitespace. Both string
and boolean variables may be tested. Boolean variables must be
tested against the values on and off. The following example isequivalent to the mode=emacs test described above:$if editing-mode == emacs
set show-mode-in-prompt on$endif$endifThis command, as seen in the previous example, terminates an $if command.

$else

Commands in this branch of the $if directive are executed if the test fails.

$includeThis directive takes a single filename as an argument and reads commands
and bindings from that file. For example, the following directive reads from/etc/inputrc:$include /etc/inputrc

33.3.3 Sample Init File
Here is an example of an inputrc file. This illustrates key binding, variable assignment, andconditional syntax.

726

Debugging with gdb# This file controls the behaviour of line input editing for# programs that use the GNU Readline library. Existing# programs include FTP, Bash, and GDB.
## You can re-read the inputrc file with C-x C-r.
# Lines beginning with ’#’ are comments.
## First, include any system-wide bindings and variable# assignments from /etc/Inputrc$include /etc/Inputrc## Set various bindings for emacs mode.
set editing-mode emacs$if mode=emacs
Meta-Control-h:

backward-kill-word Text after the function name is ignored## Arrow keys in keypad mode##"\M-OD":
backward-char#"\M-OC":
forward-char#"\M-OA":
previous-history#"\M-OB":
next-history## Arrow keys in ANSI mode#"\M-[D":
backward-char"\M-[C":
forward-char"\M-[A":previous-history"\M-[B":next-history## Arrow keys in 8 bit keypad mode##"\M-\C-OD":
backward-char#"\M-\C-OC":
forward-char#"\M-\C-OA":
previous-history#"\M-\C-OB":
next-history## Arrow keys in 8 bit ANSI mode##"\M-\C-[D":backward-char#"\M-\C-[C":forward-charChapter 33: Command Line Editing#"\M-\C-[A":#"\M-\C-[B":previous-historynext-history

C-q: quoted-insert$endif# An old-style binding.
TAB: complete

This happens to be the default.

# Macros that are convenient for shell interaction$if Bash# edit the path"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"# prepare to type a quoted word -# insert open and close double quotes# and move to just after the open quote"\C-x\"": "\"\"\C-b"# insert a backslash (testing backslash escapes# in sequences and macros)"\C-x\\": "\\"# Quote the current or previous word"\C-xq": "\eb\"\ef\""# Add a binding to refresh the line, which is unbound"\C-xr": redraw-current-line# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="$endif# use a visible bell if one is available
set bell-style visible# don’t strip characters to 7 bits when reading
set input-meta on# allow iso-latin1 characters to be inserted rather# than converted to prefix-meta sequences
set convert-meta off# display characters with the eighth bit set directly# rather than as meta-prefixed charactersset output-meta on# if there are 150 or more possible completions for a word,# ask whether or not the user wants to see all of themset completion-query-items 150

727

728

Debugging with gdb# For FTP
$if Ftp"\C-xg": "get \M-?""\C-xt": "put \M-?""\M-.": yank-last-arg$endif33.4 Bindable Readline Commands
This section describes Readline commands that may be bound to key sequences. Command
names without an accompanying key sequence are unbound by default.
In the following descriptions, point refers to the current cursor position, and mark refers
to a cursor position saved by the set-mark command. The text between the point andmark is referred to as the region.

33.4.1 Commands For Moving
beginning-of-line (C-a)
Move to the start of the current line.
end-of-line (C-e)
Move to the end of the line.
forward-char (C-f)
Move forward a character.
backward-char (C-b)
Move back a character.
forward-word (M-f)
Move forward to the end of the next word. Words are composed of letters anddigits.
backward-word (M-b)
Move back to the start of the current or previous word. Words are composedof letters and digits.
previous-screen-line ()Attempt to move point to the same physical screen column on the previous
physical screen line. This will not have the desired effect if the current Readline
line does not take up more than one physical line or if point is not greater thanthe length of the prompt plus the screen width.
next-screen-line ()Attempt to move point to the same physical screen column on the next physicalscreen line. This will not have the desired effect if the current Readline line does
not take up more than one physical line or if the length of the current Readline
line is not greater than the length of the prompt plus the screen width.
clear-display (M-C-l)
Clear the screen and, if possible, the terminal’s scrollback buffer, then redraw
the current line, leaving the current line at the top of the screen.

Chapter 33: Command Line Editing729

clear-screen (C-l)
Clear the screen, then redraw the current line, leaving the current line at the
top of the screen.
redraw-current-line ()Refresh the current line. By default, this is unbound.

33.4.2 Commands For Manipulating The History
accept-line (Newline or Return)Accept the line regardless of where the cursor is. If this line is non-empty, it
may be added to the history list for future recall with add_history(). If thisline is a modified history line, the history line is restored to its original state.
previous-history (C-p)
Move ‘back’ through the history list, fetching the previous command.
next-history (C-n)
Move ‘forward’ through the history list, fetching the next command.
beginning-of-history (M-<)
Move to the first line in the history.
end-of-history (M->)
Move to the end of the input history, i.e., the line currently being entered.
reverse-search-history (C-r)
Search backward starting at the current line and moving ‘up’ through the history as necessary. This is an incremental search. This command sets the region
to the matched text and activates the mark.
forward-search-history (C-s)
Search forward starting at the current line and moving ‘down’ through thehistory as necessary. This is an incremental search. This command sets theregion to the matched text and activates the mark.
non-incremental-reverse-search-history (M-p)
Search backward starting at the current line and moving ‘up’ through the history as necessary using a non-incremental search for a string supplied by theuser. The search string may match anywhere in a history line.
non-incremental-forward-search-history (M-n)
Search forward starting at the current line and moving ‘down’ through thehistory as necessary using a non-incremental search for a string supplied by theuser. The search string may match anywhere in a history line.
history-search-forward ()Search forward through the history for the string of characters between thestart of the current line and the point. The search string must match at the
beginning of a history line. This is a non-incremental search. By default, thiscommand is unbound.
history-search-backward ()Search backward through the history for the string of characters between thestart of the current line and the point. The search string must match at the730

Debugging with gdb

beginning of a history line. This is a non-incremental search. By default, thiscommand is unbound.
history-substring-search-forward ()Search forward through the history for the string of characters between thestart of the current line and the point. The search string may match anywhere
in a history line. This is a non-incremental search. By default, this commandis unbound.
history-substring-search-backward ()Search backward through the history for the string of characters between thestart of the current line and the point. The search string may match anywhere
in a history line. This is a non-incremental search. By default, this commandis unbound.
yank-nth-arg (M-C-y)Insert the first argument to the previous command (usually the second wordon the previous line) at point. With an argument n, insert the nth word fromthe previous command (the words in the previous command begin with word
0). A negative argument inserts the nth word from the end of the previous
command. Once the argument n is computed, the argument is extracted as if
the ‘!n’ history expansion had been specified.
yank-last-arg (M-. or M-_)
Insert last argument to the previous command (the last word of the previous
history entry). With a numeric argument, behave exactly like yank-nth-arg.
Successive calls to yank-last-arg move back through the history list, inserting
the last word (or the word specified by the argument to the first call) of each line
in turn. Any numeric argument supplied to these successive calls determines
the direction to move through the history. A negative argument switches the
direction through the history (back or forward). The history expansion facilities
are used to extract the last argument, as if the ‘!$’ history expansion had been
specified.
operate-and-get-next (C-o)
Accept the current line for return to the calling application as if a newline had
been entered, and fetch the next line relative to the current line from the history
for editing. A numeric argument, if supplied, specifies the history entry to use
instead of the current line.

33.4.3 Commands For Changing Text
end-of-file (usually C-d)
The character indicating end-of-file as set, for example, by stty. If this character is read when there are no characters on the line, and point is at the beginningof the line, Readline interprets it as the end of input and returns eof.
delete-char (C-d)
Delete the character at point. If this function is bound to the same characteras the tty eof character, as C-d commonly is, see above for the effects.

Chapter 33: Command Line Editing731

backward-delete-char (Rubout)
Delete the character behind the cursor. A numeric argument means to kill thecharacters instead of deleting them.
forward-backward-delete-char ()Delete the character under the cursor, unless the cursor is at the end of theline, in which case the character behind the cursor is deleted. By default, thisis not bound to a key.
quoted-insert (C-q or C-v)
Add the next character typed to the line verbatim. This is how to insert key
sequences like C-q, for example.
tab-insert (M-TAB)
Insert a tab character.
self-insert (a, b, A, 1, !, ...)
Insert yourself.
bracketed-paste-begin ()This function is intended to be bound to the "bracketed paste" escape sequence
sent by some terminals, and such a binding is assigned by default. It allows
Readline to insert the pasted text as a single unit without treating each character as if it had been read from the keyboard. The characters are inserted
as if each one was bound to self-insert instead of executing any editing
commands.
Bracketed paste sets the region (the characters between point and the mark)to the inserted text. It uses the concept of an active mark : when the markis active, Readline redisplay uses the terminal’s standout mode to denote theregion.
transpose-chars (C-t)
Drag the character before the cursor forward over the character at the cursor,
moving the cursor forward as well. If the insertion point is at the end of theline, then this transposes the last two characters of the line. Negative arguments
have no effect.
transpose-words (M-t)
Drag the word before point past the word after point, moving point past thatword as well. If the insertion point is at the end of the line, this transposes thelast two words on the line.
upcase-word (M-u)
Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move the cursor.
downcase-word (M-l)
Lowercase the current (or following) word. With a negative argument, lowercase
the previous word, but do not move the cursor.
capitalize-word (M-c)
Capitalize the current (or following) word. With a negative argument, capitalize
the previous word, but do not move the cursor.

732

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overwrite-mode ()Toggle overwrite mode. With an explicit positive numeric argument, switches
to overwrite mode. With an explicit non-positive numeric argument, switches toinsert mode. This command affects only emacs mode; vi mode does overwrite
differently. Each call to readline() starts in insert mode.
In overwrite mode, characters bound to self-insert replace the text at
point rather than pushing the text to the right. Characters bound to
backward-delete-char replace the character before point with a space.
By default, this command is unbound.

33.4.4 Killing And Yanking
kill-line (C-k)
Kill the text from point to the end of the line. With a negative numeric argument, kill backward from the cursor to the beginning of the current line.
backward-kill-line (C-x Rubout)
Kill backward from the cursor to the beginning of the current line. With anegative numeric argument, kill forward from the cursor to the end of thecurrent line.
unix-line-discard (C-u)
Kill backward from the cursor to the beginning of the current line.
kill-whole-line ()Kill all characters on the current line, no matter where point is. By default,
this is unbound.
kill-word (M-d)
Kill from point to the end of the current word, or if between words, to the endof the next word. Word boundaries are the same as forward-word.
backward-kill-word (M-DEL)
Kill the word behind point. Word boundaries are the same as backward-word.
shell-transpose-words (M-C-t)
Drag the word before point past the word after point, moving point past thatword as well. If the insertion point is at the end of the line, this transposes thelast two words on the line. Word boundaries are the same as shell-forwardword and shell-backward-word.
unix-word-rubout (C-w)
Kill the word behind point, using white space as a word boundary. The killed
text is saved on the kill-ring.
unix-filename-rubout ()Kill the word behind point, using white space and the slash character as theword boundaries. The killed text is saved on the kill-ring.
delete-horizontal-space ()Delete all spaces and tabs around point. By default, this is unbound.

Chapter 33: Command Line Editing733

kill-region ()Kill the text in the current region. By default, this command is unbound.
copy-region-as-kill ()Copy the text in the region to the kill buffer, so it can be yanked right away.
By default, this command is unbound.
copy-backward-word ()Copy the word before point to the kill buffer. The word boundaries are thesame as backward-word. By default, this command is unbound.
copy-forward-word ()Copy the word following point to the kill buffer. The word boundaries are thesame as forward-word. By default, this command is unbound.
yank (C-y)
Yank the top of the kill ring into the buffer at point.
yank-pop (M-y)
Rotate the kill-ring, and yank the new top. You can only do this if the priorcommand is yank or yank-pop.

33.4.5 Specifying Numeric Arguments
digit-argument (M-0, M-1, ... M--)
Add this digit to the argument already accumulating, or start a new argument.
M-- starts a negative argument.
universal-argument ()This is another way to specify an argument. If this command is followed by one
or more digits, optionally with a leading minus sign, those digits define the argument. If the command is followed by digits, executing universal-argument
again ends the numeric argument, but is otherwise ignored. As a special case,if this command is immediately followed by a character that is neither a digit
nor minus sign, the argument count for the next command is multiplied byfour. The argument count is initially one, so executing this function the firsttime makes the argument count four, a second time makes the argument countsixteen, and so on. By default, this is not bound to a key.

33.4.6 Letting Readline Type For You
complete (TAB)
Attempt to perform completion on the text before point. The actual completion
performed is application-specific. The default is filename completion.
possible-completions (M-?)
List the possible completions of the text before point. When displaying completions, Readline sets the number of columns used for display to the value ofcompletion-display-width, the value of the environment variable COLUMNS,or the screen width, in that order.
insert-completions (M-*)
Insert all completions of the text before point that would have been generated
by possible-completions.

734

Debugging with gdb

menu-complete ()Similar to complete, but replaces the word to be completed with a single match
from the list of possible completions. Repeated execution of menu-complete
steps through the list of possible completions, inserting each match in turn.
At the end of the list of completions, the bell is rung (subject to the settingof bell-style) and the original text is restored. An argument of n moves n
positions forward in the list of matches; a negative argument may be used tomove backward through the list. This command is intended to be bound to
TAB, but is unbound by default.
menu-complete-backward ()Identical to menu-complete, but moves backward through the list of possible
completions, as if menu-complete had been given a negative argument.
delete-char-or-list ()Deletes the character under the cursor if not at the beginning or end of theline (like delete-char). If at the end of the line, behaves identically topossible-completions. This command is unbound by default.

33.4.7 Keyboard Macros
start-kbd-macro (C-x ()Begin saving the characters typed into the current keyboard macro.
end-kbd-macro (C-x ))Stop saving the characters typed into the current keyboard macro and save thedefinition.
call-last-kbd-macro (C-x e)
Re-execute the last keyboard macro defined, by making the characters in themacro appear as if typed at the keyboard.
print-last-kbd-macro ()Print the last keboard macro defined in a format suitable for the inputrc file.

33.4.8 Some Miscellaneous Commands
re-read-init-file (C-x C-r)
Read in the contents of the inputrc file, and incorporate any bindings or variableassignments found there.
abort (C-g)
Abort the current editing command and ring the terminal’s bell (subject to thesetting of bell-style).
do-lowercase-version (M-A, M-B, M-x, ...)
If the metafied character x is upper case, run the command that is bound tothe corresponding metafied lower case character. The behavior is undefined if
x is already lower case.
prefix-meta (ESC)
Metafy the next character typed. This is for keyboards without a meta key.
Typing ‘ESC f’ is equivalent to typing M-f.

Chapter 33: Command Line Editing

735

undo (C-_ or C-x C-u)
Incremental undo, separately remembered for each line.
revert-line (M-r)
Undo all changes made to this line. This is like executing the undo commandenough times to get back to the beginning.
tilde-expand (M-~)
Perform tilde expansion on the current word.
set-mark (C-@)
Set the mark to the point. If a numeric argument is supplied, the mark is set
to that position.
exchange-point-and-mark (C-x C-x)
Swap the point with the mark. The current cursor position is set to the saved
position, and the old cursor position is saved as the mark.
character-search (C-])
A character is read and point is moved to the next occurrence of that character.
A negative count searches for previous occurrences.
character-search-backward (M-C-])
A character is read and point is moved to the previous occurrence of thatcharacter. A negative count searches for subsequent occurrences.
skip-csi-sequence ()Read enough characters to consume a multi-key sequence such as those definedfor keys like Home and End. Such sequences begin with a Control Sequence
Indicator (CSI), usually ESC-[. If this sequence is bound to "\e[", keys producing such sequences will have no effect unless explicitly bound to a readline
command, instead of inserting stray characters into the editing buffer. This isunbound by default, but usually bound to ESC-[.
insert-comment (M-#)
Without a numeric argument, the value of the comment-begin variable is inserted at the beginning of the current line. If a numeric argument is supplied,
this command acts as a toggle: if the characters at the beginning of the line
do not match the value of comment-begin, the value is inserted, otherwise thecharacters in comment-begin are deleted from the beginning of the line. In
either case, the line is accepted as if a newline had been typed.
dump-functions ()Print all of the functions and their key bindings to the Readline output stream.
If a numeric argument is supplied, the output is formatted in such a way thatit can be made part of an inputrc file. This command is unbound by default.
dump-variables ()Print all of the settable variables and their values to the Readline output stream.
If a numeric argument is supplied, the output is formatted in such a way thatit can be made part of an inputrc file. This command is unbound by default.

736

Debugging with gdb

dump-macros ()Print all of the Readline key sequences bound to macros and the strings they
output. If a numeric argument is supplied, the output is formatted in such a
way that it can be made part of an inputrc file. This command is unbound by
default.
emacs-editing-mode (C-e)
When in vi command mode, this causes a switch to emacs editing mode.
vi-editing-mode (M-C-j)
When in emacs editing mode, this causes a switch to vi editing mode.

33.5 Readline vi Mode
While the Readline library does not have a full set of vi editing functions, it does containenough to allow simple editing of the line. The Readline vi mode behaves as specified in
the posix standard.
In order to switch interactively between emacs and vi editing modes, use the command
M-C-j (bound to emacs-editing-mode when in vi mode and to vi-editing-mode in emacsmode). The Readline default is emacs mode.
When you enter a line in vi mode, you are already placed in ‘insertion’ mode, as if you
had typed an ‘i’. Pressing ESC switches you into ‘command’ mode, where you can edit the
text of the line with the standard vi movement keys, move to previous history lines with‘k’ and subsequent lines with ‘j’, and so forth.

737

34 Using History Interactively
This chapter describes how to use the gnu History Library interactively, from a user’s
standpoint. It should be considered a user’s guide. For information on using the gnu
History Library in your own programs, see Section “Programming with GNU History” in
GNU History Library.

34.1 History Expansion
The History library provides a history expansion feature that is similar to the history
expansion provided by csh. This section describes the syntax used to manipulate thehistory information.
History expansions introduce words from the history list into the input stream, making
it easy to repeat commands, insert the arguments to a previous command into the current
input line, or fix errors in previous commands quickly.
History expansion takes place in two parts. The first is to determine which line fromthe history list should be used during substitution. The second is to select portions ofthat line for inclusion into the current one. The line selected from the history is called theevent, and the portions of that line that are acted upon are called words. Various modifiers
are available to manipulate the selected words. The line is broken into words in the same
fashion that Bash does, so that several words surrounded by quotes are considered one word.
History expansions are introduced by the appearance of the history expansion character,which is ‘!’ by default.
History expansion implements shell-like quoting conventions: a backslash can be used toremove the special handling for the next character; single quotes enclose verbatim sequencesof characters, and can be used to inhibit history expansion; and characters enclosed withindouble quotes may be subject to history expansion, since backslash can escape the history
expansion character, but single quotes may not, since they are not treated specially withindouble quotes.

34.1.1 Event Designators
An event designator is a reference to a command line entry in the history list. Unless thereference is absolute, events are relative to the current position in the history list.
!

Start a history substitution, except when followed by a space, tab, the end of
the line, or ‘=’.

!nRefer to command line n.

!-nRefer to the command n lines back.

!!

Refer to the previous command. This is a synonym for ‘!-1’.

!string

Refer to the most recent command preceding the current position in the history
list starting with string.

!?string[?]
Refer to the most recent command preceding the current position in the history
list containing string. The trailing ‘?’ may be omitted if the string is followed
immediately by a newline. If string is missing, the string from the most recent
search is used; it is an error if there is no previous search string.

738

Debugging with gdb^string1^string2^
Quick Substitution. Repeat the last command, replacing string1 with string2.
Equivalent to !!:s^string1^string2^.
The entire command line typed so far.

!#

34.1.2 Word Designators
Word designators are used to select desired words from the event. A ‘:’ separates the event
specification from the word designator. It may be omitted if the word designator begins
with a ‘^’, ‘$’, ‘*’, ‘-’, or ‘%’. Words are numbered from the beginning of the line, with thefirst word being denoted by 0 (zero). Words are inserted into the current line separated bysingle spaces.
For example,!!

designates the preceding command. When you type this, the preceding command is repeated in toto.

!!:$

designates the last argument of the preceding command. This may be shortened
to !$.

!fi:2

designates the second argument of the most recent command starting with theletters fi.

Here are the word designators:
0 (zero)The 0th word. For many applications, this is the command word.

n

The nth word.

^

The first argument; that is, word 1.

$

The last argument.

%

The first word matched by the most recent ‘?string?’ search, if the searchstring begins with a character that is part of a word.

x-y

A range of words; ‘-y’ abbreviates ‘0-y’.

*

All of the words, except the 0th. This is a synonym for ‘1-$’. It is not an error
to use ‘*’ if there is just one word in the event; the empty string is returned inthat case.

x*

Abbreviates ‘x-$’x-

Abbreviates ‘x-$’ like ‘x*’, but omits the last word. If ‘x’ is missing, it defaults
to 0.

If a word designator is supplied without an event specification, the previous commandis used as the event.

34.1.3 Modifiers
After the optional word designator, you can add a sequence of one or more of the following
modifiers, each preceded by a ‘:’. These modify, or edit, the word or words selected fromthe history event.
hRemove a trailing pathname component, leaving only the head.

739

t

Remove all leading pathname components, leaving the tail.

r

Remove a trailing suffix of the form ‘.suffix’, leaving the basename.

eRemove all but the trailing suffix.

pPrint the new command but do not execute it.

s/old/new/
Substitute new for the first occurrence of old in the event line. Any charactermay be used as the delimiter in place of ‘/’. The delimiter may be quoted inold and new with a single backslash. If ‘&’ appears in new, it is replaced byold. A single backslash will quote the ‘&’. If old is null, it is set to the last old
substituted, or, if no previous history substitutions took place, the last string
in a !?string[?] search. If new is is null, each matching old is deleted. The
final delimiter is optional if it is the last character on the input line.
&gaG

Repeat the previous substitution.
Cause changes to be applied over the entire event line. Used in conjunction
with ‘s’, as in gs/old/new/, or with ‘&’.
Apply the following ‘s’ or ‘&’ modifier once to each word in the event.

741

Appendix A In Memoriam
The gdb project mourns the loss of the following long-time contributors:
Fred Fish Fred was a long-standing contributor to gdb (1991-2006), and to Free Software
in general. Outside of gdb, he was known in the Amiga world for his series ofFish Disks, and the GeekGadget project.
Michael Snyder
Michael was one of the Global Maintainers of the gdb project, with contributions recorded as early as 1996, until 2011. In addition to his day to day
participation, he was a large driving force behind adding Reverse Debugging to
gdb.
Beyond their technical contributions to the project, they were also enjoyable membersof the Free Software Community. We will miss them.

743

Appendix B Formatting Documentation
The gdb 4 release includes an already-formatted reference card, ready for printing with
PostScript or Ghostscript, in the gdb subdirectory of the main source directory1 . If you can
use PostScript or Ghostscript with your printer, you can print the reference card immediately with refcard.ps.
The release also includes the source for the reference card. You can format it, using
TEX, by typing:make refcard.dvi

The gdb reference card is designed to print in landscape mode on US “letter” size paper;that is, on a sheet 11 inches wide by 8.5 inches high. You will need to specify this form of
printing as an option to your dvi output program.
All the documentation for gdb comes as part of the machine-readable distribution. The
documentation is written in Texinfo format, which is a documentation system that uses asingle source file to produce both on-line information and a printed manual. You can use
one of the Info formatting commands to create the on-line version of the documentation
and TEX (or texi2roff) to typeset the printed version.
gdb includes an already formatted copy of the on-line Info version of this manual in the
gdb subdirectory. The main Info file is gdb-16.0.50.20241106-git/gdb/gdb.info, andit refers to subordinate files matching ‘gdb.info*’ in the same directory. If necessary, you
can print out these files, or read them with any editor; but they are easier to read using
the info subsystem in gnu Emacs or the standalone info program, available as part of the
gnu Texinfo distribution.
If you want to format these Info files yourself, you need one of the Info formatting
programs, such as texinfo-format-buffer or makeinfo.
If you have makeinfo installed, and are in the top level gdb source directory(gdb-16.0.50.20241106-git, in the case of version 16.0.50.20241106-git), you can makethe Info file by typing:
cd gdbmake gdb.info

If you want to typeset and print copies of this manual, you need TEX, a program to print
its dvi output files, and texinfo.tex, the Texinfo definitions file.
TEX is a typesetting program; it does not print files directly, but produces output files
called dvi files. To print a typeset document, you need a program to print dvi files. If yoursystem has TEX installed, chances are it has such a program. The precise command to use
depends on your system; lpr -d is common; another (for PostScript devices) is dvips. The
dvi print command may require a file name without any extension or a ‘.dvi’ extension.
TEX also requires a macro definitions file called texinfo.tex. This file tells TEX how
to typeset a document written in Texinfo format. On its own, TEX cannot either reador typeset a Texinfo file. texinfo.tex is distributed with GDB and is located in the
gdb-version-number/texinfo directory.
1

In gdb-16.0.50.20241106-git/gdb/refcard.ps of the version 16.0.50.20241106-git release.

744

Debugging with gdb

If you have TEX and a dvi printer program installed, you can typeset and print thismanual. First switch to the gdb subdirectory of the main source directory (for example, to
gdb-16.0.50.20241106-git/gdb) and type:make gdb.dvi

Then give gdb.dvi to your dvi printing program.

745

Appendix C Installing gdb
C.1 Requirements for Building gdb
Building gdb requires various tools and packages to be available. Other packages will be
used only if they are found.

Tools/Packages Necessary for Building gdb
C++17 compiler
gdb is written in C++17. It should be buildable with any recent C++17 compiler,
e.g. GCC.
GNU make
gdb’s build system relies on features only found in the GNU make program.
Other variants of make will not work.
Libraries

The following libraries are mandatory for building gdb. The configure script
searches for each of these libraries in several standard locations; if some library is installed in an unusual place, you can use either the --with-lib
configure option to specify its installation directory, or the two separate options ---with-library-include (to specify the location of its header files) and--with-library-lib (to specify the location of its libraries). For example, for
the GMP library, the 3 options are --with-gmp, --with-gmp-include, and--with-gmp-lib. See Section C.5 [Configure Options], page 749. We mention
below the home site of each library, so that you could download and installthem if your system doesn’t already include them.
GMP (The GNU Multiple Precision arithmetic library)
gdb uses GMP to perform some of its extended-precision arithmetic. The latest version of GMP is available from https: / /gmplib.org/.
MPFR (The GNU Multiple-precision floating-point library)
gdb uses MPFR to emulate the target floating-point arithmetic
during expression evaluation, if the target uses different floatingpoint formats than the host. The latest version of MPFR is available from http://www.mpfr.org.

Tools/Packages Optional for Building gdb
The tools/packages and libraries listed below are optional; gdb can be build without them,at the expense of some run-time functionality that will be missing. As above, we list
the home sites for each package/library, and the command-line options supported by theconfigure script to specify their installation directories if they are non-standard. In addition, for each package you can use the option --with-package to force gdb to be compiled
with the named package, and --without-package to disable building with it even if it isavailable. See Section C.5 [Configure Options], page 749, for detailed description of theoptions to configure.

746

Debugging with gdb

Pythongdb can be scripted using Python language. See Section 23.3 [Python],page 401. The latest version is available from https: / / www . python . org /downloads / . Use the --with-python=dir to specify the non-standard
directory where Python is installed.

Guile

gdb can also be scripted using GNU Guile. See Section 23.4 [Guile], page 519.
The latest version can be found on https://www.gnu.org/software/guile/
download / . If you have more than one version of Guile installed, use the--with-guile=guile-version to specify the Guile version to include in thebuild.

Expat

If available, gdb uses the Expat library for parsing XML files. gdb uses XML
files for the following functionalities:• Remote protocol memory maps (see Section E.17 [Memory Map Format],page 843)• Target descriptions (see Appendix G [Target Descriptions], page 859)
• Remote shared library lists (See Section E.15 [Library List Format],page 841, or alternatively see Section E.16 [Library List Format for SVR4
Targets], page 842)
• MS-Windows shared libraries (see [Shared Libraries], page 296)
• Traceframe info (see Section E.19 [Traceframe Info Format], page 845)
• Branch trace (see Section E.20 [Branch Trace Format], page 845, see
Section E.21 [Branch Trace Configuration Format], page 846)
The latest version of Expat is available from http://expat.sourceforge.net.
Use the --with-libexpat-prefix to specify non-standard installation places
for Expat.

iconv

gdb’s features related to character sets (see Section 10.21 [Character Sets],page 187) require a functioning iconv implementation. If you are on a GNU
system, then this is provided by the GNU C Library. Some other systems also
provide a working iconv. Use the option --with-iconv-bin to specify whereto find the iconv program.
On systems without iconv, you can install the GNU Libiconv library; its latest version can be found on https://ftp.gnu.org/pub/gnu/libiconv/ ifyour system doesn’t provide it. Use the --with-libiconv-prefix option toconfigure to specify non-standard installation place for it.
Alternatively, gdb’s top-level configure and Makefile will arrange to build
Libiconv if a directory named libiconv appears in the top-most source directory. If Libiconv is built this way, and if the operating system does not provide
a suitable iconv implementation, then the just-built library will automaticallybe used by gdb. One easy way to set this up is to download GNU Libiconv,
unpack it inside the top-level directory of the gdb source tree, and then rename
the directory holding the Libiconv source code to ‘libiconv’.

lzma

gdb can support debugging sections that are compressed with the LZMA library. See Section 18.4 [MiniDebugInfo], page 304. If this library is not included
with your operating system, you can find it in the xz package at http: / /Appendix C: Installing gdb

747

tukaani . org / xz / . Use the --with-liblzma-prefix option to specify its
non-standard location.
zlib

gdb will use the ‘zlib’ library, if available, to read compressed debug sections.
Some linkers, such as GNU gold, are capable of producing binaries with compressed debug sections. If gdb is compiled with ‘zlib’, it will be able to readthe debug information in such binaries.
The ‘zlib’ library is likely included with your operating system distribution; if
it is not, you can get the latest version from http://zlib.net.

C.2 Invoking the gdb configure Script
gdb comes with a configure script that automates the process of preparing gdb for installation; you can then use make to build the gdb program.1
The gdb distribution includes all the source code you need for gdb in a single directory,
whose name is usually composed by appending the version number to ‘gdb’.
For example, the gdb version 16.0.50.20241106-git distribution is in the
gdb-16.0.50.20241106-git directory. That directory contains:
gdb-16.0.50.20241106-git/configure (and supporting files)
script for configuring gdb and all its supporting libraries
gdb-16.0.50.20241106-git/gdb
the source specific to gdb itself
gdb-16.0.50.20241106-git/bfd
source for the Binary File Descriptor library
gdb-16.0.50.20241106-git/include
gnu include files
gdb-16.0.50.20241106-git/libiberty
source for the ‘-liberty’ free software library
gdb-16.0.50.20241106-git/opcodessource for the library of opcode tables and disassemblers
gdb-16.0.50.20241106-git/readline
source for the gnu command-line interface
There may be other subdirectories as well.
The simplest way to configure and build gdb is to run configure from the gdb-versionnumber source directory, which in this example is the gdb-16.0.50.20241106-git directory.
First switch to the gdb-version-number source directory if you are not already in it;then run configure. Pass the identifier for the platform on which gdb will run as anargument.
For example:
cd gdb-16.0.50.20241106-git
1

If you have a more recent version of gdb than 16.0.50.20241106-git, look at the README file in the sources;
we may have improved the installation procedures since publishing this manual.

748

Debugging with gdb./configuremake

Running ‘configure’ and then running make builds the included supporting libraries,
then gdb itself. The configured source files, and the binaries, are left in the corresponding
source directories.
configure is a Bourne-shell (/bin/sh) script; if your system does not recognize thisautomatically when you run a different shell, you may need to run sh on it explicitly:
sh configure

You should run the configure script from the top directory in the source tree, thegdb-version-number directory. If you run configure from one of the subdirectories, youwill configure only that subdirectory. That is usually not what you want. In particular, if
you run the first configure from the gdb subdirectory of the gdb-version-number directory, you will omit the configuration of bfd, readline, and other sibling directories of the
gdb subdirectory. This leads to build errors about missing include files such as bfd/bfd.h.
You can install gdb anywhere. The best way to do this is to pass the --prefix option
to configure, and then install it with make install.

C.3 Compiling gdb in Another Directory
If you want to run gdb versions for several host or target machines, you need a different
gdb compiled for each combination of host and target. configure is designed to make thiseasy by allowing you to generate each configuration in a separate subdirectory, rather thanin the source directory. If your make program handles the ‘VPATH’ feature (gnu make does),running make in each of these directories builds the gdb program specified there.
To build gdb in a separate directory, run configure with the ‘--srcdir’ option to
specify where to find the source. (You also need to specify a path to find configure itself
from your working directory. If the path to configure would be the same as the argumentto ‘--srcdir’, you can leave out the ‘--srcdir’ option; it is assumed.)For example, with version 16.0.50.20241106-git, you can build gdb in a separate directory
for a Sun 4 like this:cd gdb-16.0.50.20241106-git
mkdir ../gdb-sun4
cd ../gdb-sun4../gdb-16.0.50.20241106-git/configure
makeWhen configure builds a configuration using a remote source directory, it creates a tree
for the binaries with the same structure (and using the same names) as the tree under thesource directory. In the example, you’d find the Sun 4 library libiberty.a in the directory
gdb-sun4/libiberty, and gdb itself in gdb-sun4/gdb.
Make sure that your path to the configure script has just one instance of gdb in it. If
your path to configure looks like ../gdb-16.0.50.20241106-git/gdb/configure, you
are configuring only one subdirectory of gdb, not the whole package. This leads to build
errors about missing include files such as bfd/bfd.h.
One popular reason to build several gdb configurations in separate directories is to configure gdb for cross-compiling (where gdb runs on one machine—the host—while debugging

Appendix C: Installing gdb

749

programs that run on another machine—the target). You specify a cross-debugging target
by giving the ‘--target=target’ option to configure.
When you run make to build a program or library, you must run it in a configured
directory—whatever directory you were in when you called configure (or one of its subdirectories).
The Makefile that configure generates in each source directory also runs recursively. If
you type make in a source directory such as gdb-16.0.50.20241106-git (or in a separate
configured directory configured with ‘--srcdir=dirname/gdb-16.0.50.20241106-git’),
you will build all the required libraries, and then build GDB.
When you have multiple hosts or targets configured in separate directories, you can run
make on them in parallel (for example, if they are NFS-mounted on each of the hosts); they
will not interfere with each other.

C.4 Specifying Names for Hosts and Targets
The specifications used for hosts and targets in the configure script are based on a threepart naming scheme, but some short predefined aliases are also supported. The full naming
scheme encodes three pieces of information in the following pattern:architecture-vendor-os

For example, you can use the alias sun4 as a host argument, or as the value for target
in a --target=target option. The equivalent full name is ‘sparc-sun-sunos4’.
The configure script accompanying gdb does not provide any query facility to list
all supported host and target names or aliases. configure calls the Bourne shell script
config.sub to map abbreviations to full names; you can read the script, if you wish, or
you can use it to test your guesses on abbreviations—for example:% sh config.sub i386-linux
i386-pc-linux-gnu% sh config.sub alpha-linux
alpha-unknown-linux-gnu% sh config.sub hp9k700
hppa1.1-hp-hpux% sh config.sub sun4
sparc-sun-sunos4.1.1% sh config.sub sun3
m68k-sun-sunos4.1.1% sh config.sub i986v
Invalid configuration ‘i986v’: machine ‘i986v’ not recognizedconfig.sub is also distributed in the gdb source directory (gdb-16.0.50.20241106-git,
for version 16.0.50.20241106-git).

C.5 configure Options
Here is a summary of the configure options and arguments that are most often usefulfor building gdb. configure also has several other options not listed here. See Section“Running configure Scripts” in autoconf, for a full explanation of configure.
configure [--help][--prefix=dir][--exec-prefix=dir][--srcdir=dirname]

750

Debugging with gdb[--target=target]

You may introduce options with a single ‘-’ rather than ‘--’ if you prefer; but you may
abbreviate option names if you use ‘--’.
--help

Display a quick summary of how to invoke configure.

--prefix=dir
Configure the source to install programs and files under directory dir.
--exec-prefix=dir
Configure the source to install programs under directory dir.
--srcdir=dirname
Use this option to make configurations in directories separate from the gdb
source directories. Among other things, you can use this to build (or maintain)
several configurations simultaneously, in separate directories. configure writes
configuration-specific files in the current directory, but arranges for them to use
the source in the directory dirname. configure creates directories under theworking directory in parallel to the source directories below dirname.
--target=target
Configure gdb for cross-debugging programs running on the specified target.
Without this option, gdb is configured to debug programs that run on the samemachine (host) as gdb itself.
There is no convenient way to generate a list of all available targets. Also see
the --enable-targets option, below.
There are many other options that are specific to gdb. This lists just the most common
ones; there are some very specialized options not described here.
--enable-targets=[target]...
--enable-targets=all
Configure gdb for cross-debugging programs running on the specified list oftargets. The special value ‘all’ configures gdb for debugging programs runningon any target it supports.
--with-gdb-datadir=path
Set the gdb-specific data directory. gdb will look here for certain supporting
files or scripts. This defaults to the gdb subdirectory of ‘datadir’ (which canbe set using --datadir).
--with-relocated-sources=dir
Sets up the default source path substitution rule so that directory names
recorded in debug information will be automatically adjusted for any directoryunder dir. dir should be a subdirectory of gdb’s configured prefix, the one
mentioned in the --prefix or --exec-prefix options to configure. This
option is useful if GDB is supposed to be moved to a different place after it isbuilt.
--enable-64-bit-bfd
Enable 64-bit support in BFD on 32-bit hosts.

Appendix C: Installing gdb

751--disable-gdbmi
Build gdb without the GDB/MI machine interface (see Chapter 27 [GDB/MI],page 589).
--enable-tui
Build gdb with the text-mode full-screen user interface (TUI). Requires a curses
library (ncurses and cursesX are also supported).
--with-curses
Use the curses library instead of the termcap library, for text-mode terminal
operations.
--with-debuginfod
Build gdb with libdebuginfod, the debuginfod client library. Used toautomatically fetch ELF, DWARF and source files from debuginfod servers
using build IDs associated with any missing files. Enabled by default if
libdebuginfod is installed and found at configure time. For more information
regarding debuginfod see Appendix K [Debuginfod], page 887.
--with-libunwind-ia64
Use the libunwind library for unwinding function call stack on ia64 target platforms. See http://www.nongnu.org/libunwind/index.html for details.
--with-system-readline
Use the readline library installed on the host, rather than the library supplied
as part of gdb. Readline 7 or newer is required; this is enforced by the build
system.
--with-system-zlib
Use the zlib library installed on the host, rather than the library supplied aspart of gdb.
--with-expat
Build gdb with Expat, a library for XML parsing. (Done by default if libexpat
is installed and found at configure time.) This library is used to read XML files
supplied with gdb. If it is unavailable, some features, such as remote protocol
memory maps, target descriptions, and shared library lists, that are based on
XML files, will not be available in gdb. If your host does not have libexpat
installed, you can get the latest version from http://expat.sourceforge.
net.
--with-libiconv-prefix[=dir]
Build gdb with GNU libiconv, a character set encoding conversion library. This
is not done by default, as on GNU systems the iconv that is built in to the
C library is sufficient. If your host does not have a working iconv, you can
get the latest version of GNU iconv from https://www.gnu.org/software/
libiconv/.
gdb’s build system also supports building GNU libiconv as part of the overallbuild. See Section C.1 [Requirements], page 745.
--with-lzma
Build gdb with LZMA, a compression library. (Done by default if liblzma is installed and found at configure time.) LZMA is used by gdb’s "mini debuginfo"

752

Debugging with gdb

feature, which is only useful on platforms using the ELF object file format. If
your host does not have liblzma installed, you can get the latest version fromhttps://tukaani.org/xz/.
--with-python[=python]
Build gdb with Python scripting support. (Done by default if libpython ispresent and found at configure time.) Python makes gdb scripting much more
powerful than the restricted CLI scripting language. If your host does not have
Python installed, you can find it on http://www.python.org/download/. The
oldest version of Python supported by GDB is 3.0.1. The optional argument
python is used to find the Python headers and libraries. It can be either thename of a Python executable, or the name of the directory in which Python is
installed.
--with-guile[=guile]
Build gdb with GNU Guile scripting support. (Done by default if libguile ispresent and found at configure time.) If your host does not have Guile installed,
you can find it at https://www.gnu.org/software/guile/. The optional
argument guile can be a version number, which will cause configure to try to
use that version of Guile; or the file name of a pkg-config executable, which
will be queried to find the information needed to compile and link against Guile.
--without-included-regex
Don’t use the regex library included with gdb (as part of the libiberty library).
This is the default on hosts with version 2 of the GNU C library.
--with-sysroot=dir
Use dir as the default system root directory for libraries whose file names begin
with /lib’ or /usr/lib’. (The value of dir can be modified at run time byusing the set sysroot command.) If dir is under the gdb configured prefix(set with --prefix or --exec-prefix options, the default system root will
be automatically adjusted if and when gdb is moved to a different location.
--with-system-gdbinit=fileConfigure gdb to automatically load a system-wide init file. file should be an
absolute file name. If file is in a directory under the configured prefix, and gdb
is moved to another location after being built, the location of the system-wide
init file will be adjusted accordingly.
--with-system-gdbinit-dir=directory
Configure gdb to automatically load init files from a system-wide directory.
directory should be an absolute directory name. If directory is in a directoryunder the configured prefix, and gdb is moved to another location after being
built, the location of the system-wide init directory will be adjusted accordingly.
--enable-build-warnings
When building the gdb sources, ask the compiler to warn about any code whichlooks even vaguely suspicious. It passes many different warning flags, dependingon the exact version of the compiler you are using.

Appendix C: Installing gdb

753--enable-werror
Treat compiler warnings as errors. It adds the -Werror flag to the compiler,
which will fail the compilation if the compiler outputs any warning messages.
--enable-ubsan
Enable the GCC undefined behavior sanitizer. This is disabled by default,
but passing --enable-ubsan=yes or --enable-ubsan=auto to configure will
enable it. The undefined behavior sanitizer checks for C++ undefined behavior.
It has a performance cost, so if you are looking at gdb’s performance, you should
disable it. The undefined behavior sanitizer was first introduced in GCC 4.9.

C.6 System-wide configuration and settings
gdb can be configured to have a system-wide init file and a system-wide init file directory;
this file and files in that directory (if they have a recognized file extension) will be read andexecuted at startup (see Section 2.1.3 [What gdb does during startup], page 16).
Here are the corresponding configure options:--with-system-gdbinit=file
Specify that the default location of the system-wide init file is file.
--with-system-gdbinit-dir=directorySpecify that the default location of the system-wide init file directory is
directory.
If gdb has been configured with the option --prefix=$prefix, they may be subject torelocation. Two possible cases:• If the default location of this init file/directory contains $prefix, it will be subject to relocation. Suppose that the configure options are --prefix=$prefix --with-systemgdbinit=$prefix/etc/gdbinit; if gdb is moved from $prefix to $install, the system init file is looked for as $install/etc/gdbinit instead of $prefix/etc/gdbinit.
• By contrast, if the default location does not contain the prefix, it will not
be relocated.
E.g. if gdb has been configured with --prefix=/usr/local--with-system-gdbinit=/usr/share/gdb/gdbinit, then gdb will always look for/usr/share/gdb/gdbinit, wherever gdb is installed.
If the configured location of the system-wide init file (as given by the --with-systemgdbinit option at configure time) is in the data-directory (as specified by --with-gdbdatadir at configure time) or in one of its subdirectories, then gdb will look for the systemwide init file in the directory specified by the --data-directory command-line option.
Note that the system-wide init file is only read once, during gdb initialization. If the datadirectory is changed after gdb has started with the set data-directory command, thefile will not be reread.
This applies similarly to the system-wide directory specified in --with-systemgdbinit-dir.
Any supported scripting language can be used for these init files, as long as the fileextension matches the scripting language. To be interpreted as regular gdb commands, thefiles needs to have a .gdb extension.

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C.6.1 Installed System-wide Configuration Scripts
The system-gdbinit directory, located inside the data-directory (as specified by --withgdb-datadir at configure time) contains a number of scripts which can be used as systemwide init files. To automatically source those scripts at startup, gdb should be configured
with --with-system-gdbinit. Otherwise, any user should be able to source them by handas needed.
The following scripts are currently available:• elinos.py This script is useful when debugging a program on an ELinOS target. It
takes advantage of the environment variables defined in a standard ELinOS environment in order to determine the location of the system shared libraries, and then setsthe ‘solib-absolute-prefix’ and ‘solib-search-path’ variables appropriately.
• wrs-linux.py This script is useful when debugging a program on a target runningWind River Linux. It expects the ENV_PREFIX to be set to the host-side sysroot usedby the target system.

755

Appendix D Maintenance Commands
In addition to commands intended for gdb users, gdb includes a number of commands
intended for gdb developers, that are not documented elsewhere in this manual. These
commands are provided here for reference. (For commands that turn on debugging messages, see Section 22.10 [Debugging Output], page 382.)
maint agent [-at linespec,] expression
maint agent-eval [-at linespec,] expression
Translate the given expression into remote agent bytecodes. This command isuseful for debugging the Agent Expression mechanism (see Appendix F [Agent
Expressions], page 847). The ‘agent’ version produces an expression usefulfor data collection, such as by tracepoints, while ‘maint agent-eval’ produces
an expression that evaluates directly to a result. For instance, a collection
expression for globa + globb will include bytecodes to record four bytes ofmemory at each of the addresses of globa and globb, while discarding the resultof the addition, while an evaluation expression will do the addition and returnthe sum. If -at is given, generate remote agent bytecode for all the addresses
to which linespec resolves (see Section 9.2.1 [Linespec Locations], page 127). If
not, generate remote agent bytecode for current frame PC address.
maint agent-printf format,expr,...
Translate the given format string and list of argument expressions into remote
agent bytecodes and display them as a disassembled list. This command isuseful for debugging the agent version of dynamic printf (see Section 5.1.8[Dynamic Printf], page 79).
maint info breakpoints
Using the same format as ‘info breakpoints’, display both the breakpoints
you’ve set explicitly, and those gdb is using for internal purposes. Internal
breakpoints are shown with negative breakpoint numbers. The type column
identifies what kind of breakpoint is shown:breakpoint
Normal, explicitly set breakpoint.
watchpoint
Normal, explicitly set watchpoint.
longjmpInternal breakpoint, used to handle correctly stepping throughlongjmp calls.

longjmp resume
Internal breakpoint at the target of a longjmp.
until

Temporary internal breakpoint used by the gdb until command.

finishTemporary internal breakpoint used by the gdb finish command.

shlib events
Shared library events.
maint info btrace
Pint information about raw branch tracing data.

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maint btrace packet-history
Print the raw branch trace packets that are used to compute the execution
history for the ‘record btrace’ command. Both the information and the format
in which it is printed depend on the btrace recording format.
bts

For the BTS recording format, print a list of blocks of sequentialcode. For each block, the following information is printed:
Block number
Newer blocks have higher numbers. The oldest block
has number zero.
Lowest ‘PC’
Highest ‘PC’pt

For the Intel Processor Trace recording format, print a list of Intel
Processor Trace packets. For each packet, the following information
is printed:
Packet number
Newer packets have higher numbers. The oldest packet
has number zero.
Trace offset
The packet’s offset in the trace stream.
Packet opcode and payload

maint btrace clear-packet-history
Discards the cached packet history printed by the ‘maint btrace
packet-history’ command. The history will be computed again whenneeded.
maint btrace clear
Discard the branch trace data. The data will be fetched anew and the branch
trace will be recomputed when needed.
This implicitly truncates the branch trace to a single branch trace buffer. When
updating branch trace incrementally, the branch trace available to gdb may bebigger than a single branch trace buffer.
maint set btrace pt skip-pad
maint show btrace pt skip-pad
Control whether gdb will skip PAD packets when computing the packet history.
maint info jit
Print information about JIT code objects loaded in the current inferior.
maint info python-disassemblers
This command is defined within the gdb.disassembler Python module (seeSection 23.3.2.40 [Disassembly In Python], page 502), and will only be present
after that module has been imported. To force the module to be imported do
the following:Appendix D: Maintenance Commands

757

maint info linux-lwps
Print information about LWPs under control of the Linux native target.
(gdb) python import gdb.disassembler

This command lists all the architectures for which a disassembler is currently
registered, and the name of the disassembler. If a disassembler is registered for
all architectures, then this is listed last against the ‘GLOBAL’ architecture.
If one of the disassemblers would be selected for the architecture of the current
inferior, then this disassembler will be marked.
The following example shows a situation in which two disassemblers are registered, initially the ‘i386’ disassembler matches the current architecture, thenthe architecture is changed, now the ‘GLOBAL’ disassembler matches.
(gdb) show architecture
The target architecture is set to "auto" (currently "i386").
(gdb) maint info python-disassemblers
Architecture
Disassember Name
i386
Disassembler_1 (Matches current architecture)
GLOBAL
Disassembler_2(gdb) set architecture arm
The target architecture is set to "arm".
(gdb) maint info python-disassemblers
quit
Architecture
Disassember Name
i386
Disassembler_1
GLOBAL
Disassembler_2 (Matches current architecture)

set displaced-steppingshow displaced-stepping
Control whether or not gdb will do displaced stepping if the target supports it.
Displaced stepping is a way to single-step over breakpoints without removing
them from the inferior, by executing an out-of-line copy of the instruction thatwas originally at the breakpoint location. It is also known as out-of-line singlestepping.
set displaced-stepping on
If the target architecture supports it, gdb will use displaced stepping to step over breakpoints.
set displaced-stepping off
gdb will not use displaced stepping to step over breakpoints, evenif such is supported by the target architecture.
set displaced-stepping auto
This is the default mode. gdb will use displaced stepping only
if non-stop mode is active (see Section 5.5.2 [Non-Stop Mode],
page 94) and the target architecture supports displaced stepping.
maint check-psymtabs
Check the consistency of currently expanded psymtabs versus symtabs. Use
this to check, for example, whether a symbol is in one but not the other.
maint check-symtabs
Check the consistency of currently expanded symtabs.

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maint expand-symtabs [regexp]
Expand symbol tables. If regexp is specified, only expand symbol tables for filenames matching regexp.
maint set catch-demangler-crashes [on|off]
maint show catch-demangler-crashes
Control whether gdb should attempt to catch crashes in the symbol namedemangler. The default is to attempt to catch crashes. If enabled, the firsttime a crash is caught, a core file is created, the offending symbol is displayed
and the user is presented with the option to terminate the current session.
maint cplus first_component namePrint the first C++ class/namespace component of name.
maint cplus namespace
Print the list of possible C++ namespaces.
maint deprecate command [replacement]
maint undeprecate command
Deprecate or undeprecate the named command. Deprecated commands cause
gdb to issue a warning when you use them. The optional argument replacement
says which newer command should be used in favor of the deprecated one; if it
is given, gdb will mention the replacement as part of the warning.
maint dump-me
Cause a fatal signal in the debugger and force it to dump its core. This is
supported only on systems which support aborting a program with the SIGQUIT
signal.
maint internal-error [message-text]
maint internal-warning [message-text]
maint demangler-warning [message-text]
Cause gdb to call the internal function internal_error, internal_warningor demangler_warning and hence behave as though an internal problem has
been detected. In addition to reporting the internal problem, these functions
give the user the opportunity to either quit gdb or (for internal_error andinternal_warning) create a core file of the current gdb session.
These commands take an optional parameter message-text that is used as the
text of the error or warning message.
Here’s an example of using internal-error:(gdb) maint internal-error testing, 1, 2.../maint.c:121: internal-error: testing, 1, 2
A problem internal to GDB has been detected. Further
debugging may prove unreliable.
Quit this debugging session? (y or n) n
Create a core file? (y or n) n
(gdb)

Appendix D: Maintenance Commands

759

maint set debuginfod download-sections
maint set debuginfod download-sections [on|off]
maint show debuginfod download-sections
Controls whether gdb will attempt to download individual ELF/DWARF sections from debuginfod. If disabled, only whole debug info files will be downloaded; this could result in gdb downloading larger amounts of data.
maint set internal-error action [ask|yes|no]maint show internal-error action
maint set internal-warning action [ask|yes|no]maint show internal-warning action
maint set demangler-warning action [ask|yes|no]maint show demangler-warning action
When gdb reports an internal problem (error or warning) it gives the user theopportunity to both quit gdb and create a core file of the current gdb session.
These commands let you override the default behaviour for each particularaction, described in the table below.
‘quit’

You can specify that gdb should always (yes) or never (no) quit.
The default is to ask the user what to do.

‘corefile’
You can specify that gdb should always (yes) or never (no) createa core file. The default is to ask the user what to do. Note that
there is no corefile option for demangler-warning: demangler
warnings always create a core file and this cannot be disabled.
maint set internal-error backtrace [on|off]
maint show internal-error backtrace
maint set internal-warning backtrace [on|off]
maint show internal-warning backtrace
When gdb reports an internal problem (error or warning) it is possible to havea backtrace of gdb printed to the standard error stream. This is ‘on’ by default
for internal-error and ‘off’ by default for internal-warning.
maint packet text
If gdb is talking to an inferior via the serial protocol, then this command sends
the string text to the inferior, and displays the response packet. gdb supplies
the initial ‘$’ character, the terminating ‘#’ character, and the checksum.
Any non-printable characters in the reply are printed as escaped hex, e.g.
‘\x00’, ‘\x01’, etc.
maint print architecture [file]
Print the entire architecture configuration. The optional argument file names
the file where the output goes.
maint print c-tdesc [-single-feature] [file]
Print the target description (see Appendix G [Target Descriptions], page 859)
as a C source file. By default, the target description is for the current target,
but if the optional argument file is provided, that file is used to produce thedescription. The file should be an XML document, of the form described in

760

Debugging with gdb

Section G.2 [Target Description Format], page 859. The created source file isbuilt into gdb when gdb is built again. This command is used by developers
after they add or modify XML target descriptions.
When the optional flag ‘-single-feature’ is provided then the target description being processed (either the default, or from file) must only contain a single
feature. The source file produced is different in this case.
The file argument supports escaping and quoting, see Section 3.4 [Filenames
As Command Arguments], page 27.
maint print xml-tdesc [file]
Print the target description (see Appendix G [Target Descriptions], page 859) as
an XML file. By default print the target description for the current target, but
if the optional argument file is provided, then that file is read in by GDB andthen used to produce the description. The file should be an XML document,of the form described in Section G.2 [Target Description Format], page 859.
maint check xml-descriptions dir
Check that the target descriptions dynamically created by gdb equal the descriptions created from XML files found in dir.
maint check libthread-db
Run integrity checks on the current inferior’s thread debugging library. This
exercises all libthread_db functionality used by gdb on GNU/Linux systems,
and by extension also exercises the proc_service functions provided by gdb
that libthread_db uses. Note that parts of the test may be skipped on some
platforms when debugging core files.
maint print core-file-backed-mappings
Print the file-backed mappings which were loaded from a core file note. This
output represents state internal to gdb and should be similar to the mappings
displayed by the info proc mappings command.
maint print dummy-frames
Prints the contents of gdb’s internal dummy-frame stack.
(gdb) b add...
(gdb) print add(2,3)
Breakpoint 2, add (a=2, b=3) at ...
58
return (a + b);
The program being debugged stopped while in a function called from GDB.
...
(gdb) maint print dummy-frames
0xa8206d8: id={stack=0xbfffe734,code=0xbfffe73f,!special}, ptid=process 9353
(gdb)

Takes an optional file parameter.
maint print frame-id
maint print frame-id level
Print gdb’s internal frame-id for the frame at relative level, or for the currently
selected frame when level is not given.
If used, level should be an integer, as displayed in the backtrace output.
(gdb) maint print frame-id

Appendix D: Maintenance Commands

761

frame-id for frame #0: {stack=0x7fffffffac70,code=0x0000000000401106,!special}(gdb) maint print frame-id 2
frame-id for frame #2: {stack=0x7fffffffac90,code=0x000000000040111c,!special}

maint info inline-frames
maint info inline-frames address
Print information about inlined frames which start at the current address, oraddress if specified.
In order to allow the user to correctly step into inlined functions, gdb needs
to identify which inlined functions start at a particular address, and gdb also
needs to track which of these functions was last displayed to the user as thecurrent frame.
Imagine a situation where function main calls foo, which then calls bar, something like this:intmain (){/* Some interesting code here...

*/foo ();/* More interesting code here... */}void
foo (){bar ();}voidbar (){/* Some interesting code here...
}*/As both foo and bar are inlined within main then there could be one address
within main which is also the start of foo and also the start of bar. When theuser stops at this address they will initially be told the inferior is in main, if theuser does a step then gdb doesn’t actually step the inferior, instead the user
is told the inferior entered foo. After the next step the user is told the inferior
entered bar. The maint info inline-frames command can be used to view
this internal gdb state, like this:(gdb) step24
foo ();(gdb) maintenance info inline-frames
Cached inline state information for thread 1.
program counter = 0x401137
skipped frames = 2barfoo> mainHere the user is stopped in main at the call to foo. The inline-frames information shows that at this address gdb has found the start of inlined functions

762

Debugging with gdb

bar and foo, but currently gdb has skipped 2 frames and considers main to be
the current frame, this is indicated with the ‘>’.
If the user performs a step to enter foo then the situation is updated:(gdb) stepfoo () at inline.c:14
14bar ();(gdb) maintenance info inline-frames
Cached inline state information for thread 1.
program counter = 0x401137
skipped frames = 1
bar
> foo
main

Notice that the program counter value 0x401137 hasn’t change, but now gdb
considers foo to be the current frame, and it is marked as such with the ‘>’.
Finally, the user performs another step to enter bar:(gdb) stepbar () at inline.c:6
6++global_counter;(gdb) maintenance info inline-frames
Cached inline state information for thread 1.
program counter = 0x401137
skipped frames = 0
> bar
foo
main

maint info blocks
maint info blocks address
Print information about all blocks at address, or at the current $pc if address
is not given.
For information about what blocks are in gdb see Section 23.3.2.29 [Blocks In
Python], page 482.
Blocks are listed starting from the global block, then the static block, and thenproceeding through progressively narrower scopes.
Here is an example of the command’s output:(gdb) maintenance info blocks
Blocks at 0x401137:
from objfile: [(objfile *) 0x50507d0] /tmp/inline_func_demo[(block *) 0x504da90] 0x401106..0x40119a
entry pc: 0x401106
is global block
symbol count: 2
is contiguous[(block *) 0x504d9f0] 0x401106..0x40119a
entry pc: 0x401106
is static block
symbol count: 1
is contiguous[(block *) 0x504d9a0] 0x401106..0x40119a
entry pc: 0x401106
function: main
is contiguousAppendix D: Maintenance Commands

763[(block *) 0x504d900] 0x401137..0x401166
entry pc: 0x401137
inline function: foo
symbol count: 1
is contiguous[(block *) 0x504d860] 0x401137..0x401165
entry pc: 0x401137
inline function: bar
symbol count: 1
is contiguous

The command maint info blocks lists the symbol count for each block but
doesn’t print the symbols themselves. The symbol names can be found using
maint print symbols (see [maint print symbols], page 273).
maint print registers [file]maint print raw-registers [file]maint print cooked-registers [file]maint print register-groups [file]maint print remote-registers [file]
Print gdb’s internal register data structures.
The command maint print raw-registers includes the contents of the raw
register cache; the command maint print cooked-registers includes the(cooked) value of all registers, including registers which aren’t available on
the target nor visible to user; the command maint print register-groups
includes the groups that each register is a member of; and the command
maint print remote-registers includes the remote target’s register numbers
and offsets in the ‘G’ packets, as well as an indication of which registers were
included in the last stop reply packet received by gdb (see Section E.4 [StopReply Packets], page 785). Please note that the list of registers included in astop reply can change from one stop to the next.
These commands take an optional parameter, a file name to which to write theinformation.
maint print reggroups [file]
Print gdb’s internal register group data structures. The optional argument filetells to what file to write the information.
The register groups info looks like this:(gdb) maint print reggroups
Group
Type
general
user
float
user
all
user
vectoruser
systemuser
saveinternal
restoreinternal

maint flush register-cache
flushregs
Flush the contents of the register cache and as a consequence the frame cache.
This command is useful when debugging issues related to register fetching, or764

Debugging with gdb

frame unwinding. The command flushregs is deprecated in favor of maintflush register-cache.
maint flush source-cache
Flush gdb’s cache of source code file contents. After gdb reads a source file,and optionally applies styling (see Section 22.5 [Output Styling], page 371), thefile contents are cached. This command clears that cache. The next time gdb
wants to show lines from a source file, the content will be re-read.
This command is useful when debugging issues related to source code styling.
After flushing the cache any source code displayed by gdb will be re-read andre-styled.
maint print objfiles [regexp]
Print a dump of all known object files. If regexp is specified, only print object
files whose names match regexp. For each object file, this command prints its
name, address in memory, and all of its psymtabs and symtabs.
maint print user-registers
List all currently available user registers. User registers typically provide alternate names for actual hardware registers. They include the four “standard”
registers $fp, $pc, $sp, and $ps. See [standard registers], page 179. User
registers can be used in expressions in the same way as the canonical registernames, but only the latter are listed by the info registers and maint print
registers commands.
maint print section-scripts [regexp]
Print a dump of scripts specified in the .debug_gdb_section section. If regexp
is specified, only print scripts loaded by object files matching regexp. For eachscript, this command prints its name as specified in the objfile, and the fullpath if known. See Section 23.5.2 [dotdebug gdb scripts section], page 573.
maint print statistics
This command prints, for each object file in the program, various data aboutthat object file followed by the byte cache (bcache) statistics for the object
file. The objfile data includes the number of minimal, partial, full, and stabs
symbols, the number of types defined by the objfile, the number of as yet
unexpanded psym tables, the number of line tables and string tables, and theamount of memory used by the various tables. The bcache statistics include thecounts, sizes, and counts of duplicates of all and unique objects, max, average,
and median entry size, total memory used and its overhead and savings, andvarious measures of the hash table size and chain lengths.
maint print target-stack
A target is an interface between the debugger and a particular kind of file orprocess. Targets can be stacked in strata, so that more than one target canpotentially respond to a request. In particular, memory accesses will walk down
the stack of targets until they find a target that is interested in handling thatparticular address.
This command prints a short description of each layer that was pushed on thetarget stack, starting from the top layer down to the bottom one.

Appendix D: Maintenance Commands

765

maint print type expr
Print the type chain for a type specified by expr. The argument can be either atype name or a symbol. If it is a symbol, the type of that symbol is described.
The type chain produced by this command is a recursive definition of the data
type as stored in gdb’s data structures, including its flags and contained types.
maint print record-instruction
maint print record-instruction N
print how GDB recorded a given instruction. If n is not positive number, it
prints the values stored by the inferior before the n-th previous instruction was
executed. If n is positive, print the values after the n-th following instruction
is executed. If n is not given, 0 is assumed.
maint selftest [-verbose] [filter]
Run any self tests that were compiled in to gdb. This will print a message
showing how many tests were run, and how many failed. If a filter is passed,
only the tests with filter in their name will be ran. If -verbose is passed, theself tests can be more verbose.
maint set selftest verbose
maint show selftest verbose
Control whether self tests are run verbosely or not.
maint info selftests
List the selftests compiled in to gdb.
maint set dwarf always-disassemble
maint show dwarf always-disassemble
Control the behavior of info address when using DWARF debugging information.
The default is off, which means that gdb should try to describe a variable’s
location in an easily readable format. When on, gdb will instead display the
DWARF location expression in an assembly-like format. Note that some locations are too complex for gdb to describe simply; in this case you will always
see the disassembly form.
Here is an example of the resulting disassembly:(gdb) info addr argc
Symbol "argc" is a complex DWARF expression:
1: DW_OP_fbreg 0

For more information on these expressions, see the DWARF standard (http://
www.dwarfstd.org/).
maint set dwarf max-cache-age
maint show dwarf max-cache-age
Control the DWARF compilation unit cache.
In object files with inter-compilation-unit references, such as those producedby the GCC option ‘-feliminate-dwarf2-dups’, the DWARF reader needs tofrequently refer to previously read compilation units. This setting controls how
long a compilation unit will remain in the cache if it is not referenced. A higher
limit means that cached compilation units will be stored in memory longer, and766

Debugging with gdb

more total memory will be used. Setting it to zero disables caching, which willslow down gdb startup, but reduce memory consumption.
maint set dwarf synchronous
maint show dwarf synchronous
Control whether DWARF is read asynchronously.
On hosts where threading is available, the DWARF reader is mostly asynchronous with respect to the rest of gdb. That is, the bulk of the reading isdone in the background, and gdb will only pause for completion of this task
when absolutely necessary.
When this setting is enabled, gdb will instead wait for DWARF processing tocomplete before continuing.
On hosts without threading, or where worker threads have been disabled atruntime, this setting has no effect, as DWARF reading is always done on themain thread, and is therefore always synchronous.
maint set dwarf unwinders
maint show dwarf unwinders
Control use of the DWARF frame unwinders.
Many targets that support DWARF debugging use gdb’s DWARF frame unwinders to build the backtrace. Many of these targets will also have a second
mechanism for building the backtrace for use in cases where DWARF information is not available, this second mechanism is often an analysis of a function’s
prologue.
In order to extend testing coverage of the second level stack unwinding mechanisms it is helpful to be able to disable the DWARF stack unwinders, this canbe done with this switch.
In normal use of gdb disabling the DWARF unwinders is not advisable, there
are cases that are better handled through DWARF than prologue analysis, andthe debug experience is likely to be better with the DWARF frame unwinders
enabled.
If DWARF frame unwinders are not supported for a particular target architecture, then enabling this flag does not cause them to be used.
maint info frame-unwinders
List the frame unwinders currently in effect, starting with the highest priority.
maint set worker-threads
maint show worker-threads
Control the number of worker threads that may be used by gdb. On capable
hosts, gdb may use multiple threads to speed up certain CPU-intensive operations, such as demangling symbol names. While the number of threads usedby gdb may vary, this command can be used to set an upper bound on thisnumber. The default is unlimited, which lets gdb choose a reasonable number. Note that this only controls worker threads started by gdb itself; libraries
used by gdb may start threads of their own.

Appendix D: Maintenance Commands

767

maint set profile
maint show profile
Control profiling of gdb.
Profiling will be disabled until you use the ‘maint set profile’ command toenable it. When you enable profiling, the system will begin collecting timing
and execution count data; when you disable profiling or exit gdb, the results
will be written to a log file. Remember that if you use profiling, gdb will
overwrite the profiling log file (often called gmon.out). If you have a record ofimportant profiling data in a gmon.out file, be sure to move it to a safe location.
Configuring with ‘--enable-profiling’ arranges for gdb to be compiled withthe ‘-pg’ compiler option.
maint set show-debug-regs
maint show show-debug-regs
Control whether to show variables that mirror the hardware debug registers.
Use on to enable, off to disable. If enabled, the debug registers values areshown when gdb inserts or removes a hardware breakpoint or watchpoint, andwhen the inferior triggers a hardware-assisted breakpoint or watchpoint.
maint set show-all-tib
maint show show-all-tib
Control whether to show all non zero areas within a 1k block starting at thread
local base, when using the ‘info w32 thread-information-block’ command.
maint set target-async
maint show target-async
This controls whether gdb targets operate in synchronous or asynchronousmode (see Section 5.5.3 [Background Execution], page 95). Normally the default
is asynchronous, if it is available; but this can be changed to more easily debug
problems occurring only in synchronous mode.
maint set target-non-stop
maint show target-non-stop
This controls whether gdb targets always operate in non-stop mode even if set
non-stop is off (see Section 5.5.2 [Non-Stop Mode], page 94). The default is
auto, meaning non-stop mode is enabled if supported by the target.
maint set target-non-stop auto
This is the default mode. gdb controls the target in non-stop mode
if the target supports it.
maint set target-non-stop on
gdb controls the target in non-stop mode even if the target does
not indicate support.
maint set target-non-stop off
gdb does not control the target in non-stop mode even if the target
supports it.

768

Debugging with gdb

maint set tui-resize-message
maint show tui-resize-message
Control whether gdb displays a message each time the terminal is resized when
in TUI mode. The default is off, which means that gdb is silent during resizes.
When on, gdb will display a message after a resize is completed; the message
will include a number indicating how many times the terminal has been resized.
This setting is intended for use by the test suite, where it would otherwise bedifficult to determine when a resize and refresh has been completed.
maint set tui-left-margin-verbose
maint show tui-left-margin-verbose
Control whether the left margin of the TUI source and disassembly windows
uses ‘_’ and ‘0’ at locations where otherwise there would be a space. The default
is off, which means spaces are used. The setting is intended to make it clear
where the left margin begins and ends, to avoid incorrectly interpreting a space
as being part of the the left margin.
maint set per-command
maint show per-command
gdb can display the resources used by each command. This is useful in debugging performance problems.
maint set per-command space [on|off]
maint show per-command space
Enable or disable the printing of the memory used by GDB foreach command. If enabled, gdb will display how much memory
each command took, following the command’s own output. Thiscan also be requested by invoking gdb with the --statistics
command-line switch (see Section 2.1.2 [Mode Options], page 13).
maint set per-command time [on|off]
maint show per-command time
Enable or disable the printing of the execution time of gdb foreach command. If enabled, gdb will display how much time it took
to execute each command, following the command’s own output.
Both CPU time and wallclock time are printed. Printing bothis useful when trying to determine whether the cost is CPU or,e.g., disk/network latency. Note that the CPU time printed isfor gdb only, it does not include the execution time of the inferior
because there’s no mechanism currently to compute how much time
was spent by gdb and how much time was spent by the program
been debugged. This can also be requested by invoking gdb withthe --statistics command-line switch (see Section 2.1.2 [ModeOptions], page 13).
maint set per-command symtab [on|off]
maint show per-command symtab
Enable or disable the printing of basic symbol table statistics foreach command. If enabled, gdb will display the following information:

Appendix D: Maintenance Commands

769

a. number of symbol tables
b. number of primary symbol tables
c. number of blocks in the blockvector
maint set check-libthread-db [on|off]
maint show check-libthread-db
Control whether gdb should run integrity checks on inferior specific thread
debugging libraries as they are loaded. The default is not to perform suchchecks. If any check fails gdb will unload the library and continue searchingfor a suitable candidate as described in [set libthread-db-search-path], page 51.
For more information about the tests, see [maint check libthread-db], page 760.
maint set gnu-source-highlight enabled [on|off]
maint show gnu-source-highlight enabled
Control whether gdb should use the GNU Source Highlight library for applying
styling to source code (see Section 22.5 [Output Styling], page 371). This willbe ‘on’ by default if the GNU Source Highlight library is available. If the GNU
Source Highlight library is not available, then this will be ‘off’ by default, andattempting to change this value to ‘on’ will give an error.
If the GNU Source Highlight library is not being used, then gdb will use thePython Pygments package for source code styling, if it is available.
This option is useful for debugging gdb’s use of the Pygments library when
gdb is linked against the GNU Source Highlight library.
maint set libopcodes-styling enabled [on|off]
maint show libopcodes-styling enabled
Control whether gdb should use its builtin disassembler (libopcodes) to styledisassembler output (see Section 22.5 [Output Styling], page 371). The builtin
disassembler does not support styling for all architectures.
When this option is ‘off’ the builtin disassembler will not be used for styling,
gdb will fall back to using the Python Pygments package if possible.
Trying to set this option ‘on’ for an architecture that the builtin disassembler
is unable to style will give an error, otherwise, the builtin disassembler will be
used to style disassembler output.
This option is ‘on’ by default for supported architectures.
This option is useful for debugging gdb’s use of the Pygments library when gdb
is built for an architecture that supports styling with the builtin disassembler
maint info screen
Print various characteristics of the screen, such as various notions of width andheight.
maint space value
An alias for maint set per-command space. A non-zero value enables it, zerodisables it.
maint time value
An alias for maint set per-command time. A non-zero value enables it, zerodisables it.

770

Debugging with gdb

maint translate-address [section] addr
Find the symbol stored at the location specified by the address addr and an
optional section name section. If found, gdb prints the name of the closest
symbol and an offset from the symbol’s location to the specified address. Thisis similar to the info address command (see Chapter 16 [Symbols], page 263),
except that this command also allows to find symbols in other sections.
If section was not specified, the section in which the symbol was found is also
printed. For dynamically linked executables, the name of executable or sharedlibrary containing the symbol is printed as well.
maint test-options require-delimiter
maint test-options unknown-is-error
maint test-options unknown-is-operandThese commands are used by the testsuite to validate the command options
framework. The require-delimiter variant requires a double-dash delimiterto indicate end of options. The unknown-is-error and unknown-is-operand
do not. The unknown-is-error variant throws an error on unknown option,
while unknown-is-operand treats unknown options as the start of the command’s operands. When run, the commands output the result of the processed
options. When completed, the commands store the internal result of completionin a variable exposed by the maint show test-options-completion-resultcommand.
maint show test-options-completion-result
Shows the result of completing the maint test-options subcommands. Thisis used by the testsuite to validate completion support in the command options
framework.
maint set test-settings kindmaint show test-settings kind
These are representative commands for each kind of setting type gdb supports.
They are used by the testsuite for exercising the settings infrastructure.
maint set backtrace-on-fatal-signal [on|off]
maint show backtrace-on-fatal-signal
When this setting is on, if gdb itself terminates with a fatal signal (e.g.
SIGSEGV), then a limited backtrace will be printed to the standard error
stream. This backtrace can be used to help diagnose crashes within gdb insituations where a user is unable to share a corefile with the gdb developers.
If the functionality to provide this backtrace is not available for the platform on
which GDB is running then this feature will be off by default, and attempting
to turn this feature on will give an error.
For platforms that do support creating the backtrace this feature is on bydefault.
maint wait-for-index-cache
Wait until all pending writes to the index cache have completed. This is usedby the test suite to avoid races when the index cache is being updated by aworker thread.

Appendix D: Maintenance Commands

771

maint with setting [value] [-- command]
Like the with command, but works with maintenance set variables. This isused by the testsuite to exercise the with command’s infrastructure.
maint ignore-probes [-v|-verbose] [provider [name [objfile]]]maint ignore-probes -reset
Set or reset the ignore-probes filter. The provider, name and objfile arguments
are as in enable probes and disable probes (see [enable probes], page 82).
Only supported for SystemTap probes.
Here’s an example of using maint ignore-probes:(gdb) maint ignore-probes -verbose libc ^longjmp$
ignore-probes filter has been set to:
PROVIDER: ’libc’
PROBE_NAME: ’^longjmp$’
OBJNAME: ’’(gdb) start<... more output ...>
Ignoring SystemTap probe libc longjmp in /lib64/libc.so.6.^M
Ignoring SystemTap probe libc longjmp in /lib64/libc.so.6.^M
Ignoring SystemTap probe libc longjmp in /lib64/libc.so.6.^M

The following command is useful for non-interactive invocations of gdb, such as in thetest suite.
set watchdog nsec
Set the maximum number of seconds gdb will wait for the target operation tofinish. If this time expires, gdb reports and error and the command is aborted.
show watchdog
Show the current setting of the target wait timeout.

773

Appendix E gdb Remote Serial Protocol
E.1 Overview
There may be occasions when you need to know something about the protocol—for example,
if there is only one serial port to your target machine, you might want your program to dosomething special if it recognizes a packet meant for gdb.
In the examples below, ‘->’ and ‘<-’ are used to indicate transmitted and received data,
respectively.
All gdb commands and responses (other than acknowledgments and notifications, see
Section E.10 [Notification Packets], page 826) are sent as a packet. A packet is introducedwith the character ‘$’, the actual packet-data, and the terminating character ‘#’ followed
by a two-digit checksum:$packet-data#checksum

The two-digit checksum is computed as the modulo 256 sum of all characters between theleading ‘$’ and the trailing ‘#’ (an eight bit unsigned checksum).
Implementors should note that prior to gdb 5.0 the protocol specification also included
an optional two-digit sequence-id:$sequence-id:packet-data#checksum

That sequence-id was appended to the acknowledgment. gdb has never output sequenceids. Stubs that handle packets added since gdb 5.0 must not accept sequence-id.
When either the host or the target machine receives a packet, the first response expected
is an acknowledgment: either ‘+’ (to indicate the package was received correctly) or ‘-’ (torequest retransmission):-> $packet-data#checksum<- +The ‘+’/‘-’ acknowledgments can be disabled once a connection is established. See
Section E.12 [Packet Acknowledgment], page 829, for details.
The host (gdb) sends commands, and the target (the debugging stub incorporated inyour program) sends a response. In the case of step and continue commands, the response
is only sent when the operation has completed, and the target has again stopped all threads
in all attached processes. This is the default all-stop mode behavior, but the remote protocol also supports gdb’s non-stop execution mode; see Section E.11 [Remote Non-Stop],
page 828, for details.
packet-data consists of a sequence of characters with the exception of ‘#’ and ‘$’ (see ‘X’packet for additional exceptions).
Fields within the packet should be separated using ‘,’ ‘;’ or ‘:’. Except where otherwise
noted all numbers are represented in hex with leading zeros suppressed.
Implementors should note that prior to gdb 5.0, the character ‘:’ could not appear as
the third character in a packet (as it would potentially conflict with the sequence-id).
Binary data in most packets is encoded as two hexadecimal digits per byte of binary
data. This allowed the traditional remote protocol to work over connections which were only
seven-bit clean. Some packets designed more recently assume an eight-bit clean connection,and use a more efficient encoding to send and receive binary data.

774

Debugging with gdb

The binary data representation uses 7d (ascii ‘}’) as an escape character. Any escapedbyte is transmitted as the escape character followed by the original character XORed with
0x20. For example, the byte 0x7d would be transmitted as the two bytes 0x7d 0x5d. The
bytes 0x23 (ascii ‘#’), 0x24 (ascii ‘$’), and 0x7d (ascii ‘}’) must always be escaped.
Responses sent by the stub must also escape 0x2a (ascii ‘*’), so that it is not interpreted
as the start of a run-length encoded sequence (described next).
Response data can be run-length encoded to save space. Run-length encoding replaces
runs of identical characters with one instance of the repeated character, followed by a ‘*’and a repeat count. The repeat count is itself sent encoded, to avoid binary characters in
data: a value of n is sent as n+29. For a repeat count greater or equal to 3, this producesa printable ascii character, e.g. a space (ascii code 32) for a repeat count of 3. (This isbecause run-length encoding starts to win for counts 3 or more.) Thus, for example, ‘0* ’
is a run-length encoding of “0000”: the space character after ‘*’ means repeat the leading
0 32 - 29 = 3 more times.
The printable characters ‘#’ and ‘$’ or with a numeric value greater than 126 must not
be used. Runs of six repeats (‘#’) or seven repeats (‘$’) can be expanded using a repeat
count of only five (‘"’). For example, ‘00000000’ can be encoded as ‘0*"00’.
See Section E.2 [Standard Replies], page 774, for standard error responses, and how to
respond indicating a command is not supported.
In describing packets (commands and responses), each description has a template showing the overall syntax, followed by an explanation of the packet’s meaning. We include
spaces in some of the templates for clarity; these are not part of the packet’s syntax. No
gdb packet uses spaces to separate its components. For example, a template like ‘foo bar
baz’ describes a packet beginning with the three ASCII bytes ‘foo’, followed by a bar,followed directly by a baz. gdb does not transmit a space character between the ‘foo’ andthe bar, or between the bar and the baz.
We place optional portions of a packet in [square brackets]; for example, a template
like ‘c [addr]’ describes a packet beginning with the single ASCII character ‘c’, possibly
followed by an addr.
At a minimum, a stub is required to support the ‘?’ command to tell gdb the reason
for halting, ‘g’ and ‘G’ commands for register access, and the ‘m’ and ‘M’ commands formemory access. Stubs that only control single-threaded targets can implement run control
with the ‘c’ (continue) command, and if the target architecture supports hardware-assisted
single-stepping, the ‘s’ (step) command. Stubs that support multi-threading targets should
support the ‘vCont’ command. All other commands are optional.

E.2 Standard Replies
The remote protocol specifies a few standard replies. All commands support these, except
as noted in the individual command descriptions.
empty response
An empty response (raw character sequence ‘$#00’) means the command is notsupported by the stub. This way it is possible to extend the protocol. A newer
gdb can tell if a command is supported based on that response (but see also
[qSupported], page 799).

Appendix E: gdb Remote Serial Protocol‘E xx’

775

An error has occurred; xx is a two-digit hexadecimal error number. In almost all cases, the protocol does not specify the meaning of the error numbers;
gdb usually ignores the numbers, or displays them to the user without further
interpretation.

‘E.errtext’An error has occurred; errtext is the textual error message, encoded in ascii.

E.3 Packets
The following table provides a complete list of all currently defined commands and their corresponding response data. See Section E.14 [File-I/O Remote Protocol Extension], page 830,
for details about the File I/O extension of the remote protocol.
Each packet’s description has a template showing the packet’s overall syntax, followedby an explanation of the packet’s meaning. We include spaces in some of the templates forclarity; these are not part of the packet’s syntax. No gdb packet uses spaces to separate its
components. For example, a template like ‘foo bar baz’ describes a packet beginning withthe three ASCII bytes ‘foo’, followed by a bar, followed directly by a baz. gdb does nottransmit a space character between the ‘foo’ and the bar, or between the bar and the baz.
Several packets and replies include a thread-id field to identify a thread. Normallythese are positive numbers with a target-specific interpretation, formatted as big-endianhex strings. A thread-id can also be a literal ‘-1’ to indicate all threads, or ‘0’ to pick any
thread.
In addition, the remote protocol supports a multiprocess feature in which the thread-id
syntax is extended to optionally include both process and thread ID fields, as ‘ppid.tid’.
The pid (process) and tid (thread) components each have the format described above: apositive number with target-specific interpretation formatted as a big-endian hex string,
literal ‘-1’ to indicate all processes or threads (respectively), or ‘0’ to indicate an arbitrary
process or thread. Specifying just a process, as ‘ppid’, is equivalent to ‘ppid.-1’. It is anerror to specify all processes but a specific thread, such as ‘p-1.tid’. Note that the ‘p’prefix is not used for those packets and replies explicitly documented to include a process
ID, rather than a thread-id.
The multiprocess thread-id syntax extensions are only used if both gdb and the stubreport support for the ‘multiprocess’ feature using ‘qSupported’. See [multiprocess extensions], page 806, for more information.
Note that all packet forms beginning with an upper- or lower-case letter, other thanthose described here, are reserved for future use.
Here are the packet descriptions.
‘!’

Enable extended mode. In extended mode, the remote server is made persistent.
The ‘R’ packet is used to restart the program being debugged.
Reply:‘OK’‘?’

The remote target both supports and has enabled extended mode.

This is sent when connection is first established to query the reason the target
halted. The reply is the same as for step and continue. This packet has a special

776

Debugging with gdb

interpretation when the target is in non-stop mode; see Section E.11 [Remote
Non-Stop], page 828.
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.
‘A arglen,argnum,arg,...’
Initialized argv[] array passed into program. arglen specifies the number ofbytes in the hex encoded byte stream arg. See gdbserver for more details.
Reply:‘OK’‘b baud’

The arguments were set.

(Don’t use this packet; its behavior is not well-defined.) Change the serial line
speed to baud.
JTC: When does the transport layer state change? When it’s received, or after
the ACK is transmitted. In either case, there are problems if the command or
the acknowledgment packet is dropped.
Stan: If people really wanted to add something like this, and get it working
for the first time, they ought to modify ser-unix.c to send some kind of out-ofband message to a specially-setup stub and have the switch happen "in between"
packets, so that from remote protocol’s point of view, nothing actually happened.

‘B addr,mode’Set (mode is ‘S’) or clear (mode is ‘C’) a breakpoint at addr.
Don’t use this packet. Use the ‘Z’ and ‘z’ packets instead (see [insert breakpoint
or watchpoint packet], page 783).
‘bc’

Backward continue. Execute the target system in reverse. No parameter. See
Chapter 6 [Reverse Execution], page 101, for more information.
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.

‘bs’

Backward single step. Execute one instruction in reverse. No parameter. See
Chapter 6 [Reverse Execution], page 101, for more information.
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.

‘c [addr]’

Continue at addr, which is the address to resume. If addr is omitted, resume
at current address.
This packet is deprecated for multi-threading support. See [vCont packet],page 780.
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.

‘C sig[;addr]’
Continue with signal sig (hex signal number). If ‘;addr’ is omitted, resume atsame address.
This packet is deprecated for multi-threading support. See [vCont packet],page 780.

Appendix E: gdb Remote Serial Protocol

777

Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.
‘d’‘D’‘D;pid’Toggle debug flag.
Don’t use this packet; instead, define a general set packet (see Section E.5[General Query Packets], page 789).
The first form of the packet is used to detach gdb from the remote system. It
is sent to the remote target before gdb disconnects via the detach command.
The second form, including a process ID, is used when multiprocess protocol
extensions are enabled (see [multiprocess extensions], page 806), to detach only
a specific process. The pid is specified as a big-endian hex string.
Reply:‘OK’for success‘F RC,EE,CF;XX’
A reply from gdb to an ‘F’ packet sent by the target. This is part of the FileI/O protocol extension. See Section E.14 [File-I/O Remote Protocol Extension],
page 830, for the specification.
‘g’

Read general registers.
Reply:‘XX...’

Each byte of register data is described by two hex digits. The
bytes with the register are transmitted in target byte order. The
size of each register and their position within the ‘g’ packet are
determined by the target description (see Appendix G [Target Descriptions], page 859); in the absence of a target description, this isdone using code internal to gdb; typically this is some customary
register layout for the architecture in question.
When reading registers, the stub may also return a string of literal ‘x’’s in place of the register data digits, to indicate that thecorresponding register’s value is unavailable. For example, whenreading registers from a trace frame (see Section 13.2 [Using theCollected Data], page 215), this means that the register has notbeen collected in the trace frame. When reading registers from alive program, this indicates that the stub has no means to access theregister contents, even though the corresponding register is known
to exist. Note that if a register truly does not exist on the target,then it is better to not include it in the target description in thefirst place.
For example, for an architecture with 4 registers of 4 bytes each,the following reply indicates to gdb that registers 0 and 2 are unavailable, while registers 1 and 3 are available, and both have zero
value:-> g<- xxxxxxxx00000000xxxxxxxx00000000

778‘G XX...’

Debugging with gdb

Write general registers. See [read registers packet], page 777, for a descriptionof the XX. . . data.
Reply:‘OK’for success‘H op thread-id’
Set thread for subsequent operations (‘m’, ‘M’, ‘g’, ‘G’, et.al.). Depending on theoperation to be performed, op should be ‘c’ for step and continue operations(note that this is deprecated, supporting the ‘vCont’ command is a better option), and ‘g’ for other operations. The thread designator thread-id has theformat and interpretation described in [thread-id syntax], page 775.
Reply:‘OK’for success‘i [addr[,nnn]]’
Step the remote target by a single clock cycle. If ‘,nnn’ is present, cycle step
nnn cycles. If addr is present, cycle step starting at that address.
‘I’

Signal, then cycle step. See [step with signal packet], page 779. See [cycle step
packet], page 778.

‘k’

Kill request.
The exact effect of this packet is not specified.
For a bare-metal target, it may power cycle or reset the target system. For thatreason, the ‘k’ packet has no reply.
For a single-process target, it may kill that process if possible.
A multiple-process target may choose to kill just one process, or all that areunder gdb’s control. For more precise control, use the vKill packet (see [vKill
packet], page 782).
If the target system immediately closes the connection in response to ‘k’, gdb
does not consider the lack of packet acknowledgment to be an error, and assumes
the kill was successful.
If connected using target extended-remote, and the target does not close theconnection in response to a kill request, gdb probes the target state as if a newconnection was opened (see [? packet], page 775).

‘m addr,length’
Read length addressable memory units starting at address addr (see[addressable memory unit], page 154). Note that addr may not be aligned toany particular boundary.
The stub need not use any particular size or alignment when gathering datafrom memory for the response; even if addr is word-aligned and length is amultiple of the word size, the stub is free to use byte accesses, or not. For
this reason, this packet may not be suitable for accessing memory-mapped I/O
devices.
Reply:‘XX...’

Memory contents; each byte is transmitted as a two-digit hexadecimal number. The reply may contain fewer addressable memory

Appendix E: gdb Remote Serial Protocol

779

units than requested if the server was able to read only part of theregion of memory.
Unlike most packets, this packet does not support ‘E.errtext’-style textual
error replies (see [textual error reply], page 775) by default. Stubs should
be careful to only send such a reply if gdb reported support for it with theerror-message feature (see [error-message], page 801).
‘M addr,length:XX...’
Write length addressable memory units starting at address addr (see[addressable memory unit], page 154). The data is given by XX. . . ; each byteis transmitted as a two-digit hexadecimal number.
Reply:‘OK’‘p n’

All the data was written successfully. (If only part of the data waswritten, this command returns an error.)Read the value of register n; n is in hex. See [read registers packet], page 777,
for a description of how the returned register value is encoded.
Reply:‘XX...’

the register’s value‘P n...=r...’Write register n. . . with value r. . . . The register number n is in hexadecimal,
and r. . . contains two hex digits for each byte in the register (target byte order).
Reply:‘OK’for success‘q name params...’‘Q name params...’General query (‘q’) and set (‘Q’). These packets are described fully in
Section E.5 [General Query Packets], page 789.
‘r’

Reset the entire system.
Don’t use this packet; use the ‘R’ packet instead.

‘R XX’

Restart the program being debugged. The XX, while needed, is ignored. This
packet is only available in extended mode (see [extended mode], page 775).
The ‘R’ packet has no reply.

‘s [addr]’

Single step, resuming at addr. If addr is omitted, resume at same address.
This packet is deprecated for multi-threading support. See [vCont packet],page 780.
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.

‘S sig[;addr]’
Step with signal. This is analogous to the ‘C’ packet, but requests a single-step,rather than a normal resumption of execution.

780

Debugging with gdb

This packet is deprecated for multi-threading support. See [vCont packet],page 780.
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.
‘t addr:PP,MM’
Search backwards starting at address addr for a match with pattern PP andmask MM, both of which are are 4 byte long. There must be at least 3 digits
in addr.
‘T thread-id’
Find out if the thread thread-id is alive. See [thread-id syntax], page 775.
Reply:‘OK’‘v’

thread is still alive

Packets starting with ‘v’ are identified by a multi-letter name, up to the first‘;’ or ‘?’ (or the end of the packet).

‘vAttach;pid’Attach to a new process with the specified process ID pid. The process ID is ahexadecimal integer identifying the process. In all-stop mode, all threads in theattached process are stopped; in non-stop mode, it may be attached without
being stopped if that is supported by the target.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘Any stop packet’for success in all-stop mode (see Section E.4 [Stop Reply Packets],page 785)‘OK’

for success in non-stop mode (see Section E.11 [Remote Non-Stop],
page 828)‘vCont[;action[:thread-id]]...’
Resume the inferior, specifying different actions for each thread.
For each inferior thread, the leftmost action with a matching thread-id is applied. Threads that don’t match any action remain in their current state.
Thread IDs are specified using the syntax described in [thread-id syntax],
page 775. If multiprocess extensions (see [multiprocess extensions], page 806)
are supported, actions can be specified to match all threads in a process by using the ‘ppid.-1’ form of the thread-id. An action with no thread-id matches
all threads. Specifying no actions is an error.
Currently supported actions are:‘c’

Continue.

‘C sig’Continue with signal sig. The signal sig should be two hex digits.

‘s’

Step.

‘S sig’Step with signal sig. The signal sig should be two hex digits.

Appendix E: gdb Remote Serial Protocol

‘t’

781

Stop.

‘r start,end’Step once, and then keep stepping as long as the thread stops ataddresses between start (inclusive) and end (exclusive). The remotestub reports a stop reply when either the thread goes out of therange or is stopped due to an unrelated reason, such as hitting a
breakpoint. See [range stepping], page 87.
If the range is empty (start == end), then the action becomes
equivalent to the ‘s’ action. In other words, single-step once, andreport the stop (even if the stepped instruction jumps to start).
(A stop reply may be sent at any point even if the PC is still within
the stepping range; for example, it is valid to implement this packet
in a degenerate way as a single instruction step operation.)
The optional argument addr normally associated with the ‘c’, ‘C’, ‘s’, and ‘S’packets is not supported in ‘vCont’.
The ‘t’ action is only relevant in non-stop mode (see Section E.11 [Remote NonStop], page 828) and may be ignored by the stub otherwise. A stop reply shouldbe generated for any affected thread not already stopped. When a thread is
stopped by means of a ‘t’ action, the corresponding stop reply should indicatethat the thread has stopped with signal ‘0’, regardless of whether the target
uses some other signal as an implementation detail.
The server must ignore ‘c’, ‘C’, ‘s’, ‘S’, and ‘r’ actions for threads that are
already running. Conversely, the server must ignore ‘t’ actions for threads thatare already stopped.
Note: In non-stop mode, a thread is considered running until gdb acknowledges an asynchronous stop notification for it with the ‘vStopped’ packet (seeSection E.11 [Remote Non-Stop], page 828).
The stub must support ‘vCont’ if it reports support for multiprocess extensions(see [multiprocess extensions], page 806).
Reply: See Section E.4 [Stop Reply Packets], page 785, for the reply specifications.
‘vCont?’Request a list of actions supported by the ‘vCont’ packet.
Reply:‘vCont[;action...]’The ‘vCont’ packet is supported. Each action is a supported command in the ‘vCont’ packet.

‘vCtrlC’

Interrupt remote target as if a control-C was pressed on the remote terminal.
This is the equivalent to reacting to the ^C (‘\003’, the control-C character)character in all-stop mode while the target is running, except this works in
non-stop mode. See [interrupting remote targets], page 825, for more info on
the all-stop variant.
Reply:‘OK’for success782

Debugging with gdb‘vFile:operation:parameter...’Perform a file operation on the target system. For details, see Section E.8 [HostI/O Packets], page 823.
‘vFlashErase:addr,length’
Direct the stub to erase length bytes of flash starting at addr. The region may
enclose any number of flash blocks, but its start and end must fall on blockboundaries, as indicated by the flash block size appearing in the memory map(see Section E.17 [Memory Map Format], page 843). gdb groups flash memory
programming operations together, and sends a ‘vFlashDone’ request after eachgroup; the stub is allowed to delay erase operation until the ‘vFlashDone’ packet
is received.
Reply:‘OK’for success‘vFlashWrite:addr:XX...’
Direct the stub to write data to flash address addr. The data is passed inbinary form using the same encoding as for the ‘X’ packet (see [Binary Data],
page 773). The memory ranges specified by ‘vFlashWrite’ packets preceding a‘vFlashDone’ packet must not overlap, and must appear in order of increasing
addresses (although ‘vFlashErase’ packets for higher addresses may alreadyhave been received; the ordering is guaranteed only between ‘vFlashWrite’
packets). If a packet writes to an address that was neither erased by a preceding‘vFlashErase’ packet nor by some other target-specific method, the results are
unpredictable.
Reply:‘OK’for success‘E.memtype’
for vFlashWrite addressing non-flash memory‘vFlashDone’
Indicate to the stub that flash programming operation is finished. The stubis permitted to delay or batch the effects of a group of ‘vFlashErase’ and‘vFlashWrite’ packets until a ‘vFlashDone’ packet is received. The contents of
the affected regions of flash memory are unpredictable until the ‘vFlashDone’request is completed.
‘vKill;pid’
Kill the process with the specified process ID pid, which is a hexadecimal integer identifying the process. This packet is used in preference to ‘k’ when
multiprocess protocol extensions are supported; see [multiprocess extensions],
page 806.
Reply:‘OK’for successAppendix E: gdb Remote Serial Protocol

783‘vMustReplyEmpty’
The correct reply to an unknown ‘v’ packet is to return the empty string,
however, some older versions of gdbserver would incorrectly return ‘OK’ forunknown ‘v’ packets.
The ‘vMustReplyEmpty’ is used as a feature test to check how gdbserver handles unknown packets, it is important that this packet be handled in the same
way as other unknown ‘v’ packets. If this packet is handled differently to otherunknown ‘v’ packets then it is possible that gdb may run into problems in otherareas, specifically around use of ‘vFile:setfs:’.
‘vRun;filename[;argument]...’Run the program filename, passing it each argument on its command line. The
file and arguments are hex-encoded strings. If filename is an empty string, thestub may use a default program (e.g. the last program run). The program iscreated in the stopped state.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘Any stop packet’for success (see Section E.4 [Stop Reply Packets], page 785)
‘vStopped’
See Section E.10 [Notification Packets], page 826.
‘X addr,length:XX...’
Write data to memory, where the data is transmitted in binary. Memory is
specified by its address addr and number of addressable memory units length(see [addressable memory unit], page 154); ‘XX...’ is binary data (see [BinaryData], page 773).
Reply:‘OK’for success‘z type,addr,kind’‘Z type,addr,kind’
Insert (‘Z’) or remove (‘z’) a type breakpoint or watchpoint starting at address
address of kind kind.
Each breakpoint and watchpoint packet type is documented separately.
Implementation notes: A remote target shall return an empty string for an unrecognized breakpoint or watchpoint packet type. A remote target shall support
either both or neither of a given ‘Ztype...’ and ‘ztype...’ packet pair. To
avoid potential problems with duplicate packets, the operations should be implemented in an idempotent way.
‘z0,addr,kind’‘Z0,addr,kind[;cond_list...][;cmds:persist,cmd_list...]’
Insert (‘Z0’) or remove (‘z0’) a software breakpoint at address addr of type
kind.

784

Debugging with gdb

A software breakpoint is implemented by replacing the instruction at addr witha software breakpoint or trap instruction. The kind is target-specific and typically indicates the size of the breakpoint in bytes that should be inserted. E.g.,
the arm and mips can insert either a 2 or 4 byte breakpoint. Some architectures have additional meanings for kind (see Section E.6 [Architecture-SpecificProtocol Details], page 816); if no architecture-specific value is being used, itshould be ‘0’. kind is hex-encoded. cond list is an optional list of conditional
expressions in bytecode form that should be evaluated on the target’s side.
These are the conditions that should be taken into consideration when deciding
if the breakpoint trigger should be reported back to gdb.
See also the ‘swbreak’ stop reason (see [swbreak stop reason], page 786) for
how to best report a software breakpoint event to gdb.
The cond list parameter is comprised of a series of expressions, concatenatedwithout separators. Each expression has the following form:‘X len,expr’len is the length of the bytecode expression and expr is the actual
conditional expression in bytecode form.
The optional cmd list parameter introduces commands that may be run on thetarget, rather than being reported back to gdb. The parameter starts witha numeric flag persist; if the flag is nonzero, then the breakpoint may remain
active and the commands continue to be run even when gdb disconnects fromthe target. Following this flag is a series of expressions concatenated with noseparators. Each expression has the following form:‘X len,expr’len is the length of the bytecode expression and expr is the actualcommands expression in bytecode form.
Implementation note: It is possible for a target to copy or move code that contains software breakpoints (e.g., when implementing overlays). The behavior ofthis packet, in the presence of such a target, is not defined.
Reply:‘OK’

success‘z1,addr,kind’‘Z1,addr,kind[;cond_list...][;cmds:persist,cmd_list...]’
Insert (‘Z1’) or remove (‘z1’) a hardware breakpoint at address addr.
A hardware breakpoint is implemented using a mechanism that is not dependent
on being able to modify the target’s memory. The kind, cond list, and cmd list
arguments have the same meaning as in ‘Z0’ packets.
Implementation note: A hardware breakpoint is not affected by code movement.
Reply:‘OK’

success

Appendix E: gdb Remote Serial Protocol

785‘z2,addr,kind’‘Z2,addr,kind’
Insert (‘Z2’) or remove (‘z2’) a write watchpoint at addr. The number of bytes
to watch is specified by kind.
Reply:‘OK’

success‘z3,addr,kind’‘Z3,addr,kind’
Insert (‘Z3’) or remove (‘z3’) a read watchpoint at addr. The number of bytes
to watch is specified by kind.
Reply:‘OK’

success‘z4,addr,kind’‘Z4,addr,kind’
Insert (‘Z4’) or remove (‘z4’) an access watchpoint at addr. The number ofbytes to watch is specified by kind.
Reply:‘OK’

success

E.4 Stop Reply Packets
The ‘C’, ‘c’, ‘S’, ‘s’, ‘vCont’, ‘vAttach’, ‘vRun’, ‘vStopped’, and ‘?’ packets can receive anyof the below as a reply. Except for ‘?’ and ‘vStopped’, that reply is only returned when
the target halts. In the below the exact meaning of signal number is defined by the header
include/gdb/signals.h in the gdb source code.
In non-stop mode, the server will simply reply ‘OK’ to commands such as ‘vCont’; anystop will be the subject of a future notification. See Section E.11 [Remote Non-Stop],
page 828.
As in the description of request packets, we include spaces in the reply templates forclarity; these are not part of the reply packet’s syntax. No gdb stop reply packet uses
spaces to separate its components.
‘S AA’The program received signal number AA (a two-digit hexadecimal number).
This is equivalent to a ‘T’ response with no n:r pairs.

‘T AA n1:r1;n2:r2;...’The program received signal number AA (a two-digit hexadecimal number).
This is equivalent to an ‘S’ response, except that the ‘n:r’ pairs can carry valuesof important registers and other information directly in the stop reply packet,
reducing round-trip latency. Single-step and breakpoint traps are reported thisway. Each ‘n:r’ pair is interpreted as follows:• If n is a hexadecimal number, it is a register number, and the correspondingr gives that register’s value. The data r is a series of bytes in target byteorder, with each byte given by a two-digit hex number.

786

Debugging with gdb• If n is ‘thread’, then r is the thread ID of the stopped thread, as specified
in [thread-id syntax], page 775.
• If n is ‘core’, then r is the hexadecimal number of the core on which thestop event was detected.
• If n is a recognized stop reason, it describes a more specific event that
stopped the target. The currently defined stop reasons are listed below.
The aa should be ‘05’, the trap signal. At most one stop reason should bepresent.
• Otherwise, gdb should ignore this ‘n:r’ pair and go on to the next; thisallows us to extend the protocol in the future.
The currently defined stop reasons are:‘watch’‘rwatch’‘awatch’

The packet indicates a watchpoint hit, and r is the data address,
in hex.

‘syscall_entry’‘syscall_return’
The packet indicates a syscall entry or return, and r is the syscall
number, in hex.
‘library’

The packet indicates that the loaded libraries have changed. gdb
should use ‘qXfer:libraries:read’ to fetch a new list of loaded
libraries. The r part is ignored.

‘replaylog’
The packet indicates that the target cannot continue replaying
logged execution events, because it has reached the end (or the
beginning when executing backward) of the log. The value of r
will be either ‘begin’ or ‘end’. See Chapter 6 [Reverse Execution],
page 101, for more information.
‘swbreak’

The packet indicates a software breakpoint instruction was executed, irrespective of whether it was gdb that planted the breakpoint or the breakpoint is hardcoded in the program. The r part
must be left empty.
On some architectures, such as x86, at the architecture level, whena breakpoint instruction executes the program counter points atthe breakpoint address plus an offset. On such targets, the stub isresponsible for adjusting the PC to point back at the breakpoint
address.
This packet should not be sent by default; older gdb versions
did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see [qSupported], page 799). The remotestub must also supply the appropriate ‘qSupported’ feature indicating support.
This packet is required for correct non-stop mode operation.

Appendix E: gdb Remote Serial Protocol

787‘hwbreak’

The packet indicates the target stopped for a hardware breakpoint.
The r part must be left empty.
The same remarks about ‘qSupported’ and non-stop mode above
apply.

‘fork’The packet indicates that fork was called, and r is the thread ID of
the new child process, as specified in [thread-id syntax], page 775.
This packet is only applicable to targets that support fork events.
This packet should not be sent by default; older gdb versions
did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see [qSupported], page 799). The remotestub must also supply the appropriate ‘qSupported’ feature indicating support.

‘vfork’

The packet indicates that vfork was called, and r is the thread IDof the new child process, as specified in [thread-id syntax], page 775.
This packet is only applicable to targets that support vfork events.
This packet should not be sent by default; older gdb versions
did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see [qSupported], page 799). The remotestub must also supply the appropriate ‘qSupported’ feature indicating support.

‘vforkdone’
The packet indicates that a child process created by a vfork haseither called exec or terminated, so that the address spaces of theparent and child process are no longer shared. The r part is ignored.
This packet is only applicable to targets that support vforkdone
events.
This packet should not be sent by default; older gdb versions
did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see [qSupported], page 799). The remotestub must also supply the appropriate ‘qSupported’ feature indicating support.
‘exec’The packet indicates that execve was called, and r is the absolutepathname of the file that was executed, in hex. This packet is only
applicable to targets that support exec events.
This packet should not be sent by default; older gdb versions
did not support it. gdb requests it, by supplying an appropriate ‘qSupported’ feature (see [qSupported], page 799). The remotestub must also supply the appropriate ‘qSupported’ feature indicating support.

‘clone’The packet indicates that clone was called, and r is the thread IDof the new child thread, as specified in [thread-id syntax], page 775.
This packet is only applicable to targets that support clone events.
This packet should not be sent by default; gdb requests it with the[QThreadOptions], page 797, packet.

788

Debugging with gdb‘create’The packet indicates that the thread was just created. The new
thread is stopped until gdb sets it running with a resumption
packet (see [vCont packet], page 780). This packet should not
be sent by default; gdb requests it with the [QThreadEvents],
page 797, packet. See also the ‘w’ (see [thread exit event], page 788)
remote reply below. The r part is ignored.

‘W AA’‘W AA ; process:pid’
The process exited, and AA is the exit status. This is only applicable to certain
targets.
The second form of the response, including the process ID of the exited process, can be used only when gdb has reported support for multiprocess protocol
extensions; see [multiprocess extensions], page 806. Both AA and pid are formatted as big-endian hex strings.
‘X AA’‘X AA ; process:pid’
The process terminated with signal AA.
The second form of the response, including the process ID of the terminatedprocess, can be used only when gdb has reported support for multiprocess
protocol extensions; see [multiprocess extensions], page 806. Both AA and pid
are formatted as big-endian hex strings.
‘w AA ; tid’
The thread exited, and AA is the exit status. This response should not besent by default; gdb requests it with either the [QThreadEvents], page 797, or[QThreadOptions], page 797, packets. See also [thread create event], page 787,
above. AA is formatted as a big-endian hex string.
‘N’

There are no resumed threads left in the target. In other words, even though
the process is alive, the last resumed thread has exited. For example, say thetarget process has two threads: thread 1 and thread 2. The client leaves thread
1 stopped, and resumes thread 2, which subsequently exits. At this point, eventhough the process is still alive, and thus no ‘W’ stop reply is sent, no thread is
actually executing either. The ‘N’ stop reply thus informs the client that it canstop waiting for stop replies. This packet should not be sent by default; older
gdb versions did not support it. gdb requests it, by supplying an appropriate‘qSupported’ feature (see [qSupported], page 799). The remote stub must also
supply the appropriate ‘qSupported’ feature indicating support.

‘O XX...’‘XX...’ is hex encoding of ascii data, to be written as the program’s console
output. This can happen at any time while the program is running and the
debugger should continue to wait for ‘W’, ‘T’, etc. This reply is not permitted
in non-stop mode.

‘F call-id,parameter...’call-id is the identifier which says which host system call should be called. Thisis just the name of the function. Translation into the correct system call is onlyAppendix E: gdb Remote Serial Protocol

789

applicable as it’s defined in gdb. See Section E.14 [File-I/O Remote Protocol
Extension], page 830, for a list of implemented system calls.
‘parameter...’ is a list of parameters as defined for this very system call.
The target replies with this packet when it expects gdb to call a host systemcall on behalf of the target. gdb replies with an appropriate ‘F’ packet andkeeps up waiting for the next reply packet from the target. The latest ‘C’, ‘c’,
‘S’ or ‘s’ action is expected to be continued. See Section E.14 [File-I/O Remote
Protocol Extension], page 830, for more details.

E.5 General Query Packets
Packets starting with ‘q’ are general query packets; packets starting with ‘Q’ are general set
packets. General query and set packets are a semi-unified form for retrieving and sending
information to and from the stub.
The initial letter of a query or set packet is followed by a name indicating what sortof thing the packet applies to. For example, gdb may use a ‘qSymbol’ packet to exchange
symbol definitions with the stub. These packet names follow some conventions:• The name must not contain commas, colons or semicolons.
• Most gdb query and set packets have a leading upper case letter.
• The names of custom vendor packets should use a company prefix, in lower case, followed by a period. For example, packets designed at the Acme Corporation might
begin with ‘qacme.foo’ (for querying foos) or ‘Qacme.bar’ (for setting bars).
The name of a query or set packet should be separated from any parameters by a ‘:’; theparameters themselves should be separated by ‘,’ or ‘;’. Stubs must be careful to match
the full packet name, and check for a separator or the end of the packet, in case two packet
names share a common prefix. New packets should not begin with ‘qC’, ‘qP’, or ‘qL’1 .
Like the descriptions of the other packets, each description here has a template showing
the packet’s overall syntax, followed by an explanation of the packet’s meaning. We include
spaces in some of the templates for clarity; these are not part of the packet’s syntax. No
gdb packet uses spaces to separate its components.
Here are the currently defined query and set packets:‘QAgent:1’‘QAgent:0’
Turn on or off the agent as a helper to perform some debugging operations
delegated from gdb (see [Control Agent], page 705).
‘QAllow:op:val...’Specify which operations gdb expects to request of the target, as a semicolonseparated list of operation name and value pairs. Possible values for op include‘WriteReg’, ‘WriteMem’, ‘InsertBreak’, ‘InsertTrace’, ‘InsertFastTrace’,1

The ‘qP’ and ‘qL’ packets predate these conventions, and have arguments without any terminator forthe packet name; we suspect they are in widespread use in places that are difficult to upgrade. The ‘qC’
packet has no arguments, but some existing stubs (e.g. RedBoot) are known to not check for the end of
the packet.

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and ‘Stop’. val is either 0, indicating that gdb will not request the operation, or 1, indicating that it may. (The target can then use this to set up its
own internals optimally, for instance if the debugger never expects to insert
breakpoints, it may not need to install its own trap handler.)‘qC’

Return the current thread ID.
Reply:‘QC thread-id’
Where thread-id is a thread ID as documented in [thread-id syntax],
page 775.
‘(anything else)’
Any other reply implies the old thread ID.

‘qCRC:addr,length’
Compute the CRC checksum of a block of memory using CRC-32 defined inIEEE 802.3. The CRC is computed byte at a time, taking the most significant
bit of each byte first. The initial pattern code 0xffffffff is used to ensureleading zeros affect the CRC.
Note: This is the same CRC used in validating separate debug files (seeSection 18.3 [Debugging Information in Separate Files], page 300). However
the algorithm is slightly different. When validating separate debug files, the
CRC is computed taking the least significant bit of each byte first, and thefinal result is inverted to detect trailing zeros.
Reply:‘C crc32’

The specified memory region’s checksum is crc32.

‘QDisableRandomization:value’
Some target operating systems will randomize the virtual address space of theinferior process as a security feature, but provide a feature to disable suchrandomization, e.g. to allow for a more deterministic debugging experience. On
such systems, this packet with a value of 1 directs the target to disable address
space randomization for processes subsequently started via ‘vRun’ packets, whilea packet with a value of 0 tells the target to enable address space randomization.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘OK’

The request succeeded.

This packet is not probed by default; the remote stub must request it, by
supplying an appropriate ‘qSupported’ response (see [qSupported], page 799).
This should only be done on targets that actually support disabling address
space randomization.
‘QStartupWithShell:value’
On UNIX-like targets, it is possible to start the inferior using a shell program.
This is the default behavior on both gdb and gdbserver (see [set startup-withshell], page 36). This packet is used to inform gdbserver whether it should
start the inferior using a shell or not.

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If value is ‘0’, gdbserver will not use a shell to start the inferior. If value is ‘1’,
gdbserver will use a shell to start the inferior. All other values are considered
an error.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘OK’

The request succeeded.

This packet is not probed by default; the remote stub must request it, by
supplying an appropriate ‘qSupported’ response (see [qSupported], page 799).
This should only be done on targets that actually support starting the inferior
using a shell.
Use of this packet is controlled by the set startup-with-shell command; see[set startup-with-shell], page 36.
‘QEnvironmentHexEncoded:hex-value’
On UNIX-like targets, it is possible to set environment variables that will bepassed to the inferior during the startup process. This packet is used to inform
gdbserver of an environment variable that has been defined by the user on
gdb (see [set environment], page 39).
The packet is composed by hex-value, an hex encoded representation of thename=value format representing an environment variable. The name of theenvironment variable is represented by name, and the value to be assigned tothe environment variable is represented by value. If the variable has no value(i.e., the value is null), then value will not be present.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘OK’

The request succeeded.

This packet is not probed by default; the remote stub must request it, by
supplying an appropriate ‘qSupported’ response (see [qSupported], page 799).
This should only be done on targets that actually support passing environment
variables to the starting inferior.
This packet is related to the set environment command; see [set environment],
page 39.
‘QEnvironmentUnset:hex-value’
On UNIX-like targets, it is possible to unset environment variables before starting the inferior in the remote target. This packet is used to inform gdbserverof an environment variable that has been unset by the user on gdb (see [unset
environment], page 39).
The packet is composed by hex-value, an hex encoded representation of thename of the environment variable to be unset.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘OK’

The request succeeded.

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This packet is not probed by default; the remote stub must request it, by
supplying an appropriate ‘qSupported’ response (see [qSupported], page 799).
This should only be done on targets that actually support passing environment
variables to the starting inferior.
This packet is related to the unset environment command; see [unset environment], page 39.
‘QEnvironmentReset’
On UNIX-like targets, this packet is used to reset the state of environment
variables in the remote target before starting the inferior. In this context, resetmeans unsetting all environment variables that were previously set by the user
(i.e., were not initially present in the environment). It is sent to gdbserver
before the ‘QEnvironmentHexEncoded’ (see [QEnvironmentHexEncoded],
page 791) and the ‘QEnvironmentUnset’ (see [QEnvironmentUnset], page 791)
packets.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘OK’

The request succeeded.

This packet is not probed by default; the remote stub must request it, by
supplying an appropriate ‘qSupported’ response (see [qSupported], page 799).
This should only be done on targets that actually support passing environment
variables to the starting inferior.
‘QSetWorkingDir:[directory]’
This packet is used to inform the remote server of the intended current working
directory for programs that are going to be executed.
The packet is composed by directory, an hex encoded representation of thedirectory that the remote inferior will use as its current working directory. If
directory is an empty string, the remote server should reset the inferior’s current
working directory to its original, empty value.
This packet is only available in extended mode (see [extended mode], page 775).
Reply:‘OK’

The request succeeded.

‘qfThreadInfo’‘qsThreadInfo’
Obtain a list of all active thread IDs from the target (OS). Since there may be
too many active threads to fit into one reply packet, this query works iteratively:
it may require more than one query/reply sequence to obtain the entire list of
threads. The first query of the sequence will be the ‘qfThreadInfo’ query;subsequent queries in the sequence will be the ‘qsThreadInfo’ query.
NOTE: This packet replaces the ‘qL’ query (see below).
Reply:‘m thread-id’
A single thread ID

Appendix E: gdb Remote Serial Protocol

793‘m thread-id,thread-id...’a comma-separated list of thread IDs‘l’(lower case letter ‘L’) denotes end of list.

In response to each query, the target will reply with a list of one or more threadIDs, separated by commas. gdb will respond to each reply with a request for
more thread ids (using the ‘qs’ form of the query), until the target respondswith ‘l’ (lower-case ell, for last). Refer to [thread-id syntax], page 775, for theformat of the thread-id fields.
Note: gdb will send the qfThreadInfo query during the initial connection withthe remote target, and the very first thread ID mentioned in the reply will be
stopped by gdb in a subsequent message. Therefore, the stub should ensure thatthe first thread ID in the qfThreadInfo reply is suitable for being stopped by
gdb.
‘qGetTLSAddr:thread-id,offset,lm’
Fetch the address associated with thread local storage specified by thread-id,
offset, and lm.
thread-id is the thread ID associated with the thread for which to fetch the
TLS address. See [thread-id syntax], page 775.
offset is the (big endian, hex encoded) offset associated with the thread local
variable. (This offset is obtained from the debug information associated withthe variable.)lm is the (big endian, hex encoded) OS/ABI-specific encoding of the load module associated with the thread local storage. For example, a gnu/Linux system
will pass the link map address of the shared object associated with the thread
local storage under consideration. Other operating environments may choose torepresent the load module differently, so the precise meaning of this parameter
will vary.
Reply:‘XX...’Hex encoded (big endian) bytes representing the address of thethread local storage requested.

‘qGetTIBAddr:thread-id’
Fetch address of the Windows OS specific Thread Information Block.
thread-id is the thread ID associated with the thread.
Reply:‘XX...’Hex encoded (big endian) bytes representing the linear address ofthe thread information block.

‘qL startflag threadcount nextthread’
Obtain thread information from RTOS. Where: startflag (one hex digit) is one
to indicate the first query and zero to indicate a subsequent query; threadcount(two hex digits) is the maximum number of threads the response packet cancontain; and nextthread (eight hex digits), for subsequent queries (startflag iszero), is returned in the response as argthread.

794

Debugging with gdb

Don’t use this packet; use the ‘qfThreadInfo’ query instead (see above).
Reply:‘qM count done argthread thread...’Where: count (two hex digits) is the number of threads being
returned; done (one hex digit) is zero to indicate more threads
and one indicates no further threads; argthreadid (eight hex digits) is nextthread from the request packet; thread. . . is a sequenceof thread IDs, threadid (eight hex digits), from the target. Seeremote.c:parse_threadlist_response().
‘qMemTags:start address,length:type’
Fetch memory tags of type type from the address range [start address, start address + length).
The target is responsible for calculating how many tags will be returned, as
this is architecture-specific.
start address is the starting address of the memory range.
length is the length, in bytes, of the memory range.
type is the type of tag the request wants to fetch. The type is a signed integer.
gdb will only send this packet if the stub has advertised support for memory
tagging via ‘qSupported’.
Reply:‘mxx...’Hex encoded sequence of uninterpreted bytes, xx . . . , representing
the tags found in the requested memory range.

‘qIsAddressTagged:address’
Check if address address is in a memory tagged region; if it is, it’s said to betagged. The target is responsible for checking it, as this is architecture-specific.
address is the address to be checked.
Reply:
Replies to this packet should all be in two hex digit format, as
follows:‘‘01’’

Address address is tagged.

‘‘00’’

Address address is not tagged.

‘QMemTags:start address,length:type:tag bytes’Store memory tags of type type to the address range [start address, start address + length).
The target is responsible for interpreting the type, the tag bytes and modifying
the memory tag granules accordingly, given this is architecture-specific.
The interpretation of how many tags (nt) should be written to how many
memory tag granules (ng) is also architecture-specific. The behavior is
implementation-specific, but the following is suggested.
If the number of memory tags, nt, is greater than or equal to the number ofmemory tag granules, ng, only ng tags will be stored.
If nt is less than ng, the behavior is that of a fill operation, and the tag bytes
will be used as a pattern that will get repeated until ng tags are stored.

Appendix E: gdb Remote Serial Protocol

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start address is the starting address of the memory range. The address does
not have any restriction on alignment or size.
length is the length, in bytes, of the memory range.
type is the type of tag the request wants to fetch. The type is a signed integer.
tag bytes is a sequence of hex encoded uninterpreted bytes which will be interpreted by the target. Each pair of hex digits is interpreted as a single byte.
gdb will only send this packet if the stub has advertised support for memory
tagging via ‘qSupported’.
Reply:‘OK’

The request was successful and the memory tag granules were modified accordingly.

‘qOffsets’Get section offsets that the target used when relocating the downloaded image.
Reply:‘Text=xxx;Data=yyy[;Bss=zzz]’
Relocate the Text section by xxx from its original address. Relocate
the Data section by yyy from its original address. If the object fileformat provides segment information (e.g. elf ‘PT_LOAD’ program
headers), gdb will relocate entire segments by the supplied offsets.
Note: while a Bss offset may be included in the response, gdb
ignores this and instead applies the Data offset to the Bss section.
‘TextSeg=xxx[;DataSeg=yyy]’
Relocate the first segment of the object file, which conventionallycontains program code, to a starting address of xxx. If ‘DataSeg’
is specified, relocate the second segment, which conventionally contains modifiable data, to a starting address of yyy. gdb will reportan error if the object file does not contain segment information, or
does not contain at least as many segments as mentioned in the
reply. Extra segments are kept at fixed offsets relative to the last
relocated segment.
‘qP mode thread-id’
Returns information on thread-id. Where: mode is a hex encoded 32 bit mode;
thread-id is a thread ID (see [thread-id syntax], page 775).
Don’t use this packet; use the ‘qThreadExtraInfo’ query instead (see below).
Reply: see remote.c:remote_unpack_thread_info_response().
‘QNonStop:1’‘QNonStop:0’
Enter non-stop (‘QNonStop:1’) or all-stop (‘QNonStop:0’) mode.
Section E.11 [Remote Non-Stop], page 828, for more information.
Reply:‘OK’

The request succeeded.

See

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This packet is not probed by default; the remote stub must request it, by
supplying an appropriate ‘qSupported’ response (see [qSupported], page 799).
Use of this packet is controlled by the set non-stop command; see Section 5.5.2[Non-Stop Mode], page 94.
‘QCatchSyscalls:1 [;sysno]...’‘QCatchSyscalls:0’
Enable (‘QCatchSyscalls:1’) or disable (‘QCatchSyscalls:0’) catchingsyscalls from the inferior process.
For ‘QCatchSyscalls:1’, each listed syscall sysno (encoded in hex) should bereported to gdb. If no syscall sysno is listed, every system call should bereported.
Note that if a syscall not in the list is reported, gdb will still filter the event
according to its own list from all corresponding catch syscall commands.
However, it is more efficient to only report the requested syscalls.
Multiple ‘QCatchSyscalls:1’ packets do not combine;‘QCatchSyscalls:1’ list is completely replaced by the new list.

any

earlierIf the inferior process execs, the state of ‘QCatchSyscalls’ is kept for the newprocess too. On targets where exec may affect syscall numbers, for example
with exec between 32 and 64-bit processes, the client should send a new packet
with the new syscall list.
Reply:‘OK’

The request succeeded.

Use of this packet is controlled by the set remote catch-syscalls command(see Section 20.4 [Remote Configuration], page 326). This packet is not probed
by default; the remote stub must request it, by supplying an appropriate‘qSupported’ response (see [qSupported], page 799).
‘QPassSignals: signal [;signal]...’
Each listed signal should be passed directly to the inferior process. Signals arenumbered identically to continue packets and stop replies (see Section E.4 [StopReply Packets], page 785). Each signal list item should be strictly greater thanthe previous item. These signals do not need to stop the inferior, or be reported
to gdb. All other signals should be reported to gdb. Multiple ‘QPassSignals’
packets do not combine; any earlier ‘QPassSignals’ list is completely replacedby the new list. This packet improves performance when using ‘handle signal
nostop noprint pass’.
Reply:‘OK’

The request succeeded.

Use of this packet is controlled by the set remote pass-signals command(see Section 20.4 [Remote Configuration], page 326). This packet is not probed
by default; the remote stub must request it, by supplying an appropriate‘qSupported’ response (see [qSupported], page 799).

Appendix E: gdb Remote Serial Protocol

797‘QProgramSignals: signal [;signal]...’
Each listed signal may be delivered to the inferior process. Others should besilently discarded.
In some cases, the remote stub may need to decide whether to deliver a signal
to the program or not without gdb involvement. One example of that is while
detaching — the program’s threads may have stopped for signals that haven’t
yet had a chance of being reported to gdb, and so the remote stub can use thesignal list specified by this packet to know whether to deliver or ignore thosepending signals.
This does not influence whether to deliver a signal as requested by a resumption
packet (see [vCont packet], page 780).
Signals are numbered identically to continue packets and stop replies (seeSection E.4 [Stop Reply Packets], page 785). Each signal list item should bestrictly greater than the previous item. Multiple ‘QProgramSignals’ packets
do not combine; any earlier ‘QProgramSignals’ list is completely replaced by
the new list.
Reply:‘OK’

The request succeeded.

Use of this packet is controlled by the set remote program-signals command (see Section 20.4 [Remote Configuration], page 326). This packet is notprobed by default; the remote stub must request it, by supplying an appropriate‘qSupported’ response (see [qSupported], page 799).
‘QThreadEvents:1’‘QThreadEvents:0’
Enable (‘QThreadEvents:1’) or disable (‘QThreadEvents:0’) reporting of
thread create and exit events. See [thread create event], page 787, for the reply
specifications. For example, this is used in non-stop mode when gdb stops a
set of threads and synchronously waits for the their corresponding stop replies.
Without exit events, if one of the threads exits, gdb would hang forever notknowing that it should no longer expect a stop for that same thread. gdb does
not enable this feature unless the stub reports that it supports it by including‘QThreadEvents+’ in its ‘qSupported’ reply.
This packet always enables/disables event reporting for all threads of all processes under control of the remote stub. For per-thread control of optional event
reporting, see the [QThreadOptions], page 797, packet.
Reply:‘OK’

The request succeeded.

Use of this packet is controlled by the set remote thread-events command(see Section 20.4 [Remote Configuration], page 326).
‘QThreadOptions[;options[:thread-id]]...’For each inferior thread, the last options in the list with a matching thread-id
are applied. Any options previously set on a thread are discarded and replacedby the new options specified. Threads that do not match any thread-id retain

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their previously-set options. Thread IDs are specified using the syntax describedin [thread-id syntax], page 775. If multiprocess extensions (see [multiprocessextensions], page 806) are supported, options can be specified to apply to all
threads of a process by using the ‘ppid.-1’ form of thread-id. Options with no
thread-id apply to all threads. Specifying no options value is an error. Zero isa valid value.
options is an hexadecimal integer specifying the enabled thread options, andis the bitwise OR of the following values. All values are given in hexadecimal
representation.
GDB_THREAD_OPTION_CLONE (0x1)
Report thread clone events (see [thread clone event], page 787).
This is only meaningful for targets that support clone events (e.g.,
GNU/Linux systems).
GDB_THREAD_OPTION_EXIT (0x2)
Report thread exit events (see [thread exit event], page 788).
For example, gdb enables the GDB_THREAD_OPTION_EXIT and GDB_THREAD_
OPTION_CLONE options when single-stepping a thread past a breakpoint, forthe following reasons:• If the single-stepped thread exits (e.g., it executes a thread exit systemcall), enabling GDB_THREAD_OPTION_EXIT prevents gdb from waiting forever, not knowing that it should no longer expect a stop for that same
thread, and blocking other threads from progressing.
• If the single-stepped thread spawns a new clone child (i.e., it executes aclone system call), enabling GDB_THREAD_OPTION_CLONE halts the cloned
thread before it executes any instructions, and thus prevents the following
problematic situations:− If the breakpoint is stepped-over in-line, the spawned thread would
incorrectly run free while the breakpoint being stepped over is notinserted, and thus the cloned thread may potentially run past the
breakpoint without stopping for it;− If displaced (out-of-line) stepping is used, the cloned thread starts
running at the out-of-line PC, leading to undefined behavior, usuallycrashing or corrupting data.
New threads start with thread options cleared.
gdb does not enable this feature unless the stub reports that it supports it byincluding ‘QThreadOptions=supported_options’ in its ‘qSupported’ reply.
Reply:‘OK’

The request succeeded.

Use of this packet is controlled by the set remote thread-options command(see Section 20.4 [Remote Configuration], page 326).
‘qRcmd,command’command (hex encoded) is passed to the local interpreter for execution. Invalid
commands should be reported using the output string. Before the final result

Appendix E: gdb Remote Serial Protocol

799

packet, the target may also respond with a number of intermediate ‘Ooutput’console output packets. Implementors should note that providing access to a
stubs’s interpreter may have security implications.
Reply:‘OK’

A command response with no output.

‘OUTPUT’

A command response with the hex encoded output string
OUTPUT.

Unlike most packets, this packet does not support ‘E.errtext’-style textual
error replies (see [textual error reply], page 775) by default. Stubs should
be careful to only send such a reply if gdb reported support for it with theerror-message feature (see [error-message], page 801).
(Note that the qRcmd packet’s name is separated from the command by a ‘,’,not a ‘:’, contrary to the naming conventions above. Please don’t use thispacket as a model for new packets.)‘qSearch:memory:address;length;search-pattern’Search length bytes at address for search-pattern. Both address and length are
encoded in hex; search-pattern is a sequence of bytes, also hex encoded.
Reply:‘0’

The pattern was not found.

‘1,address’
The pattern was found at address.
‘QStartNoAckMode’
Request that the remote stub disable the normal ‘+’/‘-’ protocol acknowledgments (see Section E.12 [Packet Acknowledgment], page 829).
Reply:‘OK’

The stub has switched to no-acknowledgment mode. gdb acknowledges this response, but neither the stub nor gdb shall send or
expect further ‘+’/‘-’ acknowledgments in the current connection.

‘qSupported [:gdbfeature [;gdbfeature]... ]’Tell the remote stub about features supported by gdb, and query the stub forfeatures it supports. This packet allows gdb and the remote stub to take advantage of each others’ features. ‘qSupported’ also consolidates multiple featureprobes at startup, to improve gdb performance—a single larger packet performs better than multiple smaller probe packets on high-latency links. Somefeatures may enable behavior which must not be on by default, e.g. because
it would confuse older clients or stubs. Other features may describe packets
which could be automatically probed for, but are not. These features must bereported before gdb will use them. This “default unsupported” behavior is
not appropriate for all packets, but it helps to keep the initial connection time
under control with new versions of gdb which support increasing numbers of
packets.

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Reply:‘stubfeature [;stubfeature]...’The stub supports or does not support each returned stubfeature,depending on the form of each stubfeature (see below for the possible forms).
The allowed forms for each feature (either a gdbfeature in the ‘qSupported’
packet, or a stubfeature in the response) are:‘name=value’
The remote protocol feature name is supported, and associatedwith the specified value. The format of value depends on the feature, but it must not include a semicolon.
‘name+’The remote protocol feature name is supported, and does not need
an associated value.

‘name-’The remote protocol feature name is not supported.

‘name?’The remote protocol feature name may be supported, and gdb
should auto-detect support in some other way when it is needed.
This form will not be used for gdbfeature notifications, but may be
used for stubfeature responses.

Whenever the stub receives a ‘qSupported’ request, the supplied set of gdb
features should override any previous request. This allows gdb to put the stubin a known state, even if the stub had previously been communicating with adifferent version of gdb.
The following values of gdbfeature (for the packet sent by gdb) are defined:‘multiprocess’This feature indicates whether gdb supports multiprocess extensions to the remote protocol. gdb does not use such extensions
unless the stub also reports that it supports them by including‘multiprocess+’ in its ‘qSupported’ reply. See [multiprocess extensions], page 806, for details.
‘xmlRegisters’This feature indicates that gdb supports the XML target description. If the stub sees ‘xmlRegisters=’ with target specific strings
separated by a comma, it will report register description.
‘qRelocInsn’
This feature indicates whether gdb supports the ‘qRelocInsn’
packet (see Section E.7 [Relocate instruction reply packet],page 817).
‘swbreak’This feature indicates whether gdb supports the swbreak stop reason in stop replies. See [swbreak stop reason], page 786, for details.

‘hwbreak’This feature indicates whether gdb supports the hwbreak stop reason in stop replies. See [swbreak stop reason], page 786, for details.

Appendix E: gdb Remote Serial Protocol

801‘fork-events’This feature indicates whether gdb supports fork event extensions
to the remote protocol. gdb does not use such extensions
unless the stub also reports that it supports them by including‘fork-events+’ in its ‘qSupported’ reply.
‘vfork-events’This feature indicates whether gdb supports vfork event extensions to the remote protocol. gdb does not use such extensions
unless the stub also reports that it supports them by including‘vfork-events+’ in its ‘qSupported’ reply.
‘exec-events’This feature indicates whether gdb supports exec event extensions to the remote protocol. gdb does not use such extensions
unless the stub also reports that it supports them by including‘exec-events+’ in its ‘qSupported’ reply.
‘vContSupported’
This feature indicates whether gdb wants to know the supported
actions in the reply to ‘vCont?’ packet.
‘error-message’This feature indicates whether gdb supports accepting a reply in‘E.errtext’ format (See [textual error reply], page 775) from the‘qRcmd’ and ‘m’ packets. These packets, historically, didn’t support‘E.errtext’, and older versions of gdb didn’t expect to see a reply
in this format.
New packets should be written to support ‘E.errtext’ regardlessof this feature being true or not.
Stubs should ignore any unknown values for gdbfeature. Any gdb which sends
a ‘qSupported’ packet supports receiving packets of unlimited length (earlier versions of gdb may reject overly long responses). Additional values for
gdbfeature may be defined in the future to let the stub take advantage of newfeatures in gdb, e.g. incompatible improvements in the remote protocol—the‘multiprocess’ feature is an example of such a feature. The stub’s reply should
be independent of the gdbfeature entries sent by gdb; first gdb describes all thefeatures it supports, and then the stub replies with all the features it supports.
Similarly, gdb will silently ignore unrecognized stub feature responses, as longas each response uses one of the standard forms.
Some features are flags. A stub which supports a flag feature should respondwith a ‘+’ form response. Other features require values, and the stub should
respond with an ‘=’ form response.
Each feature has a default value, which gdb will use if ‘qSupported’ is notavailable or if the feature is not mentioned in the ‘qSupported’ response. The
default values are fixed; a stub is free to omit any feature responses that matchthe defaults.

802

Debugging with gdb

Not all features can be probed, but for those which can, the probing mechanism
is useful: in some cases, a stub’s internal architecture may not allow the protocol
layer to know some information about the underlying target in advance. Thisis especially common in stubs which may be configured for multiple targets.
These are the currently defined stub features and their properties:
Feature Name

Value Required

Default

Probe Allowed‘PacketSize’

Yes

‘-’

No

‘qXfer:auxv:read’

No

‘-’

Yes

‘qXfer:btrace:read’

No

‘-’

Yes

‘qXfer:btrace-conf:read’

No

‘-’

Yes

‘qXfer:exec-file:read’

No

‘-’

Yes

‘qXfer:features:read’

No

‘-’

Yes

‘qXfer:libraries:read’

No

‘-’

Yes

‘qXfer:libraries-svr4:read’

No

‘-’

Yes

‘augmented-libraries-svr4-read’
No

‘-’

No

‘qXfer:memory-map:read’

No

‘-’

Yes

‘qXfer:sdata:read’

No

‘-’

Yes

‘qXfer:siginfo:read’

No

‘-’

Yes

‘qXfer:siginfo:write’

No

‘-’

Yes

‘qXfer:threads:read’

No

‘-’

Yes

‘qXfer:traceframe-info:read’ No

‘-’

Yes

‘qXfer:uib:read’

No

‘-’

Yes

‘qXfer:fdpic:read’

No

‘-’

Yes

‘Qbtrace:off’

Yes

‘-’

Yes

‘Qbtrace:bts’

Yes

‘-’

Yes

Appendix E: gdb Remote Serial Protocol

803‘Qbtrace:pt’

Yes

‘-’

Yes

‘Qbtrace-conf:bts:size’

Yes

‘-’

Yes

‘Qbtrace-conf:pt:size’

Yes

‘-’

Yes

‘Qbtrace-conf:pt:ptwrite’

Yes

‘-’

Yes

‘Qbtrace-conf:pt:event-tracing’
Yes

‘-’

Yes

‘QNonStop’

No

‘-’

Yes

‘QCatchSyscalls’

No

‘-’

Yes

‘QPassSignals’

No

‘-’

Yes

‘QStartNoAckMode’

No

‘-’

Yes

‘multiprocess’

No

‘-’

No

‘ConditionalBreakpoints’

No

‘-’

No

‘ConditionalTracepoints’

No

‘-’

No

‘ReverseContinue’

No

‘-’

No

‘ReverseStep’

No

‘-’

No

‘TracepointSource’

No

‘-’

No

‘QAgent’

No

‘-’

No

‘QAllow’

No

‘-’

No

‘QDisableRandomization’

No

‘-’

No

‘EnableDisableTracepoints’

No

‘-’

No

‘QTBuffer:size’

No

‘-’

No

‘tracenz’

No

‘-’

No

‘BreakpointCommands’

No

‘-’

No

‘swbreak’

No

‘-’

No

804

Debugging with gdb‘hwbreak’

No

‘-’

No

‘fork-events’

No

‘-’

No

‘vfork-events’

No

‘-’

No

‘exec-events’

No

‘-’

No

‘QThreadEvents’

No

‘-’

No

‘QThreadOptions’

Yes

‘-’

No

‘no-resumed’

No

‘-’

No

‘memory-tagging’

No

‘-’

No

‘error-message’

No

‘+’

No

These are the currently defined stub features, in more detail:‘PacketSize=bytes’
The remote stub can accept packets up to at least bytes in length.
gdb will send packets up to this size for bulk transfers, and will
never send larger packets. This is a limit on the data charactersin the packet, not including the frame and checksum. There is notrailing NUL byte in a remote protocol packet; if the stub storespackets in a NUL-terminated format, it should allow an extra byte
in its buffer for the NUL. If this stub feature is not supported, gdb
guesses based on the size of the ‘g’ packet response.
‘qXfer:auxv:read’
The remote stub understands the ‘qXfer:auxv:read’ packet (see[qXfer auxiliary vector read], page 810).
‘qXfer:btrace:read’
The remote stub understands the ‘qXfer:btrace:read’ packet (see[qXfer btrace read], page 810).
‘qXfer:btrace-conf:read’
The remote stub understands the ‘qXfer:btrace-conf:read’
packet (see [qXfer btrace-conf read], page 811).
‘qXfer:exec-file:read’
The remote stub understands the ‘qXfer:exec-file:read’ packet(see [qXfer executable filename read], page 811).
‘qXfer:features:read’
The remote stub understands the ‘qXfer:features:read’ packet(see [qXfer target description read], page 811).

Appendix E: gdb Remote Serial Protocol

805‘qXfer:libraries:read’
The remote stub understands the ‘qXfer:libraries:read’ packet(see [qXfer library list read], page 811).
‘qXfer:libraries-svr4:read’
The remote stub understands the ‘qXfer:libraries-svr4:read’
packet (see [qXfer svr4 library list read], page 812).
‘augmented-libraries-svr4-read’
The remote stub understands the augmented form of the‘qXfer:libraries-svr4:read’ packet (see [qXfer svr4 library listread], page 812).
‘qXfer:memory-map:read’
The remote stub understands the ‘qXfer:memory-map:read’ packet(see [qXfer memory map read], page 813).
‘qXfer:sdata:read’
The remote stub understands the ‘qXfer:sdata:read’ packet (see[qXfer sdata read], page 813).
‘qXfer:siginfo:read’
The remote stub understands the ‘qXfer:siginfo:read’ packet(see [qXfer siginfo read], page 813).
‘qXfer:siginfo:write’
The remote stub understands the ‘qXfer:siginfo:write’ packet(see [qXfer siginfo write], page 814).
‘qXfer:threads:read’
The remote stub understands the ‘qXfer:threads:read’ packet(see [qXfer threads read], page 813).
‘qXfer:traceframe-info:read’
The remote stub understands the ‘qXfer:traceframe-info:read’
packet (see [qXfer traceframe info read], page 813).
‘qXfer:uib:read’
The remote stub understands the ‘qXfer:uib:read’ packet (see[qXfer unwind info block], page 813).
‘qXfer:fdpic:read’
The remote stub understands the ‘qXfer:fdpic:read’ packet (see[qXfer fdpic loadmap read], page 814).
‘QNonStop’
The remote stub understands the ‘QNonStop’ packet (see[QNonStop], page 795).
‘QCatchSyscalls’
The remote stub understands the ‘QCatchSyscalls’ packet (see[QCatchSyscalls], page 796).

806

Debugging with gdb‘QPassSignals’
The remote stub understands the ‘QPassSignals’ packet (see[QPassSignals], page 796).
‘QStartNoAckMode’
The remote stub understands the ‘QStartNoAckMode’ packet andprefers to operate in no-acknowledgment mode. See Section E.12
[Packet Acknowledgment], page 829.
‘multiprocess’
The remote stub understands the multiprocess extensions to theremote protocol syntax. The multiprocess extensions affect thesyntax of thread IDs in both packets and replies (see [thread-id
syntax], page 775), and add process IDs to the ‘D’ packet and ‘W’ and‘X’ replies. Note that reporting this feature indicates support forthe syntactic extensions only, not that the stub necessarily supports
debugging of more than one process at a time. The stub must notuse multiprocess extensions in packet replies unless gdb has also
indicated it supports them in its ‘qSupported’ request.
‘qXfer:osdata:read’
The remote stub understands the ‘qXfer:osdata:read’ packet((see [qXfer osdata read], page 814).
‘ConditionalBreakpoints’
The target accepts and implements evaluation of conditional expressions defined for breakpoints. The target will only report breakpoint triggers when such conditions are true (see Section 5.1.6[Break Conditions], page 76).
‘ConditionalTracepoints’
The remote stub accepts and implements conditional expressions
defined for tracepoints (see Section 13.1.4 [Tracepoint Conditions],
page 207).
‘ReverseContinue’
The remote stub accepts and implements the reverse continue
packet (see [bc], page 776).
‘ReverseStep’
The remote stub accepts and implements the reverse step packet(see [bs], page 776).
‘TracepointSource’
The remote stub understands the ‘QTDPsrc’ packet that supplies
the source form of tracepoint definitions.
‘QAgent’

The remote stub understands the ‘QAgent’ packet.

‘QAllow’

The remote stub understands the ‘QAllow’ packet.

‘QDisableRandomization’The remote stub understands the ‘QDisableRandomization’
packet.

Appendix E: gdb Remote Serial Protocol

807‘StaticTracepoint’
The remote stub supports static tracepoints.
‘InstallInTrace’The remote stub supports installing tracepoint in tracing.
‘EnableDisableTracepoints’
The remote stub supports the ‘QTEnable’ (see [QTEnable],
page 820) and ‘QTDisable’ (see [QTDisable], page 820) packets
that allow tracepoints to be enabled and disabled while a traceexperiment is running.
‘QTBuffer:size’
The remote stub supports the ‘QTBuffer:size’ (see [QTBuffersize], page 823) packet that allows to change the size of the trace
buffer.
‘tracenz’

The remote stub supports the ‘tracenz’ bytecode for collecting
strings. See Section F.2 [Bytecode Descriptions], page 849, for details about the bytecode.

‘BreakpointCommands’
The remote stub supports running a breakpoint’s command list
itself, rather than reporting the hit to gdb.
‘Qbtrace:off’
The remote stub understands the ‘Qbtrace:off’ packet.
‘Qbtrace:bts’
The remote stub understands the ‘Qbtrace:bts’ packet.
‘Qbtrace:pt’
The remote stub understands the ‘Qbtrace:pt’ packet.
‘Qbtrace-conf:bts:size’
The remote stub understands the ‘Qbtrace-conf:bts:size’
packet.
‘Qbtrace-conf:pt:size’
The remote stub understands the ‘Qbtrace-conf:pt:size’ packet.
‘Qbtrace-conf:pt:ptwrite’
The remote stub understands the ‘Qbtrace-conf:pt:ptwrite’
packet.
‘Qbtrace-conf:pt:event-tracing’
The remote stub understands the ‘Qbtrace-conf:pt:event-tracing’
packet.
‘swbreak’

The remote stub reports the ‘swbreak’ stop reason for memory
breakpoints.

‘hwbreak’

The remote stub reports the ‘hwbreak’ stop reason for hardware
breakpoints.

808

Debugging with gdb‘fork-events’
The remote stub reports the ‘fork’ stop reason for fork events.
‘vfork-events’
The remote stub reports the ‘vfork’ stop reason for vfork eventsand vforkdone events.
‘exec-events’
The remote stub reports the ‘exec’ stop reason for exec events.
‘vContSupported’
The remote stub reports the supported actions in the reply to‘vCont?’ packet.
‘QThreadEvents’
The remote stub understands the ‘QThreadEvents’ packet.
‘QThreadOptions=supported_options’
The remote stub understands the ‘QThreadOptions’ packet.
supported options indicates the set of thread options the remotestub supports. supported options has the same format as theoptions parameter of the QThreadOptions packet, described at[QThreadOptions], page 797.
‘no-resumed’
The remote stub reports the ‘N’ stop reply.
‘memory-tagging’
The remote stub supports and implements the required memory
tagging functionality and understands the ‘qMemTags’ (see[qMemTags], page 794) and ‘QMemTags’ (see [QMemTags],
page 794) packets.
For AArch64 GNU/Linux systems, this feature can require access to the /proc/pid/smaps file so memory mapping page flags
can be inspected, if ‘qIsAddressTagged’ (see [qIsAddressTagged],
page 794) packet is not supported by the stub. Access to the/proc/pid/smaps file is done via ‘vFile’ requests.
‘error-message’The remote stub supports replying with an error in a ‘E.errtext’(See [textual error reply], page 775) format from the ‘m’ and ‘qRcmd’
packets. It is not usually necessary to send this feature back to gdb
in the ‘qSupported’ reply, gdb will always support ‘E.errtext’
format replies if it sent the ‘error-message’ feature.
‘qSymbol::’
Notify the target that gdb is prepared to serve symbol lookup requests. Accept
requests from the target for the values of symbols.
Reply:‘OK’

The target does not need to look up any (more) symbols.

Appendix E: gdb Remote Serial Protocol

809‘qSymbol:sym_name’
The target requests the value of symbol sym name (hexencoded).
gdb may provide the value by using the‘qSymbol:sym_value:sym_name’ message, described below.
‘qSymbol:sym_value:sym_name’
Set the value of sym name to sym value.
sym name (hex encoded) is the name of a symbol whose value the target has
previously requested.
sym value (hex) is the value for symbol sym name. If gdb cannot supply avalue for sym name, then this field will be empty.
Reply:‘OK’

The target does not need to look up any (more) symbols.

‘qSymbol:sym_name’
The target requests the value of a new symbol sym name (hexencoded). gdb will continue to supply the values of symbols (ifavailable), until the target ceases to request them.
‘qTBuffer’‘QTBuffer’‘QTDisconnected’‘QTDP’‘QTDPsrc’‘QTDV’‘qTfP’‘qTfV’‘QTFrame’‘qTMinFTPILen’
See Section E.7 [Tracepoint Packets], page 817.
‘qThreadExtraInfo,thread-id’
Obtain from the target OS a printable string description of thread attributes forthe thread thread-id; see [thread-id syntax], page 775, for the forms of threadid. This string may contain anything that the target OS thinks is interestingfor gdb to tell the user about the thread. The string is displayed in gdb’s
info threads display. Some examples of possible thread extra info strings are‘Runnable’, or ‘Blocked on Mutex’.
Reply:‘XX...’

Where ‘XX...’ is a hex encoding of ascii data, comprising theprintable string containing the extra information about the thread’s
attributes.

(Note that the qThreadExtraInfo packet’s name is separated from the command by a ‘,’, not a ‘:’, contrary to the naming conventions above. Please
don’t use this packet as a model for new packets.)

810

Debugging with gdb‘QTNotes’‘qTP’‘QTSave’‘qTsP’‘qTsV’‘QTStart’‘QTStop’‘QTEnable’‘QTDisable’‘QTinit’‘QTro’‘qTStatus’‘qTV’‘qTfSTM’‘qTsSTM’‘qTSTMat’ See Section E.7 [Tracepoint Packets], page 817.
‘qXfer:object:read:annex:offset,length’
Read uninterpreted bytes from the target’s special data area identified by the
keyword object. Request length bytes starting at offset bytes into the data.
The content and encoding of annex is specific to object; it can supply additional
details about what data to access.
Reply:‘m data’

Data data (see [Binary Data], page 773) has been read from thetarget. There may be more data at a higher address (although it
is permitted to return ‘m’ even for the last valid block of data, as
long as at least one byte of data was read). It is possible for datato have fewer bytes than the length in the request.

‘l data’

Data data (see [Binary Data], page 773) has been read from thetarget. There is no more data to be read. It is possible for data tohave fewer bytes than the length in the request.

‘l’The offset in the request is at the end of the data. There is no moredata to be read.

Here are the specific requests of this form defined so far.
All the‘qXfer:object:read:...’ requests use the same reply formats, listed above.
‘qXfer:auxv:read::offset,length’
Access the target’s auxiliary vector. See Section 10.17 [OS Information], page 181. Note annex must be empty.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:btrace:read:annex:offset,length’
Return a description of the current branch trace. See Section E.20
[Branch Trace Format], page 845. The annex part of the generic‘qXfer’ packet may have one of the following values:Appendix E: gdb Remote Serial Protocol

811

all

Returns all available branch trace.

new

Returns all available branch trace if the branch tracechanged since the last read request.

delta

Returns the new branch trace since the last read request. Adds a new block to the end of the trace thatbegins at zero and ends at the source location of thefirst branch in the trace buffer. This extra block is used
to stitch traces together.
If the trace buffer overflowed, returns an error indicating the overflow.

This packet is not probed by default; the remote stub must request it by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:btrace-conf:read::offset,length’
Return a description of the current branch trace configuration. See
Section E.21 [Branch Trace Configuration Format], page 846.
This packet is not probed by default; the remote stub must request it by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:exec-file:read:annex:offset,length’
Return the full absolute name of the file that was executed to createa process running on the remote system. The annex specifies thenumeric process ID of the process to query, encoded as a hexadecimal number. If the annex part is empty the remote stub should
return the filename corresponding to the currently executing process.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:features:read:annex:offset,length’
Access the target description. See Appendix G [Target Descriptions], page 859. The annex specifies which XML document to access. The main description is always loaded from the ‘target.xml’
annex.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:libraries:read:annex:offset,length’
Access the target’s list of loaded libraries. See Section E.15 [Library
List Format], page 841. The annex part of the generic ‘qXfer’
packet must be empty (see [qXfer read], page 810).
Targets which maintain a list of libraries in the program’s memory
do not need to implement this packet; it is designed for platforms
where the operating system manages the list of loaded libraries.

812

Debugging with gdb

This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:libraries-svr4:read:annex:offset,length’
Access the target’s list of loaded libraries when the target is an
SVR4 platform. See Section E.16 [Library List Format for SVR4
Targets], page 842. The annex part of the generic ‘qXfer’ packet
must be empty unless the remote stub indicated it supports
the augmented form of this packet by supplying an appropriate‘qSupported’ response (see [qXfer read], page 810, [qSupported],
page 799).
This packet is optional for better performance on SVR4 targets.
gdb uses memory read packets to read the SVR4 library list otherwise.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
If the remote stub indicates it supports the augmented form of
this packet then the annex part of the generic ‘qXfer’ packet may
contain a semicolon-separated list of ‘name=value’ arguments. The
currently supported arguments are:start=address
A hexadecimal number specifying the address of the‘struct link_map’ to start reading the library list
from. If unset or zero then the first ‘struct link_map’
in the library list will be chosen as the starting point.
prev=address
A hexadecimal number specifying the address of the‘struct link_map’ immediately preceding the ‘struct
link_map’ specified by the ‘start’ argument. If unset or zero then the remote stub will expect that no‘struct link_map’ exists prior to the starting point.
lmid=lmid
A hexadecimal number specifying a namespace identifier. This is currently only used together with ‘start’
to provide the namespace identifier back to gdb in the
response. gdb will only provide values that were previously reported to it. If unset, the response will include‘lmid="0x0"’.
Arguments that are not understood by the remote stub will besilently ignored.

Appendix E: gdb Remote Serial Protocol

813‘qXfer:memory-map:read::offset,length’
Access the target’s memory-map. See Section E.17 [Memory Map
Format], page 843. The annex part of the generic ‘qXfer’ packet
must be empty (see [qXfer read], page 810).
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:sdata:read::offset,length’
Read contents of the extra collected static tracepoint marker information. The annex part of the generic ‘qXfer’ packet must be
empty (see [qXfer read], page 810). See Section 13.1.6 [Tracepoint
Action Lists], page 208.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:siginfo:read::offset,length’
Read contents of the extra signal information on the target system.
The annex part of the generic ‘qXfer’ packet must be empty (see[qXfer read], page 810).
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:threads:read::offset,length’
Access the list of threads on target. See Section E.18 [Thread List
Format], page 844. The annex part of the generic ‘qXfer’ packet
must be empty (see [qXfer read], page 810).
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:traceframe-info:read::offset,length’
Return a description of the current traceframe’s contents. See
Section E.19 [Traceframe Info Format], page 845. The annex partof the generic ‘qXfer’ packet must be empty (see [qXfer read],page 810).
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:uib:read:pc:offset,length’
Return the unwind information block for pc. This packet is used
on OpenVMS/ia64 to ask the kernel unwind information.
This packet is not probed by default.

814

Debugging with gdb‘qXfer:fdpic:read:annex:offset,length’
Read contents of loadmaps on the target system. The annex, either‘exec’ or ‘interp’, specifies which loadmap, executable loadmap orinterpreter loadmap to read.
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:osdata:read::offset,length’
Access the target’s operating system information. See Appendix H[Operating System Information], page 879.
‘qXfer:object:write:annex:offset:data...’Write uninterpreted bytes into the target’s special data area identified by the
keyword object, starting at offset bytes into the data. The binary-encoded data
(see [Binary Data], page 773) to be written is given by data. . . . The content
and encoding of annex is specific to object; it can supply additional details
about what data to access.
Reply:‘nn’

nn (hex encoded) is the number of bytes written. This may be
fewer bytes than supplied in the request.

Here are the specific requests of this form defined so far.
All the‘qXfer:object:write:...’ requests use the same reply formats, listed above.
‘qXfer:siginfo:write::offset:data...’Write data to the extra signal information on the target system.
The annex part of the generic ‘qXfer’ packet must be empty (see[qXfer write], page 814).
This packet is not probed by default; the remote stub must request it, by supplying an appropriate ‘qSupported’ response (see[qSupported], page 799).
‘qXfer:object:operation:...’
Requests of this form may be added in the future. When a stub does notrecognize the object keyword, or its support for object does not recognize theoperation keyword, the stub must respond with an empty packet.
‘qAttached:pid’
Return an indication of whether the remote server attached to an existing process or created a new process. When the multiprocess protocol extensions aresupported (see [multiprocess extensions], page 806), pid is an integer in hexadecimal format identifying the target process. Otherwise, gdb will omit thepid field and the query packet will be simplified as ‘qAttached’.
This query is used, for example, to know whether the remote process should be
detached or killed when a gdb session is ended with the quit command.
Reply:‘1’

The remote server attached to an existing process.

Appendix E: gdb Remote Serial Protocol

‘0’

815

The remote server created a new process.

‘Qbtrace:bts’Enable branch tracing for the current thread using Branch Trace Store.
Reply:‘OK’

Branch tracing has been enabled.

‘Qbtrace:pt’
Enable branch tracing for the current thread using Intel Processor Trace.
Reply:‘OK’

Branch tracing has been enabled.

‘Qbtrace:off’Disable branch tracing for the current thread.
Reply:‘OK’

Branch tracing has been disabled.

‘Qbtrace-conf:bts:size=value’
Set the requested ring buffer size for new threads that use the btrace recording
method in bts format.
Reply:‘OK’

The ring buffer size has been set.

‘Qbtrace-conf:pt:size=value’
Set the requested ring buffer size for new threads that use the btrace recording
method in pt format.
Reply:‘OK’

The ring buffer size has been set.

‘Qbtrace-conf:pt:ptwrite=(yes|no)’
Indicate support for PTWRITE packets. This allows for backwards compatibility.
Reply:‘OK’

The ptwrite config parameter has been set.

‘E.errtext’
A badly formed request or an error was encountered.
‘Qbtrace-conf:pt:event-tracing=(yes|no)’
Indicate support for event-tracing packets. This allows for backwards compatibility.
Reply:‘OK’

The event-tracing config parameter has been set.

‘E.errtext’
A badly formed request or an error was encountered.

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E.6 Architecture-Specific Protocol Details
This section describes how the remote protocol is applied to specific target architectures.
Also see Section G.5 [Standard Target Features], page 865, for details of XML target descriptions for each architecture.

E.6.1 ARM-specific Protocol Details
E.6.1.1 ARM Breakpoint Kinds
These breakpoint kinds are defined for the ‘Z0’ and ‘Z1’ packets.
2

16-bit Thumb mode breakpoint.

3

32-bit Thumb mode (Thumb-2) breakpoint.

4

32-bit ARM mode breakpoint.

E.6.1.2 ARM Memory Tag Types
These memory tag types are defined for the ‘qMemTag’ and ‘QMemTag’ packets.
0

MTE logical tag

1

MTE allocation tag

E.6.2 MIPS-specific Protocol Details
E.6.2.1 MIPS Register Packet Format
The following g/G packets have previously been defined. In the below, some thirty-two bit
registers are transferred as sixty-four bits. Those registers should be zero/sign extended(which?) to fill the space allocated. Register bytes are transferred in target byte order.
The two nibbles within a register byte are transferred most-significant – least-significant.
MIPS32All registers are transferred as thirty-two bit quantities in the order: 32 generalpurpose; sr; lo; hi; bad; cause; pc; 32 floating-point registers; fsr; fir; fp.

MIPS64All registers are transferred as sixty-four bit quantities (including thirty-two bit
registers such as sr). The ordering is the same as MIPS32.

E.6.2.2 MIPS Breakpoint Kinds
These breakpoint kinds are defined for the ‘Z0’ and ‘Z1’ packets.
2

16-bit MIPS16 mode breakpoint.

3

16-bit microMIPS mode breakpoint.

4

32-bit standard MIPS mode breakpoint.

5

32-bit microMIPS mode breakpoint.

Appendix E: gdb Remote Serial Protocol

817

E.7 Tracepoint Packets
Here we describe the packets gdb uses to implement tracepoints (see Chapter 13 [Tracepoints], page 203).
‘QTDP:n:addr:ena:step:pass[:Fflen][:Xlen,bytes][-]’Create a new tracepoint, number n, at addr. If ena is ‘E’, then the tracepointis enabled; if it is ‘D’, then the tracepoint is disabled. The step gives thetracepoint’s step count, and pass gives its pass count. If an ‘F’ is present, then
the tracepoint is to be a fast tracepoint, and the flen is the number of bytes
that the target should copy elsewhere to make room for the tracepoint. If an ‘X’is present, it introduces a tracepoint condition, which consists of a hexadecimallength, followed by a comma and hex-encoded bytes, in a manner similar toaction encodings as described below. If the trailing ‘-’ is present, further ‘QTDP’
packets will follow to specify this tracepoint’s actions.
Replies:‘OK’

The packet was understood and carried out.

‘qRelocInsn’
See Section E.7 [Relocate instruction reply packet], page 817.
‘QTDP:-n:addr:[S]action...[-]’
Define actions to be taken when a tracepoint is hit. The n and addr must be
the same as in the initial ‘QTDP’ packet for this tracepoint. This packet may
only be sent immediately after another ‘QTDP’ packet that ended with a ‘-’. If
the trailing ‘-’ is present, further ‘QTDP’ packets will follow, specifying moreactions for this tracepoint.
In the series of action packets for a given tracepoint, at most one can have an‘S’ before its first action. If such a packet is sent, it and the following packets
define “while-stepping” actions. Any prior packets define ordinary actions —that is, those taken when the tracepoint is first hit. If no action packet has an‘S’, then all the packets in the series specify ordinary tracepoint actions.
The ‘action...’ portion of the packet is a series of actions, concatenated without separators. Each action has one of the following forms:‘R mask’Collect the registers whose bits are set in mask, a hexadecimal
number whose i’th bit is set if register number i should be collected.
(The least significant bit is numbered zero.) Note that mask may
be any number of digits long; it may not fit in a 32-bit word.

‘M basereg,offset,len’Collect len bytes of memory starting at the address in register number basereg, plus offset. If basereg is ‘-1’, then the range has a fixed
address: offset is the address of the lowest byte to collect. The
basereg, offset, and len parameters are all unsigned hexadecimalvalues (the ‘-1’ value for basereg is a special case).
‘X len,expr’
Evaluate expr, whose length is len, and collect memory as it directs.
The agent expression expr is as described in Appendix F [Agent818

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Expressions], page 847. Each byte of the expression is encoded asa two-digit hex number in the packet; len is the number of bytes inthe expression (and thus one-half the number of hex digits in thepacket).
Any number of actions may be packed together in a single ‘QTDP’ packet, as longas the packet does not exceed the maximum packet length (400 bytes, for manystubs). There may be only one ‘R’ action per tracepoint, and it must precedeany ‘M’ or ‘X’ actions. Any registers referred to by ‘M’ and ‘X’ actions must becollected by a preceding ‘R’ action. (The “while-stepping” actions are treatedas if they were attached to a separate tracepoint, as far as these restrictions areconcerned.)
Replies:‘OK’

The packet was understood and carried out.

‘qRelocInsn’
See Section E.7 [Relocate instruction reply packet], page 817.
‘QTDPsrc:n:addr:type:start:slen:bytes’Specify a source string of tracepoint n at address addr. This is useful to get
accurate reproduction of the tracepoints originally downloaded at the beginningof the trace run. The type is the name of the tracepoint part, such as ‘cond’for the tracepoint’s conditional expression (see below for a list of types), whilebytes is the string, encoded in hexadecimal.
start is the offset of the bytes within the overall source string, while slen is thetotal length of the source string. This is intended for handling source strings
that are longer than will fit in a single packet.
The available string types are ‘at’ for the location, ‘cond’ for the conditional,and ‘cmd’ for an action command. gdb sends a separate packet for each command in the action list, in the same order in which the commands are stored
in the list.
The target does not need to do anything with source strings except report themback as part of the replies to the ‘qTfP’/‘qTsP’ query packets.
Although this packet is optional, and gdb will only send it if the target replies
with ‘TracepointSource’ See Section E.5 [General Query Packets], page 789, it
makes both disconnected tracing and trace files much easier to use. Otherwise
the user must be careful that the tracepoints in effect while looking at trace
frames are identical to the ones in effect during the trace run; even a small
discrepancy could cause ‘tdump’ not to work, or a particular trace frame not befound.
‘QTDV:n:value:builtin:name’
Create a new trace state variable, number n, with an initial value of value,
which is a 64-bit signed integer. Both n and value are encoded as hexadecimalvalues. gdb has the option of not using this packet for initial values of zero;
the target should simply create the trace state variables as they are mentioned
in expressions. The value builtin should be 1 (one) if the trace state variable isbuiltin and 0 (zero) if it is not builtin. gdb only sets builtin to 1 if a previous

Appendix E: gdb Remote Serial Protocol

819‘qTfV’ or ‘qTsV’ packet had it set. The contents of name is the hex-encodedname (without the leading ‘$’) of the trace state variable.
‘QTFrame:n’Select the n’th tracepoint frame from the buffer, and use the register and memory contents recorded there to answer subsequent request packets from gdb.
A successful reply from the stub indicates that the stub has found the requested
frame. The response is a series of parts, concatenated without separators,
describing the frame we selected. Each part has one of the following forms:‘F f’

The selected frame is number n in the trace frame buffer; f is ahexadecimal number. If f is ‘-1’, then there was no frame matching
the criteria in the request packet.

‘T t’

The selected trace frame records a hit of tracepoint number t; t isa hexadecimal number.

‘QTFrame:pc:addr’
Like ‘QTFrame:n’, but select the first tracepoint frame after the currently selected frame whose PC is addr; addr is a hexadecimal number.
‘QTFrame:tdp:t’Like ‘QTFrame:n’, but select the first tracepoint frame after the currently selected frame that is a hit of tracepoint t; t is a hexadecimal number.
‘QTFrame:range:start:end’
Like ‘QTFrame:n’, but select the first tracepoint frame after the currently selected frame whose PC is between start (inclusive) and end (inclusive); startand end are hexadecimal numbers.
‘QTFrame:outside:start:end’
Like ‘QTFrame:range:start:end’, but select the first frame outside the given
range of addresses (exclusive).
‘qTMinFTPILen’
This packet requests the minimum length of instruction at which a fast tracepoint (see Section 13.1 [Set Tracepoints], page 203) may be placed. For instance,on the 32-bit x86 architecture, it is possible to use a 4-byte jump, but it depends on the target system being able to create trampolines in the first 64K ofmemory, which might or might not be possible for that system. So the reply tothis packet will be 4 if it is able to arrange for that.
Replies:‘QTStart’‘0’

The minimum instruction length is currently unknown.

‘length’The minimum instruction length is length, where length is a hexadecimal number greater or equal to 1. A reply of 1 means that afast tracepoint may be placed on any instruction regardless of size.

‘E’An error has occurred.

Begin the tracepoint experiment. Begin collecting data from tracepoint hits
in the trace frame buffer. This packet supports the ‘qRelocInsn’ reply (seeSection E.7 [Relocate instruction reply packet], page 817).

820‘QTStop’

Debugging with gdb

End the tracepoint experiment. Stop collecting trace frames.

‘QTEnable:n:addr’
Enable tracepoint n at address addr in a started tracepoint experiment. If the
tracepoint was previously disabled, then collection of data from it will resume.
‘QTDisable:n:addr’
Disable tracepoint n at address addr in a started tracepoint experiment. No
more data will be collected from the tracepoint unless ‘QTEnable:n:addr’ issubsequently issued.
‘QTinit’Clear the table of tracepoints, and empty the trace frame buffer.

‘QTro:start1,end1:start2,end2:...’
Establish the given ranges of memory as “transparent”. The stub will answer
requests for these ranges from memory’s current contents, if they were notcollected as part of the tracepoint hit.
gdb uses this to mark read-only regions of memory, like those containing program code. Since these areas never change, they should still have the samecontents they did when the tracepoint was hit, so there’s no reason for the stub
to refuse to provide their contents.
‘QTDisconnected:value’
Set the choice to what to do with the tracing run when gdb disconnects fromthe target. A value of 1 directs the target to continue the tracing run, while 0
tells the target to stop tracing if gdb is no longer in the picture.
‘qTStatus’
Ask the stub if there is a trace experiment running right now.
The reply has the form:‘Trunning[;field]...’
running is a single digit 1 if the trace is presently running, or 0 if
not. It is followed by semicolon-separated optional fields that an
agent may use to report additional status.
If the trace is not running, the agent may report any of several explanations as
one of the optional fields:‘tnotrun:0’
No trace has been run yet.
‘tstop[:text]:0’
The trace was stopped by a user-originated stop command. The
optional text field is a user-supplied string supplied as part of thestop command (for instance, an explanation of why the trace wasstopped manually). It is hex-encoded.
‘tfull:0’

The trace stopped because the trace buffer filled up.

‘tdisconnected:0’
The trace stopped because gdb disconnected from the target.

Appendix E: gdb Remote Serial Protocol

821‘tpasscount:tpnum’
The trace stopped because tracepoint tpnum exceeded its passcount.
‘terror:text:tpnum’
The trace stopped because tracepoint tpnum had an error. The
string text is available to describe the nature of the error (for instance, a divide by zero in the condition expression); it is hex encoded.
‘tunknown:0’
The trace stopped for some other reason.
Additional optional fields supply statistical and other information. Although
not required, they are extremely useful for users monitoring the progress of a
trace run. If a trace has stopped, and these numbers are reported, they mustreflect the state of the just-stopped trace.
‘tframes:n’
The number of trace frames in the buffer.
‘tcreated:n’
The total number of trace frames created during the run. This may
be larger than the trace frame count, if the buffer is circular.
‘tsize:n’

The total size of the trace buffer, in bytes.

‘tfree:n’

The number of bytes still unused in the buffer.

‘circular:n’
The value of the circular trace buffer flag. 1 means that the trace
buffer is circular and old trace frames will be discarded if necessary
to make room, 0 means that the trace buffer is linear and may fillup.
‘disconn:n’
The value of the disconnected tracing flag. 1 means that tracing
will continue after gdb disconnects, 0 means that the trace run will
stop.
‘qTP:tp:addr’
Ask the stub for the current state of tracepoint number tp at address addr.
Replies:‘Vhits:usage’The tracepoint has been hit hits times so far during the trace
run, and accounts for usage in the trace buffer. Note thatwhile-stepping steps are not counted as separate hits, but thesteps’ space consumption is added into the usage number.
‘qTV:var’

Ask the stub for the value of the trace state variable number var.
Replies:‘Vvalue’The value of the variable is value. This will be the current valueof the variable if the user is examining a running target, or a saved

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value if the variable was collected in the trace frame that the user
is looking at. Note that multiple requests may result in different
reply values, such as when requesting values while the program isrunning.
‘U’‘qTfP’‘qTsP’‘qTfV’‘qTsV’‘qTfSTM’‘qTsSTM’

The value of the variable is unknown. This would occur, for example, if the user is examining a trace frame in which the requested
variable was not collected.

These packets request data about tracepoints that are being used by the target.
gdb sends qTfP to get the first piece of data, and multiple qTsP to get additional
pieces. Replies to these packets generally take the form of the QTDP packets thatdefine tracepoints. (FIXME add detailed syntax)
These packets request data about trace state variables that are on the target.
gdb sends qTfV to get the first vari of data, and multiple qTsV to get additionalvariables. Replies to these packets follow the syntax of the QTDV packets thatdefine trace state variables.
These packets request data about static tracepoint markers that exist in thetarget program. gdb sends qTfSTM to get the first piece of data, and multiple
qTsSTM to get additional pieces. Replies to these packets take the following
form:
Reply:‘m address:id:extra’
A single marker‘m address:id:extra,address:id:extra...’a comma-separated list of markers‘l’(lower case letter ‘L’) denotes end of list.

The address is encoded in hex; id and extra are strings encoded in hex.
In response to each query, the target will reply with a list of one or moremarkers, separated by commas. gdb will respond to each reply with a request
for more markers (using the ‘qs’ form of the query), until the target respondswith ‘l’ (lower-case ell, for last).
‘qTSTMat:address’
This packets requests data about static tracepoint markers in the target program at address. Replies to this packet follow the syntax of the ‘qTfSTM’ andqTsSTM packets that list static tracepoint markers.
‘QTSave:filename’This packet directs the target to save trace data to the file name filename in thetarget’s filesystem. The filename is encoded as a hex string; the interpretationof the file name (relative vs absolute, wild cards, etc) is up to the target.

Appendix E: gdb Remote Serial Protocol

823‘qTBuffer:offset,len’Return up to len bytes of the current contents of trace buffer, starting at offset.
The trace buffer is treated as if it were a contiguous collection of traceframes,
as per the trace file format. The reply consists as many hex-encoded bytes as
the target can deliver in a packet; it is not an error to return fewer than wereasked for. A reply consisting of just l indicates that no bytes are available.
‘QTBuffer:circular:value’
This packet directs the target to use a circular trace buffer if value is 1, or alinear buffer if the value is 0.
‘QTBuffer:size:size’
This packet directs the target to make the trace buffer be of size size if possible.
A value of -1 tells the target to use whatever size it prefers.
‘QTNotes:[type:text][;type:text]...’
This packet adds optional textual notes to the trace run. Allowable types include user, notes, and tstop, the text fields are arbitrary strings, hex-encoded.

E.7.1 Relocate instruction reply packet
When installing fast tracepoints in memory, the target may need to relocate the instruction
currently at the tracepoint address to a different address in memory. For most instructions,a simple copy is enough, but, for example, call instructions that implicitly push the return
address on the stack, and relative branches or other PC-relative instructions require offset
adjustment, so that the effect of executing the instruction at a different address is the sameas if it had executed in the original location.
In response to several of the tracepoint packets, the target may also respond with a number of intermediate ‘qRelocInsn’ request packets before the final result packet, to have gdb
handle this relocation operation. If a packet supports this mechanism, its documentation
will explicitly say so. See for example the above descriptions for the ‘QTStart’ and ‘QTDP’
packets. The format of the request is:‘qRelocInsn:from;to’This requests gdb to copy instruction at address from to address to, possibly
adjusted so that executing the instruction at to has the same effect as executing
it at from. gdb writes the adjusted instruction to target memory starting at
to.
Replies:‘qRelocInsn:adjusted_size’
Informs the stub the relocation is complete. The adjusted size is the length inbytes of resulting relocated instruction sequence.

E.8 Host I/O Packets
The Host I/O packets allow gdb to perform I/O operations on the far side of a remote link.
For example, Host I/O is used to upload and download files to a remote target with its own
filesystem. Host I/O uses the same constant values and data structure layout as the targetinitiated File-I/O protocol. However, the Host I/O packets are structured differently. The

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target-initiated protocol relies on target memory to store parameters and buffers. Host I/Orequests are initiated by gdb, and the target’s memory is not involved. See Section E.14
[File-I/O Remote Protocol Extension], page 830, for more details on the target-initiatedprotocol.
The Host I/O request packets all encode a single operation along with its arguments.
They have this format:‘vFile:operation: parameter...’operation is the name of the particular request; the target should compare
the entire packet name up to the second colon when checking for a supported
operation. The format of parameter depends on the operation. Numbers arealways passed in hexadecimal. Negative numbers have an explicit minus sign(i.e. two’s complement is not used). Strings (e.g. filenames) are encoded as aseries of hexadecimal bytes. The last argument to a system call may be a bufferof escaped binary data (see [Binary Data], page 773).
The valid responses to Host I/O packets are:‘F result [, errno] [; attachment]’
result is the integer value returned by this operation, usually non-negative forsuccess and -1 for errors. If an error has occurred, errno will be included in the
result specifying a value defined by the File-I/O protocol (see [Errno Values],
page 840). For operations which return data, attachment supplies the data asa binary buffer. Binary buffers in response packets are escaped in the normalway (see [Binary Data], page 773). See the individual packet documentation
for the interpretation of result and attachment.
‘’

An empty response indicates that this operation is not recognized.
These are the supported Host I/O operations:‘vFile:open: filename, flags, mode’
Open a file at filename and return a file descriptor for it, or return -1 if an error
occurs. The filename is a string, flags is an integer indicating a mask of open
flags (see [Open Flags], page 840), and mode is an integer indicating a maskof mode bits to use if the file is created (see [mode t Values], page 840). See[open], page 832, for details of the open flags and mode values.
‘vFile:close: fd’
Close the open file corresponding to fd and return 0, or -1 if an error occurs.
‘vFile:pread: fd, count, offset’
Read data from the open file corresponding to fd. Up to count bytes will beread from the file, starting at offset relative to the start of the file. The target
may read fewer bytes; common reasons include packet size limits and an endof-file condition. The number of bytes read is returned. Zero should only be
returned for a successful read at the end of the file, or if count was zero.
The data read should be returned as a binary attachment on success. If zerobytes were read, the response should include an empty binary attachment (i.e.
a trailing semicolon). The return value is the number of target bytes read; thebinary attachment may be longer if some characters were escaped.

Appendix E: gdb Remote Serial Protocol

825‘vFile:pwrite: fd, offset, data’Write data (a binary buffer) to the open file corresponding to fd. Start thewrite at offset from the start of the file. Unlike many write system calls,
there is no separate count argument; the length of data in the packet is used.
‘vFile:pwrite’ returns the number of bytes written, which may be shorter
than the length of data, or -1 if an error occurred.
‘vFile:fstat: fd’
Get information about the open file corresponding to fd. On success the information is returned as a binary attachment and the return value is the size of
this attachment in bytes. If an error occurs the return value is -1. The formatof the returned binary attachment is as described in [struct stat], page 839.
‘vFile:stat: filename’
Get information about the file filename on the target. On success the information is returned as a binary attachment and the return value is the size of this
attachment in bytes. If an error occurs the return value is -1. The format of
the returned binary attachment is as described in [struct stat], page 839.
‘vFile:unlink: filename’
Delete the file at filename on the target. Return 0, or -1 if an error occurs. The
filename is a string.
‘vFile:readlink: filename’
Read value of symbolic link filename on the target. Return the number of bytes
read, or -1 if an error occurs.
The data read should be returned as a binary attachment on success. If zerobytes were read, the response should include an empty binary attachment (i.e.
a trailing semicolon). The return value is the number of target bytes read; thebinary attachment may be longer if some characters were escaped.
‘vFile:setfs: pid’
Select the filesystem on which vFile operations with filename arguments will
operate. This is required for gdb to be able to access files on remote targets
where the remote stub does not share a common filesystem with the inferior(s).
If pid is nonzero, select the filesystem as seen by process pid. If pid is zero,select the filesystem as seen by the remote stub. Return 0 on success, or -1
if an error occurs. If vFile:setfs: indicates success, the selected filesystemremains selected until the next successful vFile:setfs: operation.

E.9 Interrupts
In all-stop mode, when a program on the remote target is running, gdb may attempt tointerrupt it by sending a ‘Ctrl-C’, BREAK or a BREAK followed by g, control of which is
specified via gdb’s ‘interrupt-sequence’.
The precise meaning of BREAK is defined by the transport mechanism and may, in fact,
be undefined. gdb does not currently define a BREAK mechanism for any of the network
interfaces except for TCP, in which case gdb sends the telnet BREAK sequence.
‘Ctrl-C’, on the other hand, is defined and implemented for all transport mechanisms.
It is represented by sending the single byte 0x03 without any of the usual packet overhead

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described in the Overview section (see Section E.1 [Overview], page 773). When a 0x03 byteis transmitted as part of a packet, it is considered to be packet data and does not represent
an interrupt. E.g., an ‘X’ packet (see [X packet], page 783), used for binary downloads, may
include an unescaped 0x03 as part of its packet.
BREAK followed by g is also known as Magic SysRq g. When Linux kernel receives thissequence from serial port, it stops execution and connects to gdb.
In non-stop mode, because packet resumptions are asynchronous (see [vCont packet],page 780), gdb is always free to send a remote command to the remote stub, even when thetarget is running. For that reason, gdb instead sends a regular packet (see [vCtrlC packet],page 781) with the usual packet framing instead of the single byte 0x03.
Stubs are not required to recognize these interrupt mechanisms and the precise meaning
associated with receipt of the interrupt is implementation defined. If the target supports
debugging of multiple threads and/or processes, it should attempt to interrupt all currentlyexecuting threads and processes. If the stub is successful at interrupting the running program, it should send one of the stop reply packets (see Section E.4 [Stop Reply Packets],page 785) to gdb as a result of successfully stopping the program in all-stop mode, and astop reply for each stopped thread in non-stop mode. Interrupts received while the programis stopped are queued and the program will be interrupted when it is resumed next time.

E.10 Notification Packets
The gdb remote serial protocol includes notifications, packets that require no acknowledgment. Both the GDB and the stub may send notifications (although the only notifications
defined at present are sent by the stub). Notifications carry information without incurring
the round-trip latency of an acknowledgment, and so are useful for low-impact communications where occasional packet loss is not a problem.
A notification packet has the form ‘% data # checksum’, where data is the content of thenotification, and checksum is a checksum of data, computed and formatted as for ordinary
gdb packets. A notification’s data never contains ‘$’, ‘%’ or ‘#’ characters. Upon receivinga notification, the recipient sends no ‘+’ or ‘-’ to acknowledge the notification’s receipt or
to report its corruption.
Every notification’s data begins with a name, which contains no colon characters, followed by a colon character.
Recipients should silently ignore corrupted notifications and notifications they do not understand. Recipients should restart timeout periods on receipt of a well-formed notification,
whether or not they understand it.
Senders should only send the notifications described here when this protocol description
specifies that they are permitted. In the future, we may extend the protocol to permit
existing notifications in new contexts; this rule helps older senders avoid confusing newer
recipients.
(Older versions of gdb ignore bytes received until they see the ‘$’ byte that begins an
ordinary packet, so new stubs may transmit notifications without fear of confusing older
clients. There are no notifications defined for gdb to send at the moment, but we assume
that most older stubs would ignore them, as well.)
Each notification is comprised of three parts:

Appendix E: gdb Remote Serial Protocol827‘name:event’
The notification packet is sent by the side that initiates the exchange (currently,
only the stub does that), with event carrying the specific information about the
notification, and name specifying the name of the notification.
‘ack’

The acknowledge sent by the other side, usually gdb, to acknowledge the exchange and request the event.

The purpose of an asynchronous notification mechanism is to report to gdb that something interesting happened in the remote stub.
The remote stub may send notification name:event at any time, but gdb acknowledges
the notification when appropriate. The notification event is pending before gdb acknowledges. Only one notification at a time may be pending; if additional events occur before
gdb has acknowledged the previous notification, they must be queued by the stub for latersynchronous transmission in response to ack packets from gdb. Because the notification
mechanism is unreliable, the stub is permitted to resend a notification if it believes gdb
may not have received it.
Specifically, notifications may appear when gdb is not otherwise reading input fromthe stub, or when gdb is expecting to read a normal synchronous response or a ‘+’/‘-’
acknowledgment to a packet it has sent. Notification packets are distinct from any othercommunication from the stub so there is no ambiguity.
After receiving a notification, gdb shall acknowledge it by sending a ack packet as aregular, synchronous request to the stub. Such acknowledgment is not required to happen
immediately, as gdb is permitted to send other, unrelated packets to the stub first, which
the stub should process normally.
Upon receiving a ack packet, if the stub has other queued events to report to gdb, it
shall respond by sending a normal event. gdb shall then send another ack packet to solicit
further responses; again, it is permitted to send other, unrelated packets as well which thestub should process normally.
If the stub receives a ack packet and there are no additional event to report, the stubshall return an ‘OK’ response. At this point, gdb has finished processing a notification andthe stub has completed sending any queued events. gdb won’t accept any new notifications
until the final ‘OK’ is received . If further notification events occur, the stub shall send a
new notification, gdb shall accept the notification, and the process shall be repeated.
The process of asynchronous notification can be illustrated by the following example:<- %Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;...
-> vStopped<- T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;-> vStopped<- T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;-> vStopped<- OK

The following notifications are defined:
Notification Ack

Event

Description

828

Stop

Debugging with gdb

vStopped reply.
The reply has theform of a stop reply, as described in Section E.4 [Stop Reply Packets], page 785. Refer
to Section E.11 [Remote NonStop], page 828, for information
on how these notifications are
acknowledged by gdb.

Report an asynchronous stop
event in non-stop mode.

E.11 Remote Protocol Support for Non-Stop Mode
gdb’s remote protocol supports non-stop debugging of multi-threaded programs, as described in Section 5.5.2 [Non-Stop Mode], page 94. If the stub supports non-stop mode,
it should report that to gdb by including ‘QNonStop+’ in its ‘qSupported’ response (see[qSupported], page 799).
gdb typically sends a ‘QNonStop’ packet only when establishing a new connection withthe stub. Entering non-stop mode does not alter the state of any currently-running threads,
but targets must stop all threads in any already-attached processes when entering all-stop
mode. gdb uses the ‘?’ packet as necessary to probe the target state after a mode change.
In non-stop mode, when an attached process encounters an event that would otherwise bereported with a stop reply, it uses the asynchronous notification mechanism (see Section E.10
[Notification Packets], page 826) to inform gdb. In contrast to all-stop mode, where all
threads in all processes are stopped when a stop reply is sent, in non-stop mode only thethread reporting the stop event is stopped. That is, when reporting a ‘S’ or ‘T’ response toindicate completion of a step operation, hitting a breakpoint, or a fault, only the affected
thread is stopped; any other still-running threads continue to run. When reporting a ‘W’ or‘X’ response, all running threads belonging to other attached processes continue to run.
In non-stop mode, the target shall respond to the ‘?’ packet as follows. First, any
incomplete stop reply notification/‘vStopped’ sequence in progress is abandoned. The target
must begin a new sequence reporting stop events for all stopped threads, whether or not it
has previously reported those events to gdb. The first stop reply is sent as a synchronous
reply to the ‘?’ packet, and subsequent stop replies are sent as responses to ‘vStopped’
packets using the mechanism described above. The target must not send asynchronous stop
reply notifications until the sequence is complete. If all threads are running when the target
receives the ‘?’ packet, or if the target is not attached to any process, it shall respond ‘OK’.
If the stub supports non-stop mode, it should also support the ‘swbreak’ stop reason if
software breakpoints are supported, and the ‘hwbreak’ stop reason if hardware breakpoints
are supported (see [swbreak stop reason], page 786). This is because given the asynchronous
nature of non-stop mode, between the time a thread hits a breakpoint and the time theevent is finally processed by gdb, the breakpoint may have already been removed from thetarget. Due to this, gdb needs to be able to tell whether a trap stop was caused by adelayed breakpoint event, which should be ignored, as opposed to a random trap signal,
which should be reported to the user. Note the ‘swbreak’ feature implies that the target is
responsible for adjusting the PC when a software breakpoint triggers, if necessary, such as
on the x86 architecture.

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E.12 Packet Acknowledgment
By default, when either the host or the target machine receives a packet, the first response
expected is an acknowledgment: either ‘+’ (to indicate the package was received correctly) or‘-’ (to request retransmission). This mechanism allows the gdb remote protocol to operateover unreliable transport mechanisms, such as a serial line.
In cases where the transport mechanism is itself reliable (such as a pipe or TCP connection), the ‘+’/‘-’ acknowledgments are redundant. It may be desirable to disable them inthat case to reduce communication overhead, or for other reasons. This can be accomplishedby means of the ‘QStartNoAckMode’ packet; see [QStartNoAckMode], page 799.
When in no-acknowledgment mode, neither the stub nor gdb shall send or expect ‘+’/‘-’
protocol acknowledgments. The packet and response format still includes the normal checksum, as described in Section E.1 [Overview], page 773, but the checksum may be ignoredby the receiver.
If the stub supports ‘QStartNoAckMode’ and prefers to operate in no-acknowledgmentmode, it should report that to gdb by including ‘QStartNoAckMode+’ in its response to‘qSupported’; see [qSupported], page 799. If gdb also supports ‘QStartNoAckMode’ and it
has not been disabled via the set remote noack-packet off command (see Section 20.4
[Remote Configuration], page 326), gdb may then send a ‘QStartNoAckMode’ packet to thestub. Only then may the stub actually turn off packet acknowledgments. gdb sends a final‘+’ acknowledgment of the stub’s ‘OK’ response, which can be safely ignored by the stub.
Note that set remote noack-packet command only affects negotiation between gdb
and the stub when subsequent connections are made; it does not affect the protocol acknowledgment state for any current connection. Since ‘+’/‘-’ acknowledgments are enabled
by default when a new connection is established, there is also no protocol request to reenable the acknowledgments for the current connection, once disabled.

E.13 Examples
Example sequence of a target being re-started. Notice how the restart does not get any
direct output:-> R00<- +target restarts
-> ?
<- +
<- T001:1234123412341234-> +Example sequence of a target being stepped by a single instruction:-> G1445...
<- +
-> s
<- +
time passes<- T001:1234123412341234
-> +
-> g
<- +
<- 1455...
-> +

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E.14 File-I/O Remote Protocol Extension
E.14.1 File-I/O Overview
The File I/O remote protocol extension (short: File-I/O) allows the target to use the host’s
file system and console I/O to perform various system calls. System calls on the target
system are translated into a remote protocol packet to the host system, which then performs
the needed actions and returns a response packet to the target system. This simulates filesystem operations even on targets that lack file systems.
The protocol is defined to be independent of both the host and target systems. It uses its
own internal representation of datatypes and values. Both gdb and the target’s gdb stubare responsible for translating the system-dependent value representations into the internal
protocol representations when data is transmitted.
The communication is synchronous. A system call is possible only when gdb is waiting
for a response from the ‘C’, ‘c’, ‘S’ or ‘s’ packets. While gdb handles the request for asystem call, the target is stopped to allow deterministic access to the target’s memory.
Therefore File-I/O is not interruptible by target signals. On the other hand, it is possible
to interrupt File-I/O by a user interrupt (‘Ctrl-C’) within gdb.
The target’s request to perform a host system call does not finish the latest ‘C’, ‘c’, ‘S’or ‘s’ action. That means, after finishing the system call, the target returns to continuing
the previous activity (continue, step). No additional continue or step request from gdb isrequired.
(gdb) continue<- target requests ’system call X’target is stopped, gdb executes system call-> gdb returns result... target continues, gdb returns to wait for the target<- target hits breakpoint and sends a Txx packet

The protocol only supports I/O on the console and to regular files on the host file system.
Character or block special devices, pipes, named pipes, sockets or any other communication
method on the host system are not supported by this protocol.
File I/O is not supported in non-stop mode.

E.14.2 Protocol Basics
The File-I/O protocol uses the F packet as the request as well as reply packet. Since a
File-I/O system call can only occur when gdb is waiting for a response from the continuing
or stepping target, the File-I/O request is a reply that gdb has to expect as a result of aprevious ‘C’, ‘c’, ‘S’ or ‘s’ packet. This F packet contains all information needed to allow
gdb to call the appropriate host system call:• A unique identifier for the requested system call.
• All parameters to the system call. Pointers are given as addresses in the target memory
address space. Pointers to strings are given as pointer/length pair. Numerical values are
given as they are. Numerical control flags are given in a protocol-specific representation.
At this point, gdb has to perform the following actions.
• If the parameters include pointer values to data needed as input to a system call, gdb
requests this data from the target with a standard m packet request. This additional

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communication has to be expected by the target implementation and is handled as anyother m packet.
• gdb translates all value from protocol representation to host representation as needed.
Datatypes are coerced into the host types.
• gdb calls the system call.
• It then coerces datatypes back to protocol representation.
• If the system call is expected to return data in buffer space specified by pointer parameters to the call, the data is transmitted to the target using a M or X packet. This
packet has to be expected by the target implementation and is handled as any other M
or X packet.
Eventually gdb replies with another F packet which contains all necessary information
for the target to continue. This at least contains• Return value.
• errno, if has been changed by the system call.
• “Ctrl-C” flag.
After having done the needed type and value coercion, the target continues the latest
continue or step action.

E.14.3 The F Request Packet
The F request packet has the following format:‘Fcall-id,parameter...’call-id is the identifier to indicate the host system call to be called. This is justthe name of the function.
parameter. . . are the parameters to the system call. Parameters are hexadecimal integer values, either the actual values in case of scalar datatypes, pointers
to target buffer space in case of compound datatypes and unspecified memoryareas, or pointer/length pairs in case of string parameters. These are appended
to the call-id as a comma-delimited list. All values are transmitted in ASCII
string representation, pointer/length pairs separated by a slash.

E.14.4 The F Reply Packet
The F reply packet has the following format:‘Fretcode,errno,Ctrl-C flag;call-specific attachment’retcode is the return code of the system call as hexadecimal value.
errno is the errno set by the call, in protocol-specific representation. Thisparameter can be omitted if the call was successful.
Ctrl-C flag is only sent if the user requested a break. In this case, errno must
be sent as well, even if the call was successful. The Ctrl-C flag itself consists ofthe character ‘C’:
F0,0,Cor, if the call was interrupted before the host call has been performed:
F-1,4,C

assuming 4 is the protocol-specific representation of EINTR.

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E.14.5 The ‘Ctrl-C’ Message
If the ‘Ctrl-C’ flag is set in the gdb reply packet (see Section E.14.4 [The F Reply Packet],page 831), the target should behave as if it had gotten a break message. The meaning forthe target is “system call interrupted by SIGINT”. Consequently, the target should actuallystop (as with a break message) and return to gdb with a T02 packet.
It’s important for the target to know in which state the system call was interrupted.
There are two possible cases:• The system call hasn’t been performed on the host yet.
• The system call on the host has been finished.
These two states can be distinguished by the target by the value of the returned errno.
If it’s the protocol representation of EINTR, the system call hasn’t been performed. Thisis equivalent to the EINTR handling on POSIX systems. In any other case, the target may
presume that the system call has been finished — successfully or not — and should behave
as if the break message arrived right after the system call.
gdb must behave reliably. If the system call has not been called yet, gdb may send the
F reply immediately, setting EINTR as errno in the packet. If the system call on the hosthas been finished before the user requests a break, the full action must be finished by gdb.
This requires sending M or X packets as necessary. The F packet may only be sent wheneither nothing has happened or the full action has been completed.

E.14.6 Console I/O
By default and if not explicitly closed by the target system, the file descriptors 0, 1 and 2
are connected to the gdb console. Output on the gdb console is handled as any other file
output operation (write(1, ...) or write(2, ...)). Console input is handled by gdb sothat after the target read request from file descriptor 0 all following typing is buffered until
either one of the following conditions is met:
• The user types Ctrl-c. The behaviour is as explained above, and the read system callis treated as finished.
• The user presses RET. This is treated as end of input with a trailing newline.
• The user types Ctrl-d. This is treated as end of input. No trailing character (neither
newline nor ‘Ctrl-D’) is appended to the input.
If the user has typed more characters than fit in the buffer given to the read call, thetrailing characters are buffered in gdb until either another read(0, ...) is requested by
the target, or debugging is stopped at the user’s request.

E.14.7 List of Supported Calls
open
Synopsis:
int open(const char *pathname, int flags);
int open(const char *pathname, int flags, mode_t mode);

Request:‘Fopen,pathptr/len,flags,mode’Appendix E: gdb Remote Serial Protocol

833

flags is the bitwise OR of the following values:
O_CREAT

If the file does not exist it will be created. The host rules apply as
far as file ownership and time stamps are concerned.

O_EXCL

When used with O_CREAT, if the file already exists it is an error andopen() fails.

O_TRUNC

If the file already exists and the open mode allows writing (O_RDWR
or O_WRONLY is given) it will be truncated to zero length.

O_APPEND

The file is opened in append mode.

O_RDONLY

The file is opened for reading only.

O_WRONLY

The file is opened for writing only.

O_RDWR

The file is opened for reading and writing.

Other bits are silently ignored.
mode is the bitwise OR of the following values:
S_IRUSR

User has read permission.

S_IWUSR

User has write permission.

S_IRGRP

Group has read permission.

S_IWGRP

Group has write permission.

S_IROTH

Others have read permission.

S_IWOTH

Others have write permission.

Other bits are silently ignored.
Return value:
open returns the new file descriptor or -1 if an error occurred.
Errors:EEXIST

pathname already exists and O_CREAT and O_EXCL were used.

EISDIR

pathname refers to a directory.

EACCES

The requested access is not allowed.

ENAMETOOLONG
pathname was too long.
ENOENT

A directory component in pathname does not exist.

ENODEVpathname refers to a device, pipe, named pipe or socket.

EROFS

pathname refers to a file on a read-only filesystem and write access
was requested.

EFAULT

pathname is an invalid pointer value.

ENOSPCNo space on device to create the file.

EMFILEThe process already has the maximum number of files open.

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Debugging with gdb

ENFILEThe limit on the total number of files open on the system has beenreached.

EINTR

The call was interrupted by the user.

close
Synopsis:
int close(int fd);

Request:‘Fclose,fd’

Return value:
close returns zero on success, or -1 if an error occurred.
Errors:EBADF

fd isn’t a valid open file descriptor.

EINTR

The call was interrupted by the user.

read
Synopsis:
int read(int fd, void *buf, unsigned int count);

Request:‘Fread,fd,bufptr,count’

Return value:
On success, the number of bytes read is returned. Zero indicates end of file. If
count is zero, read returns zero as well. On error, -1 is returned.
Errors:EBADF

fd is not a valid file descriptor or is not open for reading.

EFAULTbufptr is an invalid pointer value.

EINTR

The call was interrupted by the user.

write
Synopsis:
int write(int fd, const void *buf, unsigned int count);

Request:‘Fwrite,fd,bufptr,count’

Return value:
On success, the number of bytes written are returned. Zero indicates nothing
was written. On error, -1 is returned.
Errors:EBADF

fd is not a valid file descriptor or is not open for writing.

EFAULTbufptr is an invalid pointer value.

EFBIG

An attempt was made to write a file that exceeds the host-specificmaximum file size allowed.

ENOSPCNo space on device to write the data.

EINTR

The call was interrupted by the user.

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835

lseek
Synopsis:long lseek (int fd, long offset, int flag);

Request:‘Flseek,fd,offset,flag’
flag is one of:
SEEK_SETThe offset is set to offset bytes.

SEEK_CUR

The offset is set to its current location plus offset bytes.

SEEK_END

The offset is set to the size of the file plus offset bytes.

Return value:
On success, the resulting unsigned offset in bytes from the beginning of the fileis returned. Otherwise, a value of -1 is returned.
Errors:EBADF

fd is not a valid open file descriptor.

ESPIPEfd is associated with the gdb console.

EINVALflag is not a proper value.

EINTR

The call was interrupted by the user.

renameSynopsis:
int rename(const char *oldpath, const char *newpath);

Request:‘Frename,oldpathptr/len,newpathptr/len’Return value:
On success, zero is returned. On error, -1 is returned.
Errors:
EISDIR

newpath is an existing directory, but oldpath is not a directory.

EEXIST

newpath is a non-empty directory.

EBUSY

oldpath or newpath is a directory that is in use by some process.

EINVALAn attempt was made to make a directory a subdirectory of itself.

ENOTDIR

A component used as a directory in oldpath or new path is not a
directory. Or oldpath is a directory and newpath exists but is nota directory.

EFAULT

oldpathptr or newpathptr are invalid pointer values.

EACCESNo access to the file or the path of the file.

ENAMETOOLONG
oldpath or newpath was too long.
ENOENT

A directory component in oldpath or newpath does not exist.

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Debugging with gdb

EROFS

The file is on a read-only filesystem.

ENOSPCThe device containing the file has no room for the new directory
entry.

EINTR

The call was interrupted by the user.

unlinkSynopsis:
int unlink(const char *pathname);

Request:‘Funlink,pathnameptr/len’Return value:
On success, zero is returned. On error, -1 is returned.
Errors:EACCESNo access to the file or the path of the file.

EPERM

The system does not allow unlinking of directories.

EBUSY

The file pathname cannot be unlinked because it’s being used byanother process.

EFAULT

pathnameptr is an invalid pointer value.

ENAMETOOLONG
pathname was too long.
ENOENT

A directory component in pathname does not exist.

ENOTDIR

A component of the path is not a directory.

EROFS

The file is on a read-only filesystem.

EINTR

The call was interrupted by the user.

stat/fstat
Synopsis:
int stat(const char *pathname, struct stat *buf);
int fstat(int fd, struct stat *buf);

Request:‘Fstat,pathnameptr/len,bufptr’‘Ffstat,fd,bufptr’

Return value:
On success, zero is returned. On error, -1 is returned.
Errors:EBADF

fd is not a valid open file.

ENOENT

A directory component in pathname does not exist or the path isan empty string.

ENOTDIR

A component of the path is not a directory.

Appendix E: gdb Remote Serial Protocol

EFAULT

pathnameptr is an invalid pointer value.

EACCESNo access to the file or the path of the file.

837

ENAMETOOLONG
pathname was too long.
The call was interrupted by the user.

EINTR

gettimeofday
Synopsis:
int gettimeofday(struct timeval *tv, void *tz);

Request:‘Fgettimeofday,tvptr,tzptr’

Return value:
On success, 0 is returned, -1 otherwise.
Errors:EINVALtz is a non-NULL pointer.

EFAULT

tvptr and/or tzptr is an invalid pointer value.

isattySynopsis:
int isatty(int fd);

Request:‘Fisatty,fd’

Return value:
Returns 1 if fd refers to the gdb console, 0 otherwise.
Errors:EINTR

The call was interrupted by the user.

Note that the isatty call is treated as a special case: it returns 1 to the target if thefile descriptor is attached to the gdb console, 0 otherwise. Implementing through system
calls would require implementing ioctl and would be more complex than needed.

systemSynopsis:
int system(const char *command);

Request:‘Fsystem,commandptr/len’Return value:
If len is zero, the return value indicates whether a shell is available. A zero
return value indicates a shell is not available. For non-zero len, the value returned is -1 on error and the return status of the command otherwise. Only
the exit status of the command is returned, which is extracted from the host’ssystem return value by calling WEXITSTATUS(retval). In case /bin/sh could
not be executed, 127 is returned.

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Errors:EINTR

The call was interrupted by the user.

gdb takes over the full task of calling the necessary host calls to perform the systemcall. The return value of system on the host is simplified before it’s returned to the target.
Any termination signal information from the child process is discarded, and the return value
consists entirely of the exit status of the called command.
Due to security concerns, the system call is by default refused by gdb. The user has toallow this call explicitly with the set remote system-call-allowed 1 command.
set remote system-call-allowed
Control whether to allow the system calls in the File I/O protocol for the
remote target. The default is zero (disabled).
show remote system-call-allowed
Show whether the system calls are allowed in the File I/O protocol.

E.14.8 Protocol-specific Representation of Datatypes
Integral Datatypes
The integral datatypes used in the system calls are int, unsigned int, long, unsigned
long, mode_t, and time_t.
int, unsigned int, mode_t and time_t are implemented as 32 bit values in this protocol.
long and unsigned long are implemented as 64 bit types.
See [Limits], page 841, for corresponding MIN and MAX values (similar to those inlimits.h) to allow range checking on host and target.
time_t datatypes are defined as seconds since the Epoch.
All integral datatypes transferred as part of a memory read or write of a structured
datatype e.g. a struct stat have to be given in big endian byte order.

Pointer Values
Pointers to target data are transmitted as they are. An exception is made for pointers tobuffers for which the length isn’t transmitted as part of the function call, namely strings.
Strings are transmitted as a pointer/length pair, both as hex values, e.g.
1aaf/12which is a pointer to data of length 18 bytes at position 0x1aaf. The length is defined as thefull string length in bytes, including the trailing null byte. For example, the string "helloworld" at address 0x123456 is transmitted as
123456/d

Memory Transfer
Structured data which is transferred using a memory read or write (for example, a structstat) is expected to be in a protocol-specific format with all scalar multibyte datatypes
being big endian. Translation to this representation needs to be done both by the target
before the F packet is sent, and by gdb before it transfers memory to the target. Transferred
pointers to structured data should point to the already-coerced data at any time.

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struct stat
The buffer of type struct stat used by the target and gdb is defined as follows:
struct stat {unsigned int st_dev;
unsigned int st_ino;
mode_tst_mode;unsigned int st_nlink;unsigned int st_uid;
unsigned int st_gid;
unsigned int st_rdev;
unsigned long st_size;
unsigned long st_blksize;
unsigned long st_blocks;
time_tst_atime;
time_tst_mtime;
time_tst_ctime;};/* device *//* inode *//* protection *//* number of hard links *//* user ID of owner *//* group ID of owner *//* device type (if inode device) *//* total size, in bytes *//* blocksize for filesystem I/O *//* number of blocks allocated *//* time of last access *//* time of last modification *//* time of last change */The integral datatypes conform to the definitions given in the appropriate section (see[Integral Datatypes], page 838, for details) so this structure is of size 64 bytes.
The values of several fields have a restricted meaning and/or range of values.
st_devA value of 0 represents a file, 1 the console.

st_inoNo valid meaning for the target. Transmitted unchanged.

st_modeValid mode bits are described in Section E.14.9 [Constants], page 840. Anyother bits have currently no meaning for the target.

st_uidst_gidst_rdev
st_atime
st_mtime
st_ctime

No valid meaning for the target. Transmitted unchanged.

These values have a host and file system dependent accuracy. Especially on
Windows hosts, the file system may not support exact timing values.

The target gets a struct stat of the above representation and is responsible for coercing
it to the target representation before continuing.
Note that due to size differences between the host, target, and protocol representationsof struct stat members, these members could eventually get truncated on the target.

struct timeval
The buffer of type struct timeval used by the File-I/O protocol is defined as follows:
struct timeval {time_t tv_sec; /* second */long
tv_usec; /* microsecond */};The integral datatypes conform to the definitions given in the appropriate section (see[Integral Datatypes], page 838, for details) so this structure is of size 8 bytes.

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E.14.9 Constants
The following values are used for the constants inside of the protocol. gdb and target are
responsible for translating these values before and after the call as needed.

Open Flags
All values are given in hexadecimal representation.
O_RDONLY
O_WRONLY
O_RDWRO_APPEND
O_CREATO_TRUNC
O_EXCL

0x0
0x1
0x2
0x8
0x200
0x400
0x800

mode t Values
All values are given in octal representation.
S_IFREGS_IFDIR
S_IRUSR
S_IWUSRS_IXUSR
S_IRGRP
S_IWGRP
S_IXGRP
S_IROTH
S_IWOTH
S_IXOTH

0100000
040000
0400
0200
0100
040
020
010
04
02
01

Errno Values
All values are given in decimal representation.
EPERM
ENOENT
EINTR
EBADF
EACCESEFAULTEBUSY
EEXIST
ENODEV
ENOTDIR
EISDIR
EINVALENFILEEMFILEEFBIG
ENOSPCESPIPEEROFS
ENAMETOOLONGEUNKNOWN

1
2
4
9
13
14
16
17
19
20
21
22
23
24
27
28
29
30
91
9999

EUNKNOWN is used as a fallback error value if a host system returns any error value notin the list of supported error numbers.

Appendix E: gdb Remote Serial Protocol

841

Lseek Flags
SEEK_SETSEEK_CURSEEK_END

0
1
2

LimitsAll values are given in decimal representation.
INT_MIN
INT_MAXUINT_MAXLONG_MIN
LONG_MAXULONG_MAX-2147483648
2147483647
4294967295-9223372036854775808
9223372036854775807
18446744073709551615

E.14.10 File-I/O Examples
Example sequence of a write call, file descriptor 3, buffer is at target address 0x1234, 6
bytes should be written:<- Fwrite,3,1234,6
request memory read from target-> m1234,6<- XXXXXX
return "6 bytes written"-> F6

Example sequence of a read call, file descriptor 3, buffer is at target address 0x1234, 6
bytes should be read:<- Fread,3,1234,6
request memory write to target-> X1234,6:XXXXXX
return "6 bytes read"-> F6

Example sequence of a read call, call fails on the host due to invalid file descriptor(EBADF):<- Fread,3,1234,6-> F-1,9

Example sequence of a read call, user presses Ctrl-c before syscall on host is called:<- Fread,3,1234,6-> F-1,4,C<- T02

Example sequence of a read call, user presses Ctrl-c after syscall on host is called:<- Fread,3,1234,6-> X1234,6:XXXXXX<- T02E.15 Library List Format
On some platforms, a dynamic loader (e.g. ld.so) runs in the same process as your application to manage libraries. In this case, gdb can use the loader’s symbol table and normal
memory operations to maintain a list of shared libraries. On other platforms, the operating
system manages loaded libraries. gdb can not retrieve the list of currently loaded libraries

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through memory operations, so it uses the ‘qXfer:libraries:read’ packet (see [qXfer library list read], page 811) instead. The remote stub queries the target’s operating system
and reports which libraries are loaded.
The ‘qXfer:libraries:read’ packet returns an XML document which lists loaded libraries and their offsets. Each library has an associated name and one or more segment orsection base addresses, which report where the library was loaded in memory.
For the common case of libraries that are fully linked binaries, the library should havea list of segments. If the target supports dynamic linking of a relocatable object file, its
library XML element should instead include a list of allocated sections. The segment orsection bases are start addresses, not relocation offsets; they do not depend on the library’s
link-time base addresses.
gdb must be linked with the Expat library to support XML library lists. See [Expat],
page 746.
A simple memory map, with one loaded library relocated by a single offset, looks likethis:<library-list><library name="/lib/libc.so.6"><segment address="0x10000000"/></library></library-list>

Another simple memory map, with one loaded library with three allocated sections (.text,.data, .bss), looks like this:<library-list><library name="sharedlib.o"><section address="0x10000000"/><section address="0x20000000"/><section address="0x30000000"/></library></library-list>

The format of a library list is described by this DTD:<!-- library-list: Root element with versioning --><!ELEMENT library-list (library)*><!ATTLIST library-list version CDATA#FIXED "1.0"><!ELEMENT library(segment*, section*)><!ATTLIST library
name
CDATA
#REQUIRED><!ELEMENT segment
EMPTY><!ATTLIST segment
address CDATA#REQUIRED><!ELEMENT section
EMPTY><!ATTLIST section
address CDATA#REQUIRED>In addition, segments and section descriptors cannot be mixed within a single libraryelement, and you must supply at least one segment or section for each library.

E.16 Library List Format for SVR4 Targets
On SVR4 platforms gdb can use the symbol table of a dynamic loader (e.g. ld.so) andnormal memory operations to maintain a list of shared libraries. Still a special library list
provided by this packet is more efficient for the gdb remote protocol.
The ‘qXfer:libraries-svr4:read’ packet returns an XML document which lists loaded
libraries and their SVR4 linker parameters. For each library on SVR4 target, the following
parameters are reported:

Appendix E: gdb Remote Serial Protocol

843− name, the absolute file name from the l_name field of struct link_map.
− lm with address of struct link_map used for TLS (Thread Local Storage) access.
− l_addr, the displacement as read from the field l_addr of struct link_map. For
prelinked libraries this is not an absolute memory address. It is a displacement of
absolute memory address against address the file was prelinked to during the libraryload.
− l_ld, which is memory address of the PT_DYNAMIC segment− lmid, which is an identifier for a linker namespace, such as the memory address of ther_debug object that contains this namespace’s load map or the namespace identifier
returned by dlinfo (3).
Additionally the single main-lm attribute specifies address of struct link_map used forthe main executable. This parameter is used for TLS access and its presence is optional.
gdb must be linked with the Expat library to support XML SVR4 library lists. See[Expat], page 746.
A simple memory map, with two loaded libraries (which do not use prelink), looks likethis:<library-list-svr4 version="1.0" main-lm="0xe4f8f8"><library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000"
l_ld="0xe4eefc" lmid="0xfffe0"/><library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000"
l_ld="0x152350" lmid="0xfffe0"/></library-list-svr>

The format of an SVR4 library list is described by this DTD:<!-- library-list-svr4: Root element with versioning --><!ELEMENT library-list-svr4 (library)*><!ATTLIST library-list-svr4 version CDATA#FIXED "1.0"><!ATTLIST library-list-svr4 main-lm CDATA#IMPLIED><!ELEMENT library
EMPTY><!ATTLIST library
name
CDATA
#REQUIRED><!ATTLIST librarylm
CDATA#REQUIRED><!ATTLIST libraryl_addr CDATA#REQUIRED><!ATTLIST library
l_ld
CDATA
#REQUIRED><!ATTLIST library
lmid
CDATA
#IMPLIED>

E.17 Memory Map Format
To be able to write into flash memory, gdb needs to obtain a memory map from the target.
This section describes the format of the memory map.
The memory map is obtained using the ‘qXfer:memory-map:read’ (see [qXfer memory
map read], page 813) packet and is an XML document that lists memory regions.
gdb must be linked with the Expat library to support XML memory maps. See [Expat],
page 746.
The top-level structure of the document is shown below:<?xml version="1.0"?><!DOCTYPE memory-map
PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN""http://sourceware.org/gdb/gdb-memory-map.dtd"><memory-map>

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Debugging with gdb

region...
</memory-map>

Each region can be either:• A region of RAM starting at addr and extending for length bytes from there:<memory type="ram" start="addr" length="length"/>• A region of read-only memory:<memory type="rom" start="addr" length="length"/>• A region of flash memory, with erasure blocks blocksize bytes in length:<memory type="flash" start="addr" length="length"><property name="blocksize">blocksize</property></memory>

Regions must not overlap. gdb assumes that areas of memory not covered by the memory
map are RAM, and uses the ordinary ‘M’ and ‘X’ packets to write to addresses in such ranges.
The formal DTD for memory map format is given below:<!-- ................................................... --><!-- Memory Map XML DTD ................................ --><!-- File: memory-map.dtd .............................. --><!-- .................................... .............. --><!-- memory-map.dtd --><!-- memory-map: Root element with versioning --><!ELEMENT memory-map (memory)*><!ATTLIST memory-map
version CDATA#FIXED "1.0.0"><!ELEMENT memory (property)*><!-- memory: Specifies a memory region,and its type, or device. --><!ATTLIST memory
type(ram|rom|flash) #REQUIRED
start
CDATA
#REQUIRED
length CDATA#REQUIRED><!-- property: Generic attribute tag --><!ELEMENT property (#PCDATA | property)*><!ATTLIST property
name(blocksize) #REQUIRED>

E.18 Thread List Format
To efficiently update the list of threads and their attributes, gdb issues the‘qXfer:threads:read’ packet (see [qXfer threads read], page 813) and obtains the XML
document with the following structure:<?xml version="1.0"?><threads><thread id="id" core="0" name="name" handle="1a2b3c">... description ...
</thread></threads>

Each ‘thread’ element must have the ‘id’ attribute that identifies the thread (see [threadid syntax], page 775). The ‘core’ attribute, if present, specifies which processor core thethread was last executing on. The ‘name’ attribute, if present, specifies the human-readable
name of the thread. The content of the of ‘thread’ element is interpreted as human-readable
auxiliary information. The ‘handle’ attribute, if present, is a hex encoded representationof the thread handle.

Appendix E: gdb Remote Serial Protocol

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E.19 Traceframe Info Format
To be able to know which objects in the inferior can be examined when inspecting a tracepoint hit, gdb needs to obtain the list of memory ranges, registers and trace state variables
that have been collected in a traceframe.
This list is obtained using the ‘qXfer:traceframe-info:read’ (see [qXfer traceframe
info read], page 813) packet and is an XML document.
gdb must be linked with the Expat library to support XML traceframe info discovery.
See [Expat], page 746.
The top-level structure of the document is shown below:<?xml version="1.0"?><!DOCTYPE traceframe-info
PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN""http://sourceware.org/gdb/gdb-traceframe-info.dtd"><traceframe-info>
block...
</traceframe-info>

Each traceframe block can be either:• A region of collected memory starting at addr and extending for length bytes fromthere:<memory start="addr" length="length"/>• A block indicating trace state variable numbered number has been collected:<tvar id="number"/>

The formal DTD for the traceframe info format is given below:<!ELEMENT traceframe-info<!ATTLIST traceframe-info<!ELEMENT memory<!ATTLIST memory<!ELEMENT tvar><!ATTLIST tvar

(memory | tvar)* >version CDATA#FIXEDEMPTY>
start
length

CDATA
CDATA

#REQUIRED#REQUIRED>

id

CDATA

#REQUIRED>"1.0">

E.20 Branch Trace Format
In order to display the branch trace of an inferior thread, gdb needs to obtain the list of
branches. This list is represented as list of sequential code blocks that are connected via
branches. The code in each block has been executed sequentially.
This list is obtained using the ‘qXfer:btrace:read’ (see [qXfer btrace read], page 810)
packet and is an XML document.
gdb must be linked with the Expat library to support XML traceframe info discovery.
See [Expat], page 746.
The top-level structure of the document is shown below:<?xml version="1.0"?><!DOCTYPE btrace
PUBLIC "+//IDN gnu.org//DTD GDB Branch Trace V1.0//EN""http://sourceware.org/gdb/gdb-btrace.dtd"><btrace>block...

846

Debugging with gdb</btrace>• A block of sequentially executed instructions starting at begin and ending at end:
<block begin="begin" end="end"/>

The formal DTD for the branch trace format is given below:<!ELEMENT btrace<!ATTLIST btrace<!ELEMENT block<!ATTLIST block(block* | pt) >version CDATA#FIXED "1.0">
EMPTY>
begin CDATA
end
CDATA

#REQUIRED#REQUIRED><!ELEMENT pt (pt-config?, raw?)><!ELEMENT pt-config (cpu?)><!ELEMENT cpu EMPTY><!ATTLIST cpu vendor
CDATA #REQUIRED
family
CDATA #REQUIRED
model
CDATA #REQUIRED
stepping CDATA #REQUIRED><!ELEMENT raw (#PCDATA)>

E.21 Branch Trace Configuration Format
For each inferior thread, gdb can obtain the branch trace configuration using the‘qXfer:btrace-conf:read’ (see [qXfer btrace-conf read], page 811) packet.
The configuration describes the branch trace format and configuration settings for thatformat. The following information is described:btsThis thread uses the Branch Trace Store (BTS) format.
size

pt

The size of the BTS ring buffer in bytes.

This thread uses the Intel Processor Trace (Intel PT) format.
size

The size of the Intel PT ring buffer in bytes.

gdb must be linked with the Expat library to support XML branch trace configuration
discovery. See [Expat], page 746.
The formal DTD for the branch trace configuration format is given below:<!ELEMENT btrace-conf (bts?, pt?)><!ATTLIST btrace-conf version CDATA #FIXED "1.0"><!ELEMENT bts EMPTY><!ATTLIST bts size CDATA #IMPLIED><!ELEMENT pt EMPTY><!ATTLIST pt size CDATA #IMPLIED><!ATTLIST pt ptwrite (yes | no) #IMPLIED><!ATTLIST pt event-tracing (yes | no) #IMPLIED>

847

Appendix F The GDB Agent Expression
Mechanism
In some applications, it is not feasible for the debugger to interrupt the program’s execution
long enough for the developer to learn anything helpful about its behavior. If the program’s
correctness depends on its real-time behavior, delays introduced by a debugger might cause
the program to fail, even when the code itself is correct. It is useful to be able to observe
the program’s behavior without interrupting it.
Using GDB’s trace and collect commands, the user can specify locations in the program, and arbitrary expressions to evaluate when those locations are reached. Later, using
the tfind command, she can examine the values those expressions had when the program
hit the trace points. The expressions may also denote objects in memory — structures orarrays, for example — whose values GDB should record; while visiting a particular tracepoint, the user may inspect those objects as if they were in memory at that moment.
However, because GDB records these values without interacting with the user, it can do soquickly and unobtrusively, hopefully not disturbing the program’s behavior.
When GDB is debugging a remote target, the GDB agent code running on the target
computes the values of the expressions itself. To avoid having a full symbolic expression
evaluator on the agent, GDB translates expressions in the source language into a simpler
bytecode language, and then sends the bytecode to the agent; the agent then executes thebytecode, and records the values for GDB to retrieve later.
The bytecode language is simple; there are forty-odd opcodes, the bulk of which are theusual vocabulary of C operands (addition, subtraction, shifts, and so on) and various sizesof literals and memory reference operations. The bytecode interpreter operates strictly onmachine-level values — various sizes of integers and floating point numbers — and requires
no information about types or symbols; thus, the interpreter’s internal data structures are
simple, and each bytecode requires only a few native machine instructions to implement
it. The interpreter is small, and strict limits on the memory and time required to evaluate
an expression are easy to determine, making it suitable for use by the debugging agent inreal-time applications.

F.1 General Bytecode Design
The agent represents bytecode expressions as an array of bytes. Each instruction is one
byte long (thus the term bytecode). Some instructions are followed by operand bytes; forexample, the goto instruction is followed by a destination for the jump.
The bytecode interpreter is a stack-based machine; most instructions pop their operands
off the stack, perform some operation, and push the result back on the stack for the next
instruction to consume. Each element of the stack may contain either a integer or a floating
point value; these values are as many bits wide as the largest integer that can be directly
manipulated in the source language. Stack elements carry no record of their type; bytecode
could push a value as an integer, then pop it as a floating point value. However, GDB will
not generate code which does this. In C, one might define the type of a stack element asfollows:
union agent_val {LONGEST l;
DOUBLEST d;

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where LONGEST and DOUBLEST are typedef names for the largest integer and floating pointtypes on the machine.
By the time the bytecode interpreter reaches the end of the expression, the value ofthe expression should be the only value left on the stack. For tracing applications, trace
bytecodes in the expression will have recorded the necessary data, and the value on thestack may be discarded. For other applications, like conditional breakpoints, the value may
be useful.
Separate from the stack, the interpreter has two registers:pc

The address of the next bytecode to execute.

start

The address of the start of the bytecode expression, necessary for interpreting
the goto and if_goto instructions.

Neither of these registers is directly visible to the bytecode language itself, but they areuseful for defining the meanings of the bytecode operations.
There are no instructions to perform side effects on the running program, or call the program’s functions; we assume that these expressions are only used for unobtrusive debugging,not for patching the running code.
Most bytecode instructions do not distinguish between the various sizes of values, andoperate on full-width values; the upper bits of the values are simply ignored, since they do
not usually make a difference to the value computed. The exceptions to this rule are:memory reference instructions (refn)
There are distinct instructions to fetch different word sizes from memory. Onceon the stack, however, the values are treated as full-size integers. They may
need to be sign-extended; the ext instruction exists for this purpose.
the sign-extension instruction (ext n)
These clearly need to know which portion of their operand is to be extended tooccupy the full length of the word.
If the interpreter is unable to evaluate an expression completely for some reason (a memory location is inaccessible, or a divisor is zero, for example), we say that interpretation“terminates with an error”. This means that the problem is reported back to the interpreter’s caller in some helpful way. In general, code using agent expressions should assume
that they may attempt to divide by zero, fetch arbitrary memory locations, and misbehave
in other ways.
Even complicated C expressions compile to a few bytecode instructions; for example, theexpression x + y * z would typically produce code like the following, assuming that x andy live in registers, and z is a global variable holding a 32-bit int:
reg 1
reg 2
const32 address of z
ref32
ext 32mul
addAppendix F: The GDB Agent Expression Mechanism

849

end
In detail, these mean:
reg 1

Push the value of register 1 (presumably holding x) onto the stack.

reg 2

Push the value of register 2 (holding y).

const32 address of z
Push the address of z onto the stack.
ref32

Fetch a 32-bit word from the address at the top of the stack; replace the addresson the stack with the value. Thus, we replace the address of z with z’s value.

ext 32Sign-extend the value on the top of the stack from 32 bits to full length. Thisis necessary because z is a signed integer.

mul

Pop the top two numbers on the stack, multiply them, and push their product.
Now the top of the stack contains the value of the expression y * z.

add

Pop the top two numbers, add them, and push the sum. Now the top of thestack contains the value of x + y * z.

end

Stop executing; the value left on the stack top is the value to be recorded.

F.2 Bytecode Descriptions
Each bytecode description has the following form:
add (0x02): a b ⇒ a+b
Pop the top two stack items, a and b, as integers; push their sum, as an integer.
In this example, add is the name of the bytecode, and (0x02) is the one-byte value used
to encode the bytecode, in hexadecimal. The phrase “a b ⇒ a+b” shows the stack before
and after the bytecode executes. Beforehand, the stack must contain at least two values,a and b; since the top of the stack is to the right, b is on the top of the stack, and a isunderneath it. After execution, the bytecode will have popped a and b from the stack, andreplaced them with a single value, a+b. There may be other values on the stack below thoseshown, but the bytecode affects only those shown.
Here is another example:
const8 (0x22) n: ⇒ nPush the 8-bit integer constant n on the stack, without sign extension.
In this example, the bytecode const8 takes an operand n directly from the bytecodestream; the operand follows the const8 bytecode itself. We write any such operands immediately after the name of the bytecode, before the colon, and describe the exact encodingof the operand in the bytecode stream in the body of the bytecode description.
For the const8 bytecode, there are no stack items given before the ⇒; this simply meansthat the bytecode consumes no values from the stack. If a bytecode consumes no values, or
produces no values, the list on either side of the ⇒ may be empty.
If a value is written as a, b, or n, then the bytecode treats it as an integer. If a value iswritten is addr, then the bytecode treats it as an address.

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We do not fully describe the floating point operations here; although this design can beextended in a clean way to handle floating point values, they are not of immediate interest
to the customer, so we avoid describing them, to save time.
float (0x01): ⇒Prefix for floating-point bytecodes. Not implemented yet.
add (0x02): a b ⇒ a+b
Pop two integers from the stack, and push their sum, as an integer.
sub (0x03): a b ⇒ a-b
Pop two integers from the stack, subtract the top value from the next-to-top
value, and push the difference.
mul (0x04): a b ⇒ a*b
Pop two integers from the stack, multiply them, and push the product on thestack. Note that, when one multiplies two n-bit numbers yielding another n-bit
number, it is irrelevant whether the numbers are signed or not; the results are
the same.
div_signed (0x05): a b ⇒ a/b
Pop two signed integers from the stack; divide the next-to-top value by the top
value, and push the quotient. If the divisor is zero, terminate with an error.
div_unsigned (0x06): a b ⇒ a/b
Pop two unsigned integers from the stack; divide the next-to-top value by the
top value, and push the quotient. If the divisor is zero, terminate with an error.
rem_signed (0x07): a b ⇒ a modulo b
Pop two signed integers from the stack; divide the next-to-top value by the top
value, and push the remainder. If the divisor is zero, terminate with an error.
rem_unsigned (0x08): a b ⇒ a modulo b
Pop two unsigned integers from the stack; divide the next-to-top value by the
top value, and push the remainder. If the divisor is zero, terminate with anerror.
lsh (0x09): a b ⇒ a<<b
Pop two integers from the stack; let a be the next-to-top value, and b be the
top value. Shift a left by b bits, and push the result.
rsh_signed (0x0a): a b ⇒ (signed)a>>b
Pop two integers from the stack; let a be the next-to-top value, and b be the
top value. Shift a right by b bits, inserting copies of the top bit at the highend, and push the result.
rsh_unsigned (0x0b): a b ⇒ a>>b
Pop two integers from the stack; let a be the next-to-top value, and b be the
top value. Shift a right by b bits, inserting zero bits at the high end, and push
the result.
log_not (0x0e): a ⇒ !a
Pop an integer from the stack; if it is zero, push the value one; otherwise, pushthe value zero.

Appendix F: The GDB Agent Expression Mechanism

851

bit_and (0x0f): a b ⇒ a&b
Pop two integers from the stack, and push their bitwise and.
bit_or (0x10): a b ⇒ a|b
Pop two integers from the stack, and push their bitwise or.
bit_xor (0x11): a b ⇒ a^b
Pop two integers from the stack, and push their bitwise exclusive-or.
bit_not (0x12): a ⇒ ~a
Pop an integer from the stack, and push its bitwise complement.
equal (0x13): a b ⇒ a=b
Pop two integers from the stack; if they are equal, push the value one; otherwise,push the value zero.
less_signed (0x14): a b ⇒ a<b
Pop two signed integers from the stack; if the next-to-top value is less than the
top value, push the value one; otherwise, push the value zero.
less_unsigned (0x15): a b ⇒ a<b
Pop two unsigned integers from the stack; if the next-to-top value is less than
the top value, push the value one; otherwise, push the value zero.
ext (0x16) n: a ⇒ a, sign-extended from n bits
Pop an unsigned value from the stack; treating it as an n-bit twos-complement
value, extend it to full length. This means that all bits to the left of bit n-1(where the least significant bit is bit 0) are set to the value of bit n-1. Notethat n may be larger than or equal to the width of the stack elements of thebytecode engine; in this case, the bytecode should have no effect.
The number of source bits to preserve, n, is encoded as a single byte unsigned
integer following the ext bytecode.
zero_ext (0x2a) n: a ⇒ a, zero-extended from n bits
Pop an unsigned value from the stack; zero all but the bottom n bits.
The number of source bits to preserve, n, is encoded as a single byte unsigned
integer following the zero_ext bytecode.
ref8 (0x17): addr ⇒ a
ref16 (0x18): addr ⇒ a
ref32 (0x19): addr ⇒ a
ref64 (0x1a): addr ⇒ a
Pop an address addr from the stack. For bytecode refn, fetch an n-bit value
from addr, using the natural target endianness. Push the fetched value as an
unsigned integer.
Note that addr may not be aligned in any particular way; the refn bytecodesshould operate correctly for any address.
If attempting to access memory at addr would cause a processor exception ofsome sort, terminate with an error.

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ref_float (0x1b): addr ⇒ d
ref_double (0x1c): addr ⇒ d
ref_long_double (0x1d): addr ⇒ dl_to_d (0x1e): a ⇒ dd_to_l (0x1f): d ⇒ a
Not implemented yet.
dup (0x28): a => a a
Push another copy of the stack’s top element.
swap (0x2b): a b => b a
Exchange the top two items on the stack.
pop (0x29): a =>Discard the top value on the stack.
pick (0x32) n: a . . . b => a . . . b a
Duplicate an item from the stack and push it on the top of the stack. n, a single
byte, indicates the stack item to copy. If n is zero, this is the same as dup; if n
is one, it copies the item under the top item, etc. If n exceeds the number of
items on the stack, terminate with an error.
rot (0x33): a b c => c a b
Rotate the top three items on the stack. The top item (c) becomes the third
item, the next-to-top item (b) becomes the top item and the third item (a)from the top becomes the next-to-top item.
if_goto (0x20) offset: a ⇒Pop an integer off the stack; if it is non-zero, branch to the given offset in the
bytecode string. Otherwise, continue to the next instruction in the bytecodestream. In other words, if a is non-zero, set the pc register to start + offset.
Thus, an offset of zero denotes the beginning of the expression.
The offset is stored as a sixteen-bit unsigned value, stored immediately following the if_goto bytecode. It is always stored most significant byte first,
regardless of the target’s normal endianness. The offset is not guaranteed tofall at any particular alignment within the bytecode stream; thus, on machines
where fetching a 16-bit on an unaligned address raises an exception, you should
fetch the offset one byte at a time.
goto (0x21) offset: ⇒Branch unconditionally to offset; in other words, set the pc register to start +offset.
The offset is stored in the same way as for the if_goto bytecode.
const8 (0x22) n: ⇒ nconst16 (0x23) n: ⇒ nconst32 (0x24) n: ⇒ nconst64 (0x25) n: ⇒ nPush the integer constant n on the stack, without sign extension. To produce asmall negative value, push a small twos-complement value, and then sign-extend
it using the ext bytecode.

Appendix F: The GDB Agent Expression Mechanism

853

The constant n is stored in the appropriate number of bytes following theconstb bytecode. The constant n is always stored most significant byte first,
regardless of the target’s normal endianness. The constant is not guaranteed tofall at any particular alignment within the bytecode stream; thus, on machines
where fetching a 16-bit on an unaligned address raises an exception, you should
fetch n one byte at a time.
reg (0x26) n: ⇒ aPush the value of register number n, without sign extension. The registers arenumbered following GDB’s conventions.
The register number n is encoded as a 16-bit unsigned integer immediately following the reg bytecode. It is always stored most significant byte first, regardless of the target’s normal endianness. The register number is not guaranteed tofall at any particular alignment within the bytecode stream; thus, on machines
where fetching a 16-bit on an unaligned address raises an exception, you should
fetch the register number one byte at a time.
getv (0x2c) n: ⇒ v
Push the value of trace state variable number n, without sign extension.
The variable number n is encoded as a 16-bit unsigned integer immediately
following the getv bytecode. It is always stored most significant byte first,
regardless of the target’s normal endianness. The variable number is not guaranteed to fall at any particular alignment within the bytecode stream; thus, onmachines where fetching a 16-bit on an unaligned address raises an exception,
you should fetch the register number one byte at a time.
setv (0x2d) n: v ⇒ v
Set trace state variable number n to the value found on the top of the stack.
The stack is unchanged, so that the value is readily available if the assignmentis part of a larger expression. The handling of n is as described for getv.
trace (0x0c): addr size ⇒Record the contents of the size bytes at addr in a trace buffer, for later retrieval
by GDB.
trace_quick (0x0d) size: addr ⇒ addr
Record the contents of the size bytes at addr in a trace buffer, for later retrieval
by GDB. size is a single byte unsigned integer following the trace opcode.
This bytecode is equivalent to the sequence dup const8 size trace, but weprovide it anyway to save space in bytecode strings.
trace16 (0x30) size: addr ⇒ addr
Identical to trace quick, except that size is a 16-bit big-endian unsigned integer,
not a single byte. This should probably have been named trace_quick16, forconsistency.
tracev (0x2e) n: ⇒ a
Record the value of trace state variable number n in the trace buffer. The
handling of n is as described for getv.

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tracenz (0x2f) addr size ⇒Record the bytes at addr in a trace buffer, for later retrieval by GDB. Stopat either the first zero byte, or when size bytes have been recorded, whicheveroccurs first.
printf (0x34) numargs string ⇒Do a formatted print, in the style of the C function printf). The value ofnumargs is the number of arguments to expect on the stack, while string is
the format string, prefixed with a two-byte length. The last byte of the string
must be zero, and is included in the length. The format string includes escaped
sequences just as it appears in C source, so for instance the format string"\t%d\n" is six characters long, and the output will consist of a tab character,a decimal number, and a newline. At the top of the stack, above the values tobe printed, this bytecode will pop a “function” and “channel”. If the function
is nonzero, then the target may treat it as a function and call it, passing thechannel as a first argument, as with the C function fprintf. If the functionis zero, then the target may simply call a standard formatted print function of
its choice. In all, this bytecode pops 2 + numargs stack elements, and pushes
nothing.
end (0x27): ⇒Stop executing bytecode; the result should be the top element of the stack. If
the purpose of the expression was to compute an lvalue or a range of memory,then the next-to-top of the stack is the lvalue’s address, and the top of the stackis the lvalue’s size, in bytes.

F.3 Using Agent Expressions
Agent expressions can be used in several different ways by gdb, and the debugger can
generate different bytecode sequences as appropriate.
One possibility is to do expression evaluation on the target rather than the host, suchas for the conditional of a conditional tracepoint. In such a case, gdb compiles the source
expression into a bytecode sequence that simply gets values from registers or memory, does
arithmetic, and returns a result.
Another way to use agent expressions is for tracepoint data collection. gdb generates adifferent bytecode sequence for collection; in addition to bytecodes that do the calculation,
gdb adds trace bytecodes to save the pieces of memory that were used.
• The user selects trace points in the program’s code at which GDB should collect data.
• The user specifies expressions to evaluate at each trace point. These expressions may
denote objects in memory, in which case those objects’ contents are recorded as the
program runs, or computed values, in which case the values themselves are recorded.
• GDB transmits the tracepoints and their associated expressions to the GDB agent,running on the debugging target.
• The agent arranges to be notified when a trace point is hit.
• When execution on the target reaches a trace point, the agent evaluates the expressions
associated with that trace point, and records the resulting values and memory ranges.

Appendix F: The GDB Agent Expression Mechanism

855• Later, when the user selects a given trace event and inspects the objects and expression
values recorded, GDB talks to the agent to retrieve recorded data as necessary to meetthe user’s requests. If the user asks to see an object whose contents have not beenrecorded, GDB reports an error.

F.4 Varying Target Capabilities
Some targets don’t support floating-point, and some would rather not have to deal withlong long operations. Also, different targets will have different stack sizes, and different
bytecode buffer lengths.
Thus, GDB needs a way to ask the target about itself. We haven’t worked out the details
yet, but in general, GDB should be able to send the target a packet asking it to describe
itself. The reply should be a packet whose length is explicit, so we can add new information
to the packet in future revisions of the agent, without confusing old versions of GDB, andit should contain a version number. It should contain at least the following information:• whether floating point is supported• whether long long is supported• maximum acceptable size of bytecode stack• maximum acceptable length of bytecode expressions• which registers are actually available for collection• whether the target supports disabled tracepoints

F.5 Rationale
Some of the design decisions apparent above are arguable.
What about stack overflow/underflow?
GDB should be able to query the target to discover its stack size. Given that
information, GDB can determine at translation time whether a given expression
will overflow the stack. But this spec isn’t about what kinds of error-checking
GDB ought to do.
Why are you doing everything in LONGEST?
Speed isn’t important, but agent code size is; using LONGEST brings in a bunchof support code to do things like division, etc. So this is a serious concern.
First, note that you don’t need different bytecodes for different operand sizes.
You can generate code without knowing how big the stack elements actually
are on the target. If the target only supports 32-bit ints, and you don’t send
any 64-bit bytecodes, everything just works. The observation here is that the
MIPS and the Alpha have only fixed-size registers, and you can still get C’s
semantics even though most instructions only operate on full-sized words. You
just need to make sure everything is properly sign-extended at the right times.
So there is no need for 32- and 64-bit variants of the bytecodes. Just implement
everything using the largest size you support.
GDB should certainly check to see what sizes the target supports, so the user
can get an error earlier, rather than later. But this information is not necessary
for correctness.

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Why don’t you have > or <= operators?
I want to keep the interpreter small, and we don’t need them. We can combine
the less_ opcodes with log_not, and swap the order of the operands, yielding
all four asymmetrical comparison operators. For example, (x <= y) is ! (x >y), which is ! (y < x).
Why do you have log_not?
Why do you have ext?
Why do you have zero_ext?
These are all easily synthesized from other instructions, but I expect them to be
used frequently, and they’re simple, so I include them to keep bytecode strings
short.
log_not is equivalent to const8 0 equal; it’s used in half the relational operators.
ext n is equivalent to const8 s-n lsh const8 s-n rsh_signed, where s is thesize of the stack elements; it follows refm and reg bytecodes when the value
should be signed. See the next bulleted item.
zero_ext n is equivalent to constm mask log_and; it’s used whenever we pushthe value of a register, because we can’t assume the upper bits of the registeraren’t garbage.
Why not have sign-extending variants of the ref operators?
Because that would double the number of ref operators, and we need the ext
bytecode anyway for accessing bitfields.
Why not have constant-address variants of the ref operators?
Because that would double the number of ref operators again, and const32
address ref32 is only one byte longer.
Why do the refn operators have to support unaligned fetches?
GDB will generate bytecode that fetches multi-byte values at unaligned addresses whenever the executable’s debugging information tells it to. Furthermore, GDB does not know the value the pointer will have when GDB generates
the bytecode, so it cannot determine whether a particular fetch will be aligned
or not.
In particular, structure bitfields may be several bytes long, but follow no alignment rules; members of packed structures are not necessarily aligned either.
In general, there are many cases where unaligned references occur in correct C
code, either at the programmer’s explicit request, or at the compiler’s discretion.
Thus, it is simpler to make the GDB agent bytecodes work correctly in all
circumstances than to make GDB guess in each case whether the compiler did
the usual thing.
Why are there no side-effecting operators?
Because our current client doesn’t want them? That’s a cheap answer. I think
the real answer is that I’m afraid of implementing function calls. We should
re-visit this issue after the present contract is delivered.

857

Why aren’t the goto ops PC-relative?
The interpreter has the base address around anyway for PC bounds checking,and it seemed simpler.
Why is there only one offset size for the goto ops?
Offsets are currently sixteen bits. I’m not happy with this situation either:
Suppose we have multiple branch ops with different offset sizes. As I generate
code left-to-right, all my jumps are forward jumps (there are no loops in expressions), so I never know the target when I emit the jump opcode. Thus, I
have to either always assume the largest offset size, or do jump relaxation on
the code after I generate it, which seems like a big waste of time.
I can imagine a reasonable expression being longer than 256 bytes. I can’t
imagine one being longer than 64k. Thus, we need 16-bit offsets. This kind of
reasoning is so bogus, but relaxation is pathetic.
The other approach would be to generate code right-to-left. Then I’d always
know my offset size. That might be fun.
Where is the function call bytecode?
When we add side-effects, we should add this.
Why does the reg bytecode take a 16-bit register number?
Intel’s IA-64 architecture has 128 general-purpose registers, and 128 floatingpoint registers, and I’m sure it has some random control registers.
Why do we need trace and trace_quick?
Because GDB needs to record all the memory contents and registers an expression touches. If the user wants to evaluate an expression x->y->z, the agent
must record the values of x and x->y as well as the value of x->y->z.
Don’t the trace bytecodes make the interpreter less general?
They do mean that the interpreter contains special-purpose code, but that
doesn’t mean the interpreter can only be used for that purpose. If an expression
doesn’t use the trace bytecodes, they don’t get in its way.
Why doesn’t trace_quick consume its arguments the way everything else does?
In general, you do want your operators to consume their arguments; it’s consistent, and generally reduces the amount of stack rearrangement necessary.
However, trace_quick is a kludge to save space; it only exists so we needn’t
write dup const8 SIZE trace before every memory reference. Therefore, it’sokay for it not to consume its arguments; it’s meant for a specific context inwhich we know exactly what it should do with the stack. If we’re going to havea kludge, it should be an effective kludge.
Why does trace16 exist?
That opcode was added by the customer that contracted Cygnus for the data
tracing work. I personally think it is unnecessary; objects that large will bequite rare, so it is okay to use dup const16 size trace in those cases.
Whatever we decide to do with trace16, we should at least leave opcode 0x30
reserved, to remain compatible with the customer who added it.

859

Appendix G Target Descriptions
One of the challenges of using gdb to debug embedded systems is that there are so many
minor variants of each processor architecture in use. It is common practice for vendors tostart with a standard processor core — ARM, PowerPC, or MIPS, for example — and thenmake changes to adapt it to a particular market niche. Some architectures have hundredsof variants, available from dozens of vendors. This leads to a number of problems:• With so many different customized processors, it is difficult for the gdb maintainers tokeep up with the changes.
• Since individual variants may have short lifetimes or limited audiences, it may not beworthwhile to carry information about every variant in the gdb source tree.
• When gdb does support the architecture of the embedded system at hand, the task offinding the correct architecture name to give the set architecture command can beerror-prone.
To address these problems, the gdb remote protocol allows a target system to not
only identify itself to gdb, but to actually describe its own features. This lets gdb support
processor variants it has never seen before — to the extent that the descriptions are accurate,
and that gdb understands them.
gdb must be linked with the Expat library to support XML target descriptions. See[Expat], page 746.

G.1 Retrieving Descriptions
Target descriptions can be read from the target automatically, or specified by the user
manually. The default behavior is to read the description from the target. gdb retrieves
it via the remote protocol using ‘qXfer’ requests (see Section E.5 [General Query Packets],page 789). The annex in the ‘qXfer’ packet will be ‘target.xml’. The contents of the‘target.xml’ annex are an XML document, of the form described in Section G.2 [Target
Description Format], page 859.
Alternatively, you can specify a file to read for the target description. If a file is set, thetarget will not be queried. The commands to specify a file are:set tdesc filename path
Read the target description from path.
unset tdesc filename
Do not read the XML target description from a file. gdb will use the description
supplied by the current target.
show tdesc filename
Show the filename to read for a target description, if any.

G.2 Target Description Format
A target description annex is an XML (http: / / www . w3 . org / XML / ) document
which complies with the Document Type Definition provided in the gdb sources in
gdb/features/gdb-target.dtd. This means you can use generally available tools like
xmllint to check that your feature descriptions are well-formed and valid. However, to860

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help people unfamiliar with XML write descriptions for their targets, we also describe thegrammar here.
Target descriptions can identify the architecture of the remote target and (for somearchitectures) provide information about custom register sets. They can also identify the
OS ABI of the remote target. gdb can use this information to autoconfigure for your target,or to warn you if you connect to an unsupported target.
Here is a simple target description:<target version="1.0"><architecture>i386:x86-64</architecture></target>This minimal description only says that the target uses the x86-64 architecture.
A target description has the following overall form, with [ ] marking optional elements
and . . . marking repeatable elements. The elements are explained further below.
<?xml version="1.0"?><!DOCTYPE target SYSTEM "gdb-target.dtd"><target version="1.0">[architecture][osabi][compatible][feature...]</target>

The description is generally insensitive to whitespace and line breaks, under the usualcommon-sense rules. The XML version declaration and document type declaration can
generally be omitted (gdb does not require them), but specifying them may be usefulfor XML validation tools. The ‘version’ attribute for ‘<target>’ may also be omitted,
but we recommend including it; if future versions of gdb use an incompatible revision of
gdb-target.dtd, they will detect and report the version mismatch.

G.2.1 Inclusion
It can sometimes be valuable to split a target description up into several different annexes,
either for organizational purposes, or to share files between different possible target descriptions. You can divide a description into multiple files by replacing any element of the target
description with an inclusion directive of the form:<xi:include href="document"/>

When gdb encounters an element of this form, it will retrieve the named XML document,
and replace the inclusion directive with the contents of that document. If the current
description was read using ‘qXfer’, then so will be the included document; document will
be interpreted as the name of an annex. If the current description was read from a file, gdb
will look for document as a file in the same directory where it found the original description.

G.2.2 ArchitectureAn ‘<architecture>’ element has this form:<architecture>arch</architecture>arch is one of the architectures from the set accepted by set architecture (seeChapter 19 [Specifying a Debugging Target], page 311).

Appendix G: Target Descriptions

861

G.2.3 OS ABIThis optional field was introduced in gdb version 7.0. Previous versions of gdb ignore it.
An ‘<osabi>’ element has this form:<osabi>abi-name</osabi>

abi-name is an OS ABI name from the same selection accepted by set osabi (seeSection 22.7 [Configuring the Current ABI], page 375).

G.2.4 Compatible ArchitectureThis optional field was introduced in gdb version 7.0. Previous versions of gdb ignore it.
A ‘<compatible>’ element has this form:<compatible>arch</compatible>

arch is one of the architectures from the set accepted by set architecture (seeChapter 19 [Specifying a Debugging Target], page 311).
A ‘<compatible>’ element is used to specify that the target is able to run binaries
in some other than the main target architecture given by the ‘<architecture>’ element.
For example, on the Cell Broadband Engine, the main architecture is powerpc:common or
powerpc:common64, but the system is able to run binaries in the spu architecture as well.
The way to describe this capability with ‘<compatible>’ is as follows:<architecture>powerpc:common</architecture><compatible>spu</compatible>

G.2.5 Features
Each ‘<feature>’ describes some logical portion of the target system. Features are currently
used to describe available CPU registers and the types of their contents. A ‘<feature>’element has this form:<feature name="name">[type...]
reg...
</feature>

Each feature’s name should be unique within the description. The name of a feature does
not matter unless gdb has some special knowledge of the contents of that feature; if it does,
the feature should have its standard name. See Section G.5 [Standard Target Features],page 865.

G.2.6 Types
Any register’s value is a collection of bits which gdb must interpret. The default interpretation is a two’s complement integer, but other types can be requested by name in the register
description. Some predefined types are provided by gdb (see Section G.3 [Predefined Target
Types], page 863), and the description can define additional composite and enum types.
Each type element must have an ‘id’ attribute, which gives a unique (within the containing ‘<feature>’) name to the type. Types must be defined before they are used.
Some targets offer vector registers, which can be treated as arrays of scalar elements.
These types are written as ‘<vector>’ elements, specifying the array element type, type,
and the number of elements, count:<vector id="id" type="type" count="count"/>

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If a register’s value is usefully viewed in multiple ways, define it with a union type containing the useful representations. The ‘<union>’ element contains one or more ‘<field>’
elements, each of which has a name and a type:<union id="id"><field name="name" type="type"/>...
</union>If a register’s value is composed from several separate values, define it with either astructure type or a flags type. A flags type may only contain bitfields. A structure typemay either contain only bitfields or contain no bitfields. If the value contains only bitfields,
its total size in bytes must be specified.
Non-bitfield values have a name and type.
<struct id="id"><field name="name" type="type"/>...
</struct>

Both name and type values are required. No implicit padding is added.
Bitfield values have a name, start, end and type.
<struct id="id" size="size"><field name="name" start="start" end="end" type="type"/>...
</struct><flags id="id" size="size"><field name="name" start="start" end="end" type="type"/>...
</flags>

The name value is required. Bitfield values may be named with the empty string, ‘""’, inwhich case the field is “filler” and its value is not printed. Not all bits need to be specified,so “filler” fields are optional.
The start and end values are required, and type is optional. The field’s start must be
less than or equal to its end, and zero represents the least significant bit.
The default value of type is bool for single bit fields, and an unsigned integer otherwise.
Which to choose? Structures or flags?
Registers defined with ‘flags’ have these advantages over defining them with ‘struct’:• Arithmetic may be performed on them as if they were integers.
• They are printed in a more readable fashion.
Registers defined with ‘struct’ have one advantage over defining them with ‘flags’:• One can fetch individual fields like in ‘C’.
(gdb) print $my_struct_reg.field3$1 = 42G.2.7 Registers
Each register is represented as an element with this form:<reg name="name"bitsize="size"[regnum="num"][save-restore="save-restore"]

Appendix G: Target Descriptions

863[type="type"][group="group"]/>

The components are as follows:name

The register’s name; it must be unique within the target description.

bitsize

The register’s size, in bits.

regnumThe register’s number. If omitted, a register’s number is one greater than thatof the previous register (either in the current feature or in a preceding feature);
the first register in the target description defaults to zero. This register number
is used to read or write the register; e.g. it is used in the remote p and P
packets, and registers appear in the g and G packets in order of increasing
register number.

save-restore
Whether the register should be preserved across inferior function calls; this mustbe either yes or no. The default is yes, which is appropriate for most registers
except for some system control registers; this is not related to the target’s ABI.
type

The type of the register. It may be a predefined type, a type defined in thecurrent feature, or one of the special types int and float. int is an integer
type of the correct size for bitsize, and float is a floating point type (in thearchitecture’s normal floating point format) of the correct size for bitsize. The
default is int.

group

The register group to which this register belongs. It can be one of the standard
register groups general, float, vector or an arbitrary string. Group names
should be limited to alphanumeric characters. If a group name is made up ofmultiple words the words may be separated by hyphens; e.g. special-groupor ultra-special-group. If no group is specified, gdb will not display theregister in info registers.

G.3 Predefined Target Types
Type definitions in the self-description can build up composite types from basic building
blocks, but can not define fundamental types. Instead, standard identifiers are provided by
gdb for the fundamental types. The currently supported types are:bool

Boolean type, occupying a single bit.

int8
int16
int24
int32
int64
int128Signed integer types holding the specified number of bits.

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uint8
uint16
uint24
uint32
uint64
uint128
code_ptr
data_ptr

Unsigned integer types holding the specified number of bits.
Pointers to unspecified code and data. The program counter and any dedicatedreturn address register may be marked as code pointers; printing a code pointerconverts it into a symbolic address. The stack pointer and any dedicated address
registers may be marked as data pointers.

ieee_half
Half precision IEEE floating point.
ieee_single
Single precision IEEE floating point.
ieee_double
Double precision IEEE floating point.
bfloat16

The 16-bit brain floating point format used e.g. by x86 and ARM.

arm_fpa_ext
The 12-byte extended precision format used by ARM FPA registers.
i387_ext

The 10-byte extended precision format used by x87 registers.

i386_eflags
32bit eflags register used by x86.
i386_mxcsr
32bit mxcsr register used by x86.

G.4 Enum Target Types
Enum target types are useful in ‘struct’ and ‘flags’ register descriptions. See Section G.2[Target Description Format], page 859.
Enum types have a name, size and a list of name/value pairs.
<enum id="id" size="size"><evalue name="name" value="value"/>...
</enum>Enums must be defined before they are used.
<enum id="levels_type" size="4"><evalue name="low" value="0"/><evalue name="high" value="1"/></enum><flags id="flags_type" size="4"><field name="X" start="0"/><field name="LEVEL" start="1" end="1" type="levels_type"/></flags><reg name="flags" bitsize="32" type="flags_type"/>Appendix G: Target Descriptions

865

Given that description, a value of 3 for the ‘flags’ register would be printed as:(gdb) info register flags
flags 0x3 [ X LEVEL=high ]G.5 Standard Target Features
A target description must contain either no registers or all the target’s registers. If thedescription contains no registers, then gdb will assume a default register layout, selectedbased on the architecture. If the description contains any registers, the default layout will
not be used; the standard registers must be described in the target description, in such a
way that gdb can recognize them.
This is accomplished by giving specific names to feature elements which contain standard
registers. gdb will look for features with those names and verify that they contain the
expected registers; if any known feature is missing required registers, or if any requiredfeature is missing, gdb will reject the target description. You can add additional registers
to any of the standard features — gdb will display them just as if they were added to an
unrecognized feature.
This section lists the known features and their expected contents. Sample XML documents for these features are included in the gdb source tree, in the directory gdb/features.
Names recognized by gdb should include the name of the company or organization
which selected the name, and the overall architecture to which the feature applies; so e.g.
the feature containing ARM core registers is named ‘org.gnu.gdb.arm.core’.
The names of registers are not case sensitive for the purpose of recognizing standard
features, but gdb will only display registers using the capitalization used in the description.

G.5.1 AArch64 Features
G.5.1.1 AArch64 core registers feature
The ‘org.gnu.gdb.aarch64.core’ feature is required for AArch64 targets. It must containthe following:− ‘x0’ through ‘x30’, the general purpose registers, with size of 64 bits. Register ‘x30’ isalso known as the link register, or ‘lr’.
− ‘sp’, the stack pointer register or ‘x31’. It is 64 bits in size and has a type of ‘data_ptr’.
− ‘pc’, the program counter register. It is 64 bits in size and has a type of ‘code_ptr’.
− ‘cpsr’, the current program status register. It is 32 bits in size and has a custom flags
type.
The semantics of the individual flags and fields in ‘cpsr’ can change as new architecturalfeatures are added. The current layout can be found in the aarch64-core.xml file.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.1.2 AArch64 floating-point registers feature
The ‘org.gnu.gdb.aarch64.fpu’ feature is optional. If present, it must contain the following registers:− ‘v0’ through ‘v31’, the vector registers with size of 128 bits. The type is a custom
vector type.

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Debugging with gdb− ‘fpsr’, the floating-point status register. It is 32 bits in size and has a custom flags
type.
− ‘fpcr’, the floating-point control register. It is 32 bits in size and has a custom flags
type.
The semantics of the individual flags and fields in ‘fpsr’ and ‘fpcr’ can change as newarchitectural features are added.
The types for the vector registers, ‘fpsr’ and ‘fpcr’ registers can be found in the aarch64fpu.xml file.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.1.3 AArch64 SVE registers feature
The ‘org.gnu.gdb.aarch64.sve’ feature is optional. If present, it means the target supports the Scalable Vector Extension and must contain the following registers:− ‘z0’ through ‘z31’, the scalable vector registers. Their sizes are variable and a multipleof 128 bits up to a maximum of 2048 bit. Their type is a custom union type that helps
visualize different sizes of sub-vectors.
− ‘fpsr’, the floating-point status register. It is 32 bits in size and has a custom flags
type.
− ‘fpcr’, the floating-point control register. It is 32 bits in size and has a custom flags
type.
− ‘p0’ through ‘p15’, the predicate registers. Their sizes are variable, based on the current
vector length, and a multiple of 16 bits. Their types are a custom union to help visualize
sub-elements.
− ‘ffr’, the First Fault register. It has a variable size based on the current vector lengthand is a multiple of 16 bits. The type is the same as the predicate registers.
− ‘vg’, the vector granule. It represents the number of 64 bits chunks in a ‘z’ register. It
is closely associated with the current vector length. It has a type of ‘int’.
When gdb sees the SVE feature, it will assume the Scalable Vector Extension is supported, and will adjust the sizes of the ‘z’, ‘p’ and ‘ffr’ registers accordingly, based on thevalue of ‘vg’.
gdb will also create pseudo-registers equivalent to the ‘v’ vector registers from the‘org.gnu.gdb.aarch64.fpu’ feature.
The first 128 bits of the ‘z’ registers overlap the 128 bits of the ‘v’ registers, so changing
one will trigger a change to the other.
For the types of the ‘z’, ‘p’ and ‘ffr’ registers, please check the aarch64-sve.c file. No
XML file is available for this feature because it is dynamically generated based on thecurrent vector length.
The semantics of the individual flags and fields in ‘fpsr’ and ‘fpcr’ can change as newarchitectural features are added.
The types for the ‘fpsr’ and ‘fpcr’ registers can be found in the aarch64-sve.c file, andshould match what is described in aarch64-fpu.xml.
Extra registers are allowed in this feature, but they will not affect gdb.

Appendix G: Target Descriptions

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G.5.1.4 AArch64 Pointer Authentication registers feature
The ‘org.gnu.gdb.aarch64.pauth’ optional feature was introduced so gdb could detectsupport for the Pointer Authentication extension. If present, it must contain one of two
possible register sets.
Pointer Authentication masks for user-mode:− ‘pauth_dmask’, the user-mode pointer authentication mask for data pointers. It is 64
bits in size.
− ‘pauth_cmask’, the user-mode pointer authentication mask for code pointers. It is 64
bits in size.
Pointer Authentication masks for user-mode and kernel-mode:− ‘pauth_dmask’, the user-mode pointer authentication mask for data pointers. It is 64
bits in size.
− ‘pauth_cmask’, the user-mode pointer authentication mask for code pointers. It is 64
bits in size.
− ‘pauth_dmask_high’, the kernel-mode pointer authentication mask for data pointers.
It is 64 bits in size.
− ‘pauth_cmask_high’, the kernel-mode pointer authentication mask for code pointers.
It is 64 bits in size.
If gdb sees any of the two sets of registers in this feature, it will assume the target is capable of signing pointers. If so, gdb will decorate backtraces with a ‘[PAC]’ marker alongsidea function that has a signed link register value that needs to be unmasked/decoded.
gdb will also use the masks to remove non-address bits from pointers.
Extra registers are allowed in this feature, but they will not affect gdb.
Please note the ‘org.gnu.gdb.aarch64.pauth’ feature string is deprecated and must
only be used for backwards compatibility with older releases of gdb and gdbserver. Targets that support Pointer Authentication must advertise such capability by using the‘org.gnu.gdb.aarch64.pauth_v2’ feature string instead.
The ‘org.gnu.gdb.aarch64.pauth_v2’ feature has the exact same contents as feature‘org.gnu.gdb.aarch64.pauth’.
The reason for having feature ‘org.gnu.gdb.aarch64.pauth_v2’ is a bug inprevious versions of gdb (versions 9, 10, 11 and 12). This bug caused gdb to crash
whenever the target reported support for Pointer Authentication (using feature string‘org.gnu.gdb.aarch64.pauth’) and also reported additional system registers that were
not accounted for by gdb. This is more common when using emulators and on bare-metal
debugging scenarios.
It can also happen if a newer gdbserver is used with an old gdb that has the bug.
In such a case, the newer gdbserver might report Pointer Authentication support via the‘org.gnu.gdb.aarch64.pauth’ feature string and also report additional registers the older
gdb does not know about, potentially leading to a crash.

G.5.1.5 AArch64 TLS registers feature
The ‘org.gnu.gdb.aarch64.tls’ optional feature was introduced to expose the TLS registers to gdb. If present, it must contain either one of the following register sets.

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Debugging with gdb

Only ‘tpidr’:− ‘tpidr’, the software thread id register. It is 64 bits in size and has a type of ‘data_ptr’.
Both ‘tpidr’ and ‘tpidr2’.
− ‘tpidr’, the software thread id register. It is 64 bits in size and has a type of ‘data_ptr’.
− ‘tpidr2’, the second software thread id register. It is 64 bits in size and has a type of‘data_ptr’. It may be used in the future alongside the Scalable Matrix Extension fora lazy restore scheme.
If gdb sees this feature, it will attempt to find one of the variations of the register set.
If ‘tpidr2’ is available, gdb may act on it to display additional data in the future.
There is no XML for this feature as the presence of ‘tpidr2’ is determined dynamicallyat runtime.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.1.6 AArch64 MTE registers feature
The ‘org.gnu.gdb.aarch64.mte’ optional feature was introduced so gdb could detect support for the Memory Tagging Extension and control memory tagging settings. If present,
this feature must have the following register:− ‘tag_ctl’, the tag control register. It is 64 bits in size and has a type of ‘uint64’.
Memory Tagging detection is done via a runtime check though, so the presence of thisfeature and register is not enough to enable memory tagging support.
This restriction may be lifted in the future.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.1.7 AArch64 SME registers feature
The ‘org.gnu.gdb.aarch64.sme’ feature is optional. If present, it should contain registers
ZA, SVG and SVCR. See [AArch64 SME], page 355.
− ZA is a register represented by a vector of svlxsvl bytes. See [svl], page 355.
− SVG is a 64-bit register containing the value of svg. See [svg], page 355.
− SVCR is a 64-bit status pseudo-register with two valid bits. Bit 0 (sm) shows whether
the streaming SVE mode is enabled or disabled. Bit 1 (ZA) shows whether the ZA
register state is active (in use) or not. See [aarch64 sme svcr], page 355.
The rest of the unused bits of the SVCR pseudo-register is undefined and reserved. Suchbits should not be used and may be defined by future extensions of the architecture.
Extra registers are allowed in this feature, but they will not affect gdb.
The ‘org.gnu.gdb.aarch64.sme’ feature is required when the target also reports support for the ‘org.gnu.gdb.aarch64.sme2’ feature.

G.5.1.8 AArch64 SME2 registers feature
The ‘org.gnu.gdb.aarch64.sme2’ feature is optional.
If present, then the‘org.gnu.gdb.aarch64.sme’ feature must also be present. The ‘org.gnu.gdb.aarch64.sme2’
feature should contain the following: See [AArch64 SME2], page 357.
− ZT0 is a register of 512 bits (64 bytes). It is defined as a vector of bytes.
Extra registers are allowed in this feature, but they will not affect gdb.

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G.5.2 ARC Features
ARC processors are so configurable that even core registers and their numbers are notpredetermined completely. Moreover, flags and PC registers, which are important to gdb,
are not “core” registers in ARC. Therefore, there are two features that their presence ismandatory: ‘org.gnu.gdb.arc.core’ and ‘org.gnu.gdb.arc.aux’.
The ‘org.gnu.gdb.arc.core’ feature is required for all targets. It must contain registers:− ‘r0’ through ‘r25’ for normal register file targets.
− ‘r0’ through ‘r3’, and ‘r10’ through ‘r15’ for reduced register file targets.
− ‘gp’, ‘fp’, ‘sp’, ‘r30’1 , ‘blink’, ‘lp_count’, ‘pcl’.
In case of an ARCompact target (ARCv1 ISA), the ‘org.gnu.gdb.arc.core’ feature
may contain registers ‘ilink1’ and ‘ilink2’. While in case of ARC EM and ARC HStargets (ARCv2 ISA), register ‘ilink’ may be present. The difference between ARCv1 andARCv2 is the naming of registers 29th and 30th. They are called ‘ilink1’ and ‘ilink2’ for
ARCv1 and are optional. For ARCv2, they are called ‘ilink’ and ‘r30’ and only ‘ilink’
is optional. The optionality of ‘ilink*’ registers is because of their inaccessibility during
user space debugging sessions.
Extension core registers ‘r32’ through ‘r59’ are optional and their existence depends
on the configuration. When debugging GNU/Linux applications, i.e. user space debugging,these core registers are not available.
The ‘org.gnu.gdb.arc.aux’ feature is required for all ARC targets. Here is the list ofregisters pertinent to this feature:− mandatory: ‘pc’ and ‘status32’.
− optional: ‘lp_start’, ‘lp_end’, and ‘bta’.

G.5.3 ARM Features
G.5.3.1 Core register set for non-M-profile
The ‘org.gnu.gdb.arm.core’ feature is required for non-M-profile ARM targets. It must
contain the following registers:− ‘r0’ through ‘r12’. The general purpose registers. They are 32 bits in size and have atype of ‘uint32’.
− ‘sp’, the stack pointer register, also known as ‘r13’. It is 32 bits in size and has a typeof ‘data_ptr’.
− ‘lr’, the link register. It is 32 bits in size.
− ‘pc’, the program counter register. It is 32 bit in size and of type ‘code_ptr’.
− ‘cpsr’, the current program status register containing all the status bits. It is 32 bits insize. Historically this register was hardwired to number 25, but debugging stubs thatreport XML do not need to use this number anymore.
Extra registers are allowed in this feature, but they will not affect gdb.
1

Not necessary for ARCv1.

870

Debugging with gdb

G.5.3.2 Core register set for M-profile
For M-profile targets (e.g. Cortex-M3), the ‘org.gnu.gdb.arm.core’ feature is replaced by‘org.gnu.gdb.arm.m-profile’, and it is a required feature. It must contain the following
registers:− ‘r0’ through ‘r12’, the general purpose registers. They have a size of 32 bits and atype of ‘uint32’.
− ‘sp’, the stack pointer register, also known as ‘r13’. It has a size of 32 bits and a typeof ‘data_ptr’.
− ‘lr’, the link register. It has a size of 32 bits.
− ‘pc’, the program counter register. It has a size of 32 bits and a type of ‘code_ptr’.
− ‘xpsr’, the program status register containing all the status bits. It has a size of 32
bits. Historically this register was hardwired to number 25, but debugging stubs thatreport XML do not need to use this number anymore.
Upon seeing this feature, gdb will acknowledge that it is dealing with an M-profile target.
This means gdb will use hooks and configurations that are meaningful to M-profiles.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.3 FPA registers feature (obsolete)
The ‘org.gnu.gdb.arm.fpa’ feature is obsolete and should not be advertised by debugging
stubs anymore. It used to advertise registers for the old FPA architecture that has long
been discontinued in toolchains.
It is kept in gdb for backward compatibility purposes so older debugging stubs that
don’t support XML target descriptions still work correctly. One such example is the KGDB
debugging stub from Linux or BSD kernels.
The description below is for historical purposes only. This feature used to contain thefollowing registers:− ‘f0’ through ‘f8’. The floating point registers. They are 96 bits in size and of type
‘arm_fpa_ext’. ‘f0’ is pinned to register number 16.
− ‘fps’, the status register. It has a size of 32 bits.

G.5.3.4 M-profile Vector Extension (MVE)
Also known as Helium, the M-profile Vector Extension is advertised via the optional‘org.gnu.gdb.arm.m-profile-mve’ feature.
It must contain the following:− ‘vpr’, the vector predication status and control register. It is 32 bits in size and has acustom flags type. The flags type is laid out in a way that exposes the ‘P0’ field frombits 0 to 15, the ‘MASK01’ field from bits 16 to 19 and the ‘MASK23’ field from bits 20
to 23.
Bits 24 through 31 are reserved.
When this feature is available, gdb will synthesize the ‘p0’ pseudo-register from ‘vpr’
contents.

Appendix G: Target Descriptions

871

This feature must only be advertised if the target is M-profile. Advertising this feature
for targets that are not M-profile may cause gdb to assume the target is M-profile when it
isn’t.
If the ‘org.gnu.gdb.arm.vfp’ feature is available alongside the ‘org.gnu.gdb.arm.m-profile-mve’
feature, gdb will synthesize the ‘q’ pseudo-registers from ‘d’ register contents.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.5 XScale iwMMXt feature
The XScale ‘org.gnu.gdb.xscale.iwmmxt’ feature is optional. If present, it must containthe following:− ‘wR0’ through ‘wR15’, registers with size 64 bits and a custom type ‘iwmmxt_vec64i’.
‘iwmmxt_vec64i’ is a union of four other types: ‘uint64’, a 2-element vector of‘uint32’, a 4-element vector of ‘uint16’ and a 8-element vector of ‘uint8’.
− ‘wCGR0’ through ‘wCGR3’, registers with size 32 bits and type ‘int’.
The following registers are optional:− ‘wCID’, register with size of 32 bits and type ‘int’.
− ‘wCon’, register with size 32 bits and type ‘int’.
− ‘wCSSF’, register with size 32 bits and type ‘int’.
− ‘wCASF’, register with size 32 bit and type ‘int’.
This feature should only be reported if the target is XScale.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.6 Vector Floating-Point (VFP) feature
The ‘org.gnu.gdb.arm.vfp’ feature is optional. If present, it should contain one of two
possible sets of values depending on whether VFP version 2 or VFP version 3 is in use.
For VFP v2:− ‘d0’ through ‘d15’. The double-precision registers. They are 64 bits in size and havetype ‘ieee_double’.
− ‘fpscr’, the floating-point status and control register. It has a size of 32 bits and atype of ‘int’.
For VFP v3:− ‘d0’ through ‘d31’. The double-precision registers. They are 64 bits in size and havetype ‘ieee_double’.
− ‘fpscr’, the floating-point status and control register. It has a size of 32 bits and atype of ‘int’.
If this feature is available, gdb will synthesize the single-precision floating-point registers
from halves of the double-precision registers as pseudo-registers.
Extra registers are allowed in this feature, but they will not affect gdb.

872

Debugging with gdb

G.5.3.7 NEON architecture feature
The ‘org.gnu.gdb.arm.neon’ feature is optional. It does not need to contain registers; it
instructs gdb to display the VFP double-precision registers as vectors and to synthesize thequad-precision registers from pairs of double-precision registers. If this feature is present,‘org.gnu.gdb.arm.vfp’ must also be present and include 32 double-precision registers.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.8 M-profile Pointer Authentication and Branch Target
Identification feature
The ‘org.gnu.gdb.arm.m-profile-pacbti’ feature is optional, and acknowledges support
for the ARMv8.1-m PACBTI extensions.
This feature doesn’t contain any required registers, and it only serves as a hint to gdbthat the debugging stub supports the ARMv8.1-m PACBTI extensions.
When gdb sees this feature, it will track return address signing states and will decorate
backtraces using the [PAC] marker, similar to AArch64’s PAC extension. See [AArch64
PAC], page 357.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.9 M-profile system registers feature
The ‘org.gnu.gdb.arm.m-system’ optional feature was introduced as a way to inform gdb
about additional system registers.
At the moment this feature must contain the following:− ‘msp’, the main stack pointer register. It is 32 bits in size with type ‘data_ptr’.
− ‘psp’, the process stack pointer register. It is 32 bits in size with type ‘data_ptr’.
This feature must only be advertised for M-profile targets. When gdb sees this feature,
it will attempt to track the values of ‘msp’ and ‘psp’ across frames.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.10 M-profile Security Extensions feature
The ‘org.gnu.gdb.arm.secext’ optional feature was introduced so gdb could better support the switching of stack pointers and secure states in the Security Extensions.
At the moment this feature must contain the following:− ‘msp_ns’, the main stack pointer register (non-secure state). It is 32 bits in size with
type ‘data_ptr’.
− ‘psp_ns’, the process stack pointer register (non-secure state). It is 32 bits in size with
type ‘data_ptr’.
− ‘msp_s’, the main stack pointer register (secure state). It is 32 bits in size with type
‘data_ptr’.
− ‘psp_s’, the process stack pointer register (secure state). It is 32 bits in size with type
‘data_ptr’.
When gdb sees this feature, it will attempt to track the values of all 4 stack pointers
across secure state transitions, potentially improving unwinding when applications switch
between security states.

Appendix G: Target Descriptions

873

Extra registers are allowed in this feature, but they will not affect gdb.

G.5.3.11 TLS registers feature
The optional ‘org.gnu.gdb.arm.tls’ feature contains TLS registers.
Currently it contains the following:− ‘tpidruro’, the user read-only thread id register. It is 32 bits in size and has type
‘data_ptr’.
At the moment gdb looks for this feature, but doesn’t do anything with it other thandisplaying it.
Extra registers are allowed in this feature, but they will not affect gdb.

G.5.4 i386 Features
The ‘org.gnu.gdb.i386.core’ feature is required for i386/amd64 targets. It should describe the following registers:− ‘eax’ through ‘edi’ plus ‘eip’ for i386
− ‘rax’ through ‘r15’ plus ‘rip’ for amd64− ‘eflags’, ‘cs’, ‘ss’, ‘ds’, ‘es’, ‘fs’, ‘gs’
− ‘st0’ through ‘st7’− ‘fctrl’, ‘fstat’, ‘ftag’, ‘fiseg’, ‘fioff’, ‘foseg’, ‘fooff’ and ‘fop’
The register sets may be different, depending on the target.
The ‘org.gnu.gdb.i386.sse’ feature is optional. It should describe registers:− ‘xmm0’ through ‘xmm7’ for i386
− ‘xmm0’ through ‘xmm15’ for amd64− ‘mxcsr’The ‘org.gnu.gdb.i386.avx’ feature is optional and requires the ‘org.gnu.gdb.i386.sse’feature. It should describe the upper 128 bits of ymm registers:− ‘ymm0h’ through ‘ymm7h’ for i386
− ‘ymm0h’ through ‘ymm15h’ for amd64
The ‘org.gnu.gdb.i386.linux’ feature is optional. It should describe a single register,‘orig_eax’.
The ‘org.gnu.gdb.i386.segments’ feature is optional. It should describe two system
registers: ‘fs_base’ and ‘gs_base’.
The ‘org.gnu.gdb.i386.avx512’ feature is optional and requires‘org.gnu.gdb.i386.avx’ feature. It should describe additional xmm registers:− ‘xmm16’ through ‘xmm31’, only valid for amd64.
It should describe the upper 128 bits of additional ymm registers:− ‘ymm16h’ through ‘ymm31h’, only valid for amd64.
It should describe the upper 256 bits of zmm registers:− ‘zmm0h’ through ‘zmm7h’ for i386.

the

874

Debugging with gdb− ‘zmm0h’ through ‘zmm15h’ for amd64.
It should describe the additional zmm registers:− ‘zmm16h’ through ‘zmm31h’, only valid for amd64.
It should describe the additional 64-bit k registers:− ‘k0’ through ‘k7’, valid for amd64 and i386.
The ‘org.gnu.gdb.i386.pkeys’ feature is optional. It should describe a single register,‘pkru’. It is a 32-bit register valid for i386 and amd64.

G.5.5 LoongArch Features
The ‘org.gnu.gdb.loongarch.base’ feature is required for LoongArch targets. It should
contain the registers ‘r0’ through ‘r31’, ‘pc’, and ‘badv’. Either the architectural names(‘r0’, ‘r1’, etc) can be used, or the ABI names (‘zero’, ‘ra’, etc).
The ‘org.gnu.gdb.loongarch.fpu’ feature is optional. If present, it should containregisters ‘f0’ through ‘f31’, ‘fcc’, and ‘fcsr’.

G.5.6 MicroBlaze Features
The ‘org.gnu.gdb.microblaze.core’ feature is required for MicroBlaze targets. It should
contain registers ‘r0’ through ‘r31’, ‘rpc’, ‘rmsr’, ‘rear’, ‘resr’, ‘rfsr’, ‘rbtr’, ‘rpvr’,‘rpvr1’ through ‘rpvr11’, ‘redr’, ‘rpid’, ‘rzpr’, ‘rtlbx’, ‘rtlbsx’, ‘rtlblo’, and ‘rtlbhi’.
The ‘org.gnu.gdb.microblaze.stack-protect’ feature is optional.
should contain registers ‘rshr’ and ‘rslr’

If present, it

G.5.7 MIPS Features
The ‘org.gnu.gdb.mips.cpu’ feature is required for MIPS targets. It should contain registers ‘r0’ through ‘r31’, ‘lo’, ‘hi’, and ‘pc’. They may be 32-bit or 64-bit depending on thetarget.
The ‘org.gnu.gdb.mips.cp0’ feature is also required. It should contain at least the‘status’, ‘badvaddr’, and ‘cause’ registers. They may be 32-bit or 64-bit depending on thetarget.
The ‘org.gnu.gdb.mips.fpu’ feature is currently required, though it may be optional
in a future version of gdb. It should contain registers ‘f0’ through ‘f31’, ‘fcsr’, and ‘fir’.
They may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.dsp’ feature is optional. It should contain registers ‘hi1’
through ‘hi3’, ‘lo1’ through ‘lo3’, and ‘dspctl’. The ‘dspctl’ register should be 32-bit
and the rest may be 32-bit or 64-bit depending on the target.
The ‘org.gnu.gdb.mips.linux’ feature is optional. It should contain a single register,‘restart’, which is used by the Linux kernel to control restartable syscalls.

Appendix G: Target Descriptions

875

G.5.8 M68K Features‘org.gnu.gdb.m68k.core’‘org.gnu.gdb.coldfire.core’‘org.gnu.gdb.fido.core’
One of those features must be always present. The feature that is present
determines which flavor of m68k is used. The feature that is present should
contain registers ‘d0’ through ‘d7’, ‘a0’ through ‘a5’, ‘fp’, ‘sp’, ‘ps’ and ‘pc’.
‘org.gnu.gdb.coldfire.fp’
This feature is optional. If present, it should contain registers ‘fp0’ through‘fp7’, ‘fpcontrol’, ‘fpstatus’ and ‘fpiaddr’.
Note that, despite the fact that this feature’s name says ‘coldfire’, it is used
to describe any floating point registers. The size of the registers must matchthe main m68k flavor; so, for example, if the primary feature is reported as‘coldfire’, then 64-bit floating point registers are required.

G.5.9 NDS32 Features
The ‘org.gnu.gdb.nds32.core’ feature is required for NDS32 targets. It should containat least registers ‘r0’ through ‘r10’, ‘r15’, ‘fp’, ‘gp’, ‘lp’, ‘sp’, and ‘pc’.
The ‘org.gnu.gdb.nds32.fpu’ feature is optional. If present, it should contain 64-bit
double-precision floating-point registers ‘fd0’ through fdN, which should be ‘fd3’, ‘fd7’,‘fd15’, or ‘fd31’ based on the FPU configuration implemented.
Note: The first sixteen 64-bit double-precision floating-point registers are overlappedwith the thirty-two 32-bit single-precision floating-point registers. The 32-bit singleprecision registers, if not being listed explicitly, will be synthesized from halves of theoverlapping 64-bit double-precision registers. Listing 32-bit single-precision registers
explicitly is deprecated, and the support to it could be totally removed some day.

G.5.10 Nios II Features
The ‘org.gnu.gdb.nios2.cpu’ feature is required for Nios II targets. It should contain the
32 core registers (‘zero’, ‘at’, ‘r2’ through ‘r23’, ‘et’ through ‘ra’), ‘pc’, and the 16 control
registers (‘status’ through ‘mpuacc’).

G.5.11 Openrisc 1000 Features
The ‘org.gnu.gdb.or1k.group0’ feature is required for OpenRISC 1000 targets. It should
contain the 32 general purpose registers (‘r0’ through ‘r31’), ‘ppc’, ‘npc’ and ‘sr’.

G.5.12 PowerPC Features
The ‘org.gnu.gdb.power.core’ feature is required for PowerPC targets. It should containregisters ‘r0’ through ‘r31’, ‘pc’, ‘msr’, ‘cr’, ‘lr’, ‘ctr’, and ‘xer’. They may be 32-bit or
64-bit depending on the target.
The ‘org.gnu.gdb.power.fpu’ feature is optional. It should contain registers ‘f0’
through ‘f31’ and ‘fpscr’.
The ‘org.gnu.gdb.power.altivec’ feature is optional. It should contain registers ‘vr0’
through ‘vr31’, ‘vscr’, and ‘vrsave’. gdb will define pseudo-registers ‘v0’ through ‘v31’ asaliases for the corresponding ‘vrX’ registers.

876

Debugging with gdb

The ‘org.gnu.gdb.power.vsx’ feature is optional. It should contain registers ‘vs0h’
through ‘vs31h’. gdb will combine these registers with the floating point registers (‘f0’through ‘f31’) and the altivec registers (‘vr0’ through ‘vr31’) to present the 128-bit wide
registers ‘vs0’ through ‘vs63’, the set of vector-scalar registers for POWER7. Therefore,
this feature requires both ‘org.gnu.gdb.power.fpu’ and ‘org.gnu.gdb.power.altivec’.
The ‘org.gnu.gdb.power.spe’ feature is optional. It should contain registers ‘ev0h’
through ‘ev31h’, ‘acc’, and ‘spefscr’. SPE targets should provide 32-bit registers in‘org.gnu.gdb.power.core’ and provide the upper halves in ‘ev0h’ through ‘ev31h’. gdb
will combine these to present registers ‘ev0’ through ‘ev31’ to the user.
The ‘org.gnu.gdb.power.ppr’ feature is optional. It should contain the 64-bit register‘ppr’.
The ‘org.gnu.gdb.power.dscr’ feature is optional. It should contain the 64-bit register‘dscr’.
The ‘org.gnu.gdb.power.tar’ feature is optional. It should contain the 64-bit register‘tar’.
The ‘org.gnu.gdb.power.ebb’ feature is optional. It should contain registers ‘bescr’,‘ebbhr’ and ‘ebbrr’, all 64-bit wide.
The ‘org.gnu.gdb.power.linux.pmu’ feature is optional. It should contain registers‘mmcr0’, ‘mmcr2’, ‘siar’, ‘sdar’ and ‘sier’, all 64-bit wide. This is the subset of the isa 2.07
server PMU registers provided by gnu/Linux.
The ‘org.gnu.gdb.power.htm.spr’ feature is optional.
‘tfhar’, ‘texasr’ and ‘tfiar’, all 64-bit wide.

It should contain registers

The ‘org.gnu.gdb.power.htm.core’ feature is optional. It should contain the checkpointed general-purpose registers ‘cr0’ through ‘cr31’, as well as the checkpointed registers‘clr’ and ‘cctr’. These registers may all be either 32-bit or 64-bit depending on the target.
It should also contain the checkpointed registers ‘ccr’ and ‘cxer’, which should both be
32-bit wide.
The ‘org.gnu.gdb.power.htm.fpu’ feature is optional. It should contain the checkpointed 64-bit floating-point registers ‘cf0’ through ‘cf31’, as well as the checkpointed
64-bit register ‘cfpscr’.
The ‘org.gnu.gdb.power.htm.altivec’ feature is optional. It should contain the checkpointed altivec registers ‘cvr0’ through ‘cvr31’, all 128-bit wide. It should also contain the
checkpointed registers ‘cvscr’ and ‘cvrsave’, both 32-bit wide.
The ‘org.gnu.gdb.power.htm.vsx’ feature is optional. It should contain registers‘cvs0h’ through ‘cvs31h’. gdb will combine these registers with the checkpointed floating point registers (‘cf0’ through ‘cf31’) and the checkpointed altivec registers (‘cvr0’
through ‘cvr31’) to present the 128-bit wide checkpointed vector-scalar registers ‘cvs0’
through ‘cvs63’. Therefore, this feature requires both ‘org.gnu.gdb.power.htm.altivec’and ‘org.gnu.gdb.power.htm.fpu’.
The ‘org.gnu.gdb.power.htm.ppr’ feature is optional. It should contain the 64-bit
checkpointed register ‘cppr’.
The ‘org.gnu.gdb.power.htm.dscr’ feature is optional. It should contain the 64-bit
checkpointed register ‘cdscr’.

Appendix G: Target Descriptions

877

The ‘org.gnu.gdb.power.htm.tar’ feature is optional. It should contain the 64-bit
checkpointed register ‘ctar’.

G.5.13 RISC-V Features
The ‘org.gnu.gdb.riscv.cpu’ feature is required for RISC-V targets. It should containthe registers ‘x0’ through ‘x31’, and ‘pc’. Either the architectural names (‘x0’, ‘x1’, etc)
can be used, or the ABI names (‘zero’, ‘ra’, etc).
The ‘org.gnu.gdb.riscv.fpu’ feature is optional. If present, it should contain registers ‘f0’ through ‘f31’, ‘fflags’, ‘frm’, and ‘fcsr’. As with the cpu feature, either thearchitectural register names, or the ABI names can be used.
The ‘org.gnu.gdb.riscv.virtual’ feature is optional. If present, it should containregisters that are not backed by real registers on the target, but are instead virtual, where
the register value is derived from other target state. In many ways these are like gdbs
pseudo-registers, except implemented by the target. Currently the only register expected inthis set is the one byte ‘priv’ register that contains the target’s privilege level in the leastsignificant two bits.
The ‘org.gnu.gdb.riscv.csr’ feature is optional. If present, it should contain all of
the target’s standard CSRs. Standard CSRs are those defined in the RISC-V specification
documents. There is some overlap between this feature and the fpu feature; the ‘fflags’,‘frm’, and ‘fcsr’ registers could be in either feature. The expectation is that these registers
will be in the fpu feature if the target has floating point hardware, but can be moved into
the csr feature if the target has the floating point control registers, but no other floating
point hardware.
The ‘org.gnu.gdb.riscv.vector’ feature is optional. If present, it should contain registers ‘v0’ through ‘v31’, all of which must be the same size.

G.5.14 RX Features
The ‘org.gnu.gdb.rx.core’ feature is required for RX targets. It should contain theregisters ‘r0’ through ‘r15’, ‘usp’, ‘isp’, ‘psw’, ‘pc’, ‘intb’, ‘bpsw’, ‘bpc’, ‘fintv’, ‘fpsw’,and ‘acc’.

G.5.15 S/390 and System z Features
The ‘org.gnu.gdb.s390.core’ feature is required for S/390 and System z targets. It should
contain the PSW and the 16 general registers. In particular, System z targets should provide
the 64-bit registers ‘pswm’, ‘pswa’, and ‘r0’ through ‘r15’. S/390 targets should provide the32-bit versions of these registers. A System z target that runs in 31-bit addressing mode
should provide 32-bit versions of ‘pswm’ and ‘pswa’, as well as the general register’s upper
halves ‘r0h’ through ‘r15h’, and their lower halves ‘r0l’ through ‘r15l’.
The ‘org.gnu.gdb.s390.fpr’ feature is required. It should contain the 64-bit registers‘f0’ through ‘f15’, and ‘fpc’.
The ‘org.gnu.gdb.s390.acr’ feature is required. It should contain the 32-bit registers‘acr0’ through ‘acr15’.
The ‘org.gnu.gdb.s390.linux’ feature is optional. It should contain the register‘orig_r2’, which is 64-bit wide on System z targets and 32-bit otherwise. In addition, the878

Debugging with gdb

feature may contain the ‘last_break’ register, whose width depends on the addressing
mode, as well as the ‘system_call’ register, which is always 32-bit wide.
The ‘org.gnu.gdb.s390.tdb’ feature is optional. It should contain the 64-bit registers‘tdb0’, ‘tac’, ‘tct’, ‘atia’, and ‘tr0’ through ‘tr15’.
The ‘org.gnu.gdb.s390.vx’ feature is optional. It should contain 64-bit wide registers‘v0l’ through ‘v15l’, which will be combined by gdb with the floating point registers ‘f0’
through ‘f15’ to present the 128-bit wide vector registers ‘v0’ through ‘v15’. In addition,
this feature should contain the 128-bit wide vector registers ‘v16’ through ‘v31’.
The ‘org.gnu.gdb.s390.gs’ feature is optional. It should contain the 64-bit wide
guarded-storage-control registers ‘gsd’, ‘gssm’, and ‘gsepla’.
The ‘org.gnu.gdb.s390.gsbc’ feature is optional. It should contain the 64-bit wide
guarded-storage broadcast control registers ‘bc_gsd’, ‘bc_gssm’, and ‘bc_gsepla’.

G.5.16 Sparc Features
The ‘org.gnu.gdb.sparc.cpu’ feature is required for sparc32/sparc64 targets. It should
describe the following registers:− ‘g0’ through ‘g7’
− ‘o0’ through ‘o7’
− ‘l0’ through ‘l7’
− ‘i0’ through ‘i7’
They may be 32-bit or 64-bit depending on the target.
Also the ‘org.gnu.gdb.sparc.fpu’ feature is required for sparc32/sparc64 targets. It
should describe the following registers:− ‘f0’ through ‘f31’− ‘f32’ through ‘f62’ for sparc64
The ‘org.gnu.gdb.sparc.cp0’ feature is required for sparc32/sparc64 targets. It should
describe the following registers:− ‘y’, ‘psr’, ‘wim’, ‘tbr’, ‘pc’, ‘npc’, ‘fsr’, and ‘csr’ for sparc32− ‘pc’, ‘npc’, ‘state’, ‘fsr’, ‘fprs’, and ‘y’ for sparc64

G.5.17 TMS320C6x Features
The ‘org.gnu.gdb.tic6x.core’ feature is required for TMS320C6x targets. It should contain registers ‘A0’ through ‘A15’, registers ‘B0’ through ‘B15’, ‘CSR’ and ‘PC’.
The ‘org.gnu.gdb.tic6x.gp’ feature is optional. It should contain registers ‘A16’
through ‘A31’ and ‘B16’ through ‘B31’.
The ‘org.gnu.gdb.tic6x.c6xp’ feature is optional. It should contain registers ‘TSR’,‘ILC’ and ‘RILC’.

879

Appendix H Operating System Information
Users of gdb often wish to obtain information about the state of the operating systemrunning on the target—for example the list of processes, or the list of open files. Thissection describes the mechanism that makes it possible. This mechanism is similar to thetarget features mechanism (see Appendix G [Target Descriptions], page 859), but focuses
on a different aspect of target.
Operating system information is retrieved from the target via the remote protocol, using‘qXfer’ requests (see [qXfer osdata read], page 814). The object name in the request shouldbe ‘osdata’, and the annex identifies the data to be fetched.

H.1 Process list
When requesting the process list, the annex field in the ‘qXfer’ request should be‘processes’. The returned data is an XML document. The formal syntax of this document
is defined in gdb/features/osdata.dtd.
An example document is:<?xml version="1.0"?><!DOCTYPE target SYSTEM "osdata.dtd"><osdata type="processes"><item><column name="pid">1</column><column name="user">root</column><column name="command">/sbin/init</column><column name="cores">1,2,3</column></item></osdata>

Each item should include a column whose name is ‘pid’. The value of that column should
identify the process on the target. The ‘user’ and ‘command’ columns are optional, and will
be displayed by gdb. The ‘cores’ column, if present, should contain a comma-separated
list of cores that this process is running on. Target may provide additional columns, which
gdb currently ignores.

881

Appendix I Trace File Format
The trace file comes in three parts: a header, a textual description section, and a trace
frame section with binary data.
The header has the form \x7fTRACE0\n. The first byte is 0x7f so as to indicate thatthe file contains binary data, while the 0 is a version number that may have different values
in the future.
The description section consists of multiple lines of ascii text separated by newline
characters (0xa). The lines may include a variety of optional descriptive or context-setting
information, such as tracepoint definitions or register set size. gdb will ignore any line thatit does not recognize. An empty line marks the end of this section.
R sizeSpecifies the size of a register block in bytes. This is equal to the size of a g
packet payload in the remote protocol. size is an ascii decimal number. There
should be only one such line in a single trace file.

status status
Trace status. status has the same format as a qTStatus remote packet reply.
There should be only one such line in a single trace file.
tp payload
Tracepoint definition. The payload has the same format as qTfP/qTsP remote
packet reply payload. A single tracepoint may take multiple lines of definition,corresponding to the multiple reply packets.
tsv payload
Trace state variable definition. The payload has the same format as qTfV/qTsV
remote packet reply payload. A single variable may take multiple lines of definition, corresponding to the multiple reply packets.
tdesc payload
Target description in XML format. The payload is a single line of the XML
file. All such lines should be concatenated together to get the original XML file.
This file is in the same format as qXfer features payload, and corresponds tothe main target.xml file. Includes are not allowed.
The trace frame section consists of a number of consecutive frames. Each frame begins
with a two-byte tracepoint number, followed by a four-byte size giving the amount of datain the frame. The data in the frame consists of a number of blocks, each introduced by acharacter indicating its type (at least register, memory, and trace state variable). The datain this section is raw binary, not a hexadecimal or other encoding; its endianness matches
the target’s endianness.
R bytes

Register block. The number and ordering of bytes matches that of a g packet
in the remote protocol. Note that these are the actual bytes, in target order,
not a hexadecimal encoding.

M address length bytes...
Memory block. This is a contiguous block of memory, at the 8-byte address
address, with a 2-byte length length, followed by length bytes.

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V number value
Trace state variable block. This records the 8-byte signed value value of tracestate variable numbered number.
Future enhancements of the trace file format may include additional types of blocks.

883

Appendix J .gdb_index section format
This section documents the index section that is created by save gdb-index (seeSection 18.5 [Index Files], page 305). The index section is DWARF-specific; someknowledge of DWARF is assumed in this description.
The mapped index file format is designed to be directly mmapable on any architecture.
In most cases, a datum is represented using a little-endian 32-bit integer value, called anoffset_type. Big endian machines must byte-swap the values before using them. Exceptions to this rule are noted. The data is laid out such that alignment is always respected.
A mapped index consists of several areas, laid out in order.
1. The file header. This is a sequence of values, of offset_type unless otherwise noted:
1. The version number, currently 9. Versions 1, 2 and 3 are obsolete. Version 4 uses
a different hashing function from versions 5 and 6. Version 6 includes symbols forinlined functions, whereas versions 4 and 5 do not. Version 7 adds attributes to
the CU indices in the symbol table. Version 8 specifies that symbols from DWARF
type units (‘DW_TAG_type_unit’) refer to the type unit’s symbol table and not thecompilation unit (‘DW_TAG_comp_unit’) using the type. Version 9 adds the nameand the language of the main function to the index.
gdb will only read version 4, 5, or 6 indices by specifying set use-deprecatedindex-sections on. GDB has a workaround for potentially broken version 7
indices so it is currently not flagged as deprecated.
2. The offset, from the start of the file, of the CU list.
3. The offset, from the start of the file, of the types CU list. Note that this area canbe empty, in which case this offset will be equal to the next offset.
4. The offset, from the start of the file, of the address area.
5. The offset, from the start of the file, of the symbol table.
6. The offset, from the start of the file, of the shortcut table.
7. The offset, from the start of the file, of the constant pool.
2. The CU list. This is a sequence of pairs of 64-bit little-endian values, sorted by the CU
offset. The first element in each pair is the offset of a CU in the .debug_info section.
The second element in each pair is the length of that CU. References to a CU elsewherein the map are done using a CU index, which is just the 0-based index into this table.
Note that if there are type CUs, then conceptually CUs and type CUs form a single
list for the purposes of CU indices.
3. The types CU list. This is a sequence of triplets of 64-bit little-endian values. In a
triplet, the first value is the CU offset, the second value is the type offset in the CU,
and the third value is the type signature. The types CU list is not sorted.
4. The address area. The address area consists of a sequence of address entries. Each
address entry has three elements:
1. The low address. This is a 64-bit little-endian value.
2. The high address. This is a 64-bit little-endian value. Like DW_AT_high_pc, thevalue is one byte beyond the end.
3. The CU index. This is an offset_type value.

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5. The symbol table. This is an open-addressed hash table. The size of the hash table isalways a power of 2.
Each slot in the hash table consists of a pair of offset_type values. The first value isthe offset of the symbol’s name in the constant pool. The second value is the offset of
the CU vector in the constant pool.
If both values are 0, then this slot in the hash table is empty. This is ok because while
0 is a valid constant pool index, it cannot be a valid index for both a string and a CU
vector.
The hash value for a table entry is computed by applying an iterative hash function to
the symbol’s name. Starting with an initial value of r = 0, each (unsigned) character‘c’ in the string is incorporated into the hash using the formula depending on the index
version:Version 4

The formula is r = r * 67 + c - 113.

Versions 5 to 7
The formula is r = r * 67 + tolower (c) - 113.
The terminating ‘\0’ is not incorporated into the hash.
The step size used in the hash table is computed via ((hash * 17) & (size - 1)) | 1,
where ‘hash’ is the hash value, and ‘size’ is the size of the hash table. The step size
is used to find the next candidate slot when handling a hash collision.
The names of C++ symbols in the hash table are canonicalized. We don’t currently
have a simple description of the canonicalization algorithm; if you intend to create newindex sections, you must read the code.
6. The shortcut table This is a data structure with the following fields:
Language of main
An offset_type value indicating the language of the main function as a
DW_LANG_ constant. This value will be zero if main function information is
not present.
Name of main
An offset_type value indicating the offset of the main function’s name inthe constant pool. This value must be ignored if the value for the languageof main is zero.
7. The constant pool. This is simply a bunch of bytes. It is organized so that alignment
is correct: CU vectors are stored first, followed by strings.
A CU vector in the constant pool is a sequence of offset_type values. The first value
is the number of CU indices in the vector. Each subsequent value is the index andsymbol attributes of a CU in the CU list. This element in the hash table is used toindicate which CUs define the symbol and how the symbol is used. See below for theformat of each CU index+attributes entry.
A string in the constant pool is zero-terminated.
Attributes were added to CU index values in .gdb_index version 7. If a symbol has
multiple uses within a CU then there is one CU index+attributes value for each use.
The format of each CU index+attributes entry is as follows (bit 0 = LSB):
Bits 0-23

This is the index of the CU in the CU list.

Appendix J: .gdb_index section format

885

Bits 24-27 These bits are reserved for future purposes and must be zero.
Bits 28-30 The kind of the symbol in the CU.

Bit 310This value is reserved and should not be used. By reserving zerothe full offset_type value is backwards compatible with previous
versions of the index.

1

The symbol is a type.

2

The symbol is a variable or an enum value.

3

The symbol is a function.

4

Any other kind of symbol.

5,6,7

These values are reserved.

This bit is zero if the value is global and one if it is static.
The determination of whether a symbol is global or static is complicated. The
authoritative reference is the file dwarf2read.c in gdb sources.

This pseudo-code describes the computation of a symbol’s kind and global/static attributes in the index.
is_external = get_attribute (die, DW_AT_external);
language = get_attribute (cu_die, DW_AT_language);
switch (die->tag){case DW_TAG_typedef:
case DW_TAG_base_type:case DW_TAG_subrange_type:kind = TYPE;
is_static = 1;
break;
case DW_TAG_enumerator:
kind = VARIABLE;
is_static = language != CPLUS;
break;
case DW_TAG_subprogram:kind = FUNCTION;
is_static = ! (is_external || language == ADA);
break;
case DW_TAG_constant:kind = VARIABLE;
is_static = ! is_external;
break;
case DW_TAG_variable:
kind = VARIABLE;
is_static = ! is_external;
break;
case DW_TAG_namespace:kind = TYPE;
is_static = 0;
break;
case DW_TAG_class_type:case DW_TAG_interface_type:case DW_TAG_structure_type:case DW_TAG_union_type:886

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case DW_TAG_enumeration_type:kind = TYPE;
is_static = language != CPLUS;
break;
default:
assert (0);}887

Appendix K Download debugging resources with
Debuginfod
debuginfod is an HTTP server for distributing ELF, DWARF and source files.
With the debuginfod client library, libdebuginfod, gdb can query servers using thebuild IDs associated with missing debug info, executables and source files in order to download them on demand.
For instructions on building gdb with libdebuginfod, see Section C.5 [–withdebuginfod], page 749. debuginfod is packaged with elfutils, starting with version
0.178. See https://sourceware.org/elfutils/Debuginfod.html for more information
regarding debuginfod.

K.1 Debuginfod Settings
gdb provides the following commands for configuring debuginfod.
set debuginfod enabled
set debuginfod enabled on
gdb may query debuginfod servers for missing debug info and source files.
gdb may also download individual ELF/DWARF sections such as .gdb_index
to help reduce the total amount of data downloaded from debuginfod servers;
this can be controlled by maint set debuginfod download-sections (seeAppendix D [Maintenance Commands], page 755).
set debuginfod enabled off
gdb will not attempt to query debuginfod servers when missing debug info orsource files. By default, debuginfod enabled is set to off for non-interactive
sessions.
set debuginfod enabled ask
gdb will prompt the user to enable or disable debuginfod before attempting
to perform the next query. By default, debuginfod enabled is set to ask forinteractive sessions.
show debuginfod enabled
Display whether debuginfod enabled is set to on, off or ask.
set debuginfod urls
set debuginfod urls urls
Set the space-separated list of URLs that debuginfod will attempt to query.
Only http://, https:// and file:// protocols should be used. The default
value of debuginfod urls is copied from the DEBUGINFOD URLS environment variable.
show debuginfod urls
Display the list of URLs that debuginfod will attempt to query.
set debuginfod verbose
set debuginfod verbose n
Enable or disable debuginfod-related output. Use a non-zero value to enable
and 0 to disable. debuginfod output is shown by default.

888

show debuginfod verbose
Show the current verbosity setting.

Debugging with gdb

889

Appendix L Manual pages
gdb mangdb [OPTIONS] [prog|prog procID|prog core]
The purpose of a debugger such as gdb is to allow you to see what is going on “inside”
another program while it executes – or what another program was doing at the moment it
crashed.
gdb can do four main kinds of things (plus other things in support of these) to help you
catch bugs in the act:
• Start your program, specifying anything that might affect its behavior.
• Make your program stop on specified conditions.
• Examine what has happened, when your program has stopped.
• Change things in your program, so you can experiment with correcting the effects of
one bug and go on to learn about another.
You can use gdb to debug programs written in C, C++, Fortran and Modula-2.
gdb is invoked with the shell command gdb. Once started, it reads commands from theterminal until you tell it to exit with the gdb command quit or exit. You can get online
help from gdb itself by using the command help.
You can run gdb with no arguments or options; but the most usual way to start gdb iswith one argument or two, specifying an executable program as the argument:
gdb program

You can also start with both an executable program and a core file specified:
gdb program core

You can, instead, specify a process ID as a second argument or use option -p, if you
want to debug a running process:gdb program 1234
gdb -p 1234

would attach gdb to process 1234. With option -p you can omit the program filename.
Here are some of the most frequently needed gdb commands:
break [file:][function|line]
Set a breakpoint at function or line (in file).
run [arglist]
Start your program (with arglist, if specified).
bt

Backtrace: display the program stack.

print expr
Display the value of an expression.
cContinue running your program (after stopping, e.g. at a breakpoint).

next

Execute next program line (after stopping); step over any function calls in the
line.

890

Debugging with gdb

edit [file:]function
look at the program line where it is presently stopped.
list [file:]function
type the text of the program in the vicinity of where it is presently stopped.
step

Execute next program line (after stopping); step into any function calls in theline.

help [name]Show information about gdb command name, or general information about
using gdb.
quit
exit

Exit from gdb.

Any arguments other than options specify an executable file and core file (or processID); that is, the first argument encountered with no associated option flag is equivalent toa --se option, and the second, if any, is equivalent to a -c option if it’s the name of a file.
Many options have both long and abbreviated forms; both are shown here. The long forms
are also recognized if you truncate them, so long as enough of the option is present to beunambiguous.
The abbreviated forms are shown here with ‘-’ and long forms are shown with ‘--’to reflect how they are shown in --help. However, gdb recognizes all of the following
conventions for most options:--option=value--option value-option=value-option value--o=value--o value-o=value-o value
All the options and command line arguments you give are processed in sequential order.
The order makes a difference when the -x option is used.
--help-h

List all options, with brief explanations.

--symbols=file-s fileRead symbol table from file.
--writeEnable writing into executable and core files.

--exec=file-e fileUse file as the executable file to execute when appropriate, and for examining
pure data in conjunction with a core dump.
--se=file
Read symbol table from file and use it as the executable file.

Appendix L: Manual pages

891--core=file-c fileUse file as a core dump to examine.
--command=file-x fileExecute gdb commands from file.
--eval-command=command-ex command
Execute given gdb command.
--init-eval-command=command-iex
Execute gdb command before loading the inferior.
--directory=directory-d directory
Add directory to the path to search for source files.
--nh
--nx
-n

Do not execute commands from ~/.config/gdb/gdbinit, ~/.gdbinit,~/.config/gdb/gdbearlyinit, or ~/.gdbearlyinit
Do not execute commands from any .gdbinit or .gdbearlyinit initialization
files.

--quiet--silent-q--batch“Quiet”. Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.
Run in batch mode. Exit with status 0 after processing all the command files
specified with -x (and .gdbinit, if not inhibited). Exit with nonzero status if
an error occurs in executing the gdb commands in the command files.
Batch mode may be useful for running gdb as a filter, for example to download
and run a program on another computer; in order to make this more useful, themessage
Program exited normally.

(which is ordinarily issued whenever a program running under gdb control
terminates) is not issued when running in batch mode.
--batch-silent
Run in batch mode, just like --batch, but totally silent. All gdb output issuppressed (stderr is unaffected). This is much quieter than --silent andwould be useless for an interactive session.
This is particularly useful when using targets that give ‘Loading section’ messages, for example.
Note that targets that give their output via gdb, as opposed to writing directly
to stdout, will also be made silent.
--args prog [arglist]
Change interpretation of command line so that arguments following this option
are passed as arguments to the inferior. As an example, take the following
command:gdb ./a.out -q

892

Debugging with gdb

It would start gdb with -q, not printing the introductory message. On theother hand, using:gdb --args ./a.out -q

starts gdb with the introductory message, and passes the option to the inferior.
--pid=pidAttach gdb to an already running program, with the PID pid.
--tui

Open the terminal user interface.

--readnow
Read all symbols from the given symfile on the first access.
--readneverDo not read symbol files.
--return-child-result
gdb’s exit code will be the same as the child’s exit code.
--configuration
Print details about GDB configuration and then exit.
--version
Print version information and then exit.
--cd=directory
Run gdb using directory as its working directory, instead of the current directory.
--data-directory=directory-D
Run gdb using directory as its data directory. The data directory is where gdb
searches for its auxiliary files.
--fullname-fEmacs sets this option when it runs gdb as a subprocess. It tells gdb to output
the full file name and line number in a standard, recognizable fashion each timea stack frame is displayed (which includes each time the program stops). This
recognizable format looks like two ‘\032’ characters, followed by the file name,line number and character position separated by colons, and a newline. The
Emacs-to-gdb interface program uses the two ‘\032’ characters as a signal todisplay the source code for the frame.
-b baudrate
Set the line speed (baud rate or bits per second) of any serial interface used by
gdb for remote debugging.
-l timeout
Set timeout, in seconds, for remote debugging.
--tty=device
Run using device for your program’s standard input and output.

Appendix L: Manual pages893

gdbserver man
gdbserver comm prog [args . . . ]gdbserver –attach comm pid
gdbserver –multi commgdbserver is a program that allows you to run gdb on a different machine than the one
which is running the program being debugged.

Usage (server (target) side)
First, you need to have a copy of the program you want to debug put onto the target
system. The program can be stripped to save space if needed, as gdbserver doesn’t careabout symbols. All symbol handling is taken care of by the gdb running on the host system.
To use the server, you log on to the target system, and run the gdbserver program.
You must tell it (a) how to communicate with gdb, (b) the name of your program, and (c)its arguments. The general syntax is:target> gdbserver comm program [args ...]For example, using a serial port, you might say:target> gdbserver /dev/com1 emacs foo.txt

This tells gdbserver to debug emacs with an argument of foo.txt, and to communicate
with gdb via /dev/com1. gdbserver now waits patiently for the host gdb to communicate
with it.
To use a TCP connection, you could say:target> gdbserver host:2345 emacs foo.txt

This says pretty much the same thing as the last example, except that we are going tocommunicate with the host gdb via TCP. The host:2345 argument means that we are
expecting to see a TCP connection from host to local TCP port 2345. (Currently, the hostpart is ignored.) You can choose any number you want for the port number as long as it
does not conflict with any existing TCP ports on the target system. This same port number
must be used in the host gdbs target remote command, which will be described shortly.
Note that if you chose a port number that conflicts with another service, gdbserver will
print an error message and exit.
gdbserver can also attach to running programs. This is accomplished via the --attachargument. The syntax is:target> gdbserver --attach comm pid

pid is the process ID of a currently running process. It isn’t necessary to point gdbserver
at a binary for the running process.
To start gdbserver without supplying an initial command to run or process ID to
attach, use the --multi command line option. In such case you should connect using
target extended-remote to start the program you want to debug.
target> gdbserver --multi comm

894

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Usage (host side)
You need an unstripped copy of the target program on your host system, since gdb needs
to examine its symbol tables and such. Start up gdb as you normally would, with thetarget program as the first argument. (You may need to use the --baud option if the serialline is running at anything except 9600 baud.) That is gdb TARGET-PROG, or gdb --baud
BAUD TARGET-PROG. After that, the only new command you need to know about is target
remote (or target extended-remote). Its argument is either a device name (usually a
serial device, like /dev/ttyb), or a HOST:PORT descriptor. For example:(gdb) target remote /dev/ttyb

communicates with the server via serial line /dev/ttyb, and:(gdb) target remote the-target:2345

communicates via a TCP connection to port 2345 on host ‘the-target’, where you previously
started up gdbserver with the same port number. Note that for TCP connections, youmust start up gdbserver prior to using the ‘target remote’ command, otherwise you may
get an error that looks something like ‘Connection refused’.
gdbserver can also debug multiple inferiors at once, described in Section 4.9 [Inferiors
Connections and Programs], page 42. In such case use the extended-remote gdb commandvariant:(gdb) target extended-remote the-target:2345

The gdbserver option --multi may or may not be used in such case.
There are three different modes for invoking gdbserver:• Debug a specific program specified by its program name:gdbserver comm prog [args...]

The comm parameter specifies how should the server communicate with gdb; it iseither a device name (to use a serial line), a TCP port number (:1234), or - or stdio
to use stdin/stdout of gdbserver. Specify the name of the program to debug in prog.
Any remaining arguments will be passed to the program verbatim. When the program
exits, gdb will close the connection, and gdbserver will exit.
• Debug a specific program by specifying the process ID of a running program:
gdbserver --attach comm pid

The comm parameter is as described above. Supply the process ID of a running programin pid; gdb will do everything else. Like with the previous mode, when the process pid
exits, gdb will close the connection, and gdbserver will exit.
• Multi-process mode – debug more than one program/process:gdbserver --multi commIn this mode, gdb can instruct gdbserver which command(s) to run. Unlike the other2 modes, gdb will not close the connection when a process being debugged exits, so
you can debug several processes in the same session.
In each of the modes you may specify these options:--helpList all options, with brief explanations.

--version
This option causes gdbserver to print its version number and exit.

Appendix L: Manual pages--attach895

gdbserver will attach to a running program. The syntax is:target> gdbserver --attach comm pid

pid is the process ID of a currently running process. It isn’t necessary to point
gdbserver at a binary for the running process.
--multi

To start gdbserver without supplying an initial command to run or process ID
to attach, use this command line option. Then you can connect using target
extended-remote and start the program you want to debug. The syntax is:target> gdbserver --multi comm--debug[=option1,option2,...]
Instruct gdbserver to display extra status information about the debugging
process. This option is intended for gdbserver development and for bug reports
to the developers.
Each option is the name of a component for which debugging should be enabled.
The list of possible options is all, threads, event-loop, remote. The special
option all enables all components. The option list is processed left to right,
and an option can be prefixed with the - character to disable output for thatcomponent, so you could write:target> gdbserver --debug=all,-event-loop

to turn on debug output for all components except event-loop. If no options
are passed to --debug then this is treated as equivalent to --debug=threads.
This could change in future releases of gdbserver.
--debug-file=filename
Instruct gdbserver to send any debug output to the given filename. This option
is intended for gdbserver development and for bug reports to the developers.
--debug-format=option1[,option2,...]
Instruct gdbserver to include extra information in each line of debugging output. See [Other Command-Line Arguments for gdbserver], page 322.
--wrapper
Specify a wrapper to launch programs for debugging. The option should be
followed by the name of the wrapper, then any command-line arguments topass to the wrapper, then -- indicating the end of the wrapper arguments.
--onceBy default, gdbserver keeps the listening TCP port open, so that additional
connections are possible. However, if you start gdbserver with the --once
option, it will stop listening for any further connection attempts after connecting
to the first gdb session.

gcore
gcore [-a] [-o prefix] [-d directory] pid1 [pid2...pidN ]Generate core dumps of one or more running programs with process IDs pid1, pid2, etc.
A core file produced by gcore is equivalent to one produced by the kernel when the processcrashes (and when ulimit -c was used to set up an appropriate core dump limit). However,896

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unlike after a crash, after gcore finishes its job the program remains running without any
change.
Dump all memory mappings. The actual effect of this option depends on the
Operating System. On gnu/Linux, it will disable use-coredump-filter (see[set use-coredump-filter], page 186) and enable dump-excluded-mappings (see[set dump-excluded-mappings], page 187).

-a-o prefix The optional argument prefix specifies the prefix to be used when composing
the file names of the core dumps. The file name is composed as prefix.pid,
where pid is the process ID of the running program being analyzed by gcore.
If not specified, prefix defaults to gcore.
-d directory
Use directory as the data directory when invoking gdb for running the gcorecommand. This argument is optional.

gdbinit~/.config/gdb/gdbinit~/.gdbinit./.gdbinit
These files contain gdb commands to automatically execute during gdb startup. Thelines of contents are canned sequences of commands, described in Section 23.1 [Sequences],
page 391.
Please read more in Section 2.1.3 [Startup], page 16.
(not enabled with --with-system-gdbinit during compilation)
System-wide initialization file. It is executed unless user specified gdb option-nx or -n. See more in(not enabled with --with-system-gdbinit-dir during compilation)
System-wide initialization directory. All files in this directory are executed onstartup unless user specified gdb option -nx or -n, as long as they have arecognized file extension. See more in Section C.6 [System-wide configuration],
page 753.
~/.config/gdb/gdbinit or ~/.gdbinit
User initialization file. It is executed unless user specified gdb options -nx, -n
or -nh.
.gdbinit

Initialization file for current directory. It may need to be enabled with gdb
security command set auto-load local-gdbinit. See more in Section 22.8.1[Init File in the Current Directory], page 378.

Appendix L: Manual pages897

gdb-add-index
gdb-add-index filename
When gdb finds a symbol file, it scans the symbols in the file in order to construct aninternal symbol table. This lets most gdb operations work quickly–at the cost of a delay
early on. For large programs, this delay can be quite lengthy, so gdb provides a way tobuild an index, which speeds up startup.
To determine whether a file contains such an index, use the command readelf -S
filename: the index is stored in a section named .gdb_index. The index file can only
be produced on systems which use ELF binaries and DWARF debug information (i.e.,
sections named .debug_*).
gdb-add-index uses gdb and objdump found in the PATH environment variable. If you
want to use different versions of these programs, you can specify them through the GDB and
OBJDUMP environment variables.
See more in Section 18.5 [Index Files], page 305.

899

Appendix M GNU GENERAL PUBLIC
LICENSE
Version 3, 29 June 2007
Copyright c 2007 Free Software Foundation, Inc. http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies of thislicense document, but changing it is not allowed.

Preamble
The GNU General Public License is a free, copyleft license for software and other kinds ofworks.
The licenses for most software and other practical works are designed to take away yourfreedom to share and change the works. By contrast, the GNU General Public License isintended to guarantee your freedom to share and change all versions of a program—to makesure it remains free software for all its users. We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to any other work
released this way by its authors. You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General
Public Licenses are designed to make sure that you have the freedom to distribute copies
of free software (and charge for them if you wish), that you receive source code or can get
it if you want it, that you can change the software or use pieces of it in new free programs,
and that you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or asking
you to surrender the rights. Therefore, you have certain responsibilities if you distributecopies of the software, or if you modify it: responsibilities to respect the freedom of others.
For example, if you distribute copies of such a program, whether gratis or for a fee, youmust pass on to the recipients the same freedoms that you received. You must make surethat they, too, receive or can get the source code. And you must show them these terms sothey know their rights.
Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy,
distribute and/or modify it.
For the developers’ and authors’ protection, the GPL clearly explains that there is no
warranty for this free software. For both users’ and authors’ sake, the GPL requires thatmodified versions be marked as changed, so that their problems will not be attributed
erroneously to authors of previous versions.
Some devices are designed to deny users access to install or run modified versions of thesoftware inside them, although the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users’ freedom to change the software. The systematic
pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL
to prohibit the practice for those products. If such problems arise substantially in otherdomains, we stand ready to extend this provision to those domains in future versions of theGPL, as needed to protect the freedom of users.

900

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Finally, every program is threatened constantly by software patents. States should notallow patents to restrict development and use of software on general-purpose computers, but
in those that do, we wish to avoid the special danger that patents applied to a free program
could make it effectively proprietary. To prevent this, the GPL assures that patents cannot
be used to render the program non-free.
The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS
0. Definitions.
“This License” refers to version 3 of the GNU General Public License.
“Copyright” also means copyright-like laws that apply to other kinds of works, such as
semiconductor masks.
“The Program” refers to any copyrightable work licensed under this License. Eachlicensee is addressed as “you”. “Licensees” and “recipients” may be individuals ororganizations.
To “modify” a work means to copy from or adapt all or part of the work in a fashionrequiring copyright permission, other than the making of an exact copy. The resulting
work is called a “modified version” of the earlier work or a work “based on” the earlier
work.
A “covered work” means either the unmodified Program or a work based on the Program.
To “propagate” a work means to do anything with it that, without permission, would
make you directly or secondarily liable for infringement under applicable copyright law,
except executing it on a computer or modifying a private copy. Propagation includes
copying, distribution (with or without modification), making available to the public,
and in some countries other activities as well.
To “convey” a work means any kind of propagation that enables other parties to makeor receive copies. Mere interaction with a user through a computer network, with notransfer of a copy, is not conveying.
An interactive user interface displays “Appropriate Legal Notices” to the extent that it
includes a convenient and prominently visible feature that (1) displays an appropriate
copyright notice, and (2) tells the user that there is no warranty for the work (except
to the extent that warranties are provided), that licensees may convey the work under
this License, and how to view a copy of this License. If the interface presents a listof user commands or options, such as a menu, a prominent item in the list meets thiscriterion.
1. Source Code.
The “source code” for a work means the preferred form of the work for making modifications to it. “Object code” means any non-source form of a work.
A “Standard Interface” means an interface that either is an official standard definedby a recognized standards body, or, in the case of interfaces specified for a particular
programming language, one that is widely used among developers working in that
language.

Appendix M: GNU GENERAL PUBLIC LICENSE

901

The “System Libraries” of an executable work include anything, other than the work as
a whole, that (a) is included in the normal form of packaging a Major Component, butwhich is not part of that Major Component, and (b) serves only to enable use of thework with that Major Component, or to implement a Standard Interface for which an
implementation is available to the public in source code form. A “Major Component”,
in this context, means a major essential component (kernel, window system, and soon) of the specific operating system (if any) on which the executable work runs, or acompiler used to produce the work, or an object code interpreter used to run it.
The “Corresponding Source” for a work in object code form means all the source codeneeded to generate, install, and (for an executable work) run the object code and to
modify the work, including scripts to control those activities. However, it does notinclude the work’s System Libraries, or general-purpose tools or generally available
free programs which are used unmodified in performing those activities but which are
not part of the work. For example, Corresponding Source includes interface definition
files associated with source files for the work, and the source code for shared libraries
and dynamically linked subprograms that the work is specifically designed to require,
such as by intimate data communication or control flow between those subprograms
and other parts of the work.
The Corresponding Source need not include anything that users can regenerate automatically from other parts of the Corresponding Source.
The Corresponding Source for a work in source code form is that same work.
2. Basic Permissions.
All rights granted under this License are granted for the term of copyright on the
Program, and are irrevocable provided the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program. The output
from running a covered work is covered by this License only if the output, given its
content, constitutes a covered work. This License acknowledges your rights of fair use
or other equivalent, as provided by copyright law.
You may make, run and propagate covered works that you do not convey, without
conditions so long as your license otherwise remains in force. You may convey covered
works to others for the sole purpose of having them make modifications exclusively
for you, or provide you with facilities for running those works, provided that youcomply with the terms of this License in conveying all material for which you do notcontrol copyright. Those thus making or running the covered works for you must do
so exclusively on your behalf, under your direction and control, on terms that prohibit
them from making any copies of your copyrighted material outside their relationshipwith you.
Conveying under any other circumstances is permitted solely under the conditions
stated below. Sublicensing is not allowed; section 10 makes it unnecessary.
3. Protecting Users’ Legal Rights From Anti-Circumvention Law.
No covered work shall be deemed part of an effective technological measure under
any applicable law fulfilling obligations under article 11 of the WIPO copyright treaty
adopted on 20 December 1996, or similar laws prohibiting or restricting circumventionof such measures.

902

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When you convey a covered work, you waive any legal power to forbid circumvention oftechnological measures to the extent such circumvention is effected by exercising rights
under this License with respect to the covered work, and you disclaim any intention
to limit operation or modification of the work as a means of enforcing, against thework’s users, your or third parties’ legal rights to forbid circumvention of technologicalmeasures.
4. Conveying Verbatim Copies.
You may convey verbatim copies of the Program’s source code as you receive it, in any
medium, provided that you conspicuously and appropriately publish on each copy anappropriate copyright notice; keep intact all notices stating that this License and any
non-permissive terms added in accord with section 7 apply to the code; keep intact all
notices of the absence of any warranty; and give all recipients a copy of this Licensealong with the Program.
You may charge any price or no price for each copy that you convey, and you may offer
support or warranty protection for a fee.
5. Conveying Modified Source Versions.
You may convey a work based on the Program, or the modifications to produce it fromthe Program, in the form of source code under the terms of section 4, provided thatyou also meet all of these conditions:a. The work must carry prominent notices stating that you modified it, and giving a
relevant date.
b. The work must carry prominent notices stating that it is released under this License and any conditions added under section 7. This requirement modifies therequirement in section 4 to “keep intact all notices”.
c. You must license the entire work, as a whole, under this License to anyone whocomes into possession of a copy. This License will therefore apply, along with any
applicable section 7 additional terms, to the whole of the work, and all its parts,
regardless of how they are packaged. This License gives no permission to license
the work in any other way, but it does not invalidate such permission if you haveseparately received it.
d. If the work has interactive user interfaces, each must display Appropriate Legal
Notices; however, if the Program has interactive interfaces that do not display
Appropriate Legal Notices, your work need not make them do so.
A compilation of a covered work with other separate and independent works, which
are not by their nature extensions of the covered work, and which are not combinedwith it such as to form a larger program, in or on a volume of a storage or distribution
medium, is called an “aggregate” if the compilation and its resulting copyright are
not used to limit the access or legal rights of the compilation’s users beyond what theindividual works permit. Inclusion of a covered work in an aggregate does not cause
this License to apply to the other parts of the aggregate.
6. Conveying Non-Source Forms.
You may convey a covered work in object code form under the terms of sections 4 and5, provided that you also convey the machine-readable Corresponding Source under
the terms of this License, in one of these ways:

Appendix M: GNU GENERAL PUBLIC LICENSE

903

a. Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by the Corresponding Source fixed on adurable physical medium customarily used for software interchange.
b. Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by a written offer, valid for at least three
years and valid for as long as you offer spare parts or customer support for that
product model, to give anyone who possesses the object code either (1) a copy of
the Corresponding Source for all the software in the product that is covered by thisLicense, on a durable physical medium customarily used for software interchange,
for a price no more than your reasonable cost of physically performing this conveying of source, or (2) access to copy the Corresponding Source from a network
server at no charge.
c. Convey individual copies of the object code with a copy of the written offer toprovide the Corresponding Source. This alternative is allowed only occasionallyand noncommercially, and only if you received the object code with such an offer,in accord with subsection 6b.
d. Convey the object code by offering access from a designated place (gratis or fora charge), and offer equivalent access to the Corresponding Source in the same
way through the same place at no further charge. You need not require recipients
to copy the Corresponding Source along with the object code. If the place tocopy the object code is a network server, the Corresponding Source may be ona different server (operated by you or a third party) that supports equivalentcopying facilities, provided you maintain clear directions next to the object code
saying where to find the Corresponding Source. Regardless of what server hosts
the Corresponding Source, you remain obligated to ensure that it is available foras long as needed to satisfy these requirements.
e. Convey the object code using peer-to-peer transmission, provided you inform otherpeers where the object code and Corresponding Source of the work are being offeredto the general public at no charge under subsection 6d.
A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object
code work.
A “User Product” is either (1) a “consumer product”, which means any tangible personal property which is normally used for personal, family, or household purposes, or(2) anything designed or sold for incorporation into a dwelling. In determining whether
a product is a consumer product, doubtful cases shall be resolved in favor of coverage.
For a particular product received by a particular user, “normally used” refers to atypical or common use of that class of product, regardless of the status of the particular user or of the way in which the particular user actually uses, or expects or is
expected to use, the product. A product is a consumer product regardless of whether
the product has substantial commercial, industrial or non-consumer uses, unless suchuses represent the only significant mode of use of the product.
“Installation Information” for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of acovered work in that User Product from a modified version of its Corresponding Source.

904

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The information must suffice to ensure that the continued functioning of the modified
object code is in no case prevented or interfered with solely because modification has
been made.
If you convey an object code work under this section in, or with, or specifically foruse in, a User Product, and the conveying occurs as part of a transaction in which
the right of possession and use of the User Product is transferred to the recipient inperpetuity or for a fixed term (regardless of how the transaction is characterized),
the Corresponding Source conveyed under this section must be accompanied by the
Installation Information. But this requirement does not apply if neither you nor any
third party retains the ability to install modified object code on the User Product (forexample, the work has been installed in ROM).
The requirement to provide Installation Information does not include a requirement
to continue to provide support service, warranty, or updates for a work that has been
modified or installed by the recipient, or for the User Product in which it has been
modified or installed. Access to a network may be denied when the modification itself
materially and adversely affects the operation of the network or violates the rules andprotocols for communication across the network.
Corresponding Source conveyed, and Installation Information provided, in accord withthis section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password
or key for unpacking, reading or copying.
7. Additional Terms.
“Additional permissions” are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are
applicable to the entire Program shall be treated as though they were included in thisLicense, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under thosepermissions, but the entire Program remains governed by this License without regard
to the additional permissions.
When you convey a copy of a covered work, you may at your option remove any
additional permissions from that copy, or from any part of it. (Additional permissions
may be written to require their own removal in certain cases when you modify thework.) You may place additional permissions on material, added by you to a covered
work, for which you have or can give appropriate copyright permission.
Notwithstanding any other provision of this License, for material you add to a covered
work, you may (if authorized by the copyright holders of that material) supplement
the terms of this License with terms:
a. Disclaiming warranty or limiting liability differently from the terms of sections 15
and 16 of this License; orb. Requiring preservation of specified reasonable legal notices or author attributionsin that material or in the Appropriate Legal Notices displayed by works containing
it; orc. Prohibiting misrepresentation of the origin of that material, or requiring that modified versions of such material be marked in reasonable ways as different from theoriginal version; orAppendix M: GNU GENERAL PUBLIC LICENSE

905

d. Limiting the use for publicity purposes of names of licensors or authors of thematerial; ore. Declining to grant rights under trademark law for use of some trade names, trademarks, or service marks; or
f. Requiring indemnification of licensors and authors of that material by anyone who
conveys the material (or modified versions of it) with contractual assumptionsof liability to the recipient, for any liability that these contractual assumptions
directly impose on those licensors and authors.
All other non-permissive additional terms are considered “further restrictions” within
the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is afurther restriction, you may remove that term. If a license document contains a further
restriction but permits relicensing or conveying under this License, you may add to acovered work material governed by the terms of that license document, provided thatthe further restriction does not survive such relicensing or conveying.
If you add terms to a covered work in accord with this section, you must place, in therelevant source files, a statement of the additional terms that apply to those files, or a
notice indicating where to find the applicable terms.
Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply eitherway.
8. Termination.
You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and willautomatically terminate your rights under this License (including any patent licenses
granted under the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular
copyright holder is reinstated (a) provisionally, unless and until the copyright holder
explicitly and finally terminates your license, and (b) permanently, if the copyrightholder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if
the copyright holder notifies you of the violation by some reasonable means, this is thefirst time you have received notice of violation of this License (for any work) from thatcopyright holder, and you cure the violation prior to 30 days after your receipt of thenotice.
Termination of your rights under this section does not terminate the licenses of parties
who have received copies or rights from you under this License. If your rights havebeen terminated and not permanently reinstated, you do not qualify to receive newlicenses for the same material under section 10.
9. Acceptance Not Required for Having Copies.
You are not required to accept this License in order to receive or run a copy of theProgram. Ancillary propagation of a covered work occurring solely as a consequence ofusing peer-to-peer transmission to receive a copy likewise does not require acceptance.

906

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However, nothing other than this License grants you permission to propagate or modify
any covered work. These actions infringe copyright if you do not accept this License.
Therefore, by modifying or propagating a covered work, you indicate your acceptanceof this License to do so.
10. Automatic Licensing of Downstream Recipients.
Each time you convey a covered work, the recipient automatically receives a licensefrom the original licensors, to run, modify and propagate that work, subject to thisLicense. You are not responsible for enforcing compliance by third parties with thisLicense.
An “entity transaction” is a transaction transferring control of an organization, or
substantially all assets of one, or subdividing an organization, or merging organizations.
If propagation of a covered work results from an entity transaction, each party to thattransaction who receives a copy of the work also receives whatever licenses to the work
the party’s predecessor in interest had or could give under the previous paragraph, plus
a right to possession of the Corresponding Source of the work from the predecessor ininterest, if the predecessor has it or can get it with reasonable efforts.
You may not impose any further restrictions on the exercise of the rights granted oraffirmed under this License. For example, you may not impose a license fee, royalty, orother charge for exercise of rights granted under this License, and you may not initiate
litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patentclaim is infringed by making, using, selling, offering for sale, or importing the Programor any portion of it.
11. Patents.
A “contributor” is a copyright holder who authorizes use under this License of theProgram or a work on which the Program is based. The work thus licensed is called
the contributor’s “contributor version”.
A contributor’s “essential patent claims” are all patent claims owned or controlled by
the contributor, whether already acquired or hereafter acquired, that would be infringed
by some manner, permitted by this License, of making, using, or selling its contributor
version, but do not include claims that would be infringed only as a consequence offurther modification of the contributor version. For purposes of this definition, “control” includes the right to grant patent sublicenses in a manner consistent with therequirements of this License.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent licenseunder the contributor’s essential patent claims, to make, use, sell, offer for sale, importand otherwise run, modify and propagate the contents of its contributor version.
In the following three paragraphs, a “patent license” is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission
to practice a patent or covenant not to sue for patent infringement). To “grant” sucha patent license to a party means to make such an agreement or commitment not toenforce a patent against the party.
If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under
the terms of this License, through a publicly available network server or other readily
accessible means, then you must either (1) cause the Corresponding Source to be soAppendix M: GNU GENERAL PUBLIC LICENSE

907

available, or (2) arrange to deprive yourself of the benefit of the patent license for thisparticular work, or (3) arrange, in a manner consistent with the requirements of thisLicense, to extend the patent license to downstream recipients. “Knowingly relying”
means you have actual knowledge that, but for the patent license, your conveying thecovered work in a country, or your recipient’s use of the covered work in a country,
would infringe one or more identifiable patents in that country that you have reason
to believe are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey,
or propagate by procuring conveyance of, a covered work, and grant a patent license
to some of the parties receiving the covered work authorizing them to use, propagate,
modify or convey a specific copy of the covered work, then the patent license you grantis automatically extended to all recipients of the covered work and works based on it.
A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of therights that are specifically granted under this License. You may not convey a covered
work if you are a party to an arrangement with a third party that is in the business of
distributing software, under which you make payment to the third party based on theextent of your activity of conveying the work, and under which the third party grants,
to any of the parties who would receive the covered work from you, a discriminatory
patent license (a) in connection with copies of the covered work conveyed by you (orcopies made from those copies), or (b) primarily for and in connection with specificproducts or compilations that contain the covered work, unless you entered into that
arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license orother defenses to infringement that may otherwise be available to you under applicablepatent law.
12. No Surrender of Others’ Freedom.
If conditions are imposed on you (whether by court order, agreement or otherwise) that
contradict the conditions of this License, they do not excuse you from the conditionsof this License. If you cannot convey a covered work so as to satisfy simultaneously
your obligations under this License and any other pertinent obligations, then as aconsequence you may not convey it at all. For example, if you agree to terms thatobligate you to collect a royalty for further conveying from those to whom you convey
the Program, the only way you could satisfy both those terms and this License would
be to refrain entirely from conveying the Program.
13. Use with the GNU Affero General Public License.
Notwithstanding any other provision of this License, you have permission to link or
combine any covered work with a work licensed under version 3 of the GNU Affero
General Public License into a single combined work, and to convey the resulting work.
The terms of this License will continue to apply to the part which is the covered work,
but the special requirements of the GNU Affero General Public License, section 13,
concerning interaction through a network will apply to the combination as such.
14. Revised Versions of this License.

908

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The Free Software Foundation may publish revised and/or new versions of the GNU
General Public License from time to time. Such new versions will be similar in spirit
to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies thata certain numbered version of the GNU General Public License “or any later version”
applies to it, you have the option of following the terms and conditions either of that
numbered version or of any later version published by the Free Software Foundation.
If the Program does not specify a version number of the GNU General Public License,
you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU
General Public License can be used, that proxy’s public statement of acceptance of aversion permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no
additional obligations are imposed on any author or copyright holder as a result of yourchoosing to follow a later version.
15. Disclaimer of Warranty.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN
WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDETHE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIEDWARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCEOF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.
16. Limitation of Liability.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO INWRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO
MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE
LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO
LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM
TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OROTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
17. Interpretation of Sections 15 and 16.
If the disclaimer of warranty and limitation of liability provided above cannot be given
local legal effect according to their terms, reviewing courts shall apply local law thatmost closely approximates an absolute waiver of all civil liability in connection with
the Program, unless a warranty or assumption of liability accompanies a copy of theProgram in return for a fee.

Appendix M: GNU GENERAL PUBLIC LICENSE

909

END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest possible use to the public,
the best way to achieve this is to make it free software which everyone can redistribute andchange under these terms.
To do so, attach the following notices to the program. It is safest to attach them to thestart of each source file to most effectively state the exclusion of warranty; and each fileshould have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program’s name and a brief idea of what it does.
Copyright (C) year name of author
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (atyour option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public Licensealong with this program. If not, see http://www.gnu.org/licenses/.

Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it
starts in an interactive mode:
program Copyright (C) year name of author
This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’.
This is free software, and you are welcome to redistribute it
under certain conditions; type ‘show c’ for details.

The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of
the General Public License. Of course, your program’s commands might be different; for a
GUI interface, you would use an “about box”.
You should also get your employer (if you work as a programmer) or school, if any, tosign a “copyright disclaimer” for the program, if necessary. For more information on this,and how to apply and follow the GNU GPL, see http://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into
proprietary programs. If your program is a subroutine library, you may consider it more
useful to permit linking proprietary applications with the library. If this is what you want
to do, use the GNU Lesser General Public License instead of this License. But first, please
read http://www.gnu.org/philosophy/why-not-lgpl.html.

911

Appendix N GNU Free Documentation License
Version 1.3, 3 November 2008c
Copyright
2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/
Everyone is permitted to copy and distribute verbatim copiesof this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other functional anduseful document free in the sense of freedom: to assure everyone the effective freedom
to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible for modifications
made by others.
This License is a kind of “copyleft”, which means that derivative works of the document
must themselves be free in the same sense. It complements the GNU General Public
License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because
free software needs free documentation: a free program should come with manuals
providing the same freedoms that the software does. But this License is not limited tosoftware manuals; it can be used for any textual work, regardless of subject matter orwhether it is published as a printed book. We recommend this License principally forworks whose purpose is instruction or reference.
1. APPLICABILITY AND DEFINITIONSThis License applies to any manual or other work, in any medium, that contains a
notice placed by the copyright holder saying it can be distributed under the termsof this License. Such a notice grants a world-wide, royalty-free license, unlimited in
duration, to use that work under the conditions stated herein. The “Document”,
below, refers to any such manual or work. Any member of the public is a licensee, andis addressed as “you”. You accept the license if you copy, modify or distribute the workin a way requiring permission under copyright law.
A “Modified Version” of the Document means any work containing the Document or
a portion of it, either copied verbatim, or with modifications and/or translated intoanother language.
A “Secondary Section” is a named appendix or a front-matter section of the Documentthat deals exclusively with the relationship of the publishers or authors of the Document
to the Document’s overall subject (or to related matters) and contains nothing that
could fall directly within that overall subject. (Thus, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any mathematics.) The
relationship could be a matter of historical connection with the subject or with related
matters, or of legal, commercial, philosophical, ethical or political position regardingthem.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as
being those of Invariant Sections, in the notice that says that the Document is released

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under this License. If a section does not fit the above definition of Secondary then it is
not allowed to be designated as Invariant. The Document may contain zero Invariant
Sections. If the Document does not identify any Invariant Sections then there are none.
The “Cover Texts” are certain short passages of text that are listed, as Front-CoverTexts or Back-Cover Texts, in the notice that says that the Document is released under
this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A “Transparent” copy of the Document means a machine-readable copy, represented
in a format whose specification is available to the general public, that is suitable forrevising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing
editor, and that is suitable for input to text formatters or for automatic translation toa variety of formats suitable for input to text formatters. A copy made in an otherwise
Transparent file format whose markup, or absence of markup, has been arranged tothwart or discourage subsequent modification by readers is not Transparent. An image
format is not Transparent if used for any substantial amount of text. A copy that is
not “Transparent” is called “Opaque”.
Examples of suitable formats for Transparent copies include plain ascii without
markup, Texinfo input format, LaTEX input format, SGML or XML using a publicly
available DTD, and standard-conforming simple HTML, PostScript or PDF designed
for human modification. Examples of transparent image formats include PNG, XCF
and JPG. Opaque formats include proprietary formats that can be read and edited
only by proprietary word processors, SGML or XML for which the DTD and/or
processing tools are not generally available, and the machine-generated HTML,PostScript or PDF produced by some word processors for output purposes only.
The “Title Page” means, for a printed book, the title page itself, plus such following
pages as are needed to hold, legibly, the material this License requires to appear in thetitle page. For works in formats which do not have any title page as such, “Title Page”
means the text near the most prominent appearance of the work’s title, preceding the
beginning of the body of the text.
The “publisher” means any person or entity that distributes copies of the Document
to the public.
A section “Entitled XYZ” means a named subunit of the Document whose title either
is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in
another language. (Here XYZ stands for a specific section name mentioned below, suchas “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve
the Title” of such a section when you modify the Document means that it remains asection “Entitled XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that
this License applies to the Document. These Warranty Disclaimers are considered to
be included by reference in this License, but only as regards disclaiming warranties:
any other implication that these Warranty Disclaimers may have is void and has noeffect on the meaning of this License.
2. VERBATIM COPYING

Appendix N: GNU Free Documentation License

913

You may copy and distribute the Document in any medium, either commercially or
noncommercially, provided that this License, the copyright notices, and the license
notice saying this License applies to the Document are reproduced in all copies, andthat you add no other conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further copying of the copies
you make or distribute. However, you may accept compensation in exchange for copies.
If you distribute a large enough number of copies you must also follow the conditions
in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly
display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of
the Document, numbering more than 100, and the Document’s license notice requires
Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, allthese Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify you as the publisherof these copies. The front cover must present the full title with all words of the title
equally prominent and visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve the title of theDocument and satisfy these conditions, can be treated as verbatim copying in otherrespects.
If the required texts for either cover are too voluminous to fit legibly, you should put
the first ones listed (as many as fit reasonably) on the actual cover, and continue therest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100,
you must either include a machine-readable Transparent copy along with each Opaquecopy, or state in or with each Opaque copy a computer-network location from which
the general network-using public has access to download using public-standard network
protocols a complete Transparent copy of the Document, free of added material. If
you use the latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent copy willremain thus accessible at the stated location until at least one year after the last time
you distribute an Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the Document wellbefore redistributing any large number of copies, to give them a chance to provide youwith an updated version of the Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditionsof sections 2 and 3 above, provided that you release the Modified Version under precisely
this License, with the Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever possesses a copy of
it. In addition, you must do these things in the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title distinct from that of theDocument, and from those of previous versions (which should, if there were any,

914

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be listed in the History section of the Document). You may use the same title asa previous version if the original publisher of that version gives permission.
B. List on the Title Page, as authors, one or more persons or entities responsible forauthorship of the modifications in the Modified Version, together with at least fiveof the principal authors of the Document (all of its principal authors, if it has fewer
than five), unless they release you from this requirement.
C. State on the Title page the name of the publisher of the Modified Version, as the
publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to the othercopyright notices.
F. Include, immediately after the copyright notices, a license notice giving the public
permission to use the Modified Version under the terms of this License, in the formshown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections and required CoverTexts given in the Document’s license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled “History”, Preserve its Title, and add to it an item
stating at least the title, year, new authors, and publisher of the Modified Version
as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document
as given on its Title Page, then add an item describing the Modified Version as
stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for public access toa Transparent copy of the Document, and likewise the network locations given in
the Document for previous versions it was based on. These may be placed in the“History” section. You may omit a network location for a work that was publishedat least four years before the Document itself, or if the original publisher of theversion it refers to gives permission.
K. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Titleof the section, and preserve in the section all the substance and tone of each of thecontributor acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered in their text andin their titles. Section numbers or the equivalent are not considered part of thesection titles.
M. Delete any section Entitled “Endorsements”. Such a section may not be includedin the Modified Version.
N. Do not retitle any existing section to be Entitled “Endorsements” or to conflict intitle with any Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify
as Secondary Sections and contain no material copied from the Document, you may atyour option designate some or all of these sections as invariant. To do this, add theirAppendix N: GNU Free Documentation License

915

titles to the list of Invariant Sections in the Modified Version’s license notice. These
titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but
endorsements of your Modified Version by various parties—for example, statements ofpeer review or that the text has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up
to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified
Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be
added by (or through arrangements made by) any one entity. If the Document alreadyincludes a cover text for the same cover, previously added by you or by arrangement
made by the same entity you are acting on behalf of, you may not add another; but
you may replace the old one, on explicit permission from the previous publisher that
added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission
to use their names for publicity for or to assert or imply endorsement of any Modified
Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License,
under the terms defined in section 4 above for modified versions, provided that you
include in the combination all of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your combined work in its license
notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identicalInvariant Sections may be replaced with a single copy. If there are multiple Invariant
Sections with the same name but different contents, make the title of each such section
unique by adding at the end of it, in parentheses, the name of the original author or
publisher of that section if known, or else a unique number. Make the same adjustment
to the section titles in the list of Invariant Sections in the license notice of the combinedwork.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any
sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You
must delete all sections Entitled “Endorsements.”
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released
under this License, and replace the individual copies of this License in the various
documents with a single copy that is included in the collection, provided that you
follow the rules of this License for verbatim copying of each of the documents in allother respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted
document, and follow this License in all other respects regarding verbatim copying ofthat document.

916

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7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent
documents or works, in or on a volume of a storage or distribution medium, is called
an “aggregate” if the copyright resulting from the compilation is not used to limit thelegal rights of the compilation’s users beyond what the individual works permit. When
the Document is included in an aggregate, this License does not apply to the otherworks in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document,
then if the Document is less than one half of the entire aggregate, the Document’s CoverTexts may be placed on covers that bracket the Document within the aggregate, or theelectronic equivalent of covers if the Document is in electronic form. Otherwise theymust appear on printed covers that bracket the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may distribute translationsof the Document under the terms of section 4. Replacing Invariant Sections withtranslations requires special permission from their copyright holders, but you may
include translations of some or all Invariant Sections in addition to the original versionsof these Invariant Sections. You may include a translation of this License, and all thelicense notices in the Document, and any Warranty Disclaimers, provided that you
also include the original English version of this License and the original versions of
those notices and disclaimers. In case of a disagreement between the translation andthe original version of this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically requirechanging the actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly
provided under this License. Any attempt otherwise to copy, modify, sublicense, or
distribute it is void, and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license from a particular
copyright holder is reinstated (a) provisionally, unless and until the copyright holder
explicitly and finally terminates your license, and (b) permanently, if the copyrightholder fails to notify you of the violation by some reasonable means prior to 60 days
after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if
the copyright holder notifies you of the violation by some reasonable means, this is thefirst time you have received notice of violation of this License (for any work) from thatcopyright holder, and you cure the violation prior to 30 days after your receipt of thenotice.
Termination of your rights under this section does not terminate the licenses of parties
who have received copies or rights from you under this License. If your rights havebeen terminated and not permanently reinstated, receipt of a copy of some or all of thesame material does not give you any rights to use it.

Appendix N: GNU Free Documentation License

917

10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free
Documentation License from time to time. Such new versions will be similar in spirit
to the present version, but may differ in detail to address new problems or concerns.
See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document
specifies that a particular numbered version of this License “or any later version”
applies to it, you have the option of following the terms and conditions either of thatspecified version or of any later version that has been published (not as a draft) by
the Free Software Foundation. If the Document does not specify a version number ofthis License, you may choose any version ever published (not as a draft) by the Free
Software Foundation. If the Document specifies that a proxy can decide which futureversions of this License can be used, that proxy’s public statement of acceptance of aversion permanently authorizes you to choose that version for the Document.
11. RELICENSING“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide
Web server that publishes copyrightable works and also provides prominent facilities
for anybody to edit those works. A public wiki that anybody can edit is an example ofsuch a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in thesite means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal
place of business in San Francisco, California, as well as future copyleft versions of thatlicense published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as partof another Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works
that were first published under this License somewhere other than this MMC, andsubsequently incorporated in whole or in part into the MMC, (1) had no cover texts
or invariant sections, and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under
CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is
eligible for relicensing.

918

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ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the
document and put the following copyright and license notices just after the title page:
Copyright (C) year your name.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;with no Invariant Sections, no Front-Cover Texts, and no Back-CoverTexts. A copy of the license is included in the section entitled ‘‘GNUFree Documentation License’’.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the“with. . . Texts.” line with this:with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.

If you have Invariant Sections without Cover Texts, or some other combination of thethree, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasingthese examples in parallel under your choice of free software license, such as the GNU
General Public License, to permit their use in free software.

919

Concept Index!
‘!’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775## in Modula-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250$$ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170$$ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170$_ and info breakpoints . . . . . . . . . . . . . . . . . . . . . . 61$_ and info line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136$_, $__, and value history . . . . . . . . . . . . . . . . . . . . . 154&&, background execution of commands . . . . . . . . . . 95–--annotate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--args. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--attach, gdbserver option . . . . . . . . . . . . . . . . . . 321--batch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14--batch-silent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14--baud. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--cd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14--command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16--core. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--data-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--debug, gdbserver option. . . . . . . . . . . . . . . . . . . . 322--debug-file, gdbserver option . . . . . . . . . . . . . . 323--debug-format, gdbserver option . . . . . . . . . . . 323--directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13--early-init-command . . . . . . . . . . . . . . . . . . . . . . . . 13--early-init-eval-command . . . . . . . . . . . . . . . . . . . 13--eval-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--exec. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--fullname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--init-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--init-eval-command. . . . . . . . . . . . . . . . . . . . . . . . . . 13--interpreter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--multi, gdbserver option. . . . . . . . . . . . . . . . . . . . 315--nh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13--nowindows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14--nx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13--once, gdbserver option . . . . . . . . . . . . . . . . . . . . . 322--pid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--quiet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13--readnever, command-line option . . . . . . . . . . . . . 13--readnow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13--return-child-result . . . . . . . . . . . . . . . . . . . . . . . 14--se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--selftest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323--silent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13--statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16--symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12--tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--tui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15--version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16--windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14‘--with-gdb-datadir’ . . . . . . . . . . . . . . . . . . . . . . . . 308‘--with-relocated-sources’ . . . . . . . . . . . . . . . . . 134‘--with-sysroot’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298--wrapper, gdbserver option . . . . . . . . . . . . . . . . . 323--write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
-b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
-c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
-d . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
-e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
-eiex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-eix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-ex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
-f . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
-iex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-info-gdb-mi-command . . . . . . . . . . . . . . . . . . . . . . . 684-ix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
-l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
-n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-nw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
-p . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
-q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
-readnever, option for symbol-file command . . 292-s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
-t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
-w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
-x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.
., Modula-2 scope operator . . . . . . . . . . . . . . . . . . . 249.build-id directory . . . . . . . . . . . . . . . . . . . . . . . . . . 300.debug subdirectories . . . . . . . . . . . . . . . . . . . . . . . . . 300.debug_gdb_scripts section . . . . . . . . . . . . . . . . . . 573‘.debug_names’ section . . . . . . . . . . . . . . . . . . . . . . . . 307‘.gdb_index’ section . . . . . . . . . . . . . . . . . . . . . . . . . . 305.gdb index section format . . . . . . . . . . . . . . . . . . . . . 883.gdbinit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19‘.gnu_debugdata’ section . . . . . . . . . . . . . . . . . . . . . 304.gnu_debuglink sections . . . . . . . . . . . . . . . . . . . . . . 302.note.gnu.build-id sections . . . . . . . . . . . . . . . . . 302.o files, reading symbols from . . . . . . . . . . . . . . . . . 293

920//proc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337:::, context for variables/functions. . . . . . . . . . . . . 147<<architecture> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860<compatible> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<feature> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<flags> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862<not saved> values . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180<osabi> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<reg> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862<struct> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862<union> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<vector> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<xi:include>. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860?
‘?’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775_NSPrintForDebugger, and printing
Objective-C objects. . . . . . . . . . . . . . . . . . . . . . . . . 239‘“No symbol "foo" in current context” . . . . . . . . . 148{{type} . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

A‘A’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
AArch64 Memory Tagging Extension. . . . . . . . . . 358
AArch64 Pointer Authentication.. . . . . . . . . . . . . . 357
AArch64 SME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
AArch64 SME2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
AArch64 support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
AArch64 SVE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
abbreviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
acknowledgment, for gdb remote . . . . . . . . . . . . . . 829
active targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
Ada exception catching . . . . . . . . . . . . . . . . . . . . . . . . 70
Ada exception handlers catching . . . . . . . . . . . . . . . 70
Ada mode, general . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
Ada task switching . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
Ada tasking and core file debugging . . . . . . . . . . . 258
Ada, deviations from . . . . . . . . . . . . . . . . . . . . . . . . . . 252

Debugging with gdb

Ada, omissions from . . . . . . . . . . . . . . . . . . . . . . . . . . 251
Ada, problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
Ada, source character set . . . . . . . . . . . . . . . . . . . . . 259
Ada, tasking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
add new commands for external monitor . . . . . . 320
address locations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
address of a symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
address size for remote targets . . . . . . . . . . . . . . . . 326
addressable memory unit. . . . . . . . . . . . . . . . . . . . . . 154
aggregates (Ada) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
AIX threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
aliases for commands . . . . . . . . . . . . . . . . . . . . . . . . . 399
aliases for commands, default arguments . . . . . . 400
alignment of remote memory accesses . . . . . . . . . 778
all-stop mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Alpha stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
always-read-ctf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
ambiguous expressions . . . . . . . . . . . . . . . . . . . . . . . . 146
AMD GPU debugging info . . . . . . . . . . . . . . . . . . . . 383
AMD GPU precise memory event reporting . . . 365
AMD GPU support . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
annotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
annotations for errors, warnings
and interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
annotations for invalidation messages. . . . . . . . . . 697
annotations for prompts . . . . . . . . . . . . . . . . . . . . . . 696
annotations for running programs . . . . . . . . . . . . . 697
annotations for source display . . . . . . . . . . . . . . . . . 698
append data to a file . . . . . . . . . . . . . . . . . . . . . . . . . . 185
Application Data Integrity . . . . . . . . . . . . . . . . . . . . 361
apply a command to all frames (ignoringerrors and empty output) . . . . . . . . . . . . . . . . . . . 122
apply a command to all frames of all threads(ignoring errors and empty output) . . . . . . . . . . 50
apply command to all threads (ignoring errors
and empty output) . . . . . . . . . . . . . . . . . . . . . . . . . . 50
apply command to several frames . . . . . . . . . . . . . 120
apply command to several threads. . . . . . . . . . . . . . 49
ARC EM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
ARC HS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
ARC specific commands . . . . . . . . . . . . . . . . . . . . . . 348
ARC600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
ARC700 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
architecture debugging info . . . . . . . . . . . . . . . . . . . 383
argument count in user-defined commands . . . . 392
arguments (to your program). . . . . . . . . . . . . . . . . . . 38
arguments, to gdbserver . . . . . . . . . . . . . . . . . . . . . . 321
arguments, to user-defined commands . . . . . . . . . 391
ARM 32-bit mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
ARM AArch64 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
array aggregates (Ada). . . . . . . . . . . . . . . . . . . . . . . . 251
arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
arrays in expressions . . . . . . . . . . . . . . . . . . . . . . . . . . 145
arrays slices (Fortran). . . . . . . . . . . . . . . . . . . . . . . . . 242
artificial array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
assembly instructions . . . . . . . . . . . . . . . . . . . . . . . . . 136
assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
async output in gdb/mi. . . . . . . . . . . . . . . . . . . . . . . 595

Concept Index

async records in gdb/mi . . . . . . . . . . . . . . . . . . . . . . 598
asynchronous execution . . . . . . . . . . . . . . . . . . . 95, 591
asynchronous execution, and process
record and replay . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
AT&T disassembly flavor . . . . . . . . . . . . . . . . . . . . . 139
attach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
attach to a program, gdbserver . . . . . . . . . . . . . . . 321
auto-loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
auto-loading extensions . . . . . . . . . . . . . . . . . . . . . . . 571
auto-loading init file in the current directory . . 378
auto-loading libthread db.so.1. . . . . . . . . . . . . . . . . 378
auto-loading safe-path . . . . . . . . . . . . . . . . . . . . . . . . 379
auto-loading verbose mode . . . . . . . . . . . . . . . . . . . . 381
auto-retry, for remote TCP target . . . . . . . . . . . . . 328
automatic display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
automatic hardware breakpoints . . . . . . . . . . . . . . . 64
automatic overlay debugging . . . . . . . . . . . . . . . . . . 224
automatic symbol index cache . . . . . . . . . . . . . . . . . 306
automatic thread selection . . . . . . . . . . . . . . . . . . . . . 93
auxiliary vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
AVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

B‘b’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776‘B’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
background execution . . . . . . . . . . . . . . . . . . . . . 95, 591
backtrace beyond main function . . . . . . . . . . . . . . . 116
backtrace limit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
base name differences . . . . . . . . . . . . . . . . . . . . . . . . . 299
baud rate for remote targets . . . . . . . . . . . . . . . . . . 326‘bc’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
bcache statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
bits in remote address . . . . . . . . . . . . . . . . . . . . . . . . 326
blocks in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
blocks in python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
bookmark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
branch trace configuration format . . . . . . . . . . . . . 846
branch trace format . . . . . . . . . . . . . . . . . . . . . . . . . . . 845
branch trace store . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
break in overloaded functions . . . . . . . . . . . . . . . . . 235
break on a system call. . . . . . . . . . . . . . . . . . . . . . . . . . 70
break on fork/exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
BREAK signal instead of Ctrl-C . . . . . . . . . . . . . . 326
breakpoint address adjusted . . . . . . . . . . . . . . . . . . . . 83
breakpoint at static probe point . . . . . . . . . . . . . . . 128
breakpoint commands . . . . . . . . . . . . . . . . . . . . . . . . . . 77
breakpoint commands for gdb/mi . . . . . . . . . . . . . 607
breakpoint commands, in remote protocol . . . . . 807
breakpoint conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 76
breakpoint debugging info. . . . . . . . . . . . . . . . . . . . . 388
breakpoint kinds, ARM . . . . . . . . . . . . . . . . . . . . . . . 816
breakpoint kinds, MIPS . . . . . . . . . . . . . . . . . . . . . . . 816
breakpoint lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
breakpoint numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
breakpoint on events . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
breakpoint on memory address . . . . . . . . . . . . . . . . . 57
breakpoint on variable modification . . . . . . . . . . . . 57

921

breakpoint ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
breakpoint subroutine, remote. . . . . . . . . . . . . . . . 334
breakpointing Ada elaboration code . . . . . . . . . . . 254
breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
breakpoints and inferiors . . . . . . . . . . . . . . . . . . . . . . . 46
breakpoints and tasks, in Ada . . . . . . . . . . . . . . . . . 258
breakpoints and threads. . . . . . . . . . . . . . . . . . . . . . . . 96
breakpoints at functions matching a regexp . . . . . 61
breakpoints in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
breakpoints in overlays . . . . . . . . . . . . . . . . . . . . . . . . 224
breakpoints in python . . . . . . . . . . . . . . . . . . . . . . . . . 491
breakpoints, multiple locations . . . . . . . . . . . . . . . . . 62
‘bs’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
bug criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
bug reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
bugs in gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
build ID sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
build ID, and separate debugging files . . . . . . . . . 300
building gdb, requirements for . . . . . . . . . . . . . . . . 745
built-in simulator target . . . . . . . . . . . . . . . . . . . . . . 313
builtin Go functions . . . . . . . . . . . . . . . . . . . . . . . . . . 238
builtin Go types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

C‘c’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
C and C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
C and C++ checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
C and C++ constants . . . . . . . . . . . . . . . . . . . . . . . . . . 233
C and C++ defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
C and C++ operators . . . . . . . . . . . . . . . . . . . . . . . . . . 231‘C’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 776
C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
C++ compilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
C++ demangling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
C++ exception handling . . . . . . . . . . . . . . . . . . . . . . . 235
C++ overload debugging info . . . . . . . . . . . . . . . . . . 386
C++ scope resolution . . . . . . . . . . . . . . . . . . . . . . . . . . 148
C++ symbol decoding style . . . . . . . . . . . . . . . . . . . . 166
C++ symbol display . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
caching data of targets . . . . . . . . . . . . . . . . . . . . . . . . 190
caching of bfd objects . . . . . . . . . . . . . . . . . . . . . . . . . 300
caching of opened files . . . . . . . . . . . . . . . . . . . . . . . . 300
call dummy stack unwinding . . . . . . . . . . . . . . . . . . 281
call dummy stack unwinding on timeout. . . . . . . 282
call dummy stack unwinding on
unhandled exception. . . . . . . . . . . . . . . . . . . . . . . . 282
call overloaded functions . . . . . . . . . . . . . . . . . . . . . . 234
call stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
call stack traces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
call-clobbered registers . . . . . . . . . . . . . . . . . . . . . . . . 180
caller-saved registers . . . . . . . . . . . . . . . . . . . . . . . . . . 180
calling functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
calling functions in the program, disabling. . . . . 282
calling make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
case sensitivity in symbol names . . . . . . . . . . . . . . 263
case-insensitive symbol names . . . . . . . . . . . . . . . . . 263
casts, in expressions. . . . . . . . . . . . . . . . . . . . . . . . . . . 145

922

casts, to view memory . . . . . . . . . . . . . . . . . . . . . . . . 145
catch Ada exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . 70
catch Ada exceptions when handled . . . . . . . . . . . . 70
catch syscalls from inferior, remote request . . . . 796
catchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
catchpoints, setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
change gdb’s working directory . . . . . . . . . . . . . . . . 40
change inferior’s working directory . . . . . . . . . . . . . 40
character sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
check if a given address is in amemory tagged region . . . . . . . . . . . . . . . . . . . . . . 794
checkpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
checkpoints and process id . . . . . . . . . . . . . . . . . . . . . 55
checks, range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
checks, type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
checksum, for gdb remote . . . . . . . . . . . . . . . . . . . . . 773
choosing target byte order . . . . . . . . . . . . . . . . . . . . 314
circular trace buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
clearing breakpoints, watchpoints, catchpoints . . 73
CLI commands in python . . . . . . . . . . . . . . . . . . . . . 463
close, file-i/o system call . . . . . . . . . . . . . . . . . . . . . . 834
closest symbol and offset for an address . . . . . . . 264
code address and its source line . . . . . . . . . . . . . . . 135
code compression, MIPS . . . . . . . . . . . . . . . . . . . . . . . 360
code location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
COFF/PE exported symbols . . . . . . . . . . . . . . . . . . 383
collected data discarded . . . . . . . . . . . . . . . . . . . . . . . 212
colon, doubled as scope operator . . . . . . . . . . . . . . 249
colon-colon, context for variables/functions . . . . 147
colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
command editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
command files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
command history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
command hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
command interpreters . . . . . . . . . . . . . . . . . . . . . . . . . 577
command line editing . . . . . . . . . . . . . . . . . . . . . . . . . 367
command options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
command options, boolean . . . . . . . . . . . . . . . . . . . . . 28
command options, raw input . . . . . . . . . . . . . . . . . . . 28
command scripts, debugging . . . . . . . . . . . . . . . . . . 382
command tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
commands for C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
commands in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
commands in python, CLI . . . . . . . . . . . . . . . . . . . . 463
commands in python, GDB/MI . . . . . . . . . . . . . . . 467
commands to access guile . . . . . . . . . . . . . . . . . . . . . 519
commands to access python . . . . . . . . . . . . . . . . . . . 402
comment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
common targets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
COMMON blocks, Fortran . . . . . . . . . . . . . . . . . . . . . . . . 242
compatibility, gdb/mi and CLI . . . . . . . . . . . . . . . . 595
compilation directory . . . . . . . . . . . . . . . . . . . . . . . . . 132
compile C++ type conversion . . . . . . . . . . . . . . . . . . 286
compile command debugging info . . . . . . . . . . . . . 286
compile command driver filename override. . . . . 290
compile command options override . . . . . . . . . . . . 287
compiling code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

Debugging with gdb

completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
completion of Guile commands . . . . . . . . . . . . . . . . 543
completion of Python commands . . . . . . . . . . . . . . 464
completion of quoted strings . . . . . . . . . . . . . . . . . . . 26
completion of structure field names . . . . . . . . . . . . . 26
completion of union field names . . . . . . . . . . . . . . . . 26
compressed debug sections . . . . . . . . . . . . . . . . . . . . 746
conditional breakpoints . . . . . . . . . . . . . . . . . . . . . . . . 76
conditional tracepoints . . . . . . . . . . . . . . . . . . . . . . . . 207
configure debuginfod URLs . . . . . . . . . . . . . . . . . . . 887
configuring gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747
confirmation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
connection timeout, for remote TCP target . . . . 328
connections in python . . . . . . . . . . . . . . . . . . . . . . . . . 499
console i/o as part of file-i/o . . . . . . . . . . . . . . . . . . 832
console interpreter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
console output in gdb/mi . . . . . . . . . . . . . . . . . . . . . 595
constants, in file-i/o protocol . . . . . . . . . . . . . . . . . . 840
continuing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
continuing threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
control C, and remote debugging . . . . . . . . . . . . . . 335
controlling terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
convenience functions . . . . . . . . . . . . . . . . . . . . . . . . . 174
convenience functions in python . . . . . . . . . . . . . . . 473
convenience variables . . . . . . . . . . . . . . . . . . . . . . . . . 171
convenience variables for tracepoints . . . . . . . . . . 218
convenience variables, and tracestate variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
convenience variables, initializing . . . . . . . . . . . . . . 171
core dump file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
core dump file target . . . . . . . . . . . . . . . . . . . . . . . . . . 312
crash of debugger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
CRC algorithm definition . . . . . . . . . . . . . . . . . . . . . 302
CRC of memory block, remote request . . . . . . . . 790
CRIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
CRIS mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
CRIS version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
CTF info, when to read . . . . . . . . . . . . . . . . . . . . . . . 275
Ctrl-BREAK, MS-Windows . . . . . . . . . . . . . . . . . . . 342
ctrl-c message, in file-i/o protocol . . . . . . . . . . . . . 832
current Ada task ID . . . . . . . . . . . . . . . . . . . . . . . . . . 256
current directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
current Go package . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
current thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
current thread, remote request . . . . . . . . . . . . . . . . 790
custom JIT debug info . . . . . . . . . . . . . . . . . . . . . . . . 702
Cygwin DLL, debugging . . . . . . . . . . . . . . . . . . . . . . 342
Cygwin-specific commands . . . . . . . . . . . . . . . . . . . . 342

Concept IndexD‘d’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777‘D’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777
DAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
Darwin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
data breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
data manipulation, in gdb/mi . . . . . . . . . . . . . . . . . 651
dcache line-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
dcache size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
dcache, flushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
dead names, gnu Hurd . . . . . . . . . . . . . . . . . . . . . . . 346
debug expression parser . . . . . . . . . . . . . . . . . . . . . . . 386
debug formats and C++ . . . . . . . . . . . . . . . . . . . . . . . 234
debug link sections. . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
debug remote protocol . . . . . . . . . . . . . . . . . . . . . . . . 386
Debugger Adapter Protocol . . . . . . . . . . . . . . . . . . . 577
debugger crash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
debugging agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
debugging C++ programs . . . . . . . . . . . . . . . . . . . . . . 234
debugging information directory, global . . . . . . . 300
debugging information in separate files . . . . . . . . 300
debugging libthread_db . . . . . . . . . . . . . . . . . . . . . . . 52
debugging multiple processes . . . . . . . . . . . . . . . . . . . 53
debugging optimized code . . . . . . . . . . . . . . . . . . . . . 195
debugging stub, example . . . . . . . . . . . . . . . . . . . . . . 333
debugging target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
debugging the Cygwin DLL . . . . . . . . . . . . . . . . . . . 342
debugging threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
debuginfod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 887
debuginfod verbosity . . . . . . . . . . . . . . . . . . . . . . . . . . 887
debuginfod, maintenance commands . . . . . . . . . . . 758
decimal floating point format . . . . . . . . . . . . . . . . . 237
default behavior of commands, changing . . . . . . . . 23
default collection action . . . . . . . . . . . . . . . . . . . . . . . 210
default data directory . . . . . . . . . . . . . . . . . . . . . . . . . 308
default settings, changing . . . . . . . . . . . . . . . . . . . . . . 23
default source path substitution . . . . . . . . . . . . . . . 134
default system root . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
define trace state variable, remote request . . . . . 818
defining macros interactively . . . . . . . . . . . . . . . . . . 199
definition of a macro, showing . . . . . . . . . . . . . . . . . 199
delete breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
deleting breakpoints,
watchpoints, catchpoints . . . . . . . . . . . . . . . . . . . . . 73
deliver a signal to a program . . . . . . . . . . . . . . . . . . 279
demangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
demangler crashes . . . . . . . . . . . . . . . . . . . . . . . . 758, 759
demangling C++ names . . . . . . . . . . . . . . . . . . . . . . . 166
deprecated commands. . . . . . . . . . . . . . . . . . . . . . . . . 758
derived type of an object, printing . . . . . . . . . . . . 167
descriptor tables display . . . . . . . . . . . . . . . . . . . . . . 340
detach from task, gnu Hurd . . . . . . . . . . . . . . . . . . 346
detach from thread, gnu Hurd . . . . . . . . . . . . . . . . 347
direct memory access (DMA) on MS-DOS . . . . . 340
directories for source files . . . . . . . . . . . . . . . . . . . . . 131
directory, compilation . . . . . . . . . . . . . . . . . . . . . . . . . 132
directory, current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

923

disable address space
randomization, remote request . . . . . . . . . . . . . . 790
disabling calling functions in the program . . . . . 282
disassembler in Python, global vs. specific . . . . . 509
disassembler options . . . . . . . . . . . . . . . . . . . . . . . . . . 139
disconnected tracing . . . . . . . . . . . . . . . . . . . . . . . . . . 212
displaced stepping debugging info . . . . . . . . . . . . . 384
displaced stepping support . . . . . . . . . . . . . . . . . . . . 757
displaced stepping, and process
record and replay . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
display command history. . . . . . . . . . . . . . . . . . . . . . 370
display derived types. . . . . . . . . . . . . . . . . . . . . . . . . . 167
display disabled out of scope . . . . . . . . . . . . . . . . . . 157
display gdb copyright . . . . . . . . . . . . . . . . . . . . . . . . . . 31
display of expressions . . . . . . . . . . . . . . . . . . . . . . . . . 155
display remote monitor communications . . . . . . . 313
display remote packets . . . . . . . . . . . . . . . . . . . . . . . . 386
djgpp debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
DLLs with no debugging symbols . . . . . . . . . . . . . 343
do not print frame arguments . . . . . . . . . . . . . . . . . 160
documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743
don’t repeat command . . . . . . . . . . . . . . . . . . . . . . . . 393
don’t repeat Guile command . . . . . . . . . . . . . . . . . . 542
don’t repeat Python command . . . . . . . . . . . . . . . . 464
DOS file-name semantics of file names. . . . . . . . . 299
DOS serial data link, remote debugging . . . . . . . 341
DOS serial port status . . . . . . . . . . . . . . . . . . . . . . . . 341
DPMI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
dprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
dump all data collected at tracepoint . . . . . . . . . . 217
dump core from inferior . . . . . . . . . . . . . . . . . . . . . . . 186
dump data to a file . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
dump/restore files . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
DVC register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
DWARF compilation units cache . . . . . . . . . . . . . . 765
DWARF DIEs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
DWARF frame unwinders . . . . . . . . . . . . . . . . . . . . . 766
DWARF Line Tables . . . . . . . . . . . . . . . . . . . . . . . . . . 384
DWARF Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
DWARF-2 CFI and CRIS . . . . . . . . . . . . . . . . . . . . . 353
dynamic linking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
dynamic printf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
dynamic varobj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643

Eearly initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
early initialization file . . . . . . . . . . . . . . . . . . . . . . . . . . 16
editing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
editing command lines . . . . . . . . . . . . . . . . . . . . . . . . 713
editing source files . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
eight-bit characters in strings . . . . . . . . . . . . . . . . . 165
elaboration phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
ELinOS system-wide configuration script . . . . . . 754
Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587
empty response, for unsupported packets . . . . . . 774
enable debuginfod . . . . . . . . . . . . . . . . . . . . . . . . . . . . 887

924

enable/disable a breakpoint . . . . . . . . . . . . . . . . . . . . 74
enabling and disabling probes . . . . . . . . . . . . . . . . . . 82
entering numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
environment (of your program) . . . . . . . . . . . . . . . . . 38
errno values, in file-i/o protocol . . . . . . . . . . . . . . . 840
error on valid input . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
event debugging info . . . . . . . . . . . . . . . . . . . . . . . . . . 384
event designators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
event handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
event-loop debugging . . . . . . . . . . . . . . . . . . . . . . . . . 384
examine process image . . . . . . . . . . . . . . . . . . . . . . . . 337
examining data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
examining memory. . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
exception handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
exceptions, guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
exceptions, python . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
exec events, remote reply . . . . . . . . . . . . . . . . . . . . . 787
executable file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
executable file target . . . . . . . . . . . . . . . . . . . . . . . . . . 312
executable file, for remote target . . . . . . . . . . . . . . 328
execute commands from a file . . . . . . . . . . . . . . . . . 395
execute forward or backward in time . . . . . . . . . . 102
execute remote command, remote request . . . . . 798
execution, foreground, backgroundand asynchronous . . . . . . . . . . . . . . . . . . . . . . . 95, 591
exit status of shell commands . . . . . . . . . . . . . . . . . 174
exiting gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
expand macro once . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
expanding preprocessor macros . . . . . . . . . . . . . . . . 199
explicit locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
explore type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
explore value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
exploring hierarchical data structures . . . . . . . . . 143
expression debugging info . . . . . . . . . . . . . . . . . . . . . 384
expression parser, debugging info . . . . . . . . . . . . . . 386
expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
expressions in Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
expressions in C or C++ . . . . . . . . . . . . . . . . . . . . . . . 231
expressions in C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
expressions in Modula-2. . . . . . . . . . . . . . . . . . . . . . . 244
extend gdb for remote targets . . . . . . . . . . . . . . . . 320
extending GDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
extra signal information . . . . . . . . . . . . . . . . . . . . . . . . 92

F‘F’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777
F reply packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
F request packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
fast tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
fast tracepoints, setting . . . . . . . . . . . . . . . . . . . . . . . 205
fatal signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
fatal signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
features of the remote protocol . . . . . . . . . . . . . . . . 799
fetch memory tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
file name canonicalization . . . . . . . . . . . . . . . . . . . . . 299
file names, quoting and escaping . . . . . . . . . . . . . . . 27
file transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

Debugging with gdb

file transfer, remote protocol . . . . . . . . . . . . . . . . . . 823
file-i/o examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
file-i/o overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830
file-i/o reply packet . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
file-i/o request packet . . . . . . . . . . . . . . . . . . . . . . . . . 831
File-I/O remote protocol extension . . . . . . . . . . . . 830
filename-display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
find trace snapshot . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
flinching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
float promotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
floating point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
floating point registers . . . . . . . . . . . . . . . . . . . . . . . . 179
floating point, MIPS remote . . . . . . . . . . . . . . . . . . . 351
focus of debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
foo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
foreground execution . . . . . . . . . . . . . . . . . . . . . . 95, 591
fork events, remote reply . . . . . . . . . . . . . . . . . . . . . . 787
fork, debugging programs which call . . . . . . . . . . . . 52
format options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
formatted output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Fortran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
fortran array slicing debugging info . . . . . . . . . . . 385
Fortran Defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Fortran Intrinsics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Fortran modules, information about . . . . . . . . . . . 272
Fortran operators and expressions . . . . . . . . . . . . . 241
Fortran Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Fortran-specific support in gdb . . . . . . . . . . . . . . . 240
frame debugging info. . . . . . . . . . . . . . . . . . . . . . . . . . 385
frame decorator api . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
frame filters api . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
frame information, printing . . . . . . . . . . . . . . . . . . . 163
frame level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
frame number. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
frame pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
frame pointer register . . . . . . . . . . . . . . . . . . . . . . . . . 179
frame, definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
frameless execution . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
frames in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
frames in python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479
frames of inlined functions . . . . . . . . . . . . . . . . . . . . 761
free memory information (MS-DOS). . . . . . . . . . . 339
FreeBSD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
FreeBSD LWP debug messages . . . . . . . . . . . . . . . . 384
FreeBSD native target debug messages . . . . . . . . 385
fstat, file-i/o system call . . . . . . . . . . . . . . . . . . . . . . 836
Fujitsu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
full symbol tables, listing gdb’s internal . . . . . . . 273
function call arguments, optimized out . . . . . . . . 116
function entry/exit, wrong
values of variables . . . . . . . . . . . . . . . . . . . . . . . . . . 148
functions and variables by Fortran module . . . . 272
functions without line info, and stepping . . . . . . . 85

Concept Index

G‘g’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 777
g++, gnu C++ compiler. . . . . . . . . . . . . . . . . . . . . . . . 231‘G’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
garbled pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
gcc and C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
gdb bugs, reporting. . . . . . . . . . . . . . . . . . . . . . . . . . . 709
gdb internal error . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
gdb module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
gdb objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
gdb reference card . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743
gdb startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
gdb version number. . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
gdb.ini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
gdb.printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
gdb.prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516
gdb.ptwrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
gdb.types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
gdb.Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
gdb/mi development . . . . . . . . . . . . . . . . . . . . . . . . . . 595
gdb/mi, async records . . . . . . . . . . . . . . . . . . . . . . . . 598
gdb/mi, breakpoint commands . . . . . . . . . . . . . . . . 607
gdb/mi, compatibility with CLI . . . . . . . . . . . . . . . 595
gdb/mi, data manipulation . . . . . . . . . . . . . . . . . . . 651
gdb/mi, input syntax . . . . . . . . . . . . . . . . . . . . . . . . . 593
gdb/mi, its purpose. . . . . . . . . . . . . . . . . . . . . . . . . . . 589
gdb/mi, output syntax. . . . . . . . . . . . . . . . . . . . . . . . 593
gdb/mi, result records . . . . . . . . . . . . . . . . . . . . . . . . 597
gdb/mi, simple examples . . . . . . . . . . . . . . . . . . . . . 605
gdb/mi, stream records . . . . . . . . . . . . . . . . . . . . . . . 597
GDB/MI General Design . . . . . . . . . . . . . . . . . . . . . 589
gdbarch debugging info . . . . . . . . . . . . . . . . . . . . . . . 383
GDBHISTFILE, environment variable . . . . . . . . . . . . 368
GDBHISTSIZE, environment variable . . . . . . . . . . . . 369
gdbinit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
gdbserver, command-line arguments . . . . . . . . . . 321
gdbserver, connecting . . . . . . . . . . . . . . . . . . . . . . . . 315
gdbserver, search path for libthread_db . . . . . . 325
gdbserver, send all debug output
to a single file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
gdbserver, target extended-remote mode . . . . 315
gdbserver, target remote mode . . . . . . . . . . . . . . 315
gdbserver, types of connections . . . . . . . . . . . . . . . 315
GDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
general initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
get thread information block address . . . . . . . . . . 793
get thread-local storage address,
remote request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793
gettimeofday, file-i/o system call . . . . . . . . . . . . . . 837
getting structure elements using gdb.Field
objects as subscripts . . . . . . . . . . . . . . . . . . . . . . . . 411
global debugging information directories. . . . . . . 300
global thread identifier (GDB) . . . . . . . . . . . . . . . . . 48
global thread number . . . . . . . . . . . . . . . . . . . . . . . . . . 48
GNAT descriptive types . . . . . . . . . . . . . . . . . . . . . . 260
GNAT encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
gnu C++. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
gnu Emacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587

925

gnu Hurd debugging . . . . . . . . . . . . . . . . . . . . . . . . . . 345
gnu/Hurd debug messages . . . . . . . . . . . . . . . . . . . . 385
gnu/Linux namespaces debug messages . . . . . . . 386
gnu/Linux native target debug messages . . . . . . 385
Go (programming language) . . . . . . . . . . . . . . . . . . 238
guile api . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
guile architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
guile auto-loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
guile commands . . . . . . . . . . . . . . . . . . . . . . . . . . 519, 541
guile configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
guile exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524
guile gdb module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
guile iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
guile modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
guile pagination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
guile parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
guile pretty printing api . . . . . . . . . . . . . . . . . . . . . . . 537
guile scripting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
guile scripts directory . . . . . . . . . . . . . . . . . . . . . . . . . 519
guile stdout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
guile, working with types . . . . . . . . . . . . . . . . . . . . . 532
guile, working with values from inferior. . . . . . . . 525

H‘H’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
handling signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
hardware breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . 60
hardware debug registers . . . . . . . . . . . . . . . . . . . . . . 767
hardware watchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . 66
hash mark while downloading . . . . . . . . . . . . . . . . . 313
heuristic-fence-post (Alpha, MIPS) . . . . . . . . 359
history events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
history expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737
history expansion, turn on/off . . . . . . . . . . . . . . . . . 369
history file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
history number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
history of values printed by gdb . . . . . . . . . . . . . . 170
history size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
history substitution . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
hooks, for commands . . . . . . . . . . . . . . . . . . . . . . . . . 394
hooks, post-command . . . . . . . . . . . . . . . . . . . . . . . . . 394
hooks, pre-command . . . . . . . . . . . . . . . . . . . . . . . . . . 394
host character set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Host I/O, remote protocol . . . . . . . . . . . . . . . . . . . . 823
how many arguments(user-defined commands) . . . . . . . . . . . . . . . . . . . 392
HPPA support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

926

I‘i’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
i/o. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
i386 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
i386-stub.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333‘I’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
I/O registers (Atmel AVR) . . . . . . . . . . . . . . . . . . . . 353
ID list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
IDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
ignore count (of breakpoint) . . . . . . . . . . . . . . . . . . . . 77
in-process agent protocol . . . . . . . . . . . . . . . . . . . . . . 705
incomplete type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
indentation in structure display . . . . . . . . . . . . . . . 165
index files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305, 307
index section format . . . . . . . . . . . . . . . . . . . . . . . . . . 883
inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
inferior debugging info . . . . . . . . . . . . . . . . . . . . . . . . 385
inferior events in Python . . . . . . . . . . . . . . . . . . . . . . 451
inferior function call debugging info . . . . . . . . . . . 385
inferior functions, calling . . . . . . . . . . . . . . . . . . . . . . 281
inferior tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
inferior-specific breakpoints . . . . . . . . . . . . . . . . . . . . 46
inferiors in Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
infinite recursion in user-defined commands . . . 394
info for known.debug gdb scripts-loaded scripts . . . . . . . . . . . 764
info for known object files . . . . . . . . . . . . . . . . . . . . . 764
info line, repeated calls. . . . . . . . . . . . . . . . . . . . . . . . 136
info proc cmdline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
info proc cwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
info proc exe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
info proc files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
information about static tracepoint markers . . . 211
information about tracepoints . . . . . . . . . . . . . . . . . 210
inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
init file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
init file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
initial frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
initialization file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
initialization file, readline . . . . . . . . . . . . . . . . . . . . . 716
injecting code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
inline functions, debugging . . . . . . . . . . . . . . . . . . . . 195
innermost frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
input syntax for gdb/mi . . . . . . . . . . . . . . . . . . . . . . 593
installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
instructions, assembly . . . . . . . . . . . . . . . . . . . . . . . . . 136
integral datatypes, in file-i/o protocol . . . . . . . . . 838
Intel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
Intel disassembly flavor . . . . . . . . . . . . . . . . . . . . . . . 139
Intel Processor Trace . . . . . . . . . . . . . . . . . . . . . . . . . 104
interaction, readline . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
internal commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
internal errors, control of gdb behavior. . . . . . . . 759
internal gdb breakpoints . . . . . . . . . . . . . . . . . . . . . . . 65
interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
interrupt debuggee on MS-Windows . . . . . . . . . . . 342
interrupt remote programs . . . . . . . . . . . . . . . 326, 328
interrupting remote programs . . . . . . . . . . . . . . . . . 319

Debugging with gdb

interrupting remote targets . . . . . . . . . . . . . . . . . . . 335
interrupts (remote protocol) . . . . . . . . . . . . . . . . . . 825
invalid input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709
invoke another interpreter . . . . . . . . . . . . . . . . . . . . . 577
ipa protocol commands . . . . . . . . . . . . . . . . . . . . . . . 707
ipa protocol objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 706
isatty, file-i/o system call . . . . . . . . . . . . . . . . . . . . . 837

J
JIT compilation interface . . . . . . . . . . . . . . . . . . . . . 701
JIT debug info reader . . . . . . . . . . . . . . . . . . . . . . . . . 702
just-in-time compilation . . . . . . . . . . . . . . . . . . . . . . . 701
just-in-time compilation,
debugging messages . . . . . . . . . . . . . . . . . . . . . . . . 385

K‘k’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
kernel crash dump . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
kernel memory image . . . . . . . . . . . . . . . . . . . . . . . . . 337
kill ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
killing text. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714

Llanguages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
last tracepoint number . . . . . . . . . . . . . . . . . . . . . . . . 206
latest breakpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
lazy strings in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
lazy strings in python . . . . . . . . . . . . . . . . . . . . . . . . . 497
LDT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
leaving gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
libkvm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
library list format, remote protocol . . . . . . . 841, 842
limit hardware breakpoints and watchpoints . . . 327
limit hardware watchpoints length . . . . . . . . . . . . 327
limit on number of printed array elements . . . . . 160
limit on number of printed string characters . . . 159
limits, in file-i/o protocol . . . . . . . . . . . . . . . . . . . . . 841
line tables in python . . . . . . . . . . . . . . . . . . . . . . . . . . 490
line tables, listing gdb’s internal . . . . . . . . . . . . . . 274
linespec locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Linux native targets . . . . . . . . . . . . . . . . . . . . . . . . . . 385
list active threads, remote request . . . . . . . . . . . . . 792
list of supported file-i/o calls . . . . . . . . . . . . . . . . . . 832
list output in gdb/mi . . . . . . . . . . . . . . . . . . . . . . . . . 595
list, how many lines to display . . . . . . . . . . . . . . . 125
listing gdb’s internal line tables . . . . . . . . . . . . . . . 274
listing gdb’s internal symbol tables . . . . . . . . . . . 273
listing machine instructions . . . . . . . . . . . . . . . . . . . 136
listing mapped overlays . . . . . . . . . . . . . . . . . . . . . . . 223
lists of breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
load address, overlay’s . . . . . . . . . . . . . . . . . . . . . . . . 221
load shared library . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
load symbols from memory. . . . . . . . . . . . . . . . . . . . 294
local socket, target remote . . . . . . . . . . . . . . . . . . . 317
local variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

Concept Index

locate address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
location resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
location spec. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
lock scheduler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
locspec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
log output in gdb/mi . . . . . . . . . . . . . . . . . . . . . . . . . 595
logging file name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
logging gdb output . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
look up of disassembler in Python . . . . . . . . . . . . . 509
lseek flags, in file-i/o protocol . . . . . . . . . . . . . . . . . 841
lseek, file-i/o system call . . . . . . . . . . . . . . . . . . . . . . 835

M‘m’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
m680x0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
m68k-stub.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333‘M’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779
Mach-O symbols processing . . . . . . . . . . . . . . . . . . . 386
machine instructions . . . . . . . . . . . . . . . . . . . . . . . . . . 136
macro definition, showing . . . . . . . . . . . . . . . . . . . . . 199
macro expansion, showing the resultsof preprocessor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
macros, example of debugging with. . . . . . . . . . . . 200
macros, from debug info . . . . . . . . . . . . . . . . . . . . . . 199
macros, user-defined . . . . . . . . . . . . . . . . . . . . . . . . . . 199
mailing lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597
maintenance commands . . . . . . . . . . . . . . . . . . . . . . . 755
Man pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 889
managing frame filters . . . . . . . . . . . . . . . . . . . . . . . . 122
manual overlay debugging . . . . . . . . . . . . . . . . . . . . . 223
map an overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
mapped address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
mapped overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
markers, static tracepoints . . . . . . . . . . . . . . . . . . . . 203
maximum value for offset of closest symbol . . . . 158
member functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
memory address space mappings . . . . . . . . . 338, 760
memory map format . . . . . . . . . . . . . . . . . . . . . . . . . . 843
memory region attributes . . . . . . . . . . . . . . . . . . . . . 183
memory tag types, ARM . . . . . . . . . . . . . . . . . . . . . . 816
memory tracing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
memory transfer, in file-i/o protocol . . . . . . . . . . . 838
memory used by commands . . . . . . . . . . . . . . . . . . . 769
memory used for symbol tables. . . . . . . . . . . . . . . . 296
memory, alignment and size of
remote accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
memory, viewing as typed object . . . . . . . . . . . . . . 145
mi interpreter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
mi2 interpreter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
mi3 interpreter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
MI commands in python . . . . . . . . . . . . . . . . . . . . . . 467
MI notifications in python . . . . . . . . . . . . . . . . . . . . 469
minimal language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
minimal symbol dump . . . . . . . . . . . . . . . . . . . . . . . . 273
Minimal symbols and DLLs . . . . . . . . . . . . . . . . . . . 343
MIPS addresses, masking . . . . . . . . . . . . . . . . . . . . . . 360
MIPS remote floating point . . . . . . . . . . . . . . . . . . . . 351

927

MIPS stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

miscellaneous settings . . . . . . . . . . . . . . . . . . . . . . . . . 388
MMX registers (x86) . . . . . . . . . . . . . . . . . . . . . . . . . . 180
mode t values, in file-i/o protocol . . . . . . . . . . . . . 840
Modula-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Modula-2 built-ins . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
Modula-2 checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Modula-2 constants . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Modula-2 defaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Modula-2 operators . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Modula-2 types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Modula-2, deviations from . . . . . . . . . . . . . . . . . . . . 249
Modula-2, gdb support . . . . . . . . . . . . . . . . . . . . . . . 244
module functions and variables . . . . . . . . . . . . . . . . 272
modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
monitor commands, for gdbserver . . . . . . . . . . . . 324
Motorola 680x0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
MS Windows debugging . . . . . . . . . . . . . . . . . . . . . . 342
MS-DOS system info . . . . . . . . . . . . . . . . . . . . . . . . . . 339
MS-DOS-specific commands. . . . . . . . . . . . . . . . . . . 339
multiple locations, breakpoints . . . . . . . . . . . . . . . . . 62
multiple processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
multiple targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
multiple threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
multiple threads, backtrace . . . . . . . . . . . . . . . . . . . 115
multiple-symbols menu. . . . . . . . . . . . . . . . . . . . . . . . 146
multiprocess extensions, in remote protocol . . . . 806

Nname a thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
names of symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
namespace in C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
native Cygwin debugging . . . . . . . . . . . . . . . . . . . . . 342
native djgpp debugging . . . . . . . . . . . . . . . . . . . . . . . 339
native script auto-loading . . . . . . . . . . . . . . . . . . . . . 399
native target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
negative breakpoint numbers . . . . . . . . . . . . . . . . . . . 65
never read symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
New systag message . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
new user interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
Newlib OS ABI and its influence on the
longjmp handling . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Nios II architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
no debug info functions . . . . . . . . . . . . . . . . . . . . . . . 284
no debug info variables. . . . . . . . . . . . . . . . . . . . . . . . 149
non-member C++ functions, set breakpoint in . . . 61
non-stop mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
non-stop mode, and process
record and replay . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
non-stop mode, and ‘setdisplaced-stepping’ . . . . . . . . . . . . . . . . . . . . . . . 757
non-stop mode, remote request . . . . . . . . . . . . . . . . 795
noninvasive task options . . . . . . . . . . . . . . . . . . . . . . 346
notation, readline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
notational conventions, for gdb/mi . . . . . . . . . . . . 589
notification packets . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
notifications in python, GDB/MI. . . . . . . . . . . . . . 469

928

notify output in gdb/mi . . . . . . . . . . . . . . . . . . . . . . 595
null elements in arrays . . . . . . . . . . . . . . . . . . . . . . . 165
number of array elements to print . . . . . . . . . . . . . 160
number of string characters to print . . . . . . . . . . . 159
number representation . . . . . . . . . . . . . . . . . . . . . . . . 374
numbers for breakpoints . . . . . . . . . . . . . . . . . . . . . . . 57

O
object files, relocatable, reading
symbols from . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
Objective-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
Objective-C, classes and selectors . . . . . . . . . . . . . 272
Objective-C, print objects . . . . . . . . . . . . . . . . . . . . . 239
objfile-gdb.gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
objfile-gdb.py . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
objfile-gdb.scm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 572
objfiles in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
objfiles in python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
observer debugging info . . . . . . . . . . . . . . . . . . . . . . . 386
octal escapes in strings . . . . . . . . . . . . . . . . . . . . . . . . 165
online documentation . . . . . . . . . . . . . . . . . . . . . . . . . . 29
opaque data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
open flags, in file-i/o protocol . . . . . . . . . . . . . . . . . 840
open, file-i/o system call . . . . . . . . . . . . . . . . . . . . . . 832
OpenCL C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
OpenCL C Datatypes . . . . . . . . . . . . . . . . . . . . . . . . . 239
OpenCL C Expressions . . . . . . . . . . . . . . . . . . . . . . . 240
OpenCL C Operators . . . . . . . . . . . . . . . . . . . . . . . . . 240
OpenRISC 1000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
operate-and-get-next . . . . . . . . . . . . . . . . . . . . . . . . . . 368
operating system information . . . . . . . . . . . . . . . . . 879
operating system information, process list . . . . . 879
optimized code, debugging . . . . . . . . . . . . . . . . . . . . 195
optimized code, wrong values of variables . . . . . 148
optimized out value in guile . . . . . . . . . . . . . . . . . . . 527
optimized out value in Python . . . . . . . . . . . . . . . . 412
optimized out, in backtrace . . . . . . . . . . . . . . . . . . . 116
optional debugging messages . . . . . . . . . . . . . . . . . . 382
optional warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
OS ABI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
OS information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
out-of-line single-stepping . . . . . . . . . . . . . . . . . . . . . 757
outermost frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
output formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
output syntax of gdb/mi . . . . . . . . . . . . . . . . . . . . . . 593
overlay area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
overlay example program. . . . . . . . . . . . . . . . . . . . . . 225
overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
overlays, setting breakpoints in . . . . . . . . . . . . . . . . 224
overloaded functions, calling . . . . . . . . . . . . . . . . . . 234
overloaded functions, overload resolution . . . . . . 236
overloading in C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
overloading, Ada . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

Debugging with gdb

P‘p’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779‘P’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779
packet acknowledgment, for gdb remote . . . . . . . 829
packet size, remote protocol . . . . . . . . . . . . . . . . . . . 804
packet size, remote, configuring . . . . . . . . . . . . . . . 332
packets, notification . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
packets, reporting on stdout . . . . . . . . . . . . . . . . . . 386
packets, tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
page size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
page tables display (MS-DOS) . . . . . . . . . . . . . . . . 340
pagination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
parameters in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
parameters in python . . . . . . . . . . . . . . . . . . . . . . . . . 470
partial symbol dump . . . . . . . . . . . . . . . . . . . . . . . . . . 273
partial symbol tables, listing gdb’s internal. . . . 273
Pascal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Pascal objects, static members display . . . . . . . . 167
Pascal support in gdb, limitations . . . . . . . . . . . . 243
pass signals to inferior, remote request . . . . . . . . 796
patching binaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
patching object files. . . . . . . . . . . . . . . . . . . . . . . . . . . 291
pause current task (gnu Hurd) . . . . . . . . . . . . . . . . 346
pause current thread (gnu Hurd) . . . . . . . . . . . . . 346
pauses in output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
pending breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
physical address from linear address . . . . . . . . . . . 340
physname. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
pipe, target remote to . . . . . . . . . . . . . . . . . . . . . . . 319
pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
pointer values, in file-i/o protocol . . . . . . . . . . . . . 838
pointer, finding referent . . . . . . . . . . . . . . . . . . . . . . . 158
port rights, gnu Hurd . . . . . . . . . . . . . . . . . . . . . . . . 346
port sets, gnu Hurd . . . . . . . . . . . . . . . . . . . . . . . . . . 346
PowerPC architecture . . . . . . . . . . . . . . . . . . . . . . . . . 361
prefix for data files . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
prefix for executable and sharedlibrary file names . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
premature return from system calls . . . . . . . . . . . . . 97
preprocessor macro expansion,
showing the results of . . . . . . . . . . . . . . . . . . . . . . . 199
pretty print arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
pretty print C++ virtual function tables . . . . . . . 167
pretty-printer commands . . . . . . . . . . . . . . . . . . . . . . 169
print all frame argument values . . . . . . . . . . . . . . . 160
print an Objective-C object description . . . . . . . 239
print array indexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
print binary values in groups of four bits . . . . . . 159
print frame argument values for scalars only . . . 160
print list of auto-loaded canned sequencesof commands scripts . . . . . . . . . . . . . . . . . . . . . . . . 399
print list of auto-loaded Guile scripts . . . . . . . . . . 570
print list of auto-loaded Python scripts . . . . . . . . 513
print messages on inferior start and exit . . . . . . . . 45
print messages on thread start and exit . . . . . . . . . 51
print messages when symbols are loaded . . . . . . . 273
print settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
print structures in indented form . . . . . . . . . . . . . . 165

Concept Index

print/don’t print memory addresses . . . . . . . . . . . 157
printing byte arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
printing data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
printing frame argument values . . . . . . . . . . . . . . . 160
printing frame information . . . . . . . . . . . . . . . . . . . . 163
printing memory tag violation information . . . . 164
printing nested structures . . . . . . . . . . . . . . . . . . . . . 164
printing strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
probe static tracepoint marker . . . . . . . . . . . . . . . . 205
probing markers, static tracepoints . . . . . . . . . . . . 203
process detailed status information . . . . . . . . . . . . 339
process ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
process info via /proc. . . . . . . . . . . . . . . . . . . . . . . . . 337
process record and replay . . . . . . . . . . . . . . . . . . . . . 103
process status register. . . . . . . . . . . . . . . . . . . . . . . . . 179
processes, multiple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
procfs API calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
profiling GDB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766
program counter register . . . . . . . . . . . . . . . . . . . . . . 179
program entry point . . . . . . . . . . . . . . . . . . . . . . . . . . 116
programming in guile . . . . . . . . . . . . . . . . . . . . . . . . . 520
programming in python . . . . . . . . . . . . . . . . . . . . . . . 403
progspaces in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
progspaces in python . . . . . . . . . . . . . . . . . . . . . . . . . 474
prologue-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
protocol basics, file-i/o . . . . . . . . . . . . . . . . . . . . . . . . 830
protocol, gdb remote serial . . . . . . . . . . . . . . . . . . . 773
protocol-specific representation ofdatatypes, in file-i/o protocol . . . . . . . . . . . . . . . 838
python api . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
Python architectures . . . . . . . . . . . . . . . . . . . . . . . . . . 497
Python auto-loading . . . . . . . . . . . . . . . . . . . . . . . . . . 513
python commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
python commands, CLI . . . . . . . . . . . . . . . . . . . . . . . 463
python commands, GDB/MI . . . . . . . . . . . . . . . . . . 467
python convenience functions . . . . . . . . . . . . . . . . . 473
python directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
python exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
python finish breakpoints . . . . . . . . . . . . . . . . . . . . . 496
python functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
python instruction disassembly . . . . . . . . . . . . . . . . 502
python module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
python modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
python notifications, GDB/MI . . . . . . . . . . . . . . . . 469
python pagination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
python parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
python pretty printing api . . . . . . . . . . . . . . . . . . . . 424
python scripting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
python stdout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
Python TUI Windows . . . . . . . . . . . . . . . . . . . . . . . . 501
python, handle missing debug information . . . . . 511
Python, working with types . . . . . . . . . . . . . . . . . . . 418
python, working with values from inferior . . . . . 411

929

Q‘q’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779‘Q’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779‘QAllow’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789‘qAttached’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814‘qC’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790‘QCatchSyscalls’ packet . . . . . . . . . . . . . . . . . . . . . . 796‘qCRC’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790‘QDisableRandomization’ packet . . . . . . . . . . . . . . 790‘QEnvironmentHexEncoded’ packet . . . . . . . . . . . . . 791‘QEnvironmentReset’ packet . . . . . . . . . . . . . . . . . . 792‘QEnvironmentUnset’ packet . . . . . . . . . . . . . . . . . . 791‘qfThreadInfo’ packet . . . . . . . . . . . . . . . . . . . . . . . . 792‘qGetTIBAddr’ packet . . . . . . . . . . . . . . . . . . . . . . . . . 793‘qGetTLSAddr’ packet . . . . . . . . . . . . . . . . . . . . . . . . . 793‘qIsAddressTagged’ packet . . . . . . . . . . . . . . . . . . . . 794‘QMemTags’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794‘qMemTags’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794‘QNonStop’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795‘qOffsets’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795‘qP’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795‘QPassSignals’ packet . . . . . . . . . . . . . . . . . . . . . . . . 796‘QProgramSignals’ packet . . . . . . . . . . . . . . . . . . . . . 797‘qRcmd’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 798‘qSearch memory’ packet . . . . . . . . . . . . . . . . . . . . . . 799‘qSearch:memory’ packet . . . . . . . . . . . . . . . . . . . . . . 799‘QSetWorkingDir’ packet . . . . . . . . . . . . . . . . . . . . . . 792‘QStartNoAckMode’ packet . . . . . . . . . . . . . . . . . . . . . 799‘QStartupWithShell’ packet . . . . . . . . . . . . . . . . . . 790‘qsThreadInfo’ packet . . . . . . . . . . . . . . . . . . . . . . . . 792‘qSupported’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . 799‘qSymbol’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 808‘qTBuffer’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823‘QTBuffer size’ packet . . . . . . . . . . . . . . . . . . . . . . . 823‘QTDisable’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820‘QTDisconnected’ packet . . . . . . . . . . . . . . . . . . . . . . 820‘QTDP’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817‘QTDPsrc’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818‘QTDV’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818‘QTEnable’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820‘qTfP’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘QTFrame’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819‘qTfSTM’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘qTfV’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘QThreadEvents’ packet . . . . . . . . . . . . . . . . . . . . . . . 797‘qThreadExtraInfo’ packet . . . . . . . . . . . . . . . . . . . . 809‘QThreadOptions’ packet . . . . . . . . . . . . . . . . . . . . . . 797‘QTinit’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820‘qTMinFTPILen’ packet . . . . . . . . . . . . . . . . . . . . . . . . 819‘QTNotes’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823‘qTP’ packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821‘QTro’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820‘QTSave’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘qTsP’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘qTsSTM’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘QTStart’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 819‘qTStatus’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820‘qTSTMat’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822

930‘QTStop’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 820‘qTsV’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 822‘qTV’ packet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821
qualified thread ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
query attached, remote request . . . . . . . . . . . . . . . . 814
quotes in commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
quoting Ada internal identifiers . . . . . . . . . . . . . . . 253
quoting names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263‘qXfer’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 810

R‘r’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779‘R’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779
range checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
range stepping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
ranged breakpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
ranges of breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Ravenscar Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
Ravenscar thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
raw printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
read special object, remote request . . . . . . . . . . . . 810
read, file-i/o system call. . . . . . . . . . . . . . . . . . . . . . . 834
read-only sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
reading symbols from relocatable object files . . 293
reading symbols immediately . . . . . . . . . . . . . . . . . . 292
readline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
Readline application name . . . . . . . . . . . . . . . . . . . . 368
receive rights, gnu Hurd . . . . . . . . . . . . . . . . . . . . . . 346
recent tracepoint number . . . . . . . . . . . . . . . . . . . . . 206
record aggregates (Ada). . . . . . . . . . . . . . . . . . . . . . . 251
record mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record serial communications on file . . . . . . . . . . . 327
recording a session script . . . . . . . . . . . . . . . . . . . . . . 710
recording inferior’s execution
and replaying it . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
recordings in python . . . . . . . . . . . . . . . . . . . . . . . . . . 459
redirection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
reference card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743
reference declarations . . . . . . . . . . . . . . . . . . . . . . . . . 234
register cache, flushing . . . . . . . . . . . . . . . . . . . . . . . . 763
register packet format, MIPS . . . . . . . . . . . . . . . . . . 816
registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Registers In Python. . . . . . . . . . . . . . . . . . . . . . . . . . . 498
regular expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
reloading the overlay table . . . . . . . . . . . . . . . . . . . . 223
relocatable object files, reading
symbols from . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
remote async notification debugging info . . . . . . 386
remote connection commands . . . . . . . . . . . . . . . . . 317
remote connection without stubs . . . . . . . . . . . . . . 320
remote debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
remote debugging, connecting . . . . . . . . . . . . . . . . . 315
remote debugging, detach and program exit . . . 315
remote debugging, symbol files . . . . . . . . . . . . . . . . 316
remote debugging, types of connections . . . . . . . 315
remote memory comparison . . . . . . . . . . . . . . . . . . . 154
remote packets, enabling and disabling . . . . . . . . 329

Debugging with gdb

remote packets, standard replies. . . . . . . . . . . . . . . 774
remote programs, interrupting . . . . . . . . . . . . . . . . 319
remote protocol debugging . . . . . . . . . . . . . . . . . . . . 386
remote protocol, binary data . . . . . . . . . . . . . . . . . . 773
remote protocol, field separator . . . . . . . . . . . . . . . 773
remote query requests. . . . . . . . . . . . . . . . . . . . . . . . . 789
remote serial debugging summary . . . . . . . . . . . . . 336
remote serial debugging, overview . . . . . . . . . . . . . 333
remote serial protocol . . . . . . . . . . . . . . . . . . . . . . . . . 773
remote serial stub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
remote serial stub list . . . . . . . . . . . . . . . . . . . . . . . . . 333
remote serial stub, initialization . . . . . . . . . . . . . . . 334
remote serial stub, main routine . . . . . . . . . . . . . . . 334
remote stub, example . . . . . . . . . . . . . . . . . . . . . . . . . 333
remote stub, support routines . . . . . . . . . . . . . . . . . 334
remote target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
remote target, file transfer . . . . . . . . . . . . . . . . . . . . 320
remote target, limit break- and watchpoints . . . 327
remote target, limit watchpoints length . . . . . . . 327
remote timeout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
remove actions from a tracepoint . . . . . . . . . . . . . . 208
remove duplicate history . . . . . . . . . . . . . . . . . . . . . . 369
rename, file-i/o system call . . . . . . . . . . . . . . . . . . . . 835
Renesas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
repeated array elements . . . . . . . . . . . . . . . . . . . . . . . 163
repeating command sequences . . . . . . . . . . . . . . . . . . 23
repeating commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
replay log events, remote reply . . . . . . . . . . . . . . . . 786
replay mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
reporting bugs in gdb. . . . . . . . . . . . . . . . . . . . . . . . . 709
reprint the last value . . . . . . . . . . . . . . . . . . . . . 143, 286
reset environment, remote request . . . . . . . . . . . . . 792
resolution of location spec. . . . . . . . . . . . . . . . . . . . . 126
resources used by commands . . . . . . . . . . . . . . . . . . 768
response time, MIPS debugging . . . . . . . . . . . . . . . 359
restart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
restore data from a file . . . . . . . . . . . . . . . . . . . . . . . . 185
restrictions on Go expressions . . . . . . . . . . . . . . . . . 238
result records in gdb/mi . . . . . . . . . . . . . . . . . . . . . . 597
resume threads of multiple processes
simultaneously . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
resuming execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
returning from a function . . . . . . . . . . . . . . . . . . . . . 280
reverse execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
rewind program state . . . . . . . . . . . . . . . . . . . . . . . . . . 54
run to first instruction . . . . . . . . . . . . . . . . . . . . . . . . . 35
run to main procedure . . . . . . . . . . . . . . . . . . . . . . . . . 35
run until specified location . . . . . . . . . . . . . . . . . . . . . 85
running . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
running programs backward . . . . . . . . . . . . . . . . . . . 101

Concept Index

S‘s’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779‘S’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779
S12Z support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
save breakpoints to a file for future sessions . . . . 81
save command history . . . . . . . . . . . . . . . . . . . . . . . . 368
save gdb output to a file . . . . . . . . . . . . . . . . . . . . . . . 21
save tracepoints for future sessions . . . . . . . . . . . . 218
Scalable Matrix Extension . . . . . . . . . . . . . . . . . . . . 355
Scalable Matrix Extension 2 . . . . . . . . . . . . . . . . . . 357
scheduler locking mode . . . . . . . . . . . . . . . . . . . . . . . . . 93
scheduler-locking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
screen size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
scripting commands . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
scripting with guile . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
scripting with python . . . . . . . . . . . . . . . . . . . . . . . . . 401
search for a thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
search order for disassembler in Python . . . . . . . 509
search path for libthread_db . . . . . . . . . . . . . . . . . . 51
searching memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
searching memory, in remote debugging . . . . . . . 799
searching source files . . . . . . . . . . . . . . . . . . . . . . . . . . 131
section offsets, remote request . . . . . . . . . . . . . . . . . 795
segment descriptor tables . . . . . . . . . . . . . . . . . . . . . 340
select Ctrl-C, BREAK or BREAK-g . . . . . . . . . . . 328
select trace snapshot . . . . . . . . . . . . . . . . . . . . . . . . . . 215
selected frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
selecting guile pretty-printers . . . . . . . . . . . . . . . . . 539
selecting python pretty-printers . . . . . . . . . . . . . . . 426
self tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765
semaphores on static probe points . . . . . . . . . . . . . . 81
send command to remote monitor . . . . . . . . . . . . . 320
send command to simulator . . . . . . . . . . . . . . . . . . . 348
send interrupt-sequence on start . . . . . . . . . . . . . . 328
send rights, gnu Hurd . . . . . . . . . . . . . . . . . . . . . . . . 346
send the output of a gdb command toa shell command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
sending files to remote systems . . . . . . . . . . . . . . . . 320
separate debug sections . . . . . . . . . . . . . . . . . . . . . . . 304
separate debugging information files . . . . . . . . . . . 300
sequence-id, for gdb remote . . . . . . . . . . . . . . . . . . . 773
serial connections, debugging . . . . . . . . . . . . . . . . . . 386
serial line, target remote . . . . . . . . . . . . . . . . . . . . . 317
serial protocol, gdb remote . . . . . . . . . . . . . . . . . . . 773
server prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
server, command prefix . . . . . . . . . . . . . . . . . . . . . . 368
set ABI for MIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
set breakpoints in many functions . . . . . . . . . . . . . . 61
set breakpoints on all functions . . . . . . . . . . . . . . . . 61
set environment variable, remote request . . . . . . 791
set exec-file-mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . 41
set fast tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
set inferior controlling terminal . . . . . . . . . . . . . . . . . 41
set static tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
set tdesc filename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859
set tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
set working directory, remote request . . . . . . . . . . 792

931

setting variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
setting watchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
sh-stub.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
shared libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
shared library events, remote reply . . . . . . . . . . . . 786
shell command, exit code . . . . . . . . . . . . . . . . . . . . . 174
shell command, exit signal . . . . . . . . . . . . . . . . . . . . 174
shell escape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
show all convenience functions . . . . . . . . . . . . . . . . 178
show all user variables and functions . . . . . . . . . . 171
show exec-file-mismatch . . . . . . . . . . . . . . . . . . . . . . . . 42
show inferior’s working directory . . . . . . . . . . . . . . . 40
show last commands . . . . . . . . . . . . . . . . . . . . . . . . . . 370
show screen characteristics . . . . . . . . . . . . . . . . . . . . 769
show tdesc filename . . . . . . . . . . . . . . . . . . . . . . . . . . . 859
SH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
signals the inferior may see, remote request . . . . 797
SIGQUIT signal, dump core of gdb . . . . . . . . . . . . . 758
SingleKey keymap name . . . . . . . . . . . . . . . . . . . . . . 582
size of remote memory accesses . . . . . . . . . . . . . . . 778
size of screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
skipping over files via glob-style patterns . . . . . . . 88
skipping over functions and files . . . . . . . . . . . . . . . . 87
skipping over functions via
regular expressions. . . . . . . . . . . . . . . . . . . . . . . . . . . 88
SME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
SME2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
snapshot of a process . . . . . . . . . . . . . . . . . . . . . . . . . . 54
software watchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
source code, caching . . . . . . . . . . . . . . . . . . . . . . . . . . 764
source code, disable access . . . . . . . . . . . . . . . . . . . . 140
source file and line of a symbol . . . . . . . . . . . . . . . . 158
source line and its code address . . . . . . . . . . . . . . . 135
source location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
source path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Sparc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
sparc-stub.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
Sparc64 support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
sparcl-stub.c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
SparcLite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
Special Fortran commands . . . . . . . . . . . . . . . . . . . . 242
specifying location . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
SSE registers (x86) . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
stack frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
stack on Alpha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
stack on MIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
stack pointer register . . . . . . . . . . . . . . . . . . . . . . . . . 179
stacking targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
standard registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
standard responses for remote packets . . . . . . . . . 774
start a new independent interpreter . . . . . . . . . . . 577
start a new trace experiment . . . . . . . . . . . . . . . . . . 212
starting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
startup code, and backtrace . . . . . . . . . . . . . . . . . . . 116
startup with shell, remote request . . . . . . . . . . . . . 790
stat, file-i/o system call . . . . . . . . . . . . . . . . . . . . . . . 836

932

static members of C++ objects . . . . . . . . . . . . . . . . 167
static members of Pascal objects . . . . . . . . . . . . . . 167
static probe point, DTrace . . . . . . . . . . . . . . . . . . . . . 81
static probe point, SystemTap. . . . . . . . . . . . . . . . . . 81
static tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
static tracepoints, in remote protocol . . . . . . . . . . 807
static tracepoints, setting . . . . . . . . . . . . . . . . . . . . . 205
status of trace data collection . . . . . . . . . . . . . . . . . 212
status output in gdb/mi . . . . . . . . . . . . . . . . . . . . . . 595
stepping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
stepping and signal handlers . . . . . . . . . . . . . . . . . . . 91
stepping into functions with no line info . . . . . . . . 85
stop a running trace experiment. . . . . . . . . . . . . . . 212
stop on C++ exceptions. . . . . . . . . . . . . . . . . . . . . . . . . 69
stop reply packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
stopped threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
store memory tags . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794
stream records in gdb/mi . . . . . . . . . . . . . . . . . . . . . 597
string tracing, in remote protocol . . . . . . . . . . . . . 807
struct gdb_reader_funcs . . . . . . . . . . . . . . . . . . . . 703
struct gdb_symbol_callbacks . . . . . . . . . . . . . . . . 703
struct gdb_unwind_callbacks . . . . . . . . . . . . . . . . 703
struct return convention . . . . . . . . . . . . . . . . . . . . . . 358
struct stat, in file-i/o protocol . . . . . . . . . . . . . . . . . 839
struct timeval, in file-i/o protocol . . . . . . . . . . . . . 839
struct/union returned in registers . . . . . . . . . . . . . 358
structure field name completion . . . . . . . . . . . . . . . . 26
stub example, remote debugging . . . . . . . . . . . . . . 333
stupid questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
styling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
Super-H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
supported gdb/mi features, list . . . . . . . . . . . . . . . 684
supported packets, remote query . . . . . . . . . . . . . . 799
svg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
svl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
svq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
switching threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
switching threads automatically . . . . . . . . . . . . . . . . 93
symbol cache size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
symbol cache, flushing . . . . . . . . . . . . . . . . . . . . . . . . 275
symbol cache, printing its contents . . . . . . . . . . . . 275
symbol cache, printing usage statistics. . . . . . . . . 275
symbol decoding style, C++ . . . . . . . . . . . . . . . . . . . 166
symbol dump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
symbol file functions . . . . . . . . . . . . . . . . . . . . . . . . . . 387
symbol files, remote debugging . . . . . . . . . . . . . . . . 316
symbol from address . . . . . . . . . . . . . . . . . . . . . . . . . . 264
symbol lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
symbol lookup, remote request . . . . . . . . . . . . . . . . 808
symbol names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
symbol table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
symbol table creation . . . . . . . . . . . . . . . . . . . . . . . . . 387
symbol tables in guile . . . . . . . . . . . . . . . . . . . . . . . . . 558
symbol tables in python. . . . . . . . . . . . . . . . . . . . . . . 489
symbol tables, listing gdb’s internal . . . . . . . . . . . 273
symbol, source file and line. . . . . . . . . . . . . . . . . . . . 158
symbols in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
symbols in python . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

Debugging with gdb

symbols, never read . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
symbols, reading fromrelocatable object files . . . . . . . . . . . . . . . . . . . . . . 293
symbols, reading immediately . . . . . . . . . . . . . . . . . 292
Synopsys ARC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
syscall DSO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
system calls and thread breakpoints . . . . . . . . . . . . 97
system root, alternate . . . . . . . . . . . . . . . . . . . . . . . . . 297
system, file-i/o system call . . . . . . . . . . . . . . . . . . . . 837
system-wide configuration scripts. . . . . . . . . . . . . . 754
system-wide init file. . . . . . . . . . . . . . . . . . . . . . . . . . . 753

T‘t’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 780‘T’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 780‘T’ packet reply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785
tail call frames, debugging . . . . . . . . . . . . . . . . . . . . 196
target architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
target byte order. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
target character set . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
target debugging info . . . . . . . . . . . . . . . . . . . . . . . . . 387
target descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859
target descriptions, AArch64 features . . . . . . . . . 865
target descriptions, ARC Features . . . . . . . . . . . . . 869
target descriptions, ARM features . . . . . . . . . . . . . 869
target descriptions, enum types . . . . . . . . . . . . . . . 864
target descriptions, i386 features . . . . . . . . . . . . . . 873
target descriptions, inclusion . . . . . . . . . . . . . . . . . . 860
target descriptions, LoongArch Features . . . . . . . 874
target descriptions, M68K features . . . . . . . . . . . . 875
target descriptions, MicroBlaze features . . . . . . . 874
target descriptions, MIPS features . . . . . . . . . . . . . 874
target descriptions, NDS32 features . . . . . . . . . . . 875
target descriptions, Nios II features . . . . . . . . . . . 875
target descriptions, OpenRISC 1000 features . . 875
target descriptions, PowerPC features . . . . . . . . . 875
target descriptions, predefined types. . . . . . . . . . . 863
target descriptions, RISC-V Features . . . . . . . . . . 877
target descriptions, RX Features . . . . . . . . . . . . . . 877
target descriptions, S/390 features . . . . . . . . . . . . 877
target descriptions, sparc32 features . . . . . . . . . . . 878
target descriptions, sparc64 features . . . . . . . . . . . 878
target descriptions, standard features. . . . . . . . . . 865
target descriptions, System z features . . . . . . . . . 877
target descriptions, TIC6x features . . . . . . . . . . . . 878
target descriptions, TMS320C6x features . . . . . . 878
target descriptions, XML format . . . . . . . . . . . . . . 859
target memory comparison . . . . . . . . . . . . . . . . . . . . 154
target output in gdb/mi . . . . . . . . . . . . . . . . . . . . . . 595
target stack description . . . . . . . . . . . . . . . . . . . . . . . 764
target-assisted range stepping . . . . . . . . . . . . . . . . . . 87
task attributes (gnu Hurd) . . . . . . . . . . . . . . . . . . . 346
task breakpoints, in Ada . . . . . . . . . . . . . . . . . . . . . . 258
task exception port, gnu Hurd . . . . . . . . . . . . . . . . 346
task suspend count . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
task switching with program using
Ravenscar Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . 259

Concept Index

TCP port, target remote . . . . . . . . . . . . . . . . . . . . . 318

temporarily change settings . . . . . . . . . . . . . . . . . . . . 24
terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Text User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
thread attributes info, remote request . . . . . . . . . 809
thread breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
thread breakpoints and system calls . . . . . . . . . . . . 97
thread clone events, remote reply . . . . . . . . . . . . . 787
thread create event, remote reply . . . . . . . . . . . . . 787
thread create/exit events, remote request . . . . . . 797
thread default settings, gnu Hurd . . . . . . . . . . . . . 347
thread exit event, remote reply . . . . . . . . . . . . . . . . 788
thread ID lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
thread identifier (GDB) . . . . . . . . . . . . . . . . . . . . . . . . 47
thread identifier (system) . . . . . . . . . . . . . . . . . . . . . . 47
thread info (Solaris). . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
thread information, remote request . . . . . . . . . . . . 795
thread list format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
thread number, per inferior . . . . . . . . . . . . . . . . . . . . 47
thread options, remote request . . . . . . . . . . . . . . . . 797
thread properties, gnu Hurd . . . . . . . . . . . . . . . . . . 346
thread suspend count, gnu Hurd . . . . . . . . . . . . . . 347
thread-id, in remote protocol . . . . . . . . . . . . . . . . . . 775
threads and watchpoints . . . . . . . . . . . . . . . . . . . . . . . 68
threads in python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
threads of execution. . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
threads, automatic switching . . . . . . . . . . . . . . . . . . . 93
threads, continuing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
threads, stopped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
time of command execution . . . . . . . . . . . . . . . . . . . 769
timeout for called functions . . . . . . . . . . . . . . 283, 284
timeout for commands . . . . . . . . . . . . . . . . . . . . . . . . 771
timeout for serial communications . . . . . . . . . . . . . 327
timeout, for remote target connection . . . . . . . . . 328
timestamping debugging info . . . . . . . . . . . . . . . . . . 388
trace experiment, status of . . . . . . . . . . . . . . . . . . . . 212
trace file format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 881
trace files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
trace state variable value, remote request . . . . . . 821
trace state variables. . . . . . . . . . . . . . . . . . . . . . . . . . . 207
traceback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
traceframe info format . . . . . . . . . . . . . . . . . . . . . . . . 845
tracepoint actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
tracepoint conditions. . . . . . . . . . . . . . . . . . . . . . . . . . 207
tracepoint data, display . . . . . . . . . . . . . . . . . . . . . . . 217
tracepoint deletion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
tracepoint number . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
tracepoint packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817
tracepoint pass count . . . . . . . . . . . . . . . . . . . . . . . . . 206
tracepoint restrictions . . . . . . . . . . . . . . . . . . . . . . . . . 214
tracepoint status, remote request . . . . . . . . . . . . . . 821
tracepoint variables . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
tracepoints support in gdbserver . . . . . . . . . . . . . 325
trailing underscore, in Fortran symbols . . . . . . . . 240translating between character sets . . . . . . . . . . . . . 187
TUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
TUI commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

933

TUI configuration variables . . . . . . . . . . . . . . . . . . . 585
TUI key bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
TUI mouse support . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
TUI single key mode . . . . . . . . . . . . . . . . . . . . . . . . . . 581
type casting memory . . . . . . . . . . . . . . . . . . . . . . . . . . 145
type chain of a data type . . . . . . . . . . . . . . . . . . . . . 764
type checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
type conversions in C++ . . . . . . . . . . . . . . . . . . . . . . . 234
type printer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
type printing API for Python . . . . . . . . . . . . . . . . . 429
types in guile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
types in Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

U
UDP port, target remote . . . . . . . . . . . . . . . . . . . . . 319

union field name completion. . . . . . . . . . . . . . . . . . . . 26
unions in structures, printing. . . . . . . . . . . . . . . . . . 166
Unix domain socket . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
unknown address, locating . . . . . . . . . . . . . . . . . . . . 151
unknown type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
unlink, file-i/o system call . . . . . . . . . . . . . . . . . . . . . 836
unlinked object files . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
unload symbols from shared libraries . . . . . . . . . . 297
unmap an overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
unmapped overlays . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
unset environment variable, remote request . . . . 791
unset tdesc filename . . . . . . . . . . . . . . . . . . . . . . . . . . 859
unsupported languages . . . . . . . . . . . . . . . . . . . . . . . . 261
unsupported packets, empty response for . . . . . . 774
unwind stack in called functions . . . . . . . . . . . . . . . 281
unwind stack in called functions
when timing out . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
unwind stack in called functions withunhandled exceptions . . . . . . . . . . . . . . . . . . . . . . . 282
unwinding frames in Python . . . . . . . . . . . . . . . . . . 439
use only software watchpoints . . . . . . . . . . . . . . . . . . 67
user registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
user-defined command . . . . . . . . . . . . . . . . . . . . . . . . 391
user-defined macros . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
user-defined variables . . . . . . . . . . . . . . . . . . . . . . . . . 171

Vvalue history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
values from inferior, in guile. . . . . . . . . . . . . . . . . . . 525
values from inferior, with Python . . . . . . . . . . . . . 411
variable name conflict . . . . . . . . . . . . . . . . . . . . . . . . . 147
variable object debugging info . . . . . . . . . . . . . . . . . 388
variable objects in gdb/mi . . . . . . . . . . . . . . . . . . . . 640
variable values, wrong . . . . . . . . . . . . . . . . . . . . . . . . 148
variables, readline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 716
variables, setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277‘vAttach’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 780‘vCont’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 780‘vCont?’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781‘vCtrlC’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 781
vector unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

934

vector, auxiliary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
verbose operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
verify remote memory image . . . . . . . . . . . . . . . . . . 154
verify target memory image . . . . . . . . . . . . . . . . . . . 154‘vFile’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782‘vFlashDone’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . 782‘vFlashErase’ packet . . . . . . . . . . . . . . . . . . . . . . . . . 782‘vFlashWrite’ packet . . . . . . . . . . . . . . . . . . . . . . . . . 782
vfork events, remote reply. . . . . . . . . . . . . . . . . . . . . 787
vforkdone events, remote reply . . . . . . . . . . . . . . . . 787
vg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
virtual functions (C++) display . . . . . . . . . . . . . . . . 167‘vKill’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782
vl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354‘vMustReplyEmpty’ packet . . . . . . . . . . . . . . . . . . . . . 783
volatile registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
vq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354‘vRun’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783‘vStopped’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783
VTBL display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Wwatchdog timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771
watchpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
watchpoints and threads . . . . . . . . . . . . . . . . . . . . . . . 68
wavefronts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
where to look for shared libraries . . . . . . . . . . . . . . 297
wild pointer, interpreting . . . . . . . . . . . . . . . . . . . . . 158
Wind River Linux system-wide
configuration script . . . . . . . . . . . . . . . . . . . . . . . . . 754
word completion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
working directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
working directory (of your program) . . . . . . . . . . . . 39
working language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
write data into object, remote request . . . . . . . . . 814
write, file-i/o system call . . . . . . . . . . . . . . . . . . . . . . 834
writing a frame filter . . . . . . . . . . . . . . . . . . . . . . . . . . 435

Debugging with gdb

writing a Guile pretty-printer . . . . . . . . . . . . . . . . . 539
writing a pretty-printer . . . . . . . . . . . . . . . . . . . . . . . 427
writing convenience functions . . . . . . . . . . . . . . . . . 473
writing into corefiles . . . . . . . . . . . . . . . . . . . . . . . . . . 285
writing into executables . . . . . . . . . . . . . . . . . . . . . . . 285
writing JIT debug info readers . . . . . . . . . . . . . . . . 703
writing xmethods in Python . . . . . . . . . . . . . . . . . . 446
wrong values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

X
x command, default address . . . . . . . . . . . . . . . . . . . 136‘X’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783
Xilinx MicroBlaze . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
XInclude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860
XMD, Xilinx Microprocessor Debugger . . . . . . . . 350
xmethod API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
xmethods in Python . . . . . . . . . . . . . . . . . . . . . . . . . . 443
XML parser debugging . . . . . . . . . . . . . . . . . . . . . . . . 388

Yyanking text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714

Z‘z’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783‘z0’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783‘z1’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784‘z2’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785‘z3’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785‘z4’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785‘Z’ packets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783‘Z0’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783‘Z1’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 784‘Z2’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785‘Z3’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785‘Z4’ packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785

935

Command, Variable, and Function Index!
! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20#

$trace_file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218$trace_frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218$trace_func . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218$trace_line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218$tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218# (a comment) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23–$$_, convenience variable . . . . . . . . . . . . . . . . . . . . . . . 172$__, convenience variable . . . . . . . . . . . . . . . . . . . . . 172$_ada_exception, convenience variable . . . . . . . . . 70$_any_caller_is, convenience function . . . . . . . 178$_any_caller_matches,
convenience function . . . . . . . . . . . . . . . . . . . . . . . . 178$_as_string, convenience function . . . . . . . . . . . . 178$_caller_is, convenience function . . . . . . . . . . . . 177$_caller_matches, convenience function . . . . . . 178$_cimag, convenience function . . . . . . . . . . . . . . . . 178$_creal, convenience function . . . . . . . . . . . . . . . . 178$_exception, convenience variable . . . . . . . . . . . . . 69$_exitcode, convenience variable . . . . . . . . . . . . . 172$_exitsignal, convenience variable . . . . . . . . . . . 172$_gdb_maint_setting, convenience function . . . 176$_gdb_maint_setting_str,
convenience function . . . . . . . . . . . . . . . . . . . . . . . . 176$_gdb_major, convenience variable . . . . . . . . . . . . 174$_gdb_minor, convenience variable . . . . . . . . . . . . 174$_gdb_setting, convenience function . . . . . . . . . . 175$_gdb_setting_str, convenience function . . . . . 175$_gthread, convenience variable . . . . . . . . . . . . . . . . 48$_hit_bpnum, convenience variable . . . . . . . . . . . . . 58$_hit_locno, convenience variable . . . . . . . . . . . . . 58$_inferior, convenience variable. . . . . . . . . . . . . . . 44$_inferior_thread_count,convenience variable . . . . . . . . . . . . . . . . . . . . . . . . . 48$_isvoid, convenience function . . . . . . . . . . . . . . . 174$_memeq, convenience function . . . . . . . . . . . . . . . . 177$_probe_arg, convenience variable . . . . . . . . . . . . . 82$_regex, convenience function . . . . . . . . . . . . . . . . 177$_sdata, collect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209$_sdata, inspect, convenience variable. . . . . . . . . 173$_shell, convenience function . . . . . . . . . . . . . . . . 176$_shell_exitcode, convenience variable. . . . . . . 174$_shell_exitsignal, convenience variable . . . . 174$_siginfo, convenience variable. . . . . . . . . . . . . . . 173$_streq, convenience function . . . . . . . . . . . . . . . . 177$_strlen, convenience function . . . . . . . . . . . . . . . 177$_thread, convenience variable . . . . . . . . . . . . . . . . . 48$_tlb, convenience variable . . . . . . . . . . . . . . . . . . . 173$bpnum, convenience variable . . . . . . . . . . . . . . . . . . . 58
$cdir, convenience variable . . . . . . . . . . . . . . . . . . . 132$cwd, convenience variable . . . . . . . . . . . . . . . . . . . . 132$tpnum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206-ada-task-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626-add-inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 690-break-after . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607-break-commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608-break-condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 608-break-delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609-break-disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609-break-enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610-break-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 610-break-insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611-break-list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614-break-passcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615-break-watch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615-catch-assert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618-catch-catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621-catch-exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619-catch-handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619-catch-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 617-catch-rethrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621-catch-throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620-catch-unload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618-complete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693-data-disassemble . . . . . . . . . . . . . . . . . . . . . . . . . . . 651-data-evaluate-expression. . . . . . . . . . . . . . . . . . 654-data-list-changed-registers . . . . . . . . . . . . . . 655-data-list-register-names. . . . . . . . . . . . . . . . . . 655-data-list-register-values . . . . . . . . . . . . . . . . 656-data-read-memory . . . . . . . . . . . . . . . . . . . . . . . . . . . 657-data-read-memory-bytes . . . . . . . . . . . . . . . . . . . . 659-data-write-memory-bytes . . . . . . . . . . . . . . . . . . . 660-dprintf-insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613-enable-frame-filters . . . . . . . . . . . . . . . . . . . . . . 634-enable-pretty-printing . . . . . . . . . . . . . . . . . . . . 642-enable-timings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692-environment-cd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622-environment-directory . . . . . . . . . . . . . . . . . . . . . 623-environment-path . . . . . . . . . . . . . . . . . . . . . . . . . . . 623-environment-pwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624-exec-arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622-exec-continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627-exec-finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628-exec-interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629-exec-jump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629-exec-next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 630-exec-next-instruction . . . . . . . . . . . . . . . . . . . . . 630-exec-return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631

936-exec-run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 631-exec-step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632-exec-step-instruction . . . . . . . . . . . . . . . . . . . . . 633-exec-until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634-file-exec-and-symbols . . . . . . . . . . . . . . . . . . . . . 674-file-exec-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675-file-list-exec-source-file . . . . . . . . . . . . . . . 675-file-list-exec-source-files . . . . . . . . . . . . . . 675-file-list-shared-libraries . . . . . . . . . . . . . . . 678-file-symbol-file . . . . . . . . . . . . . . . . . . . . . . . . . . . 678-gdb-exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686-gdb-set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686-gdb-show . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 686-gdb-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687-inferior-tty-set . . . . . . . . . . . . . . . . . . . . . . . . . . . 691-inferior-tty-show . . . . . . . . . . . . . . . . . . . . . . . . . . 692-info-ada-exceptions . . . . . . . . . . . . . . . . . . . . . . . 683-info-gdb-mi-command . . . . . . . . . . . . . . . . . . . . . . . 684-info-os . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 689-interpreter-exec . . . . . . . . . . . . . . . . . . . . . . . . . . . 691-list-features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684-list-target-features . . . . . . . . . . . . . . . . . . . . . . 685-list-thread-groups . . . . . . . . . . . . . . . . . . . . . . . . 687-remove-inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691-stack-info-depth . . . . . . . . . . . . . . . . . . . . . . . . . . . 635-stack-info-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . 634-stack-list-arguments . . . . . . . . . . . . . . . . . . . . . . 635-stack-list-frames . . . . . . . . . . . . . . . . . . . . . . . . . . 637-stack-list-locals . . . . . . . . . . . . . . . . . . . . . . . . . . 639-stack-list-variables . . . . . . . . . . . . . . . . . . . . . . 639-stack-select-frame . . . . . . . . . . . . . . . . . . . . . . . . 640-symbol-info-functions . . . . . . . . . . . . . . . . . . . . . 666-symbol-info-module-functions . . . . . . . . . . . . . 668-symbol-info-module-variables . . . . . . . . . . . . . 669-symbol-info-modules . . . . . . . . . . . . . . . . . . . . . . . 670-symbol-info-types . . . . . . . . . . . . . . . . . . . . . . . . . . 671-symbol-info-variables . . . . . . . . . . . . . . . . . . . . . 672-symbol-list-lines . . . . . . . . . . . . . . . . . . . . . . . . . . 674-target-attach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678-target-detach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679-target-disconnect . . . . . . . . . . . . . . . . . . . . . . . . . . 679-target-download . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679-target-file-delete . . . . . . . . . . . . . . . . . . . . . . . . 683-target-file-get . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682-target-file-put . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682-target-flash-erase . . . . . . . . . . . . . . . . . . . . . . . . 681-target-select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681-thread-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624-thread-list-ids . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625-thread-select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625-trace-define-variable . . . . . . . . . . . . . . . . . . . . . 661-trace-find . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660-trace-frame-collected . . . . . . . . . . . . . . . . . . . . . 662-trace-list-variables . . . . . . . . . . . . . . . . . . . . . . 663-trace-save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664-trace-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664-trace-status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664-trace-stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665

Debugging with gdb-var-assign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647-var-create . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642-var-delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643-var-evaluate-expression . . . . . . . . . . . . . . . . . . . 647-var-info-expression . . . . . . . . . . . . . . . . . . . . . . . 646-var-info-num-children . . . . . . . . . . . . . . . . . . . . . 644-var-info-path-expression. . . . . . . . . . . . . . . . . . 646-var-info-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646-var-list-children . . . . . . . . . . . . . . . . . . . . . . . . . . 644-var-set-format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643-var-set-frozen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649-var-set-update-range . . . . . . . . . . . . . . . . . . . . . . 649-var-set-visualizer . . . . . . . . . . . . . . . . . . . . . . . . 650-var-show-attributes . . . . . . . . . . . . . . . . . . . . . . . 646-var-show-format . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644-var-update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647:::, in Modula-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249<<gdb:arch> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564<gdb:block> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552<gdb:breakpoint> . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559<gdb:iterator> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568<gdb:lazy-string> . . . . . . . . . . . . . . . . . . . . . . . . . . . 563<gdb:objfile> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549<gdb:progspace> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548<gdb:sal> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558<gdb:symbol> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554<gdb:symtab> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558<gdb:type> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532<gdb:value> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525@@, referencing memory as an array . . . . . . . . . . . . . 149^^connected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597^done. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597^error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597^exit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597^running . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597__init__ on TypePrinter. . . . . . . . . . . . . . . . . . . . . 516|| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Command, Variable, and Function Index

937

A

B

abort (C-g) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
accept-line (Newline or Return) . . . . . . . . . . . . 729
actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
ada-task-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
add-auto-load-safe-path . . . . . . . . . . . . . . . . . . . . 379
add-auto-load-scripts-directory . . . . . . . . . . . 573
add-inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
add-symbol-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
add-symbol-file-from-memory . . . . . . . . . . . . . . . 294
adi assign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
adi examine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
advance locspec. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
alias. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
append . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
append-pretty-printer! . . . . . . . . . . . . . . . . . . . . . 571
apropos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
arch-bool-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-char-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-disassemble . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566
arch-double-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-float-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-int-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-int16-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-int32-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-int64-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-int8-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-long-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-longdouble-type . . . . . . . . . . . . . . . . . . . . . . . 565
arch-longlong-type . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-schar-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-short-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-uchar-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-uint-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-uint16-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-uint32-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-uint64-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-uint8-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-ulong-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-ulonglong-type . . . . . . . . . . . . . . . . . . . . . . . . 565
arch-ushort-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-void-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch-wide-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
arch?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
Architecture.disassemble . . . . . . . . . . . . . . . . . . . 497
Architecture.integer_type. . . . . . . . . . . . . . . . . . 498
Architecture.name . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
Architecture.register_groups . . . . . . . . . . . . . . 498
Architecture.registers . . . . . . . . . . . . . . . . . . . . . 498
attach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
attach& . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
awatch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

b (break) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
backtrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
backward-char (C-b) . . . . . . . . . . . . . . . . . . . . . . . . . 728
backward-delete-char (Rubout) . . . . . . . . . . . . . 731
backward-kill-line (C-x Rubout) . . . . . . . . . . . 732
backward-kill-word (M-DEL) . . . . . . . . . . . . . . . . . 732
backward-word (M-b) . . . . . . . . . . . . . . . . . . . . . . . . . 728
beginning-of-history (M-<) . . . . . . . . . . . . . . . . . 729
beginning-of-line (C-a) . . . . . . . . . . . . . . . . . . . . 728
bell-style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
bfd caching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
bind-tty-special-chars . . . . . . . . . . . . . . . . . . . . . 717
blink-matching-paren . . . . . . . . . . . . . . . . . . . . . . . 717
block-end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-global-block . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-global? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-static-block . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-static? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
block-superblock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
block-symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
block-symbols-progress? . . . . . . . . . . . . . . . . . . . . 554
block-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
Block.end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.global_block . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.is_global . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.is_static . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
Block.start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.static_block . . . . . . . . . . . . . . . . . . . . . . . . . . 484
Block.superblock . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
block? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
BP_ACCESS_WATCHPOINT. . . . . . . . . . . . . . . . . . . 492, 560
BP_BREAKPOINT . . . . . . . . . . . . . . . . . . . . . . . . . . . 492, 560
BP_CATCHPOINT . . . . . . . . . . . . . . . . . . . . . . . . . . . 492, 560
BP_HARDWARE_BREAKPOINT . . . . . . . . . . . . . . . . . . . . . 492
BP_HARDWARE_WATCHPOINT . . . . . . . . . . . . . . . . 492, 560
BP_READ_WATCHPOINT . . . . . . . . . . . . . . . . . . . . . 492, 560
BP_WATCHPOINT . . . . . . . . . . . . . . . . . . . . . . . . . . . 492, 560
bracketed-paste-begin () . . . . . . . . . . . . . . . . . . . 731
break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
break ... inferior inferior-id . . . . . . . . . . . . . . 46
break ... task taskno (Ada) . . . . . . . . . . . . . . . . . 258
break ... thread thread-id . . . . . . . . . . . . . . . . . . . 96
break, and Objective-C . . . . . . . . . . . . . . . . . . . . . . . 238
break-range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
breakpoint annotation. . . . . . . . . . . . . . . . . . . . . . . 698
breakpoint-commands . . . . . . . . . . . . . . . . . . . . . . . . 563
breakpoint-condition . . . . . . . . . . . . . . . . . . . . . . . 562
breakpoint-enabled? . . . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-expression . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-hit-count . . . . . . . . . . . . . . . . . . . . . . . 562
breakpoint-ignore-count . . . . . . . . . . . . . . . . . . . . 562
breakpoint-location . . . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-notifications . . . . . . . . . . . . . . . . . . . 685

938

breakpoint-number . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-silent? . . . . . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
breakpoint-task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
breakpoint-temporary? . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-thread . . . . . . . . . . . . . . . . . . . . . . . . . . . 562
breakpoint-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . 561
breakpoint-visible? . . . . . . . . . . . . . . . . . . . . . . . . 561
Breakpoint.__init__ . . . . . . . . . . . . . . . . . . . . 491, 492
Breakpoint.commands . . . . . . . . . . . . . . . . . . . . . . . . 495
Breakpoint.condition . . . . . . . . . . . . . . . . . . . . . . . 495
Breakpoint.delete . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
Breakpoint.enabled . . . . . . . . . . . . . . . . . . . . . . . . . . 493
Breakpoint.expression . . . . . . . . . . . . . . . . . . . . . . 495
Breakpoint.hit_count . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.ignore_count . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.inferior . . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.is_valid . . . . . . . . . . . . . . . . . . . . . . . . 493
Breakpoint.location . . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.locations . . . . . . . . . . . . . . . . . . . . . . . 495
Breakpoint.number . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.pending . . . . . . . . . . . . . . . . . . . . . . . . . . 493
Breakpoint.silent . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
Breakpoint.stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
Breakpoint.task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.temporary . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.thread . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494
Breakpoint.visible . . . . . . . . . . . . . . . . . . . . . . . . . . 494
breakpoint? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
BreakpointEvent.breakpoint . . . . . . . . . . . . . . . . 453
BreakpointEvent.breakpoints . . . . . . . . . . . . . . . 453
BreakpointLocation.address . . . . . . . . . . . . . . . . 495
BreakpointLocation.enabled . . . . . . . . . . . . . . . . 495
BreakpointLocation.fullname . . . . . . . . . . . . . . . 496
BreakpointLocation.function . . . . . . . . . . . . . . . 496
BreakpointLocation.owner . . . . . . . . . . . . . . . . . . . 496
BreakpointLocation.source. . . . . . . . . . . . . . . . . . 495
BreakpointLocation.thread_groups . . . . . . . . . 496
breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
breakpoints-invalid annotation . . . . . . . . . . . . 697
bt (backtrace) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
builtin_disassemble . . . . . . . . . . . . . . . . . . . . . . . . 510

Cc (continue). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
c (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
C (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
C-L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
C-x 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
C-x 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
C-x a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
C-x A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
C-x C-a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
C-x o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
C-x s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581

Debugging with gdb

call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
call-last-kbd-macro (C-x e) . . . . . . . . . . . . . . . . 734
capitalize-word (M-c). . . . . . . . . . . . . . . . . . . . . . . 731
catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
catch assert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
catch catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
catch exception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
catch exception unhandled . . . . . . . . . . . . . . . . . . . 70
catch exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
catch fork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
catch handlers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
catch load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
catch rethrow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
catch signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
catch syscall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
catch throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
catch unload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
catch vfork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
cd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
cdir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
character-search (C-]) . . . . . . . . . . . . . . . . . . . . . 735
character-search-backward (M-C-]) . . . . . . . . . 735
checkpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
clear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
clear, and Objective-C . . . . . . . . . . . . . . . . . . . . . . . 238
clear-display (M-C-l). . . . . . . . . . . . . . . . . . . . . . . 728
clear-screen (C-l) . . . . . . . . . . . . . . . . . . . . . . . . . . 729
ClearObjFilesEvent.progspace . . . . . . . . . . . . . . 454
clone-inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
collect (tracepoints) . . . . . . . . . . . . . . . . . . . . . . . . . 209
colored-completion-prefix. . . . . . . . . . . . . . . . . . 717
colored-stats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
Command.__init__ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
Command.complete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
Command.dont_repeat . . . . . . . . . . . . . . . . . . . . . . . . 464
Command.invoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
command? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
COMMAND_BREAKPOINTS . . . . . . . . . . . . . . . . . . . . 465, 544
COMMAND_DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465, 543
COMMAND_FILES . . . . . . . . . . . . . . . . . . . . . . . . . . . 465, 544
COMMAND_MAINTENANCE . . . . . . . . . . . . . . . . . . . . 466, 544
COMMAND_NONE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465, 543
COMMAND_OBSCURE . . . . . . . . . . . . . . . . . . . . . . . . 466, 544
COMMAND_RUNNING . . . . . . . . . . . . . . . . . . . . . . . . 465, 543
COMMAND_STACK . . . . . . . . . . . . . . . . . . . . . . . . . . . 465, 544
COMMAND_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . 465, 544
COMMAND_SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . 465, 544
COMMAND_TRACEPOINTS . . . . . . . . . . . . . . . . . . . . 465, 544
COMMAND_TUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
COMMAND_USER . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466, 544
commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
commands annotation . . . . . . . . . . . . . . . . . . . . . . . . . 696
comment-begin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
compare-sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
compile code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
compile file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
complete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
complete (TAB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733

Command, Variable, and Function Index

COMPLETE_COMMAND . . . . . . . . . . . . . . . . . . . . . . . 466, 545
COMPLETE_EXPRESSION . . . . . . . . . . . . . . . . . . . . 466, 545
COMPLETE_FILENAME . . . . . . . . . . . . . . . . . . . . . . 466, 545
COMPLETE_LOCATION . . . . . . . . . . . . . . . . . . . . . . 466, 545
COMPLETE_NONE . . . . . . . . . . . . . . . . . . . . . . . . . . . 466, 544
COMPLETE_SYMBOL . . . . . . . . . . . . . . . . . . . . . . . . 466, 545
completion-display-width . . . . . . . . . . . . . . . . . . . 717
completion-ignore-case . . . . . . . . . . . . . . . . . . . . . 717
completion-map-case . . . . . . . . . . . . . . . . . . . . . . . . 717
completion-prefix-display-length . . . . . . . . . 717
completion-query-items . . . . . . . . . . . . . . . . . . . . . 718
condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
ConnectionEvent.connection . . . . . . . . . . . . . . . . 456
continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
continue& . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
convert-meta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
copy-backward-word (). . . . . . . . . . . . . . . . . . . . . . . 733
copy-forward-word () . . . . . . . . . . . . . . . . . . . . . . . . 733
copy-region-as-kill () . . . . . . . . . . . . . . . . . . . . . 733
core-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
ctf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
Ctrl-o (operate-and-get-next) . . . . . . . . . . . . . . . . . 23
current-arch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564
current-objfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
current-progspace . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
cwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Dd (delete) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
d (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
data-directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
data-disassemble-a-option. . . . . . . . . . . . . . . . . . 685
data-read-memory-bytes . . . . . . . . . . . . . . . . . . . . . 685
default-visualizer . . . . . . . . . . . . . . . . . . . . . . . . . . 538
define . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
define-prefix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
delete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
delete checkpoint checkpoint-id . . . . . . . . . . . . . 55
delete display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
delete mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
delete tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
delete tvariable . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
delete-breakpoint! . . . . . . . . . . . . . . . . . . . . . . . . . . 560
delete-char (C-d) . . . . . . . . . . . . . . . . . . . . . . . . . . . 730
delete-char-or-list () . . . . . . . . . . . . . . . . . . . . . 734
delete-horizontal-space () . . . . . . . . . . . . . . . . . 732
demangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
detach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
detach (remote) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
detach inferiors infno... . . . . . . . . . . . . . . . . . . . 45
digit-argument (M-0, M-1, ... M--) . . . . . . . . . 733
dir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
directory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
dis (disable) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
disable display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
disable frame-filter . . . . . . . . . . . . . . . . . . . . . . . . 122

939

disable mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
disable pretty-printer . . . . . . . . . . . . . . . . . . . . . 169
disable probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
disable tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . 206
disable type-printer . . . . . . . . . . . . . . . . . . . . . . . . 269
disable-completion . . . . . . . . . . . . . . . . . . . . . . . . . . 718
disassemble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
DisassembleInfo.__init__ . . . . . . . . . . . . . . . . . . . 503
DisassembleInfo.address . . . . . . . . . . . . . . . . . . . . 503
DisassembleInfo.address_part . . . . . . . . . . . . . . 504
DisassembleInfo.architecture . . . . . . . . . . . . . . 503
DisassembleInfo.is_valid . . . . . . . . . . . . . . . . . . . 503
DisassembleInfo.progspace. . . . . . . . . . . . . . . . . . 503
DisassembleInfo.read_memory . . . . . . . . . . . . . . . 503
DisassembleInfo.text_part. . . . . . . . . . . . . . . . . . 504
Disassembler.__call__ . . . . . . . . . . . . . . . . . . . . . . 504
Disassembler.__init__ . . . . . . . . . . . . . . . . . . . . . . 504
DisassemblerAddressPart.address . . . . . . . . . . . 507
DisassemblerPart.string . . . . . . . . . . . . . . . . . . . . 506
DisassemblerResult.__init__ . . . . . . . . . . . . . . . 505
DisassemblerResult.length. . . . . . . . . . . . . . . . . . 506
DisassemblerResult.parts . . . . . . . . . . . . . . . . . . . 506
DisassemblerResult.string. . . . . . . . . . . . . . . . . . 506
DisassemblerTextPart.style . . . . . . . . . . . . . . . . 507
disconnect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
do (down) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
do-lowercase-version (M-A,
M-B, M-x, ...) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
dont-repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393, 542
Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
down-silently . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
downcase-word (M-l) . . . . . . . . . . . . . . . . . . . . . . . . . 731
dprintf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
dprintf-style agent . . . . . . . . . . . . . . . . . . . . . . . . . . 80
dprintf-style call . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
dprintf-style gdb . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
dump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
dump-functions () . . . . . . . . . . . . . . . . . . . . . . . . . . . 735
dump-macros () . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736
dump-variables () . . . . . . . . . . . . . . . . . . . . . . . . . . . 735

Ee (edit) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
echo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
echo-control-characters . . . . . . . . . . . . . . . . . . . . 718
edit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
editing-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
else . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396
emacs-editing-mode (C-e) . . . . . . . . . . . . . . . . . . . 736
emacs-mode-string . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
enable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
enable display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
enable frame-filter . . . . . . . . . . . . . . . . . . . . . . . . . 123
enable mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

940

enable pretty-printer. . . . . . . . . . . . . . . . . . . . . . . 169
enable probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
enable tracepoint . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
enable type-printer . . . . . . . . . . . . . . . . . . . . . . . . . 269
enable-bracketed-paste . . . . . . . . . . . . . . . . . . . . . 718
enable-keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
enabled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
enabled of type_printer . . . . . . . . . . . . . . . . . . . . . 429
end (breakpoint commands) . . . . . . . . . . . . . . . . . . . . 78
end (if/else/while commands) . . . . . . . . . . . . . . . . . 396
end (user-defined commands) . . . . . . . . . . . . . . . . . 392
end-kbd-macro (C-x )) . . . . . . . . . . . . . . . . . . . . . . . 734
end-of-file (usually C-d) . . . . . . . . . . . . . . . . . . 730
end-of-history (M->) . . . . . . . . . . . . . . . . . . . . . . . . 729
end-of-iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
end-of-iteration? . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
end-of-line (C-e) . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
error annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
error-begin annotation . . . . . . . . . . . . . . . . . . . . . 697
error-port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398
EventRegistry.connect . . . . . . . . . . . . . . . . . . . . . . 451
EventRegistry.disconnect . . . . . . . . . . . . . . . . . . . 452
exception-args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
exception-key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
exception? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
exceptionHandler . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
exchange-point-and-mark (C-x C-x) . . . . . . . . . 735
exec-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
exec-file-mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
exec-run-start-option . . . . . . . . . . . . . . . . . . . . . . 685
ExecutableChangedEvent.progspace . . . . . . . . . 456
ExecutableChangedEvent.reload . . . . . . . . . . . . . 456
execute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
exit [expression] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
exited annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
ExitedEvent.exit_code . . . . . . . . . . . . . . . . . . . . . . 452
ExitedEvent.inferior . . . . . . . . . . . . . . . . . . . . . . . 452
expand-tilde . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
explore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Ff (frame) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
f (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
F (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
faas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
fg (resume foreground execution) . . . . . . . . . . . . . . 83
field-artificial? . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field-base-class? . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field-bitpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field-bitsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field-enumval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
field? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
fin (finish). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Debugging with gdb

find . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
find-pc-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
finish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
finish& . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
FinishBreakpoint.__init__. . . . . . . . . . . . . . . . . . 496
FinishBreakpoint.out_of_scope . . . . . . . . . . . . . 496
FinishBreakpoint.return_value . . . . . . . . . . . . . 496
flash-erase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
flush_i_cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
flushregs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
fo (forward-search) . . . . . . . . . . . . . . . . . . . . . . . . . 131
focus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
forward-backward-delete-char () . . . . . . . . . . . 731
forward-char (C-f) . . . . . . . . . . . . . . . . . . . . . . . . . . 728
forward-search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
forward-search-history (C-s) . . . . . . . . . . . . . . 729
forward-word (M-f) . . . . . . . . . . . . . . . . . . . . . . . . . . 728
frame address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
frame apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
frame function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
frame level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
frame view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
frame, selecting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
frame-arch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
frame-block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
frame-function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
frame-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
frame-newer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
frame-older . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
frame-pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
frame-read-register . . . . . . . . . . . . . . . . . . . . . . . . 552
frame-read-var . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
frame-sal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
frame-select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
frame-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
frame-unwind-stop-reason . . . . . . . . . . . . . . . . . . . 550
frame-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
Frame.architecture . . . . . . . . . . . . . . . . . . . . . . . . . . 480
Frame.block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Frame.find_sal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Frame.function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Frame.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
Frame.language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
Frame.level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
Frame.name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
Frame.newer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Frame.older . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Frame.pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
Frame.read_register . . . . . . . . . . . . . . . . . . . . . . . . 482
Frame.read_var . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
Frame.select . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
Frame.static_link . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
Frame.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480
Frame.unwind_stop_reason . . . . . . . . . . . . . . . . . . . 480
frame? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550
FrameDecorator.address . . . . . . . . . . . . . . . . . . . . . 433
FrameDecorator.elided . . . . . . . . . . . . . . . . . . . . . . 432
FrameDecorator.filename . . . . . . . . . . . . . . . . . . . . 433

Command, Variable, and Function Index

FrameDecorator.frame_args. . . . . . . . . . . . . . . . . . 433
FrameDecorator.frame_locals . . . . . . . . . . . . . . . 434
FrameDecorator.function . . . . . . . . . . . . . . . . . . . . 433
FrameDecorator.inferior_frame . . . . . . . . . . . . . 435
FrameDecorator.line . . . . . . . . . . . . . . . . . . . . . . . . 433
FrameFilter.enabled . . . . . . . . . . . . . . . . . . . . . . . . 432
FrameFilter.filter . . . . . . . . . . . . . . . . . . . . . . . . . . 431
FrameFilter.name . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
FrameFilter.priority . . . . . . . . . . . . . . . . . . . . . . . 432
frames-invalid annotation . . . . . . . . . . . . . . . . . . 697
FreeObjFileEvent.objfile . . . . . . . . . . . . . . . . . . . 454
FreeProgspaceEvent.progspace . . . . . . . . . . . . . . 457
frozen-varobjs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
ftrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
Function.__init__ . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
Function.invoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473

Ggcore. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
gdb-object-kind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
gdb-version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
gdb.add_history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
gdb.architecture_names . . . . . . . . . . . . . . . . . . . . . 408
gdb.Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482
gdb.block_for_pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
gdb.block_signals . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
gdb.BP_ACCESS_WATCHPOINT . . . . . . . . . . . . . . . . . . . 492
gdb.BP_BREAKPOINT . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
gdb.BP_CATCHPOINT . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
gdb.BP_HARDWARE_BREAKPOINT . . . . . . . . . . . . . . . . 492
gdb.BP_HARDWARE_WATCHPOINT . . . . . . . . . . . . . . . . 492
gdb.BP_READ_WATCHPOINT . . . . . . . . . . . . . . . . . . . . . 492
gdb.BP_WATCHPOINT . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
gdb.Breakpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
gdb.breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
gdb.COMMAND_BREAKPOINTS . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_FILES . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_MAINTENANCE . . . . . . . . . . . . . . . . . . . . 466
gdb.COMMAND_NONE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_OBSCURE . . . . . . . . . . . . . . . . . . . . . . . . 466
gdb.COMMAND_RUNNING . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_STACK . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_STATUS . . . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_SUPPORT . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_TRACEPOINTS . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_TUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
gdb.COMMAND_USER . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
gdb.COMPLETE_COMMAND . . . . . . . . . . . . . . . . . . . . . . . 466
gdb.COMPLETE_EXPRESSION . . . . . . . . . . . . . . . . . . . . 466
gdb.COMPLETE_FILENAME . . . . . . . . . . . . . . . . . . . . . . 466
gdb.COMPLETE_LOCATION . . . . . . . . . . . . . . . . . . . . . . 466
gdb.COMPLETE_NONE . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
gdb.COMPLETE_SYMBOL . . . . . . . . . . . . . . . . . . . . . . . . 466
gdb.connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
gdb.convenience_variable . . . . . . . . . . . . . . . . . . . 406

941

gdb.current_language . . . . . . . . . . . . . . . . . . . . . . . 409
gdb.current_objfile . . . . . . . . . . . . . . . . . . . . . . . . 477
gdb.current_progspace . . . . . . . . . . . . . . . . . . . . . . 474
gdb.current_recording . . . . . . . . . . . . . . . . . . . . . . 460
gdb.decode_line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
gdb.default_visualizer . . . . . . . . . . . . . . . . . . . . . 426
gdb.disassembler.DisassembleInfo . . . . . . . . . 503
gdb.disassembler.Disassembler . . . . . . . . . . . . . 504
gdb.disassembler.DisassemblerAddressPart . . 507
gdb.disassembler.DisassemblerPart . . . . . . . . 506
gdb.disassembler.DisassemblerResult . . . . . . 505
gdb.disassembler.DisassemblerTextPart . . . . 507
gdb.disassembler.STYLE_ADDRESS . . . . . . . . . . . . 508
gdb.disassembler.STYLE_ADDRESS_OFFSET . . . . 508
gdb.disassembler.STYLE_ASSEMBLER_DIRECTIVE . . . . . . . . . . . . . . . . . . . . . . 508
gdb.disassembler.STYLE_COMMENT_START . . . . . 509
gdb.disassembler.STYLE_IMMEDIATE . . . . . . . . . 509
gdb.disassembler.STYLE_MNEMONIC . . . . . . . . . . . 508
gdb.disassembler.STYLE_REGISTER . . . . . . . . . . . 508
gdb.disassembler.STYLE_SUB_MNEMONIC . . . . . . 508
gdb.disassembler.STYLE_SYMBOL . . . . . . . . . . . . . 509
gdb.disassembler.STYLE_TEXT . . . . . . . . . . . . . . . 507
gdb.error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
gdb.execute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
gdb.execute_mi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
gdb.find_pc_line . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
gdb.FinishBreakpoint . . . . . . . . . . . . . . . . . . . . . . . 496
gdb.flush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
gdb.format_address . . . . . . . . . . . . . . . . . . . . . . . . . . 408
gdb.frame_stop_reason_string . . . . . . . . . . . . . . 479
gdb.FrameDecorator . . . . . . . . . . . . . . . . . . . . . . . . . . 432
gdb.Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
gdb.GdbError . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
gdb.history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
gdb.history_count . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
gdb.host_charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
gdb.Inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
gdb.InferiorCallPostEvent. . . . . . . . . . . . . . . . . . 454
gdb.InferiorCallPreEvent . . . . . . . . . . . . . . . . . . . 454
gdb.inferiors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
gdb.InferiorThread . . . . . . . . . . . . . . . . . . . . . . . . . . 457
gdb.interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
gdb.invalidate_cached_frames . . . . . . . . . . . . . . 479
gdb.LazyString . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
gdb.LineTable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
gdb.lookup_global_symbol . . . . . . . . . . . . . . . . . . . 485
gdb.lookup_objfile . . . . . . . . . . . . . . . . . . . . . . . . . . 477
gdb.lookup_static_symbol . . . . . . . . . . . . . . . . . . . 485
gdb.lookup_static_symbols. . . . . . . . . . . . . . . . . . 485
gdb.lookup_symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
gdb.lookup_type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
gdb.MemoryError . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
gdb.missing_debug.MissingDebugHandler . . . . 512
gdb.missing_debug.register_handler . . . . . . . 513
gdb.newest_frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479
gdb.notify_mi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
gdb.Objfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

942

gdb.objfiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
gdb.PARAM_AUTO_BOOLEAN . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_BOOLEAN . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_ENUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
gdb.PARAM_FILENAME . . . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_INTEGER . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_OPTIONAL_FILENAME . . . . . . . . . . . . . . . 472
gdb.PARAM_STRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_STRING_NOESCAPE. . . . . . . . . . . . . . . . . . 472
gdb.PARAM_UINTEGER . . . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_ZINTEGER . . . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_ZUINTEGER . . . . . . . . . . . . . . . . . . . . . . . . 472
gdb.PARAM_ZUINTEGER_UNLIMITED . . . . . . . . . . . . . 473
gdb.Parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
gdb.parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
gdb.parse_and_eval . . . . . . . . . . . . . . . . . . . . . . . . . . 406
gdb.post_event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
gdb.pretty_printers . . . . . . . . . . . . . . . . . . . . . . . . 426
gdb.print_options . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
gdb.Progspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
gdb.progspaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
gdb.prompt_hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
gdb.ptwrite.get_filter . . . . . . . . . . . . . . . . . . . . . 518
gdb.ptwrite.register_filter_factory . . . . . . 517
gdb.PYTHONDIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
gdb.rbreak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
gdb.register_window_type . . . . . . . . . . . . . . . . . . . 501
gdb.selected_frame . . . . . . . . . . . . . . . . . . . . . . . . . . 479
gdb.selected_inferior . . . . . . . . . . . . . . . . . . . . . . 449
gdb.selected_thread . . . . . . . . . . . . . . . . . . . . . . . . 457
gdb.set_convenience_variable . . . . . . . . . . . . . . 406
gdb.set_parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
gdb.solib_name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
gdb.start_recording . . . . . . . . . . . . . . . . . . . . . . . . 459
gdb.STDERR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406, 407
gdb.STDLOG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
gdb.STDOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406, 407
gdb.stop_recording . . . . . . . . . . . . . . . . . . . . . . . . . . 460
gdb.string_to_argv . . . . . . . . . . . . . . . . . . . . . . . . . . 464
gdb.Symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
gdb.SYMBOL_COMMON_BLOCK_DOMAIN . . . . . . . . . . . . 487
gdb.SYMBOL_FUNCTION_DOMAIN . . . . . . . . . . . . . . . . 487
gdb.SYMBOL_LABEL_DOMAIN . . . . . . . . . . . . . . . . . . . . 487
gdb.SYMBOL_LOC_ARG . . . . . . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_BLOCK . . . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_COMMON_BLOCK . . . . . . . . . . . . . . . 489
gdb.SYMBOL_LOC_COMPUTED . . . . . . . . . . . . . . . . . . . . 489
gdb.SYMBOL_LOC_CONST . . . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_CONST_BYTES . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_LABEL . . . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_LOCAL . . . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_OPTIMIZED_OUT . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_REF_ARG . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_REGISTER . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_REGPARM_ADDR . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_STATIC . . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_TYPEDEF . . . . . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_LOC_UNDEF . . . . . . . . . . . . . . . . . . . . . . . 488

Debugging with gdb

gdb.SYMBOL_LOC_UNRESOLVED. . . . . . . . . . . . . . . . . . 488
gdb.SYMBOL_MODULE_DOMAIN . . . . . . . . . . . . . . . . . . . 487
gdb.SYMBOL_STRUCT_DOMAIN . . . . . . . . . . . . . . . . . . . 487
gdb.SYMBOL_TYPE_DOMAIN . . . . . . . . . . . . . . . . . . . . . 487
gdb.SYMBOL_UNDEF_DOMAIN . . . . . . . . . . . . . . . . . . . . 487
gdb.SYMBOL_VAR_DOMAIN . . . . . . . . . . . . . . . . . . . . . . 487
gdb.Symtab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
gdb.Symtab_and_line . . . . . . . . . . . . . . . . . . . . . . . . 489
gdb.target_charset . . . . . . . . . . . . . . . . . . . . . . . . . . 407
gdb.target_wide_charset . . . . . . . . . . . . . . . . . . . . 407
gdb.Thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
gdb.Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
gdb.TYPE_CODE_ARRAY . . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_BITSTRING . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_BOOL . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_CHAR . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_COMPLEX . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_DECFLOAT . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_ENUM . . . . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_ERROR . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_FIXED_POINT . . . . . . . . . . . . . 424, 536
gdb.TYPE_CODE_FLAGS . . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_FLT . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_FUNC . . . . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_INT . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_INTERNAL_FUNCTION . . . . . . . . . . . 424
gdb.TYPE_CODE_MEMBERPTR . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_METHOD . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_METHODPTR . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_NAMESPACE . . . . . . . . . . 423, 424, 536
gdb.TYPE_CODE_PTR . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_RANGE . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_REF . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_RVALUE_REF . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_SET . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_STRING . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_STRUCT . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_TYPEDEF . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_UNION . . . . . . . . . . . . . . . . . . . . . . . . 422
gdb.TYPE_CODE_VOID . . . . . . . . . . . . . . . . . . . . . . . . . . 423
gdb.TYPE_CODE_XMETHOD . . . . . . . . . . . . . . . . . 424, 536
gdb.unwinder.enabled . . . . . . . . . . . . . . . . . . . . . . . 442
gdb.unwinder.FrameId . . . . . . . . . . . . . . . . . . . . . . . 442
gdb.unwinder.FrameId.__init__(sp, . . . . . . . . 442
gdb.unwinder.name . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
gdb.unwinder.pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
gdb.unwinder.register_unwinder . . . . . . . . . . . . 442
gdb.unwinder.sp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
gdb.unwinder.special . . . . . . . . . . . . . . . . . . . . . . . 442
gdb.unwinder.Unwinder . . . . . . . . . . . . . . . . . . . . . . 441
gdb.unwinder.Unwinder.__init__(name) . . . . . 441
gdb.UnwindInfo.add_saved_register . . . . . . . . 441
gdb.with_parameter . . . . . . . . . . . . . . . . . . . . . . . . . . 405
gdb.WP_ACCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
gdb.WP_READ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
gdb.WP_WRITE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
gdb.write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
gdb:error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525

Command, Variable, and Function Index

gdb:invalid-object . . . . . . . . . . . . . . . . . . . . . . . . . . 525
gdb:memory-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
gdb:pp-type-error . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
gdb_init_reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
GdbExitingEvent.exit_code. . . . . . . . . . . . . . . . . . 456
gdbserver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
generate-core-file . . . . . . . . . . . . . . . . . . . . . . . . . . 186
get-basic-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 571
get_filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518
getDebugChar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
gnu_debuglink_crc32 . . . . . . . . . . . . . . . . . . . . . . . . 303
gr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
gu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
guile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
guile-data-directory . . . . . . . . . . . . . . . . . . . . . . . 522
guile-repl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519

Hh (help) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
handle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
handle_exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
hbreak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
help function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
help target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
help user-defined . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
history-append! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
history-preserve-point . . . . . . . . . . . . . . . . . . . . . 719
history-ref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
history-search-backward () . . . . . . . . . . . . . . . . . 729
history-search-forward () . . . . . . . . . . . . . . . . . . 729
history-size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
history-substring-search-backward () . . . . . 730
history-substring-search-forward () . . . . . . 730
hook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
hookpost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
horizontal-scroll-mode . . . . . . . . . . . . . . . . . . . . . 719
host-config . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522

Ii (info) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
i (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 582
I (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 582
if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396
ignore. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
inferior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
inferior infno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Inferior.architecture . . . . . . . . . . . . . . . . . . . . . . 450
Inferior.arguments . . . . . . . . . . . . . . . . . . . . . . . . . . 449
Inferior.clear_env . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Inferior.connection . . . . . . . . . . . . . . . . . . . . . . . . 449
Inferior.connection_num . . . . . . . . . . . . . . . . . . . . 449
Inferior.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Inferior.main_name . . . . . . . . . . . . . . . . . . . . . . . . . . 449
Inferior.num . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
Inferior.pid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449

943

Inferior.progspace . . . . . . . . . . . . . . . . . . . . . . . . . . 449
Inferior.read_memory . . . . . . . . . . . . . . . . . . . . . . . 450
Inferior.search_memory . . . . . . . . . . . . . . . . . . . . . 450
Inferior.set_env . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
Inferior.thread_from_handle . . . . . . . . . . . . . . . 450
Inferior.thread_from_thread_handle . . . . . . . 450
Inferior.threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Inferior.unset_env . . . . . . . . . . . . . . . . . . . . . . . . . . 451
Inferior.was_attached . . . . . . . . . . . . . . . . . . . . . . 449
Inferior.write_memory . . . . . . . . . . . . . . . . . . . . . . 450
InferiorCallPostEvent.address . . . . . . . . . . . . . 454
InferiorCallPostEvent.ptid . . . . . . . . . . . . . . . . 454
InferiorCallPreEvent.address . . . . . . . . . . . . . . 454
InferiorCallPreEvent.ptid. . . . . . . . . . . . . . . . . . 454
InferiorDeletedEvent.inferior . . . . . . . . . . . . . 455
InferiorThread.details . . . . . . . . . . . . . . . . . . . . . 458
InferiorThread.global_num. . . . . . . . . . . . . . . . . . 458
InferiorThread.handle . . . . . . . . . . . . . . . . . . . . . . 459
InferiorThread.inferior . . . . . . . . . . . . . . . . . . . . 458
InferiorThread.is_exited . . . . . . . . . . . . . . . . . . . 459
InferiorThread.is_running. . . . . . . . . . . . . . . . . . 458
InferiorThread.is_stopped. . . . . . . . . . . . . . . . . . 458
InferiorThread.is_valid . . . . . . . . . . . . . . . . . . . . 458
InferiorThread.name . . . . . . . . . . . . . . . . . . . . . . . . 457
InferiorThread.num . . . . . . . . . . . . . . . . . . . . . . . . . . 458
InferiorThread.ptid . . . . . . . . . . . . . . . . . . . . . . . . 458
InferiorThread.ptid_string . . . . . . . . . . . . . . . . 458
InferiorThread.switch . . . . . . . . . . . . . . . . . . . . . . 458
info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
info address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
info all-registers . . . . . . . . . . . . . . . . . . . . . . . . . . 179
info args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
info auto-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
info auto-load gdb-scripts . . . . . . . . . . . . . . . . . 399
info auto-load guile-scripts . . . . . . . . . . . . . . . 570
info auto-load libthread-db . . . . . . . . . . . . . . . . 379
info auto-load local-gdbinit . . . . . . . . . . . . . . . 378
info auto-load python-scripts . . . . . . . . . . . . . . 513
info auxv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
info breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
info checkpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
info classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
info common . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
info connections [ id... ] . . . . . . . . . . . . . . . . . . . 43
info copying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
info dcache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
info display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
info dll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
info dos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
info exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
info extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
info f (info frame) . . . . . . . . . . . . . . . . . . . . . . . . . . 119
info files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
info float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
info frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
info frame, show the source language . . . . . . . . . 229
info frame-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
info functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

944

info handle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
info inferiors [ id... ] . . . . . . . . . . . . . . . . . . . . . 43
info io_registers, AVR . . . . . . . . . . . . . . . . . . . . . 353
info line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
info line, and Objective-C . . . . . . . . . . . . . . . . . . . 238
info locals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
info macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
info macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
info main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
info mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
info module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
info modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
info os . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
info os cpus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
info os files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os msg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os procgroups . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os semaphores . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os shm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
info os sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
info os threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
info pretty-printer . . . . . . . . . . . . . . . . . . . . . . . . . 169
info probes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
info proc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
info program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
info record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
info registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
info scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
info selectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
info serial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
info set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
info share . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
info sharedlibrary . . . . . . . . . . . . . . . . . . . . . . . . . . 296
info signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
info skip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
info source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
info source, show the source language . . . . . . . . 229
info sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270, 675
info stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
info static-tracepoint-markers . . . . . . . . . . . . 211
info symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
info target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
info task taskno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
info tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
info terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
info threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
info tp [n...] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
info tracepoints [n...] . . . . . . . . . . . . . . . . . . . . . . 210
info tvariables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
info type-printers . . . . . . . . . . . . . . . . . . . . . . . . . . 269
info types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
info variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
info vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
info w32 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
info warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
info watchpoints [list...] . . . . . . . . . . . . . . . . . . . 67

Debugging with gdb

info win . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
info-gdb-mi-command . . . . . . . . . . . . . . . . . . . . . . . . 685
init-if-undefined . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
input-meta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
input-port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 566
insert-comment (M-#) . . . . . . . . . . . . . . . . . . . . . . . . 735
insert-completions (M-*) . . . . . . . . . . . . . . . . . . . 733
inspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
instantiate on type_printer . . . . . . . . . . . . . . . . 429
Instruction.data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Instruction.decoded . . . . . . . . . . . . . . . . . . . . . . . . 461
Instruction.pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Instruction.size . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
interpreter-exec . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
isearch-terminators . . . . . . . . . . . . . . . . . . . . . . . . 719
iterator->list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-for-each . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-next! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-progress . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator-until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
iterator? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569

J
j (jump) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
jit-reader-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
jit-reader-unload . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
jump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
jump, and Objective-C . . . . . . . . . . . . . . . . . . . . . . . . 238

K
KeyboardInterrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . 410
keymap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
kill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
kill inferiors infno... . . . . . . . . . . . . . . . . . . . . . . 45
kill-line (C-k) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
kill-region () . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733
kill-whole-line () . . . . . . . . . . . . . . . . . . . . . . . . . . 732
kill-word (M-d) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
kvm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337

Command, Variable, and Function IndexLl (list) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
language-option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
lazy-string->value . . . . . . . . . . . . . . . . . . . . . . . . . . 563
lazy-string-address . . . . . . . . . . . . . . . . . . . . . . . . 563
lazy-string-encoding . . . . . . . . . . . . . . . . . . . . . . . 563
lazy-string-length . . . . . . . . . . . . . . . . . . . . . . . . . . 563
lazy-string-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
lazy-string? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
LazyString.address . . . . . . . . . . . . . . . . . . . . . . . . . . 497
LazyString.encoding . . . . . . . . . . . . . . . . . . . . . . . . 497
LazyString.length . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
LazyString.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
LazyString.value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
Left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
LineTable.has_line . . . . . . . . . . . . . . . . . . . . . . . . . . 491
LineTable.line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
LineTable.source_lines . . . . . . . . . . . . . . . . . . . . . 491
LineTableEntry.line . . . . . . . . . . . . . . . . . . . . . . . . 490
LineTableEntry.pc . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
list, and Objective-C . . . . . . . . . . . . . . . . . . . . . . . . 238
load filename offset . . . . . . . . . . . . . . . . . . . . . . . . 313
lookup-block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
lookup-global-symbol . . . . . . . . . . . . . . . . . . . . . . . 556
lookup-symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
lookup-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
loop_break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396
loop_continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396

Mmacro define . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
macro exp1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
macro expand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
macro list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
macro undef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
maint ada set ignore-descriptive-types . . . . 261
maint ada show ignore-descriptive-types . . . 261
maint agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
maint agent-eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
maint agent-printf . . . . . . . . . . . . . . . . . . . . . . . . . . 755
maint btrace clear . . . . . . . . . . . . . . . . . . . . . . . . . . 756
maint btrace clear-packet-history . . . . . . . . . 756
maint btrace packet-history . . . . . . . . . . . . . . . . 755
maint check libthread-db . . . . . . . . . . . . . . . . . . . 760
maint check xml-descriptions . . . . . . . . . . . . . . . 760
maint check-psymtabs . . . . . . . . . . . . . . . . . . . . . . . . 757
maint check-symtabs . . . . . . . . . . . . . . . . . . . . . . . . . 757
maint cplus first_component . . . . . . . . . . . . . . . . 758
maint cplus namespace . . . . . . . . . . . . . . . . . . . . . . . 758
maint demangler-warning . . . . . . . . . . . . . . . . . . . . 758
maint deprecate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
maint dump-me . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
maint expand-symtabs . . . . . . . . . . . . . . . . . . . . . . . . 757
maint flush dcache . . . . . . . . . . . . . . . . . . . . . . . . . . 191
maint flush register-cache . . . . . . . . . . . . . . . . . 763

945

maint flush source-cache . . . . . . . . . . . . . . . . . . . 764
maint flush symbol-cache . . . . . . . . . . . . . . . . . . . 275
maint flush-symbol-cache . . . . . . . . . . . . . . . . . . . 275
maint ignore-probes . . . . . . . . . . . . . . . . . . . . . . . . . 771
maint info bdccsr, S12Z . . . . . . . . . . . . . . . . . . . . . 362
maint info bfds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
maint info blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
maint info breakpoints . . . . . . . . . . . . . . . . . . . . . . 755
maint info btrace. . . . . . . . . . . . . . . . . . . . . . . . . . . . 755
maint info frame-unwinders . . . . . . . . . . . . . . . . . 766
maint info inline-frames . . . . . . . . . . . . . . . . . . . 761
maint info jit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756
maint info line-table . . . . . . . . . . . . . . . . . . . . . . . 274
maint info linux-lwps . . . . . . . . . . . . . . . . . . . . . . . 756
maint info program-spaces . . . . . . . . . . . . . . . . . . . 45
maint info psymtabs . . . . . . . . . . . . . . . . . . . . . . . . . 273
maint info python-disassemblers . . . . . . . . . . . 756
maint info screen. . . . . . . . . . . . . . . . . . . . . . . . . . . . 769
maint info sections . . . . . . . . . . . . . . . . . . . . . . . . . 294
maint info selftests . . . . . . . . . . . . . . . . . . . . . . . . 765
maint info sol-threads . . . . . . . . . . . . . . . . . . . . . . . 49
maint info symtabs . . . . . . . . . . . . . . . . . . . . . . . . . . 273
maint info target-sections . . . . . . . . . . . . . . . . . 295
maint internal-error . . . . . . . . . . . . . . . . . . . . . . . . 758
maint internal-warning . . . . . . . . . . . . . . . . . . . . . 758
maint packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500, 759
maint print arc arc-instruction . . . . . . . . . . . . 348
maint print architecture . . . . . . . . . . . . . . . . . . . 759
maint print c-tdesc . . . . . . . . . . . . . . . . . . . . . . . . . 759
maint print cooked-registers . . . . . . . . . . . . . . . 763
maint print core-file-backed-mappings. . . . . 760
maint print dummy-frames . . . . . . . . . . . . . . . . . . . 760
maint print frame-id . . . . . . . . . . . . . . . . . . . . . . . . 760
maint print msymbols . . . . . . . . . . . . . . . . . . . . . . . . 273
maint print objfiles . . . . . . . . . . . . . . . . . . . . . . . . 764
maint print psymbols . . . . . . . . . . . . . . . . . . . . . . . . 273
maint print raw-registers . . . . . . . . . . . . . . . . . . 763
maint print record-instruction . . . . . . . . . . . . . 765
maint print reggroups . . . . . . . . . . . . . . . . . . . . . . . 763
maint print register-groups . . . . . . . . . . . . . . . . 763
maint print registers . . . . . . . . . . . . . . . . . . . . . . . 763
maint print remote-registers . . . . . . . . . . . . . . . 763
maint print section-scripts . . . . . . . . . . . . . . . . 764
maint print statistics . . . . . . . . . . . . . . . . . . . . . . 764
maint print symbol-cache . . . . . . . . . . . . . . . . . . . 275
maint print symbol-cache-statistics . . . . . . . 275
maint print symbols . . . . . . . . . . . . . . . . . . . . . . . . . 273
maint print target-stack . . . . . . . . . . . . . . . . . . . 764
maint print type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
maint print unwind, HPPA . . . . . . . . . . . . . . . . . . . 361
maint print user-registers . . . . . . . . . . . . . . . . . 764
maint print xml-tdesc . . . . . . . . . . . . . . . . . . . . . . . 760
maint selftest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765
maint set backtrace-on-fatal-signal . . . . . . . 770
maint set bfd-sharing . . . . . . . . . . . . . . . . . . . . . . . 300
maint set btrace pt skip-pad . . . . . . . . . . . . . . . . 756
maint set catch-demangler-crashes . . . . . . . . . 758
maint set check-libthread-db . . . . . . . . . . . . . . . 769

946

maint set debuginfod download-sections . . . . 758
maint set demangler-warning . . . . . . . . . . . . . . . . 759
maint set dwarf always-disassemble . . . . . . . . 765
maint set dwarf max-cache-age . . . . . . . . . . . . . . 765
maint set dwarf synchronous . . . . . . . . . . . . . . . . 766
maint set dwarf unwinders . . . . . . . . . . . . . . . . . . . 766
maint set gnu-source-highlight enabled . . . . 769
maint set ignore-prologue-end-flag . . . . . . . . 275
maint set internal-error . . . . . . . . . . . . . . . . . . . 759
maint set internal-warning . . . . . . . . . . . . . . . . . 759
maint set libopcodes-styling enabled . . . . . . 769
maint set per-command . . . . . . . . . . . . . . . . . . . . . . . 768
maint set profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . 766
maint set selftest verbose . . . . . . . . . . . . . . . . . . 765
maint set show-all-tib . . . . . . . . . . . . . . . . . . . . . . 767
maint set show-debug-regs . . . . . . . . . . . . . . . . . . 767
maint set symbol-cache-size . . . . . . . . . . . . . . . . 275
maint set target-async . . . . . . . . . . . . . . . . . . . . . . 767
maint set target-non-stop mode
[on|off|auto] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 767
maint set test-settings . . . . . . . . . . . . . . . . . . . . . 770
maint set tui-left-margin-verbose . . . . . . . . . 768
maint set tui-resize-message . . . . . . . . . . . . . . . 768
maint set worker-threads . . . . . . . . . . . . . . . . . . . 766
maint show backtrace-on-fatal-signal . . . . . . 770
maint show bfd-sharing . . . . . . . . . . . . . . . . . . . . . . 300
maint show btrace pt skip-pad. . . . . . . . . . . . . . . 756
maint show catch-demangler-crashes . . . . . . . . 758
maint show check-libthread-db . . . . . . . . . . . . . . 769
maint show debuginfod download-sections . . . 758
maint show demangler-warning . . . . . . . . . . . . . . . 759
maint show dwarf always-disassemble . . . . . . . 765
maint show dwarf max-cache-age . . . . . . . . . . . . . 765
maint show dwarf synchronous . . . . . . . . . . . . . . . 766
maint show dwarf unwinders . . . . . . . . . . . . . . . . . . 766
maint show gnu-source-highlight enabled . . . 769
maint show ignore-prologue-end-flag . . . . . . . 275
maint show internal-error . . . . . . . . . . . . . . . . . . 759
maint show internal-warning . . . . . . . . . . . . . . . . 759
maint show libopcodes-styling enabled . . . . . 769
maint show per-command . . . . . . . . . . . . . . . . . . . . . . 768
maint show profile . . . . . . . . . . . . . . . . . . . . . . . . . . 766
maint show selftest verbose . . . . . . . . . . . . . . . . 765
maint show show-all-tib . . . . . . . . . . . . . . . . . . . . . 767
maint show show-debug-regs . . . . . . . . . . . . . . . . . 767
maint show symbol-cache-size . . . . . . . . . . . . . . . 275
maint show target-async . . . . . . . . . . . . . . . . . . . . . 767
maint show target-non-stop . . . . . . . . . . . . . . . . . 767
maint show
test-options-completion-result. . . . . . . . . . 770
maint show test-settings . . . . . . . . . . . . . . . . . . . 770
maint show tui-left-margin-verbose . . . . . . . . 768
maint show tui-resize-message . . . . . . . . . . . . . . 768
maint show worker-threads . . . . . . . . . . . . . . . . . . 766
maint space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 769
maint test-options . . . . . . . . . . . . . . . . . . . . . . . . . . 770
maint time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 769
maint translate-address . . . . . . . . . . . . . . . . . . . . 769

Debugging with gdb

maint undeprecate . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
maint wait-for-index-cache . . . . . . . . . . . . . . . . . 770
maint with . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 770
make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
make-block-symbols-iterator . . . . . . . . . . . . . . . 554
make-breakpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
make-command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
make-enum-hashtable . . . . . . . . . . . . . . . . . . . . . . . . 571
make-exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
make-field-iterator . . . . . . . . . . . . . . . . . . . . . . . . 534
make-iterator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
make-lazy-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
make-list-iterator . . . . . . . . . . . . . . . . . . . . . . . . . . 569
make-parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
make-pretty-printer . . . . . . . . . . . . . . . . . . . . . . . . 537
make-pretty-printer-worker . . . . . . . . . . . . . . . . 537
make-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
mark-modified-lines . . . . . . . . . . . . . . . . . . . . . . . . 720
mark-symlinked-directories . . . . . . . . . . . . . . . . 720
match-hidden-files . . . . . . . . . . . . . . . . . . . . . . . . . . 720
may-insert-breakpoints . . . . . . . . . . . . . . . . . . . . . . 98
may-insert-fast-tracepoints . . . . . . . . . . . . . . . . 98
may-insert-tracepoints . . . . . . . . . . . . . . . . . . . . . . 98
may-interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
may-write-memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
may-write-registers. . . . . . . . . . . . . . . . . . . . . . . . . . 98
mem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
memory-port-range . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
memory-port-read-buffer-size . . . . . . . . . . . . . . 567
memory-port-write-buffer-size . . . . . . . . . . . . . 567
memory-port? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
memory-tag check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
memory-tag print-allocation-tag . . . . . . . . . . . 155
memory-tag print-logical-tag . . . . . . . . . . . . . . 155
memory-tag setatag . . . . . . . . . . . . . . . . . . . . . . . . . . 155
memory-tag with-logical-tag . . . . . . . . . . . . . . . . 155
MemoryChangedEvent.address . . . . . . . . . . . . . . . . 454
MemoryChangedEvent.length. . . . . . . . . . . . . . . . . . 454
memset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
menu-complete () . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
menu-complete-backward () . . . . . . . . . . . . . . . . . . 734
menu-complete-display-prefix . . . . . . . . . . . . . . 720
meta-flag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
MICommand.__init__ . . . . . . . . . . . . . . . . . . . . . . . . . . 467
MICommand.installed . . . . . . . . . . . . . . . . . . . . . . . . 468
MICommand.invoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
MICommand.name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
MissingDebugHandler.__call__ . . . . . . . . . . . . . . 512
MissingDebugHandler.__init__ . . . . . . . . . . . . . . 512
MissingDebugHandler.enabled . . . . . . . . . . . . . . . 513
MissingDebugHandler.name . . . . . . . . . . . . . . . . . . . 513
monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

Command, Variable, and Function Index

947

N

P

n (next) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
n (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
N (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
name of type_printer . . . . . . . . . . . . . . . . . . . . . . . . . 429
new-ui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 577
newest-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
NewInferiorEvent.inferior. . . . . . . . . . . . . . . . . . 455
NewObjFileEvent.new_objfile . . . . . . . . . . . . . . . 453
NewProgspaceEvent.progspace . . . . . . . . . . . . . . . 457
NewThreadEvent.inferior_thread . . . . . . . . . . . . 456
next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
next& . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
next-history (C-n) . . . . . . . . . . . . . . . . . . . . . . . . . . 729
next-screen-line () . . . . . . . . . . . . . . . . . . . . . . . . . 728
nexti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
nexti&. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
ni (nexti) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
non-incremental-forwardsearch-history (M-n) . . . . . . . . . . . . . . . . . . . . . 729
non-incremental-reversesearch-history (M-p) . . . . . . . . . . . . . . . . . . . . . 729
nosharedlibrary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

page-completions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721
PARAM_AUTO_BOOLEAN . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_BOOLEAN . . . . . . . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_ENUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473, 547
PARAM_FILENAME . . . . . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_INTEGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
PARAM_OPTIONAL_FILENAME . . . . . . . . . . . . . . . 472, 547
PARAM_STRING . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_STRING_NOESCAPE . . . . . . . . . . . . . . . . . 472, 547
PARAM_UINTEGER . . . . . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_ZINTEGER . . . . . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_ZUINTEGER . . . . . . . . . . . . . . . . . . . . . . . . 472, 547
PARAM_ZUINTEGER_UNLIMITED . . . . . . . . . . . . . 473, 547
Parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470, 545
parameter-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547
Parameter.__init__ . . . . . . . . . . . . . . . . . . . . . . . . . . 470
Parameter.get_set_string . . . . . . . . . . . . . . . . . . . 471
Parameter.get_show_string. . . . . . . . . . . . . . . . . . 472
Parameter.set_doc . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
Parameter.show_doc . . . . . . . . . . . . . . . . . . . . . . . . . . 471
Parameter.value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
parameter? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
parse-and-eval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
passcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
pending-breakpoints . . . . . . . . . . . . . . . . . . . . . . . . 685
PendingFrame.architecture. . . . . . . . . . . . . . . . . . 440
PendingFrame.block . . . . . . . . . . . . . . . . . . . . . . . . . . 441
PendingFrame.create_unwind_info . . . . . . . . . . . 440
PendingFrame.find_sal . . . . . . . . . . . . . . . . . . . . . . 441
PendingFrame.function . . . . . . . . . . . . . . . . . . . . . . 441
PendingFrame.is_valid . . . . . . . . . . . . . . . . . . . . . . 441
PendingFrame.language . . . . . . . . . . . . . . . . . . . . . . 441
PendingFrame.level . . . . . . . . . . . . . . . . . . . . . . . . . . 440
PendingFrame.name . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
PendingFrame.pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
PendingFrame.read_register . . . . . . . . . . . . . . . . 439
PgDn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
PgUp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
pi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
po (print-object) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
possible-completions (M-?) . . . . . . . . . . . . . . . . . 733
post-commands annotation . . . . . . . . . . . . . . . . . . . 696
post-overload-choice annotation . . . . . . . . . . . 696
post-prompt annotation . . . . . . . . . . . . . . . . . . . . . 696
post-prompt-for-continue annotation . . . . . . 696
post-query annotation. . . . . . . . . . . . . . . . . . . . . . . 696
pre-commands annotation . . . . . . . . . . . . . . . . . . . . 696
pre-overload-choice annotation . . . . . . . . . . . . 696
pre-prompt annotation. . . . . . . . . . . . . . . . . . . . . . . 696
pre-prompt-for-continue annotation . . . . . . . . 696
pre-query annotation . . . . . . . . . . . . . . . . . . . . . . . . 696
prefix-meta (ESC) . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
prepend-pretty-printer! . . . . . . . . . . . . . . . . . . . . 570
pretty-printer-enabled? . . . . . . . . . . . . . . . . . . . . 537
pretty-printer? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537

Oo (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
O (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
Objfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
objfile-filename . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
objfile-pretty-printers . . . . . . . . . . . . . . . . . . . . 549
objfile-progspace . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
objfile-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
Objfile.add_separate_debug_file . . . . . . . . . . . 479
Objfile.build_id . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
Objfile.filename . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
Objfile.frame_filters . . . . . . . . . . . . . . . . . . . . . . 478
Objfile.is_file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
Objfile.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
Objfile.lookup_global_symbol . . . . . . . . . . . . . . 479
Objfile.lookup_static_symbol . . . . . . . . . . . . . . 479
Objfile.owner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
Objfile.pretty_printers . . . . . . . . . . . . . . . . . . . . 478
Objfile.progspace . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
Objfile.type_printers . . . . . . . . . . . . . . . . . . . . . . 478
Objfile.username . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
objfile? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
objfiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
observer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
open-memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
operate-and-get-next (C-o) . . . . . . . . . . . . . . . . . 730
output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
output-meta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
output-port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
overload-choice annotation . . . . . . . . . . . . . . . . . 696
overwrite-mode () . . . . . . . . . . . . . . . . . . . . . . . . . . . 732

948

pretty-printers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
pretty_printer.child . . . . . . . . . . . . . . . . . . . . . . . 426
pretty_printer.children . . . . . . . . . . . . . . . . . . . . 424
pretty_printer.display_hint . . . . . . . . . . . . . . . 425
pretty_printer.num_children . . . . . . . . . . . . . . . 425
pretty_printer.to_string . . . . . . . . . . . . . . . . . . . 425
previous-history (C-p) . . . . . . . . . . . . . . . . . . . . . 729
previous-screen-line () . . . . . . . . . . . . . . . . . . . . 728
print. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
print-last-kbd-macro () . . . . . . . . . . . . . . . . . . . . 734
print-object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
printf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
proc-trace-entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
proc-trace-exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
proc-untrace-entry . . . . . . . . . . . . . . . . . . . . . . . . . . 339
proc-untrace-exit . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
Progspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
progspace-filename . . . . . . . . . . . . . . . . . . . . . . . . . . 548
progspace-objfiles . . . . . . . . . . . . . . . . . . . . . . . . . . 548
progspace-pretty-printers. . . . . . . . . . . . . . . . . . 548
progspace-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
Progspace.block_for_pc . . . . . . . . . . . . . . . . . . . . . 475
Progspace.executable_filename . . . . . . . . . . . . . 474
Progspace.filename . . . . . . . . . . . . . . . . . . . . . . . . . . 474
Progspace.find_pc_line . . . . . . . . . . . . . . . . . . . . . 475
Progspace.frame_filters . . . . . . . . . . . . . . . . . . . . 475
Progspace.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . 475
Progspace.missing_debug_handlers . . . . . . . . . 475
Progspace.objfile_for_address . . . . . . . . . . . . . 476
Progspace.objfiles . . . . . . . . . . . . . . . . . . . . . . . . . . 475
Progspace.pretty_printers. . . . . . . . . . . . . . . . . . 475
Progspace.solib_name . . . . . . . . . . . . . . . . . . . . . . . 475
Progspace.symbol_file . . . . . . . . . . . . . . . . . . . . . . 474
Progspace.type_printers . . . . . . . . . . . . . . . . . . . . 475
progspace? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
progspaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548
prompt annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
prompt-for-continue annotation . . . . . . . . . . . . 696
ptype. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
putDebugChar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
pwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
py . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402
python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402, 685
python-interactive . . . . . . . . . . . . . . . . . . . . . . . . . . 402

Q
q (quit) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
q (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
query annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 696
queue-signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
quit [expression] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
quit annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 697
quoted-insert (C-q or C-v) . . . . . . . . . . . . . . . . . . 731

Debugging with gdb

R
r (run) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
r (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
rbreak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
rc (reverse-continue) . . . . . . . . . . . . . . . . . . . . . . . 101
re-read-init-file (C-x C-r) . . . . . . . . . . . . . . . . 734
readnow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
rec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec btrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec btrace bts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec btrace pt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec bts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec del . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
rec full . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec function-call-history . . . . . . . . . . . . . . . . . . 110
rec instruction-history . . . . . . . . . . . . . . . . . . . . 109
rec pt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
rec s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
recognize on type_recognizer . . . . . . . . . . . . . . . 430
record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record btrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record btrace bts. . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record btrace pt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record bts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
record full . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record function-call-history . . . . . . . . . . . . . . 110
record goto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
record instruction-history . . . . . . . . . . . . . . . . . 109
record pt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
record restore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
record save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
record stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Record.begin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Record.clear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Record.end . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Record.format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Record.function_call_history . . . . . . . . . . . . . . 460
Record.goto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Record.instruction_history . . . . . . . . . . . . . . . . 460
Record.method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
Record.replay_position . . . . . . . . . . . . . . . . . . . . . 460
RecordAuxiliary.data . . . . . . . . . . . . . . . . . . . . . . . 461
RecordAuxiliary.number . . . . . . . . . . . . . . . . . . . . . 461
RecordFunctionSegment.instructions . . . . . . . 462
RecordFunctionSegment.level . . . . . . . . . . . . . . . 462
RecordFunctionSegment.next . . . . . . . . . . . . . . . . 462
RecordFunctionSegment.number . . . . . . . . . . . . . . 461
RecordFunctionSegment.prev . . . . . . . . . . . . . . . . 462
RecordFunctionSegment.symbol . . . . . . . . . . . . . . 462
RecordFunctionSegment.up . . . . . . . . . . . . . . . . . . . 462
RecordGap.error_code . . . . . . . . . . . . . . . . . . . . . . . 461
RecordGap.error_string . . . . . . . . . . . . . . . . . . . . . 461
RecordGap.number . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
RecordInstruction.is_speculative . . . . . . . . . 461
RecordInstruction.number . . . . . . . . . . . . . . . . . . . 461
RecordInstruction.sal . . . . . . . . . . . . . . . . . . . . . . 461
redraw-current-line () . . . . . . . . . . . . . . . . . . . . . 729

Command, Variable, and Function Index

refresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
register-breakpoint! . . . . . . . . . . . . . . . . . . . . . . . 560
register-command! . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
register-parameter! . . . . . . . . . . . . . . . . . . . . . . . . 546
register_disassembler . . . . . . . . . . . . . . . . . . . . . . 509
register_filter_factory . . . . . . . . . . . . . . . . . . . . 518
register_xmethod_matcher . . . . . . . . . . . . . . . . . . . 446
RegisterChangedEvent.frame . . . . . . . . . . . . . . . . 455
RegisterChangedEvent.regnum . . . . . . . . . . . . . . . 455
RegisterDescriptor.name . . . . . . . . . . . . . . . . . . . . 499
RegisterDescriptorIterator.find . . . . . . . . . . . 499
RegisterGroup.name . . . . . . . . . . . . . . . . . . . . . . . . . . 499
remote delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
remote get . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
remote put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
RemoteTargetConnection.send_packet . . . . . . . 500
remove-inferiors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
remove-symbol-file . . . . . . . . . . . . . . . . . . . . . . . . . . 294
restart checkpoint-id . . . . . . . . . . . . . . . . . . . . . . . . 55
restore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
RET (repeat last command) . . . . . . . . . . . . . . . . . . . . . 23
return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
reverse-continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
reverse-finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
reverse-next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
reverse-nexti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
reverse-search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
reverse-search-history (C-r) . . . . . . . . . . . . . . 729
reverse-step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
reverse-stepi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
revert-all-at-newline . . . . . . . . . . . . . . . . . . . . . . 721
revert-line (M-r) . . . . . . . . . . . . . . . . . . . . . . . . . . . 735
Right. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
rn (reverse-next) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
rni (reverse-nexti) . . . . . . . . . . . . . . . . . . . . . . . . . 102
rs (step) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
rsi (reverse-stepi) . . . . . . . . . . . . . . . . . . . . . . . . . 101
run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
run& . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
rwatch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

S
s (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 581
s (step) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
S (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 582
sal-last . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
sal-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
sal-pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559
sal-symtab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
sal-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
sal? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
save breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
save gdb-index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
save tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
save-tracepoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

949

select-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
selected-frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
self . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543
self-insert (a, b, A, 1, !, ...) . . . . . . . . . . . . 731
set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
set ada print-signatures . . . . . . . . . . . . . . . . . . . 254
set ada source-charset . . . . . . . . . . . . . . . . . . . . . . 259
set ada trust-PAD-over-XVS . . . . . . . . . . . . . . . . . 260
set agent off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
set agent on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
set always-read-ctf [on|off] . . . . . . . . . . . . . . . 275
set amdgpu precise-memory . . . . . . . . . . . . . . . . . . 365
set annotate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
set architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
set args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
set arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
set auto-connect-native-target . . . . . . . . . . . . . 36
set auto-load gdb-scripts . . . . . . . . . . . . . . . . . . 399
set auto-load guile-scripts . . . . . . . . . . . . . . . . 570
set auto-load libthread-db . . . . . . . . . . . . . . . . . 379
set auto-load local-gdbinit . . . . . . . . . . . . . . . . 378
set auto-load off. . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
set auto-load python-scripts . . . . . . . . . . . . . . . 513
set auto-load safe-path . . . . . . . . . . . . . . . . . . . . . 379
set auto-load scripts-directory . . . . . . . . . . . 572
set auto-solib-add . . . . . . . . . . . . . . . . . . . . . . . . . . 296
set backtrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
set basenames-may-differ . . . . . . . . . . . . . . . . . . . 300
set breakpoint always-inserted . . . . . . . . . . . . . . 64
set breakpoint auto-hw . . . . . . . . . . . . . . . . . . . . . . . 64
set breakpoint condition-evaluation . . . . . . . . 65
set breakpoint pending . . . . . . . . . . . . . . . . . . . . . . . 64
set can-use-hw-watchpoints . . . . . . . . . . . . . . . . . . 67
set case-sensitive . . . . . . . . . . . . . . . . . . . . . . . . . . 263
set charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
set check range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
set check type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
set circular-trace-buffer . . . . . . . . . . . . . . . . . . 213
set code-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
set coerce-float-to-double . . . . . . . . . . . . . . . . . 376
set com1base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com1irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com2base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com2irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com3base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com3irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com4base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set com4irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
set complaints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
set confirm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
set cp-abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
set cwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
set cygwin-exceptions. . . . . . . . . . . . . . . . . . . . . . . 342
set data-directory . . . . . . . . . . . . . . . . . . . . . . . . . . 308
set dcache line-size . . . . . . . . . . . . . . . . . . . . . . . . 191
set dcache size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
set debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
set debug aarch64. . . . . . . . . . . . . . . . . . . . . . . . . . . . 354

950

set debug arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
set debug auto-load . . . . . . . . . . . . . . . . . . . . . . . . . 381
set debug bfd-cache level . . . . . . . . . . . . . . . . . . . 300
set debug darwin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
set debug entry-values . . . . . . . . . . . . . . . . . . . . . . 196
set debug hppa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
set debug libthread-db . . . . . . . . . . . . . . . . . . . . . . . 52
set debug mach-o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
set debug mips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
set debug monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
set debug nios2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
set debug py-breakpoint . . . . . . . . . . . . . . . . . . . . . 403
set debug py-unwind . . . . . . . . . . . . . . . . . . . . . . . . . 403
set debug skip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
set debug threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
set debug tui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586
set debug-file-directory . . . . . . . . . . . . . . . . . . . 301
set debugevents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
set debugexceptions . . . . . . . . . . . . . . . . . . . . . . . . . 343
set debugexec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
set debuginfod enabled . . . . . . . . . . . . . . . . . . . . . . 887
set debuginfod urls . . . . . . . . . . . . . . . . . . . . . . . . . 887
set debuginfod verbose . . . . . . . . . . . . . . . . . . . . . . 887
set debugmemory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
set default-collect . . . . . . . . . . . . . . . . . . . . . . . . . 210
set demangle-style . . . . . . . . . . . . . . . . . . . . . . . . . . 166
set detach-on-fork . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
set direct-call-timeout . . . . . . . . . . . . . . . . . . . . 283
set directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
set disable-randomization . . . . . . . . . . . . . . . . . . . 37
set disassemble-next-line . . . . . . . . . . . . . . . . . . 140
set disassembler-options . . . . . . . . . . . . . . . . . . . 139
set disassembly-flavor . . . . . . . . . . . . . . . . . . . . . 139
set disconnected-dprintf . . . . . . . . . . . . . . . . . . . . 80
set disconnected-tracing . . . . . . . . . . . . . . . . . . . 213
set displaced-stepping . . . . . . . . . . . . . . . . . . . . . 757
set dump-excluded-mappings . . . . . . . . . . . . . . . . . 187
set editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
set endian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
set environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
set exceptions, Hurd command . . . . . . . . . . . . . . 345
set exec-direction . . . . . . . . . . . . . . . . . . . . . . . . . . 102
set exec-done-display. . . . . . . . . . . . . . . . . . . . . . . 382
set exec-wrapper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
set extended-prompt . . . . . . . . . . . . . . . . . . . . . . . . . 367
set extension-language . . . . . . . . . . . . . . . . . . . . . 229
set follow-exec-mode . . . . . . . . . . . . . . . . . . . . . . . . . 53
set follow-fork-mode . . . . . . . . . . . . . . . . . . . . . . . . . 52
set fortran repack-array-slices . . . . . . . . . . . 242
set frame-filter priority . . . . . . . . . . . . . . . . . . 124
set gnutarget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
set guile print-stack . . . . . . . . . . . . . . . . . . . . . . . 524
set hash, for remote monitors. . . . . . . . . . . . . . . . . 313
set height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
set history expansion . . . . . . . . . . . . . . . . . . . . . . . 369
set history filename . . . . . . . . . . . . . . . . . . . . . . . . 368
set history remove-duplicates . . . . . . . . . . . . . . 369
set history save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

Debugging with gdb

set history size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
set host-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
set index-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
set indirect-call-timeout . . . . . . . . . . . . . . . . . . 283
set inferior-tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
set input-radix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
set interactive-mode . . . . . . . . . . . . . . . . . . . . . . . . 388
set language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
set libthread-db-search-path . . . . . . . . . . . . . . . . 51
set listsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
set logging enabled . . . . . . . . . . . . . . . . . . . . . . . . . . 21
set mach-exceptions . . . . . . . . . . . . . . . . . . . . . . . . . 348
set max-completions . . . . . . . . . . . . . . . . . . . . . . . . . . 25
set max-user-call-depth . . . . . . . . . . . . . . . . . . . . 394
set max-value-size . . . . . . . . . . . . . . . . . . . . . . . . . . 192
set may-call-functions . . . . . . . . . . . . . . . . . . . . . 282
set mem inaccessible-by-default . . . . . . . . . . . 185
set mi-async . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591
set mips abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
set mips compression . . . . . . . . . . . . . . . . . . . . . . . . 360
set mips mask-address . . . . . . . . . . . . . . . . . . . . . . . 360
set mipsfpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
set multiple-symbols . . . . . . . . . . . . . . . . . . . . . . . . 146
set new-console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
set new-group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
set non-stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
set opaque-type-resolution . . . . . . . . . . . . . . . . . 272
set osabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
set output-radix . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
set overload-resolution . . . . . . . . . . . . . . . . . . . . 236
set pagination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
set powerpc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
set print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
set print entry-values . . . . . . . . . . . . . . . . . . . . . . 161
set print finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
set print frame-arguments . . . . . . . . . . . . . . . . . . 160
set print frame-info . . . . . . . . . . . . . . . . . . . . . . . . 163
set print inferior-events . . . . . . . . . . . . . . . . . . . 45
set print symbol-loading . . . . . . . . . . . . . . . . . . . 273
set print thread-events . . . . . . . . . . . . . . . . . . . . . . 51
set print type hex . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
set print type methods . . . . . . . . . . . . . . . . . . . . . . 263
set print type nested-type-limit . . . . . . . . . . . 263
set print type typedefs . . . . . . . . . . . . . . . . . . . . . 264
set processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
set procfs-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
set procfs-trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
set prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
set python dont-write-bytecode . . . . . . . . . . . . . 403
set python ignore-environment . . . . . . . . . . . . . . 402
set python print-stack . . . . . . . . . . . . . . . . . . . . . . 402
set radix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
set range-stepping . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
set ravenscar task-switching off . . . . . . . . . . . 259
set ravenscar task-switching on . . . . . . . . . . . . 259
set record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
set record btrace. . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
set record btrace bts . . . . . . . . . . . . . . . . . . . . . . . 107

Command, Variable, and Function Index

set record btrace pt . . . . . . . . . . . . . . . . . . . . . . . . 107
set record full . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
set remote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
set remote system-call-allowed . . . . . . . . . . . . . 838
set remote-mips64-transfers-32bit-regs . . . 360
set remotecache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
set remoteflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
set schedule-multiple . . . . . . . . . . . . . . . . . . . . . . . . 94
set script-extension . . . . . . . . . . . . . . . . . . . . . . . . 391
set sh calling-convention . . . . . . . . . . . . . . . . . . 354
set shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
set signal-thread . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
set signals, Hurd command . . . . . . . . . . . . . . . . . 345
set sigs, Hurd command . . . . . . . . . . . . . . . . . . . . . 345
set sigthread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
set solib-absolute-prefix . . . . . . . . . . . . . . . . . . 297
set solib-search-path. . . . . . . . . . . . . . . . . . . . . . . 298
set source open . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
set stack-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
set startup-quietly . . . . . . . . . . . . . . . . . . . . . . . . . . 13
set startup-with-shell. . . . . . . . . . . . . . . . . . . . . . . 36
set step-mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
set stop-on-solib-events . . . . . . . . . . . . . . . . . . . 297
set stopped, Hurd command . . . . . . . . . . . . . . . . . 345
set struct-convention. . . . . . . . . . . . . . . . . . . . . . . 358
set style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
set substitute-path . . . . . . . . . . . . . . . . . . . . . . . . . 134
set suppress-cli-notifications . . . . . . . . . . . . 388
set sysroot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
set target-charset . . . . . . . . . . . . . . . . . . . . . . . . . . 187
set target-file-system-kind(unix|dos-based|auto) . . . . . . . . . . . . . . . . . . . . 299
set target-wide-charset . . . . . . . . . . . . . . . . . . . . 188
set task, Hurd commands . . . . . . . . . . . . . . . . . . . . 346
set tcp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
set thread, Hurd command . . . . . . . . . . . . . . . . . . 346
set trace-buffer-size. . . . . . . . . . . . . . . . . . . . . . . 213
set trace-commands . . . . . . . . . . . . . . . . . . . . . . . . . . 382
set trace-notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
set trace-stop-notes . . . . . . . . . . . . . . . . . . . . . . . . 214
set trace-user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
set trust-readonly-sections . . . . . . . . . . . . . . . . 295
set tui active-border-mode . . . . . . . . . . . . . . . . . 585
set tui border-kind . . . . . . . . . . . . . . . . . . . . . . . . . 585
set tui border-mode . . . . . . . . . . . . . . . . . . . . . . . . . 585
set tui compact-source . . . . . . . . . . . . . . . . . . . . . . 586
set tui mouse-events . . . . . . . . . . . . . . . . . . . . . . . . 586
set tui tab-width. . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
set unwind-on-signal . . . . . . . . . . . . . . . . . . . . . . . . 281
set unwind-on-terminating-exception . . . . . . 282
set unwind-on-timeout. . . . . . . . . . . . . . . . . . . . . . . 282
set unwindonsignal . . . . . . . . . . . . . . . . . . . . . . . . . . 281
set use-coredump-filter . . . . . . . . . . . . . . . . . . . . 186
set variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
set verbose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
set watchdog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 771
set width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
set write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

951

set-breakpoint-condition!. . . . . . . . . . . . . . . . . . 562
set-breakpoint-enabled! . . . . . . . . . . . . . . . . . . . . 561
set-breakpoint-hit-count!. . . . . . . . . . . . . . . . . . 562
set-breakpoint-ignore-count! . . . . . . . . . . . . . . 562
set-breakpoint-silent! . . . . . . . . . . . . . . . . . . . . . 561
set-breakpoint-stop! . . . . . . . . . . . . . . . . . . . . . . . 562
set-breakpoint-task! . . . . . . . . . . . . . . . . . . . . . . . 562
set-breakpoint-thread! . . . . . . . . . . . . . . . . . . . . . 562
set-iterator-progress! . . . . . . . . . . . . . . . . . . . . . 569
set-mark (C-@) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735
set-memory-port-read-buffer-size! . . . . . . . . 567
set-memory-port-write-buffer-size! . . . . . . . 568
set-objfile-pretty-printers! . . . . . . . . . . . . . . 549
set-parameter-value! . . . . . . . . . . . . . . . . . . . . . . . 547
set-pretty-printer-enabled! . . . . . . . . . . . . . . . 537
set-pretty-printers! . . . . . . . . . . . . . . . . . . . . . . . 537
set-progspace-pretty-printers! . . . . . . . . . . . . 548
set_debug_traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
share. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
sharedlibrary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
shell-transpose-words (M-C-t) . . . . . . . . . . . . . 732
show . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
show ada print-signatures . . . . . . . . . . . . . . . . . . 254
show ada source-charset . . . . . . . . . . . . . . . . . . . . . 259
show ada trust-PAD-over-XVS . . . . . . . . . . . . . . . . 260
show agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705
show always-read-ctf . . . . . . . . . . . . . . . . . . . . . . . . 275
show amdgpu precise-memory . . . . . . . . . . . . . . . . . 365
show annotate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695
show architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
show args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
show arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
show auto-load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
show auto-load gdb-scripts . . . . . . . . . . . . . . . . . 399
show auto-load guile-scripts . . . . . . . . . . . . . . . 570
show auto-load libthread-db . . . . . . . . . . . . . . . . 379
show auto-load local-gdbinit . . . . . . . . . . . . . . . 378
show auto-load python-scripts . . . . . . . . . . . . . . 513
show auto-load safe-path . . . . . . . . . . . . . . . . . . . 379
show auto-load scripts-directory . . . . . . . . . . 573
show auto-solib-add . . . . . . . . . . . . . . . . . . . . . . . . . 296
show backtrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
show basenames-may-differ . . . . . . . . . . . . . . . . . . 300
show breakpoint always-inserted . . . . . . . . . . . . . 64
show breakpoint auto-hw . . . . . . . . . . . . . . . . . . . . . . 64
show breakpoint condition-evaluation . . . . . . . 65
show breakpoint pending . . . . . . . . . . . . . . . . . . . . . . 64
show can-use-hw-watchpoints . . . . . . . . . . . . . . . . . 67
show case-sensitive . . . . . . . . . . . . . . . . . . . . . . . . . 263
show charset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
show check range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
show check type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
show circular-trace-buffer . . . . . . . . . . . . . . . . . 213
show code-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
show coerce-float-to-double . . . . . . . . . . . . . . . . 376
show com1base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show com1irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

952

show com2base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show com2irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show com3base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show com3irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show com4base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show com4irq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
show commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
show complaints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
show configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
show confirm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
show convenience . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
show copying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
show cp-abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
show cwd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
show cygwin-exceptions . . . . . . . . . . . . . . . . . . . . . 342
show data-directory . . . . . . . . . . . . . . . . . . . . . . . . . 308
show dcache line-size . . . . . . . . . . . . . . . . . . . . . . . 191
show dcache size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
show debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
show debug arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
show debug auto-load . . . . . . . . . . . . . . . . . . . . . . . . 381
show debug bfd-cache . . . . . . . . . . . . . . . . . . . . . . . . 300
show debug darwin. . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
show debug entry-values . . . . . . . . . . . . . . . . . . . . . 197
show debug libthread-db . . . . . . . . . . . . . . . . . . . . . . 52
show debug mach-o. . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
show debug mips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
show debug monitor . . . . . . . . . . . . . . . . . . . . . . . . . . 313
show debug nios2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
show debug py-breakpoint . . . . . . . . . . . . . . . . . . . 403
show debug py-unwind . . . . . . . . . . . . . . . . . . . . . . . . 403
show debug skip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
show debug threads. . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
show debug tui . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586
show debug-file-directory . . . . . . . . . . . . . . . . . . 301
show debuginfod enabled . . . . . . . . . . . . . . . . . . . . . 887
show debuginfod urls . . . . . . . . . . . . . . . . . . . . . . . . 887
show debuginfod verbose . . . . . . . . . . . . . . . . . . . . . 887
show default-collect . . . . . . . . . . . . . . . . . . . . . . . . 210
show detach-on-fork . . . . . . . . . . . . . . . . . . . . . . . . . . 53
show direct-call-timeout . . . . . . . . . . . . . . . . . . . 283
show directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
show disassemble-next-line . . . . . . . . . . . . . . . . . 140
show disassembler-options . . . . . . . . . . . . . . . . . . 139
show disassembly-flavor . . . . . . . . . . . . . . . . . . . . 139
show disconnected-dprintf . . . . . . . . . . . . . . . . . . . 80
show disconnected-tracing . . . . . . . . . . . . . . . . . . 213
show displaced-stepping . . . . . . . . . . . . . . . . . . . . 757
show editing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
show environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
show exceptions, Hurd command . . . . . . . . . . . . . 345
show exec-done-display . . . . . . . . . . . . . . . . . . . . . 382
show extended-prompt . . . . . . . . . . . . . . . . . . . . . . . . 367
show follow-fork-mode . . . . . . . . . . . . . . . . . . . . . . . . 53
show fortran repack-array-slices . . . . . . . . . . 242
show frame-filter priority . . . . . . . . . . . . . . . . . 124
show gnutarget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
show hash, for remote monitors . . . . . . . . . . . . . . . 313

Debugging with gdb

show height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
show history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
show host-charset . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
show index-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
show indirect-call-timeout . . . . . . . . . . . . . . . . . 284
show inferior-tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
show input-radix . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
show interactive-mode. . . . . . . . . . . . . . . . . . . . . . . 388
show language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
show libthread-db-search-path . . . . . . . . . . . . . . 52
show listsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
show logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
show mach-exceptions . . . . . . . . . . . . . . . . . . . . . . . . 348
show max-completions . . . . . . . . . . . . . . . . . . . . . . . . . 26
show max-user-call-depth . . . . . . . . . . . . . . . . . . . 394
show max-value-size . . . . . . . . . . . . . . . . . . . . . . . . . 193
show may-call-functions . . . . . . . . . . . . . . . . . . . . 282
show mem inaccessible-by-default . . . . . . . . . . 185
show mi-async . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 591
show mips abi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
show mips compression . . . . . . . . . . . . . . . . . . . . . . . 360
show mips mask-address . . . . . . . . . . . . . . . . . . . . . . 360
show mipsfpu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
show multiple-symbols. . . . . . . . . . . . . . . . . . . . . . . 147
show new-console . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
show new-group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
show non-stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
show opaque-type-resolution . . . . . . . . . . . . . . . . 273
show osabi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
show output-radix . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
show overload-resolution . . . . . . . . . . . . . . . . . . . 236
show pagination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
show paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
show print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
show print finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
show print inferior-events . . . . . . . . . . . . . . . . . . 45
show print symbol-loading . . . . . . . . . . . . . . . . . . 273
show print thread-events . . . . . . . . . . . . . . . . . . . . . 51
show print type hex . . . . . . . . . . . . . . . . . . . . . . . . . . 264
show print type methods . . . . . . . . . . . . . . . . . . . . . 263
show print type nested-type-limit. . . . . . . . . . 263
show print type typedefs . . . . . . . . . . . . . . . . . . . . 264
show processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
show procfs-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
show procfs-trace . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
show prompt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
show radix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
show range-stepping . . . . . . . . . . . . . . . . . . . . . . . . . . 87
show ravenscar task-switching . . . . . . . . . . . . . . 259
show record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
show record btrace . . . . . . . . . . . . . . . . . . . . . . . . . . 107
show record full . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
show remote . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
show remote system-call-allowed . . . . . . . . . . . 838
show remote-mips64-transfers-32bit-regs . . 360
show remotecache . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
show remoteflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
show script-extension. . . . . . . . . . . . . . . . . . . . . . . 391

Command, Variable, and Function Index

show sh calling-convention . . . . . . . . . . . . . . . . . 354
show shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
show signal-thread . . . . . . . . . . . . . . . . . . . . . . . . . . 345
show signals, Hurd command . . . . . . . . . . . . . . . . 345
show sigs, Hurd command . . . . . . . . . . . . . . . . . . . . 345
show sigthread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
show solib-search-path . . . . . . . . . . . . . . . . . . . . . 299
show source open . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
show stack-cache . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
show startup-quietly . . . . . . . . . . . . . . . . . . . . . . . . . 13
show stop-on-solib-events . . . . . . . . . . . . . . . . . . 297
show stopped, Hurd command . . . . . . . . . . . . . . . . 345
show struct-convention . . . . . . . . . . . . . . . . . . . . . 358
show style . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
show substitute-path . . . . . . . . . . . . . . . . . . . . . . . . 135
show suppress-cli-notifications . . . . . . . . . . . 389
show sysroot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
show target-charset . . . . . . . . . . . . . . . . . . . . . . . . . 188
show target-file-system-kind . . . . . . . . . . . . . . 299
show target-wide-charset . . . . . . . . . . . . . . . . . . . 188
show task, Hurd commands . . . . . . . . . . . . . . . . . . . 346
show tcp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
show thread, Hurd command . . . . . . . . . . . . . . . . . 346
show trace-buffer-size . . . . . . . . . . . . . . . . . . . . . 214
show trace-notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
show trace-stop-notes. . . . . . . . . . . . . . . . . . . . . . . 214
show trace-user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
show unwind-on-signal. . . . . . . . . . . . . . . . . . . . . . . 282
show unwind-on-terminating-exception . . . . . 282
show unwind-on-timeout . . . . . . . . . . . . . . . . . . . . . 282
show unwindonsignal . . . . . . . . . . . . . . . . . . . . . . . . . 282
show user . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
show values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
show verbose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
show version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
show warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
show width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
show write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
show-all-if-ambiguous . . . . . . . . . . . . . . . . . . . . . . 721
show-all-if-unmodified . . . . . . . . . . . . . . . . . . . . . 721
show-mode-in-prompt . . . . . . . . . . . . . . . . . . . . . . . . 721
si (stepi) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
signal annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . 698
signal-event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
signal-name annotation . . . . . . . . . . . . . . . . . . . . . 697
signal-name-end annotation . . . . . . . . . . . . . . . . . 697
signal-string annotation . . . . . . . . . . . . . . . . . . . 697
signal-string-end annotation . . . . . . . . . . . . . . 697
SignalEvent.stop_signal . . . . . . . . . . . . . . . . . . . . 453
signalled annotation . . . . . . . . . . . . . . . . . . . . . . . . 697
silent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
sim, a command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
simple-values-ref-types . . . . . . . . . . . . . . . . . . . . 685
skip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
skip delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
skip disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
skip enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

953

skip file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
skip function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
skip-completed-text . . . . . . . . . . . . . . . . . . . . . . . . 721
skip-csi-sequence () . . . . . . . . . . . . . . . . . . . . . . . . 735
source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
source annotation . . . . . . . . . . . . . . . . . . . . . . . . . . . 698
start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
start-kbd-macro (C-x () . . . . . . . . . . . . . . . . . . . . . 734
starti. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
starting annotation . . . . . . . . . . . . . . . . . . . . . . . . . 697
STDERR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406, 407
stdio-port? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
STDLOG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
STDOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406, 407
step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
step& . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
stepi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
stepi&. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
stop, a pseudo-command . . . . . . . . . . . . . . . . . . . . . 394
StopEvent.details . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
stopping annotation . . . . . . . . . . . . . . . . . . . . . . . . . 697
strace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
string->argv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
STYLE_ADDRESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
STYLE_ADDRESS_OFFSET . . . . . . . . . . . . . . . . . . . . . . . 508
STYLE_ASSEMBLER_DIRECTIVE. . . . . . . . . . . . . . . . . . 508
STYLE_COMMENT_START . . . . . . . . . . . . . . . . . . . . . . . . 509
STYLE_IMMEDIATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
STYLE_MNEMONIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
STYLE_REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
STYLE_SUB_MNEMONIC . . . . . . . . . . . . . . . . . . . . . . . . . . 508
STYLE_SYMBOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
STYLE_TEXT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
symbol-addr-class . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-argument? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-constant? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
symbol-function? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
symbol-linkage-name . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
symbol-needs-frame? . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-print-name . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-symtab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
symbol-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
symbol-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
symbol-value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
symbol-variable? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
Symbol.addr_class . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.is_argument . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.is_constant . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.is_function . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
Symbol.is_variable . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.linkage_name . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.needs_frame . . . . . . . . . . . . . . . . . . . . . . . . . . 486

954

Symbol.print_name . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.symtab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 486
Symbol.value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
symbol? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554
SYMBOL_COMMON_BLOCK_DOMAIN . . . . . . . . . . . . . . . . 487
SYMBOL_FUNCTION_DOMAIN . . . . . . . . . . . . . . . . 487, 556
SYMBOL_FUNCTIONS_DOMAIN . . . . . . . . . . . . . . . . . . . . 556
SYMBOL_LABEL_DOMAIN . . . . . . . . . . . . . . . . . . . . 487, 556
SYMBOL_LOC_ARG . . . . . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_BLOCK . . . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_COMMON_BLOCK . . . . . . . . . . . . . . . . . . . . 489
SYMBOL_LOC_COMPUTED . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_CONST . . . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_CONST_BYTES . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_LABEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
SYMBOL_LOC_LOCAL . . . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_OPTIMIZED_OUT . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_REF_ARG . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_REGISTER . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_REGPARM_ADDR . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_STATIC . . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_TYPEDEF . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_UNDEF . . . . . . . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_LOC_UNRESOLVED . . . . . . . . . . . . . . . . . 488, 557
SYMBOL_MODULE_DOMAIN . . . . . . . . . . . . . . . . . . . . . . . 487
SYMBOL_STRUCT_DOMAIN. . . . . . . . . . . . . . . . . . . 487, 556
SYMBOL_TYPE_DOMAIN . . . . . . . . . . . . . . . . . . . . . 487, 556
SYMBOL_TYPES_DOMAIN . . . . . . . . . . . . . . . . . . . . . . . . 556
SYMBOL_UNDEF_DOMAIN . . . . . . . . . . . . . . . . . . . . 487, 556
SYMBOL_VAR_DOMAIN . . . . . . . . . . . . . . . . . . . . . . 487, 556
SYMBOL_VARIABLES_DOMAIN . . . . . . . . . . . . . . . . . . . . 556
symtab-filename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
symtab-fullname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
symtab-global-block . . . . . . . . . . . . . . . . . . . . . . . . 558
symtab-objfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
symtab-static-block . . . . . . . . . . . . . . . . . . . . . . . . 558
symtab-valid? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
Symtab.filename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
Symtab.fullname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
Symtab.global_block . . . . . . . . . . . . . . . . . . . . . . . . 490
Symtab.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
Symtab.linetable . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
Symtab.objfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
Symtab.producer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
Symtab.static_block . . . . . . . . . . . . . . . . . . . . . . . . 490
symtab? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558
Symtab_and_line.is_valid . . . . . . . . . . . . . . . . . . . 489
Symtab_and_line.last . . . . . . . . . . . . . . . . . . . . . . . 489
Symtab_and_line.line . . . . . . . . . . . . . . . . . . . . . . . 489
Symtab_and_line.pc . . . . . . . . . . . . . . . . . . . . . . . . . . 489
Symtab_and_line.symtab . . . . . . . . . . . . . . . . . . . . . 489
sysinfo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Debugging with gdb

Ttaas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
tab-insert (M-TAB) . . . . . . . . . . . . . . . . . . . . . . . . . . 731
tabset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
target ctf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
target record . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
target record-btrace . . . . . . . . . . . . . . . . . . . . . . . . 103
target record-full . . . . . . . . . . . . . . . . . . . . . . . . . . 103
target sim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
target tfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
target-config . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
TargetConnection.description . . . . . . . . . . . . . . 500
TargetConnection.details . . . . . . . . . . . . . . . . . . . 500
TargetConnection.is_valid. . . . . . . . . . . . . . . . . . 500
TargetConnection.num . . . . . . . . . . . . . . . . . . . . . . . 500
TargetConnection.type . . . . . . . . . . . . . . . . . . . . . . 500
task (Ada) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
tbreak. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
tcatch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
tdump. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
teval (tracepoints) . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
tfaas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
tfile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
tfind. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
thbreak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
this, inside C++ member functions . . . . . . . . . . . . 234
thread apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
thread find . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
thread name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
thread thread-id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
thread-info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 685
ThreadEvent.inferior_thread . . . . . . . . . . . . . . . 452
ThreadExitedEvent.inferior_thread . . . . . . . . 456
throw-user-error . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542
tilde-expand (M-~) . . . . . . . . . . . . . . . . . . . . . . . . . . 735
trace. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
transpose-chars (C-t). . . . . . . . . . . . . . . . . . . . . . . 731
transpose-words (M-t). . . . . . . . . . . . . . . . . . . . . . . 731
tsave. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
tstart [ notes ] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
tstatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
tstop [ notes ] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
tty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
tui disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
tui enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582
tui layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
tui new-layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
tui refresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
tui reg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
tui window height. . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
tui window width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
TuiStatusEvent.enabled . . . . . . . . . . . . . . . . . . . . . 457
TuiWindow.erase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
TuiWindow.height . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
TuiWindow.is_valid . . . . . . . . . . . . . . . . . . . . . . . . . . 501
TuiWindow.title . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
TuiWindow.width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

Command, Variable, and Function Index

TuiWindow.write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
tvariable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
type-array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
type-const . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
type-field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
type-fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
type-has-field-deep? . . . . . . . . . . . . . . . . . . . . . . . 571
type-has-field? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
type-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-num-fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
type-pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-print-name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-sizeof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-strip-typedefs . . . . . . . . . . . . . . . . . . . . . . . . 533
type-tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
type-target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-unqualified . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
type-vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533
type-volatile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534
Type.alignof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.const . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.dynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
Type.is_array_like . . . . . . . . . . . . . . . . . . . . . . . . . . 420
Type.is_scalar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.is_signed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420
Type.is_string_like . . . . . . . . . . . . . . . . . . . . . . . . 420
Type.name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.objfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.optimized_out . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Type.pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.sizeof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.strip_typedefs . . . . . . . . . . . . . . . . . . . . . . . . 422
Type.tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
Type.target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Type.template_argument . . . . . . . . . . . . . . . . . . . . . 422
Type.unqualified . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
Type.volatile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
type?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
TYPE_CODE_ARRAY . . . . . . . . . . . . . . . . . . . . . . . . 422, 534
TYPE_CODE_BITSTRING . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_BOOL . . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_CHAR . . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_COMPLEX . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_DECFLOAT . . . . . . . . . . . . . . . . . . . . . 423, 536
TYPE_CODE_ENUM . . . . . . . . . . . . . . . . . . . . . . . . . 422, 535
TYPE_CODE_ERROR . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_FIXED_POINT . . . . . . . . . . . . . . . . . 424, 536
TYPE_CODE_FLAGS . . . . . . . . . . . . . . . . . . . . . . . . 422, 535
TYPE_CODE_FLT . . . . . . . . . . . . . . . . . . . . . . . . . . . 423, 535

955

TYPE_CODE_FUNC . . . . . . . . . . . . . . . . . . . . . . . . . 422, 535
TYPE_CODE_INT . . . . . . . . . . . . . . . . . . . . . . . . . . . 422, 535
TYPE_CODE_INTERNAL_FUNCTION . . . . . . . . . . 423, 536
TYPE_CODE_MEMBERPTR . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_METHOD . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_METHODPTR . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_NAMESPACE . . . . . . . . . . . . . . . 423, 424, 536
TYPE_CODE_PTR . . . . . . . . . . . . . . . . . . . . . . . . . . . 422, 534
TYPE_CODE_RANGE . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_REF . . . . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_RVALUE_REF. . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_SET . . . . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_STRING . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_STRUCT . . . . . . . . . . . . . . . . . . . . . . . 422, 534
TYPE_CODE_TYPEDEF . . . . . . . . . . . . . . . . . . . . . . 423, 536
TYPE_CODE_UNION . . . . . . . . . . . . . . . . . . . . . . . . 422, 534
TYPE_CODE_VOID . . . . . . . . . . . . . . . . . . . . . . . . . 423, 535
TYPE_CODE_XMETHOD . . . . . . . . . . . . . . . . . . . . . . 424, 536

Uu (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 582
u (until) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
undefined-command-error-code . . . . . . . . . . . . . . 685
undisplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
undo (C-_ or C-x C-u) . . . . . . . . . . . . . . . . . . . . . . . . 735
universal-argument (). . . . . . . . . . . . . . . . . . . . . . . 733
unix-filename-rubout () . . . . . . . . . . . . . . . . . . . . 732
unix-line-discard (C-u) . . . . . . . . . . . . . . . . . . . . 732
unix-word-rubout (C-w) . . . . . . . . . . . . . . . . . . . . . 732
unset environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
unset substitute-path. . . . . . . . . . . . . . . . . . . . . . . 135
until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
until&. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
unwind-stop-reason-string. . . . . . . . . . . . . . . . . . 552
up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 581
up-silently . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
upcase-word (M-u) . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584

Vv (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 582
value->bool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value->bytevector . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
value->integer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value->lazy-string . . . . . . . . . . . . . . . . . . . . . . . . . . 530
value->real . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value->string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
value-abs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-add . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
value-call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value-cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
value-const-value . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value-dereference . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
value-div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531

956

value-dynamic-cast . . . . . . . . . . . . . . . . . . . . . . . . . . 528
value-dynamic-type . . . . . . . . . . . . . . . . . . . . . . . . . . 527
value-fetch-lazy! . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value-lazy? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-logand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-logior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-lognot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-logxor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-lsh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-mod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-mul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-neg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-optimized-out? . . . . . . . . . . . . . . . . . . . . . . . 527
value-pos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-pow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-reference-value . . . . . . . . . . . . . . . . . . . . . . 529
value-referenced-value . . . . . . . . . . . . . . . . . . . . . 528
value-reinterpret-cast . . . . . . . . . . . . . . . . . . . . . 528
value-rem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-rsh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value-rvalue-reference-value . . . . . . . . . . . . . . 529
value-sub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531
value-subscript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
value-type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
Value.__init__ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
Value.address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
Value.assign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
Value.bytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
Value.cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
Value.const_value . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Value.dereference . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
Value.dynamic_cast . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Value.dynamic_type . . . . . . . . . . . . . . . . . . . . . . . . . . 412
Value.fetch_lazy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Value.format_string . . . . . . . . . . . . . . . . . . . . . . . . 415
Value.is_lazy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
Value.is_optimized_out . . . . . . . . . . . . . . . . . . . . . 412
Value.lazy_string . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Value.reference_value . . . . . . . . . . . . . . . . . . . . . . 415
Value.referenced_value . . . . . . . . . . . . . . . . . . . . . 414
Value.reinterpret_cast . . . . . . . . . . . . . . . . . . . . . 415
Value.string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
Value.to_array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
Value.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
value<=? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532

Debugging with gdb

value<? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value=? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value>=? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value>? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
value? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
vi-cmd-mode-string . . . . . . . . . . . . . . . . . . . . . . . . . . 722
vi-editing-mode (M-C-j) . . . . . . . . . . . . . . . . . . . . 736
vi-ins-mode-string . . . . . . . . . . . . . . . . . . . . . . . . . . 722
visible-stats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722

Ww (SingleKey TUI key) . . . . . . . . . . . . . . . . . . . . . . . . 582
w (with) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
watch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
watchpoint annotation. . . . . . . . . . . . . . . . . . . . . . . 698
whatis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
where. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
while. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396
while-stepping (tracepoints) . . . . . . . . . . . . . . . . . 210
Window.click . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
Window.close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
Window.hscroll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
Window.render . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
Window.vscroll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
winheight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
winwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
with command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
WP_ACCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492, 560
WP_READ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492, 560
WP_WRITE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492, 560

X
x (examine memory) . . . . . . . . . . . . . . . . . . . . . . . . . . 152
x(examine), and info line . . . . . . . . . . . . . . . . . . . . 136
XMethod.__init__ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
XMethodMatcher.__init__ . . . . . . . . . . . . . . . . . . . . 445
XMethodMatcher.match . . . . . . . . . . . . . . . . . . . . . . . 445
XMethodWorker.__call__ . . . . . . . . . . . . . . . . . . . . . 445
XMethodWorker.get_arg_types . . . . . . . . . . . . . . . 445
XMethodWorker.get_result_type . . . . . . . . . . . . . 445

Yyank (C-y) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733
yank-last-arg (M-. or M-_) . . . . . . . . . . . . . . . . . . 730
yank-nth-arg (M-C-y) . . . . . . . . . . . . . . . . . . . . . . . . 730
yank-pop (M-y) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733

Command, Variable, and Function Index

The body of this manual is set in
cmr10,
with headings in cmbx10
and examples in cmtt10.
cmti10 ,cmbx10, andcmsl10are used for emphasis.

957