The “stabs” debug format

Julia Menapace, Jim Kingdon, David MacKenzie
Cygnus Support

Cygnus Support
Revision
TEXinfo 2017-08-23.19

Copyright c 1992–2024 Free Software Foundation, Inc. Contributed by Cygnus Support.
Written by Julia Menapace, Jim Kingdon, and David MacKenzie.
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 theFree Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with
no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free
Documentation License”.

iTable of Contents
1

Overview of Stabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1
1.2
1.3
1.4
1.5

2

Overview of Debugging Information Flow . . . . . . . . . . . . . . . . . . . . . . . 1
Overview of Stab Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The String Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
A Simple Example in C Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
The Simple Example at the Assembly Level . . . . . . . . . . . . . . . . . . . . . 4

Encoding the Structure of the Program . . . . . . . 7
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

Main Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Paths and Names of the Source Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Names of Include Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Line Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Nested Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Block Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Alternate Entry Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4

Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1
4.2
4.3
4.4
4.5
4.6
4.7

5

Automatic Variables Allocated on the Stack . . . . . . . . . . . . . . . . . . . 15
Global Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Register Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Common Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Static Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Fortran Based Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7.1 Passing Parameters in Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7.2 Storing Parameters as Local Variables . . . . . . . . . . . . . . . . . . . . 19
4.7.3 Passing Parameters by Reference. . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.7.4 Passing Conformant Array Parameters . . . . . . . . . . . . . . . . . . . . 20

Defining Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1

Builtin Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.1 Traditional Builtin Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.1.1 Traditional Integer Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1.1.2 Traditional Other Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.1.2 Defining Builtin Types Using Builtin Type Descriptors . . . . 22
5.1.3 Negative Type Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.2 Miscellaneous Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3 Cross-References to Other Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

ii

STABS
5.4 Subrange Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.5 Array Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.6 Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.7 Enumerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.8 Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.9 Giving a Type a Name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.10 Unions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.11 Function Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

6Representation of #define and #undef . . . . . . 33

7

Symbol Information in Symbol Tables . . . . . . . 35
7.1
7.2

8

Symbol Table Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Transformations on Symbol Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.2.1 Transformations on Static Variables . . . . . . . . . . . . . . . . . . . . . . . 35
7.2.2 Transformations on Global Variables . . . . . . . . . . . . . . . . . . . . . . 36
7.2.3 Transformations of Stabs in separate sections . . . . . . . . . . . . . 36

GNU C++ Stabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
8.1 C++ Class Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
8.2 Defining a Symbol Within Another Type . . . . . . . . . . . . . . . . . . . . . . 39
8.3 Basic Types For C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
8.4 Simple Class Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.5 Class Instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.6 Method Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
8.7 The ‘#’ Type Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
8.8 The ‘@’ Type Descriptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
8.9 Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
8.10 Method Modifiers (const, volatile, const volatile) . . . . . . . . 44
8.11 Virtual Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
8.12 Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8.13 Virtual Base Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
8.14 Static Members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Appendix A
A.1
A.2

Table of Stab Types . . . . . . . . . . . . . . . 49

Non-Stab Symbol Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Stab Symbol Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Appendix B

Table of Symbol Descriptors . . . . . . 53

Appendix C

Table of Type Descriptors . . . . . . . . . 55

iii

Appendix D Expanded Reference by Stab Type . . 57
D.1 N PC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
D.2 N NSYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
D.3 N NOMAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
D.4 N M2C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
D.5 N BROWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
D.6 N DEFD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
D.7 N EHDECL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
D.8 N MOD2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
D.9 N CATCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
D.10 N SSYM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
D.11 N SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
D.12 Non-base registers on Gould systems . . . . . . . . . . . . . . . . . . . . . . . . . 59
D.13 N LENG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Appendix E

Questions and Anomalies. . . . . . . . . . 61

Appendix F

Using Stabs in Their Own Sections . . 63

F.1
F.2

How to Embed Stabs in Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Having the Linker Relocate Stabs in ELF . . . . . . . . . . . . . . . . . . . . . . 64

Appendix G GNU Free Documentation License . . 65
Symbol Types Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

1

1 Overview of Stabs
Stabs refers to a format for information that describes a program to a debugger. This format
was apparently invented by Peter Kessler at the University of California at Berkeley, forthe pdx Pascal debugger; the format has spread widely since then.
This document is one of the few published sources of documentation on stabs. It isbelieved to be comprehensive for stabs used by C. The lists of symbol descriptors (seeAppendix B [Symbol Descriptors], page 53) and type descriptors (see Appendix C [Type Descriptors], page 55) are believed to be completely comprehensive. Stabs for COBOL-specificfeatures and for variant records (used by Pascal and Modula-2) are poorly documented here.
Other sources of information on stabs are Dbx and Dbxtool Interfaces, 2nd edition, by
Sun, 1988, and AIX Version 3.2 Files Reference, Fourth Edition, September 1992, "dbxStabstring Grammar" in the a.out section, page 2-31. This document is believed to incorporate the information from those two sources except where it explicitly directs you to themfor more information.

1.1 Overview of Debugging Information Flow
The GNU C compiler compiles C source in a .c file into assembly language in a .s file,which the assembler translates into a .o file, which the linker combines with other .o files
and libraries to produce an executable file.
With the ‘-g’ option, GCC puts in the .s file additional debugging information, whichis slightly transformed by the assembler and linker, and carried through into the final executable. This debugging information describes features of the source file like line numbers,
the types and scopes of variables, and function names, parameters, and scopes.
For some object file formats, the debugging information is encapsulated in assembler
directives known collectively as stab (symbol table) directives, which are interspersed withthe generated code. Stabs are the native format for debugging information in the a.out and
XCOFF object file formats. The GNU tools can also emit stabs in the COFF and ECOFF
object file formats.
The assembler adds the information from stabs to the symbol information it places bydefault in the symbol table and the string table of the .o file it is building. The linker
consolidates the .o files into one executable file, with one symbol table and one stringtable. Debuggers use the symbol and string tables in the executable as a source of debugging
information about the program.

1.2 Overview of Stab Format
There are three overall formats for stab assembler directives, differentiated by the firstword of the stab. The name of the directive describes which combination of four possible
data fields follows. It is either .stabs (string), .stabn (number), or .stabd (dot). IBM’s
XCOFF assembler uses .stabx (and some other directives such as .file and .bi) insteadof .stabs, .stabn or .stabd.
The overall format of each class of stab is:.stabs "string",type,other,desc,value.stabn type,other,desc,value

2

STABS

.stabd type,other,desc.stabx "string",value,type,sdb-type
For .stabn and .stabd, there is no string (the n_strx field is zero; see Chapter 7[Symbol Tables], page 35). For .stabd, the value field is implicit and has the value of thecurrent file location. For .stabx, the sdb-type field is unused for stabs and can always be
set to zero. The other field is almost always unused and can be set to zero.
The number in the type field gives some basic information about which type of stab thisis (or whether it is a stab, as opposed to an ordinary symbol). Each valid type number
defines a different stab type; further, the stab type defines the exact interpretation of, andpossible values for, any remaining string, desc, or value fields present in the stab. See
Appendix A [Stab Types], page 49, for a list in numeric order of the valid type field values
for stab directives.

1.3 The String Field
For most stabs the string field holds the meat of the debugging information. The flexible
nature of this field is what makes stabs extensible. For some stab types the string fieldcontains only a name. For other stab types the contents can be a great deal more complex.
The overall format of the string field for most stab types is:"name:symbol-descriptor type-information"
name is the name of the symbol represented by the stab; it can contain a pair of colons(see Section 8.2 [Nested Symbols], page 39). name can be omitted, which means the stab
represents an unnamed object. For example, ‘:t10=*2’ defines type 10 as a pointer to type2, but does not give the type a name. Omitting the name field is supported by AIX dbx
and GDB after about version 4.8, but not other debuggers. GCC sometimes uses a single
space as the name instead of omitting the name altogether; apparently that is supported
by most debuggers.
The symbol-descriptor following the ‘:’ is an alphabetic character that tells more specifically what kind of symbol the stab represents. If the symbol-descriptor is omitted, but
type information follows, then the stab represents a local variable. For a list of symbol
descriptors, see Appendix B [Symbol Descriptors], page 53. The ‘c’ symbol descriptor is an
exception in that it is not followed by type information. See Chapter 3 [Constants], page 13.
type-information is either a type-number, or ‘type-number=’. A type-number alone is a
type reference, referring directly to a type that has already been defined.
The ‘type-number=’ form is a type definition, where the number represents a new typewhich is about to be defined. The type definition may refer to other types by number, andthose type numbers may be followed by ‘=’ and nested definitions. Also, the Lucid compiler
will repeat ‘type-number=’ more than once if it wants to define several type numbers at
once.
In a type definition, if the character that follows the equals sign is non-numeric then it
is a type-descriptor, and tells what kind of type is about to be defined. Any other values
following the type-descriptor vary, depending on the type-descriptor. See Appendix C [TypeDescriptors], page 55, for a list of type-descriptor values. If a number follows the ‘=’ then
the number is a type-reference. For a full description of types, Chapter 5 [Types], page 21.

Chapter 1: Overview of Stabs

3

A type-number is often a single number. The GNU and Sun tools additionally permit
a type-number to be a pair (file-number,filetype-number) (the parentheses appear in thestring, and serve to distinguish the two cases). The file-number is 0 for the base source file,
1 for the first included file, 2 for the next, and so on. The filetype-number is a number
starting with 1 which is incremented for each new type defined in the file. (Separating thefile number and the type number permits the N_BINCL optimization to succeed more often;
see Section 2.3 [Include Files], page 8).
There is an AIX extension for type attributes. Following the ‘=’ are any number of typeattributes. Each one starts with ‘@’ and ends with ‘;’. Debuggers, including AIX’s dbx and
GDB 4.10, skip any type attributes they do not recognize. GDB 4.9 and other versions ofdbx may not do this. Because of a conflict with C++ (see Chapter 8 [Cplusplus], page 39),
new attributes should not be defined which begin with a digit, ‘(’, or ‘-’; GDB may beunable to distinguish those from the C++ type descriptor ‘@’. The attributes are:aboundaryboundary is an integer specifying the alignment. I assume it applies to all
variables of this type.
pinteger

Pointer class (for checking). Not sure what this means, or how integer is interpreted.

P

Indicate this is a packed type, meaning that structure fields or array elements
are placed more closely in memory, to save memory at the expense of speed.

ssizeSize in bits of a variable of this type. This is fully supported by GDB 4.11 andlater.

S

Indicate that this type is a string instead of an array of characters, or a bitstring
instead of a set. It doesn’t change the layout of the data being represented, butdoes enable the debugger to know which type it is.

V

Indicate that this type is a vector instead of an array. The only major difference
between vectors and arrays is that vectors are passed by value instead of byreference (vector coprocessor extension).

All of this can make the string field quite long. All versions of GDB, and some versionsof dbx, can handle arbitrarily long strings. But many versions of dbx (or assemblers or
linkers, I’m not sure which) cretinously limit the strings to about 80 characters, so compilers
which must work with such systems need to split the .stabs directive into several .stabs
directives. Each stab duplicates every field except the string field. The string field of every
stab except the last is marked as continued with a backslash at the end (in the assembly
code this may be written as a double backslash, depending on the assembler). Removing
the backslashes and concatenating the string fields of each stab produces the original, long
string. Just to be incompatible (or so they don’t have to worry about what the assembler
does with backslashes), AIX can use ‘?’ instead of backslash.

1.4 A Simple Example in C Source
To get the flavor of how stabs describe source information for a C program, let’s look at
the simple program:main()

4

STABS

{
printf("Hello world");}
When compiled with ‘-g’, the program above yields the following .s file. Line numbers
have been added to make it easier to refer to parts of the .s file in the description of thestabs that follows.

1.5 The Simple Example at the Assembly Level
This simple “hello world” example demonstrates several of the stab types used to describe
C language source files.
1 gcc2_compiled.:
2 .stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0
3 .stabs "hello.c",100,0,0,Ltext0
4 .text
5 Ltext0:
6 .stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0
7 .stabs "char:t2=r2;0;127;",128,0,0,0
8 .stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0
9 .stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
10 .stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0
11 .stabs "short int:t6=r1;-32768;32767;",128,0,0,0
12 .stabs "long long int:t7=r1;0;-1;",128,0,0,0
13 .stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0
14 .stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0
15 .stabs "signed char:t10=r1;-128;127;",128,0,0,0
16 .stabs "unsigned char:t11=r1;0;255;",128,0,0,0
17 .stabs "float:t12=r1;4;0;",128,0,0,0
18 .stabs "double:t13=r1;8;0;",128,0,0,0
19 .stabs "long double:t14=r1;8;0;",128,0,0,0
20 .stabs "void:t15=15",128,0,0,021.align 4
22 LC0:23.ascii "Hello, world!\12\0"24.align 4
25.global _main
26.proc 127 _main:
28 .stabn 68,0,4,LM1
29 LM1:
30!#PROLOGUE# 0
31
save %sp,-136,%sp
32!#PROLOGUE# 1
33
call ___main,034
nop
35 .stabn 68,0,5,LM2
36 LM2:

537 LBB2:
38
sethi %hi(LC0),%o1
39
or %o1,%lo(LC0),%o0
40
call _printf,041
nop
42 .stabn 68,0,6,LM3
43 LM3:
44 LBE2:
45 .stabn 68,0,6,LM4
46 LM4:47 L1:
48
ret
49
restore50 .stabs "main:F1",36,0,0,_main
51 .stabn 192,0,0,LBB2
52 .stabn 224,0,0,LBE2

7

2 Encoding the Structure of the Program
The elements of the program structure that stabs encode include the name of the mainfunction, the names of the source and include files, the line numbers, procedure names andtypes, and the beginnings and ends of blocks of code.

2.1 Main Program
Most languages allow the main program to have any name. The N_MAIN stab type tells thedebugger the name that is used in this program. Only the string field is significant; it is
the name of a function which is the main program. Most C compilers do not use this stab(they expect the debugger to assume that the name is main), but some C compilers emit
an N_MAIN stab for the main function. I’m not sure how XCOFF handles this.

2.2 Paths and Names of the Source Files
Before any other stabs occur, there must be a stab specifying the source file. This information is contained in a symbol of stab type N_SO; the string field contains the name of the file.
The value of the symbol is the start address of the portion of the text section corresponding
to that file.
Some compilers use the desc field to indicate the language of the source file. Sun’scompilers started this usage, and the first constants are derived from their documentation.
Languages added by gcc/gdb start at 0x32 to avoid conflict with languages Sun may add
in the future. A desc field with a value 0 indicates that no language has been specified via
this mechanism.
N_SO_AS (0x1)
Assembly language
N_SO_C (0x2)
K&R traditional C
N_SO_ANSI_C (0x3)
ANSI C
N_SO_CC (0x4)C++
N_SO_FORTRAN (0x5)Fortran
N_SO_PASCAL (0x6)
Pascal
N_SO_FORTRAN90 (0x7)
Fortran90
N_SO_OBJC (0x32)
Objective-C
N_SO_OBJCPLUS (0x33)
Objective-C++

8

STABS

Some compilers (for example, GCC2 and SunOS4 /bin/cc) also include the directory inwhich the source was compiled, in a second N_SO symbol preceding the one containing thefile name. This symbol can be distinguished by the fact that it ends in a slash. Code fromthe cfront C++ compiler can have additional N_SO symbols for nonexistent source files after
the N_SO for the real source file; these are believed to contain no useful information.
For example:.stabs "/cygint/s1/users/jcm/play/",100,0,0,Ltext0.stabs "hello.c",100,0,0,Ltext0.text
Ltext0:# 100 is N SO

Instead of N_SO symbols, XCOFF uses a .file assembler directive which assembles toa C_FILE symbol; explaining this in detail is outside the scope of this document.
If it is useful to indicate the end of a source file, this is done with an N_SO symbol with
an empty string for the name. The value is the address of the end of the text section for
the file. For some systems, there is no indication of the end of a source file, and you justneed to figure it ended when you see an N_SO for a different source file, or a symbol endingin .o (which at least some linkers insert to mark the start of a new .o file).

2.3 Names of Include Files
There are several schemes for dealing with include files: the traditional N_SOL approach,Sun’s N_BINCL approach, and the XCOFF C_BINCL approach (which despite the similarname has little in common with N_BINCL).
An N_SOL symbol specifies which include file subsequent symbols refer to. The string
field is the name of the file and the value is the text address corresponding to the end of
the previous include file and the start of this one. To specify the main source file again, usean N_SOL symbol with the name of the main source file.
The N_BINCL approach works as follows. An N_BINCL symbol specifies the start of an
include file. In an object file, only the string is significant; the linker puts data into some ofthe other fields. The end of the include file is marked by an N_EINCL symbol (which has no
string field). In an object file, there is no significant data in the N_EINCL symbol. N_BINCL
and N_EINCL can be nested.
If the linker detects that two source files have identical stabs between an N_BINCL and
N_EINCL pair (as will generally be the case for a header file), then it only puts out the stabs
once. Each additional occurrence is replaced by an N_EXCL symbol. I believe the GNU
linker and the Sun (both SunOS4 and Solaris) linker are the only ones which supports thisfeature.
A linker which supports this feature will set the value of a N_BINCL symbol to the total of
all the characters in the stabs strings included in the header file, omitting any file numbers.
The value of an N_EXCL symbol is the same as the value of the N_BINCL symbol it replaces.
This information can be used to match up N_EXCL and N_BINCL symbols which have thesame filename. The N_EINCL value, and the values of the other and description fields for all
three, appear to always be zero.
For the start of an include file in XCOFF, use the .bi assembler directive, which generates a C_BINCL symbol. A .ei directive, which generates a C_EINCL symbol, denotes theChapter 2: Encoding the Structure of the Program9

end of the include file. Both directives are followed by the name of the source file in quotes,
which becomes the string for the symbol. The value of each symbol, produced automaticallyby the assembler and linker, is the offset into the executable of the beginning (inclusive, as
you’d expect) or end (inclusive, as you would not expect) of the portion of the COFF line
table that corresponds to this include file. C_BINCL and C_EINCL do not nest.

2.4 Line Numbers
An N_SLINE symbol represents the start of a source line. The desc field contains the line
number and the value contains the code address for the start of that source line. On mostmachines the address is absolute; for stabs in sections (see Appendix F [Stab Sections],
page 63), it is relative to the function in which the N_SLINE symbol occurs.
GNU documents N_DSLINE and N_BSLINE symbols for line numbers in the data or bss
segments, respectively. They are identical to N_SLINE but are relocated differently by
the linker. They were intended to be used to describe the source location of a variabledeclaration, but I believe that GCC2 actually puts the line number in the desc field of thestab for the variable itself. GDB has been ignoring these symbols (unless they contain astring field) since at least GDB 3.5.
For single source lines that generate discontiguous code, such as flow of control statements, there may be more than one line number entry for the same source line. In thiscase there is a line number entry at the start of each code range, each with the same line
number.
XCOFF does not use stabs for line numbers. Instead, it uses COFF line numbers (which
are outside the scope of this document). Standard COFF line numbers cannot deal withinclude files, but in XCOFF this is fixed with the C_BINCL method of marking include files(see Section 2.3 [Include Files], page 8).

2.5 Procedures
All of the following stabs normally use the N_FUN symbol type. However, Sun’s acc compiler
on SunOS4 uses N_GSYM and N_STSYM, which means that the value of the stab for the function
is useless and the debugger must get the address of the function from the non-stab symbols
instead. On systems where non-stab symbols have leading underscores, the stabs will lackunderscores and the debugger needs to know about the leading underscore to match up thestab and the non-stab symbol. BSD Fortran is said to use N_FNAME with the same restriction;
the value of the symbol is not useful (I’m not sure it really does use this, because GDB
doesn’t handle this and no one has complained).
A function is represented by an ‘F’ symbol descriptor for a global (extern) function, and‘f’ for a static (local) function. For a.out, the value of the symbol is the address of the startof the function; it is already relocated. For stabs in ELF, the SunPRO compiler version
2.0.1 and GCC put out an address which gets relocated by the linker. In a future release
SunPRO is planning to put out zero, in which case the address can be found from the ELF(non-stab) symbol. Because looking things up in the ELF symbols would probably be slow,
I’m not sure how to find which symbol of that name is the right one, and this doesn’t provide
any way to deal with nested functions, it would probably be better to make the value ofthe stab an address relative to the start of the file, or just absolute. See Section F.2 [ELF
Linker Relocation], page 64, for more information on linker relocation of stabs in ELF files.

10

STABS

For XCOFF, the stab uses the C_FUN storage class and the value of the stab is meaningless;the address of the function can be found from the csect symbol (XTY LD/XMC PR).
The type information of the stab represents the return type of the function; thus ‘foo:f5’means that foo is a function returning type 5. There is no need to try to get the line numberof the start of the function from the stab for the function; it is in the next N_SLINE symbol.
Some compilers (such as Sun’s Solaris compiler) support an extension for specifying
the types of the arguments. I suspect this extension is not used for old (non-prototyped)
function definitions in C. If the extension is in use, the type information of the stab for thefunction is followed by type information for each argument, with each argument precededby ‘;’. An argument type of 0 means that additional arguments are being passed, whosetypes and number may vary (‘...’ in ANSI C). GDB has tolerated this extension (parsed
the syntax, if not necessarily used the information) since at least version 4.8; I don’t knowwhether all versions of dbx tolerate it. The argument types given here are not redundantwith the symbols for the formal parameters (see Section 4.7 [Parameters], page 18); they
are the types of the arguments as they are passed, before any conversions might take place.
For example, if a C function which is declared without a prototype takes a float argument,
the value is passed as a double but then converted to a float. Debuggers need to use thetypes given in the arguments when printing values, but when calling the function they need
to use the types given in the symbol defining the function.
If the return type and types of arguments of a function which is defined in anothersource file are specified (i.e., a function prototype in ANSI C), traditionally compilers emit
no stab; the only way for the debugger to find the information is if the source file where thefunction is defined was also compiled with debugging symbols. As an extension the Solaris
compiler uses symbol descriptor ‘P’ followed by the return type of the function, followed by
the arguments, each preceded by ‘;’, as in a stab with symbol descriptor ‘f’ or ‘F’. Thisuse of symbol descriptor ‘P’ can be distinguished from its use for register parameters (seeSection 4.7.1 [Register Parameters], page 18) by the fact that it has symbol type N_FUN.
The AIX documentation also defines symbol descriptor ‘J’ as an internal function. I
assume this means a function nested within another function. It also says symbol descriptor‘m’ is a module in Modula-2 or extended Pascal.
Procedures (functions which do not return values) are represented as functions returning
the void type in C. I don’t see why this couldn’t be used for all languages (inventing a void
type for this purpose if necessary), but the AIX documentation defines ‘I’, ‘P’, and ‘Q’ forinternal, global, and static procedures, respectively. These symbol descriptors are unusualin that they are not followed by type information.
The following example shows a stab for a function main which returns type number 1.
The _main specified for the value is a reference to an assembler label which is used to fillin the start address of the function.
.stabs "main:F1",36,0,0,_main# 36 is N FUN
The stab representing a procedure is located immediately following the code of theprocedure. This stab is in turn directly followed by a group of other stabs describing
elements of the procedure. These other stabs describe the procedure’s parameters, its block
local variables, and its block structure.
If functions can appear in different sections, then the debugger may not be able to findthe end of a function. Recent versions of GCC will mark the end of a function with anChapter 2: Encoding the Structure of the Program

11

N_FUN symbol with an empty string for the name. The value is the address of the end of
the current function. Without such a symbol, there is no indication of the address of theend of a function, and you must assume that it ended at the starting address of the next
function or at the end of the text section for the program.

2.6 Nested Procedures
For any of the symbol descriptors representing procedures, after the symbol descriptor andthe type information is optionally a scope specifier. This consists of a comma, the name ofthe procedure, another comma, and the name of the enclosing procedure. The first name islocal to the scope specified, and seems to be redundant with the name of the symbol (beforethe ‘:’). This feature is used by GCC, and presumably Pascal, Modula-2, etc., compilers,
for nested functions.
If procedures are nested more than one level deep, only the immediately containing scopeis specified. For example, this code:int
foo (int x){
int bar (int y){
int baz (int z){
return x + y + z;}
return baz (x + 2 * y);}return x + bar (3 * x);}
produces the stabs:.stabs "baz:f1,baz,bar",36,0,0,_baz.15# 36 is N FUN.stabs "bar:f1,bar,foo",36,0,0,_bar.12.stabs "foo:F1",36,0,0,_foo

2.7 Block Structure
The program’s block structure is represented by the N_LBRAC (left brace) and the N_RBRAC(right brace) stab types. The variables defined inside a block precede the N_LBRAC symbol
for most compilers, including GCC. Other compilers, such as the Convex, Acorn RISC
machine, and Sun acc compilers, put the variables after the N_LBRAC symbol. The values of
the N_LBRAC and N_RBRAC symbols are the start and end addresses of the code of the block,respectively. For most machines, they are relative to the starting address of this source
file. For the Gould NP1, they are absolute. For stabs in sections (see Appendix F [StabSections], page 63), they are relative to the function in which they occur.
The N_LBRAC and N_RBRAC stabs that describe the block scope of a procedure are locatedafter the N_FUN stab that represents the procedure itself.
Sun documents the desc field of N_LBRAC and N_RBRAC symbols as containing the nestinglevel of the block. However, dbx seems to not care, and GCC always sets desc to zero.

12

STABS

For XCOFF, block scope is indicated with C_BLOCK symbols. If the name of the symbolis ‘.bb’, then it is the beginning of the block; if the name of the symbol is ‘.be’; it is theend of the block.

2.8 Alternate Entry Points
Some languages, like Fortran, have the ability to enter procedures at some place other thanthe beginning. One can declare an alternate entry point. The N_ENTRY stab is for this;however, the Sun FORTRAN compiler doesn’t use it. According to AIX documentation,
only the name of a C_ENTRY stab is significant; the address of the alternate entry pointcomes from the corresponding external symbol. A previous revision of this document said
that the value of an N_ENTRY stab was the address of the alternate entry point, but I don’tknow the source for that information.

13

3 Constants
The ‘c’ symbol descriptor indicates that this stab represents a constant. This symbol
descriptor is an exception to the general rule that symbol descriptors are followed by type
information. Instead, it is followed by ‘=’ and one of the following:b value

Boolean constant. value is a numeric value; I assume it is 0 for false or 1 fortrue.

c value

Character constant. value is the numeric value of the constant.

e type-information , value
Constant whose value can be represented as integral. type-information is
the type of the constant, as it would appear after a symbol descriptor (seeSection 1.3 [String Field], page 2). value is the numeric value of the constant.
GDB 4.9 does not actually get the right value if value does not fit in ahost int, but it does not do anything violent, and future debuggers could
be extended to accept integers of any size (whether unsigned or not). This
constant type is usually documented as being only for enumeration constants,
but GDB has never imposed that restriction; I don’t know about otherdebuggers.
i value

Integer constant. value is the numeric value. The type is some sort of genericinteger type (for GDB, a host int); to specify the type explicitly, use ‘e’ instead.

r value

Real constant. value is the real value, which can be ‘INF’ (optionally precededby a sign) for infinity, ‘QNAN’ for a quiet NaN (not-a-number), or ‘SNAN’ for a
signalling NaN. If it is a normal number the format is that accepted by the C
library function atof.

s string

String constant. string is a string enclosed in either ‘’’ (in which case ‘’’characters within the string are represented as ‘\’’ or ‘"’ (in which case ‘"’characters within the string are represented as ‘\"’).

S type-information , elements , bits , pattern
Set constant. type-information is the type of the constant, as it would appear
after a symbol descriptor (see Section 1.3 [String Field], page 2). elements isthe number of elements in the set (does this means how many bits of pattern
are actually used, which would be redundant with the type, or perhaps thenumber of bits set in pattern? I don’t get it), bits is the number of bits in theconstant (meaning it specifies the length of pattern, I think), and pattern isa hexadecimal representation of the set. AIX documentation refers to a limitof 32 bytes, but I see no reason why this limit should exist. This form could
probably be used for arbitrary constants, not just sets; the only catch is thatpattern should be understood to be target, not host, byte order and format.
The boolean, character, string, and set constants are not supported by GDB 4.9, but it
ignores them. GDB 4.8 and earlier gave an error message and refused to read symbols fromthe file containing the constants.
The above information is followed by ‘;’.

15

4 Variables
Different types of stabs describe the various ways that variables can be allocated: on thestack, globally, in registers, in common blocks, statically, or as arguments to a function.

4.1 Automatic Variables Allocated on the Stack
If a variable’s scope is local to a function and its lifetime is only as long as that function
executes (C calls such variables automatic), it can be allocated in a register (see Section 4.3[Register Variables], page 16) or on the stack.
Each variable allocated on the stack has a stab with the symbol descriptor omitted. Since
type information should begin with a digit, ‘-’, or ‘(’, only those characters precluded frombeing used for symbol descriptors. However, the Acorn RISC machine (ARM) is said to get
this wrong: it puts out a mere type definition here, without the preceding ‘type-number=’.
This is a bad idea; there is no guarantee that type descriptors are distinct from symbol
descriptors. Stabs for stack variables use the N_LSYM stab type, or C_LSYM for XCOFF.
The value of the stab is the offset of the variable within the local variables. On mostmachines this is an offset from the frame pointer and is negative. The location of the stabspecifies which block it is defined in; see Section 2.7 [Block Structure], page 11.
For example, the following C code:int
main (){
int x;}
produces the following stabs:.stabs "main:F1",36,0,0,_main# 36 is N FUN.stabs "x:1",128,0,0,-12# 128 is N LSYM
.stabn 192,0,0,LBB2# 192 is N LBRAC.stabn 224,0,0,LBE2# 224 is N RBRAC
See Section 2.5 [Procedures], page 9, for more information on the N_FUN stab, andSection 2.7 [Block Structure], page 11, for more information on the N_LBRAC and N_RBRAC
stabs.

4.2 Global Variables
A variable whose scope is not specific to just one source file is represented by the ‘G’symbol descriptor. These stabs use the N_GSYM stab type (C GSYM for XCOFF). The
type information for the stab (see Section 1.3 [String Field], page 2) gives the type of thevariable.
For example, the following source code:char g_foo = ’c’;yields the following assembly code:.stabs "g_foo:G2",32,0,0,0# 32 is N GSYM
.global _g_foo

16

STABS

.data
_g_foo:.byte 99
The address of the variable represented by the N_GSYM is not contained in the N_GSYM
stab. The debugger gets this information from the external symbol for the global variable.
In the example above, the .global _g_foo and _g_foo: lines tell the assembler to produce
an external symbol.
Some compilers, like GCC, output N_GSYM stabs only once, where the variable is defined.
Other compilers, like SunOS4 /bin/cc, output a N_GSYM stab for each compilation unit
which references the variable.

4.3 Register Variables
Register variables have their own stab type, N_RSYM (C_RSYM for XCOFF), and their own
symbol descriptor, ‘r’. The stab’s value is the number of the register where the variabledata will be stored.
AIX defines a separate symbol descriptor ‘d’ for floating point registers. This seems
unnecessary; why not just just give floating point registers different register numbers? I
have not verified whether the compiler actually uses ‘d’.
If the register is explicitly allocated to a global variable, but not initialized, as in:register int g_bar asm ("%g5");then the stab may be emitted at the end of the object file, with the other bss symbols.

4.4 Common Blocks
A common block is a statically allocated section of memory which can be referred to by
several source files. It may contain several variables. I believe Fortran is the only languagewith this feature.
A N_BCOMM stab begins a common block and an N_ECOMM stab ends it. The only fieldthat is significant in these two stabs is the string, which names a normal (non-debugging)
symbol that gives the address of the common block. According to IBM documentation,
only the N_BCOMM has the name of the common block (even though their compiler actuallyputs it both places).
The stabs for the members of the common block are between the N_BCOMM and the N_
ECOMM; the value of each stab is the offset within the common block of that variable. IBM
uses the C_ECOML stab type, and there is a corresponding N_ECOML stab type, but Sun’s
Fortran compiler uses N_GSYM instead. The variables within a common block use the ‘V’symbol descriptor (I believe this is true of all Fortran variables). Other stabs (at least typedeclarations using C_DECL) can also be between the N_BCOMM and the N_ECOMM.

4.5 Static Variables
Initialized static variables are represented by the ‘S’ and ‘V’ symbol descriptors. ‘S’ means
file scope static, and ‘V’ means procedure scope static. One exception: in XCOFF, IBM’s
xlc compiler always uses ‘V’, and whether it is file scope or not is distinguished by whether
the stab is located within a function.

Chapter 4: Variables

17

In a.out files, N_STSYM means the data section, N_FUN means the text section, and N_LCSYM means the bss section. For those systems with a read-only data section separate fromthe text section (Solaris), N_ROSYM means the read-only data section.
For example, the source lines:
static const int var_const = 5;
static int var_init = 2;
static int var_noinit;
yield the following stabs:.stabs "var_const:S1",36,0,0,_var_const# 36 is N FUN...
.stabs "var_init:S1",38,0,0,_var_init# 38 is N STSYM...
.stabs "var_noinit:S1",40,0,0,_var_noinit# 40 is N LCSYMIn XCOFF files, the stab type need not indicate the section; C_STSYM can be used for all
statics. Also, each static variable is enclosed in a static block. A C_BSTAT (emitted with a‘.bs’ assembler directive) symbol begins the static block; its value is the symbol number ofthe csect symbol whose value is the address of the static block, its section is the section of
the variables in that static block, and its name is ‘.bs’. A C_ESTAT (emitted with a ‘.es’
assembler directive) symbol ends the static block; its name is ‘.es’ and its value and section
are ignored.
In ECOFF files, the storage class is used to specify the section, so the stab type need
not indicate the section.
In ELF files, for the SunPRO compiler version 2.0.1, symbol descriptor ‘S’ means thatthe address is absolute (the linker relocates it) and symbol descriptor ‘V’ means that theaddress is relative to the start of the relevant section for that compilation unit. SunPRO
has plans to have the linker stop relocating stabs; I suspect that their the debugger getsthe address from the corresponding ELF (not stab) symbol. I’m not sure how to find which
symbol of that name is the right one. The clean way to do all this would be to have thevalue of a symbol descriptor ‘S’ symbol be an offset relative to the start of the file, just likeeverything else, but that introduces obvious compatibility problems. For more information
on linker stab relocation, See Section F.2 [ELF Linker Relocation], page 64.

4.6 Fortran Based Variables
Fortran (at least, the Sun and SGI dialects of FORTRAN-77) has a feature which allows allocating arrays with malloc, but which avoids blurring the line between arrays and pointers
the way that C does. In stabs such a variable uses the ‘b’ symbol descriptor.
For example, the Fortran declarations
real foo, foo10(10), foo10_5(10,5)
pointer (foop, foo)
pointer (foo10p, foo10)
pointer (foo105p, foo10_5)
produce the stabs
foo:b6foo10:bar3;1;10;6

18

STABS

foo10_5:bar3;1;5;ar3;1;10;6
In this example, real is type 6 and type 3 is an integral type which is the type of thesubscripts of the array (probably integer).
The ‘b’ symbol descriptor is like ‘V’ in that it denotes a statically allocated symbol whose
scope is local to a function; see See Section 4.5 [Statics], page 16. The value of the symbol,
instead of being the address of the variable itself, is the address of a pointer to that variable.
So in the above example, the value of the foo stab is the address of a pointer to a real,
the value of the foo10 stab is the address of a pointer to a 10-element array of reals, andthe value of the foo10_5 stab is the address of a pointer to a 5-element array of 10-element
arrays of reals.

4.7 Parameters
Formal parameters to a function are represented by a stab (or sometimes two; see below)
for each parameter. The stabs are in the order in which the debugger should print theparameters (i.e., the order in which the parameters are declared in the source file). The
exact form of the stab depends on how the parameter is being passed.
Parameters passed on the stack use the symbol descriptor ‘p’ and the N_PSYM symbol type(or C_PSYM for XCOFF). The value of the symbol is an offset used to locate the parameteron the stack; its exact meaning is machine-dependent, but on most machines it is an offset
from the frame pointer.
As a simple example, the code:
main (argc, argv)
int argc;
char **argv;
produces the stabs:.stabs "main:F1",36,0,0,_main# 36 is N FUN.stabs "argc:p1",160,0,0,68# 160 is N PSYM
.stabs "argv:p20=*21=*2",160,0,0,72
The type definition of argv is interesting because it contains several type definitions.
Type 21 is pointer to type 2 (char) and argv (type 20) is pointer to type 21.
The following symbol descriptors are also said to go with N_PSYM. The value of thesymbol is said to be an offset from the argument pointer (I’m not sure whether this is trueor not).
pP (<<??>>)
pF Fortran function parameter
X (function result variable)

4.7.1 Passing Parameters in Registers
If the parameter is passed in a register, then traditionally there are two symbols for eachargument:.stabs "arg:p1" . . .
; N_PSYM.stabs "arg:r1" . . .
; N_RSYM
Debuggers use the second one to find the value, and the first one to know that it is anargument.

Chapter 4: Variables

19

Because that approach is kind of ugly, some compilers use symbol descriptor ‘P’ or ‘R’
to indicate an argument which is in a register. Symbol type C_RPSYM is used in XCOFF
and N_RSYM is used otherwise. The symbol’s value is the register number. ‘P’ and ‘R’ mean
the same thing; the difference is that ‘P’ is a GNU invention and ‘R’ is an IBM (XCOFF)
invention. As of version 4.9, GDB should handle either one.
There is at least one case where GCC uses a ‘p’ and ‘r’ pair rather than ‘P’; this is where
the argument is passed in the argument list and then loaded into a register.
According to the AIX documentation, symbol descriptor ‘D’ is for a parameter passed
in a floating point register. This seems unnecessary—why not just use ‘R’ with a register
number which indicates that it’s a floating point register? I haven’t verified whether thesystem actually does what the documentation indicates.
On the sparc and hppa, for a ‘P’ symbol whose type is a structure or union, the registercontains the address of the structure. On the sparc, this is also true of a ‘p’ and ‘r’ pair(using Sun cc) or a ‘p’ symbol. However, if a (small) structure is really in a register, ‘r’is used. And, to top it all off, on the hppa it might be a structure which was passed on
the stack and loaded into a register and for which there is a ‘p’ and ‘r’ pair! I believe thatsymbol descriptor ‘i’ is supposed to deal with this case (it is said to mean "value parameterby reference, indirect access"; I don’t know the source for this information), but I don’tknow details or what compilers or debuggers use it, if any (not GDB or GCC). It is notclear to me whether this case needs to be dealt with differently than parameters passed byreference (see Section 4.7.3 [Reference Parameters], page 20).

4.7.2 Storing Parameters as Local Variables
There is a case similar to an argument in a register, which is an argument that is actuallystored as a local variable. Sometimes this happens when the argument was passed in aregister and then the compiler stores it as a local variable. If possible, the compiler shouldclaim that it’s in a register, but this isn’t always done.
If a parameter is passed as one type and converted to a smaller type by the prologue(for example, the parameter is declared as a float, but the calling conventions specify that
it is passed as a double), then GCC2 (sometimes) uses a pair of symbols. The first symbol
uses symbol descriptor ‘p’ and the type which is passed. The second symbol has the typeand location which the parameter actually has after the prologue. For example, suppose
the following C code appears with no prototypes involved:
void
subr (f)float f;{
if f is passed as a double at stack offset 8, and the prologue converts it to a float inregister number 0, then the stabs look like:.stabs "f:p13",160,0,3,8# 160 is N_PSYM, here 13 is double.stabs "f:r12",64,0,3,0# 64 is N_RSYM, here 12 is float
In both stabs 3 is the line number where f is declared (see Section 2.4 [Line Numbers],
page 9).
GCC, at least on the 960, has another solution to the same problem. It uses a single‘p’ symbol descriptor for an argument which is stored as a local variable but uses N_LSYM

20

STABS

instead of N_PSYM. In this case, the value of the symbol is an offset relative to the local
variables for that function, not relative to the arguments; on some machines those are thesame thing, but not on all.
On the VAX or on other machines in which the calling convention includes the numberof words of arguments actually passed, the debugger (GDB at least) uses the parameter
symbols to keep track of whether it needs to print nameless arguments in addition to theformal parameters which it has printed because each one has a stab. For example, in
extern int fprintf (FILE *stream, char *format, ...);...
fprintf (stdout, "%d\n", x);
there are stabs for stream and format. On most machines, the debugger can only print
those two arguments (because it has no way of knowing that additional arguments werepassed), but on the VAX or other machines with a calling convention which indicates thenumber of words of arguments, the debugger can print all three arguments. To do so, theparameter symbol (symbol descriptor ‘p’) (not necessarily ‘r’ or symbol descriptor omitted
symbols) needs to contain the actual type as passed (for example, double not float if it ispassed as a double and converted to a float).

4.7.3 Passing Parameters by Reference
If the parameter is passed by reference (e.g., Pascal VAR parameters), then the symbol
descriptor is ‘v’ if it is in the argument list, or ‘a’ if it in a register. Other than the factthat these contain the address of the parameter rather than the parameter itself, they are
identical to ‘p’ and ‘R’, respectively. I believe ‘a’ is an AIX invention; ‘v’ is supported by
all stabs-using systems as far as I know.

4.7.4 Passing Conformant Array Parameters
Conformant arrays are a feature of Modula-2, and perhaps other languages, in which the sizeof an array parameter is not known to the called function until run-time. Such parameters
have two stabs: a ‘x’ for the array itself, and a ‘C’, which represents the size of the array.
The value of the ‘x’ stab is the offset in the argument list where the address of the array isstored (it this right? it is a guess); the value of the ‘C’ stab is the offset in the argument
list where the size of the array (in elements? in bytes?) is stored.

21

5 Defining Types
The examples so far have described types as references to previously defined types, or definedin terms of subranges of or pointers to previously defined types. This chapter describes theother type descriptors that may follow the ‘=’ in a type definition.

5.1 Builtin Types
Certain types are built in (int, short, void, float, etc.); the debugger recognizes thesetypes and knows how to handle them. Thus, don’t be surprised if some of the following
ways of specifying builtin types do not specify everything that a debugger would need toknow about the type—in some cases they merely specify enough information to distinguishthe type from other types.
The traditional way to define builtin types is convoluted, so new ways have been invented
to describe them. Sun’s acc uses special builtin type descriptors (‘b’ and ‘R’), and IBM uses
negative type numbers. GDB accepts all three ways, as of version 4.8; dbx just accepts the
traditional builtin types and perhaps one of the other two formats. The following sections
describe each of these formats.

5.1.1 Traditional Builtin Types
This is the traditional, convoluted method for defining builtin types. There are several
classes of such type definitions: integer, floating point, and void.

5.1.1.1 Traditional Integer Types
Often types are defined as subranges of themselves. If the bounding values fit within an
int, then they are given normally. For example:.stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0.stabs "char:t2=r2;0;127;",128,0,0,0# 128 is N LSYM

Builtin types can also be described as subranges of int:
.stabs "unsigned short:t6=r1;0;65535;",128,0,0,0
If the lower bound of a subrange is 0 and the upper bound is -1, the type is an unsigned
integral type whose bounds are too big to describe in an int. Traditionally this is only used
for unsigned int and unsigned long:.stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
For larger types, GCC 2.4.5 puts out bounds in octal, with one or more leading zeroes.
In this case a negative bound consists of a number which is a 1 bit (for the sign bit) followed
by a 0 bit for each bit in the number (except the sign bit), and a positive bound is one which
is a 1 bit for each bit in the number (except possibly the sign bit). All known versions of
dbx and GDB version 4 accept this (at least in the sense of not refusing to process the file),
but GDB 3.5 refuses to read the whole file containing such symbols. So GCC 2.3.3 did not
output the proper size for these types. As an example of octal bounds, the string fields ofthe stabs for 64 bit integer types look like:long int:t3=r1;001000000000000000000000;000777777777777777777777;
long unsigned int:t5=r1;000000000000000000000000;001777777777777777777777;

22

STABS

If the lower bound of a subrange is 0 and the upper bound is negative, the type is an
unsigned integral type whose size in bytes is the absolute value of the upper bound. I believe
this is a Convex convention for unsigned long long.
If the lower bound of a subrange is negative and the upper bound is 0, the type is asigned integral type whose size in bytes is the absolute value of the lower bound. I believe
this is a Convex convention for long long. To distinguish this from a legitimate subrange,
the type should be a subrange of itself. I’m not sure whether this is the case for Convex.

5.1.1.2 Traditional Other Types
If the upper bound of a subrange is 0 and the lower bound is positive, the type is a floating
point type, and the lower bound of the subrange indicates the number of bytes in the type:.stabs "float:t12=r1;4;0;",128,0,0,0.stabs "double:t13=r1;8;0;",128,0,0,0
However, GCC writes long double the same way it writes double, so there is no way
to distinguish.
.stabs "long double:t14=r1;8;0;",128,0,0,0Complex types are defined the same way as floating-point types; there is no way to
distinguish a single-precision complex from a double-precision floating-point type.
The C void type is defined as itself:.stabs "void:t15=15",128,0,0,0
I’m not sure how a boolean type is represented.

5.1.2 Defining Builtin Types Using Builtin Type Descriptors
This is the method used by Sun’s acc for defining builtin types. These are the type descriptors to define builtin types:
b signed char-flag width ; offset ; nbits ;Define an integral type. signed is ‘u’ for unsigned or ‘s’ for signed. char-flag is‘c’ which indicates this is a character type, or is omitted. I assume this is todistinguish an integral type from a character type of the same size, for example
it might make sense to set it for the C type wchar_t so the debugger can print
such variables differently (Solaris does not do this). Sun sets it on the C types
signed char and unsigned char which arguably is wrong. width and offset
appear to be for small objects stored in larger ones, for example a short in an
int register. width is normally the number of bytes in the type. offset seems
to always be zero. nbits is the number of bits in the type.
Note that type descriptor ‘b’ used for builtin types conflicts with its use for
Pascal space types (see Section 5.2 [Miscellaneous Types], page 26); they canbe distinguished because the character following the type descriptor will be adigit, ‘(’, or ‘-’ for a Pascal space type, or ‘u’ or ‘s’ for a builtin type.
w

Documented by AIX to define a wide character type, but their compiler actually uses negative type numbers (see Section 5.1.3 [Negative Type Numbers],
page 23).

Chapter 5: Defining Types23

R fp-type ; bytes ;Define a floating point type. fp-type has one of the following values:
1 (NF_SINGLE)
IEEE 32-bit (single precision) floating point format.
2 (NF_DOUBLE)IEEE 64-bit (double precision) floating point format.
3 (NF_COMPLEX)
4 (NF_COMPLEX16)
5 (NF_COMPLEX32)
These are for complex numbers.
A comment in the GDB
source describes them as Fortran complex, double complex, andcomplex*16, respectively, but what does that mean? (i.e., Single
precision? Double precision?).
6 (NF_LDOUBLE)Long double. This should probably only be used for Sun format
long double, and new codes should be used for other floating point
formats (NF_DOUBLE can be used if a long double is really just an
IEEE double, of course).
bytes is the number of bytes occupied by the type. This allows a debugger toperform some operations with the type even if it doesn’t understand fp-type.
g type-information ; nbits
Documented by AIX to define a floating type, but their compiler actually uses
negative type numbers (see Section 5.1.3 [Negative Type Numbers], page 23).
c type-information ; nbits
Documented by AIX to define a complex type, but their compiler actually uses
negative type numbers (see Section 5.1.3 [Negative Type Numbers], page 23).
The C void type is defined as a signed integral type 0 bits long:.stabs "void:t19=bs0;0;0",128,0,0,0
The Solaris compiler seems to omit the trailing semicolon in this case. Getting sloppy
in this way is not a swift move because if a type is embedded in a more complex expression
it is necessary to be able to tell where it ends.
I’m not sure how a boolean type is represented.

5.1.3 Negative Type Numbers
This is the method used in XCOFF for defining builtin types. Since the debugger knows
about the builtin types anyway, the idea of negative type numbers is simply to give a special
type number which indicates the builtin type. There is no stab defining these types.
There are several subtle issues with negative type numbers.
One is the size of the type. A builtin type (for example the C types int or long) might
have different sizes depending on compiler options, the target architecture, the ABI, etc.
This issue doesn’t come up for IBM tools since (so far) they just target the RS/6000; thesizes indicated below for each size are what the IBM RS/6000 tools use. To deal with

24

STABS

differing sizes, either define separate negative type numbers for each size (which works but
requires changing the debugger, and, unless you get both AIX dbx and GDB to accept
the change, introduces an incompatibility), or use a type attribute (see Section 1.3 [String
Field], page 2) to define a new type with the appropriate size (which merely requires a
debugger which understands type attributes, like AIX dbx or GDB). For example,.stabs "boolean:t10=@s8;-16",128,0,0,0
defines an 8-bit boolean type, and.stabs "boolean:t10=@s64;-16",128,0,0,0
defines a 64-bit boolean type.
A similar issue is the format of the type. This comes up most often for floating-pointtypes, which could have various formats (particularly extended doubles, which vary quite a
bit even among IEEE systems). Again, it is best to define a new negative type number foreach different format; changing the format based on the target system has various problems.
One such problem is that the Alpha has both VAX and IEEE floating types. One can easily
imagine one library using the VAX types and another library in the same executable using
the IEEE types. Another example is that the interpretation of whether a boolean is true or
false can be based on the least significant bit, most significant bit, whether it is zero, etc.,
and different compilers (or different options to the same compiler) might provide different
kinds of boolean.
The last major issue is the names of the types. The name of a given type depends only
on the negative type number given; these do not vary depending on the language, the target
system, or anything else. One can always define separate type numbers—in the following
list you will see for example separate int and integer*4 types which are identical except
for the name. But compatibility can be maintained by not inventing new negative type
numbers and instead just defining a new type with a new name. For example:.stabs "CARDINAL:t10=-8",128,0,0,0
Here is the list of negative type numbers. The phrase integral type is used to mean twoscomplement (I strongly suspect that all machines which use stabs use twos-complement;
most machines use twos-complement these days).
-1

int, 32 bit signed integral type.

-2

char, 8 bit type holding a character. Both GDB and dbx on AIX treat this as
signed. GCC uses this type whether char is signed or not, which seems like a
bad idea. The AIX compiler (xlc) seems to avoid this type; it uses -5 insteadfor char.

-3

short, 16 bit signed integral type.

-4

long, 32 bit signed integral type.

-5

unsigned char, 8 bit unsigned integral type.

-6

signed char, 8 bit signed integral type.

-7

unsigned short, 16 bit unsigned integral type.

-8

unsigned int, 32 bit unsigned integral type.

-9

unsigned, 32 bit unsigned integral type.

Chapter 5: Defining Types

25

-10

unsigned long, 32 bit unsigned integral type.

-11

void, type indicating the lack of a value.

-12

float, IEEE single precision.

-13

double, IEEE double precision.

-14

long double, IEEE double precision. The compiler claims the size will increasein a future release, and for binary compatibility you have to avoid using long
double. I hope when they increase it they use a new negative type number.

-15

integer. 32 bit signed integral type.

-16

boolean. 32 bit type. GDB and GCC assume that zero is false, one is true,
and other values have unspecified meaning. I hope this agrees with how theIBM tools use the type.

-17

short real. IEEE single precision.

-18

real. IEEE double precision.

-19

stringptr. See Section 5.6 [Strings], page 29.

-20

character, 8 bit unsigned character type.

-21

logical*1, 8 bit type. This Fortran type has a split personality in that it isused for boolean variables, but can also be used for unsigned integers. 0 is false,
1 is true, and other values are non-boolean.

-22

logical*2, 16 bit type. This Fortran type has a split personality in that it
is used for boolean variables, but can also be used for unsigned integers. 0 is
false, 1 is true, and other values are non-boolean.

-23

logical*4, 32 bit type. This Fortran type has a split personality in that it
is used for boolean variables, but can also be used for unsigned integers. 0 is
false, 1 is true, and other values are non-boolean.

-24

logical, 32 bit type. This Fortran type has a split personality in that it is used
for boolean variables, but can also be used for unsigned integers. 0 is false, 1 istrue, and other values are non-boolean.

-25

complex. A complex type consisting of two IEEE single-precision floating pointvalues.

-26

complex. A complex type consisting of two IEEE double-precision floating
point values.

-27

integer*1, 8 bit signed integral type.

-28

integer*2, 16 bit signed integral type.

-29

integer*4, 32 bit signed integral type.

-30

wchar. Wide character, 16 bits wide, unsigned (what format? Unicode?).

-31

long long, 64 bit signed integral type.

-32

unsigned long long, 64 bit unsigned integral type.

-33

logical*8, 64 bit unsigned integral type.

-34

integer*8, 64 bit signed integral type.

26

STABS

5.2 Miscellaneous Typesb type-information ; bytes
Pascal space type. This is documented by IBM; what does it mean?
This use of the ‘b’ type descriptor can be distinguished from its use for builtin
integral types (see Section 5.1.2 [Builtin Type Descriptors], page 22) because
the character following the type descriptor is always a digit, ‘(’, or ‘-’.
B type-information
A volatile-qualified version of type-information. This is a Sun extension. References and stores to a variable with a volatile-qualified type must not be optimized or cached; they must occur as the user specifies them.
d type-information
File of type type-information. As far as I know this is only used by Pascal.
k type-information
A const-qualified version of type-information. This is a Sun extension. A
variable with a const-qualified type cannot be modified.
M type-information ; length
Multiple instance type. The type seems to composed of length repetitions oftype-information, for example character*3 is represented by ‘M-2;3’, where‘-2’ is a reference to a character type (see Section 5.1.3 [Negative Type Numbers], page 23). I’m not sure how this differs from an array. This appears to bea Fortran feature. length is a bound, like those in range types; see Section 5.4[Subranges], page 27.
S type-information
Pascal set type. type-information must be a small type such as an enumeration
or a subrange, and the type is a bitmask whose length is specified by the numberof elements in type-information.
In CHILL, if it is a bitstring instead of a set, also use the ‘S’ type attribute (seeSection 1.3 [String Field], page 2).
* type-information
Pointer to type-information.

5.3 Cross-References to Other Types
A type can be used before it is defined; one common way to deal with that situation is justto use a type reference to a type which has not yet been defined.
Another way is with the ‘x’ type descriptor, which is followed by ‘s’ for a structure tag,‘u’ for a union tag, or ‘e’ for a enumerator tag, followed by the name of the tag, followedby ‘:’. If the name contains ‘::’ between a ‘<’ and ‘>’ pair (for C++ templates), such a ‘::’does not end the name—only a single ‘:’ ends the name; see Section 8.2 [Nested Symbols],
page 39.
For example, the following C declarations:struct foo;
struct foo *bar;

Chapter 5: Defining Types

27

produce:.stabs "bar:G16=*17=xsfoo:",32,0,0,0
Not all debuggers support the ‘x’ type descriptor, so on some machines GCC does notuse it. I believe that for the above example it would just emit a reference to type 17 andnever define it, but I haven’t verified that.
Modula-2 imported types, at least on AIX, use the ‘i’ type descriptor, which is followedby the name of the module from which the type is imported, followed by ‘:’, followed by
the name of the type. There is then optionally a comma followed by type information for
the type. This differs from merely naming the type (see Section 5.9 [Typedefs], page 31) inthat it identifies the module; I don’t understand whether the name of the type given here isalways just the same as the name we are giving it, or whether this type descriptor is usedwith a nameless stab (see Section 1.3 [String Field], page 2), or what. The symbol ends
with ‘;’.

5.4 Subrange Types
The ‘r’ type descriptor defines a type as a subrange of another type. It is followed bytype information for the type of which it is a subrange, a semicolon, an integral lower
bound, a semicolon, an integral upper bound, and a semicolon. The AIX documentation
does not specify the trailing semicolon, in an effort to specify array indexes more cleanly,
but a subrange which is not an array index has always included a trailing semicolon (seeSection 5.5 [Arrays], page 27).
Instead of an integer, either bound can be one of the following:
A offset

The bound is passed by reference on the stack at offset offset from the argument
list. See Section 4.7 [Parameters], page 18, for more information on such offsets.

T offset

The bound is passed by value on the stack at offset offset from the argument
list.

a register-number
The bound is passed by reference in register number register-number.
t register-number
The bound is passed by value in register number register-number.
J

There is no bound.

Subranges are also used for builtin types; see Section 5.1.1 [Traditional Builtin Types],
page 21.

5.5 Array Types
Arrays use the ‘a’ type descriptor. Following the type descriptor is the type of the index
and the type of the array elements. If the index type is a range type, it ends in a semicolon;
otherwise (for example, if it is a type reference), there does not appear to be any way to tellwhere the types are separated. In an effort to clean up this mess, IBM documents the two
types as being separated by a semicolon, and a range type as not ending in a semicolon (butthis is not right for range types which are not array indexes, see Section 5.4 [Subranges],
page 27). I think probably the best solution is to specify that a semicolon ends a range type,

28

STABS

and that the index type and element type of an array are separated by a semicolon, butthat if the index type is a range type, the extra semicolon can be omitted. GDB (at least
through version 4.9) doesn’t support any kind of index type other than a range anyway;
I’m not sure about dbx.
It is well established, and widely used, that the type of the index, unlike most types
found in the stabs, is merely a type definition, not type information (see Section 1.3 [String
Field], page 2) (that is, it need not start with ‘type-number=’ if it is defining a new type).
According to a comment in GDB, this is also true of the type of the array elements; it gives‘ar1;1;10;ar1;1;10;4’ as a legitimate way to express a two dimensional array. According
to AIX documentation, the element type must be type information. GDB accepts either.
The type of the index is often a range type, expressed as the type descriptor ‘r’ andsome parameters. It defines the size of the array. In the example below, the range ‘r1;0;2;’
defines an index type which is a subrange of type 1 (integer), with a lower bound of 0 and
an upper bound of 2. This defines the valid range of subscripts of a three-element C array.
For example, the definition:
char char_vec[3] = {’a’,’b’,’c’};
produces the output:.stabs "char_vec:G19=ar1;0;2;2",32,0,0,0.global _char_vec.align 4_char_vec:.byte 97
.byte 98
.byte 99
If an array is packed, the elements are spaced more closely than normal, saving memory
at the expense of speed. For example, an array of 3-byte objects might, if unpacked, haveeach element aligned on a 4-byte boundary, but if packed, have no padding. One way to
specify that something is packed is with type attributes (see Section 1.3 [String Field],page 2). In the case of arrays, another is to use the ‘P’ type descriptor instead of ‘a’. Other
than specifying a packed array, ‘P’ is identical to ‘a’.
An open array is represented by the ‘A’ type descriptor followed by type information
specifying the type of the array elements.
An N-dimensional dynamic array is represented by
D dimensions ; type-information
dimensions is the number of dimensions; type-information specifies the type of the arrayelements.
A subarray of an N-dimensional array is represented by
E dimensions ; type-information
dimensions is the number of dimensions; type-information specifies the type of the arrayelements.

Chapter 5: Defining Types

29

5.6 Strings
Some languages, like C or the original Pascal, do not have string types, they just haverelated things like arrays of characters. But most Pascals and various other languages havestring types, which are indicated as follows:n type-information ; bytes
bytes is the maximum length. I’m not sure what type-information is; I suspectthat it means that this is a string of type-information (thus allowing a stringof integers, a string of wide characters, etc., as well as a string of characters).
Not sure what the format of this type is. This is an AIX feature.
z type-information ; bytes
Just like ‘n’ except that this is a gstring, not an ordinary string. I don’t know
the difference.
N

Pascal Stringptr. What is this? This is an AIX feature.

Languages, such as CHILL which have a string type which is basically just an array ofcharacters use the ‘S’ type attribute (see Section 1.3 [String Field], page 2).

5.7 Enumerations
Enumerations are defined with the ‘e’ type descriptor.
The source line below declares an enumeration type at file scope. The type definition is
located after the N_RBRAC that marks the end of the previous procedure’s block scope, andbefore the N_FUN that marks the beginning of the next procedure’s block scope. Therefore
it does not describe a block local symbol, but a file local one.
The source line:
enum e_places {first,second=3,last};
generates the following stab:.stabs "e_places:T22=efirst:0,second:3,last:4,;",128,0,0,0
The symbol descriptor (‘T’) says that the stab describes a structure, enumeration, or
union tag. The type descriptor ‘e’, following the ‘22=’ of the type definition narrows it
down to an enumeration type. Following the ‘e’ is a list of the elements of the enumeration.
The format is ‘name:value,’. The list of elements ends with ‘;’. The fact that value isspecified as an integer can cause problems if the value is large. GCC 2.5.2 tries to output
it in octal in that case with a leading zero, which is probably a good thing, although GDB
4.11 supports octal only in cases where decimal is perfectly good. Negative decimal values
are supported by both GDB and dbx.
There is no standard way to specify the size of an enumeration type; it is determinedby the architecture (normally all enumerations types are 32 bits). Type attributes can beused to specify an enumeration type of another size for debuggers which support them; see
Section 1.3 [String Field], page 2.
Enumeration types are unusual in that they define symbols for the enumeration values(first, second, and third in the above example), and even though these symbols arevisible in the file as a whole (rather than being in a more local namespace like structure
member names), they are defined in the type definition for the enumeration type rather

30

STABS

than each having their own symbol. In order to be fast, GDB will only get symbols fromsuch types (in its initial scan of the stabs) if the type is the first thing defined after a ‘T’or ‘t’ symbol descriptor (the above example fulfills this requirement). If the type does nothave a name, the compiler should emit it in a nameless stab (see Section 1.3 [String Field],page 2); GCC does this.

5.8 Structures
The encoding of structures in stabs can be shown with an example.
The following source code declares a structure tag and defines an instance of the structure
in global scope. Then a typedef equates the structure tag with a new type. Separate stabs
are generated for the structure tag, the structure typedef, and the structure instance. The
stabs for the tag and the typedef are emitted when the definitions are encountered. Since
the structure elements are not initialized, the stab and code for the structure variable itself
is located at the end of the program in the bss section.
struct s_tag {int
s_int;
float s_float;char s_char_vec[8];struct s_tag* s_next;} g_an_s;
typedef struct s_tag s_typedef;
The structure tag has an N_LSYM stab type because, like the enumeration, the symbol has
file scope. Like the enumeration, the symbol descriptor is ‘T’, for enumeration, structure,or tag type. The type descriptor ‘s’ following the ‘16=’ of the type definition narrows the
symbol type to structure.
Following the ‘s’ type descriptor is the number of bytes the structure occupies, followed by a description of each structure element. The structure element descriptions areof the form ‘name:type, bit offset from the start of the struct, number of bits inthe element’.
# 128 is N LSYM
.stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0In this example, the first two structure elements are previously defined types. For these,
the type following the ‘name:’ part of the element description is a simple type reference.
The other two structure elements are new types. In this case there is a type definition
embedded after the ‘name:’. The type definition for the array element looks just like a
type definition for a stand-alone array. The s_next field is a pointer to the same kind of
structure that the field is an element of. So the definition of structure type 16 contains atype definition for an element which is a pointer to type 16.
If a field is a static member (this is a C++ feature in which a single variable appears to
be a field of every structure of a given type) it still starts out with the field name, a colon,
and the type, but then instead of a comma, bit position, comma, and bit size, there is acolon followed by the name of the variable which each such field refers to.

Chapter 5: Defining Types

31

If the structure has methods (a C++ feature), they follow the non-method fields; see
Chapter 8 [Cplusplus], page 39.

5.9 Giving a Type a Name
To give a type a name, use the ‘t’ symbol descriptor. The type is specified by the type
information (see Section 1.3 [String Field], page 2) for the stab. For example,.stabs "s_typedef:t16",128,0,0,0# 128 is N LSYM
specifies that s_typedef refers to type number 16. Such stabs have symbol type N_LSYM(or C_DECL for XCOFF). (The Sun documentation mentions using N_GSYM in some cases).
If you are specifying the tag name for a structure, union, or enumeration, use the ‘T’symbol descriptor instead. I believe C is the only language with this feature.
If the type is an opaque type (I believe this is a Modula-2 feature), AIX provides atype descriptor to specify it. The type descriptor is ‘o’ and is followed by a name. I don’tknow what the name means—is it always the same as the name of the type, or is thistype descriptor used with a nameless stab (see Section 1.3 [String Field], page 2)? There
optionally follows a comma followed by type information which defines the type of thistype. If omitted, a semicolon is used in place of the comma and the type information, andthe type is much like a generic pointer type—it has a known size but little else about it isspecified.

5.10 Unions
union u_tag {int u_int;
float u_float;
char* u_char;} an_u;This code generates a stab for a union tag and a stab for a union variable. Both use
the N_LSYM stab type. If a union variable is scoped locally to the procedure in which itis defined, its stab is located immediately preceding the N_LBRAC for the procedure’s block
start.
The stab for the union tag, however, is located preceding the code for the procedure inwhich it is defined. The stab type is N_LSYM. This would seem to imply that the union typeis file scope, like the struct type s_tag. This is not true. The contents and position of thestab for u_type do not convey any information about its procedure local scope.
# 128 is N LSYM
.stabs "u_tag:T23=u4u_int:1,0,32;u_float:12,0,32;u_char:21,0,32;;",
128,0,0,0

The symbol descriptor ‘T’, following the ‘name:’ means that the stab describes an enumeration, structure, or union tag. The type descriptor ‘u’, following the ‘23=’ of the typedefinition, narrows it down to a union type definition. Following the ‘u’ is the numberof bytes in the union. After that is a list of union element descriptions. Their format is‘name:type, bit offset into the union, number of bytes for the element;’.
The stab for the union variable is:.stabs "an_u:23",128,0,0,-20# 128 is N LSYM

32

STABS

‘-20’ specifies where the variable is stored (see Section 4.1 [Stack Variables], page 15).

5.11 Function Types
Various types can be defined for function variables. These types are not used in defining
functions (see Section 2.5 [Procedures], page 9); they are used for things like pointers tofunctions.
The simple, traditional, type is type descriptor ‘f’ is followed by type information for
the return type of the function, followed by a semicolon.
This does not deal with functions for which the number and types of the parameters arepart of the type, as in Modula-2 or ANSI C. AIX provides extensions to specify these, using
the ‘f’, ‘F’, ‘p’, and ‘R’ type descriptors.
First comes the type descriptor. If it is ‘f’ or ‘F’, this type involves a function rather thana procedure, and the type information for the return type of the function follows, followed
by a comma. Then comes the number of parameters to the function and a semicolon.
Then, for each parameter, there is the name of the parameter followed by a colon (this is
only present for type descriptors ‘R’ and ‘F’ which represent Pascal function or procedureparameters), type information for the parameter, a comma, 0 if passed by reference or 1 if
passed by value, and a semicolon. The type definition ends with a semicolon.
For example, this variable definition:
int (*g_pf)();generates the following code:.stabs "g_pf:G24=*25=f1",32,0,0,0.common _g_pf,4,"bss"
The variable defines a new type, 24, which is a pointer to another new type, 25, which
is a function returning int.

33

6 Representation of #define and #undef
This section describes the stabs support for macro define and undefine information, supported on some systems. (e.g., with -g3 -gstabs when using GCC).
A #define macro-name macro-body is represented with an N_MAC_DEFINE stab with astring field of macro-name macro-body.
An #undef macro-name is represented with an N_MAC_UNDEF stabs with a string field ofsimply macro-name.
For both N_MAC_DEFINE and N_MAC_UNDEF, the desc field is the line number within thefile where the corresponding #define or #undef occurred.
For example, the following C code:#define NONE 42#define TWO(a, b) (a + (a) + 2 * b)
#define ONE(c) (c + 19)
main(int argc, char *argv[]){
func(NONE, TWO(10, 11));func(NONE, ONE(23));#undef ONE#define ONE(c) (c + 23)
func(NONE, ONE(-23));
return (0);}int global;
func(int arg1, int arg2){
global = arg1 + arg2;}
produces the following stabs (as well as many others):.stabs "NONE 42",54,0,1,0.stabs "TWO(a,b) (a + (a) + 2 * b)",54,0,2,0.stabs "ONE(c) (c + 19)",54,0,3,0.stabs "ONE",58,0,10,0.stabs "ONE(c) (c + 23)",54,0,11,0
NOTE: In the above example, 54 is N_MAC_DEFINE and 58 is N_MAC_UNDEF.

35

7 Symbol Information in Symbol Tables
This chapter describes the format of symbol table entries and how stab assembler directives
map to them. It also describes the transformations that the assembler and linker make ondata from stabs.

7.1 Symbol Table Format
Each time the assembler encounters a stab directive, it puts each field of the stab into a
corresponding field in a symbol table entry of its output file. If the stab contains a string
field, the symbol table entry for that stab points to a string table entry containing the string
data from the stab. Assembler labels become relocatable addresses. Symbol table entries
in a.out have the format:
struct internal_nlist {unsigned long n_strx;
unsigned char n_type;unsigned char n_other;
unsigned short n_desc;
bfd_vma n_value;};/* index into string table of name *//* type of symbol *//* misc info (usually empty) *//* description field *//* value of symbol */If the stab has a string, the n_strx field holds the offset in bytes of the string within thestring table. The string is terminated by a NUL character. If the stab lacks a string (forexample, it was produced by a .stabn or .stabd directive), the n_strx field is zero.
Symbol table entries with n_type field values greater than 0x1f originated as stabs
generated by the compiler (with one random exception). The other entries were placed in
the symbol table of the executable by the assembler or the linker.

7.2 Transformations on Symbol Tables
The linker concatenates object files and does fixups of externally defined symbols.
You can see the transformations made on stab data by the assembler and linker byexamining the symbol table after each pass of the build. To do this, use ‘nm -ap’, whichdumps the symbol table, including debugging information, unsorted. For stab entries thecolumns are: value, other, desc, type, string. For assembler and linker symbols, the columns
are: value, type, string.
The low 5 bits of the stab type tell the linker how to relocate the value of the stab. Thus
for stab types like N_RSYM and N_LSYM, where the value is an offset or a register number,the low 5 bits are N_ABS, which tells the linker not to relocate the value.
Where the value of a stab contains an assembly language label, it is transformed by eachbuild step. The assembler turns it into a relocatable address and the linker turns it into an
absolute address.

7.2.1 Transformations on Static Variables
This source line defines a static variable at file scope:static int s_g_repeat

36

STABS

The following stab describes the symbol:.stabs "s_g_repeat:S1",38,0,0,_s_g_repeat
The assembler transforms the stab into this symbol table entry in the .o file. The location
is expressed as a data segment offset.
00000084 - 00 0000 STSYM s_g_repeat:S1
In the symbol table entry from the executable, the linker has made the relocatable address
absolute.
0000e00c - 00 0000 STSYM s_g_repeat:S1

7.2.2 Transformations on Global Variables
Stabs for global variables do not contain location information. In this case, the debugger
finds location information in the assembler or linker symbol table entry describing thevariable. The source line:
char g_foo = ’c’;
generates the stab:.stabs "g_foo:G2",32,0,0,0
The variable is represented by two symbol table entries in the object file (see below).
The first one originated as a stab. The second one is an external symbol. The upper case
‘D’ signifies that the n_type field of the symbol table contains 7, N_DATA with local linkage.
The stab’s value is zero since the value is not used for N_GSYM stabs. The value of the linker
symbol is the relocatable address corresponding to the variable.
00000000 - 00 0000 GSYM g_foo:G200000080 D _g_foo
These entries as transformed by the linker. The linker symbol table entry now holds anabsolute address:
00000000 - 00 0000 GSYM g_foo:G2...
0000e008 D _g_foo

7.2.3 Transformations of Stabs in separate sections
For object file formats using stabs in separate sections (see Appendix F [Stab Sections],
page 63), use objdump --stabs instead of nm to show the stabs in an object or executable
file. objdump is a GNU utility; Sun does not provide any equivalent.
The following example is for a stab whose value is an address is relative to the compilation
unit (see Section F.2 [ELF Linker Relocation], page 64). For example, if the source line
static int ld = 5;
appears within a function, then the assembly language output from the compiler contains:.Ddata.data:...
.stabs "ld:V(0,3)",0x26,0,4,.L18-Ddata.data# 0x26 is N STSYM
...
.L18:
.align 4

37.word 0x5
Because the value is formed by subtracting one symbol from another, the value is absolute, not relocatable, and so the object file contains
Symnum n_type n_othr n_desc n_value n_strx String
31
STSYM 0400000004 680
ld:V(0,3)
without any relocations, and the executable file also contains
Symnum n_type n_othr n_desc n_value n_strx String
31
STSYM 0400000004 680
ld:V(0,3)

39

8 GNU C++ Stabs
8.1 C++ Class Names
In C++, a class name which is declared with class, struct, or union, is not only a tag,as in C, but also a type name. Thus there should be stabs with both ‘t’ and ‘T’ symbol
descriptors (see Section 5.9 [Typedefs], page 31).
To save space, there is a special abbreviation for this case. If the ‘T’ symbol descriptor
is followed by ‘t’, then the stab defines both a type name and a tag.
For example, the C++ code
struct foo {int x;};can be represented as either.stabs "foo:T19=s4x:1,0,32;;",128,0,0,0# 128 is N LSYM
.stabs "foo:t19",128,0,0,0or.stabs "foo:Tt19=s4x:1,0,32;;",128,0,0,0

8.2 Defining a Symbol Within Another TypeIn C++, a symbol (such as a type name) can be defined within another type.
In stabs, this is sometimes represented by making the name of a symbol which contains‘::’. Such a pair of colons does not end the name of the symbol, the way a single colon
would (see Section 1.3 [String Field], page 2). I’m not sure how consistently used or wellthought out this mechanism is. So that a pair of colons in this position always has thismeaning, ‘:’ cannot be used as a symbol descriptor.
For example, if the string for a stab is ‘foo::bar::baz:t5=*6’, then foo::bar::baz is
the name of the symbol, ‘t’ is the symbol descriptor, and ‘5=*6’ is the type information.

8.3 Basic Types For C++<< the examples that follow are based on a01.C >>C++ adds two more builtin types to the set defined for C. These are the unknown type
and the vtable record type. The unknown type, type 16, is defined in terms of itself likethe void type.
The vtable record type, type 17, is defined as a structure type and then as a structuretag. The structure has four fields: delta, index, pfn, and delta2. pfn is the function pointer.
<< In boilerplate $vtbl ptr type, what are the fields delta, index, and delta2 used for?
>>This basic type is present in all C++ programs even if there are no virtual methods
defined.
.stabs "struct name:sym desc(type)type def(17)=type desc(struct)struct bytes(8)elem name(delta):type ref(short int),bit offset(0),field bits(16);elem name(index):type ref(short int),bit offset(16),field bits(16);elem name(pfn):type def(18)=type desc(ptr to)type ref(void),

40

STABS

bit offset(32),field bits(32);elem name(delta2):type def(short int);bit offset(32),field bits(16);;"N LSYM, NIL, NIL.stabs "$vtbl_ptr_type:t17=s8
delta:6,0,16;index:6,16,16;pfn:18=*15,32,32;delta2:6,32,16;;",128,0,0,0.stabs "name:sym dec(struct tag)type ref($vtbl ptr type)",N LSYM,NIL,NIL,NIL.stabs "$vtbl_ptr_type:T17",128,0,0,0

8.4 Simple Class Definition
The stabs describing C++ language features are an extension of the stabs describing C.
Stabs representing C++ class types elaborate extensively on the stab format used to describe
structure types in C. Stabs representing class type variables look just like stabs representing
C language variables.
Consider the following very simple class definition.
class baseA {public:int Adat;
int Ameth(int in, char other);};
The class baseA is represented by two stabs. The first stab describes the class as astructure type. The second stab describes a structure tag of the class type. Both stabs
are of stab type N_LSYM. Since the stab is not located between an N_FUN and an N_LBRAC
stab this indicates that the class is defined at file scope. If it were, then the N_LSYM would
signify a local variable.
A stab describing a C++ class type is similar in format to a stab describing a C struct,with each class member shown as a field in the structure. The part of the struct format
describing fields is expanded to include extra information relevant to C++ class members. In
addition, if the class has multiple base classes or virtual functions the struct format outsideof the field parts is also augmented.
In this simple example the field part of the C++ class stab representing member data
looks just like the field part of a C struct stab. The section on protections describes how
its format is sometimes extended for member data.
The field part of a C++ class stab representing a member function differs substantiallyfrom the field part of a C struct stab. It still begins with ‘name:’ but then goes on todefine a new type number for the member function, describe its return type, its argument
types, its protection level, any qualifiers applied to the method definition, and whether the
method is virtual or not. If the method is virtual then the method description goes on to
give the vtable index of the method, and the type number of the first base class defining
the method.
When the field name is a method name it is followed by two colons rather than one. Thisis followed by a new type definition for the method. This is a number followed by an equal
sign and the type of the method. Normally this will be a type declared using the ‘#’ typedescriptor; see Section 8.7 [Method Type Descriptor], page 42; static member functions are
declared using the ‘f’ type descriptor instead; see Section 5.11 [Function Types], page 32.

Chapter 8: GNU C++ Stabs

41

The format of an overloaded operator method name differs from that of other methods.
It is ‘op$::operator-name.’ where operator-name is the operator name such as ‘+’ or‘+=’. The name ends with a period, and any characters except the period can occur in theoperator-name string.
The next part of the method description represents the arguments to the method, preceded by a colon and ending with a semi-colon. The types of the arguments are expressedin the same way argument types are expressed in C++ name mangling. In this example an
int and a char map to ‘ic’.
This is followed by a number, a letter, and an asterisk or period, followed by anothersemicolon. The number indicates the protections that apply to the member function. Herethe 2 means public. The letter encodes any qualifier applied to the method definition. In
this case, ‘A’ means that it is a normal function definition. The dot shows that the method
is not virtual. The sections that follow elaborate further on these fields and describe theadditional information present for virtual methods.
.stabs "class name:sym desc(type)type def(20)=type desc(struct)struct bytes(4)field name(Adat):type(int),bit offset(0),field bits(32);method name(Ameth)::type def(21)=type desc(method)return type(int);:arg types(int char);protection(public)qualifier(normal)virtual(no);;"N LSYM,NIL,NIL,NIL.stabs "baseA:t20=s4Adat:1,0,32;Ameth::21=##1;:ic;2A.;;",128,0,0,0.stabs "class_name:sym_desc(struct tag)",N_LSYM,NIL,NIL,NIL.stabs "baseA:T20",128,0,0,0

8.5 Class Instance
As shown above, describing even a simple C++ class definition is accomplished by massively
extending the stab format used in C to describe structure types. However, once the class isdefined, C stabs with no modifications can be used to describe class instances. The following
source:main () {baseA AbaseA;}
yields the following stab describing the class instance. It looks no different from a standard
C stab describing a local variable.
.stabs "name:type ref(baseA)", N LSYM, NIL, NIL, frame ptr offset.stabs "AbaseA:20",128,0,0,-20

8.6 Method Definition
The class definition shown above declares Ameth. The C++ source below defines Ameth:int
baseA::Ameth(int in, char other)
{

42

STABS

return in;};This method definition yields three stabs following the code of the method. One stab
describes the method itself and following two describe its parameters. Although there
is only one formal argument all methods have an implicit argument which is the thispointer. The this pointer is a pointer to the object on which the method was called. Notethat the method name is mangled to encode the class name and argument types. Namemangling is described in the arm (The Annotated C++ Reference Manual, by Ellis andStroustrup, isbn 0-201-51459-1); gpcompare.texi in Cygnus GCC distributions describes
the differences between GNU mangling and arm mangling.
.stabs "name:symbol_descriptor(global function)return_type(int)",
N_FUN, NIL, NIL, code_addr_of_method_start.stabs "Ameth__5baseAic:F1",36,0,0,_Ameth__5baseAic
Here is the stab for the this pointer implicit argument. The name of the this pointeris always this. Type 19, the this pointer is defined as a pointer to type 20, baseA, but astab defining baseA has not yet been emitted. Since the compiler knows it will be emitted
shortly, here it just outputs a cross reference to the undefined symbol, by prefixing thesymbol name with ‘xs’.
.stabs "name:sym_desc(register param)type_def(19)=type_desc(ptr to)type_ref(baseA)=
type_desc(cross-reference to)baseA:",N_RSYM,NIL,NIL,register_number.stabs "this:P19=*20=xsbaseA:",64,0,0,8
The stab for the explicit integer argument looks just like a parameter to a C function.
The last field of the stab is the offset from the argument pointer, which in most systems isthe same as the frame pointer.
.stabs "name:sym_desc(value parameter)type_ref(int)",
N_PSYM,NIL,NIL,offset_from_arg_ptr.stabs "in:p1",160,0,0,72<< The examples that follow are based on A1.C >>8.7 The ‘#’ Type Descriptor
This is used to describe a class method. This is a function which takes an extra argument
as its first argument, for the this pointer.
If the ‘#’ is immediately followed by another ‘#’, the second one will be followed by the
return type and a semicolon. The class and argument types are not specified, and must be
determined by demangling the name of the method if it is available.
Otherwise, the single ‘#’ is followed by the class type, a comma, the return type, acomma, and zero or more parameter types separated by commas. The list of arguments is
terminated by a semicolon. In the debugging output generated by gcc, a final argument
type of void indicates a method which does not take a variable number of arguments. If
the final argument type of void does not appear, the method was declared with an ellipsis.

Chapter 8: GNU C++ Stabs

43

Note that although such a type will normally be used to describe fields in structures,
unions, or classes, for at least some versions of the compiler it can also be used in othercontexts.

8.8 The ‘@’ Type Descriptor
The ‘@’ type descriptor is used for a pointer-to-non-static-member-data type. It is followedby type information for the class (or union), a comma, and type information for the member
data.
The following C++ source:
typedef int A::*int_in_a;generates the following stab:.stabs "int_in_a:t20=21=@19,1",128,0,0,0

Note that there is a conflict between this and type attributes (see Section 1.3 [String
Field], page 2); both use type descriptor ‘@’. Fortunately, the ‘@’ type descriptor used inthis C++ sense always will be followed by a digit, ‘(’, or ‘-’, and type attributes never startwith those things.

8.9 Protections
In the simple class definition shown above all member data and functions were publicly
accessible. The example that follows contrasts public, protected and privately accessible
fields and shows how these protections are encoded in C++ stabs.
If the character following the ‘field-name:’ part of the string is ‘/’, then the next
character is the visibility. ‘0’ means private, ‘1’ means protected, and ‘2’ means public.
Debuggers should ignore visibility characters they do not recognize, and assume a reasonable
default (such as public) (GDB 4.11 does not, but this should be fixed in the next GDB
release). If no visibility is specified the field is public. The visibility ‘9’ means that the fieldhas been optimized out and is public (there is no way to specify an optimized out field witha private or protected visibility). Visibility ‘9’ is not supported by GDB 4.11; this should
be fixed in the next GDB release.
The following C++ source:class vis {
private:int
priv;
protected:
char prot;
public:float pub;};
generates the following stab:# 128 is N LSYM
.stabs "vis:T19=s12priv:/01,0,32;prot:/12,32,8;pub:12,64,32;;",128,0,0,0‘vis:T19=s12’ indicates that type number 19 is a 12 byte structure named vis The priv
field has public visibility (‘/0’), type int (‘1’), and offset and size ‘,0,32;’. The prot field

44

STABS

has protected visibility (‘/1’), type char (‘2’) and offset and size ‘,32,8;’. The pub field
has type float (‘12’), and offset and size ‘,64,32;’.
Protections for member functions are signified by one digit embedded in the field partof the stab describing the method. The digit is 0 if private, 1 if protected and 2 if public.
Consider the C++ class definition below:
class all_methods {private:int
priv_meth(int in){return in;};protected:
char protMeth(char in){return in;};public:float pubMeth(float in){return in;};};
It generates the following stab. The digit in question is to the left of an ‘A’ in each case.
Notice also that in this case two symbol descriptors apply to the class name struct tag andstruct type.
.stabs "class name:sym desc(struct tag&type)type def(21)=sym desc(struct)struct bytes(1)meth name::type def(22)=sym desc(method)returning(int);:args(int);protection(private)modifier(normal)virtual(no);meth name::type def(23)=sym desc(method)returning(char);:args(char);protection(protected)modifier(normal)virtual(no);meth name::type def(24)=sym desc(method)returning(float);:args(float);protection(public)modifier(normal)virtual(no);;",N LSYM,NIL,NIL,NIL.stabs "all_methods:Tt21=s1priv_meth::22=##1;:i;0A.;protMeth::23=##2;:c;1A.;
pubMeth::24=##12;:f;2A.;;",128,0,0,0

8.10 Method Modifiers (const, volatile, const volatile)<< based on a6.C >>In the class example described above all the methods have the normal modifier. Thismethod modifier information is located just after the protection information for the method.
This field has four possible character values. Normal methods use ‘A’, const methods use ‘B’,
volatile methods use ‘C’, and const volatile methods use ‘D’. Consider the class definition
below:
class A {public:int ConstMeth (int arg) const { return arg; };char VolatileMeth (char arg) volatile { return arg; };float ConstVolMeth (float arg) const volatile {return arg; };};This class is described by the following stab:.stabs "class(A):sym desc(struct)type def(20)=type desc(struct)struct bytes(1)meth name(ConstMeth)::type def(21)sym desc(method)
returning(int);:arg(int);protection(public)modifier(const)virtual(no);Chapter 8: GNU C++ Stabs

45

meth name(VolatileMeth)::type def(22)=sym desc(method)
returning(char);:arg(char);protection(public)modifier(volatile)virt(no)meth name(ConstVolMeth)::type def(23)=sym desc(method)
returning(float);:arg(float);protection(public)modifier(const volatile)
virtual(no);;", . . .
.stabs "A:T20=s1ConstMeth::21=##1;:i;2B.;VolatileMeth::22=##2;:c;2C.;
ConstVolMeth::23=##12;:f;2D.;;",128,0,0,0

8.11 Virtual Methods<< The following examples are based on a4.C >>The presence of virtual methods in a class definition adds additional data to the classdescription. The extra data is appended to the description of the virtual method and to
the end of the class description. Consider the class definition below:
class A {public:int Adat;virtual int A_virt (int arg) { return arg; };};This results in the stab below describing class A. It defines a new type (20) which is an
8 byte structure. The first field of the class struct is ‘Adat’, an integer, starting at structure
offset 0 and occupying 32 bits.
The second field in the class struct is not explicitly defined by the C++ class definition
but is implied by the fact that the class contains a virtual method. This field is the vtable
pointer. The name of the vtable pointer field starts with ‘$vf’ and continues with a typereference to the class it is part of. In this example the type reference for class A is 20 so
the name of its vtable pointer field is ‘$vf20’, followed by the usual colon.
Next there is a type definition for the vtable pointer type (21). This is in turn defined
as a pointer to another new type (22).
Type 22 is the vtable itself, which is defined as an array, indexed by a range of integers
between 0 and 1, and whose elements are of type 17. Type 17 was the vtable record typedefined by the boilerplate C++ type definitions, as shown earlier.
The bit offset of the vtable pointer field is 32. The number of bits in the field are notspecified when the field is a vtable pointer.
Next is the method definition for the virtual member function A_virt. Its description
starts out using the same format as the non-virtual member functions described above,
except instead of a dot after the ‘A’ there is an asterisk, indicating that the function isvirtual. Since is is virtual some addition information is appended to the end of the method
description.
The first number represents the vtable index of the method. This is a 32 bit unsigned
number with the high bit set, followed by a semi-colon.
The second number is a type reference to the first base class in the inheritance hierarchy
defining the virtual member function. In this case the class stab describes a base class so
the virtual function is not overriding any other definition of the method. Therefore thereference is to the type number of the class that the stab is describing (20).

46

STABS

This is followed by three semi-colons. One marks the end of the current sub-section, one
marks the end of the method field, and the third marks the end of the struct definition.
For classes containing virtual functions the very last section of the string part of thestab holds a type reference to the first base class. This is preceded by ‘~%’ and followed bya final semi-colon.
.stabs "class name(A):type def(20)=sym desc(struct)struct bytes(8)field name(Adat):type ref(int),bit offset(0),field bits(32);
field name(A virt func ptr):type def(21)=type desc(ptr to)type def(22)=sym desc(array)index type ref(range of int from 0 to 1);
elem type ref(vtbl elem type),
bit offset(32);meth name(A virt)::typedef(23)=sym desc(method)returning(int);:arg type(int),protection(public)normal(yes)virtual(yes)vtable index(1);class first defining(A);;;~%first base(A);",N LSYM,NIL,NIL,NIL.stabs "A:t20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32;
A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0

8.12 InheritanceStabs describing C++ derived classes include additional sections that describe the inheritancehierarchy of the class. A derived class stab also encodes the number of base classes. For
each base class it tells if the base class is virtual or not, and if the inheritance is private or
public. It also gives the offset into the object of the portion of the object corresponding toeach base class.
This additional information is embedded in the class stab following the number of bytes
in the struct. First the number of base classes appears bracketed by an exclamation point
and a comma.
Then for each base type there repeats a series: a virtual character, a visibility character,a number, a comma, another number, and a semi-colon.
The virtual character is ‘1’ if the base class is virtual and ‘0’ if not. The visibility
character is ‘2’ if the derivation is public, ‘1’ if it is protected, and ‘0’ if it is private.
Debuggers should ignore virtual or visibility characters they do not recognize, and assume
a reasonable default (such as public and non-virtual) (GDB 4.11 does not, but this should
be fixed in the next GDB release).
The number following the virtual and visibility characters is the offset from the start ofthe object to the part of the object pertaining to the base class.
After the comma, the second number is a type descriptor for the base type. Finally asemi-colon ends the series, which repeats for each base class.
The source below defines three base classes A, B, and C and the derived class D.
class A {public:int Adat;virtual int A_virt (int arg) { return arg; };};Chapter 8: GNU C++ Stabs

47

class B {public:int B_dat;
virtual int B_virt (int arg) {return arg; };};class C {public:int Cdat;virtual int C_virt (int arg) {return arg; };};class D : A, virtual B, public C {public:int Ddat;virtual int A_virt (int arg ) { return arg+1; };virtual int B_virt (int arg) { return arg+2; };virtual int C_virt (int arg) { return arg+3; };virtual int D_virt (int arg) { return arg; };};Class stabs similar to the ones described earlier are generated for each base class.
.stabs "A:T20=s8Adat:1,0,32;$vf20:21=*22=ar1;0;1;17,32;
A_virt::23=##1;:i;2A*-2147483647;20;;;~%20;",128,0,0,0.stabs "B:Tt25=s8Bdat:1,0,32;$vf25:21,32;B_virt::26=##1;:i;2A*-2147483647;25;;;~%25;",128,0,0,0.stabs "C:Tt28=s8Cdat:1,0,32;$vf28:21,32;C_virt::29=##1;:i;2A*-2147483647;28;;;~%28;",128,0,0,0In the stab describing derived class D below, the information about the derivation of thisclass is encoded as follows.
.stabs "derived class name:symbol descriptors(struct tag&type)=
type descriptor(struct)struct bytes(32)!num bases(3),base virtual(no)inheritance public(no)base offset(0),base class type ref(A);base virtual(yes)inheritance public(no)base offset(NIL),
base class type ref(B);base virtual(no)inheritance public(yes)base offset(64),base class type ref(C); . . .
.stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:
1,160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i;2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;
28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0

8.13 Virtual Base Classes
A derived class object consists of a concatenation in memory of the data areas defined byeach base class, starting with the leftmost and ending with the rightmost in the list of base

48

STABS

classes. The exception to this rule is for virtual inheritance. In the example above, class
D inherits virtually from base class B. This means that an instance of a D object will notcontain its own B part but merely a pointer to a B part, known as a virtual base pointer.
In a derived class stab, the base offset part of the derivation information, describedabove, shows how the base class parts are ordered. The base offset for a virtual base classis always given as 0. Notice that the base offset for B is given as 0 even though B is not thefirst base class. The first base class A starts at offset 0.
The field information part of the stab for class D describes the field which is the pointerto the virtual base class B. The vbase pointer name is ‘$vb’ followed by a type reference tothe virtual base class. Since the type id for B in this example is 25, the vbase pointer nameis ‘$vb25’.
.stabs "D:Tt31=s32!3,000,20;100,25;0264,28;$vb25:24,128;Ddat:1,
160,32;A_virt::32=##1;:i;2A*-2147483647;20;;B_virt::32:i;
2A*-2147483647;25;;C_virt::32:i;2A*-2147483647;28;;D_virt::32:i;2A*-2147483646;31;;;~%20;",128,0,0,0

Following the name and a semicolon is a type reference describing the type of the virtualbase class pointer, in this case 24. Type 24 was defined earlier as the type of the B classthis pointer. The this pointer for a class is a pointer to the class type.
.stabs "this:P24=*25=xsB:",64,0,0,8
Finally the field offset part of the vbase pointer field description shows that the vbase
pointer is the first field in the D object, before any data fields defined by the class. The
layout of a D class object is a follows, Adat at 0, the vtable pointer for A at 32, Cdat at 64,
the vtable pointer for C at 96, the virtual base pointer for B at 128, and Ddat at 160.

8.14 Static Members
The data area for a class is a concatenation of the space used by the data members of theclass. If the class has virtual methods, a vtable pointer follows the class data. The field
offset part of each field description in the class stab shows this ordering.
<< How is this reflected in stabs? See Cygnus bug #677 for some info. >>49

Appendix A Table of Stab Types
The following are all the possible values for the stab type field, for a.out files, in numericorder. This does not apply to XCOFF, but it does apply to stabs in sections (see Appendix F[Stab Sections], page 63). Stabs in ECOFF use these values but add 0x8f300 to distinguishthem from non-stab symbols.
The symbolic names are defined in the file include/aout/stabs.def.

A.1 Non-Stab Symbol Types
The following types are used by the linker and assembler, not by stab directives. Since
this document does not attempt to describe aspects of object file format other than the
debugging format, no details are given.
0x0 N_UNDF

Undefined symbol

0x2 N_ABS

File scope absolute symbol

0x3 N_ABS | N_EXT

External absolute symbol

0x4 N_TEXT

File scope text symbol

0x5 N_TEXT | N_EXT

External text symbol

0x6 N_DATA

File scope data symbol

0x7 N_DATA | N_EXT

External data symbol

0x8 N_BSS

File scope BSS symbol

0x9 N_BSS | N_EXT

External BSS symbol

0x0c N_FN_SEQ

Same as N_FN, for Sequent compilers

0x0a N_INDR

Symbol is indirected to another symbol

0x12 N_COMM

Common—visible after shared library dynamic link

0x14 N_SETA
0x15 N_SETA | N_EXT
Absolute set element
0x16 N_SETT
0x17 N_SETT | N_EXT
Text segment set element
0x18 N_SETD
0x19 N_SETD | N_EXT
Data segment set element
0x1a N_SETB
0x1b N_SETB | N_EXT
BSS segment set element
0x1c N_SETV
0x1d N_SETV | N_EXT
Pointer to set vector

50

STABS

0x1e N_WARNING

Print a warning message during linking

0x1f N_FN

File name of a .o file

A.2 Stab Symbol Types
The following symbol types indicate that this is a stab. This is the full list of stab numbers,
including stab types that are used in languages other than C.
0x20 N_GSYM

Global symbol; see Section 4.2 [Global Variables], page 15.

0x22 N_FNAME

Function name (for BSD Fortran); see Section 2.5 [Procedures],page 9.

0x24 N_FUN

Function name (see Section 2.5 [Procedures], page 9) or text segment
variable (see Section 4.5 [Statics], page 16).

0x26 N_STSYM

Data segment file-scope variable; see Section 4.5 [Statics], page 16.

0x28 N_LCSYM

BSS segment file-scope variable; see Section 4.5 [Statics], page 16.

0x2a N_MAIN

Name of main routine; see Section 2.1 [Main Program], page 7.

0x2c N_ROSYM

Variable in .rodata section; see Section 4.5 [Statics], page 16.

0x30 N_PC

Global symbol (for Pascal); see Section D.1 [N PC], page 57.

0x32 N_NSYMS

Number of symbols (according to Ultrix V4.0); see Section D.2[N NSYMS], page 57.

0x34 N_NOMAPNo DST map; see Section D.3 [N NOMAP], page 57.

0x36 N_MAC_DEFINE

Name and body of a #defined macro; see Chapter 6 [Macro define
and undefine], page 33.

0x38 N_OBJ

Object file (Solaris2).

0x3a N_MAC_UNDEF

Name of an #undefed macro; see Chapter 6 [Macro define and undefine], page 33.

0x3c N_OPT

Debugger options (Solaris2).

0x40 N_RSYM

Register variable; see Section 4.3 [Register Variables], page 16.

0x42 N_M2C

Modula-2 compilation unit; see Section D.4 [N M2C], page 57.

0x44 N_SLINELine number in text segment; see Section 2.4 [Line Numbers], page 9.

0x46 N_DSLINELine number in data segment; see Section 2.4 [Line Numbers], page 9.

0x48 N_BSLINELine number in bss segment; see Section 2.4 [Line Numbers], page 9.

0x48 N_BROWS

Sun source code browser, path to .cb file; see Section D.5[N BROWS], page 58.

0x4a N_DEFD

GNU Modula2 definition module dependency; see Section D.6[N DEFD], page 58.

0x4c N_FLINE

Function start/body/end line numbers (Solaris2).

0x50 N_EHDECLGNU C++ exception variable; see Section D.7 [N EHDECL], page 58.

Appendix A: Table of Stab Types

51

0x50 N_MOD2

Modula2 info "for imc" (according to Ultrix V4.0); see Section D.8[N MOD2], page 58.

0x54 N_CATCH

GNU C++ catch clause; see Section D.9 [N CATCH], page 58.

0x60 N_SSYM

Structure of union element; see Section D.10 [N SSYM], page 58.

0x62 N_ENDM

Last stab for module (Solaris2).

0x64 N_SO

Path and name of source file; see Section 2.2 [Source Files], page 7.

0x80 N_LSYM

Stack variable (see Section 4.1 [Stack Variables], page 15) or type(see Section 5.9 [Typedefs], page 31).

0x82 N_BINCL

Beginning of an include file (Sun only); see Section 2.3 [Include Files],page 8.

0x84 N_SOL

Name of include file; see Section 2.3 [Include Files], page 8.

0xa0 N_PSYM

Parameter variable; see Section 4.7 [Parameters], page 18.

0xa2 N_EINCLEnd of an include file; see Section 2.3 [Include Files], page 8.

0xa4 N_ENTRY

Alternate entry point; see Section 2.8 [Alternate Entry Points],
page 12.

0xc0 N_LBRAC

Beginning of a lexical block; see Section 2.7 [Block Structure],
page 11.

0xc2 N_EXCL

Place holder for a deleted include file; see Section 2.3 [Include Files],page 8.

0xc4 N_SCOPE

Modula2 scope information (Sun linker);[N SCOPE], page 59.

0xe0 N_RBRAC

End of a lexical block; see Section 2.7 [Block Structure], page 11.

0xe2 N_BCOMM

Begin named common block; see Section 4.4 [Common Blocks],
page 16.

0xe4 N_ECOMM

End named common block; see Section 4.4 [Common Blocks],
page 16.

0xe8 N_ECOML

Member of a common block; see Section 4.4 [Common Blocks],
page 16.

0xea N_WITH

Pascal with statement: type,,0,0,offset (Solaris2).

0xf0 N_NBTEXT

Gould non-base registers; see Section D.12 [Gould], page 59.

0xf2 N_NBDATA

Gould non-base registers; see Section D.12 [Gould], page 59.

0xf4 N_NBBSS

Gould non-base registers; see Section D.12 [Gould], page 59.

0xf6 N_NBSTS

Gould non-base registers; see Section D.12 [Gould], page 59.

0xf8 N_NBLCS

Gould non-base registers; see Section D.12 [Gould], page 59.

see Section D.11

53

Appendix B Table of Symbol Descriptors
The symbol descriptor is the character which follows the colon in many stabs, and whichtells what kind of stab it is. See Section 1.3 [String Field], page 2, for more information
about their use.
digit
(
-

Variable on the stack; see Section 4.1 [Stack Variables], page 15.

:

C++ nested symbol; see See Section 8.2 [Nested Symbols], page 39.

aParameter passed by reference in register; see Section 4.7.3 [Reference Parameters], page 20.

b

Based variable; see Section 4.6 [Based Variables], page 17.

cConstant; see Chapter 3 [Constants], page 13.

C

Conformant array bound (Pascal, maybe other languages); Section 4.7.4 [Conformant Arrays], page 20. Name of a caught exception (GNU C++). These canbe distinguished because the latter uses N_CATCH and the former uses anothersymbol type.

d

Floating point register variable; see Section 4.3 [Register Variables], page 16.

D

Parameter in floating point register; see Section 4.7.1 [Register Parameters],
page 18.

f

File scope function; see Section 2.5 [Procedures], page 9.

F

Global function; see Section 2.5 [Procedures], page 9.

G

Global variable; see Section 4.2 [Global Variables], page 15.

i

See Section 4.7.1 [Register Parameters], page 18.

I

Internal (nested) procedure; see Section 2.6 [Nested Procedures], page 11.

J

Internal (nested) function; see Section 2.6 [Nested Procedures], page 11.

L

Label name (documented by AIX, no further information known).

mModule; see Section 2.5 [Procedures], page 9.

p

Argument list parameter; see Section 4.7 [Parameters], page 18.

pP

See Section 4.7 [Parameters], page 18.

pF

Fortran Function parameter; see Section 4.7 [Parameters], page 18.

P

Unfortunately, three separate meanings have been independently invented forthis symbol descriptor. At least the GNU and Sun uses can be distinguishedby the symbol type. Global Procedure (AIX) (symbol type used unknown); see
Section 2.5 [Procedures], page 9. Register parameter (GNU) (symbol type N_
PSYM); see Section 4.7 [Parameters], page 18. Prototype of function referenced
by this file (Sun acc) (symbol type N_FUN).

Q

Static Procedure; see Section 2.5 [Procedures], page 9.

54

STABS

R

Register parameter; see Section 4.7.1 [Register Parameters], page 18.

r

Register variable; see Section 4.3 [Register Variables], page 16.

S

File scope variable; see Section 4.5 [Statics], page 16.

s

Local variable (OS9000).

t

Type name; see Section 5.9 [Typedefs], page 31.

T

Enumeration, structure, or union tag; see Section 5.9 [Typedefs], page 31.

v

Parameter passed by reference; see Section 4.7.3 [Reference Parameters],
page 20.

V

Procedure scope static variable; see Section 4.5 [Statics], page 16.

x

Conformant array; see Section 4.7.4 [Conformant Arrays], page 20.

X

Function return variable; see Section 4.7 [Parameters], page 18.

55

Appendix C Table of Type Descriptors
The type descriptor is the character which follows the type number and an equals sign. It
specifies what kind of type is being defined. See Section 1.3 [String Field], page 2, for more
information about their use.
digit(Type reference; see Section 1.3 [String Field], page 2.

-

Reference to builtin type; see Section 5.1.3 [Negative Type Numbers], page 23.

#

Method (C++); see Section 8.7 [Method Type Descriptor], page 42.

*

Pointer; see Section 5.2 [Miscellaneous Types], page 26.

&

Reference (C++).

@Type Attributes (AIX); see Section 1.3 [String Field], page 2. Member (classand variable) type (GNU C++); see Section 8.8 [Member Type Descriptor],
page 43.

a

Array; see Section 5.5 [Arrays], page 27.

A

Open array; see Section 5.5 [Arrays], page 27.

b

Pascal space type (AIX); see Section 5.2 [Miscellaneous Types], page 26. Builtin
integer type (Sun); see Section 5.1.2 [Builtin Type Descriptors], page 22. Constand volatile qualified type (OS9000).

B

Volatile-qualified type; see Section 5.2 [Miscellaneous Types], page 26.

cComplex builtin type (AIX); see Section 5.1.2 [Builtin Type Descriptors],
page 22. Const-qualified type (OS9000).

CCOBOL Picture type. See AIX documentation for details.

dFile type; see Section 5.2 [Miscellaneous Types], page 26.

DN-dimensional dynamic array; see Section 5.5 [Arrays], page 27.

eEnumeration type; see Section 5.7 [Enumerations], page 29.

E

N-dimensional subarray; see Section 5.5 [Arrays], page 27.

fFunction type; see Section 5.11 [Function Types], page 32.

F

Pascal function parameter; see Section 5.11 [Function Types], page 32,g

Builtin floating point type; see Section 5.1.2 [Builtin Type Descriptors], page 22.

G

COBOL Group. See AIX documentation for details.

i

Imported type (AIX); see Section 5.3 [Cross-References], page 26. Volatilequalified type (OS9000).

k

Const-qualified type; see Section 5.2 [Miscellaneous Types], page 26.

K

COBOL File Descriptor. See AIX documentation for details.

M

Multiple instance type; see Section 5.2 [Miscellaneous Types], page 26.

56

STABS

n

String type; see Section 5.6 [Strings], page 29.

N

Stringptr; see Section 5.6 [Strings], page 29.

oOpaque type; see Section 5.9 [Typedefs], page 31.

p

Procedure; see Section 5.11 [Function Types], page 32.

P

Packed array; see Section 5.5 [Arrays], page 27.

r

Range type; see Section 5.4 [Subranges], page 27.

R

Builtin floating type; see Section 5.1.2 [Builtin Type Descriptors], page 22,(Sun). Pascal subroutine parameter; see Section 5.11 [Function Types], page 32,(AIX). Detecting this conflict is possible with careful parsing (hint: a Pascal
subroutine parameter type will always contain a comma, and a builtin typedescriptor never will).

s

Structure type; see Section 5.8 [Structures], page 30.

S

Set type; see Section 5.2 [Miscellaneous Types], page 26.

uUnion; see Section 5.10 [Unions], page 31.

v

Variant record. This is a Pascal and Modula-2 feature which is like a union
within a struct in C. See AIX documentation for details.

w

Wide character; see Section 5.1.2 [Builtin Type Descriptors], page 22.

x

Cross-reference; see Section 5.3 [Cross-References], page 26.

Y

Used by IBM’s xlC C++ compiler (for structures, I think).

z

gstring; see Section 5.6 [Strings], page 29.

57

Appendix D Expanded Reference by Stab TypeFor a full list of stab types, and cross-references to where they are described, see Appendix A[Stab Types], page 49. This appendix just covers certain stabs which are not yet describedin the main body of this document; eventually the information will all be in one place.
Format of an entry:
The first line is the symbol type (see include/aout/stab.def).
The second line describes the language constructs the symbol type represents.
The third line is the stab format with the significant stab fields named and the rest NIL.
Subsequent lines expand upon the meaning and possible values for each significant stabfield.
Finally, any further information.

D.1 N PC[.stabs]

N_PC

Global symbol (for Pascal).
"name" -> "symbol_name" <<?>>
value -> supposedly the line number (stab.def is skeptical)
stabdump.c says:
global pascal symbol: name,,0,subtype,line<< subtype? >>D.2 N NSYMS
N_NSYMS[.stabn]

Number of symbols (according to Ultrix V4.0).
0, files,,funcs,lines (stab.def)

D.3 N NOMAP[.stabs]
No DST map for symbol (according to Ultrix V4.0). I think this means a variable
has been optimized out.
name, ,0,type,ignored (stab.def)

N_NOMAP

D.4 N M2C
N_M2C[.stabs]

Modula-2 compilation unit.
"string" -> "unit_name,unit_time_stamp[,code_time_stamp]"
desc-> unit_number
value -> 0 (main unit)
1 (any other unit)
See Dbx and Dbxtool Interfaces, 2nd edition, by Sun, 1988, for more information.

58

STABS

D.5 N BROWS
N_BROWS[.stabs]

Sun source code browser, path to .cb file<<?>> "path to associated .cb file"
Note: N BROWS has the same value as N BSLINE.

D.6 N DEFD
N_DEFD[.stabn]

GNU Modula2 definition module dependency.
GNU Modula-2 definition module dependency. The value is the modification timeof the definition file. The other field is non-zero if it is imported with the GNU M2
keyword %INITIALIZE. Perhaps N_M2C can be used if there are enough empty fields?

D.7 N EHDECL
N_EHDECL[.stabs]

GNU C++ exception variable <<?>>.
"string is variable name"Note: conflicts with N_MOD2.

D.8 N MOD2
N_MOD2[.stab?]Modula2 info "for imc" (according to Ultrix V4.0)
Note: conflicts with N_EHDECL <<?>>

D.9 N CATCH
N_CATCH[.stabn]

GNU C++ catch clause
GNU C++ catch clause. The value is its address. The desc field is nonzero if thisentry is immediately followed by a CAUGHT stab saying what exception was caught.
Multiple CAUGHT stabs means that multiple exceptions can be caught here. If desc is0, it means all exceptions are caught here.

D.10 N SSYM
N_SSYM
Structure or union element.
The value is the offset in the structure.
<<?looking at structs and unions in C I didn’t see these>>[.stabn]Appendix D: Expanded Reference by Stab Type59

D.11 N SCOPE
N_SCOPE[.stab?]Modula2 scope information (Sun linker) <<?>>

D.12 Non-base registers on Gould systems
N_NBTEXT
N_NBDATAN_NBBSS
N_NBSTS
N_NBLCS[.stab?][.stab?][.stab?][.stab?][.stab?]

These are used on Gould systems for non-base registers syms.
However, the following values are not the values used by Gould; they are the values
which GNU has been documenting for these values for a long time, without actuallychecking what Gould uses. I include these values only because perhaps some someone
actually did something with the GNU information (I hope not, why GNU knowingly
assigned wrong values to these in the header file is a complete mystery to me).
240
0xf0
N_NBTEXT ??
242
0xf2
N_NBDATA ??
244
0xf4
N_NBBSS??
246
0xf6
N_NBSTS??
248
0xf8
N_NBLCS??

D.13 N LENG[.stabn]
Second symbol entry containing a length-value for the preceding entry. The value isthe length.

N_LENG

61

Appendix E Questions and Anomalies• For GNU C stabs defining local and global variables (N_LSYM and N_GSYM), the desc
field is supposed to contain the source line number on which the variable is defined. In
reality the desc field is always 0. (This behavior is defined in dbxout.c and putting
a line number in desc is controlled by ‘#ifdef WINNING_GDB’, which defaults to false).
GDB supposedly uses this information if you say ‘list var’. In reality, var can be avariable defined in the program and GDB says ‘function var not defined’.
• In GNU C stabs, there seems to be no way to differentiate tag types: structures, unions,and enums (symbol descriptor ‘T’) and typedefs (symbol descriptor ‘t’) defined at file
scope from types defined locally to a procedure or other more local scope. They all
use the N_LSYM stab type. Types defined at procedure scope are emitted after the
N_RBRAC of the preceding function and before the code of the procedure in which they
are defined. This is exactly the same as types defined in the source file between thetwo procedure bodies. GDB over-compensates by placing all types in block #1, theblock for symbols of file scope. This is true for default, ‘-ansi’ and ‘-traditional’
compiler options. (Bugs gcc/1063, gdb/1066.)• What ends the procedure scope? Is it the proc block’s N_RBRAC or the next N_FUN? (Ibelieve it’s the first.)

63

Appendix F Using Stabs in Their Own Sections
Many object file formats allow tools to create object files with custom sections containing
any arbitrary data. For any such object file format, stabs can be embedded in special
sections. This is how stabs are used with ELF and SOM, and aside from ECOFF andXCOFF, is how stabs are used with COFF.

F.1 How to Embed Stabs in Sections
The assembler creates two custom sections, a section named .stab which contains an arrayof fixed length structures, one struct per stab, and a section named .stabstr containing all
the variable length strings that are referenced by stabs in the .stab section. The byte orderof the stabs binary data depends on the object file format. For ELF, it matches the byteorder of the ELF file itself, as determined from the EI_DATA field in the e_ident memberof the ELF header. For SOM, it is always big-endian (is this true??? FIXME). For COFF,it matches the byte order of the COFF headers. The meaning of the fields is the same as
for a.out (see Section 7.1 [Symbol Table Format], page 35), except that the n_strx fieldis relative to the strings for the current compilation unit (which can be found using thesynthetic N UNDF stab described below), rather than the entire string table.
The first stab in the .stab section for each compilation unit is synthetic, generated
entirely by the assembler, with no corresponding .stab directive as input to the assembler.
This stab contains the following fields:
n_strx

Offset in the .stabstr section to the source filename.

n_typeN_UNDF.

n_otherUnused field, always zero. This may eventually be used to hold overflows fromthe count in the n_desc field.

n_descCount of upcoming symbols, i.e., the number of remaining stabs for this source
file.

n_value

Size of the string table fragment associated with this source file, in bytes.

The .stabstr section always starts with a null byte (so that string offsets of zero reference a null string), followed by random length strings, each of which is null byte terminated.
The ELF section header for the .stab section has its sh_link member set to the section
number of the .stabstr section, and the .stabstr section has its ELF section header sh_type member set to SHT_STRTAB to mark it as a string table. SOM and COFF have no wayof linking the sections together or marking them as string tables.
For COFF, the .stab and .stabstr sections may be simply concatenated by the linker.
GDB then uses the n_desc fields to figure out the extent of the original sections. Similarly,
the n_value fields of the header symbols are added together in order to get the actual
position of the strings in a desired .stabstr section. Although this design obviates any
need for the linker to relocate or otherwise manipulate .stab and .stabstr sections, it also
requires some care to ensure that the offsets are calculated correctly. For instance, if thelinker were to pad in between the .stabstr sections before concatenating, then the offsets
to strings in the middle of the executable’s .stabstr section would be wrong.

64

STABS

The GNU linker is able to optimize stabs information by merging duplicate strings andremoving duplicate header file information (see Section 2.3 [Include Files], page 8). Whensome versions of the GNU linker optimize stabs in sections, they remove the leading N_UNDF
symbol and arranges for all the n_strx fields to be relative to the start of the .stabstr
section.

F.2 Having the Linker Relocate Stabs in ELF
This section describes some Sun hacks for Stabs in ELF; it does not apply to COFF or
SOM. While gdb no longer supports this hack for Sun Stabs in ELF, this section is kept to
document the issue.
To keep linking fast, you don’t want the linker to have to relocate very many stabs.
Making sure this is done for N_SLINE, N_RBRAC, and N_LBRAC stabs is the most important
thing (see the descriptions of those stabs for more information). But Sun’s stabs in ELF hastaken this further, to make all addresses in the n_value field (functions and static variables)
relative to the source file. For the N_SO symbol itself, Sun simply omits the address. To
find the address of each section corresponding to a given source file, the compiler puts out
symbols giving the address of each section for a given source file. Since these are ELF(not stab) symbols, the linker relocates them correctly without having to touch the stabs
section. They are named Bbss.bss for the bss section, Ddata.data for the data section, andDrodata.rodata for the rodata section. For the text section, there is no such symbol (butthere should be, see below). For an example of how these symbols work, See Section 7.2.3[Stab Section Transformations], page 36. GCC does not provide these symbols; it instead
relies on the stabs getting relocated. Thus addresses which would normally be relative to
Bbss.bss, etc., are already relocated. The Sun linker provided with Solaris 2.2 and earlier
relocates stabs using normal ELF relocation information, as it would do for any section.
Sun has been threatening to kludge their linker to not do this (to speed up linking), eventhough the correct way to avoid having the linker do these relocations is to have the compiler
no longer output relocatable values. Last I heard they had been talked out of the linker
kludge. See Sun point patch 101052-01 and Sun bug 1142109. With the Sun compiler thisaffects ‘S’ symbol descriptor stabs (see Section 4.5 [Statics], page 16) and functions (seeSection 2.5 [Procedures], page 9). In the latter case, to adopt the clean solution (making
the value of the stab relative to the start of the compilation unit), it would be necessary toinvent a Ttext.text symbol, analogous to the Bbss.bss, etc., symbols. I recommend thisrather than using a zero value and getting the address from the ELF symbols.
Finding the correct Bbss.bss, etc., symbol is difficult, because the linker simply concatenates the .stab sections from each .o file without including any information about whichpart of a .stab section comes from which .o file. The way GDB use to do this is to look for
an ELF STT_FILE symbol which has the same name as the last component of the file namefrom the N_SO symbol in the stabs (for example, if the file name is ../../gdb/main.c, it
looks for an ELF STT_FILE symbol named main.c). This loses if different files have thesame name (they could be in different directories, a library could have been copied fromone system to another, etc.). It would be much cleaner to have the Bbss.bss symbols inthe stabs themselves. Having the linker relocate them there is no more work than having
the linker relocate ELF symbols, and it solves the problem of having to associate the ELF
and stab symbols. However, no one has yet designed or implemented such a scheme.

65

Appendix G 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

66

STABS

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 G: GNU Free Documentation License

67

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,

68

STABS

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 G: GNU Free Documentation License

69

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.

70

STABS

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 G: GNU Free Documentation License

71

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.

72

STABS

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.

73

Symbol Types Index.
.bb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
.be . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

C
C_BCOMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
C_BINCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
C_BLOCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
C_BSTAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
C_DECL, for types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
C_ECOML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
C_ECOMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
C_EINCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
C_ENTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
C_ESTAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
C_FILE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
C_FUN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
C_GSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
C_LSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
C_PSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
C_RPSYM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
C_RSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
C_STSYM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

N
N_BCOMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_BINCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
N_BROWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
N_BSLINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
N_CATCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
N_DEFD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
N_DSLINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
N_ECOML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_ECOMM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_EHDECL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
N_EINCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

N_ENTRY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
N_EXCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
N_FNAME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
N_FUN, for functions . . . . . . . . . . . . . . . . . . . . . . . . . . 9
N_FUN, for variables . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_GSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
N_GSYM, for functions (Sun acc) . . . . . . . . . . . . . . 9
N_LBRAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
N_LCSYM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_LENG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_LSYM, for parameter . . . . . . . . . . . . . . . . . . . . . . . . 19
N_LSYM, for stack variables . . . . . . . . . . . . . . . . . . 15
N_LSYM, for types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
N_M2C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
N_MAC_DEFINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
N_MAC_UNDEF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
N_MAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
N_MOD2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
N_NBBSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_NBDATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_NBLCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_NBSTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_NBTEXT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_NOMAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
N_NSYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
N_PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
N_PSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
N_RBRAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
N_ROSYM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_RSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_RSYM, for parameters . . . . . . . . . . . . . . . . . . . . . . . 18
N_SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
N_SLINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
N_SO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
N_SOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
N_SSYM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
N_STSYM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
N_STSYM, for functions (Sun acc) . . . . . . . . . . . . . 9