# stap

## NAME



           stap - systemtap script translator/driver
    


## SYNOPSIS



           **stap**[ _OPTIONS_ ] _FILENAME_ [ _ARGUMENTS_ ]
           **stap**[ _OPTIONS_ ] **-**[ _ARGUMENTS_ ]
           **stap**[ _OPTIONS_ ] **-e** _SCRIPT_ [ _ARGUMENTS_ ]
           **stap**[ _OPTIONS_ ] **-l** _PROBE_ [ _ARGUMENTS_ ]
           **stap**[ _OPTIONS_ ] **-L** _PROBE_ [ _ARGUMENTS_ ]
           **stap**[ _OPTIONS_ ] **--dump-probe-types**
           **stap**[ _OPTIONS_ ] **--dump-probe-aliases**
           **stap**[ _OPTIONS_ ] **--dump-functions**
    


## DESCRIPTION



           The _stap_ program is the front-end to the Systemtap tool.  It
           accepts probing instructions written in a simple domain-specific
           language, translates those instructions into C code, compiles this
           C code, and loads the resulting module into a running Linux kernel
           or a Dyninst user-space mutator, to perform the requested system
           trace/probe functions.  You can supply the script in a named file
           (FILENAME), from standard input (use - instead of FILENAME), or
           from the command line (using -e SCRIPT).  The program runs until
           it is interrupted by the user, or if the script voluntarily
           invokes the _exit()_ function, or by sufficient number of soft
           errors.
    
           The language, which is described the _SCRIPT LANGUAGE_ section
           below, is strictly typed, expressive, declaration free,
           procedural, prototyping-friendly, and inspired by _awk_ and _C_.  It
           allows source code points or events in the system to be associated
           with handlers, which are subroutines that are executed
           synchronously.  It is somewhat similar conceptually to "breakpoint
           command lists" in the _gdb_ debugger.
    


## DOCUMENTATION OVERVIEW



           systemtap comes with a variety of educational, documentation and
           reference resources.  They come online and/or packaged for offline
           use.  Some systemtap diagnostic warning/error messages specially
           suggest reading a man page by including a string like
           [man error::pass5].  For online documentation, see the project web
           site, https://sourceware.org/systemtap/
    
           ┌───────────────────────────┬──────────────────────────────────────────────────────┐
           │ **man pages** │                                                      │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stap (this page)          │ language syntax, concepts, operation, options        │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ error::*                  │ further explanation of error conditions              │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ warning::*                │ further explanation of warning conditions            │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stapprobes                │ probe points and their $context variables            │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stapref                   │ quick reference to language syntax                   │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stappaths                 │ list of directories, including books & references    │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stap-prep                 │ program to install auxiliary dependencies like ker‐  │
           │                           │ nel debuginfo                                        │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ tapset::*                 │ generated list of tapsets                            │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ probe::*                  │ generated list of tapset probe aliases               │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ function::*               │ generated list of tapset functions                   │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ macro::*                  │ generated list of tapset macros                      │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stapvars                  │ some of the tapset global variables                  │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ staprun, stapdyn, stapbpf │ programs for executing compiled systemtap scripts    │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ systemtap                 │ initscript, boot-time probing                        │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stap-server               │ compilation server                                   │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ stapex                    │ a few very basic script examples                     │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ **books** │                                                      │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ Beginner's Guide          │ tutorial book, language essentials, examples         │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ Tutorial                  │ shorter tutorial, exercises                          │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ Language Reference        │ detailed language manual, covers statistics/analysis │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ Tapset Reference          │ the tapset man pages, reformatted into a book        │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ **references** │                                                      │
           ├───────────────────────────┼──────────────────────────────────────────────────────┤
           │ example scripts           │ over a hundred directly usable sysadmin tools, toys, │
           │                           │ hacks to learn from                                  │
           └───────────────────────────┴──────────────────────────────────────────────────────┘
    


## OPTIONS



           The systemtap translator supports the following options.  Any oth‐
           er option prints a list of supported options.  Options may be giv‐
           en on the command line, as usual.  If the file $SYSTEMTAP_DIR/rc
           exist, options are also loaded from there and interpreted first.
           ($SYSTEMTAP_DIR defaults to $HOME/.systemtap if unset.)
    
           In some cases, the default value of an option depends on particu‐
           lar system configuration and thus can't be mentioned here direct‐
           ly.  In some of those cases running "stap --help" might display
           the default.
    
           **-** Use standard input instead of a given FILENAME as probe
                  language input, unless -e SCRIPT is given.
    
           **-h --help**
                  Show help message.
    
           **-V --version**
                  Show version message.
    
           **-p** _NUM_ Stop after pass NUM.  The passes are numbered 1-5: parse,
                  elaborate, translate, compile, run.  See the **PROCESSING**
                  section for details.
    
           **-v** Increase verbosity for all passes.  Produce a larger volume
                  of informative (?) output each time option repeated.
    
           **--vp ABCDE**
                  Increase verbosity on a per-pass basis.  For example,
                  "--vp 002" adds 2 units of verbosity to pass 3 only.  The
                  combination "-v --vp 00004" adds 1 unit of verbosity for
                  all passes, and 4 more for pass 5.
    
           **-k** Keep the temporary directory after all processing.  This
                  may be useful in order to examine the generated C code, or
                  to reuse the compiled kernel object.
    
           **-g** Guru mode.  Enable parsing of unsafe expert-level con‐
                  structs like embedded C.
    
           **-P** Prologue-searching mode.  This is equivalent to --pro‐
                  logue-searching=always.  Activate heuristics to work around
                  incorrect debugging information for function parameter
                  $context variables.
    
           **-u** Unoptimized mode.  Disable unused code elision and many
                  other optimizations during elaboration / translation.
    
           **-w** Suppressed warnings mode.  Disables all warning messages.
    
           **-W** Treat all warnings as errors.
    
           **-b** Use bulk mode (percpu files) for kernel-to-user data trans‐
                  fer.  Use the _stap-merge_ program to multiplex them back to‐
                  gether later.
    
           **-i --interactive**
                  Interactive mode. Enable an interface to build the system‐
                  tap script incrementally and interactively.
    
           **-t** Collect timing information on the number of times probe ex‐
                  ecutes and average amount of time spent in each probe-
                  point. Also shows the derivation for each probe-point.
    
           **-s** _NUM_ Use NUM megabyte buffers for kernel-to-user data transfer
                  per processor.  The default is 16MB, or less on smaller
                  memory machines.
    
           **-I** _DIR_ Add the given directory to the tapset search directory.
                  See the description of pass 2 for details.
    
           **-D** _NAME=VALUE_
                  Add the given C preprocessor directive to the module Make‐
                  file.  These can be used to override limit parameters de‐
                  scribed below.
    
           **-B** _NAME=VALUE_
                  In kernel-runtime mode, add the given make directive to the
                  kernel module build's make invocation.  These can be used
                  to add or override kconfig options.  For example, use
    
                  **-B CONFIG_DEBUG_INFO=y**
    
                  to add debugging information.
    
           **-B** _FLAG_
                  In dyninst-runtime mode, add the given parameter to the
                  compiler CFLAGS used for building the dyninst shared li‐
                  brary.  For example, use
    
                  **-B -g**
    
                  to add debugging information.
    
           **-a** _ARCH_
                  Use a cross-compilation mode for the given target architec‐
                  ture.  This requires access to the cross-compiler and the
                  kernel build tree, and goes along with the
    
                  **-B CROSS_COMPILE=arch-tool-prefix-**
                  and
                  **-r /build/tree**
    
                  options.
    
           **--modinfo** _NAME=VALUE_
                  Add the name/value pair as a MODULE_INFO macro call to the
                  generated module.  This may be useful to inform or override
                  various module-related checks in the kernel.
    
           **-G** _NAME=VALUE_
                  Sets the value of global variable NAME to VALUE when
                  staprun is invoked.  This applies to scalar variables de‐
                  clared global in the script/tapset.
    
           **-R** _DIR_ Look for the systemtap runtime sources in the given direc‐
                  tory.  Your DIR default can be seen using "stap --help".
    
           **-r** _/DIR_
                  Build for kernel in given build tree. Can also be set with
                  the _SYSTEMTAP_RELEASE_ environment variable.
    
           **-r** _RELEASE_
                  Build for kernel in build tree **/lib/modules/RELEASE/build**.
                  Can also be set with the _SYSTEMTAP_RELEASE_ environment
                  variable.
    
           **-m** _MODULE_
                  Use the given name for the generated kernel object module,
                  instead of a unique randomized name.  The generated kernel
                  object module is copied to the current directory.
    
           **-d** _MODULE_
                  Add symbol/unwind information for the given module into the
                  kernel object module.  This may enable symbolic tracebacks
                  from those modules/programs, even if they do not have an
                  explicit probe placed into them.
    
           **--ldd** Add symbol/unwind information for all user-space shared li‐
                  braries suspected by ldd to be necessary for user-space bi‐
                  naries being probed or listed with the -d option.  Caution:
                  this can make the probe modules considerably larger.  Note
                  that this option does not deal with kernel-space modules:
                  see instead --all-modules below.
    
           **--all-modules**
                  Equivalent to specifying "-dkernel" and a "-d" for each
                  kernel module that is currently loaded.  Caution: this can
                  make the probe modules considerably larger.
    
           **-o** _FILE_
                  Send standard output to named file. In bulk mode, percpu
                  files will start with FILE_ (FILE_cpu with -F) followed by
                  the cpu number.  This supports strftime(3) formats for
                  FILE.
    
           **-c** _CMD_ Start the probes, run CMD, and exit when CMD finishes.
                  This also has the effect of setting target() to the pid of
                  that process.  Note that many probe types trigger indepen‐
                  dently of this setting.  Consider including something like
                  this to focus your script.
    
                     probe FOO { if (pid() != target()) next; .... }
    
           **-x** _PID_ Sets target() to PID.  The script runs independently of the
                  PID's lifespan.
    
           **-e** _SCRIPT_
                  Run the given SCRIPT specified on the command line.
    
           **-E** _SCRIPT_
                  Run the given SCRIPT specified. This SCRIPT is run in addi‐
                  tion to the main script specified, through -e, or as a
                  script file. This option can be repeated to run multiple
                  scripts, and can be used in listing mode (-l/-L).
    
           **-l** _PROBE_
                  Instead of running a probe script, just list all available
                  probe points matching the given single probe point.  The
                  pattern may include wildcards and aliases, but not comma-
                  separated multiple probe points.  The process result code
                  will indicate failure if there are no matches.
    
                  % stap -e 'probe syscall.* { }'
                  [...]
                  % stap -l 'syscall.*'
                  syscall.accept
                  [...]
                  syscall.writev
    
           **-L** _PROBE_
                  Similar to "-l", but list matching probe points plus their
                  available context variables.  When -v is set with -L, the
                  output includes duplicate probe points which are distin‐
                  guished by their PC address.
    
                  % stap -L 'process("/lib64/libpython*.so.*").mark("*")'
                  process("/usr/lib64/libpython2.7.so.1.0").mark("function__entry") $arg1:long $arg2:long $arg3:long
                  process("/usr/lib64/libpython2.7.so.1.0").mark("function__return") $arg1:long $arg2:long $arg3:long
                  process("/usr/lib64/libpython3.6m.so.1.0").mark("function__entry") $arg1:long $arg2:long $arg3:long
                  process("/usr/lib64/libpython3.6m.so.1.0").mark("function__return") $arg1:long $arg2:long $arg3:long
                  process("/usr/lib64/libpython3.6m.so.1.0").mark("gc__done") $arg1:long
                  process("/usr/lib64/libpython3.6m.so.1.0").mark("gc__start") $arg1:long
                  process("/usr/lib64/libpython3.6m.so.1.0").mark("line") $arg1:long $arg2:long $arg3:long
    
           **-F** Without -o option, load module and start probes, then de‐
                  tach from the module leaving the probes running.  With -o
                  option, run staprun in background as a daemon and show its
                  pid.
    
           **-S** _size[,N]_
                  Sets the maximum size of output file and the maximum number
                  of output files.  If the size of output file will exceed
                  **size** megabytes, systemtap switches output file to the next
                  file. And if the number of output files exceed **N** , system‐
                  tap removes the oldest output file. You can omit the second
                  argument.
    
           **-T** _TIMEOUT_
                  Exit the script after TIMEOUT seconds.
    
           **--skip-badvars**
                  Ignore unresolvable or run-time-inaccessible context vari‐
                  ables and substitute with 0, without errors.
    
           **--prologue-searching**[=_WHEN_]
                  Prologue-searching mode. Activate heuristics to work around
                  incorrect debugging information  for  function  parameter
                  $context variables. WHEN can be either "never", "always",
                  or "auto" (i.e. enabled by heuristic). If WHEN is missing,
                  then "always" is assumed. If the option is missing, then
                  "auto" is assumed.
    
           **--suppress-handler-errors**
                  Wrap all probe handlers into something like this
    
                  try { ... } catch { next }
    
                  block, which causes any runtime errors to be quietly sup‐
                  pressed.  Suppressed errors do not count against **MAXERRORS**
                  limits.  In this mode, the **MAXSKIPPED** limits are also sup‐
                  pressed, so that many errors and skipped probes may be ac‐
                  cumulated during a script's runtime.  Any overall counts
                  will still be reported at shutdown.
    
           **--compatible** _VERSION_
                  Suppress recent script language or tapset changes which are
                  incompatible with given older version of systemtap.  This
                  may be useful if a much older systemtap script fails to
                  run.  See the DEPRECATION section for more details.
    
           **--check-version**
                  This option is used to check if the active script has any
                  constructs that may be systemtap version specific.  See the
                  DEPRECATION section for more details.
    
           **--clean-cache**
                  This option prunes stale entries from the cache directory.
                  This is normally done automatically after successful runs,
                  but this option will trigger the cleanup manually and then
                  exit.  See the CACHING section for more details about cache
                  limits.
    
           **--color**[=_WHEN_], **--colour**[=_WHEN_]
                  This option controls coloring of error messages. WHEN can
                  be either "never", "always", or "auto" (i.e. enable only if
                  at a terminal). If WHEN is missing, then "always" is as‐
                  sumed. If the option is missing, then "auto" is assumed.
    
                  Colors can be modified using the SYSTEMTAP_COLORS environ‐
                  ment variable. The format must be of the form
                  **key1=val1:key2=val2:key3=val3**...etc.  Valid keys are
                  "error", "warning", "source", "caret", and "token".  Values
                  constitute Select Graphic Rendition (SGR) parameter(s).
                  Consult the documentation of your terminal for the SGRs it
                  supports. As an example, the default colors would be ex‐
                  pressed as
                  **error=01;31:warning=00;33:source=00;34:caret=01:token=01**.
                  If SYSTEMTAP_COLORS is absent, the default colors will be
                  used. If it is empty or invalid, coloring is turned off.
    
           **--disable-cache**
                  This option disables all use of the cache directory.  No
                  files will be either read from or written to the cache.
    
           **--poison-cache**
                  This option treats files in the cache directory as invalid.
                  No files will be read from the cache, but resulting files
                  from this run will still be written to the cache.  This is
                  meant as a troubleshooting aid when stap's cached behavior
                  seems to be misbehaving.  If it helped, there is a probably
                  a bug in systemtap that the developers would like you to
                  report.
    
           **--privilege**[=_stapusr_ | =_stapsys_ | =_stapdev_]
                  This option instructs _stap_ to examine the script looking
                  for constructs which are not allowed for the specified
                  privilege level (see _UNPRIVILEGED USERS_).  Compilation
                  fails if any such constructs are used.  If _stapusr_ or _stap‐_
                  _sys_ are specified when using a compile server (see
                  _--use-server_), the server will examine the script and, if
                  compilation succeeds, the server will cryptographically
                  sign the resulting kernel module, certifying that is it
                  safe for use by users at the specified privilege level.
    
                  If _--privilege_ has not been specified, _-pN_ has not been
                  specified with N < 5, and the invoking user is not _root_ ,
                  and is not a member of the group _stapdev_ , then _stap_ will
                  automatically add the appropriate _--privilege_ option to the
                  options already specified.
    
           **--unprivileged**
                  This option is equivalent to _--privilege=stapusr_.
    
           **--use-server**[=_HOSTNAME_[_:PORT_] | =_IP_ADDRESS_[_:PORT_] | =_CERT_SERIAL_]
                  Specify compile-server(s) to be used for compilation and/or
                  in conjunction with _--list-servers_ and _--trust-servers_ (see
                  below) for listing. If no argument is supplied, then the
                  default in unprivileged mode (see _--privilege_) is to select
                  compatible servers which are trusted as SSL peers and as
                  module signers and currently online. Otherwise the default
                  is to select compatible servers which are trusted as SSL
                  peers and currently online.  _--use-server_ may be specified
                  more than once, in which case a list of servers is accumu‐
                  lated in the order specified. Servers may be specified by
                  host name, ip address, or by certificate serial number (ob‐
                  tained using _--list-servers_).  The latter is most commonly
                  used when adding or revoking trust in a server (see
                  _--trust-servers_ below). If a server is specified by host
                  name or ip address, then an optional port number may be
                  specified. This is useful for accessing servers which are
                  not on the local network or to specify a particular server.
    
                  IP addresses may be IPv4 or IPv6 addresses.
    
                  If a particular IPv6 address is link local and exists on
                  more than one interface, the intended interface may be
                  specified by appending the address with a percent sign (%)
                  followed by the intended interface name. For example,
                  "fe80::5eff:35ff:fe07:55ca%eth0".
    
                  In order to specify a port number with an IPv6 address, it
                  is necessary to enclose the IPv6 address in square brackets
                  ([]) in order to separate the port number from the rest of
                  the address. For example,
                  "[fe80::5eff:35ff:fe07:55ca]:5000" or
                  "[fe80::5eff:35ff:fe07:55ca%eth0]:5000".
    
                  If _--use-server_ has not been specified, _-pN_ has not been
                  specified with N < 5, and the invoking user not _root_ , is
                  not a member of the group _stapdev_ , but is a member of the
                  group _stapusr_ , then _stap_ will automatically add _--use-serv‐_
                  _er_ to the options already specified.
    
           **--use-server-on-error**[=**yes** |=**no**]
                  Instructs stap to retry compilation of a script using a
                  compile server if compilation on the local host fails in a
                  manner which suggests that it might succeed using a server.
                  If this option is not specified, the default is _no_.  If no
                  argument is provided, then the default is _yes_. Compilation
                  will be retried for certain types of errors (e.g. insuffi‐
                  cient data or resources) which may not occur during re-com‐
                  pilation by a compile server. Compile servers will be se‐
                  lected automatically for the re-compilation attempt as if
                  _--use-server_ was specified with no arguments.
    
           **--list-servers** _[=SERVERS]_
                  Display the status of the requested _SERVERS_ , where _SERVERS_
                  is a comma-separated list of server attributes. The list of
                  attributes is combined to filter the list of servers dis‐
                  played. Supported attributes are:
    
                  **all** specifies all known servers (trusted SSL peers,
                         trusted module signers, online servers).
    
                  **specified**
                         specifies servers specified using _--use-server_.
    
                  **online** filters the output by retaining information about
                         servers which are currently online.
    
                  **trusted**
                         filters the output by retaining information about
                         servers which are trusted as SSL peers.
    
                  **signer** filters the output by retaining information about
                         servers which are trusted as module signers (see
                         _--privilege_).
    
                  **compatible**
                         filters the output by retaining information about
                         servers which are compatible with the current kernel
                         release and architecture.
    
                  If no argument is provided, then the default is **specified**.
                  If no servers were specified using _--use-server_ , then the
                  default servers for _--use-server_ are listed.
    
                  Note that _--list-servers_ uses the _avahi-daemon_ service to
                  detect online servers. If this service is not available,
                  then _--list-servers_ will fail to detect any _online_ servers.
                  In order for _--list-servers_ to detect servers listening on
                  IPv6 addresses, the _avahi-daemon_ configuration file
                  _/etc/avahi/avahi-daemon.conf_ must contain an active "use-
                  ipv6=yes" line. The service must be restarted after adding
                  this line in order for IPv6 to be enabled.
    
           **--trust-servers** _[=TRUST_SPEC]_
                  Grant or revoke trust in compile-servers, specified using
                  _--use-server_ as specified by TRUST_SPEC, where TRUST_SPEC
                  is a comma-separated list specifying the trust which is to
                  be granted or revoked. Supported elements are:
    
                  **ssl** trust the specified servers as SSL peers.
    
                  **signer** trust the specified servers as module signers (see
                         _--privilege_).  Only root can specify **signer.**
    
                  **all-users**
                         grant trust as an ssl peer for all users on the lo‐
                         cal host. The default is to grant trust as an ssl
                         peer for the current user only. Trust as a module
                         signer is always granted for all users. Only root
                         can specify **all-users**.
    
                  **revoke** revoke the specified trust. The default is to grant
                         it.
    
                  **no-prompt**
                         do not prompt the user for confirmation before car‐
                         rying out the requested action. The default is to
                         prompt the user for confirmation.
    
                  If no argument is provided, then the default is **ssl**.  If no
                  servers were specified using _--use-server_ , then no trust
                  will be granted or revoked.
    
                  Unless **no-prompt** has been specified, the user will be
                  prompted to confirm the trust to be granted or revoked be‐
                  fore the operation is performed.
    
           **--sign-module**
                  Sign the module with a MOK (Machine Owner Key) on UEFI/Se‐
                  cureBoot systems.  See the SECUREBOOT section for more de‐
                  tails.
    
           **--dump-probe-types**
                  Dumps a list of supported probe types and exits. If _--priv‐_
                  _ilege=stapusr_ is also specified, the list will be limited
                  to probe types available to unprivileged users.
    
           **--dump-probe-aliases**
                  Dumps a list of all probe aliases found in library files
                  and exits.
    
           **--dump-functions**
                  Dumps a list of all the public functions found in library
                  files and exits. Also includes their parameters and types.
                  A function of type 'unknown' indicates a function that does
                  not return a value. Note that not all function/parameter
                  types may be resolved (these are also shown by 'unknown').
                  This features is very memory-intensive and thus may not
                  work properly with _--use-server_ if the target server impos‐
                  es an rlimit on process memory (i.e. through the _~stap-_
                  _server/.systemtap/rc_ configuration file, see
                  stap-server(8)).
    
           **--remote** _URL_
                  Set the execution target to the given host.  This option
                  may be repeated to target multiple execution targets.
                  Passes 1-4 are completed locally as normal to build the
                  script, and then pass 5 will copy the module to the target
                  and run it.  Acceptable URL forms include:
    
                  **[USER@]HOSTNAME** , **ssh://[USER@]HOSTNAME**
                         This mode uses ssh, optionally using a username not
                         matching your own. If a custom ssh_config file is in
                         use, add **SendEnv LANG** to retain internationalization
                         functionality.
    
                  **libvirt://DOMAIN** , **libvirt://DOMAIN/LIBVIRT_URI**
                         This mode uses _stapvirt_ to execute the script on a
                         domain managed by libvirt. Optionally, LIBVIRT_URI
                         may be specified to connect to a specific driver
                         and/or a remote host. For example, to connect to the
                         local privileged QEMU driver, use:
    
                         --remote libvirt://MyDomain/qemu:///system
    
                         See the page at <http://libvirt.org/uri.html> for
                         supported URIs. Also see stapvirt(1) for more infor‐
                         mation on how to prepare the domain for stap prob‐
                         ing.
    
                  **unix:PATH**
                         This mode connects to a UNIX socket. This can be
                         used with a QEMU virtio-serial port for executing
                         scripts inside a running virtual machine.
    
                  **direct://**
                         Special loopback mode to run on the local host.
    
           **--remote-prefix**
                  Prefix each line of remote output with "N: ", where N is
                  the index of the remote execution target from which the
                  given line originated.
    
           **--download-debuginfo** _[=OPTION]_
                  Enable, disable or set a timeout for the automatic debugin‐
                  fo downloading feature offered by abrt as specified by OP‐
                  TION, where OPTION is one of the following:
    
                  **yes** enable automatic downloading of debuginfo with no
                         timeout. This is the same as not providing an OPTION
                         value to _--download-debuginfo_
    
                  **no** explicitly disable automatic downloading of debugin‐
                         fo. This is the same as not using the option at all.
    
                  **ask** show abrt output, and ask before continuing down‐
                         load. No timeout will be set.
    
                  **< timeout>**
                         specify a timeout as a positive number to stop the
                         download if it is taking longer than <timeout> sec‐
                         onds.
    
           **--rlimit-as** _=NUM_
                  Specify the maximum size of the process's virtual memory
                  (address space), in bytes.
    
           **--rlimit-cpu** _=NUM_
                  Specify the CPU time limit, in seconds.
    
           **--rlimit-nproc** _=NUM_
                  Specify the maximum number of processes that can be creat‐
                  ed.
    
           **--rlimit-stack** _=NUM_
                  Specify the maximum size of the process stack, in bytes.
    
           **--rlimit-fsize** _=NUM_
                  Specify the maximum size of files that the process may cre‐
                  ate, in bytes.
    
           **--sysroot** _=DIR_
                  Specify sysroot directory where target files (executables,
                  libraries, etc.)  are located.  With _-r RELEASE_ , the sys‐
                  root will be searched for the appropriate kernel build di‐
                  rectory.  With _-r /DIR_ , however, the sysroot will not be
                  used to find the kernel build.
    
           **--sysenv** _=VAR=VALUE_
                  Provide an alternate value for an environment variable
                  where the value on a remote system differs.  Path variables
                  (e.g. PATH, LD_LIBRARY_PATH) are assumed to be relative to
                  the directory provided by _--sysroot_ , if provided.
    
           **--suppress-time-limits**
                  Disable -DSTP_OVERLOAD related options as well as -DMAXAC‐
                  TION and -DMAXTRYLOCK.  This option requires guru mode.
    
           **--runtime** _=MODE_
                  Set the pass-5 runtime mode.  Valid options are _kernel_ (de‐
                  fault), _dyninst_ and _bpf_.  See **ALTERNATE RUNTIMES** below for
                  more information.
    
           **--dyninst**
                  Shorthand for _--runtime=dyninst_.
    
           **--bpf** Shorthand for _--runtime=bpf_.
    
           **--save-uprobes**
                  On machines that require SystemTap to build its own uprobes
                  module (kernels prior to version 3.5), this option in‐
                  structs SystemTap to also save a copy of the module in the
                  current directory (creating a new "uprobes" directory
                  first).
    
           **--target-namespaces** _=PID_
                  Allow for a set of target namespaces to be set based on the
                  namespaces the given PID is in. This is for namespace-aware
                  tapset functions. If the target namespaces was not set, the
                  target defaults to the stap process' namespaces.
    
           **--monitor** _=INTERVAL_
                  Enables an interface to display status information about
                  the module(uptime, module name, invoker uid, memory sizes,
                  global variables, list of probes with their statistics). An
                  optional argument INTERVAL can be supplied to set the re‐
                  fresh rate in seconds of the status window. The module can
                  also be controlled by a list of commands using the follow‐
                  ing keys:
    
                  **c** Resets all global variables to their initial values
                         or zeroes them if they did not have an initial val‐
                         ue.
    
                  **s** Rotates the attribute used to sort the list of
                         probes.
    
                  **t** Brings up a prompt to allow toggling(on/off) of
                         probes by index. Probe points are still affected by
                         their conditions.
    
                  **r** Resumes the script by toggling on all probes.
    
                  **p** Pauses the script by toggling off all probes.
    
                  **x** Hides/shows the status window. This allows for more
                         output to be seen.
    
                  **navigation-keys**
                         The navigation keys can be used to scroll up and
                         down the windows.
    
                  **Tab** Toggle scrolling between status and output windows.
    
           **--example**
                  This option is used to run example scripts without having
                  to enter the entire path to the script. Example scripts can
                  be found in the directory specified in the stappaths(7)
                  manual page.
    
           **--no-global-var-display**
                  This option is used to disable the automatic logging of un‐
                  used global variables at the end of a stap session.
    
           **--language-server**
                  Language server mode. Start a language server which will
                  communicate via stdio. The language server will respect
                  stap verbosity.
    
           **--build-as**
                  Execute passes 1-4 under specified user to increase safety.
                  This approach may have limitations.  Unprivileged users
                  might not have access to kallsyms or /proc.  At the RPM in‐
                  stall time, the stapunpriv user is created, so stap can be
                  invoked with --build-as=stapunpriv.
    


## ARGUMENTS



           Any additional arguments on the command line are passed to the
           script parser for substitution.  See below.
    


## SCRIPT LANGUAGE



           The systemtap script language resembles _awk_ and _C_.  There are two
           main outermost constructs: probes and functions.  Within these,
           statements and expressions use C-like operator syntax and prece‐
           dence.
    
       **GENERAL SYNTAX**
           Whitespace is ignored.  Three forms of comments are supported:
                  **#**... shell style, to the end of line, except for $# and @#
                  **//**... C++ style, to the end of line
                  **/***... C style ... ***/**
           Literals are either strings enclosed in double-quotes (passing
           through the usual C escape codes with backslashes, and with adja‐
           cent string literals glued together, also as in C), or integers
           (in decimal, hexadecimal, or octal, using the same notation as in
           C).  All strings are limited in length to some reasonable value (a
           few hundred bytes).  Integers are 64-bit signed quantities, al‐
           though the parser also accepts (and wraps around) values above
           positive 2**63.
    
           In addition, script arguments given at the end of the command line
           may be inserted.  Use **$1 ... $ <NN> **for insertion unquoted, **@1 ...**
           **@ <NN> **for insertion as a string literal.  The number of arguments
           may be accessed through **$#**(as an unquoted number) or through **@#**
           (as a quoted number).  These may be used at any place a token may
           begin, including within the preprocessing stage.  Reference to an
           argument number beyond what was actually given is an error.
    
       **PREPROCESSING**
           A simple conditional preprocessing stage is run as a part of pars‐
           ing.  The general form is similar to the cond **?** exp1 **:** exp2
           ternary operator:
    
                  **%(** CONDITION **%?** TRUE-TOKENS **%)**
                  **%(** CONDITION **%?** TRUE-TOKENS **%:** FALSE-TOKENS **%)**
    
           The CONDITION is either an expression whose format is determined
           by its first keyword, or a string literals comparison or a numeric
           literals comparison.  It can be also composed of many alternatives
           and conjunctions of CONDITIONs (meant as in previous sentence) us‐
           ing || and && respectively.  However, parentheses are not support‐
           ed yet, so remembering that conjunction takes precedence over al‐
           ternative is important.
    
           If the first part is the identifier **kernel_vr** or **kernel_v** to refer
           to the kernel version number, with ("2.6.13-1.322FC3smp") or with‐
           out ("2.6.13") the release code suffix, then the second part is
           one of the six standard numeric comparison operators **<** , **< =**, **==** ,
           **!=** , **>** , and **> =**, and the third part is a string literal that con‐
           tains an RPM-style version-release value.  The condition is deemed
           satisfied if the version of the target kernel (as optionally over‐
           ridden by the **-r** option) compares to the given version string.
           The comparison is performed by the glibc function **strverscmp**.  As
           a special case, if the operator is for simple equality (**==**), or
           inequality (**!=**), and the third part contains any wildcard charac‐
           ters (***** or **?** or **[**), then the expression is treated as a wildcard
           (mis)match as evaluated by **fnmatch**.
    
           If, on the other hand, the first part is the identifier **arch** to
           refer to the processor architecture (as named by the kernel build
           system ARCH/SUBARCH), then the second part is one of the two
           string comparison operators **==** or **!=** , and the third part is a
           string literal for matching it.  This comparison is a wildcard
           (mis)match.
    
           Similarly, if the first part is an identifier like **CONFIG_some‐**
           **thing** to refer to a kernel configuration option, then the second
           part is **==** or **!=** , and the third part is a string literal for
           matching the value (commonly "y" or "m").  Nonexistent or unset
           kernel configuration options are represented by the empty string.
           This comparison is also a wildcard (mis)match.
    
           If the first part is the identifier **systemtap_v** , the test refers
           to the systemtap compatibility version, which may be overridden
           for old scripts with the **--compatible** flag.  The comparison opera‐
           tor is as is for **kernel_v** and the right operand is a version
           string.  See also the DEPRECATION section below.
    
           If the first part is the identifier **systemtap_privilege** , the test
           refers to the privilege level that the systemtap script is com‐
           piled with. Here the second part is **==** or **!=** , and the third part
           is a string literal, either "stapusr" or "stapsys" or "stapdev".
    
           If the first part is the identifier **guru_mode** , the test refers to
           if the systemtap script is compiled with guru_mode. Here the sec‐
           ond part is **==** or **!=** , and the third part is a number, either 1 or
           0.
    
           If the first part is the identifier **runtime** , the test refers to
           the systemtap runtime mode. See **ALTERNATE RUNTIMES** below for more
           information on runtimes.  The second part is one of the two string
           comparison operators **==** or **!=** , and the third part is a string lit‐
           eral for matching it.  This comparison is a wildcard (mis)match.
    
           Otherwise, the CONDITION is expected to be a comparison between
           two string literals or two numeric literals.  In this case, the
           arguments are the only variables usable.
    
           The TRUE-TOKENS and FALSE-TOKENS are zero or more general parser
           tokens (possibly including nested preprocessor conditionals), and
           are passed into the input stream if the condition is true or
           false.  For example, the following code induces a parse error un‐
           less the target kernel version is newer than 2.6.5:
    
                  %( kernel_v <= "2.6.5" %? **ERROR** %) # invalid token sequence
    
           The following code might adapt to hypothetical kernel version
           drift:
    
                  probe kernel.function (
                    %( kernel_v <= "2.6.12" %? "__mm_do_fault" %:
                       %( kernel_vr == "2.6.13*smp" %? "do_page_fault" %:
                          UNSUPPORTED %) %)
                  ) { /* ... */ }
    
                  %( arch == "ia64" %?
                     probe syscall.vliw = kernel.function("vliw_widget") {}
                  %)
    
       **PREPROCESSOR MACROS**
           The preprocessor also supports a simple macro facility, run as a
           separate pass before conditional preprocessing.
    
           Macros are defined using the following construct:
    
                  @define NAME %( BODY %)
                  @define NAME(PARAM_1, PARAM_2, ...) %( BODY %)
    
           Macros, and parameters inside a macro body, are both invoked by
           prefixing the macro name with an @ symbol:
    
                  @define foo %( x %)
                  @define add(a,b) %( ((@a)+(@b)) %)
    
                     @foo = @add(2,2)
    
           Macro expansion is currently performed in a separate pass before
           conditional compilation. Therefore, both TRUE- and FALSE-tokens in
           conditional expressions will be macroexpanded regardless of how
           the condition is evaluated. This can sometimes lead to errors:
    
                  // The following results in a conflict:
                  %( CONFIG_UPROBE == "y" %?
                      @define foo %( process.syscall %)
                  %:
                      @define foo %( **ERROR** %)
                  %)
    
                  // The following works properly as expected:
                  @define foo %(
                    %( CONFIG_UPROBE == "y" %? process.syscall %: **ERROR** %)
                  %)
    
           The first example is incorrect because both @defines are evaluated
           in a pass prior to the conditional being evaluated.
    
           Normally, a macro definition is local to the file it occurs in.
           Thus, defining a macro in a tapset does not make it available to
           the user of the tapset. Publically available library macros can be
           defined by including .stpm files on the tapset search path. These
           files may only contain @define constructs, which become visible
           across all tapsets and user scripts. Optionally, within the .stpm
           files, a public macro definition can be surrounded by a preproces‐
           sor conditional as described above.
    
       **CONSTANTS**
           Tapsets or guru-mode user scripts can access header file constant
           tokens, typically macros, using built-in @const() operator.  The
           respective header file inclusion is possible either via the tapset
           library, or using a top-level guru mode embedded-C construct.
           This results in appropriate embedded C pragma comments setting.
    
                  @const("STP_SKIP_BADVARS")
    
       **VARIABLES**
           Identifiers for variables and functions are an alphanumeric se‐
           quence, and may include **_** and **$** characters.  They may not start
           with a plain digit, as in C.  Each variable is by default local to
           the probe or function statement block within which it is men‐
           tioned, and therefore its scope and lifetime is limited to a par‐
           ticular probe or function invocation.
    
           Scalar variables are implicitly typed as either string or integer.
           Associative arrays also have a string or integer value, and a tu‐
           ple of strings and/or integers serving as a key.  Here are a few
           basic expressions.
    
                  var1 = 5
                  var2 = "bar"
                  array1 [pid()] = "name"     # single numeric key
                  array2 ["foo",4,i++] += 5   # vector of string/num/num keys
                  if (["hello",5,4] in array2) println ("yes")  # membership test
    
           The translator performs _type inference_ on all identifiers, includ‐
           ing array indexes and function parameters.  Inconsistent type-re‐
           lated use of identifiers signals an error.
    
           Variables may be declared global, so that they are shared amongst
           all probes and functions and live as long as the entire systemtap
           session.  There is one namespace for all global variables, regard‐
           less of which script file they are found within.  Concurrent ac‐
           cess to global variables is automatically protected with locks,
           see the **SAFETY AND SECURITY** section for more details.  A global
           declaration may be written at the outermost level anywhere, not
           within a block of code.  Global variables which are written but
           never read will be displayed automatically at session shutdown.
           The translator will infer for each its value type, and if it is
           used as an array, its key types.  Optionally, scalar globals may
           be initialized with a string or number literal.  The following de‐
           claration marks variables as global.
    
                  **global** var1**,** var2**,** var3=4
    
           Global variables can also be set as module options. One can do
           this by either using the -G option, or the module must first be
           compiled using stap -p4.  Global variables can then be set on the
           command line when calling staprun on the module generated by stap
           -p4. See staprun(8) for more information.
    
           The scope of a global variable may be limited to a tapset or user
           script file using private keyword. The global keyword is optional
           when defining a private global variable. Following declaration
           marks var1 and var2 private globals.
    
                  **private** global **var1=2**
                  **private** var2
    
           Arrays are limited in size by the MAXMAPENTRIES variable -- see
           the **SAFETY AND SECURITY** section for details.  Optionally, global
           arrays may be declared with a maximum size in brackets, overriding
           MAXMAPENTRIES for that array only.  Note that this doesn't indi‐
           cate the type of keys for the array, just the size.
    
                  **global** tiny_array[10]**,** normal_array**,** big_array[50000]
    
           Arrays may be configured for wrapping using the '%' suffix.  This
           causes older elements to be overwritten if more elements are in‐
           serted than the array can hold. This works for both associative
           and statistics typed arrays.
    
                  **global** wrapped_array1%[10]**,** wrapped_array2%
    
           Many types of probe points provide context variables, which are
           run-time values, safely extracted from the kernel or userspace
           program being probed.  These are prefixed with the **$** character.
           The CONTEXT VARIABLES section in stapprobes(3stap) lists what is
           available for each type of probe point.  These context variables
           become normal string or numeric scalars once they are stored in
           normal script variables.  See the TYPECASTING section below on how
           to to turn them back into typed pointers for further processing as
           context variables.  There is some automation to help!
    
       **STATEMENTS**
           Statements enable procedural control flow.  They may occur within
           functions and probe handlers.  The total number of statements exe‐
           cuted in response to any single probe event is limited to some
           number defined by the MAXACTION macro in the translated C code,
           and is in the neighbourhood of 1000.
    
           EXP    Execute the string- or integer-valued expression and throw
                  away the value.
    
           **{** STMT1 STMT2 ... **}**
                  Execute each statement in sequence in this block.  Note
                  that separators or terminators are generally not necessary
                  between statements.
    
           **;** Null statement, do nothing.  It is useful as an optional
                  separator between statements to improve syntax-error detec‐
                  tion and to handle certain grammar ambiguities.
    
           **if**(EXP) STMT1 [ **else** STMT2 ]
                  Compare integer-valued EXP to zero.  Execute the first
                  (non-zero) or second STMT (zero).
    
           **while**(EXP) STMT
                  While integer-valued EXP evaluates to non-zero, execute
                  STMT.
    
           **for**(EXP1; EXP2; EXP3) STMT
                  Execute EXP1 as initialization.  While EXP2 is non-zero,
                  execute STMT, then the iteration expression EXP3.
    
           **foreach**(VAR **in** ARRAY [ **limit** EXP ]) STMT
                  Loop over each element of the named global array, assigning
                  current key to VAR.  The array may not be modified within
                  the statement.  By adding a single **+** or **-** operator after
                  the VAR or the ARRAY identifier, the iteration will proceed
                  in a sorted order, by ascending or descending index or val‐
                  ue.  If the array contains statistics aggregates, adding
                  the desired **@operator** between the ARRAY identifier and the
                  **+** or **-** will specify the sorting aggregate function.  See
                  the STATISTICS section below for the ones available.  De‐
                  fault is **@count**.  Using the optional **limit** keyword limits
                  the number of loop iterations to EXP times.  EXP is evalu‐
                  ated once at the beginning of the loop.
    
           **foreach**([VAR1, VAR2, ...] **in** ARRAY [ **limit** EXP ]) STMT
                  Same as above, used when the array is indexed with a tuple
                  of keys.  A sorting suffix may be used on at most one VAR
                  or ARRAY identifier.
    
           **foreach**([VAR1, VAR2, ...] **in** ARRAY [INDEX1, INDEX2, ...] [ **limit**
           EXP ]) STMT
                  Same as above, where iterations are limited to elements in
                  the array where the keys match the index values specified.
                  The symbol * can be used to specify an index and will be
                  treated as a wildcard.
    
           **foreach**(VAR0 = VAR **in** ARRAY [ **limit** EXP ]) STMT
                  This variant of foreach saves current value into VAR0 on
                  each iteration, so it is the same as ARRAY[VAR].  This also
                  works with a tuple of keys.  Sorting suffixes on VAR0 have
                  the same effect as on ARRAY.
    
           **foreach**(VAR0 = VAR **in** ARRAY [INDEX1, INDEX2, ...] [ **limit** EXP ])
           STMT
                  Same as above, where iterations are limited to elements in
                  the array where the keys match the index values specified.
                  The symbol * can be used to specify an index and will be
                  treated as a wildcard.
    
           **break** , **continue**
                  Exit or iterate the innermost nesting loop (**while** or **for** or
                  **foreach**) statement.
    
           **return** EXP
                  Return EXP value from enclosing function.  If the func‐
                  tion's value is not taken anywhere, then a return statement
                  is not needed, and the function will have a special "un‐
                  known" type with no return value.
    
           **next** Return now from enclosing probe handler.  This is especial‐
                  ly useful in probe aliases that apply event filtering pred‐
                  icates. When used in functions, the execution will be imme‐
                  diately transferred to the next overloaded function.
    
           **try**{ STMT1 } **catch**{ STMT2 }
                  Run the statements in the first block.  Upon any run-time
                  errors, abort STMT1 and start executing STMT2.  Any errors
                  in STMT2 will propagate to outer try/catch blocks, if any.
    
           **try**{ STMT1 } **catch**(VAR) { STMT2 }
                  Same as above, plus assign the error message to the string
                  scalar variable VAR.
    
           **delete** ARRAY[INDEX1, INDEX2, ...]
                  Remove from ARRAY the element specified by the index tuple.
                  If the index tuple contains a * in place of an index, the *
                  is treated as a wildcard and all elements with keys that
                  match the index tuple will be removed from ARRAY.  The val‐
                  ue will no longer be available, and subsequent iterations
                  will not report the element.  It is not an error to delete
                  an element that does not exist.
    
           **delete** ARRAY
                  Remove all elements from ARRAY.
    
           **delete** SCALAR
                  Removes the value of SCALAR.  Integers and strings are
                  cleared to 0 and "" respectively, while statistics are re‐
                  set to the initial empty state.
    
       **EXPRESSIONS**
           Systemtap supports a number of operators that have the same gener‐
           al syntax, semantics, and precedence as in C and awk.  Arithmetic
           is performed as per typical C rules for signed integers.  Division
           by zero or overflow is detected and results in an error.
    
           binary numeric operators
                  *** / % + - >> << & ^ | && ||**
    
           binary string operators
                  **.**(string concatenation)
    
           numeric assignment operators
                  **= *= /= %= += -= >>= <<= &= ^= |=**
    
           string assignment operators
                  **= .=**
    
           unary numeric operators
                  **+ - ! ~ ++ --**
    
           binary numeric, string comparison or regex matching operators
                  **< > <= >= == != =~ !~**
    
           ternary operator
                  cond **?** exp1 **:** exp2
    
           grouping operator
                  **(** exp **)**
    
           function call
                  fn **(**[ arg1, arg2, ... ]**)**
    
           array membership check
                  exp **in** array
                  **[** exp1**,** exp2**, ... ] in** array
                  **[** * **,** * **, ... ] in** array
    
       **REGULAR EXPRESSION MATCHING**
           The scripting language supports regular expression matching.  The
           basic syntax is as follows:
    
                  **exp** =~ **regex**
                  **exp**!~ **regex**
    
           (The first operand must be an expression evaluating to a string;
           the second operand must be a string literal containing a syntacti‐
           cally valid regular expression.)
    
           The regular expression syntax supports POSIX Extended Regular Ex‐
           pression features as documented in grep(1) except for subexpres‐
           sion reuse ("\1") functionality.
    
           After a successful match, the contents of the matched string and
           subexpressions can be extracted using the matched() and ngroups()
           tapset functions as follows:
    
                  if ("an example string" =~ "str(ing)") {
                    matched(0) // -> returns "string", the matched substring
                    matched(1) // -> returns "ing", the 1st matched subexpression
                    ngroups()  // -> returns 2, the number of matched groups
                  }
    
       **PROBES**
           The main construct in the scripting language identifies probes.
           Probes associate abstract events with a statement block ("probe
           handler") that is to be executed when any of those events occur.
           The general syntax is as follows:
    
                  **probe** PROBEPOINT [**,** PROBEPOINT] **{**[STMT ...] **}**
                  **probe** PROBEPOINT [**,** PROBEPOINT] **if (** CONDITION**) {**[STMT ...] **}**
    
           Events are specified in a special syntax called "probe points".
           There are several varieties of probe points defined by the trans‐
           lator, and tapset scripts may define further ones using aliases.
           Probe points may be wildcarded, grouped, or listed in preference
           sequences, or declared optional.  More details on probe point syn‐
           tax and semantics are listed on the stapprobes(3stap) manual page.
    
           The probe handler is interpreted relative to the context of each
           event.  For events associated with kernel code, this context may
           include _variables_ defined in the _source code_ at that spot.  These
           "context variables" are presented to the script as variables whose
           names are prefixed with "$".  They may be accessed only if the
           kernel's compiler preserved them despite optimization.  This is
           the same constraint that a debugger user faces when working with
           optimized code.  In addition, the objects must exist in paged-in
           memory at the moment of the systemtap probe handler's execution,
           because systemtap must not cause (suppresses) any additional pag‐
           ing.  Some probe types have very little context.  See the
           stapprobes(3stap) man pages to see the kinds of context variables
           available at each kind of probe point.  As of systemtap version
           4.3, functions called from the handlers of some probe point types
           may also refer to context variables.  These are treated as if a
           clone of that function was inlined into the calling probe handler
           and $variables evaluated in its context.
    
           Probes may be decorated with an _arming condition_ , consisting of a
           simple boolean expression on read-only global script variables.
           While disarmed (inactive, condition evaluates to false), some
           probe types reduce or eliminate their run-time overheads.  When an
           arming condition evaluates to true, probes will be _soon_ re-armed,
           and their probe handlers will start getting called as the events
           fire.  (Some events may be lost during the arming interval.  If
           this is unacceptable, do not use arming conditions for those
           probes.)  Example of the syntax:
    
                  probe timer.us(TIMER) if (enabled) {
                  }
    
           New probe points may be defined using "aliases".  Probe point
           aliases look similar to probe definitions, but instead of activat‐
           ing a probe at the given point, it just defines a new probe point
           name as an alias to an existing one. There are two types of alias,
           i.e. the prologue style and the epilogue style which are identi‐
           fied by "=" and "+=" respectively.
    
           For prologue style alias, the statement block that follows an
           alias definition is implicitly added as a prologue to any probe
           that refers to the alias. While for the epilogue style alias, the
           statement block that follows an alias definition is implicitly
           added as an epilogue to any probe that refers to the alias.  For
           example:
    
                  probe syscall.read = kernel.function("sys_read") {
                    fildes = $fd
                    if (execname() == "init") next  # skip rest of probe
                  }
    
           defines a new probe point _syscall.read_ , which expands to
           _kernel.function("sys_read")_ , with the given statement as a pro‐
           logue, which is useful to predefine some variables for the alias
           user and/or to skip probe processing entirely based on some condi‐
           tions.  And
    
                  probe syscall.read += kernel.function("sys_read") {
                    if (tracethis) println ($fd)
                  }
    
           defines a new probe point with the given statement as an epilogue,
           which is useful to take actions based upon variables set or left
           over by the the alias user.  Please note that in each case, the
           statements in the alias handler block are treated ordinarily, so
           that variables assigned there constitute mere initialization, not
           a macro substitution.
    
           Aliases can also be defined to include both a prologue and an epi‐
           logue.
    
                  probe syscall.read = kernel.function("sys_read") {
                    fildes = $fd
                    if (execname() == "init") next
                  },{
                    if (tracethis) println ($fd)
                  }
    
           An alias is used just like a built-in probe type.
    
                  probe syscall.read {
                    printf("reading fd=%d\n", fildes)
                    if (fildes > 10) tracethis = 1
                  }
    
           Probes with an alias can make use of the @probewrite predicate.
           This check is used to detect whether a script variable or target
           variable has been written to in the probe handler body.
    
           @probewrite(var)
                  expands to 1 iff var has been written to in the probe han‐
                  dler body, otherwise it expands to 0.
    
           In the following example, @probewrite(var) expands to 1 because
           var has been written to in the probe handler body and consequent‐
           ly, the conditional statement will run.
    
                  probe foo = begin { var = 0 }, { if (@probewrite(var)) println(var) }
    
                  probe foo {
                    var = 1
                  }
    
       **FUNCTIONS**
           Systemtap scripts may define subroutines to factor out common
           work.  Functions take any number of scalar (integer or string) ar‐
           guments, and must return a single scalar (integer or string).  An
           example function declaration looks like this:
    
                  function thisfn (arg1, arg2) {
                     return arg1 + arg2
                  }
    
           Note the general absence of type declarations, which are instead
           inferred by the translator.  However, if desired, a function defi‐
           nition may include explicit type declarations for its return value
           and/or its arguments.  This is especially helpful for embedded-C
           functions.  In the following example, the type inference engine
           need only infer type type of arg2 (a string).
    
                  function thatfn:string (arg1:long, arg2) {
                     return sprint(arg1) . arg2
                  }
    
           Functions may call others or themselves recursively, up to a fixed
           nesting limit.  This limit is defined by the MAXNESTING macro in
           the translated C code and is in the neighbourhood of 10.
    
           Functions may be marked private using the private keyword to limit
           their scope to the tapset or user script file they are defined in.
           An example definition of a private function follows:
    
                  private function three:long () { return 3 }
    
           Functions terminating without reaching an explicit return state‐
           ment will return an implicit 0 or "", determined by type infer‐
           ence.
    
           Functions may be overloaded during both runtime and compile time.
    
           Runtime overloading allows the executed function to be selected
           while the module is running based on runtime conditions and is
           achieved using the "next" statement in script functions and
           STAP_NEXT macro for embedded-C functions. For example,
    
                  function f() { if (condition) next; print("first function") }
                  function f() %{ STAP_NEXT; print("second function") %}
                  function f() { print("third function") }
    
           During a functioncall f(), the execution will transfer to the
           third function if condition evaluates to true and print "third
           function". Note that the second function is unconditionally
           nexted.
    
           Parameter overloading allows the function to be executed to be se‐
           lected at compile time based on the number of arguments provided
           to the functioncall. For example,
    
                  function g() { print("first function") }
                  function g(x) { print("second function") }
                  g() -> "first function"
                  g(1) -> "second function"
    
           Note that runtime overloading does not occur in the above example,
           as exactly one function will be resolved for the functioncall. The
           use of a next statement inside a function while no more overloads
           remain will trigger a runtime exception Runtime overloading will
           only occur if the functions have the same arity, functions with
           the same name but different number of parameters are completely
           unrelated.
    
           Execution order is determined by a priority value which may be
           specified.  If no explicit priority is specified, user script
           functions are given a higher priority than library functions. User
           script functions and library functions are assigned a default pri‐
           ority value of 0 and 1 respectively.  Functions with the same pri‐
           ority are executed in declaration order. For example,
    
                  function f():3 { if (condition) next; print("first function") }
                  function f():1 { if (condition) next; print("second function") }
                  function f():2 { print("third function") }
    
           Since the second function has highest priority, it is executed
           first.  The first function is never executed as there no "next"
           statements in the third function to transfer execution.
    
       **PRINTING**
           There are a set of function names that are specially treated by
           the translator.  They format values for printing to the standard
           systemtap output stream in a more convenient way (note that data
           generated in the kernel module need to get transferred to user-
           space in order to get printed).
    
             The _sprint*_ variants return the formatted string instead of
           printing it.
    
           **print** , **sprint**
                  Print one or more values of any type, concatenated directly
                  together.
    
           **println** , **sprintln**
                  Print values like _print_ and _sprint_ , but also append a new‐
                  line.
    
           **printd** , **sprintd**
                  Take a string delimiter and two or more values of any type,
                  and print the values with the delimiter interposed.  The
                  delimiter must be a literal string constant.
    
           **printdln** , **sprintdln**
                  Print values with a delimiter like _printd_ and _sprintd_ , but
                  also append a newline.
    
           **printf** , **sprintf**
                  Take a formatting string and a number of values of corre‐
                  sponding types, and print them all.  The format must be a
                  literal string constant.
    
           The _printf_ formatting directives similar to those of C, except
           that they are fully type-checked by the translator:
    
                  %b     Writes a binary blob of the value given, instead of
                         ASCII text.  The width specifier determines the num‐
                         ber of bytes to write; valid specifiers are %b %1b
                         %2b %4b %8b.  Default (%b) is 8 bytes.
    
                  %c     Character.
    
                  %d,%i  Signed decimal.
    
                  %m     Safely reads kernel (without #) or user (with #)
                         memory at the given address, outputs its content.
                         The optional precision specifier (not field width)
                         determines the number of bytes to read - default is
                         1 byte.  %10.4m prints 4 bytes of the memory in a
                         10-character-wide field.  Note, on some architec‐
                         tures user memory can still be read without #.
    
                  %M     Same as %m, but outputs in hexadecimal.  The minimal
                         size of output is double the optional precision
                         specifier - default is 1 byte (2 hex chars).  %10.4M
                         prints 4 bytes of the memory as 8 hexadecimal char‐
                         acters in a 10-character-wide field.   %.*M hex-
                         dumps a given number of bytes from a given buffer.
    
                  %o     Unsigned octal.
    
                  %p     Unsigned pointer address.
    
                  %s     String.
    
                  %u     Unsigned decimal.
    
                  %x     Unsigned hex value, in all lower-case.
    
                  %X     Unsigned hex value, in all upper-case.
    
                  %%     Writes a %.
    
           The _#_ flag selects the alternate forms.  For octal, this prefixes
           a 0.  For hex, this prefixes 0x or 0X, depending on case.  For
           characters, this escapes non-printing values with either C-like
           escapes or raw octal.  In the case of %#m/%#M, this safely access‐
           es user space memory rather than kernel space memory.
    
           Examples:
    
                  a = "alice", b = "bob", p = 0x1234abcd, i = 123, j = -1, id[a] = 1234, id[b] = 4567
                  print("hello")
                       Prints: hello
                  println(b)
                       Prints: bob\n
                  println(a . " is " . sprint(16))
                       Prints: alice is 16
                  foreach (name in id)  printdln("|", strlen(name), name, id[name])
                       Prints: 5|alice|1234\n3|bob|4567
                  printf("%c is %s; %x or %X or %p; %d or %u\n",97,a,p,p,p,j,j)
                       Prints: a is alice; 1234abcd or 1234ABCD or 0x1234abcd; -1 or 18446744073709551615\n
                  printf("2 bytes of kernel buffer at address %p: %2m", p, p)
                       Prints: 2 byte of kernel buffer at address 0x1234abcd: <binary data>
                  printf("%4b", p)
                       Prints (these values as binary data): 0x1234abcd
                  printf("%#o %#x %#X\n", 1, 2, 3)
                       Prints: 01 0x2 0X3
                  printf("%#c %#c %#c\n", 0, 9, 42)
                       Prints: \000 \t *
    
       **STATISTICS**
           It is often desirable to collect statistics in a way that avoids
           the penalties of repeatedly exclusive locking the global variables
           those numbers are being put into.  Systemtap provides a solution
           using a special operator to accumulate values, and several pseudo-
           functions to extract the statistical aggregates.
    
           The aggregation operator is _< <<_, and resembles an assignment, or a
           C++ output-streaming operation.  The left operand specifies a
           scalar or array-index lvalue, which must be declared global.  The
           right operand is a numeric expression.  The meaning is intuitive:
           add the given number to the pile of numbers to compute statistics
           of.  (The specific list of statistics to gather is given separate‐
           ly, by the extraction functions.)
    
                  foo <<< 1
                  stats[pid()] <<< memsize
    
           The extraction functions are also special.  For each appearance of
           a distinct extraction function operating on a given identifier,
           the translator arranges to compute a set of statistics that satis‐
           fy it.  The statistics system is thereby "on-demand".  Each execu‐
           tion of an extraction function causes the aggregation to be com‐
           puted for that moment across all processors.
    
           Here is the set of extractor functions.  The first argument of
           each is the same style of lvalue used on the left hand side of the
           accumulate operation.  The _@count(v)_ , _@sum(v)_ , _@min(v)_ , _@max(v)_ ,
           _@avg(v)_ , @variance(v[, b]) extractor functions compute the num‐
           ber/total/minimum/maximum/average/variance of all accumulated val‐
           ues.  The resulting values are all simple integers.  Arrays con‐
           taining aggregates may be sorted and iterated.  See the **foreach**
           construct above.
    
           Variance uses Welford's online algorithm.  The calculations are
           based on integer arithmetic, and so may suffer from low precision
           and overflow.  To improve this, @variance(v[, b]) accepts an op‐
           tional parameter b, the bit-shift, ranging from 0 (default) to 62,
           for internal scaling.  Only one value of bit-shift may be used
           with given global variable.  A larger bitshift value increases
           precision, but increases the likelihood of overflow.
    
                  $ stap -e \
                  > 'global x probe oneshot { for(i=1;i<=5;i++) x<<<i println(@variance(x)) }'
                  12
                  $ stap -e \
                  > 'global x probe oneshot { for(i=1;i<=5;i++) x<<<i println(@variance(x,1)) }'
                  2
                  $ python3 -c 'import statistics; print(statistics.variance([1, 2, 3, 4, 5]))'
                  2.5
                  $
    
           Overflow (from internal multiplication of large numbers) may occur
           and may cause a negative variance result.  Consider normalizing
           your input data.  Adding or subtracting a fixed value from all
           variance inputs preserves the original variance.  Dividing the
           variance inputs by a fixed value shrinks the original variance by
           that value squared.
    
           Histograms are also available, but are more complicated because
           they have a vector rather than scalar value.  _@hist_lin‐_
           _ear(v,start,stop,interval)_ represents a linear histogram from
           "start" to "stop" (inclusive) by increments of "interval".  The
           interval must be positive. Similarly, _@hist_log(v)_ represents a
           base-2 logarithmic histogram. Printing a histogram with the _print_
           family of functions renders a histogram object as a tabular "ASCII
           art" bar chart.
    
                  probe timer.profile {
                    x[1] <<< pid()
                    x[2] <<< uid()
                    y <<< tid()
                  }
                  global x // an array containing aggregates
                  global y // a scalar
                  probe end {
                    foreach ([i] in x @count+) {
                       printf ("x[%d]: avg %d = sum %d / count %d\n",
                               i, @avg(x[i]), @sum(x[i]), @count(x[i]))
                       println (@hist_log(x[i]))
                    }
                    println ("y:")
                    println (@hist_log(y))
                  }
    
           The counts of each histogram bucket may be individually accessed
           via the **[index]** operator.  Each bucket is addressed from 1 through
           N (for each natural bucket).  In addition bucket #0 counts all the
           samples beneath the start value, and bucket #N+1 counts all the
           samples above the stop value.  Histogram buckets (including the
           two out-of-range buckets) may also be iterated with **foreach**.
    
                  global x
                  probe oneshot {
                    x <<< -100
                    x <<< 1
                    x <<< 2
                    x <<< 3
                    x <<< 100
                    foreach (bucket in @hist_linear(x,1,3,1))
                      // expecting   1 out-of-range-low bucket
                      //             3 payload buckets
                      //             1 out-of-range-high bucket
                      printf("bucket %d count %d\n",
                             bucket, @hist_linear(x,1,3,1)[bucket])
                  }
    
       **TYPECASTING**
           Once a pointer (see the CONTEXT VARIABLES section of
           stapprobes(3stap)) has been saved into a script integer variable,
           the translator **attempts to** keep the type information necessary to
           access members from that pointer.
    
           The translator attempts to track DWARF typing associated with
           script variables assigned from addresses of context $variables,
           @cast or @var operators.  Depending on the complexity of the
           script code, this association may pass to related variables, so
           that _- >_ and _[]_ operators may be used on them, just as on the orig‐
           inal context variable.  For example:
    
                  foo = $param->foo; printf("x:%d y:%d\n", foo->x, foo->y)
                  printf("my value is %d\n", ($type == 42 ? $foo : $bar)->value)
                  printf("my parent pid is %d\n", task_parent(task_current())->tgid)
    
           However, if this association heuristic doesn't work for a script,
           using the _@cast()_ operator tells the translator how to interpret
           the number as a typed pointer.
    
                  @cast(p, "type_name"[, "module"])->member
    
           This will interpret _p_ as a pointer to a struct/union named
           _type_name_ and dereference the _member_ value.  Further _- >subfield_
           expressions may be appended to dereference more levels. Note that
           for direct dereferencing of a pointer {ker‐
           nel,user}_{char,int,...}($p) should be used.  (Refer to stap‐
           funcs(5) for more details.)  NOTE: the same dereferencing operator
           _- >_ is used to refer to both direct containment or pointer indirec‐
           tion.  Systemtap automatically determines which.  The optional
           _module_ tells the translator where to look for information about
           that type.  Multiple modules may be specified as a list with _:_
           separators.  If the module is not specified, it will default ei‐
           ther to the probe module for dwarf probes, or to "kernel" for
           functions and all other probes types.
    
           Previously up to systemtap version 4.2, "kernel" was inferred if
           unspecified.  Use --compatible=4.2 to activate this default.
    
           The translator can create its own module with type information
           from a header surrounded by angle brackets, in case normal debug‐
           info is not available.  For kernel headers, prefix it with "ker‐
           nel" to use the appropriate build system.  All other headers are
           built with default GCC parameters into a user module.  Multiple
           headers may be specified in sequence to resolve a codependency.
    
                  @cast(tv, "timeval", "<sys/time.h>")->tv_sec
                  @cast(task, "task_struct", "kernel<linux/sched.h>")->tgid
                  @cast(task, "task_struct",
                        "kernel<linux/sched.h><linux/fs_struct.h>")->fs->umask
    
           Values acquired by **@cast** may be pretty-printed by the **$** and **$$**
           suffix operators, the same way as described in the CONTEXT VARI‐
           ABLES section of the stapprobes(3stap) manual page.
    
           When in guru mode, the translator will also allow scripts to as‐
           sign new values to members of typecasted pointers.
    
           Typecasting is also useful in the case of _void*_ members whose type
           may be determinable at runtime.
    
                  probe foo {
                    if ($var->type == 1) {
                      value = @cast($var->data, "type1")->bar
                    } else {
                      value = @cast($var->data, "type2")->baz
                    }
                    print(value)
                  }
    
       **EMBEDDED C**
           When in guru mode, the translator accepts embedded C code in the
           top level of the script.  Such code is enclosed between _%{_ and _%}_
           markers, and is transcribed verbatim, without analysis, in some
           sequence, into the top level of the generated C code.  At the out‐
           ermost level, this may be useful to add _#include_ instructions, and
           any auxiliary definitions for use by other embedded code.
    
           Another place where embedded code is permitted is as a function
           body.  In this case, the script language body is replaced entirely
           by a piece of C code enclosed again between _%{_ and _%}_ markers.
           This C code may do anything reasonable and safe.  There are a num‐
           ber of undocumented but complex safety constraints on atomicity,
           concurrency, resource consumption, and run time limits, so this is
           an advanced technique.
    
           The memory locations set aside for input and output values are
           made available to it using macros _STAP_ARG_*_ and _STAP_RETVALUE_.
           Errors may be signalled with STAP_ERROR. Output may be written
           with STAP_PRINTF. The function may return early with STAP_RETURN.
           Here are some examples:
    
                  function integer_ops (val) %{
                    STAP_PRINTF("%d\n", STAP_ARG_val);
                    STAP_RETVALUE = STAP_ARG_val + 1;
                    if (STAP_RETVALUE == 4)
                        STAP_ERROR("wrong guess: %d", (int) STAP_RETVALUE);
                    if (STAP_RETVALUE == 3)
                        STAP_RETURN(0);
                    STAP_RETVALUE ++;
                  %}
                  function string_ops (val) %{
                    strlcpy (STAP_RETVALUE, STAP_ARG_val, MAXSTRINGLEN);
                    strlcat (STAP_RETVALUE, "one", MAXSTRINGLEN);
                    if (strcmp (STAP_RETVALUE, "three-two-one"))
                        STAP_RETURN("parameter should be three-two-");
                  %}
                  function no_ops () %{
                      STAP_RETURN(); /* function inferred with no return value */
                  %}
    
           The function argument and return value types have to be inferred
           by the translator from the call sites in order for this to work.
           The user should examine C code generated for ordinary script-lan‐
           guage functions in order to write compatible embedded-C ones.
    
           The last place where embedded code is permitted is as an expres‐
           sion rvalue.  In this case, the C code enclosed between _%{_ and _%}_
           markers is interpreted as an ordinary expression value.  It is as‐
           sumed to be a normal 64-bit signed number, unless the marker _/*_
           _string */_ is included, in which case it's treated as a string.
    
                  function add_one (val) {
                    return val + %{ 1 %}
                  }
                  function add_string_two (val) {
                    return val . %{ /* string */ "two" %}
                  }
                  @define SOME_STAP_MACRO %( %{ SOME_C_MACRO %} %)
                  probe begin {
                        printf("SOME_C_MACRO has value: %d\n", @SOME_STAP_MACRO);
                  }
    
           The embedded-C code may contain markers to assert optimization and
           safety properties.
    
           _/* pure */_
                  means that the C code has no side effects and may be elided
                  entirely if its value is not used by script code.
    
           _/* stable */_
                  means that the C code always has the same value (in any
                  given probe handler invocation), so repeated calls may be
                  automatically replaced by memoized values.  Such functions
                  must take no parameters, and also be _pure_.
    
           _/* unprivileged */_
                  means that the C code is so safe that even unprivileged
                  users are permitted to use it.
    
           _/* myproc-unprivileged */_
                  means that the C code is so safe that even unprivileged
                  users are permitted to use it, provided that the target of
                  the current probe is within the user's own process.
    
           _/* guru */_
                  means that the C code is so unsafe that a systemtap user
                  must specify _-g_ (guru mode) to use this.  (Tapsets are per‐
                  mitted and presumed to call them safely.)
    
           _/* unmangled */_
                  in an embedded-C function, means that the legacy (pre-1.8)
                  argument access syntax should be made available inside the
                  function. Hence, in addition to _STAP_ARG_foo_ and _STAP_RET‐_
                  _VALUE_ one can use _THIS- >foo_ and _THIS- >__retvalue_ respec‐
                  tively inside the function. This is useful for quickly mi‐
                  grating code written for SystemTap version 1.7 and earlier.
    
           _/* pragma:suffix */_
                  Emit the file-level containing C code near the end of the
                  resulting kernel module C source file.
    
           _/* unmodified-fnargs */_
                  in an embedded-C function, means that the function argu‐
                  ments are not modified inside the function body.
    
           _/* string */_
                  in embedded-C expressions only, means that the expression
                  has _const char *_ type and should be treated as a string
                  value, instead of the default long numeric.
    
           Script level global variables may be accessed in embedded-C func‐
           tions and blocks. To read or write the global variable _var_ , the
           _/* pragma:read:var */_ or _/* pragma:write:var */_ marker must be
           first placed in the embedded-C function or block. This provides
           the macros _STAP_GLOBAL_GET_*_ and _STAP_GLOBAL_SET_*_ macros to allow
           reading and writing, respectively. For example:
    
                  global var
                  global var2[100]
                  function increment() %{
                      /* pragma:read:var */ /* pragma:write:var */
                      /* pragma:read:var2 */ /* pragma:write:var2 */
                      STAP_GLOBAL_SET_var(STAP_GLOBAL_GET_var()+1); //var++
                      STAP_GLOBAL_SET_var2(1, 1, STAP_GLOBAL_GET_var2(1, 1)+1); //var2[1,1]++
                  %}
    
           Variables may be read and set in both embedded-C functions and ex‐
           pressions.  Strings returned from embedded-C code are decayed to
           pointers. Variables must also be assigned at script level to allow
           for type inference. Map assignment does not return the value writ‐
           ten, so chaining does not work.
    
       **BUILT-INS**
           A set of builtin probe point aliases are provided by the scripts
           installed in the directory specified in the stappaths(7) manual
           page.  The functions are described in the stapprobes(3stap) manual
           page.
    
       **DEREFERENCING**
           Integers can be dereferenced from pointers saved as a script inte‐
           ger variables using the _@kderef()_ or _@uderef()_ operators.
           _@kderef()_ is used for kernel space addresses and _@uderef()_ is used
           for user space addresses.
    
                  @kderef(SIZE, addr)
                  @uderef(SIZE, addr)
    
           This will interpret _addr_ as a kernel/user address and read _SIZE_
           bytes starting at that address.  _SIZE_ should be either 1, 2, 4 or
           8 bytes.
    
       **REGISTERS**
           The value stored within a register can be accessed using the
           _@kregister()_ or _@uregister()_ operators.  _@kregister()_ is used for
           kernel space registers and _@uregister()_ is used for user space
           registers. The register of interest is specified using its DWARF
           number.
    
                  @kregister(0)
                  @uregister(5)
    


## PROCESSING



           The translator begins pass 1 by parsing the given input script,
           and all scripts (files named _*.stp_) found in a tapset directory.
           The directories listed with **-I** are processed in sequence, each
           processed in "guru mode".  For each directory, a number of
           subdirectories are also searched.  These subdirectories are
           derived from the selected kernel version (the **-R** option), in order
           to allow more kernel-version-specific scripts to override less
           specific ones.  For example, for a kernel version _2.6.12-23.FC3_
           the following patterns would be searched, in sequence:
           _2.6.12-23.FC3/*.stp_ , _2.6.12/*.stp_ , _2.6/*.stp_ , and finally _*.stp_.
           Stopping the translator after pass 1 causes it to print the parse
           trees.
    
           In pass 2, the translator analyzes the input script to resolve
           symbols and types.  References to variables, functions, and probe
           aliases that are unresolved internally are satisfied by searching
           through the parsed tapset script files.  If any tapset script file
           is selected because it defines an unresolved symbol, then the
           entirety of that file is added to the translator's resolution
           queue.  This process iterates until all symbols are resolved and a
           subset of tapset script files is selected.
    
           Next, all probe point descriptions are validated against the wide
           variety supported by the translator.  Probe points that refer to
           code locations ("synchronous probe points") require the
           appropriate kernel debugging information to be installed.  In the
           associated probe handlers, target-side variables (whose names
           begin with "$") are found and have their run-time locations
           decoded.
    
           Next, all probes and functions are analyzed for optimization
           opportunities, in order to remove variables, expressions, and
           functions that have no useful value and no side-effect.  Embedded-
           C functions are assumed to have side-effects unless they include
           the magic string **/* pure */**.  Since this optimization can hide
           latent code errors such as type mismatches or invalid $context
           variables, it sometimes may be useful to disable the optimizations
           with the **-u** option.
    
           Finally, all variable, function, parameter, array, and index types
           are inferred from context (literals and operators).  Stopping the
           translator after pass 2 causes it to list all the probes,
           functions, and variables, along with all inferred types.  Any
           inconsistent or unresolved types cause an error.
    
           In pass 3, the translator writes C code that represents the
           actions of all selected script files, and creates a _Makefile_ to
           build that into a kernel object.  These files are placed into a
           temporary directory.  Stopping the translator at this point causes
           it to print the contents of the C file.
    
           In pass 4, the translator invokes the Linux kernel build system to
           create the actual kernel object file.  This involves running _make_
           in the temporary directory, and requires a kernel module build
           system (headers, config and Makefiles) to be installed in the
           usual spot _/lib/modules/VERSION/build_.  Stopping the translator
           after pass 4 is the last chance before running the kernel object.
           This may be useful if you want to archive the file.
    
           In pass 5, the translator invokes the systemtap auxiliary program
           _staprun_ program for the given kernel object.  This program
           arranges to load the module then communicates with it, copying
           trace data from the kernel into temporary files, until the user
           sends an interrupt signal.  Any run-time error encountered by the
           probe handlers, such as running out of memory, division by zero,
           exceeding nesting or runtime limits, results in a soft error
           indication.  Soft errors in excess of MAXERRORS block of all
           subsequent probes (except error-handling probes), and terminate
           the session.  Finally, _staprun_ unloads the module, and cleans up.
    
       **ABNORMAL TERMINATION**
           One should avoid killing the stap process forcibly, for example
           with SIGKILL, because the stapio process (a child process of the
           stap process) and the loaded module may be left running on the
           system.  If this happens, send SIGTERM or SIGINT to any remaining
           stapio processes, then use rmmod to unload the systemtap module.
    


## EXAMPLES



           See the stapex(3stap) manual page for a brief collection of
           samples, or a large set of installed samples under the systemtap
           documentation/testsuite directories.  See **stappaths**(7stap) for the
           likely location of these on the system.
    


## CACHING



           The systemtap translator caches the pass 3 output (the generated C
           code) and the pass 4 output (the compiled kernel module) if pass 4
           completes successfully.  This cached output is reused if the same
           script is translated again assuming the same conditions exist
           (same kernel version, same systemtap version, etc.).  Cached files
           are stored in the _$SYSTEMTAP_DIR/cache_ directory. The cache can be
           limited by having the file _cache_mb_limit_ placed in the cache
           directory (shown above) containing only an ASCII integer
           representing how many MiB the cache should not exceed. In the
           absence of this file, a default will be created with the limit set
           to 256MiB.  This is a 'soft' limit in that the cache will be
           cleaned after a new entry is added if the cache clean interval is
           exceeded, so the total cache size may temporarily exceed this
           limit. This interval can be specified by having the file
           _cache_clean_interval_s_ placed in the cache directory (shown above)
           containing only an ASCII integer representing the interval in
           seconds. In the absence of this file, a default will be created
           with the interval set to 300 s.
    


## SAFETY AND SECURITY



           Systemtap may be used as a powerful administrative tool.  It can
           expose kernel internal data structures and potentially private
           user information.  (In **dyninst** runtime mode, this is not the case,
           see the _ALTERNATE RUNTIMES_ section below.)
    
           The translator asserts many safety constraints during compilation
           and more during run-time.  It aims to ensure that no handler
           routine can run for very long, allocate boundless memory, perform
           unsafe operations, or in unintentionally interfere with the
           system.  Uses of script global variables are automatically
           read/write locked as appropriate, to protect against manipulation
           by concurrent probe handlers.  Locks are taken so as to run the
           global-variable manipulation portion of probe handlers atomically
           (locks are taken all-or-none).  Deadlocks are detected with
           timeouts.  Use the **-t** flag to receive reports of excessive lock
           contention.  Experimenting with scripts is therefore generally
           **safe**.  The guru-mode **-g** option allows administrators to bypass
           most safety measures, which permits invasive or state-changing
           operations, embedded-C code, and increases the risk of upset.  By
           default, overload prevention is turned on for all modules.  If you
           would like to disable overload processing, use the
           **--suppress-time-limits** option.
    
           Errors that are caught at run time normally result in a clean
           script shutdown and a pass-5 error message.  The
           **--suppress-handler-errors** option lets scripts tolerate soft errors
           without shutting down.
    
       **PERMISSIONS**
           For the normal linux-kernel-module runtime, to run the kernel
           objects systemtap builds, a user must be one of the following:
    
           •   the root user;
    
           •   a member of the _stapdev_ and _stapusr_ groups;
    
           •   a member of the _stapsys_ and _stapusr_ groups; or
    
           •   a member of the _stapusr_ group.
    
           The root user or a user who is a member of both the _stapdev_ and
           _stapusr_ groups can build and run any systemtap script.
    
           A user who is a member of both the _stapsys_ and _stapusr_ groups can
           only use pre-built modules under the following conditions:
    
           •   The module has been signed by a trusted signer. Trusted
               signers are normally systemtap compile-servers which sign
               modules when the _--privilege_ option is specified by the
               client. See the stap-server(8) manual page for more
               information.
    
           •   The module was built using the _--privilege=stapsys_ or the
               _--privilege=stapusr_ options.
    
           Members of only the _stapusr_ group can only use pre-built modules
           under the following conditions:
    
           •   The module is located in the /lib/modules/VERSION/systemtap
               directory.  This directory must be owned by root and not be
               world writable.
    
           or
    
           •   The module has been signed by a trusted signer. Trusted
               signers are normally systemtap compile-servers which sign
               modules when the _--privilege_ option is specified by the
               client. See the stap-server(8) manual page for more
               information.
    
           •   The module was built using the --privilege=stapusr option.
    
           The kernel modules generated by _stap_ program are run by the
           _staprun_ program.  The latter is a part of the Systemtap package,
           dedicated to module loading and unloading (but only in the white
           zone), and kernel-to-user data transfer.  Since _staprun_ does not
           perform any additional security checks on the kernel objects it is
           given, it would be unwise for a system administrator to add
           untrusted users to the _stapdev_ or _stapusr_ groups.
    
       **SECUREBOOT**
           If the current system has SecureBoot turned on in the UEFI
           firmware, all kernel modules must be signed.  (Some kernels may
           allow disabling SecureBoot long after booting with a key sequence
           such as SysRq-X, making it unnecessary to sign modules.)  There
           are two ways to sign a systemtap module.  The systemtap compile
           server can sign modules with a MOK (Machine Owner Key) that it has
           in common with a client system.  For example:
    
                  stap --use-server=HOSTNAME:PORT -e 'SCRIPT'
                  # If there is no mok key in common with the server's systemtap mok key
                  # list and the client's mok database then the user is directed by stap
                  # to invoke:
                  sudo mokutil --import signing_key.x509
                  # then after rebooting the system:
                  stap --use-server=HOSTNAME:PORT -e 'SCRIPT'
                  # will use the server to build and sign the module and the module will run
                  # on the client
    
           Another way to sign modules is to use the stap --sign-module op‐
           tion, which uses a MOK on the client system without using a serv‐
           er.  For example:
    
                  stap --sign-module -e 'SCRIPT'
                  # If there is no systemtap mok key in the system mok database
                  # then the user is directed by stap to invoke:
                  sudo mokutil --import /home/USER/.systemtap/ssl/server/moks/FINGERPRINT/signing_key.x509
                  # then after rebooting the system:
                  stap --sign-module -e 'SCRIPT'
                  # will sign and run the module
    
           See the following wiki page for more details:
    
                  **https://sourceware.org/systemtap/wiki/SecureBoot **
    
           Some kernels do not let systemtap guess whether module module
           signing is in effect.  On such machines, set the SYSTEMTAP_SIGN
           environment variable to any value while running stap.
    
       **RESOURCE LIMITS**
           Many resource use limits are set by macros in the generated C
           code.  These may be overridden with **-D** flags.  A selection of
           these is as follows:
    
           MAXNESTING
                  Maximum number of nested function calls.  Default deter‐
                  mined by script analysis, with a bonus 10 slots added for
                  recursive scripts.
    
           MAXSTRINGLEN
                  Maximum length of strings, default 128.
    
           MAXTRYLOCK
                  Maximum number of iterations to wait for locks on global
                  variables before declaring possible deadlock and skipping
                  the probe, default 1000.
    
           MAXACTION
                  Maximum number of statements to execute during any single
                  probe hit (with interrupts disabled), default 1000.  Note
                  that for straight-through probe handlers lacking loops or
                  recursion, due to optimization, this parameter may be in‐
                  terpreted too conservatively.
    
           MAXACTION_INTERRUPTIBLE
                  Maximum number of statements to execute during any single
                  probe hit which is executed with interrupts enabled (such
                  as begin/end probes), default (MAXACTION * 10).
    
           MAXBACKTRACE
                  Maximum number of stack frames that will be be processed by
                  the stap runtime unwinder as produced by the backtrace
                  functions in the [u]context-unwind.stp tapsets, default 20.
    
           MAXMAPENTRIES
                  Maximum number of rows in any single global array, default
                  2048.  Individual arrays may be declared with a larger or
                  smaller limit instead:
    
                  global big[10000],little[5]
    
                  or denoted with _%_ to make them wrap-around (replace old en‐
                  tries) automatically, as in
    
                  global big%
    
                  or both.
    
           MAPHASHBIAS
                  The number of powers-of-two to add or subtract from the
                  natural size of the hash table backing each global associa‐
                  tive array.  Default is 0.  Try small positive numbers to
                  get extra performance at the cost of more memory consump‐
                  tion, because that should reduce hash table collisions.
                  Try small negative numbers for the opposite tradeoff.
    
           MAXERRORS
                  Maximum number of soft errors before an exit is triggered,
                  default 0, which means that the first error will exit the
                  script.  Note that with the **--suppress-handler-errors** op‐
                  tion, this limit is not enforced.
    
           MAXSKIPPED
                  Maximum number of skipped probes before an exit is trig‐
                  gered, default 100.  Running systemtap with -t (timing)
                  mode gives more details about skipped probes.  With the de‐
                  fault -DINTERRUPTIBLE=1 setting, probes skipped due to
                  reentrancy are not accumulated against this limit.  Note
                  that with the **--suppress-handler-errors** option, this limit
                  is not enforced.
    
           MINSTACKSPACE
                  Minimum number of free kernel stack bytes required in order
                  to run a probe handler, default 1024.  This number should
                  be large enough for the probe handler's own needs, plus a
                  safety margin.
    
           MAXUPROBES
                  Maximum number of concurrently armed user-space probes (up‐
                  robes), default somewhat larger than the number of user-
                  space probe points named in the script.  This pool needs to
                  be potentially large because individual uprobe objects
                  (about 64 bytes each) are allocated for each process for
                  each matching script-level probe.
    
           STP_MAXMEMORY
                  Maximum amount of memory (in kilobytes) that the systemtap
                  module should use, default unlimited.  The memory size in‐
                  cludes the size of the module itself, plus any additional
                  allocations.  This only tracks direct allocations by the
                  systemtap runtime.  This does not track indirect alloca‐
                  tions (as done by kprobes/uprobes/etc. internals).
    
           STP_OVERLOAD_THRESHOLD, STP_OVERLOAD_INTERVAL
                  Maximum number of machine cycles spent in probes on any cpu
                  per given interval, before an overload condition is de‐
                  clared and the script shut down.  The defaults are 500 mil‐
                  lion and 1 billion, so as to limit stap script cpu consump‐
                  tion at around 50%.
    
           STP_PROCFS_BUFSIZE
                  Size of procfs probe read buffers (in bytes).  Defaults to
                  _MAXSTRINGLEN_.  This value can be overridden on a per-procfs
                  file basis using the procfs read probe _.maxsize(MAXSIZE)_
                  parameter.
    
           With scripts that contain probes on any interrupt path, it is pos‐
           sible that those interrupts may occur in the middle of another
           probe handler.  The probe in the interrupt handler would be
           skipped in this case to avoid reentrance.  To work around this is‐
           sue, execute stap with the option **-DINTERRUPTIBLE=0** to mask inter‐
           rupts throughout the probe handler.  This does add some extra
           overhead to the probes, but it may prevent reentrance for common
           problem cases.  However, probes in NMI handlers and in the call‐
           path of the stap runtime may still be skipped due to reentrance.
    
           In case something goes wrong with _stap_ or _staprun_ after a probe
           has already started running, one may safely kill both user
           processes, and remove the active probe kernel module with _rmmod_.
           Any pending trace messages may be lost.
    


## UNPRIVILEGED USERS



           Systemtap exposes kernel internal data structures and potentially
           private user information. Because of this, use of systemtap's full
           capabilities are restricted to root and to users who are members
           of the groups stapdev and stapusr.
    
           However, a restricted set of systemtap's features can be made
           available to trusted, unprivileged users. These users are members
           of the group stapusr only, or members of the groups stapusr and
           stapsys.  These users can load systemtap modules which have been
           compiled and certified by a trusted systemtap compile-server. See
           the descriptions of the options _--privilege_ and _--use-server_. See
           _README.unprivileged_ in the systemtap source code for information
           about setting up a trusted compile server.
    
           The restrictions enforced when _--privilege=stapsys_ is specified
           are designed to prevent unprivileged users from:
    
                  •   harming the system maliciously.
    
           The restrictions enforced when _--privilege=stapusr_ is specified
           are designed to prevent unprivileged users from:
    
                  •   harming the system maliciously.
    
                  •   gaining access to information which would not normally
                      be available to an unprivileged user.
    
                  •   disrupting the performance of processes owned by other
                      users of the system.  Some overhead to the system in
                      general is unavoidable since the unprivileged  user's
                      probes will be triggered at the appropriate times. What
                      we would like to avoid is targeted interruption of an‐
                      other user's processes which would not normally be pos‐
                      sible by an unprivileged user.
    
       **PROBE RESTRICTIONS**
           A member of the groups stapusr and stapsys may use all probe
           points.
    
           A member of only the group stapusr may use only the following
           probes:
    
                  •   begin, begin(n)
    
                  •   end, end(n)
    
                  •   error(n)
    
                  •   never
    
                  •   process.*, where the target process is owned by the
                      user.
    
                  •   timer.{jiffies,s,sec,ms,msec,us,usec,ns,nsec}(n)*
    
                  •   timer.hz(n)
    
       **SCRIPT LANGUAGE RESTRICTIONS**
           The following scripting language features are unavailable to all
           unprivileged users:
    
                  •   any feature enabled by the Guru Mode (-g) option.
    
                  •   embedded C code.
    
       **RUNTIME RESTRICTIONS**
           The following runtime restrictions are placed upon all unprivi‐
           leged users:
    
                  •   Only the default runtime code (see _-R_) may be used.
    
           Additional restrictions are placed on members of only the group
           stapusr:
    
                  •   Probing of processes owned by other users is not per‐
                      mitted.
    
                  •   Access of kernel memory (read and write) is not permit‐
                      ted.
    
       **COMMAND LINE OPTION RESTRICTIONS**
           Some command line options provide access to features which must
           not be available to all unprivileged users:
    
                  •   -g may not be specified.
    
                  •   The following options may not be used by the compile-
                      server client:
    
                          -a, -B, -D, -I, -r, -R
    
       **ENVIRONMENT RESTRICTIONS**
           The following environment variables must not be set for all un‐
           privileged users:
    
                  SYSTEMTAP_RUNTIME
                  SYSTEMTAP_TAPSET
                  SYSTEMTAP_DEBUGINFO_PATH
    
       **TAPSET RESTRICTIONS**
           In general, tapset functions are only available for members of the
           group stapusr when they do not gather information that an ordinary
           program running with that user's privileges would be denied access
           to.
    
           There are two categories of unprivileged tapset functions. The
           first category consists of utility functions that are uncondition‐
           ally available to all users; these include such things as:
    
                  cpu:long ()
                  exit ()
                  str_replace:string (prnt_str:string, srch_str:string, rplc_str:string)
    
           The second category consists of so-called _myproc-unprivileged_
           functions that can only gather information within their own
           processes. Scripts that wish to use these functions must test the
           result of the tapset function _is_myproc_ and only call these func‐
           tions if the result is 1. The script will exit immediately if any
           of these functions are called by an unprivileged user within a
           probe within a process which is not owned by that user. Examples
           of _myproc-unprivileged_ functions include:
    
                  print_usyms (stk:string)
                  user_int:long (addr:long)
                  usymname:string (addr:long)
    
           A compile error is triggered when any function not in either of
           the above categories is used by members of only the group stapusr.
    
           No other built-in tapset functions may be used by members of only
           the group stapusr.
    


## ALTERNATE RUNTIMES



           As described above, systemtap's default runtime mode involves
           building and loading kernel modules, with various security trade‐
           offs presented.  Systemtap now includes two new prototype back‐
           ends: _--runtime=dyninst_ and _--runtime=bpf_.
    
           _--runtime=dyninst_ uses Dyninst to instrument a user's own process‐
           es at runtime. This backend does not use kernel modules, and does
           not require root privileges, but is restricted with respect to the
           kinds of probes and other constructs that a script may use.
           _dyninst_ runtime operates in target-attach mode, so it does require
           a _-c COMMAND_ or _-x PID_ process.  For example:
    
                  stap --runtime=dyninst -c 'stap -V' \
                       -e 'probe process.function("main")
                           { println("hi from dyninst!") }'
    
           It may be necessary to disable a conflicting selinux check with
    
                  # setsebool allow_execstack 1
    
           _--runtime=bpf_ compiles the user script into extended Berkeley
           Packet Filter (eBPF) programs instead of a kernel module. eBPF
           programs are verified by the kernel for safety and are executed by
           an in-kernel virtual machine.  This runtime is in an early stage
           of development and currently lacks support for a number of fea‐
           tures available in the default runtime. Please see the stapbpf(8)
           man page for more information.
    


## EXIT STATUS



           The systemtap translator generally returns with a success code of
           0 if the requested script was processed and executed successfully
           through the requested pass.  Otherwise, errors may be printed to
           stderr and a failure code is returned.  Use _-v_ or _-vp N_ to in‐
           crease (global or per-pass) verbosity to identify the source of
           the trouble.
    
           In listings mode (_-l_ and _-L_), error messages are normally sup‐
           pressed.  A success code of 0 is returned if at least one matching
           probe was found.
    
           A script executing in pass 5 that is interrupted with ^C / SIGINT
           is considered to be successful.
    


## DEPRECATION



           Over time, some features of the script language and the tapset li‐
           brary may undergo incompatible changes, so that a script written
           against an old version of systemtap may no longer run.  In these
           cases, it may help to run systemtap with the _--compatible VERSION_
           flag, specifying the last known working version.  Running system‐
           tap with the _--check-version_ flag will output a warning if any
           possible incompatible elements have been parsed.  Deprecation his‐
           torical details may be found in the NEWS file.
    
           The purpose of deprecation facility is to improve the experience
           of scripts written for newer versions of systemtap (by adding bet‐
           ter alternatives and removing conflicting or messy older alterna‐
           tives), while at the same time permitting scripts written for old‐
           er versions of systemtap to continue running.  Deprecation is thus
           intended a _service to users_ (and an inconvenience to systemtap's
           developers), rather than the other way around.
    
           Please note that underscore-prefixed identifiers in the tapset
           sometimes undergo such changes that are difficult to preserve com‐
           patibility for, even with the deprecation mechanisms.  Avoid rely‐
           ing on these in your scripts; instead propose them for promotion
           to non-underscored status.
    


## FILES



           Important files and their corresponding paths can be located in
           the
                  stappaths (7) manual page.
    


## BUGS



           Use the Bugzilla link of the project web page or our mailing list.
           **http://sourceware.org/systemtap/ **, **< systemtap@sourceware.org>**.
    
           error::reporting(7stap),
           **https://sourceware.org/systemtap/wiki/HowToReportBugs **
    


* * *