Provided by: systemtap_2.9-2ubuntu2_amd64 bug

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.

OPTIONS

       The systemtap translator supports the following options.  Any other option prints  a  list
       of  supported  options.   Options may be given 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.)

       -      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 constructs like embedded C.

       -P     Prologue-searching   mode.   This  is  equivalent  to  --prologue-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 transfer.  Use the  stap-merge
              program to multiplex them back together later.

       -t     Collect timing information on the number of times probe executes and average amount
              of time spent in each probe-point. Also shows the derivation for each probe-point.

       -sNUM  Use NUM megabyte buffers for kernel-to-user data transfer.  On a multiprocessor  in
              bulk mode, this is a per-processor amount.

       -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 Makefile.  These can  be  used
              to override limit parameters described below.

       -B NAME=VALUE
              Add  the  given make directive to the kernel module build's make invocation.  These
              can be used to add or override kconfig options.

       -a ARCH
              Use a cross-compilation mode for the  given  target  architecture.   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 declared global in the script/tapset.

       -R DIR Look for the systemtap runtime sources in the given directory.

       -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 shared  libraries  suspected  by  ldd  to  be
              necessary  for  user-space  binaries  being  probe  or  listed  with the -d option.
              Caution: this can make the probe modules considerably larger.

       --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 the command ran.

       -x PID Sets target() to PID. This allows scripts to be written that filter on  a  specific
              process. Scripts run independent 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 addition 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.

       -L PROBE
              Similar to "-l", but list probe points and script-level local variables.

       -F     Without -o option, load module and  start  probes,  then  detach  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 , systemtap switches output file to the
              next file. And if the number of output files  exceed  N  ,  systemtap  removes  the
              oldest output file. You can omit the second argument.

       --skip-badvars
              Ignore  unresolvable or run-time-inaccessible context variables 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 suppressed.  Suppressed errors
              do not count against MAXERRORS limits.  In this mode,  the  MAXSKIPPED  limits  are
              also suppressed, so that many errors and skipped probes may be accumulated 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 assumed. If the option is missing, then "auto" is assumed.

              Colors can be modified using the SYSTEMTAP_COLORS environment 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  expressed  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.

       --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 stapsys 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). 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 accumulated  in  the  order  specified.  Servers  may  be
              specified by host name, ip address, or by certificate serial number (obtained 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-server 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. insufficient data or resources) which may not occur
              during re-compilation by  a  compile  server.  Compile  servers  will  be  selected
              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 displayed. 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 local 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 carrying  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 before the operation is performed.

       --dump-probe-types
              Dumps  a  list  of  supported probe types and exits. If --privilege=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 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 imposes 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  information  on  how  to prepare the domain for stap
                     probing.

              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  debuginfo  downloading  feature
              offered by abrt as specified by OPTION, 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 debuginfo. This is the  same  as
                     not using the option at all.

              ask    show  abrt  output,  and  ask before continuing download. No timeout will be
                     set.

              <timeout>
                     specify a timeout as a positive number to stop the download if it is  taking
                     too long.

       --rlimit-as=NUM
              Specify the maximum size of the process's virtual memory (address space), in bytes.
              If nothing is specified, no limits are imposed.

       --rlimit-cpu=NUM
              Specify the CPU time limit, in seconds. If nothing  is  specified,  no  limits  are
              imposed.

       --rlimit-nproc=NUM
              Specify  the  maximum  number  of  processes  that  can  be  created. If nothing is
              specified, no limits are imposed.

       --rlimit-stack=NUM
              Specify the maximum size of the process stack, in bytes. If nothing  is  specified,
              no limits are imposed.

       --rlimit-fsize=NUM
              Specify the maximum size of files that the process may create, in bytes. If nothing
              is specified, no limits are imposed.

       --sysroot=DIR
              Specify sysroot directory where target files (executables,  libraries,  etc.)   are
              located.   With -r RELEASE, the sysroot will be searched for the appropriate kernel
              build directory.  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 -DMAXACTION and -DMAXTRYLOCK.
              This option requires guru mode.

       --runtime=MODE
              Set the pass-5 runtime mode.  Valid options are kernel (default) and dyninst.   See
              ALTERNATE RUNTIMES below for more information.

       --dyninst
              Shorthand for --runtime=dyninst.

       --save-uprobes
              On  machines  that require SystemTap to build its own uprobes module (kernels prior
              to version 3.5), this option instructs 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.

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 precedence.

   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 adjacent 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, although 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 parsing.  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) using ||
       and && respectively.  However, parentheses are not  supported  yet,  so  remembering  that
       conjunction takes precedence over alternative 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 without ("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 contains an RPM-style  version-release
       value.   The  condition  is  deemed  satisfied  if  the  version  of the target kernel (as
       optionally overridden 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 characters (* 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_something 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  operator 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 compiled 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 second 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
       literal 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  unless
       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_UTRACE == "y" %?
                  @define foo %( process.syscall %)
              %:
                  @define foo %( **ERROR** %)
              %)

              // The following works properly as expected:
              @define foo %(
                %( CONFIG_UTRACE == "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.

   VARIABLES
       Identifiers for variables and functions are an alphanumeric sequence, 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  mentioned,  and
       therefore its scope and lifetime is limited to a particular 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 tuple 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, including array indexes and
       function parameters.  Inconsistent type-related use of identifiers signals an error.

       Variables may be declared global, so that they are shared amongst all probes and  live  as
       long  as  the  entire systemtap session.  There is one namespace for all global variables,
       regardless of which script file they  are  found  within.   Concurrent  access  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 declaration 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.

       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  indicate
       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 inserted 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.

   STATEMENTS
       Statements  enable  procedural  control  flow.   They may occur within functions and probe
       handlers.  The total number of statements executed in response to any single  probe  event
       is  limited  to  some  number  defined  by a 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  detection  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 value.   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.  Default is @count.  Using the optional limit
              keyword limits the number of loop iterations to EXP times.  EXP is  evaluated  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 (VALUE = VAR in ARRAY [ limit EXP ]) STMT
              This variant of foreach saves current value into VALUE on each iteration, so it  is
              the same as ARRAY[VAR].  This also works with a tuple of keys.  Sorting suffixes on
              VALUE have the same effect as on ARRAY.

       foreach (VALUE = 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 function's  value  is  not  taken
              anywhere,  then  a  return  statement  is  not needed, and the function will have a
              special "unknown" type with no return value.

       next   Return now from enclosing probe  handler.   This  is  especially  useful  in  probe
              aliases that apply event filtering predicates.

       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 value 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 reset to the initial empty state.

   EXPRESSIONS
       Systemtap supports a number of operators that have the same general 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 syntactically valid regular expression.)

       The regular expression syntax supports most of the  features  of  POSIX  Extended  Regular
       Expressions,  except  for subexpression reuse ("\1") functionality. The ability to capture
       and extract the contents of the  matched  string  and  subexpressions  has  not  yet  been
       implemented.

   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 translator, 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  syntax  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 paging.  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.

       Probes may be  decorated  with  an  arming  condition,  consisting  of  a  simple  boolean
       expression  on  read-only global script variables.  While disarmed (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.)

       New  probe  points  may  be  defined using "aliases".  Probe point aliases look similar to
       probe definitions, but instead of activating 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  identified  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 prologue, which is useful to predefine some variables for the
       alias user and/or to skip probe processing entirely based on some conditions.  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.

       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
              }

   FUNCTIONS
       Systemtap  scripts  may  define subroutines to factor out common work.  Functions take any
       number of scalar (integer or string) arguments, 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  definition  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 a macro in the translated C code and is in the neighbourhood of 10.

   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.  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 newline.

       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 corresponding 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 number 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 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.

              %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  characters  in  a
                     10-character-wide field.

              %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.

       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 separately, 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 satisfy it.  The statistics system is thereby "on-demand".  Each execution
       of an extraction function causes the aggregation to be computed 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)      extractor       functions       compute       the
       number/total/minimum/maximum/average  of all accumulated values.  The resulting values are
       all simple integers.  Arrays containing aggregates may be sorted and  iterated.   See  the
       foreach construct above.

       Histograms  are also available, but are more complicated because they have a vector rather
       than scalar value.  @hist_linear(v,start,stop,interval) represents a linear histogram from
       "start"  to "stop" 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))
              }

   TYPECASTING
       Once  a  pointer  (see  the CONTEXT VARIABLES section of stapprobes(3stap)) has been saved
       into a script integer variable, the translator loses the  type  information  necessary  to
       access  members from that pointer.  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: the same dereferencing operator -> is used to refer to both direct  containment  or
       pointer indirection.  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
       either to the probe module for dwarf probes, or to "kernel" for functions  and  all  other
       probes types.

       The translator can create its own module with type information from a header surrounded by
       angle brackets, in case normal debuginfo is not available.  For kernel headers, prefix  it
       with  "kernel"  to  use  the  appropriate  build system.  All other headers are build 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 VARIABLES section of the stapprobes(3stap) manual page.

       When in guru mode, the translator will also allow scripts to assign 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 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  outermost
       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  number  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-language functions in order to write compatible embedded-C ones.

       The last place where embedded code is permitted is as an expression rvalue.  In this case,
       the C code enclosed between %{ and %} markers is interpreted  as  an  ordinary  expression
       value.   It is assumed 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" %}
              }

       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.

       /* 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_RETVALUE one can use THIS->foo and  THIS->__retvalue  respectively  inside
              the  function.  This  is  useful  for  quickly migrating code written for SystemTap
              version 1.7 and earlier.

       /* unmodified-fnargs */
              in an embedded-C function, means that  the  function  arguments  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.

   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.

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 is 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.  (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.)   The  systemtap
       compile  server can sign modules with a MOK (Machine Owner Key) that it has in common with
       a client system. See the following wiki page for more details:

              https://sourceware.org/systemtap/wiki/SecureBoot

   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 determined 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 interpreted
              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
              Default  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 automatically.

       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 option, this limit is not enforced.

       MAXSKIPPED
              Maximum number of skipped probes before an exit is triggered, default 100.  Running
              systemtap with -t (timing) mode gives more details about skipped probes.  With  the
              default  -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 (uprobes), 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 includes the size of the module itself, plus
              any additional allocations.  This only tracks direct allocations by  the  systemtap
              runtime.  This does not track indirect allocations (as done by kprobes/uprobes/etc.
              internals).

       STP_OVEROAD_THRESHOLD, STP_OVERLOAD_INTERVAL
              Maximum number of machine cycles spent in probes on any  cpu  per  given  interval,
              before  an  overload  condition is declared and the script shut down.  The defaults
              are 500 million and 1 billion, so as to limit stap script cpu consumption 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 possible 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 issue,
       execute stap with the option -DINTERRUPTIBLE=0 to mask  interrupts  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 callpath of the stap
       runtime may still be skipped due to reentrance.

       Multiple  scripts  can write data into a relay buffer concurrently. A host script provides
       an interface for accessing its relay buffer to guest scripts.  Then,  the  output  of  the
       guests  are  merged  into the output of the host.  To run a script as a host, execute stap
       with -DRELAYHOST[=name] option. The name identifies your host script among several  hosts.
       While running the host, execute stap with -DRELAYGUEST[=name] to add a guest script to the
       host.  Note that you must unload guests before unloading a host. If there are some  guests
       connected to the host, unloading the host will be failed.

       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 another  user's  processes  which  would  not
                  normally be possible 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 unprivileged 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 permitted.

              ·   Access of kernel memory (read and write) is not permitted.

   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 unprivileged 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  unconditionally  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 functions 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  tradeoffs  presented.   Systemtap  now  includes  a new
       prototype backend, selected with --runtime=dyninst, which uses  Dyninst  to  instrument  a
       user's  own  processes  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.

       The  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

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
       increase (global or per-pass) verbosity to identify the source of the trouble.

       In listings mode (-l and -L), error messages are normally suppressed.  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 library 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   systemtap   with   the
       --check-version flag will output a warning if any possible incompatible elements have been
       parsed.  Deprecation historical details may be found in the NEWS file.

FILES

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

SEE ALSO

       stapprobes(3stap),
       function::*(3stap),
       probe::*(3stap),
       tapset::*(3stap),
       stappaths(7),
       staprun(8),
       stapdyn(8),
       systemtap(8),
       stapvars(3stap),
       stapex(3stap),
       stap-server(8),
       stap-prep(1),
       stapref(1),
       awk(1),
       gdb(1)

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

                                                                                          STAP(1)