Provided by: systemtap_2.3-1ubuntu1_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 ]

DESCRIPTION

       The  stap program is the front-end to the Systemtap tool.  It accepts probing instructions
       (written in a simple scripting 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 in a later section, is strictly typed, declaration  free,
       procedural,  and inspired by awk.  It allows source code points or events in the kernel 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.  Activate heuristics to work  around  incorrect  debugging
              information for $target variables.

       -u     Unoptimized mode.  Disable unused code elision during elaboration.

       -w     Suppressed warnings mode.  Disables all warning messages.

       -b     Use bulk mode (percpu files) for kernel-to-user data transfer.

       -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.

       -e SCRIPT
              Run the given SCRIPT specified on the command line.

       -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.

       --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 constructors 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  or  empty,  the  default colors will be used. If it is 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. If --privilege=stapusr  is  also  specified,
              the list will be limited to probe types available to unprivileged users.

       --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 and 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.  The direct:// URL is available as a 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  dowloading 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_NO_OVERLOAD -MAXACTION -MAXTRYLOCK  options.   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.

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.  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 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 (EXPERIMENTAL)
       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%

   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 (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.

       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.   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

   REGULAR EXPRESSION MATCHING (experimental)
       The  scripting  language has proof-of-concept support for 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 ...] }

       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 "target 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.   Some  other  events  have  very little context.  See the
       stapprobes(3stap) man pages to see the kinds of context variables available at  each  kind
       of probe point.

       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=%d0, 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
                     precision specifier determines the number of bytes to read.   Default  is  1
                     byte.

              %M     Same  as  %m,  but  outputs  in  hexadecimal.  The minimal size of output is
                     double the precision specifier.

              %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 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 read a 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.  Here are some examples:
              function add_one (val) %{
                STAP_RETVALUE = STAP_ARG_val + 1;
              %}
              function add_one_str (val) %{
                strlcpy (STAP_RETVALUE, STAP_ARG_val, MAXSTRINGLEN);
                strlcat (STAP_RETVALUE, "one", MAXSTRINGLEN);
              %}
       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.

       /* 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.

       /* 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 $target 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 collection of samples.

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 30 s.

SAFETY AND SECURITY

       Systemtap  is  an  administrative  tool.   It  exposes kernel internal data structures and
       potentially private user information.

       To actually run the kernel objects it 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.

       The translator asserts certain safety constraints.  It aims  to  ensure  that  no  handler
       routine  can  run  for  very  long,  allocate  memory,  perform  unsafe  operations, or in
       unintentionally  interfere  with  the  kernel.   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.)   Use  of guru mode constructs such as
       embedded C can violate these constraints, leading to kernel crash or data corruption.

       The resource use limits are set  by  macros  in  the  generated  C  code.   These  may  be
       overridden with the -D flag.  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.

       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  potentialy  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_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.

       In addition to the methods outlined above, the generated kernel module also uses  overload
       processing   to   make   sure   that  probes  can't  run  for  too  long.   If  more  than
       STP_OVERLOAD_THRESHOLD cycles (default 500000000) have been spent in all the probes  on  a
       single  cpu  during the last STP_OVERLOAD_INTERVAL cycles (default 1000000000), the probes
       have overloaded the system and an exit is triggered.

       By default, overload processing is turned on for  all  modules.   If  you  would  like  to
       disable overload processing, define STP_NO_OVERLOAD (or its alias STAP_NO_OVERLOAD).

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)

   SCRIPTING 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),
       error::reporting(7stap),    stappaths(7),    staprun(8),    stapdyn(8),   stapvars(3stap),
       stapex(3stap), stap-server(8), stap-prep(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>.

                                                                                          STAP(1)