STAP(1)STAP(1)NAMEstap - systemtap script translator/driver
SYNOPSISstap [ 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), trans‐
lates 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, elabo‐
rate, 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 elabora‐
tion.
-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.
-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 gen‐
erated 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 ker‐
nel 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 com‐
mand 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 num‐
ber of output files exceed N , systemtap removes the oldest out‐
put 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 in‐
compatible 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 con‐
structors that may be systemtap version specific. See the DEP‐
RECATION 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 ei‐
ther "never", "always", or "auto" (i.e. enable only if at a ter‐
minal). If WHEN is missing, then "always" is assumed. If the op‐
tion 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 docu‐
mentation of your terminal for the SGRs it supports. As an exam‐
ple, 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 mis‐
behaving.
--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 exam‐
ine 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 lev‐
el.
If --privilege has not been specified, -pN has not been speci‐
fied 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 speci‐
fied.
--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 ac‐
cumulated 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 be‐
low). If a server is specified by host name or ip address, then
an optional port number may be specified. This is useful for ac‐
cessing 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 speci‐
fied 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 provid‐
ed, 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-compi‐
lation attempt as if --use-server was specified with no argu‐
ments.
--list-servers[=SERVERS]
Display the status of the requested SERVERS, where SERVERS is a
comma-separated list of server attributes. The list of at‐
tributes 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 address‐
es, the avahi-daemon configuration file /etc/avahi/avahi-dae‐
mon.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 opera‐
tion 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 avail‐
able 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, 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 function‐
ality.
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 speci‐
fied to connect to a specific driver and/or a remote
host. For example, to connect to the local privileged QE‐
MU driver, use:
--remote libvirt://MyDomain/qemu:///system
See the page at <http://libvirt.org/uri.html> for sup‐
ported 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 in‐
side 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 in‐
dex 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 time‐
out. 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 down‐
load if it is taking too long.
--rlimit-as=NUM
Specify the maximum size of the process's virtual memory (ad‐
dress 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, li‐
braries, 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 outer‐
most 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, hexa‐
decimal, or octal, using the same notation as in C). All strings are
limited in length to some reasonable value (a few hundred bytes). In‐
tegers 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 conjunc‐
tions of CONDITIONs (meant as in previous sentence) using || and && re‐
spectively. 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 (com‐
monly "y" or "m"). Nonexistent or unset kernel configuration options
are represented by the empty string. This comparison is also a wild‐
card (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 informa‐
tion 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 ver‐
sion 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 sepa‐
rate 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 prefix‐
ing 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 condi‐
tional compilation. Therefore, both TRUE- and FALSE-tokens in condi‐
tional expressions will be macroexpanded regardless of how the condi‐
tion 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 in‐
cluding .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 in‐
vocation.
Scalar variables are implicitly typed as either string or integer. As‐
sociative 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 expres‐
sions.
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 auto‐
matically 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 shut‐
down. 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 caus‐
es 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 func‐
tions 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 separa‐
tor 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-ze‐
ro) 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 cur‐
rent 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 or‐
der, by ascending or descending index or value. If the array
contains statistics aggregates, adding the desired @operator be‐
tween the ARRAY identifier and the + or - will specify the sort‐
ing aggregate function. See the STATISTICS section below for
the ones available. Default is @count. Using the optional lim‐
it 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 er‐
rors, 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 ini‐
tial 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 per‐
formed 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 expres‐
sion 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 vari‐
ables defined in the source code at that spot. These "target vari‐
ables" are presented to the script as variables whose names are pre‐
fixed 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 "+=" respective‐
ly.
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 substitu‐
tion.
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 in‐
ferred 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 to‐
gether.
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. De‐
fault (%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 num‐
ber 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 oc‐
tal.
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 spe‐
cial operator to accumulate values, and several pseudo-functions to ex‐
tract the statistical aggregates.
The aggregation operator is <<<, and resembles an assignment, or a C++
output-streaming operation. The left operand specifies a scalar or ar‐
ray-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 ex‐
traction 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 accu‐
mulated values. The resulting values are all simple integers. Arrays
containing aggregates may be sorted and iterated. See the foreach con‐
struct above.
Histograms are also available, but are more complicated because they
have a vector rather than scalar value. @hist_linear(v,start,stop,in‐
terval) represents a linear histogram from "start" to "stop" by incre‐
ments of "interval". The interval must be positive. Similarly,
@hist_log(v) represents a base-2 logarithmic histogram. Printing a his‐
togram 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 in‐
direction. 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 ap‐
propriate 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 lev‐
el 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 consump‐
tion, 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 includ‐
ed, 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 en‐
tirely 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) argu‐
ment 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, in‐
stead of the default long numeric.
BUILT-INS
A set of builtin probe point aliases are provided by the scripts in‐
stalled 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 directo‐
ries 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 ver‐
sion 2.6.12-23.FC3 the following patterns would be searched, in se‐
quence: 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 vari‐
ety supported by the translator. Probe points that refer to code loca‐
tions ("synchronous probe points") require the appropriate kernel de‐
bugging 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 opportuni‐
ties, in order to remove variables, expressions, and functions that
have no useful value and no side-effect. Embedded-C functions are as‐
sumed 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 transla‐
tor after pass 2 causes it to list all the probes, functions, and vari‐
ables, 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 cre‐
ate the actual kernel object file. This involves running make in the
temporary directory, and requires a kernel module build system (head‐
ers, config and Makefiles) to be installed in the usual spot /lib/mod‐
ules/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 ter‐
minate 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 com‐
pletes 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) con‐
taining only an ASCII integer representing how many MiB the cache
should not exceed. In the absence of this file, a default will be cre‐
ated 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 in‐
terval 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) con‐
taining 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-serv‐
er(8) manual page for more information.
· The module was built using the --privilege=stapsys or the --privi‐
lege=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 direc‐
tory. 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-serv‐
er(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 han‐
dlers. (Deadlocks are detected with timeouts. Use the -t flag to re‐
ceive reports of excessive lock contention.) Use of guru mode con‐
structs 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 vari‐
ables 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, de‐
fault 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, de‐
fault 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 -DINTERRUPT‐
IBLE=1 setting, probes skipped due to reentrancy are not accumu‐
lated against this limit. Note that with the --suppress-han‐
dler-errors option, this limit is not enforced.
MINSTACKSPACE
Minimum number of free kernel stack bytes required in order to
run a probe handler, default 1024. This number should be large
enough for the probe handler's own needs, plus a safety margin.
MAXUPROBES
Maximum number of concurrently armed user-space probes (up‐
robes), default somewhat larger than the number of user-space
probe points named in the script. This pool needs to be poten‐
tialy 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 mod‐
ule 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/up‐
robes/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 op‐
tion -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 out‐
put of the host. To run a script as a host, execute stap with -DRELAY‐
HOST[=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 al‐
ready started running, one may safely kill both user processes, and re‐
move the active probe kernel module with rmmod. Any pending trace mes‐
sages 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 pri‐
vate user information. Because of this, use of systemtap's full capa‐
bilities 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 op‐
tions --privilege and --use-server. See README.unprivileged in the sys‐
temtap source code for information about setting up a trusted compile
server.
The restrictions enforced when --privilege=stapsys is specified are de‐
signed to prevent unprivileged users from:
· harming the system maliciously.
The restrictions enforced when --privilege=stapusr is specified are de‐
signed 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 us‐
er.
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 un‐
privileged 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 sta‐
pusr:
· 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 unprivi‐
leged 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 pro‐
gram 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 avail‐
able 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 --run‐
time=dyninst, which uses Dyninst to instrument a user's own processes
at runtime. This backend does not use kernel modules, and does not re‐
quire 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 ALSOstapprobes(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)
