NAME
stap - systemtap script translator/driverSYNOPSIS
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 kernel module into a running Linux kernel to perform the requested system trace/probe functions. You can supply the script in a named file, from standard input, or from the command line. 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.)- -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.
- --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.
- -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 }
- --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.
- --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 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.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 stapwill 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.
- --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.
-
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 ... */
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 %)
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 forkernel_v and the right operand is a version string. See also the DEPRECATION section below.
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
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") {} %)
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
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 tiny_array[10], normal_array, big_array[50000]
- 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. 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 or string comparison operators
- < > <= >= == !=
- ternary operator
- cond ? exp1 : exp2
- grouping operator
- ( exp )
- function call
- fn ([ arg1, arg2, ... ])
- array membership check
- exp in array
[exp1, exp2, ...] in array
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 ...] }
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 = $fd if (execname() == "init") next # skip rest of probe }
probe syscall.read += kernel.function("sys_read") { if (tracethis) println ($fd) }
probe syscall.read { printf("reading fd=%d, 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 }
function thatfn:string (arg1:long, arg2) { return sprint(arg1) . arg2 }
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.
-
- %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 %.
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
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
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.
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 foo { x <<< $value } probe end { printf ("avg %d = sum %d / count %d\n", @avg(x), @sum(x), @count(x)) print (@hist_log(v)) }
TYPECASTING
Once a pointer has been saved into a script integer variable, the translator loses the type information necessary to access members from that pointer. Using the @cast() operator tells the translator how to read a pointer.@cast(p, "type_name"[, "module"])->member
The translator can create its own module with type information from a header surrounded by angle brackets, in case normal debuginfo is not available. For kernel headers, prefix it with "kernel" to use the appropriate build system. All other headers are build with default GCC parameters into a user module. Multiple headers may be specified in sequence to resolve a codependency.
@cast(tv, "timeval", "<sys/time.h>")->tv_sec @cast(task, "task_struct", "kernel<linux/sched.h>")->tgid @cast(task, "task_struct", "kernel<linux/sched.h><linux/fs_struct.h>")->fs->umask
When in guru mode, the translator will also allow scripts to assign new values to members of typecasted pointers.
Typecasting is also useful in the case of void* members whose type may be determinable at runtime.
probe foo { if ($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 script. Such code is enclosed between %{ and %} markers, and is transcribed verbatim, without analysis, in some sequence, into 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 a macro THIS. Here are some examples:
function add_one (val) %{ THIS->__retvalue = THIS->val + 1; %} function add_one_str (val) %{ strlcpy (THIS->__retvalue, THIS->val, MAXSTRINGLEN); strlcat (THIS->__retvalue, "one", MAXSTRINGLEN); %}
function add_one (val) { return val + %{ 1 %} } function add_string_two (val) { return val . %{ /* string */ "two" %} }
- /* 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.
- /* 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 functions and 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 stapfuncs(3stap) andstapprobes(3stap) manual pages.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 *.stpStopping 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 scripts. If any tapset script is selected because it defines an unresolved symbol, then the entirety of that script is added to the translator's resolution queue. This process iterates until all symbols are resolved and a subset of tapset scripts 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.
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.
- *
- The module is located in the /lib/modules/VERSION/systemtap directory. This directory must be owned by root and not be world writable.
- *
- 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 FI--privilege=stapusr option.
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]
- 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.
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. SeeREADME.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.
-
- *
- 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: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.
-
- *
- 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
The following built-in tapset functions are unconditionally available to all users:_ehostunreach:long () _enetunreach:long () _icmp_dest_unreach:long () _icmp_exc_fragtime:long () _icmp_prot_unreach:long () _icmp_time_exceeded:long () _MM_ANONPAGES:long() _MM_FILEPAGES:long() _net_rx_drop:long () _rtn_broadcast:long () _rtn_multicast:long () _rtn_unspec:long () _sys_pipe2_flag_str:string (f:long) AF_INET:long() cpu:long () cputime_to_msecs:long (cputime:long) egid:long () error (msg:string) euid:long () execname:string () exit () get_cycles:long () gettimeofday_ns:long () GFP_KERNEL:long() gid:long () HZ:long () is_myproc:long () isdigit:long(str:string) isinstr:long(s1:string,s2:string) jiffies:long () log (msg:string) mem_page_size:long () module_name:string () pexecname:string () pgrp:long () pid:long () pn:string () pp:string () ppid:long () randint:long(n:long) registers_valid:long () sid:long () str_replace:string (prnt_str:string, srch_str:string, rplc_str:string) stringat:long(str:string, pos:long) strlen:long(s:string) strtol:long(str:string, base:long) substr:string(str:string,start:long, length:long) target:long () task_utime:long () task_stime:long () text_str:string(input:string) text_strn:string(input:string, len:long, quoted:long) tid:long () tokenize:string(input:string, delim:string) tz_gmtoff() { tz_name() { uid:long () user_mode:long () warn (msg:string)
_utrace_syscall_nr:long () _utrace_syscall_arg:long (n:long) _utrace_syscall_return:long () print_ubacktrace () print_ubacktrace_brief () print_ustack(stk:string) sprint_ubacktrace:string () uaddr:long () ubacktrace:string () umodname:string (addr:long) user_char:long (addr:long) user_char_warn:long (addr:long) user_int:long (addr:long) user_int_warn:long (addr:long) user_int16:long (addr:long) user_int32:long (addr:long) user_int64:long (addr:long) user_int8:long (addr:long) user_long:long (addr:long) user_long_warn:long (addr:long) user_short:long (addr:long) user_short_warn:long (addr:long) user_string_quoted:string (addr:long) user_string_n_quoted:string (addr:long, n:long) user_string_n_warn:string (addr:long, n:long) user_string_n2:string (addr:long, n:long, err_msg:string) user_string_warn:string (addr:long) user_string2:string (addr:long, err_msg:string) user_uint16:long (addr:long) user_uint32:long (addr:long) user_uint8:long (addr:long) user_ushort:long (addr:long) user_ushort_warn:long (addr:long) usymdata:string (addr: long) usymname:string (addr: long)
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 of systemtap. Running systemtap with the --check-version flag will output a warning if any possible incompatible elements have been parsed. Below is a table of recently deprecated tapset functions and syntax elements that require the given --compatible flag to use:- --compatible=1.2
- (none yet)
- --compatible=1.3
- The tapset alias 'syscall.compat_pselect7a' was misnamed. It should have been 'syscall.compat_pselect7' (without the trailing 'a'). Starting in release 1.4, the old name will be deprecated.
- --compatible=1.4
- In the 'syscall.add_key' probe, the 'description_auddr' variable has been deprecated in favor of the new 'description_uaddr' variable.
- In the 'syscall.fgetxattr', 'syscall.fsetxattr', 'syscall.getxattr', 'syscall.lgetxattr', 'syscall.lremovexattr', 'nd_syscall.fgetxattr', 'nd_syscall.fremovexattr', 'nd_syscall.fsetxattr', 'nd_syscall.getxattr', and 'nd_syscall.lremovexattr' probes, the 'name2' variable has been deprecated in favor of the new 'name_str' variable.
- In the 'nd_syscall.accept' probe the 'flag_str' variable has been deprecated in favor of the new 'flags_str' variable.
- In the 'nd_syscall.dup' probe the 'old_fd' variable has been deprecated in favor of the new 'oldfd' variable.
- The tapset alias 'nd_syscall.compat_pselect7a' was misnamed. It should have been 'nd_syscall.compat_pselect7' (without the trailing 'a').
- The tapset function 'cpuid' is deprecated in favor of the better known 'cpu'.
- In the i386 'syscall.sigaltstack' probe, the 'ussp' variable has been deprecated in favor of the new 'uss_uaddr' variable.
- In the ia64 'syscall.sigaltstack' probe, the 'ss_uaddr' and 'oss_uaddr' variables have been deprecated in favor of the new 'uss_uaddr' and 'uoss_uaddr' variables.
- The powerpc tapset alias 'syscall.compat_sysctl' was deprecated and renamed 'syscall.sysctl32'.
- In the x86_64 'syscall.sigaltstack' probe, the 'regs_uaddr' variable has been deprecated in favor of the new 'regs' variable.
- --compatible=1.7
- In the 'kprocess.release probe, the 'pid variable has been deprecated in favor of the new 'released_pid' variable.
- In the '_sunrpc.clnt.create_client.rpc_new_client_inline' probe, the 'args' variable in the has been deprecated in favor of the new internal-only '__args' variable.
- The following probe types have been deprecated:
-
- kernel.function(number).inline
module(string).function(number).inline
process.function(number).inline
process.library(string).function(number).inline
process(string).function(number).inline
process(string).library(string).function(number).inline
- kernel.function(number).inline
-
FILES
- Important files and their corresponding paths can be located in the
- stappaths (7) manual page.
