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SunOS man pages : prex (1)

User Commands                                             prex(1)


prex - control tracing and manipulate probe points in a pro- cess or the kernel


prex [ -o trace_file_name ] [ -l libraries ] [ -s kbytes_size ] cmd [ cmd-args ... ] prex [ -o trace_file_name ] [ -l libraries ] [ -s kbytes_size ] -p pid prex -k [ -s kbytes_size ]


The prex command is the part of the Solaris tracing archi- tecture that controls probes in a process or the kernel. See tracing(3TNF) for an overview of this tracing architecture, including example source code using it. prex is the application used for external control of probes. It automatically preloads the libtnfprobe library. prex locates all the probes in a target executable or the kernel and provides an interface for the user to manipulate them. It allows a probe to be turned on for tracing, debugging, or both. Tracing generates a TNF (Trace Normal Form) trace file that can be converted to ASCII by tnfdump(1) and used for performance analysis. Debugging generates a line to standard error whenever the probe is hit at run time. prex does not work on static executables. It only works on dynamic executables. Invoking prex There are three ways to invoke prex: 1. Use prex to start the target application cmd. In this case, the target application need not be built with a dependency on libtnfprobe. See TNF_PROBE(3TNF). prex sets the environment variable LD_PRELOAD to load libtnfprobe into the target process. See ld(1). prex then uses the environment variable PATH to find the target application. 2. Attach prex to a running application. In this case, the running target application should have libtnfprobe already linked in. Alternatively, the user may manually set LD_PRELOAD to include prior to invoking the target. 3. Use prex with the -k option to set prex to kernel mode. prex can then be used to control probes in the Solaris kernel. In kernel mode, additional commands are defined, SunOS 5.8 Last change: 1 Nov 1999 1 User Commands prex(1) and some commands that are valid in other modes are invalid. See Kernel Mode below. Control File Format and Command Language In a future release of prex, the command language may be moved to a syntax that is supported by an existing scripting language like ksh(1). In the mean time, the interface to prex is uncommitted. o Commands should be in ASCII. o Each command is terminated with the NEWLINE character. o A command can be continued onto the next line by end- ing the previous line with the backslash (`\') charac- ter. o Tokens in a command must be separated by whitespace (one or more spaces or tabs). o The "#" character implies that the rest of the line is a comment. Basic prex Commands Command Result % prex a.out Attaches prex to your pro- gram and starts prex. prex> enable $all Enables all the probes. prex> quit resume Quits prex and resumes exe- cution of program. Control File Search Path There are two different methods of communicating with prex: o By specifications in a control file. During start-up, prex searches for a file named .prexrc in the direc- tories specified below. prex does not stop at the first one it finds. This way a user can override any defaults that are set up. The search order is: $HOME/ ./ o By typing commands at the prex prompt. The command language for both methods is the same and is specified in USAGE. The commands that return output will not make sense in a control file. The output will go to standard output. SunOS 5.8 Last change: 1 Nov 1999 2 User Commands prex(1) When using prex on a target process, the target will be in one of two states, running or stopped. This can be detected by the presence or absence of the prex> prompt. If the prompt is absent, it means that the target process is run- ning. Typing <CTRL-C> will stop the target process and return the user to the prompt. There is no guarantee that <CTRL-C> will return to a prex prompt immediately. For exam- ple, if the target process is stopped on a job control stop (SIGSTOP), then <CTRL-C> in prex will wait until the target has been continued (SIGCONT). See Signals to Target Program below for more information on signals and the target pro- cess.


The following options are supported: -k kernel mode: prex is used to control probes in the Solaris kernel. In kernel mode, additional commands are defined, and some commands valid in other modes are invalid. See Kernel Mode below. -l libraries The libraries mentioned are linked in to the target application using LD_PRELOAD (see ld(1)). This option cannot be used when attaching to a running process. The argument to the -l option should be a space- separated string enclosed in double quotes. Each token in the string is a library name. It follows the LD_PRELOAD rules on how libraries should be specified and where they will be found. -o trace_file_name File to be used for the trace output. trace_file_name is assumed to be relative to the current working directory of prex (that is, the directory that the user was in when prex was started). If prex attaches to a process that is already tracing, the new trace_file_name (if provided) will not be used. If no trace_file_name is specified, the default is /$TMPDIR/trace-pid where pid is the process id of the target program. If TMPDIR is not set, /tmp is used. -s kbytes_size Maximum size of the output trace file in Kbytes. The default size of the trace kbytes_size is 4096 (2**10) bytes or 4 Mbytes for normal usage, and 384 or 384 kbytes in kernel mode. The minimum size that can be specified is 128 Kbytes. The trace file can be thought of as a least recently used circular buffer. Once the file has been filled, newer events will overwrite the SunOS 5.8 Last change: 1 Nov 1999 3 User Commands prex(1) older ones.


Grammar Probes are specified by a list of space-separated selectors. Selectors are of the form: attribute=value (see TNF_PROBE(3TNF)). The "attribute=" is optional. If it is not specified, it defaults to "keys=". The attribute or value (generically called "spec") can be any of the following: IDENT Any sequence of letters, digits, _, \, ., % not begin- ning with a digit. IDENT implies an exact match. QUOTED_STR Usually used to escape reserved words (any commands in the command language). QUOTED_STR implies an exact match and has to be enclosed in single quotes (' '). REGEXP An ed(1) regular expression pattern match. REGEXP has to be enclosed in slashes (/ /), A / can be included in a REGEXP by escaping it with a backslash \. The following grammar explains the syntax. selector_list ::= | /* empty */ selector_list selector selector ::= spec=spec | /* whitespace around `=' opt */ spec spec ::= IDENT | QUOTED_STR | REGEXP The terminals in the above grammar are: IDENT = [a-zA-Z_\.%]{[a-zA-Z0-9_\.%]}+ QUOTED_STR = '[^\n']*' /* any string in single quotes */ REGEXP = /[^\n/]*/ /* regexp's have to be in / / */ This is a list of the remaining grammar that is needed to understand the syntax of the command language (defined in next subsection): filename ::= QUOTED_STR /* QUOTED_STR defined above */ spec_list ::= /* empty */ | spec_list spec /* spec defined above */ SunOS 5.8 Last change: 1 Nov 1999 4 User Commands prex(1) fcn_handle ::= &IDENT /* IDENT defined above */ set_name ::= $IDENT /* IDENT defined above */ Command Language 1. Set Creation and Set Listing create $set_name selector_list list sets # list the defined sets create can be used to define a set which contains probes that match the selector_list. The set $all is pre-defined as /.*/ and it matches all the probes. 2. Function Listing list fcns # list the available fcn_handle The user can list the different functions that can be connected to probe points. Currently, only the debug function called &debug is available. 3. Commands to Connect and Disconnect Probe Functions" 6 connect &fcn_handle $set_name connect &fcn_handle selector_list clear $set_name clear selector_list The connect command is used to connect probe functions (which must be prefixed by &) to probes. The probes are specified either as a single set (with a `$'), or by explicitly listing the probe selectors in the com- mand. The probe function has to be one that is listed by the list fcns command. This command does not enable the probes. The clear command is used to disconnect all connected probe functions from the specified probes. 4. Commands to Toggle the Tracing Mode trace $set_name trace selector_list untrace $set_name untrace selector_list The trace and untrace commands are used to toggle the SunOS 5.8 Last change: 1 Nov 1999 5 User Commands prex(1) tracing action of a probe point (that is, whether a probe will emit a trace record or not if it is hit). This command does not enable the probes specified. Probes have tracing on by default. The most efficient way to turn off tracing is by using the disable com- mand. untrace is useful if you want debug output but no tracing. If so, set the state of the probe to enabled, untraced, and the debug function connected. 5. Commands to Enable and Disable Probes enable $set_name enable selector_list disable $set_name disable selector_list The enable and disable commands are used to control whether the probes perform the action that they have been set up for. To trace a probe, it has to be both enabled and traced (using the trace command). Probes are disabled by default. The list history command is used to list the probe control commands issued: con- nect, clear, trace, untrace, enable, and disable. These are the commands that are executed whenever a new shared object is brought in to the target program by dlopen(3DL). See the subsection, dlopen'ed Libraries, below for more information. The following table shows the actions that result from specific combinations of tracing, enabling, and con- necting: Enabled or Tracing State Debug State Results Disabled (On/Off) (Connected/Cleared) In ------------------------------------------------------------ Enabled On Connected Tracing and Debugging Enabled On Cleared Tracing only Enabled Off Connected Debugging only Enabled Off Cleared Nothing Disabled On Connected Nothing Disabled On Cleared Nothing Disabled Off Connected Nothing SunOS 5.8 Last change: 1 Nov 1999 6 User Commands prex(1) Disabled Off Cleared Nothing 6. List History list history # lists probe control command history The list history command displays a list of the probe control commands previously issued in the tracing ses- sion, for example, connect, clear, trace, disable. Commands in the history list are executed wherever a new shared object is brought into the target program by dlopen(3DL). 7. Commands to List Probes or List Values list spec_list probes $set_name # that is, list probes $all list spec_list probes selector_list # that is, list name probes\ # file=test.c list values spec_list # that is, list values keys The first two commands list the selected attributes and values of the specified probes. They can be used to check the state of a probe. The third command lists the various values associated with the selected attri- butes. 8. Help Command help topic To get a list of the help topics that are available, invoke the help command with no arguments. If a topic argument is specified, help is printed for that topic. 9. Source a File source filename The source command can be used to source a file of prex commands. source can be nested (that is, a file can source another file). filename is a quoted string. 10. Process Control continue # resumes the target process quit kill # quit prex, kill target quit resume # quit prex, continue target SunOS 5.8 Last change: 1 Nov 1999 7 User Commands prex(1) quit suspend # quit prex, leave target suspended quit # quit prex (continue or kill target) The default quit will continue the target process if prex attached to it. Instead, if prex had started the target program, quit will kill the target process. dlopen'ed Libraries Probes in shared objects that are brought in by dlopen(3DL) are automatically set up according to the command history of prex. When a shared object is removed by a dlclose(3DL), prex again needs to refresh its understanding of the probes in the target program. This implies that there is more work to do for dlopen(3DL) and dlclose(3DL) -so they will take slightly longer. If a user is not interested in this feature and doesn't want to interfere with dlopen(3DL) and dlclose(3DL), detach prex from the target to inhibit this feature. Signals to Target Program prex does not interfere with signals that are delivered directly to the target program. However, prex receives all signals normally generated from the terminal, for example, <CTRL-C> (SIGINT), and <CTRL-Z> (SIGSTOP), and does not for- ward them to the target program. To signal the target pro- gram, use the kill(1) command from a shell. Interactions with Other Applications Process managing applications like dbx, truss(1), and prex cannot operate on the same target program simultaneously. prex will not be able to attach to a target which is being controlled by another application. A user can trace and debug a program serially by the following method: first attach prex to target (or start target through prex), set up the probes using the command language, and then type quit suspend. The user can then attach dbx to the suspended pro- cess and debug it. A user can also suspend the target by sending it a SIGSTOP signal, and then by typing quit resume to prex. In this case, the user should also send a SIGCONT signal after invoking dbx on the stopped process (else dbx will be hung). Failure of Event Writing Operations There are a few failure points that are possible when writ- ing out events to a trace file, for example, system call failures. These failures result in a failure code being set in the target process. The target process continues nor- mally, but no trace records are written. Whenever a user types <CTRL-C> to prex to get to a prex prompt, prex will check the failure code in the target and inform the user if there was a tracing failure. SunOS 5.8 Last change: 1 Nov 1999 8 User Commands prex(1) Target Executing a Fork or exec If the target program does a fork(2), any probes that the child encounters will cause events to be logged to the same trace file. Events are annotated with a process id, so it will be possible to determine which process a particular event came from. In multi-threaded programs, there is a race condition with a thread doing a fork while the other threads are still running. For the trace file not to get corrupted, the user should either use fork1(2), or make sure that all other threads are quiescent when doing a fork(2), If the target program itself (not any children it may fork(2)) does an exec(2), prex detaches from the target and exits. The user can reconnect prex with prex -p pid. A vfork(2) is generally followed quickly by an exec(2) in the child, and in the interim, the child borrows the parent's process while the parent waits for the exec(2). Any events logged by the child from the parent process will appear to have been logged by the parent. Kernel Mode Invoking prex with the -k flag causes prex to run in kernel mode. In kernel mode, prex controls probes in the Solaris kernel. See tnf_kernel_probes(4) for a list of available probes in the Solaris kernel. A few prex commands are una- vailable in kernel mode; many other commands are valid in kernel mode only. The -l, -o, and -p command-line options are not valid in kernel mode (that is, they may not be combined with the -k flag). The rest of this section describes the differences in the prex command language when running prex in kernel mode. 1. prex will not stop the kernel When prex attaches to a running user program, it stops the user program. Obviously, it cannot do this when attaching to the kernel. Instead, prex provides a ``tracing master switch'': no probes will have any effect unless the tracing master switch is on. This allows the user to iteratively select probes to enable, then enable them all at once by turning on the master switch. The command ktrace [ on | off ] SunOS 5.8 Last change: 1 Nov 1999 9 User Commands prex(1) is used to inspect and set the value of the master switch. Without an argument, prex reports the current state of the master switch. Since prex will not stop or kill the kernel, the quit resume and quit kill commands are not valid in kernel mode. 2. No functions may be attached to probes in the kernel" 6 In particular, the debug function is unavailable in kernel mode. 3. Trace output is written to an in-core buffer In kernel mode, a trace output file is not generated directly, in order to allow probes to be placed in time-critical code. Instead, trace output is written to an in-core buffer, and copied out by a separate program, tnfxtract(1). The in-core buffer is not automatically created. The following prex command controls buffer allocation and deallocation: buffer [ alloc [ size ] | dealloc ] Without an argument, the buffer command reports the size of the currently allocated buffer, if any. With an argument of alloc [ size], prex allocates a buffer of the given size. size is in bytes, with an optional suffix of 'k' or 'm' specifying a multiplier of 1024 or 1048576, respectively. If no size is speci- fied, the size specified on the command line with the -s option is used as a default. If the -s command line option was not used, the ``default default'' is 384 kilobytes. With an argument of dealloc, prex deallocates the trace buffer in the kernel. prex will reject attempts to turn the tracing master switch on when no buffer is allocated, and to deallo- cate the buffer when the tracing master switch is on. SunOS 5.8 Last change: 1 Nov 1999 10 User Commands prex(1) prex will refuse to allocate a buffer when one is already allocated; use buffer dealloc first. prex will not allocate a buffer larger than one-half of a machine's physical memory. 4. Prex supports per-process probe enabling in the kernel" 6 In kernel mode, it is possible to select a set of processes for which probes are enabled. No trace output will be written when other processes traverse these probe points. This is called "process filter mode." By default, process filter mode is off, and all processes cause the generation of trace records when they hit an enabled probe. Some kernel events such as interrupts cannot be asso- ciated with a particular user process. By convention, these events are considered to be generated by process id 0. prex provides commands to turn process filter mode on and off, to get the current status of the process filter mode switch, to add and delete processes (by process id) from the process filter set, and to list the current process filter set. The process filter set is maintained even when process filter mode is off, but has no effect unless process filter mode is on. When a process in the process filter set exits, its process id is automatically deleted from the process filter set. The command: pfilter [ on | off | addpidlist | deletepidlist ] controls the process filter switch, and process filter set membership. With no arguments, pfilter prints the current process filter set and the state of the process filter mode switch. on or off set the state of the process filter mode switch. add pidlist delete pidlist add or delete processes from the process filter set. pidlist is a comma-separated list of one or more process ids. SunOS 5.8 Last change: 1 Nov 1999 11 User Commands prex(1)


See tracing(3TNF) for complete examples showing, among other things, the use of prex to do simple probe control. When either the process or kernel is started, all probes are disabled. Example 1: Set creation and set listing create $out name=/out/ # $out = probes with "out" in # value of "name" attribute create $foo /page/ name=biodone # $foo = union of # probes with "page" in value of keys attribute # probes with "biodone" as value of "name" attribute list sets # list the defined sets list fcns # list the defined probe fcns Example 2: Commands to trace and connect probe functions trace foobar='on' # exact match on foobar attribute trace $all # trace all probes (predefined set $all) connect &debug $foo # connect debug func to probes in $foo Example 3: Commands to enable and disable probes enable $all # enable all probes enable /vm/ name=alloc # enable the specified probes disable $foo # disable probes in set $foo list history # list probe control commands issued Example 4: Process control continue # resumes the target process ^C # stop target; give control to prex quit resume # exit prex, leave process running and resume execution of program Example 5: Kernel mode buffer alloc 2m # allocate a 2 Megabyte buffer enable $all # enable all probes trace $all # trace all probes ktrace on # turn tracing on ktrace off # turn tracing back off pfilter on # turn process filter mode on pfilter add 1379 # add pid 1379 to process filter ktrace on # turn tracing on # (only pid 1379 will be traced)


.prexrc local prex initialization file SunOS 5.8 Last change: 1 Nov 1999 12 User Commands prex(1) ~/.prexrc user's prex initialization file /proc/nnnnn process files


See attributes(5) for descriptions of the following attri- butes: ____________________________________________________________ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |_____________________________|_____________________________| | Availability | SUNWtnfc (32-bit) | |_____________________________|_____________________________| | | SUNWtnfcx (64-bit) | |_____________________________|_____________________________|


ed(1), kill(1), ksh(1), ld(1), tnfdump(1), tnfxtract(1), truss(1), exec(2), fork(2), fork1(2), vfork(2), TNF_DECLARE_RECORD(3TNF), TNF_PROBE(3TNF), dlclose(3DL), dlopen(3DL), gethrtime(3C), libtnfctl(3TNF), tnf_process_disable(3TNF), tracing(3TNF), tnf_kernel_probes(4), attributes(5)


Currently, the only probe function that is available is the &debug function. When this function is executed, it prints out the arguments sent in to the probe as well as the value associated with the sunw%debug attribute in the detail field (if any) to stderr. For example, for the following probe point: TNF_PROBE_2(input_values, "testapp main", "sunw%debug 'have read input values successfully'", tnf_long, int_input, x, tnf_string, string_input, input); If x was 100 and input was the string "success", then the output of the debug probe function would be: probe input_values; sunw%debug "have read input values successfully"; int_input=100; string_input="success"; Some non-SPARC hardware lacks a true high-resolution timer, causing gethrtime() to return the same value multiple times in succession. This can lead to problems in how some tools interpret the trace file. This situation can be improved by interposing a version of gethrtime(), which causes these SunOS 5.8 Last change: 1 Nov 1999 13 User Commands prex(1) successive values to be artificially incremented by one nanosecond: hrtime_t gethrtime() { static mutex_t lock; static hrtime_t (*real_gethrtime)(void) = NULL; static hrtime_t last_time = 0; hrtime_t this_time; if (real_gethrtime == NULL) { real_gethrtime = (hrtime_t (*)(void)) dlsym(RTLD_NEXT, "gethrtime"); } this_time = real_gethrtime(); mutex_lock(&lock); if (this_time <= last_time) this_time = ++last_time; else last_time = this_time; mutex_unlock(&lock); return (this_time); } Of course, this does not increase the resolution of the timer, so timestamps for individual events are still rela- tively inaccurate. But this technique maintains ordering, so that if event A causes event B, B never appears to happen before or at the same time as A. dbx is available with the Sun Workshop Products.


prex should issue a notification when a process id has been automatically deleted from the filter set. There is a known bug in prex which can result in this mes- sage: Tracing shut down in target program due to an internal error - Please restart prex and target When prex runs as root, and the target process is not root, and the tracefile is placed in a directory where it cannot be removed and re-created (a directory with the sticky bit on, like /tmp),mm then the target process will not be able SunOS 5.8 Last change: 1 Nov 1999 14 User Commands prex(1) to open the tracefile when it needs to. This results in tracing being disabled. Changing any of the circumstances listed above should fix the problem. Either don't run prex as root, or run the tar- get process as root, or specify the tracefile in a directory other than /tmp. SunOS 5.8 Last change: 1 Nov 1999 15