1 \input texinfo @c -*-texinfo-*-
4 @settitle LTTng Userspace Tracer (UST) Manual
8 This manual is for program, version version.
10 Copyright @copyright{} copyright-owner.
13 Permission is granted to ...
18 @title LTTng Userspace Tracer (UST) Manual
19 @c @subtitle subtitle-if-any
20 @c @subtitle second-subtitle
23 @c The following two commands
24 @c start the copyright page.
26 @c @vskip 0pt plus 1filll
32 @c So the toc is printed at the start.
37 @top LTTng Userspace Tracer
39 This manual is for UST 0.14.
46 * Instrumenting an application::
51 * List of environment variables detected by libust::
53 @c * Copying:: Your rights and freedoms.
62 * Supported platforms::
68 The LTTng Userspace Tracer (UST) is a library accompanied by a set of tools to
71 Code may be instrumented with either markers or tracepoints. A highly efficient
72 lockless tracer records these events to a trace buffers. These buffers are reaped
73 by a deamon which writes trace data to disk.
75 High performance is achieved by the use of lockless buffering algorithms, RCU and
76 per-cpu buffers. In addition, special care is taken to minize cache impact.
80 The LTTng Userspace Tracer is intended to be linkable to open source software
81 as well as to proprietary applications. This was accomplished by licensing
82 the code that needs to be linked to the traced program as @acronym{LGPL}.
84 Components licensed as LGPL v2.1:
91 Components licensed as GPL v2:
98 @node Supported platforms
99 @section Supported platforms
101 UST can currently trace applications running on Linux, on the x86-32, x86-64
102 and PowerPC 32 architectures.
105 @chapter Installation
107 The LTTng userspace tracer is a library and a set of userspace tools.
109 The following packages are required:
115 This contains the tracing library, the ust-consumerd daemon, trace control tools
116 and other helper tools.
118 Repository: @url{http://lttng.org/ust}
123 This is the userspace read-copy update library by Mathieu Desnoyers.
125 Available in Debian as package liburcu-dev.
127 Home page: @url{http://lttng.org/urcu}
132 LTTV is a graphical (and text) viewer for LTTng traces.
134 Home page: @url{http://lttng.org}
138 Liburcu should be installed first. UST may then be compiled and installed. LTTV
139 has no dependency on the other packages; it may therefore be installed on a
140 system which does not have UST installed.
142 Refer to the README in each of these packages for installation instructions.
150 First, instrument a program with a marker.
155 #include <ust/marker.h>
157 int main(int argc, char **argv)
162 /* ... set values of v and st ... */
165 ust_marker(myevent, "firstarg %d secondarg %s", v, st);
167 /* a marker without arguments: */
168 ust_marker(myotherevent, MARK_NOARGS);
176 Then compile it in the regular way, linking it with libust. For example:
179 gcc -o foo -lust foo.c
182 Run the program with @command{usttrace}. The @command{usttrace} output says where the trace
189 Finally, open the trace in LTTV.
192 lttv-gui -t /path/to/trace
195 The trace can also be dumped as text in the console:
198 lttv -m textDump -t /path/to/trace
201 @node Instrumenting an application
202 @chapter Instrumenting an application
204 In order to record a trace of events occurring in a application, the
205 application must be instrumented. Instrumentation points resemble function
206 calls. When the program reaches an instrumentation point, an event is
209 There are no limitations on the type of code that may be instrumented.
210 Multi-threaded programs may be instrumented without problem. Signal handlers
211 may be instrumented as well.
213 There are two APIs to instrument programs: markers and tracepoints. Markers are
214 quick to add and are usually used for temporary instrumentation. Tracepoints
215 provide a way to instrument code more cleanly and are suited for permanent
218 In addition to executable programs, shared libraries may also be instrumented
219 with the methods described in this chapter.
229 Adding a marker is simply a matter of inserting one line in the program.
233 #include <ust/marker.h>
235 int main(int argc, char **argv)
240 /* ... set values of v and st ... */
243 ust_marker(myevent, "firstarg %d secondarg %s", v, st);
245 /* another marker without arguments: */
246 ust_marker(myotherevent, MARK_NOARGS);
253 The invocation of the ust_marker() macro requires at least 2 arguments. The
254 first, "myevent", is the name of the event. The second is a format string
255 that announces the names and the types of the event arguments. Its
256 format resembles that of a printf() format string; it is described
257 thoroughly in Appendix x.
259 A given Marker may appear more than once in the same program. Other Markers may
260 have the same name and a different format string, although this might induce
261 some confusion at analysis time.
266 The Tracepoint API is superseded by TRACEPOINT_EVENT() (which uses the
267 Tracepoints internally). At this stage, TRACEPOINT_EVENT() is work in
268 progress. While we complete this API, please use the ust_marker() API
269 provided by ust/marker.h.
271 @node Recording a trace
272 @chapter Recording a trace
275 * Using @command{usttrace}::
276 * Setting up the recording manually::
277 * Using early tracing::
279 * Tracing across @code{fork()} and @code{clone()}::
280 * Tracing programs and libraries that were not linked to libust::
283 @node Using @command{usttrace}
284 @section Using @command{usttrace}
286 The simplest way to record a trace is to use the @command{usttrace} script. An
287 example is given in the quickstart above.
289 The @command{usttrace} script automatically:
291 @item creates a daemon
292 @item enables all markers
293 @item runs the command specified on the command line
294 @item after the command ends, prints the location where the trace was saved
297 Each subdirectory of the save location contains the trace of one process that
298 was generated by the command. The name of a subdirectory consists in the the PID
299 of the process, followed by the timestamp of its creation.
301 The save location also contains logs of the tracing.
303 When using @command{usttrace}, the early tracing is always active, which means
304 that the tracing is guaranteed to be started by the time the process enters its
305 @code{main()} function.
307 Several @command{usttrace}'s may be run simultaneously without risk of
308 conflict. This facilitates the use of the tracer by idependent users on a
309 system. Each instance of @command{usttrace} starts its own daemon which
310 collects the events of the processes it creates.
312 @node Setting up the recording manually
313 @section Setting up the recording manually
315 Instead of using @command{usttrace}, a trace may be recorded on an already
318 First the daemon must be started.
322 # Make sure the directory for the communication sockets exists.
323 $ mkdir /tmp/ustsocks
325 # Make sure the directory where ust-consumerd will write the trace exists.
331 # We assume the program we want to trace is already running and that
334 # List the available markers
335 $ ustctl list-markers 1234
336 # A column indicates 0 for an inactive marker and 1 for an active marker.
339 $ ustctl enable-marker 1234 auto ust/mymark
342 $ ustctl create-trace 1234 auto
345 $ ustctl start-trace 1234 auto
350 $ ustctl stop-trace 1234 auto
353 $ ustctl destroy-trace 1234 auto
357 For more information about the manual mode, see the ustctl(1) man page.
359 @node Using early tracing
360 @section Using early tracing
362 Early tracing consists in starting the tracing as early as possible in the
363 program, so no events are lost between program start and the point where the
364 command to start the tracing is given. When using early tracing, it is
365 guaranteed that by the time the traced program enters its @code{main()}
366 function, the tracing will be started.
368 When using @command{usttrace}, the early tracing is always active.
370 When using the manual mode (@command{ustctl}), early tracing is enabled using
371 environment variables. Setting @env{UST_TRACE} to @code{1}, enables early
372 tracing, while setting @env{UST_AUTOPROBE} to @code{1} enables all markers
377 @section Crash recovery
379 When a process being traced crashes, the daemon is able to recover all the
380 events in its buffers that were successfully commited. This is possible because
381 the buffers are in a shared memory segment which remains available to the
382 daemon even after the termination of the traced process.
384 @node Tracing across @code{fork()} and @code{clone()}
385 @section Tracing across @code{fork()} and @code{clone()}
387 Tracing across @code{clone()} when the @code{CLONE_VM} flag is specified is
388 supported without any particular action.
390 When @code{clone()} is called without @code{CLONE_VM} or @code{fork()} is
391 called, a new address space is created and the tracer must be notified to
392 create new buffers for it.
394 This can be done automatically, by @env{LD_PRELOAD}'ing @file{libinterfork.so}.
395 This library intercepts calls to @code{fork()} and informs the tracer it is
396 being called. When using @command{usttrace}, this is accomplied by specifying
397 the @option{-f} command line argument.
399 Alternatively, the program can call @code{ust_before_fork()} before calling
400 @code{fork()} or @code{clone()} with @code{CLONE_VM}. After the call,
401 @code{ust_after_fork_parent()} must be called in the parent process and
402 @code{ust_after_fork_child()} must be called in the child process.
405 @node Tracing programs and libraries that were not linked to libust
406 @section Tracing programs and libraries that were not linked to libust
408 Some programs need to be traced even though they were not linked to libust
409 either because they were not instrumented or because it was not practical.
411 An executable that is not instrumented can still yield interesting traces when
412 at least one of its dynamic libraries is instrumented. It is also possible to
413 trace certain function calls by intercepting them with a specially crafted
414 library that is linked with @env{LD_PRELOAD} at program start.
416 In any case, a program that was not linked to libust at compile time must be
417 linked to it at run time with @env{LD_PRELOAD}. This can be accomplished with
418 @command{usttrace}'s @option{-l} option. It can also be done by setting the
419 @env{LD_PRELOAD} environment variable on the command line. For example:
423 # Run ls with usttrace, LD_PRELOAD'ing libust
424 # (assuming one of the libraries used by ls is instrumented).
427 # Run ls, manually adding the LD_PRELOAD.
428 $ LD_PRELOAD=/usr/local/lib/libust.so.0 ls
439 @chapter Viewing traces
441 Traces may be viewed with LTTV. An example of command for launching LTTV is
442 given in the quickstart.
445 * Viewing multiple traces::
446 * Combined kernel-userspace tracing::
449 @node Viewing multiple traces
450 @section Viewing multiple traces
452 When tracing multi-process applications or several applications simultaneously,
453 more than one trace will be obtained. LTTV can open and display all these
454 traces simultaneously.
456 @node Combined kernel-userspace tracing
457 @section Combined kernel-userspace tracing
459 In addition to multiple userspace traces, LTTV can open a kernel trace recorded
460 with the LTTng kernel tracer. This provides events that enable the rendering of
461 the Control Flow View and the Resource View.
463 When doing so, it is necessary to use the same time source for the kernel
464 tracer as well as the userspace tracer. Currently, the recommended method is to
465 use the timestamp counter for both. The TSC can however only be used on architectures
466 where it is synchronized across cores.
469 @chapter Resource Usage
471 The purpose of this section is to give an overview of the resource usage of libust. For
472 a developer, knowing this can be important: because libust is linked with applications, it
473 needs to share some resources with it. Some applications may make some assumptions that are in
474 conflict with libust's usage of resources.
476 In practice however, libust is designed to be transparent and is compatible
477 with the vast majority of applications. This means no changes are required in
478 the application (or library) being linked to libust.
480 Libust is initialized by a constructor, which by definition runs before the
481 @code{main()} function of the application starts. This constructor creates a
482 thread called the @emph{listener thread}. The listener thread initializes a
483 named socket and waits for connections for ust-consumerd or ustctl.
485 Libust-specific code may:
487 @item use @code{malloc()} and @code{free()}
488 @item map shared memory segment in the process adress space
489 @item intercept some library calls, specifically @code{fork()} and @code{clone()}
490 @item do interprocess communication with the daemon or ustctl
491 @item create and open named sockets
497 @item handle any signal (all signals are blocked in the listener thread)
498 @item change any process-wide setting that could confuse the application
501 @node List of environment variables detected by libust
502 @appendix List of environment variables detected by libust
504 The behavior of tracing can be influenced by setting special environment
505 variables in the environment of the traced application. This section
506 describes these variables.
513 If set to 1, start tracing as soon as the program starts. Tracing is
514 guaranteed to be started by the time the @code{main()} function starts.
519 If set to @code{1}, enable all markers by the time the @code{main()} function starts.
522 @env{UST_AUTOCOLLECT}
524 If set to @code{0}, disable notification of daemon on trace start. Useful for
530 If set to @code{1}, enable overwriting of buffers on overrun.
535 If set, defines the default number of subbuffers per buffer.
538 @env{UST_SUBBUF_SIZE}
540 If set, defines the default size of subbuffers, in bytes.
544 @node GDB integration
545 @appendix GDB integration
547 GDB, the GNU Debugger, can use UST markers as GDB tracepoints (note GDB has its
548 own concept of tracepoint). This feature is called GDB Static Tracepoints. When
549 a GDB tracepoint is hit, GDB collects the marker arguments, as well as the
550 state of the registers. Support for GDB is currently work in progress.