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1 | \input texinfo @c -*-texinfo-*- |
2 | @c %**start of header | |
3 | @setfilename ust.info | |
4 | @settitle LTTng Userspace Tracer (UST) Manual | |
5 | @c %**end of header | |
6 | ||
7 | @copying | |
8 | This manual is for program, version version. | |
9 | ||
10 | Copyright @copyright{} copyright-owner. | |
11 | ||
12 | @quotation | |
13 | Permission is granted to ... | |
14 | @end quotation | |
15 | @end copying | |
16 | ||
17 | @titlepage | |
18 | @title LTTng Userspace Tracer (UST) Manual | |
19 | @c @subtitle subtitle-if-any | |
20 | @c @subtitle second-subtitle | |
21 | @c @author author | |
22 | ||
23 | @c The following two commands | |
24 | @c start the copyright page. | |
25 | @c @page | |
26 | @c @vskip 0pt plus 1filll | |
27 | @c @insertcopying | |
28 | ||
29 | @c Published by ... | |
30 | @end titlepage | |
31 | ||
32 | @c So the toc is printed at the start. | |
33 | @contents | |
34 | ||
35 | @ifnottex | |
36 | @node Top | |
37 | @top LTTng Userspace Tracer | |
38 | ||
39 | This manual is for UST 0.1. | |
40 | @end ifnottex | |
41 | ||
42 | @menu | |
43 | * Overview:: | |
44 | * Installation:: | |
45 | * Quick start:: | |
46 | * Instrumenting an application:: | |
47 | * Recording a trace:: | |
48 | * Viewing traces:: | |
49 | * Performance:: | |
50 | @c * Copying:: Your rights and freedoms. | |
51 | @end menu | |
52 | ||
53 | @node Overview | |
54 | @chapter Overview | |
55 | ||
56 | @menu | |
57 | * Supported platforms:: | |
58 | @end menu | |
59 | ||
60 | @node Supported platforms | |
61 | @section Supported platforms | |
62 | ||
63 | UST can currently trace applications running on Linux, on the x86-32 and x86-64 architectures. | |
64 | ||
65 | @node Installation | |
66 | @chapter Installation | |
67 | ||
68 | The LTTng userspace tracer is a library and a set of userspace tools. | |
69 | ||
70 | The following packages are required: | |
71 | ||
72 | @itemize @bullet | |
73 | @item | |
74 | ust | |
75 | ||
76 | This contains the tracing library, the ustd daemon, trace control tools | |
77 | and other helper tools. | |
78 | ||
79 | Repository: http://git.dorsal.polymtl.ca | |
80 | ||
81 | @item | |
82 | libkcompat | |
83 | ||
84 | This is a library that contains a userspace port of some kernel APIs. | |
85 | ||
86 | Repository: http://git.dorsal.polymtl.ca | |
87 | ||
88 | @item | |
89 | liburcu | |
90 | ||
91 | This is the userspace read-copy update library by Mathieu Desnoyers. | |
92 | ||
93 | Available in Debian as package liburcu-dev. | |
94 | ||
95 | Home page: http://lttng.org/?q=node/18 | |
96 | ||
97 | @item | |
98 | LTTV | |
99 | ||
100 | LTTV is a graphical (and text) viewer for LTTng traces. | |
101 | ||
102 | Home page: http://lttng.org | |
103 | ||
104 | @end itemize | |
105 | ||
106 | Libkcompat and liburcu should be installed first. UST may then be compiled | |
107 | and installed. LTTV has no dependency on the other packages; it may therefore | |
108 | be installed on a system which does not have UST installed. | |
109 | ||
110 | Refer to the README in each of these packages for installation instructions. | |
111 | ||
112 | @c @menu | |
113 | @c @end menu | |
114 | ||
115 | @node Quick start | |
116 | @chapter Quick start | |
117 | ||
118 | First, instrument a program with a marker. | |
119 | ||
120 | @example | |
121 | @verbatim | |
122 | ||
123 | #include <ust/marker.h> | |
124 | ||
125 | int main(int argc, char **argv) | |
126 | { | |
127 | int v; | |
128 | char *st; | |
129 | ||
130 | /* ... set values of v and st ... */ | |
131 | ||
132 | /* a marker: */ | |
133 | trace_mark(ust, myevent, "firstarg %d secondarg %s", v, st); | |
134 | ||
135 | /* a marker without arguments: */ | |
136 | trace_mark(ust, myotherevent, MARK_NOARGS); | |
137 | ||
138 | return 0; | |
139 | } | |
140 | ||
141 | @end verbatim | |
142 | @end example | |
143 | ||
144 | Then compile it in the regular way, linking it with libust. For example: | |
145 | ||
146 | @example | |
147 | gcc -o foo -lust foo.c | |
148 | @end example | |
149 | ||
150 | Run the program with @command{usttrace}. The @command{usttrace} output says where the trace | |
151 | was written. | |
152 | ||
153 | @example | |
154 | usttrace ./foo | |
155 | @end example | |
156 | ||
157 | Finally, open the trace in LTTV. | |
158 | ||
159 | @example | |
160 | lttv-gui -t /path/to/trace | |
161 | @end example | |
162 | ||
163 | The trace can also be dumped as text in the console: | |
164 | ||
165 | @example | |
166 | lttv -m textDump -t /path/to/trace | |
167 | @end example | |
168 | ||
169 | @node Instrumenting an application | |
170 | @chapter Instrumenting an application | |
171 | ||
172 | In order to record a trace of events occurring in a application, the | |
173 | application must be instrumented. Instrumentation points resemble function | |
174 | calls. When the program reaches an instrumentation point, an event is | |
175 | generated. | |
176 | ||
177 | There are no limitations on the type of code that may be instrumented. | |
178 | Multi-threaded programs may be instrumented without problem. Signal handlers | |
179 | may be instrumented as well. | |
180 | ||
181 | There are two APIs to instrument programs: markers and tracepoints. Markers are | |
182 | quick to add and are usually used for temporary instrumentation. Tracepoints | |
183 | provide a way to instrument code more cleanly and are suited for permanent | |
184 | instrumentation. | |
185 | ||
186 | In addition to executable programs, shared libraries may also be instrumented | |
187 | with the methods described in this chapter. | |
188 | ||
189 | @menu | |
190 | * Markers:: | |
191 | * Tracepoints:: | |
192 | @end menu | |
193 | ||
194 | @node Markers | |
195 | @section Markers | |
196 | ||
197 | Adding a marker is simply a matter of insert one line in the program. | |
198 | ||
199 | @example | |
200 | @verbatim | |
201 | #include <ust/marker.h> | |
202 | ||
203 | int main(int argc, char **argv) | |
204 | { | |
205 | int v; | |
206 | char *st; | |
207 | ||
208 | /* ... set values of v and st ... */ | |
209 | ||
210 | /* a marker: */ | |
211 | trace_mark(main, myevent, "firstarg %d secondarg %s", v, st); | |
212 | ||
213 | /* a marker without arguments: */ | |
214 | trace_mark(main, myotherevent, MARK_NOARGS); | |
215 | ||
216 | return 0; | |
217 | } | |
218 | @end verbatim | |
219 | @end example | |
220 | ||
221 | The invocation of the trace_mark() macro requires at least 3 arguments. The | |
222 | first, here "main", is the name of the event category. It is also the name of | |
223 | the channel the event will go in. The second, here "myevent" is the name of the | |
224 | event. The third is a format string that announces the names and the types of | |
225 | the event arguments. Its format resembles that of a printf() format string; it | |
226 | is described thoroughly in Appendix x. | |
227 | ||
228 | A given Marker may appear more than once in the same program. Other Markers may | |
229 | have the same name and a different format string, although this might induce | |
230 | some confusion at analysis time. | |
231 | ||
232 | @node Tracepoints | |
233 | @section Tracepoints | |
234 | ||
235 | The Tracepoints API uses the Markers, but provides a higher-level abstraction. | |
236 | Whereas the markers API provides limited type checking, the Tracepoints API | |
237 | provides more thorough type checking and discharges from the need to insert | |
238 | format strings directly in the code and to have format strings appear more than | |
239 | once if a given marker is reused. | |
240 | ||
241 | @quotation Note Although this example uses @emph{mychannel} as the channel, the | |
242 | only channel name currently supported with early tracing is @strong{ust}. The | |
243 | @command{usttrace} tool always uses the early tracing mode. When using manual | |
244 | mode without early tracing, any channel name may be used. @end quotation | |
245 | ||
246 | A function instrumented with a tracepoint looks like this: | |
247 | ||
248 | @example | |
249 | @verbatim | |
250 | #include "tp.h" | |
251 | ||
252 | void function() | |
253 | { | |
254 | int v; | |
255 | char *st; | |
256 | ||
257 | /* ... set values of v and st ... */ | |
258 | ||
259 | /* a tracepoint: */ | |
260 | trace_mychannel_myevent(v, st); | |
261 | } | |
262 | @end verbatim | |
263 | @end example | |
264 | ||
265 | Another file, here tp.h, contains declarations for the tracepoint. | |
266 | ||
267 | @example | |
268 | @verbatim | |
269 | #include <ust/tracepoint.h> | |
270 | ||
271 | DECLARE_TRACE(mychannel_myevent, TPPROTO(int v, char *st), | |
272 | TPARGS(v, st)); | |
273 | @end verbatim | |
274 | @end example | |
275 | ||
276 | A third file, here tp.c, contains definitions for the tracepoint. | |
277 | ||
278 | @example | |
279 | @verbatim | |
280 | #include <ust/marker.h> | |
281 | #include "tp.h" | |
282 | ||
283 | DEFINE_TRACE(mychannel_myevent); | |
284 | ||
285 | void mychannel_myevent_probe(int v, char *st) | |
286 | { | |
287 | trace_mark(mychannel, myevent, "v %d st %s", v, st); | |
288 | } | |
289 | ||
290 | static void __attribute__((constructor)) init() | |
291 | { | |
292 | register_trace_mychannel_myevent(mychannel_myevent_probe); | |
293 | } | |
294 | @end verbatim | |
295 | @end example | |
296 | ||
297 | Here, tp.h and tp.c could contain declarations and definitions for other | |
298 | tracepoints. The constructor would contain other register_* calls. | |
299 | ||
300 | @node Recording a trace | |
301 | @chapter Recording a trace | |
302 | ||
303 | @menu | |
304 | * Using @command{usttrace}:: | |
305 | * Setting up the recording manually:: | |
306 | * Using early tracing:: | |
307 | * Crash recovery:: | |
308 | * Tracing across @code{fork()} and @code{clone()}:: | |
309 | * Tracing programs and libraries that were not linked to libust:: | |
310 | @end menu | |
311 | ||
312 | @node Using @command{usttrace} | |
313 | @section Using @command{usttrace} | |
314 | ||
315 | The simplest way to record a trace is to use the @command{usttrace} script. An | |
316 | example is given in the quickstart above. | |
317 | ||
318 | The @command{usttrace} script automatically: | |
319 | @itemize @bullet | |
320 | @item creates a daemon | |
321 | @item enables all markers | |
322 | @item runs the command specified on the command line | |
323 | @item after the command ends, prints the location where the trace was saved | |
324 | @end itemize | |
325 | ||
326 | Each subdirectory of the save location contains the trace of one process that | |
327 | was generated by the command. The name of a subdirectory consists in the the PID | |
328 | of the process, followed by the timestamp of its creation. | |
329 | ||
330 | The save location also contains logs of the tracing. | |
331 | ||
332 | When using @command{usttrace}, the early tracing is always active, which means | |
333 | that the tracing is guaranteed to be started by the time the process enters its | |
334 | main() function. | |
335 | ||
336 | Several @command{usttrace}'s may be run simultaneously without risk of | |
337 | conflict. This facilitates the use of the tracer by idependent users on a | |
338 | system. Each instance of @command{usttrace} starts its own daemon which | |
339 | collects the events of the processes it creates. | |
340 | ||
341 | @node Setting up the recording manually | |
342 | @section Setting up the recording manually | |
343 | ||
344 | Instead of using @command{usttrace}, a trace may be recorded on an already | |
345 | running process. | |
346 | ||
347 | First the daemon must be started. | |
348 | ||
349 | @example | |
350 | @verbatim | |
351 | # Make sure the directory for the communication sockets exists. | |
352 | $ mkdir /tmp/ustsocks | |
353 | ||
354 | # Make sure the directory where ustd will write the trace exists. | |
355 | $ mkdir /tmp/trace | |
356 | ||
357 | # Start the daemon | |
358 | $ ustd | |
359 | ||
360 | # We assume the program we want to trace is already running and that | |
361 | # it has pid 1234. | |
362 | ||
363 | # List the available markers | |
364 | $ ustctl --list-markers 1234 | |
365 | # A column indicates 0 for an inactive marker and 1 for an active marker. | |
366 | ||
367 | # Enable a marker | |
368 | $ ustctl --enable-marker 1234 ust/mymark | |
369 | ||
370 | # Create a trace | |
371 | $ ustctl --create-trace 1234 | |
372 | ||
373 | # Start tracing | |
374 | $ ustctl --start-trace 1234 | |
375 | ||
376 | # Do things... | |
377 | ||
378 | # Stop tracing | |
379 | $ ustctl --stop-trace 1234 | |
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380 | |
381 | # Destroy the trace | |
382 | $ ustctl --destroy-trace 1234 | |
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383 | @end verbatim |
384 | @end example | |
385 | ||
386 | @node Using early tracing | |
387 | @section Using early tracing | |
388 | ||
389 | Early tracing consists in starting the tracing as early as possible in the | |
390 | program, so no events are lost between program start and the point where the | |
391 | command to start the tracing is given. When using early tracing, it is | |
392 | guaranteed that by the time the traced program enters its @code{main()} | |
393 | function, the tracing will be started. | |
394 | ||
395 | When using @command{usttrace}, the early tracing is always active. | |
396 | ||
397 | When using the manual mode (@command{ustctl}), early tracing is enabled using | |
398 | environment variables. Setting @env{UST_TRACE} to @code{1}, enables early | |
399 | tracing, while setting @env{UST_AUTOPROBE} to @code{1} enables all markers | |
400 | automatically. | |
401 | ||
402 | ||
403 | @node Crash recovery | |
404 | @section Crash recovery | |
405 | ||
406 | When a process being traced crashes, the daemon is able to recover all the | |
407 | events in its buffers that were successfully commited. This is possible because | |
408 | the buffers are in a shared memory segment which remains available to the | |
409 | daemon even after the termination of the traced process. | |
410 | ||
411 | @node Tracing across @code{fork()} and @code{clone()} | |
412 | @section Tracing across @code{fork()} and @code{clone()} | |
413 | ||
414 | Tracing across @code{clone()} when @code{CLONE_VM} is specified is supported | |
415 | without any particular action. | |
416 | ||
417 | When @code{clone()} is called without @code{CLONE_VM} or @code{fork()} is | |
418 | called, a new address space is created and the tracer must be notified to | |
419 | create new buffers for it. @strong{TODO: specify how to do it.} | |
420 | ||
421 | This can be done automatically (for @code{fork()} only for now), by | |
422 | @env{LD_PRELOAD}'ing @file{libinterfork.so}. This library intercepts calls to | |
423 | @code{fork()} and informs the tracer it is being called. When using | |
424 | @command{usttrace}, this is accomplied by specifying the @option{-f} command | |
425 | line argument. | |
426 | ||
427 | @node Tracing programs and libraries that were not linked to libust | |
428 | @section Tracing programs and libraries that were not linked to libust | |
429 | ||
430 | Todo. | |
431 | ||
432 | @node Performance | |
433 | @chapter Performance | |
434 | ||
435 | Todo. | |
436 | ||
437 | @node Viewing traces | |
438 | @chapter Viewing traces | |
439 | ||
440 | @bye |