| 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 | * License:: |
| 58 | * Supported platforms:: |
| 59 | @end menu |
| 60 | |
| 61 | @node License |
| 62 | @section License |
| 63 | The LTTng Userspace Tracer is intended to be linkable to open source software |
| 64 | as well as to proprietary applications. This was accomplished by licensing |
| 65 | the code that needs to be linked to the traced program as @acronym{LGPL}. |
| 66 | |
| 67 | The @file{libust} library, including its headers, are licensed as @acronym{GNU} |
| 68 | @acronym{LGPL} v2.1. It is also the case of some other helper libraries |
| 69 | (@file{libmallocwrap}, @file{libinterfork}, @file{libustcomm}) that need to be linked to the traced |
| 70 | program. |
| 71 | |
| 72 | The accompanying tools of the @acronym{UST} package are licensed as |
| 73 | @acronym{GNU} @acronym{GPL} v2. These tools include the @file{ustctl} trace |
| 74 | control program and the @file{ustd} daemon. |
| 75 | |
| 76 | @node Supported platforms |
| 77 | @section Supported platforms |
| 78 | |
| 79 | UST can currently trace applications running on Linux, on the x86-32 and x86-64 architectures. |
| 80 | |
| 81 | @node Installation |
| 82 | @chapter Installation |
| 83 | |
| 84 | The LTTng userspace tracer is a library and a set of userspace tools. |
| 85 | |
| 86 | The following packages are required: |
| 87 | |
| 88 | @itemize @bullet |
| 89 | @item |
| 90 | ust |
| 91 | |
| 92 | This contains the tracing library, the ustd daemon, trace control tools |
| 93 | and other helper tools. |
| 94 | |
| 95 | Repository: http://git.dorsal.polymtl.ca |
| 96 | |
| 97 | @item |
| 98 | libkcompat |
| 99 | |
| 100 | This is a library that contains a userspace port of some kernel APIs. |
| 101 | |
| 102 | Repository: http://git.dorsal.polymtl.ca |
| 103 | |
| 104 | @item |
| 105 | liburcu |
| 106 | |
| 107 | This is the userspace read-copy update library by Mathieu Desnoyers. |
| 108 | |
| 109 | Available in Debian as package liburcu-dev. |
| 110 | |
| 111 | Home page: http://lttng.org/?q=node/18 |
| 112 | |
| 113 | @item |
| 114 | LTTV |
| 115 | |
| 116 | LTTV is a graphical (and text) viewer for LTTng traces. |
| 117 | |
| 118 | Home page: http://lttng.org |
| 119 | |
| 120 | @end itemize |
| 121 | |
| 122 | Libkcompat and liburcu should be installed first. UST may then be compiled |
| 123 | and installed. LTTV has no dependency on the other packages; it may therefore |
| 124 | be installed on a system which does not have UST installed. |
| 125 | |
| 126 | Refer to the README in each of these packages for installation instructions. |
| 127 | |
| 128 | @c @menu |
| 129 | @c @end menu |
| 130 | |
| 131 | @node Quick start |
| 132 | @chapter Quick start |
| 133 | |
| 134 | First, instrument a program with a marker. |
| 135 | |
| 136 | @example |
| 137 | @verbatim |
| 138 | |
| 139 | #include <ust/marker.h> |
| 140 | |
| 141 | int main(int argc, char **argv) |
| 142 | { |
| 143 | int v; |
| 144 | char *st; |
| 145 | |
| 146 | /* ... set values of v and st ... */ |
| 147 | |
| 148 | /* a marker: */ |
| 149 | trace_mark(ust, myevent, "firstarg %d secondarg %s", v, st); |
| 150 | |
| 151 | /* a marker without arguments: */ |
| 152 | trace_mark(ust, myotherevent, MARK_NOARGS); |
| 153 | |
| 154 | return 0; |
| 155 | } |
| 156 | |
| 157 | @end verbatim |
| 158 | @end example |
| 159 | |
| 160 | Then compile it in the regular way, linking it with libust. For example: |
| 161 | |
| 162 | @example |
| 163 | gcc -o foo -lust foo.c |
| 164 | @end example |
| 165 | |
| 166 | Run the program with @command{usttrace}. The @command{usttrace} output says where the trace |
| 167 | was written. |
| 168 | |
| 169 | @example |
| 170 | usttrace ./foo |
| 171 | @end example |
| 172 | |
| 173 | Finally, open the trace in LTTV. |
| 174 | |
| 175 | @example |
| 176 | lttv-gui -t /path/to/trace |
| 177 | @end example |
| 178 | |
| 179 | The trace can also be dumped as text in the console: |
| 180 | |
| 181 | @example |
| 182 | lttv -m textDump -t /path/to/trace |
| 183 | @end example |
| 184 | |
| 185 | @node Instrumenting an application |
| 186 | @chapter Instrumenting an application |
| 187 | |
| 188 | In order to record a trace of events occurring in a application, the |
| 189 | application must be instrumented. Instrumentation points resemble function |
| 190 | calls. When the program reaches an instrumentation point, an event is |
| 191 | generated. |
| 192 | |
| 193 | There are no limitations on the type of code that may be instrumented. |
| 194 | Multi-threaded programs may be instrumented without problem. Signal handlers |
| 195 | may be instrumented as well. |
| 196 | |
| 197 | There are two APIs to instrument programs: markers and tracepoints. Markers are |
| 198 | quick to add and are usually used for temporary instrumentation. Tracepoints |
| 199 | provide a way to instrument code more cleanly and are suited for permanent |
| 200 | instrumentation. |
| 201 | |
| 202 | In addition to executable programs, shared libraries may also be instrumented |
| 203 | with the methods described in this chapter. |
| 204 | |
| 205 | @menu |
| 206 | * Markers:: |
| 207 | * Tracepoints:: |
| 208 | @end menu |
| 209 | |
| 210 | @node Markers |
| 211 | @section Markers |
| 212 | |
| 213 | Adding a marker is simply a matter of insert one line in the program. |
| 214 | |
| 215 | @example |
| 216 | @verbatim |
| 217 | #include <ust/marker.h> |
| 218 | |
| 219 | int main(int argc, char **argv) |
| 220 | { |
| 221 | int v; |
| 222 | char *st; |
| 223 | |
| 224 | /* ... set values of v and st ... */ |
| 225 | |
| 226 | /* a marker: */ |
| 227 | trace_mark(main, myevent, "firstarg %d secondarg %s", v, st); |
| 228 | |
| 229 | /* a marker without arguments: */ |
| 230 | trace_mark(main, myotherevent, MARK_NOARGS); |
| 231 | |
| 232 | return 0; |
| 233 | } |
| 234 | @end verbatim |
| 235 | @end example |
| 236 | |
| 237 | The invocation of the trace_mark() macro requires at least 3 arguments. The |
| 238 | first, here "main", is the name of the event category. It is also the name of |
| 239 | the channel the event will go in. The second, here "myevent" is the name of the |
| 240 | event. The third is a format string that announces the names and the types of |
| 241 | the event arguments. Its format resembles that of a printf() format string; it |
| 242 | is described thoroughly in Appendix x. |
| 243 | |
| 244 | A given Marker may appear more than once in the same program. Other Markers may |
| 245 | have the same name and a different format string, although this might induce |
| 246 | some confusion at analysis time. |
| 247 | |
| 248 | @node Tracepoints |
| 249 | @section Tracepoints |
| 250 | |
| 251 | The Tracepoints API uses the Markers, but provides a higher-level abstraction. |
| 252 | Whereas the markers API provides limited type checking, the Tracepoints API |
| 253 | provides more thorough type checking and discharges from the need to insert |
| 254 | format strings directly in the code and to have format strings appear more than |
| 255 | once if a given marker is reused. |
| 256 | |
| 257 | @quotation Note Although this example uses @emph{mychannel} as the channel, the |
| 258 | only channel name currently supported with early tracing is @strong{ust}. The |
| 259 | @command{usttrace} tool always uses the early tracing mode. When using manual |
| 260 | mode without early tracing, any channel name may be used. @end quotation |
| 261 | |
| 262 | A function instrumented with a tracepoint looks like this: |
| 263 | |
| 264 | @example |
| 265 | @verbatim |
| 266 | #include "tp.h" |
| 267 | |
| 268 | void function() |
| 269 | { |
| 270 | int v; |
| 271 | char *st; |
| 272 | |
| 273 | /* ... set values of v and st ... */ |
| 274 | |
| 275 | /* a tracepoint: */ |
| 276 | trace_mychannel_myevent(v, st); |
| 277 | } |
| 278 | @end verbatim |
| 279 | @end example |
| 280 | |
| 281 | Another file, here tp.h, contains declarations for the tracepoint. |
| 282 | |
| 283 | @example |
| 284 | @verbatim |
| 285 | #include <ust/tracepoint.h> |
| 286 | |
| 287 | DECLARE_TRACE(mychannel_myevent, TPPROTO(int v, char *st), |
| 288 | TPARGS(v, st)); |
| 289 | @end verbatim |
| 290 | @end example |
| 291 | |
| 292 | A third file, here tp.c, contains definitions for the tracepoint. |
| 293 | |
| 294 | @example |
| 295 | @verbatim |
| 296 | #include <ust/marker.h> |
| 297 | #include "tp.h" |
| 298 | |
| 299 | DEFINE_TRACE(mychannel_myevent); |
| 300 | |
| 301 | void mychannel_myevent_probe(int v, char *st) |
| 302 | { |
| 303 | trace_mark(mychannel, myevent, "v %d st %s", v, st); |
| 304 | } |
| 305 | |
| 306 | static void __attribute__((constructor)) init() |
| 307 | { |
| 308 | register_trace_mychannel_myevent(mychannel_myevent_probe); |
| 309 | } |
| 310 | @end verbatim |
| 311 | @end example |
| 312 | |
| 313 | Here, tp.h and tp.c could contain declarations and definitions for other |
| 314 | tracepoints. The constructor would contain other register_* calls. |
| 315 | |
| 316 | @node Recording a trace |
| 317 | @chapter Recording a trace |
| 318 | |
| 319 | @menu |
| 320 | * Using @command{usttrace}:: |
| 321 | * Setting up the recording manually:: |
| 322 | * Using early tracing:: |
| 323 | * Crash recovery:: |
| 324 | * Tracing across @code{fork()} and @code{clone()}:: |
| 325 | * Tracing programs and libraries that were not linked to libust:: |
| 326 | @end menu |
| 327 | |
| 328 | @node Using @command{usttrace} |
| 329 | @section Using @command{usttrace} |
| 330 | |
| 331 | The simplest way to record a trace is to use the @command{usttrace} script. An |
| 332 | example is given in the quickstart above. |
| 333 | |
| 334 | The @command{usttrace} script automatically: |
| 335 | @itemize @bullet |
| 336 | @item creates a daemon |
| 337 | @item enables all markers |
| 338 | @item runs the command specified on the command line |
| 339 | @item after the command ends, prints the location where the trace was saved |
| 340 | @end itemize |
| 341 | |
| 342 | Each subdirectory of the save location contains the trace of one process that |
| 343 | was generated by the command. The name of a subdirectory consists in the the PID |
| 344 | of the process, followed by the timestamp of its creation. |
| 345 | |
| 346 | The save location also contains logs of the tracing. |
| 347 | |
| 348 | When using @command{usttrace}, the early tracing is always active, which means |
| 349 | that the tracing is guaranteed to be started by the time the process enters its |
| 350 | main() function. |
| 351 | |
| 352 | Several @command{usttrace}'s may be run simultaneously without risk of |
| 353 | conflict. This facilitates the use of the tracer by idependent users on a |
| 354 | system. Each instance of @command{usttrace} starts its own daemon which |
| 355 | collects the events of the processes it creates. |
| 356 | |
| 357 | @node Setting up the recording manually |
| 358 | @section Setting up the recording manually |
| 359 | |
| 360 | Instead of using @command{usttrace}, a trace may be recorded on an already |
| 361 | running process. |
| 362 | |
| 363 | First the daemon must be started. |
| 364 | |
| 365 | @example |
| 366 | @verbatim |
| 367 | # Make sure the directory for the communication sockets exists. |
| 368 | $ mkdir /tmp/ustsocks |
| 369 | |
| 370 | # Make sure the directory where ustd will write the trace exists. |
| 371 | $ mkdir /tmp/trace |
| 372 | |
| 373 | # Start the daemon |
| 374 | $ ustd |
| 375 | |
| 376 | # We assume the program we want to trace is already running and that |
| 377 | # it has pid 1234. |
| 378 | |
| 379 | # List the available markers |
| 380 | $ ustctl --list-markers 1234 |
| 381 | # A column indicates 0 for an inactive marker and 1 for an active marker. |
| 382 | |
| 383 | # Enable a marker |
| 384 | $ ustctl --enable-marker 1234 ust/mymark |
| 385 | |
| 386 | # Create a trace |
| 387 | $ ustctl --create-trace 1234 |
| 388 | |
| 389 | # Start tracing |
| 390 | $ ustctl --start-trace 1234 |
| 391 | |
| 392 | # Do things... |
| 393 | |
| 394 | # Stop tracing |
| 395 | $ ustctl --stop-trace 1234 |
| 396 | |
| 397 | # Destroy the trace |
| 398 | $ ustctl --destroy-trace 1234 |
| 399 | @end verbatim |
| 400 | @end example |
| 401 | |
| 402 | @node Using early tracing |
| 403 | @section Using early tracing |
| 404 | |
| 405 | Early tracing consists in starting the tracing as early as possible in the |
| 406 | program, so no events are lost between program start and the point where the |
| 407 | command to start the tracing is given. When using early tracing, it is |
| 408 | guaranteed that by the time the traced program enters its @code{main()} |
| 409 | function, the tracing will be started. |
| 410 | |
| 411 | When using @command{usttrace}, the early tracing is always active. |
| 412 | |
| 413 | When using the manual mode (@command{ustctl}), early tracing is enabled using |
| 414 | environment variables. Setting @env{UST_TRACE} to @code{1}, enables early |
| 415 | tracing, while setting @env{UST_AUTOPROBE} to @code{1} enables all markers |
| 416 | automatically. |
| 417 | |
| 418 | |
| 419 | @node Crash recovery |
| 420 | @section Crash recovery |
| 421 | |
| 422 | When a process being traced crashes, the daemon is able to recover all the |
| 423 | events in its buffers that were successfully commited. This is possible because |
| 424 | the buffers are in a shared memory segment which remains available to the |
| 425 | daemon even after the termination of the traced process. |
| 426 | |
| 427 | @node Tracing across @code{fork()} and @code{clone()} |
| 428 | @section Tracing across @code{fork()} and @code{clone()} |
| 429 | |
| 430 | Tracing across @code{clone()} when @code{CLONE_VM} is specified is supported |
| 431 | without any particular action. |
| 432 | |
| 433 | When @code{clone()} is called without @code{CLONE_VM} or @code{fork()} is |
| 434 | called, a new address space is created and the tracer must be notified to |
| 435 | create new buffers for it. @strong{TODO: specify how to do it.} |
| 436 | |
| 437 | This can be done automatically (for @code{fork()} only for now), by |
| 438 | @env{LD_PRELOAD}'ing @file{libinterfork.so}. This library intercepts calls to |
| 439 | @code{fork()} and informs the tracer it is being called. When using |
| 440 | @command{usttrace}, this is accomplied by specifying the @option{-f} command |
| 441 | line argument. |
| 442 | |
| 443 | @node Tracing programs and libraries that were not linked to libust |
| 444 | @section Tracing programs and libraries that were not linked to libust |
| 445 | |
| 446 | Todo. |
| 447 | |
| 448 | @node Performance |
| 449 | @chapter Performance |
| 450 | |
| 451 | Todo. |
| 452 | |
| 453 | @node Viewing traces |
| 454 | @chapter Viewing traces |
| 455 | |
| 456 | @bye |