doc/man/lttng-ust.3

   1 .TH "LTTNG-UST" "3" "February 16, 2012" "" ""
   2
   3 .SH "NAME"
   4 lttng-ust \(em Linux Trace Toolkit Next Generation User-Space Tracer 2.x
   5
   6 .SH "SYNOPSIS"
   7
   8 .PP
   9 .nf
  10 Link liblttng-ust.so with applications, following this manpage.
  11 .fi
  12 .SH "DESCRIPTION"
  13
  14 .PP
  15 LTTng-UST, the Linux Trace Toolkit Next Generation Userspace Tracer, is a
  16 port of the low-overhead tracing capabilities of the LTTng kernel tracer
  17 to user-space. The library "liblttng-ust" enables tracing of
  18 applications and libraries.
  19
  20 .SH "USAGE WITH TRACEF"
  21 .PP
  22 The simplest way to add instrumentation to your code is by far the
  23 tracef() API. To do it, in a nutshell:
  24
  25 1) #include <lttng/tracef.h>
  26
  27 2) /* in your code, use like a printf */
  28    tracef("my message, this integer %d", 1234);
  29
  30 3) Link your program against liblttng-ust.so.
  31
  32 4) Enable UST events when tracing with the following sequence of commands
  33    from lttng-tools:
  34
  35    lttng create
  36    lttng enable-event -u -a
  37    lttng start
  38    [... run your program ...]
  39    lttng stop
  40    lttng view
  41
  42 That's it!
  43
  44 If you want to have more flexibility and control on the event names,
  45 payload typing, etc, you can continue reading on and use the tracepoints
  46 below. "tracef()" is there for quick and dirty ad hoc instrumentation,
  47 whereas tracepoint.h is meant for thorough instrumentation of a code
  48 base to be integrated with an upstream project.
  49 .PP
  50
  51 .SH "USAGE WITH TRACELOG"
  52 .PP
  53 If you want to migrate existing logging (info, errors, ...)
  54 to LTTng UST, you can use the tracelog() interface.
  55 To do it, in a nutshell:
  56
  57 1) #include <lttng/tracelog.h>
  58
  59 2) /* in your code, use like a printf, with extra loglevel info. */
  60    tracelog(TRACE_INFO, "Message with integer %d", 1234);
  61
  62 3) Link your program against liblttng-ust.so.
  63
  64 4) Enable UST events when tracing with the following sequence of commands
  65    from lttng-tools:
  66
  67    lttng create
  68    lttng enable-event -u "lttng_ust_tracelog:*"
  69    lttng start
  70    [... run your program ...]
  71    lttng stop
  72    lttng view
  73
  74 That's it!
  75
  76 You can replace the enable-event line above with a selection of
  77 loglevels, e.g.:
  78
  79    lttng enable-event -u -a --loglevel TRACE_INFO
  80
  81 Which will gather all events from TRACE_INFO and more important
  82 loglevels.
  83
  84 .PP
  85
  86 .SH "USAGE WITH TRACEPOINT"
  87 .PP
  88 The simple way to generate the lttng-ust tracepoint probes is to use the
  89 lttng-gen-tp(1) tool. See the lttng-gen-tp(1) manpage for explanation.
  90 .PP
  91
  92 .PP
  93 Here is the way to do it manually, without the lttng-gen-tp(1) helper
  94 script, through an example:
  95 .PP
  96
  97 .SH "CREATION OF TRACEPOINT PROVIDER"
  98
  99 .nf
 100
 101 To create a tracepoint provider, within a build tree similar to
 102 examples/easy-ust installed with lttng-ust documentation, see
 103 sample_component_provider.h for the general layout. You will need to
 104 define TRACEPOINT_CREATE_PROBES before including your tracepoint
 105 provider probe in one source file of your application. See tp.c from
 106 easy-ust for an example of a tracepoint probe source file. This manpage
 107 will focus on the various types that can be recorded into a trace
 108 event:
 109
 110 TRACEPOINT_EVENT(
 111         /*
 112          * provider name, not a variable but a string starting with a
 113          * letter and containing either letters, numbers or underscores.
 114          * Needs to be the same as TRACEPOINT_PROVIDER. Needs to
 115          * follow the namespacing guide-lines in lttng/tracepoint.h:
 116          *
 117          * Must be included before include tracepoint provider
 118          * ex.: project_event
 119          * ex.: project_component_event
 120          *
 121          * Optional company name goes here
 122          *  ex.: com_efficios_project_component_event
 123          *
 124          * In this example, "sample" is the project, and "component" is the
 125          * component.
 126          */
 127         sample_component,
 128
 129         /*
 130          * tracepoint name, characters permitted follow the same
 131          * constraints as the provider name. The name of this example
 132          * event is "sample_event".
 133          */
 134         sample_event,
 135
 136         /*
 137          * TP_ARGS macro contains the arguments passed for the tracepoint
 138          * it is in the following format
 139          *            TP_ARGS(type1, name1, type2, name2, ... type10,
 140                                  name10)
 141          * where there can be from zero to ten elements.
 142          * typeN is the datatype, such as int, struct or double **.
 143          * name is the variable name (in "int myInt" the name would be
 144          * myint)
 145          *            TP_ARGS() is valid to mean no arguments
 146          *            TP_ARGS(void) is valid too
 147          */
 148         TP_ARGS(int, anint, int, netint, long *, values,
 149                  char *, text, size_t, textlen,
 150                  double, doublearg, float, floatarg),
 151
 152         /*
 153          * TP_FIELDS describes how to write the fields of the trace event.
 154          * You can put expressions in the "argument expression" area,
 155          * typically using the input arguments from TP_ARGS.
 156          */
 157         TP_FIELDS(
 158                 /*
 159                  * ctf_integer: standard integer field.
 160                  * args: (type, field name, argument expression)
 161                  */
 162                 ctf_integer(int, intfield, anint)
 163                 ctf_integer(long, longfield, anint)
 164
 165                 /*
 166                  * ctf_integer_hex: integer field printed as hexadecimal.
 167                  * args: (type, field name, argument expression)
 168                  */
 169                 ctf_integer_hex(int, intfield2, anint)
 170
 171                 /*
 172                  * ctf_integer_network: integer field in network byte
 173                  * order. (_hex: printed as hexadecimal too)
 174                  * args: (type, field name, argument expression)
 175                  */
 176                 ctf_integer_network(int, netintfield, netint)
 177                 ctf_integer_network_hex(int, netintfieldhex, netint)
 178
 179                 /*
 180                  * ctf_array: a statically-sized array.
 181                  * args: (type, field name, argument expression, value)
 182                  */
 183                 ctf_array(long, arrfield1, values, 3)
 184
 185                 /*
 186                  * ctf_array_text: a statically-sized array, printed as
 187                  * a string. No need to be terminated by a null
 188                  * character.
 189                  * Behavior is undefined if "text" argument is NULL.
 190                  */
 191                 ctf_array_text(char, arrfield2, text, 10)
 192
 193                 /*
 194                  * ctf_sequence: a dynamically-sized array.
 195                  * args: (type, field name, argument expression,
 196                  *      type of length expression, length expression)
 197                  * The "type of length expression" needs to be an
 198                  * unsigned type. As a reminder, "unsigned char" should
 199                  * be preferred to "char", since the signedness of
 200                  * "char" is implementation-defined.
 201                  * Behavior is undefined if "text" argument is NULL.
 202                  */
 203                 ctf_sequence(char, seqfield1, text,
 204                              size_t, textlen)
 205
 206                 /*
 207                  * ctf_sequence_text: a dynamically-sized array, printed
 208                  * as string. No need to be null-terminated.
 209                  * Behavior is undefined if "text" argument is NULL.
 210                  */
 211                 ctf_sequence_text(char, seqfield2, text,
 212                              size_t, textlen)
 213
 214                 /*
 215                  * ctf_string: null-terminated string.
 216                  * args: (field name, argument expression)
 217                  * Behavior is undefined if "text" argument is NULL.
 218                  */
 219                 ctf_string(stringfield, text)
 220
 221                 /*
 222                  * ctf_float: floating-point number.
 223                  * args: (type, field name, argument expression)
 224                  */
 225                 ctf_float(float, floatfield, floatarg)
 226                 ctf_float(double, doublefield, doublearg)
 227         )
 228 )
 229
 230 There can be an arbitrary number of tracepoint providers within an
 231 application, but they must each have their own provider name. Duplicate
 232 provider names are not allowed.
 233
 234 .fi
 235
 236 .SH "ASSIGNING LOGLEVEL TO EVENTS"
 237
 238 .nf
 239
 240 Optionally, a loglevel can be assigned to a TRACEPOINT_EVENT using the
 241 following construct:
 242
 243         TRACEPOINT_LOGLEVEL(< [com_company_]project[_component] >,
 244                 < event >, < loglevel_name >)
 245
 246 The first field is the provider name, the second field is the name of
 247 the tracepoint, and the third field is the loglevel name.  A
 248 TRACEPOINT_EVENT should be declared prior to the the TRACEPOINT_LOGLEVEL
 249 for a given tracepoint name. The TRACEPOINT_PROVIDER must be already
 250 declared before declaring a TRACEPOINT_LOGLEVEL.
 251
 252 The loglevels go from 0 to 14. Higher numbers imply the most verbosity
 253 (higher event throughput expected.
 254
 255 Loglevels 0 through 6, and loglevel 14, match syslog(3) loglevels
 256 semantic. Loglevels 7 through 13 offer more fine-grained selection of
 257 debug information.
 258
 259    TRACE_EMERG           0
 260    system is unusable
 261
 262    TRACE_ALERT           1
 263    action must be taken immediately
 264
 265    TRACE_CRIT            2
 266    critical conditions
 267
 268    TRACE_ERR             3
 269    error conditions
 270
 271    TRACE_WARNING         4
 272    warning conditions
 273
 274    TRACE_NOTICE          5
 275    normal, but significant, condition
 276
 277    TRACE_INFO            6
 278    informational message
 279
 280    TRACE_DEBUG_SYSTEM    7
 281    debug information with system-level scope (set of programs)
 282
 283    TRACE_DEBUG_PROGRAM   8
 284    debug information with program-level scope (set of processes)
 285
 286    TRACE_DEBUG_PROCESS   9
 287    debug information with process-level scope (set of modules)
 288
 289    TRACE_DEBUG_MODULE    10
 290    debug information with module (executable/library) scope (set of
 291    units)
 292
 293    TRACE_DEBUG_UNIT      11
 294    debug information with compilation unit scope (set of functions)
 295
 296    TRACE_DEBUG_FUNCTION  12
 297    debug information with function-level scope
 298
 299    TRACE_DEBUG_LINE      13
 300    debug information with line-level scope (TRACEPOINT_EVENT default)
 301
 302    TRACE_DEBUG           14
 303    debug-level message
 304
 305 See lttng(1) for information on how to use LTTng-UST loglevels.
 306
 307 .fi
 308
 309 .SH "ADDING TRACEPOINTS TO YOUR CODE"
 310
 311 .nf
 312
 313 Include the provider header in each C files you plan to instrument,
 314 following the building/linking directives in the next section.
 315
 316 For instance, add within a function:
 317
 318                 tracepoint(ust_tests_hello, tptest, i, netint, values,
 319                         text, strlen(text), dbl, flt);
 320
 321 As a call to the tracepoint. It will only be activated when requested by
 322 lttng(1) through lttng-sessiond(8).
 323
 324 Even though LTTng-UST supports tracepoint() call site duplicates having
 325 the same provider and event name, it is recommended to use a
 326 provider event name pair only once within the source code to help
 327 map events back to their call sites when analyzing the trace.
 328
 329 Sometimes arguments to the probe are expensive to compute (e.g.
 330 take call stack). To avoid the computation when the tracepoint is
 331 disabled one can use more 'low level' tracepoint_enabled() and
 332 do_tracepoint() macros as following:
 333
 334         if (tracepoint_enabled(ust_tests_hello, tptest)) {
 335                 /* prepare arguments */
 336                 do_tracepoint(ust_tests_hello, tptest, i, netint, values,
 337                         text, strlen(text), dbl, flt);
 338         }
 339
 340 Here do_tracepoint() doesn't contain check if the tracepoint is enabled.
 341 Using tracepoint() in such scenario is dangerous since it also contains
 342 enabled check and thus race condition is possible in the following code
 343 if the tracepoint has been enabled after check in tracepoint_enabled()
 344 but before tracepoint():
 345
 346         if (tracepoint_enabled(provider, name)) { /* tracepoint is disabled */
 347                 prepare(args);
 348         }
 349         /* tracepoint is enabled by 'lttng' tool */
 350         tracepoint(provider, name, args); /* args wasn't prepared properly */
 351
 352 Note also that neither tracepoint_enabled() nor do_tracepoint() have
 353 STAP_PROBEV() call so if you need it you should emit this call yourself.
 354
 355 .fi
 356
 357 .SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
 358
 359 .nf
 360 There are 2 ways to compile the Tracepoint Provider with the
 361 application: either statically or dynamically. Please follow
 362 carefully:
 363
 364   1) Compile the Tracepoint Provider with the application, either
 365      directly or through a static library (.a):
 366     - Into exactly one object of your application, define
 367       "TRACEPOINT_DEFINE" and include the tracepoint provider.
 368     - Use "\-I." for the compilation unit containing the tracepoint
 369       provider include (e.g., tp.c).
 370     - Link the application with "\-llttng-ust" and "\-ldl".
 371     - Include the tracepoint provider header into all C files using
 372       the provider.
 373     - Examples:
 374       - doc/examples/easy-ust/   sample.c sample_component_provider.h tp.c
 375         Makefile
 376       - doc/examples/hello-static-lib/   hello.c tp.c ust_test_hello.h Makefile
 377
 378   2) Compile the Tracepoint Provider separately from the application,
 379      using dynamic linking:
 380     - Into exactly one object of your application: define
 381       "TRACEPOINT_DEFINE" _and_ also define
 382       "TRACEPOINT_PROBE_DYNAMIC_LINKAGE", then include the tracepoint
 383       provider header.
 384     - Include the tracepoint provider header into all instrumented C
 385       files that use the provider.
 386     - Compile the tracepoint provider with "\-I.".
 387     - Link the tracepoint provider with "\-llttng-ust".
 388     - Link application with "\-ldl".
 389     - Set a LD_PRELOAD environment to preload the tracepoint provider
 390       shared object before starting the application when tracing is
 391       needed. Another way is to dlopen the tracepoint probe when needed
 392       by the application.
 393     - Example:
 394       - doc/examples/demo   demo.c  tp*.c ust_tests_demo*.h demo-trace Makefile
 395
 396   - Note about dlclose() usage: it is not safe to use dlclose on a
 397     provider shared object that is being actively used for tracing due
 398     to a lack of reference counting from lttng-ust to the used shared
 399     object.
 400   - Enable instrumentation and control tracing with the "lttng" command
 401     from lttng-tools. See lttng-tools doc/quickstart.txt.
 402   - Note for C++ support: although an application instrumented with
 403     tracepoints can be compiled with g++, tracepoint probes should be
 404     compiled with gcc (only tested with gcc so far).
 405
 406 .fi
 407
 408 .SH "USING LTTNG UST WITH DAEMONS"
 409
 410 .nf
 411 Some extra care is needed when using liblttng-ust with daemon
 412 applications that call fork(), clone(), or BSD rfork() without a
 413 following exec() family system call. The library "liblttng-ust-fork.so"
 414 needs to be preloaded for the application (launch with e.g.
 415 LD_PRELOAD=liblttng-ust-fork.so appname).
 416
 417 .fi
 418
 419 .SH "CONTEXT"
 420
 421 .PP
 422 Context information can be prepended by the tracer before each, or some,
 423 events. The following context information is supported by LTTng-UST:
 424 .PP
 425
 426 .PP
 427 .IP "vtid"
 428 Virtual thread ID: thread ID as seen from the point of view of the
 429 process namespace.
 430 .PP
 431
 432 .PP
 433 .IP "vpid"
 434 Virtual process ID: process ID as seen from the point of view of the
 435 process namespace.
 436 .PP
 437
 438 .PP
 439 .IP "ip"
 440 Instruction pointer: Enables recording of the exact location where a tracepoint
 441 was emitted. Can be used to reverse-lookup the source location that caused the
 442 event to be emitted.
 443 .PP
 444
 445 .PP
 446 .IP "procname"
 447 Thread name, as set by exec() or prctl(). It is recommended that
 448 programs set their thread name with prctl() before hitting the first
 449 tracepoint for that thread.
 450 .PP
 451
 452 .PP
 453 .IP "pthread_id"
 454 Pthread identifier. Can be used on architectures where pthread_t maps
 455 nicely to an unsigned long type.
 456 .PP
 457
 458 .SH "BASE ADDRESS STATEDUMP"
 459
 460 .PP
 461 If an application that uses liblttng-ust.so becomes part of a session,
 462 information about its currently loaded shared objects will be traced to the
 463 session at session-enable time. To record this information, the following event
 464 needs to be enabled:
 465 .PP
 466 .IP "ust_baddr_statedump:soinfo"
 467 This event is used to trace a currently loaded shared object. The base address
 468 (where the dynamic linker has placed the shared object) is recorded in the
 469 "baddr" field. The path to the shared object gets recorded in the
 470 "sopath" field (as string). The file size of the loaded object (in
 471 bytes) is recorded to the "size" field and its time of last modification
 472 (in seconds since Epoch) is recorded in the "mtime" field.
 473 .PP
 474 If the event above is enabled, a series of "ust_baddr_statedump:soinfo"
 475 events is recorded at session-enable time. It represents the state of
 476 currently loaded shared objects for the traced process. If this
 477 information gets combined with the lttng-ust-dl(3) instrumentation, all
 478 aspects of dynamic loading that are relevant for symbol and
 479 line number lookup are traced by LTTng.
 480 .PP
 481 .SH "ENVIRONMENT VARIABLES"
 482
 483 .PP
 484 .IP "LTTNG_UST_DEBUG"
 485 Activate liblttng-ust debug and error output.
 486 .PP
 487 .IP "LTTNG_UST_REGISTER_TIMEOUT"
 488 The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to
 489 specify how long the applications should wait for sessiond
 490 "registration done" command before proceeding to execute the main
 491 program. The default is 3000ms (3 seconds). The timeout value is
 492 specified in milliseconds. The value 0 means "don't wait". The value
 493 \-1 means "wait forever". Setting this environment variable to 0 is
 494 recommended for applications with time constraints on the process
 495 startup time.
 496 .PP
 497 .IP "LTTNG_UST_WITHOUT_BADDR_STATEDUMP"
 498 Prevent liblttng-ust to perform a base-address statedump on session-enable.
 499 .PP
 500
 501 .SH "SEE ALSO"
 502
 503 .PP
 504 lttng-gen-tp(1), lttng(1), babeltrace(1), lttng-ust-cyg-profile(3),
 505 lttng-ust-dl(3), lttng-sessiond(8)
 506 .PP
 507
 508 .SH "COMPATIBILITY"
 509
 510 .PP
 511 Older lttng-ust libraries reject more recent, and incompatible, probe
 512 providers. Newer lttng-ust libraries accept older probe providers, even
 513 though some newer features might not be available with those providers.
 514 .PP
 515
 516 .SH "BUGS"
 517
 518 .PP
 519 LTTng-UST 2.0 and 2.1 lttng-ust libraries do not check for probe
 520 provider version compatibility. This can lead to out-of-bound accesses
 521 when using a more recent probe provider with an older lttng-ust library.
 522 These error only trigger when tracing is active. This issue has been
 523 fixed in LTTng-UST 2.2.
 524
 525 If you encounter any issues or usability problem, please report it on
 526 our mailing list <lttng-dev@lists.lttng.org> to help improve this
 527 project.
 528 .SH "CREDITS"
 529
 530 liblttng-ust is distributed under the GNU Lesser General Public License
 531 version 2.1. The headers are distributed under the MIT license.
 532 .PP
 533 See http://lttng.org for more information on the LTTng project.
 534 .PP
 535 Mailing list for support and development: <lttng-dev@lists.lttng.org>.
 536 .PP
 537 You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
 538 .PP
 539 .SH "THANKS"
 540
 541 Thanks to Ericsson for funding this work, providing real-life use-cases,
 542 and testing.
 543
 544 Special thanks to Michel Dagenais and the DORSAL laboratory at
 545 Polytechnique de Montreal for the LTTng journey.
 546 .PP
 547 .SH "AUTHORS"
 548
 549 .PP
 550 liblttng-ust was originally written by Mathieu Desnoyers, with additional
 551 contributions from various other people. It is currently maintained by
 552 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>.
 553 .PP