| 1 | #LyX 1.6.1 created this file. For more info see http://www.lyx.org/ |
| 2 | \lyxformat 345 |
| 3 | \begin_document |
| 4 | \begin_header |
| 5 | \textclass article |
| 6 | \use_default_options true |
| 7 | \language english |
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| 23 | \use_amsmath 1 |
| 24 | \use_esint 1 |
| 25 | \cite_engine basic |
| 26 | \use_bibtopic false |
| 27 | \paperorientation portrait |
| 28 | \secnumdepth 3 |
| 29 | \tocdepth 3 |
| 30 | \paragraph_separation indent |
| 31 | \defskip medskip |
| 32 | \quotes_language english |
| 33 | \papercolumns 1 |
| 34 | \papersides 1 |
| 35 | \paperpagestyle default |
| 36 | \tracking_changes false |
| 37 | \output_changes false |
| 38 | \author "" |
| 39 | \author "" |
| 40 | \end_header |
| 41 | |
| 42 | \begin_body |
| 43 | |
| 44 | \begin_layout Title |
| 45 | LTTng Userspace Tracer Manual |
| 46 | \end_layout |
| 47 | |
| 48 | \begin_layout Author |
| 49 | Pierre-Marc Fournier |
| 50 | \end_layout |
| 51 | |
| 52 | \begin_layout Section |
| 53 | What is the LTTng Userspace Tracer? |
| 54 | \end_layout |
| 55 | |
| 56 | \begin_layout Subsection |
| 57 | Overview |
| 58 | \end_layout |
| 59 | |
| 60 | \begin_layout Standard |
| 61 | The LTTng Userspace Tracer (UST) is a tracing system for userspace applications. |
| 62 | It is designed to trace efficiently applications that produce events at |
| 63 | a very high rate. |
| 64 | UST is derived from LTTng, a tracer for the Linux kernel. |
| 65 | It has the same trace format. |
| 66 | \end_layout |
| 67 | |
| 68 | \begin_layout Standard |
| 69 | Users may choose at runtime and even at trace time what instrumentation |
| 70 | should be activated. |
| 71 | Custom probes may be used to trace events conditionally. |
| 72 | \end_layout |
| 73 | |
| 74 | \begin_layout Subsection |
| 75 | Features |
| 76 | \end_layout |
| 77 | |
| 78 | \begin_layout Itemize |
| 79 | Arbitrary number of channels |
| 80 | \end_layout |
| 81 | |
| 82 | \begin_layout Itemize |
| 83 | One buffer per process (multiple threads share the same buffer) |
| 84 | \end_layout |
| 85 | |
| 86 | \begin_layout Itemize |
| 87 | Early process tracing (from the beginning of the main() function |
| 88 | \end_layout |
| 89 | |
| 90 | \begin_layout Itemize |
| 91 | Support for custom probes |
| 92 | \end_layout |
| 93 | |
| 94 | \begin_layout Standard |
| 95 | Still to implement: |
| 96 | \end_layout |
| 97 | |
| 98 | \begin_layout Itemize |
| 99 | Support of dynamic instrumentation (being implemented in |
| 100 | \end_layout |
| 101 | |
| 102 | \begin_layout Standard |
| 103 | Complementary systems: |
| 104 | \end_layout |
| 105 | |
| 106 | \begin_layout Itemize |
| 107 | A extension to gdb tracepoints that will allow the tracing of applications |
| 108 | with dynamic instrumentation is under development. |
| 109 | \end_layout |
| 110 | |
| 111 | \begin_layout Subsection |
| 112 | Performance |
| 113 | \end_layout |
| 114 | |
| 115 | \begin_layout Section |
| 116 | Instrumenting an Application |
| 117 | \end_layout |
| 118 | |
| 119 | \begin_layout Standard |
| 120 | In order to record a trace of events occurring in a application, the application |
| 121 | must be instrumented. |
| 122 | Instrumentation points resemble function calls. |
| 123 | When the program reaches an instrumentation point, an event is generated. |
| 124 | \end_layout |
| 125 | |
| 126 | \begin_layout Standard |
| 127 | There are no limitations on the type of code that may be instrumented. |
| 128 | Multi-threaded programs may be instrumented without problem. |
| 129 | Signal handler may be instrumented as well. |
| 130 | \end_layout |
| 131 | |
| 132 | \begin_layout Standard |
| 133 | There are two APIs to instrument programs: markers and tracepoints. |
| 134 | Markers are quick to add and are usually used for temporary instrumentation. |
| 135 | Tracepoints provide a way to instrument code more cleanly and are suited |
| 136 | for permanent instrumentation. |
| 137 | \end_layout |
| 138 | |
| 139 | \begin_layout Subsection |
| 140 | Markers |
| 141 | \end_layout |
| 142 | |
| 143 | \begin_layout Standard |
| 144 | Markers were ported from the Linux Kernel Markers implementation. |
| 145 | Therefore, their usage is almost identical. |
| 146 | \end_layout |
| 147 | |
| 148 | \begin_layout Subsubsection |
| 149 | Inserting Markers |
| 150 | \end_layout |
| 151 | |
| 152 | \begin_layout Standard |
| 153 | Adding a marker is simply a matter of insert one line in the program. |
| 154 | \end_layout |
| 155 | |
| 156 | \begin_layout Standard |
| 157 | \begin_inset listings |
| 158 | inline false |
| 159 | status open |
| 160 | |
| 161 | \begin_layout Plain Layout |
| 162 | |
| 163 | #include <marker.h> |
| 164 | \end_layout |
| 165 | |
| 166 | \begin_layout Plain Layout |
| 167 | |
| 168 | void function() |
| 169 | \end_layout |
| 170 | |
| 171 | \begin_layout Plain Layout |
| 172 | |
| 173 | { |
| 174 | \end_layout |
| 175 | |
| 176 | \begin_layout Plain Layout |
| 177 | |
| 178 | int v; |
| 179 | \end_layout |
| 180 | |
| 181 | \begin_layout Plain Layout |
| 182 | |
| 183 | char *st; |
| 184 | \end_layout |
| 185 | |
| 186 | \begin_layout Plain Layout |
| 187 | |
| 188 | \end_layout |
| 189 | |
| 190 | \begin_layout Plain Layout |
| 191 | |
| 192 | /* ... |
| 193 | set values of v and st ... |
| 194 | */ |
| 195 | \end_layout |
| 196 | |
| 197 | \begin_layout Plain Layout |
| 198 | |
| 199 | \end_layout |
| 200 | |
| 201 | \begin_layout Plain Layout |
| 202 | |
| 203 | /* a marker: */ |
| 204 | \end_layout |
| 205 | |
| 206 | \begin_layout Plain Layout |
| 207 | |
| 208 | trace_mark(main, myevent, |
| 209 | \begin_inset Quotes eld |
| 210 | \end_inset |
| 211 | |
| 212 | firstarg %d secondarg %s |
| 213 | \begin_inset Quotes erd |
| 214 | \end_inset |
| 215 | |
| 216 | , v, st); |
| 217 | \end_layout |
| 218 | |
| 219 | \begin_layout Plain Layout |
| 220 | |
| 221 | \end_layout |
| 222 | |
| 223 | \begin_layout Plain Layout |
| 224 | |
| 225 | /* a marker without arguments: */ |
| 226 | \end_layout |
| 227 | |
| 228 | \begin_layout Plain Layout |
| 229 | |
| 230 | trace_mark(main, myotherevent, MARK_NOARGS); |
| 231 | \end_layout |
| 232 | |
| 233 | \begin_layout Plain Layout |
| 234 | |
| 235 | } |
| 236 | \end_layout |
| 237 | |
| 238 | \end_inset |
| 239 | |
| 240 | |
| 241 | \end_layout |
| 242 | |
| 243 | \begin_layout Standard |
| 244 | The invocation of the trace_mark() macro requires at least 3 arguments. |
| 245 | The first, here |
| 246 | \begin_inset Quotes eld |
| 247 | \end_inset |
| 248 | |
| 249 | main |
| 250 | \begin_inset Quotes erd |
| 251 | \end_inset |
| 252 | |
| 253 | , is the name of the event category. |
| 254 | It is also the name of the channel the event will go in. |
| 255 | The second, here |
| 256 | \begin_inset Quotes eld |
| 257 | \end_inset |
| 258 | |
| 259 | myevent |
| 260 | \begin_inset Quotes erd |
| 261 | \end_inset |
| 262 | |
| 263 | is the name of the event. |
| 264 | The third is a format string that announces the names and the types of |
| 265 | the event arguments. |
| 266 | Its format resembles that of a printf() format string; it is described |
| 267 | thoroughly in Appendix x. |
| 268 | \end_layout |
| 269 | |
| 270 | \begin_layout Standard |
| 271 | A given Marker may appear more than once in the same program. |
| 272 | Other Markers may have the same name and a different format string, although |
| 273 | this might induce some confusion at analysis time. |
| 274 | \end_layout |
| 275 | |
| 276 | \begin_layout Subsubsection |
| 277 | Registering the Markers |
| 278 | \end_layout |
| 279 | |
| 280 | \begin_layout Standard |
| 281 | In order to inform to register the Markers present in the module, a macro |
| 282 | must be inserted at global scope. |
| 283 | Only one such macro is needed per exacutable or per shared object. |
| 284 | Adding it more than once, however, is harmless. |
| 285 | \end_layout |
| 286 | |
| 287 | \begin_layout Standard |
| 288 | \begin_inset listings |
| 289 | inline false |
| 290 | status open |
| 291 | |
| 292 | \begin_layout Plain Layout |
| 293 | |
| 294 | MARKER_LIB; |
| 295 | \end_layout |
| 296 | |
| 297 | \end_inset |
| 298 | |
| 299 | |
| 300 | \end_layout |
| 301 | |
| 302 | \begin_layout Subsection |
| 303 | Tracepoints |
| 304 | \end_layout |
| 305 | |
| 306 | \begin_layout Standard |
| 307 | The Tracepoints API uses the Markers, but provides a higher-level abstraction. |
| 308 | Whereas the markers API provides limited type checking, the Tracepoints |
| 309 | API provides more thorough type checking and discharges from the need to |
| 310 | insert format strings directly in the code and to have format strings appear |
| 311 | more than once if a given marker is reused. |
| 312 | \end_layout |
| 313 | |
| 314 | \begin_layout Standard |
| 315 | A tracepoint in the code looks like this: |
| 316 | \end_layout |
| 317 | |
| 318 | \begin_layout Standard |
| 319 | \begin_inset listings |
| 320 | inline false |
| 321 | status open |
| 322 | |
| 323 | \begin_layout Plain Layout |
| 324 | |
| 325 | #include <marker.h> |
| 326 | \end_layout |
| 327 | |
| 328 | \begin_layout Plain Layout |
| 329 | |
| 330 | \end_layout |
| 331 | |
| 332 | \begin_layout Plain Layout |
| 333 | |
| 334 | void function() |
| 335 | \end_layout |
| 336 | |
| 337 | \begin_layout Plain Layout |
| 338 | |
| 339 | { |
| 340 | \end_layout |
| 341 | |
| 342 | \begin_layout Plain Layout |
| 343 | |
| 344 | int v; |
| 345 | \end_layout |
| 346 | |
| 347 | \begin_layout Plain Layout |
| 348 | |
| 349 | char *st; |
| 350 | \end_layout |
| 351 | |
| 352 | \begin_layout Plain Layout |
| 353 | |
| 354 | \end_layout |
| 355 | |
| 356 | \begin_layout Plain Layout |
| 357 | |
| 358 | /* ... |
| 359 | set values of v and st ... |
| 360 | */ |
| 361 | \end_layout |
| 362 | |
| 363 | \begin_layout Plain Layout |
| 364 | |
| 365 | \end_layout |
| 366 | |
| 367 | \begin_layout Plain Layout |
| 368 | |
| 369 | /* a tracepoint: */ |
| 370 | \end_layout |
| 371 | |
| 372 | \begin_layout Plain Layout |
| 373 | |
| 374 | trace_main_myevent(v, st); |
| 375 | \end_layout |
| 376 | |
| 377 | \begin_layout Plain Layout |
| 378 | |
| 379 | } |
| 380 | \end_layout |
| 381 | |
| 382 | \end_inset |
| 383 | |
| 384 | |
| 385 | \end_layout |
| 386 | |
| 387 | \begin_layout Standard |
| 388 | \begin_inset listings |
| 389 | inline false |
| 390 | status open |
| 391 | |
| 392 | \begin_layout Plain Layout |
| 393 | |
| 394 | DEFINE_TRACE(); |
| 395 | \end_layout |
| 396 | |
| 397 | \end_inset |
| 398 | |
| 399 | |
| 400 | \end_layout |
| 401 | |
| 402 | \begin_layout Standard |
| 403 | \begin_inset listings |
| 404 | inline false |
| 405 | status open |
| 406 | |
| 407 | \begin_layout Plain Layout |
| 408 | |
| 409 | TRACEPOINT_LIB; |
| 410 | \end_layout |
| 411 | |
| 412 | \end_inset |
| 413 | |
| 414 | |
| 415 | \end_layout |
| 416 | |
| 417 | \begin_layout Subsection |
| 418 | Compiling the Application |
| 419 | \end_layout |
| 420 | |
| 421 | \begin_layout Section |
| 422 | Recording a Trace |
| 423 | \end_layout |
| 424 | |
| 425 | \begin_layout Subsection |
| 426 | Basic Recording |
| 427 | \end_layout |
| 428 | |
| 429 | \begin_layout Subsection |
| 430 | Early Tracing |
| 431 | \end_layout |
| 432 | |
| 433 | \begin_layout Standard |
| 434 | Sometimes, an application must be traced as soon as it is started. |
| 435 | In these cases, the Basic Recording method is not satisfactory, as important |
| 436 | events may be lost before the tracing is started. |
| 437 | \end_layout |
| 438 | |
| 439 | \begin_layout Standard |
| 440 | By using the Early Tracing method, it is guaranteed that the tracing is |
| 441 | started when the execution of the main() function of the program starts. |
| 442 | \end_layout |
| 443 | |
| 444 | \begin_layout Standard |
| 445 | Early Tracing may be enabled by defining the UST_TRACE environment variable |
| 446 | to a non-empty value when the program starts. |
| 447 | Additionally, the UST_AUTOPROBE may be set to a non-empty value to automaticall |
| 448 | y connect all markers to the default probe. |
| 449 | For example: |
| 450 | \end_layout |
| 451 | |
| 452 | \begin_layout Standard |
| 453 | \begin_inset listings |
| 454 | inline false |
| 455 | status open |
| 456 | |
| 457 | \begin_layout Plain Layout |
| 458 | |
| 459 | $ UST_TRACE=1 UST_AUTOPROBE=1 ./prog |
| 460 | \end_layout |
| 461 | |
| 462 | \end_inset |
| 463 | |
| 464 | |
| 465 | \end_layout |
| 466 | |
| 467 | \begin_layout Standard |
| 468 | In order for the trace to be saved, ustd must be running when the traced |
| 469 | program is started. |
| 470 | \end_layout |
| 471 | |
| 472 | \begin_layout Section |
| 473 | Viewing and Analyzing the Trace |
| 474 | \end_layout |
| 475 | |
| 476 | \begin_layout Standard |
| 477 | LTTV may be used for opening the trace. |
| 478 | If an appropriate time source was used, it may be opened concurrently with |
| 479 | other application traces and kernel traces. |
| 480 | \end_layout |
| 481 | |
| 482 | \begin_layout Section |
| 483 | Advanced Concepts |
| 484 | \end_layout |
| 485 | |
| 486 | \begin_layout Subsection |
| 487 | Using Custom Probes for Conditional Tracing |
| 488 | \end_layout |
| 489 | |
| 490 | \begin_layout Subsection |
| 491 | Instrumenting Calls to Library Functions without Recompilation |
| 492 | \end_layout |
| 493 | |
| 494 | \begin_layout Standard |
| 495 | Calls to uninstrumented libraries may be instrumented by creating a wrapper |
| 496 | library that intercepts calls to the library, trigger an instrumentation |
| 497 | point. |
| 498 | \end_layout |
| 499 | |
| 500 | \begin_layout Subsection |
| 501 | Tracing Programs Without Linking them to the Tracing Library |
| 502 | \end_layout |
| 503 | |
| 504 | \begin_layout Standard |
| 505 | Programs that were not instrumented nor linked with the tracing libraries |
| 506 | may still be traced. |
| 507 | In order to produce events, they must be linked to instrumented libraries |
| 508 | or use instrumented library wrappers as described in section xx. |
| 509 | \end_layout |
| 510 | |
| 511 | \begin_layout Standard |
| 512 | \begin_inset listings |
| 513 | inline false |
| 514 | status open |
| 515 | |
| 516 | \begin_layout Plain Layout |
| 517 | |
| 518 | LD_PRELOAD=... |
| 519 | program |
| 520 | \end_layout |
| 521 | |
| 522 | \end_inset |
| 523 | |
| 524 | |
| 525 | \end_layout |
| 526 | |
| 527 | \begin_layout Section |
| 528 | \start_of_appendix |
| 529 | Format of Marker Format Strings |
| 530 | \end_layout |
| 531 | |
| 532 | \begin_layout Standard |
| 533 | The format of Marker format strings is inspired from printf() format strings. |
| 534 | As with printf(), it is used to indicate to the parsing function the type |
| 535 | of the arguments that are passed. |
| 536 | Additionally, format strings indicate the name of each argument and the |
| 537 | format of that argument in the trace. |
| 538 | The structure of a typical format string is the following. |
| 539 | \end_layout |
| 540 | |
| 541 | \begin_layout Standard |
| 542 | \begin_inset listings |
| 543 | inline false |
| 544 | status open |
| 545 | |
| 546 | \begin_layout Plain Layout |
| 547 | |
| 548 | \begin_inset Quotes eld |
| 549 | \end_inset |
| 550 | |
| 551 | field_name1 #tracetype1 %ctype1 field_name2 #tracetype2 %ctype2 |
| 552 | \begin_inset Quotes erd |
| 553 | \end_inset |
| 554 | |
| 555 | |
| 556 | \end_layout |
| 557 | |
| 558 | \end_inset |
| 559 | |
| 560 | |
| 561 | \end_layout |
| 562 | |
| 563 | \begin_layout Description |
| 564 | field_name: The name of the field, as it will be seen when the trace is |
| 565 | parsed. |
| 566 | \end_layout |
| 567 | |
| 568 | \begin_layout Description |
| 569 | tracetype: The type of the argument as it will be written in the trace. |
| 570 | \end_layout |
| 571 | |
| 572 | \begin_layout Description |
| 573 | ctype: The C type of the argument passed to the Marker (this is very similar |
| 574 | to the %... |
| 575 | types in a printf() format string) |
| 576 | \end_layout |
| 577 | |
| 578 | \begin_layout Standard |
| 579 | Both field_name and tracetype are optional. |
| 580 | These are all valid format strings: |
| 581 | \end_layout |
| 582 | |
| 583 | \begin_layout Standard |
| 584 | \begin_inset listings |
| 585 | inline false |
| 586 | status open |
| 587 | |
| 588 | \begin_layout Plain Layout |
| 589 | |
| 590 | \end_layout |
| 591 | |
| 592 | \end_inset |
| 593 | |
| 594 | |
| 595 | \end_layout |
| 596 | |
| 597 | \begin_layout Subsection |
| 598 | tracetype |
| 599 | \end_layout |
| 600 | |
| 601 | \begin_layout Standard |
| 602 | A typical Marker format string looks like this: |
| 603 | \end_layout |
| 604 | |
| 605 | \begin_layout Standard |
| 606 | The serialization format string supports the basic printf format strings. |
| 607 | \end_layout |
| 608 | |
| 609 | \begin_layout Standard |
| 610 | In addition, it defines new formats that can be used to serialize more |
| 611 | \end_layout |
| 612 | |
| 613 | \begin_layout Standard |
| 614 | complex/non portable data structures. |
| 615 | \end_layout |
| 616 | |
| 617 | \begin_layout Standard |
| 618 | Typical use: |
| 619 | \end_layout |
| 620 | |
| 621 | \begin_layout Standard |
| 622 | field_name %ctype |
| 623 | \end_layout |
| 624 | |
| 625 | \begin_layout Standard |
| 626 | field_name #tracetype %ctype |
| 627 | \end_layout |
| 628 | |
| 629 | \begin_layout Standard |
| 630 | field_name #tracetype %ctype1 %ctype2 ... |
| 631 | \end_layout |
| 632 | |
| 633 | \begin_layout Standard |
| 634 | A conversion is performed between format string types supported by GCC and |
| 635 | \end_layout |
| 636 | |
| 637 | \begin_layout Standard |
| 638 | the trace type requested. |
| 639 | GCC type is used to perform type checking on format |
| 640 | \end_layout |
| 641 | |
| 642 | \begin_layout Standard |
| 643 | strings. |
| 644 | Trace type is used to specify the exact binary representation |
| 645 | \end_layout |
| 646 | |
| 647 | \begin_layout Standard |
| 648 | in the trace. |
| 649 | A mapping is done between one or more GCC types to one trace |
| 650 | \end_layout |
| 651 | |
| 652 | \begin_layout Standard |
| 653 | type. |
| 654 | Sign extension, if required by the conversion, is performed following |
| 655 | \end_layout |
| 656 | |
| 657 | \begin_layout Standard |
| 658 | the trace type. |
| 659 | \end_layout |
| 660 | |
| 661 | \begin_layout Standard |
| 662 | If a gcc format is not declared with a trace format, the gcc format is |
| 663 | \end_layout |
| 664 | |
| 665 | \begin_layout Standard |
| 666 | also used as binary representation in the trace. |
| 667 | \end_layout |
| 668 | |
| 669 | \begin_layout Standard |
| 670 | Strings are supported with %s. |
| 671 | \end_layout |
| 672 | |
| 673 | \begin_layout Standard |
| 674 | A single tracetype (sequence) can take multiple c types as parameter. |
| 675 | \end_layout |
| 676 | |
| 677 | \begin_layout Standard |
| 678 | c types: |
| 679 | \end_layout |
| 680 | |
| 681 | \begin_layout Standard |
| 682 | see printf(3). |
| 683 | \end_layout |
| 684 | |
| 685 | \begin_layout Standard |
| 686 | Note: to write a uint32_t in a trace, the following expression is recommended |
| 687 | \end_layout |
| 688 | |
| 689 | \begin_layout Standard |
| 690 | si it can be portable: |
| 691 | \end_layout |
| 692 | |
| 693 | \begin_layout Standard |
| 694 | ("#4u%lu", (unsigned long)var) |
| 695 | \end_layout |
| 696 | |
| 697 | \begin_layout Standard |
| 698 | trace types: |
| 699 | \end_layout |
| 700 | |
| 701 | \begin_layout Standard |
| 702 | Serialization specific formats : |
| 703 | \end_layout |
| 704 | |
| 705 | \begin_layout Standard |
| 706 | Fixed size integers |
| 707 | \end_layout |
| 708 | |
| 709 | \begin_layout Standard |
| 710 | #1u writes uint8_t |
| 711 | \end_layout |
| 712 | |
| 713 | \begin_layout Standard |
| 714 | #2u writes uint16_t |
| 715 | \end_layout |
| 716 | |
| 717 | \begin_layout Standard |
| 718 | #4u writes uint32_t |
| 719 | \end_layout |
| 720 | |
| 721 | \begin_layout Standard |
| 722 | #8u writes uint64_t |
| 723 | \end_layout |
| 724 | |
| 725 | \begin_layout Standard |
| 726 | #1d writes int8_t |
| 727 | \end_layout |
| 728 | |
| 729 | \begin_layout Standard |
| 730 | #2d writes int16_t |
| 731 | \end_layout |
| 732 | |
| 733 | \begin_layout Standard |
| 734 | #4d writes int32_t |
| 735 | \end_layout |
| 736 | |
| 737 | \begin_layout Standard |
| 738 | #8d writes int64_t |
| 739 | \end_layout |
| 740 | |
| 741 | \begin_layout Standard |
| 742 | i.e.: |
| 743 | \end_layout |
| 744 | |
| 745 | \begin_layout Standard |
| 746 | #1u%lu #2u%lu #4d%lu #8d%lu #llu%hu #d%lu |
| 747 | \end_layout |
| 748 | |
| 749 | \begin_layout Standard |
| 750 | * Attributes: |
| 751 | \end_layout |
| 752 | |
| 753 | \begin_layout Standard |
| 754 | n: (for network byte order) |
| 755 | \end_layout |
| 756 | |
| 757 | \begin_layout Standard |
| 758 | #ntracetype%ctype |
| 759 | \end_layout |
| 760 | |
| 761 | \begin_layout Standard |
| 762 | is written in the trace in network byte order. |
| 763 | \end_layout |
| 764 | |
| 765 | \begin_layout Standard |
| 766 | i.e.: #bn4u%lu, #n%lu, #b%u |
| 767 | \end_layout |
| 768 | |
| 769 | \begin_layout Standard |
| 770 | TODO (eventually) |
| 771 | \end_layout |
| 772 | |
| 773 | \begin_layout Standard |
| 774 | Variable length sequence |
| 775 | \end_layout |
| 776 | |
| 777 | \begin_layout Standard |
| 778 | #a #tracetype1 #tracetype2 %array_ptr %elem_size %num_elems |
| 779 | \end_layout |
| 780 | |
| 781 | \begin_layout Standard |
| 782 | In the trace: |
| 783 | \end_layout |
| 784 | |
| 785 | \begin_layout Standard |
| 786 | #a specifies that this is a sequence |
| 787 | \end_layout |
| 788 | |
| 789 | \begin_layout Standard |
| 790 | #tracetype1 is the type of elements in the sequence |
| 791 | \end_layout |
| 792 | |
| 793 | \begin_layout Standard |
| 794 | #tracetype2 is the type of the element count |
| 795 | \end_layout |
| 796 | |
| 797 | \begin_layout Standard |
| 798 | GCC input: |
| 799 | \end_layout |
| 800 | |
| 801 | \begin_layout Standard |
| 802 | array_ptr is a pointer to an array that contains members of size |
| 803 | \end_layout |
| 804 | |
| 805 | \begin_layout Standard |
| 806 | elem_size. |
| 807 | \end_layout |
| 808 | |
| 809 | \begin_layout Standard |
| 810 | num_elems is the number of elements in the array. |
| 811 | \end_layout |
| 812 | |
| 813 | \begin_layout Standard |
| 814 | i.e.: #a #lu #lu %p %lu %u |
| 815 | \end_layout |
| 816 | |
| 817 | \begin_layout Standard |
| 818 | Callback |
| 819 | \end_layout |
| 820 | |
| 821 | \begin_layout Standard |
| 822 | #k callback (taken from the probe data) |
| 823 | \end_layout |
| 824 | |
| 825 | \begin_layout Standard |
| 826 | The following % arguments are exepected by the callback |
| 827 | \end_layout |
| 828 | |
| 829 | \begin_layout Standard |
| 830 | i.e.: #a #lu #lu #k %p |
| 831 | \end_layout |
| 832 | |
| 833 | \begin_layout Standard |
| 834 | Note: No conversion is done from floats to integers, nor from integers to |
| 835 | \end_layout |
| 836 | |
| 837 | \begin_layout Standard |
| 838 | floats between c types and trace types. |
| 839 | float conversion from double to float |
| 840 | \end_layout |
| 841 | |
| 842 | \begin_layout Standard |
| 843 | or from float to double is also not supported. |
| 844 | \end_layout |
| 845 | |
| 846 | \end_body |
| 847 | \end_document |