1 This is gprof.info, produced by makeinfo version 4.8 from 2 /home/jingyu/projects/gcc/android-toolchain/binutils-2.19/gprof/gprof.texi. 3 4 START-INFO-DIR-ENTRY 5 * gprof: (gprof). Profiling your program's execution 6 END-INFO-DIR-ENTRY 7 8 This file documents the gprof profiler of the GNU system. 9 10 Copyright (C) 1988, 92, 97, 98, 99, 2000, 2001, 2003, 2007 Free 11 Software Foundation, Inc. 12 13 Permission is granted to copy, distribute and/or modify this document 14 under the terms of the GNU Free Documentation License, Version 1.1 or 15 any later version published by the Free Software Foundation; with no 16 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 17 Texts. A copy of the license is included in the section entitled "GNU 18 Free Documentation License". 19 20 21 File: gprof.info, Node: Top, Next: Introduction, Up: (dir) 22 23 Profiling a Program: Where Does It Spend Its Time? 24 ************************************************** 25 26 This manual describes the GNU profiler, `gprof', and how you can use it 27 to determine which parts of a program are taking most of the execution 28 time. We assume that you know how to write, compile, and execute 29 programs. GNU `gprof' was written by Jay Fenlason. 30 31 This manual is for `gprof' (GNU Binutils) version 2.19. 32 33 This document is distributed under the terms of the GNU Free 34 Documentation License. A copy of the license is included in the 35 section entitled "GNU Free Documentation License". 36 37 * Menu: 38 39 * Introduction:: What profiling means, and why it is useful. 40 41 * Compiling:: How to compile your program for profiling. 42 * Executing:: Executing your program to generate profile data 43 * Invoking:: How to run `gprof', and its options 44 45 * Output:: Interpreting `gprof''s output 46 47 * Inaccuracy:: Potential problems you should be aware of 48 * How do I?:: Answers to common questions 49 * Incompatibilities:: (between GNU `gprof' and Unix `gprof'.) 50 * Details:: Details of how profiling is done 51 * GNU Free Documentation License:: GNU Free Documentation License 52 53 54 File: gprof.info, Node: Introduction, Next: Compiling, Prev: Top, Up: Top 55 56 1 Introduction to Profiling 57 *************************** 58 59 Profiling allows you to learn where your program spent its time and 60 which functions called which other functions while it was executing. 61 This information can show you which pieces of your program are slower 62 than you expected, and might be candidates for rewriting to make your 63 program execute faster. It can also tell you which functions are being 64 called more or less often than you expected. This may help you spot 65 bugs that had otherwise been unnoticed. 66 67 Since the profiler uses information collected during the actual 68 execution of your program, it can be used on programs that are too 69 large or too complex to analyze by reading the source. However, how 70 your program is run will affect the information that shows up in the 71 profile data. If you don't use some feature of your program while it 72 is being profiled, no profile information will be generated for that 73 feature. 74 75 Profiling has several steps: 76 77 * You must compile and link your program with profiling enabled. 78 *Note Compiling a Program for Profiling: Compiling. 79 80 * You must execute your program to generate a profile data file. 81 *Note Executing the Program: Executing. 82 83 * You must run `gprof' to analyze the profile data. *Note `gprof' 84 Command Summary: Invoking. 85 86 The next three chapters explain these steps in greater detail. 87 88 Several forms of output are available from the analysis. 89 90 The "flat profile" shows how much time your program spent in each 91 function, and how many times that function was called. If you simply 92 want to know which functions burn most of the cycles, it is stated 93 concisely here. *Note The Flat Profile: Flat Profile. 94 95 The "call graph" shows, for each function, which functions called 96 it, which other functions it called, and how many times. There is also 97 an estimate of how much time was spent in the subroutines of each 98 function. This can suggest places where you might try to eliminate 99 function calls that use a lot of time. *Note The Call Graph: Call 100 Graph. 101 102 The "annotated source" listing is a copy of the program's source 103 code, labeled with the number of times each line of the program was 104 executed. *Note The Annotated Source Listing: Annotated Source. 105 106 To better understand how profiling works, you may wish to read a 107 description of its implementation. *Note Implementation of Profiling: 108 Implementation. 109 110 111 File: gprof.info, Node: Compiling, Next: Executing, Prev: Introduction, Up: Top 112 113 2 Compiling a Program for Profiling 114 *********************************** 115 116 The first step in generating profile information for your program is to 117 compile and link it with profiling enabled. 118 119 To compile a source file for profiling, specify the `-pg' option when 120 you run the compiler. (This is in addition to the options you normally 121 use.) 122 123 To link the program for profiling, if you use a compiler such as `cc' 124 to do the linking, simply specify `-pg' in addition to your usual 125 options. The same option, `-pg', alters either compilation or linking 126 to do what is necessary for profiling. Here are examples: 127 128 cc -g -c myprog.c utils.c -pg 129 cc -o myprog myprog.o utils.o -pg 130 131 The `-pg' option also works with a command that both compiles and 132 links: 133 134 cc -o myprog myprog.c utils.c -g -pg 135 136 Note: The `-pg' option must be part of your compilation options as 137 well as your link options. If it is not then no call-graph data will 138 be gathered and when you run `gprof' you will get an error message like 139 this: 140 141 gprof: gmon.out file is missing call-graph data 142 143 If you add the `-Q' switch to suppress the printing of the call 144 graph data you will still be able to see the time samples: 145 146 Flat profile: 147 148 Each sample counts as 0.01 seconds. 149 % cumulative self self total 150 time seconds seconds calls Ts/call Ts/call name 151 44.12 0.07 0.07 zazLoop 152 35.29 0.14 0.06 main 153 20.59 0.17 0.04 bazMillion 154 155 If you run the linker `ld' directly instead of through a compiler 156 such as `cc', you may have to specify a profiling startup file 157 `gcrt0.o' as the first input file instead of the usual startup file 158 `crt0.o'. In addition, you would probably want to specify the 159 profiling C library, `libc_p.a', by writing `-lc_p' instead of the 160 usual `-lc'. This is not absolutely necessary, but doing this gives 161 you number-of-calls information for standard library functions such as 162 `read' and `open'. For example: 163 164 ld -o myprog /lib/gcrt0.o myprog.o utils.o -lc_p 165 166 If you compile only some of the modules of the program with `-pg', 167 you can still profile the program, but you won't get complete 168 information about the modules that were compiled without `-pg'. The 169 only information you get for the functions in those modules is the 170 total time spent in them; there is no record of how many times they 171 were called, or from where. This will not affect the flat profile 172 (except that the `calls' field for the functions will be blank), but 173 will greatly reduce the usefulness of the call graph. 174 175 If you wish to perform line-by-line profiling you should use the 176 `gcov' tool instead of `gprof'. See that tool's manual or info pages 177 for more details of how to do this. 178 179 Note, older versions of `gcc' produce line-by-line profiling 180 information that works with `gprof' rather than `gcov' so there is 181 still support for displaying this kind of information in `gprof'. *Note 182 Line-by-line Profiling: Line-by-line. 183 184 It also worth noting that `gcc' implements a 185 `-finstrument-functions' command line option which will insert calls to 186 special user supplied instrumentation routines at the entry and exit of 187 every function in their program. This can be used to implement an 188 alternative profiling scheme. 189 190 191 File: gprof.info, Node: Executing, Next: Invoking, Prev: Compiling, Up: Top 192 193 3 Executing the Program 194 *********************** 195 196 Once the program is compiled for profiling, you must run it in order to 197 generate the information that `gprof' needs. Simply run the program as 198 usual, using the normal arguments, file names, etc. The program should 199 run normally, producing the same output as usual. It will, however, run 200 somewhat slower than normal because of the time spent collecting and 201 writing the profile data. 202 203 The way you run the program--the arguments and input that you give 204 it--may have a dramatic effect on what the profile information shows. 205 The profile data will describe the parts of the program that were 206 activated for the particular input you use. For example, if the first 207 command you give to your program is to quit, the profile data will show 208 the time used in initialization and in cleanup, but not much else. 209 210 Your program will write the profile data into a file called 211 `gmon.out' just before exiting. If there is already a file called 212 `gmon.out', its contents are overwritten. There is currently no way to 213 tell the program to write the profile data under a different name, but 214 you can rename the file afterwards if you are concerned that it may be 215 overwritten. 216 217 In order to write the `gmon.out' file properly, your program must 218 exit normally: by returning from `main' or by calling `exit'. Calling 219 the low-level function `_exit' does not write the profile data, and 220 neither does abnormal termination due to an unhandled signal. 221 222 The `gmon.out' file is written in the program's _current working 223 directory_ at the time it exits. This means that if your program calls 224 `chdir', the `gmon.out' file will be left in the last directory your 225 program `chdir''d to. If you don't have permission to write in this 226 directory, the file is not written, and you will get an error message. 227 228 Older versions of the GNU profiling library may also write a file 229 called `bb.out'. This file, if present, contains an human-readable 230 listing of the basic-block execution counts. Unfortunately, the 231 appearance of a human-readable `bb.out' means the basic-block counts 232 didn't get written into `gmon.out'. The Perl script `bbconv.pl', 233 included with the `gprof' source distribution, will convert a `bb.out' 234 file into a format readable by `gprof'. Invoke it like this: 235 236 bbconv.pl < bb.out > BH-DATA 237 238 This translates the information in `bb.out' into a form that `gprof' 239 can understand. But you still need to tell `gprof' about the existence 240 of this translated information. To do that, include BB-DATA on the 241 `gprof' command line, _along with `gmon.out'_, like this: 242 243 gprof OPTIONS EXECUTABLE-FILE gmon.out BB-DATA [YET-MORE-PROFILE-DATA-FILES...] [> OUTFILE] 244 245 246 File: gprof.info, Node: Invoking, Next: Output, Prev: Executing, Up: Top 247 248 4 `gprof' Command Summary 249 ************************* 250 251 After you have a profile data file `gmon.out', you can run `gprof' to 252 interpret the information in it. The `gprof' program prints a flat 253 profile and a call graph on standard output. Typically you would 254 redirect the output of `gprof' into a file with `>'. 255 256 You run `gprof' like this: 257 258 gprof OPTIONS [EXECUTABLE-FILE [PROFILE-DATA-FILES...]] [> OUTFILE] 259 260 Here square-brackets indicate optional arguments. 261 262 If you omit the executable file name, the file `a.out' is used. If 263 you give no profile data file name, the file `gmon.out' is used. If 264 any file is not in the proper format, or if the profile data file does 265 not appear to belong to the executable file, an error message is 266 printed. 267 268 You can give more than one profile data file by entering all their 269 names after the executable file name; then the statistics in all the 270 data files are summed together. 271 272 The order of these options does not matter. 273 274 * Menu: 275 276 * Output Options:: Controlling `gprof''s output style 277 * Analysis Options:: Controlling how `gprof' analyzes its data 278 * Miscellaneous Options:: 279 * Deprecated Options:: Options you no longer need to use, but which 280 have been retained for compatibility 281 * Symspecs:: Specifying functions to include or exclude 282 283 284 File: gprof.info, Node: Output Options, Next: Analysis Options, Up: Invoking 285 286 4.1 Output Options 287 ================== 288 289 These options specify which of several output formats `gprof' should 290 produce. 291 292 Many of these options take an optional "symspec" to specify 293 functions to be included or excluded. These options can be specified 294 multiple times, with different symspecs, to include or exclude sets of 295 symbols. *Note Symspecs: Symspecs. 296 297 Specifying any of these options overrides the default (`-p -q'), 298 which prints a flat profile and call graph analysis for all functions. 299 300 `-A[SYMSPEC]' 301 `--annotated-source[=SYMSPEC]' 302 The `-A' option causes `gprof' to print annotated source code. If 303 SYMSPEC is specified, print output only for matching symbols. 304 *Note The Annotated Source Listing: Annotated Source. 305 306 `-b' 307 `--brief' 308 If the `-b' option is given, `gprof' doesn't print the verbose 309 blurbs that try to explain the meaning of all of the fields in the 310 tables. This is useful if you intend to print out the output, or 311 are tired of seeing the blurbs. 312 313 `-C[SYMSPEC]' 314 `--exec-counts[=SYMSPEC]' 315 The `-C' option causes `gprof' to print a tally of functions and 316 the number of times each was called. If SYMSPEC is specified, 317 print tally only for matching symbols. 318 319 If the profile data file contains basic-block count records, 320 specifying the `-l' option, along with `-C', will cause basic-block 321 execution counts to be tallied and displayed. 322 323 `-i' 324 `--file-info' 325 The `-i' option causes `gprof' to display summary information 326 about the profile data file(s) and then exit. The number of 327 histogram, call graph, and basic-block count records is displayed. 328 329 `-I DIRS' 330 `--directory-path=DIRS' 331 The `-I' option specifies a list of search directories in which to 332 find source files. Environment variable GPROF_PATH can also be 333 used to convey this information. Used mostly for annotated source 334 output. 335 336 `-J[SYMSPEC]' 337 `--no-annotated-source[=SYMSPEC]' 338 The `-J' option causes `gprof' not to print annotated source code. 339 If SYMSPEC is specified, `gprof' prints annotated source, but 340 excludes matching symbols. 341 342 `-L' 343 `--print-path' 344 Normally, source filenames are printed with the path component 345 suppressed. The `-L' option causes `gprof' to print the full 346 pathname of source filenames, which is determined from symbolic 347 debugging information in the image file and is relative to the 348 directory in which the compiler was invoked. 349 350 `-p[SYMSPEC]' 351 `--flat-profile[=SYMSPEC]' 352 The `-p' option causes `gprof' to print a flat profile. If 353 SYMSPEC is specified, print flat profile only for matching symbols. 354 *Note The Flat Profile: Flat Profile. 355 356 `-P[SYMSPEC]' 357 `--no-flat-profile[=SYMSPEC]' 358 The `-P' option causes `gprof' to suppress printing a flat profile. 359 If SYMSPEC is specified, `gprof' prints a flat profile, but 360 excludes matching symbols. 361 362 `-q[SYMSPEC]' 363 `--graph[=SYMSPEC]' 364 The `-q' option causes `gprof' to print the call graph analysis. 365 If SYMSPEC is specified, print call graph only for matching symbols 366 and their children. *Note The Call Graph: Call Graph. 367 368 `-Q[SYMSPEC]' 369 `--no-graph[=SYMSPEC]' 370 The `-Q' option causes `gprof' to suppress printing the call graph. 371 If SYMSPEC is specified, `gprof' prints a call graph, but excludes 372 matching symbols. 373 374 `-t' 375 `--table-length=NUM' 376 The `-t' option causes the NUM most active source lines in each 377 source file to be listed when source annotation is enabled. The 378 default is 10. 379 380 `-y' 381 `--separate-files' 382 This option affects annotated source output only. Normally, 383 `gprof' prints annotated source files to standard-output. If this 384 option is specified, annotated source for a file named 385 `path/FILENAME' is generated in the file `FILENAME-ann'. If the 386 underlying file system would truncate `FILENAME-ann' so that it 387 overwrites the original `FILENAME', `gprof' generates annotated 388 source in the file `FILENAME.ann' instead (if the original file 389 name has an extension, that extension is _replaced_ with `.ann'). 390 391 `-Z[SYMSPEC]' 392 `--no-exec-counts[=SYMSPEC]' 393 The `-Z' option causes `gprof' not to print a tally of functions 394 and the number of times each was called. If SYMSPEC is specified, 395 print tally, but exclude matching symbols. 396 397 `-r' 398 `--function-ordering' 399 The `--function-ordering' option causes `gprof' to print a 400 suggested function ordering for the program based on profiling 401 data. This option suggests an ordering which may improve paging, 402 tlb and cache behavior for the program on systems which support 403 arbitrary ordering of functions in an executable. 404 405 The exact details of how to force the linker to place functions in 406 a particular order is system dependent and out of the scope of this 407 manual. 408 409 `-R MAP_FILE' 410 `--file-ordering MAP_FILE' 411 The `--file-ordering' option causes `gprof' to print a suggested 412 .o link line ordering for the program based on profiling data. 413 This option suggests an ordering which may improve paging, tlb and 414 cache behavior for the program on systems which do not support 415 arbitrary ordering of functions in an executable. 416 417 Use of the `-a' argument is highly recommended with this option. 418 419 The MAP_FILE argument is a pathname to a file which provides 420 function name to object file mappings. The format of the file is 421 similar to the output of the program `nm'. 422 423 c-parse.o:00000000 T yyparse 424 c-parse.o:00000004 C yyerrflag 425 c-lang.o:00000000 T maybe_objc_method_name 426 c-lang.o:00000000 T print_lang_statistics 427 c-lang.o:00000000 T recognize_objc_keyword 428 c-decl.o:00000000 T print_lang_identifier 429 c-decl.o:00000000 T print_lang_type 430 ... 431 432 To create a MAP_FILE with GNU `nm', type a command like `nm 433 --extern-only --defined-only -v --print-file-name program-name'. 434 435 `-T' 436 `--traditional' 437 The `-T' option causes `gprof' to print its output in 438 "traditional" BSD style. 439 440 `-w WIDTH' 441 `--width=WIDTH' 442 Sets width of output lines to WIDTH. Currently only used when 443 printing the function index at the bottom of the call graph. 444 445 `-x' 446 `--all-lines' 447 This option affects annotated source output only. By default, 448 only the lines at the beginning of a basic-block are annotated. 449 If this option is specified, every line in a basic-block is 450 annotated by repeating the annotation for the first line. This 451 behavior is similar to `tcov''s `-a'. 452 453 `--demangle[=STYLE]' 454 `--no-demangle' 455 These options control whether C++ symbol names should be demangled 456 when printing output. The default is to demangle symbols. The 457 `--no-demangle' option may be used to turn off demangling. 458 Different compilers have different mangling styles. The optional 459 demangling style argument can be used to choose an appropriate 460 demangling style for your compiler. 461 462 463 File: gprof.info, Node: Analysis Options, Next: Miscellaneous Options, Prev: Output Options, Up: Invoking 464 465 4.2 Analysis Options 466 ==================== 467 468 `-a' 469 `--no-static' 470 The `-a' option causes `gprof' to suppress the printing of 471 statically declared (private) functions. (These are functions 472 whose names are not listed as global, and which are not visible 473 outside the file/function/block where they were defined.) Time 474 spent in these functions, calls to/from them, etc., will all be 475 attributed to the function that was loaded directly before it in 476 the executable file. This option affects both the flat profile 477 and the call graph. 478 479 `-c' 480 `--static-call-graph' 481 The `-c' option causes the call graph of the program to be 482 augmented by a heuristic which examines the text space of the 483 object file and identifies function calls in the binary machine 484 code. Since normal call graph records are only generated when 485 functions are entered, this option identifies children that could 486 have been called, but never were. Calls to functions that were 487 not compiled with profiling enabled are also identified, but only 488 if symbol table entries are present for them. Calls to dynamic 489 library routines are typically _not_ found by this option. 490 Parents or children identified via this heuristic are indicated in 491 the call graph with call counts of `0'. 492 493 `-D' 494 `--ignore-non-functions' 495 The `-D' option causes `gprof' to ignore symbols which are not 496 known to be functions. This option will give more accurate 497 profile data on systems where it is supported (Solaris and HPUX for 498 example). 499 500 `-k FROM/TO' 501 The `-k' option allows you to delete from the call graph any arcs 502 from symbols matching symspec FROM to those matching symspec TO. 503 504 `-l' 505 `--line' 506 The `-l' option enables line-by-line profiling, which causes 507 histogram hits to be charged to individual source code lines, 508 instead of functions. This feature only works with programs 509 compiled by older versions of the `gcc' compiler. Newer versions 510 of `gcc' are designed to work with the `gcov' tool instead. 511 512 If the program was compiled with basic-block counting enabled, 513 this option will also identify how many times each line of code 514 was executed. While line-by-line profiling can help isolate where 515 in a large function a program is spending its time, it also 516 significantly increases the running time of `gprof', and magnifies 517 statistical inaccuracies. *Note Statistical Sampling Error: 518 Sampling Error. 519 520 `-m NUM' 521 `--min-count=NUM' 522 This option affects execution count output only. Symbols that are 523 executed less than NUM times are suppressed. 524 525 `-nSYMSPEC' 526 `--time=SYMSPEC' 527 The `-n' option causes `gprof', in its call graph analysis, to 528 only propagate times for symbols matching SYMSPEC. 529 530 `-NSYMSPEC' 531 `--no-time=SYMSPEC' 532 The `-n' option causes `gprof', in its call graph analysis, not to 533 propagate times for symbols matching SYMSPEC. 534 535 `-z' 536 `--display-unused-functions' 537 If you give the `-z' option, `gprof' will mention all functions in 538 the flat profile, even those that were never called, and that had 539 no time spent in them. This is useful in conjunction with the 540 `-c' option for discovering which routines were never called. 541 542 543 544 File: gprof.info, Node: Miscellaneous Options, Next: Deprecated Options, Prev: Analysis Options, Up: Invoking 545 546 4.3 Miscellaneous Options 547 ========================= 548 549 `-d[NUM]' 550 `--debug[=NUM]' 551 The `-d NUM' option specifies debugging options. If NUM is not 552 specified, enable all debugging. *Note Debugging `gprof': 553 Debugging. 554 555 `-h' 556 `--help' 557 The `-h' option prints command line usage. 558 559 `-ONAME' 560 `--file-format=NAME' 561 Selects the format of the profile data files. Recognized formats 562 are `auto' (the default), `bsd', `4.4bsd', `magic', and `prof' 563 (not yet supported). 564 565 `-s' 566 `--sum' 567 The `-s' option causes `gprof' to summarize the information in the 568 profile data files it read in, and write out a profile data file 569 called `gmon.sum', which contains all the information from the 570 profile data files that `gprof' read in. The file `gmon.sum' may 571 be one of the specified input files; the effect of this is to 572 merge the data in the other input files into `gmon.sum'. 573 574 Eventually you can run `gprof' again without `-s' to analyze the 575 cumulative data in the file `gmon.sum'. 576 577 `-v' 578 `--version' 579 The `-v' flag causes `gprof' to print the current version number, 580 and then exit. 581 582 583 584 File: gprof.info, Node: Deprecated Options, Next: Symspecs, Prev: Miscellaneous Options, Up: Invoking 585 586 4.4 Deprecated Options 587 ====================== 588 589 These options have been replaced with newer versions that use 590 symspecs. 591 592 `-e FUNCTION_NAME' 593 The `-e FUNCTION' option tells `gprof' to not print information 594 about the function FUNCTION_NAME (and its children...) in the call 595 graph. The function will still be listed as a child of any 596 functions that call it, but its index number will be shown as 597 `[not printed]'. More than one `-e' option may be given; only one 598 FUNCTION_NAME may be indicated with each `-e' option. 599 600 `-E FUNCTION_NAME' 601 The `-E FUNCTION' option works like the `-e' option, but time 602 spent in the function (and children who were not called from 603 anywhere else), will not be used to compute the 604 percentages-of-time for the call graph. More than one `-E' option 605 may be given; only one FUNCTION_NAME may be indicated with each 606 `-E' option. 607 608 `-f FUNCTION_NAME' 609 The `-f FUNCTION' option causes `gprof' to limit the call graph to 610 the function FUNCTION_NAME and its children (and their 611 children...). More than one `-f' option may be given; only one 612 FUNCTION_NAME may be indicated with each `-f' option. 613 614 `-F FUNCTION_NAME' 615 The `-F FUNCTION' option works like the `-f' option, but only time 616 spent in the function and its children (and their children...) 617 will be used to determine total-time and percentages-of-time for 618 the call graph. More than one `-F' option may be given; only one 619 FUNCTION_NAME may be indicated with each `-F' option. The `-F' 620 option overrides the `-E' option. 621 622 623 Note that only one function can be specified with each `-e', `-E', 624 `-f' or `-F' option. To specify more than one function, use multiple 625 options. For example, this command: 626 627 gprof -e boring -f foo -f bar myprogram > gprof.output 628 629 lists in the call graph all functions that were reached from either 630 `foo' or `bar' and were not reachable from `boring'. 631 632 633 File: gprof.info, Node: Symspecs, Prev: Deprecated Options, Up: Invoking 634 635 4.5 Symspecs 636 ============ 637 638 Many of the output options allow functions to be included or excluded 639 using "symspecs" (symbol specifications), which observe the following 640 syntax: 641 642 filename_containing_a_dot 643 | funcname_not_containing_a_dot 644 | linenumber 645 | ( [ any_filename ] `:' ( any_funcname | linenumber ) ) 646 647 Here are some sample symspecs: 648 649 `main.c' 650 Selects everything in file `main.c'--the dot in the string tells 651 `gprof' to interpret the string as a filename, rather than as a 652 function name. To select a file whose name does not contain a 653 dot, a trailing colon should be specified. For example, `odd:' is 654 interpreted as the file named `odd'. 655 656 `main' 657 Selects all functions named `main'. 658 659 Note that there may be multiple instances of the same function name 660 because some of the definitions may be local (i.e., static). 661 Unless a function name is unique in a program, you must use the 662 colon notation explained below to specify a function from a 663 specific source file. 664 665 Sometimes, function names contain dots. In such cases, it is 666 necessary to add a leading colon to the name. For example, 667 `:.mul' selects function `.mul'. 668 669 In some object file formats, symbols have a leading underscore. 670 `gprof' will normally not print these underscores. When you name a 671 symbol in a symspec, you should type it exactly as `gprof' prints 672 it in its output. For example, if the compiler produces a symbol 673 `_main' from your `main' function, `gprof' still prints it as 674 `main' in its output, so you should use `main' in symspecs. 675 676 `main.c:main' 677 Selects function `main' in file `main.c'. 678 679 `main.c:134' 680 Selects line 134 in file `main.c'. 681 682 683 File: gprof.info, Node: Output, Next: Inaccuracy, Prev: Invoking, Up: Top 684 685 5 Interpreting `gprof''s Output 686 ******************************* 687 688 `gprof' can produce several different output styles, the most important 689 of which are described below. The simplest output styles (file 690 information, execution count, and function and file ordering) are not 691 described here, but are documented with the respective options that 692 trigger them. *Note Output Options: Output Options. 693 694 * Menu: 695 696 * Flat Profile:: The flat profile shows how much time was spent 697 executing directly in each function. 698 * Call Graph:: The call graph shows which functions called which 699 others, and how much time each function used 700 when its subroutine calls are included. 701 * Line-by-line:: `gprof' can analyze individual source code lines 702 * Annotated Source:: The annotated source listing displays source code 703 labeled with execution counts 704 705 706 File: gprof.info, Node: Flat Profile, Next: Call Graph, Up: Output 707 708 5.1 The Flat Profile 709 ==================== 710 711 The "flat profile" shows the total amount of time your program spent 712 executing each function. Unless the `-z' option is given, functions 713 with no apparent time spent in them, and no apparent calls to them, are 714 not mentioned. Note that if a function was not compiled for profiling, 715 and didn't run long enough to show up on the program counter histogram, 716 it will be indistinguishable from a function that was never called. 717 718 This is part of a flat profile for a small program: 719 720 Flat profile: 721 722 Each sample counts as 0.01 seconds. 723 % cumulative self self total 724 time seconds seconds calls ms/call ms/call name 725 33.34 0.02 0.02 7208 0.00 0.00 open 726 16.67 0.03 0.01 244 0.04 0.12 offtime 727 16.67 0.04 0.01 8 1.25 1.25 memccpy 728 16.67 0.05 0.01 7 1.43 1.43 write 729 16.67 0.06 0.01 mcount 730 0.00 0.06 0.00 236 0.00 0.00 tzset 731 0.00 0.06 0.00 192 0.00 0.00 tolower 732 0.00 0.06 0.00 47 0.00 0.00 strlen 733 0.00 0.06 0.00 45 0.00 0.00 strchr 734 0.00 0.06 0.00 1 0.00 50.00 main 735 0.00 0.06 0.00 1 0.00 0.00 memcpy 736 0.00 0.06 0.00 1 0.00 10.11 print 737 0.00 0.06 0.00 1 0.00 0.00 profil 738 0.00 0.06 0.00 1 0.00 50.00 report 739 ... 740 741 The functions are sorted first by decreasing run-time spent in them, 742 then by decreasing number of calls, then alphabetically by name. The 743 functions `mcount' and `profil' are part of the profiling apparatus and 744 appear in every flat profile; their time gives a measure of the amount 745 of overhead due to profiling. 746 747 Just before the column headers, a statement appears indicating how 748 much time each sample counted as. This "sampling period" estimates the 749 margin of error in each of the time figures. A time figure that is not 750 much larger than this is not reliable. In this example, each sample 751 counted as 0.01 seconds, suggesting a 100 Hz sampling rate. The 752 program's total execution time was 0.06 seconds, as indicated by the 753 `cumulative seconds' field. Since each sample counted for 0.01 754 seconds, this means only six samples were taken during the run. Two of 755 the samples occurred while the program was in the `open' function, as 756 indicated by the `self seconds' field. Each of the other four samples 757 occurred one each in `offtime', `memccpy', `write', and `mcount'. 758 Since only six samples were taken, none of these values can be regarded 759 as particularly reliable. In another run, the `self seconds' field for 760 `mcount' might well be `0.00' or `0.02'. *Note Statistical Sampling 761 Error: Sampling Error, for a complete discussion. 762 763 The remaining functions in the listing (those whose `self seconds' 764 field is `0.00') didn't appear in the histogram samples at all. 765 However, the call graph indicated that they were called, so therefore 766 they are listed, sorted in decreasing order by the `calls' field. 767 Clearly some time was spent executing these functions, but the paucity 768 of histogram samples prevents any determination of how much time each 769 took. 770 771 Here is what the fields in each line mean: 772 773 `% time' 774 This is the percentage of the total execution time your program 775 spent in this function. These should all add up to 100%. 776 777 `cumulative seconds' 778 This is the cumulative total number of seconds the computer spent 779 executing this functions, plus the time spent in all the functions 780 above this one in this table. 781 782 `self seconds' 783 This is the number of seconds accounted for by this function alone. 784 The flat profile listing is sorted first by this number. 785 786 `calls' 787 This is the total number of times the function was called. If the 788 function was never called, or the number of times it was called 789 cannot be determined (probably because the function was not 790 compiled with profiling enabled), the "calls" field is blank. 791 792 `self ms/call' 793 This represents the average number of milliseconds spent in this 794 function per call, if this function is profiled. Otherwise, this 795 field is blank for this function. 796 797 `total ms/call' 798 This represents the average number of milliseconds spent in this 799 function and its descendants per call, if this function is 800 profiled. Otherwise, this field is blank for this function. This 801 is the only field in the flat profile that uses call graph 802 analysis. 803 804 `name' 805 This is the name of the function. The flat profile is sorted by 806 this field alphabetically after the "self seconds" and "calls" 807 fields are sorted. 808 809 810 File: gprof.info, Node: Call Graph, Next: Line-by-line, Prev: Flat Profile, Up: Output 811 812 5.2 The Call Graph 813 ================== 814 815 The "call graph" shows how much time was spent in each function and its 816 children. From this information, you can find functions that, while 817 they themselves may not have used much time, called other functions 818 that did use unusual amounts of time. 819 820 Here is a sample call from a small program. This call came from the 821 same `gprof' run as the flat profile example in the previous section. 822 823 granularity: each sample hit covers 2 byte(s) for 20.00% of 0.05 seconds 824 825 index % time self children called name 826 <spontaneous> 827 [1] 100.0 0.00 0.05 start [1] 828 0.00 0.05 1/1 main [2] 829 0.00 0.00 1/2 on_exit [28] 830 0.00 0.00 1/1 exit [59] 831 ----------------------------------------------- 832 0.00 0.05 1/1 start [1] 833 [2] 100.0 0.00 0.05 1 main [2] 834 0.00 0.05 1/1 report [3] 835 ----------------------------------------------- 836 0.00 0.05 1/1 main [2] 837 [3] 100.0 0.00 0.05 1 report [3] 838 0.00 0.03 8/8 timelocal [6] 839 0.00 0.01 1/1 print [9] 840 0.00 0.01 9/9 fgets [12] 841 0.00 0.00 12/34 strncmp <cycle 1> [40] 842 0.00 0.00 8/8 lookup [20] 843 0.00 0.00 1/1 fopen [21] 844 0.00 0.00 8/8 chewtime [24] 845 0.00 0.00 8/16 skipspace [44] 846 ----------------------------------------------- 847 [4] 59.8 0.01 0.02 8+472 <cycle 2 as a whole> [4] 848 0.01 0.02 244+260 offtime <cycle 2> [7] 849 0.00 0.00 236+1 tzset <cycle 2> [26] 850 ----------------------------------------------- 851 852 The lines full of dashes divide this table into "entries", one for 853 each function. Each entry has one or more lines. 854 855 In each entry, the primary line is the one that starts with an index 856 number in square brackets. The end of this line says which function 857 the entry is for. The preceding lines in the entry describe the 858 callers of this function and the following lines describe its 859 subroutines (also called "children" when we speak of the call graph). 860 861 The entries are sorted by time spent in the function and its 862 subroutines. 863 864 The internal profiling function `mcount' (*note The Flat Profile: 865 Flat Profile.) is never mentioned in the call graph. 866 867 * Menu: 868 869 * Primary:: Details of the primary line's contents. 870 * Callers:: Details of caller-lines' contents. 871 * Subroutines:: Details of subroutine-lines' contents. 872 * Cycles:: When there are cycles of recursion, 873 such as `a' calls `b' calls `a'... 874 875 876 File: gprof.info, Node: Primary, Next: Callers, Up: Call Graph 877 878 5.2.1 The Primary Line 879 ---------------------- 880 881 The "primary line" in a call graph entry is the line that describes the 882 function which the entry is about and gives the overall statistics for 883 this function. 884 885 For reference, we repeat the primary line from the entry for function 886 `report' in our main example, together with the heading line that shows 887 the names of the fields: 888 889 index % time self children called name 890 ... 891 [3] 100.0 0.00 0.05 1 report [3] 892 893 Here is what the fields in the primary line mean: 894 895 `index' 896 Entries are numbered with consecutive integers. Each function 897 therefore has an index number, which appears at the beginning of 898 its primary line. 899 900 Each cross-reference to a function, as a caller or subroutine of 901 another, gives its index number as well as its name. The index 902 number guides you if you wish to look for the entry for that 903 function. 904 905 `% time' 906 This is the percentage of the total time that was spent in this 907 function, including time spent in subroutines called from this 908 function. 909 910 The time spent in this function is counted again for the callers of 911 this function. Therefore, adding up these percentages is 912 meaningless. 913 914 `self' 915 This is the total amount of time spent in this function. This 916 should be identical to the number printed in the `seconds' field 917 for this function in the flat profile. 918 919 `children' 920 This is the total amount of time spent in the subroutine calls 921 made by this function. This should be equal to the sum of all the 922 `self' and `children' entries of the children listed directly 923 below this function. 924 925 `called' 926 This is the number of times the function was called. 927 928 If the function called itself recursively, there are two numbers, 929 separated by a `+'. The first number counts non-recursive calls, 930 and the second counts recursive calls. 931 932 In the example above, the function `report' was called once from 933 `main'. 934 935 `name' 936 This is the name of the current function. The index number is 937 repeated after it. 938 939 If the function is part of a cycle of recursion, the cycle number 940 is printed between the function's name and the index number (*note 941 How Mutually Recursive Functions Are Described: Cycles.). For 942 example, if function `gnurr' is part of cycle number one, and has 943 index number twelve, its primary line would be end like this: 944 945 gnurr <cycle 1> [12] 946 947 948 File: gprof.info, Node: Callers, Next: Subroutines, Prev: Primary, Up: Call Graph 949 950 5.2.2 Lines for a Function's Callers 951 ------------------------------------ 952 953 A function's entry has a line for each function it was called by. 954 These lines' fields correspond to the fields of the primary line, but 955 their meanings are different because of the difference in context. 956 957 For reference, we repeat two lines from the entry for the function 958 `report', the primary line and one caller-line preceding it, together 959 with the heading line that shows the names of the fields: 960 961 index % time self children called name 962 ... 963 0.00 0.05 1/1 main [2] 964 [3] 100.0 0.00 0.05 1 report [3] 965 966 Here are the meanings of the fields in the caller-line for `report' 967 called from `main': 968 969 `self' 970 An estimate of the amount of time spent in `report' itself when it 971 was called from `main'. 972 973 `children' 974 An estimate of the amount of time spent in subroutines of `report' 975 when `report' was called from `main'. 976 977 The sum of the `self' and `children' fields is an estimate of the 978 amount of time spent within calls to `report' from `main'. 979 980 `called' 981 Two numbers: the number of times `report' was called from `main', 982 followed by the total number of non-recursive calls to `report' 983 from all its callers. 984 985 `name and index number' 986 The name of the caller of `report' to which this line applies, 987 followed by the caller's index number. 988 989 Not all functions have entries in the call graph; some options to 990 `gprof' request the omission of certain functions. When a caller 991 has no entry of its own, it still has caller-lines in the entries 992 of the functions it calls. 993 994 If the caller is part of a recursion cycle, the cycle number is 995 printed between the name and the index number. 996 997 If the identity of the callers of a function cannot be determined, a 998 dummy caller-line is printed which has `<spontaneous>' as the "caller's 999 name" and all other fields blank. This can happen for signal handlers. 1000 1001 1002 File: gprof.info, Node: Subroutines, Next: Cycles, Prev: Callers, Up: Call Graph 1003 1004 5.2.3 Lines for a Function's Subroutines 1005 ---------------------------------------- 1006 1007 A function's entry has a line for each of its subroutines--in other 1008 words, a line for each other function that it called. These lines' 1009 fields correspond to the fields of the primary line, but their meanings 1010 are different because of the difference in context. 1011 1012 For reference, we repeat two lines from the entry for the function 1013 `main', the primary line and a line for a subroutine, together with the 1014 heading line that shows the names of the fields: 1015 1016 index % time self children called name 1017 ... 1018 [2] 100.0 0.00 0.05 1 main [2] 1019 0.00 0.05 1/1 report [3] 1020 1021 Here are the meanings of the fields in the subroutine-line for `main' 1022 calling `report': 1023 1024 `self' 1025 An estimate of the amount of time spent directly within `report' 1026 when `report' was called from `main'. 1027 1028 `children' 1029 An estimate of the amount of time spent in subroutines of `report' 1030 when `report' was called from `main'. 1031 1032 The sum of the `self' and `children' fields is an estimate of the 1033 total time spent in calls to `report' from `main'. 1034 1035 `called' 1036 Two numbers, the number of calls to `report' from `main' followed 1037 by the total number of non-recursive calls to `report'. This 1038 ratio is used to determine how much of `report''s `self' and 1039 `children' time gets credited to `main'. *Note Estimating 1040 `children' Times: Assumptions. 1041 1042 `name' 1043 The name of the subroutine of `main' to which this line applies, 1044 followed by the subroutine's index number. 1045 1046 If the caller is part of a recursion cycle, the cycle number is 1047 printed between the name and the index number. 1048 1049 1050 File: gprof.info, Node: Cycles, Prev: Subroutines, Up: Call Graph 1051 1052 5.2.4 How Mutually Recursive Functions Are Described 1053 ---------------------------------------------------- 1054 1055 The graph may be complicated by the presence of "cycles of recursion" 1056 in the call graph. A cycle exists if a function calls another function 1057 that (directly or indirectly) calls (or appears to call) the original 1058 function. For example: if `a' calls `b', and `b' calls `a', then `a' 1059 and `b' form a cycle. 1060 1061 Whenever there are call paths both ways between a pair of functions, 1062 they belong to the same cycle. If `a' and `b' call each other and `b' 1063 and `c' call each other, all three make one cycle. Note that even if 1064 `b' only calls `a' if it was not called from `a', `gprof' cannot 1065 determine this, so `a' and `b' are still considered a cycle. 1066 1067 The cycles are numbered with consecutive integers. When a function 1068 belongs to a cycle, each time the function name appears in the call 1069 graph it is followed by `<cycle NUMBER>'. 1070 1071 The reason cycles matter is that they make the time values in the 1072 call graph paradoxical. The "time spent in children" of `a' should 1073 include the time spent in its subroutine `b' and in `b''s 1074 subroutines--but one of `b''s subroutines is `a'! How much of `a''s 1075 time should be included in the children of `a', when `a' is indirectly 1076 recursive? 1077 1078 The way `gprof' resolves this paradox is by creating a single entry 1079 for the cycle as a whole. The primary line of this entry describes the 1080 total time spent directly in the functions of the cycle. The 1081 "subroutines" of the cycle are the individual functions of the cycle, 1082 and all other functions that were called directly by them. The 1083 "callers" of the cycle are the functions, outside the cycle, that 1084 called functions in the cycle. 1085 1086 Here is an example portion of a call graph which shows a cycle 1087 containing functions `a' and `b'. The cycle was entered by a call to 1088 `a' from `main'; both `a' and `b' called `c'. 1089 1090 index % time self children called name 1091 ---------------------------------------- 1092 1.77 0 1/1 main [2] 1093 [3] 91.71 1.77 0 1+5 <cycle 1 as a whole> [3] 1094 1.02 0 3 b <cycle 1> [4] 1095 0.75 0 2 a <cycle 1> [5] 1096 ---------------------------------------- 1097 3 a <cycle 1> [5] 1098 [4] 52.85 1.02 0 0 b <cycle 1> [4] 1099 2 a <cycle 1> [5] 1100 0 0 3/6 c [6] 1101 ---------------------------------------- 1102 1.77 0 1/1 main [2] 1103 2 b <cycle 1> [4] 1104 [5] 38.86 0.75 0 1 a <cycle 1> [5] 1105 3 b <cycle 1> [4] 1106 0 0 3/6 c [6] 1107 ---------------------------------------- 1108 1109 (The entire call graph for this program contains in addition an entry 1110 for `main', which calls `a', and an entry for `c', with callers `a' and 1111 `b'.) 1112 1113 index % time self children called name 1114 <spontaneous> 1115 [1] 100.00 0 1.93 0 start [1] 1116 0.16 1.77 1/1 main [2] 1117 ---------------------------------------- 1118 0.16 1.77 1/1 start [1] 1119 [2] 100.00 0.16 1.77 1 main [2] 1120 1.77 0 1/1 a <cycle 1> [5] 1121 ---------------------------------------- 1122 1.77 0 1/1 main [2] 1123 [3] 91.71 1.77 0 1+5 <cycle 1 as a whole> [3] 1124 1.02 0 3 b <cycle 1> [4] 1125 0.75 0 2 a <cycle 1> [5] 1126 0 0 6/6 c [6] 1127 ---------------------------------------- 1128 3 a <cycle 1> [5] 1129 [4] 52.85 1.02 0 0 b <cycle 1> [4] 1130 2 a <cycle 1> [5] 1131 0 0 3/6 c [6] 1132 ---------------------------------------- 1133 1.77 0 1/1 main [2] 1134 2 b <cycle 1> [4] 1135 [5] 38.86 0.75 0 1 a <cycle 1> [5] 1136 3 b <cycle 1> [4] 1137 0 0 3/6 c [6] 1138 ---------------------------------------- 1139 0 0 3/6 b <cycle 1> [4] 1140 0 0 3/6 a <cycle 1> [5] 1141 [6] 0.00 0 0 6 c [6] 1142 ---------------------------------------- 1143 1144 The `self' field of the cycle's primary line is the total time spent 1145 in all the functions of the cycle. It equals the sum of the `self' 1146 fields for the individual functions in the cycle, found in the entry in 1147 the subroutine lines for these functions. 1148 1149 The `children' fields of the cycle's primary line and subroutine 1150 lines count only subroutines outside the cycle. Even though `a' calls 1151 `b', the time spent in those calls to `b' is not counted in `a''s 1152 `children' time. Thus, we do not encounter the problem of what to do 1153 when the time in those calls to `b' includes indirect recursive calls 1154 back to `a'. 1155 1156 The `children' field of a caller-line in the cycle's entry estimates 1157 the amount of time spent _in the whole cycle_, and its other 1158 subroutines, on the times when that caller called a function in the 1159 cycle. 1160 1161 The `called' field in the primary line for the cycle has two numbers: 1162 first, the number of times functions in the cycle were called by 1163 functions outside the cycle; second, the number of times they were 1164 called by functions in the cycle (including times when a function in 1165 the cycle calls itself). This is a generalization of the usual split 1166 into non-recursive and recursive calls. 1167 1168 The `called' field of a subroutine-line for a cycle member in the 1169 cycle's entry says how many time that function was called from 1170 functions in the cycle. The total of all these is the second number in 1171 the primary line's `called' field. 1172 1173 In the individual entry for a function in a cycle, the other 1174 functions in the same cycle can appear as subroutines and as callers. 1175 These lines show how many times each function in the cycle called or 1176 was called from each other function in the cycle. The `self' and 1177 `children' fields in these lines are blank because of the difficulty of 1178 defining meanings for them when recursion is going on. 1179 1180 1181 File: gprof.info, Node: Line-by-line, Next: Annotated Source, Prev: Call Graph, Up: Output 1182 1183 5.3 Line-by-line Profiling 1184 ========================== 1185 1186 `gprof''s `-l' option causes the program to perform "line-by-line" 1187 profiling. In this mode, histogram samples are assigned not to 1188 functions, but to individual lines of source code. This only works 1189 with programs compiled with older versions of the `gcc' compiler. 1190 Newer versions of `gcc' use a different program - `gcov' - to display 1191 line-by-line profiling information. 1192 1193 With the older versions of `gcc' the program usually has to be 1194 compiled with a `-g' option, in addition to `-pg', in order to generate 1195 debugging symbols for tracking source code lines. Note, in much older 1196 versions of `gcc' the program had to be compiled with the `-a' command 1197 line option as well. 1198 1199 The flat profile is the most useful output table in line-by-line 1200 mode. The call graph isn't as useful as normal, since the current 1201 version of `gprof' does not propagate call graph arcs from source code 1202 lines to the enclosing function. The call graph does, however, show 1203 each line of code that called each function, along with a count. 1204 1205 Here is a section of `gprof''s output, without line-by-line 1206 profiling. Note that `ct_init' accounted for four histogram hits, and 1207 13327 calls to `init_block'. 1208 1209 Flat profile: 1210 1211 Each sample counts as 0.01 seconds. 1212 % cumulative self self total 1213 time seconds seconds calls us/call us/call name 1214 30.77 0.13 0.04 6335 6.31 6.31 ct_init 1215 1216 1217 Call graph (explanation follows) 1218 1219 1220 granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds 1221 1222 index % time self children called name 1223 1224 0.00 0.00 1/13496 name_too_long 1225 0.00 0.00 40/13496 deflate 1226 0.00 0.00 128/13496 deflate_fast 1227 0.00 0.00 13327/13496 ct_init 1228 [7] 0.0 0.00 0.00 13496 init_block 1229 1230 Now let's look at some of `gprof''s output from the same program run, 1231 this time with line-by-line profiling enabled. Note that `ct_init''s 1232 four histogram hits are broken down into four lines of source code--one 1233 hit occurred on each of lines 349, 351, 382 and 385. In the call graph, 1234 note how `ct_init''s 13327 calls to `init_block' are broken down into 1235 one call from line 396, 3071 calls from line 384, 3730 calls from line 1236 385, and 6525 calls from 387. 1237 1238 Flat profile: 1239 1240 Each sample counts as 0.01 seconds. 1241 % cumulative self 1242 time seconds seconds calls name 1243 7.69 0.10 0.01 ct_init (trees.c:349) 1244 7.69 0.11 0.01 ct_init (trees.c:351) 1245 7.69 0.12 0.01 ct_init (trees.c:382) 1246 7.69 0.13 0.01 ct_init (trees.c:385) 1247 1248 1249 Call graph (explanation follows) 1250 1251 1252 granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds 1253 1254 % time self children called name 1255 1256 0.00 0.00 1/13496 name_too_long (gzip.c:1440) 1257 0.00 0.00 1/13496 deflate (deflate.c:763) 1258 0.00 0.00 1/13496 ct_init (trees.c:396) 1259 0.00 0.00 2/13496 deflate (deflate.c:727) 1260 0.00 0.00 4/13496 deflate (deflate.c:686) 1261 0.00 0.00 5/13496 deflate (deflate.c:675) 1262 0.00 0.00 12/13496 deflate (deflate.c:679) 1263 0.00 0.00 16/13496 deflate (deflate.c:730) 1264 0.00 0.00 128/13496 deflate_fast (deflate.c:654) 1265 0.00 0.00 3071/13496 ct_init (trees.c:384) 1266 0.00 0.00 3730/13496 ct_init (trees.c:385) 1267 0.00 0.00 6525/13496 ct_init (trees.c:387) 1268 [6] 0.0 0.00 0.00 13496 init_block (trees.c:408) 1269 1270 1271 File: gprof.info, Node: Annotated Source, Prev: Line-by-line, Up: Output 1272 1273 5.4 The Annotated Source Listing 1274 ================================ 1275 1276 `gprof''s `-A' option triggers an annotated source listing, which lists 1277 the program's source code, each function labeled with the number of 1278 times it was called. You may also need to specify the `-I' option, if 1279 `gprof' can't find the source code files. 1280 1281 With older versions of `gcc' compiling with `gcc ... -g -pg -a' 1282 augments your program with basic-block counting code, in addition to 1283 function counting code. This enables `gprof' to determine how many 1284 times each line of code was executed. With newer versions of `gcc' 1285 support for displaying basic-block counts is provided by the `gcov' 1286 program. 1287 1288 For example, consider the following function, taken from gzip, with 1289 line numbers added: 1290 1291 1 ulg updcrc(s, n) 1292 2 uch *s; 1293 3 unsigned n; 1294 4 { 1295 5 register ulg c; 1296 6 1297 7 static ulg crc = (ulg)0xffffffffL; 1298 8 1299 9 if (s == NULL) { 1300 10 c = 0xffffffffL; 1301 11 } else { 1302 12 c = crc; 1303 13 if (n) do { 1304 14 c = crc_32_tab[...]; 1305 15 } while (--n); 1306 16 } 1307 17 crc = c; 1308 18 return c ^ 0xffffffffL; 1309 19 } 1310 1311 `updcrc' has at least five basic-blocks. One is the function 1312 itself. The `if' statement on line 9 generates two more basic-blocks, 1313 one for each branch of the `if'. A fourth basic-block results from the 1314 `if' on line 13, and the contents of the `do' loop form the fifth 1315 basic-block. The compiler may also generate additional basic-blocks to 1316 handle various special cases. 1317 1318 A program augmented for basic-block counting can be analyzed with 1319 `gprof -l -A'. The `-x' option is also helpful, to ensure that each 1320 line of code is labeled at least once. Here is `updcrc''s annotated 1321 source listing for a sample `gzip' run: 1322 1323 ulg updcrc(s, n) 1324 uch *s; 1325 unsigned n; 1326 2 ->{ 1327 register ulg c; 1328 1329 static ulg crc = (ulg)0xffffffffL; 1330 1331 2 -> if (s == NULL) { 1332 1 -> c = 0xffffffffL; 1333 1 -> } else { 1334 1 -> c = crc; 1335 1 -> if (n) do { 1336 26312 -> c = crc_32_tab[...]; 1337 26312,1,26311 -> } while (--n); 1338 } 1339 2 -> crc = c; 1340 2 -> return c ^ 0xffffffffL; 1341 2 ->} 1342 1343 In this example, the function was called twice, passing once through 1344 each branch of the `if' statement. The body of the `do' loop was 1345 executed a total of 26312 times. Note how the `while' statement is 1346 annotated. It began execution 26312 times, once for each iteration 1347 through the loop. One of those times (the last time) it exited, while 1348 it branched back to the beginning of the loop 26311 times. 1349 1350 1351 File: gprof.info, Node: Inaccuracy, Next: How do I?, Prev: Output, Up: Top 1352 1353 6 Inaccuracy of `gprof' Output 1354 ****************************** 1355 1356 * Menu: 1357 1358 * Sampling Error:: Statistical margins of error 1359 * Assumptions:: Estimating children times 1360 1361 1362 File: gprof.info, Node: Sampling Error, Next: Assumptions, Up: Inaccuracy 1363 1364 6.1 Statistical Sampling Error 1365 ============================== 1366 1367 The run-time figures that `gprof' gives you are based on a sampling 1368 process, so they are subject to statistical inaccuracy. If a function 1369 runs only a small amount of time, so that on the average the sampling 1370 process ought to catch that function in the act only once, there is a 1371 pretty good chance it will actually find that function zero times, or 1372 twice. 1373 1374 By contrast, the number-of-calls and basic-block figures are derived 1375 by counting, not sampling. They are completely accurate and will not 1376 vary from run to run if your program is deterministic. 1377 1378 The "sampling period" that is printed at the beginning of the flat 1379 profile says how often samples are taken. The rule of thumb is that a 1380 run-time figure is accurate if it is considerably bigger than the 1381 sampling period. 1382 1383 The actual amount of error can be predicted. For N samples, the 1384 _expected_ error is the square-root of N. For example, if the sampling 1385 period is 0.01 seconds and `foo''s run-time is 1 second, N is 100 1386 samples (1 second/0.01 seconds), sqrt(N) is 10 samples, so the expected 1387 error in `foo''s run-time is 0.1 seconds (10*0.01 seconds), or ten 1388 percent of the observed value. Again, if the sampling period is 0.01 1389 seconds and `bar''s run-time is 100 seconds, N is 10000 samples, 1390 sqrt(N) is 100 samples, so the expected error in `bar''s run-time is 1 1391 second, or one percent of the observed value. It is likely to vary 1392 this much _on the average_ from one profiling run to the next. 1393 (_Sometimes_ it will vary more.) 1394 1395 This does not mean that a small run-time figure is devoid of 1396 information. If the program's _total_ run-time is large, a small 1397 run-time for one function does tell you that that function used an 1398 insignificant fraction of the whole program's time. Usually this means 1399 it is not worth optimizing. 1400 1401 One way to get more accuracy is to give your program more (but 1402 similar) input data so it will take longer. Another way is to combine 1403 the data from several runs, using the `-s' option of `gprof'. Here is 1404 how: 1405 1406 1. Run your program once. 1407 1408 2. Issue the command `mv gmon.out gmon.sum'. 1409 1410 3. Run your program again, the same as before. 1411 1412 4. Merge the new data in `gmon.out' into `gmon.sum' with this command: 1413 1414 gprof -s EXECUTABLE-FILE gmon.out gmon.sum 1415 1416 5. Repeat the last two steps as often as you wish. 1417 1418 6. Analyze the cumulative data using this command: 1419 1420 gprof EXECUTABLE-FILE gmon.sum > OUTPUT-FILE 1421 1422 1423 File: gprof.info, Node: Assumptions, Prev: Sampling Error, Up: Inaccuracy 1424 1425 6.2 Estimating `children' Times 1426 =============================== 1427 1428 Some of the figures in the call graph are estimates--for example, the 1429 `children' time values and all the time figures in caller and 1430 subroutine lines. 1431 1432 There is no direct information about these measurements in the 1433 profile data itself. Instead, `gprof' estimates them by making an 1434 assumption about your program that might or might not be true. 1435 1436 The assumption made is that the average time spent in each call to 1437 any function `foo' is not correlated with who called `foo'. If `foo' 1438 used 5 seconds in all, and 2/5 of the calls to `foo' came from `a', 1439 then `foo' contributes 2 seconds to `a''s `children' time, by 1440 assumption. 1441 1442 This assumption is usually true enough, but for some programs it is 1443 far from true. Suppose that `foo' returns very quickly when its 1444 argument is zero; suppose that `a' always passes zero as an argument, 1445 while other callers of `foo' pass other arguments. In this program, 1446 all the time spent in `foo' is in the calls from callers other than `a'. 1447 But `gprof' has no way of knowing this; it will blindly and incorrectly 1448 charge 2 seconds of time in `foo' to the children of `a'. 1449 1450 We hope some day to put more complete data into `gmon.out', so that 1451 this assumption is no longer needed, if we can figure out how. For the 1452 novice, the estimated figures are usually more useful than misleading. 1453 1454 1455 File: gprof.info, Node: How do I?, Next: Incompatibilities, Prev: Inaccuracy, Up: Top 1456 1457 7 Answers to Common Questions 1458 ***************************** 1459 1460 How can I get more exact information about hot spots in my program? 1461 Looking at the per-line call counts only tells part of the story. 1462 Because `gprof' can only report call times and counts by function, 1463 the best way to get finer-grained information on where the program 1464 is spending its time is to re-factor large functions into sequences 1465 of calls to smaller ones. Beware however that this can introduce 1466 artificial hot spots since compiling with `-pg' adds a significant 1467 overhead to function calls. An alternative solution is to use a 1468 non-intrusive profiler, e.g. oprofile. 1469 1470 How do I find which lines in my program were executed the most times? 1471 Use the `gcov' program. 1472 1473 How do I find which lines in my program called a particular function? 1474 Use `gprof -l' and lookup the function in the call graph. The 1475 callers will be broken down by function and line number. 1476 1477 How do I analyze a program that runs for less than a second? 1478 Try using a shell script like this one: 1479 1480 for i in `seq 1 100`; do 1481 fastprog 1482 mv gmon.out gmon.out.$i 1483 done 1484 1485 gprof -s fastprog gmon.out.* 1486 1487 gprof fastprog gmon.sum 1488 1489 If your program is completely deterministic, all the call counts 1490 will be simple multiples of 100 (i.e., a function called once in 1491 each run will appear with a call count of 100). 1492 1493 1494 1495 File: gprof.info, Node: Incompatibilities, Next: Details, Prev: How do I?, Up: Top 1496 1497 8 Incompatibilities with Unix `gprof' 1498 ************************************* 1499 1500 GNU `gprof' and Berkeley Unix `gprof' use the same data file 1501 `gmon.out', and provide essentially the same information. But there 1502 are a few differences. 1503 1504 * GNU `gprof' uses a new, generalized file format with support for 1505 basic-block execution counts and non-realtime histograms. A magic 1506 cookie and version number allows `gprof' to easily identify new 1507 style files. Old BSD-style files can still be read. *Note 1508 Profiling Data File Format: File Format. 1509 1510 * For a recursive function, Unix `gprof' lists the function as a 1511 parent and as a child, with a `calls' field that lists the number 1512 of recursive calls. GNU `gprof' omits these lines and puts the 1513 number of recursive calls in the primary line. 1514 1515 * When a function is suppressed from the call graph with `-e', GNU 1516 `gprof' still lists it as a subroutine of functions that call it. 1517 1518 * GNU `gprof' accepts the `-k' with its argument in the form 1519 `from/to', instead of `from to'. 1520 1521 * In the annotated source listing, if there are multiple basic 1522 blocks on the same line, GNU `gprof' prints all of their counts, 1523 separated by commas. 1524 1525 * The blurbs, field widths, and output formats are different. GNU 1526 `gprof' prints blurbs after the tables, so that you can see the 1527 tables without skipping the blurbs. 1528 1529 1530 File: gprof.info, Node: Details, Next: GNU Free Documentation License, Prev: Incompatibilities, Up: Top 1531 1532 9 Details of Profiling 1533 ********************** 1534 1535 * Menu: 1536 1537 * Implementation:: How a program collects profiling information 1538 * File Format:: Format of `gmon.out' files 1539 * Internals:: `gprof''s internal operation 1540 * Debugging:: Using `gprof''s `-d' option 1541 1542 1543 File: gprof.info, Node: Implementation, Next: File Format, Up: Details 1544 1545 9.1 Implementation of Profiling 1546 =============================== 1547 1548 Profiling works by changing how every function in your program is 1549 compiled so that when it is called, it will stash away some information 1550 about where it was called from. From this, the profiler can figure out 1551 what function called it, and can count how many times it was called. 1552 This change is made by the compiler when your program is compiled with 1553 the `-pg' option, which causes every function to call `mcount' (or 1554 `_mcount', or `__mcount', depending on the OS and compiler) as one of 1555 its first operations. 1556 1557 The `mcount' routine, included in the profiling library, is 1558 responsible for recording in an in-memory call graph table both its 1559 parent routine (the child) and its parent's parent. This is typically 1560 done by examining the stack frame to find both the address of the 1561 child, and the return address in the original parent. Since this is a 1562 very machine-dependent operation, `mcount' itself is typically a short 1563 assembly-language stub routine that extracts the required information, 1564 and then calls `__mcount_internal' (a normal C function) with two 1565 arguments--`frompc' and `selfpc'. `__mcount_internal' is responsible 1566 for maintaining the in-memory call graph, which records `frompc', 1567 `selfpc', and the number of times each of these call arcs was traversed. 1568 1569 GCC Version 2 provides a magical function 1570 (`__builtin_return_address'), which allows a generic `mcount' function 1571 to extract the required information from the stack frame. However, on 1572 some architectures, most notably the SPARC, using this builtin can be 1573 very computationally expensive, and an assembly language version of 1574 `mcount' is used for performance reasons. 1575 1576 Number-of-calls information for library routines is collected by 1577 using a special version of the C library. The programs in it are the 1578 same as in the usual C library, but they were compiled with `-pg'. If 1579 you link your program with `gcc ... -pg', it automatically uses the 1580 profiling version of the library. 1581 1582 Profiling also involves watching your program as it runs, and 1583 keeping a histogram of where the program counter happens to be every 1584 now and then. Typically the program counter is looked at around 100 1585 times per second of run time, but the exact frequency may vary from 1586 system to system. 1587 1588 This is done is one of two ways. Most UNIX-like operating systems 1589 provide a `profil()' system call, which registers a memory array with 1590 the kernel, along with a scale factor that determines how the program's 1591 address space maps into the array. Typical scaling values cause every 1592 2 to 8 bytes of address space to map into a single array slot. On 1593 every tick of the system clock (assuming the profiled program is 1594 running), the value of the program counter is examined and the 1595 corresponding slot in the memory array is incremented. Since this is 1596 done in the kernel, which had to interrupt the process anyway to handle 1597 the clock interrupt, very little additional system overhead is required. 1598 1599 However, some operating systems, most notably Linux 2.0 (and 1600 earlier), do not provide a `profil()' system call. On such a system, 1601 arrangements are made for the kernel to periodically deliver a signal 1602 to the process (typically via `setitimer()'), which then performs the 1603 same operation of examining the program counter and incrementing a slot 1604 in the memory array. Since this method requires a signal to be 1605 delivered to user space every time a sample is taken, it uses 1606 considerably more overhead than kernel-based profiling. Also, due to 1607 the added delay required to deliver the signal, this method is less 1608 accurate as well. 1609 1610 A special startup routine allocates memory for the histogram and 1611 either calls `profil()' or sets up a clock signal handler. This 1612 routine (`monstartup') can be invoked in several ways. On Linux 1613 systems, a special profiling startup file `gcrt0.o', which invokes 1614 `monstartup' before `main', is used instead of the default `crt0.o'. 1615 Use of this special startup file is one of the effects of using `gcc 1616 ... -pg' to link. On SPARC systems, no special startup files are used. 1617 Rather, the `mcount' routine, when it is invoked for the first time 1618 (typically when `main' is called), calls `monstartup'. 1619 1620 If the compiler's `-a' option was used, basic-block counting is also 1621 enabled. Each object file is then compiled with a static array of 1622 counts, initially zero. In the executable code, every time a new 1623 basic-block begins (i.e., when an `if' statement appears), an extra 1624 instruction is inserted to increment the corresponding count in the 1625 array. At compile time, a paired array was constructed that recorded 1626 the starting address of each basic-block. Taken together, the two 1627 arrays record the starting address of every basic-block, along with the 1628 number of times it was executed. 1629 1630 The profiling library also includes a function (`mcleanup') which is 1631 typically registered using `atexit()' to be called as the program 1632 exits, and is responsible for writing the file `gmon.out'. Profiling 1633 is turned off, various headers are output, and the histogram is 1634 written, followed by the call-graph arcs and the basic-block counts. 1635 1636 The output from `gprof' gives no indication of parts of your program 1637 that are limited by I/O or swapping bandwidth. This is because samples 1638 of the program counter are taken at fixed intervals of the program's 1639 run time. Therefore, the time measurements in `gprof' output say 1640 nothing about time that your program was not running. For example, a 1641 part of the program that creates so much data that it cannot all fit in 1642 physical memory at once may run very slowly due to thrashing, but 1643 `gprof' will say it uses little time. On the other hand, sampling by 1644 run time has the advantage that the amount of load due to other users 1645 won't directly affect the output you get. 1646 1647 1648 File: gprof.info, Node: File Format, Next: Internals, Prev: Implementation, Up: Details 1649 1650 9.2 Profiling Data File Format 1651 ============================== 1652 1653 The old BSD-derived file format used for profile data does not contain a 1654 magic cookie that allows to check whether a data file really is a 1655 `gprof' file. Furthermore, it does not provide a version number, thus 1656 rendering changes to the file format almost impossible. GNU `gprof' 1657 uses a new file format that provides these features. For backward 1658 compatibility, GNU `gprof' continues to support the old BSD-derived 1659 format, but not all features are supported with it. For example, 1660 basic-block execution counts cannot be accommodated by the old file 1661 format. 1662 1663 The new file format is defined in header file `gmon_out.h'. It 1664 consists of a header containing the magic cookie and a version number, 1665 as well as some spare bytes available for future extensions. All data 1666 in a profile data file is in the native format of the target for which 1667 the profile was collected. GNU `gprof' adapts automatically to the 1668 byte-order in use. 1669 1670 In the new file format, the header is followed by a sequence of 1671 records. Currently, there are three different record types: histogram 1672 records, call-graph arc records, and basic-block execution count 1673 records. Each file can contain any number of each record type. When 1674 reading a file, GNU `gprof' will ensure records of the same type are 1675 compatible with each other and compute the union of all records. For 1676 example, for basic-block execution counts, the union is simply the sum 1677 of all execution counts for each basic-block. 1678 1679 9.2.1 Histogram Records 1680 ----------------------- 1681 1682 Histogram records consist of a header that is followed by an array of 1683 bins. The header contains the text-segment range that the histogram 1684 spans, the size of the histogram in bytes (unlike in the old BSD 1685 format, this does not include the size of the header), the rate of the 1686 profiling clock, and the physical dimension that the bin counts 1687 represent after being scaled by the profiling clock rate. The physical 1688 dimension is specified in two parts: a long name of up to 15 characters 1689 and a single character abbreviation. For example, a histogram 1690 representing real-time would specify the long name as "seconds" and the 1691 abbreviation as "s". This feature is useful for architectures that 1692 support performance monitor hardware (which, fortunately, is becoming 1693 increasingly common). For example, under DEC OSF/1, the "uprofile" 1694 command can be used to produce a histogram of, say, instruction cache 1695 misses. In this case, the dimension in the histogram header could be 1696 set to "i-cache misses" and the abbreviation could be set to "1" 1697 (because it is simply a count, not a physical dimension). Also, the 1698 profiling rate would have to be set to 1 in this case. 1699 1700 Histogram bins are 16-bit numbers and each bin represent an equal 1701 amount of text-space. For example, if the text-segment is one thousand 1702 bytes long and if there are ten bins in the histogram, each bin 1703 represents one hundred bytes. 1704 1705 9.2.2 Call-Graph Records 1706 ------------------------ 1707 1708 Call-graph records have a format that is identical to the one used in 1709 the BSD-derived file format. It consists of an arc in the call graph 1710 and a count indicating the number of times the arc was traversed during 1711 program execution. Arcs are specified by a pair of addresses: the 1712 first must be within caller's function and the second must be within 1713 the callee's function. When performing profiling at the function 1714 level, these addresses can point anywhere within the respective 1715 function. However, when profiling at the line-level, it is better if 1716 the addresses are as close to the call-site/entry-point as possible. 1717 This will ensure that the line-level call-graph is able to identify 1718 exactly which line of source code performed calls to a function. 1719 1720 9.2.3 Basic-Block Execution Count Records 1721 ----------------------------------------- 1722 1723 Basic-block execution count records consist of a header followed by a 1724 sequence of address/count pairs. The header simply specifies the 1725 length of the sequence. In an address/count pair, the address 1726 identifies a basic-block and the count specifies the number of times 1727 that basic-block was executed. Any address within the basic-address can 1728 be used. 1729 1730 1731 File: gprof.info, Node: Internals, Next: Debugging, Prev: File Format, Up: Details 1732 1733 9.3 `gprof''s Internal Operation 1734 ================================ 1735 1736 Like most programs, `gprof' begins by processing its options. During 1737 this stage, it may building its symspec list (`sym_ids.c:sym_id_add'), 1738 if options are specified which use symspecs. `gprof' maintains a 1739 single linked list of symspecs, which will eventually get turned into 1740 12 symbol tables, organized into six include/exclude pairs--one pair 1741 each for the flat profile (INCL_FLAT/EXCL_FLAT), the call graph arcs 1742 (INCL_ARCS/EXCL_ARCS), printing in the call graph 1743 (INCL_GRAPH/EXCL_GRAPH), timing propagation in the call graph 1744 (INCL_TIME/EXCL_TIME), the annotated source listing 1745 (INCL_ANNO/EXCL_ANNO), and the execution count listing 1746 (INCL_EXEC/EXCL_EXEC). 1747 1748 After option processing, `gprof' finishes building the symspec list 1749 by adding all the symspecs in `default_excluded_list' to the exclude 1750 lists EXCL_TIME and EXCL_GRAPH, and if line-by-line profiling is 1751 specified, EXCL_FLAT as well. These default excludes are not added to 1752 EXCL_ANNO, EXCL_ARCS, and EXCL_EXEC. 1753 1754 Next, the BFD library is called to open the object file, verify that 1755 it is an object file, and read its symbol table (`core.c:core_init'), 1756 using `bfd_canonicalize_symtab' after mallocing an appropriately sized 1757 array of symbols. At this point, function mappings are read (if the 1758 `--file-ordering' option has been specified), and the core text space 1759 is read into memory (if the `-c' option was given). 1760 1761 `gprof''s own symbol table, an array of Sym structures, is now built. 1762 This is done in one of two ways, by one of two routines, depending on 1763 whether line-by-line profiling (`-l' option) has been enabled. For 1764 normal profiling, the BFD canonical symbol table is scanned. For 1765 line-by-line profiling, every text space address is examined, and a new 1766 symbol table entry gets created every time the line number changes. In 1767 either case, two passes are made through the symbol table--one to count 1768 the size of the symbol table required, and the other to actually read 1769 the symbols. In between the two passes, a single array of type `Sym' 1770 is created of the appropriate length. Finally, 1771 `symtab.c:symtab_finalize' is called to sort the symbol table and 1772 remove duplicate entries (entries with the same memory address). 1773 1774 The symbol table must be a contiguous array for two reasons. First, 1775 the `qsort' library function (which sorts an array) will be used to 1776 sort the symbol table. Also, the symbol lookup routine 1777 (`symtab.c:sym_lookup'), which finds symbols based on memory address, 1778 uses a binary search algorithm which requires the symbol table to be a 1779 sorted array. Function symbols are indicated with an `is_func' flag. 1780 Line number symbols have no special flags set. Additionally, a symbol 1781 can have an `is_static' flag to indicate that it is a local symbol. 1782 1783 With the symbol table read, the symspecs can now be translated into 1784 Syms (`sym_ids.c:sym_id_parse'). Remember that a single symspec can 1785 match multiple symbols. An array of symbol tables (`syms') is created, 1786 each entry of which is a symbol table of Syms to be included or 1787 excluded from a particular listing. The master symbol table and the 1788 symspecs are examined by nested loops, and every symbol that matches a 1789 symspec is inserted into the appropriate syms table. This is done 1790 twice, once to count the size of each required symbol table, and again 1791 to build the tables, which have been malloced between passes. From now 1792 on, to determine whether a symbol is on an include or exclude symspec 1793 list, `gprof' simply uses its standard symbol lookup routine on the 1794 appropriate table in the `syms' array. 1795 1796 Now the profile data file(s) themselves are read 1797 (`gmon_io.c:gmon_out_read'), first by checking for a new-style 1798 `gmon.out' header, then assuming this is an old-style BSD `gmon.out' if 1799 the magic number test failed. 1800 1801 New-style histogram records are read by `hist.c:hist_read_rec'. For 1802 the first histogram record, allocate a memory array to hold all the 1803 bins, and read them in. When multiple profile data files (or files 1804 with multiple histogram records) are read, the memory ranges of each 1805 pair of histogram records must be either equal, or non-overlapping. 1806 For each pair of histogram records, the resolution (memory region size 1807 divided by the number of bins) must be the same. The time unit must be 1808 the same for all histogram records. If the above containts are met, all 1809 histograms for the same memory range are merged. 1810 1811 As each call graph record is read (`call_graph.c:cg_read_rec'), the 1812 parent and child addresses are matched to symbol table entries, and a 1813 call graph arc is created by `cg_arcs.c:arc_add', unless the arc fails 1814 a symspec check against INCL_ARCS/EXCL_ARCS. As each arc is added, a 1815 linked list is maintained of the parent's child arcs, and of the child's 1816 parent arcs. Both the child's call count and the arc's call count are 1817 incremented by the record's call count. 1818 1819 Basic-block records are read (`basic_blocks.c:bb_read_rec'), but 1820 only if line-by-line profiling has been selected. Each basic-block 1821 address is matched to a corresponding line symbol in the symbol table, 1822 and an entry made in the symbol's bb_addr and bb_calls arrays. Again, 1823 if multiple basic-block records are present for the same address, the 1824 call counts are cumulative. 1825 1826 A gmon.sum file is dumped, if requested (`gmon_io.c:gmon_out_write'). 1827 1828 If histograms were present in the data files, assign them to symbols 1829 (`hist.c:hist_assign_samples') by iterating over all the sample bins 1830 and assigning them to symbols. Since the symbol table is sorted in 1831 order of ascending memory addresses, we can simple follow along in the 1832 symbol table as we make our pass over the sample bins. This step 1833 includes a symspec check against INCL_FLAT/EXCL_FLAT. Depending on the 1834 histogram scale factor, a sample bin may span multiple symbols, in 1835 which case a fraction of the sample count is allocated to each symbol, 1836 proportional to the degree of overlap. This effect is rare for normal 1837 profiling, but overlaps are more common during line-by-line profiling, 1838 and can cause each of two adjacent lines to be credited with half a 1839 hit, for example. 1840 1841 If call graph data is present, `cg_arcs.c:cg_assemble' is called. 1842 First, if `-c' was specified, a machine-dependent routine (`find_call') 1843 scans through each symbol's machine code, looking for subroutine call 1844 instructions, and adding them to the call graph with a zero call count. 1845 A topological sort is performed by depth-first numbering all the 1846 symbols (`cg_dfn.c:cg_dfn'), so that children are always numbered less 1847 than their parents, then making a array of pointers into the symbol 1848 table and sorting it into numerical order, which is reverse topological 1849 order (children appear before parents). Cycles are also detected at 1850 this point, all members of which are assigned the same topological 1851 number. Two passes are now made through this sorted array of symbol 1852 pointers. The first pass, from end to beginning (parents to children), 1853 computes the fraction of child time to propagate to each parent and a 1854 print flag. The print flag reflects symspec handling of 1855 INCL_GRAPH/EXCL_GRAPH, with a parent's include or exclude (print or no 1856 print) property being propagated to its children, unless they 1857 themselves explicitly appear in INCL_GRAPH or EXCL_GRAPH. A second 1858 pass, from beginning to end (children to parents) actually propagates 1859 the timings along the call graph, subject to a check against 1860 INCL_TIME/EXCL_TIME. With the print flag, fractions, and timings now 1861 stored in the symbol structures, the topological sort array is now 1862 discarded, and a new array of pointers is assembled, this time sorted 1863 by propagated time. 1864 1865 Finally, print the various outputs the user requested, which is now 1866 fairly straightforward. The call graph (`cg_print.c:cg_print') and 1867 flat profile (`hist.c:hist_print') are regurgitations of values already 1868 computed. The annotated source listing 1869 (`basic_blocks.c:print_annotated_source') uses basic-block information, 1870 if present, to label each line of code with call counts, otherwise only 1871 the function call counts are presented. 1872 1873 The function ordering code is marginally well documented in the 1874 source code itself (`cg_print.c'). Basically, the functions with the 1875 most use and the most parents are placed first, followed by other 1876 functions with the most use, followed by lower use functions, followed 1877 by unused functions at the end. 1878 1879 1880 File: gprof.info, Node: Debugging, Prev: Internals, Up: Details 1881 1882 9.4 Debugging `gprof' 1883 ===================== 1884 1885 If `gprof' was compiled with debugging enabled, the `-d' option 1886 triggers debugging output (to stdout) which can be helpful in 1887 understanding its operation. The debugging number specified is 1888 interpreted as a sum of the following options: 1889 1890 2 - Topological sort 1891 Monitor depth-first numbering of symbols during call graph analysis 1892 1893 4 - Cycles 1894 Shows symbols as they are identified as cycle heads 1895 1896 16 - Tallying 1897 As the call graph arcs are read, show each arc and how the total 1898 calls to each function are tallied 1899 1900 32 - Call graph arc sorting 1901 Details sorting individual parents/children within each call graph 1902 entry 1903 1904 64 - Reading histogram and call graph records 1905 Shows address ranges of histograms as they are read, and each call 1906 graph arc 1907 1908 128 - Symbol table 1909 Reading, classifying, and sorting the symbol table from the object 1910 file. For line-by-line profiling (`-l' option), also shows line 1911 numbers being assigned to memory addresses. 1912 1913 256 - Static call graph 1914 Trace operation of `-c' option 1915 1916 512 - Symbol table and arc table lookups 1917 Detail operation of lookup routines 1918 1919 1024 - Call graph propagation 1920 Shows how function times are propagated along the call graph 1921 1922 2048 - Basic-blocks 1923 Shows basic-block records as they are read from profile data (only 1924 meaningful with `-l' option) 1925 1926 4096 - Symspecs 1927 Shows symspec-to-symbol pattern matching operation 1928 1929 8192 - Annotate source 1930 Tracks operation of `-A' option 1931 1932 1933 File: gprof.info, Node: GNU Free Documentation License, Prev: Details, Up: Top 1934 1935 Appendix A GNU Free Documentation License 1936 ***************************************** 1937 1938 Version 1.1, March 2000 1939 1940 Copyright (C) 2000, 2003 Free Software Foundation, Inc. 1941 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 1942 1943 Everyone is permitted to copy and distribute verbatim copies 1944 of this license document, but changing it is not allowed. 1945 1946 1947 0. 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A copy that is not "Transparent" is called "Opaque." 2015 2016 Examples of suitable formats for Transparent copies include plain 2017 ASCII without markup, Texinfo input format, LaTeX input format, 2018 SGML or XML using a publicly available DTD, and 2019 standard-conforming simple HTML designed for human modification. 2020 Opaque formats include PostScript, PDF, proprietary formats that 2021 can be read and edited only by proprietary word processors, SGML 2022 or XML for which the DTD and/or processing tools are not generally 2023 available, and the machine-generated HTML produced by some word 2024 processors for output purposes only. 2025 2026 The "Title Page" means, for a printed book, the title page itself, 2027 plus such following pages as are needed to hold, legibly, the 2028 material this License requires to appear in the title page. For 2029 works in formats which do not have any title page as such, "Title 2030 Page" means the text near the most prominent appearance of the 2031 work's title, preceding the beginning of the body of the text. 2032 2033 2. VERBATIM COPYING 2034 2035 You may copy and distribute the Document in any medium, either 2036 commercially or noncommercially, provided that this License, the 2037 copyright notices, and the license notice saying this License 2038 applies to the Document are reproduced in all copies, and that you 2039 add no other conditions whatsoever to those of this License. You 2040 may not use technical measures to obstruct or control the reading 2041 or further copying of the copies you make or distribute. However, 2042 you may accept compensation in exchange for copies. If you 2043 distribute a large enough number of copies you must also follow 2044 the conditions in section 3. 2045 2046 You may also lend copies, under the same conditions stated above, 2047 and you may publicly display copies. 2048 2049 3. COPYING IN QUANTITY 2050 2051 If you publish printed copies of the Document numbering more than 2052 100, and the Document's license notice requires Cover Texts, you 2053 must enclose the copies in covers that carry, clearly and legibly, 2054 all these Cover Texts: Front-Cover Texts on the front cover, and 2055 Back-Cover Texts on the back cover. Both covers must also clearly 2056 and legibly identify you as the publisher of these copies. The 2057 front cover must present the full title with all words of the 2058 title equally prominent and visible. You may add other material 2059 on the covers in addition. Copying with changes limited to the 2060 covers, as long as they preserve the title of the Document and 2061 satisfy these conditions, can be treated as verbatim copying in 2062 other respects. 2063 2064 If the required texts for either cover are too voluminous to fit 2065 legibly, you should put the first ones listed (as many as fit 2066 reasonably) on the actual cover, and continue the rest onto 2067 adjacent pages. 2068 2069 If you publish or distribute Opaque copies of the Document 2070 numbering more than 100, you must either include a 2071 machine-readable Transparent copy along with each Opaque copy, or 2072 state in or with each Opaque copy a publicly-accessible 2073 computer-network location containing a complete Transparent copy 2074 of the Document, free of added material, which the general 2075 network-using public has access to download anonymously at no 2076 charge using public-standard network protocols. If you use the 2077 latter option, you must take reasonably prudent steps, when you 2078 begin distribution of Opaque copies in quantity, to ensure that 2079 this Transparent copy will remain thus accessible at the stated 2080 location until at least one year after the last time you 2081 distribute an Opaque copy (directly or through your agents or 2082 retailers) of that edition to the public. 2083 2084 It is requested, but not required, that you contact the authors of 2085 the Document well before redistributing any large number of 2086 copies, to give them a chance to provide you with an updated 2087 version of the Document. 2088 2089 4. MODIFICATIONS 2090 2091 You may copy and distribute a Modified Version of the Document 2092 under the conditions of sections 2 and 3 above, provided that you 2093 release the Modified Version under precisely this License, with 2094 the Modified Version filling the role of the Document, thus 2095 licensing distribution and modification of the Modified Version to 2096 whoever possesses a copy of it. In addition, you must do these 2097 things in the Modified Version: 2098 2099 A. Use in the Title Page (and on the covers, if any) a title 2100 distinct from that of the Document, and from those of previous 2101 versions (which should, if there were any, be listed in the 2102 History section of the Document). You may use the same title 2103 as a previous version if the original publisher of that version 2104 gives permission. 2105 B. List on the Title Page, as authors, one or more persons or 2106 entities responsible for authorship of the modifications in the 2107 Modified Version, together with at least five of the principal 2108 authors of the Document (all of its principal authors, if it 2109 has less than five). 2110 C. State on the Title page the name of the publisher of the 2111 Modified Version, as the publisher. 2112 D. Preserve all the copyright notices of the Document. 2113 E. Add an appropriate copyright notice for your modifications 2114 adjacent to the other copyright notices. 2115 F. Include, immediately after the copyright notices, a license 2116 notice giving the public permission to use the Modified Version 2117 under the terms of this License, in the form shown in the 2118 Addendum below. 2119 G. Preserve in that license notice the full lists of Invariant 2120 Sections and required Cover Texts given in the Document's 2121 license notice. 2122 H. Include an unaltered copy of this License. 2123 I. Preserve the section entitled "History", and its title, and add 2124 to it an item stating at least the title, year, new authors, and 2125 publisher of the Modified Version as given on the Title Page. 2126 If there is no section entitled "History" in the Document, 2127 create one stating the title, year, authors, and publisher of 2128 the Document as given on its Title Page, then add an item 2129 describing the Modified Version as stated in the previous 2130 sentence. 2131 J. Preserve the network location, if any, given in the Document for 2132 public access to a Transparent copy of the Document, and 2133 likewise the network locations given in the Document for 2134 previous versions it was based on. These may be placed in the 2135 "History" section. You may omit a network location for a work 2136 that was published at least four years before the Document 2137 itself, or if the original publisher of the version it refers 2138 to gives permission. 2139 K. In any section entitled "Acknowledgements" or "Dedications", 2140 preserve the section's title, and preserve in the section all the 2141 substance and tone of each of the contributor acknowledgements 2142 and/or dedications given therein. 2143 L. Preserve all the Invariant Sections of the Document, 2144 unaltered in their text and in their titles. Section numbers 2145 or the equivalent are not considered part of the section titles. 2146 M. Delete any section entitled "Endorsements." Such a section 2147 may not be included in the Modified Version. 2148 N. Do not retitle any existing section as "Endorsements" or to 2149 conflict in title with any Invariant Section. 2150 2151 If the Modified Version includes new front-matter sections or 2152 appendices that qualify as Secondary Sections and contain no 2153 material copied from the Document, you may at your option 2154 designate some or all of these sections as invariant. To do this, 2155 add their titles to the list of Invariant Sections in the Modified 2156 Version's license notice. These titles must be distinct from any 2157 other section titles. 2158 2159 You may add a section entitled "Endorsements", provided it contains 2160 nothing but endorsements of your Modified Version by various 2161 parties-for example, statements of peer review or that the text has 2162 been approved by an organization as the authoritative definition 2163 of a standard. 2164 2165 You may add a passage of up to five words as a Front-Cover Text, 2166 and a passage of up to 25 words as a Back-Cover Text, to the end 2167 of the list of Cover Texts in the Modified Version. Only one 2168 passage of Front-Cover Text and one of Back-Cover Text may be 2169 added by (or through arrangements made by) any one entity. If the 2170 Document already includes a cover text for the same cover, 2171 previously added by you or by arrangement made by the same entity 2172 you are acting on behalf of, you may not add another; but you may 2173 replace the old one, on explicit permission from the previous 2174 publisher that added the old one. 2175 2176 The author(s) and publisher(s) of the Document do not by this 2177 License give permission to use their names for publicity for or to 2178 assert or imply endorsement of any Modified Version. 2179 2180 5. COMBINING DOCUMENTS 2181 2182 You may combine the Document with other documents released under 2183 this License, under the terms defined in section 4 above for 2184 modified versions, provided that you include in the combination 2185 all of the Invariant Sections of all of the original documents, 2186 unmodified, and list them all as Invariant Sections of your 2187 combined work in its license notice. 2188 2189 The combined work need only contain one copy of this License, and 2190 multiple identical Invariant Sections may be replaced with a single 2191 copy. If there are multiple Invariant Sections with the same name 2192 but different contents, make the title of each such section unique 2193 by adding at the end of it, in parentheses, the name of the 2194 original author or publisher of that section if known, or else a 2195 unique number. Make the same adjustment to the section titles in 2196 the list of Invariant Sections in the license notice of the 2197 combined work. 2198 2199 In the combination, you must combine any sections entitled 2200 "History" in the various original documents, forming one section 2201 entitled "History"; likewise combine any sections entitled 2202 "Acknowledgements", and any sections entitled "Dedications." You 2203 must delete all sections entitled "Endorsements." 2204 2205 6. COLLECTIONS OF DOCUMENTS 2206 2207 You may make a collection consisting of the Document and other 2208 documents released under this License, and replace the individual 2209 copies of this License in the various documents with a single copy 2210 that is included in the collection, provided that you follow the 2211 rules of this License for verbatim copying of each of the 2212 documents in all other respects. 2213 2214 You may extract a single document from such a collection, and 2215 distribute it individually under this License, provided you insert 2216 a copy of this License into the extracted document, and follow 2217 this License in all other respects regarding verbatim copying of 2218 that document. 2219 2220 7. AGGREGATION WITH INDEPENDENT WORKS 2221 2222 A compilation of the Document or its derivatives with other 2223 separate and independent documents or works, in or on a volume of 2224 a storage or distribution medium, does not as a whole count as a 2225 Modified Version of the Document, provided no compilation 2226 copyright is claimed for the compilation. Such a compilation is 2227 called an "aggregate", and this License does not apply to the 2228 other self-contained works thus compiled with the Document, on 2229 account of their being thus compiled, if they are not themselves 2230 derivative works of the Document. 2231 2232 If the Cover Text requirement of section 3 is applicable to these 2233 copies of the Document, then if the Document is less than one 2234 quarter of the entire aggregate, the Document's Cover Texts may be 2235 placed on covers that surround only the Document within the 2236 aggregate. Otherwise they must appear on covers around the whole 2237 aggregate. 2238 2239 8. TRANSLATION 2240 2241 Translation is considered a kind of modification, so you may 2242 distribute translations of the Document under the terms of section 2243 4. Replacing Invariant Sections with translations requires special 2244 permission from their copyright holders, but you may include 2245 translations of some or all Invariant Sections in addition to the 2246 original versions of these Invariant Sections. You may include a 2247 translation of this License provided that you also include the 2248 original English version of this License. In case of a 2249 disagreement between the translation and the original English 2250 version of this License, the original English version will prevail. 2251 2252 9. TERMINATION 2253 2254 You may not copy, modify, sublicense, or distribute the Document 2255 except as expressly provided for under this License. Any other 2256 attempt to copy, modify, sublicense or distribute the Document is 2257 void, and will automatically terminate your rights under this 2258 License. However, parties who have received copies, or rights, 2259 from you under this License will not have their licenses 2260 terminated so long as such parties remain in full compliance. 2261 2262 10. FUTURE REVISIONS OF THIS LICENSE 2263 2264 The Free Software Foundation may publish new, revised versions of 2265 the GNU Free Documentation License from time to time. Such new 2266 versions will be similar in spirit to the present version, but may 2267 differ in detail to address new problems or concerns. See 2268 http://www.gnu.org/copyleft/. 2269 2270 Each version of the License is given a distinguishing version 2271 number. If the Document specifies that a particular numbered 2272 version of this License "or any later version" applies to it, you 2273 have the option of following the terms and conditions either of 2274 that specified version or of any later version that has been 2275 published (not as a draft) by the Free Software Foundation. If 2276 the Document does not specify a version number of this License, 2277 you may choose any version ever published (not as a draft) by the 2278 Free Software Foundation. 2279 2280 2281 ADDENDUM: How to use this License for your documents 2282 ==================================================== 2283 2284 To use this License in a document you have written, include a copy of 2285 the License in the document and put the following copyright and license 2286 notices just after the title page: 2287 2288 Copyright (C) YEAR YOUR NAME. 2289 Permission is granted to copy, distribute and/or modify this document 2290 under the terms of the GNU Free Documentation License, Version 1.1 2291 or any later version published by the Free Software Foundation; 2292 with the Invariant Sections being LIST THEIR TITLES, with the 2293 Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. 2294 A copy of the license is included in the section entitled "GNU 2295 Free Documentation License." 2296 2297 If you have no Invariant Sections, write "with no Invariant Sections" 2298 instead of saying which ones are invariant. If you have no Front-Cover 2299 Texts, write "no Front-Cover Texts" instead of "Front-Cover Texts being 2300 LIST"; likewise for Back-Cover Texts. 2301 2302 If your document contains nontrivial examples of program code, we 2303 recommend releasing these examples in parallel under your choice of 2304 free software license, such as the GNU General Public License, to 2305 permit their use in free software. 2306 2307 2308 2309 Tag Table: 2310 Node: Top783 2311 Node: Introduction2094 2312 Node: Compiling4586 2313 Node: Executing8057 2314 Node: Invoking10845 2315 Node: Output Options12260 2316 Node: Analysis Options19349 2317 Node: Miscellaneous Options22750 2318 Node: Deprecated Options24005 2319 Node: Symspecs26084 2320 Node: Output27910 2321 Node: Flat Profile28950 2322 Node: Call Graph33903 2323 Node: Primary37135 2324 Node: Callers39723 2325 Node: Subroutines41840 2326 Node: Cycles43681 2327 Node: Line-by-line50458 2328 Node: Annotated Source54531 2329 Node: Inaccuracy57530 2330 Node: Sampling Error57788 2331 Node: Assumptions60358 2332 Node: How do I?61828 2333 Node: Incompatibilities63382 2334 Node: Details64876 2335 Node: Implementation65269 2336 Node: File Format71166 2337 Node: Internals75456 2338 Node: Debugging83951 2339 Node: GNU Free Documentation License85552 2340 2341 End Tag Table 2342
