1 This is gprof.info, produced by makeinfo version 4.8 from gprof.texi. 2 3 START-INFO-DIR-ENTRY 4 * gprof: (gprof). Profiling your program's execution 5 END-INFO-DIR-ENTRY 6 7 This file documents the gprof profiler of the GNU system. 8 9 Copyright (C) 1988, 92, 97, 98, 99, 2000, 2001, 2003, 2007 Free 10 Software Foundation, Inc. 11 12 Permission is granted to copy, distribute and/or modify this document 13 under the terms of the GNU Free Documentation License, Version 1.1 or 14 any later version published by the Free Software Foundation; with no 15 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover 16 Texts. A copy of the license is included in the section entitled "GNU 17 Free Documentation License". 18 19 20 File: gprof.info, Node: Top, Next: Introduction, Up: (dir) 21 22 Profiling a Program: Where Does It Spend Its Time? 23 ************************************************** 24 25 This manual describes the GNU profiler, `gprof', and how you can use it 26 to determine which parts of a program are taking most of the execution 27 time. We assume that you know how to write, compile, and execute 28 programs. GNU `gprof' was written by Jay Fenlason. 29 30 This manual is for `gprof' (GNU Binutils) version 2.18.90. 31 32 This document is distributed under the terms of the GNU Free 33 Documentation License. A copy of the license is included in the 34 section entitled "GNU Free Documentation License". 35 36 * Menu: 37 38 * Introduction:: What profiling means, and why it is useful. 39 40 * Compiling:: How to compile your program for profiling. 41 * Executing:: Executing your program to generate profile data 42 * Invoking:: How to run `gprof', and its options 43 44 * Output:: Interpreting `gprof''s output 45 46 * Inaccuracy:: Potential problems you should be aware of 47 * How do I?:: Answers to common questions 48 * Incompatibilities:: (between GNU `gprof' and Unix `gprof'.) 49 * Details:: Details of how profiling is done 50 * GNU Free Documentation License:: GNU Free Documentation License 51 52 53 File: gprof.info, Node: Introduction, Next: Compiling, Prev: Top, Up: Top 54 55 1 Introduction to Profiling 56 *************************** 57 58 Profiling allows you to learn where your program spent its time and 59 which functions called which other functions while it was executing. 60 This information can show you which pieces of your program are slower 61 than you expected, and might be candidates for rewriting to make your 62 program execute faster. It can also tell you which functions are being 63 called more or less often than you expected. This may help you spot 64 bugs that had otherwise been unnoticed. 65 66 Since the profiler uses information collected during the actual 67 execution of your program, it can be used on programs that are too 68 large or too complex to analyze by reading the source. However, how 69 your program is run will affect the information that shows up in the 70 profile data. If you don't use some feature of your program while it 71 is being profiled, no profile information will be generated for that 72 feature. 73 74 Profiling has several steps: 75 76 * You must compile and link your program with profiling enabled. 77 *Note Compiling a Program for Profiling: Compiling. 78 79 * You must execute your program to generate a profile data file. 80 *Note Executing the Program: Executing. 81 82 * You must run `gprof' to analyze the profile data. *Note `gprof' 83 Command Summary: Invoking. 84 85 The next three chapters explain these steps in greater detail. 86 87 Several forms of output are available from the analysis. 88 89 The "flat profile" shows how much time your program spent in each 90 function, and how many times that function was called. If you simply 91 want to know which functions burn most of the cycles, it is stated 92 concisely here. *Note The Flat Profile: Flat Profile. 93 94 The "call graph" shows, for each function, which functions called 95 it, which other functions it called, and how many times. There is also 96 an estimate of how much time was spent in the subroutines of each 97 function. This can suggest places where you might try to eliminate 98 function calls that use a lot of time. *Note The Call Graph: Call 99 Graph. 100 101 The "annotated source" listing is a copy of the program's source 102 code, labeled with the number of times each line of the program was 103 executed. *Note The Annotated Source Listing: Annotated Source. 104 105 To better understand how profiling works, you may wish to read a 106 description of its implementation. *Note Implementation of Profiling: 107 Implementation. 108 109 110 File: gprof.info, Node: Compiling, Next: Executing, Prev: Introduction, Up: Top 111 112 2 Compiling a Program for Profiling 113 *********************************** 114 115 The first step in generating profile information for your program is to 116 compile and link it with profiling enabled. 117 118 To compile a source file for profiling, specify the `-pg' option when 119 you run the compiler. (This is in addition to the options you normally 120 use.) 121 122 To link the program for profiling, if you use a compiler such as `cc' 123 to do the linking, simply specify `-pg' in addition to your usual 124 options. The same option, `-pg', alters either compilation or linking 125 to do what is necessary for profiling. Here are examples: 126 127 cc -g -c myprog.c utils.c -pg 128 cc -o myprog myprog.o utils.o -pg 129 130 The `-pg' option also works with a command that both compiles and 131 links: 132 133 cc -o myprog myprog.c utils.c -g -pg 134 135 Note: The `-pg' option must be part of your compilation options as 136 well as your link options. If it is not then no call-graph data will 137 be gathered and when you run `gprof' you will get an error message like 138 this: 139 140 gprof: gmon.out file is missing call-graph data 141 142 If you add the `-Q' switch to suppress the printing of the call 143 graph data you will still be able to see the time samples: 144 145 Flat profile: 146 147 Each sample counts as 0.01 seconds. 148 % cumulative self self total 149 time seconds seconds calls Ts/call Ts/call name 150 44.12 0.07 0.07 zazLoop 151 35.29 0.14 0.06 main 152 20.59 0.17 0.04 bazMillion 153 154 If you run the linker `ld' directly instead of through a compiler 155 such as `cc', you may have to specify a profiling startup file 156 `gcrt0.o' as the first input file instead of the usual startup file 157 `crt0.o'. In addition, you would probably want to specify the 158 profiling C library, `libc_p.a', by writing `-lc_p' instead of the 159 usual `-lc'. This is not absolutely necessary, but doing this gives 160 you number-of-calls information for standard library functions such as 161 `read' and `open'. For example: 162 163 ld -o myprog /lib/gcrt0.o myprog.o utils.o -lc_p 164 165 If you compile only some of the modules of the program with `-pg', 166 you can still profile the program, but you won't get complete 167 information about the modules that were compiled without `-pg'. The 168 only information you get for the functions in those modules is the 169 total time spent in them; there is no record of how many times they 170 were called, or from where. This will not affect the flat profile 171 (except that the `calls' field for the functions will be blank), but 172 will greatly reduce the usefulness of the call graph. 173 174 If you wish to perform line-by-line profiling you should use the 175 `gcov' tool instead of `gprof'. See that tool's manual or info pages 176 for more details of how to do this. 177 178 Note, older versions of `gcc' produce line-by-line profiling 179 information that works with `gprof' rather than `gcov' so there is 180 still support for displaying this kind of information in `gprof'. *Note 181 Line-by-line Profiling: Line-by-line. 182 183 It also worth noting that `gcc' implements a 184 `-finstrument-functions' command line option which will insert calls to 185 special user supplied instrumentation routines at the entry and exit of 186 every function in their program. This can be used to implement an 187 alternative profiling scheme. 188 189 190 File: gprof.info, Node: Executing, Next: Invoking, Prev: Compiling, Up: Top 191 192 3 Executing the Program 193 *********************** 194 195 Once the program is compiled for profiling, you must run it in order to 196 generate the information that `gprof' needs. Simply run the program as 197 usual, using the normal arguments, file names, etc. The program should 198 run normally, producing the same output as usual. It will, however, run 199 somewhat slower than normal because of the time spent collecting and 200 writing the profile data. 201 202 The way you run the program--the arguments and input that you give 203 it--may have a dramatic effect on what the profile information shows. 204 The profile data will describe the parts of the program that were 205 activated for the particular input you use. For example, if the first 206 command you give to your program is to quit, the profile data will show 207 the time used in initialization and in cleanup, but not much else. 208 209 Your program will write the profile data into a file called 210 `gmon.out' just before exiting. If there is already a file called 211 `gmon.out', its contents are overwritten. There is currently no way to 212 tell the program to write the profile data under a different name, but 213 you can rename the file afterwards if you are concerned that it may be 214 overwritten. 215 216 In order to write the `gmon.out' file properly, your program must 217 exit normally: by returning from `main' or by calling `exit'. Calling 218 the low-level function `_exit' does not write the profile data, and 219 neither does abnormal termination due to an unhandled signal. 220 221 The `gmon.out' file is written in the program's _current working 222 directory_ at the time it exits. This means that if your program calls 223 `chdir', the `gmon.out' file will be left in the last directory your 224 program `chdir''d to. If you don't have permission to write in this 225 directory, the file is not written, and you will get an error message. 226 227 Older versions of the GNU profiling library may also write a file 228 called `bb.out'. This file, if present, contains an human-readable 229 listing of the basic-block execution counts. Unfortunately, the 230 appearance of a human-readable `bb.out' means the basic-block counts 231 didn't get written into `gmon.out'. The Perl script `bbconv.pl', 232 included with the `gprof' source distribution, will convert a `bb.out' 233 file into a format readable by `gprof'. Invoke it like this: 234 235 bbconv.pl < bb.out > BH-DATA 236 237 This translates the information in `bb.out' into a form that `gprof' 238 can understand. But you still need to tell `gprof' about the existence 239 of this translated information. To do that, include BB-DATA on the 240 `gprof' command line, _along with `gmon.out'_, like this: 241 242 gprof OPTIONS EXECUTABLE-FILE gmon.out BB-DATA [YET-MORE-PROFILE-DATA-FILES...] [> OUTFILE] 243 244 245 File: gprof.info, Node: Invoking, Next: Output, Prev: Executing, Up: Top 246 247 4 `gprof' Command Summary 248 ************************* 249 250 After you have a profile data file `gmon.out', you can run `gprof' to 251 interpret the information in it. The `gprof' program prints a flat 252 profile and a call graph on standard output. Typically you would 253 redirect the output of `gprof' into a file with `>'. 254 255 You run `gprof' like this: 256 257 gprof OPTIONS [EXECUTABLE-FILE [PROFILE-DATA-FILES...]] [> OUTFILE] 258 259 Here square-brackets indicate optional arguments. 260 261 If you omit the executable file name, the file `a.out' is used. If 262 you give no profile data file name, the file `gmon.out' is used. If 263 any file is not in the proper format, or if the profile data file does 264 not appear to belong to the executable file, an error message is 265 printed. 266 267 You can give more than one profile data file by entering all their 268 names after the executable file name; then the statistics in all the 269 data files are summed together. 270 271 The order of these options does not matter. 272 273 * Menu: 274 275 * Output Options:: Controlling `gprof''s output style 276 * Analysis Options:: Controlling how `gprof' analyzes its data 277 * Miscellaneous Options:: 278 * Deprecated Options:: Options you no longer need to use, but which 279 have been retained for compatibility 280 * Symspecs:: Specifying functions to include or exclude 281 282 283 File: gprof.info, Node: Output Options, Next: Analysis Options, Up: Invoking 284 285 4.1 Output Options 286 ================== 287 288 These options specify which of several output formats `gprof' should 289 produce. 290 291 Many of these options take an optional "symspec" to specify 292 functions to be included or excluded. These options can be specified 293 multiple times, with different symspecs, to include or exclude sets of 294 symbols. *Note Symspecs: Symspecs. 295 296 Specifying any of these options overrides the default (`-p -q'), 297 which prints a flat profile and call graph analysis for all functions. 298 299 `-A[SYMSPEC]' 300 `--annotated-source[=SYMSPEC]' 301 The `-A' option causes `gprof' to print annotated source code. If 302 SYMSPEC is specified, print output only for matching symbols. 303 *Note The Annotated Source Listing: Annotated Source. 304 305 `-b' 306 `--brief' 307 If the `-b' option is given, `gprof' doesn't print the verbose 308 blurbs that try to explain the meaning of all of the fields in the 309 tables. This is useful if you intend to print out the output, or 310 are tired of seeing the blurbs. 311 312 `-C[SYMSPEC]' 313 `--exec-counts[=SYMSPEC]' 314 The `-C' option causes `gprof' to print a tally of functions and 315 the number of times each was called. If SYMSPEC is specified, 316 print tally only for matching symbols. 317 318 If the profile data file contains basic-block count records, 319 specifying the `-l' option, along with `-C', will cause basic-block 320 execution counts to be tallied and displayed. 321 322 `-i' 323 `--file-info' 324 The `-i' option causes `gprof' to display summary information 325 about the profile data file(s) and then exit. The number of 326 histogram, call graph, and basic-block count records is displayed. 327 328 `-I DIRS' 329 `--directory-path=DIRS' 330 The `-I' option specifies a list of search directories in which to 331 find source files. Environment variable GPROF_PATH can also be 332 used to convey this information. Used mostly for annotated source 333 output. 334 335 `-J[SYMSPEC]' 336 `--no-annotated-source[=SYMSPEC]' 337 The `-J' option causes `gprof' not to print annotated source code. 338 If SYMSPEC is specified, `gprof' prints annotated source, but 339 excludes matching symbols. 340 341 `-L' 342 `--print-path' 343 Normally, source filenames are printed with the path component 344 suppressed. The `-L' option causes `gprof' to print the full 345 pathname of source filenames, which is determined from symbolic 346 debugging information in the image file and is relative to the 347 directory in which the compiler was invoked. 348 349 `-p[SYMSPEC]' 350 `--flat-profile[=SYMSPEC]' 351 The `-p' option causes `gprof' to print a flat profile. If 352 SYMSPEC is specified, print flat profile only for matching symbols. 353 *Note The Flat Profile: Flat Profile. 354 355 `-P[SYMSPEC]' 356 `--no-flat-profile[=SYMSPEC]' 357 The `-P' option causes `gprof' to suppress printing a flat profile. 358 If SYMSPEC is specified, `gprof' prints a flat profile, but 359 excludes matching symbols. 360 361 `-q[SYMSPEC]' 362 `--graph[=SYMSPEC]' 363 The `-q' option causes `gprof' to print the call graph analysis. 364 If SYMSPEC is specified, print call graph only for matching symbols 365 and their children. *Note The Call Graph: Call Graph. 366 367 `-Q[SYMSPEC]' 368 `--no-graph[=SYMSPEC]' 369 The `-Q' option causes `gprof' to suppress printing the call graph. 370 If SYMSPEC is specified, `gprof' prints a call graph, but excludes 371 matching symbols. 372 373 `-t' 374 `--table-length=NUM' 375 The `-t' option causes the NUM most active source lines in each 376 source file to be listed when source annotation is enabled. The 377 default is 10. 378 379 `-y' 380 `--separate-files' 381 This option affects annotated source output only. Normally, 382 `gprof' prints annotated source files to standard-output. If this 383 option is specified, annotated source for a file named 384 `path/FILENAME' is generated in the file `FILENAME-ann'. If the 385 underlying file system would truncate `FILENAME-ann' so that it 386 overwrites the original `FILENAME', `gprof' generates annotated 387 source in the file `FILENAME.ann' instead (if the original file 388 name has an extension, that extension is _replaced_ with `.ann'). 389 390 `-Z[SYMSPEC]' 391 `--no-exec-counts[=SYMSPEC]' 392 The `-Z' option causes `gprof' not to print a tally of functions 393 and the number of times each was called. If SYMSPEC is specified, 394 print tally, but exclude matching symbols. 395 396 `-r' 397 `--function-ordering' 398 The `--function-ordering' option causes `gprof' to print a 399 suggested function ordering for the program based on profiling 400 data. This option suggests an ordering which may improve paging, 401 tlb and cache behavior for the program on systems which support 402 arbitrary ordering of functions in an executable. 403 404 The exact details of how to force the linker to place functions in 405 a particular order is system dependent and out of the scope of this 406 manual. 407 408 `-R MAP_FILE' 409 `--file-ordering MAP_FILE' 410 The `--file-ordering' option causes `gprof' to print a suggested 411 .o link line ordering for the program based on profiling data. 412 This option suggests an ordering which may improve paging, tlb and 413 cache behavior for the program on systems which do not support 414 arbitrary ordering of functions in an executable. 415 416 Use of the `-a' argument is highly recommended with this option. 417 418 The MAP_FILE argument is a pathname to a file which provides 419 function name to object file mappings. The format of the file is 420 similar to the output of the program `nm'. 421 422 c-parse.o:00000000 T yyparse 423 c-parse.o:00000004 C yyerrflag 424 c-lang.o:00000000 T maybe_objc_method_name 425 c-lang.o:00000000 T print_lang_statistics 426 c-lang.o:00000000 T recognize_objc_keyword 427 c-decl.o:00000000 T print_lang_identifier 428 c-decl.o:00000000 T print_lang_type 429 ... 430 431 To create a MAP_FILE with GNU `nm', type a command like `nm 432 --extern-only --defined-only -v --print-file-name program-name'. 433 434 `-T' 435 `--traditional' 436 The `-T' option causes `gprof' to print its output in 437 "traditional" BSD style. 438 439 `-w WIDTH' 440 `--width=WIDTH' 441 Sets width of output lines to WIDTH. Currently only used when 442 printing the function index at the bottom of the call graph. 443 444 `-x' 445 `--all-lines' 446 This option affects annotated source output only. By default, 447 only the lines at the beginning of a basic-block are annotated. 448 If this option is specified, every line in a basic-block is 449 annotated by repeating the annotation for the first line. This 450 behavior is similar to `tcov''s `-a'. 451 452 `--demangle[=STYLE]' 453 `--no-demangle' 454 These options control whether C++ symbol names should be demangled 455 when printing output. The default is to demangle symbols. The 456 `--no-demangle' option may be used to turn off demangling. 457 Different compilers have different mangling styles. The optional 458 demangling style argument can be used to choose an appropriate 459 demangling style for your compiler. 460 461 462 File: gprof.info, Node: Analysis Options, Next: Miscellaneous Options, Prev: Output Options, Up: Invoking 463 464 4.2 Analysis Options 465 ==================== 466 467 `-a' 468 `--no-static' 469 The `-a' option causes `gprof' to suppress the printing of 470 statically declared (private) functions. (These are functions 471 whose names are not listed as global, and which are not visible 472 outside the file/function/block where they were defined.) Time 473 spent in these functions, calls to/from them, etc., will all be 474 attributed to the function that was loaded directly before it in 475 the executable file. This option affects both the flat profile 476 and the call graph. 477 478 `-c' 479 `--static-call-graph' 480 The `-c' option causes the call graph of the program to be 481 augmented by a heuristic which examines the text space of the 482 object file and identifies function calls in the binary machine 483 code. Since normal call graph records are only generated when 484 functions are entered, this option identifies children that could 485 have been called, but never were. Calls to functions that were 486 not compiled with profiling enabled are also identified, but only 487 if symbol table entries are present for them. Calls to dynamic 488 library routines are typically _not_ found by this option. 489 Parents or children identified via this heuristic are indicated in 490 the call graph with call counts of `0'. 491 492 `-D' 493 `--ignore-non-functions' 494 The `-D' option causes `gprof' to ignore symbols which are not 495 known to be functions. This option will give more accurate 496 profile data on systems where it is supported (Solaris and HPUX for 497 example). 498 499 `-k FROM/TO' 500 The `-k' option allows you to delete from the call graph any arcs 501 from symbols matching symspec FROM to those matching symspec TO. 502 503 `-l' 504 `--line' 505 The `-l' option enables line-by-line profiling, which causes 506 histogram hits to be charged to individual source code lines, 507 instead of functions. This feature only works with programs 508 compiled by older versions of the `gcc' compiler. Newer versions 509 of `gcc' are designed to work with the `gcov' tool instead. 510 511 If the program was compiled with basic-block counting enabled, 512 this option will also identify how many times each line of code 513 was executed. While line-by-line profiling can help isolate where 514 in a large function a program is spending its time, it also 515 significantly increases the running time of `gprof', and magnifies 516 statistical inaccuracies. *Note Statistical Sampling Error: 517 Sampling Error. 518 519 `-m NUM' 520 `--min-count=NUM' 521 This option affects execution count output only. Symbols that are 522 executed less than NUM times are suppressed. 523 524 `-nSYMSPEC' 525 `--time=SYMSPEC' 526 The `-n' option causes `gprof', in its call graph analysis, to 527 only propagate times for symbols matching SYMSPEC. 528 529 `-NSYMSPEC' 530 `--no-time=SYMSPEC' 531 The `-n' option causes `gprof', in its call graph analysis, not to 532 propagate times for symbols matching SYMSPEC. 533 534 `-z' 535 `--display-unused-functions' 536 If you give the `-z' option, `gprof' will mention all functions in 537 the flat profile, even those that were never called, and that had 538 no time spent in them. This is useful in conjunction with the 539 `-c' option for discovering which routines were never called. 540 541 542 543 File: gprof.info, Node: Miscellaneous Options, Next: Deprecated Options, Prev: Analysis Options, Up: Invoking 544 545 4.3 Miscellaneous Options 546 ========================= 547 548 `-d[NUM]' 549 `--debug[=NUM]' 550 The `-d NUM' option specifies debugging options. If NUM is not 551 specified, enable all debugging. *Note Debugging `gprof': 552 Debugging. 553 554 `-h' 555 `--help' 556 The `-h' option prints command line usage. 557 558 `-ONAME' 559 `--file-format=NAME' 560 Selects the format of the profile data files. Recognized formats 561 are `auto' (the default), `bsd', `4.4bsd', `magic', and `prof' 562 (not yet supported). 563 564 `-s' 565 `--sum' 566 The `-s' option causes `gprof' to summarize the information in the 567 profile data files it read in, and write out a profile data file 568 called `gmon.sum', which contains all the information from the 569 profile data files that `gprof' read in. The file `gmon.sum' may 570 be one of the specified input files; the effect of this is to 571 merge the data in the other input files into `gmon.sum'. 572 573 Eventually you can run `gprof' again without `-s' to analyze the 574 cumulative data in the file `gmon.sum'. 575 576 `-v' 577 `--version' 578 The `-v' flag causes `gprof' to print the current version number, 579 and then exit. 580 581 582 583 File: gprof.info, Node: Deprecated Options, Next: Symspecs, Prev: Miscellaneous Options, Up: Invoking 584 585 4.4 Deprecated Options 586 ====================== 587 588 These options have been replaced with newer versions that use 589 symspecs. 590 591 `-e FUNCTION_NAME' 592 The `-e FUNCTION' option tells `gprof' to not print information 593 about the function FUNCTION_NAME (and its children...) in the call 594 graph. The function will still be listed as a child of any 595 functions that call it, but its index number will be shown as 596 `[not printed]'. More than one `-e' option may be given; only one 597 FUNCTION_NAME may be indicated with each `-e' option. 598 599 `-E FUNCTION_NAME' 600 The `-E FUNCTION' option works like the `-e' option, but time 601 spent in the function (and children who were not called from 602 anywhere else), will not be used to compute the 603 percentages-of-time for the call graph. More than one `-E' option 604 may be given; only one FUNCTION_NAME may be indicated with each 605 `-E' option. 606 607 `-f FUNCTION_NAME' 608 The `-f FUNCTION' option causes `gprof' to limit the call graph to 609 the function FUNCTION_NAME and its children (and their 610 children...). More than one `-f' option may be given; only one 611 FUNCTION_NAME may be indicated with each `-f' option. 612 613 `-F FUNCTION_NAME' 614 The `-F FUNCTION' option works like the `-f' option, but only time 615 spent in the function and its children (and their children...) 616 will be used to determine total-time and percentages-of-time for 617 the call graph. More than one `-F' option may be given; only one 618 FUNCTION_NAME may be indicated with each `-F' option. The `-F' 619 option overrides the `-E' option. 620 621 622 Note that only one function can be specified with each `-e', `-E', 623 `-f' or `-F' option. To specify more than one function, use multiple 624 options. For example, this command: 625 626 gprof -e boring -f foo -f bar myprogram > gprof.output 627 628 lists in the call graph all functions that were reached from either 629 `foo' or `bar' and were not reachable from `boring'. 630 631 632 File: gprof.info, Node: Symspecs, Prev: Deprecated Options, Up: Invoking 633 634 4.5 Symspecs 635 ============ 636 637 Many of the output options allow functions to be included or excluded 638 using "symspecs" (symbol specifications), which observe the following 639 syntax: 640 641 filename_containing_a_dot 642 | funcname_not_containing_a_dot 643 | linenumber 644 | ( [ any_filename ] `:' ( any_funcname | linenumber ) ) 645 646 Here are some sample symspecs: 647 648 `main.c' 649 Selects everything in file `main.c'--the dot in the string tells 650 `gprof' to interpret the string as a filename, rather than as a 651 function name. To select a file whose name does not contain a 652 dot, a trailing colon should be specified. For example, `odd:' is 653 interpreted as the file named `odd'. 654 655 `main' 656 Selects all functions named `main'. 657 658 Note that there may be multiple instances of the same function name 659 because some of the definitions may be local (i.e., static). 660 Unless a function name is unique in a program, you must use the 661 colon notation explained below to specify a function from a 662 specific source file. 663 664 Sometimes, function names contain dots. In such cases, it is 665 necessary to add a leading colon to the name. For example, 666 `:.mul' selects function `.mul'. 667 668 In some object file formats, symbols have a leading underscore. 669 `gprof' will normally not print these underscores. When you name a 670 symbol in a symspec, you should type it exactly as `gprof' prints 671 it in its output. For example, if the compiler produces a symbol 672 `_main' from your `main' function, `gprof' still prints it as 673 `main' in its output, so you should use `main' in symspecs. 674 675 `main.c:main' 676 Selects function `main' in file `main.c'. 677 678 `main.c:134' 679 Selects line 134 in file `main.c'. 680 681 682 File: gprof.info, Node: Output, Next: Inaccuracy, Prev: Invoking, Up: Top 683 684 5 Interpreting `gprof''s Output 685 ******************************* 686 687 `gprof' can produce several different output styles, the most important 688 of which are described below. The simplest output styles (file 689 information, execution count, and function and file ordering) are not 690 described here, but are documented with the respective options that 691 trigger them. *Note Output Options: Output Options. 692 693 * Menu: 694 695 * Flat Profile:: The flat profile shows how much time was spent 696 executing directly in each function. 697 * Call Graph:: The call graph shows which functions called which 698 others, and how much time each function used 699 when its subroutine calls are included. 700 * Line-by-line:: `gprof' can analyze individual source code lines 701 * Annotated Source:: The annotated source listing displays source code 702 labeled with execution counts 703 704 705 File: gprof.info, Node: Flat Profile, Next: Call Graph, Up: Output 706 707 5.1 The Flat Profile 708 ==================== 709 710 The "flat profile" shows the total amount of time your program spent 711 executing each function. Unless the `-z' option is given, functions 712 with no apparent time spent in them, and no apparent calls to them, are 713 not mentioned. Note that if a function was not compiled for profiling, 714 and didn't run long enough to show up on the program counter histogram, 715 it will be indistinguishable from a function that was never called. 716 717 This is part of a flat profile for a small program: 718 719 Flat profile: 720 721 Each sample counts as 0.01 seconds. 722 % cumulative self self total 723 time seconds seconds calls ms/call ms/call name 724 33.34 0.02 0.02 7208 0.00 0.00 open 725 16.67 0.03 0.01 244 0.04 0.12 offtime 726 16.67 0.04 0.01 8 1.25 1.25 memccpy 727 16.67 0.05 0.01 7 1.43 1.43 write 728 16.67 0.06 0.01 mcount 729 0.00 0.06 0.00 236 0.00 0.00 tzset 730 0.00 0.06 0.00 192 0.00 0.00 tolower 731 0.00 0.06 0.00 47 0.00 0.00 strlen 732 0.00 0.06 0.00 45 0.00 0.00 strchr 733 0.00 0.06 0.00 1 0.00 50.00 main 734 0.00 0.06 0.00 1 0.00 0.00 memcpy 735 0.00 0.06 0.00 1 0.00 10.11 print 736 0.00 0.06 0.00 1 0.00 0.00 profil 737 0.00 0.06 0.00 1 0.00 50.00 report 738 ... 739 740 The functions are sorted first by decreasing run-time spent in them, 741 then by decreasing number of calls, then alphabetically by name. The 742 functions `mcount' and `profil' are part of the profiling apparatus and 743 appear in every flat profile; their time gives a measure of the amount 744 of overhead due to profiling. 745 746 Just before the column headers, a statement appears indicating how 747 much time each sample counted as. This "sampling period" estimates the 748 margin of error in each of the time figures. A time figure that is not 749 much larger than this is not reliable. In this example, each sample 750 counted as 0.01 seconds, suggesting a 100 Hz sampling rate. The 751 program's total execution time was 0.06 seconds, as indicated by the 752 `cumulative seconds' field. Since each sample counted for 0.01 753 seconds, this means only six samples were taken during the run. Two of 754 the samples occurred while the program was in the `open' function, as 755 indicated by the `self seconds' field. Each of the other four samples 756 occurred one each in `offtime', `memccpy', `write', and `mcount'. 757 Since only six samples were taken, none of these values can be regarded 758 as particularly reliable. In another run, the `self seconds' field for 759 `mcount' might well be `0.00' or `0.02'. *Note Statistical Sampling 760 Error: Sampling Error, for a complete discussion. 761 762 The remaining functions in the listing (those whose `self seconds' 763 field is `0.00') didn't appear in the histogram samples at all. 764 However, the call graph indicated that they were called, so therefore 765 they are listed, sorted in decreasing order by the `calls' field. 766 Clearly some time was spent executing these functions, but the paucity 767 of histogram samples prevents any determination of how much time each 768 took. 769 770 Here is what the fields in each line mean: 771 772 `% time' 773 This is the percentage of the total execution time your program 774 spent in this function. These should all add up to 100%. 775 776 `cumulative seconds' 777 This is the cumulative total number of seconds the computer spent 778 executing this functions, plus the time spent in all the functions 779 above this one in this table. 780 781 `self seconds' 782 This is the number of seconds accounted for by this function alone. 783 The flat profile listing is sorted first by this number. 784 785 `calls' 786 This is the total number of times the function was called. If the 787 function was never called, or the number of times it was called 788 cannot be determined (probably because the function was not 789 compiled with profiling enabled), the "calls" field is blank. 790 791 `self ms/call' 792 This represents the average number of milliseconds spent in this 793 function per call, if this function is profiled. Otherwise, this 794 field is blank for this function. 795 796 `total ms/call' 797 This represents the average number of milliseconds spent in this 798 function and its descendants per call, if this function is 799 profiled. Otherwise, this field is blank for this function. This 800 is the only field in the flat profile that uses call graph 801 analysis. 802 803 `name' 804 This is the name of the function. The flat profile is sorted by 805 this field alphabetically after the "self seconds" and "calls" 806 fields are sorted. 807 808 809 File: gprof.info, Node: Call Graph, Next: Line-by-line, Prev: Flat Profile, Up: Output 810 811 5.2 The Call Graph 812 ================== 813 814 The "call graph" shows how much time was spent in each function and its 815 children. From this information, you can find functions that, while 816 they themselves may not have used much time, called other functions 817 that did use unusual amounts of time. 818 819 Here is a sample call from a small program. This call came from the 820 same `gprof' run as the flat profile example in the previous section. 821 822 granularity: each sample hit covers 2 byte(s) for 20.00% of 0.05 seconds 823 824 index % time self children called name 825 <spontaneous> 826 [1] 100.0 0.00 0.05 start [1] 827 0.00 0.05 1/1 main [2] 828 0.00 0.00 1/2 on_exit [28] 829 0.00 0.00 1/1 exit [59] 830 ----------------------------------------------- 831 0.00 0.05 1/1 start [1] 832 [2] 100.0 0.00 0.05 1 main [2] 833 0.00 0.05 1/1 report [3] 834 ----------------------------------------------- 835 0.00 0.05 1/1 main [2] 836 [3] 100.0 0.00 0.05 1 report [3] 837 0.00 0.03 8/8 timelocal [6] 838 0.00 0.01 1/1 print [9] 839 0.00 0.01 9/9 fgets [12] 840 0.00 0.00 12/34 strncmp <cycle 1> [40] 841 0.00 0.00 8/8 lookup [20] 842 0.00 0.00 1/1 fopen [21] 843 0.00 0.00 8/8 chewtime [24] 844 0.00 0.00 8/16 skipspace [44] 845 ----------------------------------------------- 846 [4] 59.8 0.01 0.02 8+472 <cycle 2 as a whole> [4] 847 0.01 0.02 244+260 offtime <cycle 2> [7] 848 0.00 0.00 236+1 tzset <cycle 2> [26] 849 ----------------------------------------------- 850 851 The lines full of dashes divide this table into "entries", one for 852 each function. Each entry has one or more lines. 853 854 In each entry, the primary line is the one that starts with an index 855 number in square brackets. The end of this line says which function 856 the entry is for. The preceding lines in the entry describe the 857 callers of this function and the following lines describe its 858 subroutines (also called "children" when we speak of the call graph). 859 860 The entries are sorted by time spent in the function and its 861 subroutines. 862 863 The internal profiling function `mcount' (*note The Flat Profile: 864 Flat Profile.) is never mentioned in the call graph. 865 866 * Menu: 867 868 * Primary:: Details of the primary line's contents. 869 * Callers:: Details of caller-lines' contents. 870 * Subroutines:: Details of subroutine-lines' contents. 871 * Cycles:: When there are cycles of recursion, 872 such as `a' calls `b' calls `a'... 873 874 875 File: gprof.info, Node: Primary, Next: Callers, Up: Call Graph 876 877 5.2.1 The Primary Line 878 ---------------------- 879 880 The "primary line" in a call graph entry is the line that describes the 881 function which the entry is about and gives the overall statistics for 882 this function. 883 884 For reference, we repeat the primary line from the entry for function 885 `report' in our main example, together with the heading line that shows 886 the names of the fields: 887 888 index % time self children called name 889 ... 890 [3] 100.0 0.00 0.05 1 report [3] 891 892 Here is what the fields in the primary line mean: 893 894 `index' 895 Entries are numbered with consecutive integers. Each function 896 therefore has an index number, which appears at the beginning of 897 its primary line. 898 899 Each cross-reference to a function, as a caller or subroutine of 900 another, gives its index number as well as its name. The index 901 number guides you if you wish to look for the entry for that 902 function. 903 904 `% time' 905 This is the percentage of the total time that was spent in this 906 function, including time spent in subroutines called from this 907 function. 908 909 The time spent in this function is counted again for the callers of 910 this function. Therefore, adding up these percentages is 911 meaningless. 912 913 `self' 914 This is the total amount of time spent in this function. This 915 should be identical to the number printed in the `seconds' field 916 for this function in the flat profile. 917 918 `children' 919 This is the total amount of time spent in the subroutine calls 920 made by this function. This should be equal to the sum of all the 921 `self' and `children' entries of the children listed directly 922 below this function. 923 924 `called' 925 This is the number of times the function was called. 926 927 If the function called itself recursively, there are two numbers, 928 separated by a `+'. The first number counts non-recursive calls, 929 and the second counts recursive calls. 930 931 In the example above, the function `report' was called once from 932 `main'. 933 934 `name' 935 This is the name of the current function. The index number is 936 repeated after it. 937 938 If the function is part of a cycle of recursion, the cycle number 939 is printed between the function's name and the index number (*note 940 How Mutually Recursive Functions Are Described: Cycles.). For 941 example, if function `gnurr' is part of cycle number one, and has 942 index number twelve, its primary line would be end like this: 943 944 gnurr <cycle 1> [12] 945 946 947 File: gprof.info, Node: Callers, Next: Subroutines, Prev: Primary, Up: Call Graph 948 949 5.2.2 Lines for a Function's Callers 950 ------------------------------------ 951 952 A function's entry has a line for each function it was called by. 953 These lines' fields correspond to the fields of the primary line, but 954 their meanings are different because of the difference in context. 955 956 For reference, we repeat two lines from the entry for the function 957 `report', the primary line and one caller-line preceding it, together 958 with the heading line that shows the names of the fields: 959 960 index % time self children called name 961 ... 962 0.00 0.05 1/1 main [2] 963 [3] 100.0 0.00 0.05 1 report [3] 964 965 Here are the meanings of the fields in the caller-line for `report' 966 called from `main': 967 968 `self' 969 An estimate of the amount of time spent in `report' itself when it 970 was called from `main'. 971 972 `children' 973 An estimate of the amount of time spent in subroutines of `report' 974 when `report' was called from `main'. 975 976 The sum of the `self' and `children' fields is an estimate of the 977 amount of time spent within calls to `report' from `main'. 978 979 `called' 980 Two numbers: the number of times `report' was called from `main', 981 followed by the total number of non-recursive calls to `report' 982 from all its callers. 983 984 `name and index number' 985 The name of the caller of `report' to which this line applies, 986 followed by the caller's index number. 987 988 Not all functions have entries in the call graph; some options to 989 `gprof' request the omission of certain functions. When a caller 990 has no entry of its own, it still has caller-lines in the entries 991 of the functions it calls. 992 993 If the caller is part of a recursion cycle, the cycle number is 994 printed between the name and the index number. 995 996 If the identity of the callers of a function cannot be determined, a 997 dummy caller-line is printed which has `<spontaneous>' as the "caller's 998 name" and all other fields blank. This can happen for signal handlers. 999 1000 1001 File: gprof.info, Node: Subroutines, Next: Cycles, Prev: Callers, Up: Call Graph 1002 1003 5.2.3 Lines for a Function's Subroutines 1004 ---------------------------------------- 1005 1006 A function's entry has a line for each of its subroutines--in other 1007 words, a line for each other function that it called. These lines' 1008 fields correspond to the fields of the primary line, but their meanings 1009 are different because of the difference in context. 1010 1011 For reference, we repeat two lines from the entry for the function 1012 `main', the primary line and a line for a subroutine, together with the 1013 heading line that shows the names of the fields: 1014 1015 index % time self children called name 1016 ... 1017 [2] 100.0 0.00 0.05 1 main [2] 1018 0.00 0.05 1/1 report [3] 1019 1020 Here are the meanings of the fields in the subroutine-line for `main' 1021 calling `report': 1022 1023 `self' 1024 An estimate of the amount of time spent directly within `report' 1025 when `report' was called from `main'. 1026 1027 `children' 1028 An estimate of the amount of time spent in subroutines of `report' 1029 when `report' was called from `main'. 1030 1031 The sum of the `self' and `children' fields is an estimate of the 1032 total time spent in calls to `report' from `main'. 1033 1034 `called' 1035 Two numbers, the number of calls to `report' from `main' followed 1036 by the total number of non-recursive calls to `report'. This 1037 ratio is used to determine how much of `report''s `self' and 1038 `children' time gets credited to `main'. *Note Estimating 1039 `children' Times: Assumptions. 1040 1041 `name' 1042 The name of the subroutine of `main' to which this line applies, 1043 followed by the subroutine's index number. 1044 1045 If the caller is part of a recursion cycle, the cycle number is 1046 printed between the name and the index number. 1047 1048 1049 File: gprof.info, Node: Cycles, Prev: Subroutines, Up: Call Graph 1050 1051 5.2.4 How Mutually Recursive Functions Are Described 1052 ---------------------------------------------------- 1053 1054 The graph may be complicated by the presence of "cycles of recursion" 1055 in the call graph. A cycle exists if a function calls another function 1056 that (directly or indirectly) calls (or appears to call) the original 1057 function. For example: if `a' calls `b', and `b' calls `a', then `a' 1058 and `b' form a cycle. 1059 1060 Whenever there are call paths both ways between a pair of functions, 1061 they belong to the same cycle. If `a' and `b' call each other and `b' 1062 and `c' call each other, all three make one cycle. Note that even if 1063 `b' only calls `a' if it was not called from `a', `gprof' cannot 1064 determine this, so `a' and `b' are still considered a cycle. 1065 1066 The cycles are numbered with consecutive integers. When a function 1067 belongs to a cycle, each time the function name appears in the call 1068 graph it is followed by `<cycle NUMBER>'. 1069 1070 The reason cycles matter is that they make the time values in the 1071 call graph paradoxical. The "time spent in children" of `a' should 1072 include the time spent in its subroutine `b' and in `b''s 1073 subroutines--but one of `b''s subroutines is `a'! How much of `a''s 1074 time should be included in the children of `a', when `a' is indirectly 1075 recursive? 1076 1077 The way `gprof' resolves this paradox is by creating a single entry 1078 for the cycle as a whole. The primary line of this entry describes the 1079 total time spent directly in the functions of the cycle. The 1080 "subroutines" of the cycle are the individual functions of the cycle, 1081 and all other functions that were called directly by them. The 1082 "callers" of the cycle are the functions, outside the cycle, that 1083 called functions in the cycle. 1084 1085 Here is an example portion of a call graph which shows a cycle 1086 containing functions `a' and `b'. The cycle was entered by a call to 1087 `a' from `main'; both `a' and `b' called `c'. 1088 1089 index % time self children called name 1090 ---------------------------------------- 1091 1.77 0 1/1 main [2] 1092 [3] 91.71 1.77 0 1+5 <cycle 1 as a whole> [3] 1093 1.02 0 3 b <cycle 1> [4] 1094 0.75 0 2 a <cycle 1> [5] 1095 ---------------------------------------- 1096 3 a <cycle 1> [5] 1097 [4] 52.85 1.02 0 0 b <cycle 1> [4] 1098 2 a <cycle 1> [5] 1099 0 0 3/6 c [6] 1100 ---------------------------------------- 1101 1.77 0 1/1 main [2] 1102 2 b <cycle 1> [4] 1103 [5] 38.86 0.75 0 1 a <cycle 1> [5] 1104 3 b <cycle 1> [4] 1105 0 0 3/6 c [6] 1106 ---------------------------------------- 1107 1108 (The entire call graph for this program contains in addition an entry 1109 for `main', which calls `a', and an entry for `c', with callers `a' and 1110 `b'.) 1111 1112 index % time self children called name 1113 <spontaneous> 1114 [1] 100.00 0 1.93 0 start [1] 1115 0.16 1.77 1/1 main [2] 1116 ---------------------------------------- 1117 0.16 1.77 1/1 start [1] 1118 [2] 100.00 0.16 1.77 1 main [2] 1119 1.77 0 1/1 a <cycle 1> [5] 1120 ---------------------------------------- 1121 1.77 0 1/1 main [2] 1122 [3] 91.71 1.77 0 1+5 <cycle 1 as a whole> [3] 1123 1.02 0 3 b <cycle 1> [4] 1124 0.75 0 2 a <cycle 1> [5] 1125 0 0 6/6 c [6] 1126 ---------------------------------------- 1127 3 a <cycle 1> [5] 1128 [4] 52.85 1.02 0 0 b <cycle 1> [4] 1129 2 a <cycle 1> [5] 1130 0 0 3/6 c [6] 1131 ---------------------------------------- 1132 1.77 0 1/1 main [2] 1133 2 b <cycle 1> [4] 1134 [5] 38.86 0.75 0 1 a <cycle 1> [5] 1135 3 b <cycle 1> [4] 1136 0 0 3/6 c [6] 1137 ---------------------------------------- 1138 0 0 3/6 b <cycle 1> [4] 1139 0 0 3/6 a <cycle 1> [5] 1140 [6] 0.00 0 0 6 c [6] 1141 ---------------------------------------- 1142 1143 The `self' field of the cycle's primary line is the total time spent 1144 in all the functions of the cycle. It equals the sum of the `self' 1145 fields for the individual functions in the cycle, found in the entry in 1146 the subroutine lines for these functions. 1147 1148 The `children' fields of the cycle's primary line and subroutine 1149 lines count only subroutines outside the cycle. Even though `a' calls 1150 `b', the time spent in those calls to `b' is not counted in `a''s 1151 `children' time. Thus, we do not encounter the problem of what to do 1152 when the time in those calls to `b' includes indirect recursive calls 1153 back to `a'. 1154 1155 The `children' field of a caller-line in the cycle's entry estimates 1156 the amount of time spent _in the whole cycle_, and its other 1157 subroutines, on the times when that caller called a function in the 1158 cycle. 1159 1160 The `called' field in the primary line for the cycle has two numbers: 1161 first, the number of times functions in the cycle were called by 1162 functions outside the cycle; second, the number of times they were 1163 called by functions in the cycle (including times when a function in 1164 the cycle calls itself). This is a generalization of the usual split 1165 into non-recursive and recursive calls. 1166 1167 The `called' field of a subroutine-line for a cycle member in the 1168 cycle's entry says how many time that function was called from 1169 functions in the cycle. The total of all these is the second number in 1170 the primary line's `called' field. 1171 1172 In the individual entry for a function in a cycle, the other 1173 functions in the same cycle can appear as subroutines and as callers. 1174 These lines show how many times each function in the cycle called or 1175 was called from each other function in the cycle. The `self' and 1176 `children' fields in these lines are blank because of the difficulty of 1177 defining meanings for them when recursion is going on. 1178 1179 1180 File: gprof.info, Node: Line-by-line, Next: Annotated Source, Prev: Call Graph, Up: Output 1181 1182 5.3 Line-by-line Profiling 1183 ========================== 1184 1185 `gprof''s `-l' option causes the program to perform "line-by-line" 1186 profiling. In this mode, histogram samples are assigned not to 1187 functions, but to individual lines of source code. This only works 1188 with programs compiled with older versions of the `gcc' compiler. 1189 Newer versions of `gcc' use a different program - `gcov' - to display 1190 line-by-line profiling information. 1191 1192 With the older versions of `gcc' the program usually has to be 1193 compiled with a `-g' option, in addition to `-pg', in order to generate 1194 debugging symbols for tracking source code lines. Note, in much older 1195 versions of `gcc' the program had to be compiled with the `-a' command 1196 line option as well. 1197 1198 The flat profile is the most useful output table in line-by-line 1199 mode. The call graph isn't as useful as normal, since the current 1200 version of `gprof' does not propagate call graph arcs from source code 1201 lines to the enclosing function. The call graph does, however, show 1202 each line of code that called each function, along with a count. 1203 1204 Here is a section of `gprof''s output, without line-by-line 1205 profiling. Note that `ct_init' accounted for four histogram hits, and 1206 13327 calls to `init_block'. 1207 1208 Flat profile: 1209 1210 Each sample counts as 0.01 seconds. 1211 % cumulative self self total 1212 time seconds seconds calls us/call us/call name 1213 30.77 0.13 0.04 6335 6.31 6.31 ct_init 1214 1215 1216 Call graph (explanation follows) 1217 1218 1219 granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds 1220 1221 index % time self children called name 1222 1223 0.00 0.00 1/13496 name_too_long 1224 0.00 0.00 40/13496 deflate 1225 0.00 0.00 128/13496 deflate_fast 1226 0.00 0.00 13327/13496 ct_init 1227 [7] 0.0 0.00 0.00 13496 init_block 1228 1229 Now let's look at some of `gprof''s output from the same program run, 1230 this time with line-by-line profiling enabled. Note that `ct_init''s 1231 four histogram hits are broken down into four lines of source code--one 1232 hit occurred on each of lines 349, 351, 382 and 385. In the call graph, 1233 note how `ct_init''s 13327 calls to `init_block' are broken down into 1234 one call from line 396, 3071 calls from line 384, 3730 calls from line 1235 385, and 6525 calls from 387. 1236 1237 Flat profile: 1238 1239 Each sample counts as 0.01 seconds. 1240 % cumulative self 1241 time seconds seconds calls name 1242 7.69 0.10 0.01 ct_init (trees.c:349) 1243 7.69 0.11 0.01 ct_init (trees.c:351) 1244 7.69 0.12 0.01 ct_init (trees.c:382) 1245 7.69 0.13 0.01 ct_init (trees.c:385) 1246 1247 1248 Call graph (explanation follows) 1249 1250 1251 granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds 1252 1253 % time self children called name 1254 1255 0.00 0.00 1/13496 name_too_long (gzip.c:1440) 1256 0.00 0.00 1/13496 deflate (deflate.c:763) 1257 0.00 0.00 1/13496 ct_init (trees.c:396) 1258 0.00 0.00 2/13496 deflate (deflate.c:727) 1259 0.00 0.00 4/13496 deflate (deflate.c:686) 1260 0.00 0.00 5/13496 deflate (deflate.c:675) 1261 0.00 0.00 12/13496 deflate (deflate.c:679) 1262 0.00 0.00 16/13496 deflate (deflate.c:730) 1263 0.00 0.00 128/13496 deflate_fast (deflate.c:654) 1264 0.00 0.00 3071/13496 ct_init (trees.c:384) 1265 0.00 0.00 3730/13496 ct_init (trees.c:385) 1266 0.00 0.00 6525/13496 ct_init (trees.c:387) 1267 [6] 0.0 0.00 0.00 13496 init_block (trees.c:408) 1268 1269 1270 File: gprof.info, Node: Annotated Source, Prev: Line-by-line, Up: Output 1271 1272 5.4 The Annotated Source Listing 1273 ================================ 1274 1275 `gprof''s `-A' option triggers an annotated source listing, which lists 1276 the program's source code, each function labeled with the number of 1277 times it was called. You may also need to specify the `-I' option, if 1278 `gprof' can't find the source code files. 1279 1280 With older versions of `gcc' compiling with `gcc ... -g -pg -a' 1281 augments your program with basic-block counting code, in addition to 1282 function counting code. This enables `gprof' to determine how many 1283 times each line of code was executed. With newer versions of `gcc' 1284 support for displaying basic-block counts is provided by the `gcov' 1285 program. 1286 1287 For example, consider the following function, taken from gzip, with 1288 line numbers added: 1289 1290 1 ulg updcrc(s, n) 1291 2 uch *s; 1292 3 unsigned n; 1293 4 { 1294 5 register ulg c; 1295 6 1296 7 static ulg crc = (ulg)0xffffffffL; 1297 8 1298 9 if (s == NULL) { 1299 10 c = 0xffffffffL; 1300 11 } else { 1301 12 c = crc; 1302 13 if (n) do { 1303 14 c = crc_32_tab[...]; 1304 15 } while (--n); 1305 16 } 1306 17 crc = c; 1307 18 return c ^ 0xffffffffL; 1308 19 } 1309 1310 `updcrc' has at least five basic-blocks. One is the function 1311 itself. The `if' statement on line 9 generates two more basic-blocks, 1312 one for each branch of the `if'. A fourth basic-block results from the 1313 `if' on line 13, and the contents of the `do' loop form the fifth 1314 basic-block. The compiler may also generate additional basic-blocks to 1315 handle various special cases. 1316 1317 A program augmented for basic-block counting can be analyzed with 1318 `gprof -l -A'. The `-x' option is also helpful, to ensure that each 1319 line of code is labeled at least once. Here is `updcrc''s annotated 1320 source listing for a sample `gzip' run: 1321 1322 ulg updcrc(s, n) 1323 uch *s; 1324 unsigned n; 1325 2 ->{ 1326 register ulg c; 1327 1328 static ulg crc = (ulg)0xffffffffL; 1329 1330 2 -> if (s == NULL) { 1331 1 -> c = 0xffffffffL; 1332 1 -> } else { 1333 1 -> c = crc; 1334 1 -> if (n) do { 1335 26312 -> c = crc_32_tab[...]; 1336 26312,1,26311 -> } while (--n); 1337 } 1338 2 -> crc = c; 1339 2 -> return c ^ 0xffffffffL; 1340 2 ->} 1341 1342 In this example, the function was called twice, passing once through 1343 each branch of the `if' statement. The body of the `do' loop was 1344 executed a total of 26312 times. Note how the `while' statement is 1345 annotated. It began execution 26312 times, once for each iteration 1346 through the loop. One of those times (the last time) it exited, while 1347 it branched back to the beginning of the loop 26311 times. 1348 1349 1350 File: gprof.info, Node: Inaccuracy, Next: How do I?, Prev: Output, Up: Top 1351 1352 6 Inaccuracy of `gprof' Output 1353 ****************************** 1354 1355 * Menu: 1356 1357 * Sampling Error:: Statistical margins of error 1358 * Assumptions:: Estimating children times 1359 1360 1361 File: gprof.info, Node: Sampling Error, Next: Assumptions, Up: Inaccuracy 1362 1363 6.1 Statistical Sampling Error 1364 ============================== 1365 1366 The run-time figures that `gprof' gives you are based on a sampling 1367 process, so they are subject to statistical inaccuracy. If a function 1368 runs only a small amount of time, so that on the average the sampling 1369 process ought to catch that function in the act only once, there is a 1370 pretty good chance it will actually find that function zero times, or 1371 twice. 1372 1373 By contrast, the number-of-calls and basic-block figures are derived 1374 by counting, not sampling. They are completely accurate and will not 1375 vary from run to run if your program is deterministic. 1376 1377 The "sampling period" that is printed at the beginning of the flat 1378 profile says how often samples are taken. The rule of thumb is that a 1379 run-time figure is accurate if it is considerably bigger than the 1380 sampling period. 1381 1382 The actual amount of error can be predicted. For N samples, the 1383 _expected_ error is the square-root of N. For example, if the sampling 1384 period is 0.01 seconds and `foo''s run-time is 1 second, N is 100 1385 samples (1 second/0.01 seconds), sqrt(N) is 10 samples, so the expected 1386 error in `foo''s run-time is 0.1 seconds (10*0.01 seconds), or ten 1387 percent of the observed value. Again, if the sampling period is 0.01 1388 seconds and `bar''s run-time is 100 seconds, N is 10000 samples, 1389 sqrt(N) is 100 samples, so the expected error in `bar''s run-time is 1 1390 second, or one percent of the observed value. It is likely to vary 1391 this much _on the average_ from one profiling run to the next. 1392 (_Sometimes_ it will vary more.) 1393 1394 This does not mean that a small run-time figure is devoid of 1395 information. If the program's _total_ run-time is large, a small 1396 run-time for one function does tell you that that function used an 1397 insignificant fraction of the whole program's time. Usually this means 1398 it is not worth optimizing. 1399 1400 One way to get more accuracy is to give your program more (but 1401 similar) input data so it will take longer. Another way is to combine 1402 the data from several runs, using the `-s' option of `gprof'. Here is 1403 how: 1404 1405 1. Run your program once. 1406 1407 2. Issue the command `mv gmon.out gmon.sum'. 1408 1409 3. Run your program again, the same as before. 1410 1411 4. Merge the new data in `gmon.out' into `gmon.sum' with this command: 1412 1413 gprof -s EXECUTABLE-FILE gmon.out gmon.sum 1414 1415 5. Repeat the last two steps as often as you wish. 1416 1417 6. Analyze the cumulative data using this command: 1418 1419 gprof EXECUTABLE-FILE gmon.sum > OUTPUT-FILE 1420 1421 1422 File: gprof.info, Node: Assumptions, Prev: Sampling Error, Up: Inaccuracy 1423 1424 6.2 Estimating `children' Times 1425 =============================== 1426 1427 Some of the figures in the call graph are estimates--for example, the 1428 `children' time values and all the time figures in caller and 1429 subroutine lines. 1430 1431 There is no direct information about these measurements in the 1432 profile data itself. Instead, `gprof' estimates them by making an 1433 assumption about your program that might or might not be true. 1434 1435 The assumption made is that the average time spent in each call to 1436 any function `foo' is not correlated with who called `foo'. If `foo' 1437 used 5 seconds in all, and 2/5 of the calls to `foo' came from `a', 1438 then `foo' contributes 2 seconds to `a''s `children' time, by 1439 assumption. 1440 1441 This assumption is usually true enough, but for some programs it is 1442 far from true. Suppose that `foo' returns very quickly when its 1443 argument is zero; suppose that `a' always passes zero as an argument, 1444 while other callers of `foo' pass other arguments. In this program, 1445 all the time spent in `foo' is in the calls from callers other than `a'. 1446 But `gprof' has no way of knowing this; it will blindly and incorrectly 1447 charge 2 seconds of time in `foo' to the children of `a'. 1448 1449 We hope some day to put more complete data into `gmon.out', so that 1450 this assumption is no longer needed, if we can figure out how. For the 1451 novice, the estimated figures are usually more useful than misleading. 1452 1453 1454 File: gprof.info, Node: How do I?, Next: Incompatibilities, Prev: Inaccuracy, Up: Top 1455 1456 7 Answers to Common Questions 1457 ***************************** 1458 1459 How can I get more exact information about hot spots in my program? 1460 Looking at the per-line call counts only tells part of the story. 1461 Because `gprof' can only report call times and counts by function, 1462 the best way to get finer-grained information on where the program 1463 is spending its time is to re-factor large functions into sequences 1464 of calls to smaller ones. Beware however that this can introduce 1465 artificial hot spots since compiling with `-pg' adds a significant 1466 overhead to function calls. An alternative solution is to use a 1467 non-intrusive profiler, e.g. oprofile. 1468 1469 How do I find which lines in my program were executed the most times? 1470 Use the `gcov' program. 1471 1472 How do I find which lines in my program called a particular function? 1473 Use `gprof -l' and lookup the function in the call graph. The 1474 callers will be broken down by function and line number. 1475 1476 How do I analyze a program that runs for less than a second? 1477 Try using a shell script like this one: 1478 1479 for i in `seq 1 100`; do 1480 fastprog 1481 mv gmon.out gmon.out.$i 1482 done 1483 1484 gprof -s fastprog gmon.out.* 1485 1486 gprof fastprog gmon.sum 1487 1488 If your program is completely deterministic, all the call counts 1489 will be simple multiples of 100 (i.e., a function called once in 1490 each run will appear with a call count of 100). 1491 1492 1493 1494 File: gprof.info, Node: Incompatibilities, Next: Details, Prev: How do I?, Up: Top 1495 1496 8 Incompatibilities with Unix `gprof' 1497 ************************************* 1498 1499 GNU `gprof' and Berkeley Unix `gprof' use the same data file 1500 `gmon.out', and provide essentially the same information. But there 1501 are a few differences. 1502 1503 * GNU `gprof' uses a new, generalized file format with support for 1504 basic-block execution counts and non-realtime histograms. A magic 1505 cookie and version number allows `gprof' to easily identify new 1506 style files. Old BSD-style files can still be read. *Note 1507 Profiling Data File Format: File Format. 1508 1509 * For a recursive function, Unix `gprof' lists the function as a 1510 parent and as a child, with a `calls' field that lists the number 1511 of recursive calls. GNU `gprof' omits these lines and puts the 1512 number of recursive calls in the primary line. 1513 1514 * When a function is suppressed from the call graph with `-e', GNU 1515 `gprof' still lists it as a subroutine of functions that call it. 1516 1517 * GNU `gprof' accepts the `-k' with its argument in the form 1518 `from/to', instead of `from to'. 1519 1520 * In the annotated source listing, if there are multiple basic 1521 blocks on the same line, GNU `gprof' prints all of their counts, 1522 separated by commas. 1523 1524 * The blurbs, field widths, and output formats are different. GNU 1525 `gprof' prints blurbs after the tables, so that you can see the 1526 tables without skipping the blurbs. 1527 1528 1529 File: gprof.info, Node: Details, Next: GNU Free Documentation License, Prev: Incompatibilities, Up: Top 1530 1531 9 Details of Profiling 1532 ********************** 1533 1534 * Menu: 1535 1536 * Implementation:: How a program collects profiling information 1537 * File Format:: Format of `gmon.out' files 1538 * Internals:: `gprof''s internal operation 1539 * Debugging:: Using `gprof''s `-d' option 1540 1541 1542 File: gprof.info, Node: Implementation, Next: File Format, Up: Details 1543 1544 9.1 Implementation of Profiling 1545 =============================== 1546 1547 Profiling works by changing how every function in your program is 1548 compiled so that when it is called, it will stash away some information 1549 about where it was called from. From this, the profiler can figure out 1550 what function called it, and can count how many times it was called. 1551 This change is made by the compiler when your program is compiled with 1552 the `-pg' option, which causes every function to call `mcount' (or 1553 `_mcount', or `__mcount', depending on the OS and compiler) as one of 1554 its first operations. 1555 1556 The `mcount' routine, included in the profiling library, is 1557 responsible for recording in an in-memory call graph table both its 1558 parent routine (the child) and its parent's parent. This is typically 1559 done by examining the stack frame to find both the address of the 1560 child, and the return address in the original parent. Since this is a 1561 very machine-dependent operation, `mcount' itself is typically a short 1562 assembly-language stub routine that extracts the required information, 1563 and then calls `__mcount_internal' (a normal C function) with two 1564 arguments--`frompc' and `selfpc'. `__mcount_internal' is responsible 1565 for maintaining the in-memory call graph, which records `frompc', 1566 `selfpc', and the number of times each of these call arcs was traversed. 1567 1568 GCC Version 2 provides a magical function 1569 (`__builtin_return_address'), which allows a generic `mcount' function 1570 to extract the required information from the stack frame. However, on 1571 some architectures, most notably the SPARC, using this builtin can be 1572 very computationally expensive, and an assembly language version of 1573 `mcount' is used for performance reasons. 1574 1575 Number-of-calls information for library routines is collected by 1576 using a special version of the C library. The programs in it are the 1577 same as in the usual C library, but they were compiled with `-pg'. If 1578 you link your program with `gcc ... -pg', it automatically uses the 1579 profiling version of the library. 1580 1581 Profiling also involves watching your program as it runs, and 1582 keeping a histogram of where the program counter happens to be every 1583 now and then. Typically the program counter is looked at around 100 1584 times per second of run time, but the exact frequency may vary from 1585 system to system. 1586 1587 This is done is one of two ways. Most UNIX-like operating systems 1588 provide a `profil()' system call, which registers a memory array with 1589 the kernel, along with a scale factor that determines how the program's 1590 address space maps into the array. Typical scaling values cause every 1591 2 to 8 bytes of address space to map into a single array slot. On 1592 every tick of the system clock (assuming the profiled program is 1593 running), the value of the program counter is examined and the 1594 corresponding slot in the memory array is incremented. Since this is 1595 done in the kernel, which had to interrupt the process anyway to handle 1596 the clock interrupt, very little additional system overhead is required. 1597 1598 However, some operating systems, most notably Linux 2.0 (and 1599 earlier), do not provide a `profil()' system call. On such a system, 1600 arrangements are made for the kernel to periodically deliver a signal 1601 to the process (typically via `setitimer()'), which then performs the 1602 same operation of examining the program counter and incrementing a slot 1603 in the memory array. Since this method requires a signal to be 1604 delivered to user space every time a sample is taken, it uses 1605 considerably more overhead than kernel-based profiling. Also, due to 1606 the added delay required to deliver the signal, this method is less 1607 accurate as well. 1608 1609 A special startup routine allocates memory for the histogram and 1610 either calls `profil()' or sets up a clock signal handler. This 1611 routine (`monstartup') can be invoked in several ways. On Linux 1612 systems, a special profiling startup file `gcrt0.o', which invokes 1613 `monstartup' before `main', is used instead of the default `crt0.o'. 1614 Use of this special startup file is one of the effects of using `gcc 1615 ... -pg' to link. On SPARC systems, no special startup files are used. 1616 Rather, the `mcount' routine, when it is invoked for the first time 1617 (typically when `main' is called), calls `monstartup'. 1618 1619 If the compiler's `-a' option was used, basic-block counting is also 1620 enabled. Each object file is then compiled with a static array of 1621 counts, initially zero. In the executable code, every time a new 1622 basic-block begins (i.e., when an `if' statement appears), an extra 1623 instruction is inserted to increment the corresponding count in the 1624 array. At compile time, a paired array was constructed that recorded 1625 the starting address of each basic-block. Taken together, the two 1626 arrays record the starting address of every basic-block, along with the 1627 number of times it was executed. 1628 1629 The profiling library also includes a function (`mcleanup') which is 1630 typically registered using `atexit()' to be called as the program 1631 exits, and is responsible for writing the file `gmon.out'. Profiling 1632 is turned off, various headers are output, and the histogram is 1633 written, followed by the call-graph arcs and the basic-block counts. 1634 1635 The output from `gprof' gives no indication of parts of your program 1636 that are limited by I/O or swapping bandwidth. This is because samples 1637 of the program counter are taken at fixed intervals of the program's 1638 run time. Therefore, the time measurements in `gprof' output say 1639 nothing about time that your program was not running. For example, a 1640 part of the program that creates so much data that it cannot all fit in 1641 physical memory at once may run very slowly due to thrashing, but 1642 `gprof' will say it uses little time. On the other hand, sampling by 1643 run time has the advantage that the amount of load due to other users 1644 won't directly affect the output you get. 1645 1646 1647 File: gprof.info, Node: File Format, Next: Internals, Prev: Implementation, Up: Details 1648 1649 9.2 Profiling Data File Format 1650 ============================== 1651 1652 The old BSD-derived file format used for profile data does not contain a 1653 magic cookie that allows to check whether a data file really is a 1654 `gprof' file. Furthermore, it does not provide a version number, thus 1655 rendering changes to the file format almost impossible. GNU `gprof' 1656 uses a new file format that provides these features. For backward 1657 compatibility, GNU `gprof' continues to support the old BSD-derived 1658 format, but not all features are supported with it. For example, 1659 basic-block execution counts cannot be accommodated by the old file 1660 format. 1661 1662 The new file format is defined in header file `gmon_out.h'. It 1663 consists of a header containing the magic cookie and a version number, 1664 as well as some spare bytes available for future extensions. All data 1665 in a profile data file is in the native format of the target for which 1666 the profile was collected. GNU `gprof' adapts automatically to the 1667 byte-order in use. 1668 1669 In the new file format, the header is followed by a sequence of 1670 records. Currently, there are three different record types: histogram 1671 records, call-graph arc records, and basic-block execution count 1672 records. Each file can contain any number of each record type. When 1673 reading a file, GNU `gprof' will ensure records of the same type are 1674 compatible with each other and compute the union of all records. For 1675 example, for basic-block execution counts, the union is simply the sum 1676 of all execution counts for each basic-block. 1677 1678 9.2.1 Histogram Records 1679 ----------------------- 1680 1681 Histogram records consist of a header that is followed by an array of 1682 bins. The header contains the text-segment range that the histogram 1683 spans, the size of the histogram in bytes (unlike in the old BSD 1684 format, this does not include the size of the header), the rate of the 1685 profiling clock, and the physical dimension that the bin counts 1686 represent after being scaled by the profiling clock rate. The physical 1687 dimension is specified in two parts: a long name of up to 15 characters 1688 and a single character abbreviation. For example, a histogram 1689 representing real-time would specify the long name as "seconds" and the 1690 abbreviation as "s". This feature is useful for architectures that 1691 support performance monitor hardware (which, fortunately, is becoming 1692 increasingly common). For example, under DEC OSF/1, the "uprofile" 1693 command can be used to produce a histogram of, say, instruction cache 1694 misses. In this case, the dimension in the histogram header could be 1695 set to "i-cache misses" and the abbreviation could be set to "1" 1696 (because it is simply a count, not a physical dimension). Also, the 1697 profiling rate would have to be set to 1 in this case. 1698 1699 Histogram bins are 16-bit numbers and each bin represent an equal 1700 amount of text-space. For example, if the text-segment is one thousand 1701 bytes long and if there are ten bins in the histogram, each bin 1702 represents one hundred bytes. 1703 1704 9.2.2 Call-Graph Records 1705 ------------------------ 1706 1707 Call-graph records have a format that is identical to the one used in 1708 the BSD-derived file format. It consists of an arc in the call graph 1709 and a count indicating the number of times the arc was traversed during 1710 program execution. Arcs are specified by a pair of addresses: the 1711 first must be within caller's function and the second must be within 1712 the callee's function. When performing profiling at the function 1713 level, these addresses can point anywhere within the respective 1714 function. However, when profiling at the line-level, it is better if 1715 the addresses are as close to the call-site/entry-point as possible. 1716 This will ensure that the line-level call-graph is able to identify 1717 exactly which line of source code performed calls to a function. 1718 1719 9.2.3 Basic-Block Execution Count Records 1720 ----------------------------------------- 1721 1722 Basic-block execution count records consist of a header followed by a 1723 sequence of address/count pairs. The header simply specifies the 1724 length of the sequence. In an address/count pair, the address 1725 identifies a basic-block and the count specifies the number of times 1726 that basic-block was executed. Any address within the basic-address can 1727 be used. 1728 1729 1730 File: gprof.info, Node: Internals, Next: Debugging, Prev: File Format, Up: Details 1731 1732 9.3 `gprof''s Internal Operation 1733 ================================ 1734 1735 Like most programs, `gprof' begins by processing its options. During 1736 this stage, it may building its symspec list (`sym_ids.c:sym_id_add'), 1737 if options are specified which use symspecs. `gprof' maintains a 1738 single linked list of symspecs, which will eventually get turned into 1739 12 symbol tables, organized into six include/exclude pairs--one pair 1740 each for the flat profile (INCL_FLAT/EXCL_FLAT), the call graph arcs 1741 (INCL_ARCS/EXCL_ARCS), printing in the call graph 1742 (INCL_GRAPH/EXCL_GRAPH), timing propagation in the call graph 1743 (INCL_TIME/EXCL_TIME), the annotated source listing 1744 (INCL_ANNO/EXCL_ANNO), and the execution count listing 1745 (INCL_EXEC/EXCL_EXEC). 1746 1747 After option processing, `gprof' finishes building the symspec list 1748 by adding all the symspecs in `default_excluded_list' to the exclude 1749 lists EXCL_TIME and EXCL_GRAPH, and if line-by-line profiling is 1750 specified, EXCL_FLAT as well. These default excludes are not added to 1751 EXCL_ANNO, EXCL_ARCS, and EXCL_EXEC. 1752 1753 Next, the BFD library is called to open the object file, verify that 1754 it is an object file, and read its symbol table (`core.c:core_init'), 1755 using `bfd_canonicalize_symtab' after mallocing an appropriately sized 1756 array of symbols. At this point, function mappings are read (if the 1757 `--file-ordering' option has been specified), and the core text space 1758 is read into memory (if the `-c' option was given). 1759 1760 `gprof''s own symbol table, an array of Sym structures, is now built. 1761 This is done in one of two ways, by one of two routines, depending on 1762 whether line-by-line profiling (`-l' option) has been enabled. For 1763 normal profiling, the BFD canonical symbol table is scanned. For 1764 line-by-line profiling, every text space address is examined, and a new 1765 symbol table entry gets created every time the line number changes. In 1766 either case, two passes are made through the symbol table--one to count 1767 the size of the symbol table required, and the other to actually read 1768 the symbols. In between the two passes, a single array of type `Sym' 1769 is created of the appropriate length. Finally, 1770 `symtab.c:symtab_finalize' is called to sort the symbol table and 1771 remove duplicate entries (entries with the same memory address). 1772 1773 The symbol table must be a contiguous array for two reasons. First, 1774 the `qsort' library function (which sorts an array) will be used to 1775 sort the symbol table. Also, the symbol lookup routine 1776 (`symtab.c:sym_lookup'), which finds symbols based on memory address, 1777 uses a binary search algorithm which requires the symbol table to be a 1778 sorted array. Function symbols are indicated with an `is_func' flag. 1779 Line number symbols have no special flags set. Additionally, a symbol 1780 can have an `is_static' flag to indicate that it is a local symbol. 1781 1782 With the symbol table read, the symspecs can now be translated into 1783 Syms (`sym_ids.c:sym_id_parse'). Remember that a single symspec can 1784 match multiple symbols. An array of symbol tables (`syms') is created, 1785 each entry of which is a symbol table of Syms to be included or 1786 excluded from a particular listing. The master symbol table and the 1787 symspecs are examined by nested loops, and every symbol that matches a 1788 symspec is inserted into the appropriate syms table. This is done 1789 twice, once to count the size of each required symbol table, and again 1790 to build the tables, which have been malloced between passes. From now 1791 on, to determine whether a symbol is on an include or exclude symspec 1792 list, `gprof' simply uses its standard symbol lookup routine on the 1793 appropriate table in the `syms' array. 1794 1795 Now the profile data file(s) themselves are read 1796 (`gmon_io.c:gmon_out_read'), first by checking for a new-style 1797 `gmon.out' header, then assuming this is an old-style BSD `gmon.out' if 1798 the magic number test failed. 1799 1800 New-style histogram records are read by `hist.c:hist_read_rec'. For 1801 the first histogram record, allocate a memory array to hold all the 1802 bins, and read them in. When multiple profile data files (or files 1803 with multiple histogram records) are read, the memory ranges of each 1804 pair of histogram records must be either equal, or non-overlapping. 1805 For each pair of histogram records, the resolution (memory region size 1806 divided by the number of bins) must be the same. The time unit must be 1807 the same for all histogram records. If the above containts are met, all 1808 histograms for the same memory range are merged. 1809 1810 As each call graph record is read (`call_graph.c:cg_read_rec'), the 1811 parent and child addresses are matched to symbol table entries, and a 1812 call graph arc is created by `cg_arcs.c:arc_add', unless the arc fails 1813 a symspec check against INCL_ARCS/EXCL_ARCS. As each arc is added, a 1814 linked list is maintained of the parent's child arcs, and of the child's 1815 parent arcs. Both the child's call count and the arc's call count are 1816 incremented by the record's call count. 1817 1818 Basic-block records are read (`basic_blocks.c:bb_read_rec'), but 1819 only if line-by-line profiling has been selected. Each basic-block 1820 address is matched to a corresponding line symbol in the symbol table, 1821 and an entry made in the symbol's bb_addr and bb_calls arrays. Again, 1822 if multiple basic-block records are present for the same address, the 1823 call counts are cumulative. 1824 1825 A gmon.sum file is dumped, if requested (`gmon_io.c:gmon_out_write'). 1826 1827 If histograms were present in the data files, assign them to symbols 1828 (`hist.c:hist_assign_samples') by iterating over all the sample bins 1829 and assigning them to symbols. Since the symbol table is sorted in 1830 order of ascending memory addresses, we can simple follow along in the 1831 symbol table as we make our pass over the sample bins. This step 1832 includes a symspec check against INCL_FLAT/EXCL_FLAT. Depending on the 1833 histogram scale factor, a sample bin may span multiple symbols, in 1834 which case a fraction of the sample count is allocated to each symbol, 1835 proportional to the degree of overlap. This effect is rare for normal 1836 profiling, but overlaps are more common during line-by-line profiling, 1837 and can cause each of two adjacent lines to be credited with half a 1838 hit, for example. 1839 1840 If call graph data is present, `cg_arcs.c:cg_assemble' is called. 1841 First, if `-c' was specified, a machine-dependent routine (`find_call') 1842 scans through each symbol's machine code, looking for subroutine call 1843 instructions, and adding them to the call graph with a zero call count. 1844 A topological sort is performed by depth-first numbering all the 1845 symbols (`cg_dfn.c:cg_dfn'), so that children are always numbered less 1846 than their parents, then making a array of pointers into the symbol 1847 table and sorting it into numerical order, which is reverse topological 1848 order (children appear before parents). Cycles are also detected at 1849 this point, all members of which are assigned the same topological 1850 number. Two passes are now made through this sorted array of symbol 1851 pointers. The first pass, from end to beginning (parents to children), 1852 computes the fraction of child time to propagate to each parent and a 1853 print flag. The print flag reflects symspec handling of 1854 INCL_GRAPH/EXCL_GRAPH, with a parent's include or exclude (print or no 1855 print) property being propagated to its children, unless they 1856 themselves explicitly appear in INCL_GRAPH or EXCL_GRAPH. A second 1857 pass, from beginning to end (children to parents) actually propagates 1858 the timings along the call graph, subject to a check against 1859 INCL_TIME/EXCL_TIME. With the print flag, fractions, and timings now 1860 stored in the symbol structures, the topological sort array is now 1861 discarded, and a new array of pointers is assembled, this time sorted 1862 by propagated time. 1863 1864 Finally, print the various outputs the user requested, which is now 1865 fairly straightforward. The call graph (`cg_print.c:cg_print') and 1866 flat profile (`hist.c:hist_print') are regurgitations of values already 1867 computed. The annotated source listing 1868 (`basic_blocks.c:print_annotated_source') uses basic-block information, 1869 if present, to label each line of code with call counts, otherwise only 1870 the function call counts are presented. 1871 1872 The function ordering code is marginally well documented in the 1873 source code itself (`cg_print.c'). Basically, the functions with the 1874 most use and the most parents are placed first, followed by other 1875 functions with the most use, followed by lower use functions, followed 1876 by unused functions at the end. 1877 1878 1879 File: gprof.info, Node: Debugging, Prev: Internals, Up: Details 1880 1881 9.4 Debugging `gprof' 1882 ===================== 1883 1884 If `gprof' was compiled with debugging enabled, the `-d' option 1885 triggers debugging output (to stdout) which can be helpful in 1886 understanding its operation. The debugging number specified is 1887 interpreted as a sum of the following options: 1888 1889 2 - Topological sort 1890 Monitor depth-first numbering of symbols during call graph analysis 1891 1892 4 - Cycles 1893 Shows symbols as they are identified as cycle heads 1894 1895 16 - Tallying 1896 As the call graph arcs are read, show each arc and how the total 1897 calls to each function are tallied 1898 1899 32 - Call graph arc sorting 1900 Details sorting individual parents/children within each call graph 1901 entry 1902 1903 64 - Reading histogram and call graph records 1904 Shows address ranges of histograms as they are read, and each call 1905 graph arc 1906 1907 128 - Symbol table 1908 Reading, classifying, and sorting the symbol table from the object 1909 file. For line-by-line profiling (`-l' option), also shows line 1910 numbers being assigned to memory addresses. 1911 1912 256 - Static call graph 1913 Trace operation of `-c' option 1914 1915 512 - Symbol table and arc table lookups 1916 Detail operation of lookup routines 1917 1918 1024 - Call graph propagation 1919 Shows how function times are propagated along the call graph 1920 1921 2048 - Basic-blocks 1922 Shows basic-block records as they are read from profile data (only 1923 meaningful with `-l' option) 1924 1925 4096 - Symspecs 1926 Shows symspec-to-symbol pattern matching operation 1927 1928 8192 - Annotate source 1929 Tracks operation of `-A' option 1930 1931 1932 File: gprof.info, Node: GNU Free Documentation License, Prev: Details, Up: Top 1933 1934 Appendix A GNU Free Documentation License 1935 ***************************************** 1936 1937 Version 1.1, March 2000 1938 1939 Copyright (C) 2000, 2003 Free Software Foundation, Inc. 1940 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 1941 1942 Everyone is permitted to copy and distribute verbatim copies 1943 of this license document, but changing it is not allowed. 1944 1945 1946 0. 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A copy that is not "Transparent" is called "Opaque." 2014 2015 Examples of suitable formats for Transparent copies include plain 2016 ASCII without markup, Texinfo input format, LaTeX input format, 2017 SGML or XML using a publicly available DTD, and 2018 standard-conforming simple HTML designed for human modification. 2019 Opaque formats include PostScript, PDF, proprietary formats that 2020 can be read and edited only by proprietary word processors, SGML 2021 or XML for which the DTD and/or processing tools are not generally 2022 available, and the machine-generated HTML produced by some word 2023 processors for output purposes only. 2024 2025 The "Title Page" means, for a printed book, the title page itself, 2026 plus such following pages as are needed to hold, legibly, the 2027 material this License requires to appear in the title page. For 2028 works in formats which do not have any title page as such, "Title 2029 Page" means the text near the most prominent appearance of the 2030 work's title, preceding the beginning of the body of the text. 2031 2032 2. VERBATIM COPYING 2033 2034 You may copy and distribute the Document in any medium, either 2035 commercially or noncommercially, provided that this License, the 2036 copyright notices, and the license notice saying this License 2037 applies to the Document are reproduced in all copies, and that you 2038 add no other conditions whatsoever to those of this License. You 2039 may not use technical measures to obstruct or control the reading 2040 or further copying of the copies you make or distribute. However, 2041 you may accept compensation in exchange for copies. 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Copying with changes limited to the 2059 covers, as long as they preserve the title of the Document and 2060 satisfy these conditions, can be treated as verbatim copying in 2061 other respects. 2062 2063 If the required texts for either cover are too voluminous to fit 2064 legibly, you should put the first ones listed (as many as fit 2065 reasonably) on the actual cover, and continue the rest onto 2066 adjacent pages. 2067 2068 If you publish or distribute Opaque copies of the Document 2069 numbering more than 100, you must either include a 2070 machine-readable Transparent copy along with each Opaque copy, or 2071 state in or with each Opaque copy a publicly-accessible 2072 computer-network location containing a complete Transparent copy 2073 of the Document, free of added material, which the general 2074 network-using public has access to download anonymously at no 2075 charge using public-standard network protocols. If you use the 2076 latter option, you must take reasonably prudent steps, when you 2077 begin distribution of Opaque copies in quantity, to ensure that 2078 this Transparent copy will remain thus accessible at the stated 2079 location until at least one year after the last time you 2080 distribute an Opaque copy (directly or through your agents or 2081 retailers) of that edition to the public. 2082 2083 It is requested, but not required, that you contact the authors of 2084 the Document well before redistributing any large number of 2085 copies, to give them a chance to provide you with an updated 2086 version of the Document. 2087 2088 4. MODIFICATIONS 2089 2090 You may copy and distribute a Modified Version of the Document 2091 under the conditions of sections 2 and 3 above, provided that you 2092 release the Modified Version under precisely this License, with 2093 the Modified Version filling the role of the Document, thus 2094 licensing distribution and modification of the Modified Version to 2095 whoever possesses a copy of it. In addition, you must do these 2096 things in the Modified Version: 2097 2098 A. Use in the Title Page (and on the covers, if any) a title 2099 distinct from that of the Document, and from those of previous 2100 versions (which should, if there were any, be listed in the 2101 History section of the Document). You may use the same title 2102 as a previous version if the original publisher of that version 2103 gives permission. 2104 B. List on the Title Page, as authors, one or more persons or 2105 entities responsible for authorship of the modifications in the 2106 Modified Version, together with at least five of the principal 2107 authors of the Document (all of its principal authors, if it 2108 has less than five). 2109 C. State on the Title page the name of the publisher of the 2110 Modified Version, as the publisher. 2111 D. Preserve all the copyright notices of the Document. 2112 E. Add an appropriate copyright notice for your modifications 2113 adjacent to the other copyright notices. 2114 F. Include, immediately after the copyright notices, a license 2115 notice giving the public permission to use the Modified Version 2116 under the terms of this License, in the form shown in the 2117 Addendum below. 2118 G. Preserve in that license notice the full lists of Invariant 2119 Sections and required Cover Texts given in the Document's 2120 license notice. 2121 H. Include an unaltered copy of this License. 2122 I. Preserve the section entitled "History", and its title, and add 2123 to it an item stating at least the title, year, new authors, and 2124 publisher of the Modified Version as given on the Title Page. 2125 If there is no section entitled "History" in the Document, 2126 create one stating the title, year, authors, and publisher of 2127 the Document as given on its Title Page, then add an item 2128 describing the Modified Version as stated in the previous 2129 sentence. 2130 J. Preserve the network location, if any, given in the Document for 2131 public access to a Transparent copy of the Document, and 2132 likewise the network locations given in the Document for 2133 previous versions it was based on. These may be placed in the 2134 "History" section. You may omit a network location for a work 2135 that was published at least four years before the Document 2136 itself, or if the original publisher of the version it refers 2137 to gives permission. 2138 K. In any section entitled "Acknowledgements" or "Dedications", 2139 preserve the section's title, and preserve in the section all the 2140 substance and tone of each of the contributor acknowledgements 2141 and/or dedications given therein. 2142 L. Preserve all the Invariant Sections of the Document, 2143 unaltered in their text and in their titles. Section numbers 2144 or the equivalent are not considered part of the section titles. 2145 M. Delete any section entitled "Endorsements." Such a section 2146 may not be included in the Modified Version. 2147 N. Do not retitle any existing section as "Endorsements" or to 2148 conflict in title with any Invariant Section. 2149 2150 If the Modified Version includes new front-matter sections or 2151 appendices that qualify as Secondary Sections and contain no 2152 material copied from the Document, you may at your option 2153 designate some or all of these sections as invariant. To do this, 2154 add their titles to the list of Invariant Sections in the Modified 2155 Version's license notice. These titles must be distinct from any 2156 other section titles. 2157 2158 You may add a section entitled "Endorsements", provided it contains 2159 nothing but endorsements of your Modified Version by various 2160 parties-for example, statements of peer review or that the text has 2161 been approved by an organization as the authoritative definition 2162 of a standard. 2163 2164 You may add a passage of up to five words as a Front-Cover Text, 2165 and a passage of up to 25 words as a Back-Cover Text, to the end 2166 of the list of Cover Texts in the Modified Version. Only one 2167 passage of Front-Cover Text and one of Back-Cover Text may be 2168 added by (or through arrangements made by) any one entity. If the 2169 Document already includes a cover text for the same cover, 2170 previously added by you or by arrangement made by the same entity 2171 you are acting on behalf of, you may not add another; but you may 2172 replace the old one, on explicit permission from the previous 2173 publisher that added the old one. 2174 2175 The author(s) and publisher(s) of the Document do not by this 2176 License give permission to use their names for publicity for or to 2177 assert or imply endorsement of any Modified Version. 2178 2179 5. COMBINING DOCUMENTS 2180 2181 You may combine the Document with other documents released under 2182 this License, under the terms defined in section 4 above for 2183 modified versions, provided that you include in the combination 2184 all of the Invariant Sections of all of the original documents, 2185 unmodified, and list them all as Invariant Sections of your 2186 combined work in its license notice. 2187 2188 The combined work need only contain one copy of this License, and 2189 multiple identical Invariant Sections may be replaced with a single 2190 copy. If there are multiple Invariant Sections with the same name 2191 but different contents, make the title of each such section unique 2192 by adding at the end of it, in parentheses, the name of the 2193 original author or publisher of that section if known, or else a 2194 unique number. Make the same adjustment to the section titles in 2195 the list of Invariant Sections in the license notice of the 2196 combined work. 2197 2198 In the combination, you must combine any sections entitled 2199 "History" in the various original documents, forming one section 2200 entitled "History"; likewise combine any sections entitled 2201 "Acknowledgements", and any sections entitled "Dedications." You 2202 must delete all sections entitled "Endorsements." 2203 2204 6. COLLECTIONS OF DOCUMENTS 2205 2206 You may make a collection consisting of the Document and other 2207 documents released under this License, and replace the individual 2208 copies of this License in the various documents with a single copy 2209 that is included in the collection, provided that you follow the 2210 rules of this License for verbatim copying of each of the 2211 documents in all other respects. 2212 2213 You may extract a single document from such a collection, and 2214 distribute it individually under this License, provided you insert 2215 a copy of this License into the extracted document, and follow 2216 this License in all other respects regarding verbatim copying of 2217 that document. 2218 2219 7. AGGREGATION WITH INDEPENDENT WORKS 2220 2221 A compilation of the Document or its derivatives with other 2222 separate and independent documents or works, in or on a volume of 2223 a storage or distribution medium, does not as a whole count as a 2224 Modified Version of the Document, provided no compilation 2225 copyright is claimed for the compilation. Such a compilation is 2226 called an "aggregate", and this License does not apply to the 2227 other self-contained works thus compiled with the Document, on 2228 account of their being thus compiled, if they are not themselves 2229 derivative works of the Document. 2230 2231 If the Cover Text requirement of section 3 is applicable to these 2232 copies of the Document, then if the Document is less than one 2233 quarter of the entire aggregate, the Document's Cover Texts may be 2234 placed on covers that surround only the Document within the 2235 aggregate. Otherwise they must appear on covers around the whole 2236 aggregate. 2237 2238 8. TRANSLATION 2239 2240 Translation is considered a kind of modification, so you may 2241 distribute translations of the Document under the terms of section 2242 4. Replacing Invariant Sections with translations requires special 2243 permission from their copyright holders, but you may include 2244 translations of some or all Invariant Sections in addition to the 2245 original versions of these Invariant Sections. You may include a 2246 translation of this License provided that you also include the 2247 original English version of this License. In case of a 2248 disagreement between the translation and the original English 2249 version of this License, the original English version will prevail. 2250 2251 9. TERMINATION 2252 2253 You may not copy, modify, sublicense, or distribute the Document 2254 except as expressly provided for under this License. Any other 2255 attempt to copy, modify, sublicense or distribute the Document is 2256 void, and will automatically terminate your rights under this 2257 License. However, parties who have received copies, or rights, 2258 from you under this License will not have their licenses 2259 terminated so long as such parties remain in full compliance. 2260 2261 10. FUTURE REVISIONS OF THIS LICENSE 2262 2263 The Free Software Foundation may publish new, revised versions of 2264 the GNU Free Documentation License from time to time. Such new 2265 versions will be similar in spirit to the present version, but may 2266 differ in detail to address new problems or concerns. See 2267 http://www.gnu.org/copyleft/. 2268 2269 Each version of the License is given a distinguishing version 2270 number. If the Document specifies that a particular numbered 2271 version of this License "or any later version" applies to it, you 2272 have the option of following the terms and conditions either of 2273 that specified version or of any later version that has been 2274 published (not as a draft) by the Free Software Foundation. If 2275 the Document does not specify a version number of this License, 2276 you may choose any version ever published (not as a draft) by the 2277 Free Software Foundation. 2278 2279 2280 ADDENDUM: How to use this License for your documents 2281 ==================================================== 2282 2283 To use this License in a document you have written, include a copy of 2284 the License in the document and put the following copyright and license 2285 notices just after the title page: 2286 2287 Copyright (C) YEAR YOUR NAME. 2288 Permission is granted to copy, distribute and/or modify this document 2289 under the terms of the GNU Free Documentation License, Version 1.1 2290 or any later version published by the Free Software Foundation; 2291 with the Invariant Sections being LIST THEIR TITLES, with the 2292 Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. 2293 A copy of the license is included in the section entitled "GNU 2294 Free Documentation License." 2295 2296 If you have no Invariant Sections, write "with no Invariant Sections" 2297 instead of saying which ones are invariant. 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