| This is gprof.info, produced by makeinfo version 4.8 from gprof.texi. |
| |
| START-INFO-DIR-ENTRY |
| * gprof: (gprof). Profiling your program's execution |
| END-INFO-DIR-ENTRY |
| |
| This file documents the gprof profiler of the GNU system. |
| |
| Copyright (C) 1988, 92, 97, 98, 99, 2000, 2001, 2003, 2007 Free |
| Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.1 or |
| any later version published by the Free Software Foundation; with no |
| Invariant Sections, with no Front-Cover Texts, and with no Back-Cover |
| Texts. A copy of the license is included in the section entitled "GNU |
| Free Documentation License". |
| |
| |
| File: gprof.info, Node: Top, Next: Introduction, Up: (dir) |
| |
| Profiling a Program: Where Does It Spend Its Time? |
| ************************************************** |
| |
| This manual describes the GNU profiler, `gprof', and how you can use it |
| to determine which parts of a program are taking most of the execution |
| time. We assume that you know how to write, compile, and execute |
| programs. GNU `gprof' was written by Jay Fenlason. |
| |
| This manual is for `gprof' (GNU Binutils) version 2.18.90. |
| |
| This document is distributed under the terms of the GNU Free |
| Documentation License. A copy of the license is included in the |
| section entitled "GNU Free Documentation License". |
| |
| * Menu: |
| |
| * Introduction:: What profiling means, and why it is useful. |
| |
| * Compiling:: How to compile your program for profiling. |
| * Executing:: Executing your program to generate profile data |
| * Invoking:: How to run `gprof', and its options |
| |
| * Output:: Interpreting `gprof''s output |
| |
| * Inaccuracy:: Potential problems you should be aware of |
| * How do I?:: Answers to common questions |
| * Incompatibilities:: (between GNU `gprof' and Unix `gprof'.) |
| * Details:: Details of how profiling is done |
| * GNU Free Documentation License:: GNU Free Documentation License |
| |
| |
| File: gprof.info, Node: Introduction, Next: Compiling, Prev: Top, Up: Top |
| |
| 1 Introduction to Profiling |
| *************************** |
| |
| Profiling allows you to learn where your program spent its time and |
| which functions called which other functions while it was executing. |
| This information can show you which pieces of your program are slower |
| than you expected, and might be candidates for rewriting to make your |
| program execute faster. It can also tell you which functions are being |
| called more or less often than you expected. This may help you spot |
| bugs that had otherwise been unnoticed. |
| |
| Since the profiler uses information collected during the actual |
| execution of your program, it can be used on programs that are too |
| large or too complex to analyze by reading the source. However, how |
| your program is run will affect the information that shows up in the |
| profile data. If you don't use some feature of your program while it |
| is being profiled, no profile information will be generated for that |
| feature. |
| |
| Profiling has several steps: |
| |
| * You must compile and link your program with profiling enabled. |
| *Note Compiling a Program for Profiling: Compiling. |
| |
| * You must execute your program to generate a profile data file. |
| *Note Executing the Program: Executing. |
| |
| * You must run `gprof' to analyze the profile data. *Note `gprof' |
| Command Summary: Invoking. |
| |
| The next three chapters explain these steps in greater detail. |
| |
| Several forms of output are available from the analysis. |
| |
| The "flat profile" shows how much time your program spent in each |
| function, and how many times that function was called. If you simply |
| want to know which functions burn most of the cycles, it is stated |
| concisely here. *Note The Flat Profile: Flat Profile. |
| |
| The "call graph" shows, for each function, which functions called |
| it, which other functions it called, and how many times. There is also |
| an estimate of how much time was spent in the subroutines of each |
| function. This can suggest places where you might try to eliminate |
| function calls that use a lot of time. *Note The Call Graph: Call |
| Graph. |
| |
| The "annotated source" listing is a copy of the program's source |
| code, labeled with the number of times each line of the program was |
| executed. *Note The Annotated Source Listing: Annotated Source. |
| |
| To better understand how profiling works, you may wish to read a |
| description of its implementation. *Note Implementation of Profiling: |
| Implementation. |
| |
| |
| File: gprof.info, Node: Compiling, Next: Executing, Prev: Introduction, Up: Top |
| |
| 2 Compiling a Program for Profiling |
| *********************************** |
| |
| The first step in generating profile information for your program is to |
| compile and link it with profiling enabled. |
| |
| To compile a source file for profiling, specify the `-pg' option when |
| you run the compiler. (This is in addition to the options you normally |
| use.) |
| |
| To link the program for profiling, if you use a compiler such as `cc' |
| to do the linking, simply specify `-pg' in addition to your usual |
| options. The same option, `-pg', alters either compilation or linking |
| to do what is necessary for profiling. Here are examples: |
| |
| cc -g -c myprog.c utils.c -pg |
| cc -o myprog myprog.o utils.o -pg |
| |
| The `-pg' option also works with a command that both compiles and |
| links: |
| |
| cc -o myprog myprog.c utils.c -g -pg |
| |
| Note: The `-pg' option must be part of your compilation options as |
| well as your link options. If it is not then no call-graph data will |
| be gathered and when you run `gprof' you will get an error message like |
| this: |
| |
| gprof: gmon.out file is missing call-graph data |
| |
| If you add the `-Q' switch to suppress the printing of the call |
| graph data you will still be able to see the time samples: |
| |
| Flat profile: |
| |
| Each sample counts as 0.01 seconds. |
| % cumulative self self total |
| time seconds seconds calls Ts/call Ts/call name |
| 44.12 0.07 0.07 zazLoop |
| 35.29 0.14 0.06 main |
| 20.59 0.17 0.04 bazMillion |
| |
| If you run the linker `ld' directly instead of through a compiler |
| such as `cc', you may have to specify a profiling startup file |
| `gcrt0.o' as the first input file instead of the usual startup file |
| `crt0.o'. In addition, you would probably want to specify the |
| profiling C library, `libc_p.a', by writing `-lc_p' instead of the |
| usual `-lc'. This is not absolutely necessary, but doing this gives |
| you number-of-calls information for standard library functions such as |
| `read' and `open'. For example: |
| |
| ld -o myprog /lib/gcrt0.o myprog.o utils.o -lc_p |
| |
| If you compile only some of the modules of the program with `-pg', |
| you can still profile the program, but you won't get complete |
| information about the modules that were compiled without `-pg'. The |
| only information you get for the functions in those modules is the |
| total time spent in them; there is no record of how many times they |
| were called, or from where. This will not affect the flat profile |
| (except that the `calls' field for the functions will be blank), but |
| will greatly reduce the usefulness of the call graph. |
| |
| If you wish to perform line-by-line profiling you should use the |
| `gcov' tool instead of `gprof'. See that tool's manual or info pages |
| for more details of how to do this. |
| |
| Note, older versions of `gcc' produce line-by-line profiling |
| information that works with `gprof' rather than `gcov' so there is |
| still support for displaying this kind of information in `gprof'. *Note |
| Line-by-line Profiling: Line-by-line. |
| |
| It also worth noting that `gcc' implements a |
| `-finstrument-functions' command line option which will insert calls to |
| special user supplied instrumentation routines at the entry and exit of |
| every function in their program. This can be used to implement an |
| alternative profiling scheme. |
| |
| |
| File: gprof.info, Node: Executing, Next: Invoking, Prev: Compiling, Up: Top |
| |
| 3 Executing the Program |
| *********************** |
| |
| Once the program is compiled for profiling, you must run it in order to |
| generate the information that `gprof' needs. Simply run the program as |
| usual, using the normal arguments, file names, etc. The program should |
| run normally, producing the same output as usual. It will, however, run |
| somewhat slower than normal because of the time spent collecting and |
| writing the profile data. |
| |
| The way you run the program--the arguments and input that you give |
| it--may have a dramatic effect on what the profile information shows. |
| The profile data will describe the parts of the program that were |
| activated for the particular input you use. For example, if the first |
| command you give to your program is to quit, the profile data will show |
| the time used in initialization and in cleanup, but not much else. |
| |
| Your program will write the profile data into a file called |
| `gmon.out' just before exiting. If there is already a file called |
| `gmon.out', its contents are overwritten. There is currently no way to |
| tell the program to write the profile data under a different name, but |
| you can rename the file afterwards if you are concerned that it may be |
| overwritten. |
| |
| In order to write the `gmon.out' file properly, your program must |
| exit normally: by returning from `main' or by calling `exit'. Calling |
| the low-level function `_exit' does not write the profile data, and |
| neither does abnormal termination due to an unhandled signal. |
| |
| The `gmon.out' file is written in the program's _current working |
| directory_ at the time it exits. This means that if your program calls |
| `chdir', the `gmon.out' file will be left in the last directory your |
| program `chdir''d to. If you don't have permission to write in this |
| directory, the file is not written, and you will get an error message. |
| |
| Older versions of the GNU profiling library may also write a file |
| called `bb.out'. This file, if present, contains an human-readable |
| listing of the basic-block execution counts. Unfortunately, the |
| appearance of a human-readable `bb.out' means the basic-block counts |
| didn't get written into `gmon.out'. The Perl script `bbconv.pl', |
| included with the `gprof' source distribution, will convert a `bb.out' |
| file into a format readable by `gprof'. Invoke it like this: |
| |
| bbconv.pl < bb.out > BH-DATA |
| |
| This translates the information in `bb.out' into a form that `gprof' |
| can understand. But you still need to tell `gprof' about the existence |
| of this translated information. To do that, include BB-DATA on the |
| `gprof' command line, _along with `gmon.out'_, like this: |
| |
| gprof OPTIONS EXECUTABLE-FILE gmon.out BB-DATA [YET-MORE-PROFILE-DATA-FILES...] [> OUTFILE] |
| |
| |
| File: gprof.info, Node: Invoking, Next: Output, Prev: Executing, Up: Top |
| |
| 4 `gprof' Command Summary |
| ************************* |
| |
| After you have a profile data file `gmon.out', you can run `gprof' to |
| interpret the information in it. The `gprof' program prints a flat |
| profile and a call graph on standard output. Typically you would |
| redirect the output of `gprof' into a file with `>'. |
| |
| You run `gprof' like this: |
| |
| gprof OPTIONS [EXECUTABLE-FILE [PROFILE-DATA-FILES...]] [> OUTFILE] |
| |
| Here square-brackets indicate optional arguments. |
| |
| If you omit the executable file name, the file `a.out' is used. If |
| you give no profile data file name, the file `gmon.out' is used. If |
| any file is not in the proper format, or if the profile data file does |
| not appear to belong to the executable file, an error message is |
| printed. |
| |
| You can give more than one profile data file by entering all their |
| names after the executable file name; then the statistics in all the |
| data files are summed together. |
| |
| The order of these options does not matter. |
| |
| * Menu: |
| |
| * Output Options:: Controlling `gprof''s output style |
| * Analysis Options:: Controlling how `gprof' analyzes its data |
| * Miscellaneous Options:: |
| * Deprecated Options:: Options you no longer need to use, but which |
| have been retained for compatibility |
| * Symspecs:: Specifying functions to include or exclude |
| |
| |
| File: gprof.info, Node: Output Options, Next: Analysis Options, Up: Invoking |
| |
| 4.1 Output Options |
| ================== |
| |
| These options specify which of several output formats `gprof' should |
| produce. |
| |
| Many of these options take an optional "symspec" to specify |
| functions to be included or excluded. These options can be specified |
| multiple times, with different symspecs, to include or exclude sets of |
| symbols. *Note Symspecs: Symspecs. |
| |
| Specifying any of these options overrides the default (`-p -q'), |
| which prints a flat profile and call graph analysis for all functions. |
| |
| `-A[SYMSPEC]' |
| `--annotated-source[=SYMSPEC]' |
| The `-A' option causes `gprof' to print annotated source code. If |
| SYMSPEC is specified, print output only for matching symbols. |
| *Note The Annotated Source Listing: Annotated Source. |
| |
| `-b' |
| `--brief' |
| If the `-b' option is given, `gprof' doesn't print the verbose |
| blurbs that try to explain the meaning of all of the fields in the |
| tables. This is useful if you intend to print out the output, or |
| are tired of seeing the blurbs. |
| |
| `-C[SYMSPEC]' |
| `--exec-counts[=SYMSPEC]' |
| The `-C' option causes `gprof' to print a tally of functions and |
| the number of times each was called. If SYMSPEC is specified, |
| print tally only for matching symbols. |
| |
| If the profile data file contains basic-block count records, |
| specifying the `-l' option, along with `-C', will cause basic-block |
| execution counts to be tallied and displayed. |
| |
| `-i' |
| `--file-info' |
| The `-i' option causes `gprof' to display summary information |
| about the profile data file(s) and then exit. The number of |
| histogram, call graph, and basic-block count records is displayed. |
| |
| `-I DIRS' |
| `--directory-path=DIRS' |
| The `-I' option specifies a list of search directories in which to |
| find source files. Environment variable GPROF_PATH can also be |
| used to convey this information. Used mostly for annotated source |
| output. |
| |
| `-J[SYMSPEC]' |
| `--no-annotated-source[=SYMSPEC]' |
| The `-J' option causes `gprof' not to print annotated source code. |
| If SYMSPEC is specified, `gprof' prints annotated source, but |
| excludes matching symbols. |
| |
| `-L' |
| `--print-path' |
| Normally, source filenames are printed with the path component |
| suppressed. The `-L' option causes `gprof' to print the full |
| pathname of source filenames, which is determined from symbolic |
| debugging information in the image file and is relative to the |
| directory in which the compiler was invoked. |
| |
| `-p[SYMSPEC]' |
| `--flat-profile[=SYMSPEC]' |
| The `-p' option causes `gprof' to print a flat profile. If |
| SYMSPEC is specified, print flat profile only for matching symbols. |
| *Note The Flat Profile: Flat Profile. |
| |
| `-P[SYMSPEC]' |
| `--no-flat-profile[=SYMSPEC]' |
| The `-P' option causes `gprof' to suppress printing a flat profile. |
| If SYMSPEC is specified, `gprof' prints a flat profile, but |
| excludes matching symbols. |
| |
| `-q[SYMSPEC]' |
| `--graph[=SYMSPEC]' |
| The `-q' option causes `gprof' to print the call graph analysis. |
| If SYMSPEC is specified, print call graph only for matching symbols |
| and their children. *Note The Call Graph: Call Graph. |
| |
| `-Q[SYMSPEC]' |
| `--no-graph[=SYMSPEC]' |
| The `-Q' option causes `gprof' to suppress printing the call graph. |
| If SYMSPEC is specified, `gprof' prints a call graph, but excludes |
| matching symbols. |
| |
| `-t' |
| `--table-length=NUM' |
| The `-t' option causes the NUM most active source lines in each |
| source file to be listed when source annotation is enabled. The |
| default is 10. |
| |
| `-y' |
| `--separate-files' |
| This option affects annotated source output only. Normally, |
| `gprof' prints annotated source files to standard-output. If this |
| option is specified, annotated source for a file named |
| `path/FILENAME' is generated in the file `FILENAME-ann'. If the |
| underlying file system would truncate `FILENAME-ann' so that it |
| overwrites the original `FILENAME', `gprof' generates annotated |
| source in the file `FILENAME.ann' instead (if the original file |
| name has an extension, that extension is _replaced_ with `.ann'). |
| |
| `-Z[SYMSPEC]' |
| `--no-exec-counts[=SYMSPEC]' |
| The `-Z' option causes `gprof' not to print a tally of functions |
| and the number of times each was called. If SYMSPEC is specified, |
| print tally, but exclude matching symbols. |
| |
| `-r' |
| `--function-ordering' |
| The `--function-ordering' option causes `gprof' to print a |
| suggested function ordering for the program based on profiling |
| data. This option suggests an ordering which may improve paging, |
| tlb and cache behavior for the program on systems which support |
| arbitrary ordering of functions in an executable. |
| |
| The exact details of how to force the linker to place functions in |
| a particular order is system dependent and out of the scope of this |
| manual. |
| |
| `-R MAP_FILE' |
| `--file-ordering MAP_FILE' |
| The `--file-ordering' option causes `gprof' to print a suggested |
| .o link line ordering for the program based on profiling data. |
| This option suggests an ordering which may improve paging, tlb and |
| cache behavior for the program on systems which do not support |
| arbitrary ordering of functions in an executable. |
| |
| Use of the `-a' argument is highly recommended with this option. |
| |
| The MAP_FILE argument is a pathname to a file which provides |
| function name to object file mappings. The format of the file is |
| similar to the output of the program `nm'. |
| |
| c-parse.o:00000000 T yyparse |
| c-parse.o:00000004 C yyerrflag |
| c-lang.o:00000000 T maybe_objc_method_name |
| c-lang.o:00000000 T print_lang_statistics |
| c-lang.o:00000000 T recognize_objc_keyword |
| c-decl.o:00000000 T print_lang_identifier |
| c-decl.o:00000000 T print_lang_type |
| ... |
| |
| To create a MAP_FILE with GNU `nm', type a command like `nm |
| --extern-only --defined-only -v --print-file-name program-name'. |
| |
| `-T' |
| `--traditional' |
| The `-T' option causes `gprof' to print its output in |
| "traditional" BSD style. |
| |
| `-w WIDTH' |
| `--width=WIDTH' |
| Sets width of output lines to WIDTH. Currently only used when |
| printing the function index at the bottom of the call graph. |
| |
| `-x' |
| `--all-lines' |
| This option affects annotated source output only. By default, |
| only the lines at the beginning of a basic-block are annotated. |
| If this option is specified, every line in a basic-block is |
| annotated by repeating the annotation for the first line. This |
| behavior is similar to `tcov''s `-a'. |
| |
| `--demangle[=STYLE]' |
| `--no-demangle' |
| These options control whether C++ symbol names should be demangled |
| when printing output. The default is to demangle symbols. The |
| `--no-demangle' option may be used to turn off demangling. |
| Different compilers have different mangling styles. The optional |
| demangling style argument can be used to choose an appropriate |
| demangling style for your compiler. |
| |
| |
| File: gprof.info, Node: Analysis Options, Next: Miscellaneous Options, Prev: Output Options, Up: Invoking |
| |
| 4.2 Analysis Options |
| ==================== |
| |
| `-a' |
| `--no-static' |
| The `-a' option causes `gprof' to suppress the printing of |
| statically declared (private) functions. (These are functions |
| whose names are not listed as global, and which are not visible |
| outside the file/function/block where they were defined.) Time |
| spent in these functions, calls to/from them, etc., will all be |
| attributed to the function that was loaded directly before it in |
| the executable file. This option affects both the flat profile |
| and the call graph. |
| |
| `-c' |
| `--static-call-graph' |
| The `-c' option causes the call graph of the program to be |
| augmented by a heuristic which examines the text space of the |
| object file and identifies function calls in the binary machine |
| code. Since normal call graph records are only generated when |
| functions are entered, this option identifies children that could |
| have been called, but never were. Calls to functions that were |
| not compiled with profiling enabled are also identified, but only |
| if symbol table entries are present for them. Calls to dynamic |
| library routines are typically _not_ found by this option. |
| Parents or children identified via this heuristic are indicated in |
| the call graph with call counts of `0'. |
| |
| `-D' |
| `--ignore-non-functions' |
| The `-D' option causes `gprof' to ignore symbols which are not |
| known to be functions. This option will give more accurate |
| profile data on systems where it is supported (Solaris and HPUX for |
| example). |
| |
| `-k FROM/TO' |
| The `-k' option allows you to delete from the call graph any arcs |
| from symbols matching symspec FROM to those matching symspec TO. |
| |
| `-l' |
| `--line' |
| The `-l' option enables line-by-line profiling, which causes |
| histogram hits to be charged to individual source code lines, |
| instead of functions. This feature only works with programs |
| compiled by older versions of the `gcc' compiler. Newer versions |
| of `gcc' are designed to work with the `gcov' tool instead. |
| |
| If the program was compiled with basic-block counting enabled, |
| this option will also identify how many times each line of code |
| was executed. While line-by-line profiling can help isolate where |
| in a large function a program is spending its time, it also |
| significantly increases the running time of `gprof', and magnifies |
| statistical inaccuracies. *Note Statistical Sampling Error: |
| Sampling Error. |
| |
| `-m NUM' |
| `--min-count=NUM' |
| This option affects execution count output only. Symbols that are |
| executed less than NUM times are suppressed. |
| |
| `-nSYMSPEC' |
| `--time=SYMSPEC' |
| The `-n' option causes `gprof', in its call graph analysis, to |
| only propagate times for symbols matching SYMSPEC. |
| |
| `-NSYMSPEC' |
| `--no-time=SYMSPEC' |
| The `-n' option causes `gprof', in its call graph analysis, not to |
| propagate times for symbols matching SYMSPEC. |
| |
| `-z' |
| `--display-unused-functions' |
| If you give the `-z' option, `gprof' will mention all functions in |
| the flat profile, even those that were never called, and that had |
| no time spent in them. This is useful in conjunction with the |
| `-c' option for discovering which routines were never called. |
| |
| |
| |
| File: gprof.info, Node: Miscellaneous Options, Next: Deprecated Options, Prev: Analysis Options, Up: Invoking |
| |
| 4.3 Miscellaneous Options |
| ========================= |
| |
| `-d[NUM]' |
| `--debug[=NUM]' |
| The `-d NUM' option specifies debugging options. If NUM is not |
| specified, enable all debugging. *Note Debugging `gprof': |
| Debugging. |
| |
| `-h' |
| `--help' |
| The `-h' option prints command line usage. |
| |
| `-ONAME' |
| `--file-format=NAME' |
| Selects the format of the profile data files. Recognized formats |
| are `auto' (the default), `bsd', `4.4bsd', `magic', and `prof' |
| (not yet supported). |
| |
| `-s' |
| `--sum' |
| The `-s' option causes `gprof' to summarize the information in the |
| profile data files it read in, and write out a profile data file |
| called `gmon.sum', which contains all the information from the |
| profile data files that `gprof' read in. The file `gmon.sum' may |
| be one of the specified input files; the effect of this is to |
| merge the data in the other input files into `gmon.sum'. |
| |
| Eventually you can run `gprof' again without `-s' to analyze the |
| cumulative data in the file `gmon.sum'. |
| |
| `-v' |
| `--version' |
| The `-v' flag causes `gprof' to print the current version number, |
| and then exit. |
| |
| |
| |
| File: gprof.info, Node: Deprecated Options, Next: Symspecs, Prev: Miscellaneous Options, Up: Invoking |
| |
| 4.4 Deprecated Options |
| ====================== |
| |
| These options have been replaced with newer versions that use |
| symspecs. |
| |
| `-e FUNCTION_NAME' |
| The `-e FUNCTION' option tells `gprof' to not print information |
| about the function FUNCTION_NAME (and its children...) in the call |
| graph. The function will still be listed as a child of any |
| functions that call it, but its index number will be shown as |
| `[not printed]'. More than one `-e' option may be given; only one |
| FUNCTION_NAME may be indicated with each `-e' option. |
| |
| `-E FUNCTION_NAME' |
| The `-E FUNCTION' option works like the `-e' option, but time |
| spent in the function (and children who were not called from |
| anywhere else), will not be used to compute the |
| percentages-of-time for the call graph. More than one `-E' option |
| may be given; only one FUNCTION_NAME may be indicated with each |
| `-E' option. |
| |
| `-f FUNCTION_NAME' |
| The `-f FUNCTION' option causes `gprof' to limit the call graph to |
| the function FUNCTION_NAME and its children (and their |
| children...). More than one `-f' option may be given; only one |
| FUNCTION_NAME may be indicated with each `-f' option. |
| |
| `-F FUNCTION_NAME' |
| The `-F FUNCTION' option works like the `-f' option, but only time |
| spent in the function and its children (and their children...) |
| will be used to determine total-time and percentages-of-time for |
| the call graph. More than one `-F' option may be given; only one |
| FUNCTION_NAME may be indicated with each `-F' option. The `-F' |
| option overrides the `-E' option. |
| |
| |
| Note that only one function can be specified with each `-e', `-E', |
| `-f' or `-F' option. To specify more than one function, use multiple |
| options. For example, this command: |
| |
| gprof -e boring -f foo -f bar myprogram > gprof.output |
| |
| lists in the call graph all functions that were reached from either |
| `foo' or `bar' and were not reachable from `boring'. |
| |
| |
| File: gprof.info, Node: Symspecs, Prev: Deprecated Options, Up: Invoking |
| |
| 4.5 Symspecs |
| ============ |
| |
| Many of the output options allow functions to be included or excluded |
| using "symspecs" (symbol specifications), which observe the following |
| syntax: |
| |
| filename_containing_a_dot |
| | funcname_not_containing_a_dot |
| | linenumber |
| | ( [ any_filename ] `:' ( any_funcname | linenumber ) ) |
| |
| Here are some sample symspecs: |
| |
| `main.c' |
| Selects everything in file `main.c'--the dot in the string tells |
| `gprof' to interpret the string as a filename, rather than as a |
| function name. To select a file whose name does not contain a |
| dot, a trailing colon should be specified. For example, `odd:' is |
| interpreted as the file named `odd'. |
| |
| `main' |
| Selects all functions named `main'. |
| |
| Note that there may be multiple instances of the same function name |
| because some of the definitions may be local (i.e., static). |
| Unless a function name is unique in a program, you must use the |
| colon notation explained below to specify a function from a |
| specific source file. |
| |
| Sometimes, function names contain dots. In such cases, it is |
| necessary to add a leading colon to the name. For example, |
| `:.mul' selects function `.mul'. |
| |
| In some object file formats, symbols have a leading underscore. |
| `gprof' will normally not print these underscores. When you name a |
| symbol in a symspec, you should type it exactly as `gprof' prints |
| it in its output. For example, if the compiler produces a symbol |
| `_main' from your `main' function, `gprof' still prints it as |
| `main' in its output, so you should use `main' in symspecs. |
| |
| `main.c:main' |
| Selects function `main' in file `main.c'. |
| |
| `main.c:134' |
| Selects line 134 in file `main.c'. |
| |
| |
| File: gprof.info, Node: Output, Next: Inaccuracy, Prev: Invoking, Up: Top |
| |
| 5 Interpreting `gprof''s Output |
| ******************************* |
| |
| `gprof' can produce several different output styles, the most important |
| of which are described below. The simplest output styles (file |
| information, execution count, and function and file ordering) are not |
| described here, but are documented with the respective options that |
| trigger them. *Note Output Options: Output Options. |
| |
| * Menu: |
| |
| * Flat Profile:: The flat profile shows how much time was spent |
| executing directly in each function. |
| * Call Graph:: The call graph shows which functions called which |
| others, and how much time each function used |
| when its subroutine calls are included. |
| * Line-by-line:: `gprof' can analyze individual source code lines |
| * Annotated Source:: The annotated source listing displays source code |
| labeled with execution counts |
| |
| |
| File: gprof.info, Node: Flat Profile, Next: Call Graph, Up: Output |
| |
| 5.1 The Flat Profile |
| ==================== |
| |
| The "flat profile" shows the total amount of time your program spent |
| executing each function. Unless the `-z' option is given, functions |
| with no apparent time spent in them, and no apparent calls to them, are |
| not mentioned. Note that if a function was not compiled for profiling, |
| and didn't run long enough to show up on the program counter histogram, |
| it will be indistinguishable from a function that was never called. |
| |
| This is part of a flat profile for a small program: |
| |
| Flat profile: |
| |
| Each sample counts as 0.01 seconds. |
| % cumulative self self total |
| time seconds seconds calls ms/call ms/call name |
| 33.34 0.02 0.02 7208 0.00 0.00 open |
| 16.67 0.03 0.01 244 0.04 0.12 offtime |
| 16.67 0.04 0.01 8 1.25 1.25 memccpy |
| 16.67 0.05 0.01 7 1.43 1.43 write |
| 16.67 0.06 0.01 mcount |
| 0.00 0.06 0.00 236 0.00 0.00 tzset |
| 0.00 0.06 0.00 192 0.00 0.00 tolower |
| 0.00 0.06 0.00 47 0.00 0.00 strlen |
| 0.00 0.06 0.00 45 0.00 0.00 strchr |
| 0.00 0.06 0.00 1 0.00 50.00 main |
| 0.00 0.06 0.00 1 0.00 0.00 memcpy |
| 0.00 0.06 0.00 1 0.00 10.11 print |
| 0.00 0.06 0.00 1 0.00 0.00 profil |
| 0.00 0.06 0.00 1 0.00 50.00 report |
| ... |
| |
| The functions are sorted first by decreasing run-time spent in them, |
| then by decreasing number of calls, then alphabetically by name. The |
| functions `mcount' and `profil' are part of the profiling apparatus and |
| appear in every flat profile; their time gives a measure of the amount |
| of overhead due to profiling. |
| |
| Just before the column headers, a statement appears indicating how |
| much time each sample counted as. This "sampling period" estimates the |
| margin of error in each of the time figures. A time figure that is not |
| much larger than this is not reliable. In this example, each sample |
| counted as 0.01 seconds, suggesting a 100 Hz sampling rate. The |
| program's total execution time was 0.06 seconds, as indicated by the |
| `cumulative seconds' field. Since each sample counted for 0.01 |
| seconds, this means only six samples were taken during the run. Two of |
| the samples occurred while the program was in the `open' function, as |
| indicated by the `self seconds' field. Each of the other four samples |
| occurred one each in `offtime', `memccpy', `write', and `mcount'. |
| Since only six samples were taken, none of these values can be regarded |
| as particularly reliable. In another run, the `self seconds' field for |
| `mcount' might well be `0.00' or `0.02'. *Note Statistical Sampling |
| Error: Sampling Error, for a complete discussion. |
| |
| The remaining functions in the listing (those whose `self seconds' |
| field is `0.00') didn't appear in the histogram samples at all. |
| However, the call graph indicated that they were called, so therefore |
| they are listed, sorted in decreasing order by the `calls' field. |
| Clearly some time was spent executing these functions, but the paucity |
| of histogram samples prevents any determination of how much time each |
| took. |
| |
| Here is what the fields in each line mean: |
| |
| `% time' |
| This is the percentage of the total execution time your program |
| spent in this function. These should all add up to 100%. |
| |
| `cumulative seconds' |
| This is the cumulative total number of seconds the computer spent |
| executing this functions, plus the time spent in all the functions |
| above this one in this table. |
| |
| `self seconds' |
| This is the number of seconds accounted for by this function alone. |
| The flat profile listing is sorted first by this number. |
| |
| `calls' |
| This is the total number of times the function was called. If the |
| function was never called, or the number of times it was called |
| cannot be determined (probably because the function was not |
| compiled with profiling enabled), the "calls" field is blank. |
| |
| `self ms/call' |
| This represents the average number of milliseconds spent in this |
| function per call, if this function is profiled. Otherwise, this |
| field is blank for this function. |
| |
| `total ms/call' |
| This represents the average number of milliseconds spent in this |
| function and its descendants per call, if this function is |
| profiled. Otherwise, this field is blank for this function. This |
| is the only field in the flat profile that uses call graph |
| analysis. |
| |
| `name' |
| This is the name of the function. The flat profile is sorted by |
| this field alphabetically after the "self seconds" and "calls" |
| fields are sorted. |
| |
| |
| File: gprof.info, Node: Call Graph, Next: Line-by-line, Prev: Flat Profile, Up: Output |
| |
| 5.2 The Call Graph |
| ================== |
| |
| The "call graph" shows how much time was spent in each function and its |
| children. From this information, you can find functions that, while |
| they themselves may not have used much time, called other functions |
| that did use unusual amounts of time. |
| |
| Here is a sample call from a small program. This call came from the |
| same `gprof' run as the flat profile example in the previous section. |
| |
| granularity: each sample hit covers 2 byte(s) for 20.00% of 0.05 seconds |
| |
| index % time self children called name |
| <spontaneous> |
| [1] 100.0 0.00 0.05 start [1] |
| 0.00 0.05 1/1 main [2] |
| 0.00 0.00 1/2 on_exit [28] |
| 0.00 0.00 1/1 exit [59] |
| ----------------------------------------------- |
| 0.00 0.05 1/1 start [1] |
| [2] 100.0 0.00 0.05 1 main [2] |
| 0.00 0.05 1/1 report [3] |
| ----------------------------------------------- |
| 0.00 0.05 1/1 main [2] |
| [3] 100.0 0.00 0.05 1 report [3] |
| 0.00 0.03 8/8 timelocal [6] |
| 0.00 0.01 1/1 print [9] |
| 0.00 0.01 9/9 fgets [12] |
| 0.00 0.00 12/34 strncmp <cycle 1> [40] |
| 0.00 0.00 8/8 lookup [20] |
| 0.00 0.00 1/1 fopen [21] |
| 0.00 0.00 8/8 chewtime [24] |
| 0.00 0.00 8/16 skipspace [44] |
| ----------------------------------------------- |
| [4] 59.8 0.01 0.02 8+472 <cycle 2 as a whole> [4] |
| 0.01 0.02 244+260 offtime <cycle 2> [7] |
| 0.00 0.00 236+1 tzset <cycle 2> [26] |
| ----------------------------------------------- |
| |
| The lines full of dashes divide this table into "entries", one for |
| each function. Each entry has one or more lines. |
| |
| In each entry, the primary line is the one that starts with an index |
| number in square brackets. The end of this line says which function |
| the entry is for. The preceding lines in the entry describe the |
| callers of this function and the following lines describe its |
| subroutines (also called "children" when we speak of the call graph). |
| |
| The entries are sorted by time spent in the function and its |
| subroutines. |
| |
| The internal profiling function `mcount' (*note The Flat Profile: |
| Flat Profile.) is never mentioned in the call graph. |
| |
| * Menu: |
| |
| * Primary:: Details of the primary line's contents. |
| * Callers:: Details of caller-lines' contents. |
| * Subroutines:: Details of subroutine-lines' contents. |
| * Cycles:: When there are cycles of recursion, |
| such as `a' calls `b' calls `a'... |
| |
| |
| File: gprof.info, Node: Primary, Next: Callers, Up: Call Graph |
| |
| 5.2.1 The Primary Line |
| ---------------------- |
| |
| The "primary line" in a call graph entry is the line that describes the |
| function which the entry is about and gives the overall statistics for |
| this function. |
| |
| For reference, we repeat the primary line from the entry for function |
| `report' in our main example, together with the heading line that shows |
| the names of the fields: |
| |
| index % time self children called name |
| ... |
| [3] 100.0 0.00 0.05 1 report [3] |
| |
| Here is what the fields in the primary line mean: |
| |
| `index' |
| Entries are numbered with consecutive integers. Each function |
| therefore has an index number, which appears at the beginning of |
| its primary line. |
| |
| Each cross-reference to a function, as a caller or subroutine of |
| another, gives its index number as well as its name. The index |
| number guides you if you wish to look for the entry for that |
| function. |
| |
| `% time' |
| This is the percentage of the total time that was spent in this |
| function, including time spent in subroutines called from this |
| function. |
| |
| The time spent in this function is counted again for the callers of |
| this function. Therefore, adding up these percentages is |
| meaningless. |
| |
| `self' |
| This is the total amount of time spent in this function. This |
| should be identical to the number printed in the `seconds' field |
| for this function in the flat profile. |
| |
| `children' |
| This is the total amount of time spent in the subroutine calls |
| made by this function. This should be equal to the sum of all the |
| `self' and `children' entries of the children listed directly |
| below this function. |
| |
| `called' |
| This is the number of times the function was called. |
| |
| If the function called itself recursively, there are two numbers, |
| separated by a `+'. The first number counts non-recursive calls, |
| and the second counts recursive calls. |
| |
| In the example above, the function `report' was called once from |
| `main'. |
| |
| `name' |
| This is the name of the current function. The index number is |
| repeated after it. |
| |
| If the function is part of a cycle of recursion, the cycle number |
| is printed between the function's name and the index number (*note |
| How Mutually Recursive Functions Are Described: Cycles.). For |
| example, if function `gnurr' is part of cycle number one, and has |
| index number twelve, its primary line would be end like this: |
| |
| gnurr <cycle 1> [12] |
| |
| |
| File: gprof.info, Node: Callers, Next: Subroutines, Prev: Primary, Up: Call Graph |
| |
| 5.2.2 Lines for a Function's Callers |
| ------------------------------------ |
| |
| A function's entry has a line for each function it was called by. |
| These lines' fields correspond to the fields of the primary line, but |
| their meanings are different because of the difference in context. |
| |
| For reference, we repeat two lines from the entry for the function |
| `report', the primary line and one caller-line preceding it, together |
| with the heading line that shows the names of the fields: |
| |
| index % time self children called name |
| ... |
| 0.00 0.05 1/1 main [2] |
| [3] 100.0 0.00 0.05 1 report [3] |
| |
| Here are the meanings of the fields in the caller-line for `report' |
| called from `main': |
| |
| `self' |
| An estimate of the amount of time spent in `report' itself when it |
| was called from `main'. |
| |
| `children' |
| An estimate of the amount of time spent in subroutines of `report' |
| when `report' was called from `main'. |
| |
| The sum of the `self' and `children' fields is an estimate of the |
| amount of time spent within calls to `report' from `main'. |
| |
| `called' |
| Two numbers: the number of times `report' was called from `main', |
| followed by the total number of non-recursive calls to `report' |
| from all its callers. |
| |
| `name and index number' |
| The name of the caller of `report' to which this line applies, |
| followed by the caller's index number. |
| |
| Not all functions have entries in the call graph; some options to |
| `gprof' request the omission of certain functions. When a caller |
| has no entry of its own, it still has caller-lines in the entries |
| of the functions it calls. |
| |
| If the caller is part of a recursion cycle, the cycle number is |
| printed between the name and the index number. |
| |
| If the identity of the callers of a function cannot be determined, a |
| dummy caller-line is printed which has `<spontaneous>' as the "caller's |
| name" and all other fields blank. This can happen for signal handlers. |
| |
| |
| File: gprof.info, Node: Subroutines, Next: Cycles, Prev: Callers, Up: Call Graph |
| |
| 5.2.3 Lines for a Function's Subroutines |
| ---------------------------------------- |
| |
| A function's entry has a line for each of its subroutines--in other |
| words, a line for each other function that it called. These lines' |
| fields correspond to the fields of the primary line, but their meanings |
| are different because of the difference in context. |
| |
| For reference, we repeat two lines from the entry for the function |
| `main', the primary line and a line for a subroutine, together with the |
| heading line that shows the names of the fields: |
| |
| index % time self children called name |
| ... |
| [2] 100.0 0.00 0.05 1 main [2] |
| 0.00 0.05 1/1 report [3] |
| |
| Here are the meanings of the fields in the subroutine-line for `main' |
| calling `report': |
| |
| `self' |
| An estimate of the amount of time spent directly within `report' |
| when `report' was called from `main'. |
| |
| `children' |
| An estimate of the amount of time spent in subroutines of `report' |
| when `report' was called from `main'. |
| |
| The sum of the `self' and `children' fields is an estimate of the |
| total time spent in calls to `report' from `main'. |
| |
| `called' |
| Two numbers, the number of calls to `report' from `main' followed |
| by the total number of non-recursive calls to `report'. This |
| ratio is used to determine how much of `report''s `self' and |
| `children' time gets credited to `main'. *Note Estimating |
| `children' Times: Assumptions. |
| |
| `name' |
| The name of the subroutine of `main' to which this line applies, |
| followed by the subroutine's index number. |
| |
| If the caller is part of a recursion cycle, the cycle number is |
| printed between the name and the index number. |
| |
| |
| File: gprof.info, Node: Cycles, Prev: Subroutines, Up: Call Graph |
| |
| 5.2.4 How Mutually Recursive Functions Are Described |
| ---------------------------------------------------- |
| |
| The graph may be complicated by the presence of "cycles of recursion" |
| in the call graph. A cycle exists if a function calls another function |
| that (directly or indirectly) calls (or appears to call) the original |
| function. For example: if `a' calls `b', and `b' calls `a', then `a' |
| and `b' form a cycle. |
| |
| Whenever there are call paths both ways between a pair of functions, |
| they belong to the same cycle. If `a' and `b' call each other and `b' |
| and `c' call each other, all three make one cycle. Note that even if |
| `b' only calls `a' if it was not called from `a', `gprof' cannot |
| determine this, so `a' and `b' are still considered a cycle. |
| |
| The cycles are numbered with consecutive integers. When a function |
| belongs to a cycle, each time the function name appears in the call |
| graph it is followed by `<cycle NUMBER>'. |
| |
| The reason cycles matter is that they make the time values in the |
| call graph paradoxical. The "time spent in children" of `a' should |
| include the time spent in its subroutine `b' and in `b''s |
| subroutines--but one of `b''s subroutines is `a'! How much of `a''s |
| time should be included in the children of `a', when `a' is indirectly |
| recursive? |
| |
| The way `gprof' resolves this paradox is by creating a single entry |
| for the cycle as a whole. The primary line of this entry describes the |
| total time spent directly in the functions of the cycle. The |
| "subroutines" of the cycle are the individual functions of the cycle, |
| and all other functions that were called directly by them. The |
| "callers" of the cycle are the functions, outside the cycle, that |
| called functions in the cycle. |
| |
| Here is an example portion of a call graph which shows a cycle |
| containing functions `a' and `b'. The cycle was entered by a call to |
| `a' from `main'; both `a' and `b' called `c'. |
| |
| index % time self children called name |
| ---------------------------------------- |
| 1.77 0 1/1 main [2] |
| [3] 91.71 1.77 0 1+5 <cycle 1 as a whole> [3] |
| 1.02 0 3 b <cycle 1> [4] |
| 0.75 0 2 a <cycle 1> [5] |
| ---------------------------------------- |
| 3 a <cycle 1> [5] |
| [4] 52.85 1.02 0 0 b <cycle 1> [4] |
| 2 a <cycle 1> [5] |
| 0 0 3/6 c [6] |
| ---------------------------------------- |
| 1.77 0 1/1 main [2] |
| 2 b <cycle 1> [4] |
| [5] 38.86 0.75 0 1 a <cycle 1> [5] |
| 3 b <cycle 1> [4] |
| 0 0 3/6 c [6] |
| ---------------------------------------- |
| |
| (The entire call graph for this program contains in addition an entry |
| for `main', which calls `a', and an entry for `c', with callers `a' and |
| `b'.) |
| |
| index % time self children called name |
| <spontaneous> |
| [1] 100.00 0 1.93 0 start [1] |
| 0.16 1.77 1/1 main [2] |
| ---------------------------------------- |
| 0.16 1.77 1/1 start [1] |
| [2] 100.00 0.16 1.77 1 main [2] |
| 1.77 0 1/1 a <cycle 1> [5] |
| ---------------------------------------- |
| 1.77 0 1/1 main [2] |
| [3] 91.71 1.77 0 1+5 <cycle 1 as a whole> [3] |
| 1.02 0 3 b <cycle 1> [4] |
| 0.75 0 2 a <cycle 1> [5] |
| 0 0 6/6 c [6] |
| ---------------------------------------- |
| 3 a <cycle 1> [5] |
| [4] 52.85 1.02 0 0 b <cycle 1> [4] |
| 2 a <cycle 1> [5] |
| 0 0 3/6 c [6] |
| ---------------------------------------- |
| 1.77 0 1/1 main [2] |
| 2 b <cycle 1> [4] |
| [5] 38.86 0.75 0 1 a <cycle 1> [5] |
| 3 b <cycle 1> [4] |
| 0 0 3/6 c [6] |
| ---------------------------------------- |
| 0 0 3/6 b <cycle 1> [4] |
| 0 0 3/6 a <cycle 1> [5] |
| [6] 0.00 0 0 6 c [6] |
| ---------------------------------------- |
| |
| The `self' field of the cycle's primary line is the total time spent |
| in all the functions of the cycle. It equals the sum of the `self' |
| fields for the individual functions in the cycle, found in the entry in |
| the subroutine lines for these functions. |
| |
| The `children' fields of the cycle's primary line and subroutine |
| lines count only subroutines outside the cycle. Even though `a' calls |
| `b', the time spent in those calls to `b' is not counted in `a''s |
| `children' time. Thus, we do not encounter the problem of what to do |
| when the time in those calls to `b' includes indirect recursive calls |
| back to `a'. |
| |
| The `children' field of a caller-line in the cycle's entry estimates |
| the amount of time spent _in the whole cycle_, and its other |
| subroutines, on the times when that caller called a function in the |
| cycle. |
| |
| The `called' field in the primary line for the cycle has two numbers: |
| first, the number of times functions in the cycle were called by |
| functions outside the cycle; second, the number of times they were |
| called by functions in the cycle (including times when a function in |
| the cycle calls itself). This is a generalization of the usual split |
| into non-recursive and recursive calls. |
| |
| The `called' field of a subroutine-line for a cycle member in the |
| cycle's entry says how many time that function was called from |
| functions in the cycle. The total of all these is the second number in |
| the primary line's `called' field. |
| |
| In the individual entry for a function in a cycle, the other |
| functions in the same cycle can appear as subroutines and as callers. |
| These lines show how many times each function in the cycle called or |
| was called from each other function in the cycle. The `self' and |
| `children' fields in these lines are blank because of the difficulty of |
| defining meanings for them when recursion is going on. |
| |
| |
| File: gprof.info, Node: Line-by-line, Next: Annotated Source, Prev: Call Graph, Up: Output |
| |
| 5.3 Line-by-line Profiling |
| ========================== |
| |
| `gprof''s `-l' option causes the program to perform "line-by-line" |
| profiling. In this mode, histogram samples are assigned not to |
| functions, but to individual lines of source code. This only works |
| with programs compiled with older versions of the `gcc' compiler. |
| Newer versions of `gcc' use a different program - `gcov' - to display |
| line-by-line profiling information. |
| |
| With the older versions of `gcc' the program usually has to be |
| compiled with a `-g' option, in addition to `-pg', in order to generate |
| debugging symbols for tracking source code lines. Note, in much older |
| versions of `gcc' the program had to be compiled with the `-a' command |
| line option as well. |
| |
| The flat profile is the most useful output table in line-by-line |
| mode. The call graph isn't as useful as normal, since the current |
| version of `gprof' does not propagate call graph arcs from source code |
| lines to the enclosing function. The call graph does, however, show |
| each line of code that called each function, along with a count. |
| |
| Here is a section of `gprof''s output, without line-by-line |
| profiling. Note that `ct_init' accounted for four histogram hits, and |
| 13327 calls to `init_block'. |
| |
| Flat profile: |
| |
| Each sample counts as 0.01 seconds. |
| % cumulative self self total |
| time seconds seconds calls us/call us/call name |
| 30.77 0.13 0.04 6335 6.31 6.31 ct_init |
| |
| |
| Call graph (explanation follows) |
| |
| |
| granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds |
| |
| index % time self children called name |
| |
| 0.00 0.00 1/13496 name_too_long |
| 0.00 0.00 40/13496 deflate |
| 0.00 0.00 128/13496 deflate_fast |
| 0.00 0.00 13327/13496 ct_init |
| [7] 0.0 0.00 0.00 13496 init_block |
| |
| Now let's look at some of `gprof''s output from the same program run, |
| this time with line-by-line profiling enabled. Note that `ct_init''s |
| four histogram hits are broken down into four lines of source code--one |
| hit occurred on each of lines 349, 351, 382 and 385. In the call graph, |
| note how `ct_init''s 13327 calls to `init_block' are broken down into |
| one call from line 396, 3071 calls from line 384, 3730 calls from line |
| 385, and 6525 calls from 387. |
| |
| Flat profile: |
| |
| Each sample counts as 0.01 seconds. |
| % cumulative self |
| time seconds seconds calls name |
| 7.69 0.10 0.01 ct_init (trees.c:349) |
| 7.69 0.11 0.01 ct_init (trees.c:351) |
| 7.69 0.12 0.01 ct_init (trees.c:382) |
| 7.69 0.13 0.01 ct_init (trees.c:385) |
| |
| |
| Call graph (explanation follows) |
| |
| |
| granularity: each sample hit covers 4 byte(s) for 7.69% of 0.13 seconds |
| |
| % time self children called name |
| |
| 0.00 0.00 1/13496 name_too_long (gzip.c:1440) |
| 0.00 0.00 1/13496 deflate (deflate.c:763) |
| 0.00 0.00 1/13496 ct_init (trees.c:396) |
| 0.00 0.00 2/13496 deflate (deflate.c:727) |
| 0.00 0.00 4/13496 deflate (deflate.c:686) |
| 0.00 0.00 5/13496 deflate (deflate.c:675) |
| 0.00 0.00 12/13496 deflate (deflate.c:679) |
| 0.00 0.00 16/13496 deflate (deflate.c:730) |
| 0.00 0.00 128/13496 deflate_fast (deflate.c:654) |
| 0.00 0.00 3071/13496 ct_init (trees.c:384) |
| 0.00 0.00 3730/13496 ct_init (trees.c:385) |
| 0.00 0.00 6525/13496 ct_init (trees.c:387) |
| [6] 0.0 0.00 0.00 13496 init_block (trees.c:408) |
| |
| |
| File: gprof.info, Node: Annotated Source, Prev: Line-by-line, Up: Output |
| |
| 5.4 The Annotated Source Listing |
| ================================ |
| |
| `gprof''s `-A' option triggers an annotated source listing, which lists |
| the program's source code, each function labeled with the number of |
| times it was called. You may also need to specify the `-I' option, if |
| `gprof' can't find the source code files. |
| |
| With older versions of `gcc' compiling with `gcc ... -g -pg -a' |
| augments your program with basic-block counting code, in addition to |
| function counting code. This enables `gprof' to determine how many |
| times each line of code was executed. With newer versions of `gcc' |
| support for displaying basic-block counts is provided by the `gcov' |
| program. |
| |
| For example, consider the following function, taken from gzip, with |
| line numbers added: |
| |
| 1 ulg updcrc(s, n) |
| 2 uch *s; |
| 3 unsigned n; |
| 4 { |
| 5 register ulg c; |
| 6 |
| 7 static ulg crc = (ulg)0xffffffffL; |
| 8 |
| 9 if (s == NULL) { |
| 10 c = 0xffffffffL; |
| 11 } else { |
| 12 c = crc; |
| 13 if (n) do { |
| 14 c = crc_32_tab[...]; |
| 15 } while (--n); |
| 16 } |
| 17 crc = c; |
| 18 return c ^ 0xffffffffL; |
| 19 } |
| |
| `updcrc' has at least five basic-blocks. One is the function |
| itself. The `if' statement on line 9 generates two more basic-blocks, |
| one for each branch of the `if'. A fourth basic-block results from the |
| `if' on line 13, and the contents of the `do' loop form the fifth |
| basic-block. The compiler may also generate additional basic-blocks to |
| handle various special cases. |
| |
| A program augmented for basic-block counting can be analyzed with |
| `gprof -l -A'. The `-x' option is also helpful, to ensure that each |
| line of code is labeled at least once. Here is `updcrc''s annotated |
| source listing for a sample `gzip' run: |
| |
| ulg updcrc(s, n) |
| uch *s; |
| unsigned n; |
| 2 ->{ |
| register ulg c; |
| |
| static ulg crc = (ulg)0xffffffffL; |
| |
| 2 -> if (s == NULL) { |
| 1 -> c = 0xffffffffL; |
| 1 -> } else { |
| 1 -> c = crc; |
| 1 -> if (n) do { |
| 26312 -> c = crc_32_tab[...]; |
| 26312,1,26311 -> } while (--n); |
| } |
| 2 -> crc = c; |
| 2 -> return c ^ 0xffffffffL; |
| 2 ->} |
| |
| In this example, the function was called twice, passing once through |
| each branch of the `if' statement. The body of the `do' loop was |
| executed a total of 26312 times. Note how the `while' statement is |
| annotated. It began execution 26312 times, once for each iteration |
| through the loop. One of those times (the last time) it exited, while |
| it branched back to the beginning of the loop 26311 times. |
| |
| |
| File: gprof.info, Node: Inaccuracy, Next: How do I?, Prev: Output, Up: Top |
| |
| 6 Inaccuracy of `gprof' Output |
| ****************************** |
| |
| * Menu: |
| |
| * Sampling Error:: Statistical margins of error |
| * Assumptions:: Estimating children times |
| |
| |
| File: gprof.info, Node: Sampling Error, Next: Assumptions, Up: Inaccuracy |
| |
| 6.1 Statistical Sampling Error |
| ============================== |
| |
| The run-time figures that `gprof' gives you are based on a sampling |
| process, so they are subject to statistical inaccuracy. If a function |
| runs only a small amount of time, so that on the average the sampling |
| process ought to catch that function in the act only once, there is a |
| pretty good chance it will actually find that function zero times, or |
| twice. |
| |
| By contrast, the number-of-calls and basic-block figures are derived |
| by counting, not sampling. They are completely accurate and will not |
| vary from run to run if your program is deterministic. |
| |
| The "sampling period" that is printed at the beginning of the flat |
| profile says how often samples are taken. The rule of thumb is that a |
| run-time figure is accurate if it is considerably bigger than the |
| sampling period. |
| |
| The actual amount of error can be predicted. For N samples, the |
| _expected_ error is the square-root of N. For example, if the sampling |
| period is 0.01 seconds and `foo''s run-time is 1 second, N is 100 |
| samples (1 second/0.01 seconds), sqrt(N) is 10 samples, so the expected |
| error in `foo''s run-time is 0.1 seconds (10*0.01 seconds), or ten |
| percent of the observed value. Again, if the sampling period is 0.01 |
| seconds and `bar''s run-time is 100 seconds, N is 10000 samples, |
| sqrt(N) is 100 samples, so the expected error in `bar''s run-time is 1 |
| second, or one percent of the observed value. It is likely to vary |
| this much _on the average_ from one profiling run to the next. |
| (_Sometimes_ it will vary more.) |
| |
| This does not mean that a small run-time figure is devoid of |
| information. If the program's _total_ run-time is large, a small |
| run-time for one function does tell you that that function used an |
| insignificant fraction of the whole program's time. Usually this means |
| it is not worth optimizing. |
| |
| One way to get more accuracy is to give your program more (but |
| similar) input data so it will take longer. Another way is to combine |
| the data from several runs, using the `-s' option of `gprof'. Here is |
| how: |
| |
| 1. Run your program once. |
| |
| 2. Issue the command `mv gmon.out gmon.sum'. |
| |
| 3. Run your program again, the same as before. |
| |
| 4. Merge the new data in `gmon.out' into `gmon.sum' with this command: |
| |
| gprof -s EXECUTABLE-FILE gmon.out gmon.sum |
| |
| 5. Repeat the last two steps as often as you wish. |
| |
| 6. Analyze the cumulative data using this command: |
| |
| gprof EXECUTABLE-FILE gmon.sum > OUTPUT-FILE |
| |
| |
| File: gprof.info, Node: Assumptions, Prev: Sampling Error, Up: Inaccuracy |
| |
| 6.2 Estimating `children' Times |
| =============================== |
| |
| Some of the figures in the call graph are estimates--for example, the |
| `children' time values and all the time figures in caller and |
| subroutine lines. |
| |
| There is no direct information about these measurements in the |
| profile data itself. Instead, `gprof' estimates them by making an |
| assumption about your program that might or might not be true. |
| |
| The assumption made is that the average time spent in each call to |
| any function `foo' is not correlated with who called `foo'. If `foo' |
| used 5 seconds in all, and 2/5 of the calls to `foo' came from `a', |
| then `foo' contributes 2 seconds to `a''s `children' time, by |
| assumption. |
| |
| This assumption is usually true enough, but for some programs it is |
| far from true. Suppose that `foo' returns very quickly when its |
| argument is zero; suppose that `a' always passes zero as an argument, |
| while other callers of `foo' pass other arguments. In this program, |
| all the time spent in `foo' is in the calls from callers other than `a'. |
| But `gprof' has no way of knowing this; it will blindly and incorrectly |
| charge 2 seconds of time in `foo' to the children of `a'. |
| |
| We hope some day to put more complete data into `gmon.out', so that |
| this assumption is no longer needed, if we can figure out how. For the |
| novice, the estimated figures are usually more useful than misleading. |
| |
| |
| File: gprof.info, Node: How do I?, Next: Incompatibilities, Prev: Inaccuracy, Up: Top |
| |
| 7 Answers to Common Questions |
| ***************************** |
| |
| How can I get more exact information about hot spots in my program? |
| Looking at the per-line call counts only tells part of the story. |
| Because `gprof' can only report call times and counts by function, |
| the best way to get finer-grained information on where the program |
| is spending its time is to re-factor large functions into sequences |
| of calls to smaller ones. Beware however that this can introduce |
| artificial hot spots since compiling with `-pg' adds a significant |
| overhead to function calls. An alternative solution is to use a |
| non-intrusive profiler, e.g. oprofile. |
| |
| How do I find which lines in my program were executed the most times? |
| Use the `gcov' program. |
| |
| How do I find which lines in my program called a particular function? |
| Use `gprof -l' and lookup the function in the call graph. The |
| callers will be broken down by function and line number. |
| |
| How do I analyze a program that runs for less than a second? |
| Try using a shell script like this one: |
| |
| for i in `seq 1 100`; do |
| fastprog |
| mv gmon.out gmon.out.$i |
| done |
| |
| gprof -s fastprog gmon.out.* |
| |
| gprof fastprog gmon.sum |
| |
| If your program is completely deterministic, all the call counts |
| will be simple multiples of 100 (i.e., a function called once in |
| each run will appear with a call count of 100). |
| |
| |
| |
| File: gprof.info, Node: Incompatibilities, Next: Details, Prev: How do I?, Up: Top |
| |
| 8 Incompatibilities with Unix `gprof' |
| ************************************* |
| |
| GNU `gprof' and Berkeley Unix `gprof' use the same data file |
| `gmon.out', and provide essentially the same information. But there |
| are a few differences. |
| |
| * GNU `gprof' uses a new, generalized file format with support for |
| basic-block execution counts and non-realtime histograms. A magic |
| cookie and version number allows `gprof' to easily identify new |
| style files. Old BSD-style files can still be read. *Note |
| Profiling Data File Format: File Format. |
| |
| * For a recursive function, Unix `gprof' lists the function as a |
| parent and as a child, with a `calls' field that lists the number |
| of recursive calls. GNU `gprof' omits these lines and puts the |
| number of recursive calls in the primary line. |
| |
| * When a function is suppressed from the call graph with `-e', GNU |
| `gprof' still lists it as a subroutine of functions that call it. |
| |
| * GNU `gprof' accepts the `-k' with its argument in the form |
| `from/to', instead of `from to'. |
| |
| * In the annotated source listing, if there are multiple basic |
| blocks on the same line, GNU `gprof' prints all of their counts, |
| separated by commas. |
| |
| * The blurbs, field widths, and output formats are different. GNU |
| `gprof' prints blurbs after the tables, so that you can see the |
| tables without skipping the blurbs. |
| |
| |
| File: gprof.info, Node: Details, Next: GNU Free Documentation License, Prev: Incompatibilities, Up: Top |
| |
| 9 Details of Profiling |
| ********************** |
| |
| * Menu: |
| |
| * Implementation:: How a program collects profiling information |
| * File Format:: Format of `gmon.out' files |
| * Internals:: `gprof''s internal operation |
| * Debugging:: Using `gprof''s `-d' option |
| |
| |
| File: gprof.info, Node: Implementation, Next: File Format, Up: Details |
| |
| 9.1 Implementation of Profiling |
| =============================== |
| |
| Profiling works by changing how every function in your program is |
| compiled so that when it is called, it will stash away some information |
| about where it was called from. From this, the profiler can figure out |
| what function called it, and can count how many times it was called. |
| This change is made by the compiler when your program is compiled with |
| the `-pg' option, which causes every function to call `mcount' (or |
| `_mcount', or `__mcount', depending on the OS and compiler) as one of |
| its first operations. |
| |
| The `mcount' routine, included in the profiling library, is |
| responsible for recording in an in-memory call graph table both its |
| parent routine (the child) and its parent's parent. This is typically |
| done by examining the stack frame to find both the address of the |
| child, and the return address in the original parent. Since this is a |
| very machine-dependent operation, `mcount' itself is typically a short |
| assembly-language stub routine that extracts the required information, |
| and then calls `__mcount_internal' (a normal C function) with two |
| arguments--`frompc' and `selfpc'. `__mcount_internal' is responsible |
| for maintaining the in-memory call graph, which records `frompc', |
| `selfpc', and the number of times each of these call arcs was traversed. |
| |
| GCC Version 2 provides a magical function |
| (`__builtin_return_address'), which allows a generic `mcount' function |
| to extract the required information from the stack frame. However, on |
| some architectures, most notably the SPARC, using this builtin can be |
| very computationally expensive, and an assembly language version of |
| `mcount' is used for performance reasons. |
| |
| Number-of-calls information for library routines is collected by |
| using a special version of the C library. The programs in it are the |
| same as in the usual C library, but they were compiled with `-pg'. If |
| you link your program with `gcc ... -pg', it automatically uses the |
| profiling version of the library. |
| |
| Profiling also involves watching your program as it runs, and |
| keeping a histogram of where the program counter happens to be every |
| now and then. Typically the program counter is looked at around 100 |
| times per second of run time, but the exact frequency may vary from |
| system to system. |
| |
| This is done is one of two ways. Most UNIX-like operating systems |
| provide a `profil()' system call, which registers a memory array with |
| the kernel, along with a scale factor that determines how the program's |
| address space maps into the array. Typical scaling values cause every |
| 2 to 8 bytes of address space to map into a single array slot. On |
| every tick of the system clock (assuming the profiled program is |
| running), the value of the program counter is examined and the |
| corresponding slot in the memory array is incremented. Since this is |
| done in the kernel, which had to interrupt the process anyway to handle |
| the clock interrupt, very little additional system overhead is required. |
| |
| However, some operating systems, most notably Linux 2.0 (and |
| earlier), do not provide a `profil()' system call. On such a system, |
| arrangements are made for the kernel to periodically deliver a signal |
| to the process (typically via `setitimer()'), which then performs the |
| same operation of examining the program counter and incrementing a slot |
| in the memory array. Since this method requires a signal to be |
| delivered to user space every time a sample is taken, it uses |
| considerably more overhead than kernel-based profiling. Also, due to |
| the added delay required to deliver the signal, this method is less |
| accurate as well. |
| |
| A special startup routine allocates memory for the histogram and |
| either calls `profil()' or sets up a clock signal handler. This |
| routine (`monstartup') can be invoked in several ways. On Linux |
| systems, a special profiling startup file `gcrt0.o', which invokes |
| `monstartup' before `main', is used instead of the default `crt0.o'. |
| Use of this special startup file is one of the effects of using `gcc |
| ... -pg' to link. On SPARC systems, no special startup files are used. |
| Rather, the `mcount' routine, when it is invoked for the first time |
| (typically when `main' is called), calls `monstartup'. |
| |
| If the compiler's `-a' option was used, basic-block counting is also |
| enabled. Each object file is then compiled with a static array of |
| counts, initially zero. In the executable code, every time a new |
| basic-block begins (i.e., when an `if' statement appears), an extra |
| instruction is inserted to increment the corresponding count in the |
| array. At compile time, a paired array was constructed that recorded |
| the starting address of each basic-block. Taken together, the two |
| arrays record the starting address of every basic-block, along with the |
| number of times it was executed. |
| |
| The profiling library also includes a function (`mcleanup') which is |
| typically registered using `atexit()' to be called as the program |
| exits, and is responsible for writing the file `gmon.out'. Profiling |
| is turned off, various headers are output, and the histogram is |
| written, followed by the call-graph arcs and the basic-block counts. |
| |
| The output from `gprof' gives no indication of parts of your program |
| that are limited by I/O or swapping bandwidth. This is because samples |
| of the program counter are taken at fixed intervals of the program's |
| run time. Therefore, the time measurements in `gprof' output say |
| nothing about time that your program was not running. For example, a |
| part of the program that creates so much data that it cannot all fit in |
| physical memory at once may run very slowly due to thrashing, but |
| `gprof' will say it uses little time. On the other hand, sampling by |
| run time has the advantage that the amount of load due to other users |
| won't directly affect the output you get. |
| |
| |
| File: gprof.info, Node: File Format, Next: Internals, Prev: Implementation, Up: Details |
| |
| 9.2 Profiling Data File Format |
| ============================== |
| |
| The old BSD-derived file format used for profile data does not contain a |
| magic cookie that allows to check whether a data file really is a |
| `gprof' file. Furthermore, it does not provide a version number, thus |
| rendering changes to the file format almost impossible. GNU `gprof' |
| uses a new file format that provides these features. For backward |
| compatibility, GNU `gprof' continues to support the old BSD-derived |
| format, but not all features are supported with it. For example, |
| basic-block execution counts cannot be accommodated by the old file |
| format. |
| |
| The new file format is defined in header file `gmon_out.h'. It |
| consists of a header containing the magic cookie and a version number, |
| as well as some spare bytes available for future extensions. All data |
| in a profile data file is in the native format of the target for which |
| the profile was collected. GNU `gprof' adapts automatically to the |
| byte-order in use. |
| |
| In the new file format, the header is followed by a sequence of |
| records. Currently, there are three different record types: histogram |
| records, call-graph arc records, and basic-block execution count |
| records. Each file can contain any number of each record type. When |
| reading a file, GNU `gprof' will ensure records of the same type are |
| compatible with each other and compute the union of all records. For |
| example, for basic-block execution counts, the union is simply the sum |
| of all execution counts for each basic-block. |
| |
| 9.2.1 Histogram Records |
| ----------------------- |
| |
| Histogram records consist of a header that is followed by an array of |
| bins. The header contains the text-segment range that the histogram |
| spans, the size of the histogram in bytes (unlike in the old BSD |
| format, this does not include the size of the header), the rate of the |
| profiling clock, and the physical dimension that the bin counts |
| represent after being scaled by the profiling clock rate. The physical |
| dimension is specified in two parts: a long name of up to 15 characters |
| and a single character abbreviation. For example, a histogram |
| representing real-time would specify the long name as "seconds" and the |
| abbreviation as "s". This feature is useful for architectures that |
| support performance monitor hardware (which, fortunately, is becoming |
| increasingly common). For example, under DEC OSF/1, the "uprofile" |
| command can be used to produce a histogram of, say, instruction cache |
| misses. In this case, the dimension in the histogram header could be |
| set to "i-cache misses" and the abbreviation could be set to "1" |
| (because it is simply a count, not a physical dimension). Also, the |
| profiling rate would have to be set to 1 in this case. |
| |
| Histogram bins are 16-bit numbers and each bin represent an equal |
| amount of text-space. For example, if the text-segment is one thousand |
| bytes long and if there are ten bins in the histogram, each bin |
| represents one hundred bytes. |
| |
| 9.2.2 Call-Graph Records |
| ------------------------ |
| |
| Call-graph records have a format that is identical to the one used in |
| the BSD-derived file format. It consists of an arc in the call graph |
| and a count indicating the number of times the arc was traversed during |
| program execution. Arcs are specified by a pair of addresses: the |
| first must be within caller's function and the second must be within |
| the callee's function. When performing profiling at the function |
| level, these addresses can point anywhere within the respective |
| function. However, when profiling at the line-level, it is better if |
| the addresses are as close to the call-site/entry-point as possible. |
| This will ensure that the line-level call-graph is able to identify |
| exactly which line of source code performed calls to a function. |
| |
| 9.2.3 Basic-Block Execution Count Records |
| ----------------------------------------- |
| |
| Basic-block execution count records consist of a header followed by a |
| sequence of address/count pairs. The header simply specifies the |
| length of the sequence. In an address/count pair, the address |
| identifies a basic-block and the count specifies the number of times |
| that basic-block was executed. Any address within the basic-address can |
| be used. |
| |
| |
| File: gprof.info, Node: Internals, Next: Debugging, Prev: File Format, Up: Details |
| |
| 9.3 `gprof''s Internal Operation |
| ================================ |
| |
| Like most programs, `gprof' begins by processing its options. During |
| this stage, it may building its symspec list (`sym_ids.c:sym_id_add'), |
| if options are specified which use symspecs. `gprof' maintains a |
| single linked list of symspecs, which will eventually get turned into |
| 12 symbol tables, organized into six include/exclude pairs--one pair |
| each for the flat profile (INCL_FLAT/EXCL_FLAT), the call graph arcs |
| (INCL_ARCS/EXCL_ARCS), printing in the call graph |
| (INCL_GRAPH/EXCL_GRAPH), timing propagation in the call graph |
| (INCL_TIME/EXCL_TIME), the annotated source listing |
| (INCL_ANNO/EXCL_ANNO), and the execution count listing |
| (INCL_EXEC/EXCL_EXEC). |
| |
| After option processing, `gprof' finishes building the symspec list |
| by adding all the symspecs in `default_excluded_list' to the exclude |
| lists EXCL_TIME and EXCL_GRAPH, and if line-by-line profiling is |
| specified, EXCL_FLAT as well. These default excludes are not added to |
| EXCL_ANNO, EXCL_ARCS, and EXCL_EXEC. |
| |
| Next, the BFD library is called to open the object file, verify that |
| it is an object file, and read its symbol table (`core.c:core_init'), |
| using `bfd_canonicalize_symtab' after mallocing an appropriately sized |
| array of symbols. At this point, function mappings are read (if the |
| `--file-ordering' option has been specified), and the core text space |
| is read into memory (if the `-c' option was given). |
| |
| `gprof''s own symbol table, an array of Sym structures, is now built. |
| This is done in one of two ways, by one of two routines, depending on |
| whether line-by-line profiling (`-l' option) has been enabled. For |
| normal profiling, the BFD canonical symbol table is scanned. For |
| line-by-line profiling, every text space address is examined, and a new |
| symbol table entry gets created every time the line number changes. In |
| either case, two passes are made through the symbol table--one to count |
| the size of the symbol table required, and the other to actually read |
| the symbols. In between the two passes, a single array of type `Sym' |
| is created of the appropriate length. Finally, |
| `symtab.c:symtab_finalize' is called to sort the symbol table and |
| remove duplicate entries (entries with the same memory address). |
| |
| The symbol table must be a contiguous array for two reasons. First, |
| the `qsort' library function (which sorts an array) will be used to |
| sort the symbol table. Also, the symbol lookup routine |
| (`symtab.c:sym_lookup'), which finds symbols based on memory address, |
| uses a binary search algorithm which requires the symbol table to be a |
| sorted array. Function symbols are indicated with an `is_func' flag. |
| Line number symbols have no special flags set. Additionally, a symbol |
| can have an `is_static' flag to indicate that it is a local symbol. |
| |
| With the symbol table read, the symspecs can now be translated into |
| Syms (`sym_ids.c:sym_id_parse'). Remember that a single symspec can |
| match multiple symbols. An array of symbol tables (`syms') is created, |
| each entry of which is a symbol table of Syms to be included or |
| excluded from a particular listing. The master symbol table and the |
| symspecs are examined by nested loops, and every symbol that matches a |
| symspec is inserted into the appropriate syms table. This is done |
| twice, once to count the size of each required symbol table, and again |
| to build the tables, which have been malloced between passes. From now |
| on, to determine whether a symbol is on an include or exclude symspec |
| list, `gprof' simply uses its standard symbol lookup routine on the |
| appropriate table in the `syms' array. |
| |
| Now the profile data file(s) themselves are read |
| (`gmon_io.c:gmon_out_read'), first by checking for a new-style |
| `gmon.out' header, then assuming this is an old-style BSD `gmon.out' if |
| the magic number test failed. |
| |
| New-style histogram records are read by `hist.c:hist_read_rec'. For |
| the first histogram record, allocate a memory array to hold all the |
| bins, and read them in. When multiple profile data files (or files |
| with multiple histogram records) are read, the memory ranges of each |
| pair of histogram records must be either equal, or non-overlapping. |
| For each pair of histogram records, the resolution (memory region size |
| divided by the number of bins) must be the same. The time unit must be |
| the same for all histogram records. If the above containts are met, all |
| histograms for the same memory range are merged. |
| |
| As each call graph record is read (`call_graph.c:cg_read_rec'), the |
| parent and child addresses are matched to symbol table entries, and a |
| call graph arc is created by `cg_arcs.c:arc_add', unless the arc fails |
| a symspec check against INCL_ARCS/EXCL_ARCS. As each arc is added, a |
| linked list is maintained of the parent's child arcs, and of the child's |
| parent arcs. Both the child's call count and the arc's call count are |
| incremented by the record's call count. |
| |
| Basic-block records are read (`basic_blocks.c:bb_read_rec'), but |
| only if line-by-line profiling has been selected. Each basic-block |
| address is matched to a corresponding line symbol in the symbol table, |
| and an entry made in the symbol's bb_addr and bb_calls arrays. Again, |
| if multiple basic-block records are present for the same address, the |
| call counts are cumulative. |
| |
| A gmon.sum file is dumped, if requested (`gmon_io.c:gmon_out_write'). |
| |
| If histograms were present in the data files, assign them to symbols |
| (`hist.c:hist_assign_samples') by iterating over all the sample bins |
| and assigning them to symbols. Since the symbol table is sorted in |
| order of ascending memory addresses, we can simple follow along in the |
| symbol table as we make our pass over the sample bins. This step |
| includes a symspec check against INCL_FLAT/EXCL_FLAT. Depending on the |
| histogram scale factor, a sample bin may span multiple symbols, in |
| which case a fraction of the sample count is allocated to each symbol, |
| proportional to the degree of overlap. This effect is rare for normal |
| profiling, but overlaps are more common during line-by-line profiling, |
| and can cause each of two adjacent lines to be credited with half a |
| hit, for example. |
| |
| If call graph data is present, `cg_arcs.c:cg_assemble' is called. |
| First, if `-c' was specified, a machine-dependent routine (`find_call') |
| scans through each symbol's machine code, looking for subroutine call |
| instructions, and adding them to the call graph with a zero call count. |
| A topological sort is performed by depth-first numbering all the |
| symbols (`cg_dfn.c:cg_dfn'), so that children are always numbered less |
| than their parents, then making a array of pointers into the symbol |
| table and sorting it into numerical order, which is reverse topological |
| order (children appear before parents). Cycles are also detected at |
| this point, all members of which are assigned the same topological |
| number. Two passes are now made through this sorted array of symbol |
| pointers. The first pass, from end to beginning (parents to children), |
| computes the fraction of child time to propagate to each parent and a |
| print flag. The print flag reflects symspec handling of |
| INCL_GRAPH/EXCL_GRAPH, with a parent's include or exclude (print or no |
| print) property being propagated to its children, unless they |
| themselves explicitly appear in INCL_GRAPH or EXCL_GRAPH. A second |
| pass, from beginning to end (children to parents) actually propagates |
| the timings along the call graph, subject to a check against |
| INCL_TIME/EXCL_TIME. With the print flag, fractions, and timings now |
| stored in the symbol structures, the topological sort array is now |
| discarded, and a new array of pointers is assembled, this time sorted |
| by propagated time. |
| |
| Finally, print the various outputs the user requested, which is now |
| fairly straightforward. The call graph (`cg_print.c:cg_print') and |
| flat profile (`hist.c:hist_print') are regurgitations of values already |
| computed. The annotated source listing |
| (`basic_blocks.c:print_annotated_source') uses basic-block information, |
| if present, to label each line of code with call counts, otherwise only |
| the function call counts are presented. |
| |
| The function ordering code is marginally well documented in the |
| source code itself (`cg_print.c'). Basically, the functions with the |
| most use and the most parents are placed first, followed by other |
| functions with the most use, followed by lower use functions, followed |
| by unused functions at the end. |
| |
| |
| File: gprof.info, Node: Debugging, Prev: Internals, Up: Details |
| |
| 9.4 Debugging `gprof' |
| ===================== |
| |
| If `gprof' was compiled with debugging enabled, the `-d' option |
| triggers debugging output (to stdout) which can be helpful in |
| understanding its operation. The debugging number specified is |
| interpreted as a sum of the following options: |
| |
| 2 - Topological sort |
| Monitor depth-first numbering of symbols during call graph analysis |
| |
| 4 - Cycles |
| Shows symbols as they are identified as cycle heads |
| |
| 16 - Tallying |
| As the call graph arcs are read, show each arc and how the total |
| calls to each function are tallied |
| |
| 32 - Call graph arc sorting |
| Details sorting individual parents/children within each call graph |
| entry |
| |
| 64 - Reading histogram and call graph records |
| Shows address ranges of histograms as they are read, and each call |
| graph arc |
| |
| 128 - Symbol table |
| Reading, classifying, and sorting the symbol table from the object |
| file. For line-by-line profiling (`-l' option), also shows line |
| numbers being assigned to memory addresses. |
| |
| 256 - Static call graph |
| Trace operation of `-c' option |
| |
| 512 - Symbol table and arc table lookups |
| Detail operation of lookup routines |
| |
| 1024 - Call graph propagation |
| Shows how function times are propagated along the call graph |
| |
| 2048 - Basic-blocks |
| Shows basic-block records as they are read from profile data (only |
| meaningful with `-l' option) |
| |
| 4096 - Symspecs |
| Shows symspec-to-symbol pattern matching operation |
| |
| 8192 - Annotate source |
| Tracks operation of `-A' option |
| |
| |
| File: gprof.info, Node: GNU Free Documentation License, Prev: Details, Up: Top |
| |
| Appendix A GNU Free Documentation License |
| ***************************************** |
| |
| Version 1.1, March 2000 |
| |
| Copyright (C) 2000, 2003 Free Software Foundation, Inc. |
| 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| |
| Everyone is permitted to copy and distribute verbatim copies |
| of this license document, but changing it is not allowed. |
| |
| |
| 0. PREAMBLE |
| |
| The purpose of this License is to make a manual, textbook, or other |
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| |
| This License is a kind of "copyleft", which means that derivative |
| works of the document must themselves be free in the same sense. |
| It complements the GNU General Public License, which is a copyleft |
| license designed for free software. |
| |
| We have designed this License in order to use it for manuals for |
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| free program should come with manuals providing the same freedoms |
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| We recommend this License principally for works whose purpose is |
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| |
| |
| 1. APPLICABILITY AND DEFINITIONS |
| |
| This License applies to any manual or other work that contains a |
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| 2. VERBATIM COPYING |
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| 4. MODIFICATIONS |
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| 5. COMBINING DOCUMENTS |
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| 6. COLLECTIONS OF DOCUMENTS |
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| 7. AGGREGATION WITH INDEPENDENT WORKS |
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| 9. TERMINATION |
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| 10. FUTURE REVISIONS OF THIS LICENSE |
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| The Free Software Foundation may publish new, revised versions of |
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| |
| |
| ADDENDUM: How to use this License for your documents |
| ==================================================== |
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| To use this License in a document you have written, include a copy of |
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| Copyright (C) YEAR YOUR NAME. |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.1 |
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| with the Invariant Sections being LIST THEIR TITLES, with the |
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| |
| |
| Tag Table: |
| Node: Top719 |
| Node: Introduction2033 |
| Node: Compiling4525 |
| Node: Executing7996 |
| Node: Invoking10784 |
| Node: Output Options12199 |
| Node: Analysis Options19288 |
| Node: Miscellaneous Options22689 |
| Node: Deprecated Options23944 |
| Node: Symspecs26023 |
| Node: Output27849 |
| Node: Flat Profile28889 |
| Node: Call Graph33842 |
| Node: Primary37074 |
| Node: Callers39662 |
| Node: Subroutines41779 |
| Node: Cycles43620 |
| Node: Line-by-line50397 |
| Node: Annotated Source54470 |
| Node: Inaccuracy57469 |
| Node: Sampling Error57727 |
| Node: Assumptions60297 |
| Node: How do I?61767 |
| Node: Incompatibilities63321 |
| Node: Details64815 |
| Node: Implementation65208 |
| Node: File Format71105 |
| Node: Internals75395 |
| Node: Debugging83890 |
| Node: GNU Free Documentation License85491 |
| |
| End Tag Table |