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 2.18.50.

   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.