2001-05-28 Philip Blundell <philb@gnu.org>

[binutils.git] / gprof / gprof.info-1

This is gprof.info, produced by makeinfo version 4.0 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 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".

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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 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

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File: gprof.info,  Node: Introduction,  Next: Compiling,  Prev: Top,  Up: Top

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::.

   * You must execute your program to generate a profile data file.
     *Note Executing::.

   * You must run `gprof' to analyze the profile data.  *Note
     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 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 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 Annotated Source::.

   To better understand how profiling works, you may wish to read a
description of its implementation.  *Note Implementation::.

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File: gprof.info,  Node: Compiling,  Next: Executing,  Prev: Introduction,  Up: Top

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

   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 will also need to
specify the `-g' option, instructing the compiler to insert debugging
symbols into the program that match program addresses to source code
lines.  *Note Line-by-line::.

   In addition to the `-pg' and `-g' options, you may also wish to
specify the `-a' option when compiling.  This will instrument the
program to perform basic-block counting.  As the program runs, it will
count how many times it executed each branch of each `if' statement,
each iteration of each `do' loop, etc.  This will enable `gprof' to
construct an annotated source code listing showing how many times each
line of code was executed.

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File: gprof.info,  Node: Executing,  Next: Invoking,  Prev: Compiling,  Up: Top

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 the 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 afterward 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'.

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File: gprof.info,  Node: Invoking,  Next: Output,  Prev: Executing,  Up: Top

`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' analyses 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

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File: gprof.info,  Node: Output Options,  Next: Analysis Options,  Up: Invoking

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::.

   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 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 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 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.

`-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 filesystem 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.

`--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.

`--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.

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File: gprof.info,  Node: Analysis Options,  Next: Miscellaneous Options,  Prev: Output Options,  Up: Invoking

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.  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
     Sampling Error::.

`-m NUM'
`--min-count=NUM'
     This option affects execution count output only.  Symbols that are
     executed less than NUM times are suppressed.

`-n[SYMSPEC]'
`--time[=SYMSPEC]'
     The `-n' option causes `gprof', in its call graph analysis, to
     only propagate times for symbols matching SYMSPEC.

`-N[SYMSPEC]'
`--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.

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File: gprof.info,  Node: Miscellaneous Options,  Next: Deprecated Options,  Prev: Analysis Options,  Up: Invoking

Miscellaneous Options
=====================

`-d[NUM]'
`--debug[=NUM]'
     The `-d NUM' option specifies debugging options.  If NUM is not
     specified, enable all debugging.  *Note Debugging::.

`-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.

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File: gprof.info,  Node: Deprecated Options,  Next: Symspecs,  Prev: Miscellaneous Options,  Up: Invoking

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'.

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File: gprof.info,  Node: Symspecs,  Prev: Deprecated Options,  Up: Invoking

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'.

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File: gprof.info,  Node: Output,  Next: Inaccuracy,  Prev: Invoking,  Up: Top

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::.

* 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

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File: gprof.info,  Node: Flat Profile,  Next: Call Graph,  Up: Output

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 by 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 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.

\x1f
File: gprof.info,  Node: Call Graph,  Next: Line-by-line,  Prev: Flat Profile,  Up: Output

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 chapter.

     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 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'...

\x1f
File: gprof.info,  Node: Primary,  Next: Callers,  Up: Call Graph

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
     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]

\x1f
File: gprof.info,  Node: Callers,  Next: Subroutines,  Prev: Primary,  Up: Call Graph

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.

\x1f
File: gprof.info,  Node: Subroutines,  Next: Cycles,  Prev: Callers,  Up: Call Graph

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 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.

\x1f
File: gprof.info,  Node: Cycles,  Prev: Subroutines,  Up: Call Graph

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 `calls' 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 `calls' 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 `calls' 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.