gcov.texi

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@c Copyright (C) 1996, 1997, 1999, 2000, 2001,
@c 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.

@ignore
@c man begin COPYRIGHT
Copyright @copyright{} 1996, 1997, 1999, 2000, 2001, 2002, 2003, 2004, 2005
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 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``GNU General Public License'' and ``Funding
Free Software'', the Front-Cover texts being (a) (see below), and with
the Back-Cover Texts being (b) (see below).  A copy of the license is
included in the gfdl(7) man page.

(a) The FSF's Front-Cover Text is:

     A GNU Manual

(b) The FSF's Back-Cover Text is:

     You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development.
@c man end
@c Set file name and title for the man page.
@setfilename gcov
@settitle coverage testing tool
@end ignore

@node Gcov
@chapter @command{gcov}---a Test Coverage Program

@command{gcov} is a tool you can use in conjunction with GCC to
test code coverage in your programs.

@menu
* Gcov Intro::         	        Introduction to gcov.
* Invoking Gcov::       	How to use gcov.
* Gcov and Optimization::       Using gcov with GCC optimization.
* Gcov Data Files::             The files used by gcov.
* Cross-profiling::             Data file relocation.
@end menu

@node Gcov Intro
@section Introduction to @command{gcov}
@c man begin DESCRIPTION

@command{gcov} is a test coverage program.  Use it in concert with GCC
to analyze your programs to help create more efficient, faster running
code and to discover untested parts of your program.  You can use
@command{gcov} as a profiling tool to help discover where your
optimization efforts will best affect your code.  You can also use
@command{gcov} along with the other profiling tool, @command{gprof}, to
assess which parts of your code use the greatest amount of computing
time.

Profiling tools help you analyze your code's performance.  Using a
profiler such as @command{gcov} or @command{gprof}, you can find out some
basic performance statistics, such as:

@itemize @bullet
@item
how often each line of code executes

@item
what lines of code are actually executed

@item
how much computing time each section of code uses
@end itemize

Once you know these things about how your code works when compiled, you
can look at each module to see which modules should be optimized.
@command{gcov} helps you determine where to work on optimization.

Software developers also use coverage testing in concert with
testsuites, to make sure software is actually good enough for a release.
Testsuites can verify that a program works as expected; a coverage
program tests to see how much of the program is exercised by the
testsuite.  Developers can then determine what kinds of test cases need
to be added to the testsuites to create both better testing and a better
final product.

You should compile your code without optimization if you plan to use
@command{gcov} because the optimization, by combining some lines of code
into one function, may not give you as much information as you need to
look for `hot spots' where the code is using a great deal of computer
time.  Likewise, because @command{gcov} accumulates statistics by line (at
the lowest resolution), it works best with a programming style that
places only one statement on each line.  If you use complicated macros
that expand to loops or to other control structures, the statistics are
less helpful---they only report on the line where the macro call
appears.  If your complex macros behave like functions, you can replace
them with inline functions to solve this problem.

@command{gcov} creates a logfile called @file{@var{sourcefile}.gcov} which
indicates how many times each line of a source file @file{@var{sourcefile}.c}
has executed.  You can use these logfiles along with @command{gprof} to aid
in fine-tuning the performance of your programs.  @command{gprof} gives
timing information you can use along with the information you get from
@command{gcov}.

@command{gcov} works only on code compiled with GCC@.  It is not
compatible with any other profiling or test coverage mechanism.

@c man end

@node Invoking Gcov
@section Invoking @command{gcov}

@smallexample
gcov @r{[}@var{options}@r{]} @var{sourcefiles}
@end smallexample

@command{gcov} accepts the following options:

@ignore
@c man begin SYNOPSIS
gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}]
     [@option{-a}|@option{--all-blocks}]
     [@option{-b}|@option{--branch-probabilities}]
     [@option{-c}|@option{--branch-counts}]
     [@option{-n}|@option{--no-output}]
     [@option{-l}|@option{--long-file-names}]
     [@option{-p}|@option{--preserve-paths}]
     [@option{-f}|@option{--function-summaries}]
     [@option{-o}|@option{--object-directory} @var{directory|file}] @var{sourcefiles}
     [@option{-u}|@option{--unconditional-branches}]
@c man end
@c man begin SEEALSO
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for @file{gcc}.
@c man end
@end ignore

@c man begin OPTIONS
@table @gcctabopt
@item -h
@itemx --help
Display help about using @command{gcov} (on the standard output), and
exit without doing any further processing.

@item -v
@itemx --version
Display the @command{gcov} version number (on the standard output),
and exit without doing any further processing.

@item -a
@itemx --all-blocks
Write individual execution counts for every basic block.  Normally gcov
outputs execution counts only for the main blocks of a line.  With this
option you can determine if blocks within a single line are not being
executed.

@item -b
@itemx --branch-probabilities
Write branch frequencies to the output file, and write branch summary
info to the standard output.  This option allows you to see how often
each branch in your program was taken.  Unconditional branches will not
be shown, unless the @option{-u} option is given.

@item -c
@itemx --branch-counts
Write branch frequencies as the number of branches taken, rather than
the percentage of branches taken.

@item -n
@itemx --no-output
Do not create the @command{gcov} output file.

@item -l
@itemx --long-file-names
Create long file names for included source files.  For example, if the
header file @file{x.h} contains code, and was included in the file
@file{a.c}, then running @command{gcov} on the file @file{a.c} will produce
an output file called @file{a.c##x.h.gcov} instead of @file{x.h.gcov}.
This can be useful if @file{x.h} is included in multiple source
files.  If you use the @samp{-p} option, both the including and
included file names will be complete path names.

@item -p
@itemx --preserve-paths
Preserve complete path information in the names of generated
@file{.gcov} files.  Without this option, just the filename component is
used.  With this option, all directories are used, with @samp{/} characters
translated to @samp{#} characters, @file{.} directory components
removed and @file{..}
components renamed to @samp{^}.  This is useful if sourcefiles are in several
different directories.  It also affects the @samp{-l} option.

@item -f
@itemx --function-summaries
Output summaries for each function in addition to the file level summary.

@item -o @var{directory|file}
@itemx --object-directory @var{directory}
@itemx --object-file @var{file}
Specify either the directory containing the gcov data files, or the
object path name.  The @file{.gcno}, and
@file{.gcda} data files are searched for using this option.  If a directory
is specified, the data files are in that directory and named after the
source file name, without its extension.  If a file is specified here,
the data files are named after that file, without its extension.  If this
option is not supplied, it defaults to the current directory.

@item -u
@itemx --unconditional-branches
When branch probabilities are given, include those of unconditional branches.
Unconditional branches are normally not interesting.

@end table

@command{gcov} should be run with the current directory the same as that
when you invoked the compiler.  Otherwise it will not be able to locate
the source files.  @command{gcov} produces files called
@file{@var{mangledname}.gcov} in the current directory.  These contain
the coverage information of the source file they correspond to.
One @file{.gcov} file is produced for each source file containing code,
which was compiled to produce the data files.  The @var{mangledname} part
of the output file name is usually simply the source file name, but can
be something more complicated if the @samp{-l} or @samp{-p} options are
given.  Refer to those options for details.

The @file{.gcov} files contain the @samp{:} separated fields along with
program source code.  The format is

@smallexample
@var{execution_count}:@var{line_number}:@var{source line text}
@end smallexample

Additional block information may succeed each line, when requested by
command line option.  The @var{execution_count} is @samp{-} for lines
containing no code and @samp{#####} for lines which were never executed.
Some lines of information at the start have @var{line_number} of zero.

The preamble lines are of the form

@smallexample
-:0:@var{tag}:@var{value}
@end smallexample

The ordering and number of these preamble lines will be augmented as
@command{gcov} development progresses --- do not rely on them remaining
unchanged.  Use @var{tag} to locate a particular preamble line.

The additional block information is of the form

@smallexample
@var{tag} @var{information}
@end smallexample

The @var{information} is human readable, but designed to be simple
enough for machine parsing too.

When printing percentages, 0% and 100% are only printed when the values
are @emph{exactly} 0% and 100% respectively.  Other values which would
conventionally be rounded to 0% or 100% are instead printed as the
nearest non-boundary value.

When using @command{gcov}, you must first compile your program with two
special GCC options: @samp{-fprofile-arcs -ftest-coverage}.
This tells the compiler to generate additional information needed by
gcov (basically a flow graph of the program) and also includes
additional code in the object files for generating the extra profiling
information needed by gcov.  These additional files are placed in the
directory where the object file is located.

Running the program will cause profile output to be generated.  For each
source file compiled with @option{-fprofile-arcs}, an accompanying
@file{.gcda} file will be placed in the object file directory.

Running @command{gcov} with your program's source file names as arguments
will now produce a listing of the code along with frequency of execution
for each line.  For example, if your program is called @file{tmp.c}, this
is what you see when you use the basic @command{gcov} facility:

@smallexample
$ gcc -fprofile-arcs -ftest-coverage tmp.c
$ a.out
$ gcov tmp.c
90.00% of 10 source lines executed in file tmp.c
Creating tmp.c.gcov.
@end smallexample