path: root/man-pages/gcov3.1

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.\" ======================================================================
.\"
.IX Title "GCOV 1"
.TH GCOV 1 "gcc-3.1" "2002-06-19" "GNU"
.UC
.SH "NAME"
gcov \- coverage testing tool
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
gcov [\fB\-v\fR|\fB\*(--version\fR] [\fB\-h\fR|\fB\*(--help\fR]
     [\fB\-b\fR|\fB\*(--branch-probabilities\fR] [\fB\-c\fR|\fB\*(--branch-counts\fR]
     [\fB\-n\fR|\fB\*(--no-output\fR] [\fB\-l\fR|\fB\*(--long-file-names\fR]
     [\fB\-f\fR|\fB\*(--function-summaries\fR]
     [\fB\-o\fR|\fB\*(--object-directory\fR \fIdirectory\fR] \fIsourcefile\fR
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBgcov\fR is a test coverage program.  Use it in concert with \s-1GCC\s0
to analyze your programs to help create more efficient, faster
running code.  You can use \fBgcov\fR as a profiling tool to help
discover where your optimization efforts will best affect your code.  You
can also use \fBgcov\fR along with the other profiling tool,
\&\fBgprof\fR, to assess which parts of your code use the greatest amount
of computing time.
.PP
Profiling tools help you analyze your code's performance.  Using a
profiler such as \fBgcov\fR or \fBgprof\fR, you can find out some
basic performance statistics, such as:
.Ip "\(bu" 4
how often each line of code executes
.Ip "\(bu" 4
what lines of code are actually executed
.Ip "\(bu" 4
how much computing time each section of code uses
.PP
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.
\&\fBgcov\fR helps you determine where to work on optimization.
.PP
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.
.PP
You should compile your code without optimization if you plan to use
\&\fBgcov\fR 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 \fBgcov\fR 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.
.PP
\&\fBgcov\fR creates a logfile called \fI\fIsourcefile\fI.gcov\fR which
indicates how many times each line of a source file \fI\fIsourcefile\fI.c\fR
has executed.  You can use these logfiles along with \fBgprof\fR to aid
in fine-tuning the performance of your programs.  \fBgprof\fR gives
timing information you can use along with the information you get from
\&\fBgcov\fR.
.PP
\&\fBgcov\fR works only on code compiled with \s-1GCC\s0.  It is not
compatible with any other profiling or test coverage mechanism.
.SH "OPTIONS"
.IX Header "OPTIONS"
.Ip "\fB\-h\fR" 4
.IX Item "-h"
.PD 0
.Ip "\fB\*(--help\fR" 4
.IX Item "help"
.PD
Display help about using \fBgcov\fR (on the standard output), and
exit without doing any further processing.
.Ip "\fB\-v\fR" 4
.IX Item "-v"
.PD 0
.Ip "\fB\*(--version\fR" 4
.IX Item "version"
.PD
Display the \fBgcov\fR version number (on the standard output),
and exit without doing any further processing.
.Ip "\fB\-b\fR" 4
.IX Item "-b"
.PD 0
.Ip "\fB\*(--branch-probabilities\fR" 4
.IX Item "branch-probabilities"
.PD
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.
.Ip "\fB\-c\fR" 4
.IX Item "-c"
.PD 0
.Ip "\fB\*(--branch-counts\fR" 4
.IX Item "branch-counts"
.PD
Write branch frequencies as the number of branches taken, rather than
the percentage of branches taken.
.Ip "\fB\-n\fR" 4
.IX Item "-n"
.PD 0
.Ip "\fB\*(--no-output\fR" 4
.IX Item "no-output"
.PD
Do not create the \fBgcov\fR output file.
.Ip "\fB\-l\fR" 4
.IX Item "-l"
.PD 0
.Ip "\fB\*(--long-file-names\fR" 4
.IX Item "long-file-names"
.PD
Create long file names for included source files.  For example, if the
header file \fIx.h\fR contains code, and was included in the file
\&\fIa.c\fR, then running \fBgcov\fR on the file \fIa.c\fR will produce
an output file called \fIa.c.x.h.gcov\fR instead of \fIx.h.gcov\fR.
This can be useful if \fIx.h\fR is included in multiple source files.
.Ip "\fB\-f\fR" 4
.IX Item "-f"
.PD 0
.Ip "\fB\*(--function-summaries\fR" 4
.IX Item "function-summaries"
.PD
Output summaries for each function in addition to the file level summary.
.Ip "\fB\-o\fR \fIdirectory\fR" 4
.IX Item "-o directory"
.PD 0
.Ip "\fB\*(--object-directory\fR \fIdirectory\fR" 4
.IX Item "object-directory directory"
.PD
The directory where the object files live.  Gcov will search for \fI.bb\fR,
\&\fI.bbg\fR, and \fI.da\fR files in this directory.
.PP
When using \fBgcov\fR, you must first compile your program with two
special \s-1GCC\s0 options: \fB\-fprofile-arcs \-ftest-coverage\fR.
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 source code is located.
.PP
Running the program will cause profile output to be generated.  For each
source file compiled with \fB\-fprofile-arcs\fR, an accompanying \fI.da\fR
file will be placed in the source directory.
.PP
Running \fBgcov\fR 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 \fItmp.c\fR, this
is what you see when you use the basic \fBgcov\fR facility:
.PP
.Vb 5
\&        $ gcc -fprofile-arcs -ftest-coverage tmp.c
\&        $ a.out
\&        $ gcov tmp.c
\&         87.50% of 8 source lines executed in file tmp.c
\&        Creating tmp.c.gcov.
.Ve
The file \fItmp.c.gcov\fR contains output from \fBgcov\fR.
Here is a sample:
.PP
.Vb 3
\&                        main()
\&                        {
\&                   1      int i, total;
.Ve
.Vb 1
\&                   1      total = 0;
.Ve
.Vb 2
\&                  11      for (i = 0; i < 10; i++)
\&                  10        total += i;
.Ve
.Vb 5
\&                   1      if (total != 45)
\&              ######        printf ("Failure\en");
\&                          else
\&                   1        printf ("Success\en");
\&                   1    }
.Ve
When you use the \fB\-b\fR option, your output looks like this:
.PP
.Vb 6
\&        $ gcov -b tmp.c
\&         87.50% of 8 source lines executed in file tmp.c
\&         80.00% of 5 branches executed in file tmp.c
\&         80.00% of 5 branches taken at least once in file tmp.c
\&         50.00% of 2 calls executed in file tmp.c
\&        Creating tmp.c.gcov.
.Ve
Here is a sample of a resulting \fItmp.c.gcov\fR file:
.PP
.Vb 3
\&                        main()
\&                        {
\&                   1      int i, total;
.Ve
.Vb 1
\&                   1      total = 0;
.Ve
.Vb 5
\&                  11      for (i = 0; i < 10; i++)
\&        branch 0 taken = 91%
\&        branch 1 taken = 100%
\&        branch 2 taken = 100%
\&                  10        total += i;
.Ve
.Vb 9
\&                   1      if (total != 45)
\&        branch 0 taken = 100%
\&              ######        printf ("Failure\en");
\&        call 0 never executed
\&        branch 1 never executed
\&                          else
\&                   1        printf ("Success\en");
\&        call 0 returns = 100%
\&                   1    }
.Ve
For each basic block, a line is printed after the last line of the basic
block describing the branch or call that ends the basic block.  There can
be multiple branches and calls listed for a single source line if there
are multiple basic blocks that end on that line.  In this case, the
branches and calls are each given a number.  There is no simple way to map
these branches and calls back to source constructs.  In general, though,
the lowest numbered branch or call will correspond to the leftmost construct
on the source line.
.PP
For a branch, if it was executed at least once, then a percentage
indicating the number of times the branch was taken divided by the
number of times the branch was executed will be printed.  Otherwise, the
message ``never executed'' is printed.
.PP
For a call, if it was executed at least once, then a percentage
indicating the number of times the call returned divided by the number
of times the call was executed will be printed.  This will usually be
100%, but may be less for functions call \f(CW\*(C`exit\*(C'\fR or \f(CW\*(C`longjmp\*(C'\fR,
and thus may not return every time they are called.
.PP
The execution counts are cumulative.  If the example program were
executed again without removing the \fI.da\fR file, the count for the
number of times each line in the source was executed would be added to
the results of the previous \fIrun\fR\|(s).  This is potentially useful in
several ways.  For example, it could be used to accumulate data over a
number of program runs as part of a test verification suite, or to
provide more accurate long-term information over a large number of
program runs.
.PP
The data in the \fI.da\fR files is saved immediately before the program
exits.  For each source file compiled with \fB\-fprofile-arcs\fR, the profiling
code first attempts to read in an existing \fI.da\fR file; if the file
doesn't match the executable (differing number of basic block counts) it
will ignore the contents of the file.  It then adds in the new execution
counts and finally writes the data to the file.
.Sh "Using \fBgcov\fP with \s-1GCC\s0 Optimization"
.IX Subsection "Using gcov with GCC Optimization"
If you plan to use \fBgcov\fR to help optimize your code, you must
first compile your program with two special \s-1GCC\s0 options:
\&\fB\-fprofile-arcs \-ftest-coverage\fR.  Aside from that, you can use any
other \s-1GCC\s0 options; but if you want to prove that every single line
in your program was executed, you should not compile with optimization
at the same time.  On some machines the optimizer can eliminate some
simple code lines by combining them with other lines.  For example, code
like this:
.PP
.Vb 4
\&        if (a != b)
\&          c = 1;
\&        else
\&          c = 0;
.Ve
can be compiled into one instruction on some machines.  In this case,
there is no way for \fBgcov\fR to calculate separate execution counts
for each line because there isn't separate code for each line.  Hence
the \fBgcov\fR output looks like this if you compiled the program with
optimization:
.PP
.Vb 4
\&              100  if (a != b)
\&              100    c = 1;
\&              100  else
\&              100    c = 0;
.Ve
The output shows that this block of code, combined by optimization,
executed 100 times.  In one sense this result is correct, because there
was only one instruction representing all four of these lines.  However,
the output does not indicate how many times the result was 0 and how
many times the result was 1.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIgpl\fR\|(7), \fIgfdl\fR\|(7), \fIfsf-funding\fR\|(7), \fIgcc\fR\|(1) and the Info entry for \fIgcc\fR.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 1996, 1997, 1999, 2000, 2001 Free Software Foundation, Inc.
.PP
Permission is granted to copy, distribute and/or modify this document
under the terms of the \s-1GNU\s0 Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``\s-1GNU\s0 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 \fIgfdl\fR\|(7) man page.
.PP
(a) The \s-1FSF\s0's Front-Cover Text is:
.PP
.Vb 1
\&     A GNU Manual
.Ve
(b) The \s-1FSF\s0's Back-Cover Text is:
.PP
.Vb 3
\&     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.
.Ve