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<h3 class="section">10.2 Invoking <samp><span class="command">gcov</span></samp></h3>

<pre class="smallexample">     gcov <span class="roman">[</span><var>options</var><span class="roman">]</span> <var>sourcefiles</var>
</pre>
 <p><samp><span class="command">gcov</span></samp> accepts the following options:

<!-- man begin OPTIONS -->
     <dl>
<dt><code>-h</code><dt><code>--help</code><dd>Display help about using <samp><span class="command">gcov</span></samp> (on the standard output), and
exit without doing any further processing.

     <br><dt><code>-v</code><dt><code>--version</code><dd>Display the <samp><span class="command">gcov</span></samp> version number (on the standard output),
and exit without doing any further processing.

     <br><dt><code>-a</code><dt><code>--all-blocks</code><dd>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.

     <br><dt><code>-b</code><dt><code>--branch-probabilities</code><dd>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 <samp><span class="option">-u</span></samp> option is given.

     <br><dt><code>-c</code><dt><code>--branch-counts</code><dd>Write branch frequencies as the number of branches taken, rather than
the percentage of branches taken.

     <br><dt><code>-n</code><dt><code>--no-output</code><dd>Do not create the <samp><span class="command">gcov</span></samp> output file.

     <br><dt><code>-l</code><dt><code>--long-file-names</code><dd>Create long file names for included source files.  For example, if the
header file <samp><span class="file">x.h</span></samp> contains code, and was included in the file
<samp><span class="file">a.c</span></samp>, then running <samp><span class="command">gcov</span></samp> on the file <samp><span class="file">a.c</span></samp> will produce
an output file called <samp><span class="file">a.c##x.h.gcov</span></samp> instead of <samp><span class="file">x.h.gcov</span></samp>. 
This can be useful if <samp><span class="file">x.h</span></samp> is included in multiple source
files.  If you use the &lsquo;<samp><span class="samp">-p</span></samp>&rsquo; option, both the including and
included file names will be complete path names.

     <br><dt><code>-p</code><dt><code>--preserve-paths</code><dd>Preserve complete path information in the names of generated
<samp><span class="file">.gcov</span></samp> files.  Without this option, just the filename component is
used.  With this option, all directories are used, with &lsquo;<samp><span class="samp">/</span></samp>&rsquo; characters
translated to &lsquo;<samp><span class="samp">#</span></samp>&rsquo; characters, <samp><span class="file">.</span></samp> directory components
removed and <samp><span class="file">..</span></samp>
components renamed to &lsquo;<samp><span class="samp">^</span></samp>&rsquo;.  This is useful if sourcefiles are in several
different directories.  It also affects the &lsquo;<samp><span class="samp">-l</span></samp>&rsquo; option.

     <br><dt><code>-f</code><dt><code>--function-summaries</code><dd>Output summaries for each function in addition to the file level summary.

     <br><dt><code>-o </code><var>directory|file</var><dt><code>--object-directory </code><var>directory</var><dt><code>--object-file </code><var>file</var><dd>Specify either the directory containing the gcov data files, or the
object path name.  The <samp><span class="file">.gcno</span></samp>, and
<samp><span class="file">.gcda</span></samp> 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.

     <br><dt><code>-u</code><dt><code>--unconditional-branches</code><dd>When branch probabilities are given, include those of unconditional branches. 
Unconditional branches are normally not interesting.

 </dl>

 <p><samp><span class="command">gcov</span></samp> 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.  <samp><span class="command">gcov</span></samp> produces files called
<samp><var>mangledname</var><span class="file">.gcov</span></samp> in the current directory.  These contain
the coverage information of the source file they correspond to. 
One <samp><span class="file">.gcov</span></samp> file is produced for each source file containing code,
which was compiled to produce the data files.  The <var>mangledname</var> part
of the output file name is usually simply the source file name, but can
be something more complicated if the &lsquo;<samp><span class="samp">-l</span></samp>&rsquo; or &lsquo;<samp><span class="samp">-p</span></samp>&rsquo; options are
given.  Refer to those options for details.

 <p>The <samp><span class="file">.gcov</span></samp> files contain the &lsquo;<samp><span class="samp">:</span></samp>&rsquo; separated fields along with
program source code.  The format is

<pre class="smallexample">     <var>execution_count</var>:<var>line_number</var>:<var>source line text</var>
</pre>
 <p>Additional block information may succeed each line, when requested by
command line option.  The <var>execution_count</var> is &lsquo;<samp><span class="samp">-</span></samp>&rsquo; for lines
containing no code and &lsquo;<samp><span class="samp">#####</span></samp>&rsquo; for lines which were never executed. 
Some lines of information at the start have <var>line_number</var> of zero.

 <p>The preamble lines are of the form

<pre class="smallexample">     -:0:<var>tag</var>:<var>value</var>
</pre>
 <p>The ordering and number of these preamble lines will be augmented as
<samp><span class="command">gcov</span></samp> development progresses &mdash; do not rely on them remaining
unchanged.  Use <var>tag</var> to locate a particular preamble line.

 <p>The additional block information is of the form

<pre class="smallexample">     <var>tag</var> <var>information</var>
</pre>
 <p>The <var>information</var> is human readable, but designed to be simple
enough for machine parsing too.

 <p>When printing percentages, 0% and 100% are only printed when the values
are <em>exactly</em> 0% and 100% respectively.  Other values which would
conventionally be rounded to 0% or 100% are instead printed as the
nearest non-boundary value.

 <p>When using <samp><span class="command">gcov</span></samp>, you must first compile your program with two
special GCC options: &lsquo;<samp><span class="samp">-fprofile-arcs -ftest-coverage</span></samp>&rsquo;. 
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.

 <p>Running the program will cause profile output to be generated.  For each
source file compiled with <samp><span class="option">-fprofile-arcs</span></samp>, an accompanying
<samp><span class="file">.gcda</span></samp> file will be placed in the object file directory.

 <p>Running <samp><span class="command">gcov</span></samp> 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 <samp><span class="file">tmp.c</span></samp>, this
is what you see when you use the basic <samp><span class="command">gcov</span></samp> facility:

<pre class="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.
</pre>
 <p>The file <samp><span class="file">tmp.c.gcov</span></samp> contains output from <samp><span class="command">gcov</span></samp>. 
Here is a sample:

<pre class="smallexample">             -:    0:Source:tmp.c
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include &lt;stdio.h&gt;
             -:    2:
             -:    3:int main (void)
             1:    4:{
             1:    5:  int i, total;
             -:    6:
             1:    7:  total = 0;
             -:    8:
            11:    9:  for (i = 0; i &lt; 10; i++)
            10:   10:    total += i;
             -:   11:
             1:   12:  if (total != 45)
         #####:   13:    printf ("Failure\n");
             -:   14:  else
             1:   15:    printf ("Success\n");
             1:   16:  return 0;
             -:   17:}
</pre>
 <p>When you use the <samp><span class="option">-a</span></samp> option, you will get individual block
counts, and the output looks like this:

<pre class="smallexample">             -:    0:Source:tmp.c
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include &lt;stdio.h&gt;
             -:    2:
             -:    3:int main (void)
             1:    4:{
             1:    4-block  0
             1:    5:  int i, total;
             -:    6:
             1:    7:  total = 0;
             -:    8:
            11:    9:  for (i = 0; i &lt; 10; i++)
            11:    9-block  0
            10:   10:    total += i;
            10:   10-block  0
             -:   11:
             1:   12:  if (total != 45)
             1:   12-block  0
         #####:   13:    printf ("Failure\n");
         $$$$$:   13-block  0
             -:   14:  else
             1:   15:    printf ("Success\n");
             1:   15-block  0
             1:   16:  return 0;
             1:   16-block  0
             -:   17:}
</pre>
 <p>In this mode, each basic block is only shown on one line &ndash; the last
line of the block.  A multi-line block will only contribute to the
execution count of that last line, and other lines will not be shown
to contain code, unless previous blocks end on those lines. 
The total execution count of a line is shown and subsequent lines show
the execution counts for individual blocks that end on that line.  After each
block, the branch and call counts of the block will be shown, if the
<samp><span class="option">-b</span></samp> option is given.

 <p>Because of the way GCC instruments calls, a call count can be shown
after a line with no individual blocks. 
As you can see, line 13 contains a basic block that was not executed.

 <p>When you use the <samp><span class="option">-b</span></samp> option, your output looks like this:

<pre class="smallexample">     $ gcov -b tmp.c
     90.00% of 10 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.
</pre>
 <p>Here is a sample of a resulting <samp><span class="file">tmp.c.gcov</span></samp> file:

<pre class="smallexample">             -:    0:Source:tmp.c
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include &lt;stdio.h&gt;
             -:    2:
             -:    3:int main (void)
     function main called 1 returned 1 blocks executed 75%
             1:    4:{
             1:    5:  int i, total;
             -:    6:
             1:    7:  total = 0;
             -:    8:
            11:    9:  for (i = 0; i &lt; 10; i++)
     branch  0 taken 91% (fallthrough)
     branch  1 taken 9%
            10:   10:    total += i;
             -:   11:
             1:   12:  if (total != 45)
     branch  0 taken 0% (fallthrough)
     branch  1 taken 100%
         #####:   13:    printf ("Failure\n");
     call    0 never executed
             -:   14:  else
             1:   15:    printf ("Success\n");
     call    0 called 1 returned 100%
             1:   16:  return 0;
             -:   17:}
</pre>
 <p>For each function, a line is printed showing how many times the function
is called, how many times it returns and what percentage of the
function's blocks were executed.

 <p>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.

 <p>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 &ldquo;never executed&rdquo; is printed.

 <p>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 that call <code>exit</code> or <code>longjmp</code>,
and thus may not return every time they are called.

 <p>The execution counts are cumulative.  If the example program were
executed again without removing the <samp><span class="file">.gcda</span></samp> file, the count for the
number of times each line in the source was executed would be added to
the results of the previous run(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.

 <p>The data in the <samp><span class="file">.gcda</span></samp> files is saved immediately before the program
exits.  For each source file compiled with <samp><span class="option">-fprofile-arcs</span></samp>, the
profiling code first attempts to read in an existing <samp><span class="file">.gcda</span></samp> 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.

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