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 <a name="Gcov_002dtool-Intro"></a>
 <div class="header">
 <p>
 Next: <a href="Invoking-Gcov_002dtool.html#Invoking-Gcov_002dtool" accesskey="n" rel="next">Invoking Gcov-tool</a>, Up: <a href="Gcov_002dtool.html#Gcov_002dtool" accesskey="u" rel="up">Gcov-tool</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Introduction-to-gcov_002dtool"></a>
 <h3 class="section">11.1 Introduction to <code>gcov-tool</code></h3>

 <p><code>gcov-tool</code> is an offline tool to process gcc&rsquo;s gcda profile files.
 </p>
 <p>Current gcov-tool supports the following functionalities:
 </p>
 <ul>
 <li> merge two sets of profiles with weights.

 </li><li> read one set of profile and rewrite profile contents. One can scale or
 normalize the count values.
 </li></ul>

 <p>Examples of the use cases for this tool are:
 </p><ul>
 <li> Collect the profiles for different set of inputs, and use this tool to merge
 them. One can specify the weight to factor in the relative importance of
 each input.

 </li><li> Rewrite the profile after removing a subset of the gcda files, while maintaining
 the consistency of the summary and the histogram.

 </li><li> It can also be used to debug or libgcov code as the tools shares the majority
 code as the runtime library.
 </li></ul>

 <p>Note that for the merging operation, this profile generated offline may
 contain slight different values from the online merged profile. Here are
 a list of typical differences:
 </p>
 <ul>
 <li> histogram difference: This offline tool recomputes the histogram after merging
 the counters. The resulting histogram, therefore, is precise. The online
 merging does not have this capability &ndash; the histogram is merged from two
 histograms and the result is an approximation.

 </li><li> summary checksum difference: Summary checksum uses a CRC32 operation. The value
 depends on the link list order of gcov-info objects. This order is different in
 gcov-tool from that in the online merge. It&rsquo;s expected to have different
 summary checksums. It does not really matter as the compiler does not use this
 checksum anywhere.

 </li><li> value profile counter values difference: Some counter values for value profile
 are runtime dependent, like heap addresses. It&rsquo;s normal to see some difference
 in these kind of counters.
 </li></ul>


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 Next: <a href="Invoking-Gcov_002dtool.html#Invoking-Gcov_002dtool" accesskey="n" rel="next">Invoking Gcov-tool</a>, Up: <a href="Gcov_002dtool.html#Gcov_002dtool" accesskey="u" rel="up">Gcov-tool</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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	Invariant Sections being "Funding Free Software", the Front-Cover
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	(a) The FSF's Front-Cover Text is:

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	<a name="Gcov_002dtool-Intro"></a>
	<div class="header">
	<p>
	Next: <a href="Invoking-Gcov_002dtool.html#Invoking-Gcov_002dtool" accesskey="n" rel="next">Invoking Gcov-tool</a>, Up: <a href="Gcov_002dtool.html#Gcov_002dtool" accesskey="u" rel="up">Gcov-tool</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Introduction-to-gcov_002dtool"></a>
	<h3 class="section">11.1 Introduction to <code>gcov-tool</code></h3>

	<p><code>gcov-tool</code> is an offline tool to process gcc’s gcda profile files.
	</p>
	<p>Current gcov-tool supports the following functionalities:
	</p>
	<ul>
	<li> merge two sets of profiles with weights.

	</li><li> read one set of profile and rewrite profile contents. One can scale or
	normalize the count values.
	</li></ul>

	<p>Examples of the use cases for this tool are:
	</p><ul>
	<li> Collect the profiles for different set of inputs, and use this tool to merge
	them. One can specify the weight to factor in the relative importance of
	each input.

	</li><li> Rewrite the profile after removing a subset of the gcda files, while maintaining
	the consistency of the summary and the histogram.

	</li><li> It can also be used to debug or libgcov code as the tools shares the majority
	code as the runtime library.
	</li></ul>

	<p>Note that for the merging operation, this profile generated offline may
	contain slight different values from the online merged profile. Here are
	a list of typical differences:
	</p>
	<ul>
	<li> histogram difference: This offline tool recomputes the histogram after merging
	the counters. The resulting histogram, therefore, is precise. The online
	merging does not have this capability – the histogram is merged from two
	histograms and the result is an approximation.

	</li><li> summary checksum difference: Summary checksum uses a CRC32 operation. The value
	depends on the link list order of gcov-info objects. This order is different in
	gcov-tool from that in the online merge. It’s expected to have different
	summary checksums. It does not really matter as the compiler does not use this
	checksum anywhere.

	</li><li> value profile counter values difference: Some counter values for value profile
	are runtime dependent, like heap addresses. It’s normal to see some difference
	in these kind of counters.
	</li></ul>


	<hr>
	<div class="header">
	<p>
	Next: <a href="Invoking-Gcov_002dtool.html#Invoking-Gcov_002dtool" accesskey="n" rel="next">Invoking Gcov-tool</a>, Up: <a href="Gcov_002dtool.html#Gcov_002dtool" accesskey="u" rel="up">Gcov-tool</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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