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<title>Using the GNU Compiler Collection (GCC): Gcov-tool Intro</title>
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<a name="Gcov_002dtool-Intro"></a>
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<div class="header">
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<p>
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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> [<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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</div>
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<hr>
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<a name="Introduction-to-gcov_002dtool"></a>
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<h3 class="section">11.1 Introduction to <code>gcov-tool</code></h3>
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<p><code>gcov-tool</code> is an offline tool to process gcc’s gcda profile files.
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</p>
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<p>Current gcov-tool supports the following functionalities:
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</p>
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<ul>
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<li> merge two sets of profiles with weights.
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</li><li> read one set of profile and rewrite profile contents. One can scale or
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normalize the count values.
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</li></ul>
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<p>Examples of the use cases for this tool are:
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</p><ul>
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<li> Collect the profiles for different set of inputs, and use this tool to merge
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them. One can specify the weight to factor in the relative importance of
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each input.
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</li><li> Rewrite the profile after removing a subset of the gcda files, while maintaining
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the consistency of the summary and the histogram.
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</li><li> It can also be used to debug or libgcov code as the tools shares the majority
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code as the runtime library.
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</li></ul>
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<p>Note that for the merging operation, this profile generated offline may
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contain slight different values from the online merged profile. Here are
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a list of typical differences:
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</p>
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<ul>
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<li> histogram difference: This offline tool recomputes the histogram after merging
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the counters. The resulting histogram, therefore, is precise. The online
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merging does not have this capability – the histogram is merged from two
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histograms and the result is an approximation.
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</li><li> summary checksum difference: Summary checksum uses a CRC32 operation. The value
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depends on the link list order of gcov-info objects. This order is different in
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gcov-tool from that in the online merge. It’s expected to have different
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summary checksums. It does not really matter as the compiler does not use this
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checksum anywhere.
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</li><li> value profile counter values difference: Some counter values for value profile
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are runtime dependent, like heap addresses. It’s normal to see some difference
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in these kind of counters.
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</li></ul>
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<hr>
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<div class="header">
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<p>
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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> [<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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