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105 lines
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<title>Gcov-tool Intro - Using the GNU Compiler Collection (GCC)</title>
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<link rel="next" href="Invoking-Gcov_002dtool.html#Invoking-Gcov_002dtool" title="Invoking Gcov-tool">
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<a name="Gcov-tool-Intro"></a>
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<a name="Gcov_002dtool-Intro"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Invoking-Gcov_002dtool.html#Invoking-Gcov_002dtool">Invoking Gcov-tool</a>,
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Up: <a rel="up" accesskey="u" href="Gcov_002dtool.html#Gcov_002dtool">Gcov-tool</a>
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<hr>
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</div>
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<h3 class="section">11.1 Introduction to <samp><span class="command">gcov-tool</span></samp></h3>
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<!-- man begin DESCRIPTION -->
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<p><samp><span class="command">gcov-tool</span></samp> is an offline tool to process gcc's gcda profile files.
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<p>Current gcov-tool supports the following functionalities:
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<ul>
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<li>merge two sets of profiles with weights.
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<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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</ul>
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<p>Examples of the use cases for this tool are:
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<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>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>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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</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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<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>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>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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</ul>
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<!-- man end -->
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