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<title>Debugging with GDB: Index Files</title>
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<a name="Index-Files"></a>
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<div class="header">
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<p>
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Next: <a href="Symbol-Errors.html#Symbol-Errors" accesskey="n" rel="next">Symbol Errors</a>, Previous: <a href="MiniDebugInfo.html#MiniDebugInfo" accesskey="p" rel="prev">MiniDebugInfo</a>, Up: <a href="GDB-Files.html#GDB-Files" accesskey="u" rel="up">GDB Files</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="Index-Files-Speed-Up-GDB"></a>
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<h3 class="section">18.5 Index Files Speed Up <small>GDB</small></h3>
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<a name="index-index-files"></a>
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<a name="index-_002egdb_005findex-section"></a>
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<p>When <small>GDB</small> finds a symbol file, it scans the symbols in the
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file in order to construct an internal symbol table. This lets most
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<small>GDB</small> operations work quickly—at the cost of a delay early
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on. For large programs, this delay can be quite lengthy, so
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<small>GDB</small> provides a way to build an index, which speeds up
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startup.
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</p>
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<p>The index is stored as a section in the symbol file. <small>GDB</small> can
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write the index to a file, then you can put it into the symbol file
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using <code>objcopy</code>.
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</p>
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<p>To create an index file, use the <code>save gdb-index</code> command:
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</p>
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<dl compact="compact">
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<dt><code>save gdb-index <var>directory</var></code></dt>
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<dd><a name="index-save-gdb_002dindex"></a>
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<p>Create an index file for each symbol file currently known by
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<small>GDB</small>. Each file is named after its corresponding symbol file,
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with ‘<samp>.gdb-index</samp>’ appended, and is written into the given
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<var>directory</var>.
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</p></dd>
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</dl>
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<p>Once you have created an index file you can merge it into your symbol
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file, here named <samp>symfile</samp>, using <code>objcopy</code>:
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</p>
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<div class="smallexample">
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<pre class="smallexample">$ objcopy --add-section .gdb_index=symfile.gdb-index \
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--set-section-flags .gdb_index=readonly symfile symfile
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</pre></div>
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<p><small>GDB</small> will normally ignore older versions of <samp>.gdb_index</samp>
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sections that have been deprecated. Usually they are deprecated because
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they are missing a new feature or have performance issues.
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To tell <small>GDB</small> to use a deprecated index section anyway
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specify <code>set use-deprecated-index-sections on</code>.
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The default is <code>off</code>.
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This can speed up startup, but may result in some functionality being lost.
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See <a href="Index-Section-Format.html#Index-Section-Format">Index Section Format</a>.
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</p>
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<p><em>Warning:</em> Setting <code>use-deprecated-index-sections</code> to <code>on</code>
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must be done before gdb reads the file. The following will not work:
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</p>
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<div class="smallexample">
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<pre class="smallexample">$ gdb -ex "set use-deprecated-index-sections on" <program>
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</pre></div>
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<p>Instead you must do, for example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">$ gdb -iex "set use-deprecated-index-sections on" <program>
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</pre></div>
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<p>There are currently some limitation on indices. They only work when
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for DWARF debugging information, not stabs. And, they do not
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currently work for programs using Ada.
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</p>
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Next: <a href="Symbol-Errors.html#Symbol-Errors" accesskey="n" rel="next">Symbol Errors</a>, Previous: <a href="MiniDebugInfo.html#MiniDebugInfo" accesskey="p" rel="prev">MiniDebugInfo</a>, Up: <a href="GDB-Files.html#GDB-Files" accesskey="u" rel="up">GDB Files</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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