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| <a name="Index-Files-Speed-Up-GDB"></a> |
| <h3 class="section">18.4 Index Files Speed Up <small>GDB</small></h3> |
| <a name="index-index-files"></a> |
| <a name="index-_002egdb_005findex-section"></a> |
| |
| <p>When <small>GDB</small> finds a symbol file, it scans the symbols in the |
| file in order to construct an internal symbol table. This lets most |
| <small>GDB</small> operations work quickly—at the cost of a delay early |
| on. For large programs, this delay can be quite lengthy, so |
| <small>GDB</small> provides a way to build an index, which speeds up |
| startup. |
| </p> |
| <p>The index is stored as a section in the symbol file. <small>GDB</small> can |
| write the index to a file, then you can put it into the symbol file |
| using <code>objcopy</code>. |
| </p> |
| <p>To create an index file, use the <code>save gdb-index</code> command: |
| </p> |
| <dl compact="compact"> |
| <dt><code>save gdb-index <var>directory</var></code></dt> |
| <dd><a name="index-save-gdb_002dindex"></a> |
| <p>Create an index file for each symbol file currently known by |
| <small>GDB</small>. Each file is named after its corresponding symbol file, |
| with ‘<samp>.gdb-index</samp>’ appended, and is written into the given |
| <var>directory</var>. |
| </p></dd> |
| </dl> |
| |
| <p>Once you have created an index file you can merge it into your symbol |
| file, here named <samp>symfile</samp>, using <code>objcopy</code>: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">$ objcopy --add-section .gdb_index=symfile.gdb-index \ |
| --set-section-flags .gdb_index=readonly symfile symfile |
| </pre></div> |
| |
| <p><small>GDB</small> will normally ignore older versions of <samp>.gdb_index</samp> |
| sections that have been deprecated. Usually they are deprecated because |
| they are missing a new feature or have performance issues. |
| To tell <small>GDB</small> to use a deprecated index section anyway |
| specify <code>set use-deprecated-index-sections on</code>. |
| The default is <code>off</code>. |
| This can speed up startup, but may result in some functionality being lost. |
| See <a href="Index-Section-Format.html#Index-Section-Format">Index Section Format</a>. |
| </p> |
| <p><em>Warning:</em> Setting <code>use-deprecated-index-sections</code> to <code>on</code> |
| must be done before gdb reads the file. The following will not work: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">$ gdb -ex "set use-deprecated-index-sections on" <program> |
| </pre></div> |
| |
| <p>Instead you must do, for example, |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">$ gdb -iex "set use-deprecated-index-sections on" <program> |
| </pre></div> |
| |
| <p>There are currently some limitation on indices. They only work when |
| for DWARF debugging information, not stabs. And, they do not |
| currently work for programs using Ada. |
| </p> |
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