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### 18.5 Index Files Speed Up GDB

When GDB finds a symbol file, it scans the symbols in the file in order to construct an internal symbol table. This lets most GDB operations work quickly—at the cost of a delay early on. For large programs, this delay can be quite lengthy, so GDB provides a way to build an index, which speeds up startup.

The index is stored as a section in the symbol file. GDB can write the index to a file, then you can put it into the symbol file using `objcopy`.

To create an index file, use the `save gdb-index` command:

`save gdb-index directory`

  Create an index file for each symbol file currently known by GDB. Each file is named after its corresponding symbol file, with ‘`.gdb-index`’ appended, and is written into the given directory.

Once you have created an index file you can merge it into your symbol file, here named `symfile`, using `objcopy`:

    $ objcopy --add-section .gdb_index=symfile.gdb-index \
        --set-section-flags .gdb_index=readonly symfile symfile

GDB will normally ignore older versions of `.gdb_index` sections that have been deprecated. Usually they are deprecated because they are missing a new feature or have performance issues. To tell GDB to use a deprecated index section anyway specify `set use-deprecated-index-sections on`. The default is `off`. This can speed up startup, but may result in some functionality being lost. See Index Section Format.

Warning: Setting `use-deprecated-index-sections` to `on` must be done before gdb reads the file. The following will not work:

    $ gdb -ex "set use-deprecated-index-sections on" <program>

Instead you must do, for example,

    $ gdb -iex "set use-deprecated-index-sections on" <program>

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.

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