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| <a name="Debugging-information-in-a-special-section"></a> |
| <h3 class="section">18.3 Debugging information in a special section</h3> |
| <a name="index-separate-debug-sections"></a> |
| <a name="index-_002egnu_005fdebugdata-section"></a> |
| |
| <p>Some systems ship pre-built executables and libraries that have a |
| special ‘<samp>.gnu_debugdata</samp>’ section. This feature is called |
| <em>MiniDebugInfo</em>. This section holds an LZMA-compressed object and |
| is used to supply extra symbols for backtraces. |
| </p> |
| <p>The intent of this section is to provide extra minimal debugging |
| information for use in simple backtraces. It is not intended to be a |
| replacement for full separate debugging information (see <a href="Separate-Debug-Files.html#Separate-Debug-Files">Separate Debug Files</a>). The example below shows the intended use; however, |
| <small>GDB</small> does not currently put restrictions on what sort of |
| debugging information might be included in the section. |
| </p> |
| <p><small>GDB</small> has support for this extension. If the section exists, |
| then it is used provided that no other source of debugging information |
| can be found, and that <small>GDB</small> was configured with LZMA support. |
| </p> |
| <p>This section can be easily created using <code>objcopy</code> and other |
| standard utilities: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample"># Extract the dynamic symbols from the main binary, there is no need |
| # to also have these in the normal symbol table. |
| nm -D <var>binary</var> --format=posix --defined-only \ |
| | awk '{ print $1 }' | sort > dynsyms |
| |
| # Extract all the text (i.e. function) symbols from the debuginfo. |
| # (Note that we actually also accept "D" symbols, for the benefit |
| # of platforms like PowerPC64 that use function descriptors.) |
| nm <var>binary</var> --format=posix --defined-only \ |
| | awk '{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 }' \ |
| | sort > funcsyms |
| |
| # Keep all the function symbols not already in the dynamic symbol |
| # table. |
| comm -13 dynsyms funcsyms > keep_symbols |
| |
| # Separate full debug info into debug binary. |
| objcopy --only-keep-debug <var>binary</var> debug |
| |
| # Copy the full debuginfo, keeping only a minimal set of symbols and |
| # removing some unnecessary sections. |
| objcopy -S --remove-section .gdb_index --remove-section .comment \ |
| --keep-symbols=keep_symbols debug mini_debuginfo |
| |
| # Drop the full debug info from the original binary. |
| strip --strip-all -R .comment <var>binary</var> |
| |
| # Inject the compressed data into the .gnu_debugdata section of the |
| # original binary. |
| xz mini_debuginfo |
| objcopy --add-section .gnu_debugdata=mini_debuginfo.xz <var>binary</var> |
| </pre></div> |
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