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<a name="MiniDebugInfo"></a>
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<p>
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Next: <a href="Index-Files.html#Index-Files" accesskey="n" rel="next">Index Files</a>, Previous: <a href="Separate-Debug-Files.html#Separate-Debug-Files" accesskey="p" rel="previous">Separate Debug Files</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="Debugging-Information-in-a-Special-Section"></a>
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<h3 class="section">18.4 Debugging Information in a Special Section</h3>
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<a name="index-separate-debug-sections"></a>
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<a name="index-_002egnu_005fdebugdata-section"></a>
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<p>Some systems ship pre-built executables and libraries that have a
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special ‘<samp>.gnu_debugdata</samp>’ section. This feature is called
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<em>MiniDebugInfo</em>. This section holds an LZMA-compressed object and
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is used to supply extra symbols for backtraces.
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</p>
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<p>The intent of this section is to provide extra minimal debugging
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information for use in simple backtraces. It is not intended to be a
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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,
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<small>GDB</small> does not currently put restrictions on what sort of
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debugging information might be included in the section.
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</p>
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<p><small>GDB</small> has support for this extension. If the section exists,
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then it is used provided that no other source of debugging information
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can be found, and that <small>GDB</small> was configured with LZMA support.
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</p>
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<p>This section can be easily created using <code>objcopy</code> and other
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standard utilities:
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</p>
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<div class="smallexample">
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<pre class="smallexample"># Extract the dynamic symbols from the main binary, there is no need
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# to also have these in the normal symbol table.
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nm -D <var>binary</var> --format=posix --defined-only \
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| awk '{ print $1 }' | sort > dynsyms
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# Extract all the text (i.e. function) symbols from the debuginfo.
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# (Note that we actually also accept "D" symbols, for the benefit
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# of platforms like PowerPC64 that use function descriptors.)
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nm <var>binary</var> --format=posix --defined-only \
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| awk '{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 }' \
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| sort > funcsyms
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# Keep all the function symbols not already in the dynamic symbol
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# table.
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comm -13 dynsyms funcsyms > keep_symbols
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# Separate full debug info into debug binary.
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objcopy --only-keep-debug <var>binary</var> debug
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# Copy the full debuginfo, keeping only a minimal set of symbols and
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# removing some unnecessary sections.
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objcopy -S --remove-section .gdb_index --remove-section .comment \
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--keep-symbols=keep_symbols debug mini_debuginfo
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# Drop the full debug info from the original binary.
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strip --strip-all -R .comment <var>binary</var>
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# Inject the compressed data into the .gnu_debugdata section of the
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# original binary.
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xz mini_debuginfo
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objcopy --add-section .gnu_debugdata=mini_debuginfo.xz <var>binary</var>
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</pre></div>
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Next: <a href="Index-Files.html#Index-Files" accesskey="n" rel="next">Index Files</a>, Previous: <a href="Separate-Debug-Files.html#Separate-Debug-Files" accesskey="p" rel="previous">Separate Debug Files</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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