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<title>Debugging with GDB: Core File Generation</title>
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<a name="Core-File-Generation"></a>
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<div class="header">
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<p>
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Next: <a href="Character-Sets.html#Character-Sets" accesskey="n" rel="next">Character Sets</a>, Previous: <a href="Dump_002fRestore-Files.html#Dump_002fRestore-Files" accesskey="p" rel="previous">Dump/Restore Files</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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="How-to-Produce-a-Core-File-from-Your-Program"></a>
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<h3 class="section">10.19 How to Produce a Core File from Your Program</h3>
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<a name="index-dump-core-from-inferior"></a>
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<p>A <em>core file</em> or <em>core dump</em> is a file that records the memory
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image of a running process and its process status (register values
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etc.). Its primary use is post-mortem debugging of a program that
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crashed while it ran outside a debugger. A program that crashes
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automatically produces a core file, unless this feature is disabled by
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the user. See <a href="Files.html#Files">Files</a>, for information on invoking <small>GDB</small> in
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the post-mortem debugging mode.
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</p>
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<p>Occasionally, you may wish to produce a core file of the program you
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are debugging in order to preserve a snapshot of its state.
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<small>GDB</small> has a special command for that.
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</p>
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<dl compact="compact">
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<dd><a name="index-gcore"></a>
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<a name="index-generate_002dcore_002dfile"></a>
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</dd>
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<dt><code>generate-core-file [<var>file</var>]</code></dt>
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<dt><code>gcore [<var>file</var>]</code></dt>
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<dd><p>Produce a core dump of the inferior process. The optional argument
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<var>file</var> specifies the file name where to put the core dump. If not
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specified, the file name defaults to <samp>core.<var>pid</var></samp>, where
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<var>pid</var> is the inferior process ID.
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</p>
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<p>Note that this command is implemented only for some systems (as of
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this writing, <small>GNU</small>/Linux, FreeBSD, Solaris, and S390).
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</p>
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<p>On <small>GNU</small>/Linux, this command can take into account the value of the
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file <samp>/proc/<var>pid</var>/coredump_filter</samp> when generating the core
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dump (see <a href="#set-use_002dcoredump_002dfilter">set use-coredump-filter</a>), and by default honors the
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<code>VM_DONTDUMP</code> flag for mappings where it is present in the file
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<samp>/proc/<var>pid</var>/smaps</samp> (see <a href="#set-dump_002dexcluded_002dmappings">set dump-excluded-mappings</a>).
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</p>
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<a name="index-set-use_002dcoredump_002dfilter"></a>
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<a name="set-use_002dcoredump_002dfilter"></a></dd>
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<dt><code>set use-coredump-filter on</code></dt>
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<dt><code>set use-coredump-filter off</code></dt>
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<dd><p>Enable or disable the use of the file
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<samp>/proc/<var>pid</var>/coredump_filter</samp> when generating core dump
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files. This file is used by the Linux kernel to decide what types of
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memory mappings will be dumped or ignored when generating a core dump
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file. <var>pid</var> is the process ID of a currently running process.
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</p>
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<p>To make use of this feature, you have to write in the
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<samp>/proc/<var>pid</var>/coredump_filter</samp> file a value, in hexadecimal,
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which is a bit mask representing the memory mapping types. If a bit
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is set in the bit mask, then the memory mappings of the corresponding
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types will be dumped; otherwise, they will be ignored. This
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configuration is inherited by child processes. For more information
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about the bits that can be set in the
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<samp>/proc/<var>pid</var>/coredump_filter</samp> file, please refer to the
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manpage of <code>core(5)</code>.
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</p>
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<p>By default, this option is <code>on</code>. If this option is turned
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<code>off</code>, <small>GDB</small> does not read the <samp>coredump_filter</samp> file
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and instead uses the same default value as the Linux kernel in order
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to decide which pages will be dumped in the core dump file. This
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value is currently <code>0x33</code>, which means that bits <code>0</code>
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(anonymous private mappings), <code>1</code> (anonymous shared mappings),
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<code>4</code> (ELF headers) and <code>5</code> (private huge pages) are active.
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This will cause these memory mappings to be dumped automatically.
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</p>
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<a name="index-set-dump_002dexcluded_002dmappings"></a>
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<a name="set-dump_002dexcluded_002dmappings"></a></dd>
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<dt><code>set dump-excluded-mappings on</code></dt>
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<dt><code>set dump-excluded-mappings off</code></dt>
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<dd><p>If <code>on</code> is specified, <small>GDB</small> will dump memory mappings
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marked with the <code>VM_DONTDUMP</code> flag. This flag is represented in
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the file <samp>/proc/<var>pid</var>/smaps</samp> with the acronym <code>dd</code>.
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</p>
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<p>The default value is <code>off</code>.
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</p></dd>
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</dl>
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<div class="header">
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<p>
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Next: <a href="Character-Sets.html#Character-Sets" accesskey="n" rel="next">Character Sets</a>, Previous: <a href="Dump_002fRestore-Files.html#Dump_002fRestore-Files" accesskey="p" rel="previous">Dump/Restore Files</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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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