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| <h3 class="section">10.19 How to Produce a Core File from Your Program</h3> |
| |
| <p><a name="index-dump-core-from-inferior-798"></a> |
| A <dfn>core file</dfn> or <dfn>core dump</dfn> is a file that records the memory |
| image of a running process and its process status (register values |
| etc.). Its primary use is post-mortem debugging of a program that |
| crashed while it ran outside a debugger. A program that crashes |
| automatically produces a core file, unless this feature is disabled by |
| the user. See <a href="Files.html#Files">Files</a>, for information on invoking <span class="sc">gdb</span> in |
| the post-mortem debugging mode. |
| |
| <p>Occasionally, you may wish to produce a core file of the program you |
| are debugging in order to preserve a snapshot of its state. |
| <span class="sc">gdb</span> has a special command for that. |
| |
| |
| <a name="index-gcore-799"></a> |
| <a name="index-generate_002dcore_002dfile-800"></a> |
| <dl><dt><code>generate-core-file [</code><var>file</var><code>]</code><dt><code>gcore [</code><var>file</var><code>]</code><dd>Produce a core dump of the inferior process. The optional argument |
| <var>file</var> specifies the file name where to put the core dump. If not |
| specified, the file name defaults to <samp><span class="file">core.</span><var>pid</var></samp>, where |
| <var>pid</var> is the inferior process ID. |
| |
| <p>Note that this command is implemented only for some systems (as of |
| this writing, <span class="sc">gnu</span>/Linux, FreeBSD, Solaris, and S390). |
| |
| <p>On <span class="sc">gnu</span>/Linux, this command can take into account the value of the |
| file <samp><span class="file">/proc/</span><var>pid</var><span class="file">/coredump_filter</span></samp> when generating the core |
| dump (see <a href="set-use_002dcoredump_002dfilter.html#set-use_002dcoredump_002dfilter">set use-coredump-filter</a>), and by default honors the |
| <code>VM_DONTDUMP</code> flag for mappings where it is present in the file |
| <samp><span class="file">/proc/</span><var>pid</var><span class="file">/smaps</span></samp> (see <a href="set-dump_002dexcluded_002dmappings.html#set-dump_002dexcluded_002dmappings">set dump-excluded-mappings</a>). |
| |
| <p><a name="index-set-use_002dcoredump_002dfilter-801"></a><a name="set-use_002dcoredump_002dfilter"></a><br><dt><code>set use-coredump-filter on</code><dt><code>set use-coredump-filter off</code><dd>Enable or disable the use of the file |
| <samp><span class="file">/proc/</span><var>pid</var><span class="file">/coredump_filter</span></samp> when generating core dump |
| files. This file is used by the Linux kernel to decide what types of |
| memory mappings will be dumped or ignored when generating a core dump |
| file. <var>pid</var> is the process ID of a currently running process. |
| |
| <p>To make use of this feature, you have to write in the |
| <samp><span class="file">/proc/</span><var>pid</var><span class="file">/coredump_filter</span></samp> file a value, in hexadecimal, |
| which is a bit mask representing the memory mapping types. If a bit |
| is set in the bit mask, then the memory mappings of the corresponding |
| types will be dumped; otherwise, they will be ignored. This |
| configuration is inherited by child processes. For more information |
| about the bits that can be set in the |
| <samp><span class="file">/proc/</span><var>pid</var><span class="file">/coredump_filter</span></samp> file, please refer to the |
| manpage of <code>core(5)</code>. |
| |
| <p>By default, this option is <code>on</code>. If this option is turned |
| <code>off</code>, <span class="sc">gdb</span> does not read the <samp><span class="file">coredump_filter</span></samp> file |
| and instead uses the same default value as the Linux kernel in order |
| to decide which pages will be dumped in the core dump file. This |
| value is currently <code>0x33</code>, which means that bits <code>0</code> |
| (anonymous private mappings), <code>1</code> (anonymous shared mappings), |
| <code>4</code> (ELF headers) and <code>5</code> (private huge pages) are active. |
| This will cause these memory mappings to be dumped automatically. |
| |
| <p><a name="index-set-dump_002dexcluded_002dmappings-802"></a><a name="set-dump_002dexcluded_002dmappings"></a><br><dt><code>set dump-excluded-mappings on</code><dt><code>set dump-excluded-mappings off</code><dd>If <code>on</code> is specified, <span class="sc">gdb</span> will dump memory mappings |
| marked with the <code>VM_DONTDUMP</code> flag. This flag is represented in |
| the file <samp><span class="file">/proc/</span><var>pid</var><span class="file">/smaps</span></samp> with the acronym <code>dd</code>. |
| |
| <p>The default value is <code>off</code>. |
| </dl> |
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