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<title>Debugging with GDB: Patching</title>

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<a name="Patching"></a>
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Next: <a href="Compiling-and-Injecting-Code.html#Compiling-and-Injecting-Code" accesskey="n" rel="next">Compiling and Injecting Code</a>, Previous: <a href="Calling.html#Calling" accesskey="p" rel="previous">Calling</a>, Up: <a href="Altering.html#Altering" accesskey="u" rel="up">Altering</a> &nbsp; [<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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<a name="Patching-Programs"></a>
<h3 class="section">17.6 Patching Programs</h3>

<a name="index-patching-binaries"></a>
<a name="index-writing-into-executables"></a>
<a name="index-writing-into-corefiles"></a>

<p>By default, <small>GDB</small> opens the file containing your program&rsquo;s
executable code (or the corefile) read-only.  This prevents accidental
alterations to machine code; but it also prevents you from intentionally
patching your program&rsquo;s binary.
</p>
<p>If you&rsquo;d like to be able to patch the binary, you can specify that
explicitly with the <code>set write</code> command.  For example, you might
want to turn on internal debugging flags, or even to make emergency
repairs.
</p>
<dl compact="compact">
<dd><a name="index-set-write"></a>
</dd>
<dt><code>set write on</code></dt>
<dt><code>set write off</code></dt>
<dd><p>If you specify &lsquo;<samp>set write on</samp>&rsquo;, <small>GDB</small> opens executable and
core files for both reading and writing; if you specify <kbd>set write
off</kbd> (the default), <small>GDB</small> opens them read-only.
</p>
<p>If you have already loaded a file, you must load it again (using the
<code>exec-file</code> or <code>core-file</code> command) after changing <code>set
write</code>, for your new setting to take effect.
</p>
</dd>
<dt><code>show write</code></dt>
<dd><a name="index-show-write"></a>
<p>Display whether executable files and core files are opened for writing
as well as reading.
</p></dd>
</dl>


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