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<a name="Overlay-Commands"></a>
<div class="header">
<p>
Next: <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging" accesskey="n" rel="next">Automatic Overlay Debugging</a>, Previous: <a href="How-Overlays-Work.html#How-Overlays-Work" accesskey="p" rel="prev">How Overlays Work</a>, Up: <a href="Overlays.html#Overlays" accesskey="u" rel="up">Overlays</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>
</div>
<hr>
<a name="Overlay-Commands-1"></a>
<h3 class="section">14.2 Overlay Commands</h3>

<p>To use <small>GDB</small>&rsquo;s overlay support, each overlay in your program must
correspond to a separate section of the executable file.  The section&rsquo;s
virtual memory address and load memory address must be the overlay&rsquo;s
mapped and load addresses.  Identifying overlays with sections allows
<small>GDB</small> to determine the appropriate address of a function or
variable, depending on whether the overlay is mapped or not.
</p>
<p><small>GDB</small>&rsquo;s overlay commands all start with the word <code>overlay</code>;
you can abbreviate this as <code>ov</code> or <code>ovly</code>.  The commands are:
</p>
<dl compact="compact">
<dt><code>overlay off</code></dt>
<dd><a name="index-overlay"></a>
<p>Disable <small>GDB</small>&rsquo;s overlay support.  When overlay support is
disabled, <small>GDB</small> assumes that all functions and variables are
always present at their mapped addresses.  By default, <small>GDB</small>&rsquo;s
overlay support is disabled.
</p>
</dd>
<dt><code>overlay manual</code></dt>
<dd><a name="index-manual-overlay-debugging"></a>
<p>Enable <em>manual</em> overlay debugging.  In this mode, <small>GDB</small>
relies on you to tell it which overlays are mapped, and which are not,
using the <code>overlay map-overlay</code> and <code>overlay unmap-overlay</code>
commands described below.
</p>
</dd>
<dt><code>overlay map-overlay <var>overlay</var></code></dt>
<dt><code>overlay map <var>overlay</var></code></dt>
<dd><a name="index-map-an-overlay"></a>
<p>Tell <small>GDB</small> that <var>overlay</var> is now mapped; <var>overlay</var> must
be the name of the object file section containing the overlay.  When an
overlay is mapped, <small>GDB</small> assumes it can find the overlay&rsquo;s
functions and variables at their mapped addresses.  <small>GDB</small> assumes
that any other overlays whose mapped ranges overlap that of
<var>overlay</var> are now unmapped.
</p>
</dd>
<dt><code>overlay unmap-overlay <var>overlay</var></code></dt>
<dt><code>overlay unmap <var>overlay</var></code></dt>
<dd><a name="index-unmap-an-overlay"></a>
<p>Tell <small>GDB</small> that <var>overlay</var> is no longer mapped; <var>overlay</var>
must be the name of the object file section containing the overlay.
When an overlay is unmapped, <small>GDB</small> assumes it can find the
overlay&rsquo;s functions and variables at their load addresses.
</p>
</dd>
<dt><code>overlay auto</code></dt>
<dd><p>Enable <em>automatic</em> overlay debugging.  In this mode, <small>GDB</small>
consults a data structure the overlay manager maintains in the inferior
to see which overlays are mapped.  For details, see <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging">Automatic Overlay Debugging</a>.
</p>
</dd>
<dt><code>overlay load-target</code></dt>
<dt><code>overlay load</code></dt>
<dd><a name="index-reloading-the-overlay-table"></a>
<p>Re-read the overlay table from the inferior.  Normally, <small>GDB</small>
re-reads the table <small>GDB</small> automatically each time the inferior
stops, so this command should only be necessary if you have changed the
overlay mapping yourself using <small>GDB</small>.  This command is only
useful when using automatic overlay debugging.
</p>
</dd>
<dt><code>overlay list-overlays</code></dt>
<dt><code>overlay list</code></dt>
<dd><a name="index-listing-mapped-overlays"></a>
<p>Display a list of the overlays currently mapped, along with their mapped
addresses, load addresses, and sizes.
</p>
</dd>
</dl>

<p>Normally, when <small>GDB</small> prints a code address, it includes the name
of the function the address falls in:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) print main
$3 = {int ()} 0x11a0 &lt;main&gt;
</pre></div>
<p>When overlay debugging is enabled, <small>GDB</small> recognizes code in
unmapped overlays, and prints the names of unmapped functions with
asterisks around them.  For example, if <code>foo</code> is a function in an
unmapped overlay, <small>GDB</small> prints it this way:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) overlay list
No sections are mapped.
(gdb) print foo
$5 = {int (int)} 0x100000 &lt;*foo*&gt;
</pre></div>
<p>When <code>foo</code>&rsquo;s overlay is mapped, <small>GDB</small> prints the function&rsquo;s
name normally:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) overlay list
Section .ov.foo.text, loaded at 0x100000 - 0x100034,
        mapped at 0x1016 - 0x104a
(gdb) print foo
$6 = {int (int)} 0x1016 &lt;foo&gt;
</pre></div>

<p>When overlay debugging is enabled, <small>GDB</small> can find the correct
address for functions and variables in an overlay, whether or not the
overlay is mapped.  This allows most <small>GDB</small> commands, like
<code>break</code> and <code>disassemble</code>, to work normally, even on unmapped
code.  However, <small>GDB</small>&rsquo;s breakpoint support has some limitations:
</p>
<ul>
<li> <a name="index-breakpoints-in-overlays"></a>
<a name="index-overlays_002c-setting-breakpoints-in"></a>
You can set breakpoints in functions in unmapped overlays, as long as
<small>GDB</small> can write to the overlay at its load address.
</li><li> <small>GDB</small> can not set hardware or simulator-based breakpoints in
unmapped overlays.  However, if you set a breakpoint at the end of your
overlay manager (and tell <small>GDB</small> which overlays are now mapped, if
you are using manual overlay management), <small>GDB</small> will re-set its
breakpoints properly.
</li></ul>


<hr>
<div class="header">
<p>
Next: <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging" accesskey="n" rel="next">Automatic Overlay Debugging</a>, Previous: <a href="How-Overlays-Work.html#How-Overlays-Work" accesskey="p" rel="prev">How Overlays Work</a>, Up: <a href="Overlays.html#Overlays" accesskey="u" rel="up">Overlays</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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