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<title>Debugging with GDB: Overlay Commands</title>
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<a name="Overlay-Commands"></a>
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<div class="header">
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<p>
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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> [<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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</div>
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<hr>
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<a name="Overlay-Commands-1"></a>
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<h3 class="section">14.2 Overlay Commands</h3>
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<p>To use <small>GDB</small>’s overlay support, each overlay in your program must
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correspond to a separate section of the executable file. The section’s
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virtual memory address and load memory address must be the overlay’s
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mapped and load addresses. Identifying overlays with sections allows
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<small>GDB</small> to determine the appropriate address of a function or
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variable, depending on whether the overlay is mapped or not.
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</p>
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<p><small>GDB</small>’s overlay commands all start with the word <code>overlay</code>;
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you can abbreviate this as <code>ov</code> or <code>ovly</code>. The commands are:
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</p>
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<dl compact="compact">
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<dt><code>overlay off</code></dt>
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<dd><a name="index-overlay"></a>
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<p>Disable <small>GDB</small>’s overlay support. When overlay support is
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disabled, <small>GDB</small> assumes that all functions and variables are
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always present at their mapped addresses. By default, <small>GDB</small>’s
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overlay support is disabled.
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</p>
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</dd>
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<dt><code>overlay manual</code></dt>
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<dd><a name="index-manual-overlay-debugging"></a>
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<p>Enable <em>manual</em> overlay debugging. In this mode, <small>GDB</small>
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relies on you to tell it which overlays are mapped, and which are not,
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using the <code>overlay map-overlay</code> and <code>overlay unmap-overlay</code>
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commands described below.
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</p>
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</dd>
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<dt><code>overlay map-overlay <var>overlay</var></code></dt>
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<dt><code>overlay map <var>overlay</var></code></dt>
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<dd><a name="index-map-an-overlay"></a>
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<p>Tell <small>GDB</small> that <var>overlay</var> is now mapped; <var>overlay</var> must
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be the name of the object file section containing the overlay. When an
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overlay is mapped, <small>GDB</small> assumes it can find the overlay’s
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functions and variables at their mapped addresses. <small>GDB</small> assumes
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that any other overlays whose mapped ranges overlap that of
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<var>overlay</var> are now unmapped.
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</p>
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</dd>
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<dt><code>overlay unmap-overlay <var>overlay</var></code></dt>
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<dt><code>overlay unmap <var>overlay</var></code></dt>
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<dd><a name="index-unmap-an-overlay"></a>
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<p>Tell <small>GDB</small> that <var>overlay</var> is no longer mapped; <var>overlay</var>
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must be the name of the object file section containing the overlay.
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When an overlay is unmapped, <small>GDB</small> assumes it can find the
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overlay’s functions and variables at their load addresses.
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</p>
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</dd>
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<dt><code>overlay auto</code></dt>
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<dd><p>Enable <em>automatic</em> overlay debugging. In this mode, <small>GDB</small>
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consults a data structure the overlay manager maintains in the inferior
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to see which overlays are mapped. For details, see <a href="Automatic-Overlay-Debugging.html#Automatic-Overlay-Debugging">Automatic Overlay Debugging</a>.
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</p>
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</dd>
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<dt><code>overlay load-target</code></dt>
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<dt><code>overlay load</code></dt>
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<dd><a name="index-reloading-the-overlay-table"></a>
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<p>Re-read the overlay table from the inferior. Normally, <small>GDB</small>
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re-reads the table <small>GDB</small> automatically each time the inferior
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stops, so this command should only be necessary if you have changed the
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overlay mapping yourself using <small>GDB</small>. This command is only
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useful when using automatic overlay debugging.
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</p>
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</dd>
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<dt><code>overlay list-overlays</code></dt>
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<dt><code>overlay list</code></dt>
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<dd><a name="index-listing-mapped-overlays"></a>
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<p>Display a list of the overlays currently mapped, along with their mapped
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addresses, load addresses, and sizes.
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</p>
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</dd>
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</dl>
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<p>Normally, when <small>GDB</small> prints a code address, it includes the name
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of the function the address falls in:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) print main
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$3 = {int ()} 0x11a0 <main>
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</pre></div>
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<p>When overlay debugging is enabled, <small>GDB</small> recognizes code in
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unmapped overlays, and prints the names of unmapped functions with
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asterisks around them. For example, if <code>foo</code> is a function in an
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unmapped overlay, <small>GDB</small> prints it this way:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) overlay list
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No sections are mapped.
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(gdb) print foo
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$5 = {int (int)} 0x100000 <*foo*>
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</pre></div>
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<p>When <code>foo</code>’s overlay is mapped, <small>GDB</small> prints the function’s
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name normally:
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</p>
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<div class="smallexample">
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<pre class="smallexample">(gdb) overlay list
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Section .ov.foo.text, loaded at 0x100000 - 0x100034,
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mapped at 0x1016 - 0x104a
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(gdb) print foo
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$6 = {int (int)} 0x1016 <foo>
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</pre></div>
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<p>When overlay debugging is enabled, <small>GDB</small> can find the correct
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address for functions and variables in an overlay, whether or not the
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overlay is mapped. This allows most <small>GDB</small> commands, like
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<code>break</code> and <code>disassemble</code>, to work normally, even on unmapped
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code. However, <small>GDB</small>’s breakpoint support has some limitations:
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</p>
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<ul>
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<li> <a name="index-breakpoints-in-overlays"></a>
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<a name="index-overlays_002c-setting-breakpoints-in"></a>
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You can set breakpoints in functions in unmapped overlays, as long as
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<small>GDB</small> can write to the overlay at its load address.
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</li><li> <small>GDB</small> can not set hardware or simulator-based breakpoints in
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unmapped overlays. However, if you set a breakpoint at the end of your
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overlay manager (and tell <small>GDB</small> which overlays are now mapped, if
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you are using manual overlay management), <small>GDB</small> will re-set its
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breakpoints properly.
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</li></ul>
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<hr>
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<div class="header">
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<p>
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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> [<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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