105 lines
4.7 KiB
HTML
105 lines
4.7 KiB
HTML
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<title>Automatic Overlay Debugging - Debugging with GDB</title>
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<a name="Automatic-Overlay-Debugging"></a>
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Next: <a rel="next" accesskey="n" href="Overlay-Sample-Program.html#Overlay-Sample-Program">Overlay Sample Program</a>,
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Previous: <a rel="previous" accesskey="p" href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>,
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Up: <a rel="up" accesskey="u" href="Overlays.html#Overlays">Overlays</a>
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<h3 class="section">14.3 Automatic Overlay Debugging</h3>
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<p><a name="index-automatic-overlay-debugging-963"></a>
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<span class="sc">gdb</span> can automatically track which overlays are mapped and which
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are not, given some simple co-operation from the overlay manager in the
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inferior. If you enable automatic overlay debugging with the
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<code>overlay auto</code> command (see <a href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>), <span class="sc">gdb</span>
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looks in the inferior's memory for certain variables describing the
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current state of the overlays.
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<p>Here are the variables your overlay manager must define to support
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<span class="sc">gdb</span>'s automatic overlay debugging:
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<dl>
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<dt><code>_ovly_table</code>:<dd>This variable must be an array of the following structures:
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<pre class="smallexample"> struct
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{
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/* The overlay's mapped address. */
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unsigned long vma;
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/* The size of the overlay, in bytes. */
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unsigned long size;
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/* The overlay's load address. */
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unsigned long lma;
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/* Non-zero if the overlay is currently mapped;
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zero otherwise. */
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unsigned long mapped;
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}
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</pre>
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<br><dt><code>_novlys</code>:<dd>This variable must be a four-byte signed integer, holding the total
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number of elements in <code>_ovly_table</code>.
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</dl>
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<p>To decide whether a particular overlay is mapped or not, <span class="sc">gdb</span>
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looks for an entry in <code>_ovly_table</code><!-- /@w --> whose <code>vma</code> and
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<code>lma</code> members equal the VMA and LMA of the overlay's section in the
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executable file. When <span class="sc">gdb</span> finds a matching entry, it consults
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the entry's <code>mapped</code> member to determine whether the overlay is
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currently mapped.
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<p>In addition, your overlay manager may define a function called
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<code>_ovly_debug_event</code>. If this function is defined, <span class="sc">gdb</span>
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will silently set a breakpoint there. If the overlay manager then
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calls this function whenever it has changed the overlay table, this
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will enable <span class="sc">gdb</span> to accurately keep track of which overlays
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are in program memory, and update any breakpoints that may be set
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in overlays. This will allow breakpoints to work even if the
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overlays are kept in ROM or other non-writable memory while they
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are not being executed.
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