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| <a name="Automatic-Overlay-Debugging"></a> |
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| Next: <a href="Overlay-Sample-Program.html#Overlay-Sample-Program" accesskey="n" rel="next">Overlay Sample Program</a>, Previous: <a href="Overlay-Commands.html#Overlay-Commands" accesskey="p" rel="prev">Overlay Commands</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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| <a name="Automatic-Overlay-Debugging-1"></a> |
| <h3 class="section">14.3 Automatic Overlay Debugging</h3> |
| <a name="index-automatic-overlay-debugging"></a> |
| |
| <p><small>GDB</small> can automatically track which overlays are mapped and which |
| are not, given some simple co-operation from the overlay manager in the |
| inferior. If you enable automatic overlay debugging with the |
| <code>overlay auto</code> command (see <a href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>), <small>GDB</small> |
| looks in the inferior’s memory for certain variables describing the |
| current state of the overlays. |
| </p> |
| <p>Here are the variables your overlay manager must define to support |
| <small>GDB</small>’s automatic overlay debugging: |
| </p> |
| <dl compact="compact"> |
| <dt><code>_ovly_table</code>:</dt> |
| <dd><p>This variable must be an array of the following structures: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">struct |
| { |
| /* The overlay's mapped address. */ |
| unsigned long vma; |
| |
| /* The size of the overlay, in bytes. */ |
| unsigned long size; |
| |
| /* The overlay's load address. */ |
| unsigned long lma; |
| |
| /* Non-zero if the overlay is currently mapped; |
| zero otherwise. */ |
| unsigned long mapped; |
| } |
| </pre></div> |
| |
| </dd> |
| <dt><code>_novlys</code>:</dt> |
| <dd><p>This variable must be a four-byte signed integer, holding the total |
| number of elements in <code>_ovly_table</code>. |
| </p> |
| </dd> |
| </dl> |
| |
| <p>To decide whether a particular overlay is mapped or not, <small>GDB</small> |
| looks for an entry in <code><span class="nolinebreak">_ovly_table</span></code><!-- /@w --> whose <code>vma</code> and |
| <code>lma</code> members equal the VMA and LMA of the overlay’s section in the |
| executable file. When <small>GDB</small> finds a matching entry, it consults |
| the entry’s <code>mapped</code> member to determine whether the overlay is |
| currently mapped. |
| </p> |
| <p>In addition, your overlay manager may define a function called |
| <code>_ovly_debug_event</code>. If this function is defined, <small>GDB</small> |
| will silently set a breakpoint there. If the overlay manager then |
| calls this function whenever it has changed the overlay table, this |
| will enable <small>GDB</small> to accurately keep track of which overlays |
| are in program memory, and update any breakpoints that may be set |
| in overlays. This will allow breakpoints to work even if the |
| overlays are kept in ROM or other non-writable memory while they |
| are not being executed. |
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