Automatic-Overlay-Debugging.html 6.3 KB

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  58. <a name="Automatic-Overlay-Debugging"></a>
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  60. <p>
  61. 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> &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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  64. <a name="Automatic-Overlay-Debugging-1"></a>
  65. <h3 class="section">14.3 Automatic Overlay Debugging</h3>
  66. <a name="index-automatic-overlay-debugging"></a>
  67. <p><small>GDB</small> can automatically track which overlays are mapped and which
  68. are not, given some simple co-operation from the overlay manager in the
  69. inferior. If you enable automatic overlay debugging with the
  70. <code>overlay auto</code> command (see <a href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>), <small>GDB</small>
  71. looks in the inferior&rsquo;s memory for certain variables describing the
  72. current state of the overlays.
  73. </p>
  74. <p>Here are the variables your overlay manager must define to support
  75. <small>GDB</small>&rsquo;s automatic overlay debugging:
  76. </p>
  77. <dl compact="compact">
  78. <dt><code>_ovly_table</code>:</dt>
  79. <dd><p>This variable must be an array of the following structures:
  80. </p>
  81. <div class="smallexample">
  82. <pre class="smallexample">struct
  83. {
  84. /* The overlay's mapped address. */
  85. unsigned long vma;
  86. /* The size of the overlay, in bytes. */
  87. unsigned long size;
  88. /* The overlay's load address. */
  89. unsigned long lma;
  90. /* Non-zero if the overlay is currently mapped;
  91. zero otherwise. */
  92. unsigned long mapped;
  93. }
  94. </pre></div>
  95. </dd>
  96. <dt><code>_novlys</code>:</dt>
  97. <dd><p>This variable must be a four-byte signed integer, holding the total
  98. number of elements in <code>_ovly_table</code>.
  99. </p>
  100. </dd>
  101. </dl>
  102. <p>To decide whether a particular overlay is mapped or not, <small>GDB</small>
  103. looks for an entry in <code><span class="nolinebreak">_ovly_table</span></code><!-- /@w --> whose <code>vma</code> and
  104. <code>lma</code> members equal the VMA and LMA of the overlay&rsquo;s section in the
  105. executable file. When <small>GDB</small> finds a matching entry, it consults
  106. the entry&rsquo;s <code>mapped</code> member to determine whether the overlay is
  107. currently mapped.
  108. </p>
  109. <p>In addition, your overlay manager may define a function called
  110. <code>_ovly_debug_event</code>. If this function is defined, <small>GDB</small>
  111. will silently set a breakpoint there. If the overlay manager then
  112. calls this function whenever it has changed the overlay table, this
  113. will enable <small>GDB</small> to accurately keep track of which overlays
  114. are in program memory, and update any breakpoints that may be set
  115. in overlays. This will allow breakpoints to work even if the
  116. overlays are kept in ROM or other non-writable memory while they
  117. are not being executed.
  118. </p>
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