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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

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  10. and with the Back-Cover Texts as in (a) below.

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  16. <head>

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  18. <title>Automatic Overlay Debugging (Debugging with GDB)</title>

  19. 

  20. <meta name="description" content="Automatic Overlay Debugging (Debugging with GDB)">

  21. <meta name="keywords" content="Automatic Overlay Debugging (Debugging with GDB)">

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  26. <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">

  27. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  28. <link href="Overlays.html#Overlays" rel="up" title="Overlays">

  29. <link href="Overlay-Sample-Program.html#Overlay-Sample-Program" rel="next" title="Overlay Sample Program">

  30. <link href="Overlay-Commands.html#Overlay-Commands" rel="prev" title="Overlay Commands">

  31. <style type="text/css">

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  62. <body lang="en">

  63. <a name="Automatic-Overlay-Debugging"></a>

  64. <div class="header">

  65. <p>

  66. 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>

  67. </div>

  68. <hr>

  69. <a name="Automatic-Overlay-Debugging-1"></a>

  70. <h3 class="section">14.3 Automatic Overlay Debugging</h3>

  71. <a name="index-automatic-overlay-debugging"></a>

  72. 

  73. <p><small>GDB</small> can automatically track which overlays are mapped and which

  74. are not, given some simple co-operation from the overlay manager in the

  75. inferior.  If you enable automatic overlay debugging with the

  76. <code>overlay auto</code> command (see <a href="Overlay-Commands.html#Overlay-Commands">Overlay Commands</a>), <small>GDB</small>

  77. looks in the inferior&rsquo;s memory for certain variables describing the

  78. current state of the overlays.

  79. </p>

  80. <p>Here are the variables your overlay manager must define to support

  81. <small>GDB</small>&rsquo;s automatic overlay debugging:

  82. </p>

  83. <dl compact="compact">

  84. <dt><code>_ovly_table</code>:</dt>

  85. <dd><p>This variable must be an array of the following structures:

  86. </p>

  87. <div class="smallexample">

  88. <pre class="smallexample">struct

  89. {

  90.   /* The overlay's mapped address.  */

  91.   unsigned long vma;

  92. 

  93.   /* The size of the overlay, in bytes.  */

  94.   unsigned long size;

  95. 

  96.   /* The overlay's load address.  */

  97.   unsigned long lma;

  98. 

  99.   /* Non-zero if the overlay is currently mapped;

  100.      zero otherwise.  */

  101.   unsigned long mapped;

  102. }

  103. </pre></div>

  104. 

  105. </dd>

  106. <dt><code>_novlys</code>:</dt>

  107. <dd><p>This variable must be a four-byte signed integer, holding the total

  108. number of elements in <code>_ovly_table</code>.

  109. </p>

  110. </dd>

  111. </dl>

  112. 

  113. <p>To decide whether a particular overlay is mapped or not, <small>GDB</small>

  114. looks for an entry in <code><span class="nolinebreak">_ovly_table</span></code><!-- /@w --> whose <code>vma</code> and

  115. <code>lma</code> members equal the VMA and LMA of the overlay&rsquo;s section in the

  116. executable file.  When <small>GDB</small> finds a matching entry, it consults

  117. the entry&rsquo;s <code>mapped</code> member to determine whether the overlay is

  118. currently mapped.

  119. </p>

  120. <p>In addition, your overlay manager may define a function called

  121. <code>_ovly_debug_event</code>.  If this function is defined, <small>GDB</small>

  122. will silently set a breakpoint there.  If the overlay manager then

  123. calls this function whenever it has changed the overlay table, this

  124. will enable <small>GDB</small> to accurately keep track of which overlays

  125. are in program memory, and update any breakpoints that may be set

  126. in overlays.  This will allow breakpoints to work even if the

  127. overlays are kept in ROM or other non-writable memory while they

  128. are not being executed.

  129. </p>

  130. <hr>

  131. <div class="header">

  132. <p>

  133. 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>

  134. </div>

  135. 

  136. 

  137. 

  138. </body>

  139. </html>