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

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  18. <title>Writing JIT Debug Info Readers (Debugging with GDB)</title>

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  28. <link href="Custom-Debug-Info.html#Custom-Debug-Info" rel="up" title="Custom Debug Info">

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  62. <body lang="en">

  63. <a name="Writing-JIT-Debug-Info-Readers"></a>

  64. <div class="header">

  65. <p>

  66. Previous: <a href="Using-JIT-Debug-Info-Readers.html#Using-JIT-Debug-Info-Readers" accesskey="p" rel="prev">Using JIT Debug Info Readers</a>, Up: <a href="Custom-Debug-Info.html#Custom-Debug-Info" accesskey="u" rel="up">Custom Debug Info</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="Writing-JIT-Debug-Info-Readers-1"></a>

  70. <h4 class="subsection">29.4.2 Writing JIT Debug Info Readers</h4>

  71. <a name="index-writing-JIT-debug-info-readers"></a>

  72. 

  73. <p>As mentioned, a reader is essentially a shared object conforming to a

  74. certain ABI.  This ABI is described in <samp>jit-reader.h</samp>.

  75. </p>

  76. <p><samp>jit-reader.h</samp> defines the structures, macros and functions

  77. required to write a reader.  It is installed (along with

  78. <small>GDB</small>), in <samp><var>includedir</var>/gdb</samp> where <var>includedir</var> is

  79. the system include directory.

  80. </p>

  81. <p>Readers need to be released under a GPL compatible license.  A reader

  82. can be declared as released under such a license by placing the macro

  83. <code>GDB_DECLARE_GPL_COMPATIBLE_READER</code> in a source file.

  84. </p>

  85. <p>The entry point for readers is the symbol <code>gdb_init_reader</code>,

  86. which is expected to be a function with the prototype

  87. </p>

  88. <a name="index-gdb_005finit_005freader"></a>

  89. <div class="smallexample">

  90. <pre class="smallexample">extern struct gdb_reader_funcs *gdb_init_reader (void);

  91. </pre></div>

  92. 

  93. <a name="index-struct-gdb_005freader_005ffuncs"></a>

  94. 

  95. <p><code>struct gdb_reader_funcs</code> contains a set of pointers to callback

  96. functions.  These functions are executed to read the debug info

  97. generated by the JIT compiler (<code>read</code>), to unwind stack frames

  98. (<code>unwind</code>) and to create canonical frame IDs

  99. (<code>get_frame_id</code>).  It also has a callback that is called when the

  100. reader is being unloaded (<code>destroy</code>).  The struct looks like this

  101. </p>

  102. <div class="smallexample">

  103. <pre class="smallexample">struct gdb_reader_funcs

  104. {

  105.   /* Must be set to GDB_READER_INTERFACE_VERSION.  */

  106.   int reader_version;

  107. 

  108.   /* For use by the reader.  */

  109.   void *priv_data;

  110. 

  111.   gdb_read_debug_info *read;

  112.   gdb_unwind_frame *unwind;

  113.   gdb_get_frame_id *get_frame_id;

  114.   gdb_destroy_reader *destroy;

  115. };

  116. </pre></div>

  117. 

  118. <a name="index-struct-gdb_005fsymbol_005fcallbacks"></a>

  119. <a name="index-struct-gdb_005funwind_005fcallbacks"></a>

  120. 

  121. <p>The callbacks are provided with another set of callbacks by

  122. <small>GDB</small> to do their job.  For <code>read</code>, these callbacks are

  123. passed in a <code>struct gdb_symbol_callbacks</code> and for <code>unwind</code>

  124. and <code>get_frame_id</code>, in a <code>struct gdb_unwind_callbacks</code>.

  125. <code>struct gdb_symbol_callbacks</code> has callbacks to create new object

  126. files and new symbol tables inside those object files.  <code>struct

  127. gdb_unwind_callbacks</code> has callbacks to read registers off the current

  128. frame and to write out the values of the registers in the previous

  129. frame.  Both have a callback (<code>target_read</code>) to read bytes off the

  130. target&rsquo;s address space.

  131. </p>

  132. <hr>

  133. <div class="header">

  134. <p>

  135. Previous: <a href="Using-JIT-Debug-Info-Readers.html#Using-JIT-Debug-Info-Readers" accesskey="p" rel="prev">Using JIT Debug Info Readers</a>, Up: <a href="Custom-Debug-Info.html#Custom-Debug-Info" accesskey="u" rel="up">Custom Debug Info</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>

  136. </div>

  137. 

  138. 

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