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 <a name="Writing-JIT-Debug-Info-Readers"></a>
 <div class="header">
 <p>
 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>
 </div>
 <hr>
 <a name="Writing-JIT-Debug-Info-Readers-1"></a>
 <h4 class="subsection">29.4.2 Writing JIT Debug Info Readers</h4>
 <a name="index-writing-JIT-debug-info-readers"></a>

 <p>As mentioned, a reader is essentially a shared object conforming to a
 certain ABI.  This ABI is described in <samp>jit-reader.h</samp>.
 </p>
 <p><samp>jit-reader.h</samp> defines the structures, macros and functions
 required to write a reader.  It is installed (along with
 <small>GDB</small>), in <samp><var>includedir</var>/gdb</samp> where <var>includedir</var> is
 the system include directory.
 </p>
 <p>Readers need to be released under a GPL compatible license.  A reader
 can be declared as released under such a license by placing the macro
 <code>GDB_DECLARE_GPL_COMPATIBLE_READER</code> in a source file.
 </p>
 <p>The entry point for readers is the symbol <code>gdb_init_reader</code>,
 which is expected to be a function with the prototype
 </p>
 <a name="index-gdb_005finit_005freader"></a>
 <div class="smallexample">
 <pre class="smallexample">extern struct gdb_reader_funcs *gdb_init_reader (void);
 </pre></div>

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

 <p><code>struct gdb_reader_funcs</code> contains a set of pointers to callback
 functions.  These functions are executed to read the debug info
 generated by the JIT compiler (<code>read</code>), to unwind stack frames
 (<code>unwind</code>) and to create canonical frame IDs
 (<code>get_Frame_id</code>).  It also has a callback that is called when the
 reader is being unloaded (<code>destroy</code>).  The struct looks like this
 </p>
 <div class="smallexample">
 <pre class="smallexample">struct gdb_reader_funcs
 {
   /* Must be set to GDB_READER_INTERFACE_VERSION.  */
   int reader_version;

   /* For use by the reader.  */
   void *priv_data;

   gdb_read_debug_info *read;
   gdb_unwind_frame *unwind;
   gdb_get_frame_id *get_frame_id;
   gdb_destroy_reader *destroy;
 };
 </pre></div>

 <a name="index-struct-gdb_005fsymbol_005fcallbacks"></a>
 <a name="index-struct-gdb_005funwind_005fcallbacks"></a>

 <p>The callbacks are provided with another set of callbacks by
 <small>GDB</small> to do their job.  For <code>read</code>, these callbacks are
 passed in a <code>struct gdb_symbol_callbacks</code> and for <code>unwind</code>
 and <code>get_frame_id</code>, in a <code>struct gdb_unwind_callbacks</code>.
 <code>struct gdb_symbol_callbacks</code> has callbacks to create new object
 files and new symbol tables inside those object files.  <code>struct
 gdb_unwind_callbacks</code> has callbacks to read registers off the current
 frame and to write out the values of the registers in the previous
 frame.  Both have a callback (<code>target_read</code>) to read bytes off the
 target&rsquo;s address space.
 </p>
 <hr>
 <div class="header">
 <p>
 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>
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	<a name="Writing-JIT-Debug-Info-Readers"></a>
	<div class="header">
	<p>
	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>   [<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>
	</div>
	<hr>
	<a name="Writing-JIT-Debug-Info-Readers-1"></a>
	<h4 class="subsection">29.4.2 Writing JIT Debug Info Readers</h4>
	<a name="index-writing-JIT-debug-info-readers"></a>

	<p>As mentioned, a reader is essentially a shared object conforming to a
	certain ABI. This ABI is described in <samp>jit-reader.h</samp>.
	</p>
	<p><samp>jit-reader.h</samp> defines the structures, macros and functions
	required to write a reader. It is installed (along with
	<small>GDB</small>), in <samp><var>includedir</var>/gdb</samp> where <var>includedir</var> is
	the system include directory.
	</p>
	<p>Readers need to be released under a GPL compatible license. A reader
	can be declared as released under such a license by placing the macro
	<code>GDB_DECLARE_GPL_COMPATIBLE_READER</code> in a source file.
	</p>
	<p>The entry point for readers is the symbol <code>gdb_init_reader</code>,
	which is expected to be a function with the prototype
	</p>
	<a name="index-gdb_005finit_005freader"></a>
	<div class="smallexample">
	<pre class="smallexample">extern struct gdb_reader_funcs *gdb_init_reader (void);
	</pre></div>

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

	<p><code>struct gdb_reader_funcs</code> contains a set of pointers to callback
	functions. These functions are executed to read the debug info
	generated by the JIT compiler (<code>read</code>), to unwind stack frames
	(<code>unwind</code>) and to create canonical frame IDs
	(<code>get_Frame_id</code>). It also has a callback that is called when the
	reader is being unloaded (<code>destroy</code>). The struct looks like this
	</p>
	<div class="smallexample">
	<pre class="smallexample">struct gdb_reader_funcs
	{
	/* Must be set to GDB_READER_INTERFACE_VERSION. */
	int reader_version;

	/* For use by the reader. */
	void *priv_data;

	gdb_read_debug_info *read;
	gdb_unwind_frame *unwind;
	gdb_get_frame_id *get_frame_id;
	gdb_destroy_reader *destroy;
	};
	</pre></div>

	<a name="index-struct-gdb_005fsymbol_005fcallbacks"></a>
	<a name="index-struct-gdb_005funwind_005fcallbacks"></a>

	<p>The callbacks are provided with another set of callbacks by
	<small>GDB</small> to do their job. For <code>read</code>, these callbacks are
	passed in a <code>struct gdb_symbol_callbacks</code> and for <code>unwind</code>
	and <code>get_frame_id</code>, in a <code>struct gdb_unwind_callbacks</code>.
	<code>struct gdb_symbol_callbacks</code> has callbacks to create new object
	files and new symbol tables inside those object files. <code>struct
	gdb_unwind_callbacks</code> has callbacks to read registers off the current
	frame and to write out the values of the registers in the previous
	frame. Both have a callback (<code>target_read</code>) to read bytes off the
	target’s address space.
	</p>
	<hr>
	<div class="header">
	<p>
	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>   [<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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