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| <h4 class="subsection">29.4.2 Writing JIT Debug Info Readers</h4> |
| |
| <p><a name="index-writing-JIT-debug-info-readers-3156"></a> |
| As mentioned, a reader is essentially a shared object conforming to a |
| certain ABI. This ABI is described in <samp><span class="file">jit-reader.h</span></samp>. |
| |
| <p><samp><span class="file">jit-reader.h</span></samp> defines the structures, macros and functions |
| required to write a reader. It is installed (along with |
| <span class="sc">gdb</span>), in <samp><var>includedir</var><span class="file">/gdb</span></samp> where <var>includedir</var> is |
| the system include directory. |
| |
| <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>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-3157"></a> |
| <pre class="smallexample"> extern struct gdb_reader_funcs *gdb_init_reader (void); |
| </pre> |
| <p><a name="index-g_t_0040code_007bstruct-gdb_005freader_005ffuncs_007d-3158"></a> |
| <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 |
| |
| <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> |
| <p><a name="index-g_t_0040code_007bstruct-gdb_005fsymbol_005fcallbacks_007d-3159"></a><a name="index-g_t_0040code_007bstruct-gdb_005funwind_005fcallbacks_007d-3160"></a> |
| The callbacks are provided with another set of callbacks by |
| <span class="sc">gdb</span> 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. |
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