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Re: [RFA] epilogue unwinder for i386 (reverse 1/2)


I tried this patch with ubuntu i386.  Everything is OK.

Thanks,
Hui

On Sat, Jul 4, 2009 at 08:34, Michael Snyder<msnyder@vmware.com> wrote:
> Michael Snyder wrote:
>>
>> This comes out of a discussion with Daniel, about how gcc
>> does not generate the right dwarf info to allow correct
>> frame unwinding in function epilogues, causing frame_unwind
>> to return bad results.
>>
>> It's necessary for reverse-step, which will frequently step
>> backward to the return instruction of a function. ?But it also
>> provides an improvement for forward debugging, in that now,
>> without this change, if you STEPI until you are at the return
>> instruction, you will get a bad backtrace.
>>
>> The infrun changes that take advantage of this patch will follow
>> separately.
>>
>> Michael
>
> Oops, the patch wasn't meant to have that "#if 0" in it...
> corrected patch below.
>
>
>
> 2009-07-03 ?Michael Snyder ?<msnyder@vmware.com>
>
> ? ? ? ?* i386-tdep.c: Add a frame unwinder for function epilogues.
> ? ? ? ?(i386_in_function_epilogue_p): New function.
> ? ? ? ?(i386_epilogue_frame_sniffer): New function.
> ? ? ? ?(i386_epilogue_frame_cache): New function.
> ? ? ? ?(i386_epilogue_frame_this_id): New function.
> ? ? ? ?(i386_epilogue_frame_unwind): New struct frame_unwind.
> ? ? ? ?(i386_gdbarch_init): Hook the new unwinder.
>
> Index: i386-tdep.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/i386-tdep.c,v
> retrieving revision 1.280
> diff -u -p -r1.280 i386-tdep.c
> --- i386-tdep.c 2 Jul 2009 17:25:54 -0000 ? ? ? 1.280
> +++ i386-tdep.c 4 Jul 2009 00:37:12 -0000
> @@ -1487,6 +1487,89 @@ static const struct frame_unwind i386_fr
> ? NULL,
> ? default_frame_sniffer
> ?};
> +
> +/* Normal frames, but in a function epilogue. ?*/
> +
> +/* The epilogue is defined here as the RET instruction, which will
> + ? follow any instruction such as LEAVE or POP EBP that destroys the
> + ? function's stack frame. ?*/
> +
> +static int
> +i386_in_function_epilogue_p (struct gdbarch *gdbarch, CORE_ADDR pc)
> +{
> + ?gdb_byte insn;
> +
> + ?if (target_read_memory (pc, &insn, 1) != 0)
> + ? ?return 0; ?/* Can't read memory at pc. ?*/
> +
> + ?if (insn != 0xc3) ? ?/* RET */
> + ? ?return 0;
> +
> + ?return 1;
> +}
> +
> +static int
> +i386_epilogue_frame_sniffer (const struct frame_unwind *self,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ?struct frame_info *this_frame,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ?void **this_prologue_cache)
> +{
> + ?if (frame_relative_level (this_frame) == 0)
> + ? ?return i386_in_function_epilogue_p (get_frame_arch (this_frame),
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? get_frame_pc (this_frame));
> + ?else
> + ? ?return 0;
> +}
> +
> +static struct i386_frame_cache *
> +i386_epilogue_frame_cache (struct frame_info *this_frame, void
> **this_cache)
> +{
> + ?struct gdbarch *gdbarch = get_frame_arch (this_frame);
> + ?enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
> + ?struct i386_frame_cache *cache;
> + ?gdb_byte buf[4];
> +
> + ?if (*this_cache)
> + ? ?return *this_cache;
> +
> + ?cache = i386_alloc_frame_cache ();
> + ?*this_cache = cache;
> +
> + ?/* Cache base will be ESP plus cache->sp_offset (-4). ?*/
> + ?get_frame_register (this_frame, I386_ESP_REGNUM, buf);
> + ?cache->base = extract_unsigned_integer (buf, 4,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? byte_order) + cache->sp_offset;
> +
> + ?/* Cache pc will be the frame func. ?*/
> + ?cache->pc = get_frame_pc (this_frame);
> +
> + ?/* The saved ESP will be at cache->base plus 8. ?*/
> + ?cache->saved_sp = cache->base + 8;
> +
> + ?/* The saved EIP will be at cache->base plus 4. ?*/
> + ?cache->saved_regs[I386_EIP_REGNUM] = cache->base + 4;
> +
> + ?return cache;
> +}
> +
> +static void
> +i386_epilogue_frame_this_id (struct frame_info *this_frame,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ?void **this_cache,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ?struct frame_id *this_id)
> +{
> + ?struct i386_frame_cache *cache = i386_epilogue_frame_cache (this_frame,
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? this_cache);
> +
> + ?(*this_id) = frame_id_build (cache->base + 8, cache->pc);
> +}
> +
> +static const struct frame_unwind i386_epilogue_frame_unwind =
> +{
> + ?NORMAL_FRAME,
> + ?i386_epilogue_frame_this_id,
> + ?i386_frame_prev_register,
> + ?NULL,
> + ?i386_epilogue_frame_sniffer
> +};
>
>
> ?/* Signal trampolines. ?*/
> @@ -5328,7 +5411,10 @@ i386_gdbarch_init (struct gdbarch_info i
>
> ? /* Helper for function argument information. ?*/
> ? set_gdbarch_fetch_pointer_argument (gdbarch, i386_fetch_pointer_argument);
> -
> +#if 0
> + ?/* Hook the function epilogue frame unwinder. ?*/
> + ?frame_unwind_append_unwinder (gdbarch, &i386_epilogue_frame_unwind);
> +#endif
> ? /* Hook in the DWARF CFI frame unwinder. ?*/
> ? dwarf2_append_unwinders (gdbarch);
>
>
>


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