Re: [RFC/TileGX 2/6] simplify the handling of skip prologue for plt stub

[Jiong Wang <jiwang at tilera dot com>]

On 03/01/2013 07:30 PM, Pedro Alves wrote
> I do agree that trying to find the end of the prologue of a plt stub is futile.  We know plt stubs
> aren't "normal" functions, and don't have prologues.
>
> But, I do think the prologue analyzer still has a problem.  You should see this
> same issue with any small normal function (with no debug info) that happens to
> end up close enough to the end of its section.

  I agree, but normally there will be crtn* files which will placed 
after the noraml
function, so that the distance to the section with different alignment, 
for example .eh_frame_hdr,
will be long enough to prevent this happen.

> I suggest limiting the end address of the analysis with something like
> in tilegx_skip_prologue
>
> + /* Don't straddle a section boundary.  */
> + s = find_pc_section (start_pc);
> + end_pc = start_pc + 8 * TILEGX_BUNDLE_SIZE_IN_BYTES;
> + if (s != NULL)
> +   end_pc = min (end_pc, obj_section_endaddr (s));
>
>    return tilegx_analyze_prologue (gdbarch,
> 				  start_pc,
> -				  start_pc + 8 * TILEGX_BUNDLE_SIZE_IN_BYTES,
> +				  end_pc,
>
> and also, make tilegx_analyze_prologue never touch memory
> over end_addr.  It doesn't seem to take that care currently?
   I think this fix make sense, and tilegx_analyze_prologue has glitch, 
it will ignore "end_pc" to some extent.
 the prefetch buffer in tilegx_analyze_prologue should consider the end_pc.

   I have tested the new patch by rerun dejagnu, please review, thanks.

   gdb/ChangeLog:

        * tilegx-tdep.c (tilegx_analyze_prologue): Improve the evaluation
        of "instbuf_size".
        (tilegx_skip_prologue): Improve the evaluation of the end address
        for prologue analyze.

--
Regards,
Jiong. Wang
Tilera Corporation.

---
 gdb/tilegx-tdep.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/gdb/tilegx-tdep.c b/gdb/tilegx-tdep.c
index f45c20f..b398507 100644
--- a/gdb/tilegx-tdep.c
+++ b/gdb/tilegx-tdep.c
@@ -433,6 +433,8 @@ tilegx_analyze_prologue (struct gdbarch* gdbarch,
 
 	  if (instbuf_size > size_on_same_page)
 	    instbuf_size = size_on_same_page;
+
+	  instbuf_size = min (instbuf_size, (end_addr - next_addr));
 	  instbuf_start = next_addr;
 
 	  status = safe_frame_unwind_memory (next_frame, instbuf_start,
@@ -745,7 +747,8 @@ tilegx_analyze_prologue (struct gdbarch* gdbarch,
 static CORE_ADDR
 tilegx_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
 {
-  CORE_ADDR func_start;
+  CORE_ADDR func_start, end_pc;
+  struct obj_section *s = NULL;
 
   /* This is the preferred method, find the end of the prologue by
      using the debugging information.  */
@@ -758,10 +761,16 @@ tilegx_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
         return max (start_pc, post_prologue_pc);
     }
 
+  /* Don't straddle a section boundary.  */
+  s = find_pc_section (start_pc);
+  end_pc = start_pc + 8 * TILEGX_BUNDLE_SIZE_IN_BYTES;
+  if (s != NULL)
+    end_pc = min (end_pc, obj_section_endaddr (s));
+
   /* Otherwise, try to skip prologue the hard way.  */
   return tilegx_analyze_prologue (gdbarch,
 				  start_pc,
-				  start_pc + 8 * TILEGX_BUNDLE_SIZE_IN_BYTES,
+				  end_pc,
 				  NULL, NULL);
 }