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

Jiong Wang
2013-03-01T14:08:16Z

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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.

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---
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);
}