[patch 2/3] Align stack for SSE (PR tdep/14222)
Mark Kettenis
mark.kettenis@xs4all.nl
Wed Jun 13 21:20:00 GMT 2012
> Date: Wed, 13 Jun 2012 17:50:20 +0200
> From: Jan Kratochvil <jan.kratochvil@redhat.com>
>
> Hi,
>
> this is mostly independent patch. But it does not make sense to discuss
> alignment in [patch 3/3] when it has been already broken.
>
> http://groups.google.com/group/ia32-abi/browse_thread/thread/4f9b3e5069943bf1
> says that gcc-4.6 aligns stack to 32 bytes. I do not see it anywhere:
> 80482e8: 83 e4 f0 and $0xfffffff0,%esp
> It is aligned just to 16 bytes. Also checked that Intel CPU documentation
> does not require any more alignment than 16 bytes (sure it may be less
> effective but traps never occur). Therefore I consider amd64-tdep.c to be
> correct and I have not changed its existing 16-bytes alignment.
>
> gdb/
> 2012-06-13 Jan Kratochvil <jan.kratochvil@redhat.com>
>
> PR tdep/14222
> * i386-tdep.c (i386_push_dummy_call): Align to 16 bytes unconditionally.
Committed a better diff (see below) that removes the now unused
have_16_byte_aligned_arg variable.
> gdb/testsuite/
> 2012-06-13 Jan Kratochvil <jan.kratochvil@redhat.com>
>
> PR tdep/14222
> * gdb.arch/i386-sse-stack-align.S: New file.
> * gdb.arch/i386-sse-stack-align.c: New file.
> * gdb.arch/i386-sse-stack-align.exp: New file.
Can you commit this testsuite bit?
2012-06-13 Mark Kettenis <kettenis@gnu.org>
Jan Kratochvil <jan.kratochvil@redhat.com>
PR tdep/14222
* i386-tdep.c (i386_push_dummy_call): Unconditionally align the
stack on a 16-byte boundary.
Index: i386-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/i386-tdep.c,v
retrieving revision 1.352
diff -u -p -r1.352 i386-tdep.c
--- i386-tdep.c 13 Jun 2012 20:29:15 -0000 1.352
+++ i386-tdep.c 13 Jun 2012 21:15:44 -0000
@@ -2351,7 +2351,6 @@ i386_push_dummy_call (struct gdbarch *gd
for (write_pass = 0; write_pass < 2; write_pass++)
{
int args_space_used = 0;
- int have_16_byte_aligned_arg = 0;
if (struct_return)
{
@@ -2389,19 +2388,20 @@ i386_push_dummy_call (struct gdbarch *gd
else
{
if (i386_16_byte_align_p (value_enclosing_type (args[i])))
- {
- args_space = align_up (args_space, 16);
- have_16_byte_aligned_arg = 1;
- }
+ args_space = align_up (args_space, 16);
args_space += align_up (len, 4);
}
}
if (!write_pass)
{
- if (have_16_byte_aligned_arg)
- args_space = align_up (args_space, 16);
sp -= args_space;
+
+ /* The original System V ABI only requires word alignment,
+ but modern incarnations need 16-byte alignment in order
+ to support SSE. Since wasting a few bytes here isn't
+ harmful we unconditionally enforce 16-byte alignment. */
+ sp &= ~0xf;
}
}
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