The following patch align stack for mcount and there should be no
problems with unwind as ix86_frame_pointer_required is true when
crtl->profile is true and flag_fentry is false (we call mcount after
function prolog).
When flag_fentry is true it is set to false in 32bit PIC mode:
if (!TARGET_64BIT_P (opts->x_ix86_isa_flags) && opts->x_flag_pic)
{
if (opts->x_flag_fentry > 0)
sorry ("-mfentry isn%'t supported for 32-bit in combination "
"with -fpic");
opts->x_flag_fentry = 0;
}
2014-10-24 Evgeny Stupachenko <evstu...@gmail.com>
PR target/63534
* config/i386/i386.c (x86_function_profiler): Add GOT register init
for mcount call.
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 6235c4f..2dff29c 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -39124,13 +39124,22 @@ x86_function_profiler (FILE *file, int
labelno ATTRIBUTE_UNUSED)
else
x86_print_call_or_nop (file, mcount_name);
}
+ /* At this stage we can't detrmine where GOT register is, as RA can allocate
+ it to any hard register. Therefore we need to set it once again. */
else if (flag_pic)
{
+ pic_labels_used |= 1 << BX_REG;
+ fprintf (file,"\tsub\t$16, %%esp\n");
+ fprintf (file,"\tmovl\t%%ebx, (%%esp)\n");
+ fprintf (file,"\tcall\t__x86.get_pc_thunk.bx\n");
+ fprintf (file,"\taddl\t$_GLOBAL_OFFSET_TABLE_, %%ebx\n");
#ifndef NO_PROFILE_COUNTERS
fprintf (file, "\tleal\t%sP%d@GOTOFF(%%ebx),%%"
PROFILE_COUNT_REGISTER "\n",
LPREFIX, labelno);
#endif
fprintf (file, "1:\tcall\t*%s@GOT(%%ebx)\n", mcount_name);
+ fprintf (file,"\tmovl\t(%%esp), %%ebx\n");
+ fprintf (file,"\tadd\t$16, %%esp\n");
}
else
{
On Fri, Oct 17, 2014 at 6:38 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> On Fri, Oct 17, 2014 at 06:30:42PM +0400, Evgeny Stupachenko wrote:
>> Hi,
>>
>> The patch fixes profile in 32bits PIC mode (only -p option affected).
>>
>> x86 bootstrap, make check passed
>>
>> spec2000 o2 -p train data on Corei7:
>> CINT -5%
>> CFP +1,5
>> compared to a compiler before "enabling ebx".
>>
>> There is a potential performance improve after the patch applied
>> suggested by Jakub:
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63534#c8
>> There is opened bug on this: PR63527. However the fix of the bug is
>> more complicated.
>>
>> Is it ok?
>
> Unfortunately I don't think it is ok.
> 1) you don't set the appropriate bit in pic_labels_used (for ebx)
> 2) more importantly, it causes the stack to be misaligned (i.e. violating
> ABI) for the _mcount call, and, break unwind info.
>
>> 2014-10-16 Evgeny Stupachenko <evstu...@gmail.com>
>>
>> PR target/63534
>> * config/i386/i386.c (x86_function_profiler): Add GOT register init
>> for mcount call.
>>
>> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
>> index a3ca2ed..5117572 100644
>> --- a/gcc/config/i386/i386.c
>> +++ b/gcc/config/i386/i386.c
>> @@ -39119,11 +39126,15 @@ x86_function_profiler (FILE *file, int
>> labelno ATTRIBUTE_UNUSED)
>> }
>> else if (flag_pic)
>> {
>> + fprintf (file,"\tpush\t%%ebx\n");
>> + fprintf (file,"\tcall\t__x86.get_pc_thunk.bx\n");
>> + fprintf (file,"\taddl\t$_GLOBAL_OFFSET_TABLE_, %%ebx\n");
>> #ifndef NO_PROFILE_COUNTERS
>> fprintf (file, "\tleal\t%sP%d@GOTOFF(%%ebx),%%"
>> PROFILE_COUNT_REGISTER "\n",
>> LPREFIX, labelno);
>> #endif
>> fprintf (file, "1:\tcall\t*%s@GOT(%%ebx)\n", mcount_name);
>> + fprintf (file,"\tpop\t%%ebx\n");
>> }
>> else
>> {
>
> Jakub
