[Mesa-dev] [PATCH] mesa: Ensure stack is realigned on x86.

[Jose Fonseca]

On 02/12/14 21:10, Brian Paul wrote:
> On 12/02/2014 01:27 PM, Jose Fonseca wrote:
>> From: José Fonseca <jfonseca at vmware.com>
>>
>> Nowadays GCC assumes stack pointer is 16-byte aligned even on 32-bits,
>> but that is an assumption OpenGL drivers (or any dynamic library for
>> that matter) can affort to make as there are many closed- and open-
>
> can or cannot?

Oops. "cannot".

>
> affort -> afford

Thanks.

>
>
>> source application binaries out there that only assume 4-byte stack
>> alignment.
>>
>> This fix uses force_align_arg_pointer GCC attribute, and is only a
>> stop-gap measure.
>>
>> The right fix would be to pass -mstackrealign or
>> -mincoming-stack-boundary=2 to all source fails that use any -msse*
>> option, as there is no way to guarantee if/when GCC will decide to spill
>> SSE registers to the stack.
>>
>> https://bugs.freedesktop.org/show_bug.cgi?id=86788
>> ---
>>   src/mesa/main/sse_minmax.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/src/mesa/main/sse_minmax.c b/src/mesa/main/sse_minmax.c
>> index 222ac14..93cf2a6 100644
>> --- a/src/mesa/main/sse_minmax.c
>> +++ b/src/mesa/main/sse_minmax.c
>> @@ -31,6 +31,9 @@
>>   #include <stdint.h>
>>
>>   void
>> +#if !defined(__x86_64__)
>> +   __attribute__((force_align_arg_pointer))
>> +#endif
>>   _mesa_uint_array_min_max(const unsigned *ui_indices, unsigned
>> *min_index,
>>                            unsigned *max_index, const unsigned count)
>>   {
>>
>
> I don't remember if this code is compiled with MSVC.  If so, do you also
> need a gcc check for the __attribute__ part?

No, it doesn't compile on MSVC yet -- there are a few non-standard GCC 
"__attribute__" below already, plus MSVC doesn't define __SSE4_1__, so 
the whole thing would be no-oped.

Getting this to compile on MSVC/MinGW is something I rather leave to 
another time, as it will involve updating scons to set -msse4.1 
correctly, and port a few defines from 
src/gallium/include/pipe/p_config.h and 
src/gallium/auxiliary/util/u_sse.h for portability.


Jose