Re: BUG: GCC-4.4.x changes the function frame on some functions

[Richard Guenther]

On Thu, Nov 19, 2009 at 4:49 PM, Richard Guenther
<richard.guenther@xxxxxxxxx> wrote:
> On Thu, Nov 19, 2009 at 4:45 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> On 11/19/2009 07:37 AM, Thomas Gleixner wrote:
>>>
>>> modified function start on a handful of functions only seen with gcc
>>> 4.4.x on x86 32 bit:
>>>
>>>       push   %edi
>>>       lea    0x8(%esp),%edi
>>>       and    $0xfffffff0,%esp
>>>       pushl  -0x4(%edi)
>>>       push   %ebp
>>>       mov    %esp,%ebp
>>>       ...
>>>       call   mcount
>>>
>>
>> The real questions is why we're aligning the stack in the kernel.  It is
>> probably not what we want -- we don't use SSE for anything but a handful
>> of special cases in the kernel, and we don't want the overhead.
>
> It's likely because you have long long vars on the stack which is
> faster when they are aligned.  -mno-stackrealign may do what you
> want (or may not, I have not checked).  I assume you already
> use -mpreferred-stack-boundary=2.

Just checking it seems you must be using -mincoming-stack-boundary=2
instead but keep the preferred stack boundary at 4.

Richard.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/