What does the FreeBSD/i386 ABI say about stack alignment?

[Peter Blok]

Hi Ryan,

Well I think gcc should not generate movdqa if it cannot guarantee the area
it is working on is aligned. If the stack is not aligned, it should generate
­ probably less efficient ­ code that works.

What is this area, if it is not a local variable allocated somewhere? Is it
some sort of stack probing? Is alloca used? Are variable length arrays used?

Peter




On 1/14/11 13:11 PM, "Ryan Stone" <rysto32 at gmail.com> wrote:

> On Fri, Jan 14, 2011 at 3:52 AM, Peter Blok <peter.blok at bsd4all.org> wrote:
>> > Hi,
>> >
>> > I¹m probably missing something but if you require a stack variable to be
>> > aligned why not use a type attribute like __attribute__ ((aligned (8)))
>> >
>> > Peter
> 
> In my case I had no stack variable that required alignment.  gcc
> issued some movdqa instructions in order to initialize a memory region
> on the stack to all-zeros.
>