Date: Fri, 14 Jan 2011 13:52:29 +0100 From: Peter Blok <peter.blok@bsd4all.org> To: Ryan Stone <rysto32@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: What does the FreeBSD/i386 ABI say about stack alignment? Message-ID: <C956059D.389E8%peter.blok@bsd4all.org> In-Reply-To: <AANLkTim1KcKRXqrPoZDHOAKWtnVpUj6QBzJ-addyCvHe@mail.gmail.com>
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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@gmail.com> wrote: > On Fri, Jan 14, 2011 at 3:52 AM, Peter Blok <peter.blok@bsd4all.org> wrote: >> > Hi, >> > >> > Iım 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. >
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