linux-kernel - Re: PATCH] Use -mpreferred-stack-boundary=3 on x86-64 if supported

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Message-ID: <CAMe9rOrH6_0mDzCnfTtydEVCn11A9wqn7MD0xHz9dOhPw1WZ1w@mail.gmail.com>
Date:	Sat, 23 Jun 2012 09:49:22 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: PATCH] Use -mpreferred-stack-boundary=3 on x86-64 if supported

On Sat, Jun 23, 2012 at 9:17 AM, H. Peter Anvin <hpa@...or.com> wrote:
> To keep gcc from paddong the stack to maintain a nonexistent alignment.
>
> Andi Kleen <andi@...stfloor.org> wrote:
>
>>> This patch uses -mpreferred-stack-boundary=3 on x86-64 if it is
>>supported.
>>> I have been running 3.4 kernel compiled with this option for weeks.
>>
>>But why?
>>
>>All the SSE code in the kernel should adjust manually. And the other
>>code doesn't need it.
>>
>>Besides the entry points do not guarantee alignment.
>>
>>For the kernel it would be probably more useful to have a attribute
>>per function that forces alignment.

There was an attempt from you to do it in 2007:

http://lkml.indiana.edu/hypermail/linux/kernel/0708.2/2604.html
http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01697.html

But the gcc patch was never checked in.


-- 
H.J.
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