From: Randy Dunlap <rdunlap@xenotime.net>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
Andi Kleen <andi@firstfloor.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: PATCH] Use -mpreferred-stack-boundary=3 on x86-64 if supported
Date: Sat, 23 Jun 2012 15:57:44 -0700 [thread overview]
Message-ID: <4FE649E8.5090103@xenotime.net> (raw)
In-Reply-To: <CAMe9rOrH6_0mDzCnfTtydEVCn11A9wqn7MD0xHz9dOhPw1WZ1w@mail.gmail.com>
On 06/23/2012 09:49 AM, H.J. Lu wrote:
> On Sat, Jun 23, 2012 at 9:17 AM, H. Peter Anvin <hpa@zytor.com> wrote:
>> To keep gcc from paddong the stack to maintain a nonexistent alignment.
>>
>> Andi Kleen <andi@firstfloor.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.
>
>
Some (most) of this explanation needs to be in the patch description.
--
~Randy
next prev parent reply other threads:[~2012-06-23 22:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-23 16:06 PATCH] Use -mpreferred-stack-boundary=3 on x86-64 if supported H.J. Lu
2012-06-23 16:13 ` Andi Kleen
2012-06-23 16:17 ` H. Peter Anvin
2012-06-23 16:49 ` H.J. Lu
2012-06-23 22:57 ` Randy Dunlap [this message]
2012-06-23 19:27 ` Andi Kleen
2012-06-23 19:45 ` H. Peter Anvin
2012-06-24 3:13 ` [tip:x86/build] x86-64, gcc: Use -mpreferred-stack-boundary= 3 " tip-bot for H.J. Lu
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