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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 19 Nov 2009 16:52:24 +0100
From:	Richard Guenther <richard.guenther@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	feng.tang@...el.com, "Fr??d??ric Weisbecker" <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>, jakub@...hat.com,
	gcc@....gnu.org
Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions

On Thu, Nov 19, 2009 at 4:49 PM, Richard Guenther
<richard.guenther@...il.com> wrote:
> On Thu, Nov 19, 2009 at 4:45 PM, H. Peter Anvin <hpa@...or.com> 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@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/