From: Andi Kleen <ak@suse.de>
Organization: SUSE Linux Products GmbH, Nuernberg, GF: Markus Rex, HRB 16746 (AG Nuernberg)
To: Jakub Jelinek <jakub@redhat.com>
Subject: Re: [PATCH] [20/45] x86_64: Use 8 byte stack alignment when possible
Date: Mon, 1 Oct 2007 00:07:59 +0200
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Cc: patches@x86-64.org, linux-kernel@vger.kernel.org
References: <200709211044.901175000@suse.de> <20070921204502.2C61D14EFF@wotan.suse.de> <20070921211935.GW2625@devserv.devel.redhat.com>
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On Friday 21 September 2007 23:19:35 Jakub Jelinek wrote:
> On Fri, Sep 21, 2007 at 10:45:02PM +0200, Andi Kleen wrote:
> > 
> > Kernel doesn't use SSE2, so it doesn't need 16 byte alignment. Also
> > the stack can be already unaligned so letting the compiler align
> > is useless. This may make some stack frames smaller.
> 
> Shouldn't sources that are compiled into the VDSO or VSYSCALL pages
> revert this to the default?

I see not reason. vdso/vsyscall don't contain any SSE code and also don't 
do any callbacks to other user code. Except for signals and signals 
already align the stack by themselves.

-Andi
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