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Message-ID: <87wswwsjcz.fsf@depni.sinp.msu.ru>
Date: Thu, 19 Jul 2007 15:50:20 +0400
From: Serge Belyshev <belyshev@...ni.sinp.msu.ru>
To: Andi Kleen <ak@...e.de>
Cc: patches@...-64.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [2/58] x86_64: Tell gcc to only align stack to 8 bytes
Andi Kleen <ak@...e.de> writes:
> Don't need 16 byte alignment because kernel doesn't use SSE2
>
...
> cflags-y += -maccumulate-outgoing-args
> +cflags-y += -mpreferred-stack-boundary=4
>
>From gcc manpage:
-mpreferred-stack-boundary=num
Attempt to keep the stack boundary aligned to a 2 raised to num
byte boundary. If -mpreferred-stack-boundary is not specified, the
default is 4 (16 bytes or 128 bits), except when optimizing for
code size (-Os), in which case the default is the minimum correct
alignment (4 bytes for x86, and 8 bytes for x86-64).
So -mpreferred-stack-boundary=4 is the default and to align stack
to 8 bytes you want -mpreferred-stack-boundary=3, not 4, IIUC.
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