Date: Thu, 23 Aug 2007 14:22:15 +0200
From: Andi Kleen <ak@suse.de>
To: Andy Whitcroft <apw@shadowen.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mel@csn.ul.ie>,
       linux-kernel@vger.kernel.org, Sam Ravnborg <sam@ravnborg.org>,
       Andi Kleen <ak@suse.de>
Subject: Re: 2.6.23-rc3-mm1
Message-ID: <20070823122215.GS8058@bingen.suse.de>
References: <20070822020648.5ea3a612.akpm@linux-foundation.org> <46CC6FB2.1010801@csn.ul.ie> <20070822111029.46db0ab7.akpm@linux-foundation.org> <20070823120318.GA7506@shadowen.org>
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On Thu, Aug 23, 2007 at 01:03:18PM +0100, Andy Whitcroft wrote:
> It seems that this is a problem caused by the way we check for
> compiler options in x86_64.  Each compiler flag is checked for
> individually and if available added to cflags-y, later that is
> added to CFLAGS.  However, this means that each flag is checked
> in total isolation.  On x86_64 (on this compiler at least) the
> -mpreferred-stack-boundary and -m{32,64} flags are actually mutually
> dependant, the alignment constraints vary based on the word size.
> This leads to the compile failure:
> 
>     # gcc -mpreferred-stack-boundary=3 -S -xc /dev/null  -o FOO
>     # echo $?
>     0
>     # gcc -m64 -mpreferred-stack-boundary=3 -S -xc /dev/null  -o FOO
>     /dev/null:1: error: -mpreferred-stack-boundary=3 is not between 4 and 12
>     # echo $?
>     1
> 
> In the main Makefile we always add each flag directly to CFLAGS
> which means we check them all in combination, perhaps this is
> prudent here also?  Either way I suspect that changing the -m64
> check to add itself directly to CFLAGS will fix this us.

Ok that makes sense. Most people don't see it because they don't
need -m64. 

I fixed it up with 
ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/cflags-probe
and then
ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/less-stack-alignment
(replacement for the mm patch)

Can you test?

-Andi

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