linux-kernel - Re: 2.6.23-rc3-mm1

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Date:	Thu, 23 Aug 2007 14:22:15 +0200
From:	Andi Kleen <ak@...e.de>
To:	Andy Whitcroft <apw@...dowen.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	Sam Ravnborg <sam@...nborg.org>, Andi Kleen <ak@...e.de>
Subject: Re: 2.6.23-rc3-mm1

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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