linux-kernel - Re: [PATCH 1/3] make page-aligned data and bss less fragile

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Date:	Thu, 29 May 2008 13:16:31 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH 1/3] make page-aligned data and bss less fragile

On Wed, May 28, 2008 at 05:04:34PM +0100, Jeremy Fitzhardinge wrote:
> Making a variable page-aligned by using
> __attribute__((section(".data.page_aligned"))) is fragile because if
> sizeof(variable) is not also a multiple of page size, it leaves
> variables in the remainder of the section unaligned.
> 
> This patch introduces two new qualifiers, __page_aligned_data and
> __page_aligned_bss to set the section *and* the alignment of
> variables.  This makes page-aligned variables more robust because the
> linker will make sure they're aligned properly.  Unfortunately it
> requires *all* page-aligned data to use these macros...
> 
> It also updates arch/x86's use of page-aligned variables, since its
> the heaviest user of them in the kernel.  The change to
> arch/x86/xen/mmu.c fixes an actual bug, but the rest are cleanups
> and to set a precident.
> 
> [ I don't know if this would be easier to manage by splitting the
>  x86 part out from the common part. Two following patches apply to
>  powerpc and sh; they're purely decorative. ]
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> Cc: Paul Mundt <lethal@...ux-sh.org>
> Cc: Paul Mackerras <paulus@...ba.org>

Acked-by: Paul Mundt <lethal@...ux-sh.org>
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