linux-kernel - Re: [PATCH] FLAT: allow arches to declare a larger alignment than the slab

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Message-ID: <20100526073334.GD26696@linux-sh.org>
Date:	Wed, 26 May 2010 16:33:34 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Jie Zhang <jie@...esourcery.com>, uclinux-dev@...inux.org,
	David Howells <dhowells@...hat.com>,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	microblaze-uclinux@...e.uq.edu.au, Michal Simek <monstr@...str.eu>,
	linux-m32r@...linux-m32r.org,
	Hirokazu Takata <takata@...ux-m32r.org>,
	linux-kernel@...r.kernel.org,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH] FLAT: allow arches to declare a larger alignment than the slab

On Wed, May 26, 2010 at 03:23:02AM -0400, Mike Frysinger wrote:
> On Wed, May 26, 2010 at 02:59, Geert Uytterhoeven wrote:
> > From looking at <linux/flat.h>, it looks like the FLAT binary format
> > doesn't contain any
> > alignment information? So if I put __attribute__((aligned(4096))) in a
> > file, there's still
> > no guarantee it will actually be in memory at a 4Ki-aligned address?
> 
> i believe that is correct.  FLAT behavior today provides alignment of
> either sizeof(unsigned long) or ARCH_SLAB_MINALIGN.
> 
> i imagine something like this would work today because everyone
> defines it to a constant:
> -#ifdef ARCH_SLAB_MINALIGN
> +#if defined(ARCH_SLAB_MINALIGN) && ARCH_SLAB_MINALIGN != 0
> but this would break if someone tried using gcc sizeof/alignof/etc...

alignof is used by SLUB/SLOB to set the ARCH_SLAB_MINALIGN value if the
architecture hasn't already specified one, so that wouldn't work.
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