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

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Date:	Wed, 26 May 2010 09:24:52 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Mike Frysinger <vapier@...too.org>
CC:	uclinux-dev@...inux.org, David Howells <dhowells@...hat.com>,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	microblaze-uclinux@...e.uq.edu.au, linux-m32r@...linux-m32r.org,
	Hirokazu Takata <takata@...ux-m32r.org>,
	linux-kernel@...r.kernel.org,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Jie Zhang <jie.zhang@...log.com>
Subject: Re: [PATCH] FLAT: allow arches to declare a larger alignment than
 the slab

Mike Frysinger wrote:
> From: Jie Zhang <jie.zhang@...log.com>
> 
> The recent commit 1f0ce8b3dd667dca7 which moved the ARCH_SLAB_MINALIGN
> default into the global header inadvertently broke FLAT for a bunch of
> systems.  Blackfin systems now fail on any FLAT exec with:
> Unable to read code+data+bss, errno 14
> When your /init is a FLAT binary, obviously this can be annoying ;).
> 
> This stems from the alignment usage in the FLAT loader.  The behavior
> before was that FLAT would default to ARCH_SLAB_MINALIGN only if it was
> defined, and this was only defined by arches when they wanted a larger
> alignment value.  Otherwise it'd default to pointer alignment.  Arguably,
> this is kind of hokey that the FLAT is semi-abusing defines it shouldn't.
> 
> But let's ignore that and let arches declare a larger FLAT alignment
> specifically anyways as some arches are OK with the default slab alignment
> but need stricter FLAT alignments for shared FLAT libraries.
> 
> The nommu arches might want to check to see if they need to declare this
> in their headers as well ...

Microblaze noMMU contains this fault too. I registered it yesterday.
I will use the same fix as you when you find out the correct solution. :-)

Michal



> 
> Signed-off-by: Jie Zhang <jie.zhang@...log.com>
> Signed-off-by: Mike Frysinger <vapier@...too.org>
> ---
>  arch/blackfin/include/asm/flat.h |    2 ++
>  fs/binfmt_flat.c                 |   11 ++++++++---
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/blackfin/include/asm/flat.h b/arch/blackfin/include/asm/flat.h
> index c1314c5..cf2a73e 100644
> --- a/arch/blackfin/include/asm/flat.h
> +++ b/arch/blackfin/include/asm/flat.h
> @@ -11,6 +11,8 @@
>  
>  #include <asm/unaligned.h>
>  
> +#define ARCH_FLAT_DATA_ALIGN			0x20
> +
>  #define	flat_argvp_envp_on_stack()		0
>  #define	flat_old_ram_flag(flags)		(flags)
>  
> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
> index 49566c1..6906170 100644
> --- a/fs/binfmt_flat.c
> +++ b/fs/binfmt_flat.c
> @@ -56,12 +56,17 @@
>  #endif
>  
>  /*
> - * User data (stack, data section and bss) needs to be aligned
> - * for the same reasons as SLAB memory is, and to the same amount.
> + * User data (stack, data section and bss) needs to be aligned.
> + * If ARCH_FLAT_DATA_ALIGN is defined, use it.
> + */
> +#ifdef ARCH_FLAT_DATA_ALIGN
> +#define FLAT_DATA_ALIGN	(ARCH_FLAT_DATA_ALIGN)
> +/* Otherwise user data nees to be aligned for the same reasons
> + * as SLAB memory is aligned, and to the same amount.
>   * Avoid duplicating architecture specific code by using the same
>   * macro as with SLAB allocation:
>   */
> -#ifdef ARCH_SLAB_MINALIGN
> +#elif defined(ARCH_SLAB_MINALIGN)
>  #define FLAT_DATA_ALIGN	(ARCH_SLAB_MINALIGN)
>  #else
>  #define FLAT_DATA_ALIGN	(sizeof(void *))


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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