[PATCH] ARM: Allow kernel unaligned accesses on ARMv6+ processors

[PATCH] ARM: Allow kernel unaligned accesses on ARMv6+ processors

[Catalin Marinas]

Recent gcc versions generate unaligned accesses by default on ARMv6 and
later processors. This patch ensures that the SCTLR.A bit is always
cleared on such processors to avoid kernel traping before
alignment_init() is called.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: John Linn <John.Linn@xilinx.com>
---
 arch/arm/kernel/head.S |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index a400a4d..1768db2 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -394,7 +394,7 @@ __secondary_data:
  *  r13 = *virtual* address to jump to upon completion
  */
 __enable_mmu:
-#ifdef CONFIG_ALIGNMENT_TRAP
+#if defined(CONFIG_ALIGNMENT_TRAP) && __LINUX_ARM_ARCH__ < 6
 	orr	r0, r0, #CR_A
 #else
 	bic	r0, r0, #CR_A

[PATCH] ARM: Allow kernel unaligned accesses on ARMv6+ processors

[Nicolas Pitre]

On Sat, 5 Nov 2011, Catalin Marinas wrote:

> Recent gcc versions generate unaligned accesses by default on ARMv6 and
> later processors. This patch ensures that the SCTLR.A bit is always
> cleared on such processors to avoid kernel traping before
> alignment_init() is called.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: John Linn <John.Linn@xilinx.com>

Acked-by: Nicolas Pitre <nico@linaro.org>

> ---
>  arch/arm/kernel/head.S |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index a400a4d..1768db2 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -394,7 +394,7 @@ __secondary_data:
>   *  r13 = *virtual* address to jump to upon completion
>   */
>  __enable_mmu:
> -#ifdef CONFIG_ALIGNMENT_TRAP
> +#if defined(CONFIG_ALIGNMENT_TRAP) && __LINUX_ARM_ARCH__ < 6
>  	orr	r0, r0, #CR_A
>  #else
>  	bic	r0, r0, #CR_A
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

[PATCH] ARM: Allow kernel unaligned accesses on ARMv6+ processors

[John Linn]

> -----Original Message-----
> From: Catalin Marinas [mailto:catalin.marinas at gmail.com] On Behalf Of
> Catalin Marinas
> Sent: Saturday, November 05, 2011 3:41 AM
> To: linux-arm-kernel at lists.infradead.org
> Cc: John Linn
> Subject: [PATCH] ARM: Allow kernel unaligned accesses on ARMv6+
> processors
> 
> Recent gcc versions generate unaligned accesses by default on ARMv6
and
> later processors. This patch ensures that the SCTLR.A bit is always
> cleared on such processors to avoid kernel traping before
> alignment_init() is called.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: John Linn <John.Linn@xilinx.com>

It worked great, thanks Catalin. I'd love to see a solution merged in
the mainline and this seems reasonable.
I'm being pushed to newer tools which require a solution.

Tested-by: John Linn <john.linn@xilinx.com>

> ---
>  arch/arm/kernel/head.S |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index a400a4d..1768db2 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -394,7 +394,7 @@ __secondary_data:
>   *  r13 = *virtual* address to jump to upon completion
>   */
>  __enable_mmu:
> -#ifdef CONFIG_ALIGNMENT_TRAP
> +#if defined(CONFIG_ALIGNMENT_TRAP) && __LINUX_ARM_ARCH__ < 6
>  	orr	r0, r0, #CR_A
>  #else
>  	bic	r0, r0, #CR_A

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[PATCH] ARM: Allow kernel unaligned accesses on ARMv6+ processors

[Catalin Marinas]

On Mon, Nov 07, 2011 at 02:11:24AM +0000, John Linn wrote:
> > -----Original Message-----
> > From: Catalin Marinas [mailto:catalin.marinas at gmail.com] On Behalf Of
> > Catalin Marinas
> > Sent: Saturday, November 05, 2011 3:41 AM
> > To: linux-arm-kernel at lists.infradead.org
> > Cc: John Linn
> > Subject: [PATCH] ARM: Allow kernel unaligned accesses on ARMv6+
> > processors
> > 
> > Recent gcc versions generate unaligned accesses by default on ARMv6
> and
> > later processors. This patch ensures that the SCTLR.A bit is always
> > cleared on such processors to avoid kernel traping before
> > alignment_init() is called.
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: John Linn <John.Linn@xilinx.com>
> 
> It worked great, thanks Catalin. I'd love to see a solution merged in
> the mainline and this seems reasonable.
> I'm being pushed to newer tools which require a solution.
> 
> Tested-by: John Linn <john.linn@xilinx.com>

Thanks. I pushed it to Russell's patch system as:

http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=7150/1

-- 
Catalin