linux-kernel - Re: [PATCH] arm64: mm: support instruction SETEND

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Message-ID: <54AD061A.6090602@arm.com>
Date:	Wed, 07 Jan 2015 10:10:34 +0000
From:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
To:	Leo Yan <leo.yan@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>
CC:	Xiaolong Ye <yexl@...vell.com>
Subject: Re: [PATCH] arm64: mm: support instruction SETEND

On 07/01/15 05:52, Leo Yan wrote:
> Currently kernel has set the bit SCTLR_EL1.SED, so the SETEND
> instruction will be treated as UNALLOCATED; this error can be
> reproduced when ARMv8 cpu runs with EL1/aarch64 and EL0/aarch32
> mode, finally kernel will trap the exception if the userspace
> libs use SETEND instruction.
>
> So this patch clears bit SCTLR_EL1.SED to support SETEND instruction.
>
The best way to do this, is via the instruction emulation framework 
added by Punit, which handles the armv8 deprecated/obsoleted 
instructions. This is now queued for 3.19.
I have a patchset which adds the 'SETEND' emulation support to the 
framework. This will enable better handling of the feature, including 
finding out the users of the deprecated instruction (when we switch to 
the emulation mode).

Btw, there is one open question that I am seeking answer for.

What should be the endianness of the signal handlers ? Should we leave 
it to the application ? Or restore the 'default' endianness for the 
signal handler ?


Thanks
Suzuki


> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> Signed-off-by: Xiaolong Ye <yexl@...vell.com>
> ---
>   arch/arm64/mm/proc.S | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 4e778b1..66a7363 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -249,9 +249,9 @@ ENDPROC(__cpu_setup)
>   	 *       CE0      XWHW CZ     ME TEEA S
>   	 * .... .IEE .... NEAI TE.I ..AD DEN0 ACAM
>   	 * 0011 0... 1101 ..0. ..0. 10.. .... .... < hardware reserved
> -	 * .... .1.. .... 01.1 11.1 ..01 0001 1101 < software settings
> +	 * .... .1.. .... 01.1 11.1 ..00 0001 1101 < software settings
>   	 */
>   	.type	crval, #object
>   crval:
> -	.word	0x000802e2			// clear
> -	.word	0x0405d11d			// set
> +	.word	0x000803e2			// clear
> +	.word	0x0405d01d			// set
>


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