linux-kernel - Re: [PATCH] ARM: Fix find_next_zero

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Date:	Tue, 23 Nov 2010 16:26:47 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	James Jones <jajones@...dia.com>
Cc:	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Fix find_next_zero_bit and related assembly

On Thu, 11 Nov 2010, James Jones wrote:

> The find_next_bit, find_first_bit, find_next_zero_bit
> and find_first_zero_bit functions were not properly
> clamping to the maxbit argument at the bit level. They
> were instead only checking maxbit at the byte level.
> To fix this, add a compare and a conditional move
> instruction to the end of the common bit-within-the-
> byte code used by all the functions and be sure not to
> clobber the maxbit argument before it is used.
> 
> Signed-off-by: James Jones <jajones@...dia.com>
> Tested-by: Stephen Warren <swarren@...dia.com>

Reviewed-by: Nicolas Pitre <nicolas.pitre@...aro.org>

Please send to RMK's patch system.



> ---
>  arch/arm/lib/findbit.S |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/lib/findbit.S b/arch/arm/lib/findbit.S
> index 1e4cbd4..64f6bc1 100644
> --- a/arch/arm/lib/findbit.S
> +++ b/arch/arm/lib/findbit.S
> @@ -174,8 +174,8 @@ ENDPROC(_find_next_bit_be)
>   */
>  .L_found:
>  #if __LINUX_ARM_ARCH__ >= 5
> -		rsb	r1, r3, #0
> -		and	r3, r3, r1
> +		rsb	r0, r3, #0
> +		and	r3, r3, r0
>  		clz	r3, r3
>  		rsb	r3, r3, #31
>  		add	r0, r2, r3
> @@ -190,5 +190,7 @@ ENDPROC(_find_next_bit_be)
>  		addeq	r2, r2, #1
>  		mov	r0, r2
>  #endif
> +		cmp	r1, r0			@ Clamp to maxbit
> +		movlo	r0, r1
>  		mov	pc, lr
>  
> -- 
> 1.7.1
> 
> --
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