linux-kernel - Re: [PATCH] ARM: alignment: Use is_wide_instruction() to check wide instruction

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Message-ID: <20150413124832.GA15504@e103592.cambridge.arm.com>
Date:	Mon, 13 Apr 2015 13:48:39 +0100
From:	Dave Martin <Dave.Martin@....com>
To:	Yingjoe Chen <yingjoe.chen@...iatek.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	srv_heupstream@...iatek.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: alignment: Use is_wide_instruction() to check wide
 instruction

On Fri, Apr 10, 2015 at 10:05:41PM +0800, Yingjoe Chen wrote:
> 
> I first notice the comment is incorrect, then I realize there's another
> macro which do exactly the same thing.
> Tested with hand written userspace program with a few wide instructions
> to make sure this still work as expect.
> 
> 8<-------------------------------------------------
> do_alignment() is using locally added IS_T32() macro to check if an
> instruction is a Thumb-2 32 bit instruction. The macro
> is_wide_instruction() is doing the same thing, with slightly faster
> implementation.
> Change to use is_wide_instruction() in do_alignment() and remove
> IS_T32().

Reviewed-by: Dave Martin <Dave.Martin@....com>

The existing code is correct, but the comment is indeed wrong.
Consolidating this with one of the other existing macros makes sense.

!__opcode_is_thumb16() could also be used here (or is_wide_instruction()
redefined in terms of it), but that's not essential.

Cheers
---Dave

> 
> Signed-off-by: Yingjoe Chen <yingjoe.chen@...iatek.com>
> ---
>  arch/arm/mm/alignment.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/arch/arm/mm/alignment.c b/arch/arm/mm/alignment.c
> index 2c0c541..f8e82f5 100644
> --- a/arch/arm/mm/alignment.c
> +++ b/arch/arm/mm/alignment.c
> @@ -71,10 +71,6 @@
>  
>  #define BAD_INSTR 	0xdeadc0de
>  
> -/* Thumb-2 32 bit format per ARMv7 DDI0406A A6.3, either f800h,e800h,f800h */
> -#define IS_T32(hi16) \
> -	(((hi16) & 0xe000) == 0xe000 && ((hi16) & 0x1800))
> -
>  static unsigned long ai_user;
>  static unsigned long ai_sys;
>  static void *ai_sys_last_pc;
> @@ -770,7 +766,7 @@ do_alignment(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
>  		tinstr = __mem_to_opcode_thumb16(tinstr);
>  		if (!fault) {
>  			if (cpu_architecture() >= CPU_ARCH_ARMv7 &&
> -			    IS_T32(tinstr)) {
> +			    is_wide_instruction(tinstr)) {
>  				/* Thumb-2 32-bit */
>  				u16 tinst2 = 0;
>  				fault = probe_kernel_address(ptr + 1, tinst2);
> -- 
> 1.8.1.1.dirty
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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