linux-kernel - Re: [PATCH 4/7] arch/x86/mm/kmemcheck: Remove double test

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Date:	Sun, 29 Aug 2010 13:26:16 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Julia Lawall <julia@...u.dk>
CC:	Vegard Nossum <vegardno@....uio.no>,
	kernel-janitors@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] arch/x86/mm/kmemcheck: Remove double test

On 28.8.2010 18.41, Julia Lawall wrote:
> The opcodes 0x2e and 0x3e are tested for in the first Group 2 line as well.
>
> The sematic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)
>
> //<smpl>
> @expression@
> expression E;
> @@
>
> (
> * E
>    || ... || E
> |
> * E
>    &&  ...&&  E
> )
> //</smpl>
>
> Signed-off-by: Julia Lawall<julia@...u.dk>
>
> ---
> This is a guess as to what the code should be.  Perhaps something else
> should have been tested instead.

The last two items are branch hint prefixes that use same encoding as CS 
and DS segment override prefixes.

Reviewed-by: Pekka Enberg <penberg@...nel.org>

Can you pick this up in the x86.git tree, please?

>   arch/x86/mm/kmemcheck/opcode.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/mm/kmemcheck/opcode.c b/arch/x86/mm/kmemcheck/opcode.c
> index 63c19e2..324aa3f 100644
> --- a/arch/x86/mm/kmemcheck/opcode.c
> +++ b/arch/x86/mm/kmemcheck/opcode.c
> @@ -9,7 +9,7 @@ static bool opcode_is_prefix(uint8_t b)
>   		b == 0xf0 || b == 0xf2 || b == 0xf3
>   		/* Group 2 */
>   		|| b == 0x2e || b == 0x36 || b == 0x3e || b == 0x26
> -		|| b == 0x64 || b == 0x65 || b == 0x2e || b == 0x3e
> +		|| b == 0x64 || b == 0x65
>   		/* Group 3 */
>   		|| b == 0x66
>   		/* Group 4 */
>

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