linux-kernel - Re: [PATCH] kprobes: x86: mark 2 bytes NOP as boostable.

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Message-ID: <54D94415.8070206@hitachi.com>
Date:	Tue, 10 Feb 2015 08:34:45 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, lizefan@...wei.com
Subject: Re: [PATCH] kprobes: x86: mark 2 bytes NOP as boostable.

(2015/02/09 21:45), Wang Nan wrote:
> x86 kprobes is unable to probe at 2 bytes nop like:
                           ^^^^^ boost

> 
> nopl 0x0(%rax,%rax,1)
> 
> which is 0x0f 0x1f 0x44 0x00 0x00.
> 
> Such nops have exactly 5 bytes which is able to hold a relative jmp
> instruction. Boosting them should be obviously safe.
> 
> This patch enable boosting such nops by simply updating
> twobyte_is_boostable[] array.

Anyway, this looks good to me.
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thank you!

> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---
>  arch/x86/kernel/kprobes/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 98f654d..6a1146e 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -84,7 +84,7 @@ static volatile u32 twobyte_is_boostable[256 / 32] = {
>  	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f          */
>  	/*      ----------------------------------------------          */
>  	W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */
> -	W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 10 */
> +	W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1) , /* 10 */
>  	W(0x20, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 20 */
>  	W(0x30, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 30 */
>  	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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