linux-kernel - Re: [PATCH] fix a bug in emitting the 16-bit immediate operand of AND

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Message-ID: <1333021525.3402.22.camel@edumazet-laptop>
Date:	Thu, 29 Mar 2012 13:45:25 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"zhuangfeiran@....ac.cn" <zhuangfeiran@....ac.cn>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix a bug in emitting the 16-bit immediate operand of
 AND

Le jeudi 29 mars 2012 à 17:27 +0800, zhuangfeiran@....ac.cn a écrit :
> When K >= 0xFFFF0000, AND needs the two least significant bytes of K as
> its operand, but EMIT2() gives it the least significant byte of K and
> 0x2. EMIT() should be used here to replace EMIT2().
> 
> Signed-off-by: Feiran Zhuang  <zhuangfeiran@....ac.cn>
> ---
>  arch/x86/net/bpf_jit_comp.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 5671752..5a5b6e4 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -289,7 +289,7 @@ void bpf_jit_compile(struct sk_filter *fp)
>  					EMIT2(0x24, K & 0xFF); /* and imm8,%al */
>  				} else if (K >= 0xFFFF0000) {
>  					EMIT2(0x66, 0x25);	/* and imm16,%ax */
> -					EMIT2(K, 2);
> +					EMIT(K, 2);
>  				} else {
>  					EMIT1_off32(0x25, K);	/* and imm32,%eax */
>  				}

Good catch, thanks !

Acked-by: Eric Dumazet <eric.dumazet@...il.com>



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