linux-kernel - Re: [PATCH] ARM: net: bpf_jit: fix emit

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Message-ID: <511C0662.8010309@gmail.com>
Date:	Wed, 13 Feb 2013 22:32:18 +0100
From:	Mircea Gherzan <mgherzan@...il.com>
To:	Nicolas Schichan <nschichan@...ebox.fr>
CC:	Russell King <linux@....linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel.borkmann@....ee.ethz.ch>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: net: bpf_jit: fix emit_swap16() for non ARMv6+.

Am 13.02.2013 18:30, schrieb Nicolas Schichan:
> The original code was generating an lsl instructions using the value
> of ARM_R8 (skb_headlen, possibly uninitialized if no skb_headlen
> access was required) as a shift amount.
> 
> Signed-off-by: Nicolas Schichan <nschichan@...ebox.fr>
> ---
> Resent due to missing Signed-off-by
> 
>  arch/arm/net/bpf_jit_32.c |   15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index a34f1e2..6828ef6 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -341,10 +341,17 @@ static void emit_load_be16(u8 cond, u8 r_res, u8 r_addr, struct jit_ctx *ctx)
>  
>  static inline void emit_swap16(u8 r_dst, u8 r_src, struct jit_ctx *ctx)
>  {
> -	emit(ARM_LSL_R(ARM_R1, r_src, 8), ctx);
> -	emit(ARM_ORR_S(r_dst, ARM_R1, r_src, SRTYPE_LSL, 8), ctx);
> -	emit(ARM_LSL_I(r_dst, r_dst, 8), ctx);
> -	emit(ARM_LSL_R(r_dst, r_dst, 8), ctx);
> +	/* r_dst = (r_src << 8) | (r_src >> 8) */
> +	emit(ARM_LSL_I(ARM_R1, r_src, 8), ctx);
> +	emit(ARM_ORR_S(r_dst, ARM_R1, r_src, SRTYPE_LSR, 8), ctx);
> +
> +	/*
> +	 * we need to mask out the bits set in r_dst[23:16] due to
> +	 * the first shift instruction.
> +	 *
> +	 * note that 0x8ff is the encoded immediate 0x00ff0000.
> +	 */
> +	emit(ARM_BIC_I(r_dst, r_dst, 0x8ff), ctx);
>  }
>  
>  #else  /* ARMv6+ */

Acked-by: Mircea Gherzan <mgherzan@...il.com>
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