Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751881AbbEDR5q (ORCPT ); Mon, 4 May 2015 13:57:46 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:50289 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751559AbbEDR50 (ORCPT ); Mon, 4 May 2015 13:57:26 -0400 Date: Mon, 4 May 2015 18:57:09 +0100 From: Russell King - ARM Linux To: Nicolas Schichan Cc: "David S. Miller" , Alexei Starovoitov , Daniel Borkmann , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/4] ARM: net fix emit_udiv() for BPF_ALU | BPF_DIV | BPF_K intruction. Message-ID: <20150504175708.GA2067@n2100.arm.linux.org.uk> References: <1430314657-2552-1-git-send-email-nschichan@freebox.fr> <1430314657-2552-5-git-send-email-nschichan@freebox.fr> <20150501173721.GO12732@n2100.arm.linux.org.uk> <55479B5E.2070901@freebox.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55479B5E.2070901@freebox.fr> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2334 Lines: 65 On Mon, May 04, 2015 at 06:16:30PM +0200, Nicolas Schichan wrote: > On 05/01/2015 07:37 PM, Russell King - ARM Linux wrote: > > On Wed, Apr 29, 2015 at 03:37:37PM +0200, Nicolas Schichan wrote: > [...] > >> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c > >> index b5f470d..ffaf311 100644 > >> --- a/arch/arm/net/bpf_jit_32.c > >> +++ b/arch/arm/net/bpf_jit_32.c > >> @@ -449,10 +449,10 @@ static inline void emit_udiv(u8 rd, u8 rm, u8 rn, struct jit_ctx *ctx) > >> return; > >> } > >> #endif > >> - if (rm != ARM_R0) > >> - emit(ARM_MOV_R(ARM_R0, rm), ctx); > >> if (rn != ARM_R1) > >> emit(ARM_MOV_R(ARM_R1, rn), ctx); > >> + if (rm != ARM_R0) > >> + emit(ARM_MOV_R(ARM_R0, rm), ctx); > > > > I don't think you've thought enough about this. What if rm is ARM_R1? > > What if rn = ARM_R0 and rm = ARM_R1? > > > > How about: > > > > if (rn == ARM_R0 && rm == ARM_R1) { > > emit(ARM_MOV_R(ARM_R3, rn), ctx); // r3 <- r0(rn) > > emit(ARM_MOV_R(ARM_R0, rm), ctx); // r0 <- r1(rm) > > emit(ARM_MOV_R(ARM_R1, ARM_R3), ctx); // r1 <- r3 > > } else if (rn == ARM_R0) { > > emit(ARM_MOV_R(ARM_R1, rn), ctx); // r1 <- rn > > if (rm != ARM_R0) > > emit(ARM_MOV_R(ARM_R0, rm), ctx); // r0 <- rm > > } else { > > if (rm != ARM_R0) > > emit(ARM_MOV_R(ARM_R0, rm), ctx); // r0 <- rm > > if (rn != ARM_R1) > > emit(ARM_MOV_R(ARM_R1, rn), ctx); // r1 <- rn > > } > > > > Hello Russell, > > In the current JIT, emit_udiv() is only being called with: > > - rm = ARM_R4 (r_A) and rn = ARM_R0 (r_scrach) for BPF_ALU | BPF_DIV | BPF_K > > - rm = ARM_R4 (r_A) and rn = ARM_R5 (r_X) for BPF_ALU | BPF_DIV | BPF_X > > so it should not cause any issue in the current code state. > > But yes, I'll rework the patch to avoid any other nasty surprises should the > code change. Maybe then add a comment detailing the current conditions that this is coded for so that if you're not around when the code changes, others are aware of the issue. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/