Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937833AbdDZWGV (ORCPT ); Wed, 26 Apr 2017 18:06:21 -0400 Received: from mail-it0-f45.google.com ([209.85.214.45]:37555 "EHLO mail-it0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754218AbdDZWGK (ORCPT ); Wed, 26 Apr 2017 18:06:10 -0400 MIME-Version: 1.0 In-Reply-To: <20170426205504.133693-1-mka@chromium.org> References: <20170426205504.133693-1-mka@chromium.org> From: Kees Cook Date: Wed, 26 Apr 2017 15:06:09 -0700 X-Google-Sender-Auth: nkKGhQ_rvyGqss0qoD-HvjdVaVY Message-ID: Subject: Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication To: Matthias Kaehlcke , Ingo Molnar Cc: Thomas Gleixner , "H . Peter Anvin" , "x86@kernel.org" , LKML , Grant Grundler , Greg Hackmann , Michael Davidson Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2137 Lines: 70 On Wed, Apr 26, 2017 at 1:55 PM, Matthias Kaehlcke wrote: > In difference to gas clang doesn't seem to infer the size from the > operands. Add and use the _ASM_MUL macro which determines the operand > size and resolves to the 'mul' instruction with the corresponding > suffix. > > This fixes the following error when building with clang: > > CC arch/x86/lib/kaslr.o > /tmp/kaslr-dfe1ad.s: Assembler messages: > /tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given and > no register operands; can't size instruction > > Signed-off-by: Matthias Kaehlcke Acked-by: Kees Cook -Kees > --- > Changes in v2: > - use _ASM_MUL instead of #ifdef > - updated commit message > > arch/x86/include/asm/asm.h | 1 + > arch/x86/lib/kaslr.c | 3 ++- > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h > index 7acb51c49fec..7a9df3beb89b 100644 > --- a/arch/x86/include/asm/asm.h > +++ b/arch/x86/include/asm/asm.h > @@ -32,6 +32,7 @@ > #define _ASM_ADD __ASM_SIZE(add) > #define _ASM_SUB __ASM_SIZE(sub) > #define _ASM_XADD __ASM_SIZE(xadd) > +#define _ASM_MUL __ASM_SIZE(mul) > > #define _ASM_AX __ASM_REG(ax) > #define _ASM_BX __ASM_REG(bx) > diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c > index 121f59c6ee54..0c7fe444dcdd 100644 > --- a/arch/x86/lib/kaslr.c > +++ b/arch/x86/lib/kaslr.c > @@ -5,6 +5,7 @@ > * kernel starts. This file is included in the compressed kernel and > * normally linked in the regular. > */ > +#include > #include > #include > #include > @@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(const char *purpose) > } > > /* Circular multiply for better bit diffusion */ > - asm("mul %3" > + asm(_ASM_MUL "%3" > : "=a" (random), "=d" (raw) > : "a" (random), "rm" (mix_const)); > random += raw; > -- > 2.13.0.rc0.306.g87b477812d-goog > -- Kees Cook Pixel Security