Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967767AbdDZVbT convert rfc822-to-8bit (ORCPT ); Wed, 26 Apr 2017 17:31:19 -0400 Received: from terminus.zytor.com ([65.50.211.136]:49613 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967641AbdDZVbL (ORCPT ); Wed, 26 Apr 2017 17:31:11 -0400 Date: Wed, 26 Apr 2017 14:24:25 -0700 User-Agent: K-9 Mail for Android In-Reply-To: References: <20170426205504.133693-1-mka@chromium.org> <02F6E6C7-5AC0-431A-9008-DBDB4EFC1A6D@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Subject: Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication To: Kees Cook CC: Matthias Kaehlcke , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , LKML , Grant Grundler , Greg Hackmann , Michael Davidson From: hpa@zytor.com Message-ID: <3FE94529-1D0B-4B23-8D3A-0543E08B12F2@zytor.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2576 Lines: 72 On April 26, 2017 2:21:25 PM PDT, Kees Cook wrote: >On Wed, Apr 26, 2017 at 2:00 PM, wrote: >> On April 26, 2017 1:55:04 PM PDT, 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 >>>--- >>>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; >> >> This really feels like a "fix your compiler" issue. > >We already use the other forms, what's so bad about adding mul too? >And if this lets us build under clang, all the better. > >-Kees It's not bad per se, but if this doesn't eventually gets fixed in clang we'll have no end of this crap. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.