From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753699Ab1G0AfJ (ORCPT ); Tue, 26 Jul 2011 20:35:09 -0400 Received: from mga09.intel.com ([134.134.136.24]:52724 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753369Ab1G0AfA (ORCPT ); Tue, 26 Jul 2011 20:35:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,272,1309762800"; d="scan'208";a="30471005" From: Andi Kleen References: <20110726534.972201586@firstfloor.org> In-Reply-To: <20110726534.972201586@firstfloor.org> To: jim876@xs4all.nl, jakub@redhat.com, andi@firstfloor.org, schwab@linux-m68k.org, torvalds@linux-foundation.org, ak@linux.intel.com, linux-kernel@vger.kernel.org, stable@kernel.org, tim.bird@am.sony.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] [8/98] Fix gcc 4.5.1 miscompiling drivers/char/i8k.c (again) Message-Id: <20110727003500.2034B2403FF@tassilo.jf.intel.com> Date: Tue, 26 Jul 2011 17:35:00 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.35-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Jim Bos [ upstream commit 22d3243de86bc92d874abb7c5b185d5c47aba323 ] The fix in commit 6b4e81db2552 ("i8k: Tell gcc that *regs gets clobbered") to work around the gcc miscompiling i8k.c to add "+m (*regs)" caused register pressure problems and a build failure. Changing the 'asm' statement to 'asm volatile' instead should prevent that and works around the gcc bug as well, so we can remove the "+m". [ Background on the gcc bug: a memory clobber fails to mark the function the asm resides in as non-pure (aka "__attribute__((const))"), so if the function does nothing else that triggers the non-pure logic, gcc will think that that function has no side effects at all. As a result, callers will be mis-compiled. Adding the "+m" made gcc see that it's not a pure function, and so does "asm volatile". The problem was never really the need to mark "*regs" as changed, since the memory clobber did that part - the problem was just a bug in the gcc "pure" function analysis - Linus ] Signed-off-by: Jim Bos Acked-by: Jakub Jelinek Cc: Andi Kleen Cc: Andreas Schwab Signed-off-by: Linus Torvalds Signed-off-by: Andi Kleen Index: linux-2.6.35.y/drivers/char/i8k.c =================================================================== --- linux-2.6.35.y.orig/drivers/char/i8k.c +++ linux-2.6.35.y/drivers/char/i8k.c @@ -119,7 +119,7 @@ static int i8k_smm(struct smm_regs *regs int eax = regs->eax; #if defined(CONFIG_X86_64) - asm("pushq %%rax\n\t" + asm volatile("pushq %%rax\n\t" "movl 0(%%rax),%%edx\n\t" "pushq %%rdx\n\t" "movl 4(%%rax),%%ebx\n\t" @@ -141,11 +141,11 @@ static int i8k_smm(struct smm_regs *regs "lahf\n\t" "shrl $8,%%eax\n\t" "andl $1,%%eax\n" - :"=a"(rc), "+m" (*regs) + :"=a"(rc) : "a"(regs) : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory"); #else - asm("pushl %%eax\n\t" + asm volatile("pushl %%eax\n\t" "movl 0(%%eax),%%edx\n\t" "push %%edx\n\t" "movl 4(%%eax),%%ebx\n\t" @@ -167,7 +167,7 @@ static int i8k_smm(struct smm_regs *regs "lahf\n\t" "shrl $8,%%eax\n\t" "andl $1,%%eax\n" - :"=a"(rc), "+m" (*regs) + :"=a"(rc) : "a"(regs) : "%ebx", "%ecx", "%edx", "%esi", "%edi", "memory"); #endif