From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754152AbaJASpN (ORCPT ); Wed, 1 Oct 2014 14:45:13 -0400 Received: from mail-lb0-f177.google.com ([209.85.217.177]:52680 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754109AbaJASpG (ORCPT ); Wed, 1 Oct 2014 14:45:06 -0400 MIME-Version: 1.0 In-Reply-To: <542C496F.80003@zytor.com> References: <542C496F.80003@zytor.com> From: Andy Lutomirski Date: Wed, 1 Oct 2014 11:44:44 -0700 Message-ID: Subject: Re: [PATCH v3 2/2] x86_64: Don't save flags on context switch To: "H. Peter Anvin" Cc: Thomas Gleixner , X86 ML , Ingo Molnar , Sebastian Lackner , Anish Bhatt , "linux-kernel@vger.kernel.org" , Chuck Ebbert Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 1, 2014 at 11:35 AM, H. Peter Anvin wrote: > On 10/01/2014 11:28 AM, Andy Lutomirski wrote: >> >> #define __EXTRA_CLOBBER \ >> , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \ >> - "r12", "r13", "r14", "r15" >> + "r12", "r13", "r14", "r15", "flags" >> > > I was under the impression that gcc *always* assumes the flags were > clobbered for an asm statement. Otherwise I think we'd have a lot of > problems. > I have no idea, but I doubt that adding the explicit "flags" clobber hurts, and it will make other people who are unsure about this less worried. --Andy > -hpa > > -- Andy Lutomirski AMA Capital Management, LLC