From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 19970 invoked by alias); 25 Nov 2009 21:01:02 -0000 Received: (qmail 19945 invoked by uid 22791); 25 Nov 2009 21:01:01 -0000 X-SWARE-Spam-Status: No, hits=-2.5 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 25 Nov 2009 21:00:56 +0000 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id nAPL0eVL008306 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 25 Nov 2009 16:00:41 -0500 Received: from zebedee.pink (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by int-mx03.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id nAPL0aUR025084; Wed, 25 Nov 2009 16:00:37 -0500 Message-ID: <4B0D9AF3.6000702@redhat.com> Date: Wed, 25 Nov 2009 21:01:00 -0000 From: Andrew Haley User-Agent: Thunderbird 2.0.0.23 (X11/20090825) MIME-Version: 1.0 To: "H. Peter Anvin" CC: Jakub Jelinek , Ingo Molnar , Thomas Gleixner , "H.J. Lu" , rostedt@goodmis.org, LKML , Andrew Morton , Heiko Carstens , feng.tang@intel.com, Peter Zijlstra , Frederic Weisbecker , David Daney , Richard Guenther , gcc , Linus Torvalds Subject: Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue References: <1258736456.22249.1032.camel@gandalf.stny.rr.com> <4B06EF6F.2050507@redhat.com> <6dc9ffc80911220138y15bfa91agccf5c29f1c30e09a@mail.gmail.com> <4B0972C9.302@redhat.com> <6dc9ffc80911221530t38d83cf6je739743c8d756667@mail.gmail.com> <4B0BF119.4070704@redhat.com> <20091124150604.GJ22813@hs20-bc2-1.build.redhat.com> <20091125154452.GA9456@elte.hu> <20091125164434.GS22813@hs20-bc2-1.build.redhat.com> <4B0D8FC1.1010608@zytor.com> In-Reply-To: <4B0D8FC1.1010608@zytor.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-IsSubscribed: yes Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org X-SW-Source: 2009-11/txt/msg00720.txt.bz2 H. Peter Anvin wrote: > On 11/25/2009 08:44 AM, Jakub Jelinek wrote: >> If you compile kernels 90%+ people out there run with -p on i?86/x86_64, >> then certainly coming up with a new gcc switch and new profiling ABI is >> desirable. -p on i?86/x86_64 e.g. forces -fno-omit-frame-pointer, which >> makes code on these register starved arches significantly worse. >> Making GCC output profiling call before prologue instead of after prologue >> is a 4 liner in generic code and a few lines in target specific code. >> The important thing is that we shouldn't have 100 different profiling ABIs, >> so it is desirable to agree on something that will be generally useful not >> just for the kernel, but perhaps for other purposes. > > There is really just one that makes sense, which is providing the > ABI-defined entry state, which means intercepting at the point of entry. > > Anything else is/was a mistake. Indeed. The problem, though, is that the "naked call" approach, while attractive, requires the back end to be modified and so requires the help of the gcc maintainers for every Linux target. Not that this is a terrible idea, but such co-ordination is going to take time. Andrew.