Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933536AbZKXQmu (ORCPT ); Tue, 24 Nov 2009 11:42:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933508AbZKXQms (ORCPT ); Tue, 24 Nov 2009 11:42:48 -0500 Received: from terminus.zytor.com ([198.137.202.10]:57939 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933520AbZKXQmp (ORCPT ); Tue, 24 Nov 2009 11:42:45 -0500 Message-ID: <4B0C0C12.7040907@zytor.com> Date: Tue, 24 Nov 2009 08:38:42 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20091014 Fedora/3.0-2.8.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Andrew Haley CC: Jakub Jelinek , Thomas Gleixner , "H.J. Lu" , rostedt@goodmis.org, Ingo Molnar , 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: <1258694593.22249.1012.camel@gandalf.stny.rr.com> <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> <4B0BFC84.7070806@redhat.com> <20091124153634.GK22813@hs20-bc2-1.build.redhat.com> <4B0BFFD0.2080203@redhat.com> In-Reply-To: <4B0BFFD0.2080203@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1543 Lines: 36 On 11/24/2009 07:46 AM, Andrew Haley wrote: >> >> Yes, a lot. The difference is that -maccumulate-outgoing-args allocates >> space for arguments of the callee with most arguments in the prologue, using >> subtraction from sp, then to pass arguments uses movl XXX, 4(%esp) etc. >> and the stack pointer doesn't usually change within the function (except for >> alloca/VLAs). >> With -mno-accumulate-outgoing-args args are pushed using push instructions >> and stack pointer is constantly changing. > > Alright. So, it is possible in theory for gcc to generate code that > only uses -maccumulate-outgoing-args when it needs to realign SP. > And, therefore, we could have a nice option for the kernel: one with > (mostly) good code density and never generates the bizarre code > sequence in the prologue. > If we're changing gcc anyway, then let's add the option of intercepting the function at the point where the machine state is well-defined by ABI, which is before the function stack frame is set up. -maccumulate-outgoing-args sounds like it would be painful on x86 (not using its cheap push/pop instructions), but I guess since it's only when tracing it's less of an issue. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/