From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 25809 invoked by alias); 19 Nov 2009 19:29:14 -0000 Received: (qmail 25800 invoked by uid 22791); 19 Nov 2009 19:29:13 -0000 X-SWARE-Spam-Status: No, hits=-2.3 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from hrndva-omtalb.mail.rr.com (HELO hrndva-omtalb.mail.rr.com) (71.74.56.122) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 19 Nov 2009 19:28:09 +0000 Received: from [192.168.23.10] (really [74.67.89.75]) by hrndva-omta04.mail.rr.com with ESMTP id <20091119192807542.PIYW20219@hrndva-omta04.mail.rr.com>; Thu, 19 Nov 2009 19:28:07 +0000 Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions From: Steven Rostedt Reply-To: rostedt@goodmis.org To: David Daney Cc: Linus Torvalds , Andrew Haley , Richard Guenther , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , LKML , Andrew Morton , Heiko Carstens , feng.tang@intel.com, Fr??d??ric Weisbecker , Peter Zijlstra , jakub@redhat.com, gcc@gcc.gnu.org In-Reply-To: <4B05982B.6060200@caviumnetworks.com> References: <20091119072040.GA23579@elte.hu> <1258653562.22249.682.camel@gandalf.stny.rr.com> <84fc9c000911191003t244eb864o3d5b355ab5485f@mail.gmail.com> <4B058CCD.8050605@redhat.com> <4B05982B.6060200@caviumnetworks.com> Content-Type: text/plain Date: Thu, 19 Nov 2009 19:29:00 -0000 Message-Id: <1258658886.22249.874.camel@gandalf.stny.rr.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit 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/msg00525.txt.bz2 On Thu, 2009-11-19 at 11:10 -0800, David Daney wrote: > Linus Torvalds wrote: > For the MIPS port of GCC and Linux I recently added the > -mmcount-ra-address switch. It causes the location of the return > address (on the stack) to be passed to mcount in a scratch register. Hehe, scratch register on i686 ;-) i686 has no extra regs. It just has: %eax, %ebx, %ecx, %edx - as the general purpose regs %esp - stack %ebp - frame pointer %edi, %esi - counter regs That's just 8 regs, and half of those are special. > > Perhaps something similar could be done for x86. It would make this > patching of the return location more reliable at the expense of more > code at the mcount invocation site. I rather not put any more code in the call site. > > For the MIPS case the code size doesn't increase, as it is done in the > delay slot of the call instruction, which would otherwise be a nop. I showed in a previous post what the best would be for x86. That is just calling mcount at the very beginning of the function. The return address is automatically pushed onto the stack. Perhaps we could create another profiler? Instead of calling mcount, call a new function: __fentry__ or something. Have it activated with another switch. This could make the performance of the function tracer even better without all these exceptions. : call __fentry__ [...] -- Steve