Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757059AbZKSPqK (ORCPT ); Thu, 19 Nov 2009 10:46:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753469AbZKSPqK (ORCPT ); Thu, 19 Nov 2009 10:46:10 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43304 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752484AbZKSPqJ (ORCPT ); Thu, 19 Nov 2009 10:46:09 -0500 Message-ID: <4B0567E0.5080803@redhat.com> Date: Thu, 19 Nov 2009 15:44:32 +0000 From: Andrew Haley User-Agent: Thunderbird 2.0.0.23 (X11/20090825) MIME-Version: 1.0 To: Thomas Gleixner CC: Ingo Molnar , "H. Peter Anvin" , LKML , Andrew Morton , Heiko Carstens , feng.tang@intel.com, Fr??d??ric Weisbecker , Steven Rostedt , Peter Zijlstra , jakub@redhat.com, gcc@gcc.gnu.org Subject: Re: BUG: GCC-4.4.x changes the function frame on some functions References: <20091119072040.GA23579@elte.hu> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1451 Lines: 53 Thomas Gleixner wrote: > On Thu, 19 Nov 2009, Thomas Gleixner wrote: > > Can the GCC folks please shed some light on this: > > standard function start: > > push %ebp > mov %esp, %ebp > .... > call mcount > > modified function start on a handful of functions only seen with gcc > 4.4.x on x86 32 bit: > > push %edi > lea 0x8(%esp),%edi > and $0xfffffff0,%esp > pushl -0x4(%edi) > push %ebp > mov %esp,%ebp > ... > call mcount > > This modification leads to a hard to solve problem in the kernel > function graph tracer which assumes that the stack looks like: > > return address > saved ebp > > With the modified function start sequence this is not longer true and > the manipulation of the return address on the stack fails silently. > > Neither gcc 4.3 nor gcc 3.4 are generating such function frames, so it > looks like a gcc 4.4.x feature. > > There is no real obvious reason why the edi magic needs to be done > _before_ > > push %ebp > mov %esp,%ebp Sure there is: unless you do the adjustment first %ebp won't be 16-aligned. We're aligning the stack properly, as per the ABI requirements. Can't you just fix the tracer? Andrew. -- 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/