Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030903AbbD1OFd (ORCPT ); Tue, 28 Apr 2015 10:05:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56084 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030765AbbD1OFb (ORCPT ); Tue, 28 Apr 2015 10:05:31 -0400 Date: Tue, 28 Apr 2015 09:04:54 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Michal Marek , x86@kernel.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] x86, stackvalidate: Compile-time stack frame pointer validation Message-ID: <20150428140454.GA17315@treble.redhat.com> References: <0c54981fcba75d6a32ad4074786b99bbf0fc0810.1430142416.git.jpoimboe@redhat.com> <20150428121606.GX23123@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150428121606.GX23123@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1601 Lines: 32 On Tue, Apr 28, 2015 at 02:16:06PM +0200, Peter Zijlstra wrote: > On Mon, Apr 27, 2015 at 08:56:27AM -0500, Josh Poimboeuf wrote: > > Frame pointer based stack traces aren't always reliable. One big reason > > is that most asm functions don't set up the frame pointer. > > > > Fix that by enforcing that all asm functions honor CONFIG_FRAME_POINTER. > > This is done with a new stackvalidate host tool which is automatically > > run for every compiled .S file and which validates that every asm > > function does the proper frame pointer setup. > > Would it make sense (maybe as an additional CONFIG_*_DEBUG thing) to > also process the output of GCC with this tool? To both double check GCC > and to give the tool more input? I tried that, but I discovered that gcc's usage of frame pointers would be a lot harder to validate. It only sets up the frame pointer in code paths which have call instructions. There are a lot of functions which have conditional jumps at the beginning which can jump straight to a return instruction without first doing the frame pointer setup. So it would really need to have a much more sophisticated static code analysis. But I think the possibility of gcc messing up frame pointers is very slim. I doubt it would be worth the complexity (and added compile time) needed to try to find any gcc bugs there. -- Josh -- 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/