From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 21 Oct 2009 19:11:36 +0200 (CEST) Received: from mail3.caviumnetworks.com ([12.108.191.235]:6740 "EHLO mail3.caviumnetworks.com" rhost-flags-OK-OK-OK-OK) by ftp.linux-mips.org with ESMTP id S1493558AbZJURLa (ORCPT ); Wed, 21 Oct 2009 19:11:30 +0200 Received: from caexch01.caveonetworks.com (Not Verified[192.168.16.9]) by mail3.caviumnetworks.com with MailMarshal (v6,5,4,7535) id ; Wed, 21 Oct 2009 10:08:23 -0700 Received: from caexch01.caveonetworks.com ([192.168.16.9]) by caexch01.caveonetworks.com with Microsoft SMTPSVC(6.0.3790.3959); Wed, 21 Oct 2009 10:07:44 -0700 Received: from dd1.caveonetworks.com ([12.108.191.236]) by caexch01.caveonetworks.com over TLS secured channel with Microsoft SMTPSVC(6.0.3790.3959); Wed, 21 Oct 2009 10:07:44 -0700 Message-ID: <4ADF3FE0.5090104@caviumnetworks.com> Date: Wed, 21 Oct 2009 10:07:44 -0700 From: David Daney User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: rostedt@goodmis.org CC: Wu Zhangjin , linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, Thomas Gleixner , Ralf Baechle , Nicholas Mc Guire Subject: Re: [PATCH -v4 9/9] tracing: add function graph tracer support for MIPS References: <028867b99ec532b84963a35e7d552becc783cafc.1256135456.git.wuzhangjin@gmail.com> <2f73eae542c47ac5bbb9f7280e6c0271d193e90d.1256135456.git.wuzhangjin@gmail.com> <3f0d3515f74a58f4cfd11e61b62a129fdc21e3a7.1256135456.git.wuzhangjin@gmail.com> <96110ea5dd4d3d54eb97d0bb708a5bd81c7a50b5.1256135456.git.wuzhangjin@gmail.com> <5dda13e8e3a9c9dba4bb7179183941bda502604f.1256135456.git.wuzhangjin@gmail.com> <53bdfdd95ec4fa00d4cc505bb5972cf21243a14d.1256135456.git.wuzhangjin@gmail.com> <1256141540.18347.3118.camel@gandalf.stny.rr.com> <4ADF38D5.9060100@caviumnetworks.com> <1256143568.18347.3169.camel@gandalf.stny.rr.com> In-Reply-To: <1256143568.18347.3169.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 21 Oct 2009 17:07:44.0373 (UTC) FILETIME=[01849A50:01CA5271] Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 24427 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ddaney@caviumnetworks.com Precedence: bulk X-list: linux-mips Steven Rostedt wrote: > On Wed, 2009-10-21 at 09:37 -0700, David Daney wrote: > >> There is no deterministic way to identify MIPS function prologs. This >> is especially true for leaf functions, but also for functions with >> multiple return sites. >> >> For certain GCC versions there may be a set of command line options that >> would give good results, but in general it is not possible. Attempts at >> fast backtrace generation using code inspection are not reliable and >> will invariably result in faults and panics when they fail. > > Thanks for the update. > > We can easily protect against panics, since we do fault protection > within the code (although currently it will panic on fault, but we can > fix that ;-). We can limit the search to a couple of 100 instructions, > as well as fail on first panic. > > But are you sure that when compiled with -pg, that GCC does not give a > reliable prologue. Things are different when GCC is compiled with -pg, > it may indeed always have something that we can flag. > > We could also add other tests, like the subtraction of the stack too. > I have not used -pg, so I don't know for sure, I think all it does is add the calls to _mcount. Someone could investigate -fno-omit-frame-pointer, with that you may be able to use: move s8,sp To identify function prologs, but it would still be ad hoc, as modern versions of GCC will reorder instructions in the prolog for better scheduling. David Daney