Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754651AbZJURvN (ORCPT ); Wed, 21 Oct 2009 13:51:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753929AbZJURvL (ORCPT ); Wed, 21 Oct 2009 13:51:11 -0400 Received: from mail3.caviumnetworks.com ([12.108.191.235]:8370 "EHLO mail3.caviumnetworks.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754064AbZJURvJ (ORCPT ); Wed, 21 Oct 2009 13:51:09 -0400 Message-ID: <4ADF4982.9010306@caviumnetworks.com> Date: Wed, 21 Oct 2009 10:48:50 -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> <4ADF3FE0.5090104@caviumnetworks.com> <1256145813.18347.3210.camel@gandalf.stny.rr.com> In-Reply-To: <1256145813.18347.3210.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 21 Oct 2009 17:48:50.0836 (UTC) FILETIME=[BFA4FD40:01CA5276] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1520 Lines: 41 Steven Rostedt wrote: > On Wed, 2009-10-21 at 10:07 -0700, David Daney wrote: > >> 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: > > Note, -pg assumes -fno-omit-frame-pointer, since -fomit-frame-pointer > and -pg are incompatible. > >> 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. > > I'll have to search the ABI documentation about calling _mcount in MIPS. > There are assumptions with _mcount that are made. It may very well be > safe to assume that the move s8,sp will always be there before an mcount > call. > Although I am quite interested in ftrace for MIPS, I a haven't spent the effort to try to figure out how many levels of backtrace we need to be generating here. If you only need the caller's address, that is passed in register 'at'. If you need more than that, then things get tricky. I would do one of two things: 1) Use the mechanism used by the OOPS dump. 2) Implement back traces based on DWARF2 unwinding data that is generated by the compiler. David Daney -- 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/