Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753468AbZJVQAz (ORCPT ); Thu, 22 Oct 2009 12:00:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752392AbZJVQAy (ORCPT ); Thu, 22 Oct 2009 12:00:54 -0400 Received: from mail3.caviumnetworks.com ([12.108.191.235]:16444 "EHLO mail3.caviumnetworks.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752430AbZJVQAx (ORCPT ); Thu, 22 Oct 2009 12:00:53 -0400 Message-ID: <4AE08173.7070500@caviumnetworks.com> Date: Thu, 22 Oct 2009 08:59:47 -0700 From: David Daney User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: wuzhangjin@gmail.com CC: rostedt@goodmis.org, 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> <1256211516.3852.47.camel@falcon> In-Reply-To: <1256211516.3852.47.camel@falcon> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 22 Oct 2009 15:59:49.0705 (UTC) FILETIME=[AF3D5B90:01CA5330] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3389 Lines: 81 Wu Zhangjin wrote: > Hi, > > On Wed, 2009-10-21 at 13:23 -0400, 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. > > Ralf have told me -pg really works with -fomit-frame-pointer, although > the gcc tool tell us they are not incompatible when we use both of them > together, but when I remove -fno-omit-frame-pointer in > KBUILD_FLAGS(enabled by CONFIG_FRAME_POINTER), it definitely remove the > s8(fp) relative source code(Seems -fomit-frame-pionter is used by > default by gcc), the leaf function becomes this: > > function: > > 80101144 : > 80101144: 03e00821 move at,ra > 80101148: 0c04271c jal 80109c70 <_mcount> > > No more instruction, > > and the non-leaf function becomes, > > 80126590 : > 80126590: 27bdffa0 addiu sp,sp,-96 > 80126594: afbf005c sw ra,92(sp) > 80126598: afbe0058 sw s8,88(sp) > 8012659c: afb70054 sw s7,84(sp) > 801265a0: afb60050 sw s6,80(sp) > 801265a4: afb5004c sw s5,76(sp) > 801265a8: afb40048 sw s4,72(sp) > 801265ac: afb30044 sw s3,68(sp) > 801265b0: afb20040 sw s2,64(sp) > 801265b4: afb1003c sw s1,60(sp) > 801265b8: afb00038 sw s0,56(sp) > 801265bc: 03e00821 move at,ra > 801265c0: 0c04271c jal 80109c70 <_mcount> > > It may save about two instructions for us. > > sw s8, offset(sp) > move s8, fp > > and also, I have tried to just search "Save" instruction, if I find one, > that should be a non-leaf function, otherwise, it's leaf function, but I > can not prove no "Save" instruction before the leaf function's "move at, > ra", for example: > > 8010113c: 03e00008 jr ra > 80101140: 00020021 nop > > 80101144 : > 80101144: 03e00821 move at,ra > 80101148: 0c04271c jal 80109c70 <_mcount> > > if there is "save" instruction at address 80101140, it will fail. > Although, I met not failure with several tries, but no prove on it! any > ABI protection for this? if YES, this should be a better solution, for > it may works without -fno-omit-frame-pointer and save several > instructions for us. This is what I was talking about up-thread. Leaf functions may have no function prolog. If you do code scanning you will fail. While scanning backwards, there is no way to know when you have entered a new function. Looking for function return sequences 'jr ra' doesn't work as there may be functions with multiple return sites, functions that never return, or arbitrary data before the function. I think you have to force a frame pointer to be established if you want this to work. 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/