From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756270Ab3AOVe4 (ORCPT ); Tue, 15 Jan 2013 16:34:56 -0500 Received: from mail-da0-f46.google.com ([209.85.210.46]:52912 "EHLO mail-da0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751280Ab3AOVez (ORCPT ); Tue, 15 Jan 2013 16:34:55 -0500 Message-ID: <50F5CB78.20800@gmail.com> Date: Tue, 15 Jan 2013 13:34:48 -0800 From: David Daney User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Steven Rostedt CC: Al Cooper , ralf@linux-mips.org, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mips: function tracer: Fix broken function tracing References: <1357914810-20656-1-git-send-email-alcooperx@gmail.com> <50F0454D.5060109@gmail.com> <20130115034006.GA3854@home.goodmis.org> <50F59812.6040806@gmail.com> <1358284049.4068.21.camel@gandalf.local.home> In-Reply-To: <1358284049.4068.21.camel@gandalf.local.home> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/15/2013 01:07 PM, Steven Rostedt wrote: > On Tue, 2013-01-15 at 09:55 -0800, David Daney wrote: > >>> There's nothing that states what the ftrace caller must be. We can have >>> it do a proper stack update. That is, only at boot up do we need to >>> handle the defined mcount. After that, those instructions are just place >>> holders for our own algorithms. If the addiu was needed for the defined >>> mcount, there's no reason to keep it for our own ftrace_caller. >>> >>> Would that work? >> >> ... either do as you suggest and dynamically change the ABI of the >> target function. > > We already change the ABI. We have it call ftrace_caller instead of > mcount. > > BTW, I've just compiled with gcc 4.6.3 against mips, and I don't see the > issue. I have: > > 0000000000000000 : > 0: 03e0082d move at,ra > 4: 0c000000 jal 0 > 4: R_MIPS_26 _mcount > 4: R_MIPS_NONE *ABS* > 4: R_MIPS_NONE *ABS* > 8: 0000602d move t0,zero > c: 2402000d li v0,13 > 10: 3c030000 lui v1,0x0 > 10: R_MIPS_HI16 mem_section > 10: R_MIPS_NONE *ABS* > 10: R_MIPS_NONE *ABS* > 14: 000216fc dsll32 v0,v0,0x1b > 18: 64630000 daddiu v1,v1,0 > > Is it dependent on the config? Yes. You need to select a 32-bit kernel (which in turn may require selecting a board type that also supports it). The ABI is different for 32-bit and 64-bit _mcount. David Daney > >> >> Or add support to GCC for a better tracing ABI (as I already said we did >> for mips64). > > I wouldn't waste time changing gcc for this. If you're going to change > gcc than please implement the -mfentry option. Look at x86_64 to > understand this more. A good point. But I don't really plan on doing any work related to 32-bit mips things at this point, so any such change would have to be done by someone else. David Daney