Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753496AbZJYPzj (ORCPT ); Sun, 25 Oct 2009 11:55:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752273AbZJYPzi (ORCPT ); Sun, 25 Oct 2009 11:55:38 -0400 Received: from ey-out-2122.google.com ([74.125.78.25]:27925 "EHLO ey-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752230AbZJYPzh (ORCPT ); Sun, 25 Oct 2009 11:55:37 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=to:mail-followup-to:cc:subject:references:from:date:in-reply-to :message-id:user-agent:mime-version:content-type; b=BO8pF0lxauexkC0RaDocu4em969cfEOq4UVtL+EgxWwr52ZWRE2BoRZO/mzdz2R2dG E9RanD/Yz25wOoCMFVVqIkQOpInUrGhEm2dRnFtneWKxuQ6llgmx/aJsyKiM+AQ+hjlj HyQdjiGPnnxEBlukNqE1Q3NyKRTEZPh+cOoEY= To: wuzhangjin@gmail.com Mail-Followup-To: wuzhangjin@gmail.com,pajko , linux-kernel@vger.kernel.org, GCC Patches , Adam Nemet , rostedt@goodmis.org, linux-mips@linux-mips.org, Thomas Gleixner , Ralf Baechle , Nicholas Mc Guire , David Daney , rdsandiford@googlemail.com Cc: pajko , linux-kernel@vger.kernel.org, GCC Patches , Adam Nemet , rostedt@goodmis.org, linux-mips@linux-mips.org, Thomas Gleixner , Ralf Baechle , Nicholas Mc Guire , David Daney 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> <53bdfdd95ec4fa00d4cc505bb5972cf21243a14d.1256135456.git.wuzhangjin@gmail.com> <26008418.post@talk.nabble.com> <1256467717.6143.13.camel@falcon> From: Richard Sandiford Date: Sun, 25 Oct 2009 15:55:34 +0000 In-Reply-To: <1256467717.6143.13.camel@falcon> (Wu Zhangjin's message of "Sun\, 25 Oct 2009 18\:48\:37 +0800") Message-ID: <87hbtn1n9l.fsf@firetop.home> User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2127 Lines: 47 Wu Zhangjin writes: > (Added linux-mips mailing list and the other people to the CC list.) > > On Thu, 2009-10-22 at 04:37 -0700, pajko wrote: > [...] >> > >> >> All this stuff can be avoided having PROFILE_BEFORE_PROLOGUE enabled in GCC >> (gcc/config/mips/mips.h), like it is done one several other architectures. >> Some of them even require it to be set for a working _mcount. >> Putting the call of _mcount before the function prologue should make no harm >> (it's working for me), and this way RA can be hooked for function graph >> tracing >> before it is saved to stack in the function prologue. Thus there will be no >> difference between leaf and non-leaf functions. > > Good idea! Seems PROFILE_BEFORE_PROLOGUE is commented by default in > gcc/config/mips/mips.h of gcc 4.4: > > /* #define PROFILE_BEFORE_PROLOGUE */ > > if we enable this macro, the handling will be the same to non-leaf and > leaf function, so, David's patch to gcc is not need again. Defining PROFILE_BEFORE_PROLOGUE isn't correct for abicalls code, because "jal _mcount" is a macro that loads _mcount from the GOT into $25. We don't have access to $28 at the beginning of the function, and we mustn't clobber the incoming value of $25. So we could only make this change for non-abicalls code. It's then a choice between (a) having new non-abicalls-specific behaviour or (b) going with David's patch. The advantage of (a) is that the linux code is slightly simpler. The disadvantage is that it makes the _mcount interface differ between -mabicalls and -mno-abicalls. And IMO the disadvantage outweights the advantage. If this new behaviour is useful for linux, it could easily be useful for userspace too. And with the new PLT support, non-shared abicalls code is supposed to be link-compatible with non-abicalls code. I think David's patch is the way to go. Richard -- 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/