From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754931AbZJEWgF (ORCPT ); Mon, 5 Oct 2009 18:36:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754234AbZJEWgE (ORCPT ); Mon, 5 Oct 2009 18:36:04 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51099 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753501AbZJEWgD (ORCPT ); Mon, 5 Oct 2009 18:36:03 -0400 Message-ID: <4ACA7577.30407@redhat.com> Date: Mon, 05 Oct 2009 18:38:47 -0400 From: Masami Hiramatsu User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.1) Gecko/20090814 Fedora/3.0-2.6.b3.fc11 Thunderbird/3.0b3 MIME-Version: 1.0 To: Frederic Weisbecker CC: Steven Rostedt , Ingo Molnar , lkml , systemtap , DLE , Thomas Gleixner , Arnaldo Carvalho de Melo , Mike Galbraith , Paul Mackerras , Peter Zijlstra , Christoph Hellwig , Ananth N Mavinakayanahalli , Jim Keniston , "Frank Ch. Eigler" Subject: Re: [PATCH tracing/kprobes v2 1/5] tracing/kprobes: Rename special variables syntax References: <20091002214834.30906.86502.stgit@dhcp-100-2-132.bos.redhat.com> <20091002214842.30906.49220.stgit@dhcp-100-2-132.bos.redhat.com> <20091003015444.GE4828@nowhere> <4AC830F0.2010003@redhat.com> <20091005191829.GA6071@nowhere> <4ACA549F.9010300@redhat.com> <20091005205826.GE6071@nowhere> <4ACA60E9.30404@redhat.com> <20091005212137.GG6071@nowhere> <4ACA6660.7020607@redhat.com> <20091005215548.GH6071@nowhere> In-Reply-To: <20091005215548.GH6071@nowhere> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Frederic Weisbecker wrote: > On Mon, Oct 05, 2009 at 05:34:24PM -0400, Masami Hiramatsu wrote: >> Hmm, one idea hits me, how about this? :) >> - %register >> - %%spvars (%%retval, %%arg0) > > > The problem is that such % or %% symbols have a specific > mean in some other well known areas. > > If we borrow the % from the AT&T assembly syntax style > to use register names, that we can retrieve in gcc inline > assembly, then one may expect %% to have a meaning inspired > from the same area. %% has its sense in gcc inline assembly, > but applied there, it looks confusing. > > I mean, I'm trying to think like someone reading a perf probe > command line without any documentation. The more this person > can understand this command line without documentation, the better. > We know that % is used for register names, some people know that %% > is used for register names too but when we are in gcc inline assembly > with var to reg resolution and need true registers name. Hmm, but %%reg syntax is only for the special case of gcc-inline assembly (e.g. assembler template, see http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html#s3). So, I guess it will not be so confusing. > Then if I try to mirror this sense from gcc to perf probe use, > I feel confused, especially in the case of %%arg1. > > In this case, we should rather have %%register and %arg0 :) > > Hm, %register is a clear pattern. > > Somehow, %retval looks clear too, retval is verbose enough and > % is still logical as return values are most of the time (always?) > put in a register. > > But %%arg0 looks confusing. Then, can we use @@ for prefix of special variables?? :-) I'm so anxious about collision between register name and those vars. Thank you, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.com