From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754555AbXIRUrd (ORCPT ); Tue, 18 Sep 2007 16:47:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754617AbXIRUr0 (ORCPT ); Tue, 18 Sep 2007 16:47:26 -0400 Received: from tomts10.bellnexxia.net ([209.226.175.54]:38819 "EHLO tomts10-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754335AbXIRUrZ (ORCPT ); Tue, 18 Sep 2007 16:47:25 -0400 Date: Tue, 18 Sep 2007 16:47:18 -0400 From: Mathieu Desnoyers To: Denys Vlasenko Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [patch 1/7] Immediate Values - Architecture Independent Code Message-ID: <20070918204718.GB12994@Krystal> References: <20070917184224.549435917@polymtl.ca> <200709181847.22905.vda.linux@googlemail.com> <20070918175902.GB2915@Krystal> <200709182101.12284.vda.linux@googlemail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <200709182101.12284.vda.linux@googlemail.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 16:44:52 up 50 days, 21:03, 4 users, load average: 0.15, 0.48, 0.67 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Denys Vlasenko (vda.linux@googlemail.com) wrote: > On Tuesday 18 September 2007 18:59, Mathieu Desnoyers wrote: > > * Denys Vlasenko (vda.linux@googlemail.com) wrote: > > > On Monday 17 September 2007 19:42, Mathieu Desnoyers wrote: > > > > Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h > > > > =================================================================== > > > > --- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h 2007-09-17 13:25:06.000000000 -0400 > > > > +++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h 2007-09-17 13:35:50.000000000 -0400 > > > > @@ -122,6 +122,13 @@ > > > > VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .; \ > > > > } \ > > > > \ > > > > + /* Immediate values: pointers */ \ > > > > + __immediate : AT(ADDR(__immediate) - LOAD_OFFSET) { \ > > > > + VMLINUX_SYMBOL(__start___immediate) = .; \ > > > > + *(__immediate) \ > > > > + VMLINUX_SYMBOL(__stop___immediate) = .; \ > > > > + } \ > > > > + \ > > > > > > Why do you need an output section for that? IOW: will this work too? > > > > > > .data : ... { > > > ... > > > > > > VMLINUX_SYMBOL(__start___immediate) = .; \ > > > *(__immediate) \ > > > VMLINUX_SYMBOL(__stop___immediate) = .; \ > > > ... > > > } > > > > > > > This last one could cause alignment problems. We either have to use the > > proper ALIGN() before the section, or let AT(ADDR(__immediate) - > > LOAD_OFFSET) take care of it. I prefer the latter. > > This adds yet another output section in vmlinux, and there is > no tools which need that. We already have 30+ sections there while we need ~20. > > I am trying to fix the mess. Please don't add to it. > > Re alignment: (1) do you really realy REALLY need it? Last I checked, > i386 was handling unaligned accesses just fine; and > (2) this works: > > . = ALIGN(4) > VMLINUX_SYMBOL(__start___immediate) = .; \ > *(__immediate) \ > VMLINUX_SYMBOL(__stop___immediate) = .; \ > > Alignment: I need the __start___immediate and __stop___immediate values to be at the same alignment as the *(__immediate) content, or else we end up thinking that padding is data. . = ALIGN(4) works fine as long as the structure within the section is not bigger or equal to 32 bytes: gcc has the habit to align 32 bytes structure on 32 bytes multiples. The safest way I found to do it is to declare the section as I do: it will cause no breakage if anybody append data to the structure. Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68