Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754347AbYGZMh0 (ORCPT ); Sat, 26 Jul 2008 08:37:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751846AbYGZMhP (ORCPT ); Sat, 26 Jul 2008 08:37:15 -0400 Received: from gate.crashing.org ([63.228.1.57]:49765 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750934AbYGZMhO (ORCPT ); Sat, 26 Jul 2008 08:37:14 -0400 Subject: Re: CONFIG_FRAME_POINTER [was [PATCH] x86: BUILD_IRQ say .text] From: Benjamin Herrenschmidt Reply-To: benh@kernel.crashing.org To: Hugh Dickins Cc: Ingo Molnar , Mike Travis , linux-kernel@vger.kernel.org, the arch/x86 maintainers , Linuxppc-dev@ozlabs.org In-Reply-To: References: <20080724104459.GI28817@elte.hu> <1217022373.11188.115.camel@pasglop> Content-Type: text/plain Date: Sat, 26 Jul 2008 22:36:42 +1000 Message-Id: <1217075802.11188.129.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.22.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1275 Lines: 32 On Sat, 2008-07-26 at 12:02 +0100, Hugh Dickins wrote: > > Hmm, perhaps it is doing sibling calls differently even without the > explicit -fno-optimize-sibling-calls (but when I add that option, > the vmlinux size does go up another 4400). > > Sorry, I'm most probably fussing over nothing, > and wasting your time with my ignorance. No you aren't, there is indeed something happening. It looks like gcc is keeping a copy of each stack frame in r31, thus forcing to save/restore that register, along function calls, possibly to help get reliable frames for leaf functions. I don't think we use that "feature" in our backtrace code though... so it won't harm in the sense that it won't break things, but it will indeed bloat the code a little bit. Maybe we should totally disable -fno-omit-frame-pointers on powerpc ... either that or see about actually using that r31 linkage, though I'm not sure it would be that useful. I'll have to talk to our toolchain folks to figure out exactly what's going on there. Cheers, Ben. -- 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/