Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757510AbZGQVM3 (ORCPT ); Fri, 17 Jul 2009 17:12:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757025AbZGQVM3 (ORCPT ); Fri, 17 Jul 2009 17:12:29 -0400 Received: from mx2.redhat.com ([66.187.237.31]:51780 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755090AbZGQVM2 (ORCPT ); Fri, 17 Jul 2009 17:12:28 -0400 Message-ID: <4A60E972.1060301@redhat.com> Date: Fri, 17 Jul 2009 17:13:22 -0400 From: Masami Hiramatsu User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: Steven Rostedt , Ingo Molnar , Ananth N Mavinakayanahalli , lkml , systemtap , DLE , Jim Keniston , Srikar Dronamraju , Christoph Hellwig , Frederic Weisbecker , "H. Peter Anvin" , Anders Kaseorg , Tim Abbott Subject: Re: [RFC][ PATCH -tip v2 3/7] Kbuild: disable gcc crossjumping References: <20090622212255.5384.53732.stgit@localhost.localdomain> <20090622212313.5384.84166.stgit@localhost.localdomain> <20090717202825.GA6872@merkur.ravnborg.org> In-Reply-To: <20090717202825.GA6872@merkur.ravnborg.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2407 Lines: 80 Sam Ravnborg wrote: > On Sat, Jun 27, 2009 at 04:13:04PM -0400, Steven Rostedt wrote: >> A change like this requires an ACK from Sam Ravnborg. >> >> -- Steve > > Overdue review... > > I do not know the gcc option so I cannot comment on theeffect of it. Thanks for comment. however, as far as I can see, I couldn't find in the difference between binary with -fno-crossjump and without it. So I decided to drop this patch... > >>> diff --git a/Makefile b/Makefile >>> index 2903e13..f73b139 100644 >>> --- a/Makefile >>> +++ b/Makefile >>> @@ -524,6 +524,10 @@ else >>> KBUILD_CFLAGS += -O2 >>> endif >>> >>> +ifdef CONFIG_DISABLE_CROSSJUMP >>> +KBUILD_CFLAGS += -fno-crossjumping >>> +endif >>> + >>> include $(srctree)/arch/$(SRCARCH)/Makefile > > Why do we add this option _before_ we include the arch specific Makefile? > If we do not want the arch specific Makefile to undo this then move it lower. > > Also please add a comment what the effect of the disabling is. > There is no reason I should fire up info gcc to find out > what -fno-crossjumping is about. Sure, I'll write a comment on, next time. > > >>> >>> ifneq ($(CONFIG_FRAME_WARN),0) >>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug >>> index 8da7467..f88e6b8 100644 >>> --- a/lib/Kconfig.debug >>> +++ b/lib/Kconfig.debug >>> @@ -673,6 +673,13 @@ config FRAME_POINTER >>> larger and slower, but it gives very useful debugging information >>> in case of kernel bugs. (precise oopses/stacktraces/warnings) >>> >>> +config DISABLE_CROSSJUMP >>> + bool "Disable cross-function jump optimization" >>> + help >>> + This build option disables cross-function jump optimization >>> + (crossjumping) of gcc. Disabling crossjumping might increase >>> + kernel binary size a little. > > So the above comment tells me that is I disable crossjumping I will > increase the kernel image a little. > That is by no means a good explanation. > > Please explain the potential advantage of disabling crossjumping. Agreed. Thank you, -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division e-mail: mhiramat@redhat.com -- 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/