Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753477AbZGQU2a (ORCPT ); Fri, 17 Jul 2009 16:28:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751397AbZGQU2a (ORCPT ); Fri, 17 Jul 2009 16:28:30 -0400 Received: from pfepa.post.tele.dk ([195.41.46.235]:53316 "EHLO pfepa.post.tele.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751295AbZGQU23 (ORCPT ); Fri, 17 Jul 2009 16:28:29 -0400 Date: Fri, 17 Jul 2009 22:28:25 +0200 From: Sam Ravnborg To: Steven Rostedt Cc: Masami Hiramatsu , 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 Message-ID: <20090717202825.GA6872@merkur.ravnborg.org> Mail-Followup-To: Steven Rostedt , Masami Hiramatsu , Ingo Molnar , Ananth N Mavinakayanahalli , lkml , systemtap , DLE , Jim Keniston , Srikar Dronamraju , Christoph Hellwig , Frederic Weisbecker , "H. Peter Anvin" , Anders Kaseorg , Tim Abbott References: <20090622212255.5384.53732.stgit@localhost.localdomain> <20090622212313.5384.84166.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1983 Lines: 63 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. > > > > > 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. > > > > 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. Sam -- 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/