From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 1795 invoked by alias); 17 Jul 2009 21:12:01 -0000 Received: (qmail 1782 invoked by uid 22791); 17 Jul 2009 21:12:01 -0000 X-SWARE-Spam-Status: No, hits=-1.8 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (66.187.233.31) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 17 Jul 2009 21:11:54 +0000 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id n6HLBpI6009432 for ; Fri, 17 Jul 2009 17:11:51 -0400 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id n6HLBpi3016470 for ; Fri, 17 Jul 2009 17:11:51 -0400 Received: from [10.11.8.6] (vpn-8-6.rdu.redhat.com [10.11.8.6]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id n6HLBnre007220; Fri, 17 Jul 2009 17:11:49 -0400 Message-ID: <4A60E972.1060301@redhat.com> Date: Fri, 17 Jul 2009 21:12:00 -0000 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 X-IsSubscribed: yes Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2009-q3/txt/msg00156.txt.bz2 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