From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934755Ab0HDU2Q (ORCPT ); Wed, 4 Aug 2010 16:28:16 -0400 Received: from pfepb.post.tele.dk ([195.41.46.236]:36027 "EHLO pfepb.post.tele.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758986Ab0HDU2J (ORCPT ); Wed, 4 Aug 2010 16:28:09 -0400 Date: Wed, 4 Aug 2010 22:28:06 +0200 From: Sam Ravnborg To: Mike Frysinger Cc: Linux kernel mailing list , Rusty Russell , Alan Jenkins Subject: Re: missing .data.shared_align placement in vmlinux Message-ID: <20100804202806.GA22134@merkur.ravnborg.org> References: <20100804115658.GA21357@merkur.ravnborg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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 On Wed, Aug 04, 2010 at 02:12:03PM -0400, Mike Frysinger wrote: > On Wed, Aug 4, 2010 at 07:56, Sam Ravnborg wrote: > > On Fri, May 21, 2010 at 04:58:53PM -0400, Mike Frysinger wrote: > >> am i missing something or does the .data.shared_align section lack > >> definition in vmlinux.lds.h and all arch vmlinux.lds.S files ? > >> > >> with the recent change "net: remove time limit in process_backlog()", > >> the softnet_data variable changed from "DEFINE_PER_CPU()" to > >> "DEFINE_PER_CPU_ALIGNED()" which moved it from the .data section to > >> the .data.shared_align section.  i'm not saying this patch is wrong, > >> just that is what caused me to notice this larger problem.  no one > >> else in the kernel is using this aligned macro variant, so i imagine > >> that's why no one has noticed yet. > >> > >> since .data.shared_align isnt declared in any vmlinux files that i can > >> see, the linker just places it last.  this "just works" for most > >> people, but when building a ROM kernel on Blackfin systems, it causes > >> section overlap errors: > >> bfin-uclinux-ld.real: section .init.data [00000000202e06b8 -> > >> 00000000202e48b7] overlaps section .data.shared_aligned > >> [00000000202e06b8 -> 00000000202e0723] > >> i imagine other arches which support the ROM config option and thus do > >> funky placement would see similar issues ... > >> > >> on x86, it is stuck in a dedicated section: > >>   [ 8] .data             PROGBITS        ffffffff810ec000 2ec000 > >> 0303a8 00  WA  0   0 4096 > >>   [ 9] .data.shared_alig PROGBITS        ffffffff8111c3c0 31c3c0 > >> 0000c8 00  WA  0   0 64 > >> > >> the ifdef forest in asm-generic/percpu.h is beyond a quick glance & > >> fix, so i leave it up to someone else ;) > > > > as there any resolution on this? > > I briefly looked at it some time ago. > > And it looks like a plain oversight. > > no, it's still broken in 2.6.35 :( > $ make ARCH=blackfin BF537-STAMP_defconfig > $ make ARCH=blackfin -s -j4 > $ readelf -WS vmlinux | grep '\' > [10] .data PROGBITS 0018369c 17269c 012964 00 WA 0 0 4 > [11] .data..shared_aligned PROGBITS 00196000 185000 00006c 00 > WA 0 0 4 Following simple patch should deal with it. Jeremy - you introduced this in ("x86/i386: Put aligned stack-canary in percpu shared_aligned section") 53f824520b6d84ca5b4a8fd71addc91dbf64357e Does the following simple fix look correct to you? Sam diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 030a954..e87260f 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -150,6 +150,7 @@ #define DATA_DATA \ *(.data) \ *(.ref.data) \ + *(.data..shared_aligned) /* percpu related */ \ DEV_KEEP(init.data) \ DEV_KEEP(exit.data) \ CPU_KEEP(init.data) \