From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934422Ab1IOSmb (ORCPT ); Thu, 15 Sep 2011 14:42:31 -0400 Received: from wolverine02.qualcomm.com ([199.106.114.251]:5220 "EHLO wolverine02.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934209Ab1IOSma (ORCPT ); Thu, 15 Sep 2011 14:42:30 -0400 X-IronPort-AV: E=McAfee;i="5400,1158,6470"; a="118829119" Message-ID: <4E724715.1030505@codeaurora.org> Date: Thu, 15 Sep 2011 11:42:29 -0700 From: Stephen Boyd User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:6.0.2) Gecko/20110902 Thunderbird/6.0.2 MIME-Version: 1.0 To: Russell King - ARM Linux CC: Rob Herring , "linux-arm-kernel@lists.infradead.org" , linux-kbuild@vger.kernel.org, Linux Kernel Mailing List Subject: Re: 3.1-rc1 link failure References: <4E402FBB.2070401@gmail.com> <20110808195804.GD19367@n2100.arm.linux.org.uk> In-Reply-To: <20110808195804.GD19367@n2100.arm.linux.org.uk> 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 ( Including full text for other lists) On 08/08/11 12:58, Russell King - ARM Linux wrote: > On Mon, Aug 08, 2011 at 01:49:31PM -0500, Rob Herring wrote: >> Russell, >> >> This commit is causing some link failures: >> >> ARM: vmlinux.lds: move discarded sections to beginning >> >> Rather than scattering the discarded sections throughout the linker >> file, move them to the start. >> >> Acked-by: Nicolas Pitre >> Tested-by: Stephen Boyd >> Signed-off-by: Russell King >> >> The error is this: >> >> `.exit.text' referenced in section `.alt.smp.init' of >> drivers/built-in.o: defined in discarded section `.exit.text' of >> drivers/built >> -in.o >> `.exit.text' referenced in section `.alt.smp.init' of net/built-in.o: >> defined in discarded section `.exit.text' of net/built-in.o >> >> I traced the one in net/ to CONFIG_SMP_ON_UP=y and CONFIG_DCB=y. >> dcbnl_exit calls dcb_flushapp which contains a spinlock. dcb_flushapp is >> getting inlined into dcbnl_exit. > Argh. This is going to be an absolute _pig_ to fix. > > This is the relevent part of the linker script (reformatted to make it > clearer): > > | SECTIONS > | { > | /* > | * unwind exit sections must be discarded before the rest of the > | * unwind sections get included. > | */ > | /DISCARD/ : { > | *(.ARM.exidx.exit.text) > | *(.ARM.extab.exit.text) > | } > | ... > | .exit.text : { > | *(.exit.text) > | *(.memexit.text) > | } > | ... > | /DISCARD/ : { > | *(.exit.text) > | *(.memexit.text) > | *(.exit.data) > | *(.memexit.data) > | *(.memexit.rodata) > | *(.exitcall.exit) > | *(.discard) > | *(.discard.*) > | } > | } > > Now, this is what the linker manual says about discarded output sections: > > | The special output section name `/DISCARD/' may be used to discard > | input sections. Any input sections which are assigned to an output > | section named `/DISCARD/' are not included in the output file. > > No questions, no exceptions. It doesn't say "unless they are listed > before the /DISCARD/ section." Now, this is what asn-generic/vmlinux.lds.S > says: > > | /* > | * Default discarded sections. > | * > | * Some archs want to discard exit text/data at runtime rather than > | * link time due to cross-section references such as alt instructions, > | * bug table, eh_frame, etc. DISCARDS must be the last of output > | * section definitions so that such archs put those in earlier section > | * definitions. > | */ > > And guess what - the list _always_ includes .exit.text etc. > > Now, what's actually happening is that the linker is reading the script, > and it finds the first /DISCARD/ output section at the beginning of the > script. It continues reading the script, and finds the 'DISCARD' macro > at the end, which having been postprocessed results in another > /DISCARD/ output section. As the linker already contains the earlier > /DISCARD/ output section, it adds it to that existing section, so it > effectively is placed at the start. This can be seen by using the -M > option to ld: > > | Linker script and memory map > | > | 0xc037c080 jiffies = jiffies_64 > | > | /DISCARD/ > | *(.ARM.exidx.exit.text) > | *(.ARM.extab.exit.text) > | *(.exit.text) > | *(.memexit.text) > | *(.exit.data) > | *(.memexit.data) > | *(.memexit.rodata) > | *(.exitcall.exit) > | *(.discard) > | *(.discard.*) > | > | 0xc0008000 . = 0xc0008000 > | > | .head.text 0xc0008000 0x1d0 > | 0xc0008000 _text = . > | *(.head.text) > | .head.text 0xc0008000 0x1d0 arch/arm/kernel/head.o > | 0xc0008000 stext > | > | .text 0xc0008200 0x2d78d0 > | 0xc0008200 _stext = . > | 0xc0008200 __exception_text_start = . > | *(.exception.text) > | .exception.text > | ... > > As you can see, all the discarded sections are grouped together - and > as a result of it being the first output section, they all appear before > any other section. > > The result is that not only is the unwind information discarded (as > intended), but also the .exit.text, despite us wanting to have the > .exit.text preserved. > > We can't move the unwind information elsewhere, because it'll then be > included even when we do actually discard the .exit.text (and similar) > sections. > > The only solution that I can think of is to stop using this > asm-generic/vmlinux.lds.S and write our own fully conditionalized > linker script, ensuring that no input section is mentioned more than > once in the output sections. > > Or someone sorts out the asm-generic/vmlinux.lds.S stuff to actually > conform to the linker manual, and stop relying on implementation defined > behaviour of the linker - again by having it fully conditionalized. > Now that the generic bug patch has been merged to linux-next a lot of ARM builds are failing like so: `.exit.text' referenced in section `__bug_table' of net/built-in.o: defined in discarded section `.exit.text' of net/built-in.o `.exit.text' referenced in section `__bug_table' of net/built-in.o: defined in discarded section `.exit.text' of net/built-in.o `.exit.text' referenced in section `__bug_table' of net/built-in.o: defined in discarded section `.exit.text' of net/built-in.o I'm not sure what the fix is here. Hopefully we can figure out how to keep using the asm-generic stuff. -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.