Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759143AbZGILOl (ORCPT ); Thu, 9 Jul 2009 07:14:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756216AbZGILOb (ORCPT ); Thu, 9 Jul 2009 07:14:31 -0400 Received: from ozlabs.org ([203.10.76.45]:50494 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753821AbZGILOa (ORCPT ); Thu, 9 Jul 2009 07:14:30 -0400 From: Rusty Russell To: "Jan Beulich" Subject: Re: [PATCH] reduce export symbol CRC table size on 64-bit archs Date: Thu, 9 Jul 2009 20:44:21 +0930 User-Agent: KMail/1.11.2 (Linux/2.6.28-13-generic; KDE/4.2.2; i686; ; ) Cc: "Michal Marek" , "Ingo Molnar" , tony.luck@intel.com, "Thomas Gleixner" , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-modules@vger.kernel.org, hpa@zytor.com, Jon Masters References: <4A4A18780200007800008345@vpn.id2.novell.com> <4A4E671C.2090201@suse.cz> <4A51C71B0200007800008EE2@vpn.id2.novell.com> In-Reply-To: <4A51C71B0200007800008EE2@vpn.id2.novell.com> MIME-Version: 1.0 Content-Disposition: inline Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200907092044.22108.rusty@rustcorp.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2329 Lines: 63 On Mon, 6 Jul 2009 05:12:51 pm Jan Beulich wrote: > >Jan Beulich napsal(a): > >> Since these CRCs are really only 32-bit quantities, there's no need to > >> store them in 64-bit slots. Since, however, gcc doesn't allow > >> respective initializations, asm() constructs get used to create the CRC > >> tables (and its for that reason that the patch only makes x86-64 and > >> ia64 utilize that functionality, as I can't verify this doesn't break > >> in some subtle way elsewhere). > > > >... > > > >> struct modversion_info > >> { > >> - unsigned long crc; > >> + ksym_crc_t crc; > >> char name[MODULE_NAME_LEN]; > >> }; > > > >This change breaks module-init-tools: > >Before: > >$ /sbin/modprobe --dump-modversions _build/drivers/usb/core/usbcore.ko > > > >| head > > > >0xb49b735a module_layout > >0xdb7e6a70 bus_register > >... > >After: > >$ /sbin/modprobe --dump-modversions > >_build-crc-int/drivers/usb/core/usbcore.ko | head > >0x75646f6d91ea7b5c le_layout > >0x5f7375623e215f43 register > >... > >It also breaks the newly added depmod -E option (check symbol versions), > >which also reads the struct modversion_info array (*). Is it possible > >name the section differently (__versions2?) on those architectures where > >the size changes, so that it is possible to fix m-i-t in a > >backwards-compatible manner? > > First of all I'd view it as a design bug if user mode code assumptions > prevent changes to the kernel. Yes, but unfortunately it happens. We do it much less than we used to, but there are limits. > But taking this as an uncorrectable fact, I'd think that renaming the > section would certainly be an option (though I'm unsure whether that would > have other consequences - Rusty?), however I could also imagine other means > to communicate to user land the width of a CRC value (e.g. adding an > absolute symbol during the .ko linking stage). No, just break it once. And I still like the idea that we should do something more radical if we're going to break this anyway, rather than these nasty asm hacks. Thanks, Rusty. -- 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/