From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.17.10]:54482 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750775AbcLCKoI (ORCPT ); Sat, 3 Dec 2016 05:44:08 -0500 From: Arnd Bergmann Subject: Re: [RFC, PATCH, v3.9] default exported asm symbols to zero Date: Sat, 03 Dec 2016 11:43:07 +0100 Message-ID: <55460922.iQ4WX6OtHo@wuerfel> In-Reply-To: <1480739797.16599.118.camel@decadent.org.uk> References: <20161129131922.GA31466@angband.pl> <8452191.39CeLIHTBT@wuerfel> <1480739797.16599.118.camel@decadent.org.uk> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Ben Hutchings Cc: Linus Torvalds , Adam Borowski , Greg Kroah-Hartman , Linux Kbuild mailing list , Michal Marek , Debian kernel maintainers , "linux-arch@vger.kernel.org" , Ingo Molnar , Nicholas Piggin , Linux Kernel Mailing List , Alan Modra On Saturday, December 3, 2016 4:36:37 AM CET Ben Hutchings wrote: > On Fri, 2016-12-02 at 13:40 +0100, Arnd Bergmann wrote: > > With binutils-2.16 and before, a weak missing symbol was kept during the > > final link, and a missing CRC for an export would lead to that CRC > > being treated as zero implicitly. With binutils-2.17, the crc > > symbol gets dropped, and any module trying to use it will fail to > > load. > > > > This sets the weak CRC symbol to zero explicitly, making it defined > > in vmlinux, which in turn lets us load the modules referring to > > that CRC. > > > > The comment above the __CRC_SYMBOL macro suggests that this was > > always the intention, although it also seems that all symbols > > defined in C have a correct CRC these days, and only the exports > > that are now done in assembly need this. > > > > > Signed-off-by: Arnd Bergmann > > --- > > Not sure if this is the correct way of doing it, but this seems trivial > > enough and lets me build the kernel with missing CRCs with any binutils > > version. > > I tried this along with Adam's patch on x86_64, with Debian's binutils > 2.27.51.20161127. The result was that the kernel's __kcrctab held 0 > for several symbols, even though there was type information in asm- > prototypes.h and Module.symvers and the modules had a non-zero CRC for > those symbols. With just Adam's patch, the kernel and modules agreed. Can you be more specific? Which symbols are those? I would have expected modpost to generate Module.symvers from the vmlinux file, so I wonder where that difference comes from. Arnd