From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752448AbdI2UqL (ORCPT ); Fri, 29 Sep 2017 16:46:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50056 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752003AbdI2UqK (ORCPT ); Fri, 29 Sep 2017 16:46:10 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 0D635C04AC52 Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com Date: Fri, 29 Sep 2017 15:46:09 -0500 From: Josh Poimboeuf To: Guenter Roeck Cc: linux-kernel@vger.kernel.org Subject: Re: Problems compiling with KCFLAGS="-frecord-gcc-switches" Message-ID: <20170929204609.d5bv3hevx6bjfo6m@treble> References: <20170929200056.GA3303@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170929200056.GA3303@roeck-us.net> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Fri, 29 Sep 2017 20:46:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 29, 2017 at 01:00:56PM -0700, Guenter Roeck wrote: > Hi Josh, > > when trying to compile an image with KCFLAGS="-frecord-gcc-switches", > I get the folllowing build warning/error. > > make allmodconfig > KCFLAGS="-frecord-gcc-switches" make arch/x86/kvm/emulate.o > ./tools/objtool/objtool check --no-unreachable "arch/x86/kvm/emulate.o" > > arch/x86/kvm/emulate.o: warning: > objtool: .GCC.command.line+0x0: special: can't find new instruction > > Building a full image aborts with: > > WARNING: arch/x86/kvm/kvm.o(__ex_table+0x4c): Section mismatch in reference > from the (unknown reference) (unknown) > to the variable .GCC.command.line:kvm_fastop_exception > FATAL: The relocation at __ex_table+0x4c references > section ".GCC.command.line" which is not executable, IOW > the kernel will fault if it ever tries to > jump to it. Something is seriously wrong > and should be fixed. > make[2]: *** [arch/x86/kvm/kvm.o] Error 1 > > Any idea what might cause this problem ? I think this is a GCC bug with the -frecord-gcc-switches feature. Due to some ambiguity in some inline asm in emulate.c, it's placing some kernel code in the .GCC.command.line section. This seems to fix it: diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index a36254cbf776..d90cdc77e077 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -425,8 +425,10 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *)); #op " %al \n\t" \ FOP_RET -asm(".global kvm_fastop_exception \n" - "kvm_fastop_exception: xor %esi, %esi; ret"); +asm(".pushsection .fixup, \"ax\"\n" + ".global kvm_fastop_exception \n" + "kvm_fastop_exception: xor %esi, %esi; ret\n" + ".popsection"); FOP_START(setcc) FOP_SETCC(seto)