Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754052AbdDMX7t (ORCPT ); Thu, 13 Apr 2017 19:59:49 -0400 Received: from terminus.zytor.com ([65.50.211.136]:36993 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752635AbdDMX7r (ORCPT ); Thu, 13 Apr 2017 19:59:47 -0400 Subject: Re: [PATCH 3/7] x86, LLVM: suppress clang warnings about unaligned accesses To: Matthias Kaehlcke References: <20170317001520.85223-1-md@google.com> <20170317001520.85223-4-md@google.com> <20170403230158.GA145051@google.com> <20170413231439.GG28657@google.com> Cc: Michael Davidson , Michal Marek , Thomas Gleixner , Ingo Molnar , Herbert Xu , "David S. Miller" , Shaohua Li , Alexander Potapenko , Dmitry Vyukov , x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, linux-raid@vger.kernel.org From: "H. Peter Anvin" Message-ID: <3b743cf7-3d81-1fd6-b3a9-2f58a3bd8817@zytor.com> Date: Thu, 13 Apr 2017 16:55:00 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170413231439.GG28657@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1659 Lines: 49 On 04/13/17 16:14, Matthias Kaehlcke wrote: > El Mon, Apr 03, 2017 at 04:01:58PM -0700 Matthias Kaehlcke ha dit: > >> El Fri, Mar 17, 2017 at 04:50:19PM -0700 hpa@zytor.com ha dit: >> >>> On March 16, 2017 5:15:16 PM PDT, Michael Davidson wrote: >>>> Suppress clang warnings about potential unaliged accesses >>>> to members in packed structs. This gets rid of almost 10,000 >>>> warnings about accesses to the ring 0 stack pointer in the TSS. >>>> >>>> Signed-off-by: Michael Davidson >>>> --- >>>> arch/x86/Makefile | 5 +++++ >>>> 1 file changed, 5 insertions(+) >>>> >>>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile >>>> index 894a8d18bf97..7f21703c475d 100644 >>>> --- a/arch/x86/Makefile >>>> +++ b/arch/x86/Makefile >>>> @@ -128,6 +128,11 @@ endif >>>> KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args) >>>> endif >>>> >>>> +ifeq ($(cc-name),clang) >>>> +# Suppress clang warnings about potential unaligned accesses. >>>> +KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) >>>> +endif >>>> + >>>> ifdef CONFIG_X86_X32 >>>> x32_ld_ok := $(call try-run,\ >>>> /bin/echo -e '1: .quad 1b' | \ >>> >>> Why conditional on clang? >> >> My understanding is that this warning is clang specific, it is not >> listed on https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html > > Actually this warning affects other platforms besides x86 > (e.g. arm64), I'll submit a patch that disables the warning on all > platforms. > Drop the ifeq ($(cc-name),clang). You should assume that if you have to add one of those ifeq's then you are doing something fundamentally wrong. -hpa