From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753286AbaIYNeL (ORCPT ); Thu, 25 Sep 2014 09:34:11 -0400 Received: from cantor2.suse.de ([195.135.220.15]:41210 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751650AbaIYNeI (ORCPT ); Thu, 25 Sep 2014 09:34:08 -0400 Message-ID: <542419CB.3090902@suse.cz> Date: Thu, 25 Sep 2014 15:34:03 +0200 From: Michal Marek User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.0 MIME-Version: 1.0 To: Behan Webster CC: ak@linux.intel.com, yamada.m@jp.panasonic.com, hpa@linux.intel.com, linux-kernel@vger.kernel.org, sam@ravnborg.org, Mark Charlebois Subject: Re: [PATCH] kbuild, LLVMLinux: Add -Werror to cc-option to support clang References: <1411500522-11480-1-git-send-email-behanw@converseincode.com> <5422B3EF.4000800@suse.cz> <5423128D.8070708@converseincode.com> In-Reply-To: <5423128D.8070708@converseincode.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 On 2014-09-24 20:50, Behan Webster wrote: > On 09/24/14 05:07, Michal Marek wrote: >> On 2014-09-23 21:28, behanw@converseincode.com wrote: >>> From: Mark Charlebois >>> >>> Clang will warn about unknown warnings but will not return false >> You mean unknown options, right? > 2 kinds of options: flags and warnings. clang used to merely warn about > unused/unsupported flags/warnings. It now returns errors for unknown > flags, but not warnings (unless you specify -Werror). Ah, unknown warning options. Now I understand. > Getting clang to error on unused flags wasn't trivial (this change broke > a lot of builds apparently). Fortunately we weren't the only ones who > wanted it to behave like gcc in this case. I think it's going to be > *much* harder to do the same for warnings. The argument given by > supporters of the current situation is that if a warning isn't > supported, why break the build? *sigh* I guess the reason to accept unknown warnings opentions is compatibility with Makefiles with hardcoded gcc-isms. BTW, GCC at some point started to ignore unknown -Wno-* options, for everyone's good of course. That's why we ended up with the cc-disable-warning function. If -W* options for clang need special care, then it might be a good idea to introduce cc-warning with the conditional -Werror for clang. There are not that many places where we add warnings, so the patch would be still short. That way, the possible silent failure is limited only to warning options with clang, which is not such a big deal. Michal