From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1FC98C636C9 for ; Fri, 16 Jul 2021 01:35:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED34B613C9 for ; Fri, 16 Jul 2021 01:35:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231347AbhGPBif (ORCPT ); Thu, 15 Jul 2021 21:38:35 -0400 Received: from gateway22.websitewelcome.com ([192.185.47.129]:24898 "EHLO gateway22.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229603AbhGPBie (ORCPT ); Thu, 15 Jul 2021 21:38:34 -0400 X-Greylist: delayed 1265 seconds by postgrey-1.27 at vger.kernel.org; Thu, 15 Jul 2021 21:38:34 EDT Received: from cm10.websitewelcome.com (cm10.websitewelcome.com [100.42.49.4]) by gateway22.websitewelcome.com (Postfix) with ESMTP id 3F99B4B25 for ; Thu, 15 Jul 2021 20:14:33 -0500 (CDT) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id 4CQzmZxYioIHn4CQzmp1ge; Thu, 15 Jul 2021 20:14:33 -0500 X-Authority-Reason: nr=8 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=embeddedor.com; s=default; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Vg9ITUv3dvdluW4XbvT6qOkw4QFMgdzrrGPJ8XWGWaE=; b=Uj6B+gUH7WDB2k4RRHo4GqNNkM TvZwhKmRn7zBbRJ8hvUYvUbBPfBo6jTM5HMkRHHuVo3qUNIizZFKN2BGi6HbVuACoAj+RwYcSSAj2 DFVFR9+w+rm4+7PtNhF0PJnfgwc5NsAlKtJMa3SnLEP5X6l5693Kf/wzBUgZWlNnYQPvhyr9Twgjn DXDg4i+PRkhli9YSA0t00beomVDCDwtai/NdTRna5SH34rMd+5a0G64n7whB/S2D1Ofj6eWQ4GHRx YVb9GqtcokiZ8GosuTiOuUSUGyMRY6Y2xn3mzfY2KdTWChL3ZebBfXQtCDxd7FNOQjgeYv4t9sxcV jOdCQDhg==; Received: from 187-162-31-110.static.axtel.net ([187.162.31.110]:40422 helo=[192.168.15.8]) by gator4166.hostgator.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1m4CQw-003OJB-57; Thu, 15 Jul 2021 20:14:30 -0500 Subject: Re: [GIT PULL] fallthrough fixes for Clang for 5.14-rc2 To: Linus Torvalds , "Gustavo A. R. Silva" , Nathan Chancellor , Nick Desaulniers Cc: Kees Cook , Linux Kernel Mailing List , clang-built-linux References: <20210714200523.GA10606@embeddedor> From: "Gustavo A. R. Silva" Message-ID: <5d170cc8-501d-0cec-bf03-2f53108a8486@embeddedor.com> Date: Thu, 15 Jul 2021 20:16:37 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 187.162.31.110 X-Source-L: No X-Exim-ID: 1m4CQw-003OJB-57 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 187-162-31-110.static.axtel.net ([192.168.15.8]) [187.162.31.110]:40422 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 6 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/15/21 20:04, Linus Torvalds wrote: > On Wed, Jul 14, 2021 at 1:03 PM Gustavo A. R. Silva > wrote: >> >> git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git tags/Wimplicit-fallthrough-clang-5.14-rc2 > > Grr. > > I merged this, but when I actually tested it on my clang build, it > turns out that the clang "-Wimplicit-fallthrough" flag is unbelievable > garbage. > > I get > > warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough] Kees just opened a bug report for this: https://bugs.llvm.org/show_bug.cgi?id=51094 -- Gustavo > > and the stupid warning doesn't even say WHERE THE PROBLEM HAPPENS. > > No file name, no line numbers. Just this pointless garbage warning. > > Honestly, how does a compiler even do something that broken? Am I > supposed to use my sixth sense to guide me in finding the warning? > > I like the concept of the fallthrough warning, but it looks like the > clang implementation of it is so unbelievably broken that it's getting > disabled again. > > Yeah, I can > > (a) build the kernel without any parallelism > > (b) use ">&" to get both output and errors into the same file > > (c) see that it says > > CC kernel/sched/core.o > warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough] > 1 warning generated. > > and now I see at least which _file_ it is that causes that warning. > > I can then use my incredible powers of deduction (it's almost like a > sixth sense, but helped by the fact that there's only one single > "fallthrough" statement in that file) to figure out that it's > triggered by this code: > > case cpuset: > if (IS_ENABLED(CONFIG_CPUSETS)) { > cpuset_cpus_allowed_fallback(p); > state = possible; > break; > } > fallthrough; > case possible: > > and it all makes it clear that the clang warning is just incredibly > broken garbage not only in that lack of filename and line number, but > just in general. > > Yeah, I'm a bit pissed off at this. This clang warning really is > WRONG. It's so wrong in so many ways that I don't know what to say. > > Except "yeah, that broken option is getting reverted again, because > the clang people messed up completely". > > It's sad to see that people wasted time and effort on trying to make > clang happy, when it turns out that clang just gets this so _totally_ > wrong. > > Linus >