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=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 73988C64E90 for ; Wed, 25 Nov 2020 22:45:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2E75D206B5 for ; Wed, 25 Nov 2020 22:45:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="mE3/9/w1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732958AbgKYWoo (ORCPT ); Wed, 25 Nov 2020 17:44:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727365AbgKYWol (ORCPT ); Wed, 25 Nov 2020 17:44:41 -0500 Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com [IPv6:2a00:1450:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9CDD7C0617A7; Wed, 25 Nov 2020 14:44:40 -0800 (PST) Received: by mail-wm1-x342.google.com with SMTP id h21so247913wmb.2; Wed, 25 Nov 2020 14:44:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=mMrMdknFbsC77SFRvwwD3pm1cwl3V2MP65kzVJE6tY4=; b=mE3/9/w1S1BsFafykdzrNl6nUKLQtv3irXzEz/AwtJdLppuZQnzVWeoYFC7Qb5OQef 2DAcZ7D6Froq/rlKPIBwqGtt0C/0XmhDJf/Ua0btTGl1wBl77rh04suLM7Drqc/fd1vb erjCUGXrwTRfKAEK60/5plkWP59Lm5M7QZ9ENMraFyUEU5TYdKtuuKGBjQ65xtLyj0UE nayIBzzwS8QdOAkDbWxTvDHZJGPoguOAiztDitejPSo1Rp931ceTN4KgHMls79AEVEp8 0UjkiGW0It0CwNfB/koaXcS1sEgjLFm2K1jcT9QDdZUmcgiCMPoll+6KvJ2hAfFlaA1V 8PSw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=mMrMdknFbsC77SFRvwwD3pm1cwl3V2MP65kzVJE6tY4=; b=R38/AmTlsvIM12T7AyYl9h5ED9p/mJot6malZaFBOIhS1UbeLy13OmOyiz1xgjm04T /HydEJD7nW6ZSDAP65iNZ4ZyQpQlKfNvvG8Zrwvv8uLZSOWvDS2YWdYP5VxYEjwyVAE8 YSM+eHBamHifsktd0Jjq0qynS/ayYPbhL9PwSiXdby3yGWsiEU1fpts0VkT3C/7OPWXj ocRKFhPpzn6ePa6qPzRQhHBuDfNd4agXbMDyMhpJ4ap7fdFyO0BWuBv8VWH5RgyxCUwY 6Y0qWuDQb3TIvXwQT3pLdiSqYvZXlMRLdWDiZDbV/WByUr20I1nWQ2LPTZlO1wjSr71m 2AEQ== X-Gm-Message-State: AOAM532eKSvBjVG+OsfR5iiFXRN7Ljtttg7gTeLIoTGmff0y9VxAQec7 jDz3jNowF+BUGdrP0/LKn/s= X-Google-Smtp-Source: ABdhPJzVXPr1uOlB1vaw2cfl6zSoOiLq1F6oo5r6Yg/UanqxqpZONWe00UKvdrBaRFZ4o0pgYT/ByA== X-Received: by 2002:a7b:cf0a:: with SMTP id l10mr6364382wmg.103.1606344279394; Wed, 25 Nov 2020 14:44:39 -0800 (PST) Received: from [192.168.1.122] (cpc92720-cmbg20-2-0-cust364.5-4.cable.virginm.net. [82.21.83.109]) by smtp.gmail.com with ESMTPSA id h15sm6411655wrw.15.2020.11.25.14.44.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Nov 2020 14:44:38 -0800 (PST) Subject: Re: [PATCH 000/141] Fix fall-through warnings for Clang To: Miguel Ojeda , James Bottomley Cc: Kees Cook , Jakub Kicinski , "Gustavo A. R. Silva" , linux-kernel , alsa-devel@alsa-project.org, amd-gfx@lists.freedesktop.org, bridge@lists.linux-foundation.org, ceph-devel@vger.kernel.org, cluster-devel@redhat.com, coreteam@netfilter.org, devel@driverdev.osuosl.org, dm-devel@redhat.com, drbd-dev@lists.linbit.com, dri-devel@lists.freedesktop.org, GR-everest-linux-l2@marvell.com, GR-Linux-NIC-Dev@marvell.com, intel-gfx@lists.freedesktop.org, intel-wired-lan@lists.osuosl.org, keyrings@vger.kernel.org, linux1394-devel@lists.sourceforge.net, linux-acpi@vger.kernel.org, linux-afs@lists.infradead.org, Linux ARM , linux-arm-msm@vger.kernel.org, linux-atm-general@lists.sourceforge.net, linux-block@vger.kernel.org, linux-can@vger.kernel.org, linux-cifs@vger.kernel.org, Linux Crypto Mailing List , linux-decnet-user@lists.sourceforge.net, Ext4 Developers List , linux-fbdev@vger.kernel.org, linux-geode@lists.infradead.org, linux-gpio@vger.kernel.org, linux-hams@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-i3c@lists.infradead.org, linux-ide@vger.kernel.org, linux-iio@vger.kernel.org, linux-input , linux-integrity@vger.kernel.org, linux-mediatek@lists.infradead.org, Linux Media Mailing List , linux-mmc@vger.kernel.org, Linux-MM , linux-mtd@lists.infradead.org, linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-scsi@vger.kernel.org, linux-sctp@vger.kernel.org, linux-security-module@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-usb@vger.kernel.org, linux-watchdog@vger.kernel.org, linux-wireless , Network Development , netfilter-devel@vger.kernel.org, nouveau@lists.freedesktop.org, op-tee@lists.trustedfirmware.org, oss-drivers@netronome.com, patches@opensource.cirrus.com, rds-devel@oss.oracle.com, reiserfs-devel@vger.kernel.org, samba-technical@lists.samba.org, selinux@vger.kernel.org, target-devel@vger.kernel.org, tipc-discussion@lists.sourceforge.net, usb-storage@lists.one-eyed-alien.net, virtualization@lists.linux-foundation.org, wcn36xx@lists.infradead.org, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , xen-devel@lists.xenproject.org, linux-hardening@vger.kernel.org, Nick Desaulniers , Nathan Chancellor , Miguel Ojeda , Joe Perches References: <20201120105344.4345c14e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <202011201129.B13FDB3C@keescook> <20201120115142.292999b2@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <202011220816.8B6591A@keescook> <9b57fd4914b46f38d54087d75e072d6e947cb56d.camel@HansenPartnership.com> <1c7d7fde126bc0acf825766de64bf2f9b888f216.camel@HansenPartnership.com> <4993259d01a0064f8bb22770503490f9252f3659.camel@HansenPartnership.com> From: Edward Cree Message-ID: <44005bde-f6d4-5eaa-39b8-1a5efeedb2d3@gmail.com> Date: Wed, 25 Nov 2020 22:44:35 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: On 25/11/2020 00:32, Miguel Ojeda wrote: > I have said *authoring* lines of *this* kind takes a minute per line. > Specifically: lines fixing the fallthrough warning mechanically and > repeatedly where the compiler tells you to, and doing so full-time for > a month. > It is useful since it makes intent clear. To make the intent clear, you have to first be certain that you understand the intent; otherwise by adding either a break or a fallthrough to suppress the warning you are just destroying the information that "the intent of this code is unknown". Figuring out the intent of a piece of unfamiliar code takes more than 1 minute; just because case foo: thing; case bar: break; produces identical code to case foo: thing; break; case bar: break; doesn't mean that *either* is correct — maybe the author meant to write case foo: return thing; case bar: break; and by inserting that break you've destroyed the marker that would direct someone who knew what the code was about to look at that point in the code and spot the problem. Thus, you *always* have to look at more than just the immediate mechanical context of the code, to make a proper judgement that yes, this was the intent. If you think that that sort of thing can be done in an *average* time of one minute, then I hope you stay away from code I'm responsible for! One minute would be an optimistic target for code that, as the maintainer, one is already somewhat familiar with. For code that you're seeing for the first time, as is usually the case with the people doing these mechanical fix-a-warning patches, it's completely unrealistic. A warning is only useful because it makes you *think* about the code. If you suppress the warning without doing that thinking, then you made the warning useless; and if the warning made you think about code that didn't *need* it, then the warning was useless from the start. So make your mind up: does Clang's stricter -Wimplicit-fallthrough flag up code that needs thought (in which case the fixes take effort both to author and to review) or does it flag up code that can be mindlessly "fixed" (in which case the warning is worthless)? Proponents in this thread seem to be trying to have it both ways. -ed