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=-2.7 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,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 10C3EC64E7B for ; Tue, 24 Nov 2020 23:47:11 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9ED602100A for ; Tue, 24 Nov 2020 23:47:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="rGjC6KnG" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9ED602100A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.37054.69204 (Exim 4.92) (envelope-from ) id 1khi17-00040C-B0; Tue, 24 Nov 2020 23:46:37 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 37054.69204; Tue, 24 Nov 2020 23:46:37 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1khi17-000405-75; Tue, 24 Nov 2020 23:46:37 +0000 Received: by outflank-mailman (input) for mailman id 37054; Tue, 24 Nov 2020 23:46:35 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1khi15-000400-Q8 for xen-devel@lists.xenproject.org; Tue, 24 Nov 2020 23:46:35 +0000 Received: from mail-qk1-x744.google.com (unknown [2607:f8b0:4864:20::744]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 976f89c0-f7cb-48ac-b69b-db25c4fb0b5b; Tue, 24 Nov 2020 23:46:34 +0000 (UTC) Received: by mail-qk1-x744.google.com with SMTP id z188so1152979qke.9 for ; Tue, 24 Nov 2020 15:46:34 -0800 (PST) Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1khi15-000400-Q8 for xen-devel@lists.xenproject.org; Tue, 24 Nov 2020 23:46:35 +0000 X-Inumbo-ID: 976f89c0-f7cb-48ac-b69b-db25c4fb0b5b Received: from mail-qk1-x744.google.com (unknown [2607:f8b0:4864:20::744]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 976f89c0-f7cb-48ac-b69b-db25c4fb0b5b; Tue, 24 Nov 2020 23:46:34 +0000 (UTC) Received: by mail-qk1-x744.google.com with SMTP id z188so1152979qke.9 for ; Tue, 24 Nov 2020 15:46:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=H+rGPaoJ9R3rr7zK4cuxMwlBlLpdlGUAwlQnvIZjZd8=; b=rGjC6KnGzC9NIfLo6IfoTM7C5TiZmv4q08vYNRt8cewMWpFhbX886WW47/gIiopas/ e2jKhT73QJs/dRAIbILcJdQSFnVW9dal1rOBoIKd0ECBe+nqcukIgJrBRfX2wbZlPbrR 27L+0GE9CXpbAta7TZEIdoDweQHp+sEvmypYMH9hyutdrnRkkklGbspFfFiZY+HYfDHj jsH/8tjPy+0JiTdJWitSDoQxXZntWXoEWL0cWLR+fmdpM332GBoSCjfuWUHY88IWDiPh 04ztpEPYlCjpB7IXy1yQhW/otwe7DgKcwtOpyIrk5XdAw3ZKiOAkll08YWpT8S+NhzMx e/Gw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=H+rGPaoJ9R3rr7zK4cuxMwlBlLpdlGUAwlQnvIZjZd8=; b=jKCChMaaqp2d8GzLpmjekjR+kGHikGCYTN+yaf0giyU1d1YrwwmkSviccMBxw8F+IH 4OPVc3mE5DYhpM0COwUGxS4+jvWzIcCtLUvw6tE4aPMSmiDUbxDwm6yz9r8ZwUwnWBcS 21FmrKorudsqCRc+ybvJj/YZnDEAroigAeHnShK5ykHrob9hVDtAj7y5ruq992lZVIaZ +r57PyfRjXoCr9j61iXdjjUERD7d5pBomTcK3qDqn2dmqs/yx0QM2fADvtFkOSR/qpkH MNa9Dx0mOmOM6J95T+iRGTJXSTEUp0aMJKGqi5RunMf8AuDUNvs/Q+cZ/KglTgGjP17H VZaw== X-Gm-Message-State: AOAM531Jt4bSEYiqpYHmNDS36s+fk1uM+cddaye0wwR+Yot8FHSVDVUO 8Ni+QRP08Jk6P5dXsNno7hYvOwpw04HolnEM9Eg= X-Google-Smtp-Source: ABdhPJzOwu2wFsHHn8A1YNPfZeoFLdmnMgNDFogUYxSXdSyfkKR4RJ+IXZpEdbdh4p7RHhstmUROclNZOq0Hltp8jFg= X-Received: by 2002:a5b:40e:: with SMTP id m14mr627984ybp.33.1606261594309; Tue, 24 Nov 2020 15:46:34 -0800 (PST) MIME-Version: 1.0 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> In-Reply-To: From: Miguel Ojeda Date: Wed, 25 Nov 2020 00:46:23 +0100 Message-ID: Subject: Re: [PATCH 000/141] Fix fall-through warnings for Clang To: Finn Thain Cc: James Bottomley , 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 Content-Type: text/plain; charset="UTF-8" On Tue, Nov 24, 2020 at 1:58 AM Finn Thain wrote: > > What I meant was that you've used pessimism as if it was fact. "future mistakes that it might prevent" is neither pessimism nor states a fact. > For example, "There is no way to guess what the effect would be if the > compiler trained programmers to add a knee-jerk 'break' statement to avoid > a warning". It is only knee-jerk if you think you are infallible. > Moreover, what I meant was that preventing programmer mistakes is a > problem to be solved by development tools This warning comes from a development tool -- the compiler. > The idea that retro-fitting new > language constructs onto mature code is somehow necessary to "prevent > future mistakes" is entirely questionable. The kernel is not a frozen codebase. Further, "mature code vs. risk of change" arguments don't apply here because the semantics of the program and binary output isn't changing. > Sure. And if you put -Wimplicit-fallthrough into the Makefile and if that > leads to well-intentioned patches that cause regressions, it is partly on > you. Again: adding a `fallthrough` does not change the program semantics. If you are a maintainer and want to cross-check, compare the codegen. > Have you ever considered the overall cost of the countless > -Wpresume-incompetence flags? Yeah: negative. On the other hand, the overall cost of the countless -fI-am-infallible flags is very noticeable. > Perhaps you pay the power bill for a build farm that produces logs that > no-one reads? Perhaps you've run git bisect, knowing that the compiler > messages are not interesting? Or compiled software in using a language > that generates impenetrable messages? If so, here's a tip: > > # grep CFLAGS /etc/portage/make.conf > CFLAGS="... -Wno-all -Wno-extra ..." > CXXFLAGS="${CFLAGS}" > > Now allow me some pessimism: the hardware upgrades, gigawatt hours and > wait time attributable to obligatory static analyses are a net loss. If you really believe compiler warnings and static analysis are useless and costly, I think there is not much point in continuing the discussion. > No, it's not for me to prove that such patches don't affect code > generation. That's for the patch author and (unfortunately) for reviewers. I was not asking you to prove it. I am stating that proving it is very easy. Cheers, Miguel