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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id d10sm4785681pjj.38.2020.11.20.11.30.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Nov 2020 11:30:41 -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 1kgC7J-0005Y5-9d for xen-devel@lists.xenproject.org; Fri, 20 Nov 2020 19:30:45 +0000 X-Inumbo-ID: 63ce36ce-f553-459b-bcf9-fef181120414 Received: from mail-pf1-x441.google.com (unknown [2607:f8b0:4864:20::441]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 63ce36ce-f553-459b-bcf9-fef181120414; Fri, 20 Nov 2020 19:30:43 +0000 (UTC) Received: by mail-pf1-x441.google.com with SMTP id v5so4785493pff.10 for ; Fri, 20 Nov 2020 11:30:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=3bv50j9tOMZCSWAChUvUk5K6TgooTRt3SRcQZBJ9fcA=; b=GgFl3K9IS/lWsdMjkEVVAtTSDzsQ0sxEOabPKwuHzNJyTA7s1nVN/P5Py+wtAIOvbE i43RryzoLL4QMDFVI6bDxTe0ngekUN0rycJ/u5dixn0o4ZWxiMdHtnF6M1zgV7bxdmjG OxnZTS8PQwcd6ZCwnahaxVB8GYQEw6f4nxFx4= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=3bv50j9tOMZCSWAChUvUk5K6TgooTRt3SRcQZBJ9fcA=; b=C81oHXFBnc1R1VLX8TJSepa3ep/2K7xvYWasFP6JYRB6QuKqeJ1loLVIjkUqLRmGTr giDDRebxTD3OL63LifnIoa5caZYeObeYbqmGJGFnFf/F8rmBOCVWXzjp0z8wOaHR0OGS BL/UK4zj/YjujrV7wrtu9Yk75Xq7R381ahwjtruITSil2UOgnVvOsF9uwLHZ1EV9ImOF Gs29Uq2S89Crh16xhIXLINAjM3C2hpP4SvNK0faL4cw1jMJSPqyvQK+EEFPIFB+kOyPI 2XFu8PApBpv7KGlWotx26iRpJCK+mrrpquuBC271+tzA6hpWb0fCoz31mg2kxO79nrFQ l2Sw== X-Gm-Message-State: AOAM531RWUdY+z6mRBsghiPIOSNUxofkB2VwYSsbXERtIu3W3XUsdeFC VlryjWbkPV1MBcznxMx7cDAP8g== X-Google-Smtp-Source: ABdhPJwl3VgOHP/MWhG5DtpaEL0Yyt6dBbRzpe/94BRgWnGkgcq6AJ5JXkZmDK0TJqDkyAhq9Y3Q+Q== X-Received: by 2002:a63:5043:: with SMTP id q3mr17907345pgl.137.1605900643099; Fri, 20 Nov 2020 11:30:43 -0800 (PST) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id d10sm4785681pjj.38.2020.11.20.11.30.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Nov 2020 11:30:41 -0800 (PST) Date: Fri, 20 Nov 2020 11:30:40 -0800 From: Kees Cook To: Jakub Kicinski Cc: "Gustavo A. R. Silva" , linux-kernel@vger.kernel.org, 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-kernel@lists.infradead.org, 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@vger.kernel.org, linux-decnet-user@lists.sourceforge.net, linux-ext4@vger.kernel.org, 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@vger.kernel.org, linux-integrity@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-media@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, 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@vger.kernel.org, netdev@vger.kernel.org, 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, x86@kernel.org, xen-devel@lists.xenproject.org, linux-hardening@vger.kernel.org, Nick Desaulniers , Nathan Chancellor , Miguel Ojeda , Joe Perches Subject: Re: [PATCH 000/141] Fix fall-through warnings for Clang Message-ID: <202011201129.B13FDB3C@keescook> References: <20201120105344.4345c14e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201120105344.4345c14e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> On Fri, Nov 20, 2020 at 10:53:44AM -0800, Jakub Kicinski wrote: > On Fri, 20 Nov 2020 12:21:39 -0600 Gustavo A. R. Silva wrote: > > This series aims to fix almost all remaining fall-through warnings in > > order to enable -Wimplicit-fallthrough for Clang. > > > > In preparation to enable -Wimplicit-fallthrough for Clang, explicitly > > add multiple break/goto/return/fallthrough statements instead of just > > letting the code fall through to the next case. > > > > Notice that in order to enable -Wimplicit-fallthrough for Clang, this > > change[1] is meant to be reverted at some point. So, this patch helps > > to move in that direction. > > > > Something important to mention is that there is currently a discrepancy > > between GCC and Clang when dealing with switch fall-through to empty case > > statements or to cases that only contain a break/continue/return > > statement[2][3][4]. > > Are we sure we want to make this change? Was it discussed before? > > Are there any bugs Clangs puritanical definition of fallthrough helped > find? > > IMVHO compiler warnings are supposed to warn about issues that could > be bugs. Falling through to default: break; can hardly be a bug?! It's certainly a place where the intent is not always clear. I think this makes all the cases unambiguous, and doesn't impact the machine code, since the compiler will happily optimize away any behavioral redundancy. -- Kees Cook