From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752296AbdK1SK0 (ORCPT ); Tue, 28 Nov 2017 13:10:26 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:34979 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751443AbdK1SKZ (ORCPT ); Tue, 28 Nov 2017 13:10:25 -0500 Date: Tue, 28 Nov 2017 19:10:07 +0100 (CET) From: Thomas Gleixner To: "Gustavo A. R. Silva" cc: Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Kees Cook Subject: Re: [PATCH] x86/syscalls: Mark expected switch fall-throughs In-Reply-To: <20171128120512.Horde.1mz61Up1PsNtyHbrjWmK8L7@gator4166.hostgator.com> Message-ID: References: <20171127235253.GA20384@embeddedor.com> <20171128120512.Horde.1mz61Up1PsNtyHbrjWmK8L7@gator4166.hostgator.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 28 Nov 2017, Gustavo A. R. Silva wrote: > Quoting Thomas Gleixner : > > > On Mon, 27 Nov 2017, Gustavo A. R. Silva wrote: > > > > > In preparation to enabling -Wimplicit-fallthrough, mark switch cases > > > where we are expecting to fall through. > > > > > case 0: > > > if (!n--) break; > > > *args++ = regs->bx; > > > + /* fall through */ > > > > And these gazillions of pointless comments help enabling of > > -Wimplicit-fallthrough in which way? > > > > The -Wimplicit-fallthrough option was added to GCC 7. We want to add that > option to the top-level Makefile so we can have the compiler help us not make > mistakes as missing "break"s or "continue"s. This also documents the intention > for humans and provides a way for analyzers to report issues or ignore False > Positives. > > So prior to adding such option to the Makefile, we have to properly add a code > comment wherever the code is intended to fall through. > > During the process of placing these comments I have identified actual bugs > (missing "break"s/"continue"s) in a variety of components in the kernel, so I > think this effort is valuable. Lastly, such a simple comment in the code can > save a person plenty of time during a code review. To be honest, such comments annoy me during a code review especially when the fallthrough is so obvious as in this case. There might be cases where its worth to document because it's non obvious, but documenting the obvious just for the sake of documenting it is just wrong. Thanks, tglx