Return-Path: Received: from mail-pg1-f194.google.com ([209.85.215.194]:40853 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728435AbeJWCNp (ORCPT ); Mon, 22 Oct 2018 22:13:45 -0400 Received: by mail-pg1-f194.google.com with SMTP id o14-v6so3652753pgv.7 for ; Mon, 22 Oct 2018 10:54:15 -0700 (PDT) MIME-Version: 1.0 References: <20181021171414.22674-1-miguel.ojeda.sandonis@gmail.com> <20181021171414.22674-2-miguel.ojeda.sandonis@gmail.com> <20181021222712.GI1617@thunk.org> <8fb78062-b6d4-6f2d-d943-44bec6b95ff0@petrovitsch.priv.at> <20181022102743.nua5fgbscyeymzal@mwanda> <1474d995-1b5a-2efb-f077-33eb4a5d9e31@petrovitsch.priv.at> <20181022105314.j6djkrpwbnokhai5@mwanda> <3cbb5345-0270-5575-7563-6ad37d888e42@petrovitsch.priv.at> In-Reply-To: <3cbb5345-0270-5575-7563-6ad37d888e42@petrovitsch.priv.at> From: Nick Desaulniers Date: Mon, 22 Oct 2018 10:54:02 -0700 Message-ID: Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough (gcc >= 7.1) To: bernd@petrovitsch.priv.at Cc: Miguel Ojeda , dan.carpenter@oracle.com, "Theodore Ts'o" , Greg KH , LKML , adilger.kernel@dilger.ca, Masahiro Yamada , Michal Marek , rostedt@goodmis.org, mchehab+samsung@kernel.org, olof@lxom.net, Konstantin Ryabitsev , "David S. Miller" , Andrey Ryabinin , Kees Cook , Thomas Gleixner , Ingo Molnar , Paul Lawrence , sandipan@linux.vnet.ibm.com, Andrey Konovalov , David Woodhouse , Will Deacon , Philippe Ombredanne , paul.burton@mips.com, David Rientjes , Willy Tarreau , msebor@gmail.com, sparse@chrisli.org, Jonathan Corbet , Geert Uytterhoeven , Rasmus Villemoes , joe@perches.com, Arnd Bergmann , asmadeus@codewreck.org, Stefan Agner , Luc Van Oostenryck , Andrew Morton , Linus Torvalds , linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, linux-sparse@vger.kernel.org, Linux Kbuild mailing list Content-Type: text/plain; charset="UTF-8" Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Oct 22, 2018 at 10:50 AM Bernd Petrovitsch wrote: > > Hi all! > > On 22/10/18 13:07, Miguel Ojeda wrote: > > On Mon, Oct 22, 2018 at 12:54 PM Dan Carpenter wrote: > >> > >> Doing both is super ugly. Let's just do comments until Eclipse gets > >> updated. > > Yes, "Eclipse" as the IDE. > > And yes but IMHO better super ugly than loosing the warning - YMMV. > > For the archives: I have Eclipse Photon/June 2016 here. And "no break" > is the (default) string in a comment used by Eclipse (it can be > customized and is actually a regexp but it must be in a comment). > > >> I had wanted to move to the attribute because that would simplify things > >> in Smatch but it's not a huge deal to delay for another year. > > > > I can re-send them later on, no problem. On the other hand, doing the > > changes will push tools to get updated sooner ;-) > > > > If tools were doing something as fancy as comment parsing for > > diagnostics, they should have been updated with the attribute support > > (either gcc's or C++17's) -- it has been more than a year now since > > gcc 7.1 and the C++17 final draft. (Note that this does not apply for > > things like clang, since they weren't doing comment parsing to begin > > with.) > > That would be nice. And if they agree on the same texts (or accept per > default all somewhat widely used and/or old ones). > > After stumbling over > https://stackoverflow.com/questions/16935935/how-do-i-turn-off-a-static-code-analysis-warning-on-a-line-by-line-warning-in-cd, > looking into Eclipses Window -> Preferences -> C/C++ -> Code Analysis -> > "No break at the end of case" screen (that's the screenshot there) and I > tried various things: > > Preface: > I have > ---- snip ---- > #define __fallthrough __attribute__((fallthrough)) > ---- snip ---- > for gcc >= 7 (because clang doesn't know it and I had also older > gcc's in use before). > > So: > - Adding a comment to the #define doesn't change anything for Eclipse. > - Eclipse looks *only* in comments for the string/regexp given > the warnings configuration (and that comment must be on the line > directly before the "case"). > - Eclipse understands [[fallthrough]] out-of-the-box though (which > is C++11 AFAIK) as does g++-7 (I use -std=gnu++17 - most of the > sources are C++, but not all) and clang++-6 (all the current standard > Ubuntu-18.06/Bionic packages). > Eclipse "accepts" [[fallthrough]] only in C++ sources (and not in C > sources). > - Neither gcc nor clang understand [[fallthrough]] (so it's probably a > no-go for the Kernel with C89 anyways). > > MfG, > Bernd > > PS: clang++ errors with "fallthrough annotation in unreachable code" if > [[fallthrough]] is after an assert(). clang-devs there, please, the > fallthrough doesn't really generated code (I hope;-). > I have lots of switch()es which catch undefined values (for enums > et. al.) with "default"+assert() and fall through to the most safe > case (for the deployed version). Can you send me a link to a simple reproducer in godbolt (godbolt.org) and we'll take a look? > -- > "I dislike type abstraction if it has no real reason. And saving > on typing is not a good reason - if your typing speed is the main > issue when you're coding, you're doing something seriously wrong." > - Linus Torvalds -- Thanks, ~Nick Desaulniers