Return-Path: Received: from mail-lj1-f193.google.com ([209.85.208.193]:47047 "EHLO mail-lj1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726038AbeJWFyr (ORCPT ); Tue, 23 Oct 2018 01:54:47 -0400 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: Miguel Ojeda Date: Mon, 22 Oct 2018 23:34:16 +0200 Message-ID: Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough (gcc >= 7.1) To: bernd@petrovitsch.priv.at Cc: Dan , "Ted Ts'o" , Greg KH , linux-kernel , Andreas Dilger , Masahiro Yamada , Michal Marek , Steven Rostedt , Mauro Carvalho Chehab , Olof Johansson , Konstantin Ryabitsev , David Miller , Andrey Ryabinin , Kees Cook , Thomas Gleixner , Ingo Molnar , Paul Lawrence , Sandipan Das , Andrey Konovalov , David Woodhouse , Will Deacon , Philippe Ombredanne , Paul Burton , David Rientjes , Willy Tarreau , Martin Sebor , Christopher Li , Jonathan Corbet , Geert Uytterhoeven , Rasmus Villemoes , Joe Perches , Arnd Bergmann , Dominique Martinet , Stefan Agner , Luc Van Oostenryck , Nick Desaulniers , Andrew Morton , Linus Torvalds , Linux Doc Mailing List , Ext4 Developers List , linux-sparse@vger.kernel.org, linux-kbuild@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Oct 22, 2018 at 7:50 PM 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. I think Dan meant too simply not touch anything (i.e. not losing the warning anywhere). > > 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). > Hm... that means they don't support (by default) the same regexps as GCC; which is bad: it means that it is only equivalent to the most relaxed level in gcc, 1: """ -Wimplicit-fallthrough=1 matches .* regular expression, any comment is used as fallthrough comment. """ See https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html i.e. any other level above will either not match Eclipse or not match gcc. > >> 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. It shouldn't according to the standard -- but who knows... :-) > - 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 understanding [[fallthrough]] is very good, actually. > Eclipse "accepts" [[fallthrough]] only in C++ sources (and not in C > sources). Bad, but I guess they will add it to C eventually, since it is probably coming for C2x. > - Neither gcc nor clang understand [[fallthrough]] (so it's probably a > no-go for the Kernel with C89 anyways). clang does it if you enable -fdouble-square-bracket-attributes (please see my other messages). gcc will at some point (if C2x gets the attributes), but at the moment the C parser is different than the C++ parser and there is no support for it on trunk that I could see, so they will have to copy the support; i.e. it will take a bit more time than clang, likely. Thanks a *lot* for taking a look at Eclipse! Cheers, Miguel