linux-kernel - Re: [PATCH 1/2] Compiler Attributes: add support for _

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Message-ID: <20181022102743.nua5fgbscyeymzal@mwanda>
Date:   Mon, 22 Oct 2018 13:27:43 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Bernd Petrovitsch <bernd@...rovitsch.priv.at>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Olof Johansson <olof@...m.net>,
        Konstantin Ryabitsev <konstantin@...uxfoundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Sandipan Das <sandipan@...ux.vnet.ibm.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Paul Burton <paul.burton@...s.com>,
        David Rientjes <rientjes@...gle.com>, Willy Tarreau <w@....eu>,
        Martin Sebor <msebor@...il.com>,
        Christopher Li <sparse@...isli.org>,
        Jonathan Corbet <corbet@....net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...db.de>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Stefan Agner <stefan@...er.ch>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-sparse@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough
 (gcc >= 7.1)

On Mon, Oct 22, 2018 at 11:41:56AM +0200, Bernd Petrovitsch wrote:
> On 22/10/2018 00:27, Theodore Y. Ts'o wrote:
> > On Sun, Oct 21, 2018 at 07:14:13PM +0200, Miguel Ojeda wrote:
> >> From the GCC manual:
> >>
> >>   fallthrough
> >>
> >>     The fallthrough attribute with a null statement serves as a
> >>     fallthrough statement. It hints to the compiler that a statement
> >>     that falls through to another case label, or user-defined label
> >>     in a switch statement is intentional and thus the -Wimplicit-fallthrough
> >>     warning must not trigger. The fallthrough attribute may appear
> >>     at most once in each attribute list, and may not be mixed with
> >>     other attributes. It can only be used in a switch statement
> >>     (the compiler will issue an error otherwise), after a preceding
> >>     statement and before a logically succeeding case label,
> >>     or user-defined label.
> >>
> >>   https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html
> > 
> > Do we know if coverity understands the fallthrough attribute?  One of
> > the reasons why I started using /* fallthrough */ is because it kept
> > Coverity happy.
> 
> FWIW, current "eclipse" has the same "problem".
> 
> > If the conversion from /* fallthrough */ to the __fallthrough__
> > attribute means that we start gethting a lot of Coverity warnings,
> 
> We could keep both.

What does that even mean?  Use both the attribute and the comment until
Eclipse is updated?

	case 3:
		frob();
		__fall_through; /* fall through */
	case 4:

That seems like a wrong idea...

regards,
dan carpenter