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

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Message-ID: <CAKwvOdm7Ts1ZpYV2qw1YLSg8ntjPekY8Gu=Q1CbSq_7==ekUMw@mail.gmail.com>
Date:   Mon, 22 Oct 2018 10:23:14 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>, dan.carpenter@...cle.com,
        adilger.kernel@...ger.ca,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>, rostedt@...dmis.org,
        mchehab+samsung@...nel.org, 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@...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@...s.com, David Rientjes <rientjes@...gle.com>,
        Willy Tarreau <w@....eu>, msebor@...il.com, sparse@...isli.org,
        Jonathan Corbet <corbet@....net>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>, joe@...ches.com,
        Arnd Bergmann <arnd@...db.de>, asmadeus@...ewreck.org,
        Stefan Agner <stefan@...er.ch>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.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 mailing list <linux-kbuild@...r.kernel.org>,
        Colin Ian King <colin.king@...onical.com>
Subject: Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough
 (gcc >= 7.1)

On Mon, Oct 22, 2018 at 2:26 AM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> On Mon, Oct 22, 2018 at 12:27 AM Theodore Y. Ts'o <tytso@....edu> 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.
>
> If Coverity is like gcc, they should be doing both (i.e. I see the
> comment parsing as an "extra" that gcc did, but the "basic stuff" is
> the attribute -- and I would guess it is way easier for them to
> support than the comment parsing).
>
> But I cannot test it myself :-( Someone, please?

+ Colin, who has been running Coverity on the kernel, and sending patches.

>
> However, if I understood Greg correctly in his reply to the cover
> letter, he replied that Coverity knows about it (?).
>
> >
> > If the conversion from /* fallthrough */ to the __fallthrough__
> > attribute means that we start gethting a lot of Coverity warnings,
> > that would be unfortunate.  OTOH, if this is getting standardized,
> > maybe we can get Coverity to understand this attribute?
>
> Indeed! That would be the best for everyone, including Coverity customers.
>
> Cheers,
> Miguel



-- 
Thanks,
~Nick Desaulniers