linux-ext4 - Re: [PATCH 1/2] Compiler Attributes: add support for _

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Message-ID: <20181022070547.GA22454@1wt.eu>
Date:   Mon, 22 Oct 2018 09:05:47 +0200
From:   Willy Tarreau <w@....eu>
To:     "Theodore Y. Ts'o" <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        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>,
        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 02:58:00AM -0400, Theodore Y. Ts'o wrote:
> On Sun, Oct 21, 2018 at 05:42:18PM -0700, Matthew Wilcox wrote:
> > On Sun, Oct 21, 2018 at 07:14:13PM +0200, Miguel Ojeda wrote:
> > > +#if __has_attribute(__fallthrough__)
> > > +# define __fallthrough                  __attribute__((__fallthrough__))
> > > +#else
> > > +# define __fallthrough
> > > +#endif
> > 
> > Why is the #else not:
> > 
> > # define __fallthrough		/* fallthrough */
> > 
> > Would this solve the Coverity problem, or does Coverity look at the raw
> > source code before preprocessing?
> 
> Wouldn't the "/* ... */" be eaten by the preprocessor before defining
> the __fallthrough cpp macro?  (e.g., try running the attached script)

You're right, even on older versions (4.7 here) :

$ echo -e '#define foobar quux /* foobar */\nfoobar\n' | gcc -E -
# 1 "<stdin>"
# 1 "<command-line>"
# 1 "<stdin>"

quux

Willy