Re: [PATCH] x86/syscalls: Mark expected switch fall-throughs

[Gustavo A. R. Silva]

Quoting Thomas Gleixner <tglx@xxxxxxxxxxxxx>:

> On Tue, 28 Nov 2017, Alan Cox wrote:
>
> > > I have no idea who came up with that brilliant idea of parsing comments in
> > > the code. It's so simple to make this parser completely fail that it's not
> >
> > Stephen Johnson (author of the V7 portable C compiler), which is where
> > it's from (the lint tool). He also wrote yacc so he does know a bit about
> > parsers 8).
>
> I don't doubt that.
>
> > > even funny anymore.
> >
> > The notation in question has been standard in tools like lint since the
> > end of the 1970s
>
> Fair enough.
>
> Still that does not make the GCC implementation which defaults to take 'any
> comment' as valid any better and does not solve other parsing issues which
> have been pointed out in various GCC bugs. Using the macro annotation is
> distinct and has no ifs and buts.

The thing about taking 'any comment' as valid is false if you add the  
following to your Makefile:

KBUILD_CFLAGS  += $(call cc-option,-Wimplicit-fallthrough)

This option takes the following comments as valid:

/* fall through */
/* Fall through */
/* fall through - ... */
/* Fall through - ... */

Comments as fallthru, fallthrough, FALLTHRU are invalid.

And of course if you intentionally change the option to:

KBUILD_CFLAGS  += $(call cc-option,-Wimplicit-fallthrough=1)

it means that you obviously want to ignore any warning.

Thanks
--
Gustavo A. R. Silva