Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough (gcc >= 7.1)

[Miguel Ojeda]

On Mon, Oct 22, 2018 at 12:27 AM Theodore Y. Ts'o <tytso@xxxxxxx> 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?

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