Re: [Qemu-devel] Handling of fall through code (was: [PATCH v8 04/87] target/mips: Mark switch fallthroughs with interpretable comments

[Markus Armbruster]

Peter Maydell <address@hidden> writes:

> On Sun, 7 Jul 2019 at 21:26, Stefan Weil <address@hidden> wrote:
>> This is a general problem all over the QEMU code. I usually compile with
>> nearly all warnings enabled and get now lots of errors with the latest
>> code and after updating to gcc-8.3.0 (Debian buster). It should be
>> reproducible by enabling -Werror=implicit-fallthrough.
>
> Coverity warns about implicit fallthroughs, and we are
> currently warning-free in that department, so I think
> our remaining problems are largely down to perhaps
> using idioms which the compiler doesn't spot.
> Being able to enable gcc implicit-fallthrough errors would
> definitely be better than spotting them only after the
> fact with Coverity.
>
>> I suggest to enable -Werror=implicit-fallthrough by default and add a
>> new macro to mark all fallthrough locations which are correct, but not
>> accepted by the compiler.
>
> I'm not sure why we need a macro. Our standard way to
> mark fallthrough is /* fall through */, which has hundreds
> of uses in the codebase. -Wimplicit-fallthrough=2 will match this,
> so it seems simpler to just use that rather than to rework
> how we mark fallthroughs.
>
> Since vixl is 3rd-party code it might be easier to just
> add -Wno-implicit-fallthrough to the cflags that
> disas/libvixl/Makefile.objs sets up for building those files.
> (We should check also for newer libvixl and/or suggest
> something upstream that works with gcc.)

Concur.