Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG

Arnd Bergmann
2024-04-15T15:35:52Z

On Mon, Apr 15, 2024, at 04:19, Michael Ellerman wrote:
> "Arnd Bergmann" <arnd@arndb.de> writes:
>> On Thu, Apr 11, 2024, at 11:27, Adrian Hunter wrote:
>>> On 11/04/24 11:22, Christophe Leroy wrote:
>>>
>>> That is fragile because it depends on defined(__OPTIMIZE__),
>>> so it should still be:
>>
>> If there is a function that is defined but that must never be
>> called, I think we are doing something wrong.
>
> It's a pretty inevitable result of using IS_ENABLED(), which the docs
> encourage people to use.

Using IS_ENABLED() is usually a good idea, as it helps avoid
adding extra #ifdef checks and just drops static functions as
dead code, or lets you call extern functions that are conditionally
defined in a different file.

The thing is that here it does not do either of those and
adds more complexity than it avoids.

> In this case it could easily be turned into a build error by just making
> it an extern rather than a static inline.
>
> But I think Christophe's solution is actually better, because it's more
> explicit, ie. this function should not be called and if it is that's a
> build time error.

I haven't seen a good solution here. Ideally we'd just define
the functions unconditionally and have IS_ENABLED() take care
of letting the compiler drop them silently, but that doesn't
build because of missing struct members.

I won't object to either an 'extern' declaration or the
'BUILD_BUG_ON()' if you and others prefer that, both are better
than BUG() here. I still think my suggestion would be a little
simpler.

Arnd