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

Arnd Bergmann
2024-04-11T07:05:16Z

On Wed, Apr 10, 2024, at 17:32, Adrian Hunter wrote:
> BUG() does not return, and arch implementations of BUG() use unreachable()
> or other non-returning code. However with !CONFIG_BUG, the default
> implementation is often used instead, and that does not do that. x86 always
> uses its own implementation, but powerpc with !CONFIG_BUG gives a build
> error:
>
> kernel/time/timekeeping.c: In function ‘timekeeping_debug_get_ns’:
> kernel/time/timekeeping.c:286:1: error: no return statement in function
> returning non-void [-Werror=return-type]
>
> Add unreachable() to default !CONFIG_BUG BUG() implementation.

I'm a bit worried about this patch, since we have had problems
with unreachable() inside of BUG() in the past, and as far as I
can remember, the current version was the only one that
actually did the right thing on all compilers.

One problem with an unreachable() annotation here is that if
a compiler misanalyses the endless loop, it can decide to
throw out the entire code path leading up to it and just
run into undefined behavior instead of printing a BUG()
message.

Do you know which compiler version show the warning above?

Arnd