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

[Adrian Hunter]

On 11/04/24 10:04, Arnd Bergmann wrote:
> 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?

Original report has a list

	https://lore.kernel.org/all/CA+G9fYvjdZCW=7ZGxS6A_3bysjQ56YF7S-+PNLQ_8a4DKh1Bhg@xxxxxxxxxxxxxx/