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

[Christophe Leroy]

Le 11/04/2024 à 09:16, Adrian Hunter a écrit :
> 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/
> 

Looking at the report, I think the correct fix should be to use 
BUILD_BUG() instead of BUG()