On 11/04/24 11:22, Christophe Leroy wrote: > > > Le 11/04/2024 à 10:12, Christophe Leroy a écrit : >> >> >> 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() > > I confirm the error goes away with the following change to next-20240411 > on powerpc tinyconfig with gcc 13.2 > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index 4e18db1819f8..3d5ac0cdd721 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -282,7 +282,7 @@ static inline void timekeeping_check_update(struct > timekeeper *tk, u64 offset) > } > static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr) > { > - BUG(); > + BUILD_BUG(); > } > #endif > That is fragile because it depends on defined(__OPTIMIZE__), so it should still be: BUILD_BUG(); return 0;
