Re: [PATCH v6 05/12] regmap: irq: Remove unreachable goto

Andy Shevchenko
2025-04-10T18:43:40Z

Wed, Apr 09, 2025 at 10:16:40AM -0700, Dmitry Torokhov kirjoitti:
> On Wed, Apr 09, 2025 at 07:45:42PM +0300, Andy Shevchenko wrote:
> > On Wed, Apr 09, 2025 at 05:32:55PM +0100, Mark Brown wrote:
> > > On Wed, Apr 09, 2025 at 07:00:24PM +0300, Andy Shevchenko wrote:
> > > > On Wed, Apr 09, 2025 at 04:46:04PM +0100, Mark Brown wrote:
> > >
> > > > > unreachable() just annotates things, AFAICT it doesn't actually
> > > > > guarantee to do anything in particular if the annotation turns out to be
> > > > > incorrect.
> > >
> > > > I;m not sure I follow. unreachable is a wrapper on top of
> > > > __builtin_unreachable() which is intrinsic of the compiler.
> > >
> > > > https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005funreachable
> > >
> > > That just says that the program is undefined if we get to the
> > > __builtin_undefined() and documents some behaviour around warnings. One
> > > example of undefined behaviour would be doing nothing.
> >
> > Theoretically yes, practically return after a BUG() makes no sense. Note,
> > that compiler effectively removes 'goto exit;' here (that's also mentioned
> > in the documentation independently on the control flow behaviour), so
> > I don't know what you expect from it.
>
> So unreachable() sometimes lears to weird behavior from compiler, for
> example as mentioned here where we ended up removing it to prevent
> miscompilations:
>
> https://lore.kernel.org/all/20241010222451.GA3571761@thelio-3990X/

How does it affect the BUG()?

From your link:
"I tested using BUG() in lieu of unreachable() like the second change
I mentioned above, which resolves the issue cleanly, ..."

--
With Best Regards,
Andy Shevchenko