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

Dmitry Torokhov
2025-04-09T17:16:44Z

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/

Thanks.

--
Dmitry