Re: [BUG] -next objtool build failure (bisected)

[Paul E. McKenney]

On Tue, Oct 15, 2024 at 01:45:07PM -0500, Josh Poimboeuf wrote:
> On Tue, Oct 15, 2024 at 11:10:11AM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > The next-20241011 release gets me build errors like the following:
> > 
> > 	vmlinux.o: warning: objtool: fetch_item() falls through to next function
> > 
> > Bisection leads me here:
> > 
> > 	61595012f280 ("HID: simplify code in fetch_item()")
> > 
> > This diff looks inoffensive to me, but I get this error on this commit
> > and not on its predecessor.
> > 
> > This build failure happens on quite a few different kernel configurations.
> > I bisected using this particular reproducer:
> > 
> > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --buildonly --configs SRCU-T
> 
> The problem is likely this:
> 
> +	default:
> +		unreachable();
> 
> The unreachable() annotation by itself produces undefined behavior, as
> it will just fall off the edge of the function if the default case is
> ever executed.
> 
> Better to do
> 
> 	default:
> 		BUG();
> 
> which makes the behavior defined.

And this fixes things for me, thank you!

							Thanx, Paul