If the function call doesn't allow you to specify a CPU core, then it seems like it would be testing either the logical or'ing of all core's powered-on state, or the state of the current core.

In order for the code to execute anywhere, at least one core must be powered on and not halted. Also, I would consider a halted CPU to still be powered on.

Otherwise, the function's name has no relation to it's behavior and it's a buggy function on top of being a useless but amusing thought experiment.

which implies that the power state of the whole core cluster is on, so the syscall is defined to return 1

That was one of the interesting things about BeOS - that you could turn off CPUs while it was running via the desktop. Just make sure to leave one running.