David Gwynne <david@gwynne.id.au> wrote:

> On Sun, Jul 13, 2025 at 07:17:00AM -0600, Theo de Raadt wrote:
> > David Gwynne <david@gwynne.id.au> wrote:
> > 
> > > we just went through an effort to shrink kernel code to help the install media fit. it seems a bit ungrateful to use those bytes again for something that's generally only going to be used for performance monitoring.
> > 
> > Nope, that's not a good reason at all.  Prefer not to trade tons of cpp
> > conditionals all over the place, for having more very different kernel
> > execution behaviours.
> > 
> > OTOH, it will take some time to get this into all the architectures.  Once
> > that's done, this should become a baseline feature.  Only then can MI code
> > call it.   Providing it behind an #ifdef means that it should not be called
> > from inside an #ifdef.
> 
> ok. how about hanging xcall off an archs cpu device until they're all
> implemented, and not providing "xcall.h" so we can't have
> #if NXCALL > 0?

or how about a simpler rule: noone can use it, until they're all implemented.
that means you don't need the ifdef's.