For instance, a CPUID leaf could be used in the 0x40001xxx range.
Right, I commented this in a previous mail as a much nicer way to do it,
but I was just too lazy to look up how CPUID works and instead ported
the implementation I already had in bochs :)
Although I can port it to CPUID if people find it useful to have
upstream. I just need a way to provide an immediate and a register-based
argument (at the same time), which does not require executing more than
a couple of extra instructions (right now everything fits on a single
instruction).
Being able te receive back information would be a plus, which I think
CPUID already does to return its results; although I think the ISA says
that _all_ registers are "used" after executing it.