Dave Martin writes ("Re: ARM processor mode, kernel startup, Hyp / secure state"):
There may be a safe way to do this check -- for example, on ARM1176 and Cortex-A8 there is a CP14 debug status/control register that you can read which includes a flag indicating which world you're in. This isn't part of the architecture though and may be different/not possible on some CPUs.
Yes. I don't think we can write this into a boot protocol spec unless we have some architectural way of doing it.
All in all, it's better to engineer things so that the check doesn't need to be done at all.
Yes, in principle.
Note that in real deployments, the kernel is not an ELF image and therefore cannot have notes.
Yes. But in the future it will do, surely ? I mean, we're working on bootloader protocols and this part (to do with startup cpu states and ownership of the various privilege levels) is only part of it.
Ian.