In S3, the processor has no stored state. "Resume" is equivalent to the machine being turned on
from scratch as far as it's concerned. It's up to the BIOS to check a flag to determine whether it's a
cold power on or a resume.
Performing a full resume cycle is hard. You need to reprogram the memory controller, bring the
embedded controller up, dump values back into the thermal monitoring hardware and any number
of low-level initialisations. Only once that's been done does control get passed back to the OS,
which has absolutely no idea how any of that hardware works.