The Core of PwnOS (a.k.a. kernel) is everything that runs at Privilege Level 0. It provides functionality for protected operations such as resource management and device I/O.
The root level of Core just contains an entry-point (CoreCallGate) into Core from Libraries. From this entry-point, the calls are routed to their requested functions. Most of these functions have associated preprocessing functions that retrieve the associated parameters. These preprocessing functions may also check validity/security of the parameters passed-in, since the Libraries calling the Core don’t always have the same permissions as the Core calling its own functions directly.