The registers that are saved/restored in the trap / exception frame need to be consistent between all entry/exit points as well as the functions that convert between trap/exception frame and context. The trap frame contains only the non-volatile registers and rbp, the rest is saved in the exception frame.
The previous code didn't save rbp in the syscall handler, which led to it being clobbered when exiting though KiServiceExit2 rather than returning back to the syscall exit path. Also KeContextToTrapFrame would use rbx, rsi and rdi from the trap frame, which wouldn't be saved there by the syscall handler.
This also fixes delivering APCs from the system call handler, which previously would have clobbered rax. Also don't use the thread's TrapFrame member, which is not always set, when returning.
- Deliver pending APCs on trap exit
- Pass the trapframe of KiApcInterrupt to KiDeliverApcs, not NULL.
- Fix parameter passing from KiSwapContext to KiSwapContextInternal and KiSwapContextResume, so that the ApcBypass parameter is not uninitialized
- Fix return value of KiSwapContextResume to correctly indicate whether we want to have APCs directly delivered or not (when there are non, or when delivery is suppressed)
