You can check out the xv6 64bit port by Brian Swetland. It contains code for handling the APIC https://github.com/swetland/xv6/blob/master/kernel/lapic.c https:

You can check out the xv6 64bit port by Brian Swetland. It contains code for handling the APIC https://github.com/swetland/xv6/blob/master/kernel/lapic.c https://github.com/swetland/xv6/blob/master/kernel/lapic.c / https://github.com/swetland/xv6/blob/master/kernel/ioapic.c https://github.com/swetland/xv6/blob/master/kernel/ioapic.c and getting multiprocessing to work in 64bit. Pretty concise and nice code. He's now one of the contributors to Fuchsia.