xv6

If folks want to experiment with a tiny, bare-bones unix-y OS on relatively modern platforms, xv6 (used as a teaching OS at MIT) is ~10kloc of C for the kernel and a handful of userland programs: https://github.com/mit-pdos/xv6-public More information, docs, etc: https://pdos.csail.mit.edu/6.828/2014/xv6.html A few years back I did a quick port of it to x86-64 as a project to learn more about 64bit intel (having been in the ARM world for some time) which was fun: https://github.com/swetland/xv6

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/ioapic.c and getting multiprocessing to work in 64bit. Pretty concise and nice code. He's now one of the contributors to Fuchsia.

For reference: https://github.com/swetland/xv6/blob/master/kernel/fs.c https://github.com/weiss/original-bsd/blob/master/old/sh/cmd...

Because splatting object files and intermediates all over the same directories as the source drives me nuts, I shuffled things so that it's a bit easier to find things (splitting source into kernel/, user/, ulib/, tools/, and include/ directories) and generated files are collected into kobj/, uobj/, out/, and fs/ directories. https://github.com/swetland/xv6 I also tweaked the scheduler to halt if there's nothing to schedule, per tankenmate's suggestion. A side-effect of this change is the generate-source-code-printout targets were rather severely broken, so they're simply removed for the moment.