While the in-tree hello-world kernel (originally by me, and Mikey managed to CUT THE BLOAT of a whole SEVENTEEN instructions down to a tiny ten) is very, very dumb (and does one thing, print “Hello World” to the console), there’s now an alternative for those who like to play with a more feature-rich Hello World rather than booting a more “real” OS such as Linux. In case you’re wondering, we use the hello world kernel as a tiny test that we haven’t completely and utterly broken things when merging/developing code.
https://github.com/andreiw/ppc64le_hello is a wonderful example of a small (INTERACTIVE!) starting point for a PowerNV (as it’s called in Linux) or “bare metal” (i.e. non-virtualised) OS on POWER.
What’s more impressive is that this was all developed using the simulator rather than real hardware (although I think somebody has tried it on some now).
Kind of neat!