..There is not yet code to read the e820 map from the BIOS.

This requires switching from -mcmodel=kernel to -mcmodel=large.  The
performance hit appears to be small.

Instead of using ld -b binary, build incbin.S, which uses gas' .incbin.

e.g. "make" and "make HW=qemu" build for qemu
     "make HW=josmp" builds for josmp