The new .seek assembler pseudo-op advances the location
counter to a fixed offset within a section --- or to a fixed
address, if the section is a .base'd section. It works
somewhat like the GNU assembler's .org pseudo-op, though
with a hopefully less confusing name.
This pseudo-op lets us avoid having to manually compute the
needed boot sector padding in the pc86 start-up code
plat/pc86/boot.s .
was nearly useless; lots of fixes to qemuppc and pc86 sbrk(), which was broken;
change the pc86 console to echo output to the serial port (needed for running
tests on qemu).
When the bootloader probes the drive geometry, the BIOS can clobber the
es register. If this happens, the bootloader loads the program to the
wrong address, and jumps off the code. This happens with an emulated
floppy drive in Bochs or QEMU, but not with an emulated hard disk.
