Hello. We were discussing with Robert how to move BIOS interrupt
routines out of kernel. There are following possibilities:
1) Have a .lowmem section in every concerned module which will always be
placed in low memory. Currently in experimental.
Advantages:
  a) moving functions to modules is straightforward
  b) functions grow neither in size nor in complexity
Disadvantages:
  c) needs lowmem allocators in core
2) Make every function needing bios interrupts setup its own trampoline.
Due to complexity of trampolines it's not a real option
3) Have an universal routine grub_interrupt (int intno, struct
grub_cpu_interrupt_regs *regs) which will be used by C routine to do the
interrupt calls. This would move the complexity from asm to C.
Advantages:
a) simplicity in core
b) complexity moved to a more readable language
c)  we can also rename grub_interrupt to grub_interrupt_real and make
grub_interrupt dprintf registers before and after the call. This would
make debugging BIOS quirks easier.
Disadvantages:
a) Moving functions needs effort
b) C functions are probably bigger but it may be offset by possibility
of inlining functions
c) repeadetly changing from/to real mode is an overhead when executing
multiple interrupts in series. Fortunately this condition is rare in our
codebase and is only on non performance-critical parts like halting.
d) Some functions aren't covered by this. At least grub_pxe_call is in
this case. But we can use method 2 for them

-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko