bytes of useless zeroes in the final image.

in a long loop before giving up on them.  Record method which worked
and default to that method on next attempt.

optimisation of only trying to do so when necessary.

number of (potentially very slow) gateA20_set operations.

Die with a fatal error if we are unable to set gate A20; if this fails
then we are bound to experience memory corruption at a later stage,
and I'd prefer to pick it up early.

doesn't want to go to the hassle of processing a full memory map.

do it.

set_fbms() will also update the E820 hidden region.

to start on a non-page boundary.  Make life safer by rounding out our
edited regions.

architecture-dependent and is needed by the ELF code.

anything over 0x80 is an extended character.

calls.  This does make a visible difference when clearing the screen with
werase() inside bochs or qemu.

technically be necessary, because the "enable A20" command requires
only that the keyboard controller is ready to accept input (i.e. that
its input buffer is empty), and shouldn't also require that the
keyboard is ready to send output (i.e. that its output buffer is also
empty).  See http://www.smsc.com/main/tools/io-bios/42i.pdf section
3.1 ("Command Invocation") for a justification.

gateA20_set() is called on every real-mode transition (in case some
idiot piece of external code such as Intel's PXE stack decided it
would be fun to re-disable A20), so draining the keyboard buffer means
that we end up losing keypresses on some systems.  In particular, this
makes typing at the command line almost impossible, and causes
Etherboot to ignore Ctrl-Alt-Del.

We should really implement a gateA20_test() function to verify that
gate A20 has been correctly enabled, and think about adding other
commonly-used methods such as Fast Gate A20.

defined in vsprintf.h.  (This may change, since vsprintf.h is a
non-standard name, but for now it's the one to use.)

There should be no need to include vsprintf.h just for DBG() statements,
since include/compiler.h forces it in for a debug build anyway.

skip past an empty region, otherwise we end up generating an infinitely
long e820 map.  (Yes, there *are* real systems that provide e820 maps
with a zero-length region at the end...)

as a result of our memory map editing, so strip out any empty regions.

order?

requiring each caller to decide how many entries it wants to permit.

Ignore carry flag for INT 15,88; the Ralf Brown interrupt list says
that CF is unreliable for this call.

and creating a memory map that's easier to work with than the E820 map.

down to base memory, since it is now in the base-memory-resident
.text16 section).

We now split e820 regions around ourselves, rather than just
truncating the e820 region.  This avoids the worst-case scenario of
losing all memory over 4GB.

It's more important to get the memory map right now that we're
expecting to still be loaded when the OS starts in several situations
(e.g. Linux with UNDI driver, any OS with iSCSI/AoE boot, etc.).

even when __atribute__ (( unused )) is correctly set...