At POST time some BIOSes return invalid e820 maps even though
they indicate that the data is valid.  We add a check that the first
region returned by e820 is RAM type and declare the map to be invalid
if it is not.

This extends the sanity checks from 8b20e5d ("[pcbios] Sanity-check
the INT15,e820 and INT15,e801 memory maps").

This brings us in to line with Linux definitions, and also simplifies
adding x86_64 support since both platforms have 2-byte shorts, 4-byte
ints and 8-byte long longs.

gcc 4.4 adds another few warnings, and also seems to complain if we
place %ebp in the clobber list for any inline asm.

Someone at Dell must have a full-time job designing ways to screw up
implementations of INT 15,e820.  This latest gem is courtesy of a Dell
Xanadu system, which arbitrarily decides to obliterate the contents of
%esi.

Preserve %esi, %edi and %ebp across calls to INT 15,e820, in case
someone tries a variation on this trick in future.

The ACPI specification defines an additional 4-byte field at offset 20
for an E820 memory map entry.  This field is presumably optional,
since generally E820 gets given only a 20-byte buffer to fill.
However, the bits of this optional field are defined as:

  bit 0 : region is enabled
  bit 1 : region is non-volatile memory rather than RAM

so it seems as though callers that pass in only a 20-byte buffer may
be missing out on some rather important information.

Some systems seem to report insane memory maps (particularly at POST
time).  Detect and work around some of the common failure cases.

INT 15,e801 is capable of returning a memory range that extends to
4GB, so allow for this in the debug message that shows the data
returned by INT 15,e801.

__from_data16 and __from_text16 now take a pointer to a
.data16/.text16 variable, and return the real-mode offset within the
appropriate segment.  This matches the use case for every occurrence
of these macros, and prevents potential future bugs such as that fixed
in commit d51d80f.  (The bug arose essentially because "&pointer" is
still syntactically valid.)

Added redundant call to get_memmap() in int13_boot() immediately
before jumping to boot sector, to assist in debugging.

Added redundant call to get_memmap() in int13_boot() immediately
before jumping to boot sector, to assist in debugging.

bytes of useless zeroes in the final image.

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

architecture-dependent and is needed by the ELF code.

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.

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.