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.