Reduce the number of sections within the linker script to match the
number of practical sections within the output file.

Define _section, _msection, _esection, _section_filesz, _section_memsz,
and _section_lma for each section, replacing the mixture of symbols that
previously existed.

In particular, replace _text and _end with _textdata and _etextdata, to
make it explicit within code that uses these symbols that the .text and
.data sections are always treated as a single contiguous block.

Although the E820 API allows for a caller to provide only a 20-byte
buffer, there exists at least one combination (HP BIOS, 32-bit WinPE)
that relies on information found only in the "extended attributes"
field, which requires a 24-byte buffer.

Allow for up to a 64-byte E820 buffer, in the hope of coping with
future idiocies like this one.

Our INT 15,e820 code was setting %es=%ss (as part of the "look ahead
in the memory map" logic), but failing to restore %es afterwards.
This is a serious bug, but wasn't affecting many platforms because
almost all callers seem to set %es=%ss anyway.

Some BIOSes require us to pass in not only the continuation value (in
%ebx) as returned by the previous call to INT 15,e820 but also the
unmodified buffer (at %es:%di) as returned by the previous call to INT
15,e820.  Apparently, someone thought it would be a worthwhile
optimisation to fill in only the low dword of the "length" field and
the low byte of the "type field", assuming that the buffer would
remain unaltered from the previous call.

This problem was being triggered by the "peek ahead" logic in
get_mangled_e820(), which would read the next entry into a temporary
buffer in order to be able to guarantee terminating the map with
%ebx=0 rather than CF=1.  (Terminating with CF=1 upsets some Windows
flavours, despite being documented legal behaviour.)

Work around this problem by always fetching directly into our e820
cache; that way we can guarantee that the underlying call always sees
the previous buffer contents (and the same buffer address).

Allow for an arbitrary number of splits of the system memory map via
INT 15,e820.

Features of the new map-mangling algorithm include:

  Supports random access to e820 map entries.

  Requires only sequential access support from the underlying e820
  map, even if our caller uses random access.

  Empty regions will always be stripped.

  Always terminates with %ebx=0, even if the underlying map terminates
  with CF=1.

  Allows for an arbitrary number of hidden regions, with underlying
  regions split into as many subregions as necessary.

Total size increase to achieve this is 193 bytes.

Define a list of N allowed memory regions, and split each underlying
e820 region into up to N subregions.  Strip resulting empty regions
out of the map, avoiding using the "return with CF set to strip last
empty region" trick, because it seems that bootmgr.exe in Win2k8 gets
upset if the memory map is terminated with CF set.

This is an intermediate checkin that defines a single allowed memory
region covering the entire 64-bit address space, and uses the existing
map-mangling code on top of the new region-splitting code.  This
sanitises the memory map to the point that Win2k8 is able to boot even
on a system that defines a final zero-length region at the 4GB mark.

I'm checking this in because it may be useful for future debugging
efforts to be able to run with the existing and known-working map
mangling code together with the map sanitisation capabilities of the
new map mangling code.

memory map.  (We achieve this by setting CF on the last entry if it is
zero-length; this avoids the need to look ahead to see at each entry
if the *next* entry would be both the last entry and zero-length).

This fixes the "0kB base memory" error message upon starting Windows
2003 on a SunFire X2100.

memory map.  (We achieve this by setting CF on the last entry if it is
zero-length; this avoids the need to look ahead to see at each entry
if the *next* entry would be both the last entry and zero-length).

This fixes the "0kB base memory" error message upon starting Windows
2003 on a SunFire X2100.

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?

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.).