IBM's iSCSI Firmware Initiator checks the UNDIROMID pointer in the
!PXE structure that gets created by the UNDI loader.  We didn't
previously fill this value in.

The IBM iSCSI Firmware Initiator complains that we don't have a bus
type field in the UNDI ROMID structure, so include one.

INT 1A,B101 (get PCI BIOS version) will overwrite %edi.

Include PMM allocation result in POST banner.

Include full product string in "starting execution" message.

Also mark ourselves as supporting DDIM in PnP header, for
completeness.

Commit 12f203c introduced a bug that caused the UNDI loader to attempt
to load the UNDI code and data segments to incorrect addresses.

On a system that doesn't support BBS, we end up hooking INT19 to gain
control of the boot process.  If the system is PCI3.0, we must take
care to use the runtime value for %cs, rather than the POST-time
value, otherwise we end up pointing INT19 to the temporary option ROM
POST scratch area.

Add the missing instructions to the code path that I never tested due
to not having a PCI 3.0 system available.

(D'oh)

Commit fd0aef9 introduced a typo that caused PMM detection to start at
paragraph 0xe00 rather than 0xe000.  (Detection would still work, since it
would scan until it ran out of base memory, but it would end up scanning
an unnecessarily large portion of base memory.)

Spotted by Sebastian Herbszt <herbszt@gmx.de>.

When the BIOS doesn't support BBS, hooking INT 19 is the only way to add
ourselves as a boot device.  If we have to do this, we should at least
try to chain to the original INT 19 vector if our boot fails.

Idea suggested by Andrew Schran <aschran@google.com>

The ROM prefix now prompts the user to enter the gPXE shell during POST;
this allows for configuring gPXE without needing to attempt to boot from
it.  (It also slows down system boot by three seconds per gPXE ROM, but
hey.)

This is apparently a certain OEM's requirement for option ROMs.

This allows multiple gPXE ROMs in a system to be disambiguated at boot
time; the PCI ID will show up in the boot menu for a BBS-compliant BIOS.

Minor bugfix: 4 x 2 = 8, not 16

Use BBS installation check to see if we need to hook INT19 even on a PnP
BIOS.

Verify that $PnP signature is paragraph-aligned; bochs/qemu BIOS provides
a dummy $PnP signature with no valid entry point, and deliberately
unaligns the signature to indicate that it is not properly valid.

Print message if INT19 is hooked.

Attempt to use PMM even if BBS check failed.

Move the printing functions from pxeprefix.S into libprefix.S, so they
are available for debug from any prefix.

ROM initialisation vector now attempts to allocate a 2MB block using
PMM.  If successful, it copies the ROM image to this block, then
shrinks the ROM image to allow for more option ROMs.  If unsuccessful,
it leaves the ROM as-is.

ROM BEV now attempts to return to the BIOS, resorting to INT 18 only
if the BIOS stack has been corrupted.

compressor fixup section.

flow of control through this code.

We now always add PCI and PnP headers even for ISA ROMs; there's no harm
in doing so.

UNDI loader is still missing.

mechanism has changed anyway, and so must be rewritten, but at least doing
this makes the output of "make symcheck" more legible.

 callback mechanism.