Commit 2422647 ("[prefix] Allow prefix to specify an arbitrary maximum
address for relocation") introduced a regression into the UNDI ROM
loader by preserving an extra register on the stack without modifying
the %sp-relative addresses used in the routine.

Fix by correcting the %sp-relative addresses to allow for the extra
preserved variable.

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

Many BIOSes do not construct the full system memory map until after
calling the option ROM initialisation entry points.  For several
years, we have added sanity checks and workarounds to accommodate
charming quirks such as BIOSes which report the entire 32-bit address
space (including all memory-mapped PCI BARs) as being usable RAM.

The IBM x3650 takes quirky behaviour to a new extreme.  Calling either
INT 15,e820 or INT 15,e801 during POST doesn't just get you invalid
data.  We could cope with invalid data.  Instead, these nominally
read-only API calls manage to trash some internal BIOS state, with the
result that the system memory map is _never_ constructed.  This tends
to confuse subsequent bootloaders and operating systems.

[ GRUB 0.97 fails in a particularly amusing way.  Someone thought it
would be a good idea for memcpy() to check that the destination memory
region is a valid part of the system memory map; if not, then memcpy()
will sulk, fail, and return NULL.  This breaks pretty much every use
of memcpy() including, for example, those inserted implicitly by gcc
to copy non-const initialisers.  Debugging is _fun_ when a simple call
to printf() manages to create an infinite recursion, exhaust the
available stack space, and shut down the CPU. ]

Fix by completely inhibiting calls to INT 15,e820 and INT 15,e801
during POST.

We do now allow relocation during POST up to the maximum address
returned by INT 15,88 (which seems so far to always be safe).  This
allows us to continue to have a reasonable size of external heap, even
if the PMM allocation is close to the 1MB mark.

The downside of allowing relocation during POST is that we may
overwrite PMM-allocated memory in use by other option ROMs.  However,
the downside of inhibiting relocation, when combined with also
inhibiting calls to INT 15,e820 and INT 15,e801, would be that we
might have no external heap available: this would make booting an OS
impossible and could prevent some devices from even completing
initialisation.

On balance, the lesser evil is probably to allow relocation during
POST (up to the limit provided by INT 15,88).  Entering iPXE during
POST is a rare operation; on the even rarer systems where doing so
happens to overwrite a PMM-allocated region, then there exists a
fairly simple workaround: if the user enters iPXE during POST and
wishes to exit iPXE, then the user must reboot.  This is an acceptable
cost, given the rarity of the situation and the simplicity of the
workaround.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>

undiloader.S was originally part of romprefix.S, and so inherits its
licence.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

It is common for system memory maps to be grotesquely unreliable
during POST.  Many sanity checks have been added to the memory map
reading code, but these do not catch all problems.

Skip relocation entirely if called during POST.  This should avoid the
problems typically encountered, at the cost of slightly disrupting the
memory map of an operating system booted via iPXE when iPXE was
entered during POST.  Since this is a very rare special case (used,
for example, when reflashing an experimental ROM that would otherwise
prevent the system from completing POST), this is an acceptable cost.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

For extremely tight space requirements and specific applications, it is
sometimes desirable to create gPXE images that cannot provide the PXE API
functionality to client programs. Add a configuration header option,
PXE_STACK, that can be removed to remove this stack. Also add PXE_MENU
to control the PXE boot menu, which most uses of gPXE do not need.

Signed-off-by: Marty Connor <mdc@etherboot.org>