[romprefix] Allow to enforce PnP BIOSes to be detected as non-PnP #16
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Add a define NONPNP_FORCE that controls building of the PnP detection routine. Together with the existing NONPNP_HOOK_INT19 hook this enables booting iPXE on PnP BIOSes that can not be persuaded to boot iPXE by BIOS menu configuration alone (e.g. my abit BX6 2.0). Signed-off-by: Stefan Tauner <stefan.tauner@gmx.at>
…tion
The vgabios used by bochs and qemu (and other virtualisation products)
has a bug in its implementation of INT 10,4f00 which causes the high
16 bits of %ebx and %edx to become corrupted.
The vgabios code uses a "pushaw"/"popaw" pair to preserve the low 16
bits of all non-segment registers. The vgabios code is compiled using
bcc, which generates 8086-compatible code and so never touches the
high 16 bits of the 32-bit registers. However, the function
vbe_biosfn_return_controller_information() includes the line:
size_64k = (Bit16u)((Bit32u)cur_info->info.XResolution *
cur_info->info.XResolution *
cur_info->info.BitsPerPixel) >> 19;
which generates an implicit call to the "lmulul" function. This
function is implemented in vbe.c as:
; helper function for memory size calculation
lmulul:
and eax, #0x0000FFFF
shl ebx, #16
or eax, ebx
SEG SS
mul eax, dword ptr [di]
mov ebx, eax
shr ebx, #16
ret
which modifies %eax, %ebx, and %edx (as a result of the "mul"
instruction, which places its result into %edx:%eax).
Work around this problem by marking %ebx and %edx as being clobbered
by the call to INT 10,4f00. (%eax is already used as an output
register, so does not need to be on the clobber list.)
Reported-by: Oliver Rath <rath@mglug.de>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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It's been a very long time (sorry) but: I would prefer not to include this unless it can be demonstrated that there is no better way to achieve the goal. Adding In this case, I'd need to be convinced that the BIOS in question is detected as PnP by iPXE's Closing this PR on the assumption that it is unlikely to receive any further attention after such a long delay, but please do reopen if it is still relevant. |
Add a define NONPNP_FORCE that controls building of the PnP detection
routine. Together with the existing NONPNP_HOOK_INT19 hook this enables
booting iPXE on PnP BIOSes that can not be persuaded to boot iPXE by
BIOS menu configuration alone (e.g. my abit BX6 2.0).
Signed-off-by: Stefan Tauner stefan.tauner@gmx.at