[LinuxBIOS] Specifications?

Brendan Trotter btrotter at gmail.com
Tue Jun 12 06:23:40 CEST 2007


I'm wondering if there's a specification describing the state of the
computer at the hand-off between LinuxBIOS and a payload.

So far I've got LinxBIOS booting a dummy "for(;;)" payload in Bochs,
and I've found out there's a "LinuxBIOS Table" and that it can be
found by searching for "LBIO" in the first 4 KB of RAM and in the area
between 0xF000 and 0xFFFFF. I don't know if there's a checksum or any
other validation, and have been unable to find anything describing
what this table contains.

I assume there may also be ACPI, MP specification, PIRQ routing and/or
(possibly) SMI/DMI tables, and I'm guessing that (if present) these
tables can be searched for using the same methods as described in
their corresponding specifications.

There's also other issues, for e.g:
- will an 80x86 system always be in 32-bit protected mode for 32-bit
ELF payloads, and is long mode possible for ELF64 payloads (and if so,
how is paging setup)?
- are any parameters passed on the stack to the payload's entry function?
- are AP CPUs started (or waiting for a SIPI sequence)?
- can the payload assume anything about the state of the PIC, I/O
APIC/s and local APIC/s, PIT, RTC, ISA DMA controllers, serial ports,
- what state are PCI buses and devices left in (would a payload need
to do full PCI bus enumeration, or..)?
- is there anything in the LinuxBIOS table that could be used to
determine if the computer is "headless" and which serial port or other
device to use if it is?
- can anything be assumed about AGP and the first video card (if the
computer isn't headless)?
- is there any form of "LinuxBIOS API" that can be used by the payload
for generic low level disk access (floppy/ATA/ATAPI/SCSI)?



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