Sorry about the newbie questions- I still can't get at the FAQ. Pointers to where I can get this document gladly accepted. Or a pointer to the archive of this mailing list. Or the CVS repository for the code.
Why is the bios going into protected mode? This would seem to make life difficult to load an OS. Is there a game plan for dealing with this that I'm not seeing?
The problem is that the linux load sequence is 16-bit code, which loads the idt and gdt and then performs dozens of more instructions before going into protected mode.
The solutions I see are:
1) Don't go into protected mode. So long as addresses stay below 1 meg, this shouldn't be a problem (PCI/AGP configuration is the only reason I know of why we may need to go above 1M).
2) Go into protected mode for initial configuration, then exit it to load the boot code (note that the BIOS service routines would have to run in real mode in this case).
3) Stay in protected mode, run the OS loader in V86 mode, and "cleverly" handle the protection fauls (probably by "emulating" them- on the lidt/gidt instructions we save off their offsets, and on the lmsw instruction doing all three- lidt/gidt/lmsw).
4) Same as above, but instead of emulating the instructions, we exit from protected mode at that point, and retry the instruction (and hope that no one ever tries to use a BIOS service after executing a protected instruction).
5) Beg the OS maintainers to change their code. I dislike this option intensely- while on Linux we could probably do it (by becoming OS maintainers), I doubt Microsoft would listen.
Brian
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