GSoC Project: EFI on amd64/i386

[Eric McCorkle]

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On 05/15/12 11:44, John Baldwin wrote:
> The i386 kernel assumes it starts out with a flat 32-bit mode with
> the kernel loaded into a contiguous memory region at a fixed
> physical address.  If we need a relocatable kernel (as Marcel
> hinted at I think), then that adds a fair bit of complication.
> 
> The amd64 kernel assumes it starts in long mode (the bootinfo64.c
> bits in the loader setup initial page tables, etc.).  I think the
> amd64 kernel also has to be loaded into contiguous memory at a
> fixed physical address currently.
> 

Seems like an initial workaround could be to allocate a space big
enough for all the necessary ELF segments, and split it up ourselves.

Do the kernel and modules actually do anything that depends on being
in a contiguous space in some way (ie some relocation trick)?  Because
it seems like it shouldn't really matter otherwise.

> Nah, nothing in amd64 calls the BIOS (we don't support VM86).  The
> only thing I am aware of is the VESA bits but those use an
> emulator, they don't let the CPU natively run BIOS routines.  i386
> could be adopted to do the same, but it also doesn't make BIOS
> calls on modern systems outside of the VESA driver (it used to use
> VM86 to probe memory, but now it uses the SMAP passed in by the 
> loader if it exists and only falls back to VM86 calls if it
> doesn't).

Yeah, I've seen the x86emu code, when I was trying to track down a
suspend/resume problem.  The thing I'm wondering is if the BIOS
info/code will even be there at all when EFI booting.  I suppose the
only way to really know is to get the kernel booting and see...
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