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Re: 64 Bit Support?

From: Andrei E. Warkentin
Subject: Re: 64 Bit Support?
Date: Sun, 17 Jun 2007 12:34:50 -0700

I wouldn't go as far as saying it is overly complex. If all you want to do is linearly map the first 4GB (which is likely enough), you can just pre-build the like... 6 or 7 tables you need (with 2m pages) in an assembly source along with a 64-bit GDT and dummy IDT. Obviously at start-up you're going to relocate that chunk out of ROM (for firmware), but that's like what... another 5-6 instructions?

Andrei Evgenievich Warkentin
Cell: (+1) (847) 321-15-55

17.06.2007, в 4:24, Stefan Reinauer писал(а):

* Jeroen Dekkers <address@hidden> [070617 13:03]:
Interesting would also be to boot pure 64bit kernels. I think some of
the BSDs have their bootloader switch to 64bit long mode, so the kernel
does not have to dot this anymore. Maybe grub could do the same thing.

To enable long mode you have to enable paging and I don't think the
bootloader should be doing things like that. I also don't see any
problems with the OS enabling long mode.

Yes, enabling long mode is overly complex and was not well designed,
imho. So I partly agree. We considered enabling long mode in LinuxBIOS a
while ago, to avoid the same "old cruft" situation like with 16bit BIOS
and 32bit OS. But you can not enable long mode without a huge amount of
overhead (ie. paging), so it can only be done when the RAM controller is
enabled and RAM is working. By that time accessing 64bit address space
has already become a lot less interesting for the boot firmware. So the
next place where it would make sense at all is in the bootloader.

The problem might be that Grub2 locks out existing operating systems, 
if it does not support switching to long mode itself. I read rumours
only, so I might be completely wrong.

Is anyone booting non-Linux OSes like FreeBSD, NetBSD, OpenBSD,
OpenSolaris, etc with GRUB2 yet? 


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