Re: [Qemu-devel] Merging improvements from VirtualBox OSE into qemu?

[C . W . Betts]

On Dec 24, 2008, at 7:33 AM, Liraz Siri wrote:
> I don't really understand the implementation VirtualBox uses to
> accomplish running 64bit VM guests on a 32bit host. Is it possible
> VirtualBox have figured out how to run 64bit instructions on a host
> running in 32bit mode? (otherwise they'll need to be doing some kind  
> of
> emulation)
>
> Testing this VirtualBox feature on hardware that doesn't support 64bit
> instructions will be revealing...

It probably uses something similar to the way the Mac OS X 10.4 and  
10.5 kernel works.  All versions of Mac OS X (excluding the upcoming  
Snow Leopard, and then only supported on select hardware) use a 32-bit  
Kernel, but on 10.4, and more so on 10.5, it can run 64-bit apps.  How  
it does this, I don't know, but it is possible that VirtualBox is  
using the same hardware calls.