Re: [Xen-users] baremetal to PV troubles (32/64 bit PV hybrid)

[Tom Brown <xensource.com@xxxxxxxxxxxxxxxxxxx>]

On Thu, 12 Jul 2007, Dylan Martin wrote:

> Thanks for answering!  I have loads more questions...
>
> Okay, I think I understand.  I'd use the 64 bit kernel & modules but
> the 32 bit libs, right?
>
> How does the 64 bit kernel know the userland is 32 bit?  Won't it try
> and find the 64 bit libs and freak out?
AFAIK, kernels don't find libraries... userspace programs do. The 64 bit 
kernels provide all the 32 bit system calls (as long as the default option 
to do that wasn't turned off when the kernel was built).
> Does it use memory like a 64 bit machine?
yes, raw memory allocation is a kernel thing.

> Is there any reason to run a 32 bit domU in a 64 bit dom0?
yes/no. 32 bit code is generally in more common use and better tested. If 
you're using precompiled binaries you might not even have an option of 
running 64 bit code. Or you might simply have a 32 bit install on a 
physical machine that you want to move to a paravirt on a big machine 
without rebuilding from scratch and consequently breaking things.
The one gotcha you will run into with the 32/64 bit hybrid is that some 
kernel related tools can get upset (iptables being an example, the 
simplest solution is to build a statically linked binary on a 64 bit 
machine and copy that across to your 32 bit userspace domU)
-Tom




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