Mixing amd64 kernel with i386 world

[Nathan Whitehorn]

On Sat, 28 Sep 2013, Peter Jeremy wrote:

> I have a system with 4GB RAM and hence need to use an amd64 kernel to use
> all the RAM (I can only access 3GB RAM with an i386 kernel).  OTOH, amd64
> processes are significantly (50-100%) larger than equivalent i386 processes
> and none none of the applications I'll be running on the system need to be
> 64-bit.
>
> This implies that the optimal approach is an amd64 kernel with i386
> userland (I'm ignoring PAE as a useable approach).  I've successfully
> run i386 jails on amd64 systems so I know this mostly works.  I also
> know that there are some gotchas:
> - kdump needs to match the kernel
> - anything accessing /dev/mem or /dev/kmem (which implies anything that
>  uses libkvm) probably needs to match the kernel.
>

For whatever it is worth, I have done this running a ppc32 userland with a 
ppc64 kernel (that is how ppc64 was first developed actually, before the 
64-bit userland existed) and it worked just fine.
-Nathan