[gentoo-user] how to rebuild gentoo on a somewhat different hardware

[Helmut Jarausch <jarausch@igpm.rwth-aachen.de>]

Hi,

I have an up-to-date ~amd64 GenToo installation with has been
built on a current AMD64 (Phenom II) machine where I used 
-mtune=native in etc/make.conf since I didn't think of the case
that I would need to port this system to a somewhat older Opteron
based machine (still AMD64)

But after cloning the system, some fundamental utilities die of
an illegal instruction. So I have to rebuild GenToo nearly
from scratch. emerge -e world doesn't work.

So, what is a reasonably fast method?

I'd like to keep
/etc
/usr/portage   except /usr/portage/packages
/var/lib/portage

Is there a fast method e.g. by using the Gentoo based
SystemRescueCD to reinstall a very basic system, such that
I can do  emerge -e world.
It looks as if the gcc tool-chain is intact since I could
compile a kernel without any problem.
But some utilities, e.g. find, die of an illegal instruction.

Many thanks for any hints saving me a couple of hours work,

Helmut.