[OpenBIOS] [PATCH] sparc64: fix registers dealing with client

[Igor Kovalenko]

Hi!

This patch improves previous proposal and adds:

- save/restore global registers across client interface calls.
Since OS kernel generally has it's own idea of what
the ABI is we have to follow this requirement.

- adjust stack to allow using unoptimized openbios
build with linux kernel. Linux provides only 128 bytes
on stack which is not enough to save arguments by
code generated with gcc -O0

- fix switch_to so it actually could be used to switch
to client image. context pointer must be volatile to
prevent gcc optimizing out stores to it.

Signed-off-by: [e-mail]