Re: porting arcboot

[Vivien Chappelier <vivienc@nerim.net>]

> I'm planning to try porting arcboot to ip27 (mips64).

I'm actually doing the same for ip32 (SGI O2). I've added support for
64-bit ELF while sticking to 32-bit arcboot to avoid the issues you
mention with 64-bit userland. The code is still a bit ugly and I've
hardcoded a different load address for the O2 (this should be a
'configure' option at least), but you might be interested to have a look.
The same trick used for the kernel could probably be used to relocate the
32-bit arcboot to 64-bit address space using objcopy, for the ip27 PROM
which only supports 64-bit ELF (according to Ralf).

An early patch is there:
http://www.linux-mips.org/~glaurung/arcboot-0.3.5-o2.diff

The idea is to load segments with the KSEG0 version of the physical
address, which can be done with 32-bit code (but limits kernel load
address to <512Mb). We then jump to the 64-bit entry point with a small
bit of mips4 assembly. 

Comments welcome.

Vivien.