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Re: porting arcboot

To: Andrew Clausen <clausen@melbourne.sgi.com>
Subject: Re: porting arcboot
From: Vivien Chappelier <vivienc@nerim.net>
Date: Mon, 10 Feb 2003 11:33:39 +0100 (CET)
Cc: Linux-MIPS <linux-mips@linux-mips.org>, Guido Guenther <agx@sigxcpu.org>
In-reply-to: <20030210034549.GA8408@pureza.melbourne.sgi.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
> 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.


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