[TUHS] Porting 2.11 BSD

[Hellwig Geisse]

Hi Oliver,

On Sa, 2015-11-21 at 14:00 +0100, Oliver Lehmann wrote:
> Is there a good "HOWTO" for "first things first" as implementing
> disklabel seems to require quite some "device work" before the
> first "hello world" is there - is there something else which
> should be could be done first and does not require so much to
> port (the whole disk subsystem on that machine is different
> from "usual" disk subsystems as it is handled via a PIO)

I don't have an exact HOWTO for porting BSD, but we gathered
some experience in these things while porting NetBSD to our
processor ECO32.

First and most important is a working tool-chain (which in case
of BSD means GCC). You should really know your tools, because
you will frequently dig deep into them to understand various
aspects of e.g. linker scripts. We totally underestimated the
amount of work to be done here.

Then you must decide if you will do cross-development, or if you
can do it on a running BSD system. Even if so, you will have to
generate a file system for the target BSD system from which you
boot your machine. You can do that with the tools included in BSD,
but they are not running yet. (Btw, byte-order is an especially
nasty thing in this context.)

Memory management was another area which required a fair amount
of work. I have no experience with 2.11 BSD, but in case of NetBSD
the code is divided into at least three layers to obtain a good
degree of re-usability for different architectures. Alas, the
documentation was rather poor, and the relevant book ("The Design
and Implementation of the 4.4 BSD Operating System" by McKusick
et al.) is a bit outdated.

The project of porting BSD to a yet unsupported machine is
certainly feasible, and is indeed a valuable experience. But
don't expect to have it done in only a couple of weeks... :-)

Good luck!
Hellwig