How do I go about creating a minimal GNAT runtime?

[Lucretia <lucretia9@lycos.co.uk>]

Hi (again),

It's been a while, but I'm coming back to my Ada kernel again. I've
been messing with my helo_world_kernel which I built using no runtime
(see http://www.archeia.com for more info).

Having just spoken to Ludovic on #Ada, he pointed out that the gnat
tools can use a basic cross tool set, like the ones I have built
myself (again, see the above link). My toolset comprises of a gnat1
compiler and a gnatbind for my targets. I found that it does work
using the --GCC and --GNATBIND flags, and I need to make sure the
cross tools and the host tools are of the same GCC version otherwise
GNAT throws up ALI format errors.

The thing is, I've been trying to enable exceptions, but keep coming
across big problems in that the runtime requires features that are
being restricted, such as returning aggregates and assigning
composites, returning unconstrained objects which requires the
secondary stack. So, what I really need to know is, how do I create a
runtime which is restricted in this way for bare hw access?

Thanks,
Luke.