Re: For the AdaOS folks

["Warren W. Gay VE3WWG" <ve3wwg@NoSpam.cogeco.ca>]

Marven Lee wrote:
> Warren W. Gay VE3WWG wrote:
>>Marven Lee wrote:
>>>You can end up with a microkernel that only handles cross-domain
>>>calls.  Everything else, including what you normally think
>>>a microkernel should at least include,
>>
>>I'm glad you said "normally" here. ;-)

>>>such as memory management,
>>>scheduling and IPC can be implemented outside of the microkernel.
>>
>>Exokernel?
> 
> No, I'd still call it a microkernel or perhaps a trampoline.

Ok, I know what you mean now. But I _want_ the mk to take
care of VM and port management however, since I don't want
to be bothered with those. Having the VM done in the mk
makes it a little easier to port MyOS to another hardware
platform (mind you, you still have to port your other
hardware support, but it is one less worry).

But your point that a mk could be smaller is taken.

> I've dug up an old thread from alt.os.development where
> KVP describes a single server trampoline and I follow
> up with a rough idea of how to implement a
> trampoline-microkernel that supports multiple servers.
> 
> http://tinyurl.com/6gb5b
> 
> That was an old posting of mine and I'd probably change the
> "activation" structure around a bit.  I'd more likely use
> array indices to reference other activations instead of pointers.
> I'd also change some of the needed system calls as well.

It sounds like an interesting idea. Perhaps you'd like to
work on rtmk and extend it some?

I simply don't have the time to do the mk part myself. For
now, I am more interested in the Ada components on top of
it. But it sure would be nice to have an Ada microkernel
underneath it someday ;-)

> Now for some suggested reading...
> 
...
> "Anonymous RPC" by C.Yarvin et al.  Imagine the Amiga's
> shared libraries randomly scattered around a 64-bit address
> space.  Imagine also that the Amiga library jump tables
> are execute-only and not readable, and that it was running
> on a RISC chip with instruction-alignment constraints.
> Then you've got a idea of what "Anonymous RPC" and
> probablistic memory protection is about.

I don't know much about the Amiga myself. But
There are 2 strikes against this IMHO:

   1. Single address space (my own bias)
   2. Not secure.

For # 2 they state "it is _unlikely_ that a process will
be able to locate any other segment... impossible to
corrupt a segment without knowing its location."

The word "unlikely" is not good enough for me here.

My first priority is security (efficiency and everything
else is secondary). So any approach like this one, where
security is just "good enough", is not appropriate to my
own goals.

> "Implementing Operating Systems without Kernels" and
> "Efficient Cross-domain Mechanisms for Building
> Kernel-less Operating Systems" by D.Probert and J.Bruno.
> I read it some time ago, I think it is more or less about
> the trampoline/microkernel being implemented in hardware.

Again, I am not really interested in doing all of the details
of an O/S myself. That is why I rather like the layered
microckernel concept. It is also a nice way to subdivide the
problem for those adventuresome people that _do_ have the
time to fiddle with the lower level things ;-)
--
Warren W. Gay VE3WWG
http://home.cogeco.ca/~ve3wwg