Re: GNAT and no runtime

[JCS <SANS.SPAM@MERCI.FR>]

On Thu, 27 May 2004 08:58:10 -0500, sk wrote:

> JCS <SANS.SPAM@MERCI.FR>:
>  > ... <snip>
>  >
> 
> So, in sumary, you are porting the GNAT run-time ?
Not the whole, just a very small subset of it, just to have exceptions
working. In fact, I would be perfectly happy if I didn't have to
reimplement some GNAT RT functions, but unfortunately it seems that I have
to.

> The point I am trying to make is that to port a run-time, you need to
> know what you are porting it to ! Replacing each run-time function at a
> time will probably work, but why not actually step back and write the
> kernel/executive to achieve your goals and then port the GNAT run-time
> to your kernel's capabilities ?
You probably misunderstand me, I was wishing exception because it helps to
develop my kernel, it's not a functionnality of the kernel. See it as a
debug feature.

> 
>  > Even if I disagree with your design, ...
> 
> Not "my design", it is how the Intel (>= i386) chips are built. Why not
> use the security/ring features of the chip if they are available ?
A short answer: ring 1 and 2 in the Intel protection mechanism are almost
useless, they don't provide any useful instruction that are in ring 0, but
they can access all memory of user-levels apps (ring 3).
Btw, the only system who use ring 2 is OS/2 and it was for some graphics
stuff. I don't know any real-life OS which use ring 1.
Almost all others processors have only 2 protections levels: supervisor
(ring 0 on Intel) and application (ring 3 on Intel). But again it is out
of topic here.

>  > ...it would be out of topic here.
> 
> Discussion of OS written in Ada off topic ? Sorry, I disagree, the topic
> seems appropriate to comp.lang.ada

Simply, it is more OS design relative than Ada relative.

Regards,
JC