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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: ada compiler?
Date: Fri, 16 Nov 2007 19:50:03 -0600
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Date: 2007-11-16T19:50:03-06:00
List-Id: <comp.lang.ada>

"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message
news:473b58af$0$27815$39db0f71@news.song.fi...
...
> My wishlist for stack checking support in Ada compilers:
>
> Storage_Error should be raised a bit before the stack is fully
> exhausted. The amount of "reserve" stack-space left at that point
> should be configurable by an option or an environment variable to
> an (application-specific) value that lets the exception be raised
> and handled.
>
> While the exception is being propagated and handled (that is, while
> it is possible to say "raise;") the application should be able to
> use the reserve stack capacity (with possibly a Segmentation
> Violation if the reserve capacity is exhausted).
>
> Normal checking rules (respecting the reserve capacity) should
> return into force when the exception has been handled (when it is
> no longer possible to reraise the exception).
>
> But I have no idea how hard that would be to implement...

That's pretty close to how Janus/Ada implements, actually, but there is one
issue: given that pretty much anything can be called during the handler, and
further exceptions raised and handled, it is pretty hard to both allow the
reserve capacity to be used and then not allow it to be used. (Moreover,
that probably would cause the exception to be immediately raised instantly
when the handler completed - because the finalization handlers would
overflow - probably not what was intended.)

We obviously can't make stack checks more expensive (for obvious reasons;
one of the purposes of the reserve is to allow room for interrupt handlers
and OS calls, neither of which respect Ada task stacks),.

The amount of the reserve can be configured in the runtime system (with just
a simple recompile), but we don't have an "option" for configuring it - it
seems a rare enough need.

Of course, other runtime models (especially those using hardware checking)
would be different.

                            Randy.