Re: How to get Ada to “cross the chasm”?

[Simon Wright <simon@pushface.org>]

Dennis Lee Bieber <wlfraed@ix.netcom.com> writes:

> On Fri, 4 May 2018 22:07:37 +0300, Niklas Holsti
> <niklas.holsti@tidorum.invalid> declaimed the following:
>
>>On 18-05-04 16:30 , Jere wrote:
>>> The secondary stack is another example.
>>
>>That is not even a standard concept in Ada, but an implementation
>>concept.
>>
>
> 	And usage of such is not permitted in the avionics software to
> which I've been exposed. Merely because it seemed to be a dynamically
> allocated structure.

That's true for unrestricted runtimes, but I hardly think you'd be using
those in avionics software? (mind, when I worked on a missile guidance
system, we used unrestricted GNAT on VxWorks. That work started in 2000,
so we didn't have much experience with pragma Restrictions, and I
wouldn't know how to check what restrictions GNAT supported then
(3.16a1). Nowadays we have No_Secondary_Stack[1].

OK, there may be no dynamic (heap) allocation in restricted secondary
stack, but since it's allocated as part of the task stack you'd have a
hard row to hoe proving that it won't overflow! Lick a finger and hope.

In my Cortex GNAT RTS, the secondary stack is allocated in the stack of
the wrapper procedure that calls the task body .. so secondary stack
overflow would smash the stack of another task, most likely (primary
stack grows down, secondary stack grows up). Ugh.

[1]
https://gcc.gnu.org/onlinedocs/gnat_rm/No_005fSecondary_005fStack.html