Re: Stacks, was Segments

On Sun, 19 Jan 2025 16:33:53 +0000, David Brown wrote:

>
A two-stack setup can be used in C too.  (The C standards don't require
a stack at all.)  On the AVR microcontroller, it is not uncommon for C
implementations to work with a dual stack, since it does not have any
kind of "[SP + n]" or "[SP + r]" addressing modes, but it /does/ have an
"[Y + n]" addressing mode using an index register.
>
Two stacks are also pretty much required for FORTH.
>
The use of a dual stack could also significantly improve the security of
systems by separating call/return addresses from data.

In My 66000 the code cannot read/write that other stack with LD and ST
instructions. It can only be accessed by ENTER (stores) and EXIT (LDs).
The mapping PTE is marked RWE = 000.
So, while you can still overrun buffers, you cannot damage the call/
return stack or the preserved registers !!