Re: segfault with large-ish array with GNAT

[Adam Beneschan <adam@irvine.com>]

On Mar 19, 11:02 am, Simon Wright <si...@pushface.org> wrote:
> tmo...@acm.org writes:
> > IIRC, the Burroughs 6500 had what they called a "cactus stack" where
> > branching would occur for new threads.  And there was a Texas Instruments
> > microprocessor that had no real stack, but rather a set of registers
> > that could be saved to RAM on a subroutine call.
> > These preceded DOS.
>
> The PDP-8 worked like that; the JMS instruction stored the return
> address in the first word of the subroutine, execution started at the
> next word.
>
>    JMS FOO    / CALL SUBROUTINE FOO
>
>    FOO, +0    / STORED RETURN ADDRESS
>    ...
>    JMP I FOO  / RETURN
>
> (we only had capitals)
>
> --S

Isn't that approximately how all computers used to work?  Or at least
a lot of them?  When I was first learning how computers ran, it seemed
like the common thing was for jump instructions to save the address of
the next instruction in a register, and then the subroutine code would
store the register somewhere---perhaps in the location containing the
return jump, since I don't remember those computers having "indirect
jump" instructions either.  It was a few years before I encountered a
machine that automatically saved return addresses on a stack---or even
had a concept of a stack built into it.

One thing I remember was a particular computer's implementation of
COBOL (Honeywell 200/2000 series---my dad used to work for Honeywell
so those were some of the computers I was most familiar with).  COBOL
used PERFORM statements for subroutine calls, and since you could have
PERFORM A in one part of the program and PERFORM A THROUGH B in
another part, or you could just fall into A without a PERFORM, the
paragraph A couldn't tell whether it was supposed to return to the
caller at the end of the paragraph.  So the code, before it did a
PERFORM A, would do a "move" to move a branch instruction into a
location at the end of A that would branch back to the caller.  Then,
after it returned, it would do another "move" to move a no-op to that
location.

Of course, none of these were good with recursion but I don't think
the experts understood the importance of recursion back then.

                                      -- Adam