[Info-vax] Creating an open source version of VMS, was: Re: OpenVMS Hobbyist Notification

[Simon Clubley]

On 2020-03-12, Arne Vajhøj <arne at vajhoej.dk> wrote:
> On 3/12/2020 3:20 PM, Simon Clubley wrote:
>> On 2020-03-12, Arne Vajhøj <arne at vajhoej.dk> wrote:
>>>
>>> ????
>>>
>>> When I search after $l_fab, $l_rab, $l_nam, $l_kbf, $l_rbf, $l_ubf
>>> etc. I see pointer and pointers.
>>>
>>> You don't?
>> 
>> They may be called "pointers" but they are nothing like the abstracted
>> pointers you see in a modern environment, including in C and Unix.
> >
> > They are nothing more than raw longwords that have had an address
> > forced into them.
>
> ????
>
> As far as I am aware C old or new only got one type of pointers,
> those you declare like:
>
> type *var;
>
> The C header files for RMS definition on VMS contains:
>
> struct xxx {
>     ...
>     struct yyy *xxx$l_yyy;
>     ...
> }
>
> How does your "the abstracted pointers you see in a modern environment"
> do that?
>

You are either being deliberately obtuse or you simply do not
understand what I am saying.

To answer your question: the abstraction comes from how addresses
are referenced in C source code versus how they are referenced
in Macro-32.

In a C/Unix environment (and in other higher level languages) how the
pointer to an address is implemented is a compiler/ABI implementation
detail that is hidden (ie: abstracted away) from the higher level
language source code. The source code generally doesn't care how
the pointer is implemented or even in most cases what size it is.

The same source code can be easily moved between a 32-bit and 64-bit
environment and across a range of environments.

In a Macro-32 environment, this is a very source code visible detail
that strongly affects how the program is written.

This is why in a modern Unix environment, you have to do little more
than tell the compiler whether you want the program built in 32-bit
or 64-bit mode unless you have deliberately coded the program in a
_very_ bad way.

In a modern VMS environment, you end up with a mixed 32-bit/64-bit
address space because compiling all your source code in a pure 64-bit
mode simply was not a viable option when 64-bit support was added
to VMS due to how visible this stuff is to the source code in VMS.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.