[Info-vax] VAX VMS going forward

[Simon Clubley]

On 2020-07-28, Arne Vajhøj <arne at vajhoej.dk> wrote:
> On 7/28/2020 8:51 AM, Simon Clubley wrote:
>> 
>> You tell the compiler whether you want a 32-bit or 64-bit executable
>> and it, the linker, and OS support libraries takes care of most of
>> the work for you (if not all the work).
>> 
>> I wish it was that simple on VMS.
>
> Other environments are not doing this at all.
>
> Many other environments has 32 bit mode and 64 bit mode. Different
> instruction sets and address size in the CPU. Two sets of
> libraries. Etc..
>

They do solve the same problem in a different way.

And they give you tools which makes it easy to switch between both
environments when compiling your code.

> But that is completely different from what VMS has.
>

_Very_ true.

> VMS Alpha/Itanium only has 64 bit mode and 64 bit addresses in the
> CPU, single instruction set and one set of libraries. That single set
> of libraries just have a lot of API's only passing lower half of
> addresses and a few passing full addresses.
>
> Totally apples and oranges.
>

But if the lowest-level supported language on VMS was C, then you
could still do this in the compilers and linker along with suitably
modified system headers without having to make major changes to your
code. You would tell the compiler what you wanted via qualifiers just
like you do in other operating systems.

There's enough information available in C code, along with enough
abstracted implementation details (such as pointer size) that the
code doesn't care about unless you go looking for it, that it would
be quite viable to do in software what other environments do in hardware.

The same is true for the other high-level languages which VMS supports.

That could be the basis of the flat 64-bit mode that Stephen is looking
for.

Unfortunately, VMS supports assembly language as an application
programming language. That made perfect sense 40 years ago, but
in 2020, it's a major weakness in VMS.

It's also the reason why we have a hybrid 32-bit/64-bit API interface
instead of a flat 64-bit mode in addition to the traditional 32-bit API
interface mode.

Simon.

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