[Info-vax] VAX VMS going forward

[Arne Vajhøj]

On 7/28/2020 1:36 PM, Simon Clubley wrote:
> 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.

It is pretty obvious that the AMD/Microsoft/Linus decision
worked out pretty well.

But I don't know if it really means anything for VMS.

I am not convinced that having support for VAX ISA
in Alpha and later Itanium would have been a
success!

>> 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.

As posted elsewhere then I also think there are other reasons, but
yes that is one of reason.

But it is hardly surprising that C code is more portable than
assembler code.

Arne