[Info-vax] VAX VMS going forward

[Simon Clubley]

On 2020-07-27, Stephen Hoffman <seaohveh at hoffmanlabs.invalid> wrote:
> On 2020-07-27 13:20:28 +0000, John Reagan said:
>> 
>> As I said, it is a flat 64-bit address space. There is no "mode".  We 
>> just decide to load the stack, the static data, and code into addresses 
>> that can fit in 32-bits because of the history of descriptors and 
>> itemlists with 32-bit pointers in them.  It is part of the "recompile 
>> and go" we promised back on the VAX days.  We require that anybody 
>> wanting to use memory that needs a 64-bit pointer to modify their 
>> compile command or source files. However, you can't move the stack or 
>> static data.  You just get to heap allocate or mapsection into those 
>> memory ranges.  And as I mentioned, for x86, we move your code there to 
>> leave more 32-bit room for stack and 32-bit addressable heap.
>
> I'm happy to be corrected here, but AFAIK there are no 64-bit apps on 
> OpenVMS. None. There are 32-bit (~30-bit) apps with 64-bit (50-bit?) 
> extended, or segmented, or, sure, maybe flat, addressing available. But 
> there are no 64-bit apps.
>

And this is because VMS _does_ have a 32-bit mode and a 64-bit mode
but it is implemented very differently from other operating systems.

It's just that this 32-bit mode is implemented in a way on VMS that
requires most changes to 64-bit mode to be made in the source code
manually instead of via some compiler and linker flags.

Also, the 64-bit mode on VMS is nowhere yet near a full replacement
for the 32-bit mode unlike on other operating systems.

Simon.

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