[Info-vax] How much of VMS is still in MACRO-32?

[Arne Vajhøj]

On 5/31/2021 7:23 PM, Arne Vajhøj wrote:
> On 5/31/2021 4:26 PM, Stephen Hoffman wrote:
>> On 2021-05-31 13:07:28 +0000, Simon Clubley said:
>>> Is there any self-modifying code in VMS ? (I hope the answer to that 
>>> is no, BTW. :-))
>>
>> There's DCL around that is self-modifying. Which is part of why 
>> compiling DCL can be such "fun".
>>
>> I'm not aware of self-modifying code or a JIT within OpenVMS itself, 
>> though I'm a little murky on the full "creativitity" of the debugger 
>> in this context.
>>
>> There is some related support present (INSTRUCTION_MB, EVAX_IMB, etc) 
>> which certainly implies self-modifying code does exist.
>>
>> I've written and have met self-modifying app code for OpenVMS.  As 
>> have others. Including Oracle Rdb, IIRC.
>>
>> Met some app code that invoked a compiler and linker and then FIS'd 
>> that code into the app, too. That was clunky and very limited, but 
>> workable for that app.
>>
>> There's Java and its JIT, of course.
> 
> It may be relevant to distinguish between:
> A) dynamic code generation where an application generate
>     new code and execute it
> B) code that modifies itself aka replace some of its code
>     with new code
> 
> #A probably have more legitimate uses than #B.

Note that Java can actually generate code at two levels:
* it can generate Java byte code dynamically and execute it
* Java byte code get JIT compiled to native code when the
   JVM decide it is time

Arne