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

[Stephen Hoffman]

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.

There are various parts of OpenVMS where applying a JIT could or would 
be useful.

Adding a JIT into DCL or into a replacement for DCL—any "fun" with 
self-modifying DCL aside—would be an obvious investigation.

Should it ever appear within OpenVMS, BPF uses a JIT, too. 
https://lwn.net/Articles/437981/


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