On Wednesday, 05/03/2017 at 08:29 GMT, "John P. Hartmann" 
<[email protected]> wrote:
> HNDSVC sets up a handler for SVCs.
>
> The documentation does not describe how to set the contents of a
> register upon return, only that registers are restored.  I assume this
> is from the system save area (SSAVE) and that one would have to modify
> the saved registers there.  Correct?

Yes.  That's how SVCs that return data in registers do it.

> SPIE allows for a way to resume at some other point than the interrupt
> (which often is desirable); suppose one would want to do the same for a
> SVC; perhaps the address of an error routine has been passed in the
> parameter list.  Also modify the SSAVE (SSAOPSWA)?

Yes.  In fact, that's what SPIE changes.

Alan Altmark

Senior Managing z/VM and Linux Consultant
Lab Services System z Delivery Practice
IBM Systems & Technology Group
ibm.com/systems/services/labservices
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[email protected]
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