Stacking PC routines

Stacking PC routines must meet the following requirements:

They must not use the checkpoint/restart facility.
They must be either permanently resident in LPA or the nucleus, or they must be loaded under the job step task of the address space that created the entry table.
They must issue the PR instruction to return control to the user.
Stacking PC routines that cause a space switch must:
- Run in an address space that is non-swappable
- Use only those MVS™ services that are supported in cross memory mode.