The user exit receives control in the following environment:
- Supervisor state, key zero.
- Running in the ASID of the process, except for the pre-process
termination exit, which runs in the master address space if the address
space of the process was terminated.
Register usage:
- On entry to the user exit, register 1 points to the Process Exit
Data Block (PEDB).
- For the pre-process initiation exit, if the value returned in
register 15 is > 4, the process initiation request is rejected. For
all other exit points, the return code in register 15 is ignored.