Output Register Information

When control returns to the caller, the general purpose registers (GPRs) contain:

Register: Contents
0: If GPR 15 contains a zero or X'10', GPR 0 is used as a work register by the macro; otherwise, GPR 0 contains a reason code.
1: Used as a work register by the system.
2-13: Unchanged.
14: Used as a work register by the system.
15: Return code.

When control returns to the caller, the access registers (ARs) contain:

Register: Contents
0-1: Used as work registers by the system
2-13: Unchanged
14-15: Used as work registers by the system

Some callers depend on register contents remaining the same before and after issuing a service. If the system changes the contents of registers on which the caller depends, the caller must save them before issuing the service, and restore them after the system returns control.