Registers at Entry

On entry to the group user routine, the registers contain the following information:

Register	Contents
GPR 0	Used as a work register by the system.
GPR 1	Address of the group user routine parameter list (GEPL), mapped by the IXCYGEPL macro.
GPRs 2 - 12	Used as work registers by the system.
GPR 13	Address of a 72-byte work area for use by the group user routine. The user routine does not have to save and restore XCF's registers in this work area. The user routine can use this work area in any way it chooses.
GPR 14	Return address (the group user routine must return control to XCF through a BR 14 or a BSM 0,14.)
GPR 15	Entry point address of the group user routine.
ARs 0 - 15	Used as work registers by the system.