For the user ID replaceable routine, the contents of the registers on entry are described below. The address of the environment block can be specified in either register 0 or in the environment block address parameter in the parameter list. For more information, see Using the environment block address.

Register 0

Address of the current environment block

Register 1

Address of the parameter list

Registers 2-12

Unpredictable

Register 13

Address of a register save area

Register 14

Return address

Register 15

Entry point address