The code for the external function or subroutine receives control in an unauthorized state. The contents of the registers are:

Register 0

Address of the environment block of the exec that invoked the external function or subroutine.

Register 1

Address of the external function parameter list (EFPL)

Registers 2-12

Unpredictable

Register 13

Address of a register save area

Register 14

Return address

Register 15

Entry point address