The invoker of IEBCOPY can specify the exits by using the fourth parameter on the invocation.

The addresses passed to IEBCOPY in R1 and R13 are always interpreted as 24-bit addresses regardless of the AMODE at entry to IEBCOPY. The user exit addresses (passed via the fourth parameter) are interpreted as 31-bit addresses regardless of the AMODE at entry to IEBCOPY. Those exits will always be called in AMODE(31) regardless of the AMODE at entry to IEBCOPY.

The fourth word in the IEBCOPY invocation parameter list will have a 31-bit address of the user exit parameter list. This parameter list will be mapped by the IEBCPARM mapping macro. The fourth word must have the high order bit on indicating the end of the list.

Compatibility Warning: There might be existing invocations of IEBCOPY that pass three parameters but fail to set the high order bit on the last word. The z/OS V2R1 version of IEBCOPY would examine the non-existent fourth pointer and get unpredictable results.