Register Usage

Upon entry to the exit, the register contents are as follows:

• Register 0 = not defined
• Register 1 contains the address of the input parameter list
• Register 2-13 = not defined
• Register 14 = return address
• Register 15 - entry point address

Upon entry to the exit, the access register contents are undefined.

Upon return from the exit, the register contents are expected to be:

• Register 0 = reason code if GR15 return code is non-zero
• Registers 1-14 = not defined (need not be restored to value on entry).
• Register 15 = return code

Upon return from the exit, the access register contents are unchanged.