User exit linkage conventions

To enter a user exit, DFSORT loads the address of the DFSORT return point in register 14 and the address of the user exit routine in register 15. A branch to the address in register 15 is then performed.

The general registers used by DFSORT for linkage and communication of parameters observe operating system conventions. When your routine gets control, the general registers have the following contents:

Register: Contents
1: DFSORT places the address of a parameter list in this register.
13: DFSORT places the address of a standard save area in this register. The area can be used to save contents of registers used by your user exit. The first word of the area contains the characters SM1 in its three low-order bytes.
14: Contains the address of DFSORT return point.
15: Contains the address of your user exit. This register can be used as a base register for your user exit; your user exit can also use it to pass return codes to DFSORT.

You can return control to DFSORT by performing a branch to the DFSORT return point address in register 14 or by using a RETURN macro instruction. The RETURN instruction can also be used to set return codes when multiple actions are available at a user exit.

Your user exit must save all the general registers it uses. You can use the SAVE macro instruction to do this. If you save registers, you must also restore them; you can do this with the RETURN macro instruction.