Linkage examples

When calling your user exit, DFSORT places the return address in general register 14 and your routine's entry point address in general register 15. DFSORT has already placed the register's save area address in general register 13. DFSORT then makes a branch to your routine.

Your routine for the E15 user exit might incorporate the following assembler instructions:

     ENTRY  E15
     .
     .
E15  SAVE   (5,9)
     .
     .
     RETURN (5,9)

This coding saves and restores the contents of general registers 5 through 9. The macro instructions are expanded into the following assembler language code:

     ENTRY  E15
     .
     .
E15  STM    5,9,40(13)
     .
     .
     LM     5,9,40(13)
     BR     14

If multiple actions are available at a user exit, your routine sets a return code in general register 15 to inform DFSORT of the action it is to take. The following macro instruction can be used to return to DFSORT with a return code of 12 in register 15:

RETURN  RC=12

A full explanation of linkage conventions and the macro instructions discussed in this section is in z/OS MVS Programming: Assembler Services Guide.