User Exit Requirements

The migration ID determination user exit must meet the following requirements:

The exit must be assembled and link-edited into an accessible load library. Any name is suitable (the name is specified in the SYSPARMS command to activate the user exit).
Because your product region executes in APF-authorized mode, the exit must be in an APF-authorized library.
The exit must obey standard linkage conventions:
- R1 contains the address of the parameter list.
- R2 to R12 must be saved on entry and restored on exit.
- R13 points to a standard save area.
- R14 holds the return address and AMODE.
- R15 holds the entry point address.
The exit can be AMODE 24 or 31, and RMODE 24 or ANY. All parameters are passed below the 16M line. The exit is called in the link-edited AMODE. It returns using BSM 0,14 (with the value in R14 as at entry). However, BR 14 also works.
The exit is called from the main task. It must not issue any operating system waits or use services that take a significant length of time. Doing so would severely impact processing.
If the exit abends, it is disabled.