Calling user exits

The assembler calls user exits using the standard OS Linkage conventions. The user exit can be written in any language that conforms to these constraints:

Can be called many times, using the exit module entry point
Retains storage for private variables across invocations

High Level Assembler provides an "anchor word" in the Exit Parameter List to allow you to maintain information across calls to the exit.

Refer to the language's Programming Guide to find out if you can use it to write a user exit for the assembler.

The contents of the registers upon entry to the user exit are as follows:

Register 0: Undefined
Register 1: Address of Exit Parameter List, see Figure 1.
Registers 2 through 12: Undefined
Register 13: Address of 72 byte save area
Register 14: Return address
Register 15: Address of entry point of user exit