Exit parameter list
The assembler passes an Exit Parameter List to the user exit. On entry to the exit, Register 1 contains the address of this parameter list. Each exit is passed a separate copy of the parameter list. The parameter list includes a pointer to an Exit-Specific block that contains information for each exit type. High Level Assembler provides macro ASMAXITP to map the Exit Parameter List and the Exit-Specific Information block. Figure 1 describes the format of the Exit Parameter List, Figure 1 describes the format of the Exit-Specific Information block for the LISTING exit, and Figure 2 describes the format of the Exit-Specific Information block for the other exit types.
The high-order bit of the last pointer in the I/O exit parameter list is set to 1.
The HLASM Services Interface for I/O exits is described HLASM Services Interface.

The following sections describe the Exit Parameter List.