Characteristics of the ARCINEXT Exit

The ARCINEXT installation exit receives control after the DFSMShsm startup PARMLIB member (ARCCMDxx) is processed, but before the functional subtasks become active.

The installation-reserved fields are the only fields in the MCVT control block that you are allowed to change. All other fields are reserved for IBM's use and are subject to change.

All parameters passed to ARCINEXT are located above the 16 MB line and have 31-bit addresses. If your ARCINEXT runs in AMODE 24, you can use the following example to switch to 31-bit mode before referring to 31-bit parameters from a 24-bit location:

MODE31  LA    15,*+10           GET 31-BIT TARGET ADDRESS
        O     15,=X'80000000'    SET AMODE 31 IN ADDRESS
        BSM   0,15              BRANCH INTO 31-BIT AMODE

Note: Before issuing the instructions in the preceding example, your program's base register should have a 31-bit address. If the program is running in 24-bit mode, byte 0 must contain zeros. Do not load the register with a BALR instruction while in 24-bit mode, as it sets inappropriate bits in byte 0. Instead, use LR or BASR instructions.

You can use the following example to switch back to 24-bit mode after referring to the 31-bit parameters.

*SWITCH TO 24 BIT ADDRESSING
MODE24   LA    15,*+6           GET TARGET ADDRESS
         BSM   0,15             ENTER 24 BIT MODE

This code is intended for use in RMODE 24. When used by RMODE 24 code, the AMODE can be either 24 or 31 before running either piece of switching code. The end result is the addressing mode indicated.

If ARCINEXT is link-edited in AMODE 31, then no change is needed.