Entry specifications

The contents of the registers on entry for the IRXINITX exit and the exec processing exit (the exit that is invoked by IRXEXEC) are:

Register 0: Same as on entry to the IRXINIT initialization routine (IRXINITX)
: Address of the current environment block (IRXEXEC exit)
Register 1: For the pre-environment initialization exit (IRXINITX), address of the parameter list passed to the IRXINIT routine
For the exec processing exit for IRXEXEC, address of the parameter list passed to the IRXEXEC routine
Registers 2–12: Unpredictable
Register 13: Address of a register save area
Register 14: Return address
Register 15: Exit entry point address

The contents of the registers on entry for the IRXITTS exit (integrated into TSO/E) and the IRXITMV exit (not integrated into TSO/E) are:

Register 0: Address of the new environment block
Registers 1–12: Unpredictable
Register 13: Address of a register save area
Register 14: Return address
Register 15: Exit entry point address

The contents of the registers on entry for the IRXTERMX exit are:

Register 0: Address of the terminating environment block
Registers 1–12: Unpredictable
Register 13: Address of a register save area
Register 14: Return address
Register 15: Exit entry point address

The contents of the registers on entry for the exec initialization exit, exec termination exit, and the attention handling exit are:

Register 0: Address of the current environment block
Registers 1–12: Unpredictable
Register 13: Address of a register save area
Register 14: Return address
Register 15: Exit entry point address

When an environment is initialized, the system creates the environment block (ENVBLOCK) that contains pointers to several other control blocks. Together, these control blocks define all the characteristics of the environment. The address of the environment block is passed in register 0 in all calls to REXX exits and routines, and in all calls to the REXX compiler runtime processor and compiler interface routines. Note that you can only read information from the environment block or the control blocks to which the environment block points. If you change the values, results are unpredictable. contains the format of the various control blocks.