REXX External Assembler API › Execution Interfaces › External Procedure and Function Handlers

External Procedure and Function Handlers

These programs are executed when a REXX CALL statement or function call refers to a procedure or function name that is not built in and is registered as an external user program.

The routines are called as documented in the TSO/E REXX Reference:

• R0 on entry points to the environment block.
• R1 on entry points to a parameter list.
• R13 (save area address), R14 (return address), and R15 (entry point address) are standard.
• AMODE is 31 (31-bit addressing).

The parameter list has six fullwords with the top bit set in the last word. The list contains the following parameters:

• Reserved
• Reserved
• Reserved
• Reserved
• Address of the input parameter list—An array of 8-byte entries, each consisting of the address and length of a parameter. The list is terminated by 8 bytes of X’FF’.
• Address of a fullword that points to the evaluation block—This block is used to return the value of a function call.

  Note: If IRXRLT is called, this address can become invalid.