The REXX exits must follow standard linkage conventions. They must have attributes of AMODE(31) and RMODE(ANY). They must save the registers on entry and restore the registers when they return. They must not be APF-authorized. They must be reentrant and refreshable.

The exits can use any of the TSO/E service routines if they are integrated into TSO/E. In non-TSO/E address spaces, the exits cannot use the TSO/E service routines, such as PARSE, SCAN, GETLINE, and PUTLINE. For a description of the TSO/E service routines, see .

Any of the TSO/E REXX service routines, such as IRXIC, IRXSUBCM, and IRXEXCOM, are available in non-TSO/E and TSO/E address spaces. For a description of the REXX service routines, see .