If the editing functions of the binder are used to modify a program module, the entry point to the program module must be restated when the program module is reprocessed by the binder. Otherwise, the first byte of the first control section processed by the binder becomes the entry point. To enable restatement of the original entry point, or designation of a new entry point, the entry point must have been identified originally as an external symbol; that is, it must have appeared as an entry in the external symbol dictionary. The assembler automatically identifies external symbols if the entry point is the name of a control section or START statement; otherwise, you must use an assembler ENTRY statement to identify the entry point as an external symbol.

Further discussion of program module entry points is contained in the z/OS MVS Program Management: User's Guide and Reference.