You must begin each exit routine with the JES2 $ENTRY macro, which you use to name the routine and to identify it to JES2.

For more information, see “Packaging Exit Routines” later in this topic.

Note that you have flexibility in naming your exit routines, under standard labeling conventions except for Exit 0 (see the description of Exit 0 in IBM-defined exits for more detail).

The $ENTRY macro is also used to generate a USING statement for your exit routine. The BASE= operand is used to specify the register or registers which provide addressability when the exit routine gets control. However, the $ENTRY macro does not load the base register.

The construction of a source module must follow certain conventions depending on how you intend to package the exit routine. Through these conventions, JES2 is able to locate both exit routines and exit points within a module.

When deciding on whether to implement a specific exit routine, you should consider whether installing a security product with your other system software could satisfy your requirements. You should also consider the affect an exit routine could have in terms of your installation's security policy. Your security auditing may be inaccurate if you change security information in a control block in an exit that occurs after access to a resource has already been granted without additional validation. Similarly, changes made to security information by an exit that occurs before validation, could cause the validation to fail.

DBCS (Double-byte Character Set) is an option that may be invoked when doing assemblies. DBCS is a means of providing support for languages which contain too many symbols to be represented by a single byte character set such as EBCDIC. JES2 supports the High-Level Assembler DBCS option for JES2 exit routines. All JES2 macros integral in a customer's JES2 exit will abide by DBCS option rules, including the continuation line logic. JES2 macros will not have the same characters specified in both columns 71 and 72. This would be interpreted as a special DBCS continuation character. IBM® does not support the DBCS option for reassembly of its modules.