The format of the GENCB macro used to generate an exit list is:
[label] |
GENCB |
BLK=EXLST |
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The subparameters of the GENCB macro can be expressed as absolute numeric expressions, as character strings, as codes, as expressions that generate valid relocatable A-type address constants, in register notation, as S-type address constants, and as indirect S-type address constants. Subparameters with GENCB, MODCB, SHOWCB, and TESTCB, further defines these operand expressions.
See: z/OS DFSMS Using Data Sets for the factors that determine the addressing mode and the parameter list residency mode set when the exit routine gets control.
For more information about user exit routines, see z/OS DFSMS Using Data Sets.
L may precede or follow the A or N specification.
The LOC parameter is different from other GENCB parameters. If you code it on the list form, the execute form always overrides it. If you want LOC=ANY when using the list and execute forms, you must code it on the execute form. For more information, refer to GENCB—List form and GENCB—Execute form.
If you did not specify an area in which the exit list is to be generated, VSAM obtains virtual storage space for the area (as specified by the LOC=keyword). Subpool 0 will be requested under the user's key and state. Users executing in key 0 and supervisor state will actually be assigned subpool 252. VSAM returns the address of the area in which the exit lists is to be generated in register 1, and the length of the area in register 0. You can find the length of each exit list by dividing the length of the area by the number of copies. The address of each exit list can then be calculated by this offset from the address in register 1. You can find the length of an exit list with the SHOWCB macro, described under
SHOWCB—Display fields of an exit list.If you are generating control blocks by issuing several GENCBs, specifying an area (WAREA and LENGTH) for them allows you to address all of them with one base register and to avoid repetitive requests for virtual storage.