VTAM® supplies a fixed patch area as a separate module. You can insert short service programs in this area to do maintenance-related functions. ISTPATCH is loaded into LPALIB during initialization of the operating system and is pointed to by the ATCPTCHA field in the ATCVT. The initial size of the patch area is 64 bytes, but you can change the size by link-editing a module named ISTPATCH of the required size.

Code the necessary change in the patch area. (ISTPATCH follows the same coding rules as other modules in LPALIB.) Then replace part of the failing code with a branch to the patch area, allowing you to bypass the failing code.