The CEEBXITA assembler user exit is invoked before enclave initialization is performed. You can use CEEBXITA to help establish your application runtime environment. For example, in the assembler user exit you can specify the stack and heap runtime options and allocate data sets. You can also use the user exit to interrogate program parameters supplied in the JCL and change them if you want. In addition, you can specify runtime options in the user exit by using the CEEAUE_A_OPTIONS field of the assembler interface.

z/OS® considerations: Under z/OS, CEEBXITA returns control to Language Environment initialization.