Procedures for establishing addressability to an address space

To establish the environment in which a program can add an access list entry for an address space and access data through private entries, programs in the accessing address space and the target address space must:

Place the entry in an access list
Obtain the ALET for the entry
Issue a stacking PC; programs must define the stacking PC through the ETDEF macro, and use the EAX parameter on ETDEF to specify the appropriate EAX value.
Issuing the stacking PC means that you must establish some of the same linkages that are described in Synchronous cross memory communication and have a program in the target address space help in establishing those linkages.

Remember that the EAX-authority to an address space is the same as the SSAR authority. In other words, authority for an address space to issue the SSAR instruction for the target address space is the same as the authority to add an entry for an address space to an access list or access data in that address space through ARs. The same ATSET macro that sets the PT and SSAR authority in the target address space's authority table also sets authority table bits that correspond to the EAX.

As you read the following procedures for a program in the accessing address space and a program in the target address space, keep three facts in mind:

A problem state program with PSW key 8 - F must be EAX-authorized to the target address space before it can issue the ALESERV ADD or ALESERV DELETE macros for that address space. A supervisor state or PSW key 0 - 7 program might require EAX-authorization.
The target address space must give explicit permission to the accessing program.
The only way for a program in the accessing address space to get a nonzero EAX is to issue a stacking PC instruction, which establishes the appropriate EAX.