Writing a callable service
An installation-defined callable service receives parameters from the application program when the program calls the service stub that is associated with the service. An installation-defined service can also access information in the secondary parameter block (SPB). The address of the SPB is passed in register 0. See Secondary parameter block for a description of the SPB.
- Supervisor state
- Key 0
- APF authorized
- TCB or SRB mode
- Cross memory mode
- AR mode
- AMODE(31) or AMODE(64)
- RMODE(ANY)
You must write the services in assembler, because you are in Access Register and cross memory mode, and the addresses of some of the parameters you may access are ALET-qualified. In particular, parameters passed into a callable service are in the user's address space, which you can access with an ALET of 1. See z/OS MVS Programming: Extended Addressability Guide for information about cross memory and AR mode.