Program call linkages
Db2 uses z/OS® program calls as one form of program invocation.
- PC-ss
- Permits an address
space switch
- PC-cp
- Retains an address space as
current primary
and does not cause a space switch
The z/OS architecture defines three addressable address spaces—primary, secondary and home. If a space switch occurs (because of the PC-ss instruction mentioned above), one address space is considered primary and another is considered secondary. If a space switch does not occur (because a PC-cp instruction is used), the primary and secondary address spaces are the same (that is, one address space is considered both primary and secondary).
The home address space is always present, and contains
the dispatchable unit of work before any program calls are issued.
If a space switch does not occur, then the home address space is also
both the primary and secondary address space. If a program call with
a space switch is issued by the dispatchable unit (using PC-ss), the
primary space becomes the secondary address space and the switched
to
address space becomes the primary address space. If the dispatchable
unit issues another PC with a space switch, the previous primary becomes
the secondary and the switched to
address space becomes the
new primary address space
Db2 uses PC-cp to get into supervisor state and key 7. Both PC-cp and PC-ss are used to enter 31-bit addressing mode (AMODE). In addition, PC-ss defines a new primary address space.
Each resource manager defines its PC linkage relationships using either (1) the RMVT and RMFT control blocks for RMRQ calls from one resource manager to another or (2) the RAL and FVL control blocks for RARQ calls to resource managers from an application.