A stacking PC routine can receive control in either primary mode or AR mode. The user program that issues the PC instruction can be in either primary mode or AR mode. When the user's program issues the PC instruction, the system saves the user's environment on the linkage stack. When the PC routine issues the PR instruction to return to the user, the system restores the user's environment from the stack before returning control. Thus, there is no need for the caller or the PC routine to either save or restore the environment. The system saves the caller's general registers (0 - 15), ARs (0 - 15), PASN, SASN, PKM, and PSW. If necessary, the PC routine can issue the extract stacked state instruction (ESTA) to examine the stacked entry.