This appendage is a combination of two independent appendages. The complete appendage is a reenterable subroutine with two entry points, one for the SIO appendage and one for the PGFX appendage.

The SIO entry point is located at offset +0 in the SIO subroutine; from this entry point you might have an instruction to branch to any other location in the appendage. The entry point of the PGFX appendage is at offset +4 in the SIO subroutine. The address of offset +0, the SIO appendage entry address, is set in register 15 as the entry point of the PGFX appendage, allowing you to use the same entry linkage code for both entry points.

Note that you cannot fix pages that were allocated with CONTROL=UNAUTH on the IARV64 macro. Unauthorized programs cannot override this setting, but they can allocate 64-bit storage with the IARST64 macro.