A z/OS callable stub to aid program development and test.

Business use of programs developed internally or by third parties or IBM may require load and execution during IPL or program load. The problem is the acquired storage address may change which which present difficulties in setting needed debug SLIP trap or trace such as capturing invalid storage alteration when the target keeps moving.

The idea is to set the SLIP trap or trace before IPL as done today. Instead using an unknown storage address and range signifier such as a storage alteration of address 0 for a length of 0. This will activate the requested SLIP during IPL with no effect or hits. During IPL or program load, the ailing program after obtaining the affected storage can then be temporarily modified to call a new IBM supplied SLIP stub module which when called will simply update the system control registers being used by SLIP with the needed address and range. I

IBM Support for z/OS software loaded during IPL may also provide temporary service APARs (as I once did) which call the new SLIP stub to capture an error in one program (JES3 in my case) which was being overlaid by a third party vendor.

The nice thing about the new callable SLIP stub is it is very small, simplistic and can be provided as a standalone option/APAR or integrated in any program running key zero and does not require a change or commitment of any existing z/OS service.