We have just shipped the PTFs for APAR PH42050 which allows a dependent USING instruction to be resolved using a 20-bit signed displacement provided that the specified OPTABLE is one which supports instructions with that capability.
It was apparently intended that this support should have been included as part of the original 20-bit displacement support in around 2003, but it was not implemented at that time. We prototyped the support in 2013 but ended up setting it aside for further research, partly because of unexpected results in the Active Usings headings and Using Map. When we resumed this item recently, we found that the logic to handle the dependent USING base address and range in the Using Map and Active Usings headings incorrectly assumed that any dependent USING would be basing the start of a section, which meant that various fields were being incorrectly calculated. This has now been fixed. For details, see the IBM Support page for APAR PH42050 (which at the time of writing has yet to catch up with the fact that PTF UI78085 for HLASM on z/OS is also now closed and available): https://www.ibm.com/support/pages/apar/PH42050 Jonathan Scott, HLASM IBM Hursley, UK
