On 12/1/2010 8:32 AM, Chris Craddock wrote:
PSW in a normal 8 byte PSW field when the instruction address is only 4 bytes. As you can probably imagine, there is literally no way to preserve compatibility with the near infinite number of programs that currently understand and inspect the task management control blocks, so while execution above the bar is a goal, it is a long way off yet.
There are indeed many programs that inspect the 8-byte PSW, but not that many that manipulate the address portion. And those that do typically do something "reasonable" with the address, such as a) replacing it altogether with another address or b) adjusting the address by 2, 4 or 6 bytes (or the ILC) to cause an instruction to be re-executed or skipped. z/OS can probably compare the 8-byte PSW at re-dispatch time against a copy saved at interrupt time and, if it has changed, guess right 99% of the time as to what should be done to the 16-byte PSW to effect the intended change(s) just by following just a few simple rules.
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