On Tue, 15 May 2018 11:57:55 -0500, Tom Marchant <m42tom-ibmm...@yahoo.com> wrote:
>>There are multiple ways of guaranteeing 0. The >>best is IBM guaranteeing it on entry to a program, >>as another RFE. In the single test that I requested, >>the high bits seem to be 0 already. I just want to >>formalize that. > >IBM cannot guarantee that. A basic principle in MVS is that any program >can be called by another program. You don't know how a program that >calls you might use the 64-bit registers. I don't see anything wrong with "LINK" being updated to save the high 32-bits (or more, in future) of registers and then zeroing them so that called 32-bit programs can run in AM64 or AM128 or AM256. Who will be affected? "LINK" can be updated to accept an AM64 caller at the same time. BTW, in another message I forgot to mention that to detect AM64, the "LA" instruction should be used so that it still works on S/370. That's for the solution where the 32-bit program needs a stub at entry to clear the high 32 bits itself with LMH so the rest of it can run AM64 without issue and without program change. The LMH would be bypassed if non-AM64 is detected. BFN. Paul. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
