I am exactly executing in AMODE 64. And so I need the high halves to be clear at all times.
Because I am using pure S/370 instructions. Previously I was hoping that z/OS would be changed to give a guarantee that the high halves were clear. Because the only alternative I could see was doing an LMH myself to clear them. It is only in the last week or something that I realized there was a S/370 instruction that would do the trick - LA. BFN. Paul. On Wed, 1 Feb 2023 22:46:24 -0500, Steve Smith <sasd...@gmail.com> wrote: >No. LA (and all LA variations) are modal, in that LA will not affect the >high-half of the register, unless executing in AMODE 64. > >Anyway, what's the point of clearing registers unless or until you need to >use them? > >sas > > >On Wed, Feb 1, 2023 at 8:02 PM Paul Edwards <mutazi...@gmail.com> wrote: > >> On Sun, 6 May 2018 18:34:35 -0500, Paul Edwards <mutazi...@gmail.com> >> wrote: >> >> Sorry for the necro ... >> >> >On Sun, 6 May 2018 16:11:57 -0700, Charles Mills <charl...@mcn.org> >> wrote: >> > >> >>2. A 31/32-bit program cannot count on the high >> >> halves being zero in any event. There is no >> >> guarantee that you are entered with the high >> >> halves equal to zero, >> > >> >The 32-bit program can clear all registers with >> >LMH if IBM can't guarantee high halves of 0. >> >It can do that once at startup and the rest of >> >the program doesn't need to change. >> >> I recently realized that I should be able to use "LA Rx,0" >> to clear the high 32-bits of undefined registers. (a separate >> LA for each register). >> >> This only uses S/370 instructions and future-proofs the >> code for if IBM produces a machine with 128-bit or 256-bit >> registers. >> >> I'm thinking undefined registers on program entry need to >> be cleared with LA, and whenever you call a z/OS service, >> any register documented as being trashed needs to be >> cleared (with LA) on return. >> >> I think that is sufficient? >> >> BFN. Paul. >> >> ---------------------------------------------------------------------- >> For IBM-MAIN subscribe / signoff / archive access instructions, >> send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >> > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
