On Sun, 6 May 2018 16:11:57 -0700, Charles Mills <[email protected]> wrote:
> The effort would be on the part of "service" writers -- primarily IBM > developers. Sure. >This is a new sort of-AMODE. Storage that you can > reference but cannot pass to the unwary, cannot > use with standard MVS VL=1 linkage, cannot branch to, ... The same consideration of not being able to use VL applies if you write an AM64 64-bit program too. Updating a 32-bit program to not use VL is a lot easier than converting the entire program to 64-bit AND not using VL. >> So long as the top 32 bits of 64-bit registers remain as zero (a 32-bit >> program is never going to change that), AM64 is just as good as an AM32 > >Au contraire. > >1. A 31/32 bit program can do 64-bit arithmetic. I consider that to be a 64-bit program. A 32-bit program is one that only uses 32-bit registers. I have no opinion about 64-bit programs. You can run them in AM31 as today. I am only interested in 32-bit programs. > As a writer of mixed mode programs, I can tell > you this is a real gotcha. In an AMODE 31 > program you can use some register for 64 bit > arithmetic, and a little while later load a 31-bit > address into it and use it as a pointer -- and > that all works. In AMODE 64, suddenly those > 64-bit high order leftovers byte you in the butt. Sure. >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. > and no guarantee they stay that way -- they > theoretically should, but there are no guarantees, > if you call some service. A theoretical faulty service can trash the low 32-bits just as easily as the high 32-bits. 64-bit programs rely on non-faulty services. So too 32-bit programs running in AM64 rely on it. There's no difference. >I'm not going to be as blunt as @Tony but IMHO > there is so little chance of this happening that I > think this discussion is moot. Lord knows I have > been wrong before. I'm wondering if there's a better way to word my RFE to avoid the apparent confusion. BFN. Paul. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
