In our case, the caller doesn't "know" whether the called subroutine is base 31 or base 64. So it is up to the called subroutine to "figure out" whether the caller used a 72 byte save area or a 144 byte save area. Parameters to the macro set addressing mode, RSA size, etc. This allows for a 31 bit module to call a 64 bit subroutine and vice versa. That's what I really mean by "switches between". The one caveat is that the caller must provide a large enough area to allow for the 144 byte area.
Since some subroutines accept arguments in R0 and/or R1 (and unfortunately assume other registers are pre-loaded) those can't be touched before being saved. Likewise, if the routine is called from another 64 bit subroutine, the high halves of registers are (potentially) in use. However, since (currently) all of our programs run below the bar, using the high half of R14 may be an option. I need to look into using a FPR or AR but the 4 byte literal pool works for now. Storing R14 in 8(R13) is not a bad idea either. Thanks! *Mark* On Tue, Nov 30, 2021 at 8:37 AM Charles Mills <charl...@mcn.org> wrote: > Ah! I have not been clear on the convention. As I read it now, the called > program puts one of the FnSA strings in its *new* save area to indicate how > *it* previously stored the registers in its entry save area. > > So the OP's premise is incorrect. A program cannot learn the length or > format of the incoming save area by examining it (although an FnSA string > there would give you a clue of what the caller was up to in general). > > I am inferring that there is no way for a called program to determine > programmatically the length or expected format of the incoming save area. > It > must be agreed upon by the two programs, or phrasing it differently, the > called program's save area expectations must be documented and respected by > the caller. > > Am I right, or off (pardon the pun) base? > > Charles > > > -----Original Message----- > From: IBM Mainframe Assembler List [mailto:ASSEMBLER-LIST@LISTSERV.UGA.EDU > ] > On Behalf Of Peter Relson > Sent: Tuesday, November 30, 2021 5:39 AM > To: ASSEMBLER-LIST@LISTSERV.UGA.EDU > Subject: Re: Base-less macros > > Steve Smith wrote: > >And there are other bizarre ways to return without > >restoring R14, which is not actually required by documented conventions. > > Only restoring of AR14 and the high half of R14 are required (for > non-AMODE 64 cases), in general. > (Although I would guess that there are many violations of preserving the > high half of R14). > Some interfaces might define that they preserve R14 completely. Most do > not. > > Mark Hammack wrote > >I have a macro that switches between a regular (24/31 bit style) > >save area and an extended (64 bit "F4SA") save area. > > What do you mean by "switches between"? It is fine to use a different > style than the style your caller was using (as long as the savearea > provided is big enough to accommodate your needs), without having any care > about what was being used by your caller. The string at +4 identifies how > you saved your caller's registers. > > Peter Relson > z/OS Core Technology Design >
