And IIRC in ancient days the PL1 runtime used to use word 1 of the RSA for its own purposes. Don’t know if LE and Enterprise PL1 (or Enterprise COBOL for that matter) continued that tradition or not.
Peter -----Original Message----- From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> On Behalf Of Mark Hammack Sent: Tuesday, November 30, 2021 12:37 PM To: ASSEMBLER-LIST@LISTSERV.UGA.EDU Subject: Re: Base-less macros I think it is one of those "better safe than sorry" things. If a prior subroutine call used this RSA in 31 bit mode, then 4(13) should be an address so the low order bit shouldn't be on (in theory). I remember a programmer using the first word of the RSA as temp storage...until some other subroutine (not in our control) either used it for some other reason. Not as bad as using the first 8 bits of an address for flags, but still a headache to correct. *Mark* On Tue, Nov 30, 2021 at 10:53 AM Seymour J Metz <sme...@gmu.edu> wrote: > Do you really need to test all four bytes? A test for 'SA' should be > enough. > > -- > Shmuel (Seymour J.) Metz > https://urldefense.com/v3/__http://mason.gmu.edu/*smetz3__;fg!!Ebr-cpP > eAnfNniQ8HSAI-g_K5b7VKg!fJ-ZGLII6ou2tbp7J5r5YQxS_lMe78f778iGHf8Xyncavn > D8-EgiZR1MVewdjWfyRDQ-iA$ > > ________________________________________ > From: IBM Mainframe Assembler List [ASSEMBLER-LIST@LISTSERV.UGA.EDU] > on behalf of Mark Hammack [mark.hamm...@gmail.com] > Sent: Tuesday, November 30, 2021 10:53 AM > To: ASSEMBLER-LIST@LISTSERV.UGA.EDU > Subject: Re: Base-less macros > > 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 > > -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. 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