IMHO, asking for assistance would get better results then issuing a challenge. But it's not my dog.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> on behalf of Tony Thigpen <t...@vse2pdf.com> Sent: Friday, August 14, 2020 6:23 PM To: ASSEMBLER-LIST@LISTSERV.UGA.EDU Subject: Re: how to return? Let's see how good you are. I have been reading all the "that is not a good way to do it" posts, so here it the challenge to all those nay-sayers. It's time to 'put-up' or 'shut-up'. Under the following conditions, just how would you code it? Rules: 1) You are coding the entry and exit for a called subroutine. For this exercise, you will not be the main program called by a JCL EXEC card. 2) The way the caller is calling you can not be regulated. 3) The caller may be Assembler or Cobol. 4) Existing older code, that can not be changed, calls using a BALR. 5) Existing newer code calls using BASSM. And, it can not be changed. 6) It is known that some programs calling via BALR will call in 31bit. 7) It is know that some programs calling via BALR will call in 24bit. 8) Your code needs to perform some functions that require 31bit. 9) You must return to the caller is such a way that the callers mode prior to the call and after the call is the same. 10) 64bit support is not required. 11) You must be callable from both a non-LE environment and an LE environment. 12) LE support is not only not required, you just can't use it. 13) You must be LE-tolerant is. If you are called by LE you can't mess up the LE environment, but you don't have to exploit it. 14) And to make it even more challenging, the code *must* run in a older processor that does not support branch-retaliative nor BAKR/PR instructions. Yes, this code is from a real-live vendor product that is still being used by customers on machines that don't support those instructions. And, before you complain, this is *exactly* the requirements that the original coder was facing, and still faces with this code. The requirements of this challenge is that you show everybody on the list the code you would write for these requirements. Tony Thigpen Seymour J Metz wrote on 8/14/20 5:10 PM: > Simpler is safer. > > > -- > Shmuel (Seymour J.) Metz > http://mason.gmu.edu/~smetz3 > > > ________________________________________ > From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> on > behalf of Tony Thigpen <t...@vse2pdf.com> > Sent: Tuesday, August 11, 2020 1:57 PM > To: ASSEMBLER-LIST@LISTSERV.UGA.EDU > Subject: how to return? > > I came across the following code today. The program can either be called > by JCL or from either an HLL or assembler program. While I included some > extra code for clarity, the code I am asking for comments on is the code > that 'fixes' R14 so that a BSM can be used instead of a BR. I just > thought I would ask what others think about this method. > > XXXXXXXX CSECT > XXXXXXXX AMODE ANY > XXXXXXXX RMODE 24 SOME IBM CODE IN HERE MAY REQUIRE R24 > USING XXXXXXXX,R15 > B COPYRGHTEND > ...... > COPYRGHTEND DS 0D > STM R14,R12,12(R13) SAVE CALLERS REGISTERS > BCTR R14,0 BACKUP TO CALLING INST > BCTR R14,0 . > CLI 0(R14),X'0C' BASSM? > BE R14_OK > CLI 0(R14),X'0D' BSM? > BE R14_OK > L R14,12(,R13) GET ORG R14 > LA R14,0(,R14) CLEAR HI BIT/BYTE > BSM R14,0 ADD PROPER AMODE > ST R14,12(,R13) SET R14 FOR RETURN BY BSM > R14_OK DS 0H > DROP R15 > LA R1,SAVEAREA > ST R1,8(,R13) FORWARD POINTER > ST R13,4(,R1) BACKWARD POINTER > LR R13,R1 ESTABLISH PERM R13 AREA > L R1,4(,R13) GET BACK ORG R0 & R1 > LM R0,R1,20(R1) FROM ORG SAVEAREA > * > LA R8,0(,R15) ESTABLISH ADDRESSABILITY > LA R15,1 . > LA R10,4095(R15,R8) . > USING XXXXXXXX,R8,R10 . > > The return code is: > RETURNR15 DS 0H > L R1,4(,R13) GET CALLER SAVE AREA ADDRESS > ST R15,16(,R1) SAVE RETURN CODE > LM R14,R12,12(R13) RESTORE REGISTERS > BSM 0,R14 GO BACK > > Tony Thigpen >
