-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf
Of John McKown
Sent: Tuesday, June 25, 2013 8:16 AM
To: [email protected]
Subject: z/OS subroutine in assembler, used in both batch & CICS , making
re-entrant
IMO, this is a rather involved problem.
background:
This is in CICS/TS 4.1, z/OS 1.12. We have a few highly used assembler
subroutines which are statically linked into both CICS and batch COBOL
programs. These programs are very old (20+ years). They use an "in line"
save area, and so they are not RENT. We are having a problem with some other
program (nobody can figure out which one) in which that program sometimes
overlays a CICS application program. Some time thereafter, when this overlaid
program is invoked, it abends (surprise, suprise!). We are running
RENTPGM=PROTECT. However, none of our programs are linked as RENT and so they
are not protected. We use CA-Endevor to do all our compiles.
The Endevor person changed the Endevor setup to have the RENT parm in all
CICS/COBOL links. Unfortunately, this resulted in programs which use this
assembler subroutine abending ASRA (S0C4-4) when the subroutine tried to modify
its save area (in the CSECT). I don't know why the binder requires the RENT
parameter to mark a program object as RENT if all the input CSECTs are COBOL
which is compiled with the RENT compiler option. Maybe somebody could explain?
Nobody here really understands CA-Endevor.
Bottom line: I need to change the assembler program to be RENT. And it still
needs to be callable by both CICS and COBOL programs. And I cannot have a batch
version vs. a CICS version. So I really do need it to truly be RENT. So I have
some questions.
This has worked for me in the past:
DFHAFCD TYPE=LOCATE ADDRESS AFCB
LTR R15,R15 Are we BATCH?
BZ BATCH00 YES Do Batch
CLC 0(3,R15),=CL3'AFC' Is It CICS?
BE CICS00 Yes, Do CICS
BATCH00 DS 0H
Batch Stuff
CICS00 DS 0H
CICS Stuff
1) Can I use a BAKR instruction in CICS successfully. This would put the
caller's registers in the z/OS stack. Since the program runs on the QR TCB and
does not do any CICS work, there should not be any concern about a CICS task
switch causing the program stack to be modified.
2) Convert the assembler code to be LE compliant. I think that the LE prologue
is the same for both CICS and batch. I am familiar with writing LE enabled
assembler main routines.
3) Convert the assembler to COBOL. This would be a royal PITA to code and I am
concerned about the CPU impact. This is highly used code. And, apologies to Tom
Ross, the COBOL code generation seems to be designed to stress test the entire
instruction set.
4) What about not using a save area at all? It might be poor design, but what
about using the high full word of each register as a save area for the lower
full word? I don't think that CICS or COBOL uses the full 64 bit registers. I
think that the start up code could "save" each register with a RLLG Rn,Rn,32 to
rotate bits 32-64 into 0-31 before using bits 32-64 for other purposes. Then
"restore" the register(s) with the exact same instruction to rotate the bits in
0-31 back into bits 32-64. I _assume_ that bits 0-31 at entry are not important
and need not be saved/restored.
5) What about using the access registers as a save area? I could do a series of
SAR Rx,Rx at the front of the code and then EAR Rx,Rx instructions at the end.
I don't think that the Access Registers are used in CICS application code and I
doubt their values are assumed to be anything specific in CICS management
routines. I.e. they should be available without saving.
I have more or less ordered these in my "most to least" desirable order.
Oh, rewriting into C is not an option. We don't have a C compiler. Actually all
we have is HLASM and COBOL.
--
This is a test of the Emergency Broadcast System. If this had been an actual
emergency, do you really think we'd stick around to tell you?
Maranatha! <><
John McKown
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