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 <[email protected]> on behalf of
Tony Thigpen <[email protected]>
Sent: Tuesday, August 11, 2020 1:57 PM
To: [email protected]
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
