Do we need BALR 12,0 for addressbility or just use USING will be ok?
i saw the code is written as
Code:
BALR 12,0
USING *,12
As i know USING is tell assambler which base register and address will be used in order to compute the object code and BALR is pass the address to register during the run time. I just confused since program should be loaded anywhere in memory , why need BALR to assgin the address to register ?
I try to write the simple code only few line and get abend 0C4 don't know why?
Sorry for the newbie question.
Code:
BALR 12,0
USING *,12
MOVE MVC NUM1,NUM2
NUM1 DC CL5'ABCDE'
NUM2 DC CL3'FGH'
NUM3 DC CL4'IJKL'
END
Joined: 30 Nov 2013 Posts: 917 Location: The Universe
The USING Assembler instruction is you (the programmer) promising the Assembler that you (the programmer) will insert an address into a register. For example -
Code:
MYPGM CSECT
SAVE (14,12),,*
BALR 12,0
USING *,12
AP NUM1,NUM2
RETURN (14,12),RC=0
NUM1 DC PL5'25000'
NUM2 DC PL3'12512'
END ,
In this program, you have already stored an address into a register. The Assembler generates -
Code:
Loc Object Code Addr1 Addr2 Stmt Source Statement
000000 00000 00028 1 MYPGM CSECT
2 SAVE (14,12),,*
000000 47F0 F00A 0000A 4+ B 10(0,15)
000004 05 5+ DC AL1(5)
000005 D4E8D7C7D4 6+ DC CL5'MYPGM'
00000A 90EC D00C 0000C 7+ STM 14,12,12(13)
00000E 05C0 8 BALR 12,0
R:C 00010 9 USING *,12
000010 FA42 C010 C015 00020 00025 10 AP NUM1,NUM2
11 RETURN (14,12),RC=0
000016 98EC D00C 0000C 13+ LM 14,12,12(13)
00001A 41F0 0000 00000 14+ LA 15,0(0,0)
00001E 07FE 15+ BR 14
000020 000025000C 16 NUM1 DC PL5'25000'
000025 12512C 17 NUM2 DC PL3'12512'
18 END ,
The USING statement is a convenience for you, the programmer. Without the USING statement and other Assembler aids, you would write -
Code:
MYPGM CSECT
DC X'FA42F00AF00F'
DC X'1BFF'
DC X'07FE'
DC X'000025000C'
DC X'12512C'
END ,
rather than -
Code:
MYPGM CSECT
AP NUM1-MYPGM(5,15),NUM2-MYPGM(3,15)
SR 15,15
BR 14
NUM1 DC PL5'25000'
NUM2 DC PL3'12512'
END ,
or
Code:
MYPGM CSECT
USING *,15
AP NUM1,NUM2
SR 15,15
BR 14
NUM1 DC PL5'25000'
NUM2 DC PL3'12512'
END ,
Which one would you rather write? I spent 7 years of my life writing the equivalent of the first example as AMASPZAP control statements, but it was no joy - and error prone!
Thank you for your answer. For USING instruction i think i can undersatnd what 's it or why need it . But my question is that i don't know do we really need BALR 12,0 together with USING *,12 ?
If r12 contains the address of your program when called then no - but that is normally not the case. It is good practice to set up a base register yourself at the start of the program. R15 should contain the address of your program, but r15 is changed by some macros and program calls, so is not normally considered safe to use. Hence the use of r12.
Joined: 30 Nov 2013 Posts: 917 Location: The Universe
For the USING to be useful, the address has to be placed into the register.
Code:
MYPGM CSECT
USING WORKAREA,11
USING *,12
SAVE (14,12)
LR 12,15
GETMAIN R,LV=WASIZE
LR 11,1
...
USING RECORD,10
GET ADCB
LR 10,1
...
WORKAREA DSECT
...
ADCB DCB DSORG=PS,MACRF=GL,...
WASIZE EQU *-WORKAREA
...
RECORD DSECT
...
In this arrangement, which is fairly typical, there are 3 USING statements to cover 3 different storage areas.
Register 12 defines addressability for the program area. The address started in register 15, and was copied to register 12. This follows the convention that when a program is called, it's address is stored in register 15 and the transfer to the program is achieved by BALR 14,15. It could just as well be BALR 12,0/USING *,12, where BALR stores the address in the register.
Register 11 defines addressability for a work area that is defined by the WORKAREA DSECT. The address is obtained by the GETMAIN macro, and copied to register 11.
Register 10 defines addressability to a data record. The GET macro stores the record address in register 1, and the program copies the address to register 10.
Many of my larger programs are constructed like this -
Code:
MYPGM CSECT
USING WORKAREA,11
USING *,12
SAVE (14,12)
LR 12,15
BAL 11,*+L'*+4
DC AL4(WORKAREA)
L 11,0(,11)
...
USING RECORD,10
GET ADCB
LR 10,1
...
WORKAREA CSECT
...
ADCB DCB DSORG=PS,MACRF=GL,...
...
RECORD DSECT
...
This separates the program text from the work area text. In -
Code:
BAL 11,*+L'*+4
DC AL4(WORKAREA)
L 11,0(,11)
The BAL machine instruction stores the address of the work area address in register 11.
The DC Assembler instruction specifies the address of the work area.
The L machine instruction loads the address of the work area.
Joined: 14 Jan 2008 Posts: 2501 Location: Atlanta, Georgia, USA
A heads up -
For Assembler sub-programs (not MAIN), which require addressability (or, maybe not) to the HLL/LE compliant Caller's "CEECAA" (Common Anchor Area), don't use R12 because the CAA is always based off the Caller's R12. Just leave R12 free just in case and pick another register (IE: R3).
Joined: 30 Nov 2013 Posts: 917 Location: The Universe
Mr. O'Boyle's comments are for programs that are expected to run in an LE non XPLINK environment, which doesn't apply to standalone Assembler programs. LE non XPLINK compliant programs are a whole different topic, as is true of LE XPLINK compliant programs.
BLAR 12,0 will copy the insturction address counter into Register 12 which will be the next instruction address that CPU will be exceute . R15 by standard rule is the entry point for the program .
Code:
BLAR 12,0
USING *,12
will be the same as
Code:
L R12,R15
USING *, R12
?? The address in base register R12 will be the same address in above two code ?
Nope.
L 12,15 will attempt to load r12 with contents of storage address x'15'. in older machines that itself would generate an error as 'x15' if not properly aligned. The correct instruction here is:
LR 12,15 which will copy the contents of r15 to r12.
But then you must have your using specify the start of the program. Your USINGs will make the basereg cover from position 2 and 4 respectively in your samples, and r15 points to position 0. I say position 2 and 4 respectively because 'balr' is 2 bytes and 'l' is 4 bytes in length.
So something like this:
MYPROG CSECT
LR 12,15
USING MYPROG,12
But it seems to me that you really need an assembler course, as we haven't even mentioned other necessary stuff like linkage conventions.
Joined: 30 Nov 2013 Posts: 917 Location: The Universe
No, I don't think you have learned anything.
In
Code:
MYPGM CSECT
USING *,12
SAVE (14,12)
LR 12,15
Register 12 has the address of MYPGM because that's what was in register 15.
In
Code:
MYPGM CSECT
SAVE (14,12)
BALR 12,0
USING *,12
Register 12 will have an address greater than the address of MYPGM. How much greater depends on the number of instructions in the SAVE macro, plus 2 more bytes for the BALR instruction. In both these examples, the incoming registers have been saved before the LR or BALR instruction altered register 12.
