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Transcript of Assembler Book
IBM 370 ASSEMBLY LANGUAGE 1 / 119
IBM 370 ASSEMBLY
LANGUAGE
BASIC COURSE
IBM 370 ASSEMBLY LANGUAGE 2 / 119
CONTENTS
1. Introduction 2. Basic Concepts 3. Instructions 4. Symbols, literals, expressions, Constants and data areas,
location counter 5. Integer operations 6. Decimal operations 7. Floating point operations 8. Data transfer and Logical operations 9. Bit manipulations 10. Branching 11. Assembler Directives 12. JCL aspects 13. Subroutines, linkage 24 bit mode 14. Macros and conditional assembly 15. MVS system Macros 16. VSAM Macros 17. Linkage Conventions, 24 & 31 bit addressing, mixed mode
addressing issues References
1. High level assembler for MVS & VM & VSE, Programmers Guide MVS & VM edition 2. High level assembler for MVS & VM & VSE, Language Reference MVS & VM edition 3. MVS Programming Assembler Services guide
4. MVS Programming Assembler Services reference
5. MVS assembly language by McQuillen and Prince
6. Assembly language programming for the IBM370 and compatible computers by
Michael D. Kudlick.
IBM 370 ASSEMBLY LANGUAGE 3 / 119
INTRODUCTION back What is Assembly Language
Lowest-level of programming on a system
Symbolic forms of representing machine language instructions
Usually represents a single machine instruction
Machine dependent
More Difficult to use than a high-level language Advantages over high-level language
Very efficient and tight code can be developed Disadvantages
Applications development time is more
Applications are machine dependent
Difficult to learn and understand Advantages over machine language
Use of mnemonic operation codes helps remembering the instructions
Symbols can be used
Macros can be used to generate repeated codes
Conditional assembly enables tailoring the code generated
IBM 370 ASSEMBLY LANGUAGE 4 / 119
BASIC CONCEPTS back
IBM-370 MACHINE ARCHITECTURE
Main storage Addressed by 24 bits or 31 bits
One single address space contains code and data
Byte is the least addressable unit
Instruction execution is faster if data is aligned on a full word boundary
Instruction categories
Fixed point Arithmetic,
Decimal Arithmetic,
Floating point Arithmetic,
Logical Operations,
Branching,
Status Switching,
Input Output
Programmer accessible Hardware Registers are
Program Status Word (PSW) 64 bits wide
General Purpose Registers (GPRs)
Floating Point Registers (FPRs)
Control Registers (CRs) 0-15 each 32 bits wide
Access Registers (AR'S) 0-15
PSW
64 bits in length
Contains the Condition Code (two bits)
Address of the next instruction to be executed.
PSW Key field
GPR'S
numbered 0-15 and 32 bits wide
Used as accumulators in Fixed point arithmetic
Used as base and index registers in computing the effective address
Two consecutive registers can be used to hold 64bit operands addressed by even register
AR'S
Numbered 0-15 each 32 bits wide
Used to point to address / data space
FPR
Used for floating point operations
Numbered 0,2,4,6 each 64 bits wide
64 bits in length
Can contain short or long operand
Two adjacent registers can be used as 128 bit register for extended precision
CR'S
Control registers each of 32 bits are available
Used by the IBM control program
Instructions to access / modify them are privileged and can be issued only by the OS.
INPUT/OUTPUT
Data processing and I/O processing are concurrent
Consists of Channel subsystem, Control Unit and I/O unit
IBM 370 ASSEMBLY LANGUAGE 5 / 119
ASSEMBLY STATEMENT FORMAT
1 10 16 72
Fixed Format. Can be changed only through ICTL Assembler Directive
Blank lines are invalid
Fields in a statement are separated by one or more blanks
Name / label field if present must start in column 1 and maximum 8 characters in length
To continue a statement to next line, type a non blank character in column 72 and continue the next line from column 16
Comment lines start with character ('*') on column 1
NAME FIELD OPERATION FIELD OPERAND FIELD REMARK
S
* SEQUENCE
IBM 370 ASSEMBLY LANGUAGE 6 / 119
INSTRUCTIONS back
TYPES OF INSTRUCTIONS
machine instructions
Assembler instructions (directives)
Macro instructions
Example : PRINT NOGEN TEST1 CSECT Assembler Directive STM 14,12,12(13) Machine instruction
BALR 12,0 Machine instruction USING *,12 Assembler Directive ST 13,SAVE+4 Machine instruction LA 13,SAVE Machine instruction MVC DATA1,DATA2 Machine Instruction
PUTMSG WTO 'message' Macro instruction L 13,SAVE+4 Machine instruction LM 14,12,12(13) Machine instruction SR 15,15 Machine instruction BR 14 Machine Instruction DATA1 DS CL100 Data Definition DATA2 DS CL100 Data Definition SAVE DS 18F Data Definition END Assembler Directive
INSTRUCTIONS FUNDAMENTALS
Two, four, or six bytes in length
Should begin on a half-word boundary
First byte normally contains the operation code. In some instructions it is two bytes.
Operation code specifies the function of the instruction
Operand designation follows the operation code
Operands
Entities that are involved in operations defined by operation code
Operands can be either implicit or explicit
Four types of operands
Register operand
Example AR 3,2
immediate operand
Example MVI DATA,X'F1'
Storage operand
Example L 3,FIELD1
Implied operand,
Example LM 14,12,SAVE
REGISTER OPERAND
Identified by R field in the instruction
Specifies either GPR or FPR
Operand access is faster
Example AR 1,2
IMMEDIATE OPERAND
Contained with in the instruction itself
IBM 370 ASSEMBLY LANGUAGE 7 / 119
Eight bit value
Self defining term or an absolute symbol can be used
Example : MVI DATA,B'10000000'
STORAGE OPERAND
Resides in memory
Address is not specified explicitly
Base and 12 bit offset with (in some instructions) index register is used
Program can be relocated
If Register 0 is used as a base or index register its contents are ignored
12 bit displacement
BALR instruction is used to load base register
If symbols are used assembler resolves it to base displacement form
Effective address = (base register) + (Index Register) + 12 bit displacement (note that some instruction formats do not support index register)
base register should be made to contain the base address at run time
Size of storage operand is implied by the instruction for some instructions
For some instructions Length field(s) is/are embedded in the instruction
Storage operands can be specified in implicit form as a re-locatable expression
Example L 3,DATA L 3,DATA+4
Storage operands can be specified in the Explicit form
Example L 3,4(1,2) Explicit addresses are of the form D2(X2,B2)
or D2(B2) or D2(L2,B2) or D1(L1,B1) or D1(B1)
Absolute addresses are also assembled in base displacement form. However the value in the base register will not change on relocation
Implicit addresses are those where a single re-locatable or absolute expression is specified
Example L 4,DATA L 3,DATA+4 LA 2,1000 . . DATA DS F
IMPLIED OPERAND The instruction implies the operand
Example TRT D1(L,B1),D2(B2) Registers 0,1 participate in this operation
IBM 370 ASSEMBLY LANGUAGE 8 / 119
INSTRUCTIONS CLASSIFICATION
RR FORMAT
0 8 12 15
RRE FORMAT
0 16 24 28 31
RX FORMAT
0 8 12 16 20 31
RS FORMAT
0 8 12 16 20 31
SI FORMAT
0 8 16 20 31
S FORMAT
0 16 20 31
SS FORMATS
0 8 12 16 20 32 36 47
0 8 16 20 32 36 47
EXAMPLES :
RR type instruction AR 2,3 reg 2 <== reg 2 + reg 3
RS type instruction BXH 1,3,D2(B2) reg 1 <== reg 1 + reg 3 If reg1>reg3 then branch
RX type instruction L 1,D2(X2,B2) reg 1 < == memory referenced by (D2 +X2 +B2)
FIRST HALF WORD SECOND HALF WORD THIRD HALF WORD
OP CODE R1 R2
OP CODE R1 R2
OP CODE R1 X2 B2 D2
OP CODE R1 R3 B2 D2
OP CODE I 2 B1 DI
OP CODE B2 D2
OP CODE L1 L2/I3 B1 D1 B2 D2
OP CODE L B1 D1 B2 D2
IBM 370 ASSEMBLY LANGUAGE 9 / 119
S type instruction LPSW D2(B2)
SI type instruction NI D1(B1),I2
Storage type instruction MVC D1(L,B1),D2(B2) PACK D1(L1,B1),D2(L2,B2)
IBM 370 ASSEMBLY LANGUAGE 10 / 119
SYMBOLS, LITERALS, CONSTANTS, DATA AREAS, LOCATION COUNTER back
SYMBOLS
A sequence of one to eight characters as specified below under ORDINARY,VARIABLE,SEQUENCE symbols
Absolute value assigned to a symbol by using 'EQU' assembler instruction with an absolute value operand
A re-locatable value is assigned to a symbol by using it in the name field of a machine instruction
Symbols can be used in operand fields to represent registers, displacements, lengths, immediate data, addresses etc.
Example : LABEL001 MVC S1,S2
BR QUIT QUIT BR 14 S1 DS CL100 S2 DC CL100'THE QUICK BROWN FOX' COUNT EQU 10
Ordinary Symbols
Optional
used in the name and operand field of machine/assembler instructions
Up to eight Alphanumeric characters A-Z,$,#,&,0-9
First character must be alphabetic A-Z
Rest can be alphanumeric
Example ABCD0001
Variable Symbols
First character must be an ampersand
second character must be alphabetic
Up to six alphanumeric characters
Example &ABC0001
Sequence Symbols
First Character must be a period
Next Character must be alphabetic
Up to six alphanumeric characters
Example .ABC0001
Advantages of symbols
Easier to remember and use
Meaningful symbol names instead of values
For address the assembler calculates the displacement
Change the value at one place (through an EQU) instead of several instructions
Printed in the cross-reference table by the assembler
Symbol Length attribute TO DS CL80 L'TO = 80 FROM DS CL240 L'FROM = 240 ADCON DC A(OTHER) L'ADCON = 4 CHAR DC C'YUKON' L'CHAR = 5 DUPL DC 3F'200' L'DUPL = 4
IBM 370 ASSEMBLY LANGUAGE 11 / 119
Self Defining terms
Can be used to designate registers, masks, and displacements within the operand entry
Decimal self-defining term
An unsigned decimal integer
maximum number of digits 10
Maximum value 2**31-1
Hexadecimal self-defining
A Hexadecimal integer within apostrophes and preceded by a X
Maximum number of digits 8
Maximum value 2**31-1
Character self-defining term
A character string within apostrophes and preceded by a C
Maximum number of characters 256
EXAMPLES: 15 UPTO 2,147,483,647 241 B'1101' UPTO 32 BITS X'F' UPTO 8 HEX DIGITS X'F1F2' C'ABCD' UPTO 4 CHARACTERS C'&&' TWO AMPERSANDS TO REPRESENT ONE C'''''' TWO APOSTROPHES TO REPRESENT ONE Literals
L 1,=F'200' L 2,=A(SUBRTN) MVC MESSAGE(16),=C'THIS IS AN ERROR' L 3,=F'33' BOTH ARE SAME L 3,FIELD BOTH ARE SAME FIELD DC F'33'
MVC FLAG,=X'00' SAME EFFECT MVI FLAG,X'00' SAME EFFECT MVI FLAG,ZERO SAME EFFECT . . ZERO EQU X'00' FLAG DS C LA 4,LOCORE SAME EFFECT LA 4,1000 SAME EFFECT . LOCORE EQU 1000 Absolute expressions An expression is absolute if it's value is unchanged by program relocation FIRST CSECT A DC F'2' B DC F'3' C DC F'4' ABSA EQU 100 ABSB EQU X'FF'
IBM 370 ASSEMBLY LANGUAGE 12 / 119
ABSC EQU B-A ABSD EQU *-A All these are absolute expressions:- ABSA 15 L'A ABSA+ABSC-ABSC*15 B-A ABSA+15-B+C-ABSD/(C-A+ABSA) Relocatable expressions A relocatable expression is one whose value changes with program relocation. FIRST CSECT A DC H'2' B DC H'3' C DC H'4' ABSA EQU 10 ABSB EQU *-A ABSC EQU 10*(B-A) The following are relocatable expressions:- A A+ABSA+10 B-A+C-10*ABSA Location Counter
Location counter is incremented after instruction or constant is assembled to the next available location
Assembler checks boundary alignment and adjusts location counter if reqd.
While assembling the current line the location counter value does not change Location counter Source Statements 000004 DONE DC CL3'SOB' 000007 BEFORE EQU * 000008 DURING DC F'200' 00000C AFTER EQU * 000010 NEXT DS D 000018 AFTNEXT EQU * 000018 NEXT1 DS D 000020 NEXT2 DS D 000028 ORG *+8 000030 NEXT3 DS D
Example : LOOP EQU *
B *+80 . . . B LOOP
IBM 370 ASSEMBLY LANGUAGE 13 / 119
ATTRIBUTES OF SYMBOLS :
Length attribute
Referred to as L'symbol
For a symbol defined by "DC' or 'DS', it is the implicit or explicit length.
For a symbol referring to a machine instruction, it is the length of the instruction.
For a 'EQU' symbol, it is the length of the left most term or supplied by the second operand
Example : length A DS F 4 DS 20FL4 4 DS XL3 3
AR 1,2 2 AA EQU A+4 4 S1 EQU 102 1 S2 EQU X'FF +A' 1 S3 EQU C'YUK' 1 BUF EQU A,256 256 BUF2 EQU *+10 1 BUF3 EQU *,80 80
Type attribute
Referred to as 'T' symbol
Gives the one character type code of the symbol A,Y,V,S For the related Address Constants B,C,D,E,F,H,Z,P For the related data constants I For machine instruction M For a Macro instruction J For a control section name T For a EXTRN symbol $ For a WXTRN symbol N For a self defining term O Null string
CONSTANTS AND DATA AREAS
Run Time Constants DC directive Literals Self defining terms
Assembly time constants EQU statement
Constants can be absolute/re-locatable A re-locatable constant has a unbalanced re-locatable term
DC instruction
To reserve storage and initialise it with values
Location counter advanced by the number of bytes associated with the specified type
Not true constants, the values can be changed in the program
Similar to specifying initial values in variable declarations of a high level language
DC
SYNTAX
DUPLICATING FACTOR TYPE LENGTH MODIFIER CONSTANT
IBM 370 ASSEMBLY LANGUAGE 14 / 119
{NAME} DC {DUP}TYPE{MOD}{V1,V2,...VN}
Run time constant
TYPE BYTES ALLOC DC F'100,-10,200' 12 DC F'123' 4 DC F'-123' 4 DC 3F'23' 12 DC H'20' 2 DC H'123,23,-34' 6 DC B'11000001' 1 DC X'FFFFFFFF' 4 DC X'FF01FF01' 4 DC C'ABCDEF' 6 DC C'abcdefg''A&&SS@#..' 16 , note double & and ' DC P'-1234' 3 DC P'1234' 3 DC P'-34' 2 DC Z'1234' 4 DC E'-3.25E10' 4 DC E'+.234E-10' 4 DC E'-2.3E15' 4 DC A(LOOP1) 4 DC V(LOOP1) 4 DC S(FIELD2) 2 DC C'USER01' 6
DC F'100,200' Two full words with value 100,200 DC CL3'JAN,FEB' Months contain 3 bytes value "JAN'
DC 3H'2,4,8,16' 12 half words with the given value DC B'10001000' 1
DC C'SAMPLE STRING' 13 DC P'123' 2
DC ZL10'123' 10 DC PL4'123' 4 DC E'1.25' 4 DC D'2.57E65' 8 DC AL3(THERE) 3 DC V(EXTSYM) 4
DEFINE STORAGE (DS)
To reserve storage
Storage is not initialised
Location counter advanced by bytes allocated
DS
SYNTAX
{NAME} DS {DUP}TYPE{MOD}
EXAMPLES DS F Bytes allocated 4
DS 10F 40 DS H 2
DS 2CL3 6 A DS 80C 80 L'A=1 DS CL80 80 L'A=80
DUPLICATING FACTOR TYPE LENGTH MODIFIER
IBM 370 ASSEMBLY LANGUAGE 15 / 119
DS 4D 32 DS 0F 0 used to force a word Boundary DS 0D 0 used to force a double word boundary DS 0CL8 0 length attribute is 8 DS 100H 200
A self defining term is an absolute constant that can be written as a
A binary integer B'1001'
A decimal integer 3
A hexadecimal integer X'4A'
A sequence of text characters C'ABCD'
These can be used as immediate operands in any instruction which needs an immediate operand.
Example CLI 0(8),C'Z'
A literal is a symbolic representation of a constant to which the assembler assigns an address FCON DC F'1' L 5,FCON L 5,=F'1' LOAD L 2,=F'-4'
MOVE MVC MSG,=C***Error ***' The first two statements are exactly equivalent to the third.
A convenient means of introducing constants without the use of 'DC' instruction
Storage is allocated for literals at the end of the first CSECT (Literal Pool). To avoid addressing problems, use a LTORG at end of each CSECT
Storage allocation can be forced at any point by 'LTORG" assembler instruction
Two literals are the same if their specifications are identical
Assembler translates a literal into a base register and a displacement
A equivalence constant allows a programmer to define a value for a symbol and use it wherever there is a need to employ that value.
R1 EQU 1 HERE EQU * OFF EQU X'00' ON EQU X'FF' Y DC F'4' Z EQU 4 W EQU Y W is equivalent to Y
CLI STATUS,ON BE POWERON CLI STATUS,OFF BE POWEROFF
Data Alignment
Instructions have to be aligned on half-word boundary
Data can be specified to be aligned to Double word D (Divisible by 8) Full-word F (Divisible by 4) Half-word H (Divisible by 2)
Location counter skipped as per alignment requirement
Example : 000100 DC C'ABC'
IBM 370 ASSEMBLY LANGUAGE 16 / 119
000103 skipped 000104 DC F'4' 000108 DC C'A' 000109 skipped 000110 skipped 000111 skipped 000112 DC F'560'
IF ASSEMBLER OPTION ALIGN IS SPECIFIED
Assembler checks storage addresses (labels) to ensure that they are aligned on boundaries required by the instruction.
Data areas are aligned on boundaries implicit with their type if no length modifier is present LOCTN COUNTER PROGRAM 000010 DATA DC C'ABC' 000014 DS F ASSM. AT WORD BDRY
IF NOALIGN IS SPECIFIED
Constants and data areas are not automatically aligned
Assembler does not check storage addresses for boundary alignment. LOCTN COUNTER PROGRAM 000010 DATA DC C'ABC' 000013 DS F ASSM. AT NEXT LOC
Example FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO 'ASM1 REPORTING'
L 3,=F'200'
LA 3,ABSB
MVC DATA1(6),=C'ABCDEF'
MVC DATA1,=CL20'ABCDEF'
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
DC A(SAVE1)
A DC H'2'
B DC H'3'
C DC H'4'
ABSA EQU 10
ABSB EQU *-A
DC F'100'
DC F'-100'
DC H'100'
DC 3H'100'
DC C'ABCEFGH'
DC CL20'ABCDEFGH'
DC 10C'AB'
DC P'123'
DC P'-123'
IBM 370 ASSEMBLY LANGUAGE 17 / 119
DC PL5'-123'
DC 3PL5'-123'
DATA1 DS CL20
END
IBM 370 ASSEMBLY LANGUAGE 18 / 119
INTEGER OPERATIONS back
FIXED POINT ARITHMETIC ADD AR,A,AH,ALR,AL SUBTRACT SR,S,SH,SLR,SL MULTIPLY MR,M,MH DIVIDE DR,D ARITHMETIC COMPARE CR,C,CH LOAD LR,L,LH,LTR,LCR,LPR STORE ST,STH,STM ARITHMETIC SHIFT SLA,SRA,SLDA,SRDA CONVERT TO BINARY CVB CONVERT TO DECIMAL CVD Constants used Type Fixed Point H and F Binary B Hexadecimal X Character C Decimal P Address Y,A,S,V,Q
IBM 370 ASSEMBLY LANGUAGE 19 / 119
INTEGER ARITHMETIC
GPR's are 32 bits with bit 0 as a sign bit
Negative numbers stored as two's complement
Both Full word and Half Word instructions are supported
GPR/GPR and GPR/Memory instructions available
Half words converted to full word by extending sign bit to the left Two's Complement Decimal Binary Decimal Binary 0 0000 0 0000 +1 0001 -1 1111 +2 0010 -2 1110 +3 0011 -3 1101 +4 0100 -4 1100 +5 0101 -5 1011 +6 0110 -6 1010 +7 0111 -7 1001 Addition and Subtraction +6 0110 -6 1010 +5 0101 -5 1011 +(+1) 0001 +(-1) 1111 +(+6) 0110 +(-6) 1010 ------ ------ ------ ------ 0111 1001 1011 0100 00 11 01 10 No overflow No overflow Overflow Overflow If the carry into the sign bit is different from the carry out of it, there is an overflow condition. L Copy full word from memory to GPR RX R1,D2(X2,B2) L 3,A GPR3 Memory Field A Before 0246 0357 000A 00B0 After 000A 00B0 000A 00B0 ST Copy a full word from GPR to memory RX R1,D2(X2,B2) ST 3,A GPR3 Memory field A Before 0123 0456 0ABC 0DEF 0123 0456 0123 0456 LH Copies a half word from memory to GPR RX R1,D2(X2,B2) LH 3,A GPR3 Memory Field A Before 0159 0260 4321 After 0000 4321 4321 STH Copy a half word from GPR to memory RX R1,D2(X2,B2) STH 3,A GPR3 Memory field A Before 0123 0456 0DEF 0123 0456 0456
IBM 370 ASSEMBLY LANGUAGE 20 / 119
LM Copies 1 to 16 Full words from memory RS R1,R3,D2(B2) to consecutive GPR,s LM 2,4,A GPR'S Memory Address
Before 2:00001234 A+0:0001ABCD 3:00003456 A+4:0002BCDE 4:00005678 A+8:0003CDEF
After 2:0001ABCD A+0:0001ABCD 3:0002BCDE A+4:0002BCDE 4:0003CDEF A+8:0003CDEF STM Copies 1 to 16 Full words to memory RS R1,R3,D2(B2) From consecutive GPR,s STM 2,4,A GPR'S Memory Address
Before 2:00001234 A+0:0001ABCD 3:00003456 A+4:0002BCDE 4:00005678 A+8:0003CDEF
After 2:00001234 A+0:00001234 3:00003456 A+4:00003456 4:00005678 A+8:00005678 LR Copies one GPR to another RR R1,R2 LR 3,4 GPR3 GPR4 Before ABCD EF00 1234 5678 After 1234 5678 1234 5678
ADDITION
A Adds a memory field to GPR RX R1,D2(X2,B2) Example 64+10=74. A 3,=F'10' GPR3 Memory Before 0000 0040 0000 000A After 0000 004A 0000 000A S Subtracts a memory field from GPR RX R1,D2(X2,B2) Example 64-10=54 S 3,=F'10' GPR3 Memory Before 0000 0040 0000 000A After 0000 0036 0000 000A AR Adds a GPR to another GPR RR R1,R2 Example 4096+(-1)=4095 AR 6,5 GPR6 GPR5 Before 0000 1000 FFFF FFFF After 0000 0FFF FFFF FFFF SR Subtracts a GPR from another GPR RR R1,R2 Example 4096-(-1)=4097 SR 6,5 GPR6 GPR5 Before 0000 1000 FFFF FFFF After 0000 1001 FFFF FFFF
AH Adds a half word memory field to a GPR RX R1,D2(X2,B2) Example 80+8=88 AH 10,=H'8' GPR10 Memory Before 0000 0050 0008
IBM 370 ASSEMBLY LANGUAGE 21 / 119
After 0000 0058 0008 Example 80+(-8)=72 AH 10,=H'8' GPR10 Memory Before 0000 0050 FFF8 After 0000 0048 FFF8 SH Subtracts a half word memory field from RX R1,D2(X2,B2) a GPR Example 8-80=-72 SH 10,=H'80' GPR10 Memory Before 0000 0008 0050 After FFFF FFB8 0050 AL Add Logical RX R1,D2(X2,B2) ALR Adds a GPR logically to another GPR RR R1,R2
Range of result in the GPR is from -2**31 to 2**31-1
If an overflow occurs (carry into sign bit and carry out are different) hardware interrupts occur if not suppressed through a program mask
For logical additions the operands are assumed to be unsigned Condition code is set (zero, negative, positive or overflow)
MULTIPLICATION |--------------consecutive GPR'S------------------------| |---even numbered GPR--|--odd numbered GPR---|
Before multiplication
After multiplication
M Multiply RX R1,D2(X2,B2)
Example 2 X 3 = 6 L 7,=F'2' M 6,=F'3' GPR6 GPR7 Memory Before any number 0000 0002 0003 After 0000 0000 0000 0006 0003 MR Multiply one GPR with another RX R1,D2(X2,B2)
Example 65536 X 65536 L 4,=F'65536' MR 6,4 GPR6 GPR7 GPR4 Before 0000 0000 0001 0000 0001 0000 After 0000 0001 0000 0000 0001 0000 MH Multiply a GPR with a half word RX R1,D2(X2,B2) from a memory field
Example 2 X 5 = 10 L 7,=F'2' MH 7,=F'5' GPR7 Memory Before 0000 0002 0005
Any number V1
64 bit product V1 X V2
IBM 370 ASSEMBLY LANGUAGE 22 / 119
After 0000 000A 0005
DIVISION |--------------consecutive GPR'S-----------------------------| |---even numbered GPR----|----odd numbered GPR----|
Before Division
After Division
D DIVIDE even odd GPR pair by memory RX R1,D2(X2,B2)Field
Example 7 / 2 = quotient =3, remainder=1 L 9,=F'7' L 8,=F'0' D 8,=F'2' GPR8 GPR9 Memory Before 0000 0000 0000 0007 0002 After 0000 0001 0000 0003 0002 Rem +1 Quot +3 Divisor +2 DR Divide one even/odd pair GPR with another GPR R1,R2
Example 150 / -40 L 9,=F'150' L 8,=F'0' L 10,=F'-40' DR 8,10 GPR8 GPR9 GPR10 Before 0000 0000 0000 0096 FFFF FFD4 After 0000 001E FFFF FFFD FFFF FFD4 rem +30 Quot -3 Divisor -40 Note: Since the dividend was a positive number extending the 32 bit positive quantity to 64 bit was achieved by simply setting the high order bits (next reg) to F'0'. However for a negative dividend sign extension is needed and this can be done by multiplying the low order reg by +1. The condition code is NOT set by the MULTIPLY and DIVIDE instructions. To test the result use the LTR instruction.
ARITHMETIC COMPARE
C Compare GPR with memory field RX R1,D2(X2,B2) CR Compare a GPR with another RR R1,R2 CH Compare GPR with a memory half word RX R1,D2(X2,B2)
Condition code is set ( equal, V1<V2, V2>V2) LCR Load complement register RR R1,R2
Example LCR 3,3 GPR3 Before FFFFFFFA After 00000006 LCR 3,4 GPR3 GPR4 Before 87654321 80000000 After 80000000 80000000
32 BIT REMAINDER 32 BIT QUOTIENT
64 BIT DIVIDEND V1
IBM 370 ASSEMBLY LANGUAGE 23 / 119
**ovfl set LPR Load positive register RR R1,R2
Example LPR 5,4 GPR5 GPR4 Before 000000AB FFFFFFFA After 00000006 FFFFFFFA LPR 4,5 GPR4 GPR5 Before FFFFFFFA 000000AB After 0000000AB 000000AB LPR 8,7 GPR8 GPR7 Before 12345678 80000000 After 80000000 80000000 ***ovflw LNR Load negative register RR R1,R2
Example LNR 4,5 GPR4 GPR5 Before FFFFFFFA 000000AB After FFFFFF55 000000AB LPR 4,5 GPR4 GPR5 Before 00000011 FFFFFF55 After 000000AB FFFFFF55 Condition code is set( zero, positive , negative, overflow)
IBM 370 ASSEMBLY LANGUAGE 24 / 119
DECIMAL OPERATIONS back ADD AP SUBTRACT SP MULTIPLY MP DIVIDE DP DECIMAL COMPARE CP MOVE DECIMAL DATA WITH 4 BIT OFFSET MVO SHIFT DECIMAL DATA SRP SET TO ZERO AND ADD ZAP CONVERT ZONED TO PACKED PACK CONVERT PACKED TO ZONED UNPK Constants used Type Decimal P Zoned Z BCD Representation (Packed Decimal) 0011 0010 0101 1100 +325 X’325C’ 0111 1000 1001 1101 -789 X’789D’ AREA1 DS PL5 AREA2 DC P’+12345678’
Only permissible (and mandatory) modifier is the length modifier example PLn
Padding is always at the left with Zeroes
Truncation is from the left and choice of length modifier is crucial
OPCODES are Arithmetic, Comparison, Copying from storage to storage, Conversion to and from Packed decimal format.
Most instructions are SS1 D1(L,B1),D2(B2) (length < 256) SS2 D1(L1,B1),D2(L2,B2) (length < 16) ZAP Zero and add packed SS2
Example ZAP A(3),B(4) A B Before Dont Care 0023456C After 23456C 0023456C AP Add packed SS2
Example AP A(2),B(3) A B Before 099C 00001C After 100C 00001C
Before 999C 00001C After 000C 00001C (ovfl cond)
SP Subtract packed SS2 SP A(2),B(3) A B Before 099D 00001C After 100D 00001C
IBM 370 ASSEMBLY LANGUAGE 25 / 119
Before 999C 00001C After 000C 00001C (ovfl cond)
Before 123C 00010C After 113C 00010C MP Multiply packed SS2 Length of L2 must be between 1 and 8 and less than L1. L1 must have at least L2 bytes of high order zeroes
Example MP A(4),B(2) A B Before 0000999C 999D After 0998001D 999D MP A(3),B(2) Before 00999C 999D After 98001D 999D **ovflw** MP A(2),B(2) Before 012C 012C After 012C 012C **error** DP Divide Packed SS2 DP D1(L1,B1),D2(L2,B2) L1 (Dividend) and L2(divisor) L2 < L1 1<=L2<=8 The quotient and remainder is stored in the L1(dividend field) replacing the dividend
Example A B DP A(4),B(2) Before 0000999C 998D After 001D001C 998D | DP A(4),B(2) Before 0000999C 3C After 00333C0C 3C | DP A(2),B(1) Before 999C 3C After 999C 3C **Divide exception** ***L1-L2=1 (insufficient length for quotient) DP A(2),B(3) Before 999C 00003C After 999C 00003C **specification exception** ***L1-L2=-1(impossible length for quotient)
QUOTIENT REMAINDER
L1-L2 BYTES L2 BYTES
DIVIDEND FIELD
IBM 370 ASSEMBLY LANGUAGE 26 / 119
ERRORS
Decimal overflow occurs when result is too long to fit into first operand and a significant digit would be lost
Data exception occurs whenever
Sign fields are invalid
Operands overlap
The first operand of a MP instruction does not have sufficient zeroes.
COMPARISONS
CP Compare packed SS2 D1(L1,B1),D2(L2,B2) BE V1=V2 BH V1>V2 BL V1<V2 SRP Shift and Round Packed D1(L1,B1),D2(B2),I3 SS1 The first operand represents an address The second operands low order 6 bits is the number of positions to be shifted and direction of shift. Positive represents left shift and vacated positions on the left are filled with zeroes. Negative represents a right shift and zeroes are inserted on the left. The sign is not disturbed in any case. The third operand is the rounding to be applied in case of right shift and is an immediate operand. L 8,=X’FFFFFFFD’ SRP A(5),0(8),5 before 031415926C after 000031416C
CONVERSION BETWEEN EBCDIC, BINARY AND PACKED DECIMAL FORMAT CVD converts binary to packed decimal 32 bit binary to a 8 byte packed decimal field
Example CVD 5,A REG5 A Before 7F FF FF FF any number after 7F FF FF FF 00 00 02 14 74 83 64 7C CVD 5,A REG5 A Before 80 00 00 00 dont care
after 80 00 00 00 00 00 02 14 74 83 64 8D CVB converts packed decimal to binary 8 byte packed decimal field to a 32 bit binary field
Example CVB 5,A REG5 A Before dont care 00 00 00 00 00 00 01 6C after 00 00 00 10 00 00 00 00 00 00 01 6C CVB 5,A REG5 A Before dont care 00 00 00 00 00 00 01 6D after FF FF FF F0 00 00 00 00 00 00 01 6D PACK converts EBCDIC to packed decimal D1(L1,B1),D2(L2,B2) Operand one will receive packed decimal field Operand two is the EBCDIC field in zoned decimal format
Example PACK A(4),B(4) A B
IBM 370 ASSEMBLY LANGUAGE 27 / 119
Before any F1 F2 F3 C4 after 00 01 23 4C F1 F2 F3 C4 UNPK converts packed decimal to EBCDIC D1(L1,B1),D2(L2,B2) Operand two is the packed decimal field Operand one will receive the EBCDIC field
Example UNPK A(8),B(4) A B Before any 12 34 56 7D After F0 F1 F2 F3 F4 F5 F6 D7 12 34 56 7D ED Converting a packed decimal number to EBCDIC with editing D1(L,B1),D2(B2) V1 is pattern, V2 is packed fld ED P(15),Y Before Y 0 0 1 2 3 4 5 6 7 D Before P 40 20 6B 20 20 20 6B 20 21 20 4B 20 20 60 40 After P 40 40 40 40 F1 F2 6B F3 F4 F5 4B F6 F7 60 40 1
st byte of pattern is the fill character, in this case a blank
Hex 20 is a digit selector Hex 21 is a significance starter Hex 6B is a ‘,’ Hex 4B is a ‘.’ Every byte of packed decimal needs two bytes of EBCDIC code 00 12 3C ----------------- F0 F0 F1 F2 C3
Example of Packed Decimal Divide FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
DP A,B
UNPK QUOT,A(L'A-L'B)
UNPK REM,A+L'A-L'B(L'B)
OI QUOT+3,X'F0'
OI REM+3,X'F0'
LA 3,MSG
WTO TEXT=(3)
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BR 14
SAVE DS 18F
MSG DC AL2(LEN)
DC C'QUOT='
QUOT DS CL4
DC C','
DC C'REM='
REM DS CL4
LEN EQU *-MSG-2
A DC PL4'+0000999'
IBM 370 ASSEMBLY LANGUAGE 28 / 119
B DC PL2'-998'
END
Example of displaying a Integer FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
LA 4,2345
CVD 4,DW
UNPK MSG+2(16),DW
OI MSG+17,X'F0'
LA 3,MSG
WTO TEXT=(3)
L 13,SAVE+4
LM 14,12,12(13)
LA 15,4
BR 14
SAVE DS 18F
MSG DC AL2(16)
DS CL16
DW DS D
END
IBM 370 ASSEMBLY LANGUAGE 29 / 119
FLOATING POINT OPERATIONS back ADD ADR,AD,AER,AE,AWR,AW,AUR,AU,AXR SUBTRACT SDR,SD,SER,SE,SWR,SW,SUR,SU,SXR MULTIPLY MDR,MD,MER,ME,MXR,MXDR,MXD DIVIDE DDR,DD,DER,DE ARITHMETIC COMPARE CDR,CD,CER,CE LOAD INTO FPR LDR,LD,LER,LTDR,LTER,LCDR,LCER,LPDR,LPER LNDR,LDER,LRDR,LRER STORE INTO AREAS STD,STE Constants used Type Floating point E,D,L
Floating-point Number representation
Consists of a signed hexadecimal fraction and an unsigned seven-bit binary integer ,called as characteristic
Characteristic represents signed exponent in excess-64 notation
A normalised floating -point number has a nonzero leftmost hexadecimal fraction digit.
If one or more leftmost fraction digits are zeros, the number is said to be un-normalised.
A normalised number represents a quantity with the greatest precision.
Un-normalised numbers are normalised by shifting the fraction left, one digit at a time, until the leftmost hexadecimal digit is nonzero and reducing the characteristic by the number of hexadecimal digits shifted.
Addition and subtraction with extended operands, as well as the multiply, divide, and halve operations, are performed only with normalisation. Addition and subtraction with short or long operands may be specified as either normalised or not normalised.
Floating-Point Data format
Short floating-point number
Represented by 32 bits
Bit 0 is sign bit
Bits 1-7 are characteristic
Bits 8-31 are digit fraction
Can reside in the storage or in the floating point registers
Long floating-point number
Represented by 64 bits
Bit 0 is sign bit
Bits 1-7 are characteristic
Bits 8-63 are digit fraction
Can reside in the storage or in the floating point registers
extended floating point number
Represented by 128 bits
Bit 0 of high-order 64 bits is the sign bit
Bits 1-7 of high-order 64 bits contains are characteristic
Bits 8-63 of high-order 64 bits and bits 72-127 of low order 64 bits contains the 28 digit fraction
Can only reside in the floating point registers
Floating Point instructions
Floating point registers 0,2,4,6 are used in the instructions
Only left half of FPR is used if short floating point number is specified
FPR 0 & 2,4 & 6 can be used to contain extended floating point
IBM 370 ASSEMBLY LANGUAGE 30 / 119
Instructions are available for data loading, arithmetic and comparison number
IBM 370 ASSEMBLY LANGUAGE 31 / 119
DATA TRANSFER AND LOGICAL OPERATIONS back MOVE MVI,MVC,MVZ,MVCL LOGICAL COMPARE CLR,CL,CLC,CLCL,CLM AND LOGICAL NR,N,NI,NC OR LOGICAL OR,O,OI,OC EXCLUSIVE OR XR,X,XI,XC TESTING BINARY PATTERNS TM INSERTING CHARS INTO GPR IC,ICM STORE CHARS INTO AREAS STC,STCM LOAD ADDRESS INTO GPR LA LOGICAL SHIFT OF GPR SLL,SRL,SLDL,SRDL DATA TRANSLATION TR,TRT EDIT ED,EDMK
BYTE AND STRING MANIPULATIONS IC Insert character RX Copies 1 byte from memory to 8 right most bits of a GPR
R1,D2(X2,B2) STC store Character RX Copies 1 byte (right most 8 bits) from GPR to Memory
R1,D2(X2,B2) ICM Insert Characters under mask RS Copies 1 to 4 bytes depending on the mask from memory to GPR
R1,Mask,D2(B2) STCM Store characters under mask RS Copies 1 to 4 bytes depending on the mask from GPR to memory
R1,R3,D2(B2) MVI Move Immediate SI Copies 1 byte from immediate
field of the instruction to memory D1(B1),I2
MVC Move Characters SS Copies 1 to 256 chars from one memory field to another
D1(L,B1),D2(B2)
MVCL Move Characters Long RR Copies 1 to 2**24 chars from one memory field to another
R1,R2 MVCIN Move Inverse SS Copies 1 to 256 bytes from one memory field to
another reversing the order of bytes Comparison
COMPARISON (LOGICAL)
Unsigned 8 bit numbers (logical quantity)
Smallest byte is X’00’, Largest is X’FF’
Comparison starts from left most position (high order) CL Compare logical RX Compares a 4 byte string in memory to contents of a GPR
R1,D2(X2,B2)
IBM 370 ASSEMBLY LANGUAGE 32 / 119
CLR Compare Logical Register RR Compares 4 bytes from two GPR’S R1,R2 CLM Compare Logical under mask RS Compares 1 to 4 bytes (determined by mask) from a GPR to a memory field
R1,M,D2(B2) CLI Compare Logical Immediate SI Compares an 1 byte immediate operand to a byte in memory
D1(B1),I2 CLC Compare Logical Characters SS Compares 1 to 256 bytes from one memory field to another
D1(L,B1),D2(B2) CLCL Compare Logical Characters long RR Compares 1 to 2**24 characters from one memory field to another.
BRANCHING
CC 0 CC 1 CC 2 CC3 CL,CLC,CLCL, CLI,CLM,CLR OPR1=OPR2 OPR1<OPR2 OPR1>OPR2 NA.
Opcode Meaning BE OPR1=OPR2 BNE OPR1!=OPR2 BL OPR1<OPR2 BNL OPR1=>OPR2 BH OPR1>OPR2 BNH OPR1<=OPR2
Notes: Destructive overlap occurs when a to field starts from within a from field How to modify length field at run time
EX R1,D2(X2,B2). The instruction at the memory address specified is executed after OR’ing bits 8-15(length field) with bits 24-31 of R1 If the target instruction is a branch then the branch is made. If it is a BALR / BAL then the return from the branch is made to the instruction following the EX instruction. LH 4,=H’20’ SH 4,=H’1’ EX 4,MOVEV | | MOVEV MVC TO(0),FROM | | FROM DS 10F TO DS 10F CLCL and MVCL instructions CLCL R1,R2 MVCL R1,R2
IBM 370 ASSEMBLY LANGUAGE 33 / 119
R1 bits 8 to 31 is the TO address R1+1 bits 8 to 31 is the length of TO field R2 bits 8 to 31 is the FROM address R2+1 bits 8 to 31 is the length of FROM field bits 0 to 7 is the padding character to be used to lengthen the shorter string LA 2,S L 3,=L’S LA 4,T L 5,=L’T ICM 5,X’8’,=X’00’ CLCL 2,4 | | | S DS CL1000 T DS CL2000 TR and TRT instructions TR Translate SS instructions can be used to replace certain bytes of the string with other bytes D1(L,B1),D2(B2) TRT Translate & test SS instruction can be used to find one of a set of characters in a string D1(L,B1),D2(B2)
Notes: Operand 1 is the argument string operated on by TR and searched by TRT instruction Operand 2 is the Function string set up by the programmer and is 256 bytes long
FN1 DS CL256 ORG FN1+C’+’ DC X’FF’ ORG ARG1 DS CL256 | TRT ARG1(256),FN1 BC 8,NONE BC 4,MORE BC 2,ONE
Notes: How the instruction works is as follows. Read a byte from argument string. Use it as an offset into the function string. In the TR instruction replace the argument byte with the function byte. In the TRT instruction , if the function byte is non zero, a copy of that byte is inserted in bits 24 to 31 of GPR2 and the address of the byte is set into bits 8 to 31 of GPR1. Execution terminates and a CC is set to 1 if more bytes remain to be scanned in the argument string. A CC of 2 is set if there was a non zero byte in the function string and there were no more bytes to be scanned as well. Else CC 0 is set
IBM 370 ASSEMBLY LANGUAGE 34 / 119
BIT MANIPULATIONS back SRA Shift Right Single Arithmetic RS SLA Shift Left Single Arithmetic RS SRDA Shift Right Double Arithmetic RS (first operand is even odd GPR pair) SLDA Shift Left Double Arithmetic RS
When shifting left zeroes are inserted on the right and overflow is set if a bit value other than the sign bit is lost from the shift.
When right shifting the low order bits are lost and the sign bit is propagated
If overflow occurs it can be checked by BO (branch on Overflow)
If overflow is not set condition code 0,1, or 2 is set SRL Shift Right Single Logical RS SLL Shift Left Single Logical RS SRDL Shift Right Double Logical RS (first operand is even odd GPR pair) SLDL Shift Left Double Logical RS
When right shifting the low order bits are lost and the zeroes are inserted on the right
When shifting left zeroes are inserted on the right and the high order bits are lost.
The condition code is never set
O Or RX N And RX X Exclusive Or RX
OR Or GPR’S RR NR And GPR’S RR XR XOR GPR’S RR OI Or Immediate SI NI And Immediate SI XI Exclusive Or Immediate SI OC Or Memory fields SS NC And Memory Fields SS XC Exclusive Or Mem Flds SS
TESTING BITS TM Test Under Mask SI D1(B1),I2 I2 is one byte.Bits corresponding to '0' bit(s) in the mask byte are not tested. Associated Branch Instructions BZ Branch if Zeroes All tested bits are '0' or all mask bits are '0' BO Branch if Ones All tested bits are '1' BM Branch if mixed Tested bits are a mix of '0' and '1'
IBM 370 ASSEMBLY LANGUAGE 35 / 119
BRANCHING INSTRUCTIONS back BRANCH ON CONDITION CODE BCR,BC BRANCH AND LINK BALR,BAL BRANCH ON COUNT BCTR,BCT BRANCH ON INDEX COMPARE BXH,BXLE TEMPORARY BRANCH EX BC Branch on Condition RX M1,D2(X2,B2) BE,BER,BNE,BNER,BL,BLR,BNL,BNLR BH,BHR,BNH,BNHR,BZ,BZR,BNZ,BNZR BM,BMR,BNM,BNMR,BP,BPR,BNP,BNPR BO,BOR,BNO,BNOR,
NOP,NOPR,B,BR All implemented using BC instruction
BRANCHING AND LOOPS
BCT Branch on count RX R1,D2(X2,B2)
Subtract 1 from R1 and test for non zero.
Branch if non zero BXH Branch on Index High RS R1,R2,D3(B3)
Increments or decrements Index
Counting iterations
Test to determine whether loop should be repeated
BHX is normally used with decrementing
BXLE is used with incrementing
R1 is the Index register
R2 contains the increment / R2+1 contains the limit
S3 is the branch address L 7,LIMIT L 6,INCR L 5,=F'0' LOOP L 3,X(5) A 3,Y(5) A 3,Z(5) BXLE 5,6,LOOP . X DS 20F Y DS 20F Z DS 20F LIMIT EQU Y-X INCR EQU 4
ASSEMBLER DIRECTIVES back
IBM 370 ASSEMBLY LANGUAGE 36 / 119
CSECT
Indicates the beginning of a control section
Smallest portion of the code which can be relocated
A program can have more than one CSECT
CSECTS can be continued across CSECTS or DSECTS
Separate location counter for each CSECT
Symbols are not addressable across CSECT s
RSECT
Defines a read only CSECT and makes the Assembler check for possible violations. The assembler check is not fool proof.
DSECT
Dummy Control Sections
To describe the structure of a block of data in memory without actually allocating memory
Acts as a template (for example with storage obtained dynamically at run time)
No code is generated
DC statement is not allowed in a DSECT
Example: CUSTOMER DSECT FIELD1 DS CL3 FIELD2 DS CL10 FIELD3 DS CL10 FIELD4 DS CL10 FIELD5 DS F CITY DS PL5
USING
USING <symbol>, Rn
Symbol can be any relocatable symbol defined in the program
* can be used in the place of symbol
Fields in the DSECTs are accessed after
Establishing a base register with USING instruction at Assembly time
Initialising the Base Register with the address of the storage area at run time.
Rn, base register, to be used by the assembler for resolving the symbols in the base displacement FORM
The location counter of the symbol is used as the base from which displacements are calculated
Users responsibility to load the base register with base address
BALR instruction can be used to load the base address
Range of a base register is 4096 including the base
If the code size is more than 4096 bytes, multiples base registers have to be used
Example : BALR 12,0 Load the base address USING *,12 Reg 12 is a base register USING PROG,10 Base for DSECT PROG
ORG
ORG <EXPR>
If expr is specified, location counter is set up with expr value
If expr is not specified, location counter takes previous maximum value Used to redefine the storage
Example: BUFFER DS 100F
IBM 370 ASSEMBLY LANGUAGE 37 / 119
ORG BUFFER A DS CL80 B DS CL80 C DS CL80 D DS CL80
ORG
DROP
DROP (R0,R1,...RN)
Specified registers are dropped as base registers
Example BALR 12,0 USING *,12 . . .
DROP 12
END LABEL
Signals the end of a control section or program, Label is the entry point
EJECT
Force a form feed
The directive itself not printed in the listing
LTORG
Forces assembler to dump the literals collected up to that point
EXTRN, ENTRY See example below. FIRST CSECT
ENTRY DATA
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO 'IN ASM4 BEFORE CALL TO SUB4'
LA 3,MSG
WTO TEXT=(3)
L 15,ASUB1
BALR 14,15
WTO 'IN ASM4 AFTER CALL TO SUB4'
LA 3,MSG
WTO TEXT=(3)
L 13,SAVE+4
LM 14,12,12(13)
LA 15,4
BR 14
SAVE DS 18F
DC A(SAVE)
ASUB1 DC V(SUB4)
MSG DC AL2(L'DATA)
DATA DC CL20'DATA BEFORE CALL'
END
SUB4 CSECT
IBM 370 ASSEMBLY LANGUAGE 38 / 119
EXTRN DATA
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO 'IN SUB 4 BEFORE CHANGING DATA'
L 3,ADATA
MVC 0(20,3),=CL20'DATA AFTER CHANGE'
WTO 'IN SUB 4 AFTER CHANGING DATA'
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
ADATA DC A(DATA)
END
WXTRN
defines a weak external reference. A weak external reference does not trigger a linkage editor auto call. Note that in the following example the linkage editor does not object to SAVE1 remaining unresolved.
Example FIRST CSECT
WXTRN SAVE1
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO TEXT=DATA
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
DATA DC AL2(L'MSG)
MSG DC CL30'ASM1 REPORTING'
END
COM
Defines a common section. All common sections across CSECTS with the same name map to the same storage. The storage for COMMON sections is allocated at the time the load module is built.
SUB CSECT
SUB AMODE 31
SUB RMODE ANY
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
IBM 370 ASSEMBLY LANGUAGE 39 / 119
LA 13,SAVE
L 4,ACOM
LA 5,15
STH 5,0(0,4)
MVC 2(15,4),=CL15'THIS IS SUB'
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BR 14
SAVE DS 18F
ACOM DC A(COMMON)
COMMON COM
MSG DS AL2
DS CL100
END
FIRST CSECT
FIRST AMODE 31
FIRST RMODE ANY
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
L 15,ASUB
BALR 14,15
ICM 4,B'1111',ACOM
WTO TEXT=(4)
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BR 14
SAVE DS 18F
ASUB DC V(SUB)
ACOM DC A(COMMON)
COMMON COM
MSG DS AL2
DS CL100
END
IBM 370 ASSEMBLY LANGUAGE 40 / 119
JCL ASPECTS back
program consists of Machine instructions Assembler instructions Macro Instructions. Development cycle Coding Pre Assembly Assembly Linkage Edit Program fetch JCL:- IBM supplied catalogued procedures can be used. ASMACL is given below which assembles and links a assembler program //ASMACL PROC //* //*** ASMACL //* //* THIS PROCEDURE RUNS THE HIGH LEVEL ASSEMBLER AND LINKS //* THE NEWLY ASSEMBLED PROGRAM //* //C EXEC PROG=ASMA90,PARM=(OBJECT,NODECK) //SYSLIB DD DSN=SYS1.MACLIB,DISP=SHR //SYSUTI DD DSN=&&SYSUT1,SPACE=(4096,(120,120),,,ROUND),UNIT=VIO, // DCB=BUFNO=1 //SYSPRINT DD SYSOUT=* //SYSPUNCH DD SYSOUT=B
SOURCE
ASSEMBLER
MACLIBS COPY BOOKS
OBJECT DECK OBJECT LIBRARIES
LINKER
LOAD MODULE
LOAD IN MAIN STORAGE FOR EXECUTION
IBM 370 ASSEMBLY LANGUAGE 41 / 119
//SYSLIN DD DSN=&&OBJ,SPACE=(3040,(40,40),,,ROUND),UNIT=VIO, // DISP=(MOD,PASS), // DCB=(BLKSIZE=3040,LRECL=80,RECFM=FBS,BUFNO=1) //L EXEC PGM=HEWL,PARM='MAP,LET,NCAL',COND=(8,LT,C) //SYSLIN DD DSN=&&OBJ,DISP=(OLD,DELETE) // DD DDNAME=SYSIN //SYSLMOD DD DISP=(,PASS),UNIT=SYSDA,SPACE=(CYL,(1,1,1)), // DSN=&&GOSET(GO) //SYSUT1 DD DSN=&SYSUT1,SPACE=(1024,(120,120),,,ROUND), // DCB=BUFNO=1,UNIT=VIO //SYSPRINT DD SYSOUT=*
Important linkage editor parameters
LET allows you to specify severity level of an error to determine whether the load module is to be marked as
unusable.
MAP | NOMAP Use map if you want a generated map of the load module
NCAL Do not make an automatic search of the object libraries when linking
RENT Indicates module is re-entrant, NORENT marks it as non re-entrant
AMODE 24|31|ANY . Use this parameter to override the attribute established by the assembler in the assembly process
RMODE 24|ANY overrides this attribute as set by the assembly process
Assembler
ALIGN instructs assembler to check for alignment where it is required default ALIGN
DECK Assembler generates object deck on SYSPUNCH default NODECK
ESD The External symbol dictionary is produced in the listing default ESD
OBJECT instructs the assembler to generate an object data set on SYSLIN default OBJECT
RENT instructs the assembler to check for possible violations of re-entrant default NORENT
RLD the assembler outputs the relocation dictionary in the listing default RLD
SYSPARM SYSPARM ( parmvalue………) max 55 chars
XREF(FULL) Ordinary symbol and literal cross reference listing produced including symbols that are not referred to .
XREF(SHORT) Omits symbols not referred to. Default XREF(SHORT,UNREFS)
IBM 370 ASSEMBLY LANGUAGE 42 / 119
Special Considerations when the member name and the CSECT name do not match.
Source File-1
FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO 'IN ASM3 BEFORE CALL TO SUB1'
L 15,ASUB1
BALR 14,15
WTO 'IN ASM3 AFTER CALL TO SUB1'
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
ASUB1 DC V(SUB1) Does not pose problems
*ASUB2 DC V(SUB2) Does pose a problem
END
Source File-2 SUB1 CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO 'IN SUB 1'
DC F'0'
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
SUB2 CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE1+4
LA 13,SAVE1
WTO 'IN SUB 2'
L 13,SAVE1+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE1 DS 18F note that labels cannot be the same
END
The solution is to explicitly make the Linkage Editor include the module by the linkage editor control statement input as below:- //LKED.SYSIN DD *
IBM 370 ASSEMBLY LANGUAGE 43 / 119
INCLUDE SYSLIB(SUB1) /*
IBM 370 ASSEMBLY LANGUAGE 44 / 119
SUBROUTINES AND LINKAGES 24 BIT MODE back
SUBROUTINE
Entry point Identified by a CSECT,START OR ENTRY assembler directives.
An entry is made in the ESD for each Entry point.
A CSECT can have multiple entry points specified by ENTRY directive
Internal Subroutine :-A subroutine present in the source module from which it is called.
External Subroutine :-A subroutine present in a different source module. Assembled and link edited separately
Static Subroutine :- A subroutine which is known at the link edit time. Can be an internal or an external subroutine.
Dynamic Subroutine:- A subroutine which is loaded at program run time using LOAD, LINK macros
V-type address constant:- To refer a symbol defined in another CSECT.
External symbol directory (ESD) :- A table containing information about the name, location and size off each all external symbols
Linking to subroutine BALR R1,R2 Branch and link register (R1) <--PC,PC <--R2) BAL R1,S2 Branch and link (R1) <--PC,PC <--S2 The next instruction address is loaded in the register specified by the first operand and the branch is taken to the address specified by the second operand. If R2 is zero, then no branch is taken
Return from subroutine BR R1 Branch register PC <--(R1) Branch unconditionally to the address specified in the operand 1 Example: MAIN START 0 SETUP . BAL 14,SUB1 . L 15,SUB2 BALR 14,15 * EOJ * SUB1 DS OH BR 14 SUB2 DC V(SUBROUT2) END
Saving and restoring environment Programs uses registers as base, index, and accumulators. If a program calls a subprogram, and when the control returns, these register values should not be altered. To achieve this, the calling program provides a SAVEAREA into which the called program saves the registers. Before the control is returned from the subprogram, the registers are restored to their original values. Some subprograms return to the called program a return code (set in GPR15) and a reason code. It is a good programming practice to save and restore the environment. If this is done any subroutine
IBM 370 ASSEMBLY LANGUAGE 45 / 119
can be used by any program with out the need to identify which registers are modified by the subroutine.
IBM convention for saving registers
Every calling routine has a save area of 18 full-words for the use of called routine
The calling routine passes the save area address in register 13
Every called routine saves the registers in this area before establishing addressability
Address of called routine is in register 15
Register 14 has the return address
SAVEAREA (18 Full words) layout Savearea+0 Reserved for PL/1 Savearea+4 save-area of program which called this sub-program Savearea+8 save-area of called sub-program called by this program Savearea+12 Register 14 savearea+16 Register 15 savearea+20 Register 0 . . . . . . Savearea+64 Register 11 Savearea+68 Register 12
Example MAIN START 0 STM 14,12,12(13) BALR 12,0 USING *,12 ST 13,SAVE+4 LR 2,13 LA 13,SAVE ST 13,8(2) . . . LA 15,0 L 13,SAVE+4 L 14,12(0,13) LM 0,12,20(13) * BR 14 SAVE DS 18F END
Advantages of SAVEAREA
Forward and backward pointers running through the save areas useful for trace-back
Called program can first save the environment before acquiring storage in case of re-entrant program
Parameter passing
Fixed and variable number of parameters can be passed to a subprogram
Parameters value are not passed directly
Each parameter is saved in the storage then an array is created containing he address of the parameters in the order they are expected in the called program and the register 1 is loaded
IBM 370 ASSEMBLY LANGUAGE 46 / 119
with the starting address of this address array. The last address in the array should have bit ' 0' set to ' 1'
For variable number of parameters, the high order bit of the last parameter is set to one to indicate the end of parameter list
Example LA 2,PI ST 2,PARM LA 2,P2 ST 2,PARM+4 LA 3,P3 ST 3,PARM+8 LA 1,PARM L 15,=V(PROC1) BALR 14,15
. .
LA 1,=A(P2,P1,P3) L 15,=V(PROC2) BALR 14,15
. P1 DS CL8 P2 DC F'20' P3 DC C'ABCDEFGHIJKL' PARM DS 3F
Accessing the parameters
On entry the subprogram, R 1 contains the base address to the array of pointers pointing to the parameters
Access the parameter pointer address from the array and using this access the parameter
If lot of parameters need to be accessed, them a DSECT can be used to access the parameters in which case the parameters have to be stored using the same DSECT in the calling program
Example LM 4,6,0(1) Fetch address of P1-P3 L 4,0(4) R4 has P1 L 4,0(5) R4 has P2 L 4,0(6) R4 has P3
Functions in Assembly language
To pass back a return value from function set register 0 to that value
The return value can be used to indicate error condition
A return code 0 means successful completion (return codes passed in GPR15)
Return codes are multiple of 4, so that it could be used to index into address table
Example MAIN CSECT . entry linkages . . LA 1,=A(I,J) L 15,=V(MIN) BALR 14,15 ST 0,K .
IBM 370 ASSEMBLY LANGUAGE 47 / 119
. . BR 14 I DC F'100' J DC F'120' K DS F SAVE1 DS 18F * MIN CSECT . entry linkages . LM 4,5,0(1) L 4,0(4)
L 5,0(5) CR 4,5 BGE BIG LR 0,5 B RESTORE
BIG LR 0,4 RESTORE EQU *
.
. exit linkages .
BR 14 SAVE2 DS 18F
END
Example of capturing PARM data from JCL PICKING UP PARMS
FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
L 13,SAVE+4
L 2,0(0,1)
LH 3,0(0,2)
STCM 3,B'0011',MSG
S 3,=F'1'
EX 3,IN1
LA 4,MSG
WTO TEXT=(4)
LM 14,12,12(13)
LA 15,0
BR 14
SAVE DS 18F
IN1 MVC MSG+2(0),2(2)
MSG DC AL2(0)
DS CL100
END
Passing Structures (like a COBOL 01 level item) SUB CSECT
STM 14,12,12(13)
IBM 370 ASSEMBLY LANGUAGE 48 / 119
USING SUB,15
ST 13,SAVE+4
LA 13,SAVE
LR 12,15
DROP 15
USING SUB,12
LR 2,1
WTO 'IN SUB'
LR 1,2
L 2,0(1)
USING PARMS,2
L 5,A
A 5,B
ST 5,RES
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BR 14
SAVE DS 18F
PARMS DSECT
A DS F
B DS F
RES DS F
END
FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
L 15,ASUB
LA 1,=A(PARMS)
BALR 14,15
L 5,RES
CVD 5,DW
UNPK MSG+2(16),DW
OI MSG+17,X'F0'
WTO 'RESULT IS'
LA 4,MSG
WTO TEXT=(4)
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BR 14
SAVE DS 18F
MSG DC AL2(16)
DS CL16
ASUB DC V(SUB)
DW DS D
DS 0F
PARMS DS 0CL12
A DC F'100'
B DC F'200'
IBM 370 ASSEMBLY LANGUAGE 49 / 119
RES DS F
END
IBM 370 ASSEMBLY LANGUAGE 50 / 119
MACRO AND CONDITIONAL ASSEMBLY Back
Macro
An extension of assembler language.
Provides convenient way to generate a sequence of assembler language statements
A macro definition is written only once
Macro invocation expands to the desired sequence of statements
Conditional assembly statements can be used to tailor the statements generated
Parameters can be passed to the macro
Expanded during the pre-assembly time and generates inline code
Macro definition
Can appear at beginning of a source module in which case it is called a source MACRO
System macros reside in a system library (ddname SYSLIB)
User macros reside in a user library or in the source program itself
Nested macro invocations possible
Format of a Macro definition
Header. Indicates the beginning of a macro definition (MACRO)
Prototype statement. Defines the macro name and the symbolic parameters
Body. Contains model statements, processing statements, comments statements and conditional assembly statements.
Trailer. Indicates the end of a macro definition (MEND)
Prototype
Must be the second non-comment statement in every macro definition.
Only internal comments are allowed between the macro header and the macro prototype.
Format of the prototype statement:
{Name} Operation {Operands} Name field : A variable symbol. The name entry in the calling macro instruction is assigned to this symbol. Operation field: The name of the macro. The macro is invoked with this name. Operands : Specify positional or keyword parameters. Maximum 240 parameters can be passed Macro body :
Contains the sequence of statements that are generated in the macro expansion.
Model statements from which assembler language statements are generated.
Processing statements that can alter the content and sequence off the statements generated or issue error messages.
Comments statements.
Conditional assembly instructions to compute results to be displayed in the message created by the MNOTE instruction, without causing any assembler language statements to be generated
Model Statement
Assembler language statements are generated at pre-assembly time from model statement
Variable symbols can be specified to vary the contents of the statements generated
Statements generated must not be conditional assembly instructions
Variable Symbols
Prefixed with '&' character
Can appear in macros and in conditional assembly statements
IBM 370 ASSEMBLY LANGUAGE 51 / 119
Can be symbolic parameters, system variables or set symbols
System variables are read only and their value is maintained by the Assembler
Example USER: &L &NAME &VARI &PARAM(1) SYSTEM: &SYSNDX &SYSDATE &SYSECT
Concatenation (".")
Used when a character string has to be concatenated to a variable symbol
Concatenation character is mandatory 1) when an alphanumeric character is to follow a variable symbol 2) A left parenthesis that does not enclose a subscript is to follow a variable symbol
To generate a period, two periods must be specified in the concatenated string following the variable symbol
Concatenation character is not required 1) when an ordinary character string precedes a variable symbol 2) A special character, except a left parenthesis or a period, is to follow a variable symbol 3) A variable symbol follows another variable symbol 4) Between a variable symbol and its subscript
String Symbol Value Result &FLD.A &FLD AREA AREAA &FLDA &FLDA SUM SUM &B 10 &D.(&B) &D 100 100(10) &I 99 &F 98 D'&I..&F' D'99.98' D'&I.&F' D'9988' &A+3 &A A A+3
Symbolic Parameters
Variable symbols included in macro prototype are supplied values by the macro call
Actual value supplied for a formal parameters is a character string (max=255chars)
Two kinds of symbolic parameters
Positional Parameters
Keyword Parameters
Null string for the omitted parameters
Defaults can be specified for keyword parameters
Parameters can be subscribed
Have local scope
Read only
Example MACRO MAC1 &P1,&K1=10 . MEND
Invocation of above Macro:
START 0 . . .
IBM 370 ASSEMBLY LANGUAGE 52 / 119
MAC1 ONE,K1=12 . MAC1 TWO . . END
Example MACRO DIVIDE &R1,&R2,&TYPE M &R1,=F`1' D&TYPE &R1,&R2 MEND
Invocation MAIN CSECT
.
. . DIVIDE 8,NUM + M 8,=F`1' + D 8,NUM
.
. DIVIDE 4,6,R
+ M 4,=F'1' . .
+ DR 4,6 END
Processing Statements
Macro instruction
Conditional assembly instructions
Macro instructions
MNOTE instruction <SEQ SYM> MNOTE <opt> <message>
To generate error messages or display intermediate values of variable symbols
Can be used in open code or in a macro
Opt specifies a severity code. If"," is specified then the severity code value is "1"
If opt is omitted or a `*' is specified, then the message is generated as a comment Example: MNOTE 2, `Error in syntax' MNOTE ,`Error, severity 1' MNOTE *, `A comment' MNOTE `Another comment'
MEXIT instruction <SEQ SYM> MEXIT
Exit from the current macro definition
Can be used only inside a macro definition
Comments
A "*" in column generates an ordinary comment which will appear in the listing
IBM 370 ASSEMBLY LANGUAGE 53 / 119
A ".*" sequence in column 1 generates an internal comment which will not appear in the listing
System Variables
Variables set by the system &SYSDATE, &SYSPARM, and &SYSNDX can be used only within a macro
Name Description &SYSLIST Provides alternate way of accessing positional parameters &SYSPARM To obtain the compile time parm value passed thru JCL EXEC statement &SYSECT To get the name of CSECT from where macro is invoked &SYSTIME To get time in HH.MM format &SYSDATE To get date in MM/DD/YY format
Example Prototype statement : LOOP VNAME V1,V2,,V4,(V5,V6) &SYSLIST(O) = LOOP &SYSLIST(1) = V1 &SYSLIST(2) = V2 &SYSLIST(3) = NULL STRING &SYSLIST(4) = V4 &SYSLIST(5) = V5,V6 &SYSLIST(5,1) = V5 &SYSLIST(5,2) = V6 N'&SYSLIST = 5 N'&SYSLIST(5) = 2
Sublists
To specify variable number of parameters to a macro
One or more entries separated by commas and enclosed in parenthesis
Including the parenthesis, maximum length is 255 characters
Example MACRO
&L VAR &P1,&P2,&KEY=(FO,F,O) .
&KEY(1) DC &KEY(2)'&KEY(3)' &P1(1) DC &P1(2) '&P1(3)'
DC A&P2 . MEND
invocation: MAIN START O
. VAR (H20,H,200), (A,B,C),KEY=(F1,F,1)
+F1 DC F' 1' +H20 DC H'200' + DC A(A,B,C)
END
Labels in macro If ordinary symbols are used as label, then for each macro invocation, the same label will be generated and duplicate symbol error will occur at assembly time. To avoid this &SYSNDX system variable can be concatenated with a symbol, so that the label generated is unique.
Example MACRO LOOP
IBM 370 ASSEMBLY LANGUAGE 54 / 119
LOOP&SYSNDX EQU * BNE LOOP&SYSNDX MEND
Invocation MAIN START 0
LOOP +LOOP0001 EQU * + BNE LOOP0001
LOOP +LOOP0002 EQU * + BNE LOOP0002
Conditional Assembly
Selectively assemble a sequence of instructions
Can be used in the open code or in the macros
Processed at the pre-assembly time
Many functions like a programming language is available
Variable declarations and assigning values
Arithmetic and logic functions
Character processing
Control facilities
Conditional assembly statement labels are called sequence symbols and are prefixed with "."
Set Symbols
Provides arithmetic, binary, or character data
Values can be varied at pre-assembly time
Can be subscripted (set symbol array)
Can be local(within a macro) or global (across other macros in this assembly)set symbols
Used as
Terms in conditional assembly expressions
Counters, Switches and character strings
Subscripts for variable symbol
Values for substitution
Global set symbols
Values can be accessed any where in the source
Has to be defined in each part of the program in which it is accessed (macro, open code)
Declared using GBLA, for global arithmetic set symbols GBLB, for global binary set symbols GBLC, for global character set symbols
GBLA and GBLB have a default value 0 (zero)
GBLC has null string as default value
SYNTAX GBLA <VARLIST> GBLB <VARLIST> GBLC <VARLIST>
Example GBLA &TEST,&VAL GBLC &NAME,&ID GBLB &TRUE
Local set symbols
IBM 370 ASSEMBLY LANGUAGE 55 / 119
Values can be accessed only in the macro in which it is defined
Declared using LCLA, for local arithmetic set symbols LCLB, for local binary set symbols LCLC, for local character set symbols
LCLA and LCLB have default value 0 (zero)
LCLC has null string as default value
SYNTAX LCLA <VARLIST> LCLB <VARLIST> LCLC <VARLIST>
Example LCLA &CNT,&VAL LCLC &STR1 LCLB &TRUE
Conditional Assembly Expressions
Three kinds
Arithmetic
Character
Binary
Can be used as operands of conditional branch instruction
To assign values to set symbols
Arithmetic expressions are formed using arithmetic operators
Character expressions can produce strings of up to 255 chars
Parameter substitution within quoted strings
Duplication factor for quoted strings
Boolean expression by combining arithmetic or character expressions using relational operators
Assigning Values to Set Symbols
Global set symbols have to be defined before assigning values
Undeclared set symbols are defined as local set symbols
More than one element in an array can be assigned values in a single set statements
Set Arithmetic
<VAR SYMBOL> SETA <arithmetic expression>
To assign an arithmetic value to a SETA symbol
Value represented by SETC symbol variable string can be used as a term in an arithmetic expression provided they contain only numeric digits.
Value represented by SETB symbol variable can also be used in arithmetic expression
Valid unary operators are +,-.Binary operators are +,-,*,/
Examples
&A SETA 10 10 &B SETA 2 2
&C SETA &A + 10/&B 15 &D SETA (&A+10)/&B 10 &A SETA 11 11 &B SETA &A/2 5 &A SETA 1 1 &B SETA &A/2 0
Set Binary
<VAR SYMBOL> SETB <Boolean expression>
IBM 370 ASSEMBLY LANGUAGE 56 / 119
Example &B SETB 1 &A SETB 0
To assign an binary bit value to a SETB symbol
Set Character
<VAR SYMBOL> SETC <expression>
To assign characters value to a SETC symbol
The expression could be
A type attribute reference
A character expression
A sub string notation
A concatenation of sub string notations, or character expressions, or both
A duplication factor can precede any of the first three options
Example: &C SETC 'STRING0' * * &C="STRING0" * &D SETC ‘&C(4,2)’ * * &D = "IN" * &E SETC 'L''SYMBOL' * * &E = "L'SYMBOL" * &F SETC 'HALF&&' * * &F="HALF&" * &G SETC '&D.NER' * * &G="INNER" * &C1 SETC 3('ABC') * * &C1 = ‘ABCABCABC’ *
Example MACRO
&NAME MOVE &TO,&FROM LCLA &A1 LCLB &B1,&B2 LCLC &C1
&B1 SETB (L'&TO EQ 4) &B2 SETB (S'&TO EQ 0) &A1 SETA &B1 &C1 SETC '&B2' &NAME ST 2,SAVEAREA
L 2,&FROM&A1 ST 2,&TO&C1 L 2,SAVEAREA MEND
IBM 370 ASSEMBLY LANGUAGE 57 / 119
Invocation MAIN START 0 HERE MOVE FLDA,FLDB +HERE ST 2,SAVEAREA + L 2,FLDB1 + ST 2,FLDAO + L 2,SAVEAREA
Conditional Branch
<SEQ SYMBOL> AIF (<LOGICAL EXPR>).<SEQ SYMBOL> The logical expression in the operand field is evaluated at pre-assembly time to determine if it is true or false. If the expression is true, the statement named by the sequence symbol in the operand field is the next statement processed. If the expression is false, the next sequential statement is processed by the assembler. Logical operators are EQ,NE,LE,LT,GE,GT Example
AIF (`&C' EQ `YES').OUT .ERROR ANOP . . . .OUT ANOP
Unconditional branch
<SEQ SYMBOL> AGO <SEQ SYM2>
Branches to the statement identified by "SEQ SYM2"
Conditional Assembly Loop Counter
<SEQ SYMBOL> ACTR <ARITHMETIC EXPRESSION>
Set a conditional assembly loop counter either within a macro definition or in open code.
Can appear any where in the program.
Each time AGO or AIF is executed the counter value is decremented by one and if its is zero exit from the macro or stop processing the statements in the open code
Avoids excessive looping
Assembler has a default counter and it is initialised with 4096
NOP
<sequence symbol> ANOP
Performs no operation
Used to define a sequence symbol which can be used in AIF and AGO
Data Attributes <c> 'SYMBOL Attribute Description T Type of the symbol Values returned by assembler are A,V,S,Q For the various address constants B Binary constant C Character constant D,E,L Floating point constant F,H Integer constants
IBM 370 ASSEMBLY LANGUAGE 58 / 119
P Packed decimal constant H Hexadecimal constant Z Zoned decimal constant I Machine instruction M Macro J Control section T EXTRN symbol N Self defining term O undefined (omitted)
L Length of symbol number of bytes C Number of characters contained by the variable symbol N Number of element in a sublist associated with the symbol D Defined attribute, indicates whether or not the symbol has been defined prior
Example MACRO TABLE
LCLA &I &SYSLIST(0) DS 0D .WHILE AIF (&I GT N'SYSLIST).DONE
DC D'&SYSLIST(&I) &I SETA &I+1
AGO .WHILE .DONE MEND
Macro help facility
<name> MHELP <value>
Controls a set of trace and dump facilities
Can occur anywhere in open code or in macro definitions
Remains in effect until superseded by another MHELP statement
More than one facility can be specified Value Function 1 Macro Call Trace 2 Macro Branch Trace 4 Macro AIF Dump 8 Macro Exit Dump 16 Macro Entry Dump 32 Global Suppression 64 Macro Hex Dump 128 Mhelp Suppression
IBM 370 ASSEMBLY LANGUAGE 59 / 119
Example of TPUT MACRO MACRO
&LABEL TPUT &ADDR, X &LEN, X &FULLSCR LCLC &TEMPREG
* AIF ('&LABEL' EQ '').NOLAB
&LABEL DS 0H .NOLAB ANOP .*
AIF ('&ADDR' EQ '').NOADDR AIF ('&ADDR'(1,1) EQ '(').ADDRREG LA 0,&ADDR GET ADDRESS IN R0 AGO .NOADDR
.ADDRREG ANOP &TEMPREG SETC '&ADDR'(2,K'&ADDR-2)
LR 0,&TEMPREG GET ADDRESS IN R0 .NOADDR ANOP .*
AIF ('&LEN'(1,1) EQ '(').LENREG LA 1,&LEN GET LENGTH IN R1 AGO .CONT
.LENREG ANOP &TEMPREG SETC '&LEN'(2,K'&LEN-2)
LR 1,&TEMPREG GET LENGTH IN R1 .* .CONT ANOP
AIF ('&FULLSCR' EQ '').NFS AIF ('&SYSCHARSET' EQ 'E').FLS MNOTE 4,'TPUT OPTION FULLSCR MUST USE EBCDIC CHARACTER SET'
.FLS ANOP SVC 96 MEXIT
.*
.NFS ANOP SVC 94 MEND
IBM 370 ASSEMBLY LANGUAGE 60 / 119
Example of SAVE macro MACRO
&LABEL SAVE ®S, X &T, X &ID
.* AIF ('&LABEL' EQ '').NOLAB
&LABEL DS 0H NOLAB ANOP
AIF ('&ID' EQ '').CONTINU .* This is a macro comment
B 12(15) * This is a normal assembler comment
AIF ('&ID' EQ '*').IDHERE DC CL8'&ID' AGO .CONTINU
.IDHERE ANOP AIF ('&LABEL' EQ '').NOID DC CL8'&LABEL' AGO .CONTINU
.NOID ANOP DC CL8'&SYSECT'
.CONTINU ANOP
.* AIF ('®S' EQ '').NOREGS STM ®S(1),®S(2),12(13)
.NOREGS ANOP MEND
IBM 370 ASSEMBLY LANGUAGE 61 / 119
Example of RETURN macro MACRO
&LABEL RETURN ®S, X &T, X &RC=
.* LCLA &WORK,&VALU
.* AIF ('&LABEL' EQ '').NOLAB
&LABEL DS 0H .NOLAB ANOP .*
AIF ('®S' EQ '').NOREGS AIF (®S(1) GE ®S(2)).RET1 AIF (®S(2) EQ 15).RET1 AIF ('&RC' EQ '').RCT3 AIF ('&RC'(1,1) EQ '(').RCT2 LA 15,&RC
.RCT3 ANOP LM ®S(1),®S(2),12(13) BR 14 MEXIT
.RCT2 ANOP &VALU SETA &RC(1)
LR 15,&VALU LM ®S(1),®S(2),12(13) BR 14 MEXIT
.*
.RET1 ANOP AIF ('&RC' EQ '').RCT4
&WORK SETA (15-®S(1))*4 AIF ('&RC'(1,1) EQ '(').RCT1 LA 15,&RC ST 15,12+&WORK.(13)
.RCT4 ANOP LM ®S(1),®S(2),12(13) BR 14 MEXIT
.RCT1 ANOP &VALU SETA &RC(1)
ST &VALU,12+&WORK.(13) LM ®S(1),®S(2),12(13) BR 14 MEXIT
.*
.NOREGS ANOP AIF ('&RC' EQ '').RCT6 AIF ('&RC'(1,1) EQ '(').RCT5 LA 15,&RC
.RCT6 ANOP BR 14 MEXIT
.RCT5 ANOP &WORK SETA &RC(1)
LR 15,&WORK
IBM 370 ASSEMBLY LANGUAGE 62 / 119
BR 14 MEXIT MEND
IBM 370 ASSEMBLY LANGUAGE 63 / 119
MVS SYSTEM MACROS back
QSAM
DCB Macro
Included for every data set accessed by the program
Access method depends upon the parameters passed to the DCB
All parameters are keyword parameters specifying various options for the data set
Generates non executable code (control block) and should therefore be coded in the data area
Name DCB DDNAME =External DD name in JCL, DSORG =PS | PO, MACRF =((G) | (P) | (G,P),M|L) LRECL =, BLKSIZE=, RECFM =F | FB | FBA | V |VB, DEVD=DA | TA | PR, EODAD=, Notes:- G Get, P Put, G,P Get and PUT M Move mode I/O L Locate mode I/O F Fixed unblocked FB Fixed blocked FBA Fixed blocked with first character as a ASA control character. Used only for printer output V Variable unblocked VB Variable blocked
OPEN Macro Name OPEN (DCB-name{options...})
Logically connect a data set
Data set identified in the DCB is prepared for processing
Option Meaning INPUT Input data set OUTPUT Output data set UPDAT Data set to be updated in place EXTEND Add records to the end of the data set
DISP Disp options (PASS,KEEP,DELETE,CATLG,UNCATLG)
Example OPEN (EMPLOYEE,(INPUT),SALES,(OUTPUT))
CLOSE Macro Name CLOSE (DCB-NAME {,option),...})
Logically disconnect a data set
Option Meaning REREAD Position to the beginning of the data set LEAVE Position to the logical end of the data set REWIND Magnetic tape has to be positioned at the beginning
DISP Disp options like PASS,KEEP,DELETE,CATLG, and UNCATLG
Example CLOSE (EMPLOYEE,SALES)
IBM 370 ASSEMBLY LANGUAGE 64 / 119
GET Macro (QSAM) Name GET DCB-NAME, {area name}
Retrieve the next record
Control is returned after the record is read
In locate mode the address of the record is returned in R1
In move mode the record is moved to the user area
Example GET EMPLOYEE, EMPREC
PUT Macro (QSAM) Name PUT DCB-NAME,{area name}
Write a record.
Control is returned after the record is written
In locate mode the area name parameter is omitted and the system returns the address of the I/O buffer in R 1. The data has to be moved to this area and it is written in the next PUT call.
In moved mode, the system moves the record to an output buffer before the control is returned.
Example PUT EMPLOYEE,EMPREC
Example PRINT CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
OPEN (SYSPRINT,OUTPUT)
LTR 15,15
BNZ OPENERR
LA 5,20
MVC OUTREC+1(132),=CL132'THIS IS LINE ONE.'
LOOP PUT SYSPRINT,OUTCARD
BCT 5,LOOP
CLOSE SYSPRINT
L 13,SAVE+4
RETURN (14,12),,RC=0
OPENERR L 13,SAVE+4
RETURN (14,12),,RC=16
OUTCARD DC AL2(137),AL2(0)
OUTREC DC CL133' '
SYSPRINT DCB DDNAME=SYSPRINT,MACRF=PM,DSORG=PS, X
LRECL=137,BLKSIZE=1370,RECFM=VB
SAVE DS 18F
END
JCL //SYSPRINT DD SYSOUT=*
Memory Management
GETMAIN
IBM 370 ASSEMBLY LANGUAGE 65 / 119
To allocate virtual storage
Can be allocated on double word or page boundary
Storage is not initialised
Storage allocation above or below 16MB line
Use FREEMAIN to release the storage
Register 1 contains the storage address Syntax Name GETMAIN R,LV=lv,BNDRY=bndry,LOC=1oc R Register form LV Length value BNDRY DBLWD/PAGE LOC BELOW/ANY (16MB line)
Example GETMAIN R,LV=4096,BNDRY=PAGE,LOC=ANY Note: More details on GETMAIN are available in the chapter VIRTUAL STORAGE MANAGEMENT
Example This example uses DXD, CXD data types and Q type address constant DXD refers to storage allocated in an external dummy section. A DSECT can also be considered an external dummy section if it is used in a Q type constant. The CXD is initialised by the linkage editor to the sum of the lengths of all external dummy sections in the load module. It is used to getmain storage for the external dummy sections at run time. The Q type address constants are set to the offset of the corresponding dummy sections. ROUTINE A
IBM 370 ASSEMBLY LANGUAGE 66 / 119
A CSECT . L 3,LEN GETMAIN R,LV=(3) LR 11,1 . L 15,=V(C) BALR 14,15 .
L 15,=V(B) BALR 14,15 . AX DXD 2DL8 BX DXD 4FL4 LEN CXD . DC Q(AX) DC Q(BX) . ROUTINE B Name Operation Operand B CSECT . L 3,DOFFS AR 3,11 ST 2,0(0,11) . G DXD 5D D DXD 10F . GOFFS DC Q(G) DOFFS DC Q(D) . ROUTINE C Name Operation Operand E DSECT ITEM DS F NO DS F SUM DS F C CSECT . L 3,EOFFS AR 3,11 USING E,3 ST 9,SUM . . EOFFS DC Q(E) . .
FREEMAIN
Releases the acquired virtual storage
Address should be on a double word boundary
IBM 370 ASSEMBLY LANGUAGE 67 / 119
Syntax Name FREEMAIN R,LV=lv,A=addr
R Register form lv Length value A Virtual storage address
Example FREEMAIN R,LV=4096,A=(1) Note: More details on FREEMAIN are available in the chapter VIRTUAL STORAGE MANAGEMENT
Example of a program that dynamically acquires its working storage and initialises it with
constants from static read only storage. FIRST CSECT
FIRST AMODE 31
FIRST RMODE ANY
STM 14,12,12(13)
BALR 12,0
USING *,12
LR 2,1
GETMAIN R,LV=LEN,LOC=BELOW
ST 13,4(0,1)
USING WS,13
LR 13,1
LR 1,2
MVC WS+72(LEN-72),WSCONST+72
BAL 2,INIT
LOAD EP=ADD
LTR 15,15
BNZ LOADERR
LR 15,0
LA 1,PARM
BASSM 14,15
WTO 'BACK'
L 5,RES
CVD 5,DW
UNPK MSG+2(16),DW
OI MSG+17,X'F0'
WTO 'RESULT IS'
LA 4,MSG
WTO TEXT=(4)
LR 2,13
L 13,SAVE+4
FREEMAIN R,LV=LEN,A=(2)
LM 14,12,12(13)
LA 15,0
BR 14
LOADERR L 13,SAVE+4
LM 14,12,12(13)
LA 15,16
BR 14
WSCONST DS 0F
DS 18F
DC F'100'
IBM 370 ASSEMBLY LANGUAGE 68 / 119
DC F'200'
DS F
DS F
DS F
DS F
DC AL2(16)
DS CL16
DS D
LEN EQU *-WSCONST
INIT DS 0H
LA 3,A
ST 3,PARM
LA 3,B
ST 3,PARM+4
LA 3,RES
ST 3,PARM+8
BR 2
WS DSECT
SAVE DS 18F
A DS F
B DS F
RES DS F
PARM DS F
DS F
DS F
MSG DS AL2
DS CL16
DW DS D
END
ADD CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
LR 2,1
WTO 'IN ADD'
LR 1,2
LM 2,4,0(1)
L 5,0(0,2)
A 5,0(0,3)
ST 5,0(0,4)
WTO 'EXITING ADD'
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BSM 0,14
SAVE DS 18F
END
Program Management
LOAD
Brings the load module into virtual storage
Module contains program or table
IBM 370 ASSEMBLY LANGUAGE 69 / 119
Placed above or below line
Returns
Authorisation code
Length of the module
Entry point to the module
AMODE of the module
Control is not passed to the module
Used in dynamic subroutine call
Modules can be shared
Name LOAD EP=entry name On return to caller the registers contain the following
0 Entry point address of requested load module. The high order bit reflects the load modules AMODE (1 for 31 bit AMODE, else 0 for 24 bit AMODE).
If AMODE is any then the bit reflects callers AMODE. 15 Zero if no error, else reason code
Example LOAD EP=MYPROG LTR 15,15 BNZ ERROR LR 15,0 stick to using register 15 for entry point BSSM 14,15 BSSM takes care of switch of AMODE if reqd. An important point to note is that if the module has already been loaded into the callers address space because of a earlier request ( Possibly from some asynchronous exit routine) then control is given to the existing copy of the module. Since we branch to the entry point directly, we can have a problem if the module is in use and it is not re-entrant or is only serially reusable. For this reason XCTL or LINK is preferred as the control is passed via system which checks for this possible source of error.
DELETE
Remove a module from virtual storage
Entry name same as used in load macro
Task termination removes the module
Name DELETE EP=entry name Register 15 is zero on successful completion.
CALL Name CALL entry-name | (n),(parm1,parm2,….),VL Notes Control returns only after called program returns. Hence register 15 reflects return code of called program If entry name is used, the called program gets link edited into the main program (caller) at linking time
XCTL
To transfer control to another module
Module loaded if not in virtual storage
Handles the addressing mode
Control does not return back name XCTL (reg1,reg2), EP=entry name, PARAM=(parm1,parm2,…),VL=1, MF=(E, user area | (n))
IBM 370 ASSEMBLY LANGUAGE 70 / 119
Notes:- The reg1,reg2 indicates the registers that are to be restored from save area before the called routine gets control . Usually coded (2,12). MF=(E,User area). User area points to an area where the parameter list can be generated .Since the transfer is through the system, the system takes care of the AMODE switch if required. The system also takes care of re-entrancy of the module transferred to. Control does not return back to caller in any case.
Example: XCTL (2,12),EP=MYPROG,MF=(E,ADDRDATA) . . ADDRDATA DC A(PARM1) DC A(PARM2)
LINK
To pass control to an entry point
Module loaded if not in virtual storage
Handles the addressing mode
Parameter list could be passed
Control returns back
Error handling could be specified
Name LINK EP=entry name, PARAM=(parm1,parm2,…..),VL=1, ERRET=errroutine Called routine gets control with the following values in the register
1 address of parameter list
15 Entry address of called program
If the link was unsuccessful the error routine gets control with the following
1 Abend Code that would have been issued if the caller had not provided error exit
2-12 unchanged
15 Address of the error exit
14 used as work register by system
Example LINK EP=MYPROG,PARAM=(parm1,parm2), ERRET=ERROR . . PARM1 DS F PARM2 DS F ERROR …
Process Management
ABEND Name ABEND compcode,REASON=,DUMP,STEP compcode value 0 to 4095.Register notation (2) to (12) permitted REASON This code is passed to subsequent user exits if specified. 32 bit hexadecimal
value or 31 bit decimal number DUMP Requests a dump of virtual storage assigned to task. Needs //SYSABEND, //SYSDUMP or //SYSUDUMP DD statement to be present in the JCL for the job step. STEP Requests all tasks associated with this Job step of which this task is a part to abend
ATTACH
IBM 370 ASSEMBLY LANGUAGE 71 / 119
To create a new task
New task is the subtask
Parameter list could be passed
ECB can be provided
Limit priority same as that of the creating task
Dispatching priority same as that of the creating task
Use DETACH macro to remove the sub task
Returns TCB address in reg 1 Name ATTACH EP=entry name,
PARAM=(parm1,parm2,…), VL=1, ECB=ecb addr, EXTR=Address of end of task routine
Registers on entry to subtask are
0 Used as work area by system
1 Used by macro to point to parameter list
2-12 Used as work regs by System
13 Should point to a 18F save area in callers module
14 Return address. Bit 0 is 0 if subtask gets control in 24 bit mode else 1 if subtask gets control in 31 bit mode
15 Entry point address of subtask Registers on return to caller after issue of ATTACH
1 address of TCB of subtask
15 A return code of non zero means subtask could not be attached Load Libraries searched are
Job pack area
Requesting tasks task library and all unique task libraries of parent tasks
Step library
Job library
Link Pack area
Link Library In simplest form usage can be : ATTACH EP=PROG1,ECB=ECB1 ECB1 DS F Notes:-
This macro creates a separate thread of execution in callers address space
Within the Address space this subtask will compete for processor resources 1) There is a despatching priority for address space 2) At a lower level there is a despatching priority for the subtasks
The attaching task has to wait for subtasks to end before terminating else it will abend when attempting to terminate
The attaching task has to wait on the ECB which is posted by the system when the subtask ends
The attaching task then issues a DETACH macro.
EXTR exit routine gets control with the following register values
0 used as a work register by the system
1 Address of TCB of subtask. Needed for issuing DETACH macro
2-12 Work registers
13 18F save area provided by system
14 return address
IBM 370 ASSEMBLY LANGUAGE 72 / 119
15 entry point of exit routine
DETACH
Removes a subtask
If issued before task completion, terminate the task
Should be issued if ECB or ETXR is used in ATTACH
Removing a task removes all its dependent tasks also
If ECB or ETXR is used, and the parent task does not issue DETACH, then the parent task will abend
Name DETACH tcb address | (n) Operand can be in register notation in which case regs 1 thru 12 may be used. The TCB address should have been previously obtained by EXTR exit routine
Example ATTACH EP=PROG1,EXTR=ENDOFTSK LTR 15,15 BNZ ERROR ST 1,TCB1 save address of TCB for later use
. . TCB1 DC F'0' ENDOFTSK DETACH (1) BR 14
WAIT
Wait for completion of events
Initialise the ECB before calling
A list of ECB’s can be specified for waiting on any number of events
Example of MAIN creating two subtasks TASK1 and TASK2 FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
WTO 'MAIN1 STARTING'
ATTACH EP=TASK1,ECB=ECB1
LTR 15,15
BNZ ERROR1
ST 1,TCB1
ATTACH EP=TASK2,ECB=ECB2
LTR 15,15
BNZ ERROR2
ST 1,TCB2
WTO 'MAIN1 ENTERING WAIT FOR TASK1 COMPLETION'
WAIT ECB=ECB1
WTO 'MAIN1 ENTERING WAIT FOR TASK2 COMPLETION'
WAIT ECB=ECB2
LA 4,TCB1
IBM 370 ASSEMBLY LANGUAGE 73 / 119
DETACH (4)
LA 4,TCB2
DETACH (4)
L 13,SAVE+4
RETURN (14,12),,RC=0
ERROR1 L 13,SAVE+4
RETURN (14,12),,RC=4
ERROR2 L 13,SAVE+4
RETURN (14,12),,RC=8
SAVE DS 18F
ECB1 DC F'0'
ECB2 DC F'0'
TCB1 DS F
TCB2 DS F
END
TASK1 CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
LA 5,50
LOOP WTO 'TASK1 REPORTING'
BCT 5,LOOP
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
END
TASK2 CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
LA 5,50
LOOP WTO 'TASK2 REPORTING'
BCT 5,LOOP
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
END
RETURN Name RETURN (reg1,reg2),T,RC=retcode restores reg1 to reg2 from save area pointed by R13 T sets a flag in the save area in the called program for dump analysis if required Maximum value for return code is 4095 which is set in R15
(see example of implementation under MACROS and conditional assembly)
IBM 370 ASSEMBLY LANGUAGE 74 / 119
SAVE Name SAVE (reg1,reg2) Saves reg1 thru reg2 in save area pointed to by R13
(see example of implementation under MACROS and conditional assembly)
REENTERABILITY For load modules which may be shared amongst more than one concurrent task, re-entrancy is important. Most macros (in standard form) generate an inline parameter list of data areas which are used for passing as well as receiving information from the macro call. Obviously inline parameter list makes the load module non re-entrant and at best serially re-entrant. For this reason to make a load module re-entrant, do not define data areas in the program which will be part of the load module. Instead at run time (using GETMAIN or STORAGE OBTAIN) to dynamically acquire storage. A typical example of this would be to acquire the 18 full word save area dynamically. Where the acquired area needs to be accessed by field you can use a DSECT to format the block of storage. As for MACROS IBM provides, apart from standard form which develops inline parameter lists,
LIST and EXECUTE (MF=L or MF=E) form of the macro exist. The list form does not generate any executable code. Instead it generates only a parameter list. At run time you acquire storage equivalent in size to this list and copy the list to this area. This way each thread of execution will have it's own discrete parameter area. At run time use the execute for of the macro (which can also be used to change some of the parameters generated earlier) with a pointer to the parameter list built up in virtual storage. The list form of the macro is signalled to the assembler by the parameter MF=L The execute form is signalled to the assembler by using the parameter MF=E
Example . . LA 3,MACNAME load address of the list generated LA 5,NSIADDR load address of end of list SR 5,3 GPR5 will now have length of list BAL 14,MOVERTN go to rtn to move list DEQ ,MF=(E,(1)) GPR1 points to parm list, execute form . . processing here . BR 14
* acquire storage sufficient to hold the list MOVERTN GETMAIN R,LV=(5) LR 4,1 address of area in gpr4 BCTR 5,0 subtract 1 from gpr5 EX 5,MOVEINST BR 14 MOVEINST MVC 0(0,4),0(3) change the length field and copy the list MACNAME DEQ (NAME1,NAME2,8,SYSTEM),RET=HAVE,MF=L NSIADDR EQU * NAME1 DC CL8'MAJOR' NAME2 DC CL8'MINOR'
Example using WTO FIRST CSECT
IBM 370 ASSEMBLY LANGUAGE 75 / 119
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
GETMAIN R,LV=LMSG
LR 2,1
LA 3,MSG
LA 4,LMSG
BCTR 4,0
EX 4,MV
WTO ,MF=(E,(2))
LA 13,SAVE
L 13,SAVE+4
LM 14,12,12(13)
SR 15,15
BR 14
SAVE DS 18F
MV MVC 0(0,2),0(3)
MSG WTO 'THIS IS THE MESSAGE',MF=L
LMSG EQU *-MSG
END
Re-entrancy and writable storage FIRST CSECT
STM 14,12,12(13)
BALR 12,0
USING *,12
LR 2,1
GETMAIN R,LV=WSLENGTH,LOC=BELOW
USING WS,1
ST 13,SAVE+4
LA 13,SAVE
DROP 1
LR 13,1
LR 1,2
USING WS,13
WTO 'ASM1 REPORTING'
MVC MSG+2(6),=C'ABCDEF'
LA 6,6
STH 6,MSG
LA 6,MSG
WTO TEXT=(6)
LA 15,4
LR 2,13
L 13,SAVE+4
FREEMAIN R,LV=WSLENGTH,A=(2)
L 14,12(0,13)
LM 0,12,20(13)
BR 14
WS DSECT
SAVE DS 18F
MSG DS AL2
DS CL100
WSLENGTH EQU *-WS
IBM 370 ASSEMBLY LANGUAGE 76 / 119
END
IBM 370 ASSEMBLY LANGUAGE 77 / 119
ACCESSING VSAM DATA SETS USING ASSEMBLER LANGUAGE back
Macros
Name ACB AM=VSAM,
BUFND=,
BUFNI=,
BUFSP=,
DDNAME=,
MACRF=([ADR],[,CNV][,KEY][,DIR][,SEQ][,SKP][,IN][,OUT] )
EXLST=,
PASSWD=,
NOTES: AM : Always code VSAM for access to VSAM data sets BUFND : Number of data buffers, default=2,override possible through JCL BUFNI : Number of Index buffers, default=1,override possible through JCL BUFSP : Size of area for Index and Data Buffers. Defaults to specification in catalogue DDNAME : Connects a DD statement in run time JCL with this ACB EXLST : Address of EXLST macro MACRF : ADR Access by RBA CNV Access by Control Interval KEY Access by Record Key DIR Direct Processing SEQ Sequential Processing
SKP Skip Sequential Processing IN Input only OUT Input / Output PASSWD : Address(label) of an area which contains password for the Data
set Note: This macro generates a control block and should therefore be placed in Data area of your program
Name EXLST [AM=VSAM]
[,EODAD=(address[,A|N][,L] )]
[,JRNAD=(address[,A|N][,L] )]
[,LERAD=(address[,A|N][,L] )]
[,SYNAD=(address[,A|N][,L] )]
Notes EODAD Is the exit routine for end of file JRNAD exit routine for journal file updates/deletions/insertions LERAD Logical error exit SYNAD Physical error exit A Routine is active N Routine is inactive L Routine is to be dynamically loaded when required
Name RPL ACB=,
AREA=,
AREALEN=,
RECLEN=,
ARG=,
KEYLEN=,
OPTCD=,
NXTRPL=
IBM 370 ASSEMBLY LANGUAGE 78 / 119
NOTES : ACB : Address of ACB macro (label) AM : Always code VSAM (used for documentation purposes only) AREA : In move mode address of work area for record (label of data area)
: In locate mode is used by VSAM to set address of record in VSAM buffer
AREALEN : Length of work area. In locate mode will be at least 4.(Full word) RECLEN : For a PUT request is length of record for variable length record
: For a GET request is updated by VSAM to indicate length of record read
ARG : Label of Argument Field (Key | RBA) field used with GET,PUT, : POINT KEYLEN : Used to specify key length if Generic key is used (OPTCD=GEN) NXTRPL : address of next RPL in chain if chained RPL'S are used. OPTCD : ( [ADR|CNV|KEY],[DIR|SEQ|SKP],[FWD|BWD],[ARD|LRD],
: [NSP|NUP|IPD],[LOC|MVE],[ASY|SYN],[KEQ|KGE], : [FKS|GEN]) :
: ADR Access by RBA : CNV Access by control interval : KEY Access by record key : : DIR Direct processing : SEQ Sequential Processing : SKP Skip sequential processing : : FWD Forward Sequential processing : BWD Backward Sequential processing : ARD Start sequential processing forward or backward with the : record identified by the ARG field : LRD For Backward processing start from the last record in the file : NSP No updating(for Direct processing VSAM is positioned at : the next record in the file). : NUP No updating, VSAM is not positioned for subsequent
: processing : UPD Retain position for Updating : LOC Locate mode I/O(record is processed in VSAM Buffers) : MOV Move mode I/O(records are processed in programs data area) : ASY Asynchronous operation. Program can continue with : other processing. Later uses CHECK macro to wait on : completion : SYN synchronous operation. Program waits until operation is : complete : FKS full key search : GEN generic search. KEYLEN must be specified
: KEQ search key equal : KGE search key greater than or equal.
You can code only one option from each group
The options must be consistent with one another and with ACB parameters
IBM 370 ASSEMBLY LANGUAGE 79 / 119
The first two groups correspond to the MACRF parameter in the ACB macro
The third group specifies direction of processing
The fourth group specifies whether processing is to start with last record in file or record identified by the ARG field
The fifth group specifies whether the record is being read with intention to update. If not which record is to be read next.
The last group specifies whether the MOVE or LOCATE mode of I/O is to be used.
This macro generates a control block and should therefore be placed in Data area of your program
OPEN Address of ACB Macro
CLOSE Address of ACB Macro
GET RPL=Label of RPL macro | (register) retrieve a record
PUT RPL=Label of RPL macro | (register) write a record
POINT RPL=Label of RPL macro | (register) position for subsequent access
ERASE RPL=Label of RPL macro | (register) Delete a record
Note : These MACROS generate executable code and should therefore be in the Instruction area of the Program
MACROS FOR CONTROL BLOCK MANIPULATION.
SHOWCB This macros is fetch control block fields
TESTCB This macro is used to test control block fields
MODCB This macro used to modify control block fields
GENCB This macro is used to dynamically generate a control block at run time
Name SHOWCB ACB|EXLST|RPL=,
AM=VSAM, only for documentation purpose
AREA=,
LENGTH=,
FIELDS=(keyword[,keyword]…)
Notes: ACB|EXLST|RPL : Address (label) of specified Macro AREA : Area into which VSAM will put the contents of field specified LENGTH : Length of Data area specified under AREA. Each field of the
ACB|EXLST|RPL macro fields are 4 bytes long except : DDNAME which is 8 bytes
FIELDS : Can be most of any field specified in the ACB|EXLST|RPL macro; FOR RPL : ACB,AREA,AREALEN,FDBK,KEYLEN,RECLEN
: RBA,NXTRPL all one full word of data FOR EXLST : EODAD,JRNAD,LERAD,SYNAD FOR ACB : ACBLEN length of ACB
Can be attributes of an open file as below AVSPAC number of bytes of available space BUFNO Number of buffers in use for this file CINV Size of Control Interval FS Percent of Free control intervals KEYLEN Length of key field
IBM 370 ASSEMBLY LANGUAGE 80 / 119
LRECL Maximum record length NCIS Number of Control Interval Splits NDELR Number of deleted records from file NEXT Number of Extents allocated to file NINSR Number of records inserted in file NLOGR Number of records in file NRETR Number of records retrieved from file NUPDR Number of records updated in file RKP Position of record key relative to start of record
Name TESTCB ACB|EXLST|RPL=,
AM=VSAM, only for documentation purpose
ERET=,
keyword=,
OBJECT= ACB|EXLST|RPL : Address(label) of any of the control block macros ERET : Address of error handler to be executed if test cannot be executed keyword : Any field of the ACB,EXLST,RPL,GENCB macro; The length of any ACB,EXLST,RPL macro using the keywords ACBLEN,EXLLEN,RPLLEN OBJECT : DATA or INDEX
Example TESTCB RPL=RPL1,FDBK=8 BE DUPKEY . . .
RPL1 RPL …. Notes: Some common VSAM FDBK codes are 8 Duplicate key 12 Record out of sequence 16 No record found 68 Access requested does not match access specified 92 A put for update without a corresponding get for update 104 Invalid or conflicting RPL options
Name MODCB ACB|EXLST|RPL=,
AM=VSAM, only for documentation purpose
Operand keyword= new value
Example: MODCB RPL=RPL1,OPTCD=(DIR) . . . RPL1 RPL …. FRAMEWORK OF ASSEMBLER PROGRAMS TO ACCESS VSAM FILES Keyed Direct Deletion
IBM 370 ASSEMBLY LANGUAGE 81 / 119
DELETE ACB MACRF=(KEY,DIR,OUT) LIST RPL ACB=DELETE,AREA=WORK,AREALEN=50, X ARG=KEYFIELD,OPTCD=(KEY,DIR,SYN,UPD, X
MVE,FKS,KEQ) . . LOOP MVC KEYFIELD,source GET RPL=LIST LTR 15,15 BNZ ERROR . . B LOOP if you do not want to delete this record ERASE RPL=LIST LTR 15,15 BNZ ERROR ERROR ….. WORK DS CL50 KEYFIELD DS CL5 Note that when you GET a record with UPD in the OPTCD option of the RPL vsam maintains position after the get anticipating either an ERASE or PUT (update). Instead if you issue a GET it goes ahead with the GET and position for the previous record is lost.
Example Keyed Sequential retrieval (Forward) INPUT ACB MACRF=(KEY,SEQ,IN) RETRVE RPL ACB=INPUT,AREA=IN,AREALEN=100, X OPTCD=(KEY,SEQ,SYN,NUP,MVE) LOOP GET RPL=RETRVE LTR 15,15 BNZ ERROR . . process the record B LOOP ERROR …… error handler . IN DS CL100 Example Keyed sequential retrieval (backward) INPUT ACB DDNAME=INPUT,EXLST=EXLST1 RETRVE RPL ACB=INPUT,AREA=IN,AREALEN=100, X OPTCD=(KEY,SEQ,LRD,BWD) EXLST1 EXLST EODAD=EOD POINT RPL=RETRVE LTR 15,15 BNZ ERROR LOOP GET RPL=RETRVE LTR 15,15 BNZ ERROR . . process the record here
IBM 370 ASSEMBLY LANGUAGE 82 / 119
B LOOP EOD EQU * . . come here for end of file ERROR . . come here for any error . IN DS CL100 Example Skip Sequential retrieval ksds variable length records
GENCB BLK=ACB,DDNAME=INPUT,MACRF=(KEY,SKP,IN) LTR 15,15 BNZ ERROR LR 2,1 GENCB BLK=RPL,ACB=(2),AREA=RCDADDR, X
AREALEN=4, X ARG=SRCHKEY, X
OPTCD=(KEY,SKP,SYN,NUP,KGE,FKS,LOC) LTR 15,15 BNZ CHECK0
LR 3,1 . LOOP MVC SRCHKEY,source GET RPL=(3) LTR 15,15 BNZ ERROR SHOWCB AREA=RCDLEN,FIELDS=RECLEN,LENGTH=4, X RPL=(3) LTR 15,15 BNZ CHECK0 . B LOOP ERROR …. CHECK0 …. RCDADDR DS F SRCHKEY DS CL8 RCDLEN DS F Example Keyed Direct Retrieval in LOCATE mode(KSDS, RRDS) INPUT ACB MACRF=(KEY,DIR,IN) RETRVE RPL ACB=INPUT,AREA=IN,AREALEN=4,OPTCD=(KEY, X DIR,SYN,NUP,KEQ,GEN,LOC),ARG=KEYAREA, X KEYLEN=5 . . LOOP MVC KEYAREA,source GET RPL=RETRVE LTR 15,15 BNZ ERROR . Address of record is now in IN . B LOOP
IBM 370 ASSEMBLY LANGUAGE 83 / 119
ERROR ….. . IN DS CL4 Where VSAM puts the address of the record in the I/O buffer KEYAREA DS CL5 Notes: In LOCATE mode (LOC) there is no transfer of the record from the VSAM buffer to the data area in your program. Instead VSAM supplies your program the address of the record in the VSAM (Control Interval) buffer. When Generic (GEN) is specified also specify KEYLEN=, and condition like KEQ. VSAM positions at first record which meets the condition. To continue in the sequence
Change to sequential mode and issue GET(s).
Or use GET with KGE using the key of the current record
If the data set is a RRDS the ARG field the search argument is a relative record number Example Switch from Direct to Sequential retrieval INPUT ACB MACRF=(KEY,DIR,SEQ,IN) RETRVE RPL ACB=INPUT,AREA=IN,AREALEN=100, X OPTCD=(KEY,DIR,SYN,NSP,KEQ,GEN,MVE), X ARG=KEYAREA,KEYLEN=8 . . LOOP MVC KEYAREA,source LOOP1 GET RPL=RETRVE direct get LTR 15,15 BNZ ERROR . SHOWCB RPL=RETRVE,AREA=FDBAREA,FIELDS=FDBK LTR 15,15 CLI ERRCD,8 If 8 means duplicate records BE SEQ B LOOP SEQ MODCB RPL=RETRVE,OPTCD=SEQ * * switched to sequential mode * LTR 15,15 BNZ ERROR SEQGET GET RPL=RETRVE LTR 15,15 BNZ ERROR . SHOWCB RPL=RETRVE,AREA=FDBAREA,FIELDS=FDBK LTR 15,15 BNZ ERROR CLI ERRCD,8 * check to see if still need sequential mode BE SEQGET * if not switch back to direct mode * DIR MODCB RPL=RETRVE,OPTCD=DIR LTR 15,15 BNZ ERROR B LOOP ERROR …..
IBM 370 ASSEMBLY LANGUAGE 84 / 119
IN DS CL100 KEYAREA DS CL8 FDBAREA DS 0F DS 1C TYPECD DS 1C CMPCD DS 1C ERRCD DS 1C Example Position with POINT macro BLOCK ACB DDNAME=IO POSITION RPL ACB=BLOCK,AREA=WORK,AREALEN=50, X ARG=SRCHKEY,OPTCD=(KEY,SEQ,SYN,KEQ,FKS) LOOP MVC SRCHKEY,source POINT RPL=POSITION LTR 15,15 BNZ ERROR LOOP1 GET RPL=POSITION LTR 15,15, BNZ ERROR . process record . B LOOP1 continue in sequential mode ERROR …. SRCHKEY DS CL5 WORK DS CL50 Example Keyed Sequential insertion KSDS variable length BLOCK ACB DDNAME=OUTPUT,MACRF=(KEY,SEQ,OUT) LIST RPL ACB=BLOCK,AREA=BUILDRCD,AREALEN=250, X OPTCD=(KEY,SEQ,SYN,NUP,MVE) LOOP L 2,source-length MODCB RPL=LIST,RECLEN=(2) * * alter record length field * LTR 15,15 BNZ ERROR PUT RPL=LIST LTR 15,15
BNZ ERROR B LOOP
ERROR ……. BUILDRCD DS CL250 Example Skip Sequential insertion for KSDS variable length record OUTPUT ACB MACRF=(KEY,SKP,OUT) RPL1 RPL ACB=OUTPUT,AREALEN=80, X
OPTCD=(KEY,SKP,SYN,NUP,MVE), X AREA=WORK
* * set up record in WORK *
IBM 370 ASSEMBLY LANGUAGE 85 / 119
LOOP PUT RPL=RPL1 LTR 15,15 BNZ ERROR . set up next record B LOOP ERROR ….. WORK DS 80C Note:In skip sequential insertion you do not need to have a ARG field with key value. However records have to be in sequence. Example Keyed direct insertion OUTPUT ACB MACRF=(KEY,DIR,OUT) RPL1 RPL ACB=OUTPUT,AREALEN=80, X
OPTCD=(KEY,DIR,SYN,NUP,MVE), X AREA=WORK
* * set up record in WORK * LOOP PUT RPL=RPL1 LTR 15,15 BNZ ERROR * set up next record B LOOP ERROR ….. WORK DS 80C Note VSAM extracts the keyfield from the record area. Example Keyed Direct Update INPUT ACB NACRF=(KEY,DIR,OUT) UPDTE RPL ACB=INPUT,AREA=IN,AREALEN=120, X OPTCD=(KEY,DIR,SYN,UPD,KEQ,FKS,MVE), X ARG=KEYAREA,KEYLEN=5 * * set up search argument * LOOP GET RPL=UPDTE LTR 15,15 BNZ ERROR SHOWCB RPL=UPDTE,AREA=RLNGTH,FIELDS=RECLEN, X LTR 15,15 BNZ ERROR * * update the record * does the new record have a different length BE STORE If not go to PUT L 5,length set R5 for new length MODCB RPL=UPDTE,RECLEN=(5) LTR 15,15 BNZ ERROR STORE PUT RPL=UPDTE LTR 15,15
IBM 370 ASSEMBLY LANGUAGE 86 / 119
BNZ ERROR B LOOP ERROR ….. IN DS CL120
KEYAREA DS CL5
RLGTH DS F
FULL EXAMPLE 1 SEQUENTIAL READ. PGMNAM START 0 BEGIN SAVE (14,12) BALR 3,0 USING *,3 ST 13,SAVE+4 LA 13,SAVE OPEN (ACB1) LTR 15,15 set CC based on value in register 15 BNZ OPENERR and test for open error . . LOOP GET RPL=RPL1 LTR 15,15 set CC based on value in register 15 BNZ READERR and test for read error . Process record here . B LOOP CLOSE (ACB1) L 13,SAVE+4 RETURN (14,12) ACB1 ACB AM=VSAM,MACRF=IN RPL1 RPL ACB=ACB1,AREA=REC1,AREALEN=80,RECLEN=80 REC1 DS CL80 SAVE DS 18F END BEGIN FULL EXAMPLE 2 DIRECT RETRIEVAL FOR UPDATE. EXAMPLE START 0 BEGIN SAVE (14,12) BALR 3,0 USING *,3 ST 13,SAVE+4 LA 13,SAVE OPEN (ACB1) LTR 15,15 BNZ DUMP no point continuing if file will not open LOOP MVC ITEMKEY,… Set up record key GET RPL=RPL1 now fetch record LTR 15,15 BNZ ERROR if error check what error . . modify record as desired . PUT RPL=RPL1 LTR 15,15 BNZ DUMP at this stage any error is unexpected .
IBM 370 ASSEMBLY LANGUAGE 87 / 119
. B LOOP CLOSE (ACB1) LTR 15,15 BNZ DUMP error closing files is serious L 13,SAVE+4 RETURN (14,12) ERROR TESTCB RPL=RPL1,FDBK=16 any error other than no BE LOOP record found is serious DUMP ABEND 1000,DUMP REC1 DS CL80 ITEMKEY DS CL6 SAVE DS 18F ACB1 ACB AM=VSAM,MACRF=(DIR,OUT) RPL1 RPL ACB=ACB1,AREA=REC1,AREALEN=80,RECLEN=80, X
ARG=ITEMKEY,OPTCD=(DIR,UPD)
IBM 370 ASSEMBLY LANGUAGE 88 / 119
LINKAGE CONVENTIONS / 31 BIT ADDRESSING back LINKAGE CONVENTIONS
Another program can be invoked through BALR, BASR, BASSM or LINK, XCTL and CALL macros
A primary mode program is one which operates in primary Address Space Control mode or primary ASC for short. In this mode access of machine instructions is only in the primary address space. All your application programs run in this mode. System programs, like the DB2 subsystem, etc can switch to Address Space modes.
The called program needs to save the registers when it receives control and restore them when returning. For this the caller provides a 18 Full word save area pointed to by R13.
When caller provides a 18F save area the area is used as below Word Usage 0 Used by language products 1 Address of previous ( caller) save area 2 Address of next save area 3 GPR14 4 GPR15 5-17 GPR0-12
Example of using the caller provided save area
Calling program linkage L 15,=A(PGM) BALR 14,15
Called program linkage PGM CSECT PGM AMODE 31 PGM RMODE ANY STM 14,12,12(13) save callers registers in callers save area LR 12,15 set up base register USING PGM,12 GETMAIN RU,LV=72 obtain save area ST 13,4(,1) and store callers R13 point in it ST 1,8(,13) store this programs save area in callers save area LR 13,1 set R13 to point to this save programs area . . . LR 2,13 Set R1 to the address of this programs save area L 13,4(,13) set R13 to point to callers save area FREEMAIN RU,A=(2),LV=72 release this programs save area SR 15,15 Zero R15 L 14,12(0,13) Restore R14 of caller LM 2,12,28(13) Restore R2 to R12 of caller
BR 14 Return END
Primary mode program which uses Linkage stack must do the following
On entry:-
Save callers registers 14 thru 12 in the save area pointed to by R13 + 12 bytes Offset.
Establish a GPR as a base register.
Establish a base area of 18 Full words of its own.
IBM 370 ASSEMBLY LANGUAGE 89 / 119
Save callers R13 into our own save area + 4.
Set GPR 13 to point to its own save area
Set our save area address into callers save area + 8 (optional).
On exit
Place parameter information that may be returned to caller in R1, R0
Load R13 with callers save area address and restore R0-R12,R14
Load R15 with return code
Issue the BR R14 instruction.
Passing Parameters
If the calling program is in primary mode, the parameter list should be in primary address space
Use R1 to point to a parameter list which is an array of 32 bit addresses which point to parameters.
The last element of the array should have bit 0 set to 1 to indicate it is the last element.
In Primary Mode
Example if control is passed to another program in same mode. L 15,NEXTADDR CNOP 0,4 BAL 1,GOOUT PARMLIST DS 0A DCBADDRS DC A(INDCB) DC A(OUTDCB) ANSWERAD DC A(AREA+X'80000000) NEXTADDR DC V(NEXTPGM) GOOUT BALR 14,15 RETURN . . ARE DC 12F'0'
Addressing
AMODE is the mode in which a program expects to receive control. AMODE = 31 means that the program expects to receive control in 31 bit mode (bit 32 of PSW on) and any addresses are passed as 32 bit values with bit 0 on to represent 31 bit addressing mode. AMODE = 24 means that the program expects to receive control in 24 bit addressing mode. In this case the high order 8 bits are not reckoned for computing the effective address. The mode of operation affects operation of some machine instructions like
BAL, BALR, LA
GPR1
A(PARM1)
A(PARM2)
A(PARM3)
1 A(PARMN)
2 BYTE LENGTH PARM FIELD -----------
2 BYTE LENGTH PARM FIELD-------------
IBM 370 ASSEMBLY LANGUAGE 90 / 119
In the case of BAL and BALR, in 24 bit mode the link register (first operand) which contains the return address in low order 24 bits, has the high order 8 bits set to the ILC (Instruction length code, CC (Condition code) and Program mask. When in 31 bit addressing mode the link register has bit 0 set to 1 and rest of the 31 bits represent the address. In the case of LA, in 24 bit mode the high order 8 bits are cleared and low order 24 bits are set to represent a 24 bit address. In 31 bit mode, bit 0 is set to 0 and rest of the bits represent a 31 bit address.
RMODE of a program indicate where it can be loaded by the system for execution. A RMODE of any indicates it can be loaded either above or below what is known as the 16MB line or simply the line. A RMODE of 24 indicates that it is to be loaded only below the line. AMODE and RMODE can be set in the assembler source as below: MAIN CSECT MAIN AMODE 31 AMODE can be 24 / 31 / any.Default=24 MAIN RMODE 24 RMODE can be 24 or any.Default=24. Note that the attributes are propagated by the assembler, Linkage editor to the Directory entry for the load module in the PDS. The following instructions are used for linkage:-
BAL Branch and Link
BAL Branch and Link Register
BAS Branch and Save
BASR Branch and Save register
BSM Branch and Set mode
BASSM Branch and save and set mode
BAS and BASR perform as BAL and BALR when in 31 bit mode
BSM provides an unconditional branch to the address in operand 2, saves the current AMODE in the high order bit of the Link register (operand 1) and sets the AMODE to agree with the high order bit in the to address.
BASSM does all that BSM does and in addition the link register contains the return address.
If we need to transfer control without a change of addressing mode use the following combinations
Transfer Return BAL/BALR BR BAS/BASR BR
If we need to change the AMODE as well use BASSM
Example TEST CSECT TEST AMODE 24 TEST RMODE 24 . . L 15,EPA Obtain transfer address BASSM 14,15 switch AMODE and branch . . EXTRN EP1 EPA DC A(X'80000000+EP1) set high order bit to 1 to switch AMODE . . END
IBM 370 ASSEMBLY LANGUAGE 91 / 119
EP1 CSECT EP1 AMODE 31 EP1 RMODE ANY . . SLR 15,15 set return code to 0 BSM 0,14 return and switch to callers AMODE END
31 Bit addressing
A 370/XA or a 370/ESA processor can operate in 24 or 31 bit mode (Bimodal operation).
The following kinds of programs must operate below the 16MB line
Programs with AMODE 24
Programs with AMODE any
Programs that use system services that require their callers to be in 24 bit mode
Programs that use system services that require their caller to have RMODE 24
Programs that must be addressable by 24 bit callers
Rules and conventions for 31 bit operation
Addresses are treated as 31 bit values
Any data passed by a program in 31 bit mode to a program in 24 bit mode must lie below the 16MB line
The A mode bit affect the way some H/W instructions work (BAL,BALR,LA,LRA)
A program must return control in the same mode in which it gained control
A program expects a 24 bit address from a 24 bit mode program and 31 bit addresses from a 31 bit mode program
A program must validate the high order byte of any address passed by a 24 bit mode program before using it as an address in 31 bit mode.
CALL, BALR
LINK, XCTL, ATTACH
At Execution time only the following combinations are valid
AMODE 24, RMODE 24
AMODE 31,RMODE 24
AMODE 31,RMODE any
AMODE/RMODE can be controlled and set at following levels
In the assembler source MAIN CSECT MAIN AMODE 31 MAIN RMODE 24
In the EXEC statement invoking the linkage editor
Calling module
amode 24
rmode 24
Called module
amode 24
rmode 24
Calling module
amode 24
rmode 24
Called module
amode 31
rmode 24
IBM 370 ASSEMBLY LANGUAGE 92 / 119
//LKED EXEC PGM=HEWL,PARM='AMODE=31,RMODE=24'
Linkage editor control statement MODE AMODE(31),RMODE(24)
The Linkage editor creates indicators in the load module from inputs from Object Decks and Load modules input to it
It indicates the attributes in the PDS member to reflect PARM and LKED control statements.
System obtains the AMODE and RMODE information from the PDS entry.
MVS support for AMODE and RMODE
MVS obtains storage for the module as indicated in RMODE
ATTACH,LINK,XCTL gives control as per the AMODE
LOAD brings in a module into storage as per it's RMODE and sets bit 0 in R0 to indicate the AMODE
CALL passes control in the AMODE of its caller
Programs in 24 bit mode can switch mode to access data above 16MB line as follows
Example USER CSECT USER AMODE 24 USER RMODE 24 L 15,ACTLB L 1,LABEL1 BSM 0,1 LABEL1 DC A(LABEL2+X'80000000) LABEL2 DS 0H L 2,4,(,15) LA 1,LABEL3 BSM 0,1 LABEL3 DS 0H . . END
IBM 370 ASSEMBLY LANGUAGE 93 / 119
OK
OK OK
16 MB LINE
OK
16 MB line definitely a problem
possible problem
possible problem
AMODE 31 AMODE 31
AMODE 31 AMODE 31
AMODE 31 AMODE 31
AMODE 24
AMODE 24
AMODE 31
IBM 370 ASSEMBLY LANGUAGE 94 / 119
16MB LINE
The above method can be used for dynamic loading and branching to a module with a different AMODE. The following example indicates how to make a static call where the called module has a different AMODE.
Example RTN1 CSECT EXTRN RTN2AD EXTRN RTN3AD . . L 15,=A(RTN2AD) L 15,0(,15) BASSM 14,15 . . L 15,=A(RTN3AD) L 15,0(,15) BASSM 14,15 . . END RTN2 CSECT RTN2 AMODE 24 ENTRY RTN2AD . BSM 0,14 RTN2AD DC A(RTN2) RTN3 CSECT RTN3 AMODE 31 ENTRY RTN3AD . BSM 0,14
ABOVE CSECT
ABOVE AMODE 31
ABOVE RMODE ANY .
.
.
BSM 0,14
BELOW CSECT
BELOW AMODE 24
BELOW RMODE 24
LOAD EP=ABOVE
ST 0,EPABOVE
L 15,EPABOVE
BASSM 14,15
IBM 370 ASSEMBLY LANGUAGE 95 / 119
RTN3AD DC A(X'80000000+RTN3)
Example of 31 bit program with static storage above 16 MB line. This program does not
work with ADD as ADD operates in 24 bit mode. FIRST CSECT
FIRST AMODE 31
FIRST RMODE ANY
STM 14,12,12(13)
BALR 12,0
USING *,12
ST 13,SAVE+4
LA 13,SAVE
LOAD EP=ADD
LTR 15,15
BNZ LOADERR
LR 15,0
LA 1,PARMS
BASSM 14,15
L 5,RES
CVD 5,DW
UNPK MSG+2(16),DW
OI MSG+17,X'F0'
WTO 'RESULT IS'
LA 4,MSG
WTO TEXT=(4)
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BR 14
LOADERR L 13,SAVE+4
LM 14,12,12(13)
LA 15,16
BR 14
SAVE DS 18F
B DC F'200'
A DC F'100'
RES DS F
PARMS DC A(A)
DC A(B)
DC A(X'80000000'+RES)
MSG DC AL2(16)
DS CL16
DW DS D
END
Example of 31 bit program with dynamically acquired storage below the line. This program
works fine with ADD although ADD operates in 24 bit mode. FIRST CSECT
FIRST AMODE 31
FIRST RMODE ANY
STM 14,12,12(13)
BALR 12,0
USING *,12
LR 2,1
IBM 370 ASSEMBLY LANGUAGE 96 / 119
GETMAIN R,LV=LEN,LOC=BELOW
ST 13,4(0,1)
USING WS,13
LR 13,1
LR 1,2
BAL 2,INIT
LOAD EP=ADD
LTR 15,15
BNZ LOADERR
LR 15,0
LA 1,PARMS
BASSM 14,15
WTO 'BACK'
L 5,RES
CVD 5,DW
UNPK MSG+2(16),DW
OI MSG+17,X'F0'
WTO 'RESULT IS'
LA 4,MSG
WTO TEXT=(4)
LR 2,13
L 13,SAVE+4
FREEMAIN R,LV=LEN,A=(2)
LM 14,12,12(13)
LA 15,0
BR 14
LOADERR L 13,SAVE+4
LM 14,12,12(13)
LA 15,16
BR 14
INIT LA 3,100
ST 3,A
LA 3,200
ST 3,B
LA 3,A
ST 3,PARMS
LA 3,B
ST 3,PARMS+4
LA 3,RES
ST 3,PARMS+8
LA 3,16
STH 3,MSG
BR 2
WS DSECT
SAVE DS 18F
A DS F
B DS F
RES DS F
PARMS DS F
DS F
DS F
MSG DS AL2
DS CL16
DW DS D
IBM 370 ASSEMBLY LANGUAGE 97 / 119
LEN EQU *-WS
END
By default ADD operates in 24 / 24 mode ADD CSECT
STM 14,12,12(13)
USING ADD,15
ST 13,SAVE+4
LA 13,SAVE
LR 12,15
DROP 15
USING ADD,12
LR 2,1
WTO 'IN ADD'
LR 1,2
LM 2,4,0(1)
L 5,0(0,2)
A 5,0(0,3)
ST 5,0(0,4)
WTO 'EXITING ADD'
L 13,SAVE+4
LM 14,12,12(13)
LA 15,0
BSM 0,14
SAVE DS 18F
END
IBM 370 ASSEMBLY LANGUAGE 98 / 119
ASSEMBLER COURSE LAB EXERCISES
The following exercises do not present any complex assembler programming effort. Rather they serve to reinforce basic and fundamental concepts. The instructions you may need to use may not be more than about twenty or so. Before you start you need to have the quick reference card, Assembler services reference and assembler services guide handy. The principles of operation which explain all operation codes in detail is available online (Windows network) in case you need it. Most operation codes you use would have been explained in the class handouts and that should be adequate. You may also need to have access to MVS codes in case your program abends. Good luck and happy programming !.
Setup the work environment Note:The data set space parameters are given on a rough basis only. In case you get into a data set full condition, you may have to create a larger, new data set and copy the members across. 1)Create a PDS for your assembler source as below Lrecl 80 Blksize 800
Recfm FB DSN userid.asmclass.asm Unit SYSDA or allow SMS to default Primary alloc 2 trk Sec alloc 2trk Dir 5 block Unit of allocation trk 2)Create a PDS for your assembler JCL as below Lrecl 80
Blksize 800 Recfm FB DSN userid.asmclass.cntl Unit SYSDA or allow SMS to default Primary alloc 2 trk Sec alloc 1trk Dir 5 block Unit of allocation trk 3)Creat a PDS for your assembler object files as below Lrecl 80 Blksize 800 Recfm FB DSN userid.asmclass.obj Unit SYSDA or allow SMS to default Primary alloc 2 trk Sec alloc 1trk Dir 5 block Unit of allocation trk 4)Creat a PDS for your assembler loadlib as below Lrecl 23200 Blksize 0 Recfm U DSN userid.asmclass.loadlib Unit SYSDA or allow SMS to default Primary alloc 2 trk Sec alloc 2trk
IBM 370 ASSEMBLY LANGUAGE 99 / 119
Dir 10 block Unit of allocatin trk 5)Creat a PDS for your assembler user macros as below Lrecl 80 Blksize 800 Recfm FB DSN userid.asmclass.maclib Unit SYSDA or allow SMS to default Primary alloc 2 trk Sec alloc 1trk Dir 5 block Unit of allocatin trk 6)Browse the member ASMACL in the SYS1.PROCLIB . This is the procedure to assemble and link your
assembler programs.You should be able to understand every line of the prcedure as well as the assembler and linker options. You may have to access IBM manuals for the assembler and linker options. Understand what statements need to be overridden to achieve the following:-
Program source from userid.asmclass.asm Program Loadmodule into userid.asmclass.loadlib Object code for subprograms into userid.asmclass.obj Object code for subprograms from userid.asmclass.obj User macros from userid.asmclass.maclib Change assembler and linker parms (if appropriate) when invoking the Procedure.
IBM 370 ASSEMBLY LANGUAGE 100 / 119
EXERCISES 1)Write a simple assembler program which does nothing other than return to check out the operation of the
JCL and submitting jobs to batch. Make sure that you understand the process including using the SDSF facility.
2)Write a program which can detect and copy the value passed through the PARM field in the exec
statement and output it via SYSOUT
3)Write an assembler program which converts a 26 byte character field from lower case to upper case. Verify the correct operation of the program through a SNAP dump before and after the operation.
4)Write an assembler program to convert a binary value in a full word storage field to a displayable value in another storage field. Verify correct operation through SNAP dump
5)a)Write a user macro (store it in userid.asmclass.maclib) which accepts a binary full word field in a GPR (operand one) and converts it to a displayable value in a memory field (operand two)
b)Use the program logic debugged and working from previous example. You will also have to make JCL modifications to include your maclib
c)Write your own macro to implement saving and restoring registers on entry and exit into your program.
6)Write an assembler program to open and read a QSAM PS file and output it via SYSOUT 7)Create a VSAM KSDS data set and load the data set using an assembler program which reads input from a QSAM PS file and loads it in sequential mode.
8)Run an IDCAMS job stream to ensure that the data set has been loaded (use PRINT option )
9)Insert records in the data set using DIRECT mode and input from another QSAM file where records which
may be in any order
10)Try out other modes of VSAM access like DIRECT get, SEQ get with an EODAD routine defined through EXLST macro. Use SHOWCB macro to test VSAM feedback code after each operation. Use dynamic storage allocation (Getmain / Storage macro) to acquire storage for data buffers in your program.
11)Write a main program which calls a subprogram in the same file with three storage Fullword integers as
parameters. The subprogram must add the two integers and return the sum in the third fullword. Output the result via sysout. Note that you have to convert the binary form to displayable form using the CVD and UNPACK instructions.
12)Write an assembler sub program which can be called using CALL macro. The main program and the
subprogram should share the same DCB for SYSOUT data. Main and sub programs should announce their entry and exit thru messages on SYSOUT. Note that main and sub programs are having separate source files and need separate compilation. Hint:You will need to have modified ASMACL to create the Object code for the subprogram which is to be in userid.asmclass.obj.
13)Write an assembler program to do the same function as in exercise (17) above but using a LOAD macro.
14)Write a main program which creates a subtask with the ATTACH macro. The main program and the
subprogram must share the same DCB for the SYSOUT dataset. The main and subprogram must announce their entry and exit. The main program must wait for the attached task to complete before ending.
IBM 370 ASSEMBLY LANGUAGE 101 / 119
*******************************************************************************
* USE THIS PROGRAM TO CHECK OUT YOUR JCL AND BATCH JOB SUBMISSION*
* BEFORE YOU START THE EXERCISES *
*******************************************************************************
BEGIN CSECT
SAVE (14,12)
BALR 12,0
USING *,12
ST 13,SAVE+4
L 13,SAVE+4
RETURN (14,12),,RC=0
SAVE DS 18F
END BEGIN
IBM 370 ASSEMBLY LANGUAGE 102 / 119
********************************************************************************
* EXAMPLE OF LOADING AND EXECUTING A PROGRAM AT RUN TIME *
********************************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
*
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR1 00083015
*
MVC OUTBUFF(L'MSG1),MSG1 00084018
PUT FILE2,OUTBUFF 00090218
*
LOAD EP=SUB1 00090319
LTR 15,15 00090419
BNZ LOADERR 00090519
LR 15,0 00090619
BALR 14,15 00090719
*
MVC OUTBUFF(L'MSG2),MSG2 00090820
PUT FILE2,OUTBUFF 00090918
L 13,SAVE+4 00146009
RETURN (4,12),,RC=0 00147009
ERROR1 L 13,SAVE+4 00148015
RETURN (14,12),,RC=4 00149015
LOADERR L 13,SAVE+4 00150019
RETURN (14,12),,RC=8 00151019
OUTBUFF DC CL80' ' 00160018
MSG1 DC C'INVOKING SUB1' 00161018
MSG2 DC C'EXITING MAIN1' 00162018
SAVE DS 18F 00170000
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132,LRECL=132, X 00200001
MACRF=PM,DDNAME=OUTFILE,DEVD=PR 00210005
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 103 / 119
*******************************************************************************
* SUB1 *
*******************************************************************************
SUB1 CSECT 00010019
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR1 00083015
L 2,=F'5' 00084015
LOOP PUT FILE2,OUTBUFF 00090215
BCT 2,LOOP 00110015
CLOSE (FILE2) 00120018
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
ERROR1 L 13,SAVE+4 00148015
RETURN (14,12),,RC=4 00149015
OUTBUFF DC C'THIS IS SUB 1 LOOPING' 00160015
DC CL(80-L'OUTBUFF)' ' 00161017
SAVE DS 18F 00170000
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132, X
LRECL=132,MACRF=PM,DDNAME=SUBFILE, X
DEVD=PR 00210018
END 00220019
IBM 370 ASSEMBLY LANGUAGE 104 / 119
*******************************************************************************
* EXAMPLE OF USAGE OF A CALL MACRO *
*******************************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR1 00083015
MVC OUTBUFF(L'MSG1),MSG1 00084018
PUT FILE2,OUTBUFF 00090218
CALL SUB2,(FILE2) 00090322
MVC OUTBUFF(L'MSG2),MSG2 00090820
PUT FILE2,OUTBUFF 00090918
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
ERROR1 L 13,SAVE+4 00148015
RETURN (14,12),,RC=4 00149015
LOADERR L 13,SAVE+4 00150019
RETURN (14,12),,RC=8 00151019
OUTBUFF DC CL80' ' 00160018
MSG1 DC C'INVOKING SUB1' 00161018
MSG2 DC C'EXITING MAIN1' 00162018
SAVE DS 18F 00170000
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132,LRECL=132, X00200001
MACRF=PM,DDNAME=OUTFILE,DEVD=PR 00210005
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 105 / 119
*******************************************************************************
* SUB2 *
*******************************************************************************
SUB2 CSECT 00010021
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
L 4,0(1) 00080022
L 2,=F'5' 00084015
LOOP PUT (4),OUTBUFF 00090222
BCT 2,LOOP 00110015
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
OUTBUFF DC C'THIS IS SUB 1 LOOPING' 00160015
DC CL(80-L'OUTBUFF)' ' 00161017
SAVE DS 18F 00170000
END 00220019
IBM 370 ASSEMBLY LANGUAGE 106 / 119
*******************************************************************************
* EXAMPLE OF USAGE OF ATTACH A SUBTASK USING ATTACH MACRO *
*******************************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
SYSSTATE ASCENV=P 00080026
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR1 00083015
MVC OUTBUFF(L'MSG1),MSG1 00084018
PUT FILE2,OUTBUFF 00090218
ATTACHX EP=SUB3,ETXR=ETXSUB3,PARAM=FILE2, X
SZERO=YES 00090328
LTR 15,15 00090419
BNZ ATTCHERR 00090521
WAIT 1,ECB=ECBSUB3 00090722
MVC OUTBUFF(L'MSG2),MSG2 00091020
PUT FILE2,OUTBUFF 00092018
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00146125
ETXSUB3 ST 1,TCBADDR 00146232
DETACH TCBADDR 00146332
POST ECBSUB3 00146425
BR 14 00146525
ERROR1 L 13,SAVE+4 00148015
RETURN (14,12),,RC=4 00149015
ATTCHERR L 13,SAVE+4 00150021
RETURN (14,12),,RC=8 00151019
TCBADDR DC A(0) 00151132
ECBSUB3 DC F'0' 00152021
OUTBUFF DC CL80' ' 00160018
MSG1 DC C'INVOKING SUB3' 00161021
MSG2 DC C'EXITING MAIN3' 00162021
SAVE DS 18F 00170000
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132,LRECL=132, X00200001
MACRF=PM,DDNAME=OUTFILE,DEVD=PR 00210005
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 107 / 119
*********************************************************************
* SUB3 *
*********************************************************************
SUB3 CSECT 00010023
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
L 4,0(1) 00080022
L 2,=F'20' 00084023
LOOP PUT (4),OUTBUFF 00090222
BCT 2,LOOP 00110015
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
OUTBUFF DC C'THIS IS SUB 3 LOOPING' 00160023
DC CL(80-L'OUTBUFF)' ' 00161017
SAVE DS 18F 00170000
END 00220019
IBM 370 ASSEMBLY LANGUAGE 108 / 119
***********************************************************************
* EXAMPLE OF INVOKING ANOTHER PROGRAM AT RUN TIME USING A*
* LINK MACRO *
***********************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR1 00083015
MVC OUTBUFF(L'MSG1),MSG1 00084018
PUT FILE2,OUTBUFF 00090218
LINK EP=SUB4,PARAM=FILE2 00090335
LTR 15,15 00090419
BNZ LINKERR 00090535
MVC OUTBUFF(L'MSG3),MSG3 00094028
PUT FILE2,OUTBUFF 00095028
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00146125
ERROR1 L 13,SAVE+4 00148015
RETURN (14,12),,RC=4 00149015
LINKERR L 13,SAVE+4 00150035
RETURN (14,12),,RC=8 00151019
OUTBUFF DC CL80' ' 00160018
MSG1 DC C'INVOKING SUB4' 00161029
MSG3 DC C'EXITING MAIN4' 00162034
SAVE DS 18F 00170000
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132,LRECL=132, X00200001
MACRF=PM,DDNAME=OUTFILE,DEVD=PR 00210005
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 109 / 119
***********************************************************************
* SUB4 *
***********************************************************************
SUB4 CSECT 00010024
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
L 4,0(1) 00080022
L 2,=F'2' 00084025
LOOP PUT (4),OUTBUFF 00090222
BCT 2,LOOP 00110015
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
OUTBUFF DC C'THIS IS SUB 4 LOOPING' 00160026
DC CL(80-L'OUTBUFF)' ' 00161017
SAVE DS 18F 00170000
END 00220019
IBM 370 ASSEMBLY LANGUAGE 110 / 119
************************************************************************
* EXAMPLE OF OBTAINING A SNAP DUMP *
************************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
TPUT MSG,L'MSG 00071013
OPEN (FILE1,INPUT) 00080005
LTR 15,15 00080105
BNZ ERROR1 00080205
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR2 00083005
OPEN (SNAPDCB,OUTPUT) 00084014
LTR 15,15 00085014
BNZ ERROR3 00086014
LOOP GET FILE1,INBUFF 00090002
MVC OUTBUFF,INBUFF 00090108
PUT FILE2,OUTBUFF 00090208
B LOOP 00110000
ERROR1 L 13,SAVE+4 00141005
RETURN (14,12),,RC=1 00142005
ERROR2 L 13,SAVE+4 00143005
RETURN (14,12),,RC=2 00144005
ERROR3 L 13,SAVE+4 00144114
RETURN (14,12),,RC=3 00144214
EOFRTN CLOSE (FILE1,,FILE2) 00145009
SNAP DCB=SNAPDCB,ID=1,PDATA=(REGS,SA), X
STORAGE=(BEGIN,LAST) 00145214
CLOSE SNAPDCB 00145314
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
INBUFF DS CL80 00150012
OUTBUFF DS CL80 00160012
DC 52C' ' 00161012
SAVE DS 18F 00170000
MSG DC CL15'ENTERING PGM' 00171013
FILE1 DCB DSORG=PS,RECFM=FB,BLKSIZE=800, X
LRECL=80,MACRF=GM,DDNAME=INFILE, X
EODAD=EOFRTN 00190009
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132, X
LRECL=132,MACRF=PM,DDNAME=OUTFILE, X
DEVD=PR 00210005
SNAPDCB DCB DSORG=PS,RECFM=VBA,BLKSIZE=882, X
LRECL=125,MACRF=W,DDNAME=SNAPDMP 00210214
LAST EQU * 00211014
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 111 / 119
********************************************************************
* EXAMPLE OF LOADING VSAM KSDS SEQUENTIALLY *
********************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (FILE1,INPUT) 00080005
LTR 15,15 00080105
BNZ ERROR1 00080205
OPEN (VSAMACB) 00081015
LTR 15,15 00082005
BNZ ERROR2 00083005
LOOP GET FILE1,INBUFF 00090002
MVC OUTBUFF,INBUFF 00090108
PUT RPL=VSAMRPL 00090215
B LOOP 00110000
ERROR1 L 13,SAVE+4 00141005
RETURN (14,12),,RC=1 00142005
ERROR2 L 13,SAVE+4 00143005
RETURN (14,12),,RC=2 00144005
EOFRTN CLOSE (FILE1,,VSAMACB) 00145016
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
INBUFF DS CL80 00150012
OUTBUFF DS CL80 00160012
SAVE DS 18F 00170000
FILE1 DCB DSORG=PS,RECFM=FB,BLKSIZE=800, X
LRECL=80, MACRF=GM,DDNAME=INFILE, X
EODAD=EOFRTN 00190009
VSAMACB ACB AM=VSAM,DDNAME=OUTFILE, X
MACRF=(KEY,SEQ,OUT) 00200015
VSAMRPL RPL AM=VSAM,ACB=VSAMACB,AREA=OUTBUFF,X
AREALEN=80,ARG=VSAMKEY,KEYLEN=4, X
OPTCD=(KEY,SEQ),RECLEN=80 00210115
VSAMKEY DS F 00210215
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 112 / 119
************************************************************************
* EXAMPLE OF DIRECT UPDATE OF A VSAM KSDS USING A QSAM FILE *
* INPUT *
************************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (FILE1,INPUT) 00080005
LTR 15,15 00080105
BNZ ERROR1 00080205
OPEN (VSAMACB) 00081015
LTR 15,15 00082005
BNZ ERROR2 00083005
LOOP GET FILE1,INBUFF 00090002
MVC OUTBUFF,INBUFF 00090108
MVC VSAMKEY,OUTKEY 00090217
PUT RPL=VSAMRPL 00090315
B LOOP 00110000
ERROR1 L 13,SAVE+4 00141005
RETURN (14,12),,RC=1 00142005
ERROR2 L 13,SAVE+4 00143005
RETURN (14,12),,RC=2 00144005
EOFRTN CLOSE (FILE1,,VSAMACB) 00145016
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
INBUFF DS CL80 00150012
OUTBUFF DS 0CL80 00160017
OUTKEY DS CL4 00161017
DS CL76 00162017
SAVE DS 18F 00170000
FILE1 DCB DSORG=PS,RECFM=FB,BLKSIZE=800, X
LRECL=80,MACRF=GM,DDNAME=INFILE, X
EODAD=EOFRTN 00190009
VSAMACB ACB AM=VSAM,DDNAME=OUTFILE, X
MACRF=(KEY,DIR,OUT) 00200017
VSAMRPL RPL AM=VSAM,ACB=VSAMACB, X
AREA=OUTBUFF,AREALEN=80, X
ARG=VSAMKEY,KEYLEN=4, X
OPTCD=(KEY,DIR),RECLEN=80 00210117
VSAMKEY DS F 00210215
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 113 / 119
********************************************************************
* EXAMPLE OF READING VSAM KSDS SEQUENTIALLY *
********************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (VSAMACB) 00080018
LTR 15,15 00080105
BNZ ERROR1 00080205
OPEN (FILE1,OUTPUT) 00081018
LTR 15,15 00082005
BNZ ERROR2 00083005
LOOP GET RPL=VSAMRPL 00090018
SHOWCB RPL=VSAMRPL,AREA=RETCODE,LENGTH=4, X
FIELDS=FDBK 00090120
L 4,RETCODE 00090220
LTR 4,4 00090320
BNZ ERROR3 00090420
MVC OUTBUFF,INBUFF 00090508
PUT FILE1,OUTBUFF 00090619
B LOOP 00110000
ERROR1 L 13,SAVE+4 00141005
RETURN (14,12),,RC=1 00142005
ERROR2 L 13,SAVE+4 00143005
RETURN (14,12),,RC=2 00144005
ERROR3 L 13,SAVE+4 00144120
RETURN (14,12),,RC=3 00144220
EOFRTN CLOSE (FILE1,,VSAMACB) 00145016
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
LIST EXLST AM=VSAM,EODAD=EOFRTN 00148019
INBUFF DS CL80 00150012
OUTBUFF DS CL80 00160018
DS CL52 00161018
SAVE DS 18F 00170000
RETCODE DS F 00171020
FILE1 DCB DSORG=PS,RECFM=F,BLKSIZE=132, X
LRECL=132,MACRF=PM,DDNAME=OUTFILE, X
DEVD=PR 00190018
VSAMACB ACB AM=VSAM,DDNAME=INFILE, X
MACRF=(KEY,SEQ,IN),EXLST=LIST 00201019
VSAMRPL RPL AM=VSAM,ACB=VSAMACB,AREA=INBUFF, X
AREALEN=80,ARG=VSAMKEY,KEYLEN=4, X
OPTCD=(KEY,SEQ),RECLEN=80 00210118
VSAMKEY DS F 00210215
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 114 / 119
********************************************************************
* EXAMPLE OF READING VSAM KSDS DIRECTLY BY KEY *
********************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
OPEN (VSAMACB) 00080018
LTR 15,15 00080105
BNZ ERROR1 00080205
OPEN (FILE1,OUTPUT) 00081018
LTR 15,15 00082005
BNZ ERROR2 00083005
FIRST MVC VSAMKEY,=C'0008' 00084021
GET RPL=VSAMRPL 00090021
SHOWCB RPL=VSAMRPL,AREA=RETCODE,LENGTH=4, X
FIELDS=FDBK 00090120
L 4,RETCODE 00090220
LTR 4,4 00090320
BNZ ERROR3 00090420
MVC OUTBUFF,INBUFF 00090508
PUT FILE1,OUTBUFF 00090619
SECOND MVC VSAMKEY,=C'0010' 00090721
GET RPL=VSAMRPL 00090821
SHOWCB RPL=VSAMRPL,AREA=RETCODE,LENGTH=4, X
FIELDS=FDBK 00090921
L 4,RETCODE 00091021
LTR 4,4 00092021
BNZ ERROR3 00093021
MVC OUTBUFF,INBUFF 00094021
PUT FILE1,OUTBUFF 00095021
THIRD MVC VSAMKEY,=C'0001' 00096021
GET RPL=VSAMRPL 00097021
SHOWCB RPL=VSAMRPL,AREA=RETCODE,LENGTH=4, X
FIELDS=FDBK 00098021
L 4,RETCODE 00099021
LTR 4,4 00100021
BNZ ERROR3 00101021
MVC OUTBUFF,INBUFF 00102021
PUT FILE1,OUTBUFF 00103021
FOURTH MVC VSAMKEY,=C'0050' 00103122
GET RPL=VSAMRPL 00103222
SHOWCB RPL=VSAMRPL,AREA=RETCODE,LENGTH=4, X
FIELDS=FDBK 00103322
L 4,RETCODE 00103422
LTR 4,4 00103522
BNZ ERROR3 00103622
MVC OUTBUFF,INBUFF 00103722
PUT FILE1,OUTBUFF 00103822
B ENDRTN 00104021
ERROR1 L 13,SAVE+4 00141005
RETURN (14,12),,RC=1 00142005
ERROR2 L 13,SAVE+4 00143005
IBM 370 ASSEMBLY LANGUAGE 115 / 119
RETURN (14,12),,RC=2 00144005
ERROR3 CLOSE (FILE1,,VSAMACB) 00144121
L 13,SAVE+4 00144221
RETURN (14,12),,RC=3 00144320
ENDRTN CLOSE (FILE1,,VSAMACB) 00145021
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
INBUFF DS CL80 00150012
OUTBUFF DS CL80 00160018
DS CL52 00161018
SAVE DS 18F 00170000
RETCODE DS F 00171020
FILE1 DCB DSORG=PS,RECFM=F,BLKSIZE=132, X
LRECL=132,MACRF=PM,DDNAME=OUTFILE, X
DEVD=PR 00190018
VSAMACB ACB AM=VSAM,DDNAME=INFILE, X
MACRF=(KEY,DIR,IN) 00200021
VSAMRPL RPL AM=VSAM,ACB=VSAMACB,AREA=INBUFF, X
AREALEN=80,ARG=VSAMKEY,KEYLEN=4, X
OPTCD=(KEY,DIR),RECLEN=80 00210121
VSAMKEY DS F 00210215
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 116 / 119
************************************************************************
* EXAMPLE OF DYNAMIC ALLOCATION AND USE OF DATA AREAS *
************************************************************************
BEGIN CSECT 00010000
SAVE (14,12) 00030000
BALR 3,0 00040000
USING *,3 00050000
ST 13,SAVE+4 00060000
LA 13,SAVE 00070000
GETMAIN R,LV=NOFBYTES,LOC=BELOW 00071015
LTR 15,15 00072015
BNZ GETMERR 00073015
LR 4,1 00074015
USING BUFFS,4 00075015
OPEN (FILE1,INPUT) 00080005
LTR 15,15 00080105
BNZ ERROR1 00080205
OPEN (FILE2,OUTPUT) 00081005
LTR 15,15 00082005
BNZ ERROR2 00083005
LOOP GET FILE1,INBUFF 00090002
MVC OUTBUFF,INBUFF 00090108
PUT FILE2,OUTBUFF 00090208
B LOOP 00110000
ERROR1 FREEMAIN R,LV=NOFBYTES,A=(4) 00120015
L 13,SAVE+4 00141015
RETURN (14,12),,RC=1 00142005
ERROR2 FREEMAIN R,LV=NOFBYTES,A=(4) 00142115
L 13,SAVE+4 00143015
RETURN (14,12),,RC=2 00144005
GETMERR L 13,SAVE+4 00144315
RETURN (14,12),,RC=4 00144415
EOFRTN CLOSE (FILE1,,FILE2) 00145009
FREEMAIN R,LV=NOFBYTES,A=(4) 00145115
L 13,SAVE+4 00146009
RETURN (14,12),,RC=0 00147009
FILE1 DCB DSORG=PS,RECFM=FB,BLKSIZE=800, X
LRECL=80,MACRF=GM,DDNAME=INFILE, X
EODAD=EOFRTN 00190009
FILE2 DCB DSORG=PS,RECFM=F,BLKSIZE=132, X
LRECL=132,MACRF=PM,DDNAME=OUTFILE, X
DEVD=PR 00210005
SAVE DS 18F 00210315
* 00211115
BUFFS DSECT 00211215
INBUFF DS CL80 00212015
OUTBUFF DS CL80 00213015
DS CL52 00214015
* 00216015
NOFBYTES EQU *-INBUFF 00217015
END BEGIN 00220001
IBM 370 ASSEMBLY LANGUAGE 117 / 119
ASMACL PROCEDURE TO COMPILE AND LINK YOUR ASSEMBLER PROGRAM
//*
//* ASMACL PROCEDURE PROVIDED BY IBM IN SYS1.PROCLIB
//* THIS PROCEDURE RUNS THE HIGH LEVEL ASSEMBLER, LINK-EDITS THE
//* NEWLY ASSEMBLED PROGRAM
//*
//ASMACL PROC
//C EXEC PGM=ASMA90
//SYSLIB DD DSN=SYS1.MACLIB,DISP=SHR
//SYSUT1 DD DSN=&&SYSUT1,SPACE=(4096,(120,120),,,ROUND),UNIT=VIO,
// DCB=BUFNO=1
//SYSPRINT DD SYSOUT=*
//SYSLIN DD DSN=&&OBJ,SPACE=(3040,(40,40),,,ROUND),UNIT=VIO,
// DISP=(MOD,PASS),DCB=(BLKSIZE=3040,LRECL=80,RECFM=FBS,BUFNO=1)
//L EXEC PGM=HEWL,PARM='MAP,LET,LIST,NACL',COND=(8,LT,C)
//SYSLIN DD DSN=&&OBJ,DISP=(OLD,DELETE)
// DD DDNAME=SYSIN
//SYSLMOD DD DISP=(,PASS),UNIT=SYSDA,SPACE=(CYL,(1,1,1)),
// DSN=&&GOSET(GO)
//SYSUT1 DD DSN=&&SYSUT1,SPACE=(1024,(120,120),,,ROUND),UNIT=VIO,
// DCB=BUFNO=1
//SYSPRINT DD SYSOUT=*
INVOCATION OF THE PROCEDURE
//HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //*
//* If you want copy the proc into your USERID.ASMCLASS.CNTL and edit it to make many
//* changes
//* if you do this you need to add the JCLLIB statement below
//* JCLLIB ORDER=(HCLUSR.ASMCLASS.CNTL) //* //MYSTEP EXEC PROC=ASMACL //C.SYSIN DD DSN=HCLUSR.ASMCLASS.ASM(memn),DISP=SHR //*
//* use the JCL statement below if you want to compile,link and also place the object code in
your
//* object library
//* C.SYSLIN DD DSN=HCLUSR.ASMCLASS.OBJ(SUB4),DISP=OLD //* //L.SYSLMOD DD DSN=HCLUSR.ASMCLASS.LOADLIB(SAMP9),DISP=OLD //L.SYSLIB DD DSN=HCLUSR.ASMCLASS.OBJ,DISP=SHR //*
//* use the JCL statement below if you want to compile, link and also place the object code in
your
//* object library
//* L.SYSLIN DD DSN=HCLUSR.ASMCLASS.OBJ(SUB4),DISP=SHR //
IBM 370 ASSEMBLY LANGUAGE 118 / 119
SAMPLE RUN JCL - 1 //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //JOBLIB DD DSN=HCLUSR.ASMCLASS.LOADLIB,DISP=SHR //MYSTEP EXEC PGM=SAMP9 //INFILE DD DSN=HCLUSR.ASMCLASS.DATA,DISP=SHR //SNAPDMP DD SYSOUT=* //OUTFILE DD SYSOUT=* //SUBFILE DD SYSOUT=* //
SAMPLE RUN JCL - 2 //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //JOBLIB DD DSN=HCLUSR.ASMCLASS.LOADLIB,DISP=SHR //MYSTEP EXEC PGM=PROG3 //INFILE DD DSN=HCLUSR.ASMCLASS.DATA,DISP=SHR //OUTFILE DD DSN=HCLUSR.ASMCLASS.KSDS.CLUSTER,DISP=SHR //
SAMPLE RUN JCL - 3 //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //JOBLIB DD DSN=HCLUSR.ASMCLASS.LOADLIB,DISP=SHR //MYSTEP EXEC PGM=PROG4 //INFILE DD DSN=HCLUSR.ASMCLASS.DATA1,DISP=SHR //OUTFILE DD DSN=HCLUSR.ASMCLASS.KSDS.CLUSTER,DISP=SHR //
SAMPLE RUN JCL - 4 //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //JOBLIB DD DSN=HCLUSR.ASMCLASS.LOADLIB,DISP=SHR //MYSTEP EXEC PGM=PROG5 //OUTFILE DD SYSOUT=* //INFILE DD DSN=HCLUSR.ASMCLASS.KSDS.CLUSTER,DISP=SHR //
IBM 370 ASSEMBLY LANGUAGE 119 / 119
SAMPLE JCL FOR DEFINING A KSDS VSAM CLUSTER //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //MYSTEP EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSIN DD * DEFINE CLUSTER - (NAME(HCLUSR.ASMCLASS.KSDS.CLUSTER) - TRACKS(1 1) - RECORDSIZE(80 80) - KEYS(4 0) - INDEXED - ) - DATA - (NAME(HCLUSR.ASMCLASS.KSDS.DATA) - CISZ(4096) - ) - INDEX - (NAME(HCLUSR.ASMCLASS.KSDS.INDEX)) /* //
SAMPLE JCL TO DEFINE VSAM LINEAR DATA SET //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //MYSTEP EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSIN DD * DEFINE CLUSTER - (NAME(HCLUSR.ASMCLASS.LINEAR.DATA) - TRACKS(1 1) - LINEAR - ) /* //
SAMPLE JCL TO PRINT CONTENTS OF VSAM CLUSTER //HCLUSR1 JOB MSGCLASS=A,NOTIFY=HCLUSR //MYSTEP EXEC PGM=IDCAMS //SYSPRINT DD SYSOUT=* //SYSIN DD * PRINT INDATASET(HCLUSR.ASMCLASS.KSDS.CLUSTER) CHAR /* //