lecture 4 executing an assembly program.pdf
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Micro processors Systems
Executing and Linking an assembly Executing and Linking an assembly
programprogram
Lecturer: Dr. Lecturer: Dr. HeshamHesham El El ZoukaZouka
CC421 - Computer Engineering Dept.
Lesson plan
�� Review Review
�� Program logic and controlProgram logic and control
�� Practice exercisePractice exercise
�� Assembling, Linking and Executing ProgramsAssembling, Linking and Executing Programs
�� Practice exercisePractice exercise
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Review
�� IMUL register/memoryIMUL register/memory
If If operand is a byteoperand is a byte
AXAX= = AL * operandAL * operand
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Review
MOV CX, MOV CX, 1010
BEGINLOOP :BEGINLOOP :
….….
DEC CXDEC CX
JNZ BEGINLOOPJNZ BEGINLOOP
OROR
MOV CX,MOV CX, 1010
BEGINLOOP :BEGINLOOP :
……
LOOP BEGINLOOPLOOP BEGINLOOP
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Program logic and control
�� Address: distance from the current Address: distance from the current addressaddress
� Short: distance from -128 to 127 bytes
� Near: -32768 to 32767 bytes
� Far: distance over 32K for the same segment address or in another segment
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Transfer operations
�� JMPJMP
UnconditionalUnconditional. . Transfer control under all circumstancesTransfer control under all circumstances
SyntaxSyntax::
[[label:] JMPlabel:] JMP short/near/far addressshort/near/far address
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Transfer operations
�� Backward jumpBackward jump
BEGINLOOPBEGINLOOP::
….….
JMP JMP BEGINLOOPBEGINLOOP
�� Forward Forward jumpjump
JMP JMP STARTLOOPSTARTLOOP
STARTLOOPSTARTLOOP::
….….
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Loop instruction
�� Loops a specified number of times Loops a specified number of times
Initial value is stored in CXInitial value is stored in CX
Each iteration, LOOP deducts Each iteration, LOOP deducts 1 1 from CX.from CX.
If CX is not zero, control jumps to the address specifiedIf CX is not zero, control jumps to the address specified
Otherwise,Otherwise, finish the finish the looploop
�� Syntax:Syntax:
[label:] LOOP short-address
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CMP Instruction
�� [[label:] CMP register/memory, label:] CMP register/memory, register/memory/immediateregister/memory/immediate
�� Compares the first to the second Compares the first to the second operandoperand
�� Affects: AF,Affects: AF, CF, OF, PF, SF and ZF flagCF, OF, PF, SF and ZF flag
e.g.e.g. CMP AX, DXCMP AX, DX
JE JE StartloopStartloop
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Conditional Jump instructions
�� Jump based on unsigned dataJump based on unsigned data
[[label:] JE/JZlabel:] JE/JZ shortshort--addressaddress
�� Jump if equal or Jump if zeroJump if equal or Jump if zero
[[label:] JNE/JNZlabel:] JNE/JNZ shortshort--addressaddress
�� Jump Jump if not equal or Jump if not zeroif not equal or Jump if not zero
FlagFlag: : ZFZF
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Example
MOV AL, MOV AL, 5 5
CMP AL, CMP AL, 5 5
JE labelJE label1 1
JMP exit JMP exit
labellabel11: : MOV CX, BXMOV CX, BX
exit: exit: …..…..
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Conditional Jump instructions
JG: Jump if first operand is Greater then second operand (as set by CMP JG: Jump if first operand is Greater then second operand (as set by CMP instruction). instruction). “Signed”. “Signed”.
if (ZF = if (ZF = 00) and (SF = OF) then jump ) and (SF = OF) then jump
Syntax:Syntax: [label:] JG[label:] JG shortshort--addressaddress
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Example
MOV AL, MOV AL, 5 5
CMP AL, CMP AL, --5 5
JG labelJG label1 1
JMP exit JMP exit
labellabel11: MOV CX, : MOV CX, --5 5 ; in this case AL > ; in this case AL > --5 5
exitexit: :
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Conditional Jump Instruction
�� JL: Jump if first operand is Less then second operand (as set by CMP JL: Jump if first operand is Less then second operand (as set by CMP instruction). Signed. instruction). Signed.
�� if SF <> OF then jump if SF <> OF then jump
�� Syntax: [label:] Syntax: [label:] JL shortJL short--addressaddress
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Example
MOV AL,MOV AL, --2 2
CMP AL, CMP AL, 5 5
JL labelJL label1 1
JMP exit JMP exit
labellabel11: MOV CX, : MOV CX, 55 ; ; in this case AL < in this case AL < 55
exitexit: …: …
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Conditional Jump instructions
�� JB/JNAEJB/JNAE
[label:] [label:] JB/JNAE shortJB/JNAE short--addressaddress
�� Jump Above/Equal or Jump Not Above/EqualJump Above/Equal or Jump Not Above/Equal
FlagFlag: : ZFZF
e.g. Write a program to compute sum of even integers from 1 to 100 using LOOP
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Conditional Jump instructions
�� JBE/JNAJBE/JNA
[[label:]label:] JBE/JNAJBE/JNA shortshort--addressaddress
�� Jump Below/Equal or Jump Not AboveJump Below/Equal or Jump Not Above
Flag: AF,Flag: AF, ZFZF
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Special Arithmetic Test
�� JCXZ: Jump if CX is JCXZ: Jump if CX is zerozero
�� JC: Jump if JC: Jump if carrycarry
�� JNC: Jump if no JNC: Jump if no carrycarry
�� JO: Jump if JO: Jump if overflowoverflow
�� JNP: Jump if no JNP: Jump if no overflowoverflow
e.g. Write a program that adds each value defined in BYTE_TBL and store e.g. Write a program that adds each value defined in BYTE_TBL and store
the sum in BYTE_TOTALthe sum in BYTE_TOTAL
BYTE_TBL BYTE_TBL DB DB 00,,55,,66,,44,,99,,77
BYTE_TOTAL BYTE_TOTAL DB DB 00
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Assembling, Linking and Executing Programs
Assembling: translate Assembling: translate source source program (written in assembly language) into program (written in assembly language) into
machine machine code (object code) code (object code)
Linking: complete machine code for the object program, generate an Linking: complete machine code for the object program, generate an
executable executable modulemodule
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Executing Programs
Editor
Create *.asm
Assemble *.asm
And create *.obj
Assembler
Link
And create *.exe
Linker
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Assembling a Source Program
�� Converts your source code into machine code and displays any errors.Converts your source code into machine code and displays any errors.
*.asm *.obj, *.lst, *.crf
Assembling
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Linking an Object Program
�� Combines more than one assembled module into one executable Combines more than one assembled module into one executable programprogram
�� Generates an EXE module and initializes it with special instructions to Generates an EXE module and initializes it with special instructions to facilitate its subsequent loading for executionfacilitate its subsequent loading for execution
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Linking an Object Program
�� *.map *.map
STARTSTART STOPSTOP LENGTH NAME LENGTH NAME CLASSCLASS
0000000000HH 00030003FH FH 00400040H H STACK STACK STACKSTACK
0004000040H H 0004500045H H 00060006H H DATASEG DATASEG DATADATA
0005000050H H 0006300063H H 00140014H H CODESEGCODECODESEGCODE
Program entry at Program entry at 00050005::00000000
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Procedures
�� Procedure is a part of code that can be called from your Procedure is a part of code that can be called from your program in order to make some specific task. program in order to make some specific task.
�� Procedure makes Procedure makes program more structural and easier to program more structural and easier to understand. understand.
�� Returns Returns to the same point from where it was called. to the same point from where it was called.
Syntax: Syntax:
name PROCname PROC
; ; the code of the procedure ...the code of the procedure ...
RETRETname ENDP name ENDP
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Procedure Call
�� CALL instruction is used to call a procedure CALL instruction is used to call a procedure
�� CALL is used to transfer controlsCALL is used to transfer controls
�� RET is used to end execution of procedureRET is used to end execution of procedure
Syntax:Syntax: [label:] CALL [label:] CALL procedureprocedure
[[label:]label:] RET [immediate]RET [immediate]
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Example
CALL mCALL m1 1
MOV AX, MOV AX, 2 2
RET ; return to operating system.RET ; return to operating system.
mm1 1 PROC PROC
MOV BX, MOV BX, 5 5
CALL mCALL m22
RET ; return to caller. RET ; return to caller.
mm1 1 ENDP ENDP
mm22 PROCPROC
MOV CX, MOV CX, 1010
RET;RET; return to callerreturn to caller
mm22 ENDPENDP
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