Detmer Ch2 Ppt

8/10/2019 Detmer Ch2 Ppt

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Chapter 3

Elements of Assembly Language

How to develop assembly Language Programs

Directives in MASM


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Contents

Types and formats of statements in MASM

Example program for how to assemble, link,and execute

Structure of assembly language program

Constant operands and instructionoperands


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3.2 A Complete Example

Purpose: prompt for two numbers and

then find and display their sum.


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Pseudocode design for the program1. Prompt for the first number;

2. Input ASCII characters representing the first number;

3. Convert the characters to a 2s complement doubleworld

4. Store the first number in memory;

5. Prompt for the second number;

6. Input ASCII characters representing the first number;

7. Convert the characters to a 2s complement double

world8. Add the first number to the second number;

9. Convert the sum to a string of ASCII characters;

10. Display a label and the characters representing the sum;


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;Example assembly language program -- adds two

numbers

;Author: R. Detmer

; Date: revised 7/97

.386

.MODEL FLAT

Structure of the program(1)comment

directives

Accept 80386 instruction

Flat memory model


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Structure of the program(2)

ExitProcess PROTONEAR32 stdcall, dwExitCode:DWORD

INCLUDEio.h ; header file for input/output

cr EQU 0dh ; carriage return characterLf EQU 0ah ; line feed

Prototype a function()

Copy file

Equate symbols to values


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.STACK 4096 ; reserve 4096-byte stack


Declare the Size of runtime stack


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.DATA ; reserve storage for data

number1 DWORD ?

number2 DWORD ?

Starts the data segment

Reserve a single

doubleword of storageSymbolic

name


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prompt1 BYTE "Enter first number: ", 0prompt2 BYTE "Enter second number: ", 0

string BYTE 40 DUP(?)label1 BYTE cr, Lf, "The sum is "sum BYTE 11 DUP(?)

BYTE cr, Lf, 0

Reserve a byte of

storage

Repeat items

in

parentheses


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output prompt2 ; repeat for second numberinput string, 40atod string

mov number2, eaxmov eax, number1 ; first number to EAXadd eax, number2 ; add second numberdtoa sum, eax ; convert to ASCII characters

output label1 ; output label and sum


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INVOKE ExitProcess, 0 ; exit with return code 0

PUBLIC _start ; make entry point public

END ; end of source code

Call the procedure

Make the label visible outside the file

Marks the physical ends of the program


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Template for assembly language

;Comments for your program

.386

.MODEL FLAT, stdcall

includelib lib\kernel32.lib

ExitProcess PROTO NEAR32 stdcall, dwExitCode:DWORD

.STACK 4096 ; reserve 4096-byte stack

.DATA ; reserve storage for data

{;data define;}

.CODE ; start of main program code

start:{;your codes;}

INVOKE ExitProcess, 0 ;exit with return code 0

ret

END start ;end of source code


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3.1 Assembly Language

StatementsLength: up to 512

If not enough, use backslash(\) character at

the end of a line

Comments:

Begin with the semicolon(;) and extends

until the end of the line


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Three types of functional assembly

language statements InstructionsCan be translated into machine code( object

code)DirectivesTell the assembler to take some action , not

result in machine code

macrosShorthand for a sequence of other

statements


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Components of a statement

name: mnemonic operands ;comment


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3.3 How to Assemble , Link and

Run a Program

Edit source code

Assemble source code

Link

execute


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Make executable file

Assemble

ml /c /coff /Zi example.asm

LinkLink /subsystem:console /entry:start

/out:example.exe /debug example.obj io.obj

kernel32.libRun

example


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3.4 The Assemble Listing File

Help to understand

the assembly process

Shows the sourcecode, the object code

and additional

information

ml /c /coff /Zi /Fl example.asm


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First part of listing file

Microsoft (R) Macro Assembler Version 6.14.8444 09/15/06 08:11:53

D:\masm32\HelloCon.asm Page 1 - 1

Offset address ofeach directives or

instructions

Object code ofinstructions or

value assigned by

directives

statements

Representing data in hexdicimal


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3.5 Variable Operands

Numeric operands

Directives:

Byte

Word

Dword

Radix

Changes the default number base

Assembler assumes that a number is decimal


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Constant operands

EQU

Symbol EQU value

=

Symbol = value

Can be redefined


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Model define directives

Select Instruction set

.386, .486, .586,386p, .mmx

Option

Option casemap:none

mode definemodel memory mode, [call], [others]


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Memory mode

Memory

mode

Max.

size of

seg.

File type OS Code seg. Data seg.

Tiny 64KB .com DOS One seg.

Small 64KB .exe DOS 1 1

Medium 64KB .exe DOS 1 Multi.

Compact 64KB .exe DOS Multi. 1

Large 64KB .exe DOS Multi. Multi.

Huge 64KB .exe DOS Multi. Multi.

flat 4GB .exe(PE) Windows Same seg.


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Include and includelib

Include filename

Insert other files in current file

Includelib filename

Tell the linker use library file named by

filename.

Insert function code in .exe file.


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Declare function

Function_name PROTO[call]

[parameter1name:parameter1 type],

Call:

C, stdcall,


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Data Area define

.data

Begin a data segment

.data?Not initial data

.const

Define constant .stack [size]

Define stack


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Code area define

.code

Begin code segment

END [LABEL]

The last statement in the program.

Label shows the entry point of the program.


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Laboratory Exercise1

Build the developing environment forprogramming using assembly language.

Test HelloCon.asm and HelloWin.asm.

Make a program complete the followingfunction: s=x+y. Use debugger to prove youprogram is correct.

Report:Introduce your developing environment.

Write your program. Introduce the debuggingstep that you used.


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3.6 Instruction Operands

Two operands

Destination operands

Source operands

Constants

Designate CPU registersReference memory locations


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Addressing modes

Giving the location of the data for eachmode

Immediate addressing mode:in the instruction itself

Register addressing mode:

in a registerMemory addressing mode :

at some address in memory


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MOV instruction

We use MOV instruction introduce

addressing mode.

MOV dest , src; src -> dest


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Immediate addressing mode

Operand itself is in the instruction.

Eaxmple:

MOV eax , 100; 100 -> eax

Result: eax=00000064h

Machine code: B8 00000064

MOV al , / ; 2F -> al, B0 2FADD eax,135 ; eax+135->eax

;05 00000087


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Register addressing mode

Operand is in a register.

MOV eax, ebx; ebx -> eax

MOV eax, 100 ; 100 -> eax

8-bit registers: AH, AL and DL

16-bit registers: AX, BX and DI32-bit registers: EAX, EBX and EDI

segment registers: CS, ES, DS, SS, FS and GS


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Not allowed Never

mix an 8-bit register with a 16-bit register, an8-bit register with a 32-bit register, or a 16-bit register

with a 32-bit register because this is not allowed by

the microprocessor and results in an error when

assembled. A segment-to-segment register MOV instruction is not

allowed. Changing the CS register with a MOV

instruction is notallowed.

MOV ES,DS ; not allowed

MOV BL,DX ; not allowed

MOV CS,AX ; not allowed


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Memory addressing modes

Operand is stored in memory.

How to calculate memory addressDirect:

memory address is built into the instruction

Register indirect:memory address is in a register


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Direct addressing mode

Operand has the 32-bit address built into theinstruction.

Programmer often codes a symbol that isassociated with a BYTE, DWORD, or WORDdirective in the data segment or with aninstruction in the code segment.

The location corresponding to such a symbolwill be relocatable so that the assembler listingshows an assembly-time address that may beadjusted later.


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ADD eax, number2;05 00000004

Note:

value BYTE 100

MOV eax , value

;;;;;

value EQU 100

MOV eax , value


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Example for indirect addressing

value DWORD 100

MOV edx, value ; edx=100

MOV edx , OFFSET value

; edx=offset address of valueMOV eax , [edx] ;eax=100


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Register used for indirect mode

Registers EAX, EBX, ECX, EDX, ESI, EDI

can be used for register indirect

addressing.(in data segment)

Register EBPcan be used for register indirect

addressing an address in stack segment.

ESPalso can be used for register indirectaddressing.But we seldom use it.

For 16-bit:only use BX, SI, DI, BP


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Size of the memory operand

When the size of the memory operand isambiguous, the PTR directive must be used togive the size to the assembler.

MOV [ebx] , 0

MOV BYTE PTR[ebx], 0

MOV eax, [edx];no need use PTR,the size of dest

operand is the same as the src operand.WORD PTR, DWORD PTR used for word

or doubleword operands respectively.


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Base-plus-index addressing

For 16-bit:use one base register (BX or BP),

and one index register (DI or SI) to indirectly

address memory.

MOV CX,[BX+DI] ;16-bit, CX = DS:[BX+DI]

MOV CH,[BP+SI] ;8-bit, CH = SS:[BP+SI]

For 32-bit:allows the combination of any two

32-bit extended registers except ESP.

MOV CL,[EDX+EDI] ;8-bit, CL=DS:[EDX+EDI]

MOV [EAX+EBX],ECX;32-bit, DS:[EAX+EBX] =ECX

R i t l ti dd i


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Register relative addressing

In register relative addressing, the data in asegment of memory are addressed by addingthe displacementto the contents of a base or anindex register (BX, SI, DI, or BP).

MOV AX,[DI+100H] ;16-bit, AX = DS:[DI+100H]

MOV ARRAY[SI],BL;8-bit, ARRAY[SI] = BL

For 32-bit, any of the 32-bit general-purpose

registers can be used in the register relativeaddressing.

MOV DI,[EAX+10] ;16-bit, DI = DS:[EAX+10]

MOV ARRAY[EBX],EAX;32-bit, ARRAY[EBX] = EAX


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Base relative-plus-index addressing

Adds a displacement, besides using a baseregister (BX or BP) and an index register (SI orDI), to form the memory address.

MOV DH,[BX+DI+20H]MOV AX,FILE[BX+SI]

MOV LIST[BP+DI],CL

MOV LIST[BP+SI+4],DH

MOV EAX,FILE[EBX+ECX+2] In 80386 and above, all the 32-bit extended

registers are both base register and indexregister.


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Scaled-index addressing

This data-addressing mode is unique to the80386 and above. It uses one or two 32-bitregisters to access the memory. The secondregister is multiplied by a scaling factor (1, 2, 4,

or 8).MOV EAX,[EBX+4*ECX]

MOV [EAX+2*EDI+100H],CX

MOV AL,[EBP+2*EDI-2]

MOV EAX,ARRAY[4*ECX]

MOV AL,[2*EBX]

A scaling factor of 1X is implied and need not beincluded in the assembly language instruction.


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3.7 Input/Output Using Macros

Defined in IO.HRead this part youselves, and do the

exercises. If you have any question,

please put up your hand and ask me or

discuss with others.


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Exercises

P45. Exercises3.1 1, 2

P67. Exercises3.4 2, 3, 4

P72. Exercises3.5 1-32



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