Chapter 3 Assembly Language Fundamentals 6th edition.ppt

Assembly Language for x86 Processors
Assembly Language for x86 Processors
6th Edition
6th Edition
Chapter 3: Assembly Language
Fundamentals
(c) Pearson Education, 2010. All rights reserved. You may modify and copy this slide show for your personal use, or
for use in the classroom, as long as this copyright statement, the author's name, and the title are not changed.
Slides prepared by the author
Revision date: 2/15/2010
Kip Irvine

Irvine, Kip R. Assembly Language for x86 Processors 6/e, 2010.
2
Chapter Overview
Chapter Overview
• Basic Elements of Assembly Language
• Example: Adding and Subtracting Integers
• Assembling, Linking, and Running Programs
• Defining Data
• Symbolic Constants
• Real-Address Mode Programming

3
Basic Elements of Assembly Language
Basic Elements of Assembly Language
• Integer constants
• Integer expressions
• Character and string constants
• Reserved words and identifiers
• Directives and instructions
• Labels
• Mnemonics and Operands
• Comments
• Examples

4
Integer Constants
Integer Constants
• Optional leading + or – sign
• binary, decimal, hexadecimal, or octal digits
• Common radix characters:
• h – hexadecimal
• d – decimal
• b – binary
• r – encoded real
Examples: 30d, 6Ah, 42, 1101b
Hexadecimal beginning with letter: 0A5h

5
Integer Expressions
Integer Expressions
• Operators and precedence levels:
• Examples:

6
Character and String Constants
Character and String Constants
• Enclose character in single or double quotes
• 'A', "x"
• ASCII character = 1 byte
• Enclose strings in single or double quotes
• "ABC"
• 'xyz'
• Each character occupies a single byte
• Embedded quotes:
• 'Say "Goodnight," Gracie'

7
Reserved Words and Identifiers
Reserved Words and Identifiers
• Reserved words cannot be used as identifiers
• Instruction mnemonics, directives, type attributes,
operators, predefined symbols
• See MASM reference in Appendix A
• Identifiers
• 1-247 characters, including digits
• not case sensitive
• first character must be a letter, _, @, ?, or $

8
Directives
Directives
• Commands that are recognized and acted
upon by the assembler
• Not part of the Intel instruction set
• Used to declare code, data areas, select
memory model, declare procedures, etc.
• not case sensitive
• Different assemblers have different directives
• NASM not the same as MASM, for example

9
Instructions
Instructions
• Assembled into machine code by assembler
• Executed at runtime by the CPU
• We use the Intel IA-32 instruction set
• An instruction contains:
• Label (optional)
• Mnemonic (required)
• Operand (depends on the instruction)
• Comment (optional)

10
Labels
Labels
• Act as place markers
• marks the address (offset) of code and data
• Follow identifer rules
• Data label
• must be unique
• example: myArray (not followed by colon)
• Code label
• target of jump and loop instructions
• example: L1: (followed by colon)

11
Mnemonics and Operands
Mnemonics and Operands
• Instruction Mnemonics
• memory aid
• examples: MOV, ADD, SUB, MUL, INC, DEC
• Operands
• constant
• constant expression
• register
• memory (data label)
Constants and constant expressions are often called
immediate values

12
Comments
Comments
• Comments are good!
• explain the program's purpose
• when it was written, and by whom
• revision information
• tricky coding techniques
• application-specific explanations
• Single-line comments
• begin with semicolon (;)
• Multi-line comments
• begin with COMMENT directive and a programmer-
chosen character
• end with the same programmer-chosen character

13
Instruction Format Examples
Instruction Format Examples
• No operands
• stc ; set Carry flag
• One operand
• inc eax ; register
• inc myByte ; memory
• Two operands
• add ebx,ecx ; register, register
• sub myByte,25 ; memory, constant
• add eax,36 * 25 ; register, constant-
expression

14
What's Next
What's Next
• Defining Data

15
Example: Adding and Subtracting Integers
Example: Adding and Subtracting Integers
TITLE Add and Subtract (AddSub.asm)
; This program adds and subtracts 32-bit integers.
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h ; EAX = 10000h
add eax,40000h ; EAX = 50000h
sub eax,20000h ; EAX = 30000h
call DumpRegs ; display registers
exit
main ENDP
END main

16
Example Output
Example Output
Program output, showing registers and flags:
EAX=00030000 EBX=7FFDF000 ECX=00000101 EDX=FFFFFFFF
ESI=00000000 EDI=00000000 EBP=0012FFF0 ESP=0012FFC4
EIP=00401024 EFL=00000206 CF=0 SF=0 ZF=0 OF=0

17
Suggested Coding Standards
Suggested Coding Standards (1 of 2)
(1 of 2)
• Some approaches to capitalization
• capitalize nothing
• capitalize everything
• capitalize all reserved words, including instruction
mnemonics and register names
• capitalize only directives and operators
• Other suggestions
• descriptive identifier names
• spaces surrounding arithmetic operators
• blank lines between procedures

18
Suggested Coding Standards
Suggested Coding Standards (2 of 2)
(2 of 2)
• Indentation and spacing
• code and data labels – no indentation
• executable instructions – indent 4-5 spaces
• comments: right side of page, aligned vertically
• 1-3 spaces between instruction and its operands
• ex: mov ax,bx
• 1-2 blank lines between procedures

19
Required Coding Standards
Required Coding Standards
• (to be filled in by the professor)

20
Alternative Version of AddSub
Alternative Version of AddSub
TITLE Add and Subtract (AddSubAlt.asm)
; This program adds and subtracts 32-bit integers.
.386
.MODEL flat,stdcall
.STACK 4096
ExitProcess PROTO, dwExitCode:DWORD
DumpRegs PROTO
.code
main PROC
mov eax,10000h ; EAX = 10000h
add eax,40000h ; EAX = 50000h
sub eax,20000h ; EAX = 30000h
call DumpRegs
INVOKE ExitProcess,0
main ENDP
END main

21
Program Template
Program Template
TITLE Program Template (Template.asm)
; Program Description:
; Author:
; Creation Date:
; Revisions:
; Date: Modified by:
.data
; (insert variables here)
.code
main PROC
; (insert executable instructions here)
exit
main ENDP
; (insert additional procedures here)
END main

22
What's Next
What's Next
• Defining Data

23
Assembling, Linking, and Running Programs
Assembling, Linking, and Running Programs
• Assemble-Link-Execute Cycle
• Listing File
• Map File

24
Assemble-Link Execute Cycle
Assemble-Link Execute Cycle
• The following diagram describes the steps from creating a
source program through executing the compiled program.
• If the source code is modified, Steps 2 through 4 must be
repeated.

25
Listing File
Listing File
• Use it to see how your program is compiled
• Contains
• source code
• addresses
• object code (machine language)
• segment names
• symbols (variables, procedures, and constants)
• Example: addSub.lst

26
Map File
Map File
• Information about each program segment:
• starting address
• ending address
• size
• segment type
• Example: addSub.map (16-bit version)

27
What's Next
What's Next
• Defining Data

28
Defining Data
Defining Data
• Intrinsic Data Types
• Data Definition Statement
• Defining BYTE and SBYTE Data
• Defining WORD and SWORD Data
• Defining DWORD and SDWORD Data
• Defining QWORD Data
• Defining TBYTE Data
• Defining Real Number Data
• Little Endian Order
• Adding Variables to the AddSub Program
• Declaring Uninitialized Data

29
Intrinsic Data Types
Intrinsic Data Types (1 of 2)
(1 of 2)
• BYTE, SBYTE
• 8-bit unsigned integer; 8-bit signed integer
• WORD, SWORD
• 16-bit unsigned & signed integer
• DWORD, SDWORD
• 32-bit unsigned & signed integer
• QWORD
• 64-bit integer
• TBYTE
• 80-bit integer

30
Intrinsic Data Types
Intrinsic Data Types (2 of 2)
(2 of 2)
• REAL4
• 4-byte IEEE short real
• REAL8
• 8-byte IEEE long real
• REAL10
• 10-byte IEEE extended real

31
Data Definition Statement
Data Definition Statement
• A data definition statement sets aside storage in memory for a
variable.
• May optionally assign a name (label) to the data
• Syntax:
[name] directive initializer [,initializer] . . .
value1 BYTE 10
• All initializers become binary data in memory

32
Defining BYTE and SBYTE Data
Defining BYTE and SBYTE Data
value1 BYTE 'A' ; character constant
value2 BYTE 0 ; smallest unsigned byte
value3 BYTE 255 ; largest unsigned byte
value4 SBYTE -128 ; smallest signed byte
value5 SBYTE +127 ; largest signed byte
value6 BYTE ? ; uninitialized byte
Each of the following defines a single byte of storage:
• MASM does not prevent you from initializing a BYTE with a
negative value, but it's considered poor style.
• If you declare a SBYTE variable, the Microsoft debugger will
automatically display its value in decimal with a leading sign.

33
Defining Byte Arrays
Defining Byte Arrays
list1 BYTE 10,20,30,40
list2 BYTE 10,20,30,40
BYTE 50,60,70,80
BYTE 81,82,83,84
list3 BYTE ?,32,41h,00100010b
list4 BYTE 0Ah,20h,‘A’,22h
Examples that use multiple initializers:

34
Defining Strings
Defining Strings (1 of 3)
(1 of 3)
• A string is implemented as an array of characters
• For convenience, it is usually enclosed in quotation marks
• It often will be null-terminated
• Examples:
str1 BYTE "Enter your name",0
str2 BYTE 'Error: halting program',0
str3 BYTE 'A','E','I','O','U'
greeting BYTE "Welcome to the Encryption Demo program "
BYTE "created by Kip Irvine.",0

35
Defining Strings
(2 of 3)
• To continue a single string across multiple lines, end
each line with a comma:
menu BYTE "Checking Account",0dh,0ah,0dh,0ah,
"1. Create a new account",0dh,0ah,
"2. Open an existing account",0dh,0ah,
"3. Credit the account",0dh,0ah,
"4. Debit the account",0dh,0ah,
"5. Exit",0ah,0ah,
"Choice> ",0

36
Defining Strings
(3 of 3)
• End-of-line character sequence:
• 0Dh = carriage return
• 0Ah = line feed
str1 BYTE "Enter your name: ",0Dh,0Ah
BYTE "Enter your address: ",0
newLine BYTE 0Dh,0Ah,0
Idea: Define all strings used by your program in the same
area of the data segment.

37
Using the DUP Operator
Using the DUP Operator
• Use DUP to allocate (create space for) an array or
string. Syntax: counter DUP ( argument )
• Counter and argument must be constants or constant
expressions
var1 BYTE 20 DUP(0) ; 20 bytes, all equal to zero
var2 BYTE 20 DUP(?) ; 20 bytes, uninitialized
var3 BYTE 4 DUP("STACK") ; 20 bytes: "STACKSTACKSTACKSTACK"
var4 BYTE 10,3 DUP(0),20 ; 5 bytes

38
Defining WORD and SWORD Data
Defining WORD and SWORD Data
• Define storage for 16-bit integers
• or double characters
• single value or multiple values
word1 WORD 65535 ; largest unsigned value
word2 SWORD –32768 ; smallest signed value
word3 WORD ? ; uninitialized, unsigned
word4 WORD "AB" ; double characters
myList WORD 1,2,3,4,5 ; array of words
array WORD 5 DUP(?) ; uninitialized array

39
Defining DWORD and SDWORD Data
Defining DWORD and SDWORD Data
val1 DWORD 12345678h ; unsigned
val2 SDWORD –2147483648 ; signed
val3 DWORD 20 DUP(?) ; unsigned array
val4 SDWORD –3,–2,–1,0,1 ; signed array
Storage definitions for signed and unsigned 32-bit
integers:

40
Defining QWORD, TBYTE, Real Data
Defining QWORD, TBYTE, Real Data
quad1 QWORD 1234567812345678h
val1 TBYTE 1000000000123456789Ah
rVal1 REAL4 -2.1
rVal2 REAL8 3.2E-260
rVal3 REAL10 4.6E+4096
ShortArray REAL4 20 DUP(0.0)
Storage definitions for quadwords, tenbyte values,
and real numbers:

41
Little Endian Order
Little Endian Order
• All data types larger than a byte store their individual
bytes in reverse order. The least significant byte occurs
at the first (lowest) memory address.
• Example:
val1 DWORD 12345678h

42
Adding Variables to AddSub
Adding Variables to AddSub
TITLE Add and Subtract, Version 2 (AddSub2.asm)
; This program adds and subtracts 32-bit unsigned
; integers and stores the sum in a variable.
.data
val1 DWORD 10000h
val2 DWORD 40000h
val3 DWORD 20000h
finalVal DWORD ?
.code
main PROC
mov eax,val1 ; start with 10000h
add eax,val2 ; add 40000h
sub eax,val3 ; subtract 20000h
mov finalVal,eax ; store the result (30000h)
call DumpRegs ; display the registers
exit
main ENDP
END main

43
Declaring Unitialized Data
Declaring Unitialized Data
• Use the .data? directive to declare an unintialized
data segment:
.data?
• Within the segment, declare variables with "?"
initializers:
smallArray DWORD 10 DUP(?)
Advantage: the program's EXE file size is reduced.

44
What's Next
What's Next
• Defining Data

45
Symbolic Constants
Symbolic Constants
• Equal-Sign Directive
• Calculating the Sizes of Arrays and Strings
• EQU Directive
• TEXTEQU Directive

46
Equal-Sign Directive
Equal-Sign Directive
• name = expression
• expression is a 32-bit integer (expression or constant)
• may be redefined
• name is called a symbolic constant
• good programming style to use symbols
COUNT = 500
.
.
mov ax,COUNT

47
Calculating the Size of a Byte Array
Calculating the Size of a Byte Array
• current location counter: $
• subtract address of list
• difference is the number of bytes
list BYTE 10,20,30,40
ListSize = ($ - list)

48
Calculating the Size of a Word Array
Calculating the Size of a Word Array
Divide total number of bytes by 2 (the size of a word)
list WORD 1000h,2000h,3000h,4000h
ListSize = ($ - list) / 2

49
Calculating the Size of a Doubleword Array
Calculating the Size of a Doubleword Array
Divide total number of bytes by 4 (the size of a
doubleword)
list DWORD 1,2,3,4
ListSize = ($ - list) / 4

50
EQU Directive
EQU Directive
• Define a symbol as either an integer or text expression.
• Cannot be redefined
PI EQU <3.1416>
pressKey EQU <"Press any key to continue...",0>
.data
prompt BYTE pressKey

51
TEXTEQU Directive
TEXTEQU Directive
• Define a symbol as either an integer or text expression.
• Called a text macro
• Can be redefined
continueMsg TEXTEQU <"Do you wish to continue (Y/N)?">
rowSize = 5
.data
prompt1 BYTE continueMsg
count TEXTEQU %(rowSize * 2) ; evaluates the expression
setupAL TEXTEQU <mov al,count>
.code
setupAL ; generates: "mov al,10"

52
What's Next
What's Next
• Defining Data

53
Real-Address Mode Programming
Real-Address Mode Programming (1 of 2)
(1 of 2)
• Generate 16-bit MS-DOS Programs
• Advantages
• enables calling of MS-DOS and BIOS functions
• no memory access restrictions
• Disadvantages
• must be aware of both segments and offsets
• cannot call Win32 functions (Windows 95 onward)
• limited to 640K program memory

54
Real-Address Mode Programming
Real-Address Mode Programming (2 of 2)
(2 of 2)
• Requirements
• INCLUDE Irvine16.inc
• Initialize DS to the data segment:
mov ax,@data
mov ds,ax

55
Add and Subtract, 16-Bit Version
Add and Subtract, 16-Bit Version
TITLE Add and Subtract, Version 2 (AddSub2r.asm)
.data
val1 DWORD 10000h
val2 DWORD 40000h
val3 DWORD 20000h
finalVal DWORD ?
.code
main PROC
mov ax,@data ; initialize DS
mov ds,ax
mov eax,val1 ; get first value
add eax,val2 ; add second value
sub eax,val3 ; subtract third
value
mov finalVal,eax ; store the result
call DumpRegs ; display registers
exit
main ENDP
END main

56
Summary
Summary
• Integer expression, character constant
• directive – interpreted by the assembler
• instruction – executes at runtime
• code, data, and stack segments
• source, listing, object, map, executable files
• Data definition directives:
• BYTE, SBYTE, WORD, SWORD, DWORD, SDWORD, QWORD,
TBYTE, REAL4, REAL8, and REAL10
• DUP operator, location counter ($)
• Symbolic constant
• EQU and TEXTEQU

57
4C 61 46 69 6E
4C 61 46 69 6E

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