程序代写代做代考 assembly c/c++ mips c++ flex assembler algorithm PowerPoint Presentation

PowerPoint Presentation

Introduction to
Assembly Language
CFOMSC 260

Outline
Basic Elements of Assembly Language
Flat Memory Program Template
Example: Adding and Subtracting Integers
Assembling, Linking, and Debugging Programs
Defining Data
Defining Symbolic Constants
Data-Related Operators and Directives

Constants
Integer Constants
Examples: –10, 42d, 10001101b, 0FF3Ah, 777o
Radix: b = binary, d = decimal, h = hexadecimal, and o = octal
If no radix is given, the integer constant is decimal
A hexadecimal beginning with a letter must have a leading 0
Character and String Constants
Enclose character or string in single or double quotes
Examples: ‘A’, “d”, ‘ABC’, “ABC”, ‘4096’
Embedded quotes: “single quote ‘ inside”, ‘double quote ” inside’
Each ASCII character occupies a single byte

Assembly Language Statements
Three types of statements in assembly language
Executable Instructions
Generate machine code for the processor to execute at runtime
Instructions tell the processor what to do
Assembler Directives
Provide information to the assembler while translating a program
Used to define data, select memory model, etc.
Non-executable: directives are not part of instruction set
Macros
Shorthand notation for a group of statements
Sequence of instructions, directives, or other macros

Instructions
Assembly language instructions have the format:
[label:] mnemonic [operands] [;comment]
Instruction Label (optional)
Marks the address of an instruction, must have a colon :
Used to transfer program execution to a labeled instruction
Mnemonic
Identifies the operation (e.g. MOV, ADD, SUB, JMP, CALL)
Operands
Specify the data required by the operation
Executable instructions can have zero to three operands
Operands can be registers, memory variables, or constants

Instruction Examples
No operands
stc ; set carry flag
One operand
inc eax ; increment register eax
call Clrscr ; call procedure Clrscr
jmp L1 ; jump to instruction with label L1
Two operands
add ebx, ecx ; register ebx = ebx + ecx
sub var1, 25 ; memory variable var1 = var1 – 25
Three operands
imul eax,ebx,5 ; register eax = ebx * 5

Identifiers
Identifier is a programmer chosen name
Identifies variable, constant, procedure, code label
May contain between 1 and 247 characters
Not case sensitive
First character must be a letter (A..Z, a..z), underscore(_), @, ?, or $.
Subsequent characters may also be digits.
Cannot be same as assembler reserved word.

Comments
Comments are very important!
Explain the program’s purpose
When it was written, revised, and by whom
Explain data used in the program
Explain instruction sequences and algorithms used
Application-specific explanations
Single-line comments
Begin with a semicolon ; and terminate at end of line
Multi-line comments
Begin with COMMENT and chosen character
End with the same chosen character

Next . . .
Basic Elements of Assembly Language
Flat Memory Program Template
Example: Adding and Subtracting Integers
Assembling, Linking, and Debugging Programs
Defining Data
Defining Symbolic Constants
Data-Related Operators and Directives

Flat Memory Program Template
TITLE Flat Memory Program Template (Template.asm)

; Program Description:
; Author: Creation Date:
; Modified by: Modification Date:

.386
.MODEL FLAT, STDCALL
.STACK

INCLUDE Irvine32.inc
.DATA
; (insert variables here)
.CODE
main PROC
; (insert executable instructions here)
exit
main ENDP
; (insert additional procedures here)
END main

TITLE and .MODEL Directives
TITLE line (optional)
Contains a brief heading of the program and the disk file name
.MODEL directive
Specifies the memory configuration
For our purposes, the FLAT memory model will be used
Linear 32-bit address space (no segmentation)
STDCALL directive tells the assembler to use …
Standard conventions for names and procedure calls
.386 processor directive
Used before the .MODEL directive
The CPU architecture that the program can use
At least the .386 directive should be used with the FLAT model

.STACK, .DATA, & .CODE Directives

.STACK directive
Tells the assembler to define a runtime stack for the program
The size of the stack can be optionally specified by this directive
The runtime stack is required for procedure calls
.DATA directive
Defines an area in memory for the program data
The program’s variables should be defined under this directive
Assembler will allocate and initialize the storage of variables
.CODE directive
Defines the code section of a program containing instructions
Assembler will place the instructions in the code area in memory

INCLUDE, PROC, ENDP, and END

INCLUDE directive
Causes the assembler to include code from another file
We will include Irvine32.inc provided by the author Kip Irvine
Declares procedures implemented in the Irvine32.lib library
To use this library, you should link Irvine32.lib to your programs
PROC and ENDP directives
Used to define procedures
As a convention, we will define main as the first procedure
Additional procedures can be defined after main
END directive
Marks the end of a program
Identifies the name (main) of the program’s startup procedure

TITLE Add and Subtract (AddSub.asm)
; This program adds and subtracts 32-bit integers.
.386
.MODEL FLAT, STDCALL
.STACK
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
Adding and Subtracting Integers

Example of Console Output
Procedure DumpRegs is defined in Irvine32.lib library
It produces the following console 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

Suggested Coding Standards

Some approaches to capitalization
Capitalize nothing
Capitalize everything
Capitalize all reserved words, mnemonics and register names
Capitalize only directives and operators
MASM is NOT case sensitive: does not matter what case is used
Other suggestions
Use meaningful identifier names
Use blank lines between procedures
Use indentation and spacing to align instructions and comments
Use tabs to indent instructions, but do not indent labels
Align the comments that appear after the instructions

Understanding Program Termination

The exit at the end of main procedure is a macro
Defined in Irvine32.inc
Expanded into a call to ExitProcess that terminates the program
ExitProcess function is defined in the kernel32 library
We can replace exit with the following:
push 0 ; push parameter 0 on stack
call ExitProcess ; to terminate program
You can also replace exit with: INVOKE ExitProcess, 0
PROTO directive (Prototypes)
Declares a procedure used by a program and defined elsewhere
ExitProcess PROTO, dwExitCode:DWORD
Specifies the parameters and types of a given procedure

Modified Program
TITLE Add and Subtract (AddSubAlt.asm)
; This program adds and subtracts 32-bit integers

.386
.MODEL flat,stdcall
.STACK 4096

; No need to include Irvine32.inc for exit function
ExitProcess PROTO, dwExitCode:DWORD

.code
main PROC
mov eax,10000h ; EAX = 10000h
add eax,40000h ; EAX = 50000h
sub eax,20000h ; EAX = 30000h

push 0
call ExitProcess ; to terminate program
main ENDP
END main

Assemble-Link-Debug Cycle
Editor
Write new (.asm) programs
Make changes to existing ones
Assembler: .lst file
Translate (.asm) file into object (.obj) file in machine language
Can produce a listing (.lst) file that shows the work of assembler
Linker: .exe program
Combine object (.obj) files with link library (.lib) files
Produce executable (.exe) file
Can produce (.map) file

Edit

Assemble

Link

Run

prog.asm

prog.obj

prog.lst

prog.exe

prog.map

library.lib

Debug

Assemble-Link-Debug Cycle – cont’d

Trace program execution
Either step-by-step, or
Use breakpoints
View
Source (.asm) code
Registers
Memory by name & by address
Modify register & memory content

Discover errors and go back to the editor to fix the program bugs

Edit

Assemble

Link

Run

prog.asm

prog.obj

prog.lst

prog.exe

prog.map

library.lib

Debug

Listing File
Use it to see how your program is assembled
Contains
Source code
Object code
Relative addresses
Segment names
Symbols
Variables
Procedures
Constants
Object & source code in a listing file
00000000 .code
00000000 main PROC
00000000 B8 00060000 mov eax, 60000h
00000005 05 00080000 add eax, 80000h
0000000A 2D 00020000 sub eax, 20000h

0000000F 6A 00 push 0
00000011 E8 00000000 E call ExitProcess
00000016 main ENDP
END main

object code
(hexadecimal)

source code

Relative
Addresses

Intrinsic Data Types(pre defined and always accessible)
BYTE, SBYTE
8-bit unsigned integer
8-bit signed integer
WORD, SWORD
16-bit unsigned integer
16-bit signed integer
DWORD, SDWORD
32-bit unsigned integer
32-bit signed integer
QWORD, TBYTE
64-bit integer
80-bit integer
REAL4
IEEE single-precision float
Occupies 4 bytes
REAL8
IEEE double-precision
Occupies 8 bytes
REAL10
IEEE extended-precision
Occupies 10 bytes
IEEE stands for
Institute of Electrical and Electronics Engineers

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] . . .

val1 BYTE 10

All initializers become binary data in memory

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

Defining Strings
A string is implemented as an array of characters
For convenience, it is usually enclosed in quotation marks
It is often terminated with a NULL char (byte value = 0)
Examples:
str1 BYTE “Enter your name”, 0
str2 BYTE ‘Error: halting program’, 0
str3 BYTE ‘D’,‘V’,‘C‘
greeting BYTE “Welcome to the Encryption ”
BYTE “Demo Program”, 0

Defining Strings – cont’d
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
End-of-line character sequence:
0Dh = 13 = carriage return
0Ah = 10 = line feed
Idea: Define all strings used by your program in the same area of the data segment

Using the DUP Operator
Use DUP to allocate space for an array or string
Advantage: more compact than using a list of initializers
Syntax
counter DUP ( argument )
Counter and argument must be constants expressions
The DUP operator may also be nested
var1 BYTE 20 DUP(0) ; 20 bytes, all equal to zero
var2 BYTE 20 DUP(?) ; 20 bytes, all uninitialized
var3 BYTE 4 DUP(“STACK”) ; 20 bytes: “STACKSTACKSTACKSTACK”
var4 BYTE 10,3 DUP(0),20 ; 5 bytes: 10, 0, 0, 0, 20
var5 BYTE 2 DUP(5 DUP(‘*’), 5 DUP(‘!’)) ; ‘*****!!!!!*****!!!!!’

Defining 16-bit and 32-bit Data
Define storage for 16-bit and 32-bit integers
Signed and Unsigned
Single or multiple initial values
word1 WORD 65535 ; largest unsigned 16-bit value
word2 SWORD –32768 ; smallest signed 16-bit value
word3 WORD “AB” ; two characters fit in a WORD
array1 WORD 1,2,3,4,5 ; array of 5 unsigned words
array2 SWORD 5 DUP(?) ; array of 5 signed words
dword1 DWORD 0ffffffffh ; largest unsigned 32-bit value
dword2 SDWORD –2147483648 ; smallest signed 32-bit value
array3 DWORD 20 DUP(?) ; 20 unsigned double words
array4 SDWORD –3,–2,–1,0,1 ; 5 signed double words

LEGACY DATA DIRECTIVES
DB – 8-bit integer
DW – 16 bit integer
DD – 32 bit integer or real
DQ – 64 bit integer or real
DT – define 80 bit integer

QWORD, TBYTE, and REAL Data
quad1 QWORD 1234567812345678h
val1 TBYTE 1000000000123456789Ah
rVal1 REAL4 -2.1
rVal2 REAL8 3.2E-260
rVal3 REAL10 4.6E+4096
array REAL4 20 DUP(0.0)

QWORD and TBYTE
Define storage for 64-bit and 80-bit integers
Signed and Unsigned
REAL4, REAL8, and REAL10
Defining storage for 32-bit, 64-bit, and 80-bit floating-point data

Symbol Table
Assembler builds a symbol table
So we can refer to the allocated storage space by name
Assembler keeps track of each name and its offset
Offset of a variable is relative to the address of the first variable
Example Symbol Table
.DATA Name Offset
value WORD 0 value 0
sum DWORD 0 sum 2
marks WORD 10 DUP (?) marks 6
msg BYTE ‘The grade is:’,0 msg 26
char1 BYTE ? char1 40

Byte Ordering and Endianness
Processors can order bytes within a word in two ways
Little Endian Byte Ordering
Memory address = Address of least significant byte
Examples: Intel 80×86

Big Endian Byte Ordering
Memory address = Address of most significant byte
Examples: MIPS, Motorola 68k, SPARC

Byte 0
Byte 1
Byte 2
Byte 3
32-bit Register
MSB
LSB
. . .
. . .
Byte 0
Byte 1
Byte 2
Byte 3
a
a+3
a+2
a+1

Memory
address

Byte 3
Byte 0
Byte 1
Byte 2
Byte 3
32-bit Register
MSB
LSB
. . .
. . .
Byte 0
Byte 1
Byte 2
a
a+3
a+2
a+1

Memory
address

Adding Variables to AddSub
TITLE Add and Subtract, Version 2 (AddSub2.asm)
.686
.MODEL FLAT, STDCALL
.STACK
INCLUDE Irvine32.inc
.DATA
val1 DWORD 10000h
val2 DWORD 40000h
val3 DWORD 20000h
result DWORD ?
.CODE
main PROC
mov eax,val1 ; start with 10000h
add eax,val2 ; add 40000h
sub eax,val3 ; subtract 20000h
mov result,eax ; store the result (30000h)
call DumpRegs ; display the registers
exit
main ENDP
END main

Defining Symbolic Constants
Symbolic Constant
Just a name used in the assembly language program
Processed by the assembler  pure text substitution
Assembler does NOT allocate memory for symbolic constants
Assembler provides three directives:
= directive
EQU directive
TEXTEQU directive
Defining constants has two advantages:
Improves program readability
Helps in software maintenance: changes are done in one place

Equal-Sign Directive
Name = Expression
Name is called a symbolic constant
Expression is an integer constant expression
Good programming style to use symbols

Name can be redefined in the program
COUNT = 500 ; NOT a variable (NO memory allocation)
. . .
mov eax, COUNT ; mov eax, 500
. . .
COUNT = 600 ; Processed by the assembler
. . .
mov ebx, COUNT ; mov ebx, 600

EQU Directive
Three Formats:
Name EQU Expression Integer constant expression
Name EQU Symbol Existing symbol name
Name EQU Any text may appear within < …>

No Redefinition: Name cannot be redefined with EQU
SIZE EQU 10*10 ; Integer constant expression
PI EQU <3.1416> ; Real symbolic constant
PressKey EQU <"Press any key to continue...",0>
.DATA
prompt BYTE PressKey

TEXTEQU Directive
TEXTEQU creates a text macro. Three Formats:
Name TEXTEQU assign any text to name
Name TEXTEQU textmacro assign existing text macro
Name TEXTEQU %constExpr constant integer expression
Name can be redefined at any time (unlike EQU)
ROWSIZE = 5
COUNT TEXTEQU %(ROWSIZE * 2) ; evaluates to 10
MOV TEXTEQU < mov>
setupAL TEXTEQU
Greating TEXTEQU <“Welcome to Assembly Language”>
.DATA
prompt BYTE Greating
.CODE
setUpAL ; generates: mov al,10

OFFSET Operator cont.
.DATA
bVal BYTE ? ; Assume bVal is at 00404000h
wVal WORD ?
dVal DWORD ?
dVal2 DWORD ?

.CODE
mov esi, OFFSET bVal ; ESI = 00404000h
mov esi, OFFSET wVal ; ESI = 00404001h
mov esi, OFFSET dVal ; ESI = 00404003h
mov esi, OFFSET dVal2 ; ESI = 00404007h
OFFSET = address of a variable within its segment

Relating to C/C++
// C++ version:

char array[1000];
char * p = array;
The value returned by OFFSET is a pointer. Compare the following code written for both C++ and assembly language:
; Assembly language:

.data
array BYTE 1000 DUP(?)
.code
mov esi,OFFSET array

ALIGN Directive
ALIGN directive aligns a variable in memory
Syntax: ALIGN bound
Where bound can be 1, 2, 4, or 16
Address of a variable should be a multiple of bound
Assembler inserts empty bytes to enforce alignment
.DATA ; Assume that
b1 BYTE ? ; Address of b1 = 00404000h
ALIGN 2 ; Skip one byte
w1 WORD ? ; Address of w1 = 00404002h
w2 WORD ? ; Address of w2 = 00404004h
ALIGN 4 ; Skip two bytes
d1 DWORD ? ; Address of d1 = 00404008h
d2 DWORD ? ; Address of d2 = 0040400Ch
w1

b1
404000
w2
404004
d1
404008
d2
40400C

TYPE Operator
TYPE operator
Size, in bytes, of a single element of a data declaration
.DATA
var1 BYTE ?
var2 WORD ?
var3 DWORD ?
var4 QWORD ?

.CODE
mov eax, TYPE var1 ; eax = 1
mov eax, TYPE var2 ; eax = 2
mov eax, TYPE var3 ; eax = 4
mov eax, TYPE var4 ; eax = 8

Counts the number of elements in a single data declaration
LENGTHOF Operator
.DATA
array1 WORD 30 DUP(?),0,0
array2 WORD 5 DUP(3 DUP(?))
array3 DWORD 1,2,3,4
digitStr BYTE “12345678”,0

.code
mov ecx, LENGTHOF array1 ; ecx = 32
mov ecx, LENGTHOF array2 ; ecx = 15
mov ecx, LENGTHOF array3 ; ecx = 4
mov ecx, LENGTHOF digitStr ; ecx = 9

LENGTHOF Operator
myArray BYTE 10, 20, 30, 40, 50
BYTE 60, 70, 80, 90, 100
myArray BYTE 10, 20, 30, 40, 50,
BYTE 60, 70, 80, 90, 100
LENGHTOF returns 5
LENGHTOF returns 10

SIZEOF Operator
.DATA
array1 WORD 30 DUP(?),0,0
array2 WORD 5 DUP(3 DUP(?))
array3 DWORD 1,2,3,4
digitStr BYTE “12345678”,0

.CODE
mov ecx, SIZEOF array1 ; ecx = 64
mov ecx, SIZEOF array2 ; ecx = 30
mov ecx, SIZEOF array3 ; ecx = 16
mov ecx, SIZEOF digitStr ; ecx = 9
Counts the number of bytes in a data declaration
SIZEOF returns TYPE * LENGHTOF

Multiple Line Declarations
.DATA
array WORD 10,20,
30,40,
50,60

.CODE
mov eax, LENGTHOF array ; 6
mov ebx, SIZEOF array ; 12
A data declaration spans multiple lines if each line (except the last) ends with a comma
The LENGTHOF and SIZEOF operators include all lines belonging to the declaration
.DATA
array WORD 10,20
WORD 30,40
WORD 50,60

.CODE
mov eax, LENGTHOF array ; 2
mov ebx, SIZEOF array ; 4
In the following example, array identifies the first line WORD declaration only
Compare the values returned by LENGTHOF and SIZEOF here to those on the left

PTR Provides the flexibility to access part of a variable
Can also be used to combine elements of a smaller type
Syntax: Type PTR (Overrides default type of a variable)
PTR Operator
.DATA
dval DWORD 12345678h
array BYTE 00h,10h,20h,30h

.CODE
mov al, dval
mov al, BYTE PTR dval
mov ax, dval
mov ax, WORD PTR dval
mov eax, array
mov eax, DWORD PTR array
78
56
34
12
dval

00
10
20
30
array

; error – why?
; al = 78h
; error – why?
; ax = 5678h
; error – why?
; eax = 30201000h

Little Endian Order

Little endian order refers to the way Intel stores integers in memory.

Multi-byte integers are stored in an order, thaT the least significant byte IS stored at the lowest address

For example, the doubleword 12345678h would be stored as:

When integers are loaded from memory into registers, the bytes are automatically re-reversed into their correct positions.

PTR Operator Examples
.data
myDouble DWORD 12345678h

mov al,BYTE PTR myDouble ; AL = 78h
mov al,BYTE PTR [myDouble+1] ; AL = 56h
mov al,BYTE PTR [myDouble+2] ; AL = 34h
mov ax,WORD PTR myDouble ; AX = 5678h
mov ax,WORD PTR [myDouble+2] ; AX = 1234h

Your turn . . .
.data
varB BYTE 65h,31h,02h,05h
varW WORD 6543h,1202h
varD DWORD 12345678h

.code
mov ax,WORD PTR [varB+2] ; a.
mov bl,BYTE PTR varD ; b.
mov bl,BYTE PTR [varW+2] ; c.
mov ax,WORD PTR [varD+2] ; d.
mov eax,DWORD PTR varW ; e.
Write down the value of each destination operand:

0502h
78h
02h
1234h
12026543h

LABEL Directive
Assigns an alternate name and type to a memory location
LABEL does not allocate any storage of its own
Can remove the need for the PTR operator
Format: Name LABEL Type
.DATA
dval LABEL DWORD
wval LABEL WORD
blist BYTE 00h,10h,00h,20h
.CODE
mov eax, dval
mov cx, wval
mov dl, blist
wval

00
10
00
20
blist

dval

; eax = 20001000h
; cx = 1000h
; dl = 00h

Summary
Instruction  executed at runtime
Directive  interpreted by the assembler
.STACK, .DATA, and .CODE
Define the code, data, and stack sections of a program
Edit-Assemble-Link-Debug Cycle
Data Definition
BYTE, WORD, DWORD, QWORD, etc.
DUP operator
Symbolic Constant
=, EQU, and TEXTEQU directives
Data-Related Operators
OFFSET, ALIGN, TYPE, LENGTHOF, SIZEOF, PTR, and LABEL

offset
myByte
data segment:

12345678
0000
5678
1234
78
56
34
12
0001
0002
0003
offset
doubleword
word
byte
myDouble
myDouble + 1
myDouble + 2
myDouble + 3

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