Download Adds and subtracts

CS2422 Assembly Language and System Programming
Week 7 & 8
Intro. To Assembly Programming
0
Basic Instruction Set
The x86 instruction set is extremely huge, but we usually don't need to
use them all. Here are some simple instructions you should know to get
you started:
Instruction Description
ADD
Adds the two operands and stores the result into the first operand.
SUB
Subtracts the second operand from the first and stores the result in the first
operand.
MUL
Multiplies the operand with the Accumulator Register and stores the result in
the Accumulator Register.
DIV
Divides the Accumulator Register by the operand and stores the result in the
Accumulator Register.
AND
Performs the bitwise logical AND operation on the operands and stores the
result in the first operand.
OR
Performs the bitwise logical OR operation on the operands and stores the
result in the first operand.
INC
Increases the value of the operand by 1 and stores the result in the operand.
DEC
Decreases the value of the operand by 1 and stores the result in the operand.
Basic Instruction Set …
Instruction Description
NEG
Negates the operand and stores the result in the operand.
PUSH
Pushes the value of the operand on to the top of the stack.
POP
Pops the value of the top item of the stack in to the operand.
MOV
Stores the second operand's value in the first operand.
CMP
Subtracts the second operand from the first operand and sets the respective
flags.
JMP
Jumps to label.
INT
constant
Calls the interrupt specified by the operand.
Basic instructions…

mov eax,10000h


add eax,40000h


The MOV instruction moves (copies) the integer 10000h to the EAX
register. The first operand (EAX) is called the destination operand,
and the second operand is called the source operand.
The ADD instruction adds 40000h to the EAX register.
sub eax,20000h

The SUB instruction subtracts 20000h from the EAX register.
Moving Data into Registers


The first thing we will want to learn about programming at the level of
the CPU, is how to put data into registers. For this we use the MOV
instruction.
code fragment which moves the number 47 into the EDX register:
>> MOV EDX, 47

The following code moves the hexadecimal number A4C9 into the 16
bit AX register:
>> MOV AX, 0A4C9h

Similarly, if we wished to move the binary number 01101110 into the 8
bit BH register we would type the following code:
>> MOV BH, 01101110b
Starting with an Example
TITLE Add and Subtract
(AddSub.asm)
; Adds and subtracts three 32-bit integers
; (10000h + 40000h + 20000h)
INCLUDE Irvine32.inc
.code
Title/header
main PROC
Include file
mov eax,10000h
; EAX = 10000h
add eax,40000h
; EAX = 50000h
sub eax,20000h
; EAX = 30000h
call DumpRegs
; display registers
exit
main ENDP
Code section
END main
5
Meanings of the Code
Assembly code
MOV EAX, 10000h
Machine code
B8 00010000
(Move 10000h into EAX)
Operand in instruction
ADD EAX, 40000h
05 00040000
(Add 40000h to EAX)
SUB EAX, 20000h
2D 00020000
(SUB 20000h from EAX)
6
Fetched MOV EAX, 10000h
Register
Memory
EAX
EBX
data
…
ALU
IR
B8 00010000
B8
00
01
00
00
05
00
04
00
00
MOV EAX, 10000h
ADD EAX, 40000h
SUB EAX, 20000h
PC
0000011
address
…
7
Execute MOV EAX, 10000h
Register
EAX
EBX
Memory
00010000
data
…
ALU
IR
B8 00010000
B8
00
01
00
00
05
00
04
00
00
MOV EAX, 10000h
ADD EAX, 40000h
SUB EAX, 20000h
PC
0000011
address
…
8
Fetched ADD EAX, 40000h
Register
EAX
EBX
Memory
00010000
data
…
ALU
IR
05 00040000
B8
00
01
00
00
05
00
04
00
00
MOV EAX, 10000h
ADD EAX, 40000h
SUB EAX, 20000h
PC
0001000
address
…
9
Execute ADD EAX, 40000h
Register
EAX
EBX
Memory
00010000
00050000
data
…
ALU
IR
05 00040000
B8
00
01
00
00
05
00
04
00
00
MOV EAX, 10000h
ADD EAX, 40000h
SUB EAX, 20000h
PC
0001000
address
…
10
Chapter Overview

Basic Elements of Assembly Language












Integer constants and expressions
Character and string constants
Reserved words and identifiers
Directives and instructions
Labels
Mnemonics and Operands
Comments
Example: Adding and Subtracting Integers
Assembling, Linking, and Running Programs
Defining Data
Symbolic Constants
Real-Address Mode Programming
11
Reserved Words, Directives
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main



TITLE:
 Define program listing
title
 Reserved word of
directive
Reserved words
 Instruction mnemonics,
directives, type
attributes, operators,
predefined symbols
 See MASM reference
in Appendix A
Directives:
 Commands for
assembler
12
Directive vs Instruction

Directives: tell assembler what to do




Commands that are recognized and acted upon
by the assembler, e.g. declare code, data areas,
select memory model, declare procedures, etc.
Not part of the Intel instruction set
Different assemblers have different directives
Instructions: tell CPU what to do




Assembled into machine code by assembler
Executed at runtime by the CPU
Member of the Intel IA-32 instruction set
Format:
LABEL (option), Mnemonic, Operands, Comment
13
Comments
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main

Single-line comments


begin with semicolon (;)
Multi-line comments

begin with COMMENT
directive and a
programmer-chosen
character, end with the
same character, e.g.
COMMENT !
Comment line 1
Comment line 2
!
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Include Files
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main

INCLUDE directive:

Copies necessary
definitions and setup
information from a text
file named Irvine32.inc,
located in the
assembler’s INCLUDE
directory (see Chapt 5)
15
Code Segment
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main

.code directive:

Marks the beginning of
the code segment,
where all executable
statements in a
program are located
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Procedure Definition
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main


Procedure defined by:
 [label] PROC
 [label] ENDP
Label:
 Place markers: marks
the address (offset) of
code and data
 Assigned a numeric
address by assembler
 Follow identifier rules
 Data label: must be
unique, e.g. myArray
 Code label: target of
jump and loop
instructions, e.g. L1:
17
Identifiers
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main

Identifiers:




A programmer-chosen
name to identify a
variable, a constant, a
procedure, or a code
label
1-247 characters,
including digits
not case sensitive
first character must be
a letter, _, @, ?, or $
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Instructions
[label:] mnemonic operand(s)
TITLE Add and …
[;comment]
; Adds and subtracts
 Instruction mnemonics:
; (10000h + …
 help to memorize
INCLUDE Irvine32.inc
 examples: MOV, ADD,
.code
SUB, MUL, INC, DEC
main PROC
 Operands:
 constant
mov eax,10000h
 constant expression
add eax,40000h
 register
sub eax,20000h
 memory (data label,
call DumpRegs
register)
exit
main ENDP Destination Source
immediate values
END main operand
operand
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Instruction Format Examples

No operands



; set Carry flag
; no operation
One operand



stc
nop
inc eax
inc myByte
; register
; memory
Two operands



add ebx,ecx
sub myByte,25
add eax,36 * 25
; register, register
; memory, constant
; register, constant-expr.
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I/O
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main

Not easy, if program by
ourselves


Two steps:



Will use the library
provided by the author
Include the library
(Irvine32.inc) in your
code
Call the subroutines
call DumpRegs:

Calls the procedure to
displays current values
of processor registers
21
Remaining
TITLE Add and …
; Adds and subtracts
; (10000h + …
INCLUDE Irvine32.inc
.code
main PROC
mov eax,10000h
add eax,40000h
sub eax,20000h
call DumpRegs
exit
main ENDP
END main

exit:



Halts the program
Not a MSAM keyword,
but a command
defined in Irvine32.inc
END main:


Marks the last line of
the program to be
assembled
Identifies the name of
the program’s startup
procedure
22
Example Program 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
23
What's Next






Basic Elements of Assembly Language
Example: Adding and Subtracting Integers
Assembling, Linking, and Running Programs
Defining Data
Symbolic Constants
Real-Address Mode Programming
24
Assemble-Link-Execute Cycle

Steps from creating a source program through
executing the compiled program
Link
Library
Source
File
Step 1: text editor
Step 2:
assembler
Object
File
Listing
File
Step 3:
linker
Executable
File
Step 4:
OS loader
Output
Map
File
http://kipirvine.com/asm/gettingStarted/index.htm
25
Download, Install, and Run

MASM 6.15 (with all examples of textbook)



Unzip the archive and run setup.exe
Choose the installation directory



Masm615.zip: download from the course web site
Suggest using the default directory
See index.htm in the archive for details
Go to C:\Masm615 (if installed default)

Write assembly source code
‒ TextPad, NotePad++, UltraEdit or …


make32 abc (where abc is your file name)
When assembled, just write abc to run the code.
26
Suggestion

Study make32.bat and make16.bat



Think about linking with other language (ex: C or
C++ or …)
Understand that MASM is only one of the
assemblers, and there are still many other
assemblers to use


To know where assembling stage and linking
stage are
Try to use NASM or TASM
Try to use high‐level compiler to generate
assembly codes

gcc or visual c++ or turbo c or …
27
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
28
What's Next




Basic Elements of Assembly Language
Example: Adding and Subtracting Integers
Assembling, Linking, and Running Programs
Defining Data







Intrinsic Data Types
Data Definition Statement
Defining BYTE, SBYTE, WORD, SWORD,
DWORD, SDWORD, QWORD, TBYTE
Defining Real Number Data
Little Endian Order
Symbolic Constants
Real-Address Mode Programming
29
Intrinsic Data Types
BYTE
SBYTE
WORD
SWORD
DWORD
SDWORD
8-bit unsigned integer
8-bit signed integer
16-bit unsigned integer
16-bit signed integer
32-bit unsigned integer
32-bit signed integer
30
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
Use ? if no initialization necessary

Example: Var1 BYTE ?
31
Defining BYTE and SBYTE Data

Each of following defines a single byte of storage:
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
32
Defining Byte Arrays

Examples that use multiple initializers:
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
33
Defining Strings

An array of characters



Usually enclosed in quotation marks
Will often be null-terminated
To continue a single string across multiple lines,
end each line with a comma
str1 BYTE
str2 BYTE
str3 BYTE
greeting
"Enter your name",0
'Error: halting program',0
'A','E','I','O','U'
BYTE "Welcome to the Encryption Demo program "
BYTE "created at Tabuk University.",0
menu BYTE "Checking Account",0dh,0ah,0dh,0ah,
"1. Create a new account",0dh,0ah,
"2. Open an existing account",0dh,0ah,
"Choice> ",0
End-of-line sequence:
•0Dh = carriage return
34
•0Ah = line feed
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"
35
Defining WORD and SWORD

Define storage for 16-bit integers


word1
word2
word3
word4
myList
array
or double characters
single value or multiple values
WORD
SWORD
WORD
WORD
WORD
WORD
65535
–32768
?
"AB"
1,2,3,4,5
5 DUP(?)
;
;
;
;
;
;
largest unsigned value
smallest signed value
uninitialized, unsigned
double characters
array of words
uninitialized array
36
Defining Other Types of Data

Storage definitions for 32-bit integers, quadwords,
tenbyte values, and real numbers:
val1
val2
val3
val4
DWORD
SDWORD
DWORD
SDWORD
12345678h ;
–2147483648
20 DUP(?) ;
–3,–2,–1,0,1
unsigned
; signed
unsigned array
; signed array
37
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.
INCLUDE Irvine32.inc
.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
38