Assembly
Introduction
Assembly
Content
Course Description
Basic Concepts of Assembly Language
Welcome to Assembly Language
Virtual Machine Concept
Data Representation
Boolean Operations
Course Description
Prerequisites:
 Structured Programming Language
Textbook References:
 Assembly Language for Intel-Based
Computers.
 Assembly language for x86
processors
 The Art of Assembly Language
 Resources:
 http://web.sau.edu/LillisKevinM/csci240/masmdocs/
 http://kipirvine.com/asm/4th/asmsources/
 http://forum.codecall.net/topic/62064-assembly-language-resources/
Course Description
Grading :
• Final Exam
• Year work
• Oral
• Laboratory and Practice
• Sum
65
10
10
15
100
Timing:
• Lecture
• Practice
• Exam
3
2
3
Content
Course Description
Basic Concepts of Assembly Language
Welcome to Assembly Language
Virtual Machine Concept
Data Representation
Boolean Operations
Basic Concepts
Welcome to Assembly Language
 Some Good Questions to Ask
Virtual Machine Concept
Data Representation
Boolean Operations
Welcome to Assembly Language
 Some Good Questions to Ask
 What is Assembly Language?
 Why Learn Assembly Language?
 What is Machine Language?
 How is Assembly related to Machine
Language?
 What is an Assembler?
 How is Assembly related to High-Level
Language?
 Is Assembly Language portable?
What is Assembly Language?
 A low-level processor-specific programming
language design to match the processor’s
machine instruction set.
 Each assembly language instruction matches
exactly one machine language instruction.
 We will focus
Instructions.
on
Intel
based
Assembly
 It covers many different versions of CPUs that followed, from Intel; the
80188, 80186, 80286, 80386, 80486, Pentium, Pentium Pro, and so on.
 It describes the basics of 32-bit assembly language programming.
What is Assembly Language?
 A Hierarchy of Languages
Why Learn Assembly Language?
 To learn how high-level language code gets
translated into machine language.
 To learn the computer’s hardware by direct
access to memory, video controller, sound
card, keyboard…
 To speed up applications by direct access to
hardware.
What is Machine Language ML?
 Machine languages are lowest-level programming
language and are the only languages understood
by computers without translation.
 While easily understood by computers, machine
languages are almost impossible for humans
because they consist entirely of binary digits.
 Every CPU has its own specific machine
language.
What is Machine Language ML?
 Each ML instruction contains an op code
(operation code) and zero or more operands.
 Examples:
Opcode
Operand
Meaning
------------------------------------------40
05
0005
increment the AX register
add 0005 to AX
The accumulator.
General-purpose
register.
How is Assembly related to Machine
Language?
 Machine language
 Native to a processor: executed directly by hardware
 Instructions consist of binary code: 1s and 0s
 Assembly language
 Slightly higher-level language
 Readability of instructions is better than machine
language
 One-to-one correspondence with machine language
instructions
 Assemblers translate assembly to machine code
 Compilers translate high-level programs to machine
code
 Either directly, or
 Indirectly via an assembler
What is an Assembler?
 An assembler is a type of computer program that
interprets software programs written in assembly
language into machine language, code and
instructions that can be executed by a computer.
 For Example, MASM (Macro Assembler from
Microsoft)
How is Assembly related to HighLevel Language?
Basic Concepts
Welcome to Assembly Language
 Some Good Questions to Ask
 Assembly Language Applications
Virtual Machine Concept
Data Representation
Boolean Operations
Virtual Machine Concept
 A virtual machine (VM) is a software program or
operating system that
• exhibits the behavior of a separate computer.
• is capable of performing tasks such as running
applications and programs in a separate
computer.
 VM (virtual machine) is a layer of abstraction
that gives a program one simplified interface for
interacting with a variety of physical computers
and their operating systems.
Translating languages
English: Display the sum of A times B plus C.
C++:
cout << (A * B + C);
Assembly Language:
mov eax,A
mul B
add eax,C
call WriteInt
Intel Machine Language:
A1
F7
03
E8
00000000
25 00000004
05 00000008
00500000
Virtual machines
Abstractions for computers
High-Level Language
Level 5
Assembly Language
Level 4
Operating System
Level 3
Instruction Set
Architecture
Level 2
Microarchitecture
Level 1
Digital Logic
Level 0
High-level language
Level 5
• Application-oriented languages
• Programs are compiled into assembly language
(Level 4)
cout << (A * B + C);
Assembly language
Level 4
• Instruction mnemonics that have a one-to-one
correspondence to machine language
• Calls functions written at the operating system
level (Level 3)
• Programs are translated into machine language
(Level 2)
mov eax, A
mul B
add eax, C
call WriteInt
Operating system
Level 3
• Provides services
• Programs translated and run at the instruction
set architecture level (Level 2)
High-Level Language
Level 5
Assembly Language
Level 4
Operating System
Level 3
Instruction Set
Architecture
Level 2
Microarchitecture
Level 1
Digital Logic
Level 0
Instruction set architecture
Level 2
• Also known as conventional machine language
• Executed by Level 1 program (microarchitecture,
Level 1)
A1
F7
03
E8
00000000
25 00000004
05 00000008
00500000
Micro-architecture
Level 1
• Interprets conventional machine instructions
(Level 2)
• Executed by digital hardware (Level 0)
Digital logic
Level 0
• CPU, constructed from digital logic gates
• System bus
• Memory
Basic Concepts
Welcome to Assembly Language
 Some Good Questions to Ask
 Assembly Language Applications
Virtual Machine Concept
Data Representation
Boolean Operations
Data representation
• Computer is a construction of digital circuits
with two states: on and off
• You need to have the ability to translate
between different representations to examine
the content.
• Common number systems: binary, octal,
decimal and hexadecimal
Binary representations
• Electronic Implementation
– Easy to store with bi-stable elements
– Reliably transmitted on noisy and inaccurate
wires
0
3.3V
2.8V
0.5V
0.0V
1
0
Binary numbers
• Digits are 1 and 0
(a binary digit is called a bit)
1 = true
0 = false
• MSB –most significant bit
• LSB –least significant bit
• Bit numbering:
MSB
LSB
1011001010011100
15
0
• A bit string could have different interpretations
Unsigned binary integers
• Each digit (bit) is either 1 or 0
• Each bit represents a power of 2:
Every binary
number is a
sum of powers
of 2
1
1
1
1
1
1
1
1
27
26
25
24
23
22
21
20
Translating binary to decimal
• Weighted positional notation shows how to calculate
the decimal value (Dec) of each binary bit:
dec = (Dn-1  2n-1) + (Dn-2  2n-2) + ... + (D1  21) + (D0  20)
D = binary digit
binary 00001001 = decimal 9:
(1  23) + (1  20) = 9
Translating unsigned decimal to
binary
• Repeatedly divide the decimal integer by 2.
Each remainder is a binary digit in the
translated value:
37 = 100101
Binary addition
• Starting with the LSB, add each pair of digits,
include the carry if present.
+
bit position:
carry:
1
0
0
0
0
0
1
0
0
(4)
0
0
0
0
0
1
1
1
(7)
0
0
0
0
1
0
1
1
(11)
7
6
5
4
3
2
1
0
Integer storage sizes
byte
Standard sizes:
word
doubleword
quadword
8
16
32
64
Practice: What is the largest unsigned integer that may be stored in 20
bits?
Large measurements
• Kilobyte (KB),
bytes
• Megabyte (MB),
bytes
• Gigabyte (GB),
bytes
• Terabyte (TB),
bytes
• Petabyte,
bytes
• Exabyte,
bytes
• Zettabyte,
bytes
• Yottabyte,
bytes
Hexadecimal integers
• All values in memory are stored in binary.
Because long binary numbers are hard to read, we
use hexadecimal representation.
Translating binary to hexadecimal
• Each hexadecimal digit corresponds to 4 binary
bits.
• Example: Translate the binary integer
000101101010011110010100 to hexadecimal:
Converting hexadecimal to decimal
• Multiply each digit by its corresponding power of
16:
dec = (D3  163) + (D2  162) + (D1  161) + (D0  160)
Examples:
• Hex 1234
= (1  163) + (2  162) + (3  161) + (4  160)
= decimal 4,660.
• Hex 3BA4
= (3  163) + (11 * 162) + (10  161) + (4  160)
= decimal 15,268.
Converting decimal to hexadecimal
decimal 422 = 1A6 hexadecimal
Hexadecimal addition
• Divide the sum of two digits by the number base
(16). The quotient becomes the carry value, and
the remainder is the sum digit.
36
42
78
28
45
6D
1
1
28
58
80
6A
4B
B5
Important skill: Programmers frequently add and
subtract the addresses of variables and instructions.
Hexadecimal subtraction
• When a borrow is required from the digit to the
left, add 10h to the current digit's value:
-1
C6
A2
24
75
47
2E
Practice: The address of var1 is 00400020. The address of the
next variable after var1 is 0040006A. How many bytes are
used by var1?
Signed integers
• The highest bit indicates the sign. 1 = negative,
0 = positive
sign bit
1
1
1
1
0
1
1
0
0
0
0
0
1
0
1
0
Negative
Positive
If the highest digit of a hexadecimal integer is > 7,
the value is negative. Examples: 8A, C5, A2, 9D
Two's complement notation For
Binary
Steps:
– Complement (reverse) each bit
– Add 1
Note that 00000001 + 11111111 = 00000000
Hexadecimal Two’s Complement
Steps:
– Complement (reverse) each digit (to reverse the
bits of a hexadecimal digit is to subtract the digit
from 15.)
– Add 1
Unsigned 2’s Complement Subtraction
• Example: Find 0101 01002 – 0100 00112
• 84 -67 = 84 +(-67) = 17
1
0101 0100
0101 0100
– 0100 0011
+1011 1101
2’s comp
0001 0001
• The carry of 1 indicates that no correction of
the result is required.
Unsigned 2’s Complement Subtraction
• Example: Find 010000112 – 010101002
• 67 - 84= 67+ (-84) = -17
0
01000011
01000011
– 01010100 2’s comp + 10101100
11101111
00010001
2’s comp
• The carry of 0 indicates that a correction of
the result is required.
• Result = – (00010001)
Ranges of signed integers
• The highest bit is reserved for the sign. This
limits the range:
Basic Concepts
Welcome to Assembly Language
 Some Good Questions to Ask
 Assembly Language Applications
Virtual Machine Concept
Data Representation
Boolean Operations
Boolean algebra
• Boolean expressions created from:
– NOT, AND, OR
NOT
• Inverts (reverses) a Boolean value
• Truth table for Boolean NOT operator:
Digital gate diagram for NOT:
NOT
AND
• Truth if both are true
• Truth table for Boolean AND operator:
Digital gate diagram for AND:
AND
OR
• True if either is true
• Truth table for Boolean OR operator:
Digital gate diagram for OR:
OR
Implementation of gates
Operator Precedence
• Examples showing the order of operations:
Truth Tables (1 of 2)
• A Boolean function has one or more Boolean
inputs, and returns a single Boolean output.
• A truth table shows all the inputs and outputs of
a Boolean function
Example: X  Y
Truth Tables (2 of 2)
• Example: X  Y
Summary
 Assembly language helps you learn how
software is constructed at the lowest levels
 Assembly language has a one-to-one relationship
with machine language
 Each layer in a computer's architecture is an
abstraction of a machine
 layers can be hardware or software
 Boolean expressions are essential to the design
of computer hardware and software
Lecturer Website
• http://www.bu.edu.eg/staff/rashaabdelkreem14