CS 16: Assembly Language Programming for the IBM PC and Compatibles

Transcription

1 CS 16: Assembly Language Programming for the IBM PC and Compatibles

2 First, a little about you Your name Have you ever worked with/used/played with assembly language? If so, talk about it Why are you taking this course? What are your expectations/goals from me, as well as this course? Then, a little about me Background about myself Cover the syllabus, including my expectations of you and this course Finally, any additional questions before we get started

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4 Get a quick overview of assembly language Understand the basic concept of a virtual machine See how we represent data Take a look at Boolean operations

5 Some good questions to ask Assembly language applications

6 What background should I have? You should have programmed in at least one structured high-level language, such as Java, C, Python, or C++ You should know how to use IF statements, arrays, and functions to solve programming problems What is an assembler? An assembler is a utility program that converts source code programs from assembly language into machine language

7 What hardware/software do I need? You need a computer that runs a 32-bit or 64-bit version of Microsoft Windows, along with one of the recent versions of Microsoft Visual Studio What types of programs will I create? 32-Bit Protected Mode 32-bit protected mode programs run under all 32-bit versions of Microsoft Windows They are usually easier to write and understand than real-mode programs 64-Bit Mode 64-bit programs run under all 64-bit versions of Microsoft Windows. 16-Bit Real-Address Mode 16-bit programs run under 32-bit versions of Windows and on embedded systems

8 What will I learn? Basic principles of computer architecture as applied to x86 processors Basic Boolean logic and how it applies to programming and computer hardware How x86 processors manage memory, using protected mode and virtual mode How high-level language compilers (such as C++) translate statements from their language into assembly language and native machine code How high-level languages implement arithmetic expressions, loops, and logical structures at the machine level

9 What else will I learn? Data representation, including signed and unsigned integers, real numbers, and character data How to debug programs at the machine level, as the need for this skill is vital when you work in languages such as C and C++, which generate native machine code How application programs communicate with the computer s operating system via interrupt handlers and system calls How to interface assembly language code to C++ programs How to create assembly language application programs

10 How does assembly language (AL) relate to machine language? Machine language is a numeric language specifically understood by a computer s processor (the CPU) All x86 processors understand a common machine language Assembly language consists of statements written with short mnemonics such as ADD, MOV, SUB, and CALL Assembly language has a one-to-one relationship with machine language: Each assembly language instruction corresponds to a single machine-language instruction.

11 How do C++ and Java relate to AL? High-level languages such as Python, C++, and Java have a one-tomany relationship with assembly language and machine language A single statement in C++, for example, expands into multiple assembly language or machine instructions Most people cannot read raw machine code, so in this book, we examine its closest relative, assembly language Is AL portable? Assembly language is not portable because it is designed for a specific processor family There are a number of different assembly languages widely used today, each based on a processor family

12 Beats me In all seriousness, there are applications for assembly language Embedded programs are short programs stored in a small amount of memory in single-purpose devices Real-time applications dealing with simulation and hardware monitoring require precise timing and responses Computer game consoles require their software to be highly optimized for small code size and fast execution

13 There are still more applications for assembly language Assembly language helps you to gain an overall understanding of the interaction between computer hardware, operating systems, and application programs Some high-level languages abstract their data representation to the point that it becomes awkward to perform low-level tasks such as bit manipulation Device drivers are programs that translate general operating system commands into specific references to hardware details

14 Some representative types of applications: Business application for single platform Hardware device driver Business application for multiple platforms Embedded systems & computer games

15 High-level language Formal structures, which allow: Easy organization Ability to maintain large sections of code ASM Minimal formal structure leads to programmers enforcing structure Consequence: difficult to maintain existing code

16 High-level language May not provide for direct hardware access Even if it exists, awkward coding techniques often used Consequence: difficult to maintain existing code ASM Hardware access is straightforward and simple Programs are short and welldocumented Consequence: easy to maintain existing code

17 High-level language Usually very portable Code can be recompiled on multiple operating systems with minimal changes Consequence: easy to maintain existing code ASM Must be recoded separately for each platform Often uses an assembler with different syntax Consequence: difficult to maintain existing code

18 High-level language Produces too much executable code May not run efficiently ASM Ideal because: Executable code is small Runs quickly

19 Virtual Machines Specific Machine Levels

20 Tanenbaum: Virtual machine concept Programming Language analogy: Each computer has a native machine language (language L0) that runs directly on its hardware A more human-friendly language is usually constructed above machine language, called Language L1

21 Programs written in L1 can run two different ways: INTERPRETATION: L0 program interprets and executes L1 instructions one by one TRANSLATION: L1 program is completely translated into an L0 program, which then runs on the computer hardware

22 English: Display the sum of A times B plus C. C++: cout << (A * B + C); Intel Machine Language: A F E Assembly Language: mov eax,a mul B add eax,c call WriteInt

23 High-Level Language Assembly Language Instruction Set Architecture (ISA) Digital Logic

24 Application-oriented languages C++ Java Pascal Visual Basic... Programs compile into assembly language

25 Instruction mnemonics that have a one-to-one correspondence to machine language Programs are translated into Instruction Set Architecture (ISA) Level-machine language

26 Also known as conventional machine language Executed by Digital Logic

27 CPU, constructed from digital logic gates System bus Memory Implemented using bipolar transistors

28 Binary Numbers Translating between binary and decimal Binary Addition Integer Storage Sizes Hexadecimal Integers Translating between decimal and hexadecimal Hexadecimal subtraction Signed Integers Binary subtraction Character Storage

29 Digits are 1 and 0 1 = true 0 = false MSB: most significant bit LSB: least significant bit Bit numbering

30 Each digit (bit) is either 1 or 0 Each bit represents a power of 2

31 2 n Decimal Value n Decimal Value , , , , , ,768 Every binary number is a sum of powers of 2

32 Weighted positional notation shows how to calculate the decimal value of each binary bit: dec = (D n-1 2 n-1 ) + (D n-2 2 n-2 ) (D ) + (D ) D = binary digit Binary = decimal 9: (1 2 3 ) + (1 2 0 ) = 9

33 Repeatedly divide the decimal integer by 2 Each remainder is a binary digit in the translated value: 37 = Division Quotient Remainder 37/ / / / / /2 0 1

34 Starting with the LSB, add each pair of digits, include the carry if present

35 Standard sizes Ranges of unsigned integers Storage Type Range (Low High) Powers of 2 Unsigned byte 0 to to (2 8 1) Unsigned word 0 to to (2 16 1) Unsigned doubleword 0 to 4,294,967,295 0 to (2 32 1) Unsigned quadword 0 to 18,446,744,073,709,551,615 0 to (2 64 1) What is the largest unsigned integer that may be stored in 20 bits?

36 Binary Decimal Hexadecimal Binary Decimal Hexadecimal A B C D E F

37 Each hexadecimal digit corresponds to 4 binary bits Example: Translate the binary integer to hexadecimal 1 6 A

38 Multiply each digit by its corresponding power of 16: dec = (D ) + (D ) + (D ) + (D ) Hex 1234 equals ( ) + ( ) + ( ) + ( ) or decimal 4,660 Hex 3BA4 equals ( ) + (11 * 16 2 ) + ( ) + ( ) or decimal 15,268

39 Used when calculating hexadecimal values up to 8 digits long 16 n Decimal Value , , ,048, ,777, ,435,456

40 decimal 422 = 1A6 hexadecimal Division Quotient Remainder 422/ /16 1 A 1/16 0 1

41 Divide the sum of two digits by the number base (16) The quotient becomes the carry value and the remainder is the sum digit A B 78 6D 80 B5 21 / 16 = 1, rem 5 Important skill: Programmers frequently add and subtract the addresses of variables and instructions.

42 When a borrow is required from the digit to the left, add 16 (decimal) to the current digit's value = 21-1 C6 75 A E Practice: The address of var1 is The address of the next variable after var1 is A. How many bytes are used by var1?

43 The highest bit indicates the sign 1 = negative 0 = positive If the highest digit of a hexadecimal integer is > 7, the value is negative Examples: 8A, C5, A2, 9D

44 Negative numbers are stored in two's complement notation Represents the additive inverse Starting Value Step 1: Reverse the bits Step 2: Add 1 to the value from Step Sum: 2 s Complement Representation Note that =

45 When subtracting A B, convert B to its two's complement Add A to ( B) Practice: Subtract 0101 from 1001

46 Form the two's complement of a hexadecimal integer Convert signed binary to decimal Convert signed decimal to binary Convert signed decimal to hexadecimal Convert signed hexadecimal to decimal

47 Ranges of unsigned integers Storage Type Range (Low High) Powers of 2 Signed byte -128 to to (2 7 1) Signed word -32,768 to +32, to (2 15 1) Signed doubleword -2,147,483,648 to +2,147,483, to (2 31 1) Signed quadword -9,223,372,036,854,775,808 to -9,223,372,036,854,775, to (2 63 1) What is the largest signed integer that may be stored in 20 bits?

48 Character sets Standard ASCII (0 127) Extended ASCII (0 255) ANSI (0 255) Unicode (0 65,535) Null-terminated String Array of characters followed by a null byte Using the ASCII table Back inside cover of book

49 Pure binary Can be calculated directly ASCII binary String of digits: " " ASCII decimal String of digits: "65" ASCII hexadecimal String of digits: "9C"

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51 NOT AND OR Operator Precedence Truth Tables

52 Based on symbolic logic, designed by George Boole Boolean expressions created from: NOT, AND, OR Expression X X Y X Y X Y Description NOT X X AND Y X OR Y (NOT X) OR Y (X Y) NOT (X AND Y) X Y X AND (NOT Y)

53 Inverts (reverses) a Boolean value Truth table for Boolean NOT operator Digital gate diagram for NOT: X X F T T F NOT

54 Truth table for Boolean AND operator X Y X Y F F F F T F T F F T T T Digital gate diagram for AND: AND

55 Truth table for Boolean OR operator X Y X Y F F F F T T T F T T T T Digital gate diagram for OR: OR

56 Examples showing the order of operations Expression X Y (X Y) X (Y Z) Order of Operations NOT, then OR OR, then NOT AND, then OR

57 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

58 Example: X Y X X Y X Y F T F T F T T T T F F F T F T T

59 Example: X Y X Y Y X Y F F T F F T F F T F T T T T F F

60 Example: (Y S) (X S) X Y S (Y S) S (X S) (Y S) (X S) F F F F T F F F T F F T F F T F F F T T T T T F F T T T F F T F F F F F T T T F F T T F T F F F F T T T T F F T X Y S mux Z Two-input multiplexer A multiplexer is a device that selects one of several analog or digital input signals and forwards the selected input into a single output line

61 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