CSI 212 Chapter 3 Slides, Spring 2012

Assembly Language for Intel-Based Assembly Language for Intel-Based Computers, 5 Computers, 5th th Edition Edition Chapter 3: Assembly Language Fundamentals (c) Pearson Education, 2006-2007. 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: June 4, 2006 Kip Irvine Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 3 Program Template Program Template TITLE Program Template (Template.asm) ; Program Description: ; Author: ; Creation Date: ; Revisions: ; Date: Modified by: INCLUDE Irvine32.inc .data ; (insert variables here) .code main PROC ; (insert executable instructions here) exit main ENDP ; (insert additional procedures here) END main Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 4 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 5 Integer Constants Integer Constants • Syntax: [ + | - ] digits [radix] • 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 6 Integer Expressions Integer Expressions • Operators and precedence levels: • Examples: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 7 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' Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 8 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 $ Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 9 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 10 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) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 11 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) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 12 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 13 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 14 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 15 What's Next 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 16 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 17 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 18 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 19 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: begin at column 40-45, aligned vertically • 1-3 spaces between instruction and its operands • ex: mov ax,bx • 1-2 blank lines between procedures Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 20 Required Coding Standards Required Coding Standards Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 21 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 22 Program Template Program Template TITLE Program Template (Template.asm) ; Program Description: ; Author: ; Creation Date: ; Revisions: ; Date: Modified by: INCLUDE Irvine32.inc .data ; (insert variables here) .code main PROC ; (insert executable instructions here) exit main ENDP ; (insert additional procedures here) END main Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 23 What's Next 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 24 Assembling, Linking, and Running Programs Assembling, Linking, and Running Programs • Assemble-Link-Execute Cycle • make32.bat • Listing File • Map File Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 25 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. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 26 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 27 Map File Map File • Information about each program segment: • starting address • ending address • size • segment type • Example: addSub.map (16-bit version) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 28 What's Next 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 29 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 30 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 32 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 33 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. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 34 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: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 35 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 36 Defining Strings Defining Strings (2 of 3) (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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 37 Defining Strings Defining Strings (3 of 3) (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. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 38 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 39 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 40 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: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 41 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: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 42 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 43 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. 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 44 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. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 45 What's Next 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 46 Symbolic Constants Symbolic Constants • Equal-Sign Directive • Calculating the Sizes of Arrays and Strings • EQU Directive • TEXTEQU Directive Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 47 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 al,COUNT Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 48 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) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 49 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 50 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 51 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 52 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" Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 53 What's Next 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 54 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 55 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 56 Add and Subtract, 16-Bit Version Add and Subtract, 16-Bit Version TITLE Add and Subtract, Version 2 (AddSub2r.asm) INCLUDE Irvine16.inc .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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 57 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 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers, 2007. 58 46 69 6E 69 73 46 69 6E 69 73