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CS2422 Assembly Language and System Programming Assembly Language Fundamentals Department of Computer Science National Tsing Hua University.

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1 CS2422 Assembly Language and System Programming Assembly Language Fundamentals Department of Computer Science National Tsing Hua University

2 CS2422 Assembly Language and System Programming Assembly Language for Intel- Based Computers, 5 th Edition Chapter 3: Assembly Language Fundamentals (c) Pearson Education, 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

3 2 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

4 3 Starting with an Example TITLE Add and Subtract (AddSub.asm) ; Adds and subtracts three 32-bit integers ; (10000h h h) 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 Title/header Include file Code section

5 4 Meanings of the Code Assembly code Machine code MOV EAX, 10000hB (Move 10000h into EAX) ADD EAX, 40000h (Add 40000h to EAX) SUB EAX, 20000h2D (SUB 20000h from EAX) 4 Operand in instruction

6 5 Fetched MOV EAX, 10000h 5 … ALU MemoryRegister EAX EBX address 00 … MOV EAX, 10000h SUB EAX, 20000h data PC B IR B ADD EAX, 40000h

7 6 Execute MOV EAX, 10000h 6 … ALU Register EAX EBX data PC B IR … MOV EAX, 10000h SUB EAX, 20000h B ADD EAX, 40000h Memory address

8 7 Fetched ADD EAX, 40000h 7 … ALU Register EAX EBX data PC IR Memory address 00 … MOV EAX, 10000h SUB EAX, 20000h B ADD EAX, 40000h

9 8 Execute ADD EAX, 40000h 8 … ALU Register EAX EBX data PC IR Memory address 00 … MOV EAX, 10000h SUB EAX, 20000h B ADD EAX, 40000h

10 9 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 10 Reserved Words, Directives  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 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

12 11 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 12 Comments  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 ! 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

14 13 Include Files  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) 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

15 14 Code Segment .code directive: Marks the beginning of the code segment, where all executable statements in a program are located 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

16 15 Procedure Definition  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: 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

17 16 Identifiers  Identifiers: A programmer-chosen name to identify a variable, a constant, a procedure, or a code label characters, including digits not case sensitive first character must be a letter, ?, or $ 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

18 17 Integer Constants  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

19 18 Instructions [label:] mnemonic operand(s) [;comment]  Instruction mnemonics: help to memorize examples: MOV, ADD, SUB, MUL, INC, DEC  Operands: constant constant expression register memory (data label, register) 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 immediate values Destination operand Source operand

20 19 Instruction Format Examples  No operands stc; set Carry flag nop; no operation  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-expr.

21 20 I/O  Not easy, if program by ourselves Will use the library provided by the author  Two steps: Include the library (Irvine32.inc) in your code Call the subroutines  call DumpRegs: Calls the procedure to displays current values of processor registers 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

22 21 Remaining  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 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

23 22 Example Program Output  Program output, showing registers and flags EAX= EBX=7FFDF000 ECX= EDX=FFFFFFFF ESI= EDI= EBP=0012FFF0 ESP=0012FFC4 EIP= EFL= CF=0 SF=0 ZF=0 OF=0

24 23 Alternative Version of AddSub TITLE Add and Subtract (AddSubAlt.asm) ; 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

25 24 Explanations .386 directive: Minimum processor required for this code .MODEL directive: Generate code for protected mode program Stdcall: enable calling of Windows functions  PROTO directives: Prototypes for procedures ExitProcess: Windows function to halt process  INVOKE directive: Calls a procedure or function Calls ExitProcess and passes it with a return code of zero

26 25 Suggested 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

27 26 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

28 27 Assemble-Link-Execute Cycle  Steps from creating a source program through executing the compiled program

29 28 MASM History  v6.11 Independent product  v6.15 Visual C Processor Pack  v7.0 Visual C++.NET 2002  v7.1 Visual C++.NET 2003  v8.0 Visual C++.NET 2005

30 29 Download, Install, and Run  MASM 6.15 (with all examples of textbook) Masm615.zip: download from the course web site  Unzip the archive and run setup.exe  Choose the installation directory 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 xxx (where xxx is your file name)

31 30 Suggestion  Study make32.bat and make16.bat To know where assembling stage and linking stage are  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 Try to use NASM or TASM  Try to use high ‐ level compiler to generate assembly codes gcc or visual c++ or turbo c or …

32 31 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.lstaddSub.lst

33 32 Listing File code main PROC B mov eax,10000h add eax,40000h A 2D sub eax,20000h F E Ecall DumpRegs exit A 00 *push h E E *call ExitProcess Bmain ENDP END main address memory content

34 33 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

35 34 Intrinsic Data Types BYTE8-bit unsigned integer SBYTE8-bit signed integer WORD16-bit unsigned integer SWORD16-bit signed integer DWORD32-bit unsigned integer SDWORD32-bit signed integer FWORD 48-bit integer (Far pointer in protected mode) QWORD 64-bit integer TBYTE 80-bit (10-byte) integer REAL4 32-bit (4-byte) IEEE short real REAL8 64-bit (8-byte) IEEE long real REAL10 80-bit (10-byte) IEEE extended real

36 35 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 ?

37 36 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 MASM does not prevent you from initializing a BYTE with a negative value, but it is considered poor style If you declare a SBYTE variable, the Microsoft debugger will automatically display its value in decimal with a leading sign

38 37 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, b list4 BYTE 0Ah,20h,‘A’,22h

39 38 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 "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 menu BYTE "Checking Account",0dh,0ah,0dh,0ah, "1. Create a new account",0dh,0ah, "2. Open an existing account",0dh,0ah, "Choice> ",0 Is str1 an array? End-of-line sequence: 0Dh = carriage return 0Ah = line feed End-of-line sequence: 0Dh = carriage return 0Ah = line feed

40 39 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

41 40 Defining WORD and SWORD  Define storage for 16-bit integers or double characters single value or multiple values word1 WORD ; 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

42 41 Defining Other Types of Data  Storage definitions for 32-bit integers, quadwords, tenbyte values, and real numbers: val1 DWORD h ; unsigned val2 SDWORD – ; signed val3 DWORD 20 DUP(?) ; unsigned array val4 SDWORD –3,–2,–1,0,1; signed array quad1 QWORD h val1 TBYTE Ah rVal1 REAL rVal2 REAL8 3.2E-260 rVal3 REAL10 4.6E+4096 ShortArray REAL4 20 DUP(0.0)

43 42 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

44 43 Listing File data val1 DWORD 10000h val2 DWORD 40000h val3 DWORD 20000h C finalVal DWORD ? code main PROC A Rmov eax,val1; start with 10000h Radd eax,val2; add 40000h B 2B Rsub eax,val3; subtract 20000h A C Rmov finalVal,eax; store result E Ecall DumpRegs; display registers exit main ENDP

45 44 C vs Assembly.data val1 DWORD 10000h val2 DWORD 40000h val3 DWORD 20000h finalVal DWORD ?.code main PROC mov eax,val1 add eax,val2 sub eax,val3 mov finalVal,eax call DumpRegs exit main ENDP main() { int val1=10000h; int val2=40000h; int val3=20000h; int finalVal; finalVal = val1 + val2 - val3; }

46 45 What's Next  Basic Elements of Assembly Language  Example: Adding and Subtracting Integers  Assembling, Linking, and Running Programs  Defining Data  Symbolic Constants Equal-Sign Directive Calculating the Sizes of Arrays and Strings EQU Directive TEXTEQU Directive  Real-Address Mode Programming

47 46 Equal-Sign Directive  name = expression expression is a 32-bit integer (expression or constant) may be redefined name is called a symbolic constant Also OK to use EQU  good programming style to use symbols COUNT = 500 … mov al,COUNT

48 47 Calculating the Size of Arrays  Current location counter: $  Size of a byte array Subtract address of list and difference is the number of bytes  Size of a word array Divide total number of bytes by 2 (size of a word) list BYTE 10,20,30,40 ListSize = ($ - list) list WORD 1000h,2000h,3000h,4000h ListSize = ($ - list) / 2

49 48 EQU Directive  Define a symbol as either an integer or text expression  Cannot be redefined  OK to use expressions in EQU: Matrix1 EQU 10 * 10 Matrix1 EQU  No expression evaluation if within  EQU accepts texts too PI EQU pressKey EQU.data prompt BYTE pressKey

50 49 TEXTEQU Directive  Define a symbol as either an integer or text expression  Called a text macro  Can be redefined continueMsg TEXTEQU rowSize = 5.data prompt1 BYTE continueMsg count TEXTEQU %(rowSize * 2); evaluates expression setupAL TEXTEQU.code setupAL; generates: "mov al,10"

51 50 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 (skipped)

52 51 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


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