1. Outline Learning Assembly by an Example.  Program Formats  Some Simple Instructions  Assemble and Execute Learning Another Example  Data Definition  Constants Memory Register

2. Example: Adding 3 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

3. Program Description Directives vs. Instructions.  Use Directives to tell assembler what to do.  Use Instructions to tell CPU what to do. Procedure defined by:  [Name] PROC  [Name] ENDP Instruction Format:  LABEL (optional), Mnemonic, Operands

4. 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.

5. Instructions Assembled into machine code by assembler Executed at runtime by the CPU Member of the Intel IA-32 instruction set Parts  Label  Mnemonic  Operand

6. I/O Not as easy as you think, if you program it yourself. We will use the library provided by the author of the textbook. Two steps:  Include the library (Irvine32.inc) in your code.  Call the subroutines.

7. Assemble and Run! The required software comes with the book:  MASM: Microsoft Macro Assembler  Visual Studio: A Debugger  Irvine32.inc: I/O procedures

8. 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.

9. Steps to Run AddSub.asm C:\MASM>ML -Zi -c -Fl -coff addsub.asm //generate AddSub.obj and AddSub.lst C:\MASM>LINK32 addsub.obj irvine32.lib kernel32.lib /SUBSYSTEM:CONSOLE /DEBUG /MAP //generate Addsub.exe, Addsub.ilk, Addsub.pdb, and Addsub.map C:\MASM>addsub //show the content of registers

10. Using make32.bat … ML -Zi -c -Fl -coff %1.asm … LINK32 %1.obj irvine32.lib kernel32.lib /SUBSYSTEM:CONSOLE /DEBUG /MAP … dir %1.* … C:\MASM615>make32 c:\MASM\AddSub

11. Using Visual Studio to Assemble, Run, and Debug AddSub.asm http://www.nuvisionmiami.com/books/asm/ide /vs6/index.htm http://www.nuvisionmiami.com/books/asm/ide /vs6/index.htm Demo

12. Another Example TITLE Add and Subtract (AddSub2.asm) INCLUDE Irvine32.inc.data Val1 DWORD 10000h Val2 DWORD 40000h Val3 DWORD 20000h finalVal DWORD ?.code main PROC mov eax,Val1; EAX = 10000h add eax,Val2; EAX = 50000h sub eax,Val3; EAX = 30000h mov finalVal1,eax; store the result call DumpRegs; display registers exit main ENDP END main

13. Data Declaration [Label], Type, Initialization (or just ?)  Example: Var1 BYTE 7 Use ? if no initialization necessary.  Example: Var1 BYTE ? Other data types: (See Table 3-2 in p.81)  WORD (or DW),  DWORD (or DD), …etc.

14. Signed vs. Unsigned Signed vs. Unsigned:  SBYTE vs. BYTE  SWORD vs. WORD  … etc. Example:  Var1 BYTE 255  Var1 SBYTE -1

15. Characters and Strings How about characters? A few examples:  Var1 BYTE ‘A’  Var1 BYTE 41h  S1 BYTE ‘Hello, World!’  Line BYTE ‘--------------------’

16. How About A List or Array? Just list them! For example:  List1 BYTE 10, 32, 41h You may also mix them:  List1 BYTE 10, 32, ?, ‘A’  List2 BYTE “good”, ‘o’, ‘r’, ‘b’, ‘a’, ‘d’, 0

17. DUP Good for allocating space for a string or array. Examples:  Var1 BYTE 20 DUP (0)  Var2 BYTE 20 DUP (?)  Var3 BYTE4 DUP (“STACK”)

18. Another Example INCLUDE Irvine32.inc C1 EQU 40000h.data Val1 DWORD 10000h.code main PROC mov eax,Val1; EAX = 10000h add eax,C1; EAX = 50000h call DumpRegs; display registers exit main ENDP END main

19. EQU is for Constants EQU for constants. Also OK to use = for integers. Examples:  COUNT = 500  COUNT EQU 500 Good programming style: COUNT = 500. mov al,COUNT

20. Expression and Text in EQU OK to use expressions in EQU:  Matrix1 EQU 10 * 10  Matrix1 EQU No expression evaluation if within. EQU accepts texts too:  Msg EQU

21. Memory Organized like mailboxes, numbered 0, 1, 2, 3, …, 2 n -1.  Each box can hold 8 bits (1 byte)  So it is called byte-addressing. …

22. Byte? Word? The number has limited range. 1 Byte = 8 Bits:  Binary: 0000 0000 to 1111 1111  Hexadecimal: 00 to FF  Decimal: 0 to 255 Word = 2 or 4 bytes, depending on the machine. In 80x86, it means 2 bytes.

23. Number Systems Binary & hexadecimal numbers. Conversion between them and decimal. How to represent negative numbers (in 2 ’ s compliment).

24. Memory Address Byte Addressing: each memory location has 8 bits. If we have only 16 bytes …  4 bits are enough for an address What if we have 64K? 1M? 1G? …

25. Memory Address 16-bit address is enough for up to 64K 20-bit for 1M 32-bit for 4G

26. Character String So how are strings like “ Hello, World! ” are stored in memory? ASCII Code! (or Unicode … etc.) Each character is stored as a byte. Review: how is “ 1234 ” stored in memory?

27. Integer A byte can hold an integer number:  between 0 and 255 (unsigned) or  between – 128 and 127 (2 ’ s compliment) How to store a bigger number? Review: how is 1234 stored in memory?

28. Big or Little Endian? Example: 1234 is stored in 2 bytes. = 100-1101-0010 in binary = 04 D2 in hexadecimal Do you store 04 or D2 first? Big Endian: 04 first. Little Endian: D2 first.  Intel ’ s choice

29. 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 Demo

30. Reason for Little-Endian? More consistent for variable length (e.g., 2 bytes, 4 bytes, 8 bytes … etc.)

31. Registers

32. General-Purpose:  AX, BX, CX, DX: 16 bits  Splitted into H and L parts, 8 bits each.  Extended into E?X to become 32-bit register (i.e., EAX, EBX, … etc.).

33. Convention EAX: accumulator EBX: base register ECX: count register EDX: data register

34. Other Registers We will explain their meaning when we encounter them later this semester: Segment (CS, DS, SS, ES) Pointer (EIP, ESP, EBP) Index (ESI, EDI) EFLAGS

35. Homework1 http://dclab.cs.nthu.edu.tw/~course/Assembly /Project1.doc http://dclab.cs.nthu.edu.tw/~course/Assembly /Project1.doc