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MOV destination, source The MOV instruction may have one of the following five forms: MOV register, register MOV register, immediate MOV memory, immediate MOV register, memory MOV memory, register Please note that: Both the operands in MOV operation should be of same size The value of source operand remains unchanged The MOV instruction causes ambiguity at times. For example, look at the statements: MOV EBX, [MY_TABLE] ; Effective Address of MY_TABLE in EBX MOV [EBX], 110 ; MY_TABLE[0] = 110 It is not clear whether you want to move a byte equivalent or word equivalent of the number 110. In such cases, it is wise to use a type specifier. Following table shows some of the common type specifiers: Type Specifier Bytes addressed BYTE 1 WORD 2 DWORD 4 QWORD 8 TBYTE 10 EXAMPLE: The following program illustrates some of the concepts discussed above. It stores a name 'Zara Ali' in the data section of the memory. Then changes its value to another name 'Nuha Ali' programmatically and displays both the names. section .text global main ;must be declared for linker (ld) main: ;tell linker entry point ;writing the name 'Zara Ali' mov edx,9 ;message length mov ecx, name ;message to write mov ebx,1 ;file descriptor (stdout) mov eax,4 ;system call number (sys_write) int 0x80 ;call kernel mov [name], dword 'Nuha' ; Changed the name to Nuha Ali ;writing the name 'Nuha Ali' mov edx,8 ;message length mov ecx,name ;message to write mov ebx,1 ;file descriptor (stdout) mov eax,4 ;system call number (sys_write) TUTORIALS POINT Simply Easy Learning
int 0x80 ;call kernel mov eax,1 ;system call number (sys_exit) int 0x80 ;call kernel section .data name db 'Zara Ali ' When the above code is compiled and executed, it produces following result: Zara Ali Nuha Ali TUTORIALS POINT Simply Easy Learning
Page 1 and 2: Assembly Language Tutorial
Page 3 and 4: ABOUT THE TUTORIAL Assembly Program
Page 5 and 6: Table of Content Assembly Programmi
Page 7 and 8: The XOR Instruction ...............
Page 9 and 10: CHAPTER 1 Assembly Introduction Wha
Page 11 and 12: Main use of hexadecimal numbers in
Page 13 and 14: x: memory address When the processo
Page 15 and 16: Check The netwide assembler (NASM)
Page 17 and 18: ; This program displays a message o
Page 19 and 20: CHAPTER 4 Assembly Memory Segments
Page 21 and 22: CHAPTER 5 Assembly Registers Proces
Page 23 and 24: Control Registers The 32-bit instru
Page 25 and 26: CHAPTER 6 Assembly System Calls Sys
Page 27 and 28: Please enter a number: 1234 You hav
Page 29: Direct Memory Addressing When opera
Page 33 and 34: Processor uses the little-endian by
Page 35 and 36: CHAPTER 9 Assembly Constants There
Page 37 and 38: The above code replaces PTR by [EBP
Page 39 and 40: dec [value] mov ebx, count inc word
Page 41 and 42: int 0x80 When the above code is com
Page 43 and 44: global main ;must be declared for u
Page 45 and 46: mov [res], ax mov ecx,msg mov edx,
Page 47 and 48: AND AL, 01H ; ANDing with 0000 0001
Page 49 and 50: The TEST Instruction The TEST instr
Page 51 and 52: L7: ... CMP is often used for compa
Page 53 and 54: jg _exit mov ecx, [num3] _exit: mov
Page 55 and 56: section .bss num resb 1 mov ecx, nu
Page 57 and 58: Such conversions are however, has a
Page 59 and 60: mov ecx,msg ;message to write mov e
Page 61 and 62: LODS - This instruction loads from
Page 63 and 64: mov ecx, len mov esi, s1 mov edi, s
Page 65 and 66: found! Repetition Prefixes The REP
Page 67 and 68: Example: The following example demo
Page 69 and 70: mov ecx, res mov edx, 1 mov ebx, 1
Page 71 and 72: CHAPTER 18 Assembly Recursion Arecu
Page 73 and 74: CHAPTER 19 Assembly Macros Writing
Page 75 and 76: CHAPTER 20 Assembly File Management
Page 77 and 78: Put the buffer size, i.e., the numb
Page 79 and 80: int 0x80 ;call kernel section .data
Page 81:
mov eax, 1 xor ebx, ebx int 80h sec
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