assembly_tutorial

Recommendations

Info

CHAPTER 16 Assembly Arrays We have already discussed that the data definition directives to the assembler are used for allocating storage for variables. The variable could also be initialized with some specific value. The initialized value could be specified in hexadecimal, decimal or binary form. For example, we can define a word variable months in either of the following way: MONTHS DW 12 MONTHS DW 0CH MONTHS DW 0110B The data definition directives can also be used for defining a one dimensional array. Let us define a one dimensional array of numbers. NUMBERS DW 34, 45, 56, 67, 75, 89 The above definition declares an array of six words each initialized with the numbers 34, 45, 56, 67, 75, 89. This allocates 2x6 = 12 bytes of consecutive memory space. The symbolic address of the first number will be NUMBERS and that of the second number will be NUMBERS + 2 and so on. Let us take up another example. You can define an array named inventory of size 8, and initialize all the values with zero, as: INVENTORY DW 0 DW 0 DW 0 DW 0 DW 0 DW 0 DW 0 DW 0 Which, can be abbreviated as: INVENTORY DW 0, 0 , 0 , 0 , 0 , 0 , 0 , 0 The TIMES directive can also be used for multiple initializations to the same value. Using TIMES, the INVENTORY array can be defined as INVENTORY TIMES 8 DW 0 TUTORIALS POINT Simply Easy Learning
Example: The following example demonstrates the above concepts by defining a 3 element array x, which stores three values: 2, 3 and 4. It adds the values in the array and displays the sum 9: section .text global main ;must be declared for linker (ld) main: mov eax,3 ;number bytes to be summed mov ebx,0 ;EBX will store the sum mov ecx, x ;ECX will point to the current element to be summed top: add ebx, [ecx] add ecx,1 ;move pointer to next element dec eax ;decrement counter jnz top ;if counter not 0, then loop again done: add ebx, '0' mov [sum],byte ebx ;done, store result in "sum" display: mov edx,1 ;message length mov ecx, sum ;message to write mov ebx, 1 ;file descriptor (stdout) mov eax, 4 ;system call number (sys_write) int 0x80 ;call kernel mov eax, 1 ;system call number (sys_exit) int 0x80 ;call kernel section .data global x x: db 2 db 4 db 3 sum: db 0 When the above code is compiled and executed, it produces following result: 9 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 and 30: Direct Memory Addressing When opera
Page 31 and 32: int 0x80 ;call kernel mov eax,1 ;sy
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: found! Repetition Prefixes The REP
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
show all

assembly_tutorial

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?