ALP Basic
Introduction to Assembly Language
What is Assembly Language?
l Every PC has a microprocessor that
manages computer's ALU and control activities.
l Each processor has its own set of
instructions for handling various operations like Input and output.
l To operate this activity assembly language
is used.
Why Study Assembly Language?
l It is used to Interface of programs
with OS, processor and BIOS.
l Representation of data in memory and
other external devices.
l It requires less memory and
execution time.
l It allows hardware-specific complex
jobs in an easier way.
Assembler
l Assembler is a type of converter
accept assembly language as input and convert it into equivalent machine
language.
l There are following types of popular
assembler:
1. Netwide Assembler (NASM)
2. Microsoft Assembler (MASM)
3. Borland Turbo Assembler (TASM)
Assembly Basic Syntax
An assembly
program can be divided into three sections:
1. The data section
2. The bss (Block Started Symbol) section
3. The text section
1. The Data Section
l The data section is used for
declaring initialized data or constants.
l This data does not change at runtime.
l The syntax for declaring data
section is:
Syntax: section .data
2. The bss (Block Started Symbol) section:
l The bss section is used for
declaring variables.
l These variables are accessed from
keyboard and used to display result.
l The syntax for declaring bss section
is:
Syntax: section .bss
3. The text section
l The text section is used for keeping
the actual code.
l This section must begin with the
declaration global _start:
l Which tells the kernel where the
program execution begins.
l The syntax for declaring text section
is:
section .text
global _start:
_start:
Syntax of Assembly Language Statements:
l Assembly language statements are
entered one statement per line. Each statement follows the following format:
l [label] mnemonic [operands] [;comment]
l e.g.
abc1: mov ax,
00h ;initialize acc.
The Hello World Program!!!
section
.data
msg db
'Hello, world!', 10 ;our string, 10=\n like C.
len equ $ -
msg ;length
of our dear string
section
.text
global _start ;must be declared for
linker (ld)
_start: ;tells
linker entry point
mov edx,len ;message
length
mov ecx,msg ;message to write
mov ebx,1 ;file
descriptor (stdout)
mov eax,4 ;system
call number (sys_write)
int 80h ;call
kernel
mov eax,1 ;system call number (sys_exit)
int 80h ;call kernel
Compile and execute Program
>nasm -f
elf64 progname.asm ; Compile code
>ld -o
progname progname.o ;Load & create
obj
>./progname ;Execute program
0 comments:
Post a Comment