Assembly Basic Syntax

sumber : https://www.tutorialspoint.com/assembly_programming/assembly_basic_syntax.htm

https://en.wikipedia.org/wiki/X86_instruction_listings

An assembly program can be divided into three sections :

  • The data section
  • The bss section
  • The text section

The data Section

The data section is used for declaring initialized data or constants. This data does not change at runtime. You can declare various constant values, file names, or buffer size, etc., in this section.

section.data

The bss Section

The bss section is used for declaring variables.

section.bss

The text section

The text section is used for keeping the actual code. This section must begin with the declaration global _start, which tells the kernel where the program execution begins.

section.text
    global _start
_start:

Syntax

[label]   mnemonic   [operands]   [;comment]

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	0x80        ;call kernel
	
   mov	eax,1       ;system call number (sys_exit)
   int	0x80        ;call kernel

section	.data
msg db 'Hello, world!', 0xa  ;string to be printed
len equ $ - msg     ;length of the string

nasm -f elf hello.asm
ld -m elf_i386 -s -o hello hello.o
./hello

section .data : tempat nyimpan data

text db "Hello world", 10 :

  • nama memory address 'text'
  • defining bytes 'db'
  • berisi "Hello world" dan '10' / newline