How to compile assembly code with NASM

Compiling assembly code involves translating human-readable assembly code into machine code or object code that a computer can execute.

Compilation Process

  1. Assembler: The first step is to use an assembler to convert assembly code into machine code or object code. Assemblers are specific to the architecture of the target machine.
  2. Linker: If the program consists of multiple source files or relies on external libraries, a linker may be used to combine these files into a single executable. The linker resolves addresses and references between different parts of the code.
Example

Consider a simple x86 assembly program that prints "Hello, World!" to the console:

section .data msg db 'Hello, World!', 0 section .text global _start _start: ; write the message to stdout mov eax, 4 ; system call number for sys_write mov ebx, 1 ; file descriptor 1 is stdout mov ecx, msg ; pointer to the message mov edx, 13 ; length of the message int 0x80 ; call kernel ; exit the program mov eax, 1 ; system call number for sys_exit xor ebx, ebx ; exit code 0 int 0x80 ; call kernel

Assembling

Use an assembler (e.g., NASM for x86) to convert the assembly code into object code:

nasm -f elf32 hello.asm -o hello.o

This produces an object file (hello.o) containing machine code.

Linking

If needed, use a linker (e.g., ld for Linux) to link the object file with any necessary libraries:

ld -m elf_i386 -s -o hello hello.o

This produces the final executable (hello), ready to be executed.

Execution

Run the compiled executable:

./hello

The program will execute and print "Hello, World!" to the console.

Conclusion

Compiling assembly code involves using an assembler to convert human-readable assembly code into machine code or object code, and optionally using a linker to combine multiple object files into a single executable.






Related Topics
  1. What is CPU Architecture?
  2. Registers in Assembly Language
  3. Addressing modes? in Assembly Language
  4. Assembly Language Instruction Components
  1. Writing Your First Assembly Program