how to assemble assembly with NASM assembler to 32-bit or 64-bit ELF binary with or without libc

compiling_asm.md

32-bit ELF binary

how to assemble and link:

nasm -f elf32 -o <filename>.o <filename>.asm
ld -m elf_i386 -o <filename> <filename>.o

template code (hello world):

section .text
global _start

%define system_call int 0x80

_start:
    mov ebx, 0x1
    mov ecx, hello
    mov edx, helloLen
    mov eax, 0x4
    system_call

    xor ebx, ebx
    mov eax, 0x1
    system_call

section .data
    hello db "Hello World", 0xa
    helloLen equ $-hello

64-bit ELF binary

how to assemble and link:

nasm -f elf64 -o <filename>.o <filename>.asm
ld -o <filename> <filename>.o

template code (hello world):

section .text
global _start

_start:
    mov rdi, 0x1
    mov rsi, hello
    mov rdx, helloLen
    mov rax, 0x1
    syscall

    xor rdi, rdi
    mov rax, 0x3c
    syscall

section .data
    hello db "Hello World", 0xa
    helloLen equ $-hello

32-bit ELF binary with libc

how to assemble and link:

nasm -f elf32 -o <filename>.o <filename>.asm
ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o <filename> -lc <filename>.o

template code (hello world):

extern puts
extern exit

section .text
global _start

%macro call_func 1
    call %1
    add esp, 0x4
%endmacro

_start:
    push hello
    call_func puts

    mov eax, 0xa
    call exit

section .data
    hello db "Hello World"

64-bit ELF binary with libc

how to assemble and link:

nasm -f elf64 -o <filename>.o <filename>.asm
ld -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o <filename> -lc <filename>.o

template code (hello world):

extern puts
extern exit

section .text
global _start

%macro call_func 1
    call %1
%endmacro

_start:
    mov rdi, hello
    call_func puts

    mov rax, 0xa 
    call exit

section .data
    hello db "Hello World"

---

NOTE :

• Assembler Directives: instructions for the assembler (e.g. NASM) and not a part of the ISA
  • extern: declare a symbol which is defined in another module that will later be linked with current one
  • section: identifies the section the code you write will go into. Examples of common ones are .text, .data, and .bss
  • global: defines symbols such that other modules that EXTERN those symbols can correctly reference them after linking
  • macro: a name that represents a snippet of code
  • define: a single-line macro

Ohh no need to take too much time trying to find it. If you just happen to come across it again in the future, feel free to share :)

There is (at least) one bug in the "64-bit ELF binary with libc" example:

The argument to 'puts' is passed in an register (not the stack), so the stack pointer should not be adjusted after the call!

Try returning from '_start' instead of calling libc's 'exit()'. Then it will fail miserably because the stack is messed up.

Oops, thank you for catching that @torbjo !! Code updated.

Thank you a lot for this! very useful for a beginner.

Glad to hear :)

Thanks a lot !

For sure!!

Awesome resource, I will steal it from you :D, thanks a lot !!!

For sure! Glad you found it noteworthy to steal ^^