Online Assembler (NASM) Compiler & Editor

section .data
    msg db "Hello, World!", 10
    len equ $ - msg
section .text
    global _start
_start:
    mov rax, 1
    mov rdi, 1
    mov rsi, msg
    mov rdx, len
    syscall
    mov rax, 60
    xor rdi, rdi
    syscall

section .data
    num1    dq 42
    num2    dq 58
    msg     db "Sum: ", 0
    msglen  equ $ - msg

section .text
    global _start
_start:
    mov rax, [num1]
    add rax, [num2]     ; rax = 42 + 58 = 100
    ; exit with the sum as exit code
    mov rdi, rax
    mov rax, 60
    syscall

section .data
    pos_msg db "Positive", 10
    pos_len equ $ - pos_msg
    neg_msg db "Non-positive", 10
    neg_len equ $ - neg_msg

section .text
    global _start
_start:
    mov rax, 5          ; test value
    cmp rax, 0
    jle .non_positive
    mov rax, 1
    mov rdi, 1
    mov rsi, pos_msg
    mov rdx, pos_len
    syscall
    jmp .exit
.non_positive:
    mov rax, 1
    mov rdi, 1
    mov rsi, neg_msg
    mov rdx, neg_len
    syscall
.exit:
    mov rax, 60
    xor rdi, rdi
    syscall

section .data
    newline db 10

section .bss
    buf resb 2

section .text
    global _start
_start:
    mov rcx, 5          ; loop counter
    mov rbx, 0          ; i = 0
.loop:
    test rcx, rcx
    jz .done
    ; convert rbx to ASCII digit and print
    mov rax, rbx
    add rax, 0x30
    mov [buf], al
    mov rax, 1
    mov rdi, 1
    mov rsi, buf
    mov rdx, 1
    syscall
    inc rbx
    dec rcx
    jmp .loop
.done:
    mov rax, 60
    xor rdi, rdi
    syscall

section .data
    msg db "Result: 120", 10
    len equ $ - msg

section .text
    global _start

; Compute factorial(n): n in rdi, result in rax
factorial:
    cmp rdi, 1
    jle .base
    push rdi
    dec rdi
    call factorial
    pop rdi
    imul rax, rdi
    ret
.base:
    mov rax, 1
    ret

_start:
    mov rdi, 5
    call factorial      ; rax = 120
    mov rax, 1
    mov rdi, 1
    mov rsi, msg
    mov rdx, len
    syscall
    mov rax, 60
    xor rdi, rdi
    syscall

; Array of 5 integers
section .data
    nums    dq 10, 20, 30, 40, 50
    count   equ 5

section .text
    global _start
_start:
    xor rax, rax        ; sum = 0
    xor rcx, rcx        ; i = 0
.loop:
    cmp rcx, count
    jge .done
    add rax, [nums + rcx*8]
    inc rcx
    jmp .loop
.done:
    ; exit with sum / 10 as code (15 = 150/10)
    mov rdi, rax
    mov rax, 60
    syscall

; Assembly structs via memory layout
; struct Dog { name: 32 bytes, age: 8 bytes }
section .data
    dog_name db "Rex", 0
             times 29 db 0
    dog_age  dq 3
    msg      db "Dog initialized", 10
    msg_len  equ $ - msg

section .text
    global _start
_start:
    mov rax, 1
    mov rdi, 1
    mov rsi, msg
    mov rdx, msg_len
    syscall
    mov rax, 60
    xor rdi, rdi
    syscall

; Check syscall return value for errors
section .data
    filename db "nonexistent.txt", 0
    errmsg   db "File not found", 10
    errlen   equ $ - errmsg

section .text
    global _start
_start:
    ; Try to open file
    mov rax, 2          ; sys_open
    mov rdi, filename
    mov rsi, 0          ; O_RDONLY
    mov rdx, 0
    syscall
    ; Check for error (negative return)
    test rax, rax
    jns .ok
    mov rax, 1
    mov rdi, 2          ; stderr
    mov rsi, errmsg
    mov rdx, errlen
    syscall
.ok:
    mov rax, 60
    xor rdi, rdi
    syscall

section .data
    filename db "output.txt", 0
    content  db "Hello, File!", 10
    cont_len equ $ - content

section .text
    global _start
_start:
    ; Open/create file (O_WRONLY|O_CREAT|O_TRUNC = 0o641)
    mov rax, 2
    mov rdi, filename
    mov rsi, 0o641
    mov rdx, 0o644
    syscall
    mov r8, rax         ; save fd
    ; Write to file
    mov rax, 1
    mov rdi, r8
    mov rsi, content
    mov rdx, cont_len
    syscall
    ; Close file
    mov rax, 3
    mov rdi, r8
    syscall
    ; Exit
    mov rax, 60
    xor rdi, rdi
    syscall

; Linux x86-64 system calls demo
section .data
    msg1 db "sys_write: stdout", 10
    len1 equ $ - msg1
    msg2 db "sys_write: stderr", 10
    len2 equ $ - msg2

section .text
    global _start
_start:
    ; Write to stdout (fd=1)
    mov rax, 1
    mov rdi, 1
    mov rsi, msg1
    mov rdx, len1
    syscall
    ; Write to stderr (fd=2)
    mov rax, 1
    mov rdi, 2
    mov rsi, msg2
    mov rdx, len2
    syscall
    ; Exit with code 0
    mov rax, 60
    xor rdi, rdi
    syscall