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Assembly (NASM64) targets the 64-bit x86-64 architecture using the Netwide Assembler (NASM) 2.15.5. You program directly with machine instructions, working with the wider 64-bit registers (rax, rbx, rcx, and friends), explicit memory addressing, and the modern Linux system-call interface. This gives precise, low-level control over the processor while remaining human-readable through familiar mnemonics like mov, add, and syscall.
On x86-64 Linux, system calls use the dedicated syscall instruction rather than the older interrupt approach: the call number goes in rax, and arguments are passed in rdi, rsi, rdx, r10, r8, and r9. Programs are split into sections such as .text and .data and begin at the _start label. Learning 64-bit assembly reveals exactly how the System V calling convention, registers, and the stack support the languages built on top of them.
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section .data
msg db "Hello, World!", 0x0A
len equ $ - msg
section .text
global _start
_start:
mov rax, 1 ; sys_write
mov rdi, 1 ; stdout
mov rsi, msg
mov rdx, len
syscall
mov rax, 60 ; sys_exit
xor rdi, rdi
syscallsection .text
global _start
_start:
mov rax, 60 ; sys_exit
mov rdi, 42 ; exit code
syscallsection .text
global _start
_start:
mov rax, 2
add rax, 3 ; rax = 5
mov rdi, rax ; use result as exit code
mov rax, 60 ; sys_exit
syscallsection .text
global _start
_start:
mov rcx, 5 ; loop 5 times
xor rax, rax ; accumulator
next:
add rax, rcx
loop next ; dec rcx, jump while rcx != 0
mov rdi, rax ; sum 5+4+3+2+1 = 15
mov rax, 60 ; sys_exit
syscallsection .text
global _start
_start:
mov rax, 7
cmp rax, 10
jl less ; jump if rax < 10
mov rdi, 1
jmp done
less:
mov rdi, 0
done:
mov rax, 60 ; sys_exit
syscallsection .text
global _start
_start:
sub rsp, 16 ; reserve stack space
mov byte [rsp], 'H'
mov byte [rsp+1], 'i'
mov byte [rsp+2], 0x0A
mov rax, 1 ; sys_write
mov rdi, 1 ; stdout
mov rsi, rsp ; buffer
mov rdx, 3 ; length
syscall
add rsp, 16
mov rax, 60 ; sys_exit
xor rdi, rdi
syscallsection .text
global _start
_start:
mov rax, 6
mov rbx, 7
imul rbx ; rdx:rax = rax * rbx -> 42
mov rdi, rax ; exit code = 42
mov rax, 60 ; sys_exit
syscallsection .data
arr dq 10, 20, 30, 40
count equ 4
section .text
global _start
_start:
xor rax, rax ; sum
xor rcx, rcx ; index
next:
add rax, [arr + rcx*8]
inc rcx
cmp rcx, count
jl next
mov rdi, rax ; exit code = 100
mov rax, 60 ; sys_exit
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Assembly (NASM64) is one of 46 single-file compiler scratchpads. Each run submits only main.asm; local sibling-file imports are not enabled.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme.
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