Nasm64

64-bit assembler

2026-01-16

Written by: xiaobin

git clone https://github.com/ShiftMediaProject/VSNASM.git

• x64 Native Tools Command Prompt for VS 2022

Run command prompt as administrator

cd \
cd VSNASM
install_script.bat

project

• set compile
  Project -> Build Customizations
  checked:

nasm(.targets, .props)

• set entry point
  Linker -> Advanced

Entry Point: main

compile

• manual:

nasm -f win64 hello_floats.asm

• auto:
  In the Solution Explorer, select the asm file, then right-click and select Compile.

Generate exe

run “x64 Native Tools Command Prompt for VS 2022”

link hello_floats.obj /subsystem:console /out:hello6.exe kernel32.lib msvcrt.lib ucrt.lib legacy_stdio_definitions.lib

hello_floats.asm

; Copyright 2019 Siew Yi Liang.
; 
default rel
bits 64

segment .data
    a dd 3.25
    b dd 10.53

    fmt db 'result is: %f', 0xa, 0

segment .text
global main
extern _CRT_INIT
extern ExitProcess
extern printf

main:
    call _CRT_INIT                 ; Needed since our entry point is not _DllMainCRTStartup. See https://msdn.microsoft.com/en-us/library/708by912.aspx

    push    rbp
    mov    rbp, rsp
    sub    rsp, 32

    movss    xmm0, [a]             ; Load a
    movss    xmm1, [b]             ; Load b
    vaddss    xmm2, xmm0, xmm1      ; xmm2 = xmm1 + xmm2
    lea    rcx, [fmt]
    movss    xmm1, xmm2

    ; Remember, %f actually expects a double, so we need to convert the float to double
    cvtss2sd    xmm1, xmm1

    ; Also remember: floats are passed in xmm registers, but printf wants a
    ; double! This is an aggregate so it's passed in RDX instead.
    movq    rdx, xmm1
    call    printf

    xor eax, eax                ; return 0
    call ExitProcess

Ref

• Understanding Windows x64 Assembly