Hello World in x64 Assembly (macOS)

A minimal Hello World implementation in x64 assembly for macOS systems.

Installation

macOS

Install the development tools:

xcode-select --install

Install NASM through Homebrew:

brew install nasm

Building and Running

# Assemble
nasm -f macho64 hello.asm

# Link
# Note: We link against System framework which provides C runtime
ld -macosx_version_min 10.7.0 -lSystem hello.o -o hello

# Run
./hello

Code Explanation

The program demonstrates key aspects of macOS x64 assembly programming:

System Call Interface:

• macOS uses a unique syscall numbering scheme (0x2000000 + syscall number)
• System calls follow BSD Unix conventions but with macOS-specific numbers
• Unlike Linux, system calls are prefixed with 0x2000000

Register Convention:

• System call number goes in RAX
• First argument in RDI (file descriptor)
• Second argument in RSI (buffer address)
• Third argument in RDX (buffer length)

C Runtime Integration:

• Uses _main as entry point (required by macOS)
• Links against System framework for C runtime
• Exits cleanly through C runtime _exit function

Note: This implementation specifically targets macOS on x64 processors. For other platforms, see the respective platform-specific implementations.