nasm

Assemble to object file

$ nasm -f [elf64] [source.asm] -o [output.o]

$ nasm -f elf32 [source.asm]

$ nasm -f win64 [source.asm]

$ nasm -f [elf64] -l [listing.lst] [source.asm]

$ nasm -D [MACRO_NAME]=[value] [source.asm]

$ nasm -I [/path/to/includes/] [source.asm]

$ nasm -E [source.asm]

$ nasm -hf

nasm [-f format] [-o outfile] [-l listfile] [-D name=value] [options] source.asm

NASM (Netwide Assembler) is a portable x86 and x86-64 assembler using Intel syntax. It produces object files for various operating systems and formats, making it suitable for cross-platform assembly development.
The Intel syntax NASM uses is generally considered more readable than AT&T syntax: destination comes first (mov eax, 1), memory references use brackets ([var]), and size specifiers are explicit (dword, qword).
Output formats cover major platforms: ELF for Linux/Unix, PE/COFF for Windows, Mach-O for macOS, and flat binary for bootloaders and embedded systems. The -f option selects the target format.
NASM includes a powerful macro preprocessor supporting multi-line macros, conditional assembly, string manipulation, and file inclusion. Context-local labels enable reusable code structures.
For debugging, NASM generates debugging information in formats like DWARF and CodeView, compatible with GDB, LLDB, and Visual Studio debuggers.

-f format

Output format (elf64, elf32, win64, win32, macho64, bin, etc.).

Output file name.

Generate listing file.

Generate Makefile dependencies.

Preprocess only, output to stdout.

Preprocess only, no output.

Define preprocessor macro.

Undefine preprocessor macro.

Add include file search directory.

Pre-include file before source.

Enable/disable warning type.

Generate debug information.

Debug information format.

Optimization level (0, 1, x for multi-pass).

Output errors to stdout.

Display version.

Display help.

List output formats.

Intel syntax differs from GNU as (AT&T syntax). Object files must be linked (ld, gcc, link.exe) to create executables. Platform-specific calling conventions matter for function calls. Binary output requires manual memory layout. 16-bit and 32-bit modes need attention to processor mode.

NASM was written by Simon Tatham and Julian Hall starting in 1996, aiming to create a free, portable assembler with clean Intel syntax. It became the assembler of choice for many open-source projects needing low-level code. The project has seen contributions from many developers and remains actively maintained for modern processor extensions including AVX-512.

as(1), yasm(1), ld(1), objdump(1), gdb(1)