Netwide Assembler

Netwide Assembler

Original author(s)	Simon Tatham, Julian Hall
Developer(s)	H. Peter Anvin, et al.
Stable release	2.09.09 / July 3, 2011; 4 months ago (2011-07-03)
Preview release	2.10rc6 / June 6, 2011; 5 months ago (2011-06-06)
Operating system	Microsoft Windows, Unix-like, OS/2, Mac OS, DOS
Available in	English
Type	x86 assembler
License	2-clause BSD
Website	http://www.nasm.us/

The Netwide Assembler (NASM) is an assembler and disassembler for the Intel x86 architecture. It can be used to write 16-bit, 32-bit (IA-32) and 64-bit (x86-64) programs. NASM is considered to be one of the most popular assemblers for Linux^[1].

NASM was originally written by Simon Tatham with assistance from Julian Hall, and is currently maintained by a small team led by H. Peter Anvin.^[2] It is available as free software under the terms of the simplified (2-clause) BSD license.^[3]

Features

NASM can output several binary formats including COFF, Portable Executable, a.out, ELF and Mach-O, though position-independent code is only supported for ELF object files. NASM also has its own binary format called RDOFF.^[4]

The variety of output formats allows programs to be retargetted to virtually any x86 operating system. In addition, NASM can create flat binary files, usable in writing boot loaders, ROM images, and in various facets of OS development.^[4] NASM can run on non-x86 platforms, such as SPARC and PowerPC, though it generate programs usable by those machines.

NASM uses variation of Intel assembly syntax instead of AT&T syntax.^[5] It also avoids features such as automatic generation of segment overrides (and the related ASSUME directive) used by MASM and compatible assemblers.^[4]

Examples of programs for various operating systems

This is a Hello world program for the DOS operating system.

section .text
org 0x100
        mov    ah, 0x9
        mov    dx, hello
        int    0x21
 
        mov    ax, 0x4c00
        int    0x21
 
section .data
hello: db 'Hello, world!', 13, 10, '$'

An example of a similar program for Microsoft Windows:

global _start
extern _MessageBoxA@16
extern _ExitProcess@4
 
section code use32 class=code
_start:
        push   dword 0      ; UINT uType = MB_OK
        push   dword title  ; LPCSTR lpCaption
        push   dword banner ; LPCSTR lpText
        push   dword 0      ; HWND hWnd = NULL
        call   _MessageBoxA@16
 
        push   dword 0      ; UINT uExitCode
        call   _ExitProcess@4
 
section data use32 class=data
        banner:        db 'Hello, world!', 0
        title:        db 'Hello', 0

An equivalent program for Linux:

section .data
msg:   db     "Hello, world!", 10
.len: equ    $ - msg
 
section .text
global _start
_start:
        mov    eax, 4 ; write
        mov    ebx, 1 ; stdout
        mov    ecx, msg
        mov    edx, msg.len
        int    0x80
 
        mov    eax, 1 ; exit
        mov    ebx, 0      
        int    0x80

Linking

NASM principally outputs object files, which are generally not executable in and of themselves. The only exception to this are flat binaries (e.g., .COM)^[4] which are inherently limited in modern use. To translate the object files into executable programs, an appropriate linker must be used, such as the Visual Studio "LINK" utility for Windows or ld for UNIX-like systems.

Development

On 28 November 2007, version 2.00 was released, adding support for x86-64 extensions.^[2] The development versions are not uploaded to SourceForge.net; instead, they are checked in to the project's own Git repository with binary snapshots available from the project web page.

A search engine for NASM docs is also available.^[6]

As of version 2.07, NASM is now under the Simplified (2-clause) BSD license.

See also

Free software portal

• Assembly language
• List of assemblers
• Yasm

References

1. ^ Ram Narayan. "Linux assemblers: A comparison of GAS and NASM". http://www.ibm.com/developerworks/linux/library/l-gas-nasm/index.html. "two of the most popular assemblers for Linux, GNU Assembler (GAS) and Netwide Assembler (NASM)" 
2. ^ ^{a b} "The Netwide Assembler". http://nasm.sourceforge.net/. Retrieved 2008-06-27. 
3. ^ "NASM Version History". http://www.nasm.us/doc/nasmdocc.html. Retrieved 2009-07-19. 
4. ^ ^{a b c d} "NASM Manual". http://alien.dowling.edu/~rohit/nasmdoc0.html. Retrieved 2009-08-15. 
5. ^ Randall Hyde. "NASM: The Netwide Assembler". http://webster.cs.ucr.edu/AsmTools/NASM/. Retrieved 2008-06-27. 
6. ^ "NASM Doc Search Engine". http://alien.dowling.edu/~rohit/search/srch/search.php. Retrieved 2009-09-14. 

Further reading

• Jeff Duntemann (2000). Assembly Language Step by Step. J Wiley and Sons. ISBN 0471375233. 

External links

• NASM website
• SourceForge Page
• Special edition for Win32 and BeOS.
• A comparison of GAS and NASM at IBM
• intel2gas : a converter between the source format of the NASM and GAS assemblers