View source for Netwide Assembler

{{short description|Assembler for the Intel x86 architecture}}
{{primary sources|date=February 2012}}
{{Use dmy dates|date=March 2020}}
{{Infobox software
| name = NASM
| logo = Netwide Assembler.svg
| author = [[Simon Tatham]], Julian Hall
| developer = [[H. Peter Anvin]], [[Chang Seok Bae]], [[Jim Kukunas]], [[Frank B. Kotler]], [[Cyrill Gorcunov]]
| released = {{Start date and age|df=yes|1996|10}}
| latest release version = {{wikidata|property|preferred|references|edit|P348|P548=Q2804309}}
| latest release date = {{Start date and age|{{wikidata|qualifier|preferred|single|P348|P548=Q2804309|P577}}|df=yes}}
| programming language = [[Assembly language|Assembly]], [[C (programming language)|C]]<ref>{{Cite web|url=https://github.com/netwide-assembler/nasm|title = NASM, the Netwide Assembler|website = [[GitHub]]|date = 25 October 2021}}</ref>
| operating system = [[Unix-like]], [[Microsoft Windows|Windows]], [[OS/2]], [[MS-DOS]]
| genre = [[x86 assembly language|x86]] [[assembly language|assembler]]
| language = [[English language|English]]
| license = [[BSD licenses|BSD 2-clause]]
| website = {{url|https://www.nasm.us/|nasm.us}}
}}

The '''Netwide Assembler''' ('''NASM''') is an [[Assembly language#Assembler|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. It is considered one of the most popular assemblers for [[Linux]] and [[X86|x86 chips]].<ref>{{Cite web|url=http://www.ibm.com/developerworks/linux/library/l-gas-nasm/index.html |title=Linux assemblers: A comparison of GAS and NASM |author=Ram Narayan |website=[[IBM]] |quote=two of the most popular assemblers for Linux, GNU Assembler (GAS) and Netwide Assembler (NASM) |url-status=dead |archive-url=https://web.archive.org/web/20131003180256/http://www.ibm.com/developerworks/linux/library/l-gas-nasm/index.html |archive-date=3 October 2013}}</ref>

It was originally written by [[Simon Tatham]] with assistance from Julian Hall. {{As of|2016}}, it is maintained by a small team led by [[H. Peter Anvin]].<ref name="Homepage">{{Cite web|url=https://nasm.sourceforge.net/|title=The Netwide Assembler|access-date=2008-06-27}}</ref> It is [[open-source software]] released under the terms of a simplified (2-clause) [[BSD licenses|BSD license]].<ref name="VersionHistory">{{Cite web|url=https://www.nasm.us/doc/nasmdocc.html|title=NASM Version History|access-date=2019-08-03}}</ref>

== Features ==
NASM can output several binary formats, including [[COFF]], OMF, [[a.out (file format)|a.out]], [[Executable and Linkable Format]] (ELF), [[Mach-O]] and [[binary file]] (.bin, binary disk image, used to compile [[operating system]]s), though [[position-independent code]] is supported only for ELF [[object file]]s. It also has its own binary format called RDOFF.<ref name="Manual">{{Cite web|url=http://alien.dowling.edu/~rohit/nasmdoc0.html|title=NASM Manual|access-date=2009-08-15|url-status=dead|archive-url=https://web.archive.org/web/20090223104837/http://alien.dowling.edu/~rohit/nasmdoc0.html|archive-date=23 February 2009}}</ref>

The variety of output formats allows [[retargeting]] programs to virtually any x86 operating system (OS). It can also create [[flat binary file]]s, usable to write [[Booting|boot loaders]], [[read-only memory]] (ROM) images, and in various facets of OS development.<ref name="Manual"/> It can run on non-x86 platforms (if NASM itself is compiled for that platform) as a [[Assembly language#Cross assembler|cross assembler]], such as [[PowerPC]] and [[SPARC]], though it cannot generate programs usable by those machines.

NASM uses a variant of [[Intel assembly syntax]] instead of [[AT&T syntax]].<ref name="Hyde">{{Cite web|url=http://webster.cs.ucr.edu/AsmTools/NASM/|title=NASM: The Netwide Assembler|access-date=2008-06-27|author=Randall Hyde|author-link=Randall Hyde|url-status=dead|archive-url=https://web.archive.org/web/20100912172954/http://webster.cs.ucr.edu/AsmTools/NASM/|archive-date=12 September 2010}}</ref> It also avoids features such as automatic generation of [[x86 memory segmentation|segment]] overrides (and the related ASSUME directive) used by [[MASM]] and compatible assemblers.<ref name="Manual"/>

== Development ==
NASM version 0.90 was released in October 1996.<ref name="VersionHistory"/>

Version 2.00 was released on 28 November 2007, adding support for [[x86-64]] extensions.<ref name="Homepage"/> The development versions are not uploaded to [[SourceForge.net]], but are checked into [[GitHub]] with binary snapshots available from the project web page.

In July 2009, as of version 2.07, NASM was released under the Simplified (2-clause) BSD license. Previously, because it was licensed under [[GNU Lesser General Public License|LGPL]], it led to development of Yasm, a complete rewrite of under the [[BSD licenses#3-clause|New BSD License]]. Yasm offered support for x86-64 earlier than NASM. It also added support for [[GNU Assembler]] syntax.

=== RDOFF ===
Relocatable Dynamic Object File Format (RDOFF) is used by developers to test the integrity of NASM's object file output abilities. It is based heavily on the internal structure of NASM,<ref name = "manual">{{cite web|url=https://nasm.sourceforge.net/doc/nasmdoc6.html|title=NASM Manual Ch. 6|access-date=2008-06-27}}</ref> essentially consisting of a header containing a [[serialization]] of the output driver function calls followed by an array of sections containing executable code or data.  Tools for using the format, including a linker and loader, are included in the NASM distribution.

Until version 0.90 was released in October 1996, NASM supported output of only flat-format executable files (e.g., [[COM file]]s). In version 0.90, [[Simon Tatham]] added support for an object-file output interface, and for DOS .OBJ files for 16-bit code only.<ref name="CVS">{{cite web|url=https://nasm.cvs.sourceforge.net/nasm/nasm/CHANGES?revision=1.48&view=markup|title=NASM CVS|date=2008-06-08|access-date=2008-06-27}}</ref>

NASM thus lacked a 32-bit object format.  To address this lack, and as an exercise to learn the object-file interface, developer Julian Hall put together the first version of RDOFF, which was released in NASM version 0.91.<ref name="CVS"/>

Since this initial version, there has been one major update to the RDOFF format, which added a record-length indicator on each header record,<ref>{{cite web|url=https://nasm.cvs.sourceforge.net/nasm/nasm/rdoff/doc/v1-v2.txt?revision=1.1&view=markup|title=V1-V2.txt|date=2002-12-04|access-date=2008-06-27}}</ref> allowing programs to skip over records whose format they do not recognise, and support for multiple segments; RDOFF1 only supported three segments: ''text'', ''data'' and ''bss'' (containing uninitialized data).<ref name = "manual"/>

The RDOFF format is strongly deprecated and has been disabled starting in NASM 2.15.04.{{r|RDOFF}}

== See also ==
{{Portal|Free and open-source software}}

* [[Assembly language]]
* [[Comparison of assemblers]]

== References ==
{{Reflist|refs=
<ref name=RDOFF>{{cite web
|url = https://www.nasm.us/doc/nasmdoc8.html#section-8.13
|title = Relocatable Dynamic Object File Format (deprecated)}}</ref>
}}

== Further reading ==
* {{Cite book|title=Assembly Language Step by Step|author=Jeff Duntemann|publisher=J Wiley and Sons|year=2000|isbn=0-471-37523-3|url-access=registration|url=https://archive.org/details/assemblylanguage0000dunt_c8n9}}

== External links ==
* {{Official website|https://www.nasm.us}}
* {{Sourceforge|nasm}}
* [https://web.archive.org/web/20111016034545/http://www.realtech-vr.com/nasm/ Special edition for Win32 and BeOS.]
* [https://developer.ibm.com/articles/l-gas-nasm/ A comparison of GAS and NASM] at [[IBM]]
* {{freshmeat|intel2gas}}: a converter between the source format of the assemblers NASM and [[GNU Assembler|GAS]]

{{X86 assembly topics}}

[[Category:1996 software]]
[[Category:Assemblers]]
[[Category:Disassemblers]]
[[Category:DOS software]]
[[Category:Free and open source compilers]]
[[Category:Linux programming tools]]
[[Category:MacOS]]
[[Category:MacOS programming tools]]
[[Category:Programming tools for Windows]]
[[Category:Software using the BSD license]]