The Netwide Assembler: NASM
                        ===========================

Chapter 1: Introduction
-----------------------

   1.1 What Is NASM?

       The Netwide Assembler, NASM, is an 80x86 and x86-64 assembler
       designed for portability and modularity. It supports a range of
       object file formats, including Linux and `*BSD' `a.out', `ELF',
       `COFF', `Mach-O', Microsoft 16-bit `OBJ', `Win32' and `Win64'. It
       will also output plain binary files. Its syntax is designed to be
       simple and easy to understand, similar to Intel's but less complex.
       It supports all currently known x86 architectural extensions, and
       has strong support for macros.

 1.1.1 Why Yet Another Assembler?

       The Netwide Assembler grew out of an idea on `comp.lang.asm.x86' (or
       possibly `alt.lang.asm' - I forget which), which was essentially
       that there didn't seem to be a good _free_ x86-series assembler
       around, and that maybe someone ought to write one.

       (*) `a86' is good, but not free, and in particular you don't get any
           32-bit capability until you pay. It's DOS only, too.

       (*) `gas' is free, and ports over to DOS and Unix, but it's not very
           good, since it's designed to be a back end to `gcc', which
           always feeds it correct code. So its error checking is minimal.
           Also, its syntax is horrible, from the point of view of anyone
           trying to actually _write_ anything in it. Plus you can't write
           16-bit code in it (properly.)

       (*) `as86' is specific to Minix and Linux, and (my version at least)
           doesn't seem to have much (or any) documentation.

       (*) `MASM' isn't very good, and it's (was) expensive, and it runs
           only under DOS.

       (*) `TASM' is better, but still strives for MASM compatibility,
           which means millions of directives and tons of red tape. And its
           syntax is essentially MASM's, with the contradictions and quirks
           that entails (although it sorts out some of those by means of
           Ideal mode.) It's expensive too. And it's DOS-only.

       So here, for your coding pleasure, is NASM. At present it's still in
       prototype stage - we don't promise that it can outperform any of
       these assemblers. But please, _please_ send us bug reports, fixes,
       helpful information, and anything else you can get your hands on
       (and thanks to the many people who've done this already! You all
       know who you are), and we'll improve it out of all recognition.
       Again.

 1.1.2 License Conditions

       Please see the file `COPYING', supplied as part of any NASM
       distribution archive, for the license conditions under which you may
       use NASM. NASM is now under the so-called GNU Lesser General Public
       License, LGPL.

   1.2 Contact Information

       The current version of NASM (since about 0.98.08) is maintained by a
       team of developers, accessible through the `nasm-devel' mailing list
       (see below for the link). If you want to report a bug, please read
       section 11.2 first.

       NASM has a WWW page at `http://nasm.sourceforge.net'. If it's not
       there, google for us!

       The original authors are e-mailable as `jules@dsf.org.uk' and
       `anakin@pobox.com'. The latter is no longer involved in the
       development team.

       New releases of NASM are uploaded to the official sites
       `http://nasm.sourceforge.net' and to `ftp.kernel.org' and
       `ibiblio.org'.

       Announcements are posted to `comp.lang.asm.x86', `alt.lang.asm' and
       `comp.os.linux.announce'

       If you want information about NASM beta releases, and the current
       development status, please subscribe to the `nasm-devel' email list
       by registering at `http://sourceforge.net/projects/nasm'.

   1.3 Installation

 1.3.1 Installing NASM under MS-DOS or Windows

       Once you've obtained the appropriate archive for NASM,
       `nasm-XXX-dos.zip' or `nasm-XXX-win32.zip' (where `XXX' denotes the
       version number of NASM contained in the archive), unpack it into its
       own directory (for example `c:\nasm').

       The archive will contain a set of executable files: the NASM
       executable file `nasm.exe', the NDISASM executable file
       `ndisasm.exe', and possibly additional utilities to handle the RDOFF
       file format.

       The only file NASM needs to run is its own executable, so copy
       `nasm.exe' to a directory on your PATH, or alternatively edit
       `autoexec.bat' to add the `nasm' directory to your `PATH' (to do
       that under Windows XP, go to Start > Control Panel > System >
       Advanced > Environment Variables; these instructions may work under
       other versions of Windows as well.)

       That's it - NASM is installed. You don't need the nasm directory to
       be present to run NASM (unless you've added it to your `PATH'), so
       you can delete it if you need to save space; however, you may want
       to keep the documentation or test programs.

       If you've downloaded the DOS source archive, `nasm-XXX.zip', the
       `nasm' directory will also contain the full NASM source code, and a
       selection of Makefiles you can (hopefully) use to rebuild your copy
       of NASM from scratch. See the file `INSTALL' in the source archive.

       Note that a number of files are generated from other files by Perl
       scripts. Although the NASM source distribution includes these
       generated files, you will need to rebuild them (and hence, will need
       a Perl interpreter) if you change insns.dat, standard.mac or the
       documentation. It is possible future source distributions may not
       include these files at all. Ports of Perl for a variety of
       platforms, including DOS and Windows, are available from
       www.cpan.org.

 1.3.2 Installing NASM under Unix

       Once you've obtained the Unix source archive for NASM,
       `nasm-XXX.tar.gz' (where `XXX' denotes the version number of NASM
       contained in the archive), unpack it into a directory such as
       `/usr/local/src'. The archive, when unpacked, will create its own
       subdirectory `nasm-XXX'.

       NASM is an auto-configuring package: once you've unpacked it, `cd'
       to the directory it's been unpacked into and type `./configure'.
       This shell script will find the best C compiler to use for building
       NASM and set up Makefiles accordingly.

       Once NASM has auto-configured, you can type `make' to build the
       `nasm' and `ndisasm' binaries, and then `make install' to install
       them in `/usr/local/bin' and install the man pages `nasm.1' and
       `ndisasm.1' in `/usr/local/man/man1'. Alternatively, you can give
       options such as `--prefix' to the configure script (see the file
       `INSTALL' for more details), or install the programs yourself.

       NASM also comes with a set of utilities for handling the `RDOFF'
       custom object-file format, which are in the `rdoff' subdirectory of
       the NASM archive. You can build these with `make rdf' and install
       them with `make rdf_install', if you want them.

Chapter 2: Running NASM
-----------------------

   2.1 NASM Command-Line Syntax

       To assemble a file, you issue a command of the form

       nasm -f <format> <filename> [-o <output>]

       For example,

       nasm -f elf myfile.asm

       will assemble `myfile.asm' into an `ELF' object file `myfile.o'. And

       nasm -f bin myfile.asm -o myfile.com

       will assemble `myfile.asm' into a raw binary file `myfile.com'.

       To produce a listing file, with the hex codes output from NASM
       displayed on the left of the original sources, use the `-l' option
       to give a listing file name, for example:

       nasm -f coff myfile.asm -l myfile.lst

       To get further usage instructions from NASM, try typing

       nasm -h

       As `-hf', this will also list the available output file formats, and
       what they are.

       If you use Linux but aren't sure whether your system is `a.out' or
       `ELF', type

       file nasm

       (in the directory in which you put the NASM binary when you
       installed it). If it says something like

       nasm: ELF 32-bit LSB executable i386 (386 and up) Version 1

       then your system is `ELF', and you should use the option `-f elf'
       when you want NASM to produce Linux object files. If it says

       nasm: Linux/i386 demand-paged executable (QMAGIC)

       or something similar, your system is `a.out', and you should use
       `-f aout' instead (Linux `a.out' systems have long been obsolete,
       and are rare these days.)

       Like Unix compilers and assemblers, NASM is silent unless it goes
       wrong: you won't see any output at all, unless it gives error
       messages.

 2.1.1 The `-o' Option: Specifying the Output File Name

       NASM will normally choose the name of your output file for you;
       precisely how it does this is dependent on the object file format.
       For Microsoft object file formats (`obj' and `win32'), it will
       remove the `.asm' extension (or whatever extension you like to use -
       NASM doesn't care) from your source file name and substitute `.obj'.
       For Unix object file formats (`aout', `coff', `elf', `macho' and
       `as86') it will substitute `.o'. For `rdf', it will use `.rdf', and
       for the `bin' format it will simply remove the extension, so that
       `myfile.asm' produces the output file `myfile'.

       If the output file already exists, NASM will overwrite it, unless it
       has the same name as the input file, in which case it will give a
       warning and use `nasm.out' as the output file name instead.

       For situations in which this behaviour is unacceptable, NASM
       provides the `-o' command-line option, which allows you to specify
       your desired output file name. You invoke `-o' by following it with
       the name you wish for the output file, either with or without an
       intervening space. For example:

       nasm -f bin program.asm -o program.com 
       nasm -f bin driver.asm -odriver.sys

       Note that this is a small o, and is different from a capital O ,
       which is used to specify the number of optimisation passes required.
       See section 2.1.22.

 2.1.2 The `-f' Option: Specifying the Output File Format

       If you do not supply the `-f' option to NASM, it will choose an
       output file format for you itself. In the distribution versions of
       NASM, the default is always `bin'; if you've compiled your own copy
       of NASM, you can redefine `OF_DEFAULT' at compile time and choose
       what you want the default to be.

       Like `-o', the intervening space between `-f' and the output file
       format is optional; so `-f elf' and `-felf' are both valid.

       A complete list of the available output file formats can be given by
       issuing the command `nasm -hf'.

 2.1.3 The `-l' Option: Generating a Listing File

       If you supply the `-l' option to NASM, followed (with the usual
       optional space) by a file name, NASM will generate a source-listing
       file for you, in which addresses and generated code are listed on
       the left, and the actual source code, with expansions of multi-line
       macros (except those which specifically request no expansion in
       source listings: see section 4.3.9) on the right. For example:

       nasm -f elf myfile.asm -l myfile.lst

       If a list file is selected, you may turn off listing for a section
       of your source with `[list -]', and turn it back on with `[list +]',
       (the default, obviously). There is no "user form" (without the
       brackets). This can be used to list only sections of interest,
       avoiding excessively long listings.

 2.1.4 The `-M' Option: Generate Makefile Dependencies

       This option can be used to generate makefile dependencies on stdout.
       This can be redirected to a file for further processing. For
       example:

       nasm -M myfile.asm > myfile.dep

 2.1.5 The `-MG' Option: Generate Makefile Dependencies

       This option can be used to generate makefile dependencies on stdout.