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The Netwide Assembler: NASM =========================== Chapter 1: Introduction

The Netwide Assembler: NASM =========================== Chapter 1: Introduction ----------------------- 1.1 What Is NASM? The Netwide Assembler, NASM, is an 80x86 assembler designed for portability and modularity. It supports a range of object file formats, including Linux and `NetBSD/FreeBSD' `a.out', `ELF', `COFF', `Mach-O', Microsoft 16-bit `OBJ' and `Win32'. 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 `Pentium', `P6', `MMX', `3DNow!', `SSE' and `SSE2' opcodes, and has macro capability. 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 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 Minix- and Linux-specific, 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 Licence Conditions Please see the file `COPYING', supplied as part of any NASM distribution archive, for the licence 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) are 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 10.2 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 DOS archive for NASM, `nasmXXX.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 four executable files: the NASM executable files `nasm.exe' and `nasmw.exe', and the NDISASM executable files `ndisasm.exe' and `ndisasmw.exe'. In each case, the file whose name ends in `w' is a `Win32' executable, designed to run under `Windows 95' or `Windows NT' Intel, and the other one is a 16-bit `DOS' executable. The only file NASM needs to run is its own executable, so copy (at least) one of `nasm.exe' and `nasmw.exe' to a directory on your PATH, or alternatively edit `autoexec.bat' to add the `nasm' directory to your `PATH'. (If you're only installing the `Win32' version, you may wish to rename it to `nasm.exe'.) 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, `nasmXXXs.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. Note that the source files `insnsa.c', `insnsd.c', `insnsi.h' and `insnsn.c' are automatically generated from the master instruction table `insns.dat' by a Perl script; the file `macros.c' is generated from `standard.mac' by another Perl script. 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-X.XX.tar.gz' (where `X.XX' 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-X.XX'. 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. If NASM fails to auto-configure, you may still be able to make it compile by using the fall-back Unix makefile `Makefile.unx'. Copy or rename that file to `Makefile' and try typing `make'. There is also a Makefile.unx file in the `rdoff' subdirectory. 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 uploads/S4/ nasm-guide.pdf