Assembly Language StepbyStep Programming with DOS and Linux 2nd Ed [Electronic resources] نسخه متنی

NASM for Linux

Another (minor) reason that I chose NASM as the focus assembler for this book is that a very good implementation-still free-exists for Linux. I've included NASM for Linux, version 0.98, on the CD-ROM for this book. That's the version with which I wrote all the code examples published here. However, there's no saying how long this book will remain in use, and if it's for more than a year or so (and the first edition lasted over seven years), you might check the NASM Web site to see if a newer release is available at www.web-sites.co.uk/nasm/.

This is its home page in early 2000. If it moves in subsequent years, you may have to hunt with a Web search engine. My hunch is that it will always exist somewhere. Free software never dies, though it sometimes gets a little dusty.

You can download NASM in either source code form or in assembled binary form, as an RPM (Red Hat Package Manager) archive. Installing the RPM file might seem to be easier, but there's a catch: You must choose one of two different RPM archives, depending on whether you're using libc5 or libc6. If you know your Linux system well, you probably know which version of the C library it uses; on the other hand, if you're relatively new to Linux, you might not. That's why I have not included the RPM version on the CD-ROM but NASM's full source code in C, which you rebuild in the process of installing it.

Installing NASM's Source Code

Don't faint, newcomers. It's not that hard, and rebuilding tools is a fact of Linux life. Installing the source code and rebuilding it from scratch avoids the libc version problem, as gcc (the Linux C compiler) knows what C library it has, and it uses it to build the NASM assembler binary correctly. That's why you'll find the file nasm-0.98.tar on the CD-ROM for this book. A tar file is an archive file, like a .ZIP file in the DOS world, only without compression. It's simply a way to combine multiple files into one file for easy transport over a network.

Your Linux system probably has a directory /usr/local/src on it. That's a good place to start. (If it doesn't, consider creating a directory with that pathname.) Copy the nasm-0.98.tar file from the CD-ROM into /usr/local/src, and then use tar to extract all the files from it. The tar utility is one of my least-favorite Unix utilities, because it has a whole different mindset for dealing with command-line parameters, and if you type something it doesn't understand or like, it will just sit there mute until you Ctrl-C out of it.

So, use this command line, and make sure you get it precisely as shown here:

tar xvf nasm-0.98.tar

Rebuilding NASM

Once you get tar to extract all the files from the archive, you'll notice that tar has created a new directory on your hard drive. Use cd to move to this directory:

cd nasm-0.98

There will be a fair number of files in this directory. The next step configures NASM's make files for rebuilding. You execute this step with the following command:

./configure

The configure step looks at your system, sees what C compilers you have installed, and tests those it finds for suitability. It looks to see what C library your system is using, checks a few other things, and finally creates the make files it will need to recreate the NASM binaries. Once configure has completed its job, you need to execute one very simple command:

./make

This will do a lot, though it won't take a great deal of time, especially if you have a reasonably fast machine and a fast hard drive. (Mine is a 400-MHz Pentium II and the whole build took about 15 seconds.) A great many obscure messages will flow by on your screen. Many of them will be warnings, but you don't need to be concerned about those-the compiler is simply complaining about things in the NASM source code that aren't simon-pure by its own reckoning. A warning is not an indication that the compiler can't understand something or generate correct code.

Once NASM is installed, it makes sense to add to your search path the path to the bin directory where NASM is installed. This command will do it:

PATH=$PATH:/usr/local/bin

Obviously, if you installed NASM somewhere else (and the preceding path is simply where the NASM make process installs it by default), enter the full path after the colon. At this point, NASM is there, installed as a brand-new binary, and ready to go to work.

But there's a lot to talk about first. NASM, like a lot of things in the Linux world, does not work alone, nor in a vacuum.