Conclusion: Not the End, But Only the Beginning

Overview

You never really learn assembly language.

You can improve your skills over time, by reading good books on the subject, by reading good code that others have written, and most of all, by writing lots and lots of code yourself. But at no point will you be able to stand up and say, I know it.

You shouldn't feel bad about this. In fact, I take some encouragement from occasionally hearing that Michael Abrash, author of Zen of Assembly Language, Zen of Code Optimization, and his giant compendium Michael Abrash's Graphics Programming Black Book, has learned something new about assembly language. Michael has been writing high-performance assembly code for almost 20 years and has evolved into one of the two or three best assembly language programmers in the Western hemisphere.

If Michael is still learning, is there hope for the rest of us?

Wrong question. Silly question. If Michael is still learning, it means that all of us are students and will always be students. It means that the journey is the goal, and as long as we continue to probe and hack and fiddle and try things we never tried before, that over time we will advance the state of the art and create programs that would have made the pioneers in our field catch their breath in 1977.

For the point is not to conquer the subject, but to live with it, and grow with your knowledge of it. The journey is the goal, and with this book I've tried hard to help those people who have been frozen with fear at the thought of starting the journey, staring at the complexity of it all and wondering where the first brick in that Yellow Brick Road might be.

It's here, with nothing more than the conviction that you can do it.

I got out of school in recession year 1974 with a B.A. in English, summa cum laude, and not much in reliable prospects outside of driving a cab. I finessed my way into a job with Xerox Corporation, repairing copy machines. Books were fun, but paperwork makes money-so I picked up a tool bag and had a fine old time for several years, before finessing my way into a computer programming position.

But I'll never forget that first awful moment when I looked over the shoulder of an accomplished technician at a model 660 copier with its panels off, to see what looked like a bottomless pit of little cams and gears and drums and sprocket chains turning and flipping and knocking switch actuators back and forth. Mesmerized by the complexity, I forgot to notice that a sheet of paper had been fed through the machine and turned into a copy of the original document. I was terrified of never learning what all the little cams did and missed the comforting simplicity of the Big Picture-that a copy machine makes copies.

That's Square One-discover the Big Picture. Ignore the cams and gears for a bit. You can do it. Find out what's important in holding the Big Picture together (ask someone if it's not obvious) and study that before getting down to the cams and gears. Locate the processes that happen. Divide the Big Picture into subpictures. See how things flow. Only then should you focus on something as small and as lost in the mess as an individual cam or switch.

That's how you conquer complexity, and that's how I've presented assembly language in this book. Some might say I've shorted the instruction set, but covering the instruction set was never the real goal here.

The real goal was to conquer your fear of the complexity of the subject, with some metaphors and some pictures and some funny stories to bleed the tension away.

Did it work? You tell me. I'd really like to know.

Where to Now?

If you've followed me so far, you've probably lost your fear of assembly language, picked up some skills and a good part of the instruction set, and are ready to move on. What's next? Ideally, you need an intermediate book on assembly language. The bad news is, assembly language has had a bad couple of years in the book industry, and most of the useful books I've found are now out of print. Tom Swan's masterful Mastering Turbo Assembler (Howard W. Sams & Co., 1995) is the most significant exception, and is still in print as of early 2000.

Worse, every single one of them focuses on DOS. There has never been an x86 assembly language book focusing on Linux, as best I know. This isn't to say there will never be one, but I don't see one on the immediate horizon.

On the other hand, the Internet has made it much easier to find out-of-print books. There are two sites that you simply must bookmark, and visit regularly, if you want to find books that are no longer available from the publisher or through Amazon.com. Both of these sites are brokers of used books, and what they do is direct you to an independent used bookstore somewhere that contributed listings of books to their master Web database. Here they are:

Alibris has better shipping but a more limited database. You deal directly with Alibris itself rather than the separate used book dealers. It's at www.alibris.com.

Bibliofind is less direct, but its listings are larger and I've found a number of things listed here that Alibris does not list. You send your order to Bibliofind via the Web, and Bibliofind forwards it to the bookstore that listed the book you want. You then conclude the order by sending payment to the bookstore rather than Bibliofind. It's at www.bibliofind.com.

I've used both firms very successfully and I endorse them both without hesitation.

Mastering Turbo Assembler

Tom Swan

HowardW. Sams & Co., 1995

ISBN 0-672-30526-7

Tom's intermediate-level assembly volume is a natural next step if you're working with the Borland tools. I have never seen a better intermediate-level text. It has gone through a couple of editions and is reasonably abundant on the used market. The downside, of course, is that it was published some years back and focuses on DOS real mode segmented model. The TASM assembly code is easily converted to NASM, and the principles Tom teaches apply well to Linux assembly as well, even though Tom does not mention Linux or NASM.

Mastering Turbo Debugger

Tom Swan

Howard W. Sams & Co, 1990

ISBN 0-672-48454-4

For my money, this is the only good book on debugging ever published, and for what I consider an advanced topic, it's remarkably approachable. Again, it focuses on DOS and the Borland tools, but Tom's higher-level strategies for finding and nuking bugs in your code are absolutely essential reading, no matter what assembler you're using, now or at any time in the future. It's been out of print for some time, but you can find it regularly on the used book market.

PC Magazine Programmer's Technical Reference: The Processor and Coprocessor

Robert L. Hummel

Ziff-Davis Press, 1992

ISBN 1-562-76016-5

This is not a tutorial but a reference on Intel's x86 processors through the 486, and it's by far the best one ever written or likely to be written for some time. It has the best discussion of that mysterious protected mode that I've ever seen, and its description of the individual assembly instructions is wonderfully crafted. I'm tempted to have my own copy taken apart and rebound as hardcover-if I don't, it's going to fall to pieces any day now! Alas, out of print but you should grab it if you find it.

Michael Abrash's Graphics Programming Black Book

Michael Abrash

Coriolis Group Books, 1997

ISBN 1-576-10174-6

This is a huge book (1,300+ pages) covering code optimization, largely for graphics applications (where it matters the most) but explained in a way that can be applied to almost anything. Some of it involves C programming, but much of it is pure, expert-level assembly-and on the CD-ROM is the original text of Michael's 1989 classic Zen of Assembly Language, which was barely off press when its publisher went under. The book was thus lost in the crush of a big business reorganization, and it never recovered. You'll need to get some practice and some context before all of this book will be completely comprehensible, but it's beautifully written and whether you can read it now, grab it if you see it so it'll be there on your shelf when you're ready for it. (Alas, it went out of print in early 2000, just as I am completing the book you're now reading.)

Stepping off Square One

Okay-with a couple of new books in hand and good night's sleep behind you, strike out on your own a little. Set yourself a goal, and try to achieve it: something tough, say, an assembly language utility that locates all files anywhere on a hard disk drive with a given ambiguous file name. That's ambitious for a newcomer and will take some research and study and (perhaps) a few false starts. But you can do it, and once you do it you'll be a real journeyman assembly language programmer.

Becoming a master takes work, and time. Michael Abrash's massive Graphics Programming Black Book (recently out of print but still in some stores) is a compilation of the secret knowledge of a programming master. It's not easy reading, but it will give you a good idea where your mind has to be to consider yourself an expert assembly language programmer.

Keep programming. Michael can show you things that would have taken you years to discover on your own, but they won't stick in your mind unless you use them. Set yourself a real challenge, something that has to be both correct and fast: Rotate graphics objects in 3-D, transfer data through a serial port at 19,200 bits per second, things like that.

You can do it.

Coming to believe the truth in that statement is the essence of stepping away from Square One-and the rest of the road, like all roads, is taken one step at a time.

Appendix A: Partial 8086/8088 Instruction Set

Reference

Overview

Instruction	Reference Page			Text Page
AAA		535		310
ADC		536		201
ADD		538		11
AND		540		67
BT		542		466				386	+
CALL		543		454
CLC		544
CLD		545		374
CMP		546		183
DEC		548		21
IMUL		549		309
INC		551		11
INT		552		86
IRET		553		263
J?		554		Only in			Appendix A
JCXZ		556		389
JECXZ		557		422
JMP		558		190
LEA		559		Only in			Appendix A
LOOP		560		276
LOOPNZ/LOOPNE		561		389
LOOPZ/LOOPE		562		422
MOV		563		75
NEG		564		212
NOP		565		Only in			Appendix A
NOT		566		213
OR		567		67
POP		568		214
POPA		569		253				286	+
POPAD				253				386	+
POPF		570		253
POPFD		571		465				386	+
PUSH		572		115
PUSHA		573		251				286	+
PUSHAD		574		251				386	+
PUSHF		575		85
PUSHFD		576		465				386	+

RET	577		263
ROL	578		316
ROR	580		316
SBB	582		11
SHL	583		316
SHR	585		316
STC	587		Only in			Appendix A
STD	588		376
STOS	589		596
SUB	590		140
XCHG	592		198
XOR	593		86