Category: programming

Writing Programs with Echo (DOS)

How do you input those characters as parameters for the echo command? I found no way of doing that. If you know a way, please drop me a line.

Is that possible? Yes, it is. It’s just a matter of redirecting echo output to a file. Writing the program with echo should be a straightforward task if we are able to produce the sequence of characters corresponding to the intended binary, executable file. Is that useful? Surely not. But it’s a healthy way to waste your time 🙂 This can be achieved by writing the characters of the executable file, using a simple text editor like notepad or even the old MS-DOS Editor. Of course, the program should be relatively small or we would adventure into the dangerous lands of masochism. By using the echo command of DOS we will be following the conceited style of doing things 🙂 But we’ll restrict this post to the simple hello, world! program we have been reviewing in previous entries.

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Encoding Intel x86/IA-32 Assembler Instructions

Translation of the second line is a direct and solved issue. What about jmp 114? Well, we want to jump over the data (18 bytes, one byte per each character in the string.) IASDM tell us (Appendix B) that the opcode for unconditional jumps in the same segment is 11101011, which in hexadecimal, is expressed as EB.

On the post Debugging hello, world, someone asked about the reason for translating the instruction jmp 114 into hexadecimal EB12. To answer this, we are going to recur to the “lovely” and elder Intel Architecture Software Developer Manual (IASDM), Volume 2. This volume describes the instructions set of the Intel Architecture processor (x86/IA-32) and the opcode structure. I’ll review some terms involved here:

    x86: It refers to the instruction set of the Intel-compatible CPU architectures (chips produced by Intel, AMD, VIA, and others) inaugurated by Intel’s original 16-bit 8086 CPU. A decision which proved wise was to make each new instance of x86 processors almost fully backwards compatible.
    IA-32: It is Intel’s 32-bit implementation of the x86 architecture; IA-32 distinguishes this implementation from the preceding 16-bit x86 processors. Note that when the 64-bit era arrived, Intel launched its Itanium processor, which discards compatibility with the IA-32 instruction set. Such 64-bit architecture description and implementation is referred to as IA-64, meaning “Intel Architecture, 64-bit”, but even though the names are similar, IA-32 and IA-64 are very different architectures and instructions sets. However, AMD’s response to Intel 64-bit processors, uses an instruction set that, in essence, is composed of 64-bit extensions to IA-32, i.e., it’s a superset of the x86 instruction set. Such instruction set is referred to as AMD64 (initially, x86-64.) Later, Intel cloned it under the name Intel 64. AMD’s processors Athlon 64, Terium, Opteron, Sempron, etc., are based on AMD64.
    Opcode: An opcode (operation code) is the part of a machine language instruction (pure binary code) specifying the operation to be performed. The other portion of the instruction is the operand, which is optional and represents the data to be operated on. In assembly language, mnemonics are used to represent the opcodes. Concretely, and according to the IASDM, a mnemonic is a reserved name for a class of instruction opcodes which have the same function. For example, in JMP 114, the mnemonic is JMP, and the operand is 114 (remember, 114 in hexadecimal, which is 276 in decimal.)

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Programmers from the Wild West

Analysis, Design, and related topics are for sissies, and for allowing professors of Computer Science who are bad at mathematics to make a living. SDLC is a pony. Cowboys ride horses.

We all know what happens when a project’s deadline is not met. Besides firing someone, hard, dry heroes appear. Lonesome, ruthless and distrustful heroes which brings the peace only revolvers can conquer. Sometimes, the guys with the money hire them as the ultimate saviors: they have bothered to come here, from the farthest west, to rescue the project. They are irresistible: they are the cowboy programmers. It’s men’s time.

Ben Cartwright & Sons
Ben Cartwright & Sons

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Debugging “hello, world”

The Go command (g) will run the program starting at the given address (in this case, CS:0100) If everything goes right, the program should output the intended “hello, world!” string, and finish with the message “Program terminated normally.”

Yesterday, we took a break after long hours of intensive coding, and a coworker started establishing similarities between our current frantic coding and the (fortunately) gone days of college homework. I specifically recalled a project I had to build by using MS-DEBUG: a simple calculator in assembly, which also required the hassle of dealing with pretty and safe user input. I have no intention of looking for such listings, but I thought about revisiting, for a moment, the old and dear friend MS-DEBUG 🙂 I’ll harness a previous post in this blog, and try to build a little ‘hello, world’ program in MS-DEBUG. I know this has little value outside a personal feeling and a tad of nostalgia, maybe.

I remember that a 100 tells DEBUG to accept code in memory starting out from CS:0100. Ok.

Now comes the data, which here simply consist of the string 'hello, world!'. A neat output, however, would require newlines before and after our intended string. A newline is comprised of a carriage return (CR = ASCII 13) and a line feed (LF = ASCII 10) on the display. As DEBUG only understand hexadecimal numbers, we must use 0Dh and 0Ah for CR and LF, respectively. Except in code, we will represent hexadecimal numbers by following the value with ‘h’.) Fortunately, DEBUG also admits ASCII characters directly (and the pseudo-instructions DB and DW!), so we can express our complete string as

db 0d,0a,"hello, world!",0d,0a,"$"

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A Review of OpenGL Programming on Mac OS X

All of the explanations are crystal clear, focused into the concepts and techniques OpenGL developers really need. The book comprises OpenGL architecture and configuration on OS X, and the various APIs we can use in order to create OpenGL applications, specifically, CGL, AGL, Cocoa, (our old buddy) GLUT, and X11 APIs.

OpenGL Programming on Mac OS X

The full title of this book is “OpenGL Programming on Mac OS X: Architecture, Performance and Integration.” Its fortunate authors are Robert P. Kuehne and J. D. Sullivan, two professionals who thoroughly know what they are talking about. Moreover, the book has been published by one of my favorites, Addison-Wesley. Therefore, success in conveying the details of OpenGL Programming on the Apple platform seems guaranteed. After reading it, I confirmed that any graphics programmer will learn a lot of things from this book. And nowadays, with a market saturated by rushed books, it’s a bliss.
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hello, world

Personally, by reading “hello, world”, I evoke orange and warm afternoons, with my eyes strained (and soothed) by code. Nice, and overly inefficient Pascal code. In some images, a few BASIC snippets interleave, but those are not that nice to remember…

In calm thoughts, these two words (with the comma) bring to mind plenty of images. More often that not, I hold “hello, world” in fond remembrances. For this post I’ve slightly modified the default WordPress post title, in favor of the original Kernighan‘s form: no capitalization and presence of comma. Through the years, it seems to me that this sequence lightens my worries when coping with new languages, systems, things. Somehow, the mind has understood that once “hello, world” is done, then reaching the entire system is achievable. Kind of Pavlovian Conditioning, I guess.

In K&R’s C Tutorial, this feel at ease perception it’s also intended:

The only way to learn a new programming language is by writing programs in it. The first program to write is the same for all languages: Print the words hello, world. This is the basic hurdle; to leap over it you have to be able to create the program text somewhere, compile it successfully, load it, run it, and find out where your output went.

This way, “hello, world” should be our first step for pummeling through the new beast (language).
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