Asm Basics.doc

What Is Assembly Language?

First What is Machine Language:

Although programmers tend to use C or C++ or Pascal these days, the language closest to the PC hardware

is machine language. Not one second during a PCs powered on lifetime passes where the computer is not

executing machine language.

Assembly Language or Machine Language:

To word this simply, you can say that say that assembly language is a human-readable text, and machine

language is machine-readable binary code. When you program in assembly language, you are programming

on the machine language level.

To program directly in machine language is teadious, so you use assembly language instead, and use an

assembler to produce the actual machine code.

The assembler language is the symbolic programming language that lies closest to the machine language in

form and content.

You will, therefore, find the assembler language useful when:

You need to control your program closely, down to the byte and even the bit level.

You must write subroutines for functions that are not provided by other symbolic programming languages,

such as COBOL, FORTRAN, or PL/I.

Windows Memory

The first thing you need to know that windows memory is numbered, the first byte is at offset number 0, and

the highest possible offset for a byte is just over 4.2 billion (ffffffff hex)

When a program executes it will start at the first instruction (starting at 400000 (hex) in windows 95) and then

go onto the next one in a linear fashion, that is until a jump or conditional jump happens.

Conditional jumps are like a choice. If something happens then jump to here, otherwise just keep going in the

code. For instance if a character has 0 hp after being hit it will compare the hp to 0 and if it's 0 then it will jump

to the death routine.

Disassembling (W32Dasm)

Using w32Dasm disassembler on: diablo_s.exe

Start off by loading the project. It may take awhile, go fix yourself a drink :)

After this, go to Disassembler menu/Save Disassembly Txt File and Create Project File

and then next time you load it it'll just take 5 seconds...

Ok, now that you've finshed loading it...Hmm, so what do all these funky symbols mean? :)

Well, now what ya gotta do is this: goto font under the Disassembler menu. Then goto select font and select

fixedsys. Now you can actually read it! :)

Meanings of all those numbers you see: