Assembly ProgrammingNotes for Practical 1Adan PatienceJoshua Moran

About the PracticalsCovering the Assembly Language Assembly for Intel-Based ComputersFourth edition Kip R. IrvineAlso the slides help a lot and check website7 PracticalsConsult Course outline for dates and website for more informationPracticals 3rd, 4th and 5th period every Wednesday.Homework Due Next Wednesday NO late SubmissionsExpect Surprise Tests

Programming Languages

Machine Language "... is a numeric language that is specifically understood by computer's processor (CPU)..." - consists purely of numbers: eg:1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 1011000000000101 WHAT DOES THAT MEAN?

What is Assembly Language? A programming language that is easier for humans to understand, but slightly less efficient for computers to process.

Uses names and hexadecimal pointers instead of binary numbers.

What is Assembly Language? (cont)A machine-orientated language in which mnemonics are used to represent each machine-language instruction. E.g. ADD, MOV, SUB, MUL etc, which represent machine language sequences (011000)

Translating LanguagesEnglish: Display the sum of A times B plus C.Java: System.out.println(A * B + C);Assembly Language:mov ax,Amul Badd ax,Ccall WriteIntIntel Machine Language:A1 00000000F7 25 0000000403 05 00000008E8 00500000

Download Prac 1Go to www.cs.uwc.ac.za/~masm/

Select prac1

Right click on Masm615.rar and select save link as

Save the file to C:/

Starting DosClick On Start

Then type CMD

Go to the directory Masm615: cd C:/Masm615/

A full program looks like:

What is a Batch file? Similar to a Makefile in unix

It is a text file with the extension .BAT that contains DOS commands.

Reduces repetitive typing by executing a batch of commands.

Make32

Make32.bat

To Compile: make32.bat filename in CMD.

Note: Remove (omit) the .asm extension

Make32Make32 /Zi filename.asm ; include debugging information

Make32 /Fl filename.asm ; produce a listing file (prac1.lst)

Make32 /Fm filename.asm ; produce a map file (prac1.map)

Make32 /Zm filename.asm ; use MASM 5.12 compatibility mode

Make32The following command assembles filename.asm and links filename.obj to the link library linkfile.lib in the C:\MASM615 directory:

Make32 /Zi /Zm /Fm /Fl filename.asm /link /co c:\MASM615\

Hello WorldOpen Notepad

Select File Save As

Save as type All Files

File name hello.asm

Save the file in prac1

Why Assembly language?Java: public class Hello{ public static void main(String[] args){ System.out.println("Hello World"); } } or

C++: int main(void){ cout

Hello World

title Hello World program

; ALWAYS include the following lines ; Name: (Replace with your own name) ; Purpose: This program displays "Hello world" ; Date:

Hello World

stack 100h.data

HelloString db "Hello, world", 0 ;message to write.codemain proc

Hello World

mov edx, offset HelloStringinvoke WriteString ; Write to cmdexit ; irvine.inc: a macro that calls ExitProcessmain endpend main

Possible InstructionsCopy

Move

Delete (del)

The Basics are overThe next few slides explain registers in detail and can be read in your own time.GOOD LUCK!

Segment Registers CS Code Segment 32-bit number that points to the active code-segment DS Data Segment 32-bit number that points to the active data-segment SS Stack Segment 32-bit number that points to the active stack-segment ES Extra Segment 32-bit number that points to the active extra-segment

Pointer Registers IP Instruction Pointer 32-bit number that points to the offset of the next instruction SP Stack Pointer 32-bit number that points to the offset that the stack is using BP Base Pointer used to pass data to and from the stack

General-Purpose Registers AX Accumulator Register mostly used for calculations and for input/output BX Base Register Only register that can be used as an index CX Count Register used for the loop instruction DX Data Register input/output and used by multiply and divide

Index Registers SI Source Index used by string operations as source DI Destination Index used by string operations as destination

Explanation:Explanation:.model small : Lines that start with a "." are used to provide the assembler with information. The word(s) behind it say what kind of info. In this case it just tells the assembler the program is small and doesn't need a lot of memory. I'll get back on this later..stack : Another line with info. This one tells the assembler that the "stack" segment starts here. The stack is used to store temporary data. It isn't used in the program, but it must be there, because we make an .EXE file and these files MUST have a stack..data : indicates that the data segment starts here and that the stack segment ends there..code : indicates that the code segment starts there and the data segment ends there.main proc : Code must be in procedures, just like in Java or any other language. This indicates a procedure called main starts here. main endp states that the procedure is finished. Procedures MUST have a start and end. end main : tells the assembler that the program is finished. It also tells the assembler were to start the program. At the procedure called main in this case.

Explanation:message db "xxxx" : DB means Define Byte and so it does. In the data-segment it defines a couple of bytes. These bytes contain the information between the brackets. "Message" is a name to indentify this byte-string. It's called an "identifier".mov ax, seg message : AX is a register. MOV is an instruction that moves data. It can have a few "operands". Here the operands are AX and seg message. Seg message can be seen as a number. It's the number of the segment "message" is in (The data-segment) We have to know this number, so we can load the DS register with it. Else we can't get to the bit-string in memory. We need to know WHERE the bit-string is located in memory. The number is loaded in the AX register. MOV always moves data to the operand left of the comma and from the operand right of the comma.

Explanation:mov ds,ax : The MOV instruction again. Here it moves the number in the AX register (the number of the data segment) into the DS register. We have to load this DS register this way (with two instructions) Just typing: "mov ds,segment message" isn't possible.mov ah, 09 : MOV again. This time it load the AH register with the constant value nine.lea dx, message : LEA Load Effective Address. This instructions stores the offset within the datasegment of the bit-string message into the DX register. This offset is the second thing we need to know, when we want to know where "message" is in the memory. So now we have DS:DX. See the segment explanation above.

*************************************************