Transcript lecture1 v2 - UWC Computer Science

Assembly Programming
Notes for Practical 1
COS212 Architecture
Lecturer: Prof IM Venter
Practical Assistants:
Andre Henney & Andries Kruger
About the Practicals
• Covering the Assembly Language
• Assembly for Intel-Based Computers
•Fourth edition Kip R. Irvine
•Also the slides help a lot and check website
• 7 Practicals
•Consult Course outline for dates and website for more information
• Practicals 3rd, 4th and 5th period every
Wednesday.
• Homework Due Next Wednesday
• NO late Submissions
• Expect 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 Languages
English: Display the sum of A times B plus C.
Java: System.out.println(A * B + C);
Assembly Language:
mov ax,A
mul B
add ax,C
call WriteInt
Intel Machine Language:
A1 00000000
F7 25 00000004
03 05 00000008
E8 00500000
• Download Prac 1
• Go to www.cs.uwc.ac.za/~masm/
• Download Masm615.exe
• Right click on Masm615.exe and select save link
as
• Save the file to C:/
• Install Masm615, by double left click on
executable
Starting Dos
• Click On Start
• Then type CMD
• Create a Prac 1 folder on C:\
• On MS-DOS prompt, type the command
C:\> mkdir prac1 and press Enter.
• Create and save your practical 1 files in Prac1
folder.
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
Make32
• Make32 /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
Make32
The 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\<linkfile>
Hello World
• Open 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");
}
}
• C++:
int main(void){
cout << "Hello world\n" << endl;
}
• Java and C++ obviously much easier; so why?
Hello World
title Hello World programme
; ALWAYS include the following lines
; Name: <Dane Brown> (Replace with your own
name)
; Purpose: This program displays "Hello world"
; Date: <Today's date>
(Insert todays date)
include irvine32.inc
; from Irvine CDROM
Hello World
stack 100h
.data
HelloString db "Hello, world", 0 ;message to write
.code
main proc
Hello World
mov edx, offset HelloString
invoke WriteString ; Write to cmd
exit
; irvine.inc: a macro that calls ExitProcess
main endp
end main
Possible Instructions
• Copy
• Move
• Delete (del)
The Basics are over
• The 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:
– .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.
Explanation:
– .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
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.
Explanation:
–
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 bitstring 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.
Explanation:
– 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.