CSC231 Lab 1 2014

This lab is a first lab to get you started with the process of assembling, linking, and running assembly programs for the Intel processor.

Creating a program from scratch

• Find the skeleton program on the class Web page

• Login to beowulf with your new 231a-xx account

• Create a file called skel.asm in your account, and save the skeleton program in it.

• Make a copy of skel.asm and call it lab1.asm

• Add a string variable in your data section:

             msg     db     "Welcome to csc231", 10
             MSGLEN  equ    $-msg

• Add some code to output the string in the text (code) section

             mov    eax, WRITE
             mov    ebx, STDOUT
             mov    ecx, msg      ; use the same name as the string in the data section
             mov    edx, MSGLEN   ; # of chars in string
             int      0x80

• Save your file

Assembly and Linking steps

• Assemble your program

             nasm -f elf -F stabs lab1.asm
             

• Fix any errors you may get

• Link your program

             ld -o lab1 lab1.o

You shouldn't get any errors at this stage.

Execution

• Run your program:

             ./lab1
             

Playing around with the program

• Make your program output look like this:

                    Welcome to CSC111
                    Home of the Assembly Language

• If your first solution uses two strings, modify your program so that it uses only 1 string. If your first solution uses one string, modify your program so that it uses two.

• Modify your program so that its output looks like this:

                    *********************************
                    * Welcome to CSC111             *
                    * Home of the Assembly Language *
                    *********************************

The lines of stars contain 33 *-characters. Each line is thus 34-character long (to account for the line-feed character). Can you find a solution where the number of characters in your data section is not 4 x 34 = 136 characters, but 3 x 34 = 102, instead?

Test it out!