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 (see Troubleshooting section at bottom of this page in case of trouble)

• 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 CSC231             *
                    * 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!

Troubleshooting

It is possible that if you are using ssh to connect to Beowulf the first time, and if you are using a Mac, you get a message of this form:

ssh 231a-xx@beowulf.csc.smith.edu
==================================================
   WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     
==================================================
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
bf:db:14:e6:a4:e0:f3:3d:d8:87:35:66:a9:35:68:fb.
Please contact your system administrator.
Add correct host key in /Users/alex/.ssh/known_hosts to get rid of this message. 
Offending key in /Users/xxxxx/.ssh/known_hosts:1
RSA host key for beowulf.csc.smith.edu has changed and you have requested strict checking. 
Host key verification failed.

In this case, use the editor of your choice and edit the file ~/.ssh/known_hosts and remove the lines that contains the word beowulf. Be careful, the lines are very long and wrap around to form blocks of 4 or 5 lines on your screen, so deleting one line will require a big block to disappear.