Difference between revisions of "CSC231 Lab 1 2014"
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* Login to beowulf with your new 231a-xx account (see the [[CSC231_Lab_1#Troubleshooting |'''Troubleshooting''']] section at bottom of this page in case of trouble) | * Login to beowulf with your new 231a-xx account (see the [[CSC231_Lab_1#Troubleshooting |'''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. | + | * Create a file called '''skel.asm''' in your account, and save the skeleton program in it. At the Linux prompt, type: |
| + | |||
| + | emacs skel.asm | ||
| + | |||
| + | :Use the [[Emacs Quick Reference| Emacs Quick-Reference]] page for the most often used commands. | ||
* Make a copy of [[CSC231_skel.asm | skel.asm]] and call it '''lab1.asm''' | * Make a copy of [[CSC231_skel.asm | skel.asm]] and call it '''lab1.asm''' | ||
| + | |||
| + | cp skel.asm lab1.asm | ||
* Add a string variable in your data section: | * Add a string variable in your data section: | ||
| Line 37: | Line 43: | ||
| − | mov eax, | + | mov eax, 4 |
| − | mov ebx, | + | mov ebx, 1 |
mov ecx, msg ; use the same name as the string in the data section | mov ecx, msg ; use the same name as the string in the data section | ||
mov edx, MSGLEN ; # of chars in string | mov edx, MSGLEN ; # of chars in string | ||
| Line 45: | Line 51: | ||
| − | * Save your file | + | * Save your file by typing '''Control-X''', '''Control-C''' while in emacs. |
| + | |||
==Assembly and Linking steps== | ==Assembly and Linking steps== | ||
| − | * Assemble your program | + | * You should be back at the Linux prompt. Assemble your program |
| − | + | nasm -f elf -F stabs lab1.asm | |
| − | * Fix any errors you may get | + | * Fix any errors you may get by starting emacs again and figuring out where the error is. |
* Link your program | * Link your program | ||
| − | + | ld -melf_i386 -o lab1 lab1.o | |
| − | You shouldn't get any errors at this stage. | + | :You shouldn't get any errors at this stage. |
==Execution== | ==Execution== | ||
| Line 66: | Line 73: | ||
* Run your program: | * Run your program: | ||
| − | + | ./lab1 | |
| + | :It should run and display the string. | ||
==Playing around with the program== | ==Playing around with the program== | ||
| − | * | + | * Modify the msg string to make it look like this: |
| − | + | msg db 10, 10, "Welcome", 10, "to", 10, "csc231", 10, 10 | |
| − | + | MSGLEN equ $-msg | |
| + | |||
| + | * Reassemble, link and run the new version of your program. | ||
| + | |||
| + | * Something different. Modify your program once more, as shown below: | ||
| + | |||
| + | msg db 10, 10 | ||
| + | db "Welcome", 10 | ||
| + | db "to", 10, "csc231" | ||
| + | db 10 | ||
| + | db 10 | ||
| + | MSGLEN equ $-msg | ||
| + | |||
| + | * Reassemble, link and run the new version of your program. | ||
| − | + | {| style="width:100%; background:silver" | |
| + | |- | ||
| + | | | ||
| + | == Mini Challenge of the Day == | ||
| + | |} | ||
| + | [[Image:QuestionMark3.jpg|right|120px]] | ||
| + | |||
* Modify your program so that its output looks like this: | * Modify your program so that its output looks like this: | ||
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Contents
This lab is the first lab of this course. It will 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 (or open it here)
- Login to beowulf with your new 231a-xx account (see the 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. At the Linux prompt, type:
emacs skel.asm
- Use the Emacs Quick-Reference page for the most often used commands.
- Make a copy of skel.asm and call it lab1.asm
cp skel.asm 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, 4
mov ebx, 1
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 by typing Control-X, Control-C while in emacs.
Assembly and Linking steps
- You should be back at the Linux prompt. Assemble your program
nasm -f elf -F stabs lab1.asm
- Fix any errors you may get by starting emacs again and figuring out where the error is.
- Link your program
ld -melf_i386 -o lab1 lab1.o
- You shouldn't get any errors at this stage.
Execution
- Run your program:
./lab1
- It should run and display the string.
Playing around with the program
- Modify the msg string to make it look like this:
msg db 10, 10, "Welcome", 10, "to", 10, "csc231", 10, 10
MSGLEN equ $-msg
- Reassemble, link and run the new version of your program.
- Something different. Modify your program once more, as shown below:
msg db 10, 10
db "Welcome", 10
db "to", 10, "csc231"
db 10
db 10
MSGLEN equ $-msg
- Reassemble, link and run the new version of your program.
Mini Challenge of the Day |
- 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. Bold text
