CSC231 Homework 1 2015

--D. Thiebaut (talk) 16:08, 8 September 2015 (EDT)

---

This homework assignment is concurrent with Lecture 1, which took place on 9/9/15. It is due Sunday night 9/20/15, at 11:55 p.m. It is fully understood that we haven't had a chance to fully dig into assembly and understand what instructions do, and how they work. What is asked of you today is simply to use the typical hello world! program in assembly, and modify it in various ways to get it to print a particular message. You are asked to use your programmer's logic in figuring out how to modify a program rather than creating a new one from scratch.

Preparation

Part 1

• Login to your 231a-xx account on aurora.smith.edu.
• Create the following assembly program, assemble it, link it, and run it (the commands are in the header):

;;; ; hw1prep1.asm
;;; ; D. Thiebaut
;;; ;
;;; ;
;;; ; To assemble, link, and run:
;;; ;     nasm -f elf  hw1prep1.asm
;;; ;     ld -melf_i386 -o hw1prep1 hw1prep1.o
;;; ;     ./hw1prep1
;;; ;                

		section	.data
msg1		db	"The quick red fox jumped over the dog", 10
msg1Len	equ	$-msg1

        

		section	.text
		global	_start
_start:	

;;; print message
		mov	eax, 4		; write
		mov	ebx, 1		; stdout
		mov	ecx, msg1	; address of message to print
		mov	edx, msg1Len	; # of chars to print
		int 	0x80

;;; exit
		mov	ebx, 0
		mov	eax, 1
		int	0x80

• Observe the output.

Part 2

• Same question, but with a different program. Make sure you study the code of both programs and see how they differ. Then see how their output compare.

;;; ; hw1prep2.asm
;;; ; D. Thiebaut
;;; ;
;;; ;
;;; ; To assemble, link, and run:
;;; ;     nasm -f elf  hw1prep2.asm
;;; ;     ld -melf_i386 -o hw1prep2 hw1prep2.o
;;; ;     ./hw1prep2
;;; ;                

		section	.data
msg1		db	"The quick red fox jumped"
msg1Len	equ	$-msg1
        
msg2		db	" over the dog", 10
msg2Len	equ	$-msg2

        

		section	.text
		global	_start
_start:	

;;; print message, part 1
		mov	eax, 4		; write
		mov	ebx, 1		; stdout
		mov	ecx, msg1	; address of message to print
		mov	edx, msg1Len	; # of chars to print
		int 	0x80            ; get Linux to print the message

;;; print message, part 2
		mov	eax, 4		; write
		mov	ebx, 1		; stdout
		mov	ecx, msg2	; address of message to print
		mov	edx, msg2Len	; # of chars to print
		int 	0x80            ; get Linux to print the message

;;; exit
		mov	ebx, 0
		mov	eax, 1
		int	0x80

Problem 1

• Write an assembly language program called hw1a.asm that displays the following message.

 ====================
 ====================
 = CSC231 FALL 2015 =
 ====================
 ====================

• Make the code section (text section) of your program contain as few instructions as possible.
• You will be given instructions on how to submit your program to Moodle in a few days. Stay tuned...

Problem 2

• Same question as for Problem 1, but this time using as few characters in the data section, as possible. You are not limited for the size of your code section any longer. Just the size of the data section should be as small as possible.

• Call your program hw1b.asm.
• Instructions on how to submit it on Moodle will be provided later. Stay tuned!