CSC231 Functions and the Stack

--D. Thiebaut 10:41, 31 October 2012 (EDT)

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A Shell File to Assemble and Link

• The text file below can be created with emacs. Call it nasmld (or some other name of your choosing):

#! /bin/bash
# nasmld
# a script to assemble and link assembly files
nasm -f elf -F stabs $@.asm
ld -o $@ -melf_i386 $@.o
./$@

• make sure you make your script executable by using this command:

      chmod a+rx nasmld

Program 1: funcExample.asm

;;; ------------------------------------
;;; funcExample.asm
;;; prints 2 strings using functions
;;; ------------------------------------

		section	.data
Hello		db	"Hello "
There		db	"there!", 10, 10, 10
HelloLen	equ	$-Hello

		section	.text
		global	_start
_start:	
;;; ------------------------------------
;;; main program
;;; ------------------------------------

;;; print message
		mov	ecx, Hello
		mov	edx, HelloLen
		call	printString

		mov	ecx, There
		mov	edx, 9
		call	printString
	
;;; exit
		mov	ebx, 0
		mov	eax, 1
		int	0x80

;;; ------------------------------------
;;; printString: prints string whose
;;; address is in ecx, and length in edx
;;; ------------------------------------
printString:	
		mov	eax, 4
		mov	ebx, 1
		int 	0x80
		ret

Program 2: funcExample2.asm

;;; ----------------------------------
;;; funcExample2.asm
;;; prints 2 strings with lines of stars
;;; between them
;;; ----------------------------------
		section	.data
Hello		db	"Hello "
There		db	"there!", 10, 10, 10
HelloLen	equ	$-Hello
line		db	"****************************", 10
lineLen		equ	$-line
	
		section	.text
		global	_start
_start:	
;;; ----------------------------------
;;; main program
;;; ----------------------------------
		call	printLine
	
		mov	ecx, Hello
		mov	edx, HelloLen
		call	printString
	
		call	printLine
	
		mov	ecx, There
		mov	edx, 9
		call	printString

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

;;; ----------------------------------
;;; printString: Prints a string whose
;;; address is in ecx and length in edx
;;; ----------------------------------
printString:	mov	eax, 4
		mov	ebx, 1
		int 	0x80
		ret

;;; ----------------------------------
;;; printLine: prints a line of stars.
;;; ----------------------------------
printLine:	mov	ecx, line
		mov	edx, lineLen
		call	printString
		ret