CSC231 Homework 7 2015

--D. Thiebaut (talk) 11:58, 10 November 2015 (EST)

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This assignment is due on Wednesday, 11/18/15, at 11:55 p.m. Document your program well!

Problem

Your assignment is to add a new function to 231Lib.asm called _printRegs.

• Take your 231Lib.asm library and make a copy of it, and call it 231Lib2.asm.

 cp 231Lib.asm 231Lib2.asm

• Add a global statement at the top of the program (with the other similar statements):

global _printRegs

• Go to the end of the file and add a new function called _printRegs

• Your new function should display the contents of eax, ebx, ecx, edx, edi, and esi, in this order:

• in hexadecimal (you should have a function for that)
• as an unsigned number (_printDec will do that for you)
• as a 2's complement signed number (you have to figure this part out).

• Submit you 231Lib2.asm program to Moodle when done

Testing

• To test your new function, create a new program that will be linked with your modified library, and will display all the registers.
• Example test program:

;;;  test.asm
;;;  assemble and run as follows:
;;;
;;;  nasm -f elf test.asm
;;;  nasm -f elf 231Lib2.asm
;;;  ld -melf_i386 test.o 231Lib2.o -o myTest
;;;  ./myTest
;;;

;;;  Extern functions that will be linked to this program
;;;  they are contained in 231Lib2.asm

extern  _printDec
extern  _printString
extern  _println
extern  _getInput
extern  _printRegs

;;; ------------------------------------------------------
;;; CODE SECTION
;;; ------------------------------------------------------        
                section .text
                global  _start
_start: 
                mov   eax, 0xFFFFFFFF
                mov   ebx, 0
                mov   ecx, 0x00000003
                mov   edx, 0x7FFFFFFF
                mov   esi,  2
                mov   edi, 0x80000002
 
                call    _printRegs
                call    _println
                call    _printRegs
                call    _println

                mov   eax, 0x01234567
                mov   ebx, 0x000000FF
                mov   ecx, 0x00000001
                mov   edx, 0x0
                mov   esi,  10
                mov   edi, 0xFFFFFFFE

                call    _printRegs
                call    _println

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

The output of the program above should be:

eax FFFFFFFF 4294967295 -1
ebx 00000000 0 0
ecx 00000003 3 3 
edx 7FFFFFFF 2147483647 2147483647
edi 80000002 2147483650 -2147483646
esi 00000002 2 2

eax FFFFFFFF 4294967295 -1
ebx 00000000 0 0
ecx 00000003 3 3 
edx 7FFFFFFF 2147483647 2147483647
edi 80000002 2147483650 -2147483646
esi 00000002 2 2

eax 01234567 19088743 19088743
ebx 000000FF 255 255
ecx 00000001 1 1
edx 00000000 0 0
edi FFFFFFFE 4294967294 -2
esi 0000000A 10 10

Hints

• Using temporary variables is fine for this assignment.
• If you write functions, make them "clean," in the sense that they should return to their caller without changing any of the registers. This will make your life much easier! For example, you may want to create a printSpace function. Here's how I would code it:

;;;-----------------------------------------------------------------
;;; printSpace: prints a space.  Does not modify any of the 
;;; registers.
;;;-----------------------------------------------------------------
                section  .data
space           db     ' '

                section  .text
printSpace:        
                push    ecx
                push    edx
                mov     ecx, space
                mov     edx, 1
                call    _printString
                pop     edx
                pop     ecx
                ret

• You may want to create a table of the 16 4-bit binary numbers I draw in class regularly, and available here. Assume that the most significant bit of the group of 4 bits is a sign bit, and enter the values of the numbers in a 4th column. Figure out the algorithm you have to use to actually print the numbers in the 4th column. For example, how do you print 0010 as 2, but 1111 as -1?

Submission

• Submit your 231Lib2.asm file on Moodle. It will be tested with a different main program, that will set the registers to different values and verify that your _printRegs function prints them correctly.

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