CSC231 Midterm Preparation

A List of Problems to Prepare for the In-Class Closed-Books Midterm

• Write a small assembly program (don't worry about writing a complete program: just the data and instructions necessary) that displays all the letters of the alphabet on the screen.
• Write a program that displays the first 20 fibonacci terms.
• Write a program that stores the factorial of word-variable x into word-variable y.
• What is the contents of eax, ebx, ecx, and edx after the execution of each instruction?

                       mov    eax,10
                       mov    edx,0
                       mov    bx,3
                       div    bx
                       
              

• What's a segmentation fault? Give an example of an instruction that would cause one.
• What is printed by this program?

                       section .data
               msg     db 10,10,10,"hello ",10
               msg2    db "world",10,"!"
               msg3    db 0x0a

                       section .text
                       mov     ebx,msg
                       add     byte [ebx+9],'-'-10
                       mov     byte [msg3-2],' '

                       mov     eax,4
                       mov     ebx,1
                       lea     ecx,[msg]
                       mov     edx,msg3-msg
                       int     0x80
                 

• What's a big endian processor? a small endian processor?
• Write a program that uses only one string of characters "********" and that prints this pattern:

                 ********
                 ******
                 ****
                 **
                 

• Show the memory once the following data section of a program has been loaded into memory (indicate hex values with a 0x... prefix)

                             section .data
                 a           dd        10
                 b           dd        -1
                 msg         db        1,2,3,4,5,6,7
                 c           dw        0xaa

• What is the binary and hexadecimal representations of the following 16-bit words (assume we are using 2's complement)?

                 65


                 -3


                 32767

• What is the advantage of 2's complement over other systems of representation of signed integers?
• What is the contents of the different registers after the following instructions have finished executing?

                            mov   eax,"231a"
                            and   eax,0xff00ff00
                            mov   ebx,0
                            mov   bl, '+'
                            shl   ebx,16
                            or    bl, '-'
                            or    eax,ebx
                 

• what is the purpose of the XOR instruction? When is it useful?