CS 354, version A
Fall 2014 		Name:___________________
Section:________________
ID:___________________
Exam 2
No electronic devices may be used while taking this exam. No calculators, no cell phones. Each student is allowed one 8.5 by 11 inch sheet of paper with handwritten notes. Do not write on the notes sheet during the exam.

Show all work, and do any/all calculations on the exam. Extra scratch paper may not be used. Partial credit will be given based on work shown.

Exam Score
Q1 = _____ /    10
Q2 = _____ /      5
Q3 = _____ /    10
Q4 = _____ /    10
Q5 = _____ /    10
Q6 = _____ /    30
Q7 = _____ /    20
Q8 = _____ /      5
Total = _____ / 100		 







Question 1 (10 points)


You find this x86 code within a program:


      testl %eax, %eax
      jz    next
      inc   %ecx
next:



Assume that the value in %eax 
is the integer variable aa,
and the value in %ecx 
is the integer variable count.
Write the C code fragment that this assembly language fragment implements.

 


 


 


Question 2 (5 points)


Write the equivalent of the x86 instruction


pushl %edx



as a series of x86 instructions, without using the
pushl instruction.

 


 


 


Question 3 (10 points total)



Part A (4 points)
While working on a job, you suspect that the stepA program that
you are using has a bug. You decide to investigate, before you send
an email claiming to have found a bug in stepA.
But, you only have the Linux binary executable of stepA.
What Linux program can you use to generate an assembly language
version of the stepA?








Part B (6 points)
In your divide.c program from assignment 3,
what two types of interrupts did you catch and handle?

    

  1. 


    

  2. 






Question 4 (10 points)



Write an x86 code fragment that implements the C code fragment:

   ar[i] = -36 + ar[i];


Assume ar is an
array of integers,
variable i is in %edi,
and this code initializes other variables:


   leal  ar, %ebx
   movl  $-36, %eax




 



 


 


 


Question 5 (10 points total)


The compiler is working to produce the x86 assembly language
code for a function that uses 5 integer-type local variables.
Write the prologue code for this function. 

 




Question 6 (30 points total)


Here are portions of a C program (on the left) and its x86 assembly
language version (on the right).



int f1(int a, int b) {        f1: push   %ebp
   int x;                         mov    %esp,%ebp
                                  sub    $0x10,%esp
   x = a + b;                     mov    _____(%ebp),%eax
                                  mov    _____(%ebp),%edx
                                  add    %edx, %eax
                                  mov    %eax,-0x4(%ebp)
   return __________  ;           mov    -0x4(%ebp),%eax
                                  leave
                                  ret
}                                       
 	                                
int main() {                main: push   %ebp
   int xx, yy, zz;                mov    %esp,%ebp
                                  sub    $0x18,%esp
                                  movl   $0x10,-0xc(%ebp)
   xx = _______;                  movl   $0xffffffff,-0x8(%ebp)
                                  mov    -0x8(%ebp),%eax
   yy = _______;                  mov    %eax,0x4(%esp)
                                  mov    -0xc(%ebp),%eax
                                  mov    %eax,(%esp)
   zz = f1(xx, yy);               call   f1
                                  mov    %eax,-0x4(%ebp)
                                  mov    $0x80484f4,%eax
                                  mov    -0x4(%ebp),%edx
                                  mov    %edx,0x4(%esp)
                                  mov    %eax,(%esp)
   printf("%d\n", zz);            call   printf
                                  
   return 0;                      mov    $0x0,%eax
}                                 leave
                                  ret



Part A (5 points)

Circle the prologue code within  
f1().

 

Part B (15 points)
Fill in the blanks within both the
the C code and the assembly language code to complete the
missing code. 


 

Part C (10 points)

What is the output of this program?

 


 



Question 7 (20 points total)

 
Part A (4 points)
What is the key difference between RAM and ROM?

 


 



Part B (4 points)
Identify one advantage that SSDs have over rotating disks.

 


 



Part C (4 points)
If an application invokes getc(),  
and no key has been pressed on the keyboard, 
what technique does the operating system code 
use to block to wait for input? 

 


 




Part D (4 points)
What distinguishes an interrupt from a trap?

 


 


 

Part E (4 points)
Are real world exception handlers reentrant or non-reentrant?

 


 


Question 8 (5 points)


What programming bug does a stack smashing attack rely upon?