| CS 354, version A Spring 2015 | 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 = _____ / 10 Q3 = _____ / 10 Q4 = _____ / 5 Q5 = _____ / 37 Q6 = _____ / 8 Q7 = _____ / 20 Total = _____ / 100 |
Question 1 (10 points)
Write the equivalent of the x86 instruction
popl %edx
as a series of x86 instructions, without using the
popl instruction.
Question 2 (10 points total)
Part A (4 points)
Are 2 dimensional arrays for C code stored in
row major or column major order?
Part B (6 points)
An array is declared with
int counts[240];The base address of this array at address 0x080400c4. At what address is
counts[65]?
Give your answer in hexadecimal.
Question 3 (10 points total)
Part A (5 points)
Circle the statement in this C code fragment
that could cause a SIGFPE interrupt to be sent to the program.
struct sigaction intaction;
intaction.sa_handler = divby0handler;
intaction.sa_flags = 0;
if ( sigaction(SIGFPE, &intaction, NULL) == -1 ) {
printf("sigaction() failed for arithmetic errors; quitting\n");
exit(1);
}
while (1) { /* Loop forever. */
int1 = 0;
int2 = 0;
printf("Enter first integer: ");
if ( fgets(oneline, BUFSIZE, stdin) != NULL ) {
int1 = atoi(oneline);
} else {
printf("bad input, quitting.\n");
exit(1);
}
printf("Enter second integer: ");
if ( fgets(oneline, BUFSIZE, stdin) != NULL ) {
int2 = atoi(oneline);
} else {
printf("bad input, quitting.\n");
exit(1);
}
quotient = int1 / int2;
printf("%d / %d is %d\n", int1, int2, quotient);
}
Part B (5 points)
Which statement in the C code fragment could be executing when a SIGINT
is sent to the program?
Question 4 (5 points)
What programming bug does a stack smashing attack rely upon?
Question 5 (37 points total)
Part A (18 points)
Write the C code for function f1.
Invent variable names for local variables, and show
declarations for those variables.
Hint: there is a loop that iterates 6 times.
f1: pushl %ebp
movl %esp, %ebp
subl $32, %esp
movl $0, -4(%ebp)
jmp .L2
.L3:
movl -4(%ebp), %edx
movl %edx, -28(%ebp,%edx,4)
addl $1, -4(%ebp)
.L2:
cmpl $5, -4(%ebp)
jle .L3
leave
ret
Part B (19 points)
Show the contents of the stack
and where registers %ebp and %esp point
just before the
leave instruction is fetched.
| | ^ address 0
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Question 6 (8 points total)
Here is a a C function (on the left) and its x86 assembly
language version (on the right).
int function(int a) { function:
pushl %ebp
movl %esp, %ebp
return (a - 1); movl ____(%ebp), %eax
subl $1, %eax
popl %ebp
} ret
Part A (3 points)
Circle the prologue code within
function().
Part B (5 points)
Fill in the blank in the assembly language code to complete the code.
Question 7 (20 points total)
Part A (4 points)
(Briefly) Why do we need wear leveling for SSDs?
Part B (3 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 C (6 points)
Name the 2 types of exceptions.