Homework #2: Introduction to Computer Systems - 18x13: Summer 2024

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Homework #2: Introduction to Computer Systems - 18x13: Summer 2024

Question 1 1 / 1 pts

Consider the following assembly:

addl    %eax, %edx          # %eax here is an "int x" and %edx here is an "int y"

movl    %edx, %eax

sall    $2, %eax

addl    %edx, %eax

sall    $3, %eax

Which of the following expressions matches the assembly?

32x + 32y

Correct!

40(x + y)

8x + 4y

4x + 8y

None of the above

Question 2 3 / 3 pts

Please consider the following assembly:

leaq    12(%rbx), %rax     # Assume that %rbx is the base of an "int array[ 10 ]"

movl    $6, (%rax)

leaq    16(%rbx), %rax

movl    $8, (%rax)

leaq    12(%rbx), %rax

movl    (%rax), %edx

leaq    16(%rbx), %rax

(a) Into what element of the array is the value 6 being moved? Specify the index. 3

(b) Into what element of the array is the value 8 being moved? Specify the index. 4

(c) What element is represented by 16(%rbx)? Specify the index. 4

Question 3 6 / 6 pts

Loops and Conditionals (6 points)

Consider the following code, under the assumption that it was compiled from C code in the same environment using the same "shark machine" toolset you’ve used all semester:

loop:

.LFB0:

pushq   %rbp

movq    %rsp, %rbp

pushq   %rbx

movl    %edi, -12(%rbp)

movl    %esi, -16(%rbp)

movl    %edx, -20(%rbp)

movl    $0, %ebx

movl    -12(%rbp), %eax

cmpl    -20(%rbp), %eax

jl      .L2

movl    -20(%rbp), %eax

cmpl    -16(%rbp), %eax

jg      .L2

movl    %ebx, %eax

jmp     .L3

.L2:

jmp     .L4

.L5:

addl    $1, %ebx

addl    $1, -12(%rbp)

.L4:

movl    -12(%rbp), %eax

cmpl    -20(%rbp), %eax

jl      .L5

jmp     .L6

.L7:

addl    $1, %ebx

subl    $1, -20(%rbp)

.L6:

movl    -20(%rbp), %eax

cmpl    -16(%rbp), %eax

jg      .L7

movl    %ebx, %eax

.L3:

popq    %rbx

popq    %rbp

ret

(A) (2 points): How many loops does this function have? 2

(B) (2 points): How many “if” statements does this function have? 2

Hint: Control flow from loops is not counted as "if" statements.

(C) (2 points) Consider calling the function as below. What value does the function return?

6

Hint: It returns an integer type. Enter nothing but an integer number.

loop(3, 5, 7, 9, 11, 13);

Switch Statements (8 points)

Consider the following code, which was compiled from C Programming Language source code containing one switch statement and no (zero) if statements:

Consider also the following dump:

Question 4 2 / 2 pts

Switch Statements (8 points)

(A)(2 points): What integer input values are managed by non-default cases of the switch statement?

Check all that apply.

Question 5 2 / 2 pts

Switch Statements (8 points)

(B)(2 points): If there is a default case, at what address, in hex, does the begin? If there isn't a default case, write NONE: 0x40055d

Question 6 2 / 2 pts

Switch Statements (8 points)

(C) (2 points): Which integer input values (if any), managed by non-default cases of the switch statement, consist of exactly the same code as least one other case? Check all that apply. [exact_same]

Question 7 2 / 2 pts

Switch Statements (8 points)

(D) (2 points): Which case(s), if any, fall through to the next case after executing some of their own code? [falls_through]