Week 5

Question 1

How would you find the hexadecimal address of the last item in the following array?
.data
0x44 history WORD 100 DUP(?)

Answer 1

The array effectively spans from 0-198 bytes. So add 0x44 + 198d = 0x10A

Question 2

What hexadecimal value does EIP hold immediately after “inc EAX” has executed?

0x26 inc EAX
0x2B mov EBX, z
0x30 xor EAX, EBX

Answer 2

0x2B

Question 3

The following instruction will increment the stack pointer (ESP) by how many bytes?
ret 8

Answer 3

12

Question 4

The following instruction will increment the stack pointer (ESP) by how many bytes?
ret 2

Answer 4

6

Question 5

If you reference a point beyond the end of an array i.e. the 101st element of a 100-element array, what happens?

Answer 5

You access whatever data bytes are stored there.

Question 6

Given the following register states, and using Register Indirect Addressing, how would you move the 11th element of the list array (of DWORDs) to the EAX register?
EDX = the address of list[0]
ESI = address of list[10]
EBX = 40

Answer 6

mov eax, [esi]

Question 7

Given the following register states, and using Base Indexed Addressing, how would you move the 11th element of the list array (of DWORDs) to the EAX register?
EDX = the address of list[0]
ESI = address of list[10]
EBX = 40

Answer 7

mov eax, [edx + ebx]

Question 8

Given the following register states, and using Indexed Addressing, how would you move the 11th element of the list array (of DWORDs) to the EAX register?
EDX = the address of list[0]
ESI = address of list[10]
EBX = 40

Answer 8

mov eax, list [ebx]

Question 9

Given list, an array of WORDs, what element is addressed by list[7]?

Answer 9

4th element

Question 10

The RET instruction (without operands) will pop how many bytes off the stack?

Answer 10

4

Question 11

The following two instructions are equivalent:
ret
ret 4

Answer 11

False, the second instruction pops an additional 4 bytes off the stack.

Question 12

When passing procedure parameters on the stack, why are the following lines of code often necessary?
push ebp
mov ebb, esp

Answer 12

To keep additional usage of the stack within the procedure from invalidating the stack offsets.

Question 13

Register indirect addressing is defined as?

Indexed Addressing is defined as?

Base Indexed Addressing is defined as?

Answer 13

Register indirect addressing is accessing memory through an address stored in a register. 
mov esi, OFFSET list
mov eax, [esi]
add  esi, 4
mov  eax, [esi]

Indexed addressing is adding a constant to a register to generate an effective address.
mov esi, 0
mov eax, list[esi] ; or [list + esi]

Base Indexed Addressing is accessing lists through the base pointer in procedures.
mov esi, [ebp + 12] ; @list
mov edx, 0
mov eax, [esi + edx] ; gets curr element

Question 14

What is SIZEOF myChecker (in decimal)?

.data
myChecker BYTE 12h
BYTE 34h
BYTE 56h

Answer 14

SIZEOF = 1

Question 15

How do you obtain the value of the SIZEOF operator?

Answer 15

Multiply the number of elements in a data declaration by the size in bytes.

Question 16

What is SIZEOF myChecker (in decimal)?

.data
myChecker BYTE 12h,
34h,
56h

Answer 16

SIZEOF = 3

Question 17

What is the correct formula to obtain the address of an element in matrix[r][c]?

Answer 17

base address + data size * [(row index * elements/row) + column index]

Question 18

Loading a string byte using string primitives increments or decrements which register?

Answer 18

ESI

Question 19

EAX contains what value in hexadecimal?

.data
myList BYTE 12h, 34h, 56h, 78h, 90h, ABh, CDh

.code
mov eax, DWORD PTR [myList + 2]

Answer 19

eax = AB907856h

Question 20

What is the value in decimal of y?

.data
myList WORD 12h, 34h, 56h, 78h, 90h, ABh
y DWORD SIZEOF myList

Answer 20

y = length * size
y = 6 * 2 = 12

Question 21

What is the value in decimal of x?

.data
myList WORD 12h, 34h, 56h, 78h, 90h, ABh
x DWORD LENGTHOF myList

Answer 21

x = 6

Question 22

The _____ operator overrides the default type of. a label and can also be used to combine elements of a smaller data type and move them into a larger operand.

Answer 22

PTR

Question 23

Two dimensional arrays are declared in _____ order in MASM?

Answer 23

row-major

Question 24

If the string direction flag is not set, string operations will move backwards through the string.

Answer 24

False

Question 25

Given the following array declaration, how many bytes of memory does array matrix require (in decimal)?

.data
matrix WORD 21 DUP (33 DUP(?))

Answer 25

1386

21 * 33 * 2