Lab 5: Common Instructions

Overview

The purpose of this lab is to practice analyzing some common assembly instructions.

Part 1: Arithmetic Instructions

For this exercise, assume the following:

• The value in the EAX register is 0x00001337
• The value in the ECX register is 0xFFFFFFFF
• All values are 32 bits

Assume the values do not hold across each question. (Basically the values are reset for each question).

Question 1.1

What will be the value in EAX, after the following instruction?

add eax, 0xFFFF0000

Answer

0xFFFF1337

Question 1.2

What will be the value in the EAX and ECX registers, after the following instructions?

sub ecx, 0x15
add ecx, eax
inc eax

Answer

• EAX: 0x1338
• ECX: 0x1321 (Note: it overflowed, so this is what is in the ECX register)

Question 1.3

What is the binary representation of the number 0x0000061B?

Answer

11000011011

Question 1.4

What is the 32-bit hexadecimal representation of the value -1563?

Answer

0xFFFFF9E5

Question 1.5

What is the decimal representation of 0xFFFF7867 as an unsigned value?

Answer

4294932583

Question 1.6

What is the decimal representation of 0xFFFF7867 as a signed value?

Answer

-34713

Part 2: Bitwise Instructions

For this exercise, assume the following:

• The value in the EAX register is 0xA5A50000
• The value in the ECX register is 0xFFFFFFFF
• All values are 32 bits

Assume the values do not hold across each question. (Basically the values are reset for each question).

Question 2.1

What will be the value in the EAX register after the following instruction?

and eax, 0x00FF00FF

Answer

0x00A50000

Question 2.2

What will be the value in the EAX and ECX registers, after the following instructions?

xor eax, ecx
not ecx

Answer

• EAX: 0x5A5AFFFF
• ECX: 0x00000000

Question 2.3

What will be the value in the EAX and ECX registers, after the following instructions?

neg ecx
not eax
xor eax, 0xFFFFFFFF

Answer

• EAX: 0xA5A50000
• ECX: 0x00000001