CPU Registers

Question 1

What are the 8 general purpose registers?

Answer 1

EAX, EBX, ECX, EDX, EDI, ESI, EBP, and ESP

Question 2

What is EAX?

Answer 2

The accumulator register.

• addition subtraction
• store the returned value

Question 3

What is EBX?

Answer 3

The Base Register.

- catch all for available storage

Question 4

What is EDX?

Answer 4

The Data Register
It’s often used in mathematical operations like division and multiplication to deal with overflow where the most significant bits would be stored in EDX and the least significant in EAX. It is also commonly used for storing function variables.

Question 5

What is ESI?

Answer 5

The Source Index
The counterpart to EDI, ESI is often used to store the pointer to a read location. For example, if a function is designed to read a string, ESI would hold the pointer to the location of that string.

Question 6

What is EDI?

Answer 6

The Destination Index
Though it can be (and is) used for general data storage, EDI was primarily designed to store the storage pointers of functions, such as the write address of a string operation

Question 7

What is ESP?

Answer 7

The Stack Pointer
ESP is used to track the top of the stack. As items are moved to and from the stack ESP increments/decrements accordingly. Of all of the general purpose registers, ESP is rarely/never used for anything other than it’s intended purpose.

Question 8

What is EIP?

Answer 8

The Instruction Pointer
Not a general purpose register, but fitting to cover here, EIP points to the memory address of the next instruction to be executed by the CPU. As you’ll see in the coming tutorials, control the value of EIP and you can control the execution flow of the application (to execute code of your choosing).

Question 9

What is a register?

Answer 9

A register may hold an instruction, a storage address, or any kind of data (such as a bit sequence or individual characters)

Question 10

What is the stack?

Answer 10

LIFO data structure that lives in RAM. It is an area in program memory that is used for short-term storage of information by the CPU and the program

Question 11

What are the three groups of registers?

Answer 11

General, Control, and Segment

Question 12

What are the general registers divided into?

Answer 12

Data registers, Pointer registers, and index registers

Question 13

What are the four Data registers?

Answer 13

EAX, EBX, ECX, EDX

Question 14

What are the three Pointer registers?

Answer 14

EIP, ESP, EBP

Question 15

What are the two index registers?

Answer 15

ESI, EDI

Question 16

What are control registers used for?

Answer 16

The 32-bit instruction pointer register and the 32-bit flags register combined are considered as the control registers.

Many instructions involve comparisons and mathematical calculations and change the status of the flags and some other conditional instructions test the value of these status flags to take the control flow to other location.

Question 17

What are segment registers?

Answer 17

Segments are specific areas defined in a program for containing data, code and stack

Question 18

What are the three main segments ?

Answer 18

Code, Data, Stack

Question 19

What is the Code Segment?

Answer 19

It contains all the instructions to be executed. A 16-bit Code Segment register or CS register stores the starting address of the code segment

Question 20

What is the Data Segment?

Answer 20

It contains data, constants and work areas. A 16-bit Data Segment register or DS register stores the starting address of the data segment.

Question 21

What is the Stack Segment?

Answer 21

It contains data and return addresses of procedures or subroutines. It is implemented as a ‘stack’ data structure. The Stack Segment register or SS register stores the starting address of the stack.