13 - Parameters

Question 1

What is a subroutine?

Answer 1

An asm function.

Question 2

Give the two main parameter forms?

Answer 2

• Value parameters - eg: given two numbers, has to decide which number is bigger
• Reference parameters - eg: Given two variables,
  exchange their values

Question 3

How are parameters generally passed ?

Answer 3

By using a stack in the memory (as opposed to using the limited registers)

Question 4

What is a stack frame?

Answer 4

It’s the area of the stack which holds the data related to one call of a subroutine.

Question 5

Where is the ESP is always pointing to?

Answer 5

To the top of the stack.

Question 6

What does the EBP initially contain ?

Answer 6

An address of the base of the stack.

Question 7

What happens before and during a call to a subroutine?

Answer 7

1. The parameters are pushed on the stack.
2. The return address is pushed onto the stack.
3. The address stored in EBP is pushed on the stack.
4. The current address of the top of the stack is saved in EBP.
5. The local variables are installed on the stack.

Question 8

What happens at the end of a subroutine ?

Answer 8

1. Pop all the variables from the stack.
2. Pop the address from the top of the stack and save it in the EBP.
3. Pop the return address and put it in the IP.
4. Clean the parameters off the stack.

Question 9

What is used to pass the parameters and local variables ?

Answer 9

Stack usually, as the registers are limited.