Memory Management

Question 1

What is layout of x86 / x86_74 memory structure (top to bottom)

Answer 1

1. Code/text segment
2. Initialised data segment
3. Uninitialized data segment
4. Heap / Stack

Question 2

What is the in the text/code segment?

Answer 2

Binary instruction set of the program (what the program does). Read only.

Question 3

What is in the initialised data segment?

Answer 3

• Where you store Global + static variables with non-zero values. Values are copied from the text/code segment
• Initiated before program execution

Question 4

What is in the Uninitialized data segment (.bss)?

Answer 4

Stores Global and static variables initialised to zero or not explicitly initialised in our code. Initiated before program execution.

Question 5

What does the stack store?

Answer 5

Variables created and removed through execution. First in last out.

Question 6

What does a stack pointer provide?

Answer 6

It points to the next available memory address.

Question 7

What happens to the stack pointer when a variable is created?

Answer 7

When a variable is created, the stack pointer increases by the size of variable in bytes.

Question 8

What happens to the stack when a variable is removed?

Answer 8

The stack pointer is decremented by the size of variables in bytes. The values aren’t cleared.

Question 9

What happens to the stack when you enter a function?

Answer 9

When you enter a function it pushes a stack frame onto the stack.

Question 10

What does a stack frame for functions contain?

Answer 10

A stack frame contains the return address where the function was called from, and any argument variables.

Question 11

What happens to the stack when a function declares a variable?

Answer 11

The variable is pushed onto the stack during the execution of the function call (length of the scope).

Question 12

What order are local variables removed from the stack on return of a function?

Answer 12

On returning from a function, local variables are removed in reverse order of their creation. (Push onto the top, pop off the top)

Question 13

How big is the stack?

Answer 13

Size of the stack is fixed and known at execution time

Question 14

When do stack overflows occur?

Answer 14

• If we make a large number of variables or large variables within a function
• Recursively call a function too many times.

Question 15

What is the Heap?

Answer 15

Memory dynamically allocated by the programmer.

Question 16

What are some guidelines for using the Heap?

Answer 16

Memory must be allocated and deallocated.

Question 17

What does the allocator function do?

Answer 17

Manage heap, reserving space and not double allocating it.

Question 18

What is the size of the heap?

Answer 18

Heap can use as much memory your system has available. The heap dynamically grows and shrinks, it starts at the end of the uninitialized data segment.

Question 19

What does the allocator function return?

Answer 19

Returns an address in memory reserve based on our request.

Question 20

When can allocation fail (Heap)?

Answer 20

When we run out of RAM

Question 21

What can you do with an address that has been deallocated?

Answer 21

Nothing, it cannot be used again. Read/write operations to that address are terminated.

Question 22

When can a SEGFAULT error be cause in memory managment?

Answer 22

When writing to an incorrect memory address.

Question 23

How do you manage memory in C (allocating/deallocating heap)?

Answer 23

functions:
- malloc()
- free()

Question 24

How do you manage memory in C++(allocating/deallocating heap)?

Answer 24

Keywords:
- new/new[]
- delete/delete[]

Question 25

What is the parameter for malloc()

Answer 25

(unsigned int size), the size bytes of memory on the heap.

Question 26

What doe malloc() return?

Answer 26

Returns the address to start of reserved memory.

Question 27

What does free(void *ptr) do?

Answer 27

Takes a pointer that points to something and removes the reservation of memory it was allocated with (frees memory).

Question 28

How do the stack and the heap differ?

Answer 28

Stack memory is a sort of memory allocation that the OS continuously manages and uses to store local variables in a FILO order. On the other hand, heap memory is a type of dynamic memory allocation used for storing objects and data structures that require a longer lifespan than stack memory.