Stack

Question 1

Where is stack allocated?

Answer 1

Primary memory

Question 2

___ is pushed onto the stack when function is called

Answer 2

stack frame

Question 3

stack uses high or low memory? which direction does the stack grow towards?

Answer 3

high, towards 0

Question 4

what does the frame pointer do?

Answer 4

points to local variables in a stack frame

Question 5

What size of address does ARMv8 use?

Answer 5

64 bit

Question 6

How many bytes can ARMv8 address?

Answer 6

2^64

Question 7

What is stack?

Answer 7

A space in RAM provided by the OS to store data for functions

Question 8

What does the stack frame hold?

Answer 8

A function’s parameters, lvars and return values

Question 9

What happens to the stack frame when the function returns?

Answer 9

It is popped

Question 10

What does the stack diagram look like?

Answer 10

Check notes

Question 11

Where are programs loaded (think of stack diagram)

Answer 11

Into low mem, just above the space for the OS

Question 12

What is the heap used for?

Answer 12

dynamically allocated mem in a program. done in c using malloc() and free()

Question 13

Where does the stack pointer (SP) point to and what happens to it when the stack grows?

Answer 13

The top of the stack. It is decremented when the stack grows

Question 14

How does a program allocate stack mem?

Answer 14

By subtracting the number of bytes needed from SP

Question 15

The stack must be ____ aligned. What does this mean?

Answer 15

Quadword. The address in SP must be evenly divisible by 16

Question 16

How do we guarantee alignment?

Answer 16

1. Add a negative number instead of subtracting.
2. Clear the low order 4 bits of the negative number by ANDing it with -16

Question 17

Machine instructions for “allocate 20 bytes”. Does this actually allocate 20 bytes?

Answer 17

add sp, sp, -20 & -16
No, it allocates 32 because it ANDs -20 and -16

Question 18

What is the FP used for?

Answer 18

To point to lvars in a stack frame

Question 19

Stability of FP vs SP

Answer 19

FP is stable once set at the beginning of a function.

SP is allowed to change as the function executes

Question 20

A stack frame must be at least __ bytes long.

Answer 20

16