Week 13: Stack Frame & Passing Parameters

Question 1

Computer programs and subroutines consist of

Answer 1

Data elements and procedures that operate on the data elements

Question 2

The scope of a variable defines the

Answer 2

Range of its visibility or accessibility within a program

Question 3

Global variables are visible…

Answer 3

from the moment they are loaded into memory to the moment the program stops running

Question 4

Local variables and parameters are visible…

Answer 4

Within that procedure but invisible outside the procedure

Question 5

When a language invokes a procedure , it is said to…

Answer 5

Activate the procedure

Question 6

With each invocation of a procedure, there is an…

Answer 6

Activation record

Question 7

Activation records contain…

Answer 7

All necessary information to execute the procedure

• Parameters
• Local variables
• Return address

Question 8

The activation record is also known as the…

Answer 8

Frame

Question 9

After an activation record has been used…

Answer 9

Executing a return from procedure deallocates or frees the storage taken up by the record

Question 10

The stack provides…

Answer 10

A mechanism for implementing the dynamic memory allocation

Question 11

The stack-frame is a region of

Answer 11

Temporary storage

Question 12

At the beginning of a subroutine, the temporary storage will be

Answer 12

Pushed onto the stack

Question 13

At the end of a subroutine, temporary storage will be

Answer 13

Popped from the stack

Question 14

The two pointers associated with stack frames are

Answer 14

Stack Pointer, SP (r13)

Frame Pointer, FP (r11)

Question 15

What register is the Stack Pointer?

Answer 15

r13

Question 16

What register is the Frame Pointer?

Answer 16

r11

Question 17

What is in register 11?

Answer 17

The Frame Pointer

Question 18

What is in register 13?

Answer 18

The Stack Pointer

Question 19

The stack pointer always points to the

Answer 19

Top of the stack

Question 20

The frame pointer always points to the

Answer 20

Base of the current stack frame

Question 21

The _____ may change during procedure execution, but the ______ will not

Answer 21

The stack pointer may change during procedure execution, but the frame pointer will not

Question 22

It is strongly recommended that data in the stack frame be accessed through the

Answer 22

Frame Pointer

Question 23

Reserving memory in the stack frame is done by

Answer 23

ADDing / SUBtracting x-bytes onto the Stack Pointer

Question 24

Operations on the stack are ___ meaning….

Answer 24

Balanced, meaning if you put something onto the stack you have to remove it

Question 25

Does arm have native link and unlike instructions?

Answer 25

NO

Question 26

To create a stack frame you can…

Answer 26

1. Push the old frame pointer onto the stack to save its value
2. Make the frame pointer point to the bottom of the new stack frame
3. move the stack pointer by d-bytes to create a local workplace

Question 27

At the end of a subroutine call the stack frame is collapsed by

Answer 27

MOV sp,fp ;restore the stack pointer

LDR fp,[sp] ;restore old frame pointer from the stack

ADD sp,sp,#4 ;move stack pointer down 4 bytes to
;restore stack

Question 28

To implement a program using the SP, FP, and LR…

Answer 28

Question 29

What does a function look like that is being called by a main area that uses BL and has parameters:

Answer 29

Question 30

If you store multiple the FP anf the LR, which will be put onto the stack first? If FD?

STMFD sp!, {fp, lr}

Answer 30

LR

Because it is FD, we are starting at higher memory addresses first and then descending since LDM and STM store the highest number register in the higher memory address / lowest numbered register in the lowest memory address

Question 31

To call a subroutine the following steps need to be performed…

Answer 31

Parameters need to be passed from the caller to the subroutine (can be done via the stack)

The address of the instruction after the calling instruction needs to be saved BEFORE branching (can be done using BL or the stack or both)

Inside the subroutine we must

• Push all register values that are going to be used in the subroutine onto the stack
• Make the FP point to the bottom of the frame by copying the value of the SP to the FP
• Create a space inside the stack for local variables
• Perform subroutine instructions where local variables and parameters are relative to the FP
• At the end of the the subroutine, deallocate all created local variables
• Pop all pushed registers but use the PC instead of LR to return

Finally in the calling program, all pushed parameters need to be popped

Question 32

You can pass a parameter to a subroutine by..

Answer 32

Value or by Reference

Question 33

What does a traditional call/return mechanism with parameters look like?

Answer 33