Difference between revisions of "CSC231 Exercises On Functions"
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[[CSC231_Class_Page | Back]] to Weekly Schedule. | [[CSC231_Class_Page | Back]] to Weekly Schedule. | ||
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+ | Note: For some exercises, highlight the white section on the right hand-side of each code section to see the solution. | ||
+ | [[Image:pushPop.jpg| right]] | ||
− | + | =Exercise 1= | |
+ | |||
+ | * Write a program that prints all the letters of the alphabet in a loop. All the characters appear on the same line. Do not use a function yet! Use '''ecx''' and '''loop''' to control the looping. Make your program print 1 letter per loop. | ||
+ | * use int 0x80 to print the character (which you'll store in a string). | ||
+ | |||
+ | =Exercise 2= | ||
− | =Exercise | + | * Same exercise, but this time use a function that receives the character to be printed in al. |
+ | * Explore ways to save ecx in a temporary variable | ||
+ | * Explore alternative ways using the '''push''' and '''pop''' operations | ||
+ | |||
+ | =Exercise 3= | ||
+ | |||
+ | * Print all the characters on separate lines. You cannot use a library function for printing the 0x0a line-feed character. | ||
+ | * Explore a solution where the new-line character is printed at the same time the letter of the alphabet is printed. | ||
+ | * Explore a solution where you have a separate ''myPrintLn'' function that prints a new-line character. | ||
+ | |||
+ | =Exercise 4= | ||
+ | |||
+ | * What is the behavior of the stack, and the resulting values in the registers as this program is executing: | ||
+ | <br /> | ||
+ | <source lang="asm"> | ||
+ | mov eax, 0x01234567 | ||
+ | mov ebx, 0x89ABCDEF | ||
+ | xor ecx, ecx | ||
+ | |||
+ | push ax | ||
+ | pop cx | ||
+ | |||
+ | push ax | ||
+ | push bx | ||
+ | pop ecx | ||
+ | |||
+ | call next | ||
+ | next: pop ecx | ||
+ | |||
+ | </source> | ||
+ | <br /> | ||
− | + | [[Media:file.pdf|.]] | |
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− | + | =Exercise 5= | |
− | |||
− | |||
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− | + | What is the behavior of this program? | |
− | What is the behavior of | ||
{| | {| | ||
! width="300" | | ! width="300" | | ||
Line 37: | Line 53: | ||
|- | |- | ||
| | | | ||
− | < | + | <source lang="asm"> |
− | + | mov eax, 0 | |
− | + | mov ecx, 10 | |
− | for: call func1 | + | for: call func1 |
− | + | ||
− | |||
− | |||
+ | func1: add eax, 1 | ||
+ | ret | ||
− | + | ;;; exit code | |
− | + | mov ebx, 0 | |
− | </ | + | mov eax, 1 |
+ | int 0x80 | ||
+ | </source> | ||
| | | | ||
<font color="white"> | <font color="white"> | ||
<br> | <br> | ||
− | The | + | The loop goes 10 times and the function is called 10 times, adding 1 to eax every time. Eax ends with 10 in it. |
</font> | </font> | ||
|} | |} | ||
− | =Exercise | + | =Exercise 6= |
What is the behavior of this program? Draw the stack as the processor executes this program: | What is the behavior of this program? Draw the stack as the processor executes this program: | ||
{| | {| | ||
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|- | |- | ||
| | | | ||
− | < | + | <source lang="asm"> |
mov eax, 0 | mov eax, 0 | ||
mov ebx, 0 | mov ebx, 0 | ||
Line 79: | Line 97: | ||
func2: add ebx, 1 | func2: add ebx, 1 | ||
ret | ret | ||
− | </ | + | </source> |
| | | | ||
<font color="white"> | <font color="white"> | ||
Line 86: | Line 104: | ||
|} | |} | ||
− | =Exercise | + | =Exercise 7= |
Same question, but now observe that the programmer forgot the '''ret''' instruction at the end of the first function. | Same question, but now observe that the programmer forgot the '''ret''' instruction at the end of the first function. | ||
{| | {| | ||
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|- | |- | ||
| | | | ||
− | < | + | <source lang="asm"> |
mov eax, 0 | mov eax, 0 | ||
mov ebx, 0 | mov ebx, 0 | ||
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func2: add ebx, 1 | func2: add ebx, 1 | ||
ret | ret | ||
− | </ | + | </source> |
| | | | ||
<font color="white"> | <font color="white"> | ||
Line 115: | Line 133: | ||
|} | |} | ||
− | =Exercise | + | =Exercise 8 (Push and Pop)= |
− | What are the numbers stored in eax and ebx when the loop terminates? | + | What are the numbers stored in eax and ebx when the loop terminates? If we assume that the default stack is 2 KB long, what is the largest number of times the loop can iterate before the stack overflows (trick question :-)? |
{| | {| | ||
! width="300" | | ! width="300" | | ||
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|- | |- | ||
| | | | ||
− | < | + | <source lang="asm"> |
mov eax, 0 | mov eax, 0 | ||
mov ebx, 0 | mov ebx, 0 | ||
mov ecx, 10 | mov ecx, 10 | ||
− | for: | + | for: push ebx |
call func1 | call func1 | ||
pop ebx | pop ebx | ||
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func2: add ebx, 1 | func2: add ebx, 1 | ||
ret | ret | ||
− | </ | + | </source> |
| | | | ||
<font color="white"> | <font color="white"> | ||
Line 146: | Line 164: | ||
|} | |} | ||
− | =Exercise | + | =Exercise 9= |
Same question, but now observe that we pop eax, not ebx... | Same question, but now observe that we pop eax, not ebx... | ||
{| | {| | ||
Line 153: | Line 171: | ||
|- | |- | ||
| | | | ||
− | < | + | <source lang="asm"> |
mov eax, 0 | mov eax, 0 | ||
mov ebx, 0 | mov ebx, 0 | ||
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func2: add ebx, 1 | func2: add ebx, 1 | ||
ret | ret | ||
− | </ | + | </source> |
| | | | ||
<font color="white"> | <font color="white"> | ||
Line 177: | Line 195: | ||
|} | |} | ||
− | =Exercise | + | =Exercise 10= |
What do these 2 code sections do? | What do these 2 code sections do? | ||
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|- | |- | ||
| | | | ||
− | < | + | <source lang="asm"> |
push eax | push eax | ||
mov eax, ebx | mov eax, ebx | ||
pop ebx | pop ebx | ||
− | </ | + | </source> |
and | and | ||
− | < | + | <source lang="asm"> |
xor eax, ebx | xor eax, ebx | ||
xor ebx, eax | xor ebx, eax | ||
xor eax, ebx | xor eax, ebx | ||
− | </ | + | </source> |
| | | |
Latest revision as of 09:55, 21 October 2014
Back to Weekly Schedule.
Note: For some exercises, highlight the white section on the right hand-side of each code section to see the solution.
Contents
Exercise 1
- Write a program that prints all the letters of the alphabet in a loop. All the characters appear on the same line. Do not use a function yet! Use ecx and loop to control the looping. Make your program print 1 letter per loop.
- use int 0x80 to print the character (which you'll store in a string).
Exercise 2
- Same exercise, but this time use a function that receives the character to be printed in al.
- Explore ways to save ecx in a temporary variable
- Explore alternative ways using the push and pop operations
Exercise 3
- Print all the characters on separate lines. You cannot use a library function for printing the 0x0a line-feed character.
- Explore a solution where the new-line character is printed at the same time the letter of the alphabet is printed.
- Explore a solution where you have a separate myPrintLn function that prints a new-line character.
Exercise 4
- What is the behavior of the stack, and the resulting values in the registers as this program is executing:
mov eax, 0x01234567
mov ebx, 0x89ABCDEF
xor ecx, ecx
push ax
pop cx
push ax
push bx
pop ecx
call next
next: pop ecx
Exercise 5
What is the behavior of this program?
mov eax, 0
mov ecx, 10
for: call func1
func1: add eax, 1
ret
;;; exit code
mov ebx, 0
mov eax, 1
int 0x80
|
|
Exercise 6
What is the behavior of this program? Draw the stack as the processor executes this program:
mov eax, 0
mov ebx, 0
mov ecx, 10
for: call func1
...
loop for
func1: add eax, 1
call func2
ret
func2: add ebx, 1
ret
|
|
Exercise 7
Same question, but now observe that the programmer forgot the ret instruction at the end of the first function.
mov eax, 0
mov ebx, 0
mov ecx, 10
for: call func1
...
loop for
func1: add eax, 1
call func2
func2: add ebx, 1
ret
|
|
Exercise 8 (Push and Pop)
What are the numbers stored in eax and ebx when the loop terminates? If we assume that the default stack is 2 KB long, what is the largest number of times the loop can iterate before the stack overflows (trick question :-)?
mov eax, 0
mov ebx, 0
mov ecx, 10
for: push ebx
call func1
pop ebx
loop for
...
func1: add eax, 1
call func2
ret
func2: add ebx, 1
ret
|
|
Exercise 9
Same question, but now observe that we pop eax, not ebx...
mov eax, 0
mov ebx, 0
mov ecx, 10
for: push ebx
call func1
pop eax
loop for
...
func1: add eax, 1
call func2
ret
func2: add ebx, 1
ret
|
|
Exercise 10
What do these 2 code sections do?
push eax
mov eax, ebx
pop ebx
and xor eax, ebx
xor ebx, eax
xor eax, ebx
|
|