2505 Test 2 Review

Question 1

how many bytes does pushq %rbp allocate

Answer 1

8

Question 2

subq $32, %rsp

is doing what?

Answer 2

This line moves the stack pointer down, allocating 32 bytes of room for the stack frame for the function

Question 3

a function receives a parameter. this is the assembly code where the parameter is placed in a stack frame:
movl %esi, -24(%rbp)
At what address is the parameter value stored?

Answer 3

%rbp - 24

Question 4

what is happening here:
movl -20(%rbp), %eax
imull -24(%rbp), %eax
movl %eax, -8(%rbp)

Answer 4

the code is computing the product of 2 parameters and setting it equal to a local variable

Question 5

which comes first, destination or source?

Answer 5

source

Question 6

what do registers look like?

Answer 6

%e”?”x

Question 7

what kind of assembly instructions would copy data from RAM to a register?

Answer 7

movl where first operand is address, second is register
leave
ret

Question 8

what should be done before copying a string?

Answer 8

calloc(strlen(varName)+1, sizeof(char))

Question 9

what is represented by the value 0?

Answer 9

NULL

Question 10

how many args does malloc take?

Answer 10

1

Question 11

args for calloc?

Answer 11

(num of elems, byte size per element)

Question 12

format for creating a mask

Answer 12

0x(number)(letter) (8 bits)

Question 13

what kind of mask would make everything 0?

Answer 13

& 0

Question 14

what kind of 1 byte mask would make everything 1?

Answer 14

0xF

Question 15

mask to extract bit N

Answer 15

mask = 1 &laquo_space;N;

return ((x & mask)&raquo_space; N);

Question 16

what should the most significant bit of a positive integer be?

Answer 16

0

Question 17

pattern for converting from binary to decimal

Answer 17

8421

Question 18

what goes in empty spots for left shifts?

Answer 18

0

Question 19

what is 10 in hexadecimal?

Answer 19

A

Question 20

when do we fill 1s in the empty positions after a right shift?

Answer 20

only when the number is negative (most significant bit is 1)

Question 21

how many bytes does a uint16_t occupy

Answer 21

2

Question 22

when you calloc a char array what is the first parameter?

Answer 22

strlen(str) + 1

Question 23

when using malloc or calloc with strings what should you do to the string length?

Answer 23

add 1

Question 24

difference between movq and movl?

Answer 24

movq is for 64 bit, movl is for 32 bit

Question 25

difference bw strncpy and strcpy?

Answer 25

strncpy only copies part of a string, takes dest, source, idx args

Question 26

what should you do when there are two different pointer types?

Answer 26

type cast

Question 27

what do while loops look like in assembly?

Answer 27

1) unconditional jmp (start)
2) conditional BACKWARDS jump (end)
DO WHILES will not have a jump to the test loop

Question 28

what does if-else look like in assembly?

Answer 28

1) conditional FORWARD jmp (start is right before the cmp statement, end is jump location)
2) unconditional jump

Question 29

je

Answer 29

jump if 0

Question 30

jne

Answer 30

jump if nonzero

Question 31

jg

Answer 31

jump if +

Question 32

js

Answer 32

jump if -

Question 33

jl

Answer 33

jump if signed neg

Question 34

what kind of assembly instructions would copy data from register to RAM?

Answer 34

mov where first operand is register, second is address

INCLUDES PUSH

Question 35

what would be considered a local automatic variable in the stack?

Answer 35

anything that isn’t storing a parameter

Question 36

how many bytes is uint8

Answer 36

1 byte

Question 37

which register holds the return value?

Answer 37

%eax

Question 38

if a register name starts with r…

Answer 38

a 64 bit value is being manipulated

Question 39

How would you write C2 in hexadecimal format?

Answer 39

0xC2

Question 40

How many bits in a byte?

Answer 40

8

Question 41

Little endian order…

Answer 41

flips the order of the two hexdump values GO BACKWARDS

Question 42

for hexdump problems, when you perform a typecast of uint16_t…

Answer 42

two chunks of the memory will be used and in little endian order (since its 2 bytes)

Question 43

how many bytes is 64 bit

Answer 43

8 bytes

Question 44

how many bytes is 32 bit

Answer 44

4 bytes

Question 45

8*16 =

Answer 45

128

Question 46

how many bytes are in the stack frame?

Answer 46

rbp (8) + the value associated with subq

Question 47

char* is a

Answer 47

string

Question 48

args for memcpy()

Answer 48

destination, source, total memory

Question 49

function to make a copy of a string

Answer 49

strcpy()

Question 50

function to ALLOCATE memory for a string copy

Answer 50

calloc(strlen(str)+1, size(char))

Question 51

function to copy int array

Answer 51

memcpy()

Question 52

allocate memory to make a copy of the struct PIE

Answer 52

Pie* pecan = calloc(1, sizeof(Pie));

Question 53

what does -1 look like in binary

Answer 53

a bunch of 1s

Question 54

how many bits is a nybble

Answer 54

4

Question 55

what is 0x7FFFFFFF in binary

Answer 55

0111 1111 1111 1111…

Question 56

true or false: overflow can change a positive number into a negative number with addition

Answer 56

true

Question 57

instead of saying value of a pointer say

Answer 57

target

Question 58

what does sal do

Answer 58

shift to the left by n bits

Question 59

strlen(str) + 1 is only needed when using

Answer 59

calloc

Question 60

operation needed to step into next array element

Answer 60

+ sizeof(type)

Question 61

how do you know if a value is even? (binary)

Answer 61

the low bit should be 0

Question 62

what is 0x01 in binary?

Answer 62

00000001 (8 bits)

Question 63

how to convert from decimal to hex

Answer 63

take the number
div by 16
take that answer
div 16 ...
the final hex value is the remainder from each division BACKWARDS

Question 64

when reading hex values from a hexdump the values should be written

Answer 64

BACKWARDS