Chapter 3 Machine Level Representation of Programs

Question 1

Assembly code suffix b represents…

Answer 1

C declaration: Char
Intel data type : Byte
Size: 1 byte

Question 2

Assembly code suffix w represents…

Answer 2

C declaration: short
Intel data type : Word
Size: 2 bytes

Question 3

Assembly code suffix l represents

Answer 3

C declaration: int or double
Intel data type : Double word(int), Double precision (double)
Size: 4 bytes (int), 8 bytes(double)

Question 4

Assembly code suffix q represents:

Answer 4

C declaration: long or char*
Intel data type : Quad word
Size: 8 bytes

Question 5

Assembly code suffix s

Answer 5

C declaration: float
Intel data type : Single precision
Size: 4 bytes

Question 6

in x86-64, what is the size of pointers

Answer 6

8 bytes

Question 7

Return register for 64 bit machine

Answer 7

%rax (r for 64)

Question 8

Return register for 32 bit machine

Answer 8

%eax (e for 32)

Question 9

Return register for 16 bit machine

Answer 9

%ax

Question 10

Data movement instruction

Answer 10

mov

Question 11

$

Answer 11

immediate value

Question 12

movzb

Answer 12

Move zero extending byte. These instructions have a register or memory location as the source and a register as the destination

Question 13

movsbw

Answer 13

move sign-extended byte to word (bw can change to bl, wl… meaning from one type to another)

Question 14

PC

Answer 14

Program Counter

Question 15

Importance of PC

Answer 15

Holds address of next instruction

Question 16

What do Condition codes do

Answer 16

Store status information about most recent arithmetic or logical operation
Used for conditional branching

Question 17

What is Memory

Answer 17

• Byte addressable array
• Code and user data
• Stack to support procedures

Question 18

Translate to C
movq $0x4,%rax

Answer 18

Immediate value to register
temp = 0x4

Question 19

Translate to C
movq $-147,(%rax)

Answer 19

Immediate value to memory
*p = -147

Question 20

Translate to C
movq %rax,%rdx

Answer 20

register to register
temp2 = temp1

Question 21

Translate to C
movq %rax,(%rdx)

Answer 21

Register to memory
*p = temp

Question 22

Translate to C
movq (%rax),%rdx

Answer 22

Memory to register
temp = *p

Question 23

Meaning of the following unary operation
neg

Answer 23

Arithmetic negation

Question 24

Meaning of the following unary operation
not

Answer 24

Bitwise complement

Question 25

addq

Answer 25

Dest = Dest + Src

Question 26

subq

Answer 26

Dest = Dest - Src

Question 27

imulq

Answer 27

Dest = Dest * Src

Question 28

salq or shlq

Answer 28

Dest = Dest &laquo_space;Src

Question 29

sarq

Answer 29

Dest = Dest&raquo_space; Src ARITHMETIC

Question 30

shrq

Answer 30

Dest = Dest&raquo_space; Src LOGICAL

Question 31

xorq

Answer 31

Dest = Dest ^ Src

Question 32

andq

Answer 32

Dest = Dest & Src

Question 33

orq

Answer 33

Dest = Dest | Src

Question 34

incq

Answer 34

Dest = Dest + 1

Question 35

decq

Answer 35

Dest = Dest -1

Question 36

negq

Answer 36

Dest = -Dest

Question 37

notq

Answer 37

Dest = ~Dest

Question 38

Difference between neg and not

Answer 38

NEG changes -1 to 1 because it reverses all the bits and adds 1
NOT changes -1 to 0 because it reverses all the bits only

Question 39

What is a stack

Answer 39

Data structure where values can be added or deleted according to “last-in, first out” rule

Question 40

Register to hold location of runtime stack

Answer 40

%rsp

Question 41

Register to hold location of current code
control (instruction) point

Answer 41

%rip

Question 42

CF

Answer 42

Carry Flag (for unsigned)
Set if carry out from most significant bit(unsigned overflow)

Question 43

ZF

Answer 43

Zero flag
Set if t == 0

Question 44

SF

Answer 44

Sign flag (for signed)
Set if t < 0 (as signed)

Question 45

OF

Answer 45

Overflow flag(for signed)
Set if two’s complement overflow

Question 46

cmpq b,a

Answer 46

Is like computing a - b without setting destination

Question 47

ZF in compare

Answer 47

Set if a == b

Question 48

SF in compare

Answer 48

Set if (a-b) < 0 (as signed)

Question 49

testq b,a

Answer 49

Is like computing a&b without setting destination

Question 50

ZF in test

Answer 50

Set when a&b == 0

Question 51

SF in test

Answer 51

Set when a&b <0

Question 52

Translate to C
movl (%rdi, %rsi, 4), %eax

Answer 52

%rdi + 4*%rsi