Assembly Exam 2 Terms & Definitions

reserve storage space for variables

RESB (reserve bytes)

in .bss

define storage space for constants

DB (define bytes)

in .data

DB

define byte

1 byte

DW

define word

2 bytes

DD

define doubleWord

4 bytes

DQ

define quadWord

8 bytes

DT

define ten bytes

10 bytes

TIMES

used to define multiple of the same variable (arrays)

: times 9 db ''

RESB

reserve byte

1 byte

RESW

reserve word

2 bytes

RESD

reserve doubleword

4 bytes

RESQ

reserve quadword

8 bytes

REST

reserve ten bytes

10 bytes

EQU

makes macros (text substitution)

can have expressions (AREA equ length * width)

define directive

%define

basically a function, can pass it parameters

%define ()

EX:

%define syscall(id) mov eax, id

makes a "function" called syscall which moves the passed parameter into eax

INC

increment, increments number by one and doesnt flip overflow flag

DEC

decrements number by 1 and doesnt flip overflow flag

ADD

adds 2 values and stores them in the first operand

SUB

subtracts 2 values and stores them in the first operand

MUL

unsigned multiplication

IMUL

signed multiplication

multiplying 2 bytes

AL * 8 bit source = AH AL

MUL <8 bit source> multiplies the source by AL and stores the result in AH(high order bits) and AL (low order bits)

multiplying 2 words

AX * 16 bit source = DX AX

MUL <16 bit source> multiplies the source by AX and stores the result in DX(high order bits) and AX(low order bits)

multiplying 2 doublewords

EAX * 32 bit source = EDX EAX

MUL <32 bit source> multiplies the source by EAX and stores the result in EDX(high order bits) and EAX(low order bits)

DIV

unsigned division

IDIV

signed division

dividing 2 bytes

AX(16 bit dividend) / 8 bit divider = Q: AL R:AH

DIV <8 bit divider> divides AX by the source and stores the result in AL and the remainder in AH

dividing word

DX(high) AX(low)(32 bit dividend) / 16 bit divider = Q: AX R:DX

DIV <16 bit divider> divides DX and AX by the source and stores the result in AX and the remainder in DX

dividing double word

EDX(high) EAX(low)(64 bit dividend) / 32 bit divider = Q: EAX R:EDX

DIV <32 bit divider> divides DX and AX by the source and stores the result in EAX and the remainder in EDX

AND

AND ,

if both bits are 1, result is 1

operand 1 can be in register or in memory

operand 2 can be register, memory, or immediate

cannot do memory to memory

use AND to clear some bits but not others

you can take whatever bits you want to flip and AND it with an immediate of that ammount

use AND to check if number is odd or even

AND register with one, will flip zero flag if even

OR

returns 1 if either or both bits are 1

set certain bit with OR

you can set certain bits in a register by ORing them with a value that has a 1 in the slot you want to set to 1

EX 0FH will set the last 4 bits to 1

XOR

will set bits to 1 if both bits are different

set register to zero with XOR

XOR a register with itsself to set it to zero

EX: XOR EAX, EAX

TEST

same as AND but doesnt change the first value

use TEST to determine if even or odd

same as and

TEST , 1

JZ (even)

NOT

reverses bits in operand

NOT

Unconditional jump

Jumps no matter what

JMP

Conditional jump

jumps when something is true. uses EFLAGS register

J

ex: JZ means jump zero (jump if the zero flag is true)

CMP

compare

subtracts second operand from first but only changes EFLAGS

EX:

CMP EAX, EBX

JE is_equal if EAX = EBX, jump

use unconditional jump to form loop

you can have an unconditional jump to form a loop then use another jump to leave the loop when a condition is met

JE

jump equal, checks zero flag

JZ

jump zero, checks zero flag

JG

jump greater

checks overflow flag, sign flag, zero flag

JNLE

jump not less than or equal to

checks overflow flag, sign flag, zero flag

JGE

jump greater than or equal to

checks overflow flag, sign flag

JNL

jump not less

checks overflow flag, sign flag

JL

jump less

checks overflow flag, sign flag

JLE

jump less than or equal to

checks overflow flag, sign flag, zero flag

JA

jump above

checks carry flag, zero flag

JNBE

jump not below/equal

checks carry flag, zero flag

JB

jump below

checks carry flag

JNAE

jump not above/equal to

checks carry flag

JBE

jump below/equal

checks auxiliary carry flag, carry flag

JNA

jump not above

checks auxiliary carry flag, carry flag

LOOP instruction

LOOP

assumes ECX contains loop count

FOR loop tips

to make a for loop in assembly, change it to a while loop, then implement it