CHAPTER 3: Instructions

Question 1

instruction set

Answer 1

vocabulary of commands understood by a given architecture

Question 2

stored-program concept

Answer 2

idea that instructions and data of many types can be stored in memory as numbers and thus be easy to change, leading to the stored-program computer

Question 3

word

Answer 3

natural unit of access in a computer, usually a group of 32 bits

Question 4

doubleword

Answer 4

another natural unit of access in a computer, usually a group of 64 bits; corresponds to the size of a register in the LEGv8 architecture

Question 5

Design Principle 2: Smaller is faster

Answer 5

• a very large number of registers may increase the clock cycle time simply because it takes electronic signals longer when they must travel farther

Question 6

data transfer instruction

Answer 6

command that moves data between memory and registers

Question 7

address

Answer 7

value used to delineate the location of a specific data element within a memory array

Question 8

data transfer instruction

Answer 8

command that moves data between memory and registers

Question 9

address

Answer 9

value used to delineate the location of a specific data element within a memory array

Question 10

memory

Answer 10

is just a large, single-dimensional array, with the address acting as the index to that array, starting at 0

Question 11

alignment restriction

Answer 11

requirement that data be aligned in memory on natural boundaries

Question 12

binary number

Answer 12

Question 13

least significant bit

Answer 13

rightmost bit in an LEGv8 doubleword

Question 14

most significant bit

Answer 14

leftmost bit in an LEGv8 doubleword

Question 15

two’s complement

Answer 15

signed number representation where a leading 0 indicates a positive number and a leading 1 indicates a negative number. The complement of a value is obtained by complementing each bit (0 → 1 or 1 → 0), and then adding one to the result

Question 16

one’s complement

Answer 16

notation that represents the most negative value by 10 … 000two and the most positive value by 01 … 11two, leaving an equal number of negatives and positives but ending up with two zeros, one positive (00 … 00two) and one negative (11 … 11two). The term is also used to mean the inversion of every bit in a pattern: 0 to 1 and 1 to 0

Question 17

biased notation

Answer 17

notation that represents the most negative value by 00 … 000two and the most positive value by 11 … 11two, with 0 typically having the value 10 … 00two, thereby biasing the number such that the number plus the bias has a non-negative representation

Question 18

instruction format

Answer 18

form of representation of an instruction composed of fields of binary numbers

Question 19

machine language

Answer 19

binary representation used for communication within a computer system

Question 20

hexadecimal

Answer 20

Numbers in base 16 that are easy to convert to binary

Question 21

opcode

Answer 21

field that denotes the operation and format of an instruction

Question 22

and

Answer 22

logical bit- by-bit operation with two operands that calculates a 1 only if there is a 1 in both operands

Question 23

mask

Answer 23

“conceals” some bits

Question 24

or

Answer 24

logical bit-by-bit operation with two operands that calculates a 1 if there is a 1 in either operand

Question 25

not

Answer 25

logical bit-by-bit operation with one operand that inverts the bits; that is, it replaces every 1 with a 0, and every 0 with a 1

Question 26

EOR (exclusive or)

Answer 26

logical bit-by-bit operation with two operands that calculates the exclusive OR of the two operands. That is, it calculates a 1 only if the values are different in the two operands

Question 27

conditional branch

Answer 27

instruction that tests a value and that allows for a subsequent transfer of control to a new address in the program based on the outcome of the test

Question 28

basic block

Answer 28

sequence of instructions without branches (except possibly at the end) and without branch targets or branch labels (except possibly at the beginning)

Question 29

branch address table (branch table)

Answer 29

table of addresses of alternative instruction sequences

Question 30

procedure

Answer 30

stored subroutine that performs a specific task based on the parameters with which it is provided

Question 31

branch-and-link instruction

Answer 31

instruction that branches to an address and simultaneously saves the address of the following instruction in a register (LR or X30 in LEGv8)

Question 32

return address

Answer 32

link to the calling site that allows a procedure to return to the proper address; in LEGv8 it is stored in register LR (X30)

Question 33

caller

Answer 33

program that instigates a procedure and provides the necessary parameter values

Question 34

callee

Answer 34

procedure that executes a series of stored instructions based on parameters provided by the caller and then returns control to the caller.

Question 35

program counter (PC)

Answer 35

register containing the address of the instruction in the program being executed.

Question 36

stack

Answer 36

data structure for spilling registers organized as a last-in- first-out queue

Question 37

stack pointer

Answer 37

value denoting the most recently allocated address in a stack that shows where registers should be spilled or where old register values can be found. In LEGv8, it is register SP

Question 38

push

Answer 38

add element to stack

Question 39

pop

Answer 39

remove element from stack

Question 40

global pointer

Answer 40

register that is reserved to point to the static area

Question 41

procedure frame (activation record)

Answer 41

segment of the stack containing a procedure's saved registers and local variables

Question 42

frame pointer

Answer 42

value denoting the location of the saved registers and local variables for a given procedure

Question 43

text segment

Answer 43

segment of a UNIX object file that contains the machine language code for routines in the source file

Question 44

pc-relative addressing

Answer 44

addressing regime in which the address is the sum of the program counter (PC) and a constant in the instruction

Question 45

addressing mode

Answer 45

one of several addressing regimes delimited by their varied use of operands and/or addresses

Question 46

data race

Answer 46

two memory accesses form a data race if they are from different threads to same location, at least one is a write, and they occur one after another

Question 47

assembly language

Answer 47

symbolic language that can be translated into binary machine language

Question 48

pseudoinstruction

Answer 48

common variation of assembly language instructions often treated as if it were an instruction in its own right

Question 49

symbol table

Answer 49

table that matches names of labels to the addresses of the memory words that instructions occupy

Question 50

linker (link editor)

Answer 50

systems program that combines independently assembled machine language programs and resolves all undefined labels into an executable file.

Question 51

executable file

Answer 51

functional program in the format of an object file that contains no unresolved references. It can contain symbol tables and debugging information. A "stripped executable" does not contain that information. Relocation information may be included for the loader

Question 52

loader

Answer 52

systems program that places an object program in main memory so that it is ready to execute

Question 53

dynamically linked libraries (DLL)

Answer 53

library routines that are linked to a program during execution

Question 54

java bytecode

Answer 54

instruction from an instruction set designed to interpret Java programs

Question 55

just in time compiler (JIT)

Answer 55

name commonly given to a compiler that operates at runtime, translating the interpreted code segments into the native code of the computer

Question 56

loop-unrolling

Answer 56

technique to get more performance from loops that access arrays, in which multiple copies of the loop body are made and instructions from different iterations are scheduled together.

Question 57

public

Answer 57

Java keyword that allows a method to be invoked by any other method

Question 58

protected

Answer 58

Java keyword that restricts invocation of a method to other methods in that package

Question 59

package

Answer 59

a directory that contains a group of related classes

Question 60

static method

Answer 60

method that applies to the whole class rather to an individual object. It is unrelated to static in C

Question 61

general purpose register (GPR)

Answer 61

register that can be used for addresses or for data with virtually any instruction

Question 62

fallacy: More powerful instructions mean higher performance

Answer 62

part of the power of the Intel x86 is the prefixes that can modify the execution of the following instruction

Question 63

fallacy: write in assembly language to obtain the highest performance

Answer 63

even if writing by hand resulted in faster code, the dangers of writing in assembly language are the protracted time spent coding and debugging, the loss in portability, and the difficulty of maintaining such code

Question 64

fallacy: the importance of commercial binary compatibility means successful instruction sets don't change

Answer 64

Question 65

pitfall: forgetting that sequential word or doubleword addresses in machines with byte addressing do not differ by one

Answer 65

assembly language programmer has toiled over errors made by assuming that the address of the next word or doubleword can be found by incrementing the address in a register by one instead of by the word or doubleword size in bytes.

Question 66

pitfall: using a pointer to an automatic variable outside its defining procedure

Answer 66

common mistake in dealing with pointers is to pass a result from a procedure that includes a pointer to an array that is local to that procedure