CSE 2421 Final Exam Review

A 64 bit register the CPU uses to put addresses for memory accesses on the address bus

Memory Address Register (MAR)

A 64 bit register which the CPU uses to put data on the data bus for writes, or to retrieve data from the data bus for reads from memory

Memory Data Register (MDR)

A collection of intertwined hardware and systems software that must cooperate in order to achieve the ultimate goal of running application programs

System

A directive needed by the linker for symbol resolution, followed by the name of the function

.globl

A logic element that does not store state, the output depends only on the current input

Combinatorial Logic Element

A logic element that is capable of storing state, has memory and can store prior states

Sequential (clocked) Logic Element

A method of optimizing a processor by predicting what instructions will be computed next

Speculative execution

A requirement of the x86-64 ABI, should be satisfied prior to any call.

stack alignment

A value too large for representation

overflow

A value too small to be represented, not as serious because it's comparable to a loss of precision, which can be approximated by zero.

underflow

Address displacement syntax

displacement (src, index, scale)

Adds first argument to second argument

add

Allows a name to be assigned to the assembly language source code file

.file

Arithmic logic unit, sets the condition flags

ALU

.byte data size

1 byte (byte)

Changes or sets the current section to the data section

.data

Changes or sets the current section to the text (or code) section

.text

changing a given bit pattern to a related one

Data Transformation

Computes address math, does not touch memory or affect condition codes

lea

Computes bitwise NOT

not

Computes bitwise OR

or

Computes bitwise XOR

xor

Computes biwise AND

and

Data called by the program that is likely to be called again, EX: indexes in for loops

Temporal Locality

Do displacements require dollar signs?

No

Does the stack grow towards higher or lower addresses?

Lower

Dynamic Ram, slow memory dense needs constant refresh

DRAM

faster than addq one

inc

faster than subq one

dec

Holds static variables in the file scope

Heap

How do you access a member of a structure?

use leaq to find the address, imulq may be needed

How do you access an array that is a member of a structure?

use leaq to find the address, displacement is needed for index

How do you allocate space on the stack?

Subtract from rsp

How do you call malloc in assembler?

put size in rdi and call malloc

How do you go to the value that a memory expression points to in x86-64 ASM?

Use () (this is a memory reference)

How does call figure out what the return address is?

call pushes the return address of the next call instruction

How does lea compute addresses?

lea uses displacement(base,index,scale) formula

How does someone allocate space on the stack?

Move the stack pointer (subq $40, %rsp)

How many registers are in a 64 bit architecture?

16

If a particular piece of data is accessed, nearby addresses are also likely to be accessed. Ex: arrays

Spatial Locality

If we don't ______, we don't know what.

Measure

If we don't ______, we don't know where.

Profile

In what order are multidimensional (nested) arrays created?

Row major order

increment a register

inc

Keeps track of what instruction being executed

Program Counter (PC)

Keyboards, mouse, etc

I/O Devices

Larger memory sizes take more time to access and vice versa.

Memory Hierarchy

.long data size

4 bytes (.long)

Memory that can maintain its value without power

Non-Volatile Memory

Moves a value onto the stack, subtracts quad value to rsp

push

moving data from one system component to another, or within a given component

Data Movement

movq %rsp, %rbp; pop %rbp

leave

Needed by the linker to identify the label as one associated with a function, as opposed to data

.type

Needed by the linker to identify the size of the text for the program

.size

older version of call, not really all that useful because it's slower than other instructions that do the same thing

enter

opcode conditional move

cmov

opcode for unconditional jump

jmp

opcode to jump when equal

je

opcode to jump when not equal

jne

opcode to move and sign extend as it moves

movs

opcode to move and zero extend as it moves

movz

opcode to move data from one register to another

mov

opcode to shift in the sign bit

sar

opcode to shift left

shl

opcode to shift right, add in 0's

shr

Parameter order for registers

rdi, rsi, rdx, rcx, r8, r9

.quad data size

8 bytes (q)

Registers that push values to the stack to be used later

callee-saved register

Removes a value from the stack, adds quad value to rsp

pop

Scratch pad register that will get trashed at function calls

caller-saved register

Sets the flags for SF, ZF, and PF, discards result of bitwise AND

test

Sets the flags, subtracts first argument from second argument

cmp

Similar to preprocessor directives in C, provides information helpful to execution of the file

Assembler Directives

Specifies that the characters enclosed in quotation marks are to be stored in memory, terminated by a null byte

.string

Specifies that the following data is to be placed in the read only memory portion of the executable

.rodata

Static ram, fast, memory intensive

SRAM

Storage held within processor

Cache

storing digital data in a form which balances considerations of cost, reliability, and access speed

Data Storage

Subtracts first argument from second argument

sub

Temp storage for applications being exceuted. SRAM and DRAM

Main Memory

The abstraction of hardware, what our software must comply with

Instruction Set Architecture (ISA)

The execution of a computer program using one or more threads

Process

The style used for floating point math

IEEE 754

This file format combines .o, .out, and .so into a single linking file

Executable Linkage Format (ELF)

This is used by the OS to manage each process in the system

Process Control Block (PCB)

This kind of memory storage is used for the stack, does not allow for direct memory access.

LIFO storage

This makes the specified section the current section

.section (this is important!!)

This register keeps track of the current instruction

Instruction Register (IR)

This storage location has no direct memory access

Stack

Transfers control to a function, uses the parameters in the parameter registers to execute the function as needed

call

Transfers control to the return address located on the stack. This address is usually placed on the stack by a call instruction. This transfers control to the calling function at the instruction following the call.

ret

transfers data between system components or within system components

Bus

This opcode is used for scales not in 1, 2, 4, or 8 bytes.

imul

We have a struct s with members:

{

char name[23];

int age;

int stuff[2];

double height;

int friends;

}

What's the size of the struct?

56 bytes

What are the stack housekeeping calls after a function body is executed?

leave, ret

What are the stack housekeeping calls before a function body is executed?

pushq %rbp, followed by movq rsp, rbp. this makes our stack frame

What coding style is pipeline friendly?

branchless code

What do you have to do with rax before using printf?

set rax to 0 because of floating points, printf

What do you have to do with rax before using scanf?

set rax to 0 because of floating points, scanf

What does the CF flag do?

carry flag. for carrying bits