01 introduction Flashcards by Gaara Coolest

Parts of the Machine Cycle

Fetch, Decode, and Execute

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Retrieve the instruction from the memory and increment the Program Counter

Fetch

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Decode the bit pattern in the Instruction Register

Decode

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Perform the instruction in the Instruction Register

Execute

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Decodes the bits to determine what should happen

CPU

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Is stored in memory as bunch of bits

Instruction

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Sequence of simple instructions

Executable program

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Where is the sequence stored?

Memory

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True or False
The CPU processes the simple instructions sequentialy.

True

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This is what the computer actually sees and deals with.

Machine Language

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Every command the computer sees is given as ______ or ________

a number or sequence of numbers

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The same as machine language, except the command numbers have been replaced by letter sequences which are easier to memorize

Assembly Language

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Maps human-readable mnemonics to machine instructions

Allows machine-level programming without writing in machine language

Assembly Language

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Makes programming easier

Allow you to describe the program in a more natural language

High-level Language

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Low-level language which provides the basic instructional interface to the computer processor

Is as close to the processor as you can get as a programmer

Assembly Language

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What are the direct controls that Assembly language gives

setting processor registers
accessing memory locations
interfacing with other hardware elements

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Reason NOT to use assembly

Development time: it takes much longer to develop in assembly
Maintainability: unstructured
Portability: platform-dependent

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Reasons to use assembly

To understand how CPUs and compilers work
Developing compilers, debuggers and other development tools
Hardware drivers, system code and low-level tasks such as bootloaders
embedded systems
Reverse Engineering
Address critical performance issues (Optimizing for speed or space)
Creating/fighting malware
writing low-level programs helps programmers improve algorithm development skills by practicing with a language that requires more thought and more attention to detail.

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Devices connected to the bus

Input and Output (I/O devices)

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A collection of the computer’s electrical lines where signals pass through

bus

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The bus is typically designed to transfer fixed-sized chunks of bytes known as _____

words

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The computer’s processor

Engine that interprets (or executes) instructions stored in main memory

Central Processing Unit (CPU)

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Includes the Arithmetic and Logic Unit and CPU Registers

CPU chip

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A logic circuit in the CPU that is responsible for performing mathematical and logical operations

Arithmetic and Logic Unit (ALU)

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A set of flip-flops treated as a single unit

A digital logic circuit capable of storing a single bit

Flip-flop

Temporary storage device that holds both a program and the data it manipulates while the processor is executing the program

Main memory

Size in bits and bytes of the following: 1) Byte 2) Word 3) Double-word 4) Quadword 5) Double quadword

bits bytes 8 1 16 2 32 4 64 8 128 16

A temporary storage or working location built into the CPU itself (separate from memory) Computations are typically performed by the CPU using this

General Purpose Registers (GPR)

Used to point to the current top of the stack

Stack pointer register (RSP)

Used as a base pointer during function calls

Base pointer register (RBP)

Used by the CPU to point to the next instruction to be executed

Instruction pointer register (RIP)

Used for status and CPU control information Updated by the CPU after each instruction and not directly accessible by programs Stores status information about the instruction that was just executed

Flag register (rFlags)

Used to indicate if the previous operation resulted in a carry

Carry (CF)

Used to indicate of the last byte has an even number of 1's

Parity (PF)

Used to support Binary Coded Decimal operations

Adjust (AF)

Used to indicate if the result of the previous operation resulted in a 1 in the most significant bit (indicating negative in the context of signed data)

Sign (SF)

Used to specify the direction (increment or decrement for some string operations)

Direction (DF)

Used to indicate if the previous operation resulted in an overflow

Overflow (OF)

Can be viewed as a series of bytes Each memory address holds one byte of information

Main memory

Least Significant Byte (LSB) is stored in the lowest memory address Most Significant Byte (MSB) is stored in the highest memory location

Little-Endian Architecture

General memory layout for a program

Memory layout

Where the machine language (1's an 0's representing the code) is stored

text (code)

Where the initialized data is stored

data

Where uninitialized declared variables are stored

BSS

Where dynamically allocated data will be stored (if requested)

heap

Starts in high memory and grows downward (used by subroutines)

stack

All initialized variables and constants are placed in this section

section .data (data section)

What is the format for variable definition?

example: SYS_EXIT equ 60 num1 db 21

Must start with a letter, followed by letters or numbers, including some special characters (such as the underscore)

Variable names

What do you call these: db 8-bit variable dw 16-bit variable dd 32-bit variable dq 64-bit variable

Directives

Substituted for their defined values during the assembly process Not assigned a memory location

Constant

What is the format for defining constants?

< varname> equ < initVal>

All uninitialized variables are placed in this section

section .bss (BSS section)

Includes some headers or labels that define the initial program entry point

section .text (text section)

with suffix h or x: 7Fh preceded with 0x or 0h: 0x7F

Hexadecimal

with suffix q or o: 777q preceded with 0q or 0o: 0q777

Octal

Used to start a program comment

semicolon (;)

Parts of assembly programming process or compilation system

Preprocessor Compiler Assembler Linker

Modifies the original C program according to directives that begin with '#' character

Preprocessing

Translates the output text file of the pre-processor into a text file which contains an assembly language program

Compilation

Translates compiler output to machine language instructions, generating a relocatable object program

Assembly

Handles the merging of the other necessary precompiled object files with the assembler's output, generating an executable file

Linking

Parts of Assembly Tool Chain

Assembler Linker Loader Debugger

Program that will read an assembly language input file and convert the code into a machine language binary file Comments are removed, and the variable names and labels are converted into appropriate addresses Optionally capable of creating a list file which shows the line number, the relative address, the machine language version of the instruction, and the original source line

Assembler

What is the NASM assembler command?

nasm -felf64 < asmFile>.asm

Combines one or more object files into a single executable file Any routines from user or system libraries are included as necessary

Linker

What is the GNU Linker command?

ld [-o < execFileName>] < objFile>.o

Part of the operating system that will load the program from secondary storage into primary storage (main memory) Implicitly invoked by typing the program name

Loader ./< execFileName>

Used to control execution of a program This allows for testing and debugging activities to be performed

Debugger gdb < execFileName>

GDB command to view the list of functions

info functions

GDB command to disassemble functions

disas < function name>

GDB command lets you swtich to intel syntax

set disassembly-flavor intel

GDB command to run the executable file in gdb

r [< command line arguments>]

GDB command to set a breakpoint

b*< function name>[< +offset>]

GDB command to inspect registers

info registers or i r

GDB command to execute the next instruction

GDB command to inspect specific registers

info registers < register name> or i r < register name>

GDB command to continue until next breakpoint

GDB command to examine memory location

x/< n>< f>< u> &< variable> n = number of locations f = format (dec, hex, char, str, float) u = unit size (byte, halfword, word, giant)