Download COS 318: Operating Systems Overview Kai Li and Andy Bavier

COS 318: Operating Systems
Overview
Kai Li and Andy Bavier
Computer Science Department
Princeton University
http://www.cs.princeton.edu/courses/archive/fall13/cos318/
Logistics
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Precepts:
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Design review:
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Sun 9/29 at 11:55pm
Reminder:
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Mon 9/23: 11am- - 7:40pm, 010 Friends center
Project 1 due:
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Tue: 7:30pm-8:30pm, 105 CS building
Subscribe to the cos318 mailing list!
To do:
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Lab partner? Enrollment?
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Who am I?
A builder: practical, hands-on
u  A philosopher?
u  Search for beauty J
u  Operating systems spans the spectrum
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Abstract
Simple, powerful
ideas
Concrete
Making things
work
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Today
Overview of OS structure
u  Overview of OS components
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Hardware of A Typical Computer
CPU
Memory
...
CPU
Chipset
I/O bus
ROM
Network
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Computing machinery
Analytical Engine (~1850) Charles Babbage
ENIAC (~1946) Eckert & Mauchly, UPenn
Johnniac (~1953) von Neumann, IAS
A Typical Computer System
CPU
..
.
Memory
Application
CPU
Operating System
BIOS
ROM
OS
Apps
Data
Network
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Hardware Interrupts
Raised by external events
u  Interrupt handler is in the
kernel
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Switch to another process
l  Overlap I/O with CPU
l  …
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Eventually resume the
interrupted process
0:
1:
…
Interrupt
handler
i:
i+1:
…
N:
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Typical Unix OS Structure
Application
Libraries
User level
Kernel level
Portable OS Layer
Machine-dependent layer
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Typical Unix OS Structure
Application
User function calls
written by programmers and
compiled by programmers.
Libraries
Portable OS Layer
Machine-dependent layer
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Typical Unix OS Structure
Application
Libraries
•  Written by elves
•  Objects pre-compiled
•  Defined in headers
•  Input to linker
•  Invoked like functions
•  May be “resolved”
when program is loaded
Portable OS Layer
Machine-dependent layer
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Elves
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Pipeline of Creating An Executable File
foo.c
gcc
foo.s
as
foo.o
bar.c
gcc
bar.s
as
bar.o
libc.a
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ld
a.out
…
gcc can compile, assemble, and link together
Compiler (part of gcc) compiles a program into assembly
Assembler compiles assembly code into relocatable object file
Linker links object files into an executable
For more information:
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Read man page of elf, ld, and nm
Read the document of ELF
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Execution (Run An Application)
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On Unix, “loader” does the job
Read an executable file
l  Layout the code, data, heap and stack
l  Dynamically link to shared libraries
l  Prepare for the OS kernel to run the application
l  E.g., on Linux, “man ld-linux”
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*.o, *.a
ld
a.out
loader
Application
Shared
library
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What’s An Application?
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Four segments
Code/Text – instructions
l  Data – initialized global
variables
l  Stack
l  Heap
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Why?
Separate code and data
l  Stack and heap go
towards each other
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Stack
2n -1
Heap
Initialized data
Code
0
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Responsibilities
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Stack
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Heap
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Layout by compiler
Allocate/deallocate by process creation (fork) and termination
Names are relative to stack pointer and entirely local
Linker and loader say the starting address
Allocate/deallocate by library calls such as malloc() and free()
Application program use the library calls to manage
Global data/code
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Compiler allocate statically
Compiler emit names and symbolic references
Linker translate references and relocate addresses
Loader finally lay them out in memory
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Typical Unix OS Structure
Application
Libraries
Portable OS Layer
“Guts” of system calls
Machine-dependent layer
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OS Service Examples
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Examples that are not provided at user level
System calls: file open, close, read and write
l  Control the CPU so that users won’t get stuck by
running
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•  while ( 1 ) ;
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Protection:
•  Keep user programs from crashing OS
•  Keep user programs from crashing each other
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System calls are typically traps or exceptions
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System calls are implemented in the kernel
When finishing the service, a system returns to the user code
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Typical Unix OS Structure
Application
Libraries
Portable OS Layer
•  Bootstrap
•  System initialization
•  Interrupt and exception
•  I/O device driver
•  Memory management
•  Mode switching
•  Processor management
Machine-dependent layer
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Software “Onion” Layers
Applications
Libraries
User and Kernel
boundary
OS Services
Device
Kernel
HW
Driver
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Today
Overview of OS structure
u  Overview of OS components
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Processor Management
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Goals
Overlap between I/O and
computation
l  Time sharing
l  Multiple CPU allocations
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CPU
I/O
CPU
I/O
CPU
CPU
Issues
Do not waste CPU resources
l  Synchronization and mutual
exclusion
l  Fairness and deadlock free
l 
CPU
CPU
I/O
CPU
CPU
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Memory Management
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Goals
Support programs to run
l  Allocation and management
l  Transfers from and to
secondary storage
Register: 1x
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Issues
Efficiency & convenience
l  Fairness
l  Protection
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L1 cache: 2-4x
L2 cache: ~10x
L3 cache: ~50x
DRAM: ~200-500x
Disks: ~30M x
Archive storage: >1000M x
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I/O Device Management
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Goals
Interactions between
devices and applications
l  Ability to plug in new
devices
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Issues
Efficiency
l  Fairness
l  Protection and sharing
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User 1
...
User n
Library support
Driver
Driver
I/O
device
I/O
device
...
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File System
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Goals:
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User 1
...
User n
A typical file system
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Manage disk blocks
Map between files and disk
blocks
Open a file with
authentication
Read/write data in files
Close a file
File system services
File
...
File
Issues
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Reliability
Safety
Efficiency
Manageability
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Window Systems
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Goals
Interacting with a user
l  Interfaces to examine and
manage apps and the system
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u 
Issues
Direct inputs from keyboard and
mouse
l  Display output from applications
and systems
l  Division of labor
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•  All in the kernel (Windows)
•  All at user level
•  Split between user and kernel (Unix)
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Bootstrap
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Power up a computer
Processor reset
l  Set to known state
l  Jump to ROM code (BIOS is
in ROM)
Load in the boot loader from
stable storage
Jump to the boot loader
Load the rest of the operating
system
Initialize and run
Question: Can BIOS be on disk?
Boot
loader
Boot
loader
OS
sector 1
OS
sector 2
.
.
.
OS
sector n
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Ways to Develop An Operating System
A hardware simulator
u  A virtual machine
u  A good kernel debugger
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When OS crashes, always goes to the debugger
l  Debugging over the network
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Smart people
1972
1998
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Summary
Interrupts
u  User level vs. kernel level
u  OS services
u 
Processor
l  Memory
l  I/O devices
l  File system
l  Window system
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Booting the OS
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