Recall: What is an operating system? Very Brief History of OS. Very Brief History of OS. CS162 Operating Systems and Systems Programming Lecture 2

Transcription

1 Recall: What is a operatig system? CS6 Operatig Systems ad Systems Programmig Lecture Itroductio to esses Special layer of software that provides applicatio software access to hardware resources Coveiet abstractio of complex hardware devices Protected access to shared resources Security ad autheticatio Commuicatio amogst logical etities Jauary d, 08 Profs. Athoy D. Joseph ad Joatha Raga-Kelley appl applappl Hardware Lec. Several Distict Phases: Very Brief History of Very Brief History of Several Distict Phases: Hardware Expesive, Humas C» Eiac, Multics I thik there is a world market for maybe five computers. Thomas Watso, chairma of IBM, 943 Lec.3 Lec.4

2 Very Brief History of Very Brief History of Several Distict Phases: Several Distict Phases: Hardware Expesive, Humas C Hardware Expesive, Humas C» Eiac, Multics» Eiac, Multics Hardware Cer, Humas Expesive» s, Workstatios, Rise of GUIs Thomas Watso was ofte called the worlds greatest salesma by the time of his death i 956 //8 Joseph ad Raga-Kelley CS6 UCB Sprig 08 Lec.5 //8 Joseph ad Raga-Kelley CS6 UCB Sprig 08 Very Brief History of Lec.6 Very Brief History of Several Distict Phases: Several Distict Phases: Hardware Expesive, Humas C Hardware Expesive, Humas C» Eiac, Multics» Eiac, Multics Hardware Cer, Humas Expesive Hardware Cer, Humas Expesive» s, Workstatios, Rise of GUIs» s, Workstatios, Rise of GUIs Hardware Really C, Humas Really Expesive Hardware Really C, Humas Really Expesive» Ubiquitous devices, Widespread etworkig» Ubiquitous devices, Widespread etworkig Rapid chage i hardware leads to chagig Batch Þ Multiprogrammig Þ Timesharig Þ Graphical UI Þ Ubiquitous Devices Gradual migratio of features ito smaller machies Today Small : 00K lies / Large: 0M lies (5M browser!) people-years //8 Joseph ad Raga-Kelley CS6 UCB Sprig 08 Lec.7 //8 Joseph ad Raga-Kelley CS6 UCB Sprig 08 Lec.8

3 Migratio of Cocepts ad Features Archaeology Because of the cost of developig a from scratch, most moder es have a log lieage: Multics à AT&T Uix à BSD Uix à Ultrix, Su, NetBSD, Mach (micro-kerel) + BSD à NextStep à XNU à Apple X, iphoe i, Watch MINIX à Liux à Adroid, Chrome, RedHat, Ubutu, Fedora, Debia, Suse, CP/M à QD à MS-D à Widows 3. à NT à 95 à 98 à 000 à XP à Vista à 7 à 8 à 0 à Xbox Oe à Joseph ad Raga-Kelley CS6 UCB Sprig 08 Lec.9 //8 Joseph ad Raga-Kelley CS6 UCB Sprig 08 Thread compiler editor Programs execute i a address space that is distict from the memory space of the physical machie istructios ess foo.c A istace of a executig program is a process cosistig of a address space ad oe or more threads of cotrol Dual mode operatio / Protectio Oly the system has the ability to access certai resources The ad the hardware are protected from user programs ad user programs are isolated from oe aother by cotrollig the traslatio from program virtual addresses to machie physical addresses Joseph ad Raga-Kelley CS6 UCB Sprig 08 Lec. data data a.out Load istructio ad data segmets of executable file ito memory Create ad Trasfer cotrol to program Provide services to program While protectig ad program //8 Memory Address space (with traslatio) it mai() {; } 0xFFF Executable Program Source Sigle uique executio cotext: fully describes program state Program Couter, Registers, Executio Flags, Stack //8 Lec.0 Bottom Lie: Ru Programs Today: Four Fudametal Cocepts Load & Execute //8 istructios 0x000 : Joseph ad Raga-Kelley CS6 UCB Sprig 08 registers essor Lec.

4 Recall (6C): Istructio Fetch/De/Execute The istructio cycle essor ext Memory : Istructio fetch istructio De de Registers Execute ALU data Lec.3 Recall (6C): What happes durig program executio? R0 R3 F0 F30 Fetch Exec Executio sequece: Fetch Istructio at De Execute (possibly usig registers) Write results to registers/mem = Next Istructio() Repeat Addr 3 - Data Data0 Ist37 Ist36 Ist5 Ist4 Ist3 Ist Ist Ist0 Addr 0 Lec.4 First Cocept: Thread of Cotrol Secod Cocept: Program s Address Space Certai registers hold the cotext of thread Stack poiter holds the address of the top of» Other covetios: Frame poiter, Heap poiter, Data May be defied by the istructio set architecture or by compiler covetios Thread: Sigle uique executio cotext Program Couter, Registers, Executio Flags, Stack A thread is executig o a processor whe it is residet i the processor registers. register holds the address of executig istructio i the thread Registers hold the root state of the thread. Address space Þ the set of accessible addresses + state associated with them: For a 3-bit processor there are 3 = 4 billio addresses What happes whe you read or write to a address? Perhaps othig Perhaps acts like regular memory Perhaps igores writes Perhaps causes I/O operatio» (Memory-mapped I/O) Perhaps causes exceptio (fault) 0xFFF 0x000 The rest is i memory Lec.5 Lec.6

5 : SP: Address Space: I a Picture essor registers istructio Code Segmet What s i the segmet? Static data segmet? What s i the Stack Segmet? How is it allocated? How big is it? What s i the Heap Segmet? How is it allocated? How big? 0xFFF 0x000 Multiprogrammig - Multiple Threads of Cotrol Lec.7 Lec.8 Admiistrivia: Gettig started Start homework 0 immediately Þ Due ext Moday (/9)! cs6-xx accout, Github accout, registratio survey Vagrat ad VirtualBox VM eviromet for the course» Cosistet, maaged eviromet o your machie Get familiar with all the cs6 tools, submit to autograder via git Homework slip days: You have 3 slip days THIS Friday (/6) is early drop day! Very hard to drop afterwards Should be goig to sectio already! Group sig up form will be out after drop deadlie Work o fidig groups ASAP: 4 people i a group! Try to atted either same sectio or sectios by same TA Lec.9 How ca we give the illusio of multiple processors? vcpu vcpu Shared Memory vcpu3 Assume a sigle processor. How do we provide the illusio of multiple processors? Multiplex i time! Each virtual CPU eeds a structure to hold: Program Couter (), Stack Poiter (SP) Registers (Iteger, Floatig poit, others?) How switch from oe virtual CPU to the ext? Save, SP, ad registers i curret state block Load, SP, ad registers from ew state block What triggers switch? Timer, volutary yield, I/O, other thigs vcpu vcpu vcpu3 vcpu vcpu Time Lec.0

6 The Basic Problem of Cocurrecy The basic problem of cocurrecy ivolves resources: Hardware: sigle CPU, sigle DRAM, sigle I/O devices Multiprogrammig API: processes thik they have exclusive access to shared resources has to coordiate all activity Multiple processes, I/O iterrupts, How ca it keep all these thigs straight? Basic Idea: Use Virtual Machie abstractio Simple machie abstractio for processes Multiplex these abstract machies Dijkstra did this for the THE system Few thousad lies vs millio lies i 360 (K bugs) Properties of this simple multiprogrammig techique All virtual CPUs share same o-cpu resources I/O devices the same Memory the same Cosequece of sharig: Each thread ca access the data of every other thread (good for sharig, bad for protectio) Threads ca share istructios (good for sharig, bad for protectio) Ca threads overwrite fuctios? This (uprotected) model is commo i: Embedded applicatios Widows 3./Early Macitosh (switch oly with yield) Widows 95 ME (switch with both yield ad timer) Lec. Lec. Protectio Operatig System must protect itself from user programs Reliability: compromisig the operatig system geerally causes it to crash Security: limit the scope of what processes ca do Privacy: limit each process to the data it is permitted to access Fairess: each should be limited to its appropriate share of system resources (CPU time, memory, I/O, etc) It must protect User programs from oe aother Primary Mechaism: limit the traslatio from program address space to physical memory space Ca oly touch what is mapped ito process address space Additioal Mechaisms: Privileged istructios, i/out istructios, special registers syscall processig, subsystem implemetatio» (e.g., file access rights, etc) Lec.3 Third Cocept: ess ess: executio eviromet with Restricted Rights Address Space with Oe or More Threads Ows memory (address space) Ows file descriptors, file system cotext, Ecapsulate oe or more threads sharig process resources Why processes? Protected from each other! Protected from them esses provides memory protectio Threads more efficiet tha processes (later) Fudametal tradeoff betwee protectio ad efficiecy Commuicatio easier withi a process Commuicatio harder betwee processes Applicatio istace cosists of oe or more processes Lec.4

7 Sigle ad Multithreaded esses Threads ecapsulate cocurrecy: Active compoet Address spaces ecapsulate protectio: Passive part Keeps buggy program from trashig the system Why have multiple threads per address space? Fourth Cocept: Dual Mode Operatio Hardware provides at least two modes: Kerel mode (or supervisor or protected ) User mode: Normal programs executed What is eeded i the hardware to support dual mode operatio? A bit of state (user/system mode bit) Certai operatios / actios oly permitted i system/kerel mode» I user mode they fail or trap User à Kerel trasitio sets system mode AND saves the user» Operatig system carefully puts aside user state the performs the ecessary operatios Kerel à User trasitio clears system mode AND restores appropriate user» retur-from-iterrupt Lec.5 Lec.6 User/Kerel (Privileged) Mode User Mode syscall exec iterrupt exceptio rt rfi Kerel Mode exit Admiistrivia (Cot d) Athoy s OH: Wedesdays -3PM 465F Soda startig /3 Joatha s OH : Modays -:45PM 55 Soda startig /9 Avoid private Piazza posts others have same questio Three Free Olie Textbooks: Click o Resources lik for a list of Olie Textbooks Ca read O'Reilly books for free as log as o campus or VPN» Oe book o Git, two books o C Limited HW access Full HW access Webcast: (CalNet sig i) Webcast is *NOT* a replacemet for comig to class! Lec.7 Lec.8

8 Simple Protectio: ad (B&B) 5 mi break 000 Program address >= < FFFF Lec Program address Simple Protectio: ad (B&B) 00 Addresses traslated whe program is loaded Requires relocatig loader Still protects ad isolates program No additio o address path >= < FFFF Lec.3 Aother idea: Address Space Traslatio Program operates i a address space that is distict from the physical memory space of the machie essor virtual address traslator physical address Memory 0x000 0xFFF Lec.3

9 A simple address traslatio with ad Addresses traslated o-the-fly Tyig it together: Simple B&B: loads process 000 Program address 000 Address 000 < 000 Ca the program touch? Ca it touch other programs? FFFF u xxxx xxxx xxxx FFFF FFFF Lec.33 Lec.34 Simple B&B: gets ready to execute process Simple B&B: User Code Ruig RTU FFFF FFFF 000 Privileged Ist: set special registers RTU u FF FFFF How does kerel switch betwee processes? First questio: How to retur to system? u xxxx FF FFFF Lec.35 Lec.36

10 3 types of Mode Trasfer Syscall ess requests a system service, e.g., exit Like a fuctio call, but outside the process Does ot have the address of the system fuctio to call Like a Remote edure Call (R) for later Marshall the syscall id ad args i registers ad exec syscall Iterrupt Exteral asychroous evet triggers cotext switch e. g., Timer, I/O device Idepedet of user process Trap or Exceptio Iteral sychroous evet i process triggers cotext switch e.g., Protectio violatio (segmetatio fault), Divide by zero, All 3 are a UNPROGRAMMED CONTROL TRANSFER Where does it go? How do we get the system target address of the uprogrammed cotrol trasfer? Lec.37 Lec.38 Iterrupt Vector Simple B&B: User => Kerel iterrupt umber (i) Address ad properties of each iterrupt hadler Where else do you see this dispatch patter? itrphadler_i () {. } u How to retur to system? 00 xxxx FF FFFF FFFF Lec.39 Lec.40

11 Simple B&B: Iterrupt Simple B&B: Switch User ess RTU How to save registers ad set up system? u ItrpVector[i] 00FF FFFF FFFF FF How to save registers ad set up system? u D0 FFFF FFFF Lec.4 Lec FF How to save registers ad set up system? u Simple B&B: resume xxxx xxxx D0 FFFF RTU FFFF Lec.43 Thread Coclusio: Four fudametal cocepts Sigle uique executio cotext Program Couter, Registers, Executio Flags, Stack Address Space with Traslatio Programs execute i a address space that is distict from the memory space of the physical machie ess A istace of a executig program is a process cosistig of a address space ad oe or more threads of cotrol Dual Mode operatio/protectio Oly the system has the ability to access certai resources The ad the hardware are protected from user programs ad user programs are isolated from oe aother by cotrollig the traslatio from program virtual addresses to machie physical addresses Lec.44