Introduction to System Programming

Transcription

1 Introduction to System Programming

2 Introduction to System Programming Why system programming? Basic operation of a computer system Summary Acknowledgement: slides based on the cs:app2e material 2

3 Why System Programming? I program everything in JavaScript (Python, Ruby, ). I don t need to know this stuff. 3

4 Why System Programming? Abstractions only partially reflect reality To be a good computer engineer you have to know that abstractions in computer science are only abstractions; the reality may look very different, especially in special cases To understand the limitations of these abstractions and write safe and efficient code you need to know computer architecture assembly programming system programming Programming, data structures, computer architecture, and system programming prepare you for more advanced classes in computer science & engineering operating systems, compilers, embedded systems, networks, data base systems, 4

5 Why System Programming? Graphics Programming AI, Machine Learning Theoretical CS Embedded Systems Database Systems Networking Compilers Operating Systems Programming Languages Computer Security System Programming Data Structures Programming Computer Architecture 5

6 Introduction to System Programming Why system programming? Basic operation of a computer system Summary 6

7 Hardware Organization General hardware organization Memory I/O processor I/O processor PU (*) PU PU disk NIC printer mouse kbd (*) PU = Processing Unit 7

8 From Batch To Parallel Processing 1940 s: special-purpose computers Z1, Colossus, ENIAC Programmable by rewiring the system early 1950 s: general-purpose computers EDVAC, bombe programs stored in memory CPU fetch-execute cycle single program, single user at a time 8

9 From Batch To Parallel Processing mid 1950 s: batch programming operator combines programs into batches of programs executing a batch meant executing the programs one by one results available after all jobs in the batch had completed resident monitor : a first primitive version of system software (OS) control card interpreter loader device drivers 9

10 From Batch To Parallel Processing mid 1950 s: batch programming (cont d) no protection: a faulty job reading too many cards, overwriting the resident monitor s memory, or entering an endless loop would affect the entire system lead to: operating modes (user/monitor) memory protection execution timers 10

11 From Batch To Parallel Processing early 1960 s: multiprogramming more memory keep several programs in memory at once (memory partitioning to separate the different jobs) OS monitor could switch between jobs when one became idle (i.e., waiting for I/O) e.g., IBM OS/360 mid 1960 s: timesharing switch between jobs periodically access via remote terminals e.g., CTSS, MULTICS, UNIX 11

12 From Batch To Parallel Processing early 1960 s: multiprogramming more memory keep several programs in memory at once (memory partitioning to separate the different jobs) OS monitor could switch between jobs when one became idle (i.e., waiting for I/O) e.g., IBM OS/360 mid 1960 s: timesharing switch between jobs periodically access via remote terminals e.g., CTSS, MULTICS, UNIX 12

13 From Batch To Parallel Processing late 1970 s: personal computers single user, dedicated workstation WIMP user interface peripherals connected directly single processor, time-sharing 13

14 From Batch To Parallel Processing parallel processing several physical processors several cores per physical processor hyper-threading in a single core several users, several programs 14

15 From Batch To Parallel Processing still to this day a single (single-threaded) applications executes under the assumption it runs exclusively on the hardware private memory its own CPU uninterrupted access to peripherals yet, programs may be multi-threaded communicate with each other this illusion is maintained by the operating system three core abstractions: processes, virtual memory, and files 15

16 System Software Basics The system software (operating system) manages the hardware protect H/W from misuse by buggy/malicious programs provide simple and uniform mechanisms for manipulating hardware devices Fundamental abstractions provided by the OS processes virtual memory files 16

17 Processes and Threads A process is the operating system s abstraction for a running program multiple processes can run concurrently multi-core processors: true parallelism single-cores: apparent parallelism through context-switching OS provides the illusion that the process has exclusive access to the H/W full memory address space exclusive access to the I/O devices 17

18 Processes and Threads Context-Switching OS keeps track of all state (context) that a process needs in order to run current PC register file memory contents open files switch to a new process periodically when a process has to wait for an event A process can consist of multiple threads not as heavy as full processes easier sharing of data typically more efficient scheduling 18

19 Virtual Memory An abstraction of the physical memory Provides each process with the illusion that it has exclusive use of the main memory Managed by the OS with the help of a hardware translation unit, the MMU (memory management unit) Typical layout on Linux systems 19

20 Files a file is a sequence of bytes in *nix systems, everything is modeled as a file disk keyboard mouse display network shared memory single interface to interact with files 20

21 Isolation of OS and User Processes In principle, a user process has no direct access to physical hardware resources no access to memory of the OS or other user processes unless explicitly permitted (process relations, shared memory) no direct access to disk drives direct access to the CPU, but only in user mode 21

22 Isolation of OS and User Processes Process View of the Hardware (Linux) CPU(s) OS memory (1GB/128TB) exclusive use exclusive use access through API memory (3GB/128TB) file system network printer/ 22

23 Isolation of OS and User Processes OS View of the Hardware time sharing process virtual memory physical memory CPU(s) exclusive use time access through API file system network printer/ 23

24 Isolation of OS and User Processes Hardware Support CPU user mode kernel mode Memory System address translation System timer interrupt much more these days, mostly for virtualization devices, etc 24

25 Isolation of OS and User Processes Example: Intel x86 Processors ISA four levels of protection ring 0: all instructions can be executed ring 3: only instructions that cannot compromise system state are allowed to execute source: Wikipedia example: mov $0, %eax set %eax to 0 hlt halt processor wbinvd flush caches with write-back 25

26 Introduction to System Programming Abstractions are good but don t forget reality Basic operation of a computer system Summary 26

27 System Programming System software (or systems software) is computer software or an operating system designed to operate and control the computer hardware and to provide a platform for running application software. (source: Wikipedia) System Programming concerns itself with writing system software from relatively high-level (web servers) down to very low-level (boot loaders) 27

28 Wrapping it up In this class you will learn learn how to interact with the operating system on a low level get an idea of what the operating system is doing how to write safer code how to write faster code Prerequisites some programming experience computer architecture x86 assembly SP will require a substantial effort read the book do the homework start with labs early! 28