CMSC421

1. CMSC421 Chapter 22 Operating System Concepts Windows XP

2. Windows XP • Windows XP operating system is a 32/64-bit preemptive multitasking operating system for AMD K6/K7, Intel IA32/IA64 and later microprocessors. It is the successor to Windows NT/2000 and the replacement for Windows 95/98.

3. History • Many features are from NT/2000. • Uses a client-server architecture (like Mach) to implement multiple operating system personalities, such as Win32 and POSIX. • Comes in two versions, Personal and Professional.

4. Design Principles • Security • Reliability • Windows and POSIX Application Compatibility • High Performance • Extensibility • Portability • International Support

5. Security • Adherence to the design standards to receive U.S. Government C-2 security designation. • Extensive code review and testing, plus use of sophisticated automatic analysis tools to investigate potential defects that might represent security vulnerabilities.

6. Reliability • Used extensive manual and automatic code review to identify over 63,000 lines in the source files that might contain issues not detected by testing. • Extends driver verification to catch more subtle bugs, improves the facilities for catching programming errors in user-level code,.

7. Reliability -- II • Subjects third party applications, drivers and devices to a rigorous certification process. • New facilities for monitoring the health of the PC including downloading fixes for problems before they are encountered by the users.

8. Windows/ POSIX Application Compatibility • Application compatibility is difficult to achieve because each application checks for a particular version of Windows, may have dependence on the quirks of the implementation of APIs. • XP introduces a compatibility layer that falls between applications and the Win32 API. This layer makes XP look “bug-for-bug” compatible with previous versions of Windows.

9. Windows/ POSIX Application Compatibility -- II • Maintains support for running many 16-bit applications using a “thunking layer” that translates 16-bit API calls into equivalent 32-bit calls. • 64-bit version provides a thunking layer that translates 32-bit API calls into native 64-bit calls.

10. Windows/ POSIX Application Compatibility -- III • POSIX support is a POSIX subsystem called Interix. • Most available UNIX-compatible software compiles and runs under Interix without modification.

11. High Performance • Desktop systems are largely constrained by I/O performance. • Servers, and large multi-threaded and multi-processor environments are often constrained by CPU. Locking and cache-line management are key to scalability.

12. High Performance Techniques • Asynchronous I/o • Optimized protocols for networks • Kernel-based graphics • Sophisticated caching of file-system data. • Memory management • Synchronization algorithms • Reducing code-path length in critical functions.

13. High Performance Techniques -- II • Using better algorithms and per-processor data structures. • Implementing more scalable locking protocols. • Except while executing in the kernel dispatcher, threads in the subsystems of Windows XP can be preempted by higher-priority threads.

14. Extensibility • Used a layered architecture. • Uses environmental subsystems to emulate different operating systems (DOS, Windows, POSIX). • Uses loadable drivers in the I/O system. • Uses RPCs for distributed processing.

15. Portability • Can be moved from one hardware architecture to another with relatively few changes. • Majority of the system is written in C and C++. • Processor-dependent code is isolated in DLL called hardware-abstraction layer (HAL).

16. Portability -- II • Only shipped on IA32 compatible platforms, it was also tested on DEC Alpha. • “Maintaining portability is a matter of use it or loss it.”

17. International Support • Uses National Language Support API. • Uses UNICODE as the native language character code. • ASCII is converted to UNICODE. • System text strings are kept in resource files that can be replaced to localize the system for different languages. • Multiple locales can be used concurrently.

18. System Components • Hardware-Abstraction Layer • Kernel • Executive

19. Logon process OS/2 applications Win16 applications Win32 applications MSDOS applications POSIX applications Security subsystem OS/2 subsystem Win16 VDM MSDOS VDM POSIX subsystem Authentication package Security account manager database Win32 subsystem executive I/O manager Object manager Security reference monitor Process manager Plug and play manager Virtual memory manager Local procedure call facility Window manager File system Cache manager Device drivers Graphic device drivers kernel Network drivers Hardware abstraction layer Hardware Windows XP block diagram

20. Hardware Abstraction Layer • HAL is the layer of software that hides hardware differences from upper levels of the operating system. • HAL exports a virtual-machine interface that is used by the kernel dispatcher, the executive, and the device drivers. • Only a single version of each device driver is required.

21. Kernel • Kernel Dispatcher • Threads and Scheduling • Implementation of Synchronization Primitives • Software Interrupt: Async Proc Calls • Software Interrupt: Deferred Proc Calls • Exceptions and Interrupts

22. Kernel -- II • Is object oriented • An object type is a system defined data type with a set of attributes and a set of methods. • An object is an instance of an object type. • The kernel performs its job by using a set of kernel objects whose attributes shore the kernel data, and whose methods perform the kernel activities.

23. Kernel Dispatcher • Provides the foundation for the executive and subsystems • Most is never paged out • Can not be preempted

24. Kernel Dispatcher Responsibilities • Thread scheduling • Implementation of synch primitives • Timer management • Software interrupts • Exception dispatching

25. Threads and Scheduling • Uses processes and threads for executable code. • Process has a virtual memory address space and information to initialize each thread. • Each thread is an executable unit dispatched by the kernel.

26. Thread states • Ready • Standby • running • waiting • transition • terminated

27. Priority scheme • 32-level scheme • Variable class (0 - 15) • Real-time class (16 - 31) • Uses a queue for each priority

28. Implementation of Synchronization Primitives • Dispatcher objects control dispatching and synchronization • Event objects record an event occurrence • Mutant provides mutex • Semaphore object acts as a counter or a gate • Thread object is the entity that is scheduled • Timer objects keep track of time

29. Asynchronous Procedure Call • Break into an executing thread and call procedure. • APCs are used to begin execution of a new thread, terminate processes, and deliver notification that an asynch I/O has completed. • Queued to a specific thread • Allow the system to execute both system and user code within a process’ context

30. Deferred Procedure Call • DPCs are used to postpone interrupt processing. • Process timer expirations • Preempt thread execution at end of scheduling quantum

31. Exceptions and Interrupts • Architecture-independent exceptions • memory-access violation • integer and floating point divide by zero • overflow or underflow • illegal instruction • data misalignment • privileged instruction • page read error, etc

32. Exceptions • Trap handlers deal with simple exceptions • More elaborate handling is performed by the kernel’s exception dispatcher. • If no handler is found, a system error occurs and results in a “blue screen of death” • Exception handing is more complex for user-mode processes

33. Exceptions -- II • The interrupt dispatcher in the kernel handles interrupts by calling an Interrupt Service Routine (ISR) supplied by a device driver or a kernel trap handler routine. • For portability, the interrupt dispatcher maps hardware interrupts into a standard set.

34. Executive • Provides a set of services that all environmental subsystems use: • Object manager • Virtual memory manager • Process manager • Local procedure call facility • I/O manager • Security reference monitor • Plug-and-play and security managers • registry • booting

35. Object Manager • A generic set of interfaces for managing the kernel-mode entities that is manipulated by user-mode programs. • Examples: • semaphores • mutexes • events • processes • threads

36. Handles • Each process has an object table that track the objects used by the process • User-mode code accesses these objects using an opaque value called a handle that is returned by many APIs. • Object handles can be created by duplicating an existing handle, either from either the same or different process.

37. Virtual Functions • Objects are manipulated by a set of virtual functions with implementations provided by each object type: • query - gets object’s name • parse - search for an object given the object’s name • security - makes security checks on all object operations.

38. Virtual Memory Manager • The design of the VM Manager assumes that the underlying hardware supports virtual-to-physical mapping, a paging mechanism, transparent cache coherence on multiprocessor systems and allows multiple page-table entries to map to the same physical page frame.

39. Virtual Memory Manager -- II • On IA32 processors each process has a 4GB virtual address space. • The upper 2GB are mostly identical for all processes, and are used by Windows XP in kernel mode to access the operating system code and data structures. • Key areas that are not identical are page table self-map, hyperspace and session space.

40. Page Table Self-map • The hardware uses a process’s page tables using physical page-frame numbers. • The VM manager maps the page tables into a single 4GB region in the process’ address space so they are accessed through virtual addresses.

41. Hyperspace • Hyperspace maps the current process’ working set information into the kernel-mode address.

42. Session Space • Session space is used to share the win32 and other session-specific drivers between all the processes in the same terminal-server session rather than with all the processes in the system.

43. Process Manager • Provides services for creating, deleting, and using processes, threads, and jobs. • It has no knowledge about parent-child relationships; left to environmental subsystems. • Processes contain one or more threads. • Processes can be collected together into job objects.

44. Process Creation • Once a new process is created, the initial thread is created and an APC (Async Procedure Call) is delivered to the thread to prompt the start of execution at the user-mode image loader (ntdll.DLL). • Also supports a UNIX fork( ) style of process creation.

45. Local Procedure Call Facility • XP uses a client-server model. • Environmental subsystems are servers that implement particular operating system personalities. • XP uses LPCs to pass requests and results (messages) between client and server processes within a single machine.

46. I/O Manager • Responsible for file-systems, device drivers, and network drivers. • Works with VM to provide memory mapped I/O operations. • Is fundamentally asynchronous. • Device drivers are written according to the Windows Driver Model (WDM) specification.

47. WDM • Because of the richness of the WDM, it can be an excessive amount of work to write a full WDM device driver for each new hardware device.

48. Cache Manager • Centralized facility. • Works with file-system and VM mangers. • Caching in XP is based on files rather than raw blocks. • Size of the cache changes dynamically.

49. Cache • Cache is divided into blocks of 256KB. • Each block can hold a memory-mapped region (view) of a file. • Each cache block is described by a virtual-address control block (VACB) that stores the virtual address and file offset of the view.

50. Security Reference Monitor • Centralized management of system entities in the object manager enables the use of a uniform mechanism to perform run-time access validation and audit checks for every user-accessible entity in the system.