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Lecture 3 System Mechanisms (1)

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Lecture 3 System Mechanisms (1)

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  1. Lecture 3 System Mechanisms (1) xlanchen@03/11/2005

  2. Contents • Trap dispatching • The executive object manager • Synchronization • System worker threads • Local procedure calls (LPCs) Understanding the Inside of Windows2000

  3. Trap dispatching • Interrupt & exception • Divert the processor to code outside thenormal flow of control • Trap: A processor's mechanism for • Capturing an executing thread when an exception or an interrupt occurs • Transferring control to a fixed location in the operating system Understanding the Inside of Windows2000

  4. Trap handler • a function specific to a particular interrupt or exception Understanding the Inside of Windows2000

  5. Interrupts vs. exceptions • Either hardware or software can generate exceptions and interrupts • Interrupt An asynchronous event that is unrelated to what the processor is executing • can occur at any time • I/O devices, processor clocks, … • can be enabled (turned on) or disabled (turned off) Understanding the Inside of Windows2000

  6. Interrupts vs. exceptions • ExceptionA synchronous condition that results from the execution of a particular instruction • Can be reproduced • Memory access violations, certain debugger instructions, divide-by-zero errors,… • Additionally: System service calls Understanding the Inside of Windows2000

  7. Stop and continue, how? • Trap frame • Created by the processor on the kernel stack of the interrupted thread • Used to store the execution state of the thread • Usually a subset of a thread's complete context Understanding the Inside of Windows2000

  8. Trap dispatching • Front-end trap handling functions • Perform general trap handling tasks before and after transferring control to other functions that field the trap • Example: • The kernel hardware interrupt trap handler • The general system service trap handler • Unexpected trap handler (KeBugCheckEx) Understanding the Inside of Windows2000

  9. Trap dispatching • Interrupt dispatching • Exception dispatching • System service call dispatching Understanding the Inside of Windows2000

  10. Interrupt Dispatching • I/O control methods? • Polling, interrupt, DMA • Interrupt-driven device • Allow the operating system to get the maximum use out of the processor by overlapping central processing with I/O operations • Example: pointing devices, printers, keyboards, disk drives, and network cards Understanding the Inside of Windows2000

  11. Interrupt time line for a single process doing output Understanding the Inside of Windows2000

  12. Interrupt dispatching • Interrupt trap handlers • For device interrupt • --|----> External routine, ISR | (Provided by device drivers) | |---> Internal kernel routine (Provided by kernel) Understanding the Inside of Windows2000

  13. OS CPU 8259 M device 8259 S Hardware Interrupt Processing • On x86 systems • IRQinterrupt request interrupt number • IDTinterrupt dispatch table • filled at system boot time Understanding the Inside of Windows2000

  14. EXPERIMENT • Viewing the IDT Understanding the Inside of Windows2000

  15. Hardware Interrupt Processing • PIC: Programmable Interrupt Controller • i8259A for uniprocessor systems (IBM PC) • <=15 • APIC: Advanced Programmable Interrupt Controller • i82489 for multiprocessor systems • Most new computers • <=256 Understanding the Inside of Windows2000

  16. EXPERIMENT • Viewing the PIC Understanding the Inside of Windows2000

  17. IRQL (Interrupt request levels) • Windows 2000 own interrupt priority scheme • Interrupt numbers  IRQL • Using IRQL • Raise & lower Understanding the Inside of Windows2000

  18. EXPERIMENT • Viewing the IRQL Understanding the Inside of Windows2000

  19. Lazy IRQL: a performance optimization • Accessing a PIC is relatively slow • Lazy IRQL • The changing of the interrupt mask is delayed until a lower-priority interrupt occurs • the lower-priority interrupt is postponed until the IRQL is lowered Understanding the Inside of Windows2000

  20. Mapping interrupts to IRQLs • HAL function • HalpGetSystemInterruptVector • On a uniprocessor system • IRQL for Device = 27- interrupt vector Understanding the Inside of Windows2000

  21. Important restriction • Can't wait on an object at DPC/dispatch level or above • Only nonpaged memory can be accessed at IRQL DPC/dispatch level or higher • If violated, the system crashes with an IRQL_NOT_LESS_OR_EQUAL crash code. Understanding the Inside of Windows2000

  22. Interrupt objects • Contains the information about a device ISR, including • the address of the ISR, • the IRQL, • the entry in the kernel's IDT Understanding the Inside of Windows2000

  23. Software interrupts • Including: • Initiating thread dispatching • Non-time-critical interrupt processing • Handling timer expiration • Asynchronously executing a procedure in the context of a particular thread • Supporting asynchronous I/O operations Understanding the Inside of Windows2000

  24. DPC • Interrupt routines should exit asap and some knl activity easier when current code has unwound • NT uses DPC to schedule non-immediate code, e.g. • I/O drivers queue DPCs to complete I/O • Knl uses DPC to handle timer expiration • Knl uses DPC to reschedule when thread quantum expires • Adding DPC to DPC queue causes dispatch/DPC interrupt • Dispatch/DPC has low IRQL – deferred if IRQL higher • Limits soft real-time capability of NT Understanding the Inside of Windows2000

  25. Delivering a DPC Understanding the Inside of Windows2000

  26. EXPERIMENT • Monitoring Interrupt and DPC Activity Understanding the Inside of Windows2000

  27. APC (Asynchronous procedure call) interrupts • a way for user programs and system code to execute in the context of a particular user thread • run at an IRQL less than 2 • An APC routine can acquire resources (objects), wait on object handles, incur page faults, and call system services Understanding the Inside of Windows2000

  28. Kernel mode APC Executive & device driver User mode APC Win32 APIs: ReadFileEx, WriteFileEx, and QueueUserAPC Kernel mode vs. user mode Understanding the Inside of Windows2000

  29. Exception Dispatching • Structured exception handling • allows applications to gain control when exceptions occur • The application can fix the condition and return, or declare back to the system that the exception isn't recognized • The system should continue searching for an exception handler that might process the exception. Understanding the Inside of Windows2000

  30. X86 Understanding the Inside of Windows2000

  31. Exception dispatcher • To find an exception handler that can "dispose of" the exception • Some exceptions transparently are handled by kernel • A few exceptions are allowed to filter back, untouched, to user mode • kernel-mode exceptions • If unhandled, are considered fatal operating system errors Understanding the Inside of Windows2000

  32. Dispatching an exception Understanding the Inside of Windows2000

  33. EXPERIMENT • Viewing the Real User Start Address for Win32 Threads Understanding the Inside of Windows2000

  34. EXPERIMENT • Unhandled Exceptions Understanding the Inside of Windows2000

  35. System Service Dispatching • On X86 • int 0x2e • NtWriteFile: moveax,0x0E;movebx,esp;int0x2E;ret0x2C; Understanding the Inside of Windows2000

  36. System service exceptions Understanding the Inside of Windows2000

  37. System service number to system service translation Understanding the Inside of Windows2000

  38. System service dispatching Understanding the Inside of Windows2000

  39. EXPERIMENT • Viewing System Service Activity Understanding the Inside of Windows2000