Interrupts, exceptions and system calls

Chapter 2: Interrupts, Exceptions, and System Calls

Labels (space separated): OS

---

2.1 Startup of the operating system

start up

• DISK: store the OS
• BIOS: Basic I/O Processing System
  
  • Load BootLoader from disk's boot sector (512 bytes) to 0x7cDD, jump to CS:IP=0000:7cDD
• BootLoader: load OS
  
  • Load the code and data of the operating system from the hard disk into the memory and jump to the starting address of the OS
• CS:IP = 0xf000:fff0 (CS: segment register, IP: instruction register)
• POST (Power On Self Test): Find Graphics Card and Execute BIOS

OS interacts with devices and programs

• Interface system calls, exceptions, interrupts

• defs

  • System calls (from the application)
    
    • The application actively issues a service request to the operating system
  • Exception (from application)
    
    • Illegal instruction or other bad processing state (such as memory error)
  • Interrupts (from peripherals)
    
    • Timers and network interrupts from different hardware devices

• Differences and Features

Types of	source	processing time	response
interrupt	Peripherals	asynchronous	Persistent, transparent to user applications
abnormal	Unexpected behavior of the application	Synchronize	Kill or re-execute unexpected application instructions
system call	Application requests to provide services	synchronous or asynchronous	wait and continue

2.2 OS interrupts, exceptions and system calls

(1) Interruption

hardware

• Set interrupt flag (CPU initialization)
  
  • Set interrupt flags for internal and external events
  • ID of the interrupt event

Software (OS)

• Save the current processing state
• Interrupt Service Routine Handling
• clear interrupt flag
• Restore a previously saved state

(2) Exception: exception number

• save the scene
• exception handling
  
  • kill the program that generated the exception
  • Re-execute the abnormal instruction
• restore the scene

(3) System call

• Program access is mainly through high-level API interfaces rather than direct system calls

Overhead across operating system boundaries

• Overhead in execution time over program calls
• Overhead:
  
  • Initialization overhead for establishing the mapping relationship between interrupt/exception/system call numbers and corresponding service routines
  • build kernel stack
  • Validation parameters
  • The kernel mode is mapped to the address space of the user mode, and the page mapping permission is updated
  • Kernel mode independent address space, TLB