Exception

Definition:

• used to handle conditions that arise when executing instructions on the processor
• Detected by the processor itself
• Used in:
  • Allow user programs to get service from the OS
    • A system call creates an exception that kicks out the user program and transfers control to exception handler, which will invoke a proper OS service routine
• Handle unexpected events: Memory protection violation, divide-by-zero, invalid opcode, etc.
• Handle Page Fault
  • when instruction requested is TLB-miss and Page table-miss
  • → CPU generates a page fault exception
  • → Exception handler saves program state and transfers control to the OS
  • → OS brings in the pages, updates page tables and TLB, restores program state and resum the program
  • → Execute the instruction