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05.Exceptions Handling.md

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Exceptions Handling

Interrupts

Interrupts are signals that alter the normal control flow of a program at runtime. An interrupt must be handled by a dedicated interrupt handler, and the architecture should be able to resume the normal execution of the program. Causes:

  • Asynchronous external events:
    • I/O device reply
    • timer expiration
    • HW failure
  • Synchronous internal event:
    • opcode error
    • arithmetic overflow
    • bad memory access
    • traps: traps are a mechanism used by computers to transfer control to the OS or to kernel routines in response to various events like system calls.

Interrupts can be characterized in various ways:

  • Async interrupts are caused by external sources and can be handled at the end of the execution of the current instruction, making them easier to manage than sync ones.
  • User request interrupts are predictable: they are treated as exceptions because they use the same mechanism. Coerced interrupts (forced) are caused by some HW event not under control of the program.
  • User maskable vs user nonmaskable
  • Within instructions interrupts are usually synchronous since the instruction triggers the exception. The instruction must be stopped and restarted.
  • Resume vs terminate interrupts

Super exception table

Exception type Synchronous vs. asynchronous User request vs. coerced Oser maskable vs. nonmaskable Within vs. between instructions Resume vs. terminate
I/O device request Asynchronous Coerced Nonmaskable Between Resume
Invoke operating system Tracing instruction execution Synchronous User request Nonmaskable Between Resume
Breakpoint Integer arithmetic overflow Synchronous User request User maskable Between Resume
Floating-point arithmetic overflow or underflow Synchronous Coerced User maskable Within Resume
Page fault Synchronous Coerced Nonmaskable Within Resume
Mischaligned memory accesses Synchronous Coerced User maskable Within Resume
Memory protection violations Synchronous Coerced Nonmaskable Within Resume
Using undefined instructions Synchronous Coerced Nonmaskable Within Terminate
Hardware malfunctions Asynchronous Coerced Nonmaskable Within Terminate
Power failure Asynchronous Coerced Nonmaskable Within Terminate