Triple Fault: Difference between revisions

When a fault occurs, the CPU invokes an exception handler. If a fault occurs while trying to invoke the exception handler, that's called a double fault, which the CPU tries to handle with yet another exception handler. If that invocation results in a fault too, the system reboots with a triple fault.

Note that a fault that occurs while a fault handler is already running does not of itself cause a double or triple fault. For example, if a Segment Not Present Fault occurs after a handler has already started, then the Segment Not Present handler will run as normal. However, if the code segment of the original handler is itself not Present, then the double (or triple) fault would occur since the original handler hadn't started yet.

A triple fault is usually a sign that the exception handler called is faulty, or worse, that the whole exception handling in your system is screwed up. (LDT or GDT issues, bogus pointers or faulty memory mappings are frequent offenders.)

The cleanest way to handle this is to provide a separate [[Task State Segment|TSS]] for double faults and to use a task gate for that kind of exception. Try to keep that Task as simple as possible, and give it a dedicated stack segment and pointers.