How are exceptions actually implemented in assembly?

[Jason Orendorff]

Bengt Richter wrote:
> I suppose you could eliminate the checking altogether in the normal path
> if you use an "int n" instruction on x86, to break out of a path 
> of execution like a hardware interrupt when you raise an exception,
> but it might not be so easy to do portably.

The problem is: once an exception occurs, then what?
How do you unwind the stack and find the matching "except:" clause?
An interrupt doesn't seem to solve this problem.

## Jason Orendorff    http://www.jorendorff.com/