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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.arch
Subject: Re: Privilege Levels Below User
Date: Tue, 11 Jun 2024 04:10:00 -0000 (UTC)
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On Mon, 10 Jun 2024 20:41:31 +0300, Michael S wrote:

> Intel's official terminology makes distinction between interrupts and
> exceptions. The former are external/asynchronous, the later are
> internal/synchronous. Exceptions are further sub-divided into faults,
> traps and aborts.

That all sounds very DEC-like.

In particular, the DEC definition of a “fault” is that the saved PC on the 
stack still points at the instruction that caused the exception, so a 
return-from-exception will attempt to re-execute the same instruction. 
This is exactly what you want for page faults, for example, but also for 
long-running interruptible instructions that haven’t finished yet.

Whereas a “trap” left the PC pointing at the following instruction. So a 
return from the exception handler will simply resume execution there.

Over the evolution of the VAX architecture, some exceptions which 
initially were “traps” became “faults” instead.