Path: utzoo!utgpu!water!watmath!clyde!burl!codas!killer!richardh
From: richardh@killer.UUCP (Richard Hargrove)
Newsgroups: comp.unix.questions
Subject: Re: Unix (Microport) internal question
Summary: 80286 exceptions
Keywords: Unix Microport internals
Message-ID: <2801@killer.UUCP>
Date: 12 Jan 88 04:33:04 GMT
References: <2788@killer.UUCP>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 33

In article <2788@killer.UUCP>, ajohnson@killer.UUCP (Andy Johnson) writes:
> I have been running Microport's Unix V2.2 for about 7 months now
> and have encountered the messages:
>             tss fault
>             double panic tss fault
> 
> could/would tell me what it is.  I would appreciate it if any netlanders 
> that are sufficiently versed in unix internals and know the answer to this 
> question would reply, either in mail or on the net.
> 

These are hardware exceptions generated by the 80286. The first is the
invalid task state segment fault (a task's TSS is an area of memory that
the os uses to initialize architectural elements supporting the task). 
The hardware exception handling is then generating a second hardware fault 
(it looks like a new invalid TSS fault is occurring, this time for the TSS 
for the exception handler), thus generating a double-fault. Fortunately 
the cpu is not then generating a third fault. It enters a shutdown mode if 
it does.

This looks like a uPort problem. The user is not supposed to be able to
access such things as TSS's (particularly the TSS for an exception handler)
in a protected execution environment. In weak defence of uPort, there's
not much you can do in the face of a double fault except force the user
to reboot.

If you're really curious about details, see _80286 and 80287 Programmer's 
Reference Manual_, chapter 9, published by Intel.

regards,
richard hargrove
...!killer!richardh
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