Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!sharkey!itivax!scs
From: scs@itivax.iti.org (Steve Simmons)
Newsgroups: comp.mail.elm
Subject: Re: Serious elm problems on Sun OS 3.5.2
Message-ID: <2822@itivax.iti.org>
Date: 16 Aug 89 18:24:08 GMT
References: <2311@oakhill.UUCP>
Distribution: usa
Organization: Industrial Technology Institute, Ann Arbor, MI.
Lines: 36

mikes@oakhill.UUCP (Mike Schultz) writes:

>But then it happened to me one day and I could repeat the failure, so I got out
>adb and went bug hunting!  And what did I find?  I found an illegal instruction
>in the middle of the object file.  No, I didn't disassemble in the middle of
>an instruction, it was right there in the middle of the disassembly of the 
>legal instructions,.... And then it wasn't!

>Yes, that's right.  While poking around trying to figure out how on a virtual
>memory machine with page protection, elm managed to get an instruction trashed,
>the instruction fixed itself and elm ran my test case without failure!

>Whoa!  I took my evidence to the system managers . . .

And they said "You're crazy".  We had the same thing happen (tho not
with elm) at another site where *I* was the system manager -- Suns, and
certian programs would random crash with illegal instructions.  Only
certian programs.  And relinking a new version would make the problem go
away.  The programmers complained to the system manager (me) and I said
they were crazy.

They weren't.

It turns out that there is a hardware bug in some Sun 3/50s (those made before
1988, I think).  It affects very very few programs, and requires some really
odd circumstances -- a branch instruction at the end of a virtual page
which crosses into the 'next' page, which causes a page fault, and other
I/O must be happening at the same time (I'm serious!) and sometimes it'll
happen.

So: do you have old 3/50s?  Does the problem occur only there?  Does it
come and go as versions of elm change?  If so, you been bit.
-- 
Steve Simmons		          scs@vax3.iti.org
Industrial Technology Institute     Ann Arbor, MI.
"Velveeta -- the Spam of Cheeses!" -- Uncle Bonsai