Path: utzoo!attcan!uunet!wuarchive!psuvax1!rutgers!uwvax!dip.cs.wisc.edu!cole
From: cole@dip.cs.wisc.edu (Bruce Cole)
Newsgroups: comp.unix.ultrix
Subject: Re: emacs or csh problem?
Message-ID: <10905@spool.cs.wisc.edu>
Date: 28 Jul 90 21:20:15 GMT
References: <27522@netnews.upenn.edu>
Sender: news@spool.cs.wisc.edu
Organization: U of Wisconsin CS Dept
Lines: 62

In article <27522@netnews.upenn.edu> hagan@scotty.dccs.upenn.edu (John Dotts Hagan) writes:
>   "I think I mentioned that we have hundreds of
>   people here using emacs and the reported seg fault problem has never been
>   seen here."
It is very distressing to hear DEC say this, since I QAR'ed this problem to
DEC some time ago, and gave them the fixes to the Ultrix kernel problem which
causes this to occur.

I posted this description to info-gnu-emacs:

From: cole (Bruce Cole)
To: gordon!jpd
Cc: cole, info-gnu-emacs@prep.ai.mit.edu
Subject: RISC Ultrix- Emacs problems
Date: Sat, 7 Jul 90 12:11:25 -0500

 > We're running emacs 18.54 on an Ultrix Risc Decsystem 5400. Three times
 > we've had the machine hang with the following message:
 > 
 >   panic: tblmod on invalid pte
 > 
 > Ultrix support tells us this is caused by emacs. Has anyone experienced
 > this? DEC says it only happens on RISC boxes.
This is due to a MIPS specific Ultrix kernel bug.  I sent DEC a description
of the bug with a bug fix.  The Kernel bug manifests itself with emacs 
since emacs uses a non-standard data start address on Ultrix MIPS machines.

I haven't often seen emacs cause MIPS machines to panic.  Usually you just
see one of the following errors when you try to start up emacs:
	segmentation fault (core dumped)
	emacs: Bad address
	Out of memory
	data size rlimit exceeded, pid 6523, process tcsh (for example)

Until DEC fixes their kernel, you can avoid the bug by changing the data
start address used by emacs.  Change m-pmax.h to define these values:
[...]
Here are diffs to emacs 18.55:

*** m-pmax.h	Thu Jun  8 11:53:55 1989
--- m-pmax.h.new	Mon Jul  9 10:21:21 1990
***************
*** 1,3 ****
--- 1,7 ----
  #include "m-mips.h"
  #undef LIBS_MACHINE
  #undef BIG_ENDIAN
+ #undef LD_SWITCH_MACHINE
+ #undef DATA_START
+ #define DATA_START 0x10000000
+ #define DATA_SEG_BITS 0x10000000

>I have built two newer versions of gnu emacs and it still happens.  I should
>also mention that these faults happen quite rarely to some users (I may see
>it once a month), while other users see it a few times a week or even daily!

The problem only occurs when a MIPS machine is doing a lot of paging.  Users
who don't cause their workstation to page will not see this problem.
--
Bruce Cole
Computer Sciences Dept.
U. of Wisconsin - Madison