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From: jdb@mordor.UUCP (John Bruner)
Newsgroups: net.unix
Subject: Re: rcs blows up on suns (NULL dereferencing)
Message-ID: <3440@mordor.UUCP>
Date: Wed, 11-Sep-85 13:18:30 EDT
Article-I.D.: mordor.3440
Posted: Wed Sep 11 13:18:30 1985
Date-Received: Sat, 14-Sep-85 01:46:45 EDT
References: <830@panda.UUCP> <1075@sdcsvax.UUCP> <961@sdcsla.UUCP> <967@sdcsla.UUCP> <151@maynard.UUCP>
Reply-To: jdb@mordor.UUCP (John Bruner)
Distribution: net
Organization: S-1 Project, LLNL
Lines: 20

In article <151@maynard.UUCP> campbell@maynard.UUCP (Larry Campbell) writes:
>A minor point, but dereferencing zero only "works" on Vaxen that are
>running Berkeley Unix (don't know about USG).  VMS sets page zero to
>no access; this is one of the few areas where I concede VMS a point
>over Unix.  It catches an all-too-common programming error.

I implemented an (optional) new object format with page 0 unmapped in
VAX 4.2BSD.  The changes to the kernel and a few user-level programs
(e.g. the linker) are minimal.  A program in this format (which I
call Z0MAGIC (0420) or -Z format) will receive a SIGBUS if it attempts
to indirect through NULL.  This has been very useful in finding
NULL-dereferencing bugs, both in locally-written code and in
distributed software.

I posted the set of changes to "net.unix-wizards" several months
ago.  If you missed them and would like a copy, mail me a note.
-- 
  John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
  MILNET: jdb@mordor [jdb@s1-c.ARPA]	(415) 422-0758
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