Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site rlvd.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!seismo!mcvax!ukc!warwick!rlvd!asw From: asw@rlvd.UUCP (Antony Williams) Newsgroups: net.unix Subject: Re: Re: rcs blows up on suns Message-ID: <794@rlvd.UUCP> Date: Fri, 20-Sep-85 08:17:19 EDT Article-I.D.: rlvd.794 Posted: Fri Sep 20 08:17:19 1985 Date-Received: Mon, 23-Sep-85 00:13:25 EDT References: <830@panda.UUCP> <1075@sdcsvax.UUCP> <961@sdcsla.UUCP> <967@sdcsla.UUCP> <151@maynard.UUCP> Reply-To: asw@rlvd.UUCP (Antony Williams) Distribution: net Organization: Rutherford Appleton Laboratories, Atlas Buildings, U.K. Lines: 21 Xpath: warwick ubu 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. This is a difficult decision for implementors: the error is so common that disabling address zero causes just about every Unix program to dump core under some circumstance. One instance I recall is that PIC will dereference null pointers if given syntactically incorrect input. It works fine with correct input. The problem with PIC is exacerbated in that the null pointer is used as a pointer to various kinds of structure, with further pointers at various offsets: V7 Unix on PDP11/70 used to ensure a few bytes of zeros at address zero, but behaviour like that of PIC seems to require an unknowable number of zeros to avoid the error. -- -------------------------------------------------- UK JANET: asw@uk.ac.rl.vd Usenet: {... | mcvax}!ukc!rlvd!asw ARPAnet: asw%rlvd@ucl-cs.arpa Brought to you by Super Global Mega Corp .com