Path: utzoo!mnetor!uunet!husc6!cmcl2!beta!unm-la!unmvax!turing.UNM.EDU!mike From: mike@turing.UNM.EDU (Michael I. Bushnell) Newsgroups: comp.unix.wizards Subject: Re: Referencing through a null pointer Message-ID: <1013@unmvax.unm.edu> Date: 1 May 88 01:40:37 GMT References: <4729@cup.portal.com> <1988Apr24.092740.8673@utzoo.uucp> <50676@sun.uucp> <2730@bsu-cs.UUCP> <9946@tekecs.TEK.COM> <1766@pixar.UUCP> Sender: news@unmvax.unm.edu Reply-To: mike@turing.UNM.EDU.UUCP (Michael I. Bushnell) Organization: University of New Mexico, Albuquerque Lines: 24 You know, people love railing against VAX unix...but there is one reason that you CAN'T make the bottom of "data" un-readable and thus fix the problem. The VAX has a linear address space (or the VM hardware makes it look that way). There isn't a distinction between a data address and a text address, except that one is less than _etext. If you marked the bottom page non-readable, you would have massive problems... you couldn't read start and whatever else makes it into the beginning of the text space. There is a problem; but there isn't an easy way to avoid it, short of deciding that a unix process should be loaded starting at address 1024 and make the first page non-readable. N u m q u a m G l o r i a D e o Michael I. Bushnell HASA - "A" division 14308 Skyline Rd NE Computer Science Dept. Albuquerque, NM 87123 OR Farris Engineering Ctr. OR University of New Mexico mike@turing.unm.edu Albuquerque, NM 87131 {ucbvax,gatech}!unmvax!turing.unm.edu!mike