From: utzoo!decvax!harpo!seismo!rlgvax!guy
Newsgroups: net.unix-wizards
Title: Re: Questions about nil-pointer dereferences (the "plague")
Article-I.D.: rlgvax.181
Posted: Mon Apr  4 12:50:23 1983
Received: Tue Apr  5 03:22:25 1983
References: sri-arpa.798

If a program breaks because there isn't a null string at location 0, that
program deserves to break.  It's *very* easy to generate a null string; ""
generally suffices.  And it's *very* easy to say:

if (p != NULL && whatever(p))

instead of

if (whatever(p))

or whatever the erroneous code was doing.  It's only two instructions on a
VAX....  Several machines (the SUN and the CCI Power/5, both 68000-based, for
example) use the lower part of the address space for the kernel, and
dereferencing null pointers on those systems causes a fault (as it should!).
VMS also maps page 0 out of the address space; I cast my vote either for
demand-paged pure executables (or *all* executables) explicitly starting
the text at 1024 and setting page 0's permissions to no read, no write, no
execute, no way, or adding a new executable type which does this.

						Guy Harris
						RLG Corporation
						{seismo,mcnc,we13}!rlgvax!guy