Path: utzoo!attcan!uunet!mcsun!unido!mikros!mwtech!martin
From: martin@mwtech.UUCP (Martin Weitzel)
Newsgroups: comp.unix.wizards
Subject: Re: What machines core dump on deref of NULL?
Message-ID: <816@mwtech.UUCP>
Date: 26 Jun 90 23:27:33 GMT
References: <444@mtndew.UUCP> <31079@cup.portal.com> <2389@aix.aix.kingston.ibm.com> <13226@smoke.BRL.MIL> <2392@aix.aix.kingston.ibm.com>
Reply-To: martin@mwtech.UUCP (Martin Weitzel)
Organization: MIKROS Systemware, Darmstadt/W-Germany
Lines: 49

In article <2392@aix.aix.kingston.ibm.com> rlc@aix.aix.kingston.ibm.com (Roger Collins) writes:
[some lines deleted]
>To give another example of this situation, almost all UNIX systems
>initialize .bss to zero.  This causes uninitialized global and static
>variables to be initialized to zero by default.  Many, many programs,
>including System V commands, depend on this fact.  They assume
>uninitialized global and static variables are initialized to zero
>even though the C language explicitly says the values are undetermined.

K&R1
Page 37:
	External and static variables are initialized to zero
	by default ...
Page 198:
	Static and external variables which are not initialized are
	guaranteed to start off as 0; ...

K&R2
Page 40:
	External and static variables are initialized to zero
	by default.
Page 219:
	A static object that is not explicitly initialized is
	initialized as if it (or its members) were assigned the
	constant 0.

I don't have a copy of the ANSI-C-Standard handy, but I'm pretty
sure that it gives the same guarantee. Could you please name *one*
reference for the C language which supports your claim?

>This is wrong, I know.

Yes, of course it's wrong - but wouldn't it have been easier to
leave the last two sentences out? (Of course, this would have made
all the rest of the article pointless, so I guess the last sentence
doesn't apply to the claim, but to the fact that many programs
make the - perfectly correct - assumption that all uninitialized
data is initialized with zero.)

>Now, why don't you suggest to your boss that you release a computer
>that initializes .bss to 0xffffffff? (Leaving it uninitialized is a
>security hole on multiuser systems.)  It doesn't break the C language.

Really? I'm pretty sure it breaks the C Language! Again: Please name
*one* reference for the C language that makes you think it wouldn't.

[rest deleted]
-- 
Martin Weitzel, email: martin@mwtech.UUCP, voice: 49-(0)6151-6 56 83