Subject: Re: port-xen/29887: sysctl kern.consdev coredumps
To: YAMAMOTO Takashi <>
From: Bill Studenmund <>
List: tech-userlevel
Date: 06/20/2005 21:11:42
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On Tue, Jun 21, 2005 at 10:28:00AM +0900, YAMAMOTO Takashi wrote:
> > While you are correct that the library has no way of knowing which of t=
> > two choices it should use, our common practice for printf() has been to
> > not core dump.  We have had that behavior since 4.4BSD, i.e. longer than
> > there has been a NetBSD. Thus BSD developers decided that not core dump=
> > was the better choice overall.
> >=20
> > You are the one who is championing making printf() and puts() and frien=
> > core dump when passed NULL. That's changing behavior for printf(). Thus=
> > believe you should be explaining to us how this will make our programs=
> > better, rather than telling us to change our code.
> i think you are missing the context.  my reply was about puts.
> i didn't propose to change the historical behaviour of printf.
> it's way too late to change. :(

Ahhh... Ok.

The problem though is that thanks to gcc, how puts() behaves is how=20
printf() behaves some of the time. So printf() no longer has its=20
historical behavior.

> > I agree we should not make system libraries, by default, perform a lot =
> > extra input validation. I believe that _DIAGASSERT is fine for them.=20
> > However I believe that printf() for the '%s' format and puts() are=20
> > different. I believe we should retain the printf "(null)" behavior and,=
> > especially in light of the gcc optimization, we should extend the behav=
> > to puts(). And that's it. I believe this as I see printf("%s") being us=
> > in error-case-logging code in programs, and I feel it is much simpler t=
> > let "%s" deal with NULL than to make EVERY caller be defensive.
> if you follow gcc (ie. honor compiler's right to do
> this kind of optimization), you can't use non-standard extensions anyway.
> if you don't follow gcc (ie. disable the optimization),
> you don't need to extend the extension to puts.
> in either way, i don't see any good reason to propagate
> the extention to puts.

You've defined everything in a very black & white manner, and in such a=20
way that both scenarios support your opinion. That's not really a good=20
starting point for an exchange of ideas.

Exactly what puts() does is up to us in the areas of "standards undefined"=
behavior, is it not? So we are free to add "(null)" support as I=20
understand it. I really don't see why we shouldn't. What do you think will=
be broken or what will we lose?

The reality is we will probably have to live with gcc making assumptions=20
for us. And to be honest, if we change puts(), then the assumption gcc=20
makes (that printf("%s\n", x) yields the same effect as puts(x) for all x)=
is once again true.

Take care,


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