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Date:      Mon, 15 Oct 2012 16:26:50 -0700
From:      Garrett Cooper <yanegomi@gmail.com>
To:        Gleb Smirnoff <glebius@freebsd.org>
Cc:        src-committers@freebsd.org, John Baldwin <jhb@freebsd.org>, Jilles Tjoelker <jilles@stack.nl>, svn-src-all@freebsd.org, Bruce Evans <brde@optusnet.com.au>, svn-src-head@freebsd.org
Subject:   Re: svn commit: r241546 - head/sys/contrib/ipfilter/netinet
Message-ID:  <CAGH67wSGetFXNnUTGHRTz1r5pLDTMaCRCTLWOU3thq1fWw0Yeg@mail.gmail.com>
In-Reply-To: <20121015222333.GY89655@FreeBSD.org>
References:  <201210141503.q9EF37rE087018@svn.freebsd.org> <201210150834.09553.jhb@freebsd.org> <20121015143658.GU89655@FreeBSD.org> <20121015151147.GA92923@stack.nl> <20121016045904.Q15233@besplex.bde.org> <20121015222333.GY89655@FreeBSD.org>

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On Mon, Oct 15, 2012 at 3:23 PM, Gleb Smirnoff <glebius@freebsd.org> wrote:
> On Tue, Oct 16, 2012 at 05:09:31AM +1100, Bruce Evans wrote:
> B> > On Mon, Oct 15, 2012 at 06:36:58PM +0400, Gleb Smirnoff wrote:
> B> >> On Mon, Oct 15, 2012 at 08:34:09AM -0400, John Baldwin wrote:
> B> >> J> On Sunday, October 14, 2012 11:03:07 am Gleb Smirnoff wrote:
> B> >> J> > Author: glebius
> B> >> J> > Date: Sun Oct 14 15:03:06 2012
> B> >> J> > New Revision: 241546
> B> >> J> > URL: http://svn.freebsd.org/changeset/base/241546
> B> >
> B> >> J> > Log:
> B> >> J> >   Fix defines in r241245. We actually don't define FreeBSD.
> B> >
> B> >> J> >   Reported & tested by:      Oleg Ginzburg
> B> >
> B> >> J> Seems like it should be using 'defined(__FreeBSD_version)' instead?
> B> >
> B> >> AFAIU, the construction which left after r241546 works fine. Anything
> B> >> undefined resolves to zero, so in case of non-FreeBSD build we test
> B> >> if (0 > 10000019) and this fails which is what we expect.
> B> >
> B> >> I have used this construction several times already without any side
> B> >> effects. I have also seen it in some software in ports, where it works
> B> >> okay, too.
> B> >
> B> > The C standard indeed permits this, but gcc -Wundef will warn about it.
> B> > That compiler warning is in CWARNFLAGS in sys/conf/kern.mk so I suggest
> B> > adding the 'defined(__FreeBSD_version) &&'.
> B>
> B> The C standard requires this, but some misconfigured compilers like
> B> gcc -Wundef warn about it, and some non-C compilers like gcc -Wundef
> B> -Werror fail on it.  The bug is sometimes hidden by -Wno-system-headers,
> B> but FreeBSD wants to detect bugs in system headers so it sets
> B> -Wsystem-headers at WARNS >= 1, and then the buggy compilers find this
> B> non-bug in system headers.  The result is uglification of many system
> B> headers to use if `defined(__FOO) && ...' instead of depending on this
> B> standard and useful feature.
>
> Shouldn't we then remove -Wundef from CWARNFLAGS in kern.mk?

There is some value to -Wundef if used properly:

       -Wundef
           Warn whenever an identifier which is not a macro is encountered in
           an #if directive, outside of defined.  Such identifiers are
           replaced with zero.

Thanks,
-Garrett



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