Date: Tue, 29 Jun 2004 12:44:44 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: cvs-src@freebsd.org Subject: Re: cvs commit: src/sys/vm vm_map.c Message-ID: <20040629123426.G2908@gamplex.bde.org> In-Reply-To: <16608.36423.596831.48148@grasshopper.cs.duke.edu> References: <200406281915.i5SJFeaV060231@repoman.freebsd.org> <20040628193858.GG5635@green.homeunix.org> <20040628201821.GA23618@green.homeunix.org> <16608.36423.596831.48148@grasshopper.cs.duke.edu>
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On Mon, 28 Jun 2004, Andrew Gallatin wrote:
> Brian Fundakowski Feldman writes:
> >
> > GCC not actually type-checking here is certainly a bug from my
> > viewpoint and one whose existence makes me more than a little
> > worried about further problems with min() and friends (ones that
> > I did not introduced ;). Are there any GCC experts that can help
> > out, here?
> >
>
> -Wconversion would find this..
>
> -Wconversion
> Warn if a prototype causes a type conversion that is different
> from what would happen to the same argument in the absence of a
> prototype. This includes conversions of fixed point to floating
> and vice versa, and conversions changing the width or signedness
> of a fixed point argument except when the same as the default
> promotion.
>
> However its a little bit too restrictive, as it complains about any
^^^^^^ big :-)
> mismatch and the compile doesn't get even one C file done before
> erroring out.
>
> If I add -Wconversion to my cflags, it first trips on sys/bus.h
> (harmless passing of "1" to a function taking a long),
> and then it pukes all over atomic.h:
>
> In file included from ../../../sys/systm.h:41,
> from ../../../cam/cam.c:35:
> machine/atomic.h: In function `atomic_set_acq_8':
> machine/atomic.h:308: warning: passing arg 2 of `atomic_set_8' with different width due to prototype
> machine/atomic.h: In function `atomic_set_rel_8':
> machine/atomic.h:308: warning: passing arg 2 of `atomic_set_8' with different width due to prototype
>
> Any idea what its problem is?
This is a FAQ, but I couldn't find the answer in gcc.info. The problem
is that -Wconversion doesn't do what you want. It was intended for
discovering portability problems in K&R code and/or old code that doesn't
always have prototypes in scope. The default promotions can work, but
not if there is a prototype that sometimes forces wider args. I forget
if the signedness warning was there originally. Signedness mismatches for
parameters are subtler than size mismatches and tend to get "fixed" by 2
bogus conversions canceling each other.
Bruce
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