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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