Date: Sun, 6 Nov 2011 13:13:04 -0800 From: Rui Paulo <rpaulo@FreeBSD.org> To: Alexander Best <arundel@freebsd.org> Cc: freebsd-toolchain@freebsd.org, Dimitry Andric <dim@FreeBSD.org> Subject: Re: [poc] buildkernel + clang + -Werror Message-ID: <C7A0F95A-0F55-47BF-AD60-66DDAEEC3EC7@FreeBSD.org> In-Reply-To: <20111106205805.GA78142@freebsd.org> References: <20111105102102.GA54596@freebsd.org> <20111106172835.GO2258@hoeg.nl> <20111106203316.GA73216@freebsd.org> <4EB6F38E.2080006@FreeBSD.org> <20111106205805.GA78142@freebsd.org>
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On Nov 6, 2011, at 12:58 PM, Alexander Best wrote: > On Sun Nov 6 11, Dimitry Andric wrote: >> On 2011-11-06 21:33, Alexander Best wrote: >> ...=20 >>> the problem is, something like >>>=20 >>> uint x; >>>=20 >>> if (x < 0) ... >>>=20 >>> clang will warn about this, yet it is 100% valid code so my vote = would be to >>> make such an error into a warning. >>=20 >> Sorry, but checking something unsigned to be smaller than zero is = bogus, >> or at the least superfluous, and it's perfectly sane to warn about = this, >> especially since the compiler is not going to emit code for it at = all. >=20 > there was a discussion with the topic > "disable -Wtautological-compare for clang" on freebsd-toolchain@ and = most of > the devs considered this code *not* to be bogus. ;) Tautologic checks are good because they may find problems you never = thought about. The examples pointed out are quite simple and are missing = the point. You have to thinking about crazy macros. The only argument against this tautological check that I agree with is = when the code is explicitly trying to be safe. If the developer checks = for "i < 0" when indexing an array he/she is trying to guard against = possible pitfalls in the future when someone suddenly decides to change = the variable type to become signed. One possible security vulnerability = was avoided because that developer checked for negative values. I'm against turning this off by default, but it should not cause an = error. Regards, -- Rui Paulo
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