Date: Thu, 11 Jan 2018 14:37:25 +0100 From: Dimitry Andric <dim@FreeBSD.org> To: Ed Schouten <ed@nuxi.nl> Cc: Eitan Adler <lists@eitanadler.com>, FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: 1 << 31 redux Message-ID: <CA37BE71-935C-4349-AFEF-B98160460FFE@FreeBSD.org> In-Reply-To: <CABh_MKmy3ojYO3M6YwH2wWrEp5a4C-o2XC1icN%2BNj3GDo4f%2BZA@mail.gmail.com> References: <CAF6rxg=GbfpBfPAAJg0RvpMrWW8p%2B0Ayf_Zd9i7Em2kOijFCjA@mail.gmail.com> <CABh_MKmy3ojYO3M6YwH2wWrEp5a4C-o2XC1icN%2BNj3GDo4f%2BZA@mail.gmail.com>
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On 11 Jan 2018, at 13:05, Ed Schouten <ed@nuxi.nl> wrote:
>=20
> 2018-01-11 13:03 GMT+01:00 Eitan Adler <lists@eitanadler.com>:
>> I'd also like to see if we could find some more general solution, be =
it a
>> compiler warning, bit set macro, or otherwise.
>=20
> Does Clang already offer a warning for this? If so, we should consider
> adding it to WARNS=3D6.
There is a -Wshift-sign-overflow flag, but it isn't enabled by default:
$ clang -Wshift-sign-overflow -c bar.c
bar.c:1:26: warning: signed shift result (0x80000000) sets the sign bit =
of the shift expression's type ('int') and becomes negative =
[-Wshift-sign-overflow]
int bar(void) { return 1 << 31; }
~ ^ ~~
I would expect quite a lot of stuff to break if you enable it, though. =
:)
And of course, there is -fsanitize=3Dundefined, which can catch this =
kind
of thing at runtime.
-Dimitry
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