Date: Tue, 2 May 2017 11:34:45 +0200 From: Nick Hibma <nick@van-laarhoven.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD Current Mailing List <freebsd-current@FreeBSD.ORG> Subject: Re: Compiler optimisation bug Message-ID: <AACCB2FA-1B18-4DA3-BC43-FFB1DB4115E6@van-laarhoven.org> In-Reply-To: <20170502083438.GA1622@kib.kiev.ua> References: <3626A28E-9DF5-4775-BAAB-CC6C36D2CD01@van-laarhoven.org> <20170502083438.GA1622@kib.kiev.ua>
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[-- Attachment #1 --] >> Should this be reported to the clang folks? Or is this to be expected when abusing integer overflows this way? > > You will get an answer that this is expected. Add -fwrapv compiler flag > to make signed arithmetic behave in a way different from the mine-field, > or remove the code. For kernel, we use -fwrapv. Thanks, that was what I expected. I searched for -fwrapv and found similar comments. The code has been rewritten to not depend on overflow for its checks, so it works properly with any sized time_t (assuming that it is an integer though :). I'll commit it after feedback. Nick [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.30 Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJZCFK1AAoJEB9yHO7GNHbgAsMQAMwyWY9sYIVKv1rjV/MOisj6 4SZEh638XN5cN5d7XpgwlTqyFyVhcKgutIhI5EC2wvMB1cWRdeXkcI2QyZs1rlZU mhnJHPZBtspGYF9lzY9bU5yEnepVUsoqD5/ztDXNxWfzSJLPazVAksYUcBFMsq+d pKJn/xZIGOnB1rFvLScm5Z/+40cCp4c3UDGUuLLS1JFefllCrY4ydq91H1k91bm3 qd6ULuoEwfIb72NdJ2zaXzjrAvWWffnr9ZzC01JoovKmlKMJi3MKHzE1RR+gxv8x QHn8KK2gXbUjbCmfhUEtLUha58uBN/r0NAl/FoPksHM/Voaew3/w4ozL15VvdeAT M2MHoyHw4eBGBqArp/bITZhsJZtfceOYhaj9YywTYuQ13vVm7DPJDasMXU2z6Lu7 H6RW7RogO6jlxoBSy/ywIrjxkiqgRDJ23koT3PGy5H1KlQvEookICF14qs6ZxLjA VXntqfnt1NVAMmYK5vFae2dcdMrW0GGLzM4eV133N+O/gBBABBjAdk0+zcsoNJwp bDqaCXLiqrTPixjGBGn0yQbhnWw9zX2X7sXaD8KoHnoWtas4MbZzN3dVUpLRXL47 UuHyKsHXFbuwwIENFctXAwNnQYFXFJVSxoxeLmriUwYZrGKm4ghf5lq6lTCEFSNb 67HOdmHl8zS3AlioEKMl =2gg6 -----END PGP SIGNATURE-----
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