Date: Thu, 14 Jan 2021 13:04:54 +0100 From: Dimitry Andric <dim@FreeBSD.org> To: Thierry Thomas <thierry@FreeBSD.org> Cc: FreeBSD Hackerz <hackers@freebsd.org> Subject: Re: Some fun with -O2 Message-ID: <5E0B4EA1-0F24-41C2-AEDD-F9D127B5D290@FreeBSD.org> In-Reply-To: <YAAqI08bgBtfpssP@graf.pompo.net> References: <YAAqI08bgBtfpssP@graf.pompo.net>
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--Apple-Mail=_33B68D4C-1DE7-44C6-B1EE-8E2F5E6AF82E Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 On 14 Jan 2021, at 12:25, Thierry Thomas <thierry@FreeBSD.org> wrote: >=20 > Let=C2=B4s check a small C program, check_mktime.c, fetchable from > <https://people.freebsd.org/~thierry/check_mktime.c>. >=20 > $CC -o check_mktime -O2 check_mktime.c > ./check_mktime $ gcc -fsanitize=3Dundefined check_mktime.c -o check_mktime <...lots of warnings snipped...> $ ./check_mktime check_mktime.c:109:51: runtime error: signed integer overflow: = 4611686018427387904 * 2 cannot be represented in type 'long int' check_mktime.c:111:13: runtime error: signed integer overflow: = -9223372036854775808 - 1 cannot be represented in type 'long int' check_mktime.c:123:28: runtime error: signed integer overflow: = 1073741824 * 2 cannot be represented in type 'int' check_mktime.c:125:7: runtime error: signed integer overflow: = -2147483648 - 1 cannot be represented in type 'int' This program indeed relies on -fwrapv. -Dimitry --Apple-Mail=_33B68D4C-1DE7-44C6-B1EE-8E2F5E6AF82E Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.2 iF0EARECAB0WIQR6tGLSzjX8bUI5T82wXqMKLiCWowUCYAAzZgAKCRCwXqMKLiCW o+p8AJ0RXoS2gDkHTWNSbxjyeye4WQa/8ACgmCobasaFEDND9qQodSFJkiYpg8M= =Jr7y -----END PGP SIGNATURE----- --Apple-Mail=_33B68D4C-1DE7-44C6-B1EE-8E2F5E6AF82E--
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