From: Junio C Hamano <gitster@pobox.com>
To: "Carlo Marcelo Arenas Belón" <carenas@gmail.com>
Cc: git@vger.kernel.org, davvid@gmail.com
Subject: Re: [PATCH] wrapper: avoid UB in macOS
Date: Wed, 19 Jun 2019 07:40:28 -0700 [thread overview]
Message-ID: <xmqqk1dhr63n.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20190616184003.17236-1-carenas@gmail.com> ("Carlo Marcelo Arenas Belón"'s message of "Sun, 16 Jun 2019 11:40:03 -0700")
Carlo Marcelo Arenas Belón <carenas@gmail.com> writes:
> 0620b39b3b ("compat: add a mkstemps() compatibility function", 2009-05-31)
> included a function based on code from libiberty which would result in
> undefined behaviour in platforms where timeval's tv_usec is a 32-bit signed
> type as shown by:
>
> wrapper.c:505:31: runtime error: left shift of 594546 by 16 places cannot be represented in type '__darwin_suseconds_t' (aka 'int')
I had to scratch my head wondering what an UB was (spell it out as
"undefined behaviour" if that is what you wanted to say).
> interestingly the version of this code from gcc never had this bug and the
> code had a cast that would had prevented the issue (at least in 64-bit
> platforms) but was misapplied.
>
> change the cast to uint64_t so it also works in 32-bit platforms.
Yup, regardless of the platform, that's the "right" type to use,
certainly more correct than "size_t", as value is declared to be u64
in this function.
> gettimeofday(&tv, NULL);
> - value = ((size_t)(tv.tv_usec << 16)) ^ tv.tv_sec ^ getpid();
> + value = ((uint64_t)tv.tv_usec << 16) ^ tv.tv_sec ^ getpid();
> filename_template = &pattern[len - 6 - suffix_len];
> for (count = 0; count < TMP_MAX; ++count) {
> uint64_t v = value;
Thanks.
prev parent reply other threads:[~2019-06-19 14:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-16 18:40 [PATCH] wrapper: avoid UB in macOS Carlo Marcelo Arenas Belón
2019-06-19 14:40 ` Junio C Hamano [this message]
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