From: Jeff King <peff@peff.net>
To: Duy Nguyen <pclouds@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>,
Christian Couder <christian.couder@gmail.com>
Subject: Re: [PATCH 1/2] avoid shifting signed integers 31 bits
Date: Thu, 31 Dec 2015 00:20:29 -0500 [thread overview]
Message-ID: <20151231052029.GA10238@sigill.intra.peff.net> (raw)
In-Reply-To: <CACsJy8CAAqZFQCfadUov7DFhSgh=dtGfE-onbXZQXO-0Y2652g@mail.gmail.com>
On Thu, Dec 31, 2015 at 12:10:33PM +0700, Duy Nguyen wrote:
> On Tue, Dec 29, 2015 at 1:35 PM, Jeff King <peff@peff.net> wrote:
> > We sometimes use 32-bit unsigned integers as bit-fields.
> > It's fine to access the MSB, because it's unsigned. However,
> > doing so as "1 << 31" is wrong, because the constant "1" is
> > a signed int, and we shift into the sign bit, causing
> > undefined behavior.
> >
> > We can fix this by using "1U" as the constant.
>
> We have this in cache.h, should it be fixed as well?
>
> /* CE_EXTENDED2 is for future extension */
> #define CE_EXTENDED2 (1 << 31)
Sort of. We don't actually use it, and since it's a macro, that means it
never even hits the compiler proper itself. So it's not a bug, but it's
a bug waiting to happen. :)
-Peff
next prev parent reply other threads:[~2015-12-31 5:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-29 6:34 [PATCH 0/2] compiling with -fsanitize=undefined Jeff King
2015-12-29 6:35 ` [PATCH 1/2] avoid shifting signed integers 31 bits Jeff King
2015-12-30 0:09 ` Junio C Hamano
2015-12-30 4:25 ` Jeff King
2015-12-31 5:10 ` Duy Nguyen
2015-12-31 5:20 ` Jeff King [this message]
2016-01-04 17:52 ` Junio C Hamano
2016-01-04 23:32 ` Jeff King
2015-12-29 6:36 ` [PATCH 2/2] bswap: add NO_UNALIGNED_LOADS define Jeff King
2015-12-29 6:42 ` Eric Sunshine
2015-12-29 6:45 ` Jeff King
2015-12-29 6:44 ` [PATCH 0/2] compiling with -fsanitize=undefined Jeff King
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