Re: [PATCH 1/2] avoid shifting signed integers 31 bits
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Jan 4, 2016, 17:52 UTC
- Message-ID
- <xmqqh9itp705.fsf@gitster.mtv.corp.google.com>
- In-Reply-To
- <20151231052029.GA10238@sigill.intra.peff.net>
Jeff King <peff@peff.net> writes:
Show 21 quoted lines
> 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
Let's squash an obvious change for that in to 1/2, then, before I merge the series to 'next'.
Thanks.
-- >8 -- From: Jeff King <peff@peff.net> Date: Tue, 29 Dec 2015 01:35:46 -0500 Subject: [PATCH] avoid shifting signed integers 31 bits
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.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com> --- builtin/receive-pack.c | 2 +- cache.h | 2 +- diff.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c index e6b93d0..e35ed40 100644 --- a/builtin/receive-pack.c +++ b/builtin/receive-pack.c @@ -1597,7 +1597,7 @@ static void prepare_shallow_update(struct command *commands, continue; si->need_reachability_test[i]++; for (k = 0; k < 32; k++) - if (si->used_shallow[i][j] & (1 << k)) + if (si->used_shallow[i][j] & (1U << k)) si->shallow_ref[j * 32 + k]++; } diff --git a/cache.h b/cache.h index 6f53962..9088843 100644 --- a/cache.h +++ b/cache.h @@ -214,7 +214,7 @@ struct cache_entry { #define CE_INTENT_TO_ADD (1 << 29) #define CE_SKIP_WORKTREE (1 << 30) /* CE_EXTENDED2 is for future extension */ -#define CE_EXTENDED2 (1 << 31) +#define CE_EXTENDED2 (1U << 31) #define CE_EXTENDED_FLAGS (CE_INTENT_TO_ADD | CE_SKIP_WORKTREE) diff --git a/diff.h b/diff.h index f7208ad..893f446 100644 --- a/diff.h +++ b/diff.h @@ -91,7 +91,7 @@ typedef struct strbuf *(*diff_prefix_fn_t)(struct diff_options *opt, void *data) #define DIFF_OPT_DIRSTAT_BY_LINE (1 << 28) #define DIFF_OPT_FUNCCONTEXT (1 << 29) #define DIFF_OPT_PICKAXE_IGNORE_CASE (1 << 30) -#define DIFF_OPT_DEFAULT_FOLLOW_RENAMES (1 << 31) +#define DIFF_OPT_DEFAULT_FOLLOW_RENAMES (1U << 31) #define DIFF_OPT_TST(opts, flag) ((opts)->flags & DIFF_OPT_##flag) #define DIFF_OPT_TOUCHED(opts, flag) ((opts)->touched_flags & DIFF_OPT_##flag)
-- 2.7.0-rc3-132-g73ad441