From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.92.2 #3 (Red Hat Linux)) id 1iBa7h-0001eS-Fx for barebox@lists.infradead.org; Sat, 21 Sep 2019 07:48:07 +0000 Message-ID: From: Rouven Czerwinski Date: Sat, 21 Sep 2019 09:47:47 +0200 In-Reply-To: <20190920075813.22471-3-ahmad@a3f.at> References: <20190920075813.22471-1-ahmad@a3f.at> <20190920075813.22471-3-ahmad@a3f.at> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH v1 3/4] common: ubsan: ignore shifting one into sign bit To: Ahmad Fatoum , barebox@lists.infradead.org Hi Ahmad, On Fri, 2019-09-20 at 09:58 +0200, Ahmad Fatoum wrote: > The __ubsan_handle_shift_out_of_bounds handler would be called for > code > shifting a one into the sign bit like (1 << 31), which is all too > common > in barebox. It's technically UB, but it's so prevalent that it's > highly > unlikely to be treated by a compiler as anything else than the > standard-compliant (1U << 31). > > Check for this case here and ignore it selectively. Shouldn't we rather fix the the (1 << 31) to be (1U <<31)? > Signed-off-by: Ahmad Fatoum > --- > lib/ubsan.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/lib/ubsan.c b/lib/ubsan.c > index 89ca6e580bce..41a5731dda66 100644 > --- a/lib/ubsan.c > +++ b/lib/ubsan.c > @@ -382,6 +382,26 @@ void __ubsan_handle_shift_out_of_bounds(struct > shift_out_of_bounds_data *data, > if (suppress_report(&data->location)) > return; > > + /* This handler would be called for code shifting a one into > the > + * sign bit like (1 << 31), which is all too common in barebox. > + * It's technically UB, but it's so prevalent that it's highly > + * unlikely to be treated by a compiler as anything else than > the > + * standard-compliant (1U << 31). Thus check for this case here > + * and ignore it selectively > + */ > + if (type_is_signed(lhs_type)) { > + s_max lhs_int, rhs_int; > + > + lhs_int = get_signed_val(lhs_type, lhs); > + rhs_int = get_signed_val(rhs_type, rhs); > + > + if (fls(lhs_int) + rhs_int == type_bit_width(lhs_type)) > { > + pr_debug("signed left shift of %lld by %lld > ignored.\n", > + (s64)lhs_int, (s64)rhs_int); > + return; > + } > + } > + > ubsan_prologue(&data->location, &flags); > > val_to_string(rhs_str, sizeof(rhs_str), rhs_type, rhs); - rcz _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox