From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57880) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zujsu-0002Ik-OC for qemu-devel@nongnu.org; Fri, 06 Nov 2015 11:29:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zujss-00059n-2w for qemu-devel@nongnu.org; Fri, 06 Nov 2015 11:29:04 -0500 Received: from s16892447.onlinehome-server.info ([82.165.15.123]:48550) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zujsr-00059D-R4 for qemu-devel@nongnu.org; Fri, 06 Nov 2015 11:29:01 -0500 Message-ID: <563CD52D.6000607@ilande.co.uk> Date: Fri, 06 Nov 2015 16:28:29 +0000 From: Mark Cave-Ayland MIME-Version: 1.0 References: <1446825056-7989-1-git-send-email-pbonzini@redhat.com> In-Reply-To: <1446825056-7989-1-git-send-email-pbonzini@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , qemu-devel@nongnu.org Cc: Blue Swirl , peter.maydell@linaro.org, armbru@redhat.com, rth@twiddle.net On 06/11/15 15:50, Paolo Bonzini wrote: > This is reported by Coverity. The algorithm description at > ftp://ftp.icm.edu.pl/packages/ggi/doc/hw/sparc/Sparc.pdf suggests > that the 32-bit parts of rs2, after the left shift, is treated > as a 64-bit integer. Bits 32 and above are used to do the > saturating truncation. > > Use a cast to unsigned in order to placate ubsan for negative > inputs, and do so in the other fpack* instructions too. > > Signed-off-by: Paolo Bonzini > --- > target-sparc/vis_helper.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/target-sparc/vis_helper.c b/target-sparc/vis_helper.c > index 383cc8b..a1c3343 100644 > --- a/target-sparc/vis_helper.c > +++ b/target-sparc/vis_helper.c > @@ -404,7 +404,8 @@ uint32_t helper_fpack16(uint64_t gsr, uint64_t rs2) > for (byte = 0; byte < 4; byte++) { > uint32_t val; > int16_t src = rs2 >> (byte * 16); > - int32_t scaled = src << scale; > + /* The cast to unsigned avoids undefined behavior for negative src. */ > + int32_t scaled = (uint32_t)src << scale; > int32_t from_fixed = scaled >> 7; > > val = (from_fixed < 0 ? 0 : > @@ -426,7 +427,8 @@ uint64_t helper_fpack32(uint64_t gsr, uint64_t rs1, uint64_t rs2) > for (word = 0; word < 2; word++) { > uint64_t val; > int32_t src = rs2 >> (word * 32); > - int64_t scaled = (int64_t)src << scale; > + /* The cast to unsigned avoids undefined behavior for negative src. */ > + int64_t scaled = (uint64_t)src << scale; > int64_t from_fixed = scaled >> 23; > > val = (from_fixed < 0 ? 0 : > @@ -447,7 +449,8 @@ uint32_t helper_fpackfix(uint64_t gsr, uint64_t rs2) > for (word = 0; word < 2; word++) { > uint32_t val; > int32_t src = rs2 >> (word * 32); > - int64_t scaled = src << scale; > + /* The cast to unsigned avoids undefined behavior for negative src. */ > + int64_t scaled = (uint64_t)src << scale; > int64_t from_fixed = scaled >> 16; > > val = (from_fixed < -32768 ? -32768 : Acked-by: Mark Cave-Ayland ATB, Mark.