From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55048) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZtGoO-0006Io-92 for qemu-devel@nongnu.org; Mon, 02 Nov 2015 10:14:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZtGoN-0002K0-J2 for qemu-devel@nongnu.org; Mon, 02 Nov 2015 10:14:20 -0500 Received: from mail-vk0-x235.google.com ([2607:f8b0:400c:c05::235]:36174) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZtGoN-0002Jp-AB for qemu-devel@nongnu.org; Mon, 02 Nov 2015 10:14:19 -0500 Received: by vkex70 with SMTP id x70so86416037vke.3 for ; Mon, 02 Nov 2015 07:14:18 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <563777D5.6050000@redhat.com> References: <1446473134-4330-1-git-send-email-pbonzini@redhat.com> <563777D5.6050000@redhat.com> From: Peter Maydell Date: Mon, 2 Nov 2015 15:13:59 +0000 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Blue Swirl , Mark Cave-Ayland , QEMU Developers On 2 November 2015 at 14:48, Paolo Bonzini wrote: > > > On 02/11/2015 15:09, Peter Maydell wrote: >>> > diff --git a/target-sparc/vis_helper.c b/target-sparc/vis_helper.c >>> > index 383cc8b..45fc7db 100644 >>> > --- a/target-sparc/vis_helper.c >>> > +++ b/target-sparc/vis_helper.c >>> > @@ -447,7 +447,7 @@ 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; >>> > + int64_t scaled = (int64_t)src << scale; >>> > int64_t from_fixed = scaled >> 16; >> This will now shift left into the sign bit of a signed integer, >> which is undefined behaviour. > > Why "now"? It would have done the same before. True, but I was reviewing the new code rather than the code you were taking away :-) Incidentally, that manual says the fpackfix and fpack32 insns use a 4 bit GSR.scale_factor value, but our code is masking by 0x1f in helper_fpack32 and helper_fpackfix. Which is right? thanks -- PMM