From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60786) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gWN1J-0000kH-By for qemu-devel@nongnu.org; Mon, 10 Dec 2018 09:58:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gWN1F-0006Mt-CR for qemu-devel@nongnu.org; Mon, 10 Dec 2018 09:58:53 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:58348 helo=mx0a-001b2d01.pphosted.com) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gWN1F-0006Lv-6U for qemu-devel@nongnu.org; Mon, 10 Dec 2018 09:58:49 -0500 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wBAEs0ZZ183533 for ; Mon, 10 Dec 2018 09:58:47 -0500 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0b-001b2d01.pphosted.com with ESMTP id 2p9s6741kw-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 10 Dec 2018 09:58:47 -0500 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 10 Dec 2018 14:58:46 -0000 References: <20181210135803.20208-1-peter.maydell@linaro.org> From: Farhan Ali Date: Mon, 10 Dec 2018 09:58:42 -0500 MIME-Version: 1.0 In-Reply-To: <20181210135803.20208-1-peter.maydell@linaro.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <10299eda-e310-5711-cb09-f3b725daec90@linux.ibm.com> Subject: Re: [Qemu-devel] [PATCH] hw/s390/ccw.c: Don't take address of packed members List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell , qemu-devel@nongnu.org Cc: David Hildenbrand , Cornelia Huck , "Dr . David Alan Gilbert" , Christian Borntraeger , qemu-s390x@nongnu.org, patches@linaro.org, Richard Henderson On 12/10/2018 08:58 AM, Peter Maydell wrote: > Taking the address of a field in a packed struct is a bad idea, because > it might not be actually aligned enough for that pointer type (and > thus cause a crash on dereference on some host architectures). Newer > versions of clang warn about this. > > Avoid the problem by using local copies of the PMCW and SCSW > struct fields in copy_schib_from_guest() and copy_schib_to_guest(). > > Signed-off-by: Peter Maydell > --- > This seemed like a not totally ugly and reasonably localised fix > that satisfies clang. Oddly, this makes the generated object file > 15K smaller (421K vs 406K), so it might even be better code... > > hw/s390x/css.c | 20 ++++++++++++++++---- > 1 file changed, 16 insertions(+), 4 deletions(-) > > diff --git a/hw/s390x/css.c b/hw/s390x/css.c > index 04ec5cc9705..ef07691e36b 100644 > --- a/hw/s390x/css.c > +++ b/hw/s390x/css.c > @@ -1290,9 +1290,15 @@ void copy_scsw_to_guest(SCSW *dest, const SCSW *src) > static void copy_schib_to_guest(SCHIB *dest, const SCHIB *src) > { > int i; > + PMCW srcpmcw, destpmcw; > + SCSW srcscsw, destscsw; > > - copy_pmcw_to_guest(&dest->pmcw, &src->pmcw); > - copy_scsw_to_guest(&dest->scsw, &src->scsw); > + srcpmcw = src->pmcw; > + copy_pmcw_to_guest(&destpmcw, &srcpmcw); > + dest->pmcw = destpmcw; > + srcscsw = src->scsw; > + copy_scsw_to_guest(&destscsw, &srcscsw); > + dest->scsw = destscsw; > dest->mba = cpu_to_be64(src->mba); > for (i = 0; i < ARRAY_SIZE(dest->mda); i++) { > dest->mda[i] = src->mda[i]; > @@ -1339,9 +1345,15 @@ static void copy_scsw_from_guest(SCSW *dest, const SCSW *src) > static void copy_schib_from_guest(SCHIB *dest, const SCHIB *src) > { > int i; > + PMCW srcpmcw, destpmcw; > + SCSW srcscsw, destscsw; > > - copy_pmcw_from_guest(&dest->pmcw, &src->pmcw); > - copy_scsw_from_guest(&dest->scsw, &src->scsw); > + srcpmcw = src->pmcw; > + copy_pmcw_from_guest(&destpmcw, &srcpmcw); > + dest->pmcw = destpmcw; > + srcscsw = src->scsw; > + copy_scsw_from_guest(&destscsw, &srcscsw); > + dest->scsw = destscsw; > dest->mba = be64_to_cpu(src->mba); > for (i = 0; i < ARRAY_SIZE(dest->mda); i++) { > dest->mda[i] = src->mda[i]; > Reviewed-by: Farhan Ali