From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55151) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gXQbs-000321-1t for qemu-devel@nongnu.org; Thu, 13 Dec 2018 08:01:04 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gXQbn-0007aC-V9 for qemu-devel@nongnu.org; Thu, 13 Dec 2018 08:00:59 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:43424) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gXQbn-0007QX-ES for qemu-devel@nongnu.org; Thu, 13 Dec 2018 08:00:55 -0500 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wBDCxSBl140341 for ; Thu, 13 Dec 2018 08:00:51 -0500 Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) by mx0a-001b2d01.pphosted.com with ESMTP id 2pbmrd1ppd-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 13 Dec 2018 08:00:51 -0500 Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 13 Dec 2018 13:00:50 -0000 References: <20181213120252.21697-1-peter.maydell@linaro.org> From: Farhan Ali Date: Thu, 13 Dec 2018 08:00:34 -0500 MIME-Version: 1.0 In-Reply-To: <20181213120252.21697-1-peter.maydell@linaro.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Subject: Re: [Qemu-devel] [PATCH v2] 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: patches@linaro.org, qemu-s390x@nongnu.org, David Hildenbrand , Richard Henderson , Christian Borntraeger , Cornelia Huck , Thomas Huth On 12/13/2018 07:02 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 > --- > v1->v2 changes: > * add comment about why we're using locals > * name locals with underscores, as QEMU's naming conventions recommend > > > hw/s390x/css.c | 28 ++++++++++++++++++++++++---- > 1 file changed, 24 insertions(+), 4 deletions(-) > > diff --git a/hw/s390x/css.c b/hw/s390x/css.c > index 04ec5cc9705..f92b046cd33 100644 > --- a/hw/s390x/css.c > +++ b/hw/s390x/css.c > @@ -1290,9 +1290,19 @@ void copy_scsw_to_guest(SCSW *dest, const SCSW *src) > static void copy_schib_to_guest(SCHIB *dest, const SCHIB *src) > { > int i; > + /* > + * We copy the PMCW and SCSW in and out of local variables to > + * avoid taking the address of members of a packed struct. > + */ > + PMCW src_pmcw, dest_pmcw; > + SCSW src_scsw, dest_scsw; > > - copy_pmcw_to_guest(&dest->pmcw, &src->pmcw); > - copy_scsw_to_guest(&dest->scsw, &src->scsw); > + src_pmcw = src->pmcw; > + copy_pmcw_to_guest(&dest_pmcw, &src_pmcw); > + dest->pmcw = dest_pmcw; > + src_scsw = src->scsw; > + copy_scsw_to_guest(&dest_scsw, &src_scsw); > + dest->scsw = dest_scsw; > dest->mba = cpu_to_be64(src->mba); > for (i = 0; i < ARRAY_SIZE(dest->mda); i++) { > dest->mda[i] = src->mda[i]; > @@ -1339,9 +1349,19 @@ static void copy_scsw_from_guest(SCSW *dest, const SCSW *src) > static void copy_schib_from_guest(SCHIB *dest, const SCHIB *src) > { > int i; > + /* > + * We copy the PMCW and SCSW in and out of local variables to > + * avoid taking the address of members of a packed struct. > + */ > + PMCW src_pmcw, dest_pmcw; > + SCSW src_scsw, dest_scsw; > > - copy_pmcw_from_guest(&dest->pmcw, &src->pmcw); > - copy_scsw_from_guest(&dest->scsw, &src->scsw); > + src_pmcw = src->pmcw; > + copy_pmcw_from_guest(&dest_pmcw, &src_pmcw); > + dest->pmcw = dest_pmcw; > + src_scsw = src->scsw; > + copy_scsw_from_guest(&dest_scsw, &src_scsw); > + dest->scsw = dest_scsw; > 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