From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59527) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gXPhs-0005lt-O0 for qemu-devel@nongnu.org; Thu, 13 Dec 2018 07:03:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gXPhm-0006tG-Li for qemu-devel@nongnu.org; Thu, 13 Dec 2018 07:03:08 -0500 From: Peter Maydell Date: Thu, 13 Dec 2018 12:02:52 +0000 Message-Id: <20181213120252.21697-1-peter.maydell@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [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: qemu-devel@nongnu.org Cc: patches@linaro.org, qemu-s390x@nongnu.org, David Hildenbrand , Richard Henderson , Christian Borntraeger , Cornelia Huck , Thomas Huth , Farhan Ali 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]; -- 2.19.2