From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50259) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gWMJK-0006Hx-E7 for qemu-devel@nongnu.org; Mon, 10 Dec 2018 09:13:27 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gWMJH-0002RP-9O for qemu-devel@nongnu.org; Mon, 10 Dec 2018 09:13:26 -0500 Date: Mon, 10 Dec 2018 15:13:10 +0100 From: Cornelia Huck Message-ID: <20181210151310.3f13c28f.cohuck@redhat.com> In-Reply-To: <20181210135803.20208-1-peter.maydell@linaro.org> References: <20181210135803.20208-1-peter.maydell@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Cc: qemu-devel@nongnu.org, patches@linaro.org, qemu-s390x@nongnu.org, Christian Borntraeger , Richard Henderson , David Hildenbrand , "Dr . David Alan Gilbert" On Mon, 10 Dec 2018 13:58:03 +0000 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... Nice :) > > 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; I would find src_pmcw etc. easier to read. Other opinions? > > - 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];