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Date: Wed, 12 Dec 2018 18:34:16 +0100
From: Cornelia Huck <cohuck@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] hw/s390/ccw.c: Don't take address of
 packed members
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, "patches@linaro.org" <patches@linaro.org>, qemu-s390x <qemu-s390x@nongnu.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Richard Henderson <rth@twiddle.net>, David Hildenbrand <david@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>

On Mon, 10 Dec 2018 14:23:15 +0000
Peter Maydell <peter.maydell@linaro.org> wrote:

> On Mon, 10 Dec 2018 at 14:13, Cornelia Huck <cohuck@redhat.com> wrote:
> >
> > On Mon, 10 Dec 2018 13:58:03 +0000
> > Peter Maydell <peter.maydell@linaro.org> 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 <peter.maydell@linaro.org>
> > > ---
> > > 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;  
> >
> > <bikeshed>
> > I would find src_pmcw etc. easier to read. Other opinions?
> > </bikeshed>  
> 
> CODING_STYLE's "Naming" section agrees with you...

Do you plan to send a v2, or should I just rename and apply?