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Date: Sat, 6 Mar 2010 08:53:32 +0000
From: Chris Webb <chris@arachsys.com>
Subject: Re: [Qemu-devel] Re: Another VNC crash, qemu-kvm-0.12.3
Message-ID: <20100306085332.GF7180@arachsys.com>
References: <20100221172358.GH4894@arachsys.com> <4B82462A.7050903@redhat.com>
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To: Alexander Graf <agraf@suse.de>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

Alexander Graf <agraf@suse.de> writes:

> On 05.03.2010, at 17:52, Chris Webb wrote:
>
> > Of course, if the screen width or height is 1, it doesn't really matter what
> > the value of the mouse position for the click is, so something as simple as
> > 
> > diff --git a/vnc.c b/vnc.c
> > --- a/vnc.c
> > +++ b/vnc.c
> > @@ -1421,8 +1421,10 @@
> >         dz = 1;
> > 
> >     if (vs->absolute) {
> > -        kbd_mouse_event(x * 0x7FFF / (ds_get_width(vs->ds) - 1),
> > -                        y * 0x7FFF / (ds_get_height(vs->ds) - 1),
> > +        kbd_mouse_event(ds_get_width(vs->ds) > 1 ?
> > +                          x * 0x7FFF / (ds_get_width(vs->ds) - 1) : 0x4000,
> > +                        ds_get_height(vs->ds) > 1 ?
> > +                          y * 0x7FFF / (ds_get_height(vs->ds) - 1) : 0x4000,
> >                         dz, buttons);
> >     } else if (vnc_has_feature(vs, VNC_FEATURE_POINTER_TYPE_CHANGE)) {
> >         x -= 0x7FFF;
> > 
> > will fix the symptom: the division by zero. The underlying cause of a 9x1
> > display surface is a bit mysterious though.
> 
> Is it? When booting the screen gets resized to something like 9x1 for a
> few ms. Try putting debug code in the resize callback - you'll see it.

Ah, okay. In that case, this patch could well be the correct fix rather than
just a work-around. I'll have a look for any other places in vnc.c that
might do a similar division-by-zero for small screen sizes at the same
point.

Best wishes,

Chris.