Re: [PATCH] hw/display/xenfb: Replace unreachable code by abort()

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

On Tue, Jul 29, 2025 at 02:59:46PM +0200, Philippe Mathieu-Daudé wrote:
> On 29/7/25 14:16, Markus Armbruster wrote:
> > Philippe Mathieu-Daudé <philmd@xxxxxxxxxx> writes:
> > 
> > > On 29/7/25 13:12, Markus Armbruster wrote:
> > > > xenfb_mouse_event() has a switch statement whose controlling
> > > > expression move->axis is an enum InputAxis.  The enum values are
> > > > INPUT_AXIS_X and INPUT_AXIS_Y, encoded as 0 and 1.  The switch has a
> > > > case for both axes.  In addition, it has an unreachable default label.
> > > > This convinces Coverity that move->axis can be greater than 1.  It
> > > > duly reports a buffer overrun when it is used to subscript an array
> > > > with two elements.
> > > > Replace the unreachable code by abort().
> > > > Resolves: Coverity CID 1613906
> > > > Signed-off-by: Markus Armbruster <armbru@xxxxxxxxxx>
> > > > ---
> > > >    hw/display/xenfb.c | 3 +--
> > > >    1 file changed, 1 insertion(+), 2 deletions(-)
> > > > diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
> > > > index 22822fecea..5e6c691779 100644
> > > > --- a/hw/display/xenfb.c
> > > > +++ b/hw/display/xenfb.c
> > > > @@ -283,8 +283,7 @@ static void xenfb_mouse_event(DeviceState *dev, 
> > > > QemuConsole *src,
> > > >                    scale = surface_height(surface) - 1;
> > > >                    break;
> > > >                default:
> > > > -                scale = 0x8000;
> > > > -                break;
> > > > +                abort();
> > > 
> > > We prefer GLib g_assert_not_reached() over abort() because it displays
> > > the file, line number & function before aborting.
> > 
> > The purpose of this line is to tell the compiler we can't get there,
> > with the least amount of ceremony.
> > 
> > We have ~600 calls of abort().
> 
> And ~1600 of g_assert_not_reached() =)
> 
> $ git grep -w 'abort();' | wc -l
>      556
> $ git grep -w 'g_assert_not_reached();' | wc -l
>     1551

Sounds like we could create a gitlab issue for "replace abort with
g_assert_not_reached" that could be a easy on-ramp for someone to
start contributing.

With regards,
Daniel
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