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

[Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>]

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

> Whoever merges this: feel free to replace by g_assert_not_reached().
>
> > >                }
> > >                xenfb->axis[move->axis] = move->value * scale / 0x7fff;
> > >            }