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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 29/7/25 14:16, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <philmd@linaro.org> 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@redhat.com>
>>> ---
>>>    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;
>>>            }
>