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

[Peter Maydell <peter.maydell@xxxxxxxxxx>]

On Tue, 29 Jul 2025 at 12:14, Markus Armbruster <armbru@xxxxxxxxxx> 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.

I think also that Coverity gets confused by QAPI's convention
in generated code of defining enumerations like this:

typedef enum InputAxis {
    INPUT_AXIS_X,
    INPUT_AXIS_Y,
    INPUT_AXIS__MAX,
} InputAxis;

Coverity thinks that INPUT_AXIS__MAX might be a valid
value it can see in move->axis, because we defined the
enum that way.

In theory I suppose that since the __MAX value is only
there to be an array or enumeration bound that we could
emit code that #defines it rather than making it part
of the enum.

thanks
-- PMM