Michael Roth <mdr...@linux.vnet.ibm.com> writes:
> In general QMP command parameter values are specified by consumers of the
> QMP/HMP interface, but in the case of optional parameters these values may
> be left uninitialized.
>
> It is considered a bug for code to make use of optional parameters that have
> not been flagged as being present by the marshalling code (via corresponding
> has_<parameter> parameter), however our marshalling code will still pass
> these uninitialized values on to the corresponding QMP function (to then
> be ignored). Some compilers (clang in particular) consider this unsafe
> however, and generate warnings as a result. As reported by Peter Maydell:
>
> This is something clang's -fsanitize=undefined spotted. The
> code generated by qapi-commands.py in qmp-marshal.c for
> qmp_marshal_* functions where there are some optional
> arguments looks like this:
>
> bool has_force = false;
> bool force;
>
> mi = qmp_input_visitor_new_strict(QOBJECT(args));
> v = qmp_input_get_visitor(mi);
> visit_type_str(v, &device, "device", errp);
> visit_start_optional(v, &has_force, "force", errp);
> if (has_force) {
> visit_type_bool(v, &force, "force", errp);
> }
> visit_end_optional(v, errp);
> qmp_input_visitor_cleanup(mi);
>
> if (error_is_set(errp)) {
> goto out;
> }
> qmp_eject(device, has_force, force, errp);
>
> In the case where has_force is false, we never initialize
> force, but then we use it by passing it to qmp_eject.
> I imagine we don't then actually use the value, but clang
> complains in particular for 'bool' variables because the value
> that ends up being loaded from memory for 'force' is not either
> 0 or 1 (being uninitialized stack contents).
>
> Fix this by initializing all QMP command parameters to {0} in the
> marshalling code prior to passing them on to the QMP functions.
>
> Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com>
> Reported-by: Peter Maydell <peter.mayd...@linaro.org>
> Tested-by: Peter Maydell <peter.mayd...@linaro.org>
> Reviewed-by: Eric Blake <ebl...@redhat.com>
> ---
> scripts/qapi-commands.py | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
> index 386f17e..7d93d01 100644
> --- a/scripts/qapi-commands.py
> +++ b/scripts/qapi-commands.py
> @@ -111,7 +111,7 @@ bool has_%(argname)s = false;
> argname=c_var(argname), argtype=c_type(argtype))
> else:
> ret += mcgen('''
> -%(argtype)s %(argname)s;
> +%(argtype)s %(argname)s = {0};
> ''',
> argname=c_var(argname), argtype=c_type(argtype))
Thanks for the clear commit message.
Reviewed-by: Markus Armbruster <arm...@redhat.com>
