Re: [Qemu-devel] qapi-commands.py generates code that uses uninitialized variables

[Markus Armbruster]

Peter Maydell <address@hidden> writes:

> 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

Use of FOO when !has_FOO is a bug.

> 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).
>
> Anybody understand what the codegenerator is doing well enough
> to suggest a fix? I'd guess that just initializing the variable either
> at point of declaration or in an else {) clause of the 'if (has_force)'
> conditional would suffice, but presumably you need to handle
> all the possible data types...

I can give it a try.  Will probably take a while, though.