Fix UB in Instance::supports_<prop>()

openxr/src/instance.rs

@@ -149,35 +149,44 @@ impl Instance {
  }
  }
 
+ // Note: to avoid undefined behaviour, `ext_props` should be initialized filling in all fields
+ // manually. The OpenXR spec does not guarantee that `get_system_properties()` will return an
+ // error when pushing `ext_props` to `SystemProperties::next` if the corresponding extension is
+ // unsupported. Using `T::out()` and then `assume_init()` could lead to undefined behaviour
+ // because not all fields may be initialized.
  #[inline]
- pub fn supports_render_model_loading(&self, system: SystemId) -> Result<bool> {
+ pub fn get_system_props_ext<T>(&self, system: SystemId, ext_props: &mut T) -> Result<()> {
  unsafe {
- let mut render_model = sys::SystemRenderModelPropertiesFB::out(ptr::null_mut());
- let mut p = sys::SystemProperties::out(&mut render_model as *mut _ as _);
+ let mut p = sys::SystemProperties::out(ext_props as *mut _ as _);
  cvt((self.fp().get_system_properties)(
  self.as_raw(),
  system,
  p.as_mut_ptr(),
  ))?;
- Ok(render_model
- .assume_init()
- .supports_render_model_loading
- .into())
  }
+ Ok(())
+ }
+
+ #[inline]
+ pub fn supports_render_model_loading(&self, system: SystemId) -> Result<bool> {
+ let mut props = sys::SystemRenderModelPropertiesFB {
+ ty: sys::SystemRenderModelPropertiesFB::TYPE,
+ next: ptr::null_mut(),
+ supports_render_model_loading: sys::FALSE,
+ };
+ self.get_system_props_ext(system, &mut props)?;
+ Ok(props.supports_render_model_loading.into())
  }
 
  #[inline]
  pub fn supports_hand_tracking(&self, system: SystemId) -> Result<bool> {
- unsafe {
- let mut hand = sys::SystemHandTrackingPropertiesEXT::out(ptr::null_mut());
- let mut p = sys::SystemProperties::out(&mut hand as *mut _ as _);
- cvt((self.fp().get_system_properties)(
- self.as_raw(),
- system,
- p.as_mut_ptr(),
- ))?;
- Ok(hand.assume_init().supports_hand_tracking.into())
- }
+ let mut props = sys::SystemHandTrackingPropertiesEXT {
+ ty: sys::SystemHandTrackingPropertiesEXT::TYPE,
+ next: ptr::null_mut(),
+ supports_hand_tracking: sys::FALSE,
+ };
+ self.get_system_props_ext(system, &mut props)?;
+ Ok(props.supports_hand_tracking.into())
  }
 
  /// Construct a `Path` from a string