libweston: Fix crash with mirror-of

Since c4eb15d453 we keep a copy of
native mode parameters, however we forgot to initialize the
native mode parameters in some situations, which breaks the
output mirroring code when it sees uninitialized data.

Fixes c4eb15d453
Fixes #949

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

frontend/main.c

@@ -2540,6 +2540,9 @@ wet_output_compute_output_from_mirror(struct weston_output *output,
 				      struct weston_mode *mode,
 				      int *scale)
 {
+	assert(output->native_mode_copy.width);
+	assert(output->native_mode_copy.height);
+
 	mode->width = output->native_mode_copy.width /
 			mirror->current_scale;
 

libweston/backend-drm/modes.c

@@ -912,7 +912,7 @@ drm_output_set_mode(struct weston_output *base,
 	output->base.current_mode->flags |= WL_OUTPUT_MODE_CURRENT;
 
 	/* Set native_ fields, so weston_output_mode_switch_to_native() works */
-	output->base.native_mode = output->base.current_mode;
+	weston_output_copy_native_mode(&output->base, output->base.current_mode);
 	output->base.native_scale = output->base.current_scale;
 
 	return 0;

libweston/backend-pipewire/pipewire.c

@@ -1129,7 +1129,8 @@ pipewire_switch_mode(struct weston_output *base, struct weston_mode *target_mode
 
 	base->current_mode->flags &= ~WL_OUTPUT_MODE_CURRENT;
 
-	base->current_mode = base->native_mode = local_mode;
+	base->current_mode = local_mode;
+	weston_output_copy_native_mode(base, local_mode);
 	base->current_mode->flags |= WL_OUTPUT_MODE_CURRENT;
 
 	fb_size.width = target_mode->width;
@@ -1172,8 +1173,8 @@ pipewire_output_set_size(struct weston_output *base, int width, int height)
 	current_mode = pipewire_ensure_matching_mode(&output->base, &init_mode);
 	current_mode->flags = WL_OUTPUT_MODE_CURRENT | WL_OUTPUT_MODE_PREFERRED;
 
-	output->base.current_mode = output->base.native_mode = current_mode;
-
+	output->base.current_mode = current_mode;
+	weston_output_copy_native_mode(base, current_mode);
 	output->base.start_repaint_loop = pipewire_output_start_repaint_loop;
 	output->base.repaint = pipewire_output_repaint;
 	output->base.assign_planes = NULL;

libweston/backend-x11/x11.c

@@ -1182,7 +1182,7 @@ x11_output_set_size(struct weston_output *base, int width, int height)
 	wl_list_insert(&output->base.mode_list, &output->mode.link);
 
 	output->base.current_mode = &output->mode;
-	output->base.native_mode = &output->native;
+	weston_output_copy_native_mode(&output->base, &output->mode);
 	output->base.native_scale = output->base.current_scale;
 
 	return 0;

libweston/compositor.c

@@ -525,6 +525,36 @@ static void
 weston_compositor_reflow_outputs(struct weston_compositor *compositor,
 				struct weston_output *resized_output, int delta_width);
 
+/** Set up the native mode for an output
+ *
+ * \param output     The weston_output object
+ * \param mode       The new native mode
+ *
+ * Our mode setting code does some ugly tricks, and will
+ * sometimes save pointers to ephemeral structures for
+ * comparison later.
+ *
+ * To work around this fragility, we copy the contents of
+ * the native mode at set time.
+ *
+ * This function will be removed when we fix the mode set
+ * code.
+ *
+ * \ingroup output
+ * \internal
+ */
+WL_EXPORT void
+weston_output_copy_native_mode(struct weston_output *output,
+			       struct weston_mode *mode)
+{
+	output->native_mode = mode;
+	output->native_mode_copy.width = mode->width;
+	output->native_mode_copy.height = mode->height;
+	output->native_mode_copy.flags = mode->flags;
+	output->native_mode_copy.aspect_ratio = mode->aspect_ratio;
+	output->native_mode_copy.refresh = mode->refresh;
+}
+
 /**
  * \ingroup output
  */
@@ -552,15 +582,9 @@ weston_output_mode_set_native(struct weston_output *output,
 	}
 
 	old_width = output->width;
-	output->native_mode = mode;
+	weston_output_copy_native_mode(output, mode);
 	output->native_scale = scale;
 
-	output->native_mode_copy.width = mode->width;
-	output->native_mode_copy.height = mode->height;
-	output->native_mode_copy.flags = mode->flags;
-	output->native_mode_copy.aspect_ratio = mode->aspect_ratio;
-	output->native_mode_copy.refresh = mode->refresh;
-
 	weston_mode_switch_finish(output, mode_changed, scale_changed);
 
 	if (mode_changed || scale_changed) {
@@ -8053,7 +8077,7 @@ weston_output_set_single_mode(struct weston_output *output,
 	wl_list_insert(&output->mode_list, &mode->link);
 out:
 	output->current_mode = mode;
-	output->native_mode = mode;
+	weston_output_copy_native_mode(output, mode);
 
 	if (local) {
 		wl_list_remove(&local->link);

libweston/libweston-internal.h

@@ -656,4 +656,8 @@ convert_size_by_transform_scale(int32_t *width_out, int32_t *height_out,
 bool
 weston_authenticate_user(const char *username, const char *password);
 
+void
+weston_output_copy_native_mode(struct weston_output *output,
+			       struct weston_mode *mode);
+
 #endif