noop-renderer: Read the shm buffer contents on attach

The noop-renderer doesn't read buffer contents, which means bad
buffers go undetected. Thus, read the buffer contents just for
the purpose of triggering SIGBUS (and having the client killed).

Fixes the bad-buffer test when run against the headless backend.

Signed-off-by: Emilio Pozuelo Monfort <emilio.pozuelo@collabora.co.uk>

src/noop-renderer.c

@@ -50,6 +50,9 @@ static void
 noop_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer)
 {
 	struct wl_shm_buffer *shm_buffer;
+	uint8_t *data;
+	uint32_t size, i, width, height, stride;
+	volatile unsigned char unused = 0; /* volatile so it's not optimized out */
 
 	if (!buffer)
 		return;
@@ -61,9 +64,24 @@ noop_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer)
 		return;
 	}
 
+	data = wl_shm_buffer_get_data(shm_buffer);
+	stride = wl_shm_buffer_get_stride(shm_buffer);
+	width = wl_shm_buffer_get_width(shm_buffer);
+	height = wl_shm_buffer_get_height(shm_buffer);
+	size = stride * height;
+
+	/* Access the buffer data to make sure the buffer's client gets killed
+	 * if the buffer size is invalid. This makes the bad_buffer test pass.
+	 * This can be removed if we start reading the buffer contents
+	 * somewhere else, e.g. in repaint_output(). */
+	wl_shm_buffer_begin_access(shm_buffer);
+	for (i = 0; i < size; i++)
+		unused ^= data[i];
+	wl_shm_buffer_end_access(shm_buffer);
+
 	buffer->shm_buffer = shm_buffer;
-	buffer->width = wl_shm_buffer_get_width(shm_buffer);
-	buffer->height = wl_shm_buffer_get_height(shm_buffer);
+	buffer->width = width;
+	buffer->height = height;
 }
 
 static void