static inline void vmsvga_update_rect_delayed(struct vmsvga_state_s *s,
                int x, int y, int w, int h)
{
    struct vmsvga_rect_s *rect = &s->redraw_fifo[s->redraw_fifo_last++];

    s->redraw_fifo_last &= REDRAW_FIFO_LEN - 1;
    rect->x = x;
    rect->y = y;
    rect->w = w;
    rect->h = h;
}

The product writes data past the end, or before the beginning, of the intended buffer.