[PATCH] compositor: fix overflow issue when calculate msecs of vblank

[Kristian Høgsberg]

On Wed, Sep 05, 2012 at 03:35:32AM +0000, Wang, Quanxian wrote:
> From "Quanxian Wang" <quanxian.wang at intel.com<mailto:quanxian.wang at intel.com>>
> 
> commit f7b156cef1ed8081df6f25cc0e66c8d7fbf414fc
> Author: Wang Quanxian <quanxian.wang at intel.com>
> Date:   Wed Sep 5 11:30:38 2012 +0800
> 
>     Change int to long to avoid the overflow when calculation vblank msecs
> 
>     secs and nsecs are from vblank event, the number of secs is very big(134xxxxxxx),
>     when turns secs to msecs(multiple 1000), it will exceed uint32
>     max value.
> 
>     Signed-Off-By Quanxian Wang <quanxian.wang at intel.com>

No, the overflow is itentional.  The timestamp is just a milisecond
value with an unspecified epoch, only differences between timestamps
are useful.  It may overflow and that's expected.  If you use uint32_t
math, you can subtract timestamps before and after an overflow and
still get the number of miliseconds elapsed.

Kristian

> diff --git a/src/compositor-drm.c b/src/compositor-drm.c
> index df81aba..8b6285c 100644
> --- a/src/compositor-drm.c
> +++ b/src/compositor-drm.c
> @@ -447,7 +447,7 @@ vblank_handler(int fd, unsigned int frame, unsigned int sec, unsigned int usec,
>         struct drm_sprite *s = (struct drm_sprite *)data;
>         struct drm_compositor *c = s->compositor;
>         struct drm_output *output = s->output;
> -       uint32_t msecs;
> +       uint64_t msecs = 0;
> 
>         output->vblank_pending = 0;
> 
> @@ -480,7 +480,7 @@ page_flip_handler(int fd, unsigned int frame,
>                   unsigned int sec, unsigned int usec, void *data)
>  {
>         struct drm_output *output = (struct drm_output *) data;
> -       uint32_t msecs;
> +       uint64_t msecs=0;
> 
>         output->page_flip_pending = 0;
> 
> @@ -496,7 +496,7 @@ page_flip_handler(int fd, unsigned int frame,
>         output->next = NULL;
> 
>         if (!output->vblank_pending) {
> -               msecs = sec * 1000 + usec / 1000;
> +               msecs = (uint64_t)sec * 1000 + (uint64_t)usec / 1000;
>                 weston_output_finish_frame(&output->base, msecs);
>         }
>  }
> diff --git a/src/compositor.c b/src/compositor.c
> index f4263ac..37c52bc 100644
> --- a/src/compositor.c
> +++ b/src/compositor.c
> @@ -1026,7 +1026,7 @@ weston_output_damage(struct weston_output *output)
> 
>  static void
>  fade_frame(struct weston_animation *animation,
> -          struct weston_output *output, uint32_t msecs)
> +          struct weston_output *output, uint64_t msecs)
>  {
>         struct weston_compositor *compositor =
>                 container_of(animation,
> @@ -1129,7 +1129,7 @@ surface_accumulate_damage(struct weston_surface *surface,
>  }
> 
>  static void
> -weston_output_repaint(struct weston_output *output, uint32_t msecs)
> +weston_output_repaint(struct weston_output *output, uint64_t msecs)
>  {
>         struct weston_compositor *ec = output->compositor;
>         struct weston_surface *es;
> @@ -1222,7 +1222,7 @@ weston_compositor_read_input(int fd, uint32_t mask, void *data)
>  }
> 
>  WL_EXPORT void
> -weston_output_finish_frame(struct weston_output *output, uint32_t msecs)
> +weston_output_finish_frame(struct weston_output *output, uint64_t msecs)
>  {
>         struct weston_compositor *compositor = output->compositor;
>         struct wl_event_loop *loop =
> diff --git a/src/compositor.h b/src/compositor.h
> index 7a8058e..f49da84 100644
> --- a/src/compositor.h
> +++ b/src/compositor.h
> @@ -109,7 +109,7 @@ struct weston_spring {
>         double current;
>         double target;
>         double previous;
> -       uint32_t timestamp;
> +       uint64_t timestamp;
>  };
> 
>  enum {
> @@ -164,7 +164,7 @@ struct weston_output {
>         struct weston_output_zoom zoom;
>         int dirty;
>         struct wl_signal frame_signal;
> -       uint32_t frame_time;
> +       uint64_t frame_time;
>         int disable_planes;
> 
>         char *make, *model;
> @@ -493,7 +493,7 @@ void
>  weston_spring_init(struct weston_spring *spring,
>                    double k, double current, double target);
>  void
> -weston_spring_update(struct weston_spring *spring, uint32_t msec);
> +weston_spring_update(struct weston_spring *spring, uint64_t msec);
>  int
>  weston_spring_done(struct weston_spring *spring);
> 
> @@ -543,7 +543,7 @@ void
>  weston_plane_release(struct weston_plane *plane);
> 
>  void
> -weston_output_finish_frame(struct weston_output *output, uint32_t msecs);
> +weston_output_finish_frame(struct weston_output *output, uint64_t msecs);
>  void
>  weston_output_schedule_repaint(struct weston_output *output);
>  void
> diff --git a/src/util.c b/src/util.c
> index 4ff451a..34b140e 100644
> --- a/src/util.c
> +++ b/src/util.c
> @@ -42,7 +42,7 @@ weston_spring_init(struct weston_spring *spring,
>  }
> 
>  WL_EXPORT void
> -weston_spring_update(struct weston_spring *spring, uint32_t msec)
> +weston_spring_update(struct weston_spring *spring, uint64_t msec)
>  {
>         double force, v, current, step;
> 
> 

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