Re: [PATCH v3 1/3] util/main-loop: Fix maximum number of wait objects for win32

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Aug 24, 2022 at 04:52:29PM +0800, Bin Meng wrote:
> From: Bin Meng <bin.meng@windriver.com>
> 
> The maximum number of wait objects for win32 should be
> MAXIMUM_WAIT_OBJECTS, not MAXIMUM_WAIT_OBJECTS + 1.
> 
> Signed-off-by: Bin Meng <bin.meng@windriver.com>
> ---
> 
> Changes in v3:
> - move the check of adding the same HANDLE twice to a separete patch
> 
> Changes in v2:
> - fix the logic in qemu_add_wait_object() to avoid adding
>   the same HANDLE twice
> 
>  util/main-loop.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/util/main-loop.c b/util/main-loop.c
> index f00a25451b..cb018dc33c 100644
> --- a/util/main-loop.c
> +++ b/util/main-loop.c
> @@ -363,10 +363,10 @@ void qemu_del_polling_cb(PollingFunc *func, void *opaque)
>  /* Wait objects support */
>  typedef struct WaitObjects {
>      int num;
> -    int revents[MAXIMUM_WAIT_OBJECTS + 1];
> -    HANDLE events[MAXIMUM_WAIT_OBJECTS + 1];
> -    WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS + 1];
> -    void *opaque[MAXIMUM_WAIT_OBJECTS + 1];
> +    int revents[MAXIMUM_WAIT_OBJECTS];
> +    HANDLE events[MAXIMUM_WAIT_OBJECTS];
> +    WaitObjectFunc *func[MAXIMUM_WAIT_OBJECTS];
> +    void *opaque[MAXIMUM_WAIT_OBJECTS];
>  } WaitObjects;
>  
>  static WaitObjects wait_objects = {0};
> @@ -395,6 +395,9 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc *func, void *opaque)
>          if (w->events[i] == handle) {
>              found = 1;
>          }
> +        if (i == MAXIMUM_WAIT_OBJECTS - 1) {
> +            break;
> +        }

Took me a while to realize this was protecting the body
of the next if from out of bounds access. Can we redo
this to make it explicit:

>          if (found) {

   if (found &&
       i < (MAXIMUM_WAIT_OBJECTS - 1)) {

>              w->events[i] = w->events[i + 1];
>              w->func[i] = w->func[i + 1];

With regards,
Daniel
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