In Modules/selectmodule.c it is assumed that the kevent structure is defined on FreeBSD and NetBSD as:

     struct kevent {
             uintptr_t ident;
             short     filter;
             u_short   flags;
             u_int     fflags;
             intptr_t  data;
             uintptr_t udata;
     };

and on OpenBSD as:

     struct kevent {
             u_int     ident;
             short     filter;
             u_short   flags;
             u_int     fflags;
             intptr_t  data;
             int       udata;
     };


Actually it is defined on FreeBSD as:

     struct kevent {
             uintptr_t ident;
             short     filter;
             u_short   flags;
             u_int     fflags;
             intptr_t  data;
             void      *udata;
     };

On OpenBSD as:

     struct kevent {
             uintptr_t ident;
             short     filter;
             u_short   flags;
             u_int     fflags;
             int64_t   data;
             void      *udata;
     };

And on NetBSD as:

     struct kevent {
             uintptr_t ident;
             uint32_t  filter;
             uint32_t  flags;
             uint32_t  fflags;
             int64_t   data;
             intptr_t  udata;
     };

Other issues are related to rich comparison. Due to integer overflows the ordering is not transitive. The rich comparison protocol is not properly supported, comparing a kevent_event object with a non-kevent_event object don't falls back to the rich comparison methods of the right arguments.