According to the Windows DDK header files, KSPIN_LOCK is defined like this:
typedef ULONG_PTR KSPIN_LOCK;
From basetsd.h (SDK, Feb. 2003):
typedef [public] unsigned __int3264 ULONG_PTR, *PULONG_PTR;
typedef unsigned __int64 ULONG_PTR, *PULONG_PTR;
typedef _W64 unsigned long ULONG_PTR, *PULONG_PTR;
The keyword __int3264 specifies an integral type that has the following
properties:
+ It is 32-bit on 32-bit platforms
+ It is 64-bit on 64-bit platforms
+ It is 32-bit on the wire for backward compatibility.
It gets truncated on the sending side and extended appropriately
(signed or unsigned) on the receiving side.
Thus register_t seems the proper mapping onto FreeBSD for spin locks.