Since Solaris 9, a bunch of pretty cool debugger commands have been added to mdb, among which ::print, ::sizeof and ::offsetof... Well, you might have noticed that whose commands are only available for a subset of Solaris kernel modules, in particular, they are not applicable to Sun Cluster product specific types. These new commands work only for kernel modules that are embedding a specific symbolic debugging information. This type of information, named CTF ("Compact Type Format") is derived (extracted and compressed) from the symbol table entries (stabs) generated at compile time. As of today, CTF supports only C code. Sun Cluster (Release 3 and up) kernel modules are written with C++... Now you know the rest of the story...