This is a nitpicky-details question with three parts. The context is that I wish to persuade some folks that it is safe to use <stddef.h>'s definition of offsetof unconditionally rather than (under some circumstances) rolling their own. The program in question is written entirely in plain old C, so please ignore C++ entirely when answering.
Part 1: When used in the same manner as the standard offsetof, does the expansion of this macro provoke undefined behavior per C89, why or why not, and is it different in C99?
#define offset_of(tp, member) (((char*) &((tp*)0)->member) - (char*)0)
Note: All implementations of interest to the people whose program this is supersede the standard's rule that pointers may only be subtracted from each other when they point into the same array, by defining all pointers, regardless of type or value, to point into a single global address space. Therefore, please do not rely on that rule when arguing that this macro's expansion provokes undefined behavior.
Part 2: To the best of your knowledge, has there ever been a released, production C implementation that, when fed the expansion of the above macro, would (under some circumstances) behave differently than it would have if its offsetof macro had been used instead?
Part 3: To the best of your knowledge, what is the most recently released production C implementation that either did not provide stddef.h or did not provide a working definition of offsetof in that header? Did that implementation claim conformance with any version of the C standard?
For parts 2 and 3, please answer only if you can name a specific implementation and give the date it was released. Answers that state general characteristics of implementations that may qualify are not useful to me.