[RFC] Improving compatibility of NetBSD's unwind.h (or replacing it?)

[Michał Górny <mgorny%gentoo.org@localhost>]

Hi,

While working on building more LLVM projects on NetBSD, I've noticed
that libcxxabi fails to build due to incompatible unwind.h.  The example
of problematic code is [1]:

  _Unwind_SetGR(context, __builtin_eh_return_data_regno(0),
                reinterpret_cast<uintptr_t>(unwind_exception));
  _Unwind_SetGR(context, __builtin_eh_return_data_regno(1),
                static_cast<uintptr_t>(results.ttypeIndex));
  _Unwind_SetIP(context, results.landingPad);

This fails to build because NetBSD's unwind.h expects the last argument
to _Unwind_Set{GR,IP} to be a pointer.  However, it seems that other
implementations expect an unsigned integer type instead.  The types used
for the last argument of appropriate functions (and return type of their
respective _Unwind_Get* counterparts) are:

                        SetGR/GetGR   SetIP/GetIP
  gcc 7.3.0 on Linux    _Unwind_Word  _Unwind_Ptr   (-> unsigned [a])
  clang                 _Unwind_Word  _Unwind_Word  (-> uintptr_t)
  llvm-libunwind        uintptr_t     uintptr_t
  libunwind 1.2.1       uns. long     uns. long

  [a] gcc is doing some __attribute__ magic on top of it

I think changing our header to use unsigned integer type alike other
implementations is the way to go.  Does this sound like the right thing
to do?

[1]:https://github.com/llvm-mirror/libcxxabi/blob/master/src/cxa_personality.cpp#L528

-- 
Best regards,
Michał Górny

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