debug:

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.11.20151219 for powerpc64-unknown-linux):
        dwarfReturnRegNo: Unsupported platform!
CallStack (from ImplicitParams):
  error, called at compiler/nativeGen/Dwarf/Constants.hs:224:19 in ghc:Dwarf.Constants

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Provide DWARF constants for registers.

Still TODO:

• add unwinding information to StgCRun to ensure that the unwinder can unwind from Haskell into C
• to support the RTS unwinder: add support to the initial register callback set_initial_registers in rts/Libdw.c
• Valid unwind records in stg_stop_thread (defined in rts/StgStartup.cmm)
• Support in the native code generator (by implementing the extractUnwindPoints field of NcgImpl)
• Unwinding support in libdw