[GHC] #11823: Undefined stg_sel_17_upd_info symbols on OS X

[GHC]

#11823: Undefined stg_sel_17_upd_info symbols on OS X
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  8.0.1-rc3
      Resolution:                    |             Keywords:
Operating System:  MacOS X           |         Architecture:  x86_64
 Type of failure:  Building GHC      |  (amd64)
  failed                             |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Great, thanks everyone who contributed dumps.

 This is quite bizarre: the pattern match in question appears to be
 selecting the 20th field of a `GHCiState` constructor (citing the STG),

 {{{#!hs
 let { sat_s1rNg :: [GHC.Types.Char] =
       \u srt:SRT:[] []
           case ipv146_s1rMI of
           _ { GHCi.UI.Monad.GHCiState _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
 _ ds36_s1rNa _ _ _ _ _  ->
                 ds36_s1rNa;
             };
 } in GHC.CString.unpackAppendCString# "'\n"# sat_s1rNg;
 }}}

 Somehow this emits this C--,
 {{{
        c1Mzv:
            _s1rMI::P64 = P64[_s1rNh::P64 + 16];
            I64[Hp - 16] = stg_sel_17_upd_info;
            P64[Hp] = _s1rMI::P64;
            _c1Mzq::P64 = Hp - 16;
            R3 = _c1Mzq::P64;
            R2 = c1Mzr_str;
            call GHC.CString.unpackAppendCString#_info(R3,
                                                       R2) args: 8, res: 0,
 upd: 8;
 }}}

 Which is truly strange in light of the check in `mkRhsClosure`,
 {{{#!hs
 mkRhsClosure    dflags bndr _cc _bi [NonVoid the_fv] upd_flag [] expr
   | let strip = snd . stripStgTicksTop (not . tickishIsCode)
   , StgCase (StgApp scrutinee [{-no args-}])
          _   -- ignore bndr
          (AlgAlt _)
          [(DataAlt _, params, sel_expr)] <- strip expr
   , StgApp selectee [{-no args-}] <- strip sel_expr
   , the_fv == scrutinee                -- Scrutinee is the only free
 variable

   , let (_, _, params_w_offsets) = mkVirtConstrOffsets dflags (addIdReps
 params)
                                    -- Just want the layout
   , Just the_offset <- assocMaybe params_w_offsets (NonVoid selectee)

   , let offset_into_int = bytesToWordsRoundUp dflags the_offset
                           - fixedHdrSizeW dflags
   , offset_into_int <= mAX_SPEC_SELECTEE_SIZE dflags -- Offset is small
 enough
   = let lf_info = mkSelectorLFInfo bndr offset_into_int (isUpdatable
 upd_flag)
     in cgRhsStdThunk bndr lf_info [StgVarArg the_fv]

 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11823#comment:9>
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