ghci/ByteCodeAsm.hs

    {-# LANGUAGE BangPatterns, CPP, DeriveFunctor, MagicHash, RecordWildCards #-}
    {-# OPTIONS_GHC -optc-DNON_POSIX_SOURCE #-}
    --
    --  (c) The University of Glasgow 2002-2006
    --

    -- | ByteCodeLink: Bytecode assembler and linker
    module ByteCodeAsm (
            assembleBCOs, assembleOneBCO,

            bcoFreeNames,
            SizedSeq, sizeSS, ssElts,
            iNTERP_STACK_CHECK_THRESH
      ) where

    #include "HsVersions.h"

    import GhcPrelude

    import ByteCodeInstr
    import ByteCodeItbls
    import ByteCodeTypes
    import GHCi.RemoteTypes
    import GHCi

    import HscTypes
    import Name
    import NameSet
    import Literal
    import TyCon
    import FastString
    import GHC.StgToCmm.Layout     ( ArgRep(..) )
    import SMRep
    import DynFlags
    import Outputable
    import GHC.Platform
    import Util
    import Unique
    import UniqDSet

    -- From iserv
    import SizedSeq

    import Control.Monad
    import Control.Monad.ST ( runST )
    import Control.Monad.Trans.Class
    import Control.Monad.Trans.State.Strict

    import Data.Array.MArray

    import qualified Data.Array.Unboxed as Array
    import Data.Array.Base  ( UArray(..) )

    import Data.Array.Unsafe( castSTUArray )

    import Foreign
    import Data.Char        ( ord )
    import Data.List
    import Data.Map (Map)
    import Data.Maybe (fromMaybe)
    import qualified Data.Map as Map

    -- -----------------------------------------------------------------------------
    -- Unlinked BCOs

    -- CompiledByteCode represents the result of byte-code
    -- compiling a bunch of functions and data types

    -- | Finds external references.  Remember to remove the names
    -- defined by this group of BCOs themselves
    bcoFreeNames :: UnlinkedBCO -> UniqDSet Name
    bcoFreeNames bco
      = bco_refs bco `uniqDSetMinusUniqSet` mkNameSet [unlinkedBCOName bco]
      where
        bco_refs (UnlinkedBCO _ _ _ _ nonptrs ptrs)
            = unionManyUniqDSets (
                 mkUniqDSet [ n | BCOPtrName n <- ssElts ptrs ] :
                 mkUniqDSet [ n | BCONPtrItbl n <- ssElts nonptrs ] :
                 map bco_refs [ bco | BCOPtrBCO bco <- ssElts ptrs ]
              )

    -- -----------------------------------------------------------------------------
    -- The bytecode assembler

    -- The object format for bytecodes is: 16 bits for the opcode, and 16
    -- for each field -- so the code can be considered a sequence of
    -- 16-bit ints.  Each field denotes either a stack offset or number of
    -- items on the stack (eg SLIDE), and index into the pointer table (eg
    -- PUSH_G), an index into the literal table (eg PUSH_I/D/L), or a
    -- bytecode address in this BCO.

    -- Top level assembler fn.
    assembleBCOs
      :: HscEnv -> [ProtoBCO Name] -> [TyCon] -> [RemotePtr ()]
      -> Maybe ModBreaks
      -> IO CompiledByteCode
    assembleBCOs hsc_env proto_bcos tycons top_strs modbreaks = do
      itblenv <- mkITbls hsc_env tycons
      bcos    <- mapM (assembleBCO (hsc_dflags hsc_env)) proto_bcos
      (bcos',ptrs) <- mallocStrings hsc_env bcos
      return CompiledByteCode
        { bc_bcos = bcos'
        , bc_itbls =  itblenv
        , bc_ffis = concat (map protoBCOFFIs proto_bcos)
        , bc_strs = top_strs ++ ptrs
        , bc_breaks = modbreaks
        }

    -- Find all the literal strings and malloc them together.  We want to
    -- do this because:
    --
    --  a) It should be done when we compile the module, not each time we relink it
    --  b) For -fexternal-interpreter It's more efficient to malloc the strings
    --     as a single batch message, especially when compiling in parallel.
    --
    mallocStrings :: HscEnv -> [UnlinkedBCO] -> IO ([UnlinkedBCO], [RemotePtr ()])
    mallocStrings hsc_env ulbcos = do
      let bytestrings = reverse (execState (mapM_ collect ulbcos) [])
      ptrs <- iservCmd hsc_env (MallocStrings bytestrings)
      return (evalState (mapM splice ulbcos) ptrs, ptrs)
     where
      splice bco@UnlinkedBCO{..} = do
        lits <- mapM spliceLit unlinkedBCOLits
        ptrs <- mapM splicePtr unlinkedBCOPtrs
        return bco { unlinkedBCOLits = lits, unlinkedBCOPtrs = ptrs }

      spliceLit (BCONPtrStr _) = do
        rptrs <- get
        case rptrs of
          (RemotePtr p : rest) -> do
            put rest
            return (BCONPtrWord (fromIntegral p))
          _ -> panic "mallocStrings:spliceLit"
      spliceLit other = return other

      splicePtr (BCOPtrBCO bco) = BCOPtrBCO <$> splice bco
      splicePtr other = return other

      collect UnlinkedBCO{..} = do
        mapM_ collectLit unlinkedBCOLits
        mapM_ collectPtr unlinkedBCOPtrs

      collectLit (BCONPtrStr bs) = do
        strs <- get
        put (bs:strs)
      collectLit _ = return ()

      collectPtr (BCOPtrBCO bco) = collect bco
      collectPtr _ = return ()

    assembleOneBCO :: HscEnv -> ProtoBCO Name -> IO UnlinkedBCO
    assembleOneBCO hsc_env pbco = do
      ubco <- assembleBCO (hsc_dflags hsc_env) pbco
      ([ubco'], _ptrs) <- mallocStrings hsc_env [ubco]
      return ubco'

    assembleBCO :: DynFlags -> ProtoBCO Name -> IO UnlinkedBCO
    assembleBCO dflags (ProtoBCO { protoBCOName       = nm
                                 , protoBCOInstrs     = instrs
                                 , protoBCOBitmap     = bitmap
                                 , protoBCOBitmapSize = bsize
                                 , protoBCOArity      = arity }) = do
      -- pass 1: collect up the offsets of the local labels.
      let asm = mapM_ (assembleI dflags) instrs

          initial_offset = 0

          -- Jump instructions are variable-sized, there are long and short variants
          -- depending on the magnitude of the offset.  However, we can't tell what
          -- size instructions we will need until we have calculated the offsets of
          -- the labels, which depends on the size of the instructions...  So we
          -- first create the label environment assuming that all jumps are short,
          -- and if the final size is indeed small enough for short jumps, we are
          -- done.  Otherwise, we repeat the calculation, and we force all jumps in
          -- this BCO to be long.
          (n_insns0, lbl_map0) = inspectAsm dflags False initial_offset asm
          ((n_insns, lbl_map), long_jumps)
            | isLarge n_insns0 = (inspectAsm dflags True initial_offset asm, True)
            | otherwise = ((n_insns0, lbl_map0), False)

          env :: Word16 -> Word
          env lbl = fromMaybe
            (pprPanic "assembleBCO.findLabel" (ppr lbl))
            (Map.lookup lbl lbl_map)

      -- pass 2: run assembler and generate instructions, literals and pointers
      let initial_state = (emptySS, emptySS, emptySS)
      (final_insns, final_lits, final_ptrs) <- flip execStateT initial_state $ runAsm dflags long_jumps env asm

      -- precomputed size should be equal to final size
      ASSERT(n_insns == sizeSS final_insns) return ()

      let asm_insns = ssElts final_insns
          insns_arr = Array.listArray (0, fromIntegral n_insns - 1) asm_insns
          bitmap_arr = mkBitmapArray bsize bitmap
          ul_bco = UnlinkedBCO nm arity insns_arr bitmap_arr final_lits final_ptrs

      -- 8 Aug 01: Finalisers aren't safe when attached to non-primitive
      -- objects, since they might get run too early.  Disable this until
      -- we figure out what to do.
      -- when (notNull malloced) (addFinalizer ul_bco (mapM_ zonk malloced))

      return ul_bco

    mkBitmapArray :: Word16 -> [StgWord] -> UArray Int Word64
    -- Here the return type must be an array of Words, not StgWords,
    -- because the underlying ByteArray# will end up as a component
    -- of a BCO object.
    mkBitmapArray bsize bitmap
      = Array.listArray (0, length bitmap) $
          fromIntegral bsize : map (fromInteger . fromStgWord) bitmap

    -- instrs nonptrs ptrs
    type AsmState = (SizedSeq Word16,
                     SizedSeq BCONPtr,
                     SizedSeq BCOPtr)

    data Operand
      = Op Word
      | SmallOp Word16
      | LabelOp Word16
    -- (unused)  | LargeOp Word

    data Assembler a
      = AllocPtr (IO BCOPtr) (Word -> Assembler a)
      | AllocLit [BCONPtr] (Word -> Assembler a)
      | AllocLabel Word16 (Assembler a)
      | Emit Word16 [Operand] (Assembler a)
      | NullAsm a
      deriving (Functor)

    instance Applicative Assembler where
        pure = NullAsm
        (<*>) = ap

    instance Monad Assembler where
      NullAsm x >>= f = f x
      AllocPtr p k >>= f = AllocPtr p (k >=> f)
      AllocLit l k >>= f = AllocLit l (k >=> f)
      AllocLabel lbl k >>= f = AllocLabel lbl (k >>= f)
      Emit w ops k >>= f = Emit w ops (k >>= f)

    ioptr :: IO BCOPtr -> Assembler Word
    ioptr p = AllocPtr p return

    ptr :: BCOPtr -> Assembler Word
    ptr = ioptr . return

    lit :: [BCONPtr] -> Assembler Word
    lit l = AllocLit l return

    label :: Word16 -> Assembler ()
    label w = AllocLabel w (return ())

    emit :: Word16 -> [Operand] -> Assembler ()
    emit w ops = Emit w ops (return ())

    type LabelEnv = Word16 -> Word

    largeOp :: Bool -> Operand -> Bool
    largeOp long_jumps op = case op of
       SmallOp _ -> False
       Op w      -> isLarge w
       LabelOp _ -> long_jumps
    -- LargeOp _ -> True

    runAsm :: DynFlags -> Bool -> LabelEnv -> Assembler a -> StateT AsmState IO a
    runAsm dflags long_jumps e = go
      where
        go (NullAsm x) = return x
        go (AllocPtr p_io k) = do
          p <- lift p_io
          w <- state $ \(st_i0,st_l0,st_p0) ->
            let st_p1 = addToSS st_p0 p
            in (sizeSS st_p0, (st_i0,st_l0,st_p1))
          go $ k w
        go (AllocLit lits k) = do
          w <- state $ \(st_i0,st_l0,st_p0) ->
            let st_l1 = addListToSS st_l0 lits
            in (sizeSS st_l0, (st_i0,st_l1,st_p0))
          go $ k w
        go (AllocLabel _ k) = go k
        go (Emit w ops k) = do
          let largeOps = any (largeOp long_jumps) ops
              opcode
                | largeOps = largeArgInstr w
                | otherwise = w
              words = concatMap expand ops
              expand (SmallOp w) = [w]
              expand (LabelOp w) = expand (Op (e w))
              expand (Op w) = if largeOps then largeArg dflags w else [fromIntegral w]
    --        expand (LargeOp w) = largeArg dflags w
          state $ \(st_i0,st_l0,st_p0) ->
            let st_i1 = addListToSS st_i0 (opcode : words)
            in ((), (st_i1,st_l0,st_p0))
          go k

    type LabelEnvMap = Map Word16 Word

    data InspectState = InspectState
      { instrCount :: !Word
      , ptrCount :: !Word
      , litCount :: !Word
      , lblEnv :: LabelEnvMap
      }

    inspectAsm :: DynFlags -> Bool -> Word -> Assembler a -> (Word, LabelEnvMap)
    inspectAsm dflags long_jumps initial_offset
      = go (InspectState initial_offset 0 0 Map.empty)
      where
        go s (NullAsm _) = (instrCount s, lblEnv s)
        go s (AllocPtr _ k) = go (s { ptrCount = n + 1 }) (k n)
          where n = ptrCount s
        go s (AllocLit ls k) = go (s { litCount = n + genericLength ls }) (k n)
          where n = litCount s
        go s (AllocLabel lbl k) = go s' k
          where s' = s { lblEnv = Map.insert lbl (instrCount s) (lblEnv s) }
        go s (Emit _ ops k) = go s' k
          where
            s' = s { instrCount = instrCount s + size }
            size = sum (map count ops) + 1
            largeOps = any (largeOp long_jumps) ops
            count (SmallOp _) = 1
            count (LabelOp _) = count (Op 0)
            count (Op _) = if largeOps then largeArg16s dflags else 1
    --      count (LargeOp _) = largeArg16s dflags

    -- Bring in all the bci_ bytecode constants.
    #include "rts/Bytecodes.h"

    largeArgInstr :: Word16 -> Word16
    largeArgInstr bci = bci_FLAG_LARGE_ARGS .|. bci

    largeArg :: DynFlags -> Word -> [Word16]
    largeArg dflags w
     | wORD_SIZE_IN_BITS dflags == 64
               = [fromIntegral (w `shiftR` 48),
                  fromIntegral (w `shiftR` 32),
                  fromIntegral (w `shiftR` 16),
                  fromIntegral w]
     | wORD_SIZE_IN_BITS dflags == 32
               = [fromIntegral (w `shiftR` 16),
                  fromIntegral w]
     | otherwise = error "wORD_SIZE_IN_BITS not 32 or 64?"

    largeArg16s :: DynFlags -> Word
    largeArg16s dflags | wORD_SIZE_IN_BITS dflags == 64 = 4
                       | otherwise                      = 2

    assembleI :: DynFlags
              -> BCInstr
              -> Assembler ()
    assembleI dflags i = case i of
      STKCHECK n               -> emit bci_STKCHECK [Op n]
      PUSH_L o1                -> emit bci_PUSH_L [SmallOp o1]
      PUSH_LL o1 o2            -> emit bci_PUSH_LL [SmallOp o1, SmallOp o2]
      PUSH_LLL o1 o2 o3        -> emit bci_PUSH_LLL [SmallOp o1, SmallOp o2, SmallOp o3]
      PUSH8 o1                 -> emit bci_PUSH8 [SmallOp o1]
      PUSH16 o1                -> emit bci_PUSH16 [SmallOp o1]
      PUSH32 o1                -> emit bci_PUSH32 [SmallOp o1]
      PUSH8_W o1               -> emit bci_PUSH8_W [SmallOp o1]
      PUSH16_W o1              -> emit bci_PUSH16_W [SmallOp o1]
      PUSH32_W o1              -> emit bci_PUSH32_W [SmallOp o1]
      PUSH_G nm                -> do p <- ptr (BCOPtrName nm)
                                     emit bci_PUSH_G [Op p]
      PUSH_PRIMOP op           -> do p <- ptr (BCOPtrPrimOp op)
                                     emit bci_PUSH_G [Op p]
      PUSH_BCO proto           -> do let ul_bco = assembleBCO dflags proto
                                     p <- ioptr (liftM BCOPtrBCO ul_bco)
                                     emit bci_PUSH_G [Op p]
      PUSH_ALTS proto          -> do let ul_bco = assembleBCO dflags proto
                                     p <- ioptr (liftM BCOPtrBCO ul_bco)
                                     emit bci_PUSH_ALTS [Op p]
      PUSH_ALTS_UNLIFTED proto pk
                               -> do let ul_bco = assembleBCO dflags proto
                                     p <- ioptr (liftM BCOPtrBCO ul_bco)
                                     emit (push_alts pk) [Op p]
      PUSH_PAD8                -> emit bci_PUSH_PAD8 []
      PUSH_PAD16               -> emit bci_PUSH_PAD16 []
      PUSH_PAD32               -> emit bci_PUSH_PAD32 []
      PUSH_UBX8 lit            -> do np <- literal lit
                                     emit bci_PUSH_UBX8 [Op np]
      PUSH_UBX16 lit           -> do np <- literal lit
                                     emit bci_PUSH_UBX16 [Op np]
      PUSH_UBX32 lit           -> do np <- literal lit
                                     emit bci_PUSH_UBX32 [Op np]
      PUSH_UBX lit nws         -> do np <- literal lit
                                     emit bci_PUSH_UBX [Op np, SmallOp nws]

      PUSH_APPLY_N             -> emit bci_PUSH_APPLY_N []
      PUSH_APPLY_V             -> emit bci_PUSH_APPLY_V []
      PUSH_APPLY_F             -> emit bci_PUSH_APPLY_F []
      PUSH_APPLY_D             -> emit bci_PUSH_APPLY_D []
      PUSH_APPLY_L             -> emit bci_PUSH_APPLY_L []
      PUSH_APPLY_P             -> emit bci_PUSH_APPLY_P []
      PUSH_APPLY_PP            -> emit bci_PUSH_APPLY_PP []
      PUSH_APPLY_PPP           -> emit bci_PUSH_APPLY_PPP []
      PUSH_APPLY_PPPP          -> emit bci_PUSH_APPLY_PPPP []
      PUSH_APPLY_PPPPP         -> emit bci_PUSH_APPLY_PPPPP []
      PUSH_APPLY_PPPPPP        -> emit bci_PUSH_APPLY_PPPPPP []

      SLIDE     n by           -> emit bci_SLIDE [SmallOp n, SmallOp by]
      ALLOC_AP  n              -> emit bci_ALLOC_AP [SmallOp n]
      ALLOC_AP_NOUPD n         -> emit bci_ALLOC_AP_NOUPD [SmallOp n]
      ALLOC_PAP arity n        -> emit bci_ALLOC_PAP [SmallOp arity, SmallOp n]
      MKAP      off sz         -> emit bci_MKAP [SmallOp off, SmallOp sz]
      MKPAP     off sz         -> emit bci_MKPAP [SmallOp off, SmallOp sz]
      UNPACK    n              -> emit bci_UNPACK [SmallOp n]
      PACK      dcon sz        -> do itbl_no <- lit [BCONPtrItbl (getName dcon)]
                                     emit bci_PACK [Op itbl_no, SmallOp sz]
      LABEL     lbl            -> label lbl
      TESTLT_I  i l            -> do np <- int i
                                     emit bci_TESTLT_I [Op np, LabelOp l]
      TESTEQ_I  i l            -> do np <- int i
                                     emit bci_TESTEQ_I [Op np, LabelOp l]
      TESTLT_W  w l            -> do np <- word w
                                     emit bci_TESTLT_W [Op np, LabelOp l]
      TESTEQ_W  w l            -> do np <- word w
                                     emit bci_TESTEQ_W [Op np, LabelOp l]
      TESTLT_F  f l            -> do np <- float f
                                     emit bci_TESTLT_F [Op np, LabelOp l]
      TESTEQ_F  f l            -> do np <- float f
                                     emit bci_TESTEQ_F [Op np, LabelOp l]
      TESTLT_D  d l            -> do np <- double d
                                     emit bci_TESTLT_D [Op np, LabelOp l]
      TESTEQ_D  d l            -> do np <- double d
                                     emit bci_TESTEQ_D [Op np, LabelOp l]
      TESTLT_P  i l            -> emit bci_TESTLT_P [SmallOp i, LabelOp l]
      TESTEQ_P  i l            -> emit bci_TESTEQ_P [SmallOp i, LabelOp l]
      CASEFAIL                 -> emit bci_CASEFAIL []
      SWIZZLE   stkoff n       -> emit bci_SWIZZLE [SmallOp stkoff, SmallOp n]
      JMP       l              -> emit bci_JMP [LabelOp l]
      ENTER                    -> emit bci_ENTER []
      RETURN                   -> emit bci_RETURN []
      RETURN_UBX rep           -> emit (return_ubx rep) []
      CCALL off m_addr i       -> do np <- addr m_addr
                                     emit bci_CCALL [SmallOp off, Op np, SmallOp i]
      BRK_FUN index uniq cc    -> do p1 <- ptr BCOPtrBreakArray
                                     q <- int (getKey uniq)
                                     np <- addr cc
                                     emit bci_BRK_FUN [Op p1, SmallOp index,
                                                       Op q, Op np]

      where
        literal (LitLabel fs (Just sz) _)
         | platformOS (targetPlatform dflags) == OSMinGW32
             = litlabel (appendFS fs (mkFastString ('@':show sz)))
         -- On Windows, stdcall labels have a suffix indicating the no. of
         -- arg words, e.g. foo@8.  testcase: ffi012(ghci)
        literal (LitLabel fs _ _) = litlabel fs
        literal LitNullAddr       = int 0
        literal (LitFloat r)      = float (fromRational r)
        literal (LitDouble r)     = double (fromRational r)
        literal (LitChar c)       = int (ord c)
        literal (LitString bs)    = lit [BCONPtrStr bs]
           -- LitString requires a zero-terminator when emitted
        literal (LitNumber nt i _) = case nt of
          LitNumInt     -> int (fromIntegral i)
          LitNumWord    -> int (fromIntegral i)
          LitNumInt64   -> int64 (fromIntegral i)
          LitNumWord64  -> int64 (fromIntegral i)
          LitNumInteger -> panic "ByteCodeAsm.literal: LitNumInteger"
          LitNumNatural -> panic "ByteCodeAsm.literal: LitNumNatural"
        -- We can lower 'LitRubbish' to an arbitrary constant, but @NULL@ is most
        -- likely to elicit a crash (rather than corrupt memory) in case absence
        -- analysis messed up.
        literal LitRubbish         = int 0

        litlabel fs = lit [BCONPtrLbl fs]
        addr (RemotePtr a) = words [fromIntegral a]
        float = words . mkLitF
        double = words . mkLitD dflags
        int = words . mkLitI
        int64 = words . mkLitI64 dflags
        words ws = lit (map BCONPtrWord ws)
        word w = words [w]

    isLarge :: Word -> Bool
    isLarge n = n > 65535

    push_alts :: ArgRep -> Word16
    push_alts V   = bci_PUSH_ALTS_V
    push_alts P   = bci_PUSH_ALTS_P
    push_alts N   = bci_PUSH_ALTS_N
    push_alts L   = bci_PUSH_ALTS_L
    push_alts F   = bci_PUSH_ALTS_F
    push_alts D   = bci_PUSH_ALTS_D
    push_alts V16 = error "push_alts: vector"
    push_alts V32 = error "push_alts: vector"
    push_alts V64 = error "push_alts: vector"

    return_ubx :: ArgRep -> Word16
    return_ubx V   = bci_RETURN_V
    return_ubx P   = bci_RETURN_P
    return_ubx N   = bci_RETURN_N
    return_ubx L   = bci_RETURN_L
    return_ubx F   = bci_RETURN_F
    return_ubx D   = bci_RETURN_D
    return_ubx V16 = error "return_ubx: vector"
    return_ubx V32 = error "return_ubx: vector"
    return_ubx V64 = error "return_ubx: vector"

    -- Make lists of host-sized words for literals, so that when the
    -- words are placed in memory at increasing addresses, the
    -- bit pattern is correct for the host's word size and endianness.
    mkLitI   ::             Int    -> [Word]
    mkLitF   ::             Float  -> [Word]
    mkLitD   :: DynFlags -> Double -> [Word]
    mkLitI64 :: DynFlags -> Int64  -> [Word]

    mkLitF f
       = runST (do
            arr <- newArray_ ((0::Int),0)
            writeArray arr 0 f
            f_arr <- castSTUArray arr
            w0 <- readArray f_arr 0
            return [w0 :: Word]
         )

    mkLitD dflags d
       | wORD_SIZE dflags == 4
       = runST (do
            arr <- newArray_ ((0::Int),1)
            writeArray arr 0 d
            d_arr <- castSTUArray arr
            w0 <- readArray d_arr 0
            w1 <- readArray d_arr 1
            return [w0 :: Word, w1]
         )
       | wORD_SIZE dflags == 8
       = runST (do
            arr <- newArray_ ((0::Int),0)
            writeArray arr 0 d
            d_arr <- castSTUArray arr
            w0 <- readArray d_arr 0
            return [w0 :: Word]
         )
       | otherwise
       = panic "mkLitD: Bad wORD_SIZE"

    mkLitI64 dflags ii
       | wORD_SIZE dflags == 4
       = runST (do
            arr <- newArray_ ((0::Int),1)
            writeArray arr 0 ii
            d_arr <- castSTUArray arr
            w0 <- readArray d_arr 0
            w1 <- readArray d_arr 1
            return [w0 :: Word,w1]
         )
       | wORD_SIZE dflags == 8
       = runST (do
            arr <- newArray_ ((0::Int),0)
            writeArray arr 0 ii
            d_arr <- castSTUArray arr
            w0 <- readArray d_arr 0
            return [w0 :: Word]
         )
       | otherwise
       = panic "mkLitI64: Bad wORD_SIZE"

    mkLitI i = [fromIntegral i :: Word]

    iNTERP_STACK_CHECK_THRESH :: Int
    iNTERP_STACK_CHECK_THRESH = INTERP_STACK_CHECK_THRESH