content: {-
  (c) The University of Glasgow 2006
  (c) The AQUA Project, Glasgow University, 1998
  
  
  Desugaring foreign declarations (see also DsCCall).
  -}
  
  {-# LANGUAGE CPP #-}
  {-# LANGUAGE FlexibleContexts #-}
  {-# LANGUAGE TypeFamilies #-}
  {-# LANGUAGE ViewPatterns #-}
  
  module Gen2.GHC.DsForeign where
  
  -- #include "HsVersions.h"
  -- import GhcPrelude
  import Prelude hiding ((<>))
  
  import TcRnMonad        -- temp
  
  import CoreSyn
  
  import DsCCall
  import DsMonad
  
  import GHC.Hs
  import DataCon
  import CoreUnfold
  import Id
  import Literal
  import Module
  import Name
  import Type
  import RepType
  import TyCon
  import Coercion
  import TcEnv
  import TcType
  
  import CmmExpr
  import CmmUtils
  import HscTypes
  import ForeignCall
  import TysWiredIn
  import TysPrim
  import PrelNames
  import BasicTypes
  import SrcLoc
  import Outputable
  import FastString
  import DynFlags
  import GHC.Platform
  import OrdList
  import Pair
  import Util
  import Hooks
  import Encoding
  
  import Data.Maybe
  import Data.List
  
  {-
  Desugaring of @foreign@ declarations is naturally split up into
  parts, an @import@ and an @export@  part. A @foreign import@
  declaration
  \begin{verbatim}
    foreign import cc nm f :: prim_args -> IO prim_res
  \end{verbatim}
  is the same as
  \begin{verbatim}
    f :: prim_args -> IO prim_res
    f a1 ... an = _ccall_ nm cc a1 ... an
  \end{verbatim}
  so we reuse the desugaring code in @DsCCall@ to deal with these.
  -}
  
  type Binding = (Id, CoreExpr) -- No rec/nonrec structure;
                                -- the occurrence analyser will sort it all out
  
  dsForeigns :: [LForeignDecl GhcTc]
             -> DsM (ForeignStubs, OrdList Binding)
  dsForeigns fos = getHooked dsForeignsHook dsForeigns' >>= ($ fos)
  
  dsForeigns' :: [LForeignDecl GhcTc]
              -> DsM (ForeignStubs, OrdList Binding)
  dsForeigns' []
    = return (NoStubs, nilOL)
  dsForeigns' fos = do
      mod <- getModule
      fives <- mapM do_ldecl fos
      let
          (hs, cs, idss, bindss) = unzip4 fives
          fe_ids = concat idss
          fe_init_code = foreignExportsInitialiser mod fe_ids
      --
      return (ForeignStubs
               (vcat hs)
               (vcat cs $$ fe_init_code),
              foldr (appOL . toOL) nilOL bindss)
    where
     do_ldecl (dL->L loc decl) = putSrcSpanDs loc (do_decl decl)
  
     do_decl (ForeignImport { fd_name = id, fd_i_ext = co, fd_fi = spec }) = do
        traceIf (text "fi start" <+> ppr id)
        let id' = unLoc id
        (bs, h, c) <- dsFImport id' co spec
        traceIf (text "fi end" <+> ppr id)
        return (h, c, [], bs)
  
     do_decl (ForeignExport { fd_name = (dL->L _ id)
                            , fd_e_ext = co
                            , fd_fe = CExport
                                (dL->L _ (CExportStatic _ ext_nm cconv)) _ }) = do
        (h, c, _, _) <- dsFExport id co ext_nm cconv False
        return (h, c, [id], [])
     do_decl (XForeignDecl nec) = noExtCon nec
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Foreign import}
  *                                                                      *
  ************************************************************************
  
  Desugaring foreign imports is just the matter of creating a binding
  that on its RHS unboxes its arguments, performs the external call
  (using the @CCallOp@ primop), before boxing the result up and returning it.
  
  However, we create a worker/wrapper pair, thus:
  
          foreign import f :: Int -> IO Int
  ==>
          f x = IO ( \s -> case x of { I# x# ->
                           case fw s x# of { (# s1, y# #) ->
                           (# s1, I# y# #)}})
  
          fw s x# = ccall f s x#
  
  The strictness/CPR analyser won't do this automatically because it doesn't look
  inside returned tuples; but inlining this wrapper is a Really Good Idea
  because it exposes the boxing to the call site.
  -}
  
  dsFImport :: Id
            -> Coercion
            -> ForeignImport
            -> DsM ([Binding], SDoc, SDoc)
  dsFImport id co (CImport cconv safety mHeader spec _) =
      dsCImport id co spec (unLoc cconv) (unLoc safety) mHeader
  
  dsCImport :: Id
            -> Coercion
            -> CImportSpec
            -> CCallConv
            -> Safety
            -> Maybe Header
            -> DsM ([Binding], SDoc, SDoc)
  dsCImport id co (CLabel cid) cconv _ _ = do
     dflags <- getDynFlags
     let ty  = pFst $ coercionKind co
         fod = case tyConAppTyCon_maybe (dropForAlls ty) of
               Just tycon
                | tyConUnique tycon == funPtrTyConKey ->
                   IsFunction
               _ -> IsData
     (resTy, foRhs) <- resultWrapper ty
     -- ASSERT(fromJust resTy `eqType` addrPrimTy)    -- typechecker ensures this
     let
          rhs = foRhs (Lit (LitLabel cid stdcall_info fod))
          rhs' = Cast rhs co
          stdcall_info = fun_type_arg_stdcall_info dflags cconv ty
     return ([(id, rhs')], empty, empty)
  
  dsCImport id co (CFunction target) cconv@PrimCallConv safety _
    = dsPrimCall id co (CCall (mkCCallSpec target cconv safety
                                           (panic "Missing Return PrimRep")
                                           (panic "Missing Argument PrimReps")))
  dsCImport id co (CFunction target) cconv safety mHeader
    = dsFCall id co (CCall (mkCCallSpec target cconv safety
                                        (panic "Missing Return PrimRep")
                                        (panic "Missing Argument PrimReps"))) mHeader
  dsCImport id co CWrapper cconv _ _
    = dsFExportDynamic id co cconv
  
  -- For stdcall labels, if the type was a FunPtr or newtype thereof,
  -- then we need to calculate the size of the arguments in order to add
  -- the @n suffix to the label.
  fun_type_arg_stdcall_info :: DynFlags -> CCallConv -> Type -> Maybe Int
  fun_type_arg_stdcall_info dflags StdCallConv ty
    | Just (tc,[arg_ty]) <- splitTyConApp_maybe ty,
      tyConUnique tc == funPtrTyConKey
    = let
         (bndrs, _) = tcSplitPiTys arg_ty
         fe_arg_tys = mapMaybe binderRelevantType_maybe bndrs
      in Just $ sum (map (widthInBytes . typeWidth . typeCmmType dflags . getPrimTyOf) fe_arg_tys)
  fun_type_arg_stdcall_info _ _other_conv _
    = Nothing
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Foreign calls}
  *                                                                      *
  ************************************************************************
  -}
  
  dsFCall :: Id -> Coercion -> ForeignCall -> Maybe Header
          -> DsM ([(Id, Expr TyVar)], SDoc, SDoc)
  dsFCall fn_id co (CCall (CCallSpec target cconv safety _ _)) mDeclHeader = do
      let
          ty                   = pFst $ coercionKind co
          (tv_bndrs, rho)      = tcSplitForAllVarBndrs ty
          (arg_tys, io_res_ty) = tcSplitFunTys rho
  
      args <- newSysLocalsDs arg_tys  -- no FFI levity-polymorphism
      (val_args, arg_wrappers) <- mapAndUnzipM unboxArg (map Var args)
  
      let
          work_arg_ids  = [v | Var v <- val_args] -- All guaranteed to be vars
  
      (ccall_result_ty, res_wrapper) <- boxResult io_res_ty
  
      ccall_uniq <- newUnique
      work_uniq  <- newUnique
  
      dflags <- getDynFlags
  
      let
        fcall = CCall (mkCCallSpec target cconv safety io_res_ty arg_tys)
  
      (fcall', cDoc) <- case fcall of
                CCall (CCallSpec (StaticTarget _ cName mUnitId isFun)
                                 CApiConv safety _ _) ->
                 do wrapperName <- mkWrapperName "ghc_wrapper" (unpackFS cName)
                    let fcall' = CCall (mkCCallSpec
                                        (StaticTarget NoSourceText
                                                      wrapperName mUnitId
                                                      True)
                                        CApiConv safety io_res_ty arg_tys)
                        c = includes
                         $$ fun_proto <+> braces (cRet <> semi)
                        includes = vcat [ text "#include \"" <> ftext h
                                          <> text "\""
                                        | Header _ h <- nub headers ]
                        fun_proto = cResType <+> pprCconv <+> ppr wrapperName <> parens argTypes
                        cRet
                         | isVoidRes =                   cCall
                         | otherwise = text "return" <+> cCall
                        cCall = if isFun
                                then ppr cName <> parens argVals
                                else if null arg_tys
                                      then ppr cName
                                      else panic "dsFCall: Unexpected arguments to FFI value import"
                        raw_res_ty = case tcSplitIOType_maybe io_res_ty of
                                     Just (_ioTyCon, res_ty) -> res_ty
                                     Nothing                 -> io_res_ty
                        isVoidRes = raw_res_ty `eqType` unitTy
                        (mHeader, cResType)
                         | isVoidRes = (Nothing, text "void")
                         | otherwise = toCType raw_res_ty
                        pprCconv = ccallConvAttribute CApiConv
                        mHeadersArgTypeList
                            = [ (header, cType <+> char 'a' <> int n)
                              | (t, n) <- zip arg_tys [1..]
                              , let (header, cType) = toCType t ]
                        (mHeaders, argTypeList) = unzip mHeadersArgTypeList
                        argTypes = if null argTypeList
                                   then text "void"
                                   else hsep $ punctuate comma argTypeList
                        mHeaders' = mDeclHeader : mHeader : mHeaders
                        headers = catMaybes mHeaders'
                        argVals = hsep $ punctuate comma
                                      [ char 'a' <> int n
                                      | (_, n) <- zip arg_tys [1..] ]
                    return (fcall', c)
                _ ->
                    return (fcall, empty)
      let
          -- Build the worker
          worker_ty     = mkForAllTys tv_bndrs (mkVisFunTys (map idType work_arg_ids) ccall_result_ty)
          tvs           = map binderVar tv_bndrs
          the_ccall_app = mkFCall dflags ccall_uniq fcall' val_args ccall_result_ty
          work_rhs      = mkLams tvs (mkLams work_arg_ids the_ccall_app)
          work_id       = mkSysLocal (fsLit "$wccall") work_uniq worker_ty
  
          -- Build the wrapper
          work_app     = mkApps (mkVarApps (Var work_id) tvs) val_args
          wrapper_body = foldr ($) (res_wrapper work_app) arg_wrappers
          wrap_rhs     = mkLams (tvs ++ args) wrapper_body
          wrap_rhs'    = Cast wrap_rhs co
          fn_id_w_inl  = fn_id `setIdUnfolding` mkInlineUnfoldingWithArity
                                                  (length args) wrap_rhs'
  
      return ([(work_id, work_rhs), (fn_id_w_inl, wrap_rhs')], empty, cDoc)
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Primitive calls}
  *                                                                      *
  ************************************************************************
  
  This is for `@foreign import prim@' declarations.
  
  Currently, at the core level we pretend that these primitive calls are
  foreign calls. It may make more sense in future to have them as a distinct
  kind of Id, or perhaps to bundle them with PrimOps since semantically and
  for calling convention they are really prim ops.
  -}
  
  dsPrimCall :: Id -> Coercion -> ForeignCall
             -> DsM ([(Id, Expr TyVar)], SDoc, SDoc)
  dsPrimCall fn_id co (CCall (CCallSpec target cconv safety _ _)) = do
      let
          ty                   = pFst $ coercionKind co
          (tvs, fun_ty)        = tcSplitForAllTys ty
          (arg_tys, io_res_ty) = tcSplitFunTys fun_ty
  
      args <- newSysLocalsDs arg_tys  -- no FFI levity-polymorphism
  
      ccall_uniq <- newUnique
      dflags <- getDynFlags
      let
          fcall = CCall (mkCCallSpec target cconv safety io_res_ty arg_tys)
          call_app = mkFCall dflags ccall_uniq fcall (map Var args) io_res_ty
          rhs      = mkLams tvs (mkLams args call_app)
          rhs'     = Cast rhs co
      return ([(fn_id, rhs')], empty, empty)
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection{Foreign export}
  *                                                                      *
  ************************************************************************
  
  The function that does most of the work for `@foreign export@' declarations.
  (see below for the boilerplate code a `@foreign export@' declaration expands
   into.)
  
  For each `@foreign export foo@' in a module M we generate:
  \begin{itemize}
  \item a C function `@foo@', which calls
  \item a Haskell stub `@M.\$ffoo@', which calls
  \end{itemize}
  the user-written Haskell function `@M.foo@'.
  -}
  
  dsFExport :: Id                 -- Either the exported Id,
                                  -- or the foreign-export-dynamic constructor
            -> Coercion           -- Coercion between the Haskell type callable
                                  -- from C, and its representation type
            -> CLabelString       -- The name to export to C land
            -> CCallConv
            -> Bool               -- True => foreign export dynamic
                                  --         so invoke IO action that's hanging off
                                  --         the first argument's stable pointer
            -> DsM ( SDoc         -- contents of Module_stub.h
                   , SDoc         -- contents of Module_stub.c
                   , String       -- string describing type to pass to createAdj.
                   , Int          -- size of args to stub function
                   )
  
  dsFExport fn_id co ext_name cconv isDyn = do
      let
         ty                     = pSnd $ coercionKind co
         (bndrs, orig_res_ty)   = tcSplitPiTys ty
         fe_arg_tys'            = mapMaybe binderRelevantType_maybe bndrs
         -- We must use tcSplits here, because we want to see
         -- the (IO t) in the corner of the type!
         fe_arg_tys | isDyn     = tail fe_arg_tys'
                    | otherwise = fe_arg_tys'
  
         -- Look at the result type of the exported function, orig_res_ty
         -- If it's IO t, return         (t, True)
         -- If it's plain t, return      (t, False)
         (res_ty, is_IO_res_ty) = case tcSplitIOType_maybe orig_res_ty of
                                  -- The function already returns IO t
                                  Just (_ioTyCon, res_ty) -> (res_ty, True)
                                  -- The function returns t
                                  Nothing                 -> (orig_res_ty, False)
  
      dflags <- getDynFlags
      return $
        mkFExportCBits dflags ext_name
                       (if isDyn then Nothing else Just fn_id)
                       fe_arg_tys res_ty is_IO_res_ty cconv
  
  {-
  @foreign import "wrapper"@ (previously "foreign export dynamic") lets
  you dress up Haskell IO actions of some fixed type behind an
  externally callable interface (i.e., as a C function pointer). Useful
  for callbacks and stuff.
  
  \begin{verbatim}
  type Fun = Bool -> Int -> IO Int
  foreign import "wrapper" f :: Fun -> IO (FunPtr Fun)
  
  -- Haskell-visible constructor, which is generated from the above:
  -- SUP: No check for NULL from createAdjustor anymore???
  
  f :: Fun -> IO (FunPtr Fun)
  f cback =
     bindIO (newStablePtr cback)
            (\StablePtr sp# -> IO (\s1# ->
                case _ccall_ createAdjustor cconv sp# ``f_helper'' <arg info> s1# of
                   (# s2#, a# #) -> (# s2#, A# a# #)))
  
  foreign import "&f_helper" f_helper :: FunPtr (StablePtr Fun -> Fun)
  
  -- and the helper in C: (approximately; see `mkFExportCBits` below)
  
  f_helper(StablePtr s, HsBool b, HsInt i)
  {
          Capability *cap;
          cap = rts_lock();
          rts_evalIO(&cap,
                     rts_apply(rts_apply(deRefStablePtr(s),
                                         rts_mkBool(b)), rts_mkInt(i)));
          rts_unlock(cap);
  }
  \end{verbatim}
  -}
  
  dsFExportDynamic :: Id
                   -> Coercion
                   -> CCallConv
                   -> DsM ([Binding], SDoc, SDoc)
  dsFExportDynamic id co0 cconv = do
      mod <- getModule
      dflags <- getDynFlags
      let fe_nm = mkFastString $ zEncodeString
              (moduleStableString mod ++ "$" ++ toCName dflags id)
          -- Construct the label based on the passed id, don't use names
          -- depending on Unique. See #13807 and Note [Unique Determinism].
      cback <- newSysLocalDs arg_ty
      newStablePtrId <- dsLookupGlobalId newStablePtrName
      stable_ptr_tycon <- dsLookupTyCon stablePtrTyConName
      let
          stable_ptr_ty = mkTyConApp stable_ptr_tycon [arg_ty]
          export_ty     = mkVisFunTy stable_ptr_ty arg_ty
      bindIOId <- dsLookupGlobalId bindIOName
      stbl_value <- newSysLocalDs stable_ptr_ty
      (h_code, c_code, typestring, args_size) <- dsFExport id (mkRepReflCo export_ty) fe_nm cconv True
      let
           {-
            The arguments to the external function which will
            create a little bit of (template) code on the fly
            for allowing the (stable pointed) Haskell closure
            to be entered using an external calling convention
            (stdcall, ccall).
           -}
          adj_args      = [ mkIntLit dflags (toInteger (ccallConvToInt cconv))
                          , Var stbl_value
                          , Lit (LitLabel fe_nm mb_sz_args IsFunction)
                          , Lit (mkLitString typestring)
                          ]
            -- name of external entry point providing these services.
            -- (probably in the RTS.)
          adjustor   = fsLit "createAdjustor"
  
            -- Determine the number of bytes of arguments to the stub function,
            -- so that we can attach the '@N' suffix to its label if it is a
            -- stdcall on Windows.
          mb_sz_args = case cconv of
                          StdCallConv -> Just args_size
                          _           -> Nothing
  
      ccall_adj <- dsCCall adjustor adj_args PlayRisky (mkTyConApp io_tc [res_ty])
          -- PlayRisky: the adjustor doesn't allocate in the Haskell heap or do a callback
  
      let io_app = mkLams tvs                  $
                   Lam cback                   $
                   mkApps (Var bindIOId)
                          [ Type stable_ptr_ty
                          , Type res_ty
                          , mkApps (Var newStablePtrId) [ Type arg_ty, Var cback ]
                          , Lam stbl_value ccall_adj
                          ]
  
          fed = (id `setInlineActivation` NeverActive, Cast io_app co0)
                 -- Never inline the f.e.d. function, because the litlit
                 -- might not be in scope in other modules.
  
      return ([fed], h_code, c_code)
  
   where
    ty                       = pFst (coercionKind co0)
    (tvs,sans_foralls)       = tcSplitForAllTys ty
    ([arg_ty], fn_res_ty)    = tcSplitFunTys sans_foralls
    Just (io_tc, res_ty)     = tcSplitIOType_maybe fn_res_ty
          -- Must have an IO type; hence Just
  
  
  toCName :: DynFlags -> Id -> String
  toCName dflags i = showSDoc dflags (pprCode CStyle (ppr (idName i)))
  
  {-
  *
  
  \subsection{Generating @foreign export@ stubs}
  
  *
  
  For each @foreign export@ function, a C stub function is generated.
  The C stub constructs the application of the exported Haskell function
  using the hugs/ghc rts invocation API.
  -}
  
  mkFExportCBits :: DynFlags
                 -> FastString
                 -> Maybe Id      -- Just==static, Nothing==dynamic
                 -> [Type]
                 -> Type
                 -> Bool          -- True <=> returns an IO type
                 -> CCallConv
                 -> (SDoc,
                     SDoc,
                     String,      -- the argument reps
                     Int          -- total size of arguments
                    )
  mkFExportCBits dflags c_nm maybe_target arg_htys res_hty is_IO_res_ty cc
   = (header_bits, c_bits, type_string,
      sum [ widthInBytes (typeWidth rep) | (_,_,_,rep) <- aug_arg_info] -- all the args
           -- NB. the calculation here isn't strictly speaking correct.
           -- We have a primitive Haskell type (eg. Int#, Double#), and
           -- we want to know the size, when passed on the C stack, of
           -- the associated C type (eg. HsInt, HsDouble).  We don't have
           -- this information to hand, but we know what GHC's conventions
           -- are for passing around the primitive Haskell types, so we
           -- use that instead.  I hope the two coincide --SDM
      )
   where
    -- list the arguments to the C function
    arg_info :: [(SDoc,           -- arg name
                  SDoc,           -- C type
                  Type,           -- Haskell type
                  CmmType)]       -- the CmmType
    arg_info  = [ let stg_type = showStgType ty in
                  (arg_cname n stg_type,
                   stg_type,
                   ty,
                   typeCmmType dflags (getPrimTyOf ty))
                | (ty,n) <- zip arg_htys [1::Int ..] ]
  
    arg_cname n stg_ty
          | libffi    = char '*' <> parens (stg_ty <> char '*') <>
                        text "args" <> brackets (int (n-1))
          | otherwise = text ('a':show n)
  
    -- generate a libffi-style stub if this is a "wrapper" and libffi is enabled
    libffi = platformMisc_libFFI (platformMisc dflags) && isNothing maybe_target
  
    type_string
        -- libffi needs to know the result type too:
        | libffi    = primTyDescChar dflags res_hty : arg_type_string
        | otherwise = arg_type_string
  
    arg_type_string = [primTyDescChar dflags ty | (_,_,ty,_) <- arg_info]
                  -- just the real args
  
    -- add some auxiliary args; the stable ptr in the wrapper case, and
    -- a slot for the dummy return address in the wrapper + ccall case
    aug_arg_info
      | isNothing maybe_target = stable_ptr_arg : insertRetAddr dflags cc arg_info
      | otherwise              = arg_info
  
    stable_ptr_arg =
          (text "the_stableptr", text "StgStablePtr", undefined,
           typeCmmType dflags (mkStablePtrPrimTy alphaTy))
  
    -- stuff to do with the return type of the C function
    res_hty_is_unit = res_hty `eqType` unitTy     -- Look through any newtypes
  
    cResType | res_hty_is_unit = text "void"
             | otherwise       = showStgType res_hty
  
    -- when the return type is integral and word-sized or smaller, it
    -- must be assigned as type ffi_arg (#3516).  To see what type
    -- libffi is expecting here, take a look in its own testsuite, e.g.
    -- libffi/testsuite/libffi.call/cls_align_ulonglong.c
    ffi_cResType
       | is_ffi_arg_type = text "ffi_arg"
       | otherwise       = cResType
       where
         res_ty_key = getUnique (getName (typeTyCon res_hty))
         is_ffi_arg_type = res_ty_key `notElem`
                [floatTyConKey, doubleTyConKey,
                 int64TyConKey, word64TyConKey]
  
    -- Now we can cook up the prototype for the exported function.
    pprCconv = ccallConvAttribute cc
  
    header_bits = text "extern" <+> fun_proto <> semi
  
    fun_args
      | null aug_arg_info = text "void"
      | otherwise         = hsep $ punctuate comma
                                 $ map (\(nm,ty,_,_) -> ty <+> nm) aug_arg_info
  
    fun_proto
      | libffi
        = text "void" <+> ftext c_nm <>
            parens (text "void *cif STG_UNUSED, void* resp, void** args, void* the_stableptr")
      | otherwise
        = cResType <+> pprCconv <+> ftext c_nm <> parens fun_args
  
    -- the target which will form the root of what we ask rts_evalIO to run
    the_cfun
       = case maybe_target of
            Nothing    -> text "(StgClosure*)deRefStablePtr(the_stableptr)"
            Just hs_fn -> char '&' <> ppr hs_fn <> text "_closure"
  
    cap = text "cap" <> comma
  
    -- the expression we give to rts_evalIO
    expr_to_run
       = foldl' appArg the_cfun arg_info -- NOT aug_arg_info
         where
            appArg acc (arg_cname, _, arg_hty, _)
               = text "rts_apply"
                 <> parens (cap <> acc <> comma <> mkHObj arg_hty <> parens (cap <> arg_cname))
  
    -- various other bits for inside the fn
    declareResult = text "HaskellObj ret;"
    declareCResult | res_hty_is_unit = empty
                   | otherwise       = cResType <+> text "cret;"
  
    assignCResult | res_hty_is_unit = empty
                  | otherwise       =
                          text "cret=" <> unpackHObj res_hty <> parens (text "ret") <> semi
  
    -- an extern decl for the fn being called
    extern_decl
       = case maybe_target of
            Nothing -> empty
            Just hs_fn -> text "extern StgClosure " <> ppr hs_fn <> text "_closure" <> semi
  
  
    -- finally, the whole darn thing
    c_bits =
      space $$
      extern_decl $$
      fun_proto  $$
      vcat
       [ lbrace
       ,   text "Capability *cap;"
       ,   declareResult
       ,   declareCResult
       ,   text "cap = rts_lock();"
            -- create the application + perform it.
       ,   text "rts_evalIO" <> parens (
                  char '&' <> cap <>
                  text "rts_apply" <> parens (
                      cap <>
                      text "(HaskellObj)"
                   <> ptext (if is_IO_res_ty
                                  then (sLit "runIO_closure")
                                  else (sLit "runNonIO_closure"))
                   <> comma
                   <> expr_to_run
                  ) <+> comma
                 <> text "&ret"
               ) <> semi
       ,   text "rts_checkSchedStatus" <> parens (doubleQuotes (ftext c_nm)
                                                  <> comma <> text "cap") <> semi
       ,   assignCResult
       ,   text "rts_unlock(cap);"
       ,   ppUnless res_hty_is_unit $
           if libffi
                    then char '*' <> parens (ffi_cResType <> char '*') <>
                         text "resp = cret;"
                    else text "return cret;"
       , rbrace
       ]
  
  
  foreignExportsInitialiser :: Module -> [Id] -> SDoc
  foreignExportsInitialiser mod hs_fns =
     -- Initialise foreign exports by registering a stable pointer from an
     -- __attribute__((constructor)) function.
     -- The alternative is to do this from stginit functions generated in
     -- codeGen/CodeGen.hs; however, stginit functions have a negative impact
     -- on binary sizes and link times because the static linker will think that
     -- all modules that are imported directly or indirectly are actually used by
     -- the program.
     -- (this is bad for big umbrella modules like Graphics.Rendering.OpenGL)
     --
     -- See Note [Tracking foreign exports] in rts/ForeignExports.c
     vcat
      [ text "static struct ForeignExportsList" <+> list_symbol <+> equals
           <+> braces (
             text ".exports = " <+> export_list <> comma <+>
             text ".n_entries = " <+> ppr (length hs_fns))
           <> semi
      , text "static void " <> ctor_symbol <> text "(void)"
           <+> text " __attribute__((constructor));"
      , text "static void " <> ctor_symbol <> text "()"
      , braces (text "registerForeignExports" <> parens (char '&' <> list_symbol) <> semi)
      ]
    where
      mod_str = pprModuleName (moduleName mod)
      ctor_symbol = text "stginit_export_" <> mod_str
      list_symbol = text "stg_exports_" <> mod_str
      export_list = braces $ pprWithCommas closure_ptr hs_fns
  
      closure_ptr :: Id -> SDoc
      closure_ptr fn = text "(StgPtr) &" <> ppr fn <> text "_closure"
  
  
  mkHObj :: Type -> SDoc
  mkHObj t = text "rts_mk" <> text (showFFIType t)
  
  unpackHObj :: Type -> SDoc
  unpackHObj t = text "rts_get" <> text (showFFIType t)
  
  showStgType :: Type -> SDoc
  showStgType t = text "Hs" <> text (showFFIType t)
  
  showFFIType :: Type -> String
  showFFIType t = getOccString (getName (typeTyCon t))
  
  toCType :: Type -> (Maybe Header, SDoc)
  toCType = f False
      where f voidOK t
             -- First, if we have (Ptr t) of (FunPtr t), then we need to
             -- convert t to a C type and put a * after it. If we don't
             -- know a type for t, then "void" is fine, though.
             | Just (ptr, [t']) <- splitTyConApp_maybe t
             , tyConName ptr `elem` [ptrTyConName, funPtrTyConName]
                = case f True t' of
                  (mh, cType') ->
                      (mh, cType' <> char '*')
             -- Otherwise, if we have a type constructor application, then
             -- see if there is a C type associated with that constructor.
             -- Note that we aren't looking through type synonyms or
             -- anything, as it may be the synonym that is annotated.
             | Just tycon <- tyConAppTyConPicky_maybe t
             , Just (CType _ mHeader (_,cType)) <- tyConCType_maybe tycon
                = (mHeader, ftext cType)
             -- If we don't know a C type for this type, then try looking
             -- through one layer of type synonym etc.
             | Just t' <- coreView t
                = f voidOK t'
             -- This may be an 'UnliftedFFITypes'-style ByteArray# argument
             -- (which is marshalled like a Ptr)
             | Just byteArrayPrimTyCon        == tyConAppTyConPicky_maybe t
                = (Nothing, text "const void*")
             | Just mutableByteArrayPrimTyCon == tyConAppTyConPicky_maybe t
                = (Nothing, text "void*")
             -- Otherwise we don't know the C type. If we are allowing
             -- void then return that; otherwise something has gone wrong.
             | voidOK = (Nothing, text "void")
             | otherwise
                = pprPanic "toCType" (ppr t)
  
  typeTyCon :: Type -> TyCon
  typeTyCon ty
    | Just (tc, _) <- tcSplitTyConApp_maybe (unwrapType ty)
    = tc
    | otherwise
    = pprPanic "DsForeign.typeTyCon" (ppr ty)
  
  insertRetAddr :: DynFlags -> CCallConv
                -> [(SDoc, SDoc, Type, CmmType)]
                -> [(SDoc, SDoc, Type, CmmType)]
  insertRetAddr dflags CCallConv args
      = case platformArch platform of
        ArchX86_64
         | platformOS platform == OSMinGW32 ->
            -- On other Windows x86_64 we insert the return address
            -- after the 4th argument, because this is the point
            -- at which we need to flush a register argument to the stack
            -- (See rts/Adjustor.c for details).
            let go :: Int -> [(SDoc, SDoc, Type, CmmType)]
                          -> [(SDoc, SDoc, Type, CmmType)]
                go 4 args = ret_addr_arg dflags : args
                go n (arg:args) = arg : go (n+1) args
                go _ [] = []
            in go 0 args
         | otherwise ->
            -- On other x86_64 platforms we insert the return address
            -- after the 6th integer argument, because this is the point
            -- at which we need to flush a register argument to the stack
            -- (See rts/Adjustor.c for details).
            let go :: Int -> [(SDoc, SDoc, Type, CmmType)]
                          -> [(SDoc, SDoc, Type, CmmType)]
                go 6 args = ret_addr_arg dflags : args
                go n (arg@(_,_,_,rep):args)
                 | cmmEqType_ignoring_ptrhood rep b64 = arg : go (n+1) args
                 | otherwise  = arg : go n     args
                go _ [] = []
            in go 0 args
        _ ->
            ret_addr_arg dflags : args
      where platform = targetPlatform dflags
  insertRetAddr _ _ args = args
  
  ret_addr_arg :: DynFlags -> (SDoc, SDoc, Type, CmmType)
  ret_addr_arg dflags = (text "original_return_addr", text "void*", undefined,
                         typeCmmType dflags addrPrimTy)
  
  -- This function returns the primitive type associated with the boxed
  -- type argument to a foreign export (eg. Int ==> Int#).
  getPrimTyOf :: Type -> UnaryType
  getPrimTyOf ty
    | isBoolTy rep_ty = intPrimTy
    -- Except for Bool, the types we are interested in have a single constructor
    -- with a single primitive-typed argument (see TcType.legalFEArgTyCon).
    | otherwise =
    case splitDataProductType_maybe rep_ty of
       Just (_, _, data_con, [prim_ty]) ->
          -- ASSERT(dataConSourceArity data_con == 1)
          -- ASSERT2(isUnliftedType prim_ty, ppr prim_ty)
          prim_ty
       _other -> pprPanic "DsForeign.getPrimTyOf" (ppr ty)
    where
          rep_ty = unwrapType ty
  
  -- represent a primitive type as a Char, for building a string that
  -- described the foreign function type.  The types are size-dependent,
  -- e.g. 'W' is a signed 32-bit integer.
  primTyDescChar :: DynFlags -> Type -> Char
  primTyDescChar dflags ty
   | ty `eqType` unitTy = 'v'
   | otherwise
   = case typePrimRep1 (getPrimTyOf ty) of
       IntRep      -> signed_word
       WordRep     -> unsigned_word
       Int8Rep     -> 'B'
       Word8Rep    -> 'b'
       Int16Rep    -> 'S'
       Word16Rep   -> 's'
       Int32Rep    -> 'W'
       Word32Rep   -> 'w'
       Int64Rep    -> 'L'
       Word64Rep   -> 'l'
       AddrRep     -> 'p'
       FloatRep    -> 'f'
       DoubleRep   -> 'd'
       _           -> pprPanic "primTyDescChar" (ppr ty)
    where
      (signed_word, unsigned_word)
         | wORD_SIZE dflags == 4  = ('W','w')
         | wORD_SIZE dflags == 8  = ('L','l')
         | otherwise              = panic "primTyDescChar"
  