deSugar/DsForeign.hs

    {-
    (c) The University of Glasgow 2006
    (c) The AQUA Project, Glasgow University, 1998

    Desugaring foreign declarations (see also DsCCall).
    -}

    {-# LANGUAGE CPP #-}

    module DsForeign ( dsForeigns ) where

    #include "HsVersions.h"
    import TcRnMonad        -- temp

    import CoreSyn

    import DsCCall
    import DsMonad

    import HsSyn
    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 Platform
    import Config
    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 Id]
               -> DsM (ForeignStubs, OrdList Binding)
    dsForeigns fos = getHooked dsForeignsHook dsForeigns' >>= ($ fos)

    dsForeigns' :: [LForeignDecl Id]
                -> DsM (ForeignStubs, OrdList Binding)
    dsForeigns' []
      = return (NoStubs, nilOL)
    dsForeigns' fos = do
        fives <- mapM do_ldecl fos
        let
            (hs, cs, idss, bindss) = unzip4 fives
            fe_ids = concat idss
            fe_init_code = map foreignExportInitialiser fe_ids
        --
        return (ForeignStubs
                 (vcat hs)
                 (vcat cs $$ vcat fe_init_code),
                foldr (appOL . toOL) nilOL bindss)
      where
       do_ldecl (L loc decl) = putSrcSpanDs loc (do_decl decl)

       do_decl (ForeignImport { fd_name = id, fd_co = 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 = L _ id, fd_co = co
                              , fd_fe = CExport (L _ (CExportStatic _ ext_nm cconv)) _ }) = do
          (h, c, _, _) <- dsFExport id co ext_nm cconv False
          return (h, c, [id], [])

    {-
    ************************************************************************
    *                                                                      *
    \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 (MachLabel cid stdcall_info fod))
            rhs' = Cast rhs co
            stdcall_info = fun_type_arg_stdcall_info dflags cconv ty
        in
        return ([(id, rhs')], empty, empty)

    dsCImport id co (CFunction target) cconv@PrimCallConv safety _
      = dsPrimCall id co (CCall (CCallSpec target cconv safety))
    dsCImport id co (CFunction target) cconv safety mHeader
      = dsFCall id co (CCall (CCallSpec target cconv safety)) 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 fcall mDeclHeader = do
        let
            ty                   = pFst $ coercionKind co
            (tv_bndrs, rho)      = tcSplitForAllTyVarBndrs 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
        (fcall', cDoc) <-
                  case fcall of
                  CCall (CCallSpec (StaticTarget _ cName mUnitId isFun)
                                   CApiConv safety) ->
                   do wrapperName <- mkWrapperName "ghc_wrapper" (unpackFS cName)
                      let fcall' = CCall (CCallSpec
                                          (StaticTarget NoSourceText
                                                        wrapperName mUnitId
                                                        True)
                                          CApiConv safety)
                          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 (mkFunTys (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 fcall = 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
            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     = mkFunTy 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      = [ mkIntLitInt dflags (ccallConvToInt cconv)
                            , Var stbl_value
                            , Lit (MachLabel fe_nm mb_sz_args IsFunction)
                            , Lit (mkMachString 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 = cLibFFI && 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
         ]

    foreignExportInitialiser :: Id -> SDoc
    foreignExportInitialiser hs_fn =
       -- 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)
       vcat
        [ text "static void stginit_export_" <> ppr hs_fn
             <> text "() __attribute__((constructor));"
        , text "static void stginit_export_" <> ppr hs_fn <> text "()"
        , braces (text "foreignExportStablePtr"
           <> parens (text "(StgPtr) &" <> ppr hs_fn <> text "_closure")
           <> semi)
        ]

    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
         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"