% % (c) The University of Glasgow 2005-2006 % \begin{code}

    -- | The dynamic linker for GHCi.
    --
    -- This module deals with the top-level issues of dynamic linking,
    -- calling the object-code linker and the byte-code linker where
    -- necessary.

    {-# OPTIONS -fno-cse #-}
    -- -fno-cse is needed for GLOBAL_VAR's to behave properly

    module Linker ( HValue, getHValue, showLinkerState,
    		linkExpr, unload, withExtendedLinkEnv,
                    extendLinkEnv, deleteFromLinkEnv,
                    extendLoadedPkgs,
    		linkPackages,initDynLinker,
                    dataConInfoPtrToName
    	) where

    #include "HsVersions.h"

    import LoadIface
    import ObjLink
    import ByteCodeLink
    import ByteCodeItbls
    import ByteCodeAsm
    import CgInfoTbls
    import SMRep
    import IfaceEnv
    import TcRnMonad
    import Packages
    import DriverPhases
    import Finder
    import HscTypes
    import Name
    import NameEnv
    import NameSet
    import qualified OccName
    import UniqFM
    import Module
    import ListSetOps
    import DynFlags
    import BasicTypes
    import Outputable
    import Panic
    import Util
    import StaticFlags
    import ErrUtils
    import SrcLoc
    import qualified Maybes
    import UniqSet
    import Constants
    import FastString
    import Config

    -- Standard libraries
    import Control.Monad

    import Data.Char
    import Data.IORef
    import Data.List
    import qualified Data.Map as Map
    import Foreign
    import Control.Concurrent.MVar

    import System.FilePath
    import System.IO
    import System.Directory

    import Distribution.Package hiding (depends, PackageId)

    import Exception

\end{code} %************************************************************************ %* * The Linker's state %* * %************************************************************************ The persistent linker state *must* match the actual state of the C dynamic linker at all times, so we keep it in a private global variable. The PersistentLinkerState maps Names to actual closures (for interpreted code only), for use during linking. \begin{code}

    GLOBAL_MVAR(v_PersistentLinkerState, panic "Dynamic linker not initialised", PersistentLinkerState)
    GLOBAL_VAR(v_InitLinkerDone, False, Bool)	-- Set True when dynamic linker is initialised

    data PersistentLinkerState
       = PersistentLinkerState {

    	-- Current global mapping from Names to their true values
            closure_env :: ClosureEnv,

    	-- The current global mapping from RdrNames of DataCons to
    	-- info table addresses.
    	-- When a new Unlinked is linked into the running image, or an existing
    	-- module in the image is replaced, the itbl_env must be updated
    	-- appropriately.
            itbl_env    :: !ItblEnv,

    	-- The currently loaded interpreted modules (home package)
    	bcos_loaded :: ![Linkable],

    	-- And the currently-loaded compiled modules (home package)
    	objs_loaded :: ![Linkable],

    	-- The currently-loaded packages; always object code
    	-- Held, as usual, in dependency order; though I am not sure if
    	-- that is really important
    	pkgs_loaded :: ![PackageId]
         }

    emptyPLS :: DynFlags -> PersistentLinkerState
    emptyPLS _ = PersistentLinkerState {
    			closure_env = emptyNameEnv,
    			itbl_env    = emptyNameEnv,
    			pkgs_loaded = init_pkgs,
    			bcos_loaded = [],
    			objs_loaded = [] }

      -- Packages that don't need loading, because the compiler
      -- shares them with the interpreted program.
      --
      -- The linker's symbol table is populated with RTS symbols using an
      -- explicit list.  See rts/Linker.c for details.
      where init_pkgs = [rtsPackageId]

\end{code} \begin{code}

    extendLoadedPkgs :: [PackageId] -> IO ()
    extendLoadedPkgs pkgs =
      modifyMVar_ v_PersistentLinkerState $ \s ->
          return s{ pkgs_loaded = pkgs ++ pkgs_loaded s }

    extendLinkEnv :: [(Name,HValue)] -> IO ()
    -- Automatically discards shadowed bindings
    extendLinkEnv new_bindings =
      modifyMVar_ v_PersistentLinkerState $ \pls ->
        let new_closure_env = extendClosureEnv (closure_env pls) new_bindings
        in return pls{ closure_env = new_closure_env }

    deleteFromLinkEnv :: [Name] -> IO ()
    deleteFromLinkEnv to_remove =
      modifyMVar_ v_PersistentLinkerState $ \pls ->
        let new_closure_env = delListFromNameEnv (closure_env pls) to_remove
        in return pls{ closure_env = new_closure_env }

    -- | Given a data constructor in the heap, find its Name.
    --   The info tables for data constructors have a field which records
    --   the source name of the constructor as a Ptr Word8 (UTF-8 encoded
    --   string). The format is:
    --
    --   > Package:Module.Name
    --
    --   We use this string to lookup the interpreter's internal representation of the name
    --   using the lookupOrig.
    --
    dataConInfoPtrToName :: Ptr () -> TcM (Either String Name)
    dataConInfoPtrToName x = do
       theString <- liftIO $ do
          let ptr = castPtr x :: Ptr StgInfoTable
          conDescAddress <- getConDescAddress ptr
          peekArray0 0 conDescAddress
       let (pkg, mod, occ) = parse theString
           pkgFS = mkFastStringByteList pkg
           modFS = mkFastStringByteList mod
           occFS = mkFastStringByteList occ
           occName = mkOccNameFS OccName.dataName occFS
           modName = mkModule (fsToPackageId pkgFS) (mkModuleNameFS modFS)
       return (Left$ showSDoc$ ppr modName <> dot <> ppr occName )
        `recoverM` (Right `fmap` lookupOrig modName occName)

       where

       {- To find the string in the constructor's info table we need to consider
          the layout of info tables relative to the entry code for a closure.

          An info table can be next to the entry code for the closure, or it can
          be separate. The former (faster) is used in registerised versions of ghc,
          and the latter (portable) is for non-registerised versions.

          The diagrams below show where the string is to be found relative to
          the normal info table of the closure.

          1) Code next to table:

             --------------
             |            |   <- pointer to the start of the string
             --------------
             |            |   <- the (start of the) info table structure
             |            |
             |            |
             --------------
             | entry code |
             |    ....    |

             In this case the pointer to the start of the string can be found in
             the memory location _one word before_ the first entry in the normal info
             table.

          2) Code NOT next to table:

                                     --------------
             info table structure -> |     *------------------> --------------
                                     |            |             | entry code |
                                     |            |             |    ....    |
                                     --------------
             ptr to start of str ->  |            |
                                     --------------

             In this case the pointer to the start of the string can be found
             in the memory location: info_table_ptr + info_table_size
       -}

       getConDescAddress :: Ptr StgInfoTable -> IO (Ptr Word8)
       getConDescAddress ptr
        | ghciTablesNextToCode = do
           offsetToString <- peek $ ptr `plusPtr` (- wORD_SIZE)
           return $ (ptr `plusPtr` stdInfoTableSizeB) `plusPtr` (fromIntegral (offsetToString :: StgWord))
        | otherwise =
           peek $ intPtrToPtr $ (ptrToIntPtr ptr) + fromIntegral stdInfoTableSizeB

       -- parsing names is a little bit fiddly because we have a string in the form:
       -- pkg:A.B.C.foo, and we want to split it into three parts: ("pkg", "A.B.C", "foo").
       -- Thus we split at the leftmost colon and the rightmost occurrence of the dot.
       -- It would be easier if the string was in the form pkg:A.B.C:foo, but alas
       -- this is not the conventional way of writing Haskell names. We stick with
       -- convention, even though it makes the parsing code more troublesome.
       -- Warning: this code assumes that the string is well formed.
       parse :: [Word8] -> ([Word8], [Word8], [Word8])
       parse input
          = ASSERT (all (>0) (map length [pkg, mod, occ])) (pkg, mod, occ)
          where
          dot = fromIntegral (ord '.')
          (pkg, rest1) = break (== fromIntegral (ord ':')) input
          (mod, occ)
             = (concat $ intersperse [dot] $ reverse modWords, occWord)
             where
             (modWords, occWord) = ASSERT (length rest1 > 0) (parseModOcc [] (tail rest1))
          parseModOcc :: [[Word8]] -> [Word8] -> ([[Word8]], [Word8])
          parseModOcc acc str
             = case break (== dot) str of
                  (top, []) -> (acc, top)
                  (top, _:bot) -> parseModOcc (top : acc) bot

    -- | Get the 'HValue' associated with the given name.
    --
    -- May cause loading the module that contains the name.
    --
    -- Throws a 'ProgramError' if loading fails or the name cannot be found.
    getHValue :: HscEnv -> Name -> IO HValue
    getHValue hsc_env name = do
      pls <- modifyMVar v_PersistentLinkerState $ \pls -> do
               if (isExternalName name) then do
                 (pls', ok) <- linkDependencies hsc_env pls noSrcSpan [nameModule name]
                 if (failed ok) then ghcError (ProgramError "")
                                else return (pls', pls')
                else
                 return (pls, pls)
      lookupName (closure_env pls) name

    linkDependencies :: HscEnv -> PersistentLinkerState
                     -> SrcSpan -> [Module]
                     -> IO (PersistentLinkerState, SuccessFlag)
    linkDependencies hsc_env pls span needed_mods = do
       let hpt = hsc_HPT hsc_env
           dflags = hsc_dflags hsc_env
    	-- The interpreter and dynamic linker can only handle object code built
    	-- the "normal" way, i.e. no non-std ways like profiling or ticky-ticky.
    	-- So here we check the build tag: if we're building a non-standard way
    	-- then we need to find & link object files built the "normal" way.
       maybe_normal_osuf <- checkNonStdWay dflags span

    	-- Find what packages and linkables are required
       (lnks, pkgs) <- getLinkDeps hsc_env hpt pls
    				maybe_normal_osuf span needed_mods

    	-- Link the packages and modules required
       pls1 <- linkPackages' dflags pkgs pls
       linkModules dflags pls1 lnks

    -- | Temporarily extend the linker state.

    withExtendedLinkEnv :: (MonadIO m, ExceptionMonad m) =>
                           [(Name,HValue)] -> m a -> m a
    withExtendedLinkEnv new_env action
        = gbracket (liftIO $ extendLinkEnv new_env)
                   (\_ -> reset_old_env)
                   (\_ -> action)
        where
            -- Remember that the linker state might be side-effected
            -- during the execution of the IO action, and we don't want to
            -- lose those changes (we might have linked a new module or
            -- package), so the reset action only removes the names we
            -- added earlier.
              reset_old_env = liftIO $ do
                modifyMVar_ v_PersistentLinkerState $ \pls ->
                    let cur = closure_env pls
                        new = delListFromNameEnv cur (map fst new_env)
                    in return pls{ closure_env = new }

    -- filterNameMap removes from the environment all entries except
    -- 	those for a given set of modules;
    -- Note that this removes all *local* (i.e. non-isExternal) names too
    --	(these are the temporary bindings from the command line).
    -- Used to filter both the ClosureEnv and ItblEnv

    filterNameMap :: [Module] -> NameEnv (Name, a) -> NameEnv (Name, a)
    filterNameMap mods env
       = filterNameEnv keep_elt env
       where
         keep_elt (n,_) = isExternalName n
    		      && (nameModule n `elem` mods)

\end{code} \begin{code}

    -- | Display the persistent linker state.
    showLinkerState :: IO ()
    showLinkerState
      = do pls <- readMVar v_PersistentLinkerState
           printDump (vcat [text "----- Linker state -----",
    			text "Pkgs:" <+> ppr (pkgs_loaded pls),
    			text "Objs:" <+> ppr (objs_loaded pls),
    			text "BCOs:" <+> ppr (bcos_loaded pls)])

\end{code} %************************************************************************ %* * \subsection{Initialisation} %* * %************************************************************************ \begin{code}

    -- | Initialise the dynamic linker.  This entails
    --
    --  a) Calling the C initialisation procedure,
    --
    --  b) Loading any packages specified on the command line,
    --
    --  c) Loading any packages specified on the command line, now held in the
    --     @-l@ options in @v_Opt_l@,
    --
    --  d) Loading any @.o\/.dll@ files specified on the command line, now held
    --     in @v_Ld_inputs@,
    --
    --  e) Loading any MacOS frameworks.
    --
    -- NOTE: This function is idempotent; if called more than once, it does
    -- nothing.  This is useful in Template Haskell, where we call it before
    -- trying to link.
    --
    initDynLinker :: DynFlags -> IO ()
    initDynLinker dflags =
      modifyMVar_ v_PersistentLinkerState $ \pls0 -> do
        done <- readIORef v_InitLinkerDone
        if done then return pls0
                else do writeIORef v_InitLinkerDone True
                        reallyInitDynLinker dflags

    reallyInitDynLinker :: DynFlags -> IO PersistentLinkerState
    reallyInitDynLinker dflags =
        do  {  -- Initialise the linker state
    	  let pls0 = emptyPLS dflags

    	 	-- (a) initialise the C dynamic linker
    	; initObjLinker

    		-- (b) Load packages from the command-line
    	; pls <- linkPackages' dflags (preloadPackages (pkgState dflags)) pls0

    	   	-- (c) Link libraries from the command-line
    	; let optl = getOpts dflags opt_l
    	; let minus_ls = [ lib | '-':'l':lib <- optl ]

    	   	-- (d) Link .o files from the command-line
    	; let lib_paths = libraryPaths dflags
    	; cmdline_ld_inputs <- readIORef v_Ld_inputs

    	; classified_ld_inputs <- mapM classifyLdInput cmdline_ld_inputs

    	   	-- (e) Link any MacOS frameworks
    	; let framework_paths
                   | isDarwinTarget = frameworkPaths dflags
                   | otherwise      = []
    	; let frameworks
                   | isDarwinTarget = cmdlineFrameworks dflags
                   | otherwise      = []
    		-- Finally do (c),(d),(e)
            ; let cmdline_lib_specs = [ l | Just l <- classified_ld_inputs ]
    			       ++ map DLL       minus_ls
    			       ++ map Framework frameworks
    	; if null cmdline_lib_specs then return pls
    				    else do

     	{ mapM_ (preloadLib dflags lib_paths framework_paths) cmdline_lib_specs
    	; maybePutStr dflags "final link ... "
    	; ok <- resolveObjs

    	; if succeeded ok then maybePutStrLn dflags "done"
    	  else ghcError (ProgramError "linking extra libraries/objects failed")

            ; return pls
    	}}

    classifyLdInput :: FilePath -> IO (Maybe LibrarySpec)
    classifyLdInput f
      | isObjectFilename f = return (Just (Object f))
      | isDynLibFilename f = return (Just (DLLPath f))
      | otherwise 	       = do
    	hPutStrLn stderr ("Warning: ignoring unrecognised input `" ++ f ++ "'")
    	return Nothing

    preloadLib :: DynFlags -> [String] -> [String] -> LibrarySpec -> IO ()
    preloadLib dflags lib_paths framework_paths lib_spec
      = do maybePutStr dflags ("Loading object " ++ showLS lib_spec ++ " ... ")
           case lib_spec of
              Object static_ish
                 -> do b <- preload_static lib_paths static_ish
                       maybePutStrLn dflags (if b  then "done"
                                                    else "not found")

              Archive static_ish
                 -> do b <- preload_static_archive lib_paths static_ish
                       maybePutStrLn dflags (if b  then "done"
                                                    else "not found")

              DLL dll_unadorned
                 -> do maybe_errstr <- loadDynamic lib_paths dll_unadorned
                       case maybe_errstr of
                          Nothing -> maybePutStrLn dflags "done"
                          Just mm -> preloadFailed mm lib_paths lib_spec

    	  DLLPath dll_path
    	     -> do maybe_errstr <- loadDLL dll_path
                       case maybe_errstr of
                          Nothing -> maybePutStrLn dflags "done"
                          Just mm -> preloadFailed mm lib_paths lib_spec

    	  Framework framework
               | isDarwinTarget
                 -> do maybe_errstr <- loadFramework framework_paths framework
                       case maybe_errstr of
                          Nothing -> maybePutStrLn dflags "done"
                          Just mm -> preloadFailed mm framework_paths lib_spec
               | otherwise -> panic "preloadLib Framework"

      where
        preloadFailed :: String -> [String] -> LibrarySpec -> IO ()
        preloadFailed sys_errmsg paths spec
           = do maybePutStr dflags "failed.\n"
                ghcError $
    	      CmdLineError (
                        "user specified .o/.so/.DLL could not be loaded ("
                        ++ sys_errmsg ++ ")\nWhilst trying to load:  "
                        ++ showLS spec ++ "\nAdditional directories searched:"
                        ++ (if null paths then " (none)" else
                            (concat (intersperse "\n" (map ("   "++) paths)))))

        -- Not interested in the paths in the static case.
        preload_static _paths name
           = do b <- doesFileExist name
                if not b then return False
                         else loadObj name >> return True
        preload_static_archive _paths name
           = do b <- doesFileExist name
                if not b then return False
                         else loadArchive name >> return True

\end{code} %************************************************************************ %* * Link a byte-code expression %* * %************************************************************************ \begin{code}

    -- | Link a single expression, /including/ first linking packages and
    -- modules that this expression depends on.
    --
    -- Raises an IO exception ('ProgramError') if it can't find a compiled
    -- version of the dependents to link.
    --
    linkExpr :: HscEnv -> SrcSpan -> UnlinkedBCO -> IO HValue
    linkExpr hsc_env span root_ul_bco
      = do {
    	-- Initialise the linker (if it's not been done already)
         let dflags = hsc_dflags hsc_env
       ; initDynLinker dflags

            -- Take lock for the actual work.
       ; modifyMVar v_PersistentLinkerState $ \pls0 -> do {

    	-- Link the packages and modules required
       ; (pls, ok) <- linkDependencies hsc_env pls0 span needed_mods
       ; if failed ok then
    	ghcError (ProgramError "")
         else do {

    	-- Link the expression itself
         let ie = itbl_env pls
    	 ce = closure_env pls

    	-- Link the necessary packages and linkables
       ; (_, (root_hval:_)) <- linkSomeBCOs False ie ce [root_ul_bco]
       ; return (pls, root_hval)
       }}}
       where
         free_names = nameSetToList (bcoFreeNames root_ul_bco)

         needed_mods :: [Module]
         needed_mods = [ nameModule n | n <- free_names,
    				    isExternalName n,	 	-- Names from other modules
    				    not (isWiredInName n)	-- Exclude wired-in names
    		   ]						-- (see note below)
    	-- Exclude wired-in names because we may not have read
    	-- their interface files, so getLinkDeps will fail
    	-- All wired-in names are in the base package, which we link
    	-- by default, so we can safely ignore them here.

    dieWith :: SrcSpan -> Message -> IO a
    dieWith span msg = ghcError (ProgramError (showSDoc (mkLocMessage span msg)))

    checkNonStdWay :: DynFlags -> SrcSpan -> IO (Maybe String)
    checkNonStdWay dflags srcspan = do
      let tag = buildTag dflags
      if null tag {-  || tag == "dyn" -} then return Nothing else do
        -- see #3604: object files compiled for way "dyn" need to link to the
        -- dynamic packages, so we can't load them into a statically-linked GHCi.
        -- we have to treat "dyn" in the same way as "prof".
        --
        -- In the future when GHCi is dynamically linked we should be able to relax
        -- this, but they we may have to make it possible to load either ordinary
        -- .o files or -dynamic .o files into GHCi (currently that's not possible
        -- because the dynamic objects contain refs to e.g. __stginit_base_Prelude_dyn
        -- whereas we have __stginit_base_Prelude_.
      let default_osuf = phaseInputExt StopLn
      if objectSuf dflags == default_osuf
    	then failNonStd srcspan
    	else return (Just default_osuf)

    failNonStd :: SrcSpan -> IO (Maybe String)
    failNonStd srcspan = dieWith srcspan $
      ptext (sLit "Dynamic linking required, but this is a non-standard build (eg. prof).") $$
      ptext (sLit "You need to build the program twice: once the normal way, and then") $$
      ptext (sLit "in the desired way using -osuf to set the object file suffix.")

    getLinkDeps :: HscEnv -> HomePackageTable
                -> PersistentLinkerState
    	    -> Maybe String			-- the "normal" object suffix
    	    -> SrcSpan				-- for error messages
    	    -> [Module]				-- If you need these
    	    -> IO ([Linkable], [PackageId])	-- ... then link these first
    -- Fails with an IO exception if it can't find enough files

    getLinkDeps hsc_env hpt pls maybe_normal_osuf span mods
    -- Find all the packages and linkables that a set of modules depends on
     = do {
    	-- 1.  Find the dependent home-pkg-modules/packages from each iface
            (mods_s, pkgs_s) <- follow_deps mods emptyUniqSet emptyUniqSet;

    	let {
    	-- 2.  Exclude ones already linked
    	--	Main reason: avoid findModule calls in get_linkable
    	    mods_needed = mods_s `minusList` linked_mods     ;
    	    pkgs_needed = pkgs_s `minusList` pkgs_loaded pls ;

    	    linked_mods = map (moduleName.linkableModule)
                                    (objs_loaded pls ++ bcos_loaded pls)
    	} ;

    --        putStrLn (showSDoc (ppr mods_s)) ;
    	-- 3.  For each dependent module, find its linkable
    	--     This will either be in the HPT or (in the case of one-shot
    	--     compilation) we may need to use maybe_getFileLinkable
    	lnks_needed <- mapM (get_linkable maybe_normal_osuf) mods_needed ;

    	return (lnks_needed, pkgs_needed) }
      where
        dflags = hsc_dflags hsc_env
        this_pkg = thisPackage dflags

            -- The ModIface contains the transitive closure of the module dependencies
            -- within the current package, *except* for boot modules: if we encounter
            -- a boot module, we have to find its real interface and discover the
            -- dependencies of that.  Hence we need to traverse the dependency
            -- tree recursively.  See bug #936, testcase ghci/prog007.
        follow_deps :: [Module]             -- modules to follow
                    -> UniqSet ModuleName         -- accum. module dependencies
                    -> UniqSet PackageId          -- accum. package dependencies
                    -> IO ([ModuleName], [PackageId]) -- result
        follow_deps []     acc_mods acc_pkgs
            = return (uniqSetToList acc_mods, uniqSetToList acc_pkgs)
        follow_deps (mod:mods) acc_mods acc_pkgs
            = do
              mb_iface <- initIfaceCheck hsc_env $
                            loadInterface msg mod (ImportByUser False)
              iface <- case mb_iface of
            	    Maybes.Failed err      -> ghcError (ProgramError (showSDoc err))
    	            Maybes.Succeeded iface -> return iface

              when (mi_boot iface) $ link_boot_mod_error mod

              let
                pkg = modulePackageId mod
                deps  = mi_deps iface

                pkg_deps = dep_pkgs deps
                (boot_deps, mod_deps) = partitionWith is_boot (dep_mods deps)
                        where is_boot (m,True)  = Left m
                              is_boot (m,False) = Right m

                boot_deps' = filter (not . (`elementOfUniqSet` acc_mods)) boot_deps
                acc_mods'  = addListToUniqSet acc_mods (moduleName mod : mod_deps)
                acc_pkgs'  = addListToUniqSet acc_pkgs pkg_deps
              --
              if pkg /= this_pkg
                 then follow_deps mods acc_mods (addOneToUniqSet acc_pkgs' pkg)
                 else follow_deps (map (mkModule this_pkg) boot_deps' ++ mods)
                                  acc_mods' acc_pkgs'
            where
                msg = text "need to link module" <+> ppr mod <+>
                      text "due to use of Template Haskell"

        link_boot_mod_error mod =
            ghcError (ProgramError (showSDoc (
                text "module" <+> ppr mod <+>
                text "cannot be linked; it is only available as a boot module")))

        no_obj :: Outputable a => a -> IO b
        no_obj mod = dieWith span $
    		     ptext (sLit "cannot find object file for module ") <>
    			quotes (ppr mod) $$
    		     while_linking_expr

        while_linking_expr = ptext (sLit "while linking an interpreted expression")

    	-- This one is a build-system bug

        get_linkable maybe_normal_osuf mod_name	-- A home-package module
    	| Just mod_info <- lookupUFM hpt mod_name
    	= adjust_linkable (Maybes.expectJust "getLinkDeps" (hm_linkable mod_info))
    	| otherwise
    	= do	-- It's not in the HPT because we are in one shot mode,
    		-- so use the Finder to get a ModLocation...
    	     mb_stuff <- findHomeModule hsc_env mod_name
    	     case mb_stuff of
    		  Found loc mod -> found loc mod
    		  _ -> no_obj mod_name
            where
                found loc mod = do {
    		-- ...and then find the linkable for it
    	       mb_lnk <- findObjectLinkableMaybe mod loc ;
    	       case mb_lnk of {
    		  Nothing  -> no_obj mod ;
    		  Just lnk -> adjust_linkable lnk
    	      }}

    	    adjust_linkable lnk
    		| Just osuf <- maybe_normal_osuf = do
    			new_uls <- mapM (adjust_ul osuf) (linkableUnlinked lnk)
            		return lnk{ linkableUnlinked=new_uls }
    		| otherwise =
    			return lnk

    	    adjust_ul osuf (DotO file) = do
    		let new_file = replaceExtension file osuf
    		ok <- doesFileExist new_file
    		if (not ok)
    		   then dieWith span $
    			  ptext (sLit "cannot find normal object file ")
    				<> quotes (text new_file) $$ while_linking_expr
    		   else return (DotO new_file)
    	    adjust_ul _ _ = panic "adjust_ul"

\end{code} %************************************************************************ %* * Link some linkables The linkables may consist of a mixture of byte-code modules and object modules %* * %************************************************************************ \begin{code}

    linkModules :: DynFlags -> PersistentLinkerState -> [Linkable]
                -> IO (PersistentLinkerState, SuccessFlag)
    linkModules dflags pls linkables
      = mask_ $ do  -- don't want to be interrupted by ^C in here

    	let (objs, bcos) = partition isObjectLinkable
                                  (concatMap partitionLinkable linkables)

    		-- Load objects first; they can't depend on BCOs
    	(pls1, ok_flag) <- dynLinkObjs dflags pls objs

    	if failed ok_flag then
    		return (pls1, Failed)
    	  else do
    		pls2 <- dynLinkBCOs pls1 bcos
    		return (pls2, Succeeded)

    -- HACK to support f-x-dynamic in the interpreter; no other purpose
    partitionLinkable :: Linkable -> [Linkable]
    partitionLinkable li
       = let li_uls = linkableUnlinked li
             li_uls_obj = filter isObject li_uls
             li_uls_bco = filter isInterpretable li_uls
         in
             case (li_uls_obj, li_uls_bco) of
                (_:_, _:_) -> [li {linkableUnlinked=li_uls_obj},
                               li {linkableUnlinked=li_uls_bco}]
                _ -> [li]

    findModuleLinkable_maybe :: [Linkable] -> Module -> Maybe Linkable
    findModuleLinkable_maybe lis mod
       = case [LM time nm us | LM time nm us <- lis, nm == mod] of
            []   -> Nothing
            [li] -> Just li
            _    -> pprPanic "findModuleLinkable" (ppr mod)

    linkableInSet :: Linkable -> [Linkable] -> Bool
    linkableInSet l objs_loaded =
      case findModuleLinkable_maybe objs_loaded (linkableModule l) of
    	Nothing -> False
    	Just m  -> linkableTime l == linkableTime m

\end{code} %************************************************************************ %* * \subsection{The object-code linker} %* * %************************************************************************ \begin{code}

    dynLinkObjs :: DynFlags -> PersistentLinkerState -> [Linkable]
                -> IO (PersistentLinkerState, SuccessFlag)
    dynLinkObjs dflags pls objs = do
    	-- Load the object files and link them
    	let (objs_loaded', new_objs) = rmDupLinkables (objs_loaded pls) objs
    	    pls1 		     = pls { objs_loaded = objs_loaded' }
    	    unlinkeds 		     = concatMap linkableUnlinked new_objs

    	mapM_ loadObj (map nameOfObject unlinkeds)

    	-- Link the all together
    	ok <- resolveObjs

    	-- If resolving failed, unload all our
    	-- object modules and carry on
    	if succeeded ok then do
    		return (pls1, Succeeded)
    	  else do
    		pls2 <- unload_wkr dflags [] pls1
                    return (pls2, Failed)

    rmDupLinkables :: [Linkable] 	-- Already loaded
    	       -> [Linkable]	-- New linkables
    	       -> ([Linkable],	-- New loaded set (including new ones)
    		   [Linkable])	-- New linkables (excluding dups)
    rmDupLinkables already ls
      = go already [] ls
      where
        go already extras [] = (already, extras)
        go already extras (l:ls)
    	| linkableInSet l already = go already     extras     ls
    	| otherwise		  = go (l:already) (l:extras) ls

\end{code} %************************************************************************ %* * \subsection{The byte-code linker} %* * %************************************************************************ \begin{code}

    dynLinkBCOs :: PersistentLinkerState -> [Linkable] -> IO PersistentLinkerState
    dynLinkBCOs pls bcos = do

    	let (bcos_loaded', new_bcos) = rmDupLinkables (bcos_loaded pls) bcos
    	    pls1 		     = pls { bcos_loaded = bcos_loaded' }
    	    unlinkeds :: [Unlinked]
    	    unlinkeds 		     = concatMap linkableUnlinked new_bcos

    	    cbcs :: [CompiledByteCode]
    	    cbcs      = map byteCodeOfObject unlinkeds

    	    ul_bcos    = [b | ByteCode bs _  <- cbcs, b <- bs]
    	    ies	       = [ie | ByteCode _ ie <- cbcs]
    	    gce	      = closure_env pls
                final_ie  = foldr plusNameEnv (itbl_env pls) ies

            (final_gce, _linked_bcos) <- linkSomeBCOs True final_ie gce ul_bcos
    		-- XXX What happens to these linked_bcos?

    	let pls2 = pls1 { closure_env = final_gce,
    			  itbl_env    = final_ie }

    	return pls2

    -- Link a bunch of BCOs and return them + updated closure env.
    linkSomeBCOs :: Bool 	-- False <=> add _all_ BCOs to returned closure env
                            -- True  <=> add only toplevel BCOs to closure env
                 -> ItblEnv
                 -> ClosureEnv
                 -> [UnlinkedBCO]
                 -> IO (ClosureEnv, [HValue])
    			-- The returned HValues are associated 1-1 with
    			-- the incoming unlinked BCOs.  Each gives the
    			-- value of the corresponding unlinked BCO

    linkSomeBCOs toplevs_only ie ce_in ul_bcos
       = do let nms = map unlinkedBCOName ul_bcos
            hvals <- fixIO
                        ( \ hvs -> let ce_out = extendClosureEnv ce_in (zipLazy nms hvs)
                                   in  mapM (linkBCO ie ce_out) ul_bcos )
            let ce_all_additions = zip nms hvals
                ce_top_additions = filter (isExternalName.fst) ce_all_additions
                ce_additions     = if toplevs_only then ce_top_additions
                                                   else ce_all_additions
                ce_out = -- make sure we're not inserting duplicate names into the
    		     -- closure environment, which leads to trouble.
    		     ASSERT (all (not . (`elemNameEnv` ce_in)) (map fst ce_additions))
    		     extendClosureEnv ce_in ce_additions
            return (ce_out, hvals)

\end{code} %************************************************************************ %* * Unload some object modules %* * %************************************************************************ \begin{code}

    -- ---------------------------------------------------------------------------
    -- | Unloading old objects ready for a new compilation sweep.
    --
    -- The compilation manager provides us with a list of linkables that it
    -- considers \"stable\", i.e. won't be recompiled this time around.  For
    -- each of the modules current linked in memory,
    --
    --   * if the linkable is stable (and it's the same one -- the user may have
    --     recompiled the module on the side), we keep it,
    --
    --   * otherwise, we unload it.
    --
    --   * we also implicitly unload all temporary bindings at this point.
    --
    unload :: DynFlags
           -> [Linkable] -- ^ The linkables to *keep*.
           -> IO ()
    unload dflags linkables
      = mask_ $ do -- mask, so we're safe from Ctrl-C in here

    	-- Initialise the linker (if it's not been done already)
    	initDynLinker dflags

    	new_pls
                <- modifyMVar v_PersistentLinkerState $ \pls -> do
    	         pls1 <- unload_wkr dflags linkables pls
                     return (pls1, pls1)

    	debugTraceMsg dflags 3 (text "unload: retaining objs" <+> ppr (objs_loaded new_pls))
    	debugTraceMsg dflags 3 (text "unload: retaining bcos" <+> ppr (bcos_loaded new_pls))
    	return ()

    unload_wkr :: DynFlags
               -> [Linkable]		-- stable linkables
    	   -> PersistentLinkerState
               -> IO PersistentLinkerState
    -- Does the core unload business
    -- (the wrapper blocks exceptions and deals with the PLS get and put)

    unload_wkr _ linkables pls
      = do	let (objs_to_keep, bcos_to_keep) = partition isObjectLinkable linkables

    	objs_loaded' <- filterM (maybeUnload objs_to_keep) (objs_loaded pls)
            bcos_loaded' <- filterM (maybeUnload bcos_to_keep) (bcos_loaded pls)

           	let bcos_retained = map linkableModule bcos_loaded'
    	    itbl_env'     = filterNameMap bcos_retained (itbl_env pls)
                closure_env'  = filterNameMap bcos_retained (closure_env pls)
      	    new_pls = pls { itbl_env = itbl_env',
    			    closure_env = closure_env',
    			    bcos_loaded = bcos_loaded',
    			    objs_loaded = objs_loaded' }

    	return new_pls
      where
        maybeUnload :: [Linkable] -> Linkable -> IO Bool
        maybeUnload keep_linkables lnk
          | linkableInSet lnk keep_linkables = return True
          | otherwise
          = do mapM_ unloadObj [f | DotO f <- linkableUnlinked lnk]
    		-- The components of a BCO linkable may contain
    		-- dot-o files.  Which is very confusing.
    		--
    		-- But the BCO parts can be unlinked just by
    		-- letting go of them (plus of course depopulating
    		-- the symbol table which is done in the main body)
    	   return False

\end{code} %************************************************************************ %* * Loading packages %* * %************************************************************************ \begin{code}

    data LibrarySpec
       = Object FilePath 	-- Full path name of a .o file, including trailing .o
    			-- For dynamic objects only, try to find the object
    			-- file in all the directories specified in
    			-- v_Library_paths before giving up.

       | Archive FilePath 	-- Full path name of a .a file, including trailing .a

       | DLL String		-- "Unadorned" name of a .DLL/.so
    			--  e.g.    On unix     "qt"  denotes "libqt.so"
    			--          On WinDoze  "burble"  denotes "burble.DLL"
    			--  loadDLL is platform-specific and adds the lib/.so/.DLL
    			--  suffixes platform-dependently

       | DLLPath FilePath   -- Absolute or relative pathname to a dynamic library
    			-- (ends with .dll or .so).

       | Framework String	-- Only used for darwin, but does no harm

    -- If this package is already part of the GHCi binary, we'll already
    -- have the right DLLs for this package loaded, so don't try to
    -- load them again.
    --
    -- But on Win32 we must load them 'again'; doing so is a harmless no-op
    -- as far as the loader is concerned, but it does initialise the list
    -- of DLL handles that rts/Linker.c maintains, and that in turn is
    -- used by lookupSymbol.  So we must call addDLL for each library
    -- just to get the DLL handle into the list.
    partOfGHCi :: [PackageName]
    partOfGHCi
     | isWindowsTarget || isDarwinTarget = []
     | otherwise = map PackageName
                       ["base", "template-haskell", "editline"]

    showLS :: LibrarySpec -> String
    showLS (Object nm)    = "(static) " ++ nm
    showLS (Archive nm)   = "(static archive) " ++ nm
    showLS (DLL nm)       = "(dynamic) " ++ nm
    showLS (DLLPath nm)   = "(dynamic) " ++ nm
    showLS (Framework nm) = "(framework) " ++ nm

    -- | Link exactly the specified packages, and their dependents (unless of
    -- course they are already linked).  The dependents are linked
    -- automatically, and it doesn't matter what order you specify the input
    -- packages.
    --
    linkPackages :: DynFlags -> [PackageId] -> IO ()
    -- NOTE: in fact, since each module tracks all the packages it depends on,
    --       we don't really need to use the package-config dependencies.
    --
    -- However we do need the package-config stuff (to find aux libs etc),
    -- and following them lets us load libraries in the right order, which
    -- perhaps makes the error message a bit more localised if we get a link
    -- failure.  So the dependency walking code is still here.

    linkPackages dflags new_pkgs = do
      -- It's probably not safe to try to load packages concurrently, so we take
      -- a lock.
      modifyMVar_ v_PersistentLinkerState $ \pls -> do
        linkPackages' dflags new_pkgs pls

    linkPackages' :: DynFlags -> [PackageId] -> PersistentLinkerState
                 -> IO PersistentLinkerState
    linkPackages' dflags new_pks pls = do
        pkgs' <- link (pkgs_loaded pls) new_pks
        return $! pls { pkgs_loaded = pkgs' }
      where
         pkg_map = pkgIdMap (pkgState dflags)
         ipid_map = installedPackageIdMap (pkgState dflags)

         link :: [PackageId] -> [PackageId] -> IO [PackageId]
         link pkgs new_pkgs =
             foldM link_one pkgs new_pkgs

         link_one pkgs new_pkg
    	| new_pkg `elem` pkgs	-- Already linked
    	= return pkgs

    	| Just pkg_cfg <- lookupPackage pkg_map new_pkg
    	= do { 	-- Link dependents first
                   pkgs' <- link pkgs [ Maybes.expectJust "link_one" $
                                        Map.lookup ipid ipid_map
                                      | ipid <- depends pkg_cfg ]
    		-- Now link the package itself
    	     ; linkPackage dflags pkg_cfg
    	     ; return (new_pkg : pkgs') }

    	| otherwise
    	= ghcError (CmdLineError ("unknown package: " ++ packageIdString new_pkg))

    linkPackage :: DynFlags -> PackageConfig -> IO ()
    linkPackage dflags pkg
       = do
            let dirs      =  Packages.libraryDirs pkg

            let libs      =  Packages.hsLibraries pkg
                -- The FFI GHCi import lib isn't needed as
                -- compiler/ghci/Linker.lhs + rts/Linker.c link the
                -- interpreted references to FFI to the compiled FFI.
                -- We therefore filter it out so that we don't get
                -- duplicate symbol errors.
                libs'     =  filter ("HSffi" /=) libs
            -- Because of slight differences between the GHC dynamic linker and
            -- the native system linker some packages have to link with a
            -- different list of libraries when using GHCi. Examples include: libs
            -- that are actually gnu ld scripts, and the possability that the .a
            -- libs do not exactly match the .so/.dll equivalents. So if the
            -- package file provides an "extra-ghci-libraries" field then we use
            -- that instead of the "extra-libraries" field.
                          ++ (if null (Packages.extraGHCiLibraries pkg)
                                then Packages.extraLibraries pkg
                                else Packages.extraGHCiLibraries pkg)
                          ++ [ lib | '-':'l':lib <- Packages.ldOptions pkg ]
            classifieds   <- mapM (locateOneObj dirs) libs'

            -- Complication: all the .so's must be loaded before any of the .o's.
    	let dlls = [ dll | DLL dll    <- classifieds ]
    	    objs = [ obj | Object obj <- classifieds ]
    	    archs = [ arch | Archive arch <- classifieds ]

    	maybePutStr dflags ("Loading package " ++ display (sourcePackageId pkg) ++ " ... ")

    	-- See comments with partOfGHCi
    	when (packageName pkg `notElem` partOfGHCi) $ do
    	    loadFrameworks pkg
                -- When a library A needs symbols from a library B, the order in
                -- extra_libraries/extra_ld_opts is "-lA -lB", because that's the
                -- way ld expects it for static linking. Dynamic linking is a
                -- different story: When A has no dependency information for B,
                -- dlopen-ing A with RTLD_NOW (see addDLL in Linker.c) will fail
                -- when B has not been loaded before. In a nutshell: Reverse the
                -- order of DLLs for dynamic linking.
    	    -- This fixes a problem with the HOpenGL package (see "Compiling
    	    -- HOpenGL under recent versions of GHC" on the HOpenGL list).
    	    mapM_ (load_dyn dirs) (reverse dlls)

    	-- After loading all the DLLs, we can load the static objects.
    	-- Ordering isn't important here, because we do one final link
    	-- step to resolve everything.
    	mapM_ loadObj objs
    	mapM_ loadArchive archs

            maybePutStr dflags "linking ... "
            ok <- resolveObjs
    	if succeeded ok then maybePutStrLn dflags "done."
    	      else ghcError (InstallationError ("unable to load package `" ++ display (sourcePackageId pkg) ++ "'"))

    load_dyn :: [FilePath] -> FilePath -> IO ()
    load_dyn dirs dll = do r <- loadDynamic dirs dll
    		       case r of
    			 Nothing  -> return ()
    			 Just err -> ghcError (CmdLineError ("can't load .so/.DLL for: "
                                     			      ++ dll ++ " (" ++ err ++ ")" ))

    loadFrameworks :: InstalledPackageInfo_ ModuleName -> IO ()
    loadFrameworks pkg
     | isDarwinTarget = mapM_ load frameworks
     | otherwise = return ()
      where
        fw_dirs    = Packages.frameworkDirs pkg
        frameworks = Packages.frameworks pkg

        load fw = do  r <- loadFramework fw_dirs fw
    		  case r of
    		    Nothing  -> return ()
    		    Just err -> ghcError (CmdLineError ("can't load framework: "
                                   			        ++ fw ++ " (" ++ err ++ ")" ))

    -- Try to find an object file for a given library in the given paths.
    -- If it isn't present, we assume it's a dynamic library.
    locateOneObj :: [FilePath] -> String -> IO LibrarySpec
    locateOneObj dirs lib
      | not ("HS" `isPrefixOf` lib)
        -- For non-Haskell libraries (e.g. gmp, iconv) we assume dynamic library
      = assumeDll
      | not isDynamicGhcLib
        -- When the GHC package was not compiled as dynamic library
        -- (=DYNAMIC not set), we search for .o libraries or, if they
        -- don't exist, .a libraries.
      = findObject `orElse` findArchive `orElse` assumeDll
      | otherwise
        -- When the GHC package was compiled as dynamic library (=DYNAMIC set),
        -- we search for .so libraries first.
      = findDll `orElse` findObject `orElse` findArchive `orElse` assumeDll
       where
         mk_obj_path dir = dir </> (lib <.> "o")
         mk_arch_path dir = dir </> ("lib" ++ lib <.> "a")
         dyn_lib_name = lib ++ "-ghc" ++ cProjectVersion
         mk_dyn_lib_path dir = dir </> mkSOName dyn_lib_name
         findObject  = liftM (fmap Object)  $ findFile mk_obj_path  dirs
         findArchive = liftM (fmap Archive) $ findFile mk_arch_path dirs
         findDll     = liftM (fmap DLL)     $ findFile mk_dyn_lib_path dirs
         assumeDll   = return (DLL lib)
         infixr `orElse`
         f `orElse` g = do m <- f
                           case m of
                               Just x -> return x
                               Nothing -> g

    -- ----------------------------------------------------------------------------
    -- Loading a dyanmic library (dlopen()-ish on Unix, LoadLibrary-ish on Win32)

    -- return Nothing == success, else Just error message from dlopen
    loadDynamic :: [FilePath] -> FilePath -> IO (Maybe String)
    loadDynamic paths rootname
      = do	{ mb_dll <- findFile mk_dll_path paths
    	; case mb_dll of
    	    Just dll -> loadDLL dll
    	    Nothing  -> loadDLL (mkSOName rootname) }
    			-- Tried all our known library paths, so let
    			-- dlopen() search its own builtin paths now.
      where
        mk_dll_path dir = dir </> mkSOName rootname

    mkSOName :: FilePath -> FilePath
    mkSOName root
     | isDarwinTarget  = ("lib" ++ root) <.> "dylib"
     | isWindowsTarget = -- Win32 DLLs have no .dll extension here, because
                         -- addDLL tries both foo.dll and foo.drv
                         root
     | otherwise       = ("lib" ++ root) <.> "so"

    -- Darwin / MacOS X only: load a framework
    -- a framework is a dynamic library packaged inside a directory of the same
    -- name. They are searched for in different paths than normal libraries.
    loadFramework :: [FilePath] -> FilePath -> IO (Maybe String)
    loadFramework extraPaths rootname
       = do { either_dir <- tryIO getHomeDirectory
            ; let homeFrameworkPath = case either_dir of
                                      Left _ -> []
                                      Right dir -> [dir ++ "/Library/Frameworks"]
                  ps = extraPaths ++ homeFrameworkPath ++ defaultFrameworkPaths
            ; mb_fwk <- findFile mk_fwk ps
            ; case mb_fwk of
                Just fwk_path -> loadDLL fwk_path
                Nothing       -> return (Just "not found") }
                    -- Tried all our known library paths, but dlopen()
                    -- has no built-in paths for frameworks: give up
       where
         mk_fwk dir = dir </> (rootname ++ ".framework/" ++ rootname)
            -- sorry for the hardcoded paths, I hope they won't change anytime soon:
         defaultFrameworkPaths = ["/Library/Frameworks", "/System/Library/Frameworks"]

\end{code} %************************************************************************ %* * Helper functions %* * %************************************************************************ \begin{code}

    findFile :: (FilePath -> FilePath)	-- Maps a directory path to a file path
    	 -> [FilePath]			-- Directories to look in
    	 -> IO (Maybe FilePath)		-- The first file path to match
    findFile _ []
      = return Nothing
    findFile mk_file_path (dir:dirs)
      = do	{ let file_path = mk_file_path dir
    	; b <- doesFileExist file_path
    	; if b then
    	     return (Just file_path)
    	  else
    	     findFile mk_file_path dirs }

\end{code} \begin{code}

    maybePutStr :: DynFlags -> String -> IO ()
    maybePutStr dflags s | verbosity dflags > 0 = putStr s
    		     | otherwise	    = return ()

    maybePutStrLn :: DynFlags -> String -> IO ()
    maybePutStrLn dflags s | verbosity dflags > 0 = putStrLn s
    		       | otherwise	      = return ()

\end{code}