GHC/Linker/ExtraObj.hs

    -----------------------------------------------------------------------------
    --
    -- GHC Extra object linking code
    --
    -- (c) The GHC Team 2017
    --
    -----------------------------------------------------------------------------

    module GHC.Linker.ExtraObj
       ( mkExtraObj
       , mkExtraObjToLinkIntoBinary
       , mkNoteObjsToLinkIntoBinary
       , checkLinkInfo
       , getLinkInfo
       , getCompilerInfo
       , ghcLinkInfoSectionName
       , ghcLinkInfoNoteName
       , platformSupportsSavingLinkOpts
       , haveRtsOptsFlags
       )
    where

    import GHC.Prelude
    import GHC.Platform

    import GHC.Unit
    import GHC.Unit.Env
    import GHC.Unit.State

    import GHC.Utils.Asm
    import GHC.Utils.Error
    import GHC.Utils.Misc
    import GHC.Utils.Outputable as Outputable
    import GHC.Utils.Logger
    import GHC.Utils.TmpFs

    import GHC.Driver.Session
    import GHC.Driver.Ppr

    import qualified GHC.Data.ShortText as ST

    import GHC.SysTools.Elf
    import GHC.SysTools.Tasks
    import GHC.SysTools.Info
    import GHC.Linker.Unit

    import Control.Monad.IO.Class
    import Control.Monad
    import Data.Maybe

    mkExtraObj :: Logger -> TmpFs -> DynFlags -> UnitState -> Suffix -> String -> IO FilePath
    mkExtraObj logger tmpfs dflags unit_state extn xs
     = do cFile <- newTempName logger tmpfs dflags TFL_CurrentModule extn
          oFile <- newTempName logger tmpfs dflags TFL_GhcSession "o"
          writeFile cFile xs
          ccInfo <- liftIO $ getCompilerInfo logger dflags
          runCc Nothing logger tmpfs dflags
                ([Option        "-c",
                  FileOption "" cFile,
                  Option        "-o",
                  FileOption "" oFile]
                  ++ if extn /= "s"
                        then cOpts
                        else asmOpts ccInfo)
          return oFile
        where
          -- Pass a different set of options to the C compiler depending one whether
          -- we're compiling C or assembler. When compiling C, we pass the usual
          -- set of include directories and PIC flags.
          cOpts = map Option (picCCOpts dflags)
                        ++ map (FileOption "-I" . ST.unpack)
                                (unitIncludeDirs $ unsafeLookupUnit unit_state rtsUnit)

          -- When compiling assembler code, we drop the usual C options, and if the
          -- compiler is Clang, we add an extra argument to tell Clang to ignore
          -- unused command line options. See trac #11684.
          asmOpts ccInfo =
                if any (ccInfo ==) [Clang, AppleClang, AppleClang51]
                    then [Option "-Qunused-arguments"]
                    else []

    -- When linking a binary, we need to create a C main() function that
    -- starts everything off.  This used to be compiled statically as part
    -- of the RTS, but that made it hard to change the -rtsopts setting,
    -- so now we generate and compile a main() stub as part of every
    -- binary and pass the -rtsopts setting directly to the RTS (#5373)
    --
    -- On Windows, when making a shared library we also may need a DllMain.
    --
    mkExtraObjToLinkIntoBinary :: Logger -> TmpFs -> DynFlags -> UnitState -> IO (Maybe FilePath)
    mkExtraObjToLinkIntoBinary logger tmpfs dflags unit_state = do
      when (gopt Opt_NoHsMain dflags && haveRtsOptsFlags dflags) $
         logInfo logger dflags $ withPprStyle defaultUserStyle
             (text "Warning: -rtsopts and -with-rtsopts have no effect with -no-hs-main." $$
              text "    Call hs_init_ghc() from your main() function to set these options.")

      case ghcLink dflags of
        -- Don't try to build the extra object if it is not needed.  Compiling the
        -- extra object assumes the presence of the RTS in the unit database
        -- (because the extra object imports Rts.h) but GHC's build system may try
        -- to build some helper programs before building and registering the RTS!
        -- See #18938 for an example where hp2ps failed to build because of a failed
        -- (unsafe) lookup for the RTS in the unit db.
        _ | gopt Opt_NoHsMain dflags
          -> return Nothing

        LinkDynLib
          | OSMinGW32 <- platformOS (targetPlatform dflags)
          -> mk_extra_obj dllMain

          | otherwise
          -> return Nothing

        _ -> mk_extra_obj exeMain

      where
        mk_extra_obj = fmap Just . mkExtraObj logger tmpfs dflags unit_state "c" . showSDoc dflags

        exeMain = vcat [
            text "#include <Rts.h>",
            text "extern StgClosure ZCMain_main_closure;",
            text "int main(int argc, char *argv[])",
            char '{',
            text " RtsConfig __conf = defaultRtsConfig;",
            text " __conf.rts_opts_enabled = "
                <> text (show (rtsOptsEnabled dflags)) <> semi,
            text " __conf.rts_opts_suggestions = "
                <> text (if rtsOptsSuggestions dflags
                            then "true"
                            else "false") <> semi,
            text "__conf.keep_cafs = "
                <> text (if gopt Opt_KeepCAFs dflags
                           then "true"
                           else "false") <> semi,
            case rtsOpts dflags of
                Nothing   -> Outputable.empty
                Just opts -> text "    __conf.rts_opts= " <>
                              text (show opts) <> semi,
            text " __conf.rts_hs_main = true;",
            text " return hs_main(argc,argv,&ZCMain_main_closure,__conf);",
            char '}',
            char '\n' -- final newline, to keep gcc happy
            ]

        dllMain = vcat [
            text "#include <Rts.h>",
            text "#include <windows.h>",
            text "#include <stdbool.h>",
            char '\n',
            text "bool",
            text "WINAPI",
            text "DllMain ( HINSTANCE hInstance STG_UNUSED",
            text "        , DWORD reason STG_UNUSED",
            text "        , LPVOID reserved STG_UNUSED",
            text "        )",
            text "{",
            text "  return true;",
            text "}",
            char '\n' -- final newline, to keep gcc happy
            ]

    -- Write out the link info section into a new assembly file. Previously
    -- this was included as inline assembly in the main.c file but this
    -- is pretty fragile. gas gets upset trying to calculate relative offsets
    -- that span the .note section (notably .text) when debug info is present
    mkNoteObjsToLinkIntoBinary :: Logger -> TmpFs -> DynFlags -> UnitEnv -> [UnitId] -> IO [FilePath]
    mkNoteObjsToLinkIntoBinary logger tmpfs dflags unit_env dep_packages = do
       link_info <- getLinkInfo dflags unit_env dep_packages

       if (platformSupportsSavingLinkOpts (platformOS platform ))
         then fmap (:[]) $ mkExtraObj logger tmpfs dflags unit_state "s" (showSDoc dflags (link_opts link_info))
         else return []

      where
        unit_state = ue_units unit_env
        platform   = ue_platform unit_env
        link_opts info = hcat
            [ -- "link info" section (see Note [LinkInfo section])
              makeElfNote platform ghcLinkInfoSectionName ghcLinkInfoNoteName 0 info

            -- ALL generated assembly must have this section to disable
            -- executable stacks.  See also
            -- "GHC.CmmToAsm" for another instance
            -- where we need to do this.
            , if platformHasGnuNonexecStack platform
                then text ".section .note.GNU-stack,\"\","
                     <> sectionType platform "progbits" <> char '\n'
                else Outputable.empty
            ]

    -- | Return the "link info" string
    --
    -- See Note [LinkInfo section]
    getLinkInfo :: DynFlags -> UnitEnv -> [UnitId] -> IO String
    getLinkInfo dflags unit_env dep_packages = do
        package_link_opts <- getUnitLinkOpts dflags unit_env dep_packages
        pkg_frameworks <- if not (platformUsesFrameworks (ue_platform unit_env))
          then return []
          else do
             ps <- mayThrowUnitErr (preloadUnitsInfo' unit_env dep_packages)
             return (collectFrameworks ps)
        let link_info =
                 ( package_link_opts
                 , pkg_frameworks
                 , rtsOpts dflags
                 , rtsOptsEnabled dflags
                 , gopt Opt_NoHsMain dflags
                 , map showOpt (ldInputs dflags)
                 , getOpts dflags opt_l
                 )
        return (show link_info)

    platformSupportsSavingLinkOpts :: OS -> Bool
    platformSupportsSavingLinkOpts os
     | os == OSSolaris2 = False -- see #5382
     | otherwise        = osElfTarget os

    -- See Note [LinkInfo section]
    ghcLinkInfoSectionName :: String
    ghcLinkInfoSectionName = ".debug-ghc-link-info"
      -- if we use the ".debug" prefix, then strip will strip it by default

    -- Identifier for the note (see Note [LinkInfo section])
    ghcLinkInfoNoteName :: String
    ghcLinkInfoNoteName = "GHC link info"

    -- Returns 'False' if it was, and we can avoid linking, because the
    -- previous binary was linked with "the same options".
    checkLinkInfo :: Logger -> DynFlags -> UnitEnv -> [UnitId] -> FilePath -> IO Bool
    checkLinkInfo logger dflags unit_env pkg_deps exe_file
     | not (platformSupportsSavingLinkOpts (platformOS (ue_platform unit_env)))
     -- ToDo: Windows and OS X do not use the ELF binary format, so
     -- readelf does not work there.  We need to find another way to do
     -- this.
     = return False -- conservatively we should return True, but not
                    -- linking in this case was the behaviour for a long
                    -- time so we leave it as-is.
     | otherwise
     = do
       link_info <- getLinkInfo dflags unit_env pkg_deps
       debugTraceMsg logger dflags 3 $ text ("Link info: " ++ link_info)
       m_exe_link_info <- readElfNoteAsString logger dflags exe_file
                              ghcLinkInfoSectionName ghcLinkInfoNoteName
       let sameLinkInfo = (Just link_info == m_exe_link_info)
       debugTraceMsg logger dflags 3 $ case m_exe_link_info of
         Nothing -> text "Exe link info: Not found"
         Just s
           | sameLinkInfo -> text ("Exe link info is the same")
           | otherwise    -> text ("Exe link info is different: " ++ s)
       return (not sameLinkInfo)

    {- Note [LinkInfo section]
       ~~~~~~~~~~~~~~~~~~~~~~~

    The "link info" is a string representing the parameters of the link. We save
    this information in the binary, and the next time we link, if nothing else has
    changed, we use the link info stored in the existing binary to decide whether
    to re-link or not.

    The "link info" string is stored in a ELF section called ".debug-ghc-link-info"
    (see ghcLinkInfoSectionName) with the SHT_NOTE type.  For some time, it used to
    not follow the specified record-based format (see #11022).

    -}

    haveRtsOptsFlags :: DynFlags -> Bool
    haveRtsOptsFlags dflags =
            isJust (rtsOpts dflags) || case rtsOptsEnabled dflags of
                                           RtsOptsSafeOnly -> False
                                           _ -> True