GHC/SysTools.hs

    {-# LANGUAGE CPP                 #-}
    {-# LANGUAGE ScopedTypeVariables #-}

    {-
    -----------------------------------------------------------------------------
    --
    -- (c) The University of Glasgow 2001-2003
    --
    -- Access to system tools: gcc, cp, rm etc
    --
    -----------------------------------------------------------------------------
    -}

    module GHC.SysTools (
            -- * Initialisation
            initSysTools,
            lazyInitLlvmConfig,

            -- * Interface to system tools
            module GHC.SysTools.Tasks,
            module GHC.SysTools.Info,

            copy,
            copyWithHeader,

            -- * General utilities
            Option(..),
            expandTopDir,
     ) where

    #include "HsVersions.h"

    import GHC.Prelude

    import GHC.Settings.Utils

    import GHC.Utils.Error
    import GHC.Utils.Panic
    import GHC.Utils.Logger
    import GHC.Driver.Session

    import Control.Monad.Trans.Except (runExceptT)
    import System.FilePath
    import System.IO
    import System.IO.Unsafe (unsafeInterleaveIO)
    import GHC.Linker.ExtraObj
    import GHC.SysTools.Info
    import GHC.SysTools.Tasks
    import GHC.SysTools.BaseDir
    import GHC.Settings.IO

    {-
    Note [How GHC finds toolchain utilities]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    GHC.SysTools.initSysProgs figures out exactly where all the auxiliary programs
    are, and initialises mutable variables to make it easy to call them.
    To do this, it makes use of definitions in Config.hs, which is a Haskell
    file containing variables whose value is figured out by the build system.

    Config.hs contains two sorts of things

      cGCC,         The *names* of the programs
      cCPP            e.g.  cGCC = gcc
      cUNLIT                cCPP = gcc -E
      etc           They do *not* include paths

      cUNLIT_DIR   The *path* to the directory containing unlit, split etc
      cSPLIT_DIR   *relative* to the root of the build tree,
                       for use when running *in-place* in a build tree (only)

    ---------------------------------------------
    NOTES for an ALTERNATIVE scheme (i.e *not* what is currently implemented):

    Another hair-brained scheme for simplifying the current tool location
    nightmare in GHC: Simon originally suggested using another
    configuration file along the lines of GCC's specs file - which is fine
    except that it means adding code to read yet another configuration
    file.  What I didn't notice is that the current package.conf is
    general enough to do this:

    Package
        {name = "tools",    import_dirs = [],  source_dirs = [],
         library_dirs = [], hs_libraries = [], extra_libraries = [],
         include_dirs = [], c_includes = [],   package_deps = [],
         extra_ghc_opts = ["-pgmc/usr/bin/gcc","-pgml${topdir}/bin/unlit", ... etc.],
         extra_cc_opts = [], extra_ld_opts = []}

    Which would have the advantage that we get to collect together in one
    place the path-specific package stuff with the path-specific tool
    stuff.
                    End of NOTES
    ---------------------------------------------

    ************************************************************************
    *                                                                      *
    \subsection{Initialisation}
    *                                                                      *
    ************************************************************************
    -}

    -- Note [LLVM configuration]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- The `llvm-targets` and `llvm-passes` files are shipped with GHC and contain
    -- information needed by the LLVM backend to invoke `llc` and `opt`.
    -- Specifically:
    --
    --  * llvm-targets maps autoconf host triples to the corresponding LLVM
    --    `data-layout` declarations. This information is extracted from clang using
    --    the script in utils/llvm-targets/gen-data-layout.sh and should be updated
    --    whenever we target a new version of LLVM.
    --
    --  * llvm-passes maps GHC optimization levels to sets of LLVM optimization
    --    flags that GHC should pass to `opt`.
    --
    -- This information is contained in files rather the GHC source to allow users
    -- to add new targets to GHC without having to recompile the compiler.
    --
    -- Since this information is only needed by the LLVM backend we load it lazily
    -- with unsafeInterleaveIO. Consequently it is important that we lazily pattern
    -- match on LlvmConfig until we actually need its contents.

    lazyInitLlvmConfig :: String
                   -> IO LlvmConfig
    lazyInitLlvmConfig top_dir
      = unsafeInterleaveIO $ do    -- see Note [LLVM configuration]
          targets <- readAndParse "llvm-targets"
          passes <- readAndParse "llvm-passes"
          return $ LlvmConfig { llvmTargets = fmap mkLlvmTarget <$> targets,
                                llvmPasses = passes }
      where
        readAndParse :: Read a => String -> IO a
        readAndParse name =
          do let llvmConfigFile = top_dir </> name
             llvmConfigStr <- readFile llvmConfigFile
             case maybeReadFuzzy llvmConfigStr of
               Just s -> return s
               Nothing -> pgmError ("Can't parse " ++ show llvmConfigFile)

        mkLlvmTarget :: (String, String, String) -> LlvmTarget
        mkLlvmTarget (dl, cpu, attrs) = LlvmTarget dl cpu (words attrs)

    initSysTools :: String          -- TopDir path
                 -> IO Settings     -- Set all the mutable variables above, holding
                                    --      (a) the system programs
                                    --      (b) the package-config file
                                    --      (c) the GHC usage message
    initSysTools top_dir = do
      res <- runExceptT $ initSettings top_dir
      case res of
        Right a -> pure a
        Left (SettingsError_MissingData msg) -> pgmError msg
        Left (SettingsError_BadData msg) -> pgmError msg

    {- Note [Windows stack usage]

    See: #8870 (and #8834 for related info) and #12186

    On Windows, occasionally we need to grow the stack. In order to do
    this, we would normally just bump the stack pointer - but there's a
    catch on Windows.

    If the stack pointer is bumped by more than a single page, then the
    pages between the initial pointer and the resulting location must be
    properly committed by the Windows virtual memory subsystem. This is
    only needed in the event we bump by more than one page (i.e 4097 bytes
    or more).

    Windows compilers solve this by emitting a call to a special function
    called _chkstk, which does this committing of the pages for you.

    The reason this was causing a segfault was because due to the fact the
    new code generator tends to generate larger functions, we needed more
    stack space in GHC itself. In the x86 codegen, we needed approximately
    ~12kb of stack space in one go, which caused the process to segfault,
    as the intervening pages were not committed.

    GCC can emit such a check for us automatically but only when the flag
    -fstack-check is used.

    See https://gcc.gnu.org/onlinedocs/gnat_ugn/Stack-Overflow-Checking.html
    for more information.

    -}

    copy :: Logger -> DynFlags -> String -> FilePath -> FilePath -> IO ()
    copy logger dflags purpose from to = copyWithHeader logger dflags purpose Nothing from to

    copyWithHeader :: Logger -> DynFlags -> String -> Maybe String -> FilePath -> FilePath
                   -> IO ()
    copyWithHeader logger dflags purpose maybe_header from to = do
      showPass logger dflags purpose

      hout <- openBinaryFile to   WriteMode
      hin  <- openBinaryFile from ReadMode
      ls <- hGetContents hin -- inefficient, but it'll do for now. ToDo: speed up
      maybe (return ()) (header hout) maybe_header
      hPutStr hout ls
      hClose hout
      hClose hin
     where
      -- write the header string in UTF-8.  The header is something like
      --   {-# LINE "foo.hs" #-}
      -- and we want to make sure a Unicode filename isn't mangled.
      header h str = do
       hSetEncoding h utf8
       hPutStr h str
       hSetBinaryMode h True