Move GHC.Platform into the compiler

Previously it was in ghc-boot so that ghc-pkg could use it. However it
wasn't necessary because ghc-pkg only uses a subset of it: reading
target arch and OS from the settings file. This is now done via
GHC.Platform.ArchOS (was called PlatformMini before).

7 files changed, 221 insertions, 479 deletions

diff --git a/libraries/ghc-boot/GHC/Platform.hs b/libraries/ghc-boot/GHC/Platform.hs
deleted file mode 100644
index 9191dda44f..0000000000
--- a/libraries/ghc-boot/GHC/Platform.hs
+++ /dev/null
@@ -1,356 +0,0 @@
-{-# LANGUAGE LambdaCase, ScopedTypeVariables #-}
-
--- | A description of the platform we're compiling for.
---
-module GHC.Platform
-   ( PlatformMini(..)
-   , PlatformWordSize(..)
-   , PlatformConstants(..)
-   , Platform(..)
-   , platformArch
-   , platformOS
-   , Arch(..)
-   , OS(..)
-   , ArmISA(..)
-   , ArmISAExt(..)
-   , ArmABI(..)
-   , PPC_64ABI(..)
-   , ByteOrder(..)
-   , target32Bit
-   , isARM
-   , osElfTarget
-   , osMachOTarget
-   , osSubsectionsViaSymbols
-   , platformUsesFrameworks
-   , platformWordSizeInBytes
-   , platformWordSizeInBits
-   , platformMinInt
-   , platformMaxInt
-   , platformMaxWord
-   , platformInIntRange
-   , platformInWordRange
-   , PlatformMisc(..)
-   , stringEncodeArch
-   , stringEncodeOS
-   , SseVersion (..)
-   , BmiVersion (..)
-   )
-where
-
-import Prelude -- See Note [Why do we import Prelude here?]
-import GHC.Read
-import GHC.ByteOrder (ByteOrder(..))
-import GHC.Platform.Constants
-import Data.Word
-import Data.Int
-
--- | Contains the bare-bones arch and os information. This isn't enough for
--- code gen, but useful for tasks where we can fall back upon the host
--- platform, as this is all we know about the host platform.
-data PlatformMini
-  = PlatformMini
-    { platformMini_arch :: Arch
-    , platformMini_os :: OS
-    }
-    deriving (Read, Show, Eq)
-
--- | Contains enough information for the native code generator to emit
--- code for this platform.
-data Platform = Platform
-   { platformMini                     :: !PlatformMini
-   , platformWordSize                 :: !PlatformWordSize -- ^ Word size
-   , platformByteOrder                :: !ByteOrder        -- ^ Byte order (endianness)
-   , platformUnregisterised           :: !Bool
-   , platformHasGnuNonexecStack       :: !Bool
-   , platformHasIdentDirective        :: !Bool
-   , platformHasSubsectionsViaSymbols :: !Bool
-   , platformIsCrossCompiling         :: !Bool
-   , platformLeadingUnderscore        :: !Bool             -- ^ Symbols need underscore prefix
-   , platformTablesNextToCode         :: !Bool
-      -- ^ Determines whether we will be compiling info tables that reside just
-      --   before the entry code, or with an indirection to the entry code. See
-      --   TABLES_NEXT_TO_CODE in includes/rts/storage/InfoTables.h.
-   , platformConstants                :: !PlatformConstants
-      -- ^ Constants such as structure offsets, type sizes, etc.
-   }
-   deriving (Read, Show, Eq)
-
-data PlatformWordSize
-  = PW4 -- ^ A 32-bit platform
-  | PW8 -- ^ A 64-bit platform
-  deriving (Eq)
-
-instance Show PlatformWordSize where
-  show PW4 = "4"
-  show PW8 = "8"
-
-instance Read PlatformWordSize where
-  readPrec = do
-    i :: Int <- readPrec
-    case i of
-      4 -> return PW4
-      8 -> return PW8
-      other -> fail ("Invalid PlatformWordSize: " ++ show other)
-
-platformWordSizeInBytes :: Platform -> Int
-platformWordSizeInBytes p =
-    case platformWordSize p of
-      PW4 -> 4
-      PW8 -> 8
-
-platformWordSizeInBits :: Platform -> Int
-platformWordSizeInBits p = platformWordSizeInBytes p * 8
-
--- | Legacy accessor
-platformArch :: Platform -> Arch
-platformArch = platformMini_arch . platformMini
-
--- | Legacy accessor
-platformOS :: Platform -> OS
-platformOS = platformMini_os . platformMini
-
--- | Architectures that the native code generator knows about.
---      TODO: It might be nice to extend these constructors with information
---      about what instruction set extensions an architecture might support.
---
-data Arch
-        = ArchUnknown
-        | ArchX86
-        | ArchX86_64
-        | ArchPPC
-        | ArchPPC_64
-          { ppc_64ABI :: PPC_64ABI
-          }
-        | ArchS390X
-        | ArchSPARC
-        | ArchSPARC64
-        | ArchARM
-          { armISA    :: ArmISA
-          , armISAExt :: [ArmISAExt]
-          , armABI    :: ArmABI
-          }
-        | ArchARM64
-        | ArchAlpha
-        | ArchMipseb
-        | ArchMipsel
-        | ArchJavaScript
-        deriving (Read, Show, Eq)
-
--- Note [Platform Syntax]
--- ~~~~~~~~~~~~~~~~~~~~~~
--- There is a very loose encoding of platforms shared by many tools we are
--- encoding to here. GNU Config (http://git.savannah.gnu.org/cgit/config.git),
--- and LLVM's http://llvm.org/doxygen/classllvm_1_1Triple.html are perhaps the
--- most definitional parsers. The basic syntax is a list of '-'-separated
--- components. The Unix 'uname' command syntax is related but briefer.
---
--- Those two parsers are quite forgiving, and even the 'config.sub'
--- normalization is forgiving too. The "best" way to encode a platform is
--- therefore somewhat a matter of taste.
---
--- The 'stringEncode*' functions here convert each part of GHC's structured
--- notion of a platform into one dash-separated component.
-
--- | See Note [Platform Syntax].
-stringEncodeArch :: Arch -> String
-stringEncodeArch = \case
-  ArchUnknown -> "unknown"
-  ArchX86 -> "i386"
-  ArchX86_64 -> "x86_64"
-  ArchPPC -> "powerpc"
-  ArchPPC_64 { ppc_64ABI = abi } -> case abi of
-    ELF_V1 -> "powerpc64"
-    ELF_V2 -> "powerpc64le"
-  ArchS390X -> "s390x"
-  ArchSPARC -> "sparc"
-  ArchSPARC64 -> "sparc64"
-  ArchARM { armISA = isa, armISAExt = _, armABI = _ } -> "arm" ++ vsuf
-    where
-      vsuf = case isa of
-        ARMv5 -> "v5"
-        ARMv6 -> "v6"
-        ARMv7 -> "v7"
-  ArchARM64 -> "aarch64"
-  ArchAlpha -> "alpha"
-  ArchMipseb -> "mipseb"
-  ArchMipsel -> "mipsel"
-  ArchJavaScript -> "js"
-
-isARM :: Arch -> Bool
-isARM (ArchARM {}) = True
-isARM ArchARM64    = True
-isARM _ = False
-
--- | Operating systems that the native code generator knows about.
---      Having OSUnknown should produce a sensible default, but no promises.
-data OS
-        = OSUnknown
-        | OSLinux
-        | OSDarwin
-        | OSSolaris2
-        | OSMinGW32
-        | OSFreeBSD
-        | OSDragonFly
-        | OSOpenBSD
-        | OSNetBSD
-        | OSKFreeBSD
-        | OSHaiku
-        | OSQNXNTO
-        | OSAIX
-        | OSHurd
-        deriving (Read, Show, Eq)
-
--- | See Note [Platform Syntax].
-stringEncodeOS :: OS -> String
-stringEncodeOS = \case
-  OSUnknown -> "unknown"
-  OSLinux -> "linux"
-  OSDarwin -> "darwin"
-  OSSolaris2 -> "solaris2"
-  OSMinGW32 -> "mingw32"
-  OSFreeBSD -> "freebsd"
-  OSDragonFly -> "dragonfly"
-  OSOpenBSD -> "openbsd"
-  OSNetBSD -> "netbsd"
-  OSKFreeBSD -> "kfreebsdgnu"
-  OSHaiku -> "haiku"
-  OSQNXNTO -> "nto-qnx"
-  OSAIX -> "aix"
-  OSHurd -> "hurd"
-
--- | ARM Instruction Set Architecture, Extensions and ABI
---
-data ArmISA
-    = ARMv5
-    | ARMv6
-    | ARMv7
-    deriving (Read, Show, Eq)
-
-data ArmISAExt
-    = VFPv2
-    | VFPv3
-    | VFPv3D16
-    | NEON
-    | IWMMX2
-    deriving (Read, Show, Eq)
-
-data ArmABI
-    = SOFT
-    | SOFTFP
-    | HARD
-    deriving (Read, Show, Eq)
-
--- | PowerPC 64-bit ABI
---
-data PPC_64ABI
-    = ELF_V1
-    | ELF_V2
-    deriving (Read, Show, Eq)
-
--- | This predicate tells us whether the platform is 32-bit.
-target32Bit :: Platform -> Bool
-target32Bit p =
-    case platformWordSize p of
-      PW4 -> True
-      PW8 -> False
-
--- | This predicate tells us whether the OS supports ELF-like shared libraries.
-osElfTarget :: OS -> Bool
-osElfTarget OSLinux     = True
-osElfTarget OSFreeBSD   = True
-osElfTarget OSDragonFly = True
-osElfTarget OSOpenBSD   = True
-osElfTarget OSNetBSD    = True
-osElfTarget OSSolaris2  = True
-osElfTarget OSDarwin    = False
-osElfTarget OSMinGW32   = False
-osElfTarget OSKFreeBSD  = True
-osElfTarget OSHaiku     = True
-osElfTarget OSQNXNTO    = False
-osElfTarget OSAIX       = False
-osElfTarget OSHurd      = True
-osElfTarget OSUnknown   = False
- -- Defaulting to False is safe; it means don't rely on any
- -- ELF-specific functionality.  It is important to have a default for
- -- portability, otherwise we have to answer this question for every
- -- new platform we compile on (even unreg).
-
--- | This predicate tells us whether the OS support Mach-O shared libraries.
-osMachOTarget :: OS -> Bool
-osMachOTarget OSDarwin = True
-osMachOTarget _ = False
-
-osUsesFrameworks :: OS -> Bool
-osUsesFrameworks OSDarwin = True
-osUsesFrameworks _        = False
-
-platformUsesFrameworks :: Platform -> Bool
-platformUsesFrameworks = osUsesFrameworks . platformOS
-
-osSubsectionsViaSymbols :: OS -> Bool
-osSubsectionsViaSymbols OSDarwin = True
-osSubsectionsViaSymbols _        = False
-
--- | Platform-specific settings formerly hard-coded in Config.hs.
---
--- These should probably be all be triaged whether they can be computed from
--- other settings or belong in another another place (like 'Platform' above).
-data PlatformMisc = PlatformMisc
-  { -- TODO Recalculate string from richer info?
-    platformMisc_targetPlatformString :: String
-  , platformMisc_ghcWithInterpreter   :: Bool
-  , platformMisc_ghcWithSMP           :: Bool
-  , platformMisc_ghcRTSWays           :: String
-  , platformMisc_libFFI               :: Bool
-  , platformMisc_ghcThreaded          :: Bool
-  , platformMisc_ghcDebugged          :: Bool
-  , platformMisc_ghcRtsWithLibdw      :: Bool
-  , platformMisc_llvmTarget           :: String
-  }
-
--- | Minimum representable Int value for the given platform
-platformMinInt :: Platform -> Integer
-platformMinInt p = case platformWordSize p of
-   PW4 -> toInteger (minBound :: Int32)
-   PW8 -> toInteger (minBound :: Int64)
-
--- | Maximum representable Int value for the given platform
-platformMaxInt :: Platform -> Integer
-platformMaxInt p = case platformWordSize p of
-   PW4 -> toInteger (maxBound :: Int32)
-   PW8 -> toInteger (maxBound :: Int64)
-
--- | Maximum representable Word value for the given platform
-platformMaxWord :: Platform -> Integer
-platformMaxWord p = case platformWordSize p of
-   PW4 -> toInteger (maxBound :: Word32)
-   PW8 -> toInteger (maxBound :: Word64)
-
--- | Test if the given Integer is representable with a platform Int
-platformInIntRange :: Platform -> Integer -> Bool
-platformInIntRange platform x = x >= platformMinInt platform && x <= platformMaxInt platform
-
--- | Test if the given Integer is representable with a platform Word
-platformInWordRange :: Platform -> Integer -> Bool
-platformInWordRange platform x = x >= 0 && x <= platformMaxWord platform
-
-
---------------------------------------------------
--- Instruction sets
---------------------------------------------------
-
--- | x86 SSE instructions
-data SseVersion
-   = SSE1
-   | SSE2
-   | SSE3
-   | SSE4
-   | SSE42
-   deriving (Eq, Ord)
-
--- | x86 BMI (bit manipulation) instructions
-data BmiVersion
-   = BMI1
-   | BMI2
-   deriving (Eq, Ord)
-
diff --git a/libraries/ghc-boot/GHC/Platform/ArchOS.hs b/libraries/ghc-boot/GHC/Platform/ArchOS.hs
new file mode 100644
index 0000000000..bd3ef5f4cc
--- /dev/null
+++ b/libraries/ghc-boot/GHC/Platform/ArchOS.hs
@@ -0,0 +1,152 @@
+{-# LANGUAGE LambdaCase, ScopedTypeVariables #-}
+
+-- | Platform architecture and OS
+--
+-- We need it in ghc-boot because ghc-pkg needs it.
+module GHC.Platform.ArchOS
+   ( ArchOS(..)
+   , Arch(..)
+   , OS(..)
+   , ArmISA(..)
+   , ArmISAExt(..)
+   , ArmABI(..)
+   , PPC_64ABI(..)
+   , stringEncodeArch
+   , stringEncodeOS
+   )
+where
+
+import Prelude -- See Note [Why do we import Prelude here?]
+
+-- | Platform architecture and OS.
+data ArchOS
+   = ArchOS Arch OS
+   deriving (Read, Show, Eq)
+
+-- | Architectures
+--
+-- TODO: It might be nice to extend these constructors with information about
+-- what instruction set extensions an architecture might support.
+--
+data Arch
+   = ArchUnknown
+   | ArchX86
+   | ArchX86_64
+   | ArchPPC
+   | ArchPPC_64 PPC_64ABI
+   | ArchS390X
+   | ArchSPARC
+   | ArchSPARC64
+   | ArchARM ArmISA [ArmISAExt] ArmABI
+   | ArchARM64
+   | ArchAlpha
+   | ArchMipseb
+   | ArchMipsel
+   | ArchJavaScript
+   deriving (Read, Show, Eq)
+
+-- | ARM Instruction Set Architecture
+data ArmISA
+   = ARMv5
+   | ARMv6
+   | ARMv7
+   deriving (Read, Show, Eq)
+
+-- | ARM extensions
+data ArmISAExt
+   = VFPv2
+   | VFPv3
+   | VFPv3D16
+   | NEON
+   | IWMMX2
+   deriving (Read, Show, Eq)
+
+-- | ARM ABI
+data ArmABI
+   = SOFT
+   | SOFTFP
+   | HARD
+   deriving (Read, Show, Eq)
+
+-- | PowerPC 64-bit ABI
+data PPC_64ABI
+   = ELF_V1
+   | ELF_V2
+   deriving (Read, Show, Eq)
+
+-- | Operating systems.
+--
+-- Using OSUnknown to generate code should produce a sensible default, but no
+-- promises.
+data OS
+   = OSUnknown
+   | OSLinux
+   | OSDarwin
+   | OSSolaris2
+   | OSMinGW32
+   | OSFreeBSD
+   | OSDragonFly
+   | OSOpenBSD
+   | OSNetBSD
+   | OSKFreeBSD
+   | OSHaiku
+   | OSQNXNTO
+   | OSAIX
+   | OSHurd
+   deriving (Read, Show, Eq)
+
+
+-- Note [Platform Syntax]
+-- ~~~~~~~~~~~~~~~~~~~~~~
+--
+-- There is a very loose encoding of platforms shared by many tools we are
+-- encoding to here. GNU Config (http://git.savannah.gnu.org/cgit/config.git),
+-- and LLVM's http://llvm.org/doxygen/classllvm_1_1Triple.html are perhaps the
+-- most definitional parsers. The basic syntax is a list of '-'-separated
+-- components. The Unix 'uname' command syntax is related but briefer.
+--
+-- Those two parsers are quite forgiving, and even the 'config.sub'
+-- normalization is forgiving too. The "best" way to encode a platform is
+-- therefore somewhat a matter of taste.
+--
+-- The 'stringEncode*' functions here convert each part of GHC's structured
+-- notion of a platform into one dash-separated component.
+
+-- | See Note [Platform Syntax].
+stringEncodeArch :: Arch -> String
+stringEncodeArch = \case
+  ArchUnknown       -> "unknown"
+  ArchX86           -> "i386"
+  ArchX86_64        -> "x86_64"
+  ArchPPC           -> "powerpc"
+  ArchPPC_64 ELF_V1 -> "powerpc64"
+  ArchPPC_64 ELF_V2 -> "powerpc64le"
+  ArchS390X         -> "s390x"
+  ArchSPARC         -> "sparc"
+  ArchSPARC64       -> "sparc64"
+  ArchARM ARMv5 _ _ -> "armv5"
+  ArchARM ARMv6 _ _ -> "armv6"
+  ArchARM ARMv7 _ _ -> "armv7"
+  ArchARM64         -> "aarch64"
+  ArchAlpha         -> "alpha"
+  ArchMipseb        -> "mipseb"
+  ArchMipsel        -> "mipsel"
+  ArchJavaScript    -> "js"
+
+-- | See Note [Platform Syntax].
+stringEncodeOS :: OS -> String
+stringEncodeOS = \case
+  OSUnknown   -> "unknown"
+  OSLinux     -> "linux"
+  OSDarwin    -> "darwin"
+  OSSolaris2  -> "solaris2"
+  OSMinGW32   -> "mingw32"
+  OSFreeBSD   -> "freebsd"
+  OSDragonFly -> "dragonfly"
+  OSOpenBSD   -> "openbsd"
+  OSNetBSD    -> "netbsd"
+  OSKFreeBSD  -> "kfreebsdgnu"
+  OSHaiku     -> "haiku"
+  OSQNXNTO    -> "nto-qnx"
+  OSAIX       -> "aix"
+  OSHurd      -> "hurd"
diff --git a/libraries/ghc-boot/GHC/Settings/Platform.hs b/libraries/ghc-boot/GHC/Settings/Platform.hs
deleted file mode 100644
index 95278da76e..0000000000
--- a/libraries/ghc-boot/GHC/Settings/Platform.hs
+++ /dev/null
@@ -1,103 +0,0 @@
--- Note [Settings file]
--- ~~~~~~~~~~~~~~~~~~~~
---
--- GHC has a file, `${top_dir}/settings`, which is the main source of run-time
--- configuration. ghc-pkg needs just a little bit of it: the target platform CPU
--- arch and OS. It uses that to figure out what subdirectory of `~/.ghc` is
--- associated with the current version/target.
---
--- This module has just enough code to read key value pairs from the settings
--- file, and read the target platform from those pairs.
---
--- The  "0" suffix is because the caller will partially apply it, and that will
--- in turn be used a few more times.
-module GHC.Settings.Platform where
-
-import Prelude -- See Note [Why do we import Prelude here?]
-
-import GHC.BaseDir
-import GHC.Platform
-import GHC.Settings.Utils
-
-import Data.Map (Map)
-import qualified Data.Map as Map
-
------------------------------------------------------------------------------
--- parts of settings file
-
-getTargetPlatform
-  :: FilePath     -- ^ Settings filepath (for error messages)
-  -> RawSettings  -- ^ Raw settings file contents
-  -> PlatformConstants -- ^ Platform constants
-  -> Either String Platform
-getTargetPlatform settingsFile mySettings constants = do
-  let
-    getBooleanSetting = getBooleanSetting0 settingsFile mySettings
-    readSetting :: (Show a, Read a) => String -> Either String a
-    readSetting = readSetting0 settingsFile mySettings
-
-  targetArch <- readSetting "target arch"
-  targetOS <- readSetting "target os"
-  targetWordSize <- readSetting "target word size"
-  targetWordBigEndian <- getBooleanSetting "target word big endian"
-  targetLeadingUnderscore <- getBooleanSetting "Leading underscore"
-  targetUnregisterised <- getBooleanSetting "Unregisterised"
-  targetHasGnuNonexecStack <- getBooleanSetting "target has GNU nonexec stack"
-  targetHasIdentDirective <- getBooleanSetting "target has .ident directive"
-  targetHasSubsectionsViaSymbols <- getBooleanSetting "target has subsections via symbols"
-  crossCompiling <- getBooleanSetting "cross compiling"
-  tablesNextToCode <- getBooleanSetting "Tables next to code"
-
-  pure $ Platform
-    { platformMini = PlatformMini
-      { platformMini_arch = targetArch
-      , platformMini_os = targetOS
-      }
-    , platformWordSize = targetWordSize
-    , platformByteOrder = if targetWordBigEndian then BigEndian else LittleEndian
-    , platformUnregisterised = targetUnregisterised
-    , platformHasGnuNonexecStack = targetHasGnuNonexecStack
-    , platformHasIdentDirective = targetHasIdentDirective
-    , platformHasSubsectionsViaSymbols = targetHasSubsectionsViaSymbols
-    , platformIsCrossCompiling = crossCompiling
-    , platformLeadingUnderscore = targetLeadingUnderscore
-    , platformTablesNextToCode  = tablesNextToCode
-    , platformConstants = constants
-    }
-
------------------------------------------------------------------------------
--- settings file helpers
-
-type RawSettings = Map String String
-
--- | See Note [Settings file] for "0" suffix
-getSetting0
-  :: FilePath -> RawSettings -> String -> Either String String
-getSetting0 settingsFile mySettings key = case Map.lookup key mySettings of
-  Just xs -> Right xs
-  Nothing -> Left $ "No entry for " ++ show key ++ " in " ++ show settingsFile
-
--- | See Note [Settings file] for "0" suffix
-getFilePathSetting0
-  :: FilePath -> FilePath -> RawSettings -> String -> Either String String
-getFilePathSetting0 top_dir settingsFile mySettings key =
-  expandTopDir top_dir <$> getSetting0 settingsFile mySettings key
-
--- | See Note [Settings file] for "0" suffix
-getBooleanSetting0
-  :: FilePath -> RawSettings -> String -> Either String Bool
-getBooleanSetting0 settingsFile mySettings key = do
-  rawValue <- getSetting0 settingsFile mySettings key
-  case rawValue of
-    "YES" -> Right True
-    "NO" -> Right False
-    xs -> Left $ "Bad value for " ++ show key ++ ": " ++ show xs
-
--- | See Note [Settings file] for "0" suffix
-readSetting0
-  :: (Show a, Read a) => FilePath -> RawSettings -> String -> Either String a
-readSetting0 settingsFile mySettings key = case Map.lookup key mySettings of
-  Just xs -> case maybeRead xs of
-    Just v -> Right v
-    Nothing -> Left $ "Failed to read " ++ show key ++ " value " ++ show xs
-  Nothing -> Left $ "No entry for " ++ show key ++ " in " ++ show settingsFile
diff --git a/libraries/ghc-boot/GHC/Settings/Utils.hs b/libraries/ghc-boot/GHC/Settings/Utils.hs
index 1f1cd67030..4ccbbf23b6 100644
--- a/libraries/ghc-boot/GHC/Settings/Utils.hs
+++ b/libraries/ghc-boot/GHC/Settings/Utils.hs
@@ -3,6 +3,11 @@ module GHC.Settings.Utils where
 import Prelude -- See Note [Why do we import Prelude here?]
 
 import Data.Char (isSpace)
+import Data.Map (Map)
+import qualified Data.Map as Map
+
+import GHC.BaseDir
+import GHC.Platform.ArchOS
 
 maybeRead :: Read a => String -> Maybe a
 maybeRead str = case reads str of
@@ -13,3 +18,55 @@ maybeReadFuzzy :: Read a => String -> Maybe a
 maybeReadFuzzy str = case reads str of
   [(x, s)] | all isSpace s -> Just x
   _ -> Nothing
+
+
+-- Note [Settings file]
+-- ~~~~~~~~~~~~~~~~~~~~
+--
+-- GHC has a file, `${top_dir}/settings`, which is the main source of run-time
+-- configuration. ghc-pkg needs just a little bit of it: the target platform CPU
+-- arch and OS. It uses that to figure out what subdirectory of `~/.ghc` is
+-- associated with the current version/target platform.
+--
+-- This module has just enough code to read key value pairs from the settings
+-- file, and read the target platform from those pairs.
+
+type RawSettings = Map String String
+
+-- | Read target Arch/OS from the settings
+getTargetArchOS
+  :: FilePath     -- ^ Settings filepath (for error messages)
+  -> RawSettings  -- ^ Raw settings file contents
+  -> Either String ArchOS
+getTargetArchOS settingsFile settings =
+  ArchOS <$> readRawSetting settingsFile settings "target arch"
+         <*> readRawSetting settingsFile settings "target os"
+
+
+getRawSetting
+  :: FilePath -> RawSettings -> String -> Either String String
+getRawSetting settingsFile settings key = case Map.lookup key settings of
+  Just xs -> Right xs
+  Nothing -> Left $ "No entry for " ++ show key ++ " in " ++ show settingsFile
+
+getRawFilePathSetting
+  :: FilePath -> FilePath -> RawSettings -> String -> Either String String
+getRawFilePathSetting top_dir settingsFile settings key =
+  expandTopDir top_dir <$> getRawSetting settingsFile settings key
+
+getRawBooleanSetting
+  :: FilePath -> RawSettings -> String -> Either String Bool
+getRawBooleanSetting settingsFile settings key = do
+  rawValue <- getRawSetting settingsFile settings key
+  case rawValue of
+    "YES" -> Right True
+    "NO" -> Right False
+    xs -> Left $ "Bad value for " ++ show key ++ ": " ++ show xs
+
+readRawSetting
+  :: (Show a, Read a) => FilePath -> RawSettings -> String -> Either String a
+readRawSetting settingsFile settings key = case Map.lookup key settings of
+  Just xs -> case maybeRead xs of
+    Just v -> Right v
+    Nothing -> Left $ "Failed to read " ++ show key ++ " value " ++ show xs
+  Nothing -> Left $ "No entry for " ++ show key ++ " in " ++ show settingsFile
diff --git a/libraries/ghc-boot/GHC/UniqueSubdir.hs b/libraries/ghc-boot/GHC/UniqueSubdir.hs
index b59fdc43ce..5ffaafefd8 100644
--- a/libraries/ghc-boot/GHC/UniqueSubdir.hs
+++ b/libraries/ghc-boot/GHC/UniqueSubdir.hs
@@ -6,19 +6,15 @@ import Prelude -- See Note [Why do we import Prelude here?]
 
 import Data.List (intercalate)
 
-import GHC.Platform
+import GHC.Platform.ArchOS
 import GHC.Version (cProjectVersion)
 
 -- | A filepath like @x86_64-linux-7.6.3@ with the platform string to use when
 -- constructing platform-version-dependent files that need to co-exist.
---
--- 'ghc-pkg' falls back on the host platform if the settings file is missing,
--- and so needs this since we don't have information about the host platform in
--- as much detail as 'Platform', so we use 'PlatformMini' instead.
-uniqueSubdir :: PlatformMini -> FilePath
-uniqueSubdir archOs = intercalate "-"
-  [ stringEncodeArch $ platformMini_arch archOs
-  , stringEncodeOS $ platformMini_os archOs
+uniqueSubdir :: ArchOS -> FilePath
+uniqueSubdir (ArchOS arch os) = intercalate "-"
+  [ stringEncodeArch arch
+  , stringEncodeOS os
   , cProjectVersion
   ]
   -- NB: This functionality is reimplemented in Cabal, so if you
diff --git a/libraries/ghc-boot/ghc-boot.cabal.in b/libraries/ghc-boot/ghc-boot.cabal.in
index aed65d8f0a..e320a5725f 100644
--- a/libraries/ghc-boot/ghc-boot.cabal.in
+++ b/libraries/ghc-boot/ghc-boot.cabal.in
@@ -43,10 +43,9 @@ Library
             GHC.Serialized
             GHC.ForeignSrcLang
             GHC.HandleEncoding
-            GHC.Platform
+            GHC.Platform.ArchOS
             GHC.Platform.Host
             GHC.Platform.Constants
-            GHC.Settings.Platform
             GHC.Settings.Utils
             GHC.UniqueSubdir
             GHC.Version
diff --git a/libraries/ghc-boot/ghc.mk b/libraries/ghc-boot/ghc.mk
index 9c5d695d8c..d183ccc501 100644
--- a/libraries/ghc-boot/ghc.mk
+++ b/libraries/ghc-boot/ghc.mk
@@ -42,17 +42,14 @@ libraries/ghc-boot/dist-install/build/GHC/Platform/Host.hs: mk/project.mk | $$(d
 	@echo                                                               >> $@
 	@echo 'import GHC.Platform'                                         >> $@
 	@echo                                                               >> $@
-	@echo 'cHostPlatformArch   :: Arch'                                 >> $@
-	@echo 'cHostPlatformArch   = $(HaskellHostArch)'                    >> $@
+	@echo 'hostPlatformArch   :: Arch'                                  >> $@
+	@echo 'hostPlatformArch   = $(HaskellHostArch)'                     >> $@
 	@echo                                                               >> $@
-	@echo 'cHostPlatformOS     :: OS'                                   >> $@
-	@echo 'cHostPlatformOS     = $(HaskellHostOs)'                      >> $@
+	@echo 'hostPlatformOS     :: OS'                                    >> $@
+	@echo 'hostPlatformOS     = $(HaskellHostOs)'                       >> $@
 	@echo                                                               >> $@
-	@echo 'cHostPlatformMini :: PlatformMini'                           >> $@
-	@echo 'cHostPlatformMini = PlatformMini'                            >> $@
-	@echo '  { platformMini_arch = cHostPlatformArch'                   >> $@
-	@echo '  , platformMini_os = cHostPlatformOS'                       >> $@
-	@echo '  }'                                                         >> $@
+	@echo 'hostPlatformArchOS :: ArchOS'                                >> $@
+	@echo 'hostPlatformArchOS = ArchOS hostPlatformArch hostPlatformOS' >> $@
 	@echo done.
 
 libraries/ghc-boot/dist-boot/package-data.mk: \