Use linker capability detection to improve linker use (backport #9443)

Cabal/src/Distribution/Simple/Configure.hs

@@ -73,10 +73,16 @@ import Distribution.PackageDescription.Configuration
 import Distribution.PackageDescription.Check hiding (doesFileExist)
 import Distribution.Simple.BuildToolDepends
 import Distribution.Simple.Program
+<<<<<<< HEAD
 import Distribution.Simple.Setup as Setup
 import Distribution.Simple.BuildTarget
 import Distribution.Simple.LocalBuildInfo
 import Distribution.Simple.Program.Db (appendProgramSearchPath)
+=======
+import Distribution.Simple.Program.Db (lookupProgramByName)
+import Distribution.Simple.Setup.Common as Setup
+import Distribution.Simple.Setup.Config as Setup
+>>>>>>> 53fc3d36f (Use linker capability detection to improve linker use)
 import Distribution.Simple.Utils
 import Distribution.System
 import Distribution.Types.PackageVersionConstraint
@@ -619,6 +625,7 @@ configure (pkg_descr0, pbi) cfg = do
                                       "--enable-split-sections; ignoring")
                                 return False
 
+<<<<<<< HEAD
     -- Decide if we're going to compile with split objects.
     split_objs :: Bool <-
        if not (fromFlag $ configSplitObjs cfg)
@@ -679,6 +686,44 @@ configure (pkg_descr0, pbi) cfg = do
               ++ " GHC 9.4 and later; ignoring..."
           return False
         v -> return v
+=======
+  -- Basically yes/no/unknown.
+  let linkerSupportsRelocations :: Maybe Bool
+      linkerSupportsRelocations =
+        case lookupProgramByName "ld" programDb'' of
+          Nothing -> Nothing
+          Just ld ->
+            case Map.lookup "Supports relocatable output" $ programProperties ld of
+              Just "YES" -> Just True
+              Just "NO" -> Just False
+              _other -> Nothing
+  let ghciLibByDefault =
+        case compilerId comp of
+          CompilerId GHC _ ->
+            -- If ghc is non-dynamic, then ghci needs object files,
+            -- so we build one by default.
+            --
+            -- Technically, archive files should be sufficient for ghci,
+            -- but because of GHC bug #8942, it has never been safe to
+            -- rely on them. By the time that bug was fixed, ghci had
+            -- been changed to read shared libraries instead of archive
+            -- files (see next code block).
+            not (GHC.isDynamic comp)
+          CompilerId GHCJS _ ->
+            not (GHCJS.isDynamic comp)
+          _ -> False
+
+  withGHCiLib_ <-
+    case fromFlagOrDefault ghciLibByDefault (configGHCiLib cfg) of
+      -- NOTE: If linkerSupportsRelocations is Nothing this may still fail if the
+      -- linker does not support -r.
+      True | not (fromMaybe True linkerSupportsRelocations) -> do
+        warn verbosity $
+          "--enable-library-for-ghci is not supported with the current"
+            ++ "  linker; ignoring..."
+        return False
+      v -> return v
+>>>>>>> 53fc3d36f (Use linker capability detection to improve linker use)
 
     let sharedLibsByDefault
           | fromFlag (configDynExe cfg) =

Cabal/src/Distribution/Simple/GHC/Internal.hs

@@ -95,6 +95,7 @@ configureToolchain :: GhcImplInfo
                    -> ProgramDb
                    -> ProgramDb
 configureToolchain _implInfo ghcProg ghcInfo =
+<<<<<<< HEAD
     addKnownProgram gccProgram {
       programFindLocation = findProg gccProgramName extraGccPath,
       programPostConf     = configureGcc
@@ -109,6 +110,28 @@ configureToolchain _implInfo ghcProg ghcInfo =
   . addKnownProgram stripProgram {
       programFindLocation = findProg stripProgramName extraStripPath
     }
+=======
+  addKnownProgram
+    gccProgram
+      { programFindLocation = findProg gccProgramName extraGccPath
+      , programPostConf = configureGcc
+      }
+    . addKnownProgram
+      ldProgram
+        { programFindLocation = findProg ldProgramName extraLdPath
+        , programPostConf = \v cp ->
+            -- Call any existing configuration first and then add any new configuration
+            configureLd v =<< programPostConf ldProgram v cp
+        }
+    . addKnownProgram
+      arProgram
+        { programFindLocation = findProg arProgramName extraArPath
+        }
+    . addKnownProgram
+      stripProgram
+        { programFindLocation = findProg stripProgramName extraStripPath
+        }
+>>>>>>> 4336f4c48 (Chain configuration of ldProgram)
   where
     compilerDir = takeDirectory (programPath ghcProg)
     base_dir     = takeDirectory compilerDir

Cabal/src/Distribution/Simple/Program/Builtin.hs

@@ -322,7 +322,49 @@ greencardProgram :: Program
 greencardProgram = simpleProgram "greencard"
 
 ldProgram :: Program
+<<<<<<< HEAD
 ldProgram = simpleProgram "ld"
+=======
+ldProgram =
+  (simpleProgram "ld")
+    { programPostConf = \verbosity ldProg -> do
+        -- The `lld` linker cannot create merge (relocatable) objects so we
+        -- want to detect this.
+        -- If the linker does support relocatable objects, we want to use that
+        -- to create partially pre-linked objects for GHCi, so we get much
+        -- faster loading as we do not have to do the separate loading and
+        -- in-memory linking the static linker in GHC does, but can offload
+        -- parts of this process to a pre-linking step.
+        -- However this requires the linker to support this features. Not all
+        -- linkers do, and notably as of this writing `lld` which is a popular
+        -- choice for windows linking does not support this feature. However
+        -- if using binutils ld or another linker that supports --relocatable,
+        -- we should still be good to generate pre-linked objects.
+        ldHelpOutput <-
+          getProgramInvocationOutput
+            verbosity
+            (programInvocation ldProg ["--help"])
+            -- In case the linker does not support '--help'. Eg the LLVM linker,
+            -- `lld` only accepts `-help`.
+            `catchIO` (\_ -> return "")
+        let k = "Supports relocatable output"
+            -- Standard GNU `ld` uses `--relocatable` while `ld.gold` uses
+            -- `-relocatable` (single `-`).
+            v
+              | "-relocatable" `isInfixOf` ldHelpOutput = "YES"
+              -- ld64 on macOS has this lovely response for "--help"
+              --
+              --   ld64: For information on command line options please use 'man ld'.
+              --
+              -- it does however support -r, if you read the manpage
+              -- (e.g. https://www.manpagez.com/man/1/ld64/)
+              | "ld64:" `isPrefixOf` ldHelpOutput = "YES"
+              | otherwise = "NO"
+
+            m = Map.insert k v (programProperties ldProg)
+        return $ ldProg{programProperties = m}
+    }
+>>>>>>> fb14e4e29 (Fix configuation of ldProgram)
 
 tarProgram :: Program
 tarProgram = (simpleProgram "tar") {

Cabal/src/Distribution/Simple/Program/Db.hs

@@ -32,6 +32,7 @@ module Distribution.Simple.Program.Db (
     restoreProgramDb,
 
     -- ** Query and manipulate the program db
+<<<<<<< HEAD
     addKnownProgram,
     addKnownPrograms,
     appendProgramSearchPath,
@@ -49,6 +50,25 @@ module Distribution.Simple.Program.Db (
     lookupProgram,
     updateProgram,
     configuredPrograms,
+=======
+  , addKnownProgram
+  , addKnownPrograms
+  , lookupKnownProgram
+  , knownPrograms
+  , getProgramSearchPath
+  , setProgramSearchPath
+  , modifyProgramSearchPath
+  , userSpecifyPath
+  , userSpecifyPaths
+  , userMaybeSpecifyPath
+  , userSpecifyArgs
+  , userSpecifyArgss
+  , userSpecifiedArgs
+  , lookupProgram
+  , lookupProgramByName
+  , updateProgram
+  , configuredPrograms
+>>>>>>> 53fc3d36f (Use linker capability detection to improve linker use)
 
     -- ** Query and manipulate the program db
     configureProgram,
@@ -309,7 +329,11 @@ userSpecifiedArgs prog =
 
 -- | Try to find a configured program
 lookupProgram :: Program -> ProgramDb -> Maybe ConfiguredProgram
-lookupProgram prog = Map.lookup (programName prog) . configuredProgs
+lookupProgram = lookupProgramByName . programName
+
+-- | Try to find a configured program
+lookupProgramByName :: String -> ProgramDb -> Maybe ConfiguredProgram
+lookupProgramByName name = Map.lookup name . configuredProgs
 
 
 -- | Update a configured program in the database.

changelog.d/pr-9443

@@ -0,0 +1,11 @@
+synopsis: Use linker capability detection to improve linker use
+packages: Cabal
+prs: #9443
+
+description: {
+
+- Previously the GHC version number and platform were used as a proxy for whether
+  the linker can generate relocatable objects.
+- Now, the ability of the linker to create relocatable objects is detected.
+
+}