Build a threaded stage 1 if the bootstrapping GHC supports it.

4 files changed, 66 insertions, 20 deletions

diff --git a/hadrian/cfg/system.config.in b/hadrian/cfg/system.config.in
index 016b5bc7bb..810b290d1b 100644
--- a/hadrian/cfg/system.config.in
+++ b/hadrian/cfg/system.config.in
@@ -79,6 +79,8 @@ ghc-major-version     = @GhcMajVersion@
 ghc-minor-version     = @GhcMinVersion@
 ghc-patch-level       = @GhcPatchLevel@
 
+bootstrap-threaded-rts      = @GhcThreadedRts@
+
 supports-this-unit-id = @SUPPORTS_THIS_UNIT_ID@
 
 project-name          = @ProjectName@
diff --git a/hadrian/src/Expression.hs b/hadrian/src/Expression.hs
index 197827a5f0..d0b166fdaa 100644
--- a/hadrian/src/Expression.hs
+++ b/hadrian/src/Expression.hs
@@ -6,8 +6,9 @@ module Expression (
     expr, exprIO, arg, remove,
 
     -- ** Predicates
-    (?), stage, stage0, stage1, stage2, notStage0, package, notPackage,
-     packageOneOf, libraryPackage, builder, way, input, inputs, output, outputs,
+    (?), stage, stage0, stage1, stage2, notStage0, threadedBootstrapper,
+     package, notPackage, packageOneOf, libraryPackage, builder, way, input,
+     inputs, output, outputs,
 
     -- ** Evaluation
     interpret, interpretInContext,
@@ -26,6 +27,7 @@ import Base
 import Builder
 import Context hiding (stage, package, way)
 import Expression.Type
+import Oracles.Flag
 import Hadrian.Expression hiding (Expr, Predicate, Args)
 import Hadrian.Haskell.Cabal.Type
 import Hadrian.Oracles.Cabal
@@ -86,6 +88,19 @@ instance BuilderPredicate a => BuilderPredicate (FilePath -> a) where
 way :: Way -> Predicate
 way w = (w ==) <$> getWay
 
+{-
+Note [Stage Names]
+~~~~~~~~~~~~~~~~~~
+
+Code referring to specific stages can be a bit tricky. In Hadrian, the stages
+have the same names they carried in the autoconf build system, but they are
+often referred to by the stage used to construct them. For example, the stage 1
+artifacts will be placed in _build/stage0, because they are constructed by the
+stage 0 compiler. The stage predicates in this module behave the same way,
+'stage0' will return 'True' while stage 0 is being used to build the stage 1
+compiler.
+-}
+
 -- | Is the build currently in stage 0?
 stage0 :: Predicate
 stage0 = stage Stage0
@@ -102,6 +117,13 @@ stage2 = stage Stage2
 notStage0 :: Predicate
 notStage0 = notM stage0
 
+-- | Whether or not the bootstrapping compiler provides a threaded RTS. We need
+--   to know this when building stage 1, since stage 1 links against the
+--   compiler's RTS ways. See Note [Linking ghc-bin against threaded stage0 RTS]
+--   in Settings.Packages for details.
+threadedBootstrapper :: Predicate
+threadedBootstrapper = expr (flag BootstrapThreadedRts)
+
 -- | Is a certain package /not/ built right now?
 notPackage :: Package -> Predicate
 notPackage = notM . package
diff --git a/hadrian/src/Oracles/Flag.hs b/hadrian/src/Oracles/Flag.hs
index 34713faae1..2de81cfdd6 100644
--- a/hadrian/src/Oracles/Flag.hs
+++ b/hadrian/src/Oracles/Flag.hs
@@ -24,25 +24,27 @@ data Flag = ArSupportsAtFile
           | WithLibnuma
           | HaveLibMingwEx
           | UseSystemFfi
+          | BootstrapThreadedRts
 
 -- Note, if a flag is set to empty string we treat it as set to NO. This seems
 -- fragile, but some flags do behave like this.
 flag :: Flag -> Action Bool
 flag f = do
     let key = case f of
-            ArSupportsAtFile   -> "ar-supports-at-file"
-            CrossCompiling     -> "cross-compiling"
-            CcLlvmBackend      -> "cc-llvm-backend"
-            GhcUnregisterised  -> "ghc-unregisterised"
-            TablesNextToCode   -> "tables-next-to-code"
-            GmpInTree          -> "intree-gmp"
-            GmpFrameworkPref   -> "gmp-framework-preferred"
-            LeadingUnderscore  -> "leading-underscore"
-            SolarisBrokenShld  -> "solaris-broken-shld"
-            WithLibdw          -> "with-libdw"
-            WithLibnuma        -> "with-libnuma"
-            HaveLibMingwEx     -> "have-lib-mingw-ex"
-            UseSystemFfi       -> "use-system-ffi"
+            ArSupportsAtFile     -> "ar-supports-at-file"
+            CrossCompiling       -> "cross-compiling"
+            CcLlvmBackend        -> "cc-llvm-backend"
+            GhcUnregisterised    -> "ghc-unregisterised"
+            TablesNextToCode     -> "tables-next-to-code"
+            GmpInTree            -> "intree-gmp"
+            GmpFrameworkPref     -> "gmp-framework-preferred"
+            LeadingUnderscore    -> "leading-underscore"
+            SolarisBrokenShld    -> "solaris-broken-shld"
+            WithLibdw            -> "with-libdw"
+            WithLibnuma          -> "with-libnuma"
+            HaveLibMingwEx       -> "have-lib-mingw-ex"
+            UseSystemFfi         -> "use-system-ffi"
+            BootstrapThreadedRts -> "bootstrap-threaded-rts"
     value <- lookupValueOrError configFile key
     when (value `notElem` ["YES", "NO", ""]) . error $ "Configuration flag "
         ++ quote (key ++ " = " ++ value) ++ " cannot be parsed."
diff --git a/hadrian/src/Settings/Packages.hs b/hadrian/src/Settings/Packages.hs
index eb911ef6f2..210f1c829c 100644
--- a/hadrian/src/Settings/Packages.hs
+++ b/hadrian/src/Settings/Packages.hs
@@ -64,8 +64,13 @@ packageArgs = do
             , flag GhcUnregisterised ? arg "--ghc-option=-DNO_REGS"
             , notM targetSupportsSMP ? arg "--ghc-option=-DNOSMP"
             , notM targetSupportsSMP ? arg "--ghc-option=-optc-DNOSMP"
+            -- When building stage 1 or later, use thread-safe RTS functions if
+            -- the configuration calls for a threaded GHC.
             , (any (wayUnit Threaded) rtsWays) ?
               notStage0 ? arg "--ghc-option=-optc-DTHREADED_RTS"
+            -- When building stage 1, use thread-safe RTS functions if the
+            -- bootstrapping (stage 0) compiler provides a threaded RTS way.
+            , stage0 ? threadedBootstrapper ? arg "--ghc-option=-optc-DTHREADED_RTS"
             , ghcWithInterpreter ?
               ghciWithDebugger <$> flavour ?
               notStage0 ? arg "--ghc-option=-DDEBUGGER"
@@ -90,11 +95,26 @@ packageArgs = do
           , builder (Cabal Flags) ? mconcat
             [ ghcWithInterpreter ? notStage0 ? arg "ghci"
             , cross ? arg "-terminfo"
-            -- the 'threaded' flag is True by default, but
-            -- let's record explicitly that we link all ghc
-            -- executables with the threaded runtime.
-            , stage0 ? arg "-threaded"
-            , notStage0 ? ifM (ghcThreaded <$> expr flavour) (arg "threaded") (arg "-threaded") ]
+            -- Note [Linking ghc-bin against threaded stage0 RTS]
+            -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+            -- We must maintain the invariant that GHCs linked with '-threaded'
+            -- are built with '-optc=-DTHREADED_RTS', otherwise we'll end up
+            -- with a GHC that can use the threaded runtime, but contains some
+            -- non-thread-safe functions. See
+            -- https://gitlab.haskell.org/ghc/ghc/issues/18024 for an example of
+            -- the sort of issues this can cause.
+            , ifM stage0
+                  -- We build a threaded stage 1 if the bootstrapping compiler
+                  -- supports it.
+                  (ifM threadedBootstrapper
+                       (arg "threaded")
+                       (arg "-threaded"))
+                  -- We build a threaded stage N, N>1 if the configuration calls
+                  -- for it.
+                  (ifM (ghcThreaded <$> expr flavour)
+                       (arg "threaded")
+                       (arg "-threaded"))
+            ]
           ]
 
         -------------------------------- ghcPkg --------------------------------