2 files changed, 21 insertions, 16 deletions
diff --git a/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cpp.hs b/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cpp.hs
index a9fe18bd1d..4d0a3ddef5 100644
--- a/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cpp.hs
+++ b/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Cpp.hs
@@ -3,9 +3,11 @@
 module GHC.Toolchain.Tools.Cpp (Cpp(..), findCpp) where
 
 import Control.Monad
+import System.FilePath
 
 import GHC.Toolchain.Prelude
 import GHC.Toolchain.Program
+import GHC.Toolchain.Utils (withTempDir)
 
 import GHC.Toolchain.Tools.Cc
 
@@ -30,19 +32,22 @@ findCpp progOpt cc = checking "for C preprocessor" $ do
 -- | Given a C preprocessor, figure out how it should be invoked to preprocess
 -- Haskell source.
 findHsCppArgs :: Program -> M [String]
-findHsCppArgs cpp =
-    concat <$> sequence
-        [ ["-traditional"] <$ checkFlag "-traditional"
-        , tryFlag "-undef"
-        , tryFlag "-Wno-invalid-pp-token"
-        , tryFlag "-Wno-unicode"
-        , tryFlag "-Wno-trigraphs"
-        ]
-  where
-    -- Werror to ensure that unrecognized warnings result in an error
-    checkFlag flag =
-        checking ("for "++flag++" support") $ callProgram cpp ["-E", "-Werror", flag, "/dev/null"]
-
-    tryFlag flag =
-        ([flag] <$ checkFlag flag) <|> return []
+findHsCppArgs cpp = withTempDir $ \dir -> do
+  let tmp_h = dir </> "tmp.h"
+
+      -- Werror to ensure that unrecognized warnings result in an error
+      checkFlag flag =
+          checking ("for "++flag++" support") $ callProgram cpp ["-Werror", flag, tmp_h]
+
+      tryFlag flag =
+          ([flag] <$ checkFlag flag) <|> return []
+
+  writeFile tmp_h ""
+  concat <$> sequence
+      [ ["-traditional"] <$ checkFlag "-traditional"
+      , tryFlag "-undef"
+      , tryFlag "-Wno-invalid-pp-token"
+      , tryFlag "-Wno-unicode"
+      , tryFlag "-Wno-trigraphs"
+      ]
 
diff --git a/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Link.hs b/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Link.hs
index ec0b051c09..71f53dba54 100644
--- a/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Link.hs
+++ b/utils/ghc-toolchain/src/GHC/Toolchain/Tools/Link.hs
@@ -100,7 +100,7 @@ checkSupportsNoPie ccLink = checking "whether the cc linker supports -no-pie" $
 checkSupportsCompactUnwind :: Cc -> Program -> M Bool
 checkSupportsCompactUnwind cc ccLink = checking "whether the cc linker understands -no_compact_unwind" $
   withTempDir $ \dir -> do
-    let test_o  = dir </> "o"
+    let test_o  = dir </> "test.o"
         test2_o = dir </> "test2.o"
 
     compileC cc test_o "int foo() { return 0; }"