-fPIC -fvia-C issues a warning and ignores -fvia-C

Also, -fPIC causes an error if the target is registerised and has no
native code generator.

2 files changed, 28 insertions, 4 deletions

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index 1969c3b629..55dc8c77da 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -1926,7 +1926,7 @@ parseDynamicNoPackageFlags dflags args = parseDynamicFlags_ dflags args False
 parseDynamicFlags_ :: Monad m =>
                       DynFlags -> [Located String] -> Bool
                   -> m (DynFlags, [Located String], [Located String])
-parseDynamicFlags_ dflags args pkg_flags = do
+parseDynamicFlags_ dflags0 args pkg_flags = do
   -- XXX Legacy support code
   -- We used to accept things like
   --     optdep-f  -optdepdepend
@@ -1943,10 +1943,23 @@ parseDynamicFlags_ dflags args pkg_flags = do
       flag_spec | pkg_flags = package_flags ++ dynamic_flags
                 | otherwise = dynamic_flags
 
-  let ((leftover, errs, warns), dflags')
-          = runCmdLine (processArgs flag_spec args') dflags
+  let ((leftover, errs, warns), dflags1)
+          = runCmdLine (processArgs flag_spec args') dflags0
   when (not (null errs)) $ ghcError $ errorsToGhcException errs
-  return (dflags', leftover, warns)
+
+  -- Cannot use -fPIC with registerised -fvia-C, because the mangler
+  -- isn't up to the job.  We know that if hscTarget == HscC, then the
+  -- user has explicitly used -fvia-C, because -fasm is the default,
+  -- unless there is no NCG on this platform.  The latter case is
+  -- checked when the -fPIC flag is parsed.
+  --
+  let (pic_warns, dflags2) =
+        if opt_PIC && hscTarget dflags1 == HscC && cGhcUnregisterised == "NO"
+          then ([L noSrcSpan $ "Warning: -fvia-C is incompatible with -fPIC; ignoring -fvia-C"],
+                dflags1{ hscTarget = HscAsm })
+          else ([], dflags1)
+
+  return (dflags2, leftover, pic_warns ++ warns)
 
 type DynP = CmdLineP DynFlags
 
diff --git a/compiler/main/StaticFlagParser.hs b/compiler/main/StaticFlagParser.hs
index a153435967..bcc96a676f 100644
--- a/compiler/main/StaticFlagParser.hs
+++ b/compiler/main/StaticFlagParser.hs
@@ -138,6 +138,11 @@ static_flags = [
   , Flag "Rghc-timing"    (NoArg  (enableTimingStats)) Supported
 
         ------ Compiler flags -----------------------------------------------
+
+        -- -fPIC requires extra checking: only the NCG supports it.
+        -- See also DynFlags.parseDynamicFlags.
+  , Flag "fPIC" (PassFlag setPIC) Supported
+
         -- All other "-fno-<blah>" options cancel out "-f<blah>" on the hsc cmdline
   , Flag "fno-"
          (PrefixPred (\s -> isStaticFlag ("f"++s)) (\s -> removeOpt ("-f"++s)))
@@ -147,6 +152,12 @@ static_flags = [
   , Flag "f" (AnySuffixPred isStaticFlag addOpt) Supported
   ]
 
+setPIC :: String -> IO ()
+setPIC | cGhcWithNativeCodeGen == "YES" || cGhcUnregisterised == "YES"
+       = addOpt
+       | otherwise
+       = ghcError $ CmdLineError "-fPIC is not supported on this platform"
+
 isStaticFlag :: String -> Bool
 isStaticFlag f =
   f `elem` [