[Git][ghc/ghc][wip/dcoutts/windows-rts-dll] 5 commits: Add minimal dlltool support into ./configure

6 May 2026

David Eichmann pushed to branch wip/dcoutts/windows-rts-dll at Glasgow Haskell Compiler / GHC


Commits:
3eed75d2 by Duncan Coutts at 2026-05-06T17:58:12+01:00
Add minimal dlltool support into ./configure

Find dlltool, and hopefully support finding it within the bundled llvm
toolchain on windows.

- - - - -
9a074a69 by Duncan Coutts at 2026-05-06T17:58:14+01:00
Update the default host and target files for dlltool support

- - - - -
5fdb97fd by Duncan Coutts at 2026-05-06T17:58:14+01:00
Add dlltool as a hadrian builder

Optional except on windows.

- - - - -
6b7d555f by Duncan Coutts at 2026-05-06T17:58:14+01:00
Update and generate libHSghc-internal.def from .def.in file

The only symbol that the rts imports from the ghc-internal package now
is init_ghc_hs_iface. So the rts only needs an import lib that defines
that one symbol.

Also, remove the libHSghc-prim.def because it is redundant. The rts no
longer imports anything from ghc-prim.

Keep libHSffi.def for now. We may yet need it once it is clear how
libffi is going to be built/used for ghc.

- - - - -
f195d87e by Duncan Coutts at 2026-05-06T17:58:14+01:00
Add rule to build libHSghc-internal.dll.a and link into the rts

On windows only, with dynamic linking.

This is needed because on windows, all symbols in dlls must be resolved.
No dangling symbols allowed. References to external symbols must be
explicit. We resolve this with an import library. We create an import
library for ghc-internal, a .dll.a file. This is a static archive
containing .o files that define the symbols we need, and crucially have
".idata" sections that specifies the symbols the dll imports and from
where.

Note that we do not install this libHSghc-internal.dll.a, and it does
not need to list all the symbols exported by that package. We create a
special purpose import lib and only use it when linking the rts dll, so
it only has to list the symbols that the rts uses from ghc-internal
(which is exactly one symbol: init_ghc_hs_iface).

- - - - -


15 changed files:

- configure.ac
- distrib/configure.ac.in
- hadrian/cfg/default.host.target.in
- hadrian/cfg/default.target.in
- hadrian/src/Builder.hs
- hadrian/src/Rules/Generate.hs
- hadrian/src/Rules/Library.hs
- hadrian/src/Rules/Rts.hs
- m4/find_llvm_prog.m4
- m4/fp_setup_windows_toolchain.m4
- m4/ghc_toolchain.m4
- m4/prep_target_file.m4
- rts/.gitignore
- + rts/win32/libHSghc-internal.def.in
- utils/ghc-toolchain/exe/Main.hs


Changes:

=====================================
configure.ac
=====================================
@@ -314,13 +314,16 @@ else
     AC_CHECK_TOOL([RANLIB],[ranlib])
     AC_CHECK_TOOL([OBJDUMP],[objdump])
     AC_CHECK_TOOL([WindresCmd],[windres])
+    AC_CHECK_TOOL([DlltoolCmd],[llvm-dlltool])
     AC_CHECK_TOOL([Genlib],[genlib])
 
     if test "$HostOS" = "mingw32"; then
         AC_CHECK_TARGET_TOOL([WindresCmd],[windres])
+        AC_CHECK_TARGET_TOOL([DlltoolCmd],[llvm-dlltool])
         AC_CHECK_TARGET_TOOL([OBJDUMP],[objdump])
 
         WindresCmd="$(cygpath -m $WindresCmd)"
+        DlltoolCmd="$(cygpath -m $DlltoolCmd)"
 
         if test "$Genlib" != ""; then
             GenlibCmd="$(cygpath -m $Genlib)"
@@ -568,6 +571,11 @@ FIND_LLVM_PROG([OPT], [opt], [$LlvmMinVersion], [$LlvmMaxVersion])
 OptCmd="$OPT"
 AC_SUBST([OptCmd])
 
+dnl ** Which LLVM llvm-dlltool to use?
+dnl --------------------------------------------------------------
+AC_ARG_VAR(DlltoolCmd,[Use as the path to LLVM's llvm-dlltool [default=autodetect]])
+FIND_LLVM_PROG([DlltoolCmd], [llvm-dlltool], [$LlvmMinVersion], [$LlvmMaxVersion])
+
 dnl ** look to see if we have a C compiler using an llvm back end.
 dnl
 FP_CC_LLVM_BACKEND
@@ -1080,9 +1088,10 @@ echo "\
       libdw   : $UseLibdw
 
    Using LLVM tools
-      llc   : $LlcCmd
-      opt   : $OptCmd
-      llvm-as : $LlvmAsCmd"
+      llc          : $LlcCmd
+      opt          : $OptCmd
+      llvm-as      : $LlvmAsCmd
+      llvm-dlltool : $DlltoolCmd"
 
 if test "$HSCOLOUR" = ""; then
 echo "


=====================================
distrib/configure.ac.in
=====================================
@@ -229,6 +229,13 @@ FIND_LLVM_PROG([LLVMAS], [clang], [$LlvmMinVersion], [$LlvmMaxVersion])
 LlvmAsCmd="$LLVMAS"
 AC_SUBST([LlvmAsCmd])
 
+dnl ** Which LLVM llvm-dlltool to use?
+dnl --------------------------------------------------------------
+AC_CHECK_TARGET_TOOL([DlltoolCmd],[llvm-dlltool])
+AC_ARG_VAR(DlltoolCmd,[Use as the path to LLVM's llvm-dlltool [default=autodetect]])
+FIND_LLVM_PROG([DlltoolCmd], [llvm-dlltool], [$LlvmMinVersion], [$LlvmMaxVersion])
+AC_SUBST([DlltoolCmd])
+
 dnl We know that `clang` supports `--target` and it is necessary to pass it
 dnl lest we see #25793.
 if test -z "$LlvmAsFlags" && ! test -z "$LlvmTarget"; then


=====================================
hadrian/cfg/default.host.target.in
=====================================
@@ -45,6 +45,7 @@ Target
 , tgtOpt = Nothing
 , tgtLlvmAs = Nothing
 , tgtWindres = Nothing
+, tgtDlltool = Nothing
 , tgtOtool = Nothing
 , tgtInstallNameTool = Nothing
 }


=====================================
hadrian/cfg/default.target.in
=====================================
@@ -45,6 +45,7 @@ Target
 , tgtOpt = @OptCmdMaybeProg@
 , tgtLlvmAs = @LlvmAsCmdMaybeProg@
 , tgtWindres = @WindresCmdMaybeProg@
+, tgtDlltool = @DlltoolCmdMaybeProg@
 , tgtOtool = @OtoolCmdMaybeProg@
 , tgtInstallNameTool = @InstallNameToolCmdMaybeProg@
 }


=====================================
hadrian/src/Builder.hs
=====================================
@@ -17,7 +17,7 @@ import Development.Shake.Classes
 import Development.Shake.Command
 import Development.Shake.FilePath
 import GHC.Generics
-import GHC.Platform.ArchOS (ArchOS(..), Arch(..))
+import GHC.Platform.ArchOS (ArchOS(..), Arch(..), OS(..))
 import qualified Hadrian.Builder as H
 import Hadrian.Builder hiding (Builder)
 import Hadrian.Builder.Ar
@@ -180,6 +180,7 @@ data Builder = Alex
              | Objdump
              | Python
              | Ranlib
+             | Dlltool
              | Testsuite TestMode
              | Sphinx SphinxMode
              | Tar TarMode
@@ -418,6 +419,7 @@ isOptional target = \case
     Alex     -> True
     -- Most ar implemententions no longer need ranlib, but some still do
     Ranlib   -> not $ Toolchain.arNeedsRanlib (tgtAr target)
+    Dlltool  -> archOS_OS (tgtArchOs target) /= OSMinGW32
     JsCpp    -> not $ (archOS_arch . tgtArchOs) target == ArchJavaScript -- ArchWasm32 too?
     _        -> False
 
@@ -442,6 +444,7 @@ systemBuilderPath builder = case builder of
     Objdump         -> fromKey "objdump"
     Python          -> fromKey "python"
     Ranlib          -> fromTargetTC "ranlib" (maybeProg Toolchain.ranlibProgram . tgtRanlib)
+    Dlltool         -> fromTargetTC "dlltool" (maybeProg id . tgtDlltool)
     Testsuite _     -> fromKey "python"
     Sphinx _        -> fromKey "sphinx-build"
     Tar _           -> fromKey "tar"


=====================================
hadrian/src/Rules/Generate.hs
=====================================
@@ -377,6 +377,7 @@ templateRules = do
     , interpolateSetting "ProjectPatchLevel1" ProjectPatchLevel1
     , interpolateSetting "ProjectPatchLevel2" ProjectPatchLevel2
     ]
+  templateRule "rts/win32/libHSghc-internal.def" projectVersion
   templateRule "docs/index.html" $ packageUnitIds Stage1
   templateRule "docs/users_guide/ghc_config.py" $ mconcat
     [ projectVersion


=====================================
hadrian/src/Rules/Library.hs
=====================================
@@ -4,6 +4,8 @@ import Hadrian.BuildPath
 import Hadrian.Haskell.Cabal
 import Hadrian.Haskell.Cabal.Type
 import qualified Text.Parsec      as Parsec
+import GHC.Platform.ArchOS (ArchOS(archOS_OS), OS(..))
+import GHC.Toolchain.Target (Target(tgtArchOs))
 
 import Base
 import Context
@@ -185,9 +187,13 @@ jsObjects context = do
   srcs <- interpretInContext context (getContextData jsSrcs)
   mapM (objectPath context) srcs

--- | Return extra object files needed to build the given library context. The
--- resulting list is currently non-empty only when the package from the
--- 'Context' is @ghc-internal@ built with in-tree GMP backend.
+-- | Return extra object files needed to build the given library context.
+--
+-- This is non-empty for:
+--
+-- * @ghc-internal@ when built with in-tree GMP backend
+-- * @rts@ on Windows when linking dynamically
+--
 extraObjects :: Context -> Action [FilePath]
 extraObjects context
     | package context == ghcInternal = do
@@ -195,6 +201,13 @@ extraObjects context
             "gmp" -> gmpObjects (stage context)
             _     -> return []
 
+    | package context == rts = do
+          target   <- interpretInContext context getStagedTarget
+          builddir <- buildPath context
+          return [ builddir -/- "libHSghc-internal.dll.a"
+                 | archOS_OS (tgtArchOs target) == OSMinGW32
+                 , Dynamic `wayUnit` way context ]
+
     | otherwise = return []
 
 -- | Return all the object files to be put into the library we're building for


=====================================
hadrian/src/Rules/Rts.hs
=====================================
@@ -24,6 +24,20 @@ rtsRules = priority 3 $ do
             (addRtsDummyVersion $ takeFileName rtsLibFilePath')
             rtsLibFilePath'
 
+    -- Solve the recursive dependency between the rts and ghc-internal
+    -- on Windows by creating an import lib for the ghc-internal dll,
+    -- to be linked into the rts dll.
+    forM_ [Stage1, Stage2, Stage3 ] $ \ stage -> do
+        let buildPath = root -/- buildDir (rtsContext stage)
+        buildPath -/- "libHSghc-internal.dll.a" %> buildGhcInternalImportLib
+
+buildGhcInternalImportLib :: FilePath -> Action ()
+buildGhcInternalImportLib target = do
+    let input  = "rts/win32/libHSghc-internal.def"
+        output = target -- the .dll.a import lib
+    need [input]
+    runBuilder Dlltool ["-d", input, "-l", output] [input] [output]
+
 -- Need symlinks generated by rtsRules.
 needRtsSymLinks :: Stage -> Set.Set Way -> Action ()
 needRtsSymLinks stage rtsWays


=====================================
m4/find_llvm_prog.m4
=====================================
@@ -16,9 +16,12 @@ AC_DEFUN([FIND_LLVM_PROG],[
     AS_IF([test x"$$1" != x],[
         PROG_VERSION=`$$1 --version | sed -n -e 's/.*version \(\([[0-9]][[0-9]]*\.\)\([[0-9]][[0-9]]*\.\)*[[0-9]][[0-9]]*\).*/\1/gp'`
         AS_IF([test x"$PROG_VERSION" = x],
-          [AC_MSG_RESULT(no)
-           $1=""
-           AC_MSG_NOTICE([We only support llvm $3 upto $4 (non-inclusive) (no version found).])],
+          [AS_IF(
+            [test x"$2" = x"llvm-dlltool"],
+            [AC_MSG_RESULT(yes)], # llvm-dlltool doesn't have a --version
+            [AC_MSG_RESULT(no)
+             AC_MSG_NOTICE([We only support llvm $3 upto $4 (non-inclusive) (no version found).])]
+            )],
           [AC_MSG_CHECKING([$$1 version ($PROG_VERSION) is between $3 and $4])
            AX_COMPARE_VERSION([$PROG_VERSION], [lt], [$3],
             [AC_MSG_RESULT(no)


=====================================
m4/fp_setup_windows_toolchain.m4
=====================================
@@ -131,8 +131,8 @@ AC_DEFUN([FP_SETUP_WINDOWS_TOOLCHAIN],[
     AR="${mingwbin}llvm-ar.exe"
     RANLIB="${mingwbin}llvm-ranlib.exe"
     OBJDUMP="${mingwbin}llvm-objdump.exe"
-    DLLTOOL="${mingwbin}llvm-dlltool.exe"
     WindresCmd="${mingwbin}llvm-windres.exe"
+    DlltoolCmd="${mingwbin}llvm-dlltool.exe"
     LLC="${mingwbin}llc.exe"
     OPT="${mingwbin}opt.exe"
     LLVMAS="${mingwbin}clang.exe"


=====================================
m4/ghc_toolchain.m4
=====================================
@@ -95,6 +95,7 @@ AC_DEFUN([FIND_GHC_TOOLCHAIN],
     echo "--merge-objs=$MergeObjsCmd" >> acargs
     echo "--readelf=$READELF" >> acargs
     echo "--windres=$WindresCmd" >> acargs
+    echo "--dlltool=$DlltoolCmd" >> acargs
     echo "--llc=$LlcCmd" >> acargs
     echo "--opt=$OptCmd" >> acargs
     echo "--llvm-as=$LlvmAsCmd" >> acargs


=====================================
m4/prep_target_file.m4
=====================================
@@ -191,6 +191,7 @@ AC_DEFUN([PREP_TARGET_FILE],[
     PREP_MAYBE_SIMPLE_PROGRAM([OptCmd])
     PREP_MAYBE_PROGRAM([LlvmAsCmd], [LlvmAsFlags])
     PREP_MAYBE_SIMPLE_PROGRAM([WindresCmd])
+    PREP_MAYBE_SIMPLE_PROGRAM([DlltoolCmd])
     PREP_MAYBE_SIMPLE_PROGRAM([OtoolCmd])
     PREP_MAYBE_SIMPLE_PROGRAM([InstallNameToolCmd])
     PREP_MAYBE_STRING([TargetVendor_CPP])


=====================================
rts/.gitignore
=====================================
@@ -20,3 +20,4 @@
 /ghcautoconf.h.autoconf.in
 /ghcautoconf.h.autoconf
 /include/ghcautoconf.h
+/win32/libHSghc-internal.def


=====================================
rts/win32/libHSghc-internal.def.in
=====================================
@@ -0,0 +1,4 @@
+LIBRARY libHSghc-internal-@ProjectVersionForLib@.0-ghc@ProjectVersion@.dll
+
+EXPORTS
+    init_ghc_hs_iface


=====================================
utils/ghc-toolchain/exe/Main.hs
=====================================
@@ -486,7 +486,7 @@ mkTarget opts = do
 
     -- for windows, also used for cross compiling
     windres <- optional $ findProgram "windres" (optWindres opts) ["windres"]
-    dlltool <- optional $ findProgram "dlltool" (optDlltool opts) ["dlltool", "llvm-dlltool"]
+    dlltool <- optional $ findProgram "dlltool" (optDlltool opts) ["llvm-dlltool"]
 
     -- Darwin-specific utilities
     (otool, installNameTool) <-



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/3ea6bb3f3c11c0e300ac2c627d05cf0...

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David Eichmann (＠DavidEichmann)

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