From e35ef3b7d796a174eeb35fc2595281a3285a38ea Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin@martin.st>
Date: Thu, 4 Mar 2021 22:14:13 +0200
Subject: [PATCH] Use -unwindlib=libunwind instead of merging libunwind into
 libc++

This makes the build of libcxx a bit cleaner, and simplifies later
building and testing of libcxx.
---
 build-compiler-rt.sh             | 17 ++++++++++++++++-
 build-libcxx.sh                  | 19 ++++++++++---------
 build-llvm.sh                    |  1 +
 wrappers/clang-target-wrapper.c  |  1 +
 wrappers/clang-target-wrapper.sh |  1 +
 5 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/build-compiler-rt.sh b/build-compiler-rt.sh
index e9e677a..c9f335b 100755
--- a/build-compiler-rt.sh
+++ b/build-compiler-rt.sh
@@ -100,7 +100,22 @@ for arch in $ARCHS; do
     $BUILDCMD ${CORES+-j$CORES}
     $BUILDCMD install
     mkdir -p "$PREFIX/$arch-w64-mingw32/bin"
-    if [ -n "$SANITIZERS" ]; then
+    if [ -z "$SANITIZERS" ]; then
+        # Building builtins only. If libunwind isn't built yet, linking of any
+        # executable will still fail as we're using -unwindlib=libunwind.
+        # Therefore, create a dummy libunwind.a (unless there's a real
+        # libunwind installed already) to let linking succeed.
+        #
+        # This is a workaround to avoid needing to specify -unwindlib=none
+        # for all linking until libunwind has been built. This avoids
+        # needing to build libunwind right away (allowing building plain C
+        # executables already now) and avoids needing to pass -unwindlib=none
+        # when configuring the libunwind build.
+        if [ ! -f $PREFIX/$arch-w64-mingw32/lib/libunwind.a ] && [ ! -f $PREFIX/$arch-w64-mingw32/lib/libunwind.dll.a ]; then
+            # Create an archive, don't add any members.
+            llvm-ar rcs $PREFIX/$arch-w64-mingw32/lib/libunwind.a
+        fi
+    else
         mv "$PREFIX/lib/clang/$CLANG_VERSION/lib/windows/"*.dll "$PREFIX/$arch-w64-mingw32/bin"
     fi
     cd ..
diff --git a/build-libcxx.sh b/build-libcxx.sh
index fbede0c..6fdde00 100755
--- a/build-libcxx.sh
+++ b/build-libcxx.sh
@@ -193,15 +193,6 @@ build_all() {
         cd build-$arch-$type
         $BUILDCMD ${CORES+-j$CORES}
         $BUILDCMD install
-        if [ "$type" = "shared" ]; then
-            llvm-ar qcsL \
-                "$PREFIX/$arch-w64-mingw32/lib/libc++.dll.a" \
-                "$PREFIX/$arch-w64-mingw32/lib/libunwind.dll.a"
-        else
-            llvm-ar qcsL \
-                "$PREFIX/$arch-w64-mingw32/lib/libc++.a" \
-                "$PREFIX/$arch-w64-mingw32/lib/libunwind.a"
-        fi
         cd ..
     done
     cd ..
@@ -211,3 +202,13 @@ build_all() {
 # work when linking against the DLL, but not vice versa.
 [ -z "$BUILD_SHARED" ] || build_all shared
 [ -z "$BUILD_STATIC" ] || build_all static
+
+# Remove dummy placeholder libunwind.a. If we've built a static version, it
+# already was overwritten with a proper one, but if only building a shared
+# version, remove the dummy one to avoid surprises.
+for arch in $ARCHS; do
+    # Only remove the file if it contains no members.
+    if [ -f $PREFIX/$arch-w64-mingw32/lib/libunwind.a ] && [ "$(llvm-ar t $PREFIX/$arch-w64-mingw32/lib/libunwind.a)" = "" ]; then
+        rm $PREFIX/$arch-w64-mingw32/lib/libunwind.a
+    fi
+done
diff --git a/build-llvm.sh b/build-llvm.sh
index c5f05e3..0f0b5ef 100755
--- a/build-llvm.sh
+++ b/build-llvm.sh
@@ -157,6 +157,7 @@ if [ -n "$HOST" ]; then
     # the frontend wrappers, but this makes sure they are enabled by
     # default if that wrapper is bypassed as well.
     CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_RTLIB=compiler-rt"
+    CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_UNWINDLIB=libunwind"
     CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_CXX_STDLIB=libc++"
     CMAKEFLAGS="$CMAKEFLAGS -DCLANG_DEFAULT_LINKER=lld"
     BUILDDIR=$BUILDDIR-$HOST
diff --git a/wrappers/clang-target-wrapper.c b/wrappers/clang-target-wrapper.c
index 1305be9..cd03d87 100644
--- a/wrappers/clang-target-wrapper.c
+++ b/wrappers/clang-target-wrapper.c
@@ -224,6 +224,7 @@ int _tmain(int argc, TCHAR* argv[]) {
     exec_argv[arg++] = _T("-target");
     exec_argv[arg++] = target;
     exec_argv[arg++] = _T("-rtlib=compiler-rt");
+    exec_argv[arg++] = _T("-unwindlib=libunwind");
     exec_argv[arg++] = _T("-stdlib=libc++");
     exec_argv[arg++] = _T("-fuse-ld=lld");
     exec_argv[arg++] = _T("-Qunused-arguments");
diff --git a/wrappers/clang-target-wrapper.sh b/wrappers/clang-target-wrapper.sh
index 5d75702..4cac061 100755
--- a/wrappers/clang-target-wrapper.sh
+++ b/wrappers/clang-target-wrapper.sh
@@ -84,6 +84,7 @@ esac
 
 FLAGS="$FLAGS -target $TARGET"
 FLAGS="$FLAGS -rtlib=compiler-rt"
+FLAGS="$FLAGS -unwindlib=libunwind"
 FLAGS="$FLAGS -stdlib=libc++"
 FLAGS="$FLAGS -fuse-ld=lld"
 FLAGS="$FLAGS -Qunused-arguments"