add shared library support

This adds support for building WASI shared libraries per
https://github.com/WebAssembly/tool-conventions/blob/main/DynamicLinking.md.

For the time being, the goal is to allow "pseudo-dynamic" linking using the
Component Model per
https://github.com/WebAssembly/component-model/blob/main/design/mvp/examples/SharedEverythingDynamicLinking.md.
This requires all libraries to be available when the component is created, but
still allows runtime symbol resolution via `dlopen`/`dlsym` backed by a static
lookup table.  This is sufficient to support Python native extensions, for
example.  A complete demo using `wit-component` is available at
https://github.com/dicej/component-linking-demo.

This requires https://reviews.llvm.org/D153293, which we will need to backport
to LLVM 16 we're ready to upgrade to LLVM 17, hence the
llvm-D153293-backport.patch file.

Signed-off-by: Joel Dice <[email protected]>

.gitmodules

@@ -3,7 +3,7 @@
 	url = https://github.com/llvm/llvm-project
 [submodule "src/wasi-libc"]
 	path = src/wasi-libc
-	url = https://github.com/CraneStation/wasi-libc
+	url = https://github.com/WebAssembly/wasi-libc
 [submodule "src/config"]
 	path = src/config
 	url = https://git.savannah.gnu.org/git/config.git

Makefile

@@ -60,6 +60,9 @@ clean:
 
 build/llvm.BUILT:
 	mkdir -p build/llvm
+	# Apply https://reviews.llvm.org/D153293 as a patch until we're ready to
+	# upgrade to LLVM 17
+	(cd $(LLVM_PROJ_DIR) && patch -p1 -N < ../../llvm-D153293-backport.patch) || true
 	cd build/llvm && cmake -G Ninja \
 		-DCMAKE_BUILD_TYPE=MinSizeRel \
 		-DLLVM_ENABLE_TERMINFO=OFF \
@@ -107,21 +110,24 @@ build/llvm.BUILT:
 		llvm-config
 	touch build/llvm.BUILT
 
-build/wasi-libc.BUILT: build/llvm.BUILT
+build/wasi-libc.BUILT: build/compiler-rt.BUILT
 	$(MAKE) -C $(ROOT_DIR)/src/wasi-libc \
 		CC=$(BUILD_PREFIX)/bin/clang \
 		AR=$(BUILD_PREFIX)/bin/llvm-ar \
 		NM=$(BUILD_PREFIX)/bin/llvm-nm \
-		SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot
+		SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
+		BUILTINS_LIB=$(BUILD_PREFIX)/lib/clang/$(CLANG_VERSION)/lib/wasi/libclang_rt.builtins-wasm32.a \
+		default libc_so
 	$(MAKE) -C $(ROOT_DIR)/src/wasi-libc \
 		CC=$(BUILD_PREFIX)/bin/clang \
 		AR=$(BUILD_PREFIX)/bin/llvm-ar \
 		NM=$(BUILD_PREFIX)/bin/llvm-nm \
 		SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
+		BUILTINS_LIB=$(BUILD_PREFIX)/lib/clang/$(CLANG_VERSION)/lib/wasi/libclang_rt.builtins-wasm32.a \
 		THREAD_MODEL=posix
 	touch build/wasi-libc.BUILT
 
-build/compiler-rt.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
+build/compiler-rt.BUILT: build/llvm.BUILT
 	# Do the build, and install it.
 	mkdir -p build/compiler-rt
 	cd build/compiler-rt && cmake -G Ninja \
@@ -151,6 +157,8 @@ build/compiler-rt.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
 	touch build/compiler-rt.BUILT
 
 # Flags for libcxx and libcxxabi.
+# $(1): pthreads ON or OFF
+# $(2): shared libraries ON or OFF
 LIBCXX_CMAKE_FLAGS = \
     -DCMAKE_C_COMPILER_WORKS=ON \
     -DCMAKE_CXX_COMPILER_WORKS=ON \
@@ -161,38 +169,39 @@ LIBCXX_CMAKE_FLAGS = \
     -DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
     -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
     -DCXX_SUPPORTS_CXX11=ON \
-    -DLIBCXX_ENABLE_THREADS:BOOL=@PTHREAD@ \
-    -DLIBCXX_HAS_PTHREAD_API:BOOL=@PTHREAD@ \
+    -DLIBCXX_ENABLE_THREADS:BOOL=$(1) \
+    -DLIBCXX_HAS_PTHREAD_API:BOOL=$(1) \
     -DLIBCXX_HAS_EXTERNAL_THREAD_API:BOOL=OFF \
     -DLIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY:BOOL=OFF \
     -DLIBCXX_HAS_WIN32_THREAD_API:BOOL=OFF \
     -DLLVM_COMPILER_CHECKED=ON \
     -DCMAKE_BUILD_TYPE=RelWithDebugInfo \
-    -DLIBCXX_ENABLE_SHARED:BOOL=OFF \
+    -DLIBCXX_ENABLE_SHARED:BOOL=$(2) \
     -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY:BOOL=OFF \
     -DLIBCXX_ENABLE_EXCEPTIONS:BOOL=OFF \
     -DLIBCXX_ENABLE_FILESYSTEM:BOOL=OFF \
+    -DLIBCXX_ENABLE_ABI_LINKER_SCRIPT:BOOL=OFF \
     -DLIBCXX_CXX_ABI=libcxxabi \
     -DLIBCXX_CXX_ABI_INCLUDE_PATHS=$(LLVM_PROJ_DIR)/libcxxabi/include \
     -DLIBCXX_HAS_MUSL_LIBC:BOOL=ON \
     -DLIBCXX_ABI_VERSION=2 \
     -DLIBCXXABI_ENABLE_EXCEPTIONS:BOOL=OFF \
-    -DLIBCXXABI_ENABLE_SHARED:BOOL=OFF \
+    -DLIBCXXABI_ENABLE_SHARED:BOOL=$(2) \
     -DLIBCXXABI_SILENT_TERMINATE:BOOL=ON \
-    -DLIBCXXABI_ENABLE_THREADS:BOOL=@PTHREAD@ \
-    -DLIBCXXABI_HAS_PTHREAD_API:BOOL=@PTHREAD@ \
+    -DLIBCXXABI_ENABLE_THREADS:BOOL=$(1) \
+    -DLIBCXXABI_HAS_PTHREAD_API:BOOL=$(1) \
     -DLIBCXXABI_HAS_EXTERNAL_THREAD_API:BOOL=OFF \
     -DLIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY:BOOL=OFF \
     -DLIBCXXABI_HAS_WIN32_THREAD_API:BOOL=OFF \
-    -DLIBCXXABI_ENABLE_PIC:BOOL=OFF \
+    -DLIBCXXABI_ENABLE_PIC:BOOL=$(2) \
     -DWASI_SDK_PREFIX=$(BUILD_PREFIX) \
     -DUNIX:BOOL=ON \
     --debug-trycompile
 
-build/libcxx.BUILT: build/llvm.BUILT build/compiler-rt.BUILT build/wasi-libc.BUILT
+build/libcxx.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
 	# Do the build.
 	mkdir -p build/libcxx
-	cd build/libcxx && cmake -G Ninja $(LIBCXX_CMAKE_FLAGS:@PTHREAD@=OFF) \
+	cd build/libcxx && cmake -G Ninja $(call LIBCXX_CMAKE_FLAGS,OFF,ON) \
 		-DCMAKE_SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
 		-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP) $(EXTRA_CFLAGS)" \
 		-DCMAKE_CXX_FLAGS="$(DEBUG_PREFIX_MAP) $(EXTRA_CXXFLAGS)" \
@@ -202,7 +211,7 @@ build/libcxx.BUILT: build/llvm.BUILT build/compiler-rt.BUILT build/wasi-libc.BUI
 		$(LLVM_PROJ_DIR)/runtimes
 	ninja $(NINJA_FLAGS) -C build/libcxx
 	mkdir -p build/libcxx-threads
-	cd build/libcxx-threads && cmake -G Ninja $(LIBCXX_CMAKE_FLAGS:@PTHREAD@=ON) \
+	cd build/libcxx-threads && cmake -G Ninja $(call LIBCXX_CMAKE_FLAGS,ON,OFF) \
 		-DCMAKE_SYSROOT=$(BUILD_PREFIX)/share/wasi-sysroot \
 		-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP) -pthread $(EXTRA_CFLAGS)" \
 		-DCMAKE_CXX_FLAGS="$(DEBUG_PREFIX_MAP) -pthread $(EXTRA_CXXFLAGS)" \

llvm-D153293-backport.patch

@@ -0,0 +1,40 @@
+diff --git a/clang/lib/Driver/ToolChains/WebAssembly.cpp b/clang/lib/Driver/ToolChains/WebAssembly.cpp
+index a1c4cd9ef9c7..4cbc0794f420 100644
+--- a/clang/lib/Driver/ToolChains/WebAssembly.cpp
++++ b/clang/lib/Driver/ToolChains/WebAssembly.cpp
+@@ -101,13 +101,16 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+           << CM << A->getOption().getName();
+     }
+   }
+-  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles))
++  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles, options::OPT_shared))
+     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(Crt1)));
+   if (Entry) {
+     CmdArgs.push_back(Args.MakeArgString("--entry"));
+     CmdArgs.push_back(Args.MakeArgString(Entry));
+   }
+
++  if (Args.hasArg(options::OPT_shared))
++    CmdArgs.push_back(Args.MakeArgString("-shared"));
++
+   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
+
+   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
+diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+index 630c786a3dc7..788e08e3c8a9 100644
+--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
++++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+@@ -98,13 +98,6 @@ static Reloc::Model getEffectiveRelocModel(std::optional<Reloc::Model> RM,
+     return Reloc::Static;
+   }
+
+-  if (!TT.isOSEmscripten()) {
+-    // Relocation modes other than static are currently implemented in a way
+-    // that only works for Emscripten, so disable them if we aren't targeting
+-    // Emscripten.
+-    return Reloc::Static;
+-  }
+-
+   return *RM;
+ }
+

wasi-sdk-pthread.cmake

@@ -41,3 +41,6 @@ set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+
+
+set(CMAKE_POSITION_INDEPENDENT_CODE On)

wasi-sdk.cmake

@@ -38,3 +38,5 @@ set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+
+set(CMAKE_POSITION_INDEPENDENT_CODE On)