Instructions for compiling libclang_rt.builtins-wasm32.a?

[TerrorJack]

I'm trying to use clang-9 to compile and use wasi-sysroot, but additionally the libclang_rt.builtins-wasm32.a file is required to link into the final wasm module. It is not obvious how to build this file without building the llvm/clang submodules first, so it would be much appreciated if you can add relevant instructions. Thanks a lot!

[eric-nubix]

@TerrorJack Did you ever find out how to build libclang_rt.builtins-wasm32.a from source?

[sbc100]

libclang_rt.builtins-wasm32.a built a build of llvm's compiler-rt.

You can see how we build it as part of wasi-sdk here:

wasi-sdk/Makefile

Lines 98 to 124 in 1a95329

	build/compiler-rt.BUILT: build/llvm.BUILT build/wasi-libc.BUILT
	# Do the build, and install it.
	mkdir -p build/compiler-rt
	cd build/compiler-rt && cmake -G Ninja \
	-DCMAKE_C_COMPILER_WORKS=ON \
	-DCMAKE_CXX_COMPILER_WORKS=ON \
	-DCMAKE_AR=$(BUILD_PREFIX)/bin/ar \
	-DCMAKE_MODULE_PATH=$(ROOT_DIR)/cmake \
	-DCMAKE_BUILD_TYPE=RelWithDebInfo \
	-DCMAKE_TOOLCHAIN_FILE=$(ROOT_DIR)/wasi-sdk.cmake \
	-DCOMPILER_RT_BAREMETAL_BUILD=On \
	-DCOMPILER_RT_BUILD_XRAY=OFF \
	-DCOMPILER_RT_INCLUDE_TESTS=OFF \
	-DCOMPILER_RT_HAS_FPIC_FLAG=OFF \
	-DCOMPILER_RT_ENABLE_IOS=OFF \
	-DCOMPILER_RT_DEFAULT_TARGET_ONLY=On \
	-DWASI_SDK_PREFIX=$(BUILD_PREFIX) \
	-DCMAKE_C_FLAGS="$(DEBUG_PREFIX_MAP) --sysroot=$(BUILD_PREFIX)/share/wasi-sysroot" \
	-DLLVM_CONFIG_PATH=$(ROOT_DIR)/build/llvm/bin/llvm-config \
	-DCOMPILER_RT_OS_DIR=wasi \
	-DCMAKE_INSTALL_PREFIX=$(PREFIX)/lib/clang/$(CLANG_VERSION)/ \
	-DCMAKE_VERBOSE_MAKEFILE:BOOL=ON \
	$(LLVM_PROJ_DIR)/compiler-rt/lib/builtins
	DESTDIR=$(DESTDIR) ninja $(NINJA_FLAGS) -v -C build/compiler-rt install
	# Install clang-provided headers.
	cp -R $(ROOT_DIR)/build/llvm/lib/clang $(BUILD_PREFIX)/lib/
	touch build/compiler-rt.BUILT

[sbc100]

If you don't want to build it from source you can download a prebuilt version of this library from one of the releases. e.g. https://github.com/WebAssembly/wasi-sdk/releases/tag/wasi-sdk-12

Then can most likely just copy this library into ./lib/clang/9.0.0/lib/wasi/ inside your existing clang installation.

[turbolent]

Is it possible to build libclang_rt.builtins-wasm32.a with -phread?

[abrown]

@turbolent, you mean build it manually or distribute it as a part of the release artifacts?