Nick's way of setting up Wasm toolchain

build-wasm-toolchain.sh

# Check everything out here, and build here
BUILD_DIR=~/workspace/wasm
# Install all the tools, headers, Wasm libraries here, so that
# we can use it via "-isysroot" when compiling.
INSTALL_DIR=~/workspace/wasm-root

#####
##### Get LLVM, build WebAssembly
#####
cd $BUILD_DIR
git clone https://github.com/llvm-mirror/llvm.git  llvm
git clone https://github.com/llvm-mirror/clang.git llvm/tools/clang
git clone https://github.com/llvm-mirror/lld.git   llvm/tools/lld

mdir bld
cd bld
cmake -G Ninja \
  -DCMAKE_INSTALL_PREFIX=$INSTALL_DIR \
  -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly \
  -DLLVM_TARGETS_TO_BUILD=X86 \
  -DLLVM_DEFAULT_TARGET_TRIPLE=wasm32-unknown-unknown-wasm \
  -DLLVM_USE_LINKER=gold \
  -DCMAKE_BUILD_TYPE=Debug \
  -DLLVM_ENABLE_ASSERTIONS=On \
  ..
ninja all install


#####
##### Get Musl, produce a working libc
#####
cd $BUILD_DIR
git clone git@github.com:NWilson/musl.git musl
cd musl
(
  PATH=$INSTALL_DIR/bin:$PATH # Use Wasm Clang
  export CC=clang
  export LDFLAGS=-Wl,--no-entry
  export CFLAGS=-fvisibility=hidden # Just a nicety to hide symbols
  export CROSS_COMPILE=llvm- # Essential to use llvm-ar!
  ./configure --prefix=$INSTALL_DIR/usr/
  make -j8 all
)
make install
cp arch/wasm/wasm.syms $INSTALL_DIR/share/


#####
##### libcxx/libcxxabi compilation
#####
cd $BUILD_DIR
git clone https://github.com/llvm-mirror/libcxx.git libcxx
mkdir -p libcxx/bld
cd libcxx/bld
(
  PATH=$INSTALL_DIR/bin:$PATH # Use Wasm Clang
  cmake -G Ninja \
    -DCMAKE_CXX_FLAGS="-nostdlib++ -nostdlib -isysroot/home/ncw/workspace/llvm/compile-root/ -Wl,--allow-undefined -Wl,--no-entry" \
    -DCMAKE_C_FLAGS="-nostdlib -isysroot/home/ncw/workspace/llvm/compile-root/ -Wl,--allow-undefined -Wl,--no-entry" \
    -DCMAKE_BUILD_TYPE=Release \
    -DLIBCXX_ENABLE_SHARED=False \
    -DLIBCXX_HAS_MUSL_LIBC=True \
    -DLLVM_CONFIG_PATH=$INSTALL_DIR/bin/llvm-config \
    -DLIBCXX_ENABLE_THREADS=False \
    -DCMAKE_AR=$INSTALL_DIR/bin/llvm-ar \
    ..
  ninja libc++.a
)

git clone https://github.com/llvm-mirror/libcxxabi.git libcxxabi
mkdir -p libcxxabi/bld
cd libcxxabi/bld
(
  PATH=$INSTALL_DIR/bin:$PATH # Use Wasm Clang
  LIBCXX_BINARY_DIR=$BUILD_DIR/libcxx/bld
  cmake -G Ninja \
    -DCMAKE_CXX_FLAGS="-nostdlib++ -nostdlib -isysroot/home/ncw/workspace/llvm/compile-root/ -Wl,--allow-undefined -Wl,--no-entry -include ${LIBCXX_BINARY_DIR}/__config_site" \
    -DCMAKE_C_FLAGS="-nostdlib -isysroot/home/ncw/workspace/llvm/compile-root/ -Wl,--allow-undefined -Wl,--no-entry" \
    -DCMAKE_BUILD_TYPE=Release \
    -DLLVM_CONFIG_PATH=$INSTALL_DIR/bin/llvm-config \
    -DCMAKE_AR=$INSTALL_DIR/bin/llvm-ar \
    -DLLVM_ENABLE_LIBCXX=True \
    -DLIBCXXABI_LIBCXX_PATH=$BUILD_DIR/libcxx \
    -DLIBCXXABI_ENABLE_SHARED=False \
    -DLIBCXXABI_ENABLE_THREADS=False \
    ..
  ninja libc++abi.a
)


#####
##### Using it all
#####
(
  CC=$INSTALL_DIR/bin/clang
  CFLAGS=-isysroot$INSTALL_DIR
  
  # Sadly, LLD doesn't support sysroot, so we're stuck with using -L for now.
  LDFLAGS="-L$INSTALL_DIR/usr/lib"
  # Secondly, my version of Musl isn't targeted by Clang, so we have to use
  # -nostdlib to wipe the bits it adds for Musl and add our own.
  LDFLAGS="$LDFLAGS -nostdlib -lc -Wl,--entry=_start_wasm -Wl,-allow-undefined-file -Wl,$INSTALL_DIR/share/wasm.syms"
  
  echo "int exportedFn() { return 42; }" > /tmp/test.c
  $CC $CFLAGS  -c -o /tmp/test.o /tmp/test.c
  $CC $LDFLAGS    -o /tmp/test   /tmp/test.o
)