How to compile C++?

[ElysiaEgo]

I have compiled a working LLVM 18.1.4 with WASI 22 and emscripten 3.1.58.
However, I cannot find C++ header files and libstdc++ for C++ to work. Any help?

[ElysiaEgo]

I got it working but not sure if it works perfectly. Only tested with helloworld.
Using emscripten upstream include header file for clang sysroot, and wasi sysroot for lld sysroot.
Build command

emcmake cmake -G Ninja -S llvm -B build \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=install \
  -DCMAKE_CROSSCOMPILING=True \
  -DCMAKE_C_FLAGS="" \
  -DCMAKE_CXX_FLAGS="-Dwait4=__syscall_wait4" \
  -DLLVM_TARGET_ARCH=wasm32-emscripten \
  -DLLVM_DEFAULT_TARGET_TRIPLE=wasm32-wasi \
  -DLLVM_ENABLE_PROJECTS="clang;lld" \
  -DLLVM_TARGETS_TO_BUILD=WebAssembly \
  -DLLVM_ENABLE_THREADS=OFF \
  -DLLVM_TABLEGEN=$PWD/build-host/bin/llvm-tblgen\
  -DLLVM_ENABLE_PIC=OFF\
  -DLLVM_INCLUDE_UTILS=OFF \
  -DLLVM_ENABLE_OCAMLDOC=OFF\
  -DLLVM_ENABLE_BACKTRACES=OFF\
  -DLLVM_INCLUDE_TESTS=OFF \
  -DLLVM_INCLUDE_EXAMPLES=OFF \
  -DLLVM_INCLUDE_BENCHMARKS=OFF \
  -DLLVM_CCACHE_BUILD=ON \
  -DLLVM_PARALLEL_LINK_JOBS=6

Changes to llvm/CMakeLists.txt
Note that setting $LDFLAGS is not working and may cause issues when llvm try to bootstrap

set_target_properties(lld PROPERTIES LINK_FLAGS "--preload-file=../../lld-sysroot@/ -sNO_INVOKE_RUN -sEXIT_RUNTIME -sINITIAL_MEMORY=128MB -sALLOW_MEMORY_GROWTH -sEXPORTED_RUNTIME_METHODS=FS,callMain -sMODULARIZE -sEXPORT_ES6 -sWASM_BIGINT")
set_target_properties(clang PROPERTIES LINK_FLAGS "--preload-file=../../clang-sysroot@/ -sNO_INVOKE_RUN -sEXIT_RUNTIME -sINITIAL_MEMORY=128MB -sALLOW_MEMORY_GROWTH -sEXPORTED_RUNTIME_METHODS=FS,callMain -sMODULARIZE -sEXPORT_ES6 -sWASM_BIGINT")

[anutosh491]

Hi @ElysiaEgo

I am trying to compile clang and lld against emscripten for wasm. I would be glad if you could give me clarification on some of these flags

1. Why would you need this flag -Dwait4=__syscall_wait4 here ?
2. Why would you need to use DLLVM_TABLEGEN ?

So basically I have been successful in building the projects but not too sure on if I could get it to execute or during runtime. Maybe these flags might be what I want !

[ElysiaEgo]

@anutosh491

1. wait4 is not defined in wasi in my impression so thats why we need this marco.
2. custom tablegen is used for cross-compiling according to LLVM documentation.