WebAssembly.Module doesn't parse at byte error on iOS

[lizozom]

I'm building a wasm project to run on mobile.

I'm using the following CMakeLists configurations:

project(ncnn-webassembly-project)

cmake_minimum_required(VERSION 3.10)

set(CMAKE_BUILD_TYPE release)

set(RUNTIME_OUTPUT_DIRECTORY  ${PROJECT_SOURCE_DIR}/build/)
set(EXECUTABLE_OUTPUT_PATH  ${PROJECT_SOURCE_DIR}/public/)

set(ncnn_DIR "${CMAKE_CURRENT_SOURCE_DIR}/cpp/ncnn/lib/cmake/ncnn")
find_package(ncnn REQUIRED)

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -s FORCE_FILESYSTEM=1 -s INITIAL_MEMORY=256MB -s EXIT_RUNTIME=1")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s FORCE_FILESYSTEM=1 -s INITIAL_MEMORY=256MB -s EXIT_RUNTIME=1")

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fopenmp -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=15")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fopenmp -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=15")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fopenmp -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=15")

# debug
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -sASSERTIONS")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -sASSERTIONS")

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -sEXPORTED_FUNCTIONS=['_yolo_ncnn','_detect_yolo','_free'] --preload-file ${CMAKE_CURRENT_SOURCE_DIR}/cpp/assets@.")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -sEXPORTED_FUNCTIONS=['_yolo_ncnn','_detect_yolo','_free'] --preload-file ${CMAKE_CURRENT_SOURCE_DIR}/cpp/assets@.")
set(CMAKE_EXECUTBLE_LINKER_FLAGS "${CMAKE_EXECUTBLE_LINKER_FLAGS} -sEXPORTED_FUNCTIONS=['_yolo_ncnn','_detect_yolo','_free'] --preload-file ${CMAKE_CURRENT_SOURCE_DIR}/cpp/assets@.")


add_executable(duckpuc cpp/proj.cpp)
target_link_libraries(duckpuc ncnn pthread)

add_executable(duckpuc-ios cpp/proj-ios.cpp)
target_link_libraries(duckpuc-ios ncnn pthread)

On Android everything works, but on iOS I get the following errors:

failed to asynchronously prepare wasm: CompileError: WebAssembly.Module doesn't parse at byte 885: can't get 7th argument Type
Aborted(CompileError: WebAssembly.Module doesn't parse at byte 885: can't get 7th argument Type)

Now as far as I understand, threads and atomics are supported on iOS 15.2+, so what else might be the problem?

[lizozom]

I'm trying to troubleshoot with wasm-objdump as proposed here, but I'm not sure what I should be looking for

[lizozom]

I've resolved the issue myself, posting here hoping this would help someone.

In my case I was building my project with a dependency built with simd on, which is not supported on iOS at the moment.

So I instead built my dependencies with simd disabled (see here how to build ncnn with different modes):

mkdir -p build-threads
cd build-threads
cmake -DCMAKE_TOOLCHAIN_FILE=../emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake \
    -DNCNN_THREADS=ON -DNCNN_OPENMP=ON -DNCNN_SIMPLEOMP=ON -DNCNN_RUNTIME_CPU=OFF -DNCNN_SSE2=OFF -DNCNN_AVX2=OFF -DNCNN_AVX=OFF \
    -DNCNN_BUILD_TOOLS=OFF -DNCNN_BUILD_EXAMPLES=OFF -DNCNN_BUILD_BENCHMARK=OFF ..
cmake --build . -j 4
cmake --build . --target install

Once I linked the correct version, the code works with threading on iOS as well.

If you want to build your project for iOS pre-15.2 without both threads and simd, you should build your dependencies appropriately and also be sure to remove USE_PTHREADS from your cmake file.