SVT-AV1 Emscripten build

I am trying to build svt-av1 v1.4.1 for ffmpeg with emscripten 3.1.32. I have followed Build-Guide and ended up with the following command:

cd Build

BUILD_DIR=/home/jozefchutka/ffmpeg-wasm/build/
TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake

emmake cmake .. -G"Unix Makefiles" -DCMAKE_INSTALL_PREFIX=$BUILD_DIR -DCMAKE_TOOLCHAIN_FILE=$TOOLCHAIN_FILE -DBUILD_SHARED_LIBS=OFF -DCMAKE_BUILD_TYPE=Release -DBUILD_TESTING=OFF -DCMAKE_HAVE_LIBC_PTHREAD=On -DCMAKE_C_FLAGS="-O3 -I/home/jozefchutka/ffmpeg-wasm/build/include -s USE_PTHREADS=1 -msimd128"

emmake make -j

however the process fails on:

...
[ 95%] Building C object Source/App/EncApp/CMakeFiles/SvtAv1EncApp.dir/EbTime.c.o
[ 96%] Linking C executable ../../../../Bin/Release/SvtAv1EncApp.js
emcc: error: noexecstack: No such file or directory ("noexecstack" was expected to be an input file, based on the commandline arguments provided)
make[2]: *** [Source/App/EncApp/CMakeFiles/SvtAv1EncApp.dir/build.make:213: ../Bin/Release/SvtAv1EncApp.js] Error 1
make[1]: *** [CMakeFiles/Makefile2:574: Source/App/EncApp/CMakeFiles/SvtAv1EncApp.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

Generated build.make and link.txt which contains some relevant info.

211: ../Bin/Release/SvtAv1EncApp.js: Source/App/EncApp/CMakeFiles/SvtAv1EncApp.dir/link.txt
212:	@$(CMAKE_COMMAND) -E cmake_echo_color --switch=$(COLOR) --green --bold --progress-dir=/home/jozefchutka/ffmpeg-wasm/modules/svtav1/Build/CMakeFiles --progress-num=$(CMAKE_PROGRESS_8) "Linking C executable ../../../../Bin/Release/SvtAv1EncApp.js"
213:	cd /home/jozefchutka/ffmpeg-wasm/modules/svtav1/Build/Source/App/EncApp && $(CMAKE_COMMAND) -E cmake_link_script CMakeFiles/SvtAv1EncApp.dir/link.txt --verbose=$(VERBOSE)

/home/jozefchutka/ffmpeg-wasm/modules/emsdk/upstream/emscripten/emcc -O3 -I/home/jozefchutka/ffmpeg-wasm/build/include -s USE_PTHREADS=1 -msimd128 -O3 -DNDEBUG  -z noexecstack -z relro -z now @CMakeFiles/SvtAv1EncApp.dir/objects1.rsp -o ../../../../Bin/Release/SvtAv1EncApp.js @CMakeFiles/SvtAv1EncApp.dir/linklibs.rsp

As I am not fluent in c/c++ and related build stack, I am not sure if the problem is my build misconfiguration, svt-av1 sources or emscripten.

Please help me resolve the issue or at least identify the cause, so I can continue in relevant issue tracker.

The issue was resolved by including an extra flag -DBUILD_APPS=OFF, which caused that the problematic line is not executed.

For your reference, the line that adds those linker flags is here: https://gitlab.com/AOMediaCodec/SVT-AV1/-/blob/v1.4.1/CMakeLists.txt#L211

if(UNIX)
    if(APPLE)
        ...
    else()
        set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -z noexecstack -z relro -z now")
    endif()
endif()

Since this is setting a variable (and variables are scoped to CMake directories), this variable must be applying to a target in the same or deeper directory scope, and the error is happening because these linker flags are not supported by emcc (the Emscripten compiler and linker). The reference docs for Emscripten's commandline flags can be found here: https://emscripten.org/docs/tools_reference/emcc.html#command-line-syntax. I have also found this resource useful for finding out which option flags are for compiling and which are for linking: https://emsettings.surma.technology/.

Looking through the target definitions in SVT-AV1, you'll find that executables are defined in the Source/App folder: Source/App/DecApp/CMakeLists.txt and Source/App/EncApp/CMakeLists.txt. Those executables get added by default.

See this line in the root CMakeLists.txt (notice that the default is ON):

option(BUILD_APPS "Build Enc and Dec Apps" ON)

And these lines that add_subdirectory the apps folders:

if(BUILD_APPS AND BUILD_ENC)
    add_subdirectory(Source/App/EncApp)
endif()
if(BUILD_APPS AND BUILD_DEC)
    add_subdirectory(Source/App/DecApp)
endif()

So if you don't need those apps to be built for your purposes, you can stop them from being built by adding -DBUILD_APPS=OFF in your configure command.

If you do need those to be built for your purposes, raise an issue ticket or implement changes in a Merge Request to somehow resolve that issue when the Emscripten toolchain is being used. You can use the EMSCRIPTEN CMake variable, which the Emscripten CMake toolchain file defines to do the platform check.