How to export C function in Emscripten when using CMake

Question

In this tutorial it shows the following example for exporting C functions

./emcc tests/hello_function.cpp -o function.html -s EXPORTED_FUNCTIONS='["_int_sqrt"]' -s EXPORTED_RUNTIME_METHODS='["ccall", "cwrap"]'

I would like to do the same except that I use CMake like this

cd bin
emcmake cmake ../src
emmake make

What is the canonical way of specifying -s in emmake? Should I add it to CMakeLists.txt like

set(EXPORTED_FUNCTIONS '["_int_sqrt"]')

or do something similar?

Answer 1

What I figured out so far is that it can be achieved CMake with the following settings

# Here you can add -s flag during compiling object files
add_definitions("-s EXPORTED_RUNTIME_METHODS='[\"ccall\",\"cwrap\"]'")
add_definitions("-s EXTRA_EXPORTED_RUNTIME_METHODS='[\"ccall\",\"cwrap\"]'")
add_definitions("-s EXPORTED_FUNCTIONS='[\"_testInt\"]'")
# Here you can add -s flag during linking
set_target_properties(web_mealy_compiler PROPERTIES LINK_FLAGS "-s EXTRA_EXPORTED_RUNTIME_METHODS=['ccall','cwrap']")
# Set this if you want to to generate sample html file
set(CMAKE_EXECUTABLE_SUFFIX ".html")

Then you should be able to call C functions from javascript as follows:

<script type="text/javascript">
     
    Module['onRuntimeInitialized'] = function() {
     
        console.log("wasm loaded ");
        
        console.log(Module.ccall); // make sure it's not undefined
        console.log(Module._testInt); // make sure it's not undefined
        console.log(Module._testInt()); // this should work
        console.log( Module.ccall('testInt', // name of C function
            'number', // return type
             [], // argument types
             []) // argument values
        );
    }
</script>

And this is my definition of C function:

#include <emscripten.h>
EMSCRIPTEN_KEEPALIVE
int testInt(){
    return 69420;
}