Feature request: suppress `undefined symbol` warning for specific symbols

[hoodmane]

There are some symbols that I manually add to wasmImports in the instantiateWasm hook. I would like to be able to suppress warnings about these being missing specifically, without turning off all missing symbol warnings.

[RReverser]

Isn't that the one we talked about recently, the one you can use Stub Libraries for?

[sbc100]

Do you mean you want some kind of flag like -sALLOW_UNDEFINED=foo,bar,baz and then a way to inject those symbols at runtime? With and an error at runtime if they are missing then?

[hoodmane]

I think stub libraries is a feature of wasm-ld that Emscripten can use but we can't directly access as Emscripten users. But I could be wrong. One way to deal with this for now is to define an empty EM_JS function:

EM_JS(int, some_import, (sig), {});

and then we can assign over it in Module.instantiateWasm.

[sbc100]

You could also add a dummy JS library:

$ cat libfoo.js
addToLibrary({
  foo: () => {}
  bar: () => {}
}
$ emcc --js-library=libfoo.js ....

Then you would need to somehow overwrite the empty definitions of foo and bar` in the generated JS code.

[sbc100]

Regarding the stub library feature of wasm-ld, I think can pass you own stuff libraries which will make wasm-ld happy, and it won't report errors.

$ cat libextern.so 
#STUB
foo
bar
$ cat test.c 
extern void foo();

int main() {
  foo();
}
$ ./emcc test.c libextern.so 
error: undefined symbol: foo (referenced by root reference (e.g. compiled C/C++ code))
warning: To disable errors for undefined symbols use `-sERROR_ON_UNDEFINED_SYMBOLS=0`
warning: _foo may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
Error: Aborting compilation due to previous errors
    at finalCombiner (file:///usr/local/google/home/sbc/dev/wasm/emscripten/src/jsifier.mjs:886:13)
    at Module.runJSify (file:///usr/local/google/home/sbc/dev/wasm/emscripten/src/jsifier.mjs:921:5)
    at file:///usr/local/google/home/sbc/dev/wasm/emscripten/tools/compiler.mjs:97:17
emcc: error: '/usr/local/google/home/sbc/dev/wasm/emsdk/node/22.16.0_64bit/bin/node /usr/local/google/home/sbc/dev/wasm/emscripten/tools/compiler.mjs -' failed (returned 1)

However, as you can see, while wasm-ld no longer complains about these symbols, the JS compiler still does.. so the stub library on its own is not enough here.

Could you explain a little more about your use case? Where are these unknown symbols coming from? What is stopping you creating a JS library file for contains all the symbols?