How to load dynamiclib automatically without invoke dlopen+dlsym?

[oatgnauh]

emsdk 3.1.54
multi thread browser environment
Now I download sideModule into FS and passing fs path to dlopen, then use dlsym to load apis，I wonder if there is a better way to do it automatically.

I add " \ -sMAIN_MODULE=2 \ -sAUTOLOAD_DYLIBS=1 \ ${ffmpeg_DIR}/lib/libffmpeg${WASM_SUBFFIX_NAME}.wasm \ "
to main module link flag, according to official doc, it should be load-time dynamic link

[oatgnauh]

I learn something from

AUTOLOAD_DYLIBS just help me download simd module, can not do dlopen&dlsym

also when I review this js code:

var loadDylibs = () => {
 if (!dynamicLibraries.length) {
  reportUndefinedSymbols();
  return;
 }
 addRunDependency("loadDylibs");
 dynamicLibraries.reduce((chain, lib) => chain.then(() => loadDynamicLibrary(lib, {
  loadAsync: true,
  global: true,
  nodelete: true,
  allowUndefined: true
 })), Promise.resolve()).then(() => {
  reportUndefinedSymbols();
  removeRunDependency("loadDylibs");
 });
};

seems if you want to do load-time dynamick link, you have to set the array dynamicLibraries, which is define at var dynamicLibraries = Module["dynamicLibraries"] || [];

but still have some problem. I set
Module["dynamicLibraries"] = ["libffmpeg_simd.wasm"]
and i got a crash

still confusing..

[oatgnauh]

however, I found that even if i am using load-time link, it would invoke loadDynamicLibrary automatically by createWasm -> loadDylibs ->loadDynamicLibrary, but C function symbols are not being export.

here is dlsym function in js

var __dlsym_js = (handle, symbol, symbolIndex) => {
 symbol = UTF8ToString(symbol);
 var result;
 var newSymIndex;
 var lib = LDSO.loadedLibsByHandle[handle];
 if (!lib.exports.hasOwnProperty(symbol) || lib.exports[symbol].stub) {
  dlSetError(`Tried to lookup unknown symbol "${symbol}" in dynamic lib: ${lib.name}`);
  return 0;
 }
 newSymIndex = Object.keys(lib.exports).indexOf(symbol);
 result = lib.exports[symbol];
 if (typeof result == "function") {
  var addr = getFunctionAddress(result);
  if (addr) {
   result = addr;
  } else {
   result = addFunction(result, result.sig);
   GROWABLE_HEAP_U32()[((symbolIndex) >> 2)] = newSymIndex;
  }
 }
 return result;
};

most importance call is getFunctionAddress and addFunction, none of two have been invoke in loadDynamicLibrary.
So I guess this "load-time linking" simply do stuff as dlopen ?

[oatgnauh]

thanks myself, I figure out Module["dynamicLibraries"] = ["libffmpeg_simd.wasm"] should be add in pre.js, everything work.
remember add -sAUTOLOAD_DYLIBS=1

[sbc100]

AUTOLOAD_DYLIBS is enabled by default so should need to pass -sAUTOLOAD_DYLIBS=1

When you pass libffmpeg_simd.wasm on the command line when linking your main module then libffmpeg_simd.wasm should automatically be added dynamicLibraries.. you should not need to add it manually anywhere.

[oatgnauh]

seems something wrong, ibffmpeg_simd.wasm bas been pass to command line but Module["dynamicLibraries"] = ["libffmpeg_simd.wasm"] not add to js file

here is default output

var dynamicLibraries = Module["dynamicLibraries"] || [];

[oatgnauh]

I search the whole project

only notice that in upstream/emscripten/test/test_core.py

would create an pre.js including Module['dynamicLibraries'] = ['liblib.so'].
IIUC, this is just a test file

[sbc100]

If you look at your main module it should contain dylink header which includes the libraries it depends on:

$ wasm-objdump -x a.out.wasm
a.out.wasm:     file format wasm 0x1

Section Details:

Custom:
 - name: "dylink.0"
 - mem_size     : 4688
 - mem_p2align  : 4
 - table_size   : 5
 - table_p2align: 0
 - needed_dynlibs[1]:
  - libside.wasm                    <--- here you should see `libffmpeg_simd.wasm`

The emscripten startup code will add these libraries to Module['dynamicLibraries'] on startup:

emscripten/src/preamble.js

Lines 957 to 961 in 7f8a05d

	#if AUTOLOAD_DYLIBS
	if (metadata.neededDynlibs) {
	dynamicLibraries = metadata.neededDynlibs.concat(dynamicLibraries);
	}
	#endif

Can you check this code fragment is in your generated code?

[oatgnauh]

True, you are right

Custom:
 - name: "dylink.0"
 - mem_size     : 22830136
 - mem_p2align  : 4
 - table_size   : 77119
 - table_p2align: 0
 - needed_dynlibs[1]:
  - libffmpeg_simd.wasm

Module["dynamicLibraries"] dont need to add manually