src/library_dylink.js

// ==========================================================================
// Dynamic library loading
//
// ==========================================================================

var LibraryDylink = {
#if RELOCATABLE
  $asmjsMangle: function(x) {
    var unmangledSymbols = {{{ buildStringArray(WASM_SYSTEM_EXPORTS) }}};
    return x.indexOf('dynCall_') == 0 || unmangledSymbols.indexOf(x) != -1 ? x : '_' + x;
  },

  $resolveGlobalSymbol__deps: ['$asmjsMangle'],
  $resolveGlobalSymbol: function(symName, direct) {
    var sym;
#if !WASM_BIGINT
    if (direct) {
      // First look for the orig$ symbol which is the symbols without
      // any legalization performed.   Here we look on the 'asm' object
      // to avoid any JS wrapping of the symbol.
      sym = Module['asm']['orig$' + symName];
    }
#endif
    // Then look for the unmangled name itself.
    if (!sym) {
      sym = Module['asm'][symName];
    }
    // fall back to the mangled name on the module object which could include
    // JavaScript functions and wrapped native functions.
#if !WASM_BIGINT
    if (!sym && direct) {
      sym = Module['_orig$' + symName];
    }
#endif

    if (!sym) {
      sym = Module[asmjsMangle(symName)];
    }

    if (!sym && symName.indexOf('invoke_') == 0) {
      sym = createInvokeFunction(symName.split('_')[1]);
    }

    return sym;
  },

  $GOT: {},

  // Create globals to each imported symbol.  These are all initialized to zero
  // and get assigned later in `updateGOT`
  $GOTHandler__deps: ['$GOT'],
  $GOTHandler: {
    'get': function(obj, symName) {
      if (!GOT[symName]) {
        GOT[symName] = new WebAssembly.Global({value: 'i32', mutable: true});
#if DYLINK_DEBUG
        err("new GOT entry: " + symName);
#endif
      }
      return GOT[symName]
    }
  },

  $isInternalSym: function(symName) {
    // TODO: find a way to mark these in the binary or avoid exporting them.
    return [
      '__cpp_exception',
      '__wasm_apply_data_relocs',
      '__dso_handle',
      '__set_stack_limits'
    ].indexOf(symName) != -1
#if SPLIT_MODULE
        // Exports synthesized by wasm-split should be prefixed with '%'
        || symName[0] == '%'
#endif
    ;
  },

  $updateGOT__deps: ['$GOT', '$isInternalSym'],
  $updateGOT: function(exports) {
#if DYLINK_DEBUG
    err("updateGOT: " + Object.keys(exports).length);
#endif
    for (var symName in exports) {
      if (isInternalSym(symName)) {
        continue;
      }

      var replace = false;
      var value = exports[symName];
#if !WASM_BIGINT
      if (symName.indexOf('orig$') == 0) {
        symName = symName.split('$')[1];
        replace = true;
      }
#endif

      if (!GOT[symName]) {
        GOT[symName] = new WebAssembly.Global({value: 'i32', mutable: true});
      }
      if (replace || GOT[symName].value == 0) {
        if (typeof value === 'function') {
          GOT[symName].value = addFunctionWasm(value);
#if DYLINK_DEBUG
          err("updateGOT FUNC: " + symName + ' : ' + GOT[symName].value);
#endif
        } else if (typeof value === 'number') {
          GOT[symName].value = value;
        } else {
          err("unhandled export type for `" + symName + "`: " + (typeof value));
        }
#if DYLINK_DEBUG
        err("updateGOT: " + symName + ' : ' + GOT[symName].value);
#endif
      }
#if DYLINK_DEBUG
      else if (GOT[symName].value != value) {
        err("updateGOT: EXISTING SYMBOL: " + symName + ' : ' + GOT[symName].value + " " + value);
      }
#endif
    }
#if DYLINK_DEBUG
    err("done updateGOT");
#endif
  },

  // Applies relocations to exported things.
  $relocateExports__deps: ['$updateGOT'],
  $relocateExports: function(exports, memoryBase) {
    var relocated = {};

    for (var e in exports) {
      var value = exports[e];
#if SPLIT_MODULE
      // Do not modify exports synthesized by wasm-split
      if (e.startsWith('%')) {
        relocated[e] = value
        continue;
      }
#endif
      if (typeof value === 'object') {
        // a breaking change in the wasm spec, globals are now objects
        // https://github.com/WebAssembly/mutable-global/issues/1
        value = value.value;
      }
      if (typeof value === 'number') {
        value += memoryBase;
      }
      relocated[e] = value;
    }
    updateGOT(relocated);
    return relocated;
  },

  $reportUndefinedSymbols__deps: ['$GOT', '$resolveGlobalSymbol'],
  $reportUndefinedSymbols: function() {
#if DYLINK_DEBUG
    err('reportUndefinedSymbols');
#endif
    for (var symName in GOT) {
      if (GOT[symName].value == 0) {
        var value = resolveGlobalSymbol(symName, true)
#if ASSERTIONS
        assert(value, 'undefined symbol `' + symName + '`. perhaps a side module was not linked in? if this global was expected to arrive from a system library, try to build the MAIN_MODULE with EMCC_FORCE_STDLIBS=1 in the environment');
#endif
#if DYLINK_DEBUG
        err('assigning dynamic symbol from main module: ' + symName + ' -> ' + value);
#endif
        if (typeof value === 'function') {
          GOT[symName].value = addFunctionWasm(value, value.sig);
#if DYLINK_DEBUG
          err('assigning table entry for : ' + symName + ' -> ' + GOT[symName].value);
#endif
        } else if (typeof value === 'number') {
          GOT[symName].value = value;
        } else {
          assert(false, 'bad export type for `' + symName + '`: ' + (typeof value));
        }
      }
    }
#if DYLINK_DEBUG
    err('done reportUndefinedSymbols');
#endif
  },
#endif

#if MAIN_MODULE == 0
  dlopen: function(filename, flag) {
    abort("To use dlopen, you need to use Emscripten's linking support, see https://github.com/emscripten-core/emscripten/wiki/Linking");
  },
  dlclose: function(handle) {
    abort("To use dlopen, you need to use Emscripten's linking support, see https://github.com/emscripten-core/emscripten/wiki/Linking");
  },
  dlsym: function(handle, symbol) {
    abort("To use dlopen, you need to use Emscripten's linking support, see https://github.com/emscripten-core/emscripten/wiki/Linking");
  },
  dlerror: function() {
    abort("To use dlopen, you need to use Emscripten's linking support, see https://github.com/emscripten-core/emscripten/wiki/Linking");
  },
  dladdr: function(address, info) {
    abort("To use dlopen, you need to use Emscripten's linking support, see https://github.com/emscripten-core/emscripten/wiki/Linking");
  },
#else // MAIN_MODULE != 0
  $DLFCN: {
    error: null,
    errorMsg: null,
  },

  // dynamic linker/loader (a-la ld.so on ELF systems)
  $LDSO: {
    // next free handle to use for a loaded dso.
    // (handle=0 is avoided as it means "error" in dlopen)
    nextHandle: 1,
    // handle -> dso [refcount, name, module, global]
    loadedLibs: {},
    // name   -> handle
    loadedLibNames: {},
  },

  // Dynamic version of shared.py:make_invoke.  This is needed for invokes
  // that originate from side modules since these are not known at JS
  // generation time.
  $createInvokeFunction: function(sig) {
    return function() {
      var sp = stackSave();
      try {
        return dynCall(sig, arguments[0], Array.prototype.slice.call(arguments, 1));
      } catch(e) {
        stackRestore(sp);
        if (e !== e+0 && e !== 'longjmp') throw e;
        _setThrew(1, 0);
      }
    }
  },

  // We support some amount of allocation during startup in the case of
  // dynamic linking, which needs to allocate memory for dynamic libraries that
  // are loaded. That has to happen before the main program can start to run,
  // because the main program needs those linked in before it runs (so we can't
  // use normally malloc from the main program to do these allocations).

  // Allocate memory even if malloc isn't ready yet.
  $getMemory__deps: ['$GOT'],
  $getMemory: function(size) {
    // After the runtime is initialized, we must only use sbrk() normally.
#if DYLINK_DEBUG
    err("getMemory: " + size + " runtimeInitialized=" + runtimeInitialized);
#endif
    if (runtimeInitialized)
      return _malloc(size);
    var ret = Module['___heap_base'];
    var end = (ret + size + 15) & -16;
#if ASSERTIONS
    assert(end <= HEAP8.length, 'failure to getMemory - memory growth etc. is not supported there, call malloc/sbrk directly or increase INITIAL_MEMORY');
#endif
    Module['___heap_base'] = end;
    GOT['__heap_base'].value = end;
    return ret;
  },

  // fetchBinary fetches binary data @ url. (async)
  $fetchBinary: function(url) {
    return fetch(url, { credentials: 'same-origin' }).then(function(response) {
      if (!response['ok']) {
        throw "failed to load binary file at '" + url + "'";
      }
      return response['arrayBuffer']();
    }).then(function(buffer) {
      return new Uint8Array(buffer);
    });
  },

  // returns the side module metadata as an object
  // { memorySize, memoryAlign, tableSize, tableAlign, neededDynlibs}
  $getDylinkMetadata: function(binary) {
    var next = 0;
    function getLEB() {
      var ret = 0;
      var mul = 1;
      while (1) {
        var byte = binary[next++];
        ret += ((byte & 0x7f) * mul);
        mul *= 0x80;
        if (!(byte & 0x80)) break;
      }
      return ret;
    }

    if (binary instanceof WebAssembly.Module) {
      var dylinkSection = WebAssembly.Module.customSections(binary, "dylink");
      assert(dylinkSection.length != 0, 'need dylink section');
      binary = new Int8Array(dylinkSection[0]);
    } else {
      var int32View = new Uint32Array(new Uint8Array(binary.subarray(0, 24)).buffer);
      assert(int32View[0] == 0x6d736100, 'need to see wasm magic number'); // \0asm
      // we should see the dylink section right after the magic number and wasm version
      assert(binary[8] === 0, 'need the dylink section to be first')
      next = 9;
      getLEB(); //section size
      assert(binary[next] === 6);                 next++; // size of "dylink" string
      assert(binary[next] === 'd'.charCodeAt(0)); next++;
      assert(binary[next] === 'y'.charCodeAt(0)); next++;
      assert(binary[next] === 'l'.charCodeAt(0)); next++;
      assert(binary[next] === 'i'.charCodeAt(0)); next++;
      assert(binary[next] === 'n'.charCodeAt(0)); next++;
      assert(binary[next] === 'k'.charCodeAt(0)); next++;
    }

    var customSection = {};
    customSection.memorySize = getLEB();
    customSection.memoryAlign = getLEB();
    customSection.tableSize = getLEB();
    customSection.tableAlign = getLEB();
    // shared libraries this module needs. We need to load them first, so that
    // current module could resolve its imports. (see tools/shared.py
    // WebAssembly.make_shared_library() for "dylink" section extension format)
    var neededDynlibsCount = getLEB();
    customSection.neededDynlibs = [];
    for (var i = 0; i < neededDynlibsCount; ++i) {
      var nameLen = getLEB();
      var nameUTF8 = binary.subarray(next, next + nameLen);
      next += nameLen;
      var name = UTF8ArrayToString(nameUTF8, 0);
      customSection.neededDynlibs.push(name);
    }
    return customSection;
  },

  // Module.symbols <- libModule.symbols (flags.global handler)
  $mergeLibSymbols__deps: ['$asmjsMangle'],
  $mergeLibSymbols: function(libModule, libName) {
    // add symbols into global namespace TODO: weak linking etc.
    for (var sym in libModule) {
      if (!libModule.hasOwnProperty(sym)) {
        continue;
      }

      // When RTLD_GLOBAL is enable, the symbols defined by this shared object will be made
      // available for symbol resolution of subsequently loaded shared objects.
      //
      // We should copy the symbols (which include methods and variables) from SIDE_MODULE to MAIN_MODULE.

      var module_sym = asmjsMangle(sym);

      if (!Module.hasOwnProperty(module_sym)) {
        Module[module_sym] = libModule[sym];
      }
#if ASSERTIONS == 2
      else {
        var curr = Module[sym], next = libModule[sym];
        // don't warn on functions - might be odr, linkonce_odr, etc.
        if (!(typeof curr === 'function' && typeof next === 'function')) {
          err("warning: symbol '" + sym + "' from '" + libName + "' already exists (duplicate symbol? or weak linking, which isn't supported yet?)"); // + [curr, ' vs ', next]);
        }
      }
#endif
    }
  },

  // Loads a side module from binary data or compiled Module. Returns the module's exports or a
  // promise that resolves to its exports if the loadAsync flag is set.
  $loadWebAssemblyModule__deps: ['$loadDynamicLibrary', '$createInvokeFunction', '$getMemory', '$relocateExports', '$resolveGlobalSymbol', '$GOTHandler', '$getDylinkMetadata'],
  $loadWebAssemblyModule: function(binary, flags) {
    var metadata = getDylinkMetadata(binary);
    var memorySize = metadata.memorySize;
    var memoryAlign = metadata.memoryAlign;
    var tableSize = metadata.tableSize;
    var tableAlign = metadata.tableAlign;
    var neededDynlibs = metadata.neededDynlibs;

    // loadModule loads the wasm module after all its dependencies have been loaded.
    // can be called both sync/async.
    function loadModule() {
      // alignments are powers of 2
      memoryAlign = Math.pow(2, memoryAlign);
      tableAlign = Math.pow(2, tableAlign);
      // finalize alignments and verify them
      memoryAlign = Math.max(memoryAlign, STACK_ALIGN); // we at least need stack alignment
#if ASSERTIONS
      assert(tableAlign === 1, 'invalid tableAlign ' + tableAlign);
#endif
      // prepare memory
      var memoryBase = alignMemory(getMemory(memorySize + memoryAlign), memoryAlign); // TODO: add to cleanups
#if DYLINK_DEBUG
      err("loadModule: memoryBase=" + memoryBase);
#endif
      // prepare env imports
      var env = asmLibraryArg;
      // TODO: use only __memory_base and __table_base, need to update asm.js backend
      var table = wasmTable;
      var tableBase = table.length;
      var originalTable = table;
      table.grow(tableSize);
      assert(table === originalTable);
      // zero-initialize memory and table
      // The static area consists of explicitly initialized data, followed by zero-initialized data.
      // The latter may need zeroing out if the MAIN_MODULE has already used this memory area before
      // dlopen'ing the SIDE_MODULE.  Since we don't know the size of the explicitly initialized data
      // here, we just zero the whole thing, which is suboptimal, but should at least resolve bugs
      // from uninitialized memory.
#if USE_PTHREADS
      // in a pthread the module heap was already allocated and initialized in the main thread.
      if (!ENVIRONMENT_IS_PTHREAD) {
#endif
        for (var i = memoryBase; i < memoryBase + memorySize; i++) {
          HEAP8[i] = 0;
        }
#if USE_PTHREADS
      }
#endif
      for (var i = tableBase; i < tableBase + tableSize; i++) {
        table.set(i, null);
      }

      // This is the export map that we ultimately return.  We declare it here
      // so it can be used within resolveSymbol.  We resolve symbols against
      // this local symbol map in the case there they are not present on the
      // global Module object.  We need this fallback because:
      // a) Modules sometime need to import their own symbols
      // b) Symbols from side modules are not always added to the global namespace.
      var moduleExports;

      function resolveSymbol(sym) {
        var resolved = resolveGlobalSymbol(sym, false);
        if (!resolved) {
          resolved = moduleExports[sym];
        }
#if ASSERTIONS
        assert(resolved, 'undefined symbol `' + sym + '`. perhaps a side module was not linked in? if this global was expected to arrive from a system library, try to build the MAIN_MODULE with EMCC_FORCE_STDLIBS=1 in the environment');
#endif
        return resolved;
      }

      // copy currently exported symbols so the new module can import them
      for (var x in Module) {
        if (!(x in env)) {
          env[x] = Module[x];
        }
      }

      // TODO kill ↓↓↓ (except "symbols local to this module", it will likely be
      // not needed if we require that if A wants symbols from B it has to link
      // to B explicitly: similarly to -Wl,--no-undefined)
      //
      // wasm dynamic libraries are pure wasm, so they cannot assist in
      // their own loading. When side module A wants to import something
      // provided by a side module B that is loaded later, we need to
      // add a layer of indirection, but worse, we can't even tell what
      // to add the indirection for, without inspecting what A's imports
      // are. To do that here, we use a JS proxy (another option would
      // be to inspect the binary directly).
      var proxyHandler = {
        'get': function(obj, prop) {
          // symbols that should be local to this module
          switch (prop) {
            case '__memory_base':
              return memoryBase;
            case '__table_base':
              return tableBase;
          }
          if (prop in obj) {
            return obj[prop]; // already present
          }
          // otherwise this is regular function import - call it indirectly
          var resolved;
          return obj[prop] = function() {
            if (!resolved) resolved = resolveSymbol(prop, true);
            return resolved.apply(null, arguments);
          };
        }
      };
      var proxy = new Proxy(env, proxyHandler);
      var info = {
        'GOT.mem': new Proxy(asmLibraryArg, GOTHandler),
        'GOT.func': new Proxy(asmLibraryArg, GOTHandler),
        'env': proxy,
        {{{ WASI_MODULE_NAME }}}: proxy,
      };

      function postInstantiation(instance) {
#if ASSERTIONS
        // the table should be unchanged
        assert(table === originalTable);
        assert(table === wasmTable);
#endif
        // add new entries to functionsInTableMap
        for (var i = 0; i < tableSize; i++) {
          var item = table.get(tableBase + i);
#if ASSERTIONS
          // verify that the new table region was filled in
          assert(item !== undefined, 'table entry was not filled in');
#endif
          // Ignore null values.
          if (item) {
            functionsInTableMap.set(item, tableBase + i);
          }
        }
        moduleExports = relocateExports(instance.exports, memoryBase);
        if (!flags.allowUndefined) {
          reportUndefinedSymbols();
        }
#if STACK_OVERFLOW_CHECK >= 2
        moduleExports['__set_stack_limits']({{{ STACK_BASE }}} , {{{ STACK_MAX }}});
#endif

        // initialize the module
#if USE_PTHREADS
        // The main thread does a full __post_instantiate (which includes a call
        // to emscripten_tls_init), but secondary threads should not call static
        // constructors in general - emscripten_tls_init is the exception.
        if (ENVIRONMENT_IS_PTHREAD) {
          init = moduleExports['emscripten_tls_init'];
          assert(init);
#if DYLINK_DEBUG
          out("adding to tlsInitFunctions: " + init);
#endif
          PThread.tlsInitFunctions.push(init);
        } else {
#endif
          var init = moduleExports['__post_instantiate'];
          if (init) {
            if (runtimeInitialized) {
              init();
            } else {
              // we aren't ready to run compiled code yet
              __ATINIT__.push(init);
            }
          }
#if USE_PTHREADS
        }
#endif
        return moduleExports;
      }

      if (flags.loadAsync) {
        if (binary instanceof WebAssembly.Module) {
          var instance = new WebAssembly.Instance(binary, info);
          return Promise.resolve(postInstantiation(instance));
        }
        return WebAssembly.instantiate(binary, info).then(function(result) {
          return postInstantiation(result.instance);
        });
      }

      var module = binary instanceof WebAssembly.Module ? binary : new WebAssembly.Module(binary);
      var instance = new WebAssembly.Instance(module, info);
      return postInstantiation(instance);
    }

    // now load needed libraries and the module itself.
    if (flags.loadAsync) {
      return neededDynlibs.reduce(function(chain, dynNeeded) {
        return chain.then(function() {
          return loadDynamicLibrary(dynNeeded, flags);
        });
      }, Promise.resolve()).then(function() {
        return loadModule();
      });
    }

    neededDynlibs.forEach(function(dynNeeded) {
      loadDynamicLibrary(dynNeeded, flags);
    });
    return loadModule();
  },

  // loadDynamicLibrary loads dynamic library @ lib URL / path and returns handle for loaded DSO.
  //
  // Several flags affect the loading:
  //
  // - if flags.global=true, symbols from the loaded library are merged into global
  //   process namespace. Flags.global is thus similar to RTLD_GLOBAL in ELF.
  //
  // - if flags.nodelete=true, the library will be never unloaded. Flags.nodelete
  //   is thus similar to RTLD_NODELETE in ELF.
  //
  // - if flags.loadAsync=true, the loading is performed asynchronously and
  //   loadDynamicLibrary returns corresponding promise.
  //
  // - if flags.fs is provided, it is used as FS-like interface to load library data.
  //   By default, when flags.fs=undefined, native loading capabilities of the
  //   environment are used.
  //
  // If a library was already loaded, it is not loaded a second time. However
  // flags.global and flags.nodelete are handled every time a load request is made.
  // Once a library becomes "global" or "nodelete", it cannot be removed or unloaded.
  $loadDynamicLibrary__deps: ['$LDSO', '$loadWebAssemblyModule', '$asmjsMangle', '$fetchBinary', '$isInternalSym', '$mergeLibSymbols'],
  $loadDynamicLibrary: function(lib, flags) {
    if (lib == '__main__' && !LDSO.loadedLibNames[lib]) {
      LDSO.loadedLibs[-1] = {
        refcount: Infinity,   // = nodelete
        name:     '__main__',
        module:   Module['asm'],
        global:   true
      };
      LDSO.loadedLibNames['__main__'] = -1;
    }

    // when loadDynamicLibrary did not have flags, libraries were loaded globally & permanently
    flags = flags || {global: true, nodelete: true}

    var handle = LDSO.loadedLibNames[lib];
    var dso;
    if (handle) {
      // the library is being loaded or has been loaded already.
      //
      // however it could be previously loaded only locally and if we get
      // load request with global=true we have to make it globally visible now.
      dso = LDSO.loadedLibs[handle];
      if (flags.global && !dso.global) {
        dso.global = true;
        if (dso.module !== 'loading') {
          // ^^^ if module is 'loading' - symbols merging will be eventually done by the loader.
          mergeLibSymbols(dso.module, lib)
        }
      }
      // same for "nodelete"
      if (flags.nodelete && dso.refcount !== Infinity) {
        dso.refcount = Infinity;
      }
      dso.refcount++
      return flags.loadAsync ? Promise.resolve(handle) : handle;
    }

    // allocate new DSO & handle
    handle = LDSO.nextHandle++;
    dso = {
      refcount: flags.nodelete ? Infinity : 1,
      name:     lib,
      module:   'loading',
      global:   flags.global,
    };
    LDSO.loadedLibNames[lib] = handle;
    LDSO.loadedLibs[handle] = dso;

    // libData <- libFile
    function loadLibData(libFile) {
      // for wasm, we can use fetch for async, but for fs mode we can only imitate it
      if (flags.fs) {
        var libData = flags.fs.readFile(libFile, {encoding: 'binary'});
        if (!(libData instanceof Uint8Array)) {
          libData = new Uint8Array(libData);
        }
        return flags.loadAsync ? Promise.resolve(libData) : libData;
      }

      if (flags.loadAsync) {
        return fetchBinary(libFile);
      }
      // load the binary synchronously
      return readBinary(libFile);
    }

    // libModule <- lib
    function getLibModule() {
      // lookup preloaded cache first
      if (Module['preloadedWasm'] !== undefined &&
          Module['preloadedWasm'][lib] !== undefined) {
        var libModule = Module['preloadedWasm'][lib];
        return flags.loadAsync ? Promise.resolve(libModule) : libModule;
      }

      // module not preloaded - load lib data and create new module from it
      if (flags.loadAsync) {
        return loadLibData(lib).then(function(libData) {
          return loadWebAssemblyModule(libData, flags);
        });
      }

      return loadWebAssemblyModule(loadLibData(lib), flags);
    }

    // module for lib is loaded - update the dso & global namespace
    function moduleLoaded(libModule) {
      if (dso.global) {
        mergeLibSymbols(libModule, lib);
      }
      dso.module = libModule;
    }

    if (flags.loadAsync) {
      return getLibModule().then(function(libModule) {
        moduleLoaded(libModule);
        return handle;
      })
    }

    moduleLoaded(getLibModule());
    return handle;
  },

  $preloadDylibs__deps: ['$loadDynamicLibrary', '$reportUndefinedSymbols'],
  $preloadDylibs: function() {
#if DYLINK_DEBUG
    err('preloadDylibs');
#endif
    if (!dynamicLibraries.length) {
#if DYLINK_DEBUG
      err('preloadDylibs: no libraries to preload');
#endif
      reportUndefinedSymbols();
      return;
    }

    // if we can load dynamic libraries synchronously, do so, otherwise, preload
    if (!readBinary) {
      // we can't read binary data synchronously, so preload
      addRunDependency('preloadDylibs');
      dynamicLibraries.reduce(function(chain, lib) {
        return chain.then(function() {
          return loadDynamicLibrary(lib, {loadAsync: true, global: true, nodelete: true, allowUndefined: true});
        });
      }, Promise.resolve()).then(function() {
        // we got them all, wonderful
        removeRunDependency('preloadDylibs');
        reportUndefinedSymbols();
      });
      return;
    }

    dynamicLibraries.forEach(function(lib) {
      // libraries linked to main never go away
      loadDynamicLibrary(lib, {global: true, nodelete: true, allowUndefined: true});
    });
    reportUndefinedSymbols();
  },

  // void* dlopen(const char* filename, int flags);
  dlopen__deps: ['$DLFCN', '$FS', '$ENV'],
  dlopen__proxy: 'sync',
  dlopen__sig: 'iii',
  dlopen: function(filenameAddr, flags) {
    // void *dlopen(const char *file, int mode);
    // http://pubs.opengroup.org/onlinepubs/009695399/functions/dlopen.html
    var searchpaths = [];
    var filename;
    if (filenameAddr === 0) {
      filename = '__main__';
    } else {
      filename = UTF8ToString(filenameAddr);

      var isValidFile = function (filename) {
        var target = FS.findObject(filename);
        return target && !target.isFolder && !target.isDevice;
      };

      if (!isValidFile(filename)) {
        if (ENV['LD_LIBRARY_PATH']) {
          searchpaths = ENV['LD_LIBRARY_PATH'].split(':');
        }

        for (var ident in searchpaths) {
          var searchfile = PATH.join2(searchpaths[ident], filename);
          if (isValidFile(searchfile)) {
            filename = searchfile;
            break;
          }
        }
      }
    }

    if (!(flags & ({{{ cDefine('RTLD_LAZY') }}} | {{{ cDefine('RTLD_NOW') }}}))) {
      DLFCN.errorMsg = 'invalid mode for dlopen(): Either RTLD_LAZY or RTLD_NOW is required';
      return 0;
    }

    // We don't care about RTLD_NOW and RTLD_LAZY.
    var jsflags = {
      global:   Boolean(flags & {{{ cDefine('RTLD_GLOBAL') }}}),
      nodelete: Boolean(flags & {{{ cDefine('RTLD_NODELETE') }}}),

      fs: FS, // load libraries from provided filesystem
    }

    try {
      return loadDynamicLibrary(filename, jsflags)
    } catch (e) {
#if ASSERTIONS
      err('Error in loading dynamic library ' + filename + ": " + e);
#endif
      DLFCN.errorMsg = 'Could not load dynamic lib: ' + filename + '\n' + e;
      return 0;
    }
  },

  // int dlclose(void* handle);
  dlclose__deps: ['$DLFCN'],
  dlclose__proxy: 'sync',
  dlclose__sig: 'ii',
  dlclose: function(handle) {
    // int dlclose(void *handle);
    // http://pubs.opengroup.org/onlinepubs/009695399/functions/dlclose.html
    var lib = LDSO.loadedLibs[handle];
    if (!lib) {
      DLFCN.errorMsg = 'Tried to dlclose() unopened handle: ' + handle;
      return 1;
    }
    if (--lib.refcount == 0) {
      delete LDSO.loadedLibNames[lib.name];
      delete LDSO.loadedLibs[handle];
    }
    return 0;
  },

  // void* dlsym(void* handle, const char* symbol);
  dlsym__deps: ['$DLFCN'],
  dlsym__proxy: 'sync',
  dlsym__sig: 'iii',
  dlsym: function(handle, symbol) {
    // void *dlsym(void *restrict handle, const char *restrict name);
    // http://pubs.opengroup.org/onlinepubs/009695399/functions/dlsym.html
    symbol = UTF8ToString(symbol);
    var result;

    if (handle == {{{ cDefine('RTLD_DEFAULT') }}}) {
      result = resolveGlobalSymbol(symbol, true);
      if (!result) {
        DLFCN.errorMsg = 'Tried to lookup unknown symbol "' + symbol + '" in dynamic lib: RTLD_DEFAULT'
        return 0;
      }
    } else {
      var lib = LDSO.loadedLibs[handle];
      if (!lib) {
        DLFCN.errorMsg = 'Tried to dlsym() from an unopened handle: ' + handle;
        return 0;
      }
      if (!lib.module.hasOwnProperty(symbol)) {
        DLFCN.errorMsg = 'Tried to lookup unknown symbol "' + symbol + '" in dynamic lib: ' + lib.name;
        return 0;
      }
#if !WASM_BIGINT
      result = lib.module['orig$' + symbol];
      if (!result)
#endif
      result = lib.module[symbol];
    }

    if (typeof result === 'function') {
      // Insert the function into the wasm table.  If its a direct wasm function
      // the second argument will not be needed.  If its a JS function we rely
      // on the `sig` attribute being set based on the `<func>__sig` specified
      // in library JS file.
      return addFunctionWasm(result, result.sig);
    } else {
      return result;
    }
  },

  // char* dlerror(void);
  dlerror__deps: ['$DLFCN', '$stringToNewUTF8'],
  dlerror__proxy: 'sync',
  dlerror__sig: 'i',
  dlerror: function() {
    // char *dlerror(void);
    // http://pubs.opengroup.org/onlinepubs/009695399/functions/dlerror.html
    if (DLFCN.errorMsg === null) {
      return 0;
    }
    if (DLFCN.error) _free(DLFCN.error);
    DLFCN.error = stringToNewUTF8(DLFCN.errorMsg);
    DLFCN.errorMsg = null;
    return DLFCN.error;
  },

  dladdr__deps: ['$stringToNewUTF8', '$getExecutableName'],
  dladdr__proxy: 'sync',
  dladdr__sig: 'iii',
  dladdr: function(addr, info) {
    // report all function pointers as coming from this program itself XXX not really correct in any way
    var fname = stringToNewUTF8(getExecutableName()); // XXX leak
    {{{ makeSetValue('info', 0, 'fname', 'i32') }}};
    {{{ makeSetValue('info', Runtime.QUANTUM_SIZE, '0', 'i32') }}};
    {{{ makeSetValue('info', Runtime.QUANTUM_SIZE*2, '0', 'i32') }}};
    {{{ makeSetValue('info', Runtime.QUANTUM_SIZE*3, '0', 'i32') }}};
    return 1;
  },
#endif // MAIN_MODULE != 0
};

mergeInto(LibraryManager.library, LibraryDylink);