Replace Module["asm"] with wasmExports global

This brings the regular runtime closer `MINIMAL_RUNTIME` which uses the global `asm` to refer to exports object. As a followup we should consider merging these two symbols.
emscripten-core · Jul 12, 2023 · 00e9f24 · 00e9f24
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diff --git a/ChangeLog.md b/ChangeLog.md
@@ -27,6 +27,10 @@ See docs/process.md for more on how version tagging works.
 - The internal `read_` and `readAsync` functions no longer handle date URIs.
   This only effects builds that use `-sSINGLE_FILE` or `--memory-init-file`.
   (#19792)
+- The `asm` property of the Module object (which held the raw exports of the
+  wasm module) has been removed.  Internally, this is now accessed via the
+  `wasmExports` global. If necessary, it is possible to export `wasmExports`
+  on the Module object using `-sEXPORTED_RUNTIME_METHODS=wasmExports`. (#19816)
 
 3.1.43 - 07/10/23
 -----------------

diff --git a/emscripten.py b/emscripten.py
@@ -762,7 +762,7 @@ def install_wrapper(sym):
       # first use.
       args = [f'a{i}' for i in range(nargs)]
       args = ', '.join(args)
-      wrapper += f"({args}) => ({mangled} = {exported}Module['asm']['{name}'])({args});"
+      wrapper += f"({args}) => ({mangled} = {exported}wasmExports['{name}'])({args});"
     else:
       wrapper += 'asm["%s"]' % name
 

diff --git a/site/source/docs/optimizing/Module-Splitting.rst b/site/source/docs/optimizing/Module-Splitting.rst
@@ -124,7 +124,7 @@ included in the profile.
 Here’s the function to write the profile and our new main function::
 
   EM_JS(void, write_profile, (), {
-    var __write_profile = Module['asm']['__write_profile'];
+    var __write_profile = wasmExports['__write_profile'];
     if (__write_profile) {
 
       // Get the size of the profile and allocate a buffer for it.
@@ -338,7 +338,7 @@ be called either.
 
 When eagerly instantiating the secondary module, the imports object should be::
 
-  {'primary': Module['asm']}
+  {'primary': wasmExports}
 
 Debugging
 ---------

diff --git a/src/library_async.js b/src/library_async.js
@@ -267,9 +267,9 @@ mergeInto(LibraryManager.library, {
     getDataRewindFunc: function(ptr) {
       var id = {{{ makeGetValue('ptr', C_STRUCTS.asyncify_data_s.rewind_id, 'i32') }}};
       var name = Asyncify.callStackIdToName[id];
-      var func = Module['asm'][name];
+      var func = wasmExports[name];
 #if RELOCATABLE
-      // Exported functions in side modules are not listed in `Module['asm']`,
+      // Exported functions in side modules are not listed in `wasmExports`,
       // So we should use `resolveGlobalSymbol` helper function, which is defined in `library_dylink.js`.
       if (!func) {
         func = resolveGlobalSymbol(name, false).sym;
@@ -522,8 +522,8 @@ mergeInto(LibraryManager.library, {
   _load_secondary_module__sig: 'v',
   _load_secondary_module: async function() {
     // Mark the module as loading for the wasm module (so it doesn't try to load it again).
-    Module['asm']['load_secondary_module_status'].value = 1;
-    var imports = {'primary': Module['asm']};
+    wasmExports['load_secondary_module_status'].value = 1;
+    var imports = {'primary': wasmExports};
     // Replace '.wasm' suffix with '.deferred.wasm'.
     var deferred = wasmBinaryFile.slice(0, -5) + '.deferred.wasm';
     await new Promise((resolve) => {

diff --git a/src/library_exceptions.js b/src/library_exceptions.js
@@ -331,7 +331,7 @@ var LibraryExceptions = {
 #if RELOCATABLE
     return ___cpp_exception; // defined in library.js
 #else
-    return Module['asm']['__cpp_exception'];
+    return wasmExports['__cpp_exception'];
 #endif
   },
 

diff --git a/src/library_exports.js b/src/library_exports.js
@@ -16,7 +16,7 @@ mergeInto(LibraryManager.library, {
     var exportedFunc = asm[name];
 #else
     // In regular runtime, exports are available on the Module object.
-    var exportedFunc = Module['asm'][name];
+    var exportedFunc = wasmExports[name];
 #endif
     if (exportedFunc) {
       // Record the created function pointer to each function object,

diff --git a/src/modules.js b/src/modules.js
@@ -382,6 +382,8 @@ function exportRuntime() {
     'abort',
     'keepRuntimeAlive',
     'wasmMemory',
+    'wasmTable',
+    'wasmExports',
   ];
 
   // These are actually native wasm functions these days but we allow exporting

diff --git a/src/parseTools.js b/src/parseTools.js
@@ -865,6 +865,13 @@ function hasExportedSymbol(sym) {
   return WASM_EXPORTS.has(sym);
 }
 
+function receivedSymbol(sym) {
+  if (EXPORTED_RUNTIME_METHODS.includes(sym)) {
+    return `Module['${sym}'] = ${sym};`
+  }
+  return '';
+}
+
 // JS API I64 param handling: if we have BigInt support, the ABI is simple,
 // it is a BigInt. Otherwise, we legalize into pairs of i32s.
 function defineI64Param(name) {

diff --git a/src/postamble_minimal.js b/src/postamble_minimal.js
@@ -142,7 +142,7 @@ WebAssembly.instantiate(Module['wasm'], imports).then((output) => {
 
 #if !LibraryManager.has('library_exports.js') && !EMBIND
   // If not using the emscripten_get_exported_function() API or embind, keep the
-  // 'asm' exports variable in local scope to this instantiate function to save
+  // `asm` exports variable in local scope to this instantiate function to save
   // code size.  (otherwise access it without to export it to outer scope)
   var
 #endif

diff --git a/src/preamble.js b/src/preamble.js
@@ -53,6 +53,7 @@ if (typeof WebAssembly != 'object') {
 // Wasm globals
 
 var wasmMemory;
+var wasmExports;
 
 #if SHARED_MEMORY
 // For sending to workers.
@@ -471,7 +472,7 @@ function abort(what) {
 #if WASM_EXCEPTIONS == 1
   // See above, in the meantime, we resort to wasm code for trapping.
   //
-  // In case abort() is called before the module is initialized, Module['asm']
+  // In case abort() is called before the module is initialized, wasmExports
   // and its exported '__trap' function is not available, in which case we throw
   // a RuntimeError.
   //
@@ -527,7 +528,7 @@ function createExportWrapper(name) {
 #if EXIT_RUNTIME
     assert(!runtimeExited, `native function \`${name}\` called after runtime exit (use NO_EXIT_RUNTIME to keep it alive after main() exits)`);
 #endif
-    var f = Module['asm'][name];
+    var f = wasmExports[name];
     assert(f, `exported native function \`${name}\` not found`);
     return f.apply(null, arguments);
   };
@@ -714,7 +715,7 @@ var splitModuleProxyHandler = {
       throw new Error('Placeholder function "' + prop + '" should not be called when using JSPI.');
 #else
       err('placeholder function called: ' + prop);
-      var imports = {'primary': Module['asm']};
+      var imports = {'primary': wasmExports};
       // Replace '.wasm' suffix with '.deferred.wasm'.
       var deferred = wasmBinaryFile.slice(0, -5) + '.deferred.wasm'
       loadSplitModule(deferred, imports, prop);
@@ -979,18 +980,20 @@ function createWasm() {
     exports = applySignatureConversions(exports);
 #endif
 
-    Module['asm'] = exports;
+    wasmExports = exports;
+    {{{ receivedSymbol('wasmExports') }}}
 
 #if PTHREADS
 #if MAIN_MODULE
-    registerTLSInit(Module['asm']['_emscripten_tls_init'], instance.exports, metadata);
+    registerTLSInit(wasmExports['_emscripten_tls_init'], instance.exports, metadata);
 #else
-    registerTLSInit(Module['asm']['_emscripten_tls_init']);
+    registerTLSInit(wasmExports['_emscripten_tls_init']);
 #endif
 #endif
 
 #if !IMPORTED_MEMORY
-    wasmMemory = Module['asm']['memory'];
+    wasmMemory = wasmExports['memory'];
+    {{{ receivedSymbol('wasmMemory') }}}
 #if ASSERTIONS
     assert(wasmMemory, "memory not found in wasm exports");
     // This assertion doesn't hold when emscripten is run in --post-link
@@ -1005,7 +1008,8 @@ function createWasm() {
 #endif
 
 #if !RELOCATABLE
-    wasmTable = Module['asm']['__indirect_function_table'];
+    wasmTable = wasmExports['__indirect_function_table'];
+    {{{ receivedSymbol('wasmTable') }}}
 #if ASSERTIONS && !PURE_WASI
     assert(wasmTable, "table not found in wasm exports");
 #endif
@@ -1019,11 +1023,11 @@ function createWasm() {
 #endif
 
 #if hasExportedSymbol('__wasm_call_ctors')
-    addOnInit(Module['asm']['__wasm_call_ctors']);
+    addOnInit(wasmExports['__wasm_call_ctors']);
 #endif
 
 #if hasExportedSymbol('__wasm_apply_data_relocs')
-    __RELOC_FUNCS__.push(Module['asm']['__wasm_apply_data_relocs']);
+    __RELOC_FUNCS__.push(wasmExports['__wasm_apply_data_relocs']);
 #endif
 
 #if ABORT_ON_WASM_EXCEPTIONS

diff --git a/src/runtime_debug.js b/src/runtime_debug.js
@@ -6,20 +6,22 @@
 
 #if ASSERTIONS
 
-function legacyModuleProp(prop, newName) {
+function legacyModuleProp(prop, newName, incomming=true) {
   if (!Object.getOwnPropertyDescriptor(Module, prop)) {
     Object.defineProperty(Module, prop, {
       configurable: true,
       get() {
-        abort('Module.' + prop + ' has been replaced with plain ' + newName + ' (the initial value can be provided on Module, but after startup the value is only looked for on a local variable of that name)');
+        let extra = incomming ? ' (the initial value can be provided on Module, but after startup the value is only looked for on a local variable of that name)' : '';
+        abort(`\`Module.${prop}\` has been replaced by \`${newName}\`` + extra);
+
       }
     });
   }
 }
 
 function ignoredModuleProp(prop) {
   if (Object.getOwnPropertyDescriptor(Module, prop)) {
-    abort('`Module.' + prop + '` was supplied but `' + prop + '` not included in INCOMING_MODULE_JS_API');
+    abort(`\`Module.${prop}\` was supplied but \`${prop}\` not included in INCOMING_MODULE_JS_API`);
   }
 }
 

diff --git a/src/shell.js b/src/shell.js
@@ -477,6 +477,7 @@ assert(typeof Module['readAsync'] == 'undefined', 'Module.readAsync option was r
 assert(typeof Module['readBinary'] == 'undefined', 'Module.readBinary option was removed (modify readBinary in JS)');
 assert(typeof Module['setWindowTitle'] == 'undefined', 'Module.setWindowTitle option was removed (modify setWindowTitle in JS)');
 assert(typeof Module['TOTAL_MEMORY'] == 'undefined', 'Module.TOTAL_MEMORY has been renamed Module.INITIAL_MEMORY');
+{{{ makeRemovedModuleAPIAssert('asm', 'wasmExports', false) }}}
 {{{ makeRemovedModuleAPIAssert('read', 'read_') }}}
 {{{ makeRemovedModuleAPIAssert('readAsync') }}}
 {{{ makeRemovedModuleAPIAssert('readBinary') }}}

diff --git a/test/optimizer/applyDCEGraphRemovals-output.js b/test/optimizer/applyDCEGraphRemovals-output.js
@@ -17,15 +17,15 @@ var expD5 = asm["expD5"];
 
 var expD6;
 
-var expI1 = Module["expI1"] = () => (expI1 = Module["expI1"] = Module["asm"]["expI1"])();
+var expI1 = Module["expI1"] = () => (expI1 = Module["expI1"] = wasmExports["expI1"])();
 
-var expI2 = Module["expI2"] = () => (expI2 = Module["expI2"] = Module["asm"]["expI2"])();
+var expI2 = Module["expI2"] = () => (expI2 = Module["expI2"] = wasmExports["expI2"])();
 
-var expI3 = Module["expI3"] = () => (expI3 = Module["expI3"] = Module["asm"]["expI3"])();
+var expI3 = Module["expI3"] = () => (expI3 = Module["expI3"] = wasmExports["expI3"])();
 
 var expI4;
 
-var expI5 = () => (expI5 = Module["asm"]["expI5"])();
+var expI5 = () => (expI5 = wasmExports["expI5"])();
 
 var expI6;
 

diff --git a/test/optimizer/applyDCEGraphRemovals.js b/test/optimizer/applyDCEGraphRemovals.js
@@ -11,14 +11,14 @@ var expD5 = asm['expD5'];
 var expD6 = asm['expD6'];
 
 // exports gotten indirectly (async compilation
-var expI1 = Module['expI1'] = () => (expI1 = Module['expI1'] = Module['asm']['expI1'])();
-var expI2 = Module['expI2'] = () => (expI2 = Module['expI2'] = Module['asm']['expI2'])();
-var expI3 = Module['expI3'] = () => (expI3 = Module['expI3'] = Module['asm']['expI3'])();
-var expI4 = Module['expI4'] = () => (expI4 = Module['expI4'] = Module['asm']['expI4'])();
+var expI1 = Module['expI1'] = () => (expI1 = Module['expI1'] = wasmExports['expI1'])();
+var expI2 = Module['expI2'] = () => (expI2 = Module['expI2'] = wasmExports['expI2'])();
+var expI3 = Module['expI3'] = () => (expI3 = Module['expI3'] = wasmExports['expI3'])();
+var expI4 = Module['expI4'] = () => (expI4 = Module['expI4'] = wasmExports['expI4'])();
 
 // Like above, but not exported on the Module
-var expI5 = () => (expI5 = Module['asm']['expI5'])();
-var expI6 = () => (expI6 = Module['asm']['expI6'])();
+var expI5 = () => (expI5 = wasmExports['expI5'])();
+var expI6 = () => (expI6 = wasmExports['expI6'])();
 
 // add uses for some of them, leave *4 as non-roots
 expD1;

diff --git a/test/optimizer/applyImportAndExportNameChanges-output.js b/test/optimizer/applyImportAndExportNameChanges-output.js
@@ -17,5 +17,5 @@ var wasmImports = {
 var expD1 = Module["expD1"] = asm["c"];
 
 var expI1 = Module["expI1"] = function() {
- return Module["asm"]["d"].apply(null, arguments);
+ return wasmExports["d"].apply(null, arguments);
 };
diff --git a/test/optimizer/applyImportAndExportNameChanges.js b/test/optimizer/applyImportAndExportNameChanges.js
@@ -18,7 +18,7 @@ var expD1 = Module['expD1'] = asm['expD1'];
 
 // exports gotten indirectly (async compilation
 var expI1 = Module['expI1'] = (function() {
- return Module['asm']['expI1'].apply(null, arguments);
+ return wasmExports['expI1'].apply(null, arguments);
 });
 
 // EXTRA_INFO: { "mapping": {"save1" : "a", "number": "A", "expD1": "c", "expI1": "d", "__wasm_call_ctors": "e", "stackRestore": "h", "stackAlloc": "g", "__syscall140": "d", "main": "f", "__syscall146": "q", "__syscall54": "c", "__syscall6": "b" }}

diff --git a/test/optimizer/emitDCEGraph.js b/test/optimizer/emitDCEGraph.js
@@ -53,13 +53,13 @@ var expD4 = Module['expD4'] = asm['expD4'];
 var expD5 = asm['expD5'];
 
 // exports gotten indirectly (async compilation
-var expI1 = Module['expI1'] = () => (expI1 = Module['expI1'] = Module['asm']['expI1'])();
-var expI2 = Module['expI2'] = () => (expI2 = Module['expI2'] = Module['asm']['expI2'])();
-var expI3 = Module['expI3'] = () => (expI3 = Module['expI3'] = Module['asm']['expI3'])();
-var expI4 = Module['expI4'] = () => (expI4 = Module['expI4'] = Module['asm']['expI4'])();
+var expI1 = Module['expI1'] = () => (expI1 = Module['expI1'] = wasmExports['expI1'])();
+var expI2 = Module['expI2'] = () => (expI2 = Module['expI2'] = wasmExports['expI2'])();
+var expI3 = Module['expI3'] = () => (expI3 = Module['expI3'] = wasmExports['expI3'])();
+var expI4 = Module['expI4'] = () => (expI4 = Module['expI4'] = wasmExports['expI4'])();
 
 // Same as above but not export on the Module.
-var expI5 = () => (expI5 = Module['asm']['expI5'])();
+var expI5 = () => (expI5 = wasmExports['expI5'])();
 
 // add uses for some of them
 expD1;
@@ -68,7 +68,7 @@ asm['expD3'];
 
 expI1;
 Module['expI2'];
-Module['asm']['expI3'];
+wasmExports['expI3'];
 
 // deep uses, that we can't scan
 function usedFromDeep() {
@@ -86,10 +86,10 @@ var func = function() {
 };
 
 // dyncalls
-var dynCall_v = Module["dynCall_v"] = () => Module["asm"]["dynCall_v"]();
-var dynCall_vi = Module["dynCall_vi"] = () => Module["asm"]["dynCall_vi"]();
-var dynCall_vii = Module["dynCall_vii"] = () => Module["asm"]["dynCall_vii"]();
-var dynCall_viii = Module["dynCall_viii"] = () => Module["asm"]["dynCall_viii"]();
+var dynCall_v = Module["dynCall_v"] = () => wasmExports["dynCall_v"]();
+var dynCall_vi = Module["dynCall_vi"] = () => wasmExports["dynCall_vi"]();
+var dynCall_vii = Module["dynCall_vii"] = () => wasmExports["dynCall_vii"]();
+var dynCall_viii = Module["dynCall_viii"] = () => wasmExports["dynCall_viii"]();
 
 dynCall_v(ptr); // use directly
 Module['dynCall_vi'](ptr, 1); // use on module

diff --git a/test/optimizer/emitDCEGraph2.js b/test/optimizer/emitDCEGraph2.js
@@ -1,8 +1,8 @@
 // dyncalls
-var dynCall_v = Module["dynCall_v"] = () => Module["asm"]["dynCall_v"]();
-var dynCall_vi = Module["dynCall_vi"] = () => Module["asm"]["dynCall_vi"]();
-var dynCall_vii = Module["dynCall_vii"] = () => Module["asm"]["dynCall_vii"]();
-var dynCall_viii = Module["dynCall_viii"] = () => Module["asm"]["dynCall_viii"]();
+var dynCall_v = Module["dynCall_v"] = () => wasmExports["dynCall_v"]();
+var dynCall_vi = Module["dynCall_vi"] = () => wasmExports["dynCall_vi"]();
+var dynCall_vii = Module["dynCall_vii"] = () => wasmExports["dynCall_vii"]();
+var dynCall_viii = Module["dynCall_viii"] = () => wasmExports["dynCall_viii"]();
 
 // a dynamic dynCall
 function dynCall(sig) {

diff --git a/test/optimizer/emitDCEGraph3.js b/test/optimizer/emitDCEGraph3.js
@@ -1,8 +1,8 @@
 // dyncalls
-var dynCall_v = Module["dynCall_v"] = () => Module["asm"]["dynCall_v"]();
-var dynCall_vi = Module["dynCall_vi"] = () => Module["asm"]["dynCall_vi"]();
-var dynCall_vii = Module["dynCall_vii"] = () => Module["asm"]["dynCall_vii"]();
-var dynCall_viii = Module["dynCall_viii"] = () => Module["asm"]["dynCall_viii"]();
+var dynCall_v = Module["dynCall_v"] = () => wasmExports["dynCall_v"]();
+var dynCall_vi = Module["dynCall_vi"] = () => wasmExports["dynCall_vi"]();
+var dynCall_vii = Module["dynCall_vii"] = () => wasmExports["dynCall_vii"]();
+var dynCall_viii = Module["dynCall_viii"] = () => wasmExports["dynCall_viii"]();
 
 // a dynamic dynCall
 function dynCall(sig) {

diff --git a/test/optimizer/emitDCEGraph4.js b/test/optimizer/emitDCEGraph4.js
@@ -1,8 +1,8 @@
 // dyncalls
-var dynCall_v = Module["dynCall_v"] = () => Module["asm"]["dynCall_v"]();
-var dynCall_vi = Module["dynCall_vi"] = () => Module["asm"]["dynCall_vi"]();
-var dynCall_vii = Module["dynCall_vii"] = () => Module["asm"]["dynCall_vii"]();
-var dynCall_viii = Module["dynCall_viii"] = () => Module["asm"]["dynCall_viii"]();
+var dynCall_v = Module["dynCall_v"] = () => wasmExports["dynCall_v"]();
+var dynCall_vi = Module["dynCall_vi"] = () => wasmExports["dynCall_vi"]();
+var dynCall_vii = Module["dynCall_vii"] = () => wasmExports["dynCall_vii"]();
+var dynCall_viii = Module["dynCall_viii"] = () => wasmExports["dynCall_viii"]();
 
 // a dynamic dynCall
 function dynCall(sig) {

diff --git a/test/optimizer/emitDCEGraph5.js b/test/optimizer/emitDCEGraph5.js
@@ -1,14 +1,14 @@
 // wasm backend notation has one fewer _ in the wasm
 __GLOBAL__I_000101(); // var use
-var __GLOBAL__I_000101 = Module["__GLOBAL__I_000101"] = () => Module["asm"]["_GLOBAL__I_000101"]();
+var __GLOBAL__I_000101 = Module["__GLOBAL__I_000101"] = () => wasmExports["_GLOBAL__I_000101"]();
 
 __ATINIT__.push({ func: function() { __GLOBAL__I_iostream() } }); // var use inside other scope
-var __GLOBAL__I_iostream = Module["__GLOBAL__I_iostream"] = () => Module["asm"]["_GLOBAL__I_iostream.cpp"]();
+var __GLOBAL__I_iostream = Module["__GLOBAL__I_iostream"] = () => wasmExports["_GLOBAL__I_iostream.cpp"]();
 
 Module["__DUB"](); // module use
-var __DUB = Module["__DUB"] = () => Module["asm"]["_DUB"]();
+var __DUB = Module["__DUB"] = () => wasmExports["_DUB"]();
 
-var __UNUSED = Module["__UNUSED"] = () => Module["asm"]["_UNUSED"]();
+var __UNUSED = Module["__UNUSED"] = () => wasmExports["_UNUSED"]();
 
 var wasmImports = {
 };

diff --git a/test/other/metadce/test_metadce_cxx_ctors1.jssize b/test/other/metadce/test_metadce_cxx_ctors1.jssize
@@ -1 +1 @@
-25162
+25131
diff --git a/test/other/metadce/test_metadce_cxx_ctors2.jssize b/test/other/metadce/test_metadce_cxx_ctors2.jssize
@@ -1 +1 @@
-25126
+25099
diff --git a/test/other/metadce/test_metadce_cxx_except.jssize b/test/other/metadce/test_metadce_cxx_except.jssize
@@ -1 +1 @@
-29381
+29309
diff --git a/test/other/metadce/test_metadce_cxx_except_wasm.jssize b/test/other/metadce/test_metadce_cxx_except_wasm.jssize
@@ -1 +1 @@
-24934
+24899