Detect direct/internal usage of all missing library symbols (#17418)

Previously this mechanism only worked for missing function symbols and
would only fire once the function was called.  The new mechanism will
catch any access to missing functions, even if they never called, and
will also catch access to missing number symbols.

I've also optimized the size of the `missingLibrarySymbol` block in
the generate code:

Old:

missingLibrarySymbol('foo');
missingLibrarySymbol('bar');
...

New:

var missingLibrarySymbols = ['foo', 'bar' ...];
missingLibrarySymbols.forEach(missingLibrarySymbol);

Author: sbc100

src/library.js

@@ -3680,6 +3680,8 @@ DEFAULT_LIBRARY_FUNCS_TO_INCLUDE.push(
   '$addFunction',
   '$removeFunction',
   '$allocate',
+  '$ALLOC_NORMAL',
+  '$ALLOC_STACK',
   '$AsciiToString',
   '$stringToAscii',
   '$UTF16ToString',

src/modules.js

@@ -266,23 +266,6 @@ function isFSPrefixed(name) {
   return name.length > 3 && name[0] === 'F' && name[1] === 'S' && name[2] === '_';
 }
 
-// forcing the filesystem exports a few things by default
-function isExportedByForceFilesystem(name) {
-  if (!WASMFS) {
-    // The old FS has some functionality that WasmFS lacks.
-    if (name === 'FS_createLazyFile' ||
-        name === 'FS_createDevice') {
-      return true;
-    }
-  }
-  return name === 'FS_createPath' ||
-         name === 'FS_createDataFile' ||
-         name === 'FS_createPreloadedFile' ||
-         name === 'FS_unlink' ||
-         name === 'addRunDependency' ||
-         name === 'removeRunDependency';
-}
-
 function isInternalSymbol(ident) {
   return ident + '__internal' in LibraryManager.library;
 }
@@ -297,16 +280,25 @@ function addMissingLibraryStubs() {
   if (!ASSERTIONS) return '';
   let rtn = '';
   const librarySymbolSet = new Set(librarySymbols);
+  const missingSyms = [];
   for (const ident in LibraryManager.library) {
-    if (typeof LibraryManager.library[ident] === 'function') {
+    if (typeof LibraryManager.library[ident] === 'function' || typeof LibraryManager.library[ident] === 'number') {
       if (ident[0] === '$' && !isJsLibraryConfigIdentifier(ident) && !isInternalSymbol(ident)) {
         const name = ident.substr(1);
         if (!librarySymbolSet.has(name)) {
-          rtn += `var ${name} = missingLibraryFunc('${name}');\n`;
+          missingSyms.push(name);
         }
       }
     }
   }
+  if (missingSyms.length) {
+    rtn += 'var missingLibrarySymbols = [\n';
+    for (const sym of missingSyms) {
+      rtn += `  '${sym}',\n`;
+    }
+    rtn += '];\n';
+    rtn += 'missingLibrarySymbols.forEach(missingLibrarySymbol)\n';
+  }
   return rtn;
 }
 
@@ -333,14 +325,6 @@ function exportRuntime() {
       }
       return `Module["${name}"] = ${exported};`;
     }
-    // do not export it. but if ASSERTIONS, emit a
-    // stub with an error, so the user gets a message
-    // if it is used, that they should export it
-    if (ASSERTIONS) {
-      // check if it already exists, to support EXPORT_ALL and other cases
-      const fssymbol = isExportedByForceFilesystem(name);
-      return `unexportedRuntimeSymbol('${name}', ${fssymbol});`;
-    }
   }
 
   // All possible runtime elements that can be exported
@@ -439,6 +423,7 @@ function exportRuntime() {
     }
   }
 
+  let unexportedStubs = '';
   if (ASSERTIONS) {
     // check all exported things exist, warn about typos
     const runtimeElementsSet = new Set(runtimeElements);
@@ -447,8 +432,25 @@ function exportRuntime() {
         warn(`invalid item in EXPORTED_RUNTIME_METHODS: ${name}`);
       }
     }
+
+    const unexported = [];
+    for (const name of runtimeElements) {
+      if (!EXPORTED_RUNTIME_METHODS_SET.has(name)) {
+        unexported.push(name);
+      }
+    }
+
+    if (unexported.length) {
+      unexportedStubs += 'var unexportedRuntimeSymbols = [\n';
+      for (const sym of unexported) {
+        unexportedStubs += `  '${sym}',\n`;
+      }
+      unexportedStubs += '];\n';
+      unexportedStubs += 'unexportedRuntimeSymbols.forEach(unexportedRuntimeSymbol);\n';
+    }
   }
+
   let exports = runtimeElements.map((name) => maybeExport(name));
   exports = exports.filter((name) => name);
-  return exports.join('\n') + '\n' + addMissingLibraryStubs();
+  return exports.join('\n') + '\n' + unexportedStubs + addMissingLibraryStubs();
 }

src/runtime_debug.js

@@ -22,24 +22,49 @@ function ignoredModuleProp(prop) {
   }
 }
 
-function unexportedMessage(sym, isFSSybol) {
-  var msg = "'" + sym + "' was not exported. add it to EXPORTED_RUNTIME_METHODS (see the FAQ)";
-  if (isFSSybol) {
-    msg += '. Alternatively, forcing filesystem support (-sFORCE_FILESYSTEM) can export this for you';
-  }
-  return msg;
+// forcing the filesystem exports a few things by default
+function isExportedByForceFilesystem(name) {
+  return name === 'FS_createPath' ||
+         name === 'FS_createDataFile' ||
+         name === 'FS_createPreloadedFile' ||
+         name === 'FS_unlink' ||
+         name === 'addRunDependency' ||
+#if !WASMFS
+         // The old FS has some functionality that WasmFS lacks.
+         name === 'FS_createLazyFile' ||
+         name === 'FS_createDevice' ||
+#endif
+         name === 'removeRunDependency';
 }
 
-function missingLibraryFunc(sym) {
-  return () => abort('Call to `' + sym + '` which is a library function and not included by default; add it to your library.js __deps or to DEFAULT_LIBRARY_FUNCS_TO_INCLUDE on the command line');
+function missingLibrarySymbol(sym) {
+  if (typeof globalThis !== 'undefined' && !Object.getOwnPropertyDescriptor(globalThis, sym)) {
+    Object.defineProperty(globalThis, sym, {
+      configurable: true,
+      get: function() {
+        // Can't `abort()` here because it would break code that does runtime
+        // checks.  e.g. `if (typeof SDL === 'undefined')`.
+        var msg = '`' + sym + '` is a library symbol and not included by default; add it to your library.js __deps or to DEFAULT_LIBRARY_FUNCS_TO_INCLUDE on the command line';
+        if (isExportedByForceFilesystem(sym)) {
+          msg += '. Alternatively, forcing filesystem support (-sFORCE_FILESYSTEM) can export this for you';
+        }
+        warnOnce(msg);
+        return undefined;
+      }
+    });
+  }
 }
 
-function unexportedRuntimeSymbol(sym, isFSSybol) {
+function unexportedRuntimeSymbol(sym) {
   if (!Object.getOwnPropertyDescriptor(Module, sym)) {
     Object.defineProperty(Module, sym, {
       configurable: true,
       get: function() {
-        abort(unexportedMessage(sym, isFSSybol));
+        var msg = "'" + sym + "' was not exported. add it to EXPORTED_RUNTIME_METHODS (see the FAQ)";
+        if (isExportedByForceFilesystem(sym)) {
+          msg += '. Alternatively, forcing filesystem support (-sFORCE_FILESYSTEM) can export this for you';
+        }
+        abort(msg);
       }
     });
   }

tests/core/legacy_exported_runtime_numbers.cpp

@@ -3,17 +3,19 @@
 // University of Illinois/NCSA Open Source License.  Both these licenses can be
 // found in the LICENSE file.
 
-#include<emscripten.h>
+#include <emscripten.h>
+#include <stdio.h>
 
 int main() {
+  int rtn = EM_ASM_INT({
 #ifdef DIRECT
-  EM_ASM({
-    out('|' + ALLOC_STACK + '|');
-  });
+    out('|' +  ALLOC_STACK + '|');
+    return ALLOC_STACK;
 #else
-  EM_ASM({
     out('|' + Module['ALLOC_STACK'] + '|');
-  });
+    return Module['ALLOC_STACK'];
 #endif
+  });
+  printf("|%d|\n", rtn);
+  return 0;
 }
-

tests/core/legacy_exported_runtime_numbers.out

@@ -1 +1 @@
-26679
+27500

tests/other/metadce/test_metadce_hello_O0.jssize

@@ -1 +1 @@
-21458
+22356

tests/other/metadce/test_metadce_minimal_O0.jssize

@@ -1 +1 @@
-95154
+84065

tests/other/test_unoptimized_code_size.js.size

@@ -1 +1 @@
-56605
+56607

tests/other/test_unoptimized_code_size_no_asserts.js.size

@@ -1 +1 @@
-76442
+66130