Add assertion checking the number of args passed into exports.

Fixes #21348

Author: brendandahl

src/preamble.js

@@ -512,14 +512,15 @@ Module['FS_createPreloadedFile'] = FS.createPreloadedFile;
 #include "URIUtils.js"
 
 #if ASSERTIONS
-function createExportWrapper(name) {
+function createExportWrapper(name, nargs) {
   return (...args) => {
     assert(runtimeInitialized, `native function \`${name}\` called before runtime initialization`);
 #if EXIT_RUNTIME
     assert(!runtimeExited, `native function \`${name}\` called after runtime exit (use NO_EXIT_RUNTIME to keep it alive after main() exits)`);
 #endif
     var f = wasmExports[name];
     assert(f, `exported native function \`${name}\` not found`);
+    assert(args.length <= nargs, `native function \`${name}\` called with ${args.length} args but expects ${nargs}`);
     return f(...args);
   };
 }

test/test_other.py

@@ -11985,6 +11985,20 @@ def test_native_call_after_exit(self):
     out = self.run_js('foo.js', assert_returncode=NON_ZERO)
     self.assertContained('native function `main` called after runtime exit', out)
 
+  def test_native_call_nargs(self):
+    self.set_setting('ASSERTIONS')
+    self.set_setting('EXPORTED_FUNCTIONS', ['_main', '_foo'])
+    create_file('foo.c', r'''
+      #include <emscripten.h>
+      void foo(int arg) {}
+      int main() {
+        EM_ASM(_foo(99, 100));
+      }
+    ''')
+    self.build('foo.c')
+    out = self.run_js('foo.js', assert_returncode=NON_ZERO)
+    self.assertContained('native function `foo` called with 2 args but expects 1', out)
+
   def test_metadce_wasm2js_i64(self):
     # handling i64 unsigned remainder brings in some i64 support code. metadce
     # must not remove it.

tools/emscripten.py

@@ -851,7 +851,7 @@ def install_wrapper(sym):
     if settings.ASSERTIONS and install_wrapper(name):
       # With assertions enabled we create a wrapper that are calls get routed through, for
       # the lifetime of the program.
-      wrapper += "createExportWrapper('%s');" % name
+      wrapper += f"createExportWrapper('{name}', {nargs});"
     elif settings.WASM_ASYNC_COMPILATION:
       # With WASM_ASYNC_COMPILATION wrapper will replace the global var and Module var on
       # first use.