Report more undefined symbols at wasm-ld time (#21000)

Symbols that are part of EXPORTED_FUNCTIONS are now reported by wasm-ld.

Author: sbc100

test/browser/test_sdl_key_proxy.c

@@ -64,4 +64,3 @@ int main(int argc, char **argv) {
   emscripten_runtime_keepalive_push();
   return 0;
 }
-

test/test_other.py

@@ -2375,6 +2375,15 @@ def test_undefined_exported_function(self):
     cmd = [EMXX, test_file('hello_world.cpp')]
     self.run_process(cmd)
 
+    # adding a missing symbol to EXPORTED_FUNCTIONS should cause failure
+    cmd += ['-sEXPORTED_FUNCTIONS=_foobar']
+    err = self.expect_fail(cmd)
+    self.assertContained('wasm-ld: error: symbol exported via --export not found: foobar', err)
+
+  def test_undefined_exported_js_function(self):
+    cmd = [EMXX, test_file('hello_world.cpp')]
+    self.run_process(cmd)
+
     # adding a missing symbol to EXPORTED_FUNCTIONS should cause failure
     cmd += ['-sEXPORTED_FUNCTIONS=foobar']
     err = self.expect_fail(cmd)
@@ -7226,7 +7235,7 @@ def test_no_warn_exported_jslibfunc(self):
     err = self.expect_fail([EMCC, test_file('hello_world.c'),
                             '-sDEFAULT_LIBRARY_FUNCS_TO_INCLUDE=alGetError',
                             '-sEXPORTED_FUNCTIONS=_main,_alGet'])
-    self.assertContained('error: undefined exported symbol: "_alGet" [-Wundefined] [-Werror]', err)
+    self.assertContained('wasm-ld: error: symbol exported via --export not found: alGet', err)
 
   def test_musl_syscalls(self):
     self.run_process([EMCC, test_file('hello_world.c')])
@@ -10074,7 +10083,7 @@ def test_dash_s_list_parsing(self):
       # stray slash
       ('EXPORTED_FUNCTIONS=["_a", "_b",\\ "_c", "_d"]', 'undefined exported symbol: "\\\\ "_c"'),
       # missing comma
-      ('EXPORTED_FUNCTIONS=["_a", "_b" "_c", "_d"]', 'emcc: error: undefined exported symbol: "_b" "_c" [-Wundefined] [-Werror]'),
+      ('EXPORTED_FUNCTIONS=["_a", "_b" "_c", "_d"]', 'wasm-ld: error: symbol exported via --export not found: b" "_c'),
     ]:
       print(export_arg)
       proc = self.run_process([EMCC, 'src.c', '-s', export_arg], stdout=PIPE, stderr=PIPE, check=not expected)

tools/building.py

@@ -191,20 +191,20 @@ def lld_flags_for_executable(external_symbols):
   c_exports = [e for e in settings.EXPORTED_FUNCTIONS if is_c_symbol(e)]
   # Strip the leading underscores
   c_exports = [demangle_c_symbol_name(e) for e in c_exports]
-  c_exports += settings.EXPORT_IF_DEFINED
   # Filter out symbols external/JS symbols
   c_exports = [e for e in c_exports if e not in external_symbols]
+  c_exports += settings.REQUIRED_EXPORTS
   if settings.MAIN_MODULE:
     c_exports += side_module_external_deps(external_symbols)
   for export in c_exports:
-    cmd.append('--export-if-defined=' + export)
-
-  for export in settings.REQUIRED_EXPORTS:
     if settings.ERROR_ON_UNDEFINED_SYMBOLS:
       cmd.append('--export=' + export)
     else:
       cmd.append('--export-if-defined=' + export)
 
+  for e in settings.EXPORT_IF_DEFINED:
+    cmd.append('--export-if-defined=' + e)
+
   if settings.RELOCATABLE:
     cmd.append('--experimental-pic')
     cmd.append('--unresolved-symbols=import-dynamic')

tools/emscripten.py

@@ -31,7 +31,7 @@
 from tools.utils import exit_with_error, path_from_root, removeprefix
 from tools.shared import DEBUG, asmjs_mangle
 from tools.shared import treat_as_user_export
-from tools.settings import settings
+from tools.settings import settings, user_settings
 
 sys.path.append(path_from_root('third_party'))
 import leb128
@@ -555,6 +555,7 @@ def finalize_wasm(infile, outfile, js_syms):
 
   expected_exports = set(settings.EXPORTED_FUNCTIONS)
   expected_exports.update(asmjs_mangle(s) for s in settings.REQUIRED_EXPORTS)
+  expected_exports.update(asmjs_mangle(s) for s in settings.EXPORT_IF_DEFINED)
   # Assume that when JS symbol dependencies are exported it is because they
   # are needed by by a JS symbol and are not being explicitly exported due
   # to EMSCRIPTEN_KEEPALIVE (llvm.used).
@@ -569,18 +570,21 @@ def finalize_wasm(infile, outfile, js_syms):
   unexpected_exports = [asmjs_mangle(e) for e in unexpected_exports]
   unexpected_exports = [e for e in unexpected_exports if e not in expected_exports]
 
-  # If `_main` was unexpectedly exported we assume it was added to
-  # EXPORT_IF_DEFINED by emcc.py in order that we can detect it and
-  # report this warning.  In this case we explicitly ignore the export
-  # and run as if there was no main function since that is defined is
-  # behaviour for programs that don't include `_main` in EXPORTED_FUNCTIONS.
-  if not settings.STANDALONE_WASM and '_main' in unexpected_exports:
-    diagnostics.warning('unused-main', '`main` is defined in the input files, but `_main` is not in `EXPORTED_FUNCTIONS`. Add it to this list if you want `main` to run.')
-    unexpected_exports.remove('_main')
-    if 'main' in metadata.all_exports:
-      metadata.all_exports.remove('main')
+  if not settings.STANDALONE_WASM and 'main' in metadata.all_exports or '__main_argc_argv' in metadata.all_exports:
+    if 'EXPORTED_FUNCTIONS' in user_settings and '_main' not in settings.USER_EXPORTED_FUNCTIONS:
+      # If `_main` was unexpectedly exported we assume it was added to
+      # EXPORT_IF_DEFINED by `phase_linker_setup` in order that we can detect
+      # it and report this warning.  After reporting the warning we explicitly
+      # ignore the export and run as if there was no main function since that
+      # is defined is behaviour for programs that don't include `_main` in
+      # EXPORTED_FUNCTIONS.
+      diagnostics.warning('unused-main', '`main` is defined in the input files, but `_main` is not in `EXPORTED_FUNCTIONS`. Add it to this list if you want `main` to run.')
+      if 'main' in metadata.all_exports:
+        metadata.all_exports.remove('main')
+      else:
+        metadata.all_exports.remove('__main_argc_argv')
     else:
-      metadata.all_exports.remove('__main_argc_argv')
+      unexpected_exports.append('_main')
 
   building.user_requested_exports.update(unexpected_exports)
   settings.EXPORTED_FUNCTIONS.extend(unexpected_exports)

tools/link.py

@@ -810,11 +810,13 @@ def phase_linker_setup(options, state, newargs):
     # 2. If the user doesn't export anything we default to exporting `_main` (unless `--no-entry`
     #    is specified (see above).
     if 'EXPORTED_FUNCTIONS' in user_settings:
-      if '_main' not in settings.USER_EXPORTED_FUNCTIONS:
+      if '_main' in settings.USER_EXPORTED_FUNCTIONS:
+        settings.EXPORTED_FUNCTIONS.remove('_main')
+        settings.EXPORT_IF_DEFINED.append('main')
+      else:
         settings.EXPECT_MAIN = 0
     else:
-      assert not settings.EXPORTED_FUNCTIONS
-      settings.EXPORTED_FUNCTIONS = ['_main']
+      settings.EXPORT_IF_DEFINED.append('main')
 
   if settings.STANDALONE_WASM:
     # In STANDALONE_WASM mode we either build a command or a reactor.
@@ -838,7 +840,7 @@ def phase_linker_setup(options, state, newargs):
   # Note the exports the user requested
   building.user_requested_exports.update(settings.EXPORTED_FUNCTIONS)
 
-  if '_main' in settings.EXPORTED_FUNCTIONS:
+  if '_main' in settings.EXPORTED_FUNCTIONS or 'main' in settings.EXPORT_IF_DEFINED:
     settings.EXPORT_IF_DEFINED.append('__main_argc_argv')
   elif settings.ASSERTIONS and not settings.STANDALONE_WASM:
     # In debug builds when `main` is not explicitly requested as an