Always warn/error about undefined symbols if they are explicitly exported (#11604)

ERROR_ON_UNDEFINED_SYMBOLS and WARN_ON_UNDEFINED_SYMBOLS exist
to allow build that contains undefined symbols to build created
with the missing symbols supplied at runtime somehow.

However, I think we should have a separate warning system for when function
that are explicitly exported by the user via EXPORTED_FUNCTIONS are missing
from a build.  In that case we always want to fail or warn.

ChangeLog.md

@@ -17,6 +17,10 @@ See docs/process.md for how version tagging works.
 
 Current Trunk
 -------------
+- It is now an error if a function listed in the `EXPORTED_FUNCTIONS` list is
+  missing from the build (can be disabled via `-Wno-undefined`)
+  (ERROR_ON_UNDEFINED_SYMBOLS and WARN_ON_UNDEFINED_SYMBOLS no longer apply
+  to these symbols which are explicly exported).
 - Support for pthreads with wasm2js (`WASM=0`; #11505).
 - Rename `emscripten/math.h` to `emscripten/em_math.h` because if a user adds
   `emscripten/` as an include path with `-I`, that can override libc math.h,

emcc.py

@@ -1573,11 +1573,6 @@ There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR P
       shared.Settings.ERROR_ON_UNDEFINED_SYMBOLS = 0
       shared.Settings.WARN_ON_UNDEFINED_SYMBOLS = 0
 
-    if shared.Settings.WARN_ON_UNDEFINED_SYMBOLS:
-      diagnostics.enable_warning('undefined', shared.Settings.ERROR_ON_UNDEFINED_SYMBOLS)
-    else:
-      diagnostics.disable_warning('undefined')
-
     if shared.Settings.ASYNCIFY:
       if not shared.Settings.WASM_BACKEND:
         exit_with_error('ASYNCIFY has been removed from fastcomp. There is a new implementation which can be used in the upstream wasm backend.')

emscripten.py

@@ -313,7 +313,8 @@ def function_tables_and_exports(funcs, metadata, mem_init, glue, forwarded_data,
   pre, funcs_js = get_js_funcs(pre, funcs)
   all_exported_functions = get_all_exported_functions(function_table_data)
   all_implemented = get_all_implemented(forwarded_json, metadata)
-  report_missing_symbols(all_implemented, pre)
+  all_implemented_with_aliases = set(all_implemented).union(set(metadata['aliases'].keys()))
+  report_missing_symbols(all_implemented_with_aliases, pre)
   implemented_functions = get_implemented_functions(metadata)
   pre = include_asm_consts(pre, forwarded_json, metadata)
   pre = apply_table(pre)
@@ -890,10 +891,6 @@ def get_all_implemented(forwarded_json, metadata):
 
 
 def report_missing_symbols(all_implemented, pre):
-  # we are not checking anyway, so just skip this
-  if not shared.Settings.ERROR_ON_UNDEFINED_SYMBOLS and not shared.Settings.WARN_ON_UNDEFINED_SYMBOLS:
-    return
-
   # the initial list of missing functions are that the user explicitly exported
   # but were not implemented in compiled code
   missing = list(set(shared.Settings.USER_EXPORTED_FUNCTIONS) - all_implemented)

tests/test_core.py

@@ -4324,7 +4324,7 @@ res64 - external 64\n''', header='''
       void call_side() {
         printf("side: jslib_x is %d.\n", jslib_x);
       }
-    ''', expected=['main: jslib_x is 148.\nside: jslib_x is 148.\n'], main_emcc_args=['--js-library', 'lib.js', '-s', 'EXPORTED_FUNCTIONS=["_main", "_jslib_x"]'])
+    ''', expected=['main: jslib_x is 148.\nside: jslib_x is 148.\n'], main_emcc_args=['--js-library', 'lib.js'])
 
   @needs_dlfcn
   def test_dylink_many_postsets(self):

tests/test_other.py

@@ -1553,7 +1553,7 @@ int f() {
 
   def test_export_from_archive(self):
     export_name = 'this_is_an_entry_point'
-    full_export_name = '_' + export_name
+    full_export_name = '_this_is_an_entry_point'
 
     # The wasm backend exports symbols without the leading '_'
     if self.is_wasm_backend():
@@ -1563,10 +1563,10 @@ int f() {
 
     create_test_file('export.c', r'''
       #include <stdio.h>
-      void %s(void) {
+      void this_is_an_entry_point(void) {
         printf("Hello, world!\n");
       }
-    ''' % export_name)
+    ''')
     run_process([EMCC, 'export.c', '-c', '-o', 'export.o'])
     run_process([EMAR, 'rc', 'libexport.a', 'export.o'])
 
@@ -1580,12 +1580,7 @@ int f() {
     run_process([EMCC, 'main.c', '-L.', '-lexport'])
     self.assertFalse(self.is_exported_in_wasm(expect_export, 'a.out.wasm'))
 
-    # Sanity check: exporting without a definition does not cause it to appear.
-    # Note: exporting main prevents emcc from warning that it generated no code.
-    run_process([EMCC, 'main.c', '-s', 'ERROR_ON_UNDEFINED_SYMBOLS=0', '-s', "EXPORTED_FUNCTIONS=['_main', '%s']" % full_export_name])
-    self.assertFalse(self.is_exported_in_wasm(expect_export, 'a.out.wasm'))
-
-    # Actual test: defining symbol in library and exporting it causes it to appear in the output.
+    # Exporting it causes it to appear in the output.
     run_process([EMCC, 'main.c', '-L.', '-lexport', '-s', "EXPORTED_FUNCTIONS=['%s']" % full_export_name])
     self.assertTrue(self.is_exported_in_wasm(expect_export, 'a.out.wasm'))
 
@@ -1849,7 +1844,7 @@ int f() {
 ''', output)
     self.assertNotContained('warning: library.js memcpy should not be running, it is only for testing!', output)
 
-  def test_undefined_function(self):
+  def test_undefined_exported_function(self):
     cmd = [EMCC, path_from_root('tests', 'hello_world.cpp')]
     run_process(cmd)
 
@@ -1858,8 +1853,8 @@ int f() {
     err = self.expect_fail(cmd)
     self.assertContained('undefined exported function: "foobar"', err)
 
-    # setting ERROR_ON_UNDEFINED_SYMBOLS=0 suppresses error
-    cmd += ['-s', 'ERROR_ON_UNDEFINED_SYMBOLS=0']
+    # setting `-Wno-undefined` should suppress error
+    cmd += ['-Wno-undefined']
     run_process(cmd)
 
   def test_undefined_symbols(self):

tools/diagnostics.py

@@ -158,13 +158,13 @@ def warn(msg, *args):
 class WarningManager(object):
   warnings = {}
 
-  def add_warning(self, name, enabled=True, part_of_all=True, shared=False):
+  def add_warning(self, name, enabled=True, part_of_all=True, shared=False, error=False):
     self.warnings[name] = {
       'enabled': enabled,
       'part_of_all': part_of_all,
       # True for flags that are shared with the underlying clang driver
       'shared': shared,
-      'error': False,
+      'error': error,
     }
 
   def capture_warnings(self, cmd_args):
@@ -227,8 +227,8 @@ class WarningManager(object):
       logger.debug('disabled warning: ' + msg)
 
 
-def add_warning(name, enabled=True, part_of_all=True, shared=False):
-  manager.add_warning(name, enabled, part_of_all, shared)
+def add_warning(name, enabled=True, part_of_all=True, shared=False, error=False):
+  manager.add_warning(name, enabled, part_of_all, shared, error)
 
 
 def enable_warning(name, as_error=False):

tools/shared.py

@@ -63,7 +63,7 @@ diagnostics.add_warning('legacy-settings', enabled=False, part_of_all=False)
 # Catch-all for other emcc warnings
 diagnostics.add_warning('linkflags')
 diagnostics.add_warning('emcc')
-diagnostics.add_warning('undefined')
+diagnostics.add_warning('undefined', error=True)
 diagnostics.add_warning('version-check')
 diagnostics.add_warning('fastcomp')
 diagnostics.add_warning('unused-command-line-argument', shared=True)