[EH] Make lsan/asan work with Wasm EH (emscripten-core#23552)

`std::rethrow_exception` leaked memory because dependent exceptions were
not recognized as such and thus not freed properly here:
https://github.com/emscripten-core/emscripten/blob/44fd294e8244afa710cecb2c10c9a644a6549b8e/system/lib/libcxxabi/src/cxa_exception.cpp#L575-L583
The reason for that was, in `__cxa_rethrow_primary_exception`, we were
incorrectly throwing the primary exception, not the dependent one. I
think the error was introduced during copy-pasting.

`isDependentException` method was copied from `cxa_exception.cpp`,
because it is a static function, as in the case for other utility
functions in that file.

This also adds handling for dependent exceptions in
`__get_exception_message`.

Fixes emscripten-core#21124.

system/lib/libcxxabi/src/cxa_exception.cpp

@@ -789,9 +789,9 @@ __cxa_rethrow_primary_exception(void* thrown_object)
         // In debug mode, call a JS library function to use
         // WebAssembly.Exception JS API, which enables us to include stack
         // traces
-        __throw_exception_with_stack_trace(&exception_header->unwindHeader);
+        __throw_exception_with_stack_trace(&dep_exception_header->unwindHeader);
 #else
-        _Unwind_RaiseException(&exception_header->unwindHeader);
+        _Unwind_RaiseException(&dep_exception_header->unwindHeader);
 #endif
         // Some sort of unwinding error.  Note that terminate is a handler.
         __cxa_begin_catch(&dep_exception_header->unwindHeader);

system/lib/libcxxabi/src/cxa_exception_js_utils.cpp

@@ -38,6 +38,14 @@ static inline __cxa_exception* cxa_exception_from_unwind_exception(
   return cxa_exception_from_thrown_object(unwind_exception + 1);
 }
 
+#ifdef __WASM_EXCEPTIONS__
+struct __cxa_dependent_exception;
+uint64_t __getExceptionClass(const _Unwind_Exception* unwind_exception);
+static bool isDependentException(_Unwind_Exception* unwind_exception) {
+  return (__getExceptionClass(unwind_exception) & 0xFF) == 0x01;
+}
+#endif
+
 extern "C" {
 
 void* __thrown_object_from_unwind_exception(
@@ -78,6 +86,13 @@ void __get_exception_message(void* thrown_object, char** type, char** message) {
     static_cast<const __shim_type_info*>(&typeid(std::exception));
   int can_catch = catch_type->can_catch(thrown_type, thrown_object);
   if (can_catch) {
+#if __WASM_EXCEPTIONS__
+    if (isDependentException(&exception_header->unwindHeader))
+      thrown_object =
+        reinterpret_cast<__cxa_dependent_exception*>(exception_header)
+          ->primaryException;
+#endif
+
     const char* what =
       static_cast<const std::exception*>(thrown_object)->what();
     *message = (char*)malloc(strlen(what) + 1);

test/common.py

@@ -641,9 +641,6 @@ def metafunc(self, mode, *args, **kwargs):
       # Wasm EH is currently supported only in wasm backend and V8
       if self.is_wasm2js():
         self.skipTest('wasm2js does not support wasm EH/SjLj')
-      # FIXME Temporarily disabled. Enable this later when the bug is fixed.
-      if '-fsanitize=address' in self.emcc_args:
-        self.skipTest('Wasm EH does not work with asan yet')
       self.emcc_args.append('-fwasm-exceptions')
       self.set_setting('SUPPORT_LONGJMP', 'wasm')
       if mode == 'wasm':
@@ -677,9 +674,6 @@ def metafunc(self, mode, *args, **kwargs):
     if mode in {'wasm', 'wasm_legacy'}:
       if self.is_wasm2js():
         self.skipTest('wasm2js does not support wasm SjLj')
-      # FIXME Temporarily disabled. Enable this later when the bug is fixed.
-      if '-fsanitize=address' in self.emcc_args:
-        self.skipTest('Wasm EH does not work with asan yet')
       self.set_setting('SUPPORT_LONGJMP', 'wasm')
       if mode == 'wasm':
         self.require_wasm_eh()

test/test_core.py

@@ -1328,8 +1328,6 @@ def test_exceptions_refcount(self):
 
   @with_all_eh_sjlj
   def test_exceptions_primary(self):
-    if '-fsanitize=leak' in self.emcc_args and '-fwasm-exceptions' in self.emcc_args:
-      self.skipTest('https://github.com/emscripten-core/emscripten/issues/21124')
     self.do_core_test('test_exceptions_primary.cpp')
 
   @with_all_eh_sjlj
@@ -1346,8 +1344,6 @@ def test_exceptions_multiple_inherit(self):
 
   @with_all_eh_sjlj
   def test_exceptions_multiple_inherit_rethrow(self):
-    if '-fsanitize=leak' in self.emcc_args and '-fwasm-exceptions' in self.emcc_args:
-      self.skipTest('https://github.com/emscripten-core/emscripten/issues/21124')
     self.do_core_test('test_exceptions_multiple_inherit_rethrow.cpp')
 
   @with_all_eh_sjlj
@@ -1499,8 +1495,6 @@ def test_exceptions_longjmp2(self):
 
   @with_all_eh_sjlj
   def test_exceptions_longjmp3(self):
-    if '-fwasm-exceptions' in self.emcc_args:
-      self.skipTest('https://github.com/emscripten-core/emscripten/issues/17004')
     self.do_core_test('test_exceptions_longjmp3.cpp')
 
   @with_all_eh_sjlj