Wasm demangling (emscripten-core#4851)

* Reenable test_demangle_stacks for V8

* Don't inline Aborter constructor in test_demangle_stacks.cpp

The test depends on emitting a symbol for Aborter, which wasm_backend
was inlining.

* Update js stackTrace demangling for wasm_backend

wasm_backend emits functions without an underscore prefix, which causes
mismatches with js backend when it comes to C++ symbol demangling,
particularly in stack traces.

Author: jgravelle-google

src/preamble.js

@@ -858,15 +858,20 @@ function lengthBytesUTF32(str) {
 {{{ maybeExport('lengthBytesUTF32') }}}
 
 function demangle(func) {
-  var hasLibcxxabi = !!Module['___cxa_demangle'];
-  if (hasLibcxxabi) {
+  var __cxa_demangle_func = Module['___cxa_demangle'] || Module['__cxa_demangle'];
+  if (__cxa_demangle_func) {
     try {
-      var s = func.substr(1);
+      var s =
+#if WASM_BACKEND
+        func;
+#else
+        func.substr(1);
+#endif
       var len = lengthBytesUTF8(s)+1;
       var buf = _malloc(len);
       stringToUTF8(s, buf, len);
       var status = _malloc(4);
-      var ret = Module['___cxa_demangle'](buf, 0, 0, status);
+      var ret = __cxa_demangle_func(buf, 0, 0, status);
       if (getValue(status, 'i32') === 0 && ret) {
         return Pointer_stringify(ret);
       }
@@ -886,7 +891,17 @@ function demangle(func) {
 }
 
 function demangleAll(text) {
-  return text.replace(/__Z[\w\d_]+/g, function(x) { var y = demangle(x); return x === y ? x : (x + ' [' + y + ']') });
+  var regex =
+#if WASM_BACKEND
+    /_Z[\w\d_]+/g;
+#else
+    /__Z[\w\d_]+/g;
+#endif
+  return text.replace(regex,
+    function(x) {
+      var y = demangle(x);
+      return x === y ? x : (x + ' [' + y + ']');
+    });
 }
 
 function jsStackTrace() {

tests/core/test_demangle_stacks.c tests/core/test_demangle_stacks.cpptests/core/test_demangle_stacks.c renamed to tests/core/test_demangle_stacks.cpp

@@ -4,6 +4,7 @@
 namespace NameSpace {
 class Class {
  public:
+  __attribute__((noinline))
   void Aborter(double x, char y, int *z) {
     int addr = x + y + (int)z;
     void *p = (void *)addr;

tests/test_core.py

@@ -6115,26 +6115,22 @@ def test_emulate_function_pointer_casts(self):
     '''
     self.do_run(src, '|1.266,1|\n')
 
-  @no_wasm_backend()
   def test_demangle_stacks(self):
-    if self.is_wasm():
-      self.banned_js_engines = [V8_ENGINE] # https://bugs.chromium.org/p/v8/issues/detail?id=5632
     Settings.DEMANGLE_SUPPORT = 1
     if '-O' in str(self.emcc_args):
       self.emcc_args += ['--profiling-funcs', '--llvm-opts', '0']
 
     self.do_run_in_out_file_test('tests', 'core', 'test_demangle_stacks')
 
   @no_emterpreter
-  @no_wasm_backend()
   def test_demangle_stacks_symbol_map(self):
     Settings.DEMANGLE_SUPPORT = 1
     if '-O' in str(self.emcc_args) and '-O0' not in self.emcc_args and '-O1' not in self.emcc_args and '-g' not in self.emcc_args:
       self.emcc_args += ['--llvm-opts', '0']
     else:
       return self.skip("without opts, we don't emit a symbol map")
     self.emcc_args += ['--emit-symbol-map']
-    self.do_run(open(path_from_root('tests', 'core', 'test_demangle_stacks.c')).read(), 'abort')
+    self.do_run(open(path_from_root('tests', 'core', 'test_demangle_stacks.cpp')).read(), 'abort')
     # make sure the shortened name is the right one
     symbols = open('src.cpp.o.js.symbols').read().split('\n')
     for line in symbols: