Move demangle helper to library_legacy.js

Followup to emscripten-core#21156

We no longer use this function anywhere in emscripten.

ChangeLog.md

@@ -20,6 +20,9 @@ See docs/process.md for more on how version tagging works.
 
 3.1.54 (in development)
 -----------------------
+- The `DEMANGLE_SUPPORT` setting and the associated `demangle` function are
+  now deprecated since Wasm stack traces always contain demangled symbols these
+  days. (#21346)
 - The type of `EMSCRIPTEN_WEBGL_CONTEXT_HANDLE` was changed to unsigned and
   the only valid error returned from `emscripten_webgl_create_context` is
   now zero.  This allows `EMSCRIPTEN_WEBGL_CONTEXT_HANDLE` to hold a pointer

site/source/docs/tools_reference/settings_reference.rst

@@ -409,7 +409,9 @@ Print out exceptions in emscriptened code.
 DEMANGLE_SUPPORT
 ================
 
-If 1, export `demangle` and `stackTrace` helper function.
+If 1, export `demangle` and `stackTrace` JS library functions.
+
+.. note:: This setting is deprecated
 
 .. _library_debug:
 

src/library_legacy.js

@@ -90,4 +90,34 @@ addToLibrary({
     return 0;
   },
 #endif
+
+#if LINK_AS_CXX
+  $demangle__deps: ['$withStackSave', '__cxa_demangle', 'free', '$stringToUTF8OnStack'],
+  $demangle: (func) => {
+    // If demangle has failed before, stop demangling any further function names
+    // This avoids an infinite recursion with malloc()->abort()->stackTrace()->demangle()->malloc()->...
+    demangle.recursionGuard = (demangle.recursionGuard|0)+1;
+    if (demangle.recursionGuard > 1) return func;
+    return withStackSave(() => {
+      try {
+        var s = func;
+        if (s.startsWith('__Z'))
+          s = s.substr(1);
+        var buf = stringToUTF8OnStack(s);
+        var status = stackAlloc(4);
+        var ret = ___cxa_demangle(buf, 0, 0, status);
+        if ({{{ makeGetValue('status', '0', 'i32') }}} === 0 && ret) {
+          return UTF8ToString(ret);
+        }
+        // otherwise, libcxxabi failed
+      } catch(e) {
+      } finally {
+        _free(ret);
+        if (demangle.recursionGuard < 2) --demangle.recursionGuard;
+      }
+      // failure when using libcxxabi, don't demangle
+      return func;
+    });
+  },
+#endif
 });

src/library_stack_trace.js

@@ -5,43 +5,6 @@
  */
 
 var LibraryStackTrace = {
-#if DEMANGLE_SUPPORT
-  $demangle__deps: ['$withStackSave', '__cxa_demangle', 'free', '$stringToUTF8OnStack'],
-#endif
-  $demangle: (func) => {
-#if DEMANGLE_SUPPORT
-    // If demangle has failed before, stop demangling any further function names
-    // This avoids an infinite recursion with malloc()->abort()->stackTrace()->demangle()->malloc()->...
-    demangle.recursionGuard = (demangle.recursionGuard|0)+1;
-    if (demangle.recursionGuard > 1) return func;
-    return withStackSave(() => {
-      try {
-        var s = func;
-        if (s.startsWith('__Z'))
-          s = s.substr(1);
-        var buf = stringToUTF8OnStack(s);
-        var status = stackAlloc(4);
-        var ret = ___cxa_demangle(buf, 0, 0, status);
-        if ({{{ makeGetValue('status', '0', 'i32') }}} === 0 && ret) {
-          return UTF8ToString(ret);
-        }
-        // otherwise, libcxxabi failed
-      } catch(e) {
-      } finally {
-        _free(ret);
-        if (demangle.recursionGuard < 2) --demangle.recursionGuard;
-      }
-      // failure when using libcxxabi, don't demangle
-      return func;
-    });
-#else // DEMANGLE_SUPPORT
-#if ASSERTIONS
-    warnOnce('warning: build with -sDEMANGLE_SUPPORT to link in libcxxabi demangling');
-#endif // ASSERTIONS
-    return func;
-#endif // DEMANGLE_SUPPORT
-  },
-
   $jsStackTrace: function() {
     var error = new Error();
     if (!error.stack) {

src/settings.js

@@ -337,8 +337,9 @@ var EMULATE_FUNCTION_POINTER_CASTS = false;
 // [link]
 var EXCEPTION_DEBUG = false;
 
-// If 1, export `demangle` and `stackTrace` helper function.
+// If 1, export `demangle` and `stackTrace` JS library functions.
 // [link]
+// [deprecated]
 var DEMANGLE_SUPPORT = false;
 
 // Print out when we enter a library call (library*.js). You can also unset

test/test_core.py

@@ -7213,7 +7213,6 @@ def test_emulate_function_pointer_casts(self):
   })
   def test_demangle_stacks(self, extra_args):
     self.emcc_args += extra_args
-    self.set_setting('DEMANGLE_SUPPORT')
     self.set_setting('ASSERTIONS')
     # disable aggressive inlining in binaryen
     self.set_setting('BINARYEN_EXTRA_PASSES', '--one-caller-inline-max-function-size=1')
@@ -7234,7 +7233,6 @@ def test_demangle_stacks_symbol_map(self):
     self.set_setting('BINARYEN_EXTRA_PASSES', '--one-caller-inline-max-function-size=1')
     self.set_setting('DEFAULT_LIBRARY_FUNCS_TO_INCLUDE', '$stackTrace')
 
-    self.set_setting('DEMANGLE_SUPPORT')
     self.set_setting('ENVIRONMENT', 'node,shell')
     if '-O' not in str(self.emcc_args) or '-O0' in self.emcc_args or '-O1' in self.emcc_args or '-g' in self.emcc_args:
       self.skipTest("without opts, we don't emit a symbol map")
@@ -7943,7 +7941,6 @@ def test_modularize_closure_pre(self):
   @no_wasm2js('symbol names look different wasm2js backtraces')
   @also_with_wasm_bigint
   def test_emscripten_log(self):
-    self.set_setting('DEMANGLE_SUPPORT')
     if '-g' not in self.emcc_args:
       self.emcc_args.append('-g')
     self.emcc_args += ['-DRUN_FROM_JS_SHELL', '-Wno-deprecated-pragma']

test/test_other.py

@@ -3466,10 +3466,13 @@ def test_syntax_only_invalid(self):
     self.assertContained("src.c:1:13: error: expected '}'", err)
     self.assertNotExists('a.out.js')
 
+  # `demangle` is a legacy JS function on longer used by emscripten
+  # TODO(sbc): Remove `demangle` and this test.
   def test_demangle(self):
     create_file('src.cpp', '''
       #include <stdio.h>
       #include <emscripten.h>
+
       void two(char c) {
         EM_ASM(out(stackTrace()));
       }
@@ -3547,10 +3550,10 @@ def test_demangle_cpp(self):
 
     self.do_runf('src.cpp', 'Waka::f::a23412341234::point()')
 
-  # Test that malloc() -> OOM -> abort() -> stackTrace() -> jsStackTrace() -> demangleAll() -> demangle() -> malloc()
-  # cycle will not produce an infinite loop.
+  # Test that malloc() -> OOM -> abort() -> stackTrace() -> jsStackTrace()
+  # cycle will not cycle back to malloc to produce an infinite loop.
   def test_demangle_malloc_infinite_loop_crash(self):
-    self.run_process([EMXX, test_file('malloc_demangle_infinite_loop.cpp'), '-g', '-sABORTING_MALLOC', '-sDEMANGLE_SUPPORT'])
+    self.run_process([EMXX, test_file('malloc_demangle_infinite_loop.cpp'), '-g', '-sABORTING_MALLOC'])
     output = self.run_js('a.out.js', assert_returncode=NON_ZERO)
     if output.count('Cannot enlarge memory arrays') > 5:
       print(output)
@@ -8423,7 +8426,7 @@ def test_metadce_minimal_pthreads(self):
     'except':   (['-O2', '-fexceptions'],    [], ['waka']), # noqa
     # exceptions does not pull in demangling by default, which increases code size
     'mangle':   (['-O2', '-fexceptions',
-                  '-sDEMANGLE_SUPPORT'], [], ['waka']), # noqa
+                  '-sDEMANGLE_SUPPORT', '-Wno-deprecated'], [], ['waka']), # noqa
     # Wasm EH's code size increase is smaller than that of Emscripten EH
     'except_wasm':   (['-O2', '-fwasm-exceptions'], [], ['waka']), # noqa
     # eval_ctors 1 can partially optimize, but runs into getenv() for locale

tools/link.py

@@ -701,6 +701,9 @@ def phase_linker_setup(options, state, newargs):
   if 'SUPPORT_ERRNO' in user_settings:
     diagnostics.warning('deprecated', 'SUPPORT_ERRNO is deprecated since emscripten no longer uses the setErrNo library function')
 
+  if 'DEMANGLE_SUPPORT' in user_settings:
+    diagnostics.warning('deprecated', 'DEMANGLE_SUPPORT is deprecated since mangled names no longer appear in stack traces')
+
   if settings.EXTRA_EXPORTED_RUNTIME_METHODS:
     diagnostics.warning('deprecated', 'EXTRA_EXPORTED_RUNTIME_METHODS is deprecated, please use EXPORTED_RUNTIME_METHODS instead')
     settings.EXPORTED_RUNTIME_METHODS += settings.EXTRA_EXPORTED_RUNTIME_METHODS