[sanitizer] Fix a crash when demangling Swift symbols

[kubamracek]

Summary

To invoke the Swift demangler, we use dlsym to locate swift_demangle. However, dlsym malloc's storage and stores it in thread-local storage. Since allocations from the symbolizer are done with the system allocator (at least in TSan, interceptors are skipped when inside the symbolizer), we will crash when we try to deallocate later using the sanitizer allocator again.

To fix this, let's just not call dlsym from the demangler, and call it during initialization.

[kubamracek]

Had to revert in r268723 due to test failures on Linux.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cc

const char *DemangleCXXABI(const char *name) {
   if (__cxxabiv1::__cxa_demangle)
     if (const char *demangled_name =
           __cxxabiv1::__cxa_demangle(name, 0, 0, 0))
       return demangled_name;
 
   return name;
 }
 
+// As of now, there are no headers for the Swift runtime. Once they are
+// present, we will weakly link since we do not require Swift runtime to be
+// linked.
+typedef char *(*swift_demangle_ft)(const char *mangledName,
+                                   size_t mangledNameLength, char *outputBuffer,
+                                   size_t *outputBufferSize, uint32_t flags);
+static swift_demangle_ft swift_demangle_f;
+
+// This must not happen lazily, because dlsym uses thread-local storage, which
+// is not a good thing to do during symbolication.
+static void InitializeSwiftDemangler() {
+  swift_demangle_f = (swift_demangle_ft)dlsym(RTLD_DEFAULT, "swift_demangle");
+}
+
 // Attempts to demangle a Swift name. The demangler will return nullptr
 /// if a non-Swift name is passed in.
 const char *DemangleSwift(const char *name) {
   // Not to call dlsym every time we demangle, check if we are dealing with
   // Swift mangled name first.
   if (name[0] != '_' || name[1] != 'T') {
     return nullptr;
   }
 
-  // As of now, there are no headers for the Swift runtime. Once they are
-  // present, we will weakly link since we do not require Swift runtime to be
-  // linked.
-  typedef char *(*swift_demangle_ft)(const char *mangledName,
-                                     size_t mangledNameLength,
-                                     char *outputBuffer,
-                                     size_t *outputBufferSize,
-                                     uint32_t flags);
-  swift_demangle_ft swift_demangle_f =
-    (swift_demangle_ft) dlsym(RTLD_DEFAULT, "swift_demangle");
   if (swift_demangle_f)
     return swift_demangle_f(name, internal_strlen(name), 0, 0, 0);
 
   return nullptr;
 }
 
 const char *DemangleSwiftAndCXX(const char *name) {
   CHECK(name);

 
 #if SANITIZER_MAC
   VReport(2, "Using dladdr symbolizer.\n");
   list->push_back(new(*allocator) DlAddrSymbolizer());
 #endif  // SANITIZER_MAC
 }
 
 Symbolizer *Symbolizer::PlatformInit() {
+  InitializeSwiftDemangler();
+
   IntrusiveList<SymbolizerTool> list;
   list.clear();
   ChooseSymbolizerTools(&list, &symbolizer_allocator_);
   return new(symbolizer_allocator_) Symbolizer(list);
 }
 
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_POSIX