[NFC][sanitizer] Return nullptr from PlatformDemangle

Use fallback name only on the top level, in Symbolizer::Demangle or
DlAddrSymbolizer. This makes PlatformDemangle to be more consistent with
SymbolizerTool and the loop in Symbolizer::Demangle which iterates over
all availible options.

Author: vitalybuka

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer.h

@@ -187,7 +187,7 @@ class Symbolizer final {
   // If stale, need to reload the modules before looking up addresses.
   bool modules_fresh_;
 
-  // Platform-specific default demangler, must not return nullptr.
+  // Platform-specific default demangler, returns nullptr on failure.
   const char *PlatformDemangle(const char *name);
 
   static Symbolizer *symbolizer_;

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_mac.cpp

@@ -42,7 +42,8 @@ bool DlAddrSymbolizer::SymbolizePC(uptr addr, SymbolizedStack *stack) {
   }
 
   const char *demangled = DemangleSwiftAndCXX(info.dli_sname);
-  if (!demangled) return false;
+  if (!demangled)
+    demangled = info.dli_sname;
   stack->info.function = internal_strdup(demangled);
   return true;
 }
@@ -52,6 +53,8 @@ bool DlAddrSymbolizer::SymbolizeData(uptr addr, DataInfo *datainfo) {
   int result = dladdr((const void *)addr, &info);
   if (!result) return false;
   const char *demangled = DemangleSwiftAndCXX(info.dli_sname);
+  if (!demangled)
+    demangled = info.dli_sname;
   datainfo->name = internal_strdup(demangled);
   datainfo->start = (uptr)info.dli_saddr;
   return true;

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_posix_libcdep.cpp

@@ -56,7 +56,7 @@ const char *DemangleCXXABI(const char *name) {
           __cxxabiv1::__cxa_demangle(name, 0, 0, 0))
       return demangled_name;
 
-  return name;
+  return nullptr;
 }
 
 // As of now, there are no headers for the Swift runtime. Once they are

compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_win.cpp

@@ -175,9 +175,7 @@ const char *WinSymbolizerTool::Demangle(const char *name) {
     return name;
 }
 
-const char *Symbolizer::PlatformDemangle(const char *name) {
-  return name;
-}
+const char *Symbolizer::PlatformDemangle(const char *name) { return nullptr; }
 
 namespace {
 struct ScopedHandle {

compiler-rt/lib/sanitizer_common/tests/sanitizer_symbolizer_test.cpp

@@ -58,13 +58,13 @@ TEST(Symbolizer, ExtractTokenUpToDelimiter) {
 TEST(Symbolizer, DemangleSwiftAndCXX) {
   // Swift names are not demangled in default llvm build because Swift
   // runtime is not linked in.
-  EXPECT_STREQ("_TtSd", DemangleSwiftAndCXX("_TtSd"));
+  EXPECT_STREQ(nullptr, DemangleSwiftAndCXX("_TtSd"));
   // Check that the rest demangles properly.
   EXPECT_STREQ("f1(char*, int)", DemangleSwiftAndCXX("_Z2f1Pci"));
 #if !SANITIZER_FREEBSD // QoI issue with libcxxrt on FreeBSD
-  EXPECT_STREQ("foo", DemangleSwiftAndCXX("foo"));
+  EXPECT_STREQ(nullptr, DemangleSwiftAndCXX("foo"));
 #endif
-  EXPECT_STREQ("", DemangleSwiftAndCXX(""));
+  EXPECT_STREQ(nullptr, DemangleSwiftAndCXX(""));
 }
 #endif