Implementation NonUniqueARMRTTIBit __type_name has higher bits set on arm64

[usama54321]

Summary

This problem arises because ubsan can not currently import c++ headers, and the type_info definition goes out of sync.

On arm64 Apple, we have the NonUniqueARMRTTIBit implementation of typeinfo. Copying from typeinfo header:

// When constructing the type_info,
// the compiler packs the pointer to the type name into a uintptr_t and reserves
// the high bit of that pointer, which is assumed to be free for use under that
// ABI. If that high bit is set, that specific copy of the RTTI can't be assumed
// to be unique within the program. If the high bit is unset, then the RTTI can
// be assumed to be unique within the program.

The corresponding implementation __non_unique_arm_rtti_bit_impl masks out these bits when returning the pointer to the type name in __type_name_to_string function. This patch just syncs the type_info definition in ubsan with this masking.

The fix is needed because some ubsan tests (vptr*) crash while trying to symbolicate the type name during diagnositcs.

[usama54321]

Fix commit message

[ldionne]

Can you please add a description of the change?

[ldionne]

LGTM, assuming you don't need to add a test because this is already fixing a test failure.

compiler-rt/lib/ubsan/ubsan_type_hash_itanium.cpp

 
 #include "sanitizer_common/sanitizer_platform.h"
 #include "ubsan_platform.h"
 #if CAN_SANITIZE_UB && !defined(_MSC_VER)
 #include "ubsan_type_hash.h"
 
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_ptrauth.h"
+#include <stdint.h>
 
 // The following are intended to be binary compatible with the definitions
 // given in the Itanium ABI. We make no attempt to be ODR-compatible with
 // those definitions, since existing ABI implementations aren't.
 
 namespace std {
   class type_info {
   public:
+    typedef const char *__type_name_t;
     virtual ~type_info();
 
     const char *__type_name;
+
+    __type_name_t name() const {
+#if defined(__APPLE__) && defined(__LP64__) && !defined(__x86_64__)
+      uintptr_t __non_unique_rtti_bit =
+          (1ULL << ((__CHAR_BIT__ * sizeof(__type_name_t)) - 1));
+      return (__type_name_t)((uintptr_t)__type_name & ~__non_unique_rtti_bit);
+#else
+      return __type_name;
+#endif
+    }
   };
 }
 
 namespace __cxxabiv1 {
 
 /// Type info for classes with no bases, and base class for type info for
 /// classes with bases.
 class __class_type_info : public std::type_info {
static __ubsan::HashValue *getTypeCacheHashTableBucket(__ubsan::HashValue V) {
   return &__ubsan_vptr_hash_set[First];
 }
 
 /// \brief Determine whether \p Derived has a \p Base base class subobject at
 /// offset \p Offset.
 static bool isDerivedFromAtOffset(const abi::__class_type_info *Derived,
                                   const abi::__class_type_info *Base,
                                   sptr Offset) {
-  if (Derived->__type_name == Base->__type_name ||
+  if (Derived->name() == Base->name() ||
       __ubsan::checkTypeInfoEquality(Derived, Base))
     return Offset == 0;
 
   if (const abi::__si_class_type_info *SI =
         dynamic_cast<const abi::__si_class_type_info*>(Derived))
     return isDerivedFromAtOffset(SI->__base_type, Base, Offset);
 
   const abi::__vmi_class_type_info *VTI =
__ubsan::getDynamicTypeInfoFromVtable(void *VtablePtr) {
   VtablePrefix *Vtable = getVtablePrefix(VtablePtr);
   if (!Vtable)
     return DynamicTypeInfo(nullptr, 0, nullptr);
   if (Vtable->Offset < -VptrMaxOffsetToTop || Vtable->Offset > VptrMaxOffsetToTop)
     return DynamicTypeInfo(nullptr, Vtable->Offset, nullptr);
   const abi::__class_type_info *ObjectType = findBaseAtOffset(
     static_cast<const abi::__class_type_info*>(Vtable->TypeInfo),
     -Vtable->Offset);
-  return DynamicTypeInfo(Vtable->TypeInfo->__type_name, -Vtable->Offset,
-                         ObjectType ? ObjectType->__type_name : "<unknown>");
+  return DynamicTypeInfo(Vtable->TypeInfo->name(), -Vtable->Offset,
+                         ObjectType ? ObjectType->name() : "<unknown>");
 }
 
 bool __ubsan::checkTypeInfoEquality(const void *TypeInfo1,
                                     const void *TypeInfo2) {
   auto TI1 = static_cast<const std::type_info *>(TypeInfo1);
   auto TI2 = static_cast<const std::type_info *>(TypeInfo2);
-  return SANITIZER_NON_UNIQUE_TYPEINFO && TI1->__type_name[0] != '*' &&
-         TI2->__type_name[0] != '*' &&
-         !internal_strcmp(TI1->__type_name, TI2->__type_name);
+  return SANITIZER_NON_UNIQUE_TYPEINFO && TI1->name()[0] != '*' &&
+         TI2->name()[0] != '*' && !internal_strcmp(TI1->name(), TI2->name());
 }
 
 #endif  // CAN_SANITIZE_UB && !SANITIZER_WINDOWS