[committed] Fix ubsan -fsanitize=vptr sanitization (PR sanitizer/64632)

--- gcc/testsuite/g++.dg/ubsan/pr64632.C.jj	2015-01-20 16:53:42.560478816 +0100
+++ gcc/testsuite/g++.dg/ubsan/pr64632.C	2015-01-20 16:53:37.683562024 +0100
@@ -0,0 +1,23 @@ 
+// PR sanitizer/64632
+// { dg-do run }
+// { dg-options "-fsanitize=vptr -fno-sanitize-recover=vptr" }
+
+struct S
+{
+  S () : a(0) {}
+  int a;
+  int f () { return a; }
+  virtual int v () { return 0; }
+};
+
+struct X : virtual S
+{
+  int v () { return 2; }
+};
+
+int
+main ()
+{
+  X x;
+  return x.f ();
+}
--- libsanitizer/ubsan/ubsan_type_hash.cc	(revision 224971)
+++ libsanitizer/ubsan/ubsan_type_hash.cc	(revision 224972)
@@ -115,8 +115,7 @@  __ubsan::__ubsan_vptr_type_cache[__ubsan
 
 /// \brief Determine whether \p Derived has a \p Base base class subobject at
 /// offset \p Offset.
-static bool isDerivedFromAtOffset(sptr Object,
-                                  const abi::__class_type_info *Derived,
+static bool isDerivedFromAtOffset(const abi::__class_type_info *Derived,
                                   const abi::__class_type_info *Base,
                                   sptr Offset) {
   if (Derived->__type_name == Base->__type_name)
@@ -124,7 +123,7 @@  static bool isDerivedFromAtOffset(sptr O
 
   if (const abi::__si_class_type_info *SI =
         dynamic_cast<const abi::__si_class_type_info*>(Derived))
-    return isDerivedFromAtOffset(Object, SI->__base_type, Base, Offset);
+    return isDerivedFromAtOffset(SI->__base_type, Base, Offset);
 
   const abi::__vmi_class_type_info *VTI =
     dynamic_cast<const abi::__vmi_class_type_info*>(Derived);
@@ -139,13 +138,13 @@  static bool isDerivedFromAtOffset(sptr O
     sptr OffsetHere = VTI->base_info[base].__offset_flags >>
                       abi::__base_class_type_info::__offset_shift;
     if (VTI->base_info[base].__offset_flags &
-          abi::__base_class_type_info::__virtual_mask) {
-      sptr VTable = *reinterpret_cast<const sptr *>(Object);
-      OffsetHere = *reinterpret_cast<const sptr *>(VTable + OffsetHere);
-    }
-    if (isDerivedFromAtOffset(Object + OffsetHere,
-                              VTI->base_info[base].__base_type, Base,
-                              Offset - OffsetHere))
+          abi::__base_class_type_info::__virtual_mask)
+      // For now, just punt on virtual bases and say 'yes'.
+      // FIXME: OffsetHere is the offset in the vtable of the virtual base
+      //        offset. Read the vbase offset out of the vtable and use it.
+      return true;
+    if (isDerivedFromAtOffset(VTI->base_info[base].__base_type,
+                              Base, Offset - OffsetHere))
       return true;
   }
 
@@ -154,15 +153,14 @@  static bool isDerivedFromAtOffset(sptr O
 
 /// \brief Find the derived-most dynamic base class of \p Derived at offset
 /// \p Offset.
-static const abi::__class_type_info *
-findBaseAtOffset(sptr Object, const abi::__class_type_info *Derived,
-                 sptr Offset) {
+static const abi::__class_type_info *findBaseAtOffset(
+    const abi::__class_type_info *Derived, sptr Offset) {
   if (!Offset)
     return Derived;
 
   if (const abi::__si_class_type_info *SI =
         dynamic_cast<const abi::__si_class_type_info*>(Derived))
-    return findBaseAtOffset(Object, SI->__base_type, Offset);
+    return findBaseAtOffset(SI->__base_type, Offset);
 
   const abi::__vmi_class_type_info *VTI =
     dynamic_cast<const abi::__vmi_class_type_info*>(Derived);
@@ -174,13 +172,12 @@  findBaseAtOffset(sptr Object, const abi:
     sptr OffsetHere = VTI->base_info[base].__offset_flags >>
                       abi::__base_class_type_info::__offset_shift;
     if (VTI->base_info[base].__offset_flags &
-          abi::__base_class_type_info::__virtual_mask) {
-      sptr VTable = *reinterpret_cast<const sptr *>(Object);
-      OffsetHere = *reinterpret_cast<const sptr *>(VTable + OffsetHere);
-    }
-    if (const abi::__class_type_info *Base = findBaseAtOffset(
-            Object + OffsetHere, VTI->base_info[base].__base_type,
-            Offset - OffsetHere))
+          abi::__base_class_type_info::__virtual_mask)
+      // FIXME: Can't handle virtual bases yet.
+      continue;
+    if (const abi::__class_type_info *Base =
+          findBaseAtOffset(VTI->base_info[base].__base_type,
+                           Offset - OffsetHere))
       return Base;
   }
 
@@ -232,8 +229,7 @@  bool __ubsan::checkDynamicType(void *Obj
     return false;
 
   abi::__class_type_info *Base = (abi::__class_type_info*)Type;
-  if (!isDerivedFromAtOffset(reinterpret_cast<sptr>(Object), Derived, Base,
-                             -Vtable->Offset))
+  if (!isDerivedFromAtOffset(Derived, Base, -Vtable->Offset))
     return false;
 
   // Success. Cache this result.
@@ -247,9 +243,8 @@  __ubsan::DynamicTypeInfo __ubsan::getDyn
   if (!Vtable)
     return DynamicTypeInfo(0, 0, 0);
   const abi::__class_type_info *ObjectType = findBaseAtOffset(
-      reinterpret_cast<sptr>(Object),
-      static_cast<const abi::__class_type_info *>(Vtable->TypeInfo),
-      -Vtable->Offset);
+    static_cast<const abi::__class_type_info*>(Vtable->TypeInfo),
+    -Vtable->Offset);
   return DynamicTypeInfo(Vtable->TypeInfo->__type_name, -Vtable->Offset,
                          ObjectType ? ObjectType->__type_name : "<unknown>");
 }