Merging r244101:
------------------------------------------------------------------------
r244101 | samsonov | 2015-08-05 12:35:46 -0700 (Wed, 05 Aug 2015) | 6 lines
[UBSan] Fix UBSan-vptr false positive.
Offset from vptr to the start of most-derived object can actually
be positive in some virtual base class vtables.
Patch by Stephan Bergmann!
------------------------------------------------------------------------
git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/branches/release_37@245114 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ubsan/ubsan_type_hash_itanium.cc b/lib/ubsan/ubsan_type_hash_itanium.cc
index 5cd46df..b84e88d 100644
--- a/lib/ubsan/ubsan_type_hash_itanium.cc
+++ b/lib/ubsan/ubsan_type_hash_itanium.cc
@@ -185,8 +185,8 @@
struct VtablePrefix {
/// The offset from the vptr to the start of the most-derived object.
- /// This should never be greater than zero, and will usually be exactly
- /// zero.
+ /// This will only be greater than zero in some virtual base class vtables
+ /// used during object con-/destruction, and will usually be exactly zero.
sptr Offset;
/// The type_info object describing the most-derived class type.
std::type_info *TypeInfo;
@@ -196,7 +196,7 @@
if (!Vptr)
return 0;
VtablePrefix *Prefix = Vptr - 1;
- if (Prefix->Offset > 0 || !Prefix->TypeInfo)
+ if (!Prefix->TypeInfo)
// This can't possibly be a valid vtable.
return 0;
return Prefix;
diff --git a/test/ubsan/TestCases/TypeCheck/vptr-virtual-base-construction.cpp b/test/ubsan/TestCases/TypeCheck/vptr-virtual-base-construction.cpp
new file mode 100644
index 0000000..dc27d9f
--- /dev/null
+++ b/test/ubsan/TestCases/TypeCheck/vptr-virtual-base-construction.cpp
@@ -0,0 +1,13 @@
+// RUN: %clangxx -frtti -fsanitize=vptr -fno-sanitize-recover=vptr %s -o %t
+// RUN: %run %t
+
+// REQUIRES: cxxabi
+
+int volatile n;
+
+struct A { virtual ~A() {} };
+struct B: virtual A {};
+struct C: virtual A { ~C() { n = 0; } };
+struct D: virtual B, virtual C {};
+
+int main() { delete new D; }
