Fix -fsanitize=vptr badness in <__debug>

Summary:

This patch fixes a lifetime bug when inserting a new container into the debug database. It is
diagnosed by UBSAN when debug mode is enabled. This patch corrects how nodes are constructed
during insertion.

The fix requires unconditionally breaking the debug mode ABI. Users should not expect ABI
stability from debug mode.

Reviewers: ldionne, serge-sans-paille, EricWF

Reviewed By: EricWF

Subscribers: mclow.lists, christof, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D58011

llvm-svn: 355367

1 files changed, 9 insertions, 3 deletions

diff --git a/libcxx/include/__debug b/libcxx/include/__debug
index 6ccb72cb8ad..281cf6675c9 100644
--- a/libcxx/include/__debug
+++ b/libcxx/include/__debug
@@ -250,16 +250,22 @@ public:
     __db_c_const_iterator __c_end() const;
     __db_i_const_iterator __i_end() const;
 
+    typedef __c_node*(_InsertConstruct)(void*, void*, __c_node*);
+
+    template <class _Cont>
+    _LIBCPP_INLINE_VISIBILITY static __c_node* __create_C_node(void *__mem, void *__c, __c_node *__next) {
+        return ::new(__mem) _C_node<_Cont>(__c, __next);
+    }
+
     template <class _Cont>
     _LIBCPP_INLINE_VISIBILITY
     void __insert_c(_Cont* __c)
     {
-        __c_node* __n = __insert_c(static_cast<void*>(__c));
-        ::new(__n) _C_node<_Cont>(__n->__c_, __n->__next_);
+        __insert_c(static_cast<void*>(__c), &__create_C_node<_Cont>);
     }
 
     void __insert_i(void* __i);
-    __c_node* __insert_c(void* __c);
+    void __insert_c(void* __c, _InsertConstruct* __fn);
     void __erase_c(void* __c);
 
     void __insert_ic(void* __i, const void* __c);