[libcxx-commits] [PATCH] D99624: [libc++] Remove UB in std::list

Louis Dionne via Phabricator via libcxx-commits libcxx-commits at lists.llvm.org
Tue Mar 30 15:31:17 PDT 2021

ldionne created this revision.
ldionne requested review of this revision.
Herald added a project: libc++.
Herald added a subscriber: libcxx-commits.
Herald added a reviewer: libc++.

We create list nodes by allocating them, but we never actually call the
constructor of the list node itself - we only construct its subobjects
one at a time. This patch fixes that by making sure that we construct
the list node itself. This is a different attempt to fix the underlying
issue behind D98750 <https://reviews.llvm.org/D98750>.

  rG LLVM Github Monorepo



Index: libcxx/include/list
--- libcxx/include/list
+++ libcxx/include/list
@@ -270,11 +270,14 @@
 struct __list_node
     : public __list_node_base<_Tp, _VoidPtr>
-    _Tp __value_;
+    union { _Tp __value_; };
     typedef __list_node_base<_Tp, _VoidPtr> __base;
     typedef typename __base::__link_pointer __link_pointer;
+    __list_node() { }
     __link_pointer __as_link() {
         return static_cast<__link_pointer>(__base::__self());
@@ -1113,6 +1116,7 @@
     __hold_pointer __allocate_node(__node_allocator& __na) {
       __node_pointer __p = __node_alloc_traits::allocate(__na, 1);
+      ::new ((void*)_VSTD::addressof(*__p)) __node();
       __p->__prev_ = nullptr;
       return __hold_pointer(__p, __node_destructor(__na, 1));

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