[PATCH] D50743: libcxx: Mark __temp_value::__temp_value as _LIBCPP_NO_CFI.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc created this revision.
pcc added reviewers: mclow.lists, EricWF.
Herald added a subscriber: christof.

This constructor needs to cast a pointer to uninitialized
memory to a pointer to object type in order to call
allocator_traits::construct(). This cast is not allowed when CFI cast
checks are enabled.

I did this instead of marking __addr() as _LIBCPP_NO_CFI so that we
don't lose CFI checks on get() or the dtor.


Repository:
  rL LLVM

https://reviews.llvm.org/D50743

Files:
  libcxx/include/memory


Index: libcxx/include/memory
===================================================================
--- libcxx/include/memory
+++ libcxx/include/memory
@@ -5631,8 +5631,11 @@
     _Tp &   get() { return *__addr(); }
 
     template<class... _Args>
-    __temp_value(_Alloc &__alloc, _Args&& ... __args) : __a(__alloc)
-    { _Traits::construct(__a, __addr(), _VSTD::forward<_Args>(__args)...); }
+    _LIBCPP_NO_CFI
+    __temp_value(_Alloc &__alloc, _Args&& ... __args) : __a(__alloc) {
+      _Traits::construct(__a, reinterpret_cast<_Tp*>(addressof(__v)),
+                         _VSTD::forward<_Args>(__args)...);
+    }
 
     ~__temp_value() { _Traits::destroy(__a, __addr()); }
     };


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