[libcxx] r339797 - libcxx: Mark __temp_value::__temp_value as _LIBCPP_NO_CFI.

[Peter Collingbourne via cfe-commits]

Author: pcc
Date: Wed Aug 15 10:49:30 2018
New Revision: 339797

URL: http://llvm.org/viewvc/llvm-project?rev=339797&view=rev
Log:
libcxx: Mark __temp_value::__temp_value as _LIBCPP_NO_CFI.

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.

Differential Revision: https://reviews.llvm.org/D50743

Modified:
    libcxx/trunk/include/memory

Modified: libcxx/trunk/include/memory
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/memory?rev=339797&r1=339796&r2=339797&view=diff
==============================================================================
--- libcxx/trunk/include/memory (original)
+++ libcxx/trunk/include/memory Wed Aug 15 10:49:30 2018
@@ -5631,8 +5631,11 @@ struct __temp_value {
     _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()); }
     };