[patch] libstdc++/65352 fix ubsan errors in std::array

[Jonathan Wakely]

Unsurprisingly ubsan doesn't like referencing a null pointer.

With this change __array_traits::_S_ref is only used to access an
element, which is invalid for std::array<T, 0> anyway.

Tested powerpc64le-linux, committed to trunk.


commit 0d999cf16b8f6a0d9bbf4bfe96b29e7b73a259e4
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu May 28 12:21:36 2015 +0100

    	PR libstdc++/65352
    	* include/std/array (__array_traits::_S_ptr): New function.
    	(array::data): Use _S_ptr to avoid creating invalid reference.
    	* testsuite/23_containers/array/tuple_interface/get_neg.cc: Adjust
    	dg-error line numbers.
    	* testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc:
    	likewise.

diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array
index 429506b..24be44f 100644
--- a/libstdc++-v3/include/std/array
+++ b/libstdc++-v3/include/std/array
@@ -51,6 +51,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       static constexpr _Tp&
       _S_ref(const _Type& __t, std::size_t __n) noexcept
       { return const_cast<_Tp&>(__t[__n]); }
+
+      static constexpr _Tp*
+      _S_ptr(const _Type& __t) noexcept
+      { return const_cast<_Tp*>(__t); }
     };
 
  template<typename _Tp>
@@ -61,6 +65,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
      static constexpr _Tp&
      _S_ref(const _Type&, std::size_t) noexcept
      { return *static_cast<_Tp*>(nullptr); }
+
+     static constexpr _Tp*
+     _S_ptr(const _Type&) noexcept
+     { return nullptr; }
    };
 
   /**
@@ -219,11 +227,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
       pointer
       data() noexcept
-      { return std::__addressof(_AT_Type::_S_ref(_M_elems, 0)); }
+      { return _AT_Type::_S_ptr(_M_elems); }
 
       const_pointer
       data() const noexcept
-      { return std::__addressof(_AT_Type::_S_ref(_M_elems, 0)); }
+      { return _AT_Type::_S_ptr(_M_elems); }
     };
 
   // Array comparisons.
diff --git a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
index 7604412..6830964 100644
--- a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
@@ -28,6 +28,6 @@ int n1 = std::get<1>(a);
 int n2 = std::get<1>(std::move(a));
 int n3 = std::get<1>(ca);
 
-// { dg-error "static assertion failed" "" { target *-*-* } 274 }
-// { dg-error "static assertion failed" "" { target *-*-* } 283 }
+// { dg-error "static assertion failed" "" { target *-*-* } 282 }
 // { dg-error "static assertion failed" "" { target *-*-* } 291 }
+// { dg-error "static assertion failed" "" { target *-*-* } 299 }
diff --git a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc
index 9788053..5d75366 100644
--- a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc
@@ -23,4 +23,4 @@
 
 typedef std::tuple_element<1, std::array<int, 1>>::type type;
 
-// { dg-error "static assertion failed" "" { target *-*-* } 322 }
+// { dg-error "static assertion failed" "" { target *-*-* } 330 }