From b694ada29489728a6d6764a59d7bc8c659786f74 Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Date: Fri, 27 Jan 2023 12:37:17 +0100
Subject: [PATCH] Do not memset(0) POD types

"POD" is the wrong type trait to determine if something can be safely
zero-filled in order to achieve zero initialization. Consider a type
like

  struct POD { int POD::*ptr; };

This is a POD; its value initialization needs to value initialize the
member, and since it's a pointer, that's zero initialization, and that's
setting the pointer to null.

On Itanium, a null pointer to data member is not zero filled; it actually
has the value -1u.

Hence, zero-filling via memset(0) a POD object like the one above is
erroneous. Unfortunately there is no type trait in C++ that we can use to
know if a given datatype can be value initialized by zero-filling -- we
can check for trivial constructability, but that's a necessary
condition, not a sufficient one (POD above is also trivially
constructible).

The test is disabled on MSVC because of a compiler bug.

Fixes #238
---
 doc/container.qbk                             |  4 ---
 .../boost/container/detail/copy_move_algo.hpp |  3 ---
 test/vector_test.cpp                          | 25 +++++++++++++++++++
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/doc/container.qbk b/doc/container.qbk
index 591edd9..981a151 100644
--- a/doc/container.qbk
+++ b/doc/container.qbk
@@ -1276,10 +1276,6 @@ member object and member function pointers) to be initializable using `std::mems
 Most platforms are compatible with this initialization, but in case this initialization is not desired the
 user can `#define BOOST_CONTAINER_MEMZEROED_POINTER_IS_NOT_ZERO` before including library headers.
 
-If neither `BOOST_CONTAINER_MEMZEROED_FLOATING_POINT_IS_NOT_ZERO` nor
-`BOOST_CONTAINER_MEMZEROED_POINTER_IS_NOT_ZERO` is defined [*Boost.Container] also considers POD
-types to be value initializable via `std::memset` with value zero.
-
 [endsect]
 
 [endsect]
diff --git a/include/boost/container/detail/copy_move_algo.hpp b/include/boost/container/detail/copy_move_algo.hpp
index a7d23a5..8729b30 100644
--- a/include/boost/container/detail/copy_move_algo.hpp
+++ b/include/boost/container/detail/copy_move_algo.hpp
@@ -296,9 +296,6 @@ struct is_memzero_initializable
       #if defined(BOOST_CONTAINER_MEMZEROED_FLOATING_POINT_IS_ZERO)
       || dtl::is_floating_point<value_type>::value
       #endif
-      #if defined(BOOST_CONTAINER_MEMZEROED_FLOATING_POINT_IS_ZERO) && defined(BOOST_CONTAINER_MEMZEROED_POINTER_IS_NULL)
-      || dtl::is_pod<value_type>::value
-      #endif
       );
 };
 
diff --git a/test/vector_test.cpp b/test/vector_test.cpp
index 6057ab1..e72f62c 100644
--- a/test/vector_test.cpp
+++ b/test/vector_test.cpp
@@ -220,6 +220,12 @@ bool test_span_conversion()
 
 #endif   //BOOST_VECTOR_TEST_HAS_SPAN
 
+struct POD { int POD::*ptr; };
+BOOST_STATIC_ASSERT_MSG
+   ( boost::container::dtl::is_pod<POD>::value
+   , "POD test failed"
+   );
+
 int main()
 {
    {
@@ -392,5 +398,24 @@ int main()
          );
    }
 
+   ////////////////////////////////////
+   //    POD types should not be 0-filled testing
+   ////////////////////////////////////
+#if !defined(_MSC_VER)
+   // MSVC miscompiles value initialization of pointers to data members,
+   // https://developercommunity.visualstudio.com/t/Pointer-to-data-member-is-not-initialize/10238905
+   {
+      typedef boost::container::vector<POD> cont;
+      const std::size_t size = 10;
+      cont a(size);
+      for(std::size_t i = 0; i != size; ++i) {
+         if (a[i].ptr != 0) {
+            std::cerr << "POD test failed" << std::endl;
+            return 1;
+         }
+      }
+   }
+#endif
+
    return 0;
 }