Fix multi_buffer allocation alignment

CHANGELOG.md

@@ -5,6 +5,7 @@ Version 261:
 * Remove redundant includes in websocket
 * Simplify websocket::detail::prng
 * Don't over-allocate in http::basic_fields
+* Fix multi_buffer allocation alignment
 
 --------------------------------------------------------------------------------
 

include/boost/beast/core/impl/multi_buffer.hpp

@@ -87,41 +87,6 @@ namespace beast {
           in_pos_                   out_pos_ == 0
                                     out_end_ == 0
 */
-//------------------------------------------------------------------------------
-
-template<class Allocator>
-class basic_multi_buffer<Allocator>::element
-    : public boost::intrusive::list_base_hook<
-        boost::intrusive::link_mode<
-            boost::intrusive::normal_link>>
-{
-    using size_type = typename
-        detail::allocator_traits<Allocator>::size_type;
-
-    size_type const size_;
-
-public:
-    element(element const&) = delete;
-
-    explicit
-    element(size_type n) noexcept
-        : size_(n)
-    {
-    }
-
-    size_type
-    size() const noexcept
-    {
-        return size_;
-    }
-
-    char*
-    data() const noexcept
-    {
-        return const_cast<char*>(
-            reinterpret_cast<char const*>(this + 1));
-    }
-};
 
 //------------------------------------------------------------------------------
 
@@ -486,7 +451,7 @@ template<class Allocator>
 basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     Allocator const& alloc) noexcept
-    : boost::empty_value<base_alloc_type>(
+    : boost::empty_value<Allocator>(
         boost::empty_init_t(), alloc)
     , max_(alloc_traits::max_size(this->get()))
     , out_(list_.end())
@@ -498,8 +463,8 @@ basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     std::size_t limit,
     Allocator const& alloc) noexcept
-    : boost::empty_value<
-        base_alloc_type>(boost::empty_init_t(), alloc)
+    : boost::empty_value<Allocator>(
+        boost::empty_init_t(), alloc)
     , max_(limit)
     , out_(list_.end())
 {
@@ -509,7 +474,7 @@ template<class Allocator>
 basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     basic_multi_buffer&& other) noexcept
-    : boost::empty_value<base_alloc_type>(
+    : boost::empty_value<Allocator>(
         boost::empty_init_t(), std::move(other.get()))
     , max_(other.max_)
     , in_size_(boost::exchange(other.in_size_, 0))
@@ -529,8 +494,8 @@ basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     basic_multi_buffer&& other,
     Allocator const& alloc)
-    : boost::empty_value<
-        base_alloc_type>(boost::empty_init_t(), alloc)
+    : boost::empty_value<Allocator>(
+        boost::empty_init_t(), alloc)
     , max_(other.max_)
 {
     if(this->get() != other.get())
@@ -561,7 +526,7 @@ template<class Allocator>
 basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     basic_multi_buffer const& other)
-    : boost::empty_value<base_alloc_type>(
+    : boost::empty_value<Allocator>(
         boost::empty_init_t(), alloc_traits::
             select_on_container_copy_construction(
                 other.get()))
@@ -576,7 +541,7 @@ basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     basic_multi_buffer const& other,
     Allocator const& alloc)
-    : boost::empty_value<base_alloc_type>(
+    : boost::empty_value<Allocator>(
         boost::empty_init_t(), alloc)
     , max_(other.max_)
     , out_(list_.end())
@@ -600,8 +565,8 @@ basic_multi_buffer<Allocator>::
 basic_multi_buffer(
     basic_multi_buffer<OtherAlloc> const& other,
         allocator_type const& alloc)
-    : boost::empty_value<
-        base_alloc_type>(boost::empty_init_t(), alloc)
+    : boost::empty_value<Allocator>(
+        boost::empty_init_t(), alloc)
     , max_(other.max_)
     , out_(list_.end())
 {
@@ -991,6 +956,7 @@ consume(size_type n) noexcept
 {
     if(list_.empty())
         return;
+    auto a = rebind_type{this->get()};
     for(;;)
     {
         if(list_.begin() != out_)
@@ -1013,8 +979,8 @@ consume(size_type n) noexcept
             list_.erase(list_.iterator_to(e));
             auto const len = sizeof(e) + e.size();
             e.~element();
-            alloc_traits::deallocate(this->get(),
-                reinterpret_cast<char*>(&e), len);
+            alloc_traits::deallocate(a,
+                reinterpret_cast<align_type*>(&e), len);
         #if BOOST_BEAST_MULTI_BUFFER_DEBUG_CHECK
             debug_check();
         #endif
@@ -1215,10 +1181,13 @@ void
 basic_multi_buffer<Allocator>::
 destroy(element& e)
 {
-    auto const len = sizeof(e) + e.size();
+    auto a = rebind_type{this->get()};
+    auto const n =
+        (sizeof(element) + e.size() + sizeof(align_type) - 1) /
+            sizeof(align_type);
     e.~element();
-    alloc_traits::deallocate(this->get(),
-        reinterpret_cast<char*>(&e), len);
+    alloc_traits::deallocate(a,
+        reinterpret_cast<align_type*>(&e), n);
 }
 
 template<class Allocator>
@@ -1230,9 +1199,11 @@ alloc(std::size_t size) ->
     if(size > alloc_traits::max_size(this->get()))
         BOOST_THROW_EXCEPTION(std::length_error(
         "A basic_multi_buffer exceeded the allocator's maximum size"));
-    return *::new(alloc_traits::allocate(
-        this->get(),
-        sizeof(element) + size)) element(size);
+    auto a = rebind_type{this->get()};
+    auto const p = alloc_traits::allocate(a,
+        (sizeof(element) + size + sizeof(align_type) - 1) /
+            sizeof(align_type));
+    return *(::new(p) element(size));
 }
 
 template<class Allocator>

include/boost/beast/core/multi_buffer.hpp

@@ -15,6 +15,7 @@
 #include <boost/asio/buffer.hpp>
 #include <boost/core/empty_value.hpp>
 #include <boost/intrusive/list.hpp>
+#include <boost/type_traits/type_with_alignment.hpp>
 #include <iterator>
 #include <limits>
 #include <memory>
@@ -62,14 +63,13 @@ namespace beast {
 template<class Allocator>
 class basic_multi_buffer
 #if ! BOOST_BEAST_DOXYGEN
-    : private boost::empty_value<
-        typename detail::allocator_traits<Allocator>::
-            template rebind_alloc<char>>
+    : private boost::empty_value<Allocator>
 #endif
 {
-    using base_alloc_type = typename
-        detail::allocator_traits<Allocator>::
-            template rebind_alloc<char>;
+    // Fancy pointers are not supported
+    static_assert(std::is_pointer<typename
+        std::allocator_traits<Allocator>::pointer>::value,
+        "Allocator must use regular pointers");
 
     static bool constexpr default_nothrow =
         std::is_nothrow_default_constructible<Allocator>::value;
@@ -77,19 +77,61 @@ class basic_multi_buffer
     // Storage for the list of buffers representing the input
     // and output sequences. The allocation for each element
     // contains `element` followed by raw storage bytes.
-    class element;
+    class element
+        : public boost::intrusive::list_base_hook<
+            boost::intrusive::link_mode<
+                boost::intrusive::normal_link>>
+    {
+        using size_type = typename
+            detail::allocator_traits<Allocator>::size_type;
+
+        size_type const size_;
+
+    public:
+        element(element const&) = delete;
+
+        explicit
+        element(size_type n) noexcept
+            : size_(n)
+        {
+        }
+
+        size_type
+        size() const noexcept
+        {
+            return size_;
+        }
+
+        char*
+        data() const noexcept
+        {
+            return const_cast<char*>(
+                reinterpret_cast<char const*>(this + 1));
+        }
+    };
 
     template<bool>
     class readable_bytes;
 
-    using alloc_traits =
-        beast::detail::allocator_traits<base_alloc_type>;
-    using list_type = typename boost::intrusive::make_list<element,
-        boost::intrusive::constant_time_size<true>>::type;
-    using iter = typename list_type::iterator;
-    using const_iter = typename list_type::const_iterator;
+    using size_type = typename
+        detail::allocator_traits<Allocator>::size_type;
 
-    using size_type = typename alloc_traits::size_type;
+    using align_type = typename
+        boost::type_with_alignment<alignof(element)>::type;
+
+    using rebind_type = typename
+        beast::detail::allocator_traits<Allocator>::
+            template rebind_alloc<align_type>;
+
+    using alloc_traits =
+        beast::detail::allocator_traits<rebind_type>;
+
+    using list_type = typename boost::intrusive::make_list<
+        element, boost::intrusive::constant_time_size<true>>::type;
+
+    using iter = typename list_type::iterator;
+
+    using const_iter = typename list_type::const_iterator;
 
     using pocma = typename
         alloc_traits::propagate_on_container_move_assignment;