Fix alignment issue with heap_string

danielaparker · Oct 11, 2023 · b5f5958 · b5f5958
1 parent 62e3858
commit b5f5958
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Showing 2 changed files with 33 additions and 6 deletions.
diff --git a/include/jsoncons/detail/heap_string.hpp b/include/jsoncons/detail/heap_string.hpp
@@ -18,6 +18,13 @@
 namespace jsoncons { 
 namespace detail {
 
+    inline void*
+    align_up(void* ptr, std::size_t alignment) noexcept
+    {
+        return reinterpret_cast<void*>(~(alignment - 1) &
+            (reinterpret_cast<uintptr_t>(ptr) + alignment - 1));
+    }
+
     template <class Extra,class Allocator>
     struct heap_string_base
     {
@@ -52,6 +59,7 @@ namespace detail {
 
         pointer p_;
         std::size_t length_;
+        uint16_t offset_;
 
         ~heap_string() noexcept = default; 
 
@@ -114,23 +122,29 @@ namespace detail {
             heap_string_type data;
             char_type c[1];
         };
-        typedef typename jsoncons_aligned_storage<sizeof(storage_t), alignof(storage_t)>::type json_storage_kind;
+        typedef typename jsoncons_aligned_storage<sizeof(storage_t), alignof(storage_t)>::type storage_type;
 
         static size_t aligned_size(std::size_t n)
         {
-            return sizeof(json_storage_kind) + n;
+            return sizeof(storage_type) + n;
         }
 
     public:
 
         static pointer create(const char_type* s, std::size_t length, Extra extra, const Allocator& alloc)
         {
-            std::size_t mem_size = aligned_size(length*sizeof(char_type));
+            std::size_t len = aligned_size(length*sizeof(char_type));
+
+            std::size_t align = alignof(storage_type);
+            std::size_t mem_len = align-1+len;
 
             byte_allocator_type byte_alloc(alloc);
-            byte_pointer ptr = byte_alloc.allocate(mem_size);
+            byte_pointer ptr = byte_alloc.allocate(mem_len);
+
+            char* q = extension_traits::to_plain_pointer(ptr);
+
+            void* storage = align_up(q, align);
 
-            char* storage = extension_traits::to_plain_pointer(ptr);
             heap_string_type* ps = new(storage)heap_string_type(extra, byte_alloc);
 
             auto psa = launder_cast<storage_t*>(storage); 
@@ -149,7 +163,9 @@ namespace detail {
             {
                 heap_string_type* rawp = extension_traits::to_plain_pointer(ptr);
 
-                char* p = launder_cast<char*>(rawp);
+                char* q = launder_cast<char*>(rawp);
+
+                char* p = q - ptr->offset_;
 
                 std::size_t mem_size = aligned_size(ptr->length_*sizeof(char_type));
                 byte_allocator_type byte_alloc(ptr->get_allocator());

diff --git a/test/corelib/src/detail/heap_string_tests.cpp b/test/corelib/src/detail/heap_string_tests.cpp
@@ -11,3 +11,14 @@
 
 using namespace jsoncons;
 
+using heap_string_factory_type = jsoncons::detail::heap_string_factory<char, null_type, std::allocator<char>>;
+using pointer = typename heap_string_factory_type::pointer;
+
+TEST_CASE("heap_string test")
+{
+    std::string s("Hello World");
+
+    pointer ptr = heap_string_factory_type::create(s.data(), s.length(), null_type(), std::allocator<char>());
+}
+
+