jsoncpp: force alignment of Json::Value::null to avoid crashes on ARM.

third_party/jsoncpp/overrides/src/lib_json/json_value.cpp

 // Copyright 2011 Baptiste Lepilleur
 // Distributed under MIT license, or public domain if desired and
 // recognized in your jurisdiction.
 // See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
 
 #if !defined(JSON_IS_AMALGAMATION)
 # include <json/assertions.h>
 # include <json/value.h>
 # include <json/writer.h>
 # ifndef JSON_USE_SIMPLE_INTERNAL_ALLOCATOR
 #  include "json_batchallocator.h"
 # endif // #ifndef JSON_USE_SIMPLE_INTERNAL_ALLOCATOR
 #endif // if !defined(JSON_IS_AMALGAMATION)
 #include <math.h>
 #include <sstream>
 #include <utility>
 #include <stdexcept>
 #include <cstring>
 #include <cassert>
 #ifdef JSON_USE_CPPTL
 # include <cpptl/conststring.h>
 #endif
 #include <cstddef>    // size_t
 
 #define JSON_ASSERT_UNREACHABLE assert( false )
 
 namespace Json {
 
 // This is a walkaround to avoid the static initialization of Value::null.
-// const Value Value::null;
-static const unsigned char kNull[sizeof(Value)] = { 0 };
+// kNull must be word-aligned to avoid crashing on ARM.  We use an alignment of
+// 8 (instead of 4) as a bit of future-proofing.
+#if defined(__ARMEL__)
+#define ALIGNAS(byte_alignment) __attribute__((aligned(byte_alignment)))
+#else
+#define ALIGNAS(byte_alignment)
+#endif
+static const unsigned char ALIGNAS(8) kNull[sizeof(Value)] = {0};
 const Value& Value::null = reinterpret_cast<const Value&>(kNull);
 
 const Int Value::minInt = Int( ~(UInt(-1)/2) );
 const Int Value::maxInt = Int( UInt(-1)/2 );
 const UInt Value::maxUInt = UInt(-1);
 # if defined(JSON_HAS_INT64)
 const Int64 Value::minInt64 = Int64( ~(UInt64(-1)/2) );
 const Int64 Value::maxInt64 = Int64( UInt64(-1)/2 );
 const UInt64 Value::maxUInt64 = UInt64(-1);
 // The constant is hard-coded because some compiler have trouble
@@ skipping 1873 matching lines @@
             // Error: node is not an object at position...
          }
          node = &((*node)[arg.key_]);
       }
    }
    return *node;
 }
 
 
 } // namespace Json