dnsdist: make sure we do not allocate 16-byte aligned objects through…

… lua(jit)

luajit aligns only to 8 bytes by default, and some objects require 16 byte alignment.
Fixes PowerDNS#13766

ext/luawrapper/include/LuaContext.hpp

@@ -1643,6 +1643,7 @@ class LuaContext {
               // creating the object
               // lua_newuserdata allocates memory in the internals of the lua library and returns it so we can fill it
               //   and that's what we do with placement-new
+              static_assert(alignof(TType) <= 8);
               const auto pointerLocation = static_cast<TType*>(lua_newuserdata(state, sizeof(TType)));
               new (pointerLocation) TType(std::forward<TType2>(value));
             }
@@ -2292,6 +2293,7 @@ struct LuaContext::Pusher<TReturnType (TParameters...)>
         // creating the object
         // lua_newuserdata allocates memory in the internals of the lua library and returns it so we can fill it
         //   and that's what we do with placement-new
+        // static_assert(alignof(TFunctionObject) <= 8); XXX trips on at least c++lib 17, see #13766
         const auto functionLocation = static_cast<TFunctionObject*>(lua_newuserdata(state, sizeof(TFunctionObject)));
         new (functionLocation) TFunctionObject(std::move(fn));
 
@@ -2335,6 +2337,7 @@ struct LuaContext::Pusher<TReturnType (TParameters...)>
         };
 
         // we copy the function object onto the stack
+        static_assert(alignof(TFunctionObject) <= 8);
         const auto functionObjectLocation = static_cast<TFunctionObject*>(lua_newuserdata(state, sizeof(TFunctionObject)));
         new (functionObjectLocation) TFunctionObject(std::move(fn));
 

pdns/dnsdist-lua-bindings.cc

@@ -78,16 +78,16 @@ void setupLuaBindings(LuaContext& luaCtx, bool client, bool configCheck)
   luaCtx.registerFunction("toString", &ServerPolicy::toString);
   luaCtx.registerFunction("__tostring", &ServerPolicy::toString);
 
-  ServerPolicy policies[] = {
+  static const std::array<ServerPolicy, 6> policies = {
     ServerPolicy{"firstAvailable", firstAvailable, false},
     ServerPolicy{"roundrobin", roundrobin, false},
     ServerPolicy{"wrandom", wrandom, false},
     ServerPolicy{"whashed", whashed, false},
     ServerPolicy{"chashed", chashed, false},
     ServerPolicy{"leastOutstanding", leastOutstanding, false}
   };
-  for (auto& policy : policies) {
-    luaCtx.writeVariable(policy.d_name, policy);
+  for (const auto& policy : policies) {
+    luaCtx.writeVariable(policy.d_name, &policy);
   }
 
 #endif /* DISABLE_POLICIES_BINDINGS */