rt_finalize question

[Oleg B via Digitalmars-d-learn]

Hello. In object.di rt_finalize calls for class objects in 
destroy func.
I not found it in dmd source on github and not found in druntime 
sources.
I think rt_finalize must call dtors for object and base classes, 
but I think that's not all. Or if it all has it code logic 
problems?

void myDestroy(T)( T obj ) if( is( T == class ) )
{
    mixin( callDtor!( obj.stringof, 
TypeTuple!(T,BaseClassesTuple!T) ) );
}
string callDtor( string name, BCT... )() @property
{
    import std.string;
    static if( BCT.length == 1 ) return ""; // Object has no dtor
    else
        return format( "%s.%s.__dtor();\n", name, 
BCT[0].stringof.split(".")[$-1] ) ~
               callDtor!(name, BCT[1..$]);
}

function callDtor generate string like this

obj.C.__dtor();
obj.B.__dtor();
obj.A.__dtor();

for class model

class A{}
class B : A {}
class C : B {}

I want understand why destroy for class objects call extern(C) 
function rt_finalize (not pure, with gc, can except), and how it 
works (rt_finalize gets void*).