Full name of submitter (unless configured in github; will be published with the issue): Jim X

Consider this example:

struct A{
    virtual void foo(){}
};
struct B{
    virtual void foo2(){}
};
struct D:A,B{
   virtual void foo(){

   }
};
struct No{};
int main(){
  No no;
  B* ptr = (B*)&no;
  try{
    auto r = dynamic_cast<D*>(ptr);
    std::cout<< (long long int)r;
  }catch(...){

  };
}

This example just causes the segment fault in major implementations. However, [expr.dynamic.cast] does not specify the behavior for this case.

Suggested Resolution

Append a wording before [expr.dynamic.cast] p7

If the type of the object pointed or referred to by v is not similar to the pointed or referred type by v, the behavior is undefined.