#include <exception>
#include <cassert>
#include <cstring>

class user_exception: public std::exception
{
  const char* what() const throw()
  {
    return "user exception";
  }
};

int main() {
  using namespace std;
  const exception& rhs = user_exception();
  exception lhs = rhs;
  assert( strcmp(lhs.what(), rhs.what()) == 0 );
}

t: t.cpp:18: int main(): Assertion `strcmp(lhs.what(), rhs.what()) == 0' failed.

Disallowed system call: SYS_kill