How could type_traits know all of informations about polymorphism at compile time

I'm learning how to use type_traits with C++11 and I'm told that type_traits works at compile time.

I'm really surprised. I've made a test as below:

class A {virtual void foo();};
class B : public A {};

constexpr bool b = std::is_base_of<A, B>::value;
constexpr bool bb = std::is_polymorphic<A>::value;
constexpr bool bb2 = std::is_polymorphic<B>::value;

int main()
{
    return 0;
}

I compile this piece of code with the command: g++ -std=c++11 main.cpp -g and get a binary file a.out.

Then I execute the command objdump -dj .rodata a.out and get the output:

./a.out:     file format elf64-x86-64    

Disassembly of section .rodata:

0000000000000830 <_IO_stdin_used>:
 830:   01 00 02 00                                         ....

0000000000000834 <_ZStL19piecewise_construct>:
        ...

0000000000000835 <_ZL1b>:
 835:   01                                                  .

0000000000000836 <_ZL2bb>:
 836:   01                                                  .

0000000000000837 <_ZL3bb2>:
 837:   01                                                  .

OK, type_traits does work at compile time.

But how? Or does it mean that the c++ compiler could get all of polymorphism information at compile time? I always thought that polymorphism information was all about runtime stuff...