That's not really what's happening with such C++ code. `static` variables are placed in normal writeable global memory. Only difference with such static is that compiler generates extra "bool" variable and checks it to initialize obj only on first run (threadsafe on C++11 and up).

You can see example here: https://godbolt.org/z/7f1qbh5r5

There are no code modifications - all compiler generated is extra byte check ("if" statement) and then acquire/release lock around constructor to be threadsafe.