What is the entry point of 'exec'

What is the entry point of ‘exec’ in cpython source code?
I have some custom code in ‘static void pymain_run_python(int *exitcode)’ but I have to put this code to ‘exec’

Assuming you mean the python-accessible builtin function, here: cpython/Python/bltinmodule.c at 15309329b65a285cb7b3071f0f08ac964b61411b · python/cpython · GitHub

But that is probably not the correct place to do whatever you want to do.