storage of compiled functions

Hello everyone

i have been studying postgres's function handling philosophy lately. I
got stuck at a point where i could'nt get the answer myself

All the information related to functions are stored in pg_proc system
catalog. But when a function is compiled (probably the data structure
that contains a compiled function is pgfunction) where is it stored
for persistence.

I checked plpgsql's code and noticed there that the function after
compilation was saved in
fcinfo->flinfo->fn_extra. But how do you get persistence (of compiled
functions) by storing its value in fcinfo->flinfo->fn_extra. Or in
other words how is the FmgrInfo information stored to persistence in
postgresql

Thankz