It's not about okay or not okay. Zig is designed to prevent any user code from being implicitly called, or for the resolution of user code to be done implicitly. It's not about what the CPU does internally, but whether you're able to tell, from reading the code of a single subroutine, which operations could be done, whether stack frames can be created etc.. This has pros and cons, and for some people the pros outweigh the cons and for others, the other way around, and that's why different programming languages need to prioritise different things when they target different users.