This is not concrete in any way. What guarantee do you mean? What "this information" should be "recorded in their signature"? What does this murky "information"

This is not concrete in any way. What guarantee do you mean? What "this information" should be "recorded in their signature"? What does this murky "information" have to do with enabling tail recursion? Here's a tail recursive function C function that is compiled to tail recursive machine code without any problems: https://gcc.godbolt.org/z/dc886a https://gcc.godbolt.org/z/dc886a This function can be called from external compilation units without any problems. Whether or not it is compiled to tail recursive code is an implementation detail that the caller doesn't need to know about.