How to find the end address of a function in a C prog?

Question

Start address can be obtained from the function name, how to find the end address of a function? I have been asked this question in interview:

Consider the function f() which i wrote has crossed the text section and started over writing the adjacent section (data section). How can i handle this situation? Also he added that i should handle it through C code. I should not see the symbol map file and get the address.

Answer 1

With GCC, you can take the address of a label, with the && operator (yes - &&, not &).
This can be used as follows:

void f(void) {
    printf("Start %p End %p\n", f, &&f_end);
    f_end: return;
}

This won't give you exactly the end, because there's some epilogue code after the label, but I think it's good enough for an interview answer.

Answer 2

The C standard does not guarantee that there is such a thing as then end address of a function.

In practice, functions are not necessarily a single continuous piece of memory, but can overlap, or be fragmented across several pieces by code optimisers.

For that reason there is no way to find this out at runtime.

Furthermore, there is no guarantee that the "start address" you get from GetProcAddress or by taking the address of the function (for a function pointer) bears any relation to where the code actually is.

All a function pointer guarantees is that if you call through the address the function will be executed. It does not guarantee that the code actually resides there. It may just be the address of a thunk, for example.