How to remove *ALL* unused symbols from a shared library?

Question

I have a code that I need to compile to shared library and remove ALL unused code from, but I can't find a proper solution. Here is a simple example:

// test.cpp, compiled with GCC -fPIC -shared -fvisibility=hidden
#include <stdio.h>
class Foo {
    void bar();
};
void Foo::bar() { printf("hello"); } // unused and should be removed
// I'm using printf("hello") so I can detect the symbols with `strings`

__attribute__((visibility("default"))) void test() {} // this function is "used"

-fvisibility=hidden makes it so that all functions are hidden by default, and I manually mark public functions with __attribute__((visibility("default"))). However, hidden functions are not removed unless marked as static (which I can't do to C++ methods, obviously).

No matter what I do, GCC will always keep void Foo::bar() and hello around. Is there a way to remove these symbols without hacking the compiler? (yes, I am considering it at this point!)

Thanks!

Answer 1

Compile with the flag -ffunction-sections. Then link with -Wl,--gc-sections. I think that this can also be achieved with LTO, I'm not sure of the details.

Note that all public symbols in a dylib are considered live. Only hidden symbols will be stripped this way.