Calling private method in C++

Question

This is purely a theoretical question, I know that if someone declares a method private, you probably shouldn\'t call it. I managed to call private virtual methods and chang

Answer 1

For GCC it can be done by using mangled name of a function.

#include 

class A {
public:
    A() {
        f(); //the function should be used somewhere to force gcc to generate it
    }
private:
    void f() { printf("\nf"); }
};

typedef void(A::*TF)();

union U {
    TF f;
    size_t i;
};

int main(/*int argc, char *argv[]*/) {
    A a;
    //a.f(); //error
    U u;
    //u.f = &A::f; //error

    //load effective address of the function
    asm("lea %0, _ZN1A1fEv"
    : "=r" (u.i));
    (a.*u.f)();
    return 0;
}

Mangled names can be found by nm *.o files.

Add -masm=intel compiler option

Sources: GCC error: Cannot apply offsetof to member function MyClass::MyFunction https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html