dlopen/dlsym: error getting function pointer

Question

I am attempting to get the function pointer by using dlopen and dlsym, however I have been unable to get it working correctly. It fails when trying to doing the dlsym call. Following is my code.

Any help please?

#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

int test() {
    printf("%s", "test()");
    return 123;
}

int main() {
    char * functionname = "test";
    void* handle = dlopen(NULL,RTLD_LAZY|RTLD_GLOBAL);
    if (!handle) {
        fprintf(stderr, "Couldn't open handle: %s\n",
            dlerror());
        exit(1);
    }

    int (*fun)() = (int (*)())dlsym(handle, functionname);
    if (fun == NULL) { 
        fprintf(stderr, "Couldn't find function: %s\n",functionname); 
        exit(1);
    }
    int a = fun();
    printf("result: %d \n", a);
}

Answer 1

Probably you need to specify to the linker to export the symbols as dynamic. With gcc you have to use -rdynamic.

You can check the exported dynamic symbols with objdump -T.