Here is the Question

/*A.c*/
#include <stdio.h>
int sayHi() {
  printf("Hi, this is AAAAA\n");
  return 0;
}
int sayOut() {
  sayHi();
  printf("Use this to introduce AAAAA\n");
  return 0;
}

/*B.c*/
#include <stdio.h>
int sayHi() {
  printf("Hi, this is BBBBB\n");
  return 0;
}
int sayOut() {
  sayHi();
  printf("Use this to introduce BBBBB\n");
  return 0;
}

#include <stdio.h>
extern int sayOut();

int main() {
  sayOut();
  return 0;
}

# if link A first
>gcc test.c -L. -lA -lB
>./a.out
Hi, this is AAAAA
Use this to introduce AAAAA
# if link B first
>gcc test.c -L. -lB -lA
>./a.out
Hi, this is BBBBB
Use this to introduce BBBBB

First solution

at first i use dlopen to explicitly load a dynamic library

#include <stdio.h>
#include<dlfcn.h>
extern int sayOut();

typedef int (*func_pt)();

int main() {
    void *handle = NULL;
    func_pt func = NULL;
    if((handle = dlopen("./libA.so",RTLD_LAZY))== NULL)
    {
        printf("dlopen %s\n", dlerror());
        return -1;
    }
    func = dlsym(handle, "sayOut");
    func();
    dlclose(handle);

    if((handle = dlopen("./libB.so",RTLD_LAZY))== NULL)
    {
        printf("dlopen %s\n", dlerror());
        return -1;
    }
    func = dlsym(handle, "sayOut");
    func();
    dlclose(handle);
  return 0;
}

❯gcc test.c -L. -lA -lB
❯ ./a.out
Hi, this is AAAAA
Use this to introduce AAAAA
Hi, this is AAAAA
Use this to introduce BBBBB

❯ gcc test.c -L. -lB -lA
❯ ./a.out
Hi, this is BBBBB
Use this to introduce AAAAA
Hi, this is BBBBB
Use this to introduce BBBBB

we can see the outer func sayOut is load explicitly, however the inner function still related to linking order it is because the inner function are exposed to the outside

Second solution

i use attrubute to control if a function should expose to the outside here is an example

/*A.c*/
#include <stdio.h>
#define DLL_PUBLIC __attribute__((visibility("default")))
#define DLL_LOCAL __attribute__((visibility("hidden")))

DLL_LOCAL int sayHi() {
  printf("Hi, this is AAAAA\n");
  return 0;
}
DLL_PUBLIC int sayOut() {
  sayHi();
  printf("Use this to introduce AAAAA\n");
  return 0;
}

/*B.c*/
#include <stdio.h>

#define DLL_PUBLIC __attribute__((visibility("default")))
#define DLL_LOCAL __attribute__((visibility("hidden")))

DLL_LOCAL int sayHi() {
  printf("Hi, this is BBBBB\n");
  return 0;
}
DLL_PUBLIC int sayOut() {
  sayHi();
  printf("Use this to introduce BBBBB\n");
  return 0;
}

❯ gcc test.c -L. -lA -lB
❯ ./a.out
Hi, this is AAAAA
Use this to introduce AAAAA
Hi, this is BBBBB
Use this to introduce BBBBB

❯ gcc test.c -L. -lB -lA
❯ ./a.out
Hi, this is AAAAA
Use this to introduce AAAAA
Hi, this is BBBBB
Use this to introduce BBBBB

Third solution

The third way is only set outer function to visible and compile it with -fvisibility=hidden argument

/*A.c*/
#include <stdio.h>
#define DLL_PUBLIC __attribute__((visibility("default")))

int sayHi() {
  printf("Hi, this is AAAAA\n");
  return 0;
}
DLL_PUBLIC int sayOut() {
  sayHi();
  printf("Use this to introduce AAAAA\n");
  return 0;
}

/*B.c*/
#include <stdio.h>

#define DLL_PUBLIC __attribute__((visibility("default")))

int sayHi() {
  printf("Hi, this is BBBBB\n");
  return 0;
}
DLL_PUBLIC int sayOut() {
  sayHi();
  printf("Use this to introduce BBBBB\n");
  return 0;
}

and it worked as expected
❯ gcc test.c -L. -lA -lB
❯ ./a.out
Hi, this is AAAAA
Use this to introduce AAAAA
Hi, this is BBBBB
Use this to introduce BBBBB

❯ gcc test.c -L. -lB -lA
❯ ./a.out
Hi, this is AAAAA
Use this to introduce AAAAA
Hi, this is BBBBB
Use this to introduce BBBBB

https://blog.csdn.net/giveaname/article/details/103353828