ld_preload + api

main.cc

#include <dlfcn.h>
#include "tool.h"

int main() {
  //void *handle = dlopen("./tool.so", RTLD_NOW);
  print_t func = (print_t)dlsym(RTLD_NEXT, "print");                                                                                                                   
  func();
  return 0;
}

run.sh

g++ -ldl -shared -fPIC -o tool.so tool.cc
g++ ./main.cc -ldl
LD_PRELOAD=./tool.so ./a.out

tool.cc

#include "tool.h"
#include <cstdio>

extern "C"
void print() {
  printf("tool.h\n");                                                                                                                                                  
}

tool.h

typedef void (*print_t)();