SubHook is a super-simple hooking library for C/C++ that works on both Linux and Windows. It currently supports only x86 and x86-64.

Examples

In the following examples foo is some function or a function pointer that takes a single argument of type int and uses the same calling convention as my_foo (depends on compiler).

C

#include <stdio.h>
#include <subhook.h>

subhook_t foo_hook;

void my_foo(int x) {
  /* Sometimes you want to call the original function. */
  subhook_remove(foo_hook);

  printf("foo(%d) called\n", x);
  foo(x);

  /* Install the hook back again to intercept further calls. */
  subhook_install(foo_hook);
}

int main() {
  foo_hook = subhook_new();

  /* The "source" is the function that we want to hook. */
  subhook_set_src((void*)foo);

  /* The "destination" is the function that will get called instead of the
   * original function. */
  subhook_set_dst((void*)my_foo);

  /* Install our newly created hook so from now on any call to foo()
   * will be redirected to my_foo(). */
  subhook_install(foo_hook);

  /* Free the memory when you're done. */
  subhook_free(foo_hook);
}

C++

#include <iostream>
#include <subhook.h>

SubHook foo_hook;

void my_foo(int x) {
  // ScopedRemove removes the specified hook and automatically re-installs it
  // when it goes out of scope (thanks to C++ destructors).
  SubHook::ScopedRemove remove(&foo_hook);

  std::cout << "foo(" << x < ") called" << std::endl;
  foo(x);
}

int main() {
  foo_hook.Install((void*)foo, (void*)my_foo);
}