Lipraxde / UHook

Add hook mechanism to your project

UHook

Add hook mechanism to your project

UHook can help turn a function into a hook. The hook can have different behaviors by loading different HookLibrary. It is especially useful when the project is almost complete. Because only a little modification is needed.

For example, here we have a function calc:

uint64_t calc(uint64_t i) {
  // Fibonacci
  if (i > 1)
    return calc(i - 1) + calc(i - 2);
  else
    return 1;
}

To turn calc into a hook, use PROVIDE_HOOK and ORIG_HOOK macros to help us:

#include <uhook/HookProvider.h>

PROVIDE_HOOK(uint64_t, calc, "Description about calc", uint64_t)
uint64_t ORIG_HOOK(calc)(uint64_t i) {
  // Fibonacci
  if (i > 1)
    return calc::self(i - 1) + calc::self(i - 2);
  else
    return 1;
}

Example of using the hook calc:

int main(int argc, char *argv[]) {
  // Load the hook library with the input path
  if (argc > 1 && (dlopen(argv[1], RTLD_NOW) == nullptr))
      std::cerr << "[Error] Fail to open the hook library\n";
  std::cout << "Calc(" << argc << ") = " << calc::hook(argc) << '\n';
}

The default behavior of calc::hook() is to calculate the Fibonacci number. Let's hook calc, create a hook library. The hook library contains the following code, use USE_HOOK and NEW_HOOK:

USE_HOOK(uint64_t, calc, uint64_t)
uint64_t NEW_HOOK(calc)(uint64_t i) {
  // Factorial
  if (i > 1)
    return i * calc::self(i - 1);
  else
    return 1;
}

If we execute command ./main HookLib.so 3 4 5,the main program should print Calc(5) = 120.