hook _memcpy using a trampoline approach

Here is another method to hook _memcpy using a trampoline approach:

```cpp
#include <dlfcn.h>

void* (*original_memcpy)(void* dest, const void* src, size_t n); 

// Trampoline that will contain our hook logic
void* trampoline_memcpy(void* dest, const void* src, size_t n) {

  // Manipulate data before original
  
  void* result = original_memcpy(dest, src, n); 
  
  // Manipulate data after original

  return result;
}

// Our _memcpy thunk 
void* _memcpy(void* dest, const void* src, size_t n) {

  // Jump to the trampoline 
  void* result = trampoline_memcpy(dest, src, n);
  
  return result;
}

// Hook by modifying _memcpy
void hook_memcpy() {

  // Get the original address
  original_memcpy = dlsym(RTLD_NEXT, "memcpy");

  // Override _memcpy with a jump to our trampoline
  void* _memcpy_addr = (void*)&_memcpy;
  unsigned char jump[5] = {0xE9, 0xXX, 0XX, 0XX, 0XFF};

  int trampoline_offset = (int)&trampoline_memcpy - ((int)_memcpy_addr + 5);
  memcpy(&jump[1], &trampoline_offset, 4);

  memcpy(_memcpy_addr, jump, 5); 
}
```

Instead of putting the hook logic directly in _memcpy, we redirect execution to a separate trampoline function. This avoids modifying the target function. The key steps are similar - get original, add a jump, execute custom logic.