#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int test1(char *msg);
int test2(char *msg);
void _jmp(void);
void _hook_init(char *buf, int n);
void _hook(char *ptr, char *hook, char *bak, int n);


unsigned int t2_ptr    = (unsigned int)test2;
unsigned int *t2_pptr  = &t2_ptr;
char buf1[10];
char buf2[10];


int test1(char *msg)
{
  printf("test1 call arg:'%s'\n", msg);
  return 1;
}

int test2(char *msg)
{
  printf("test2 call arg:'%s'\n", msg);
  return 2;
}

int main(void)
{
  _hook_init(buf1, sizeof(buf1));

  printf("rv: %d\n", test1("no hook"));
  _hook((char *)test1, buf1, buf2, sizeof(buf1));
  printf("rv: %d\n", test1("hooked"));
  _hook((char *)test1, buf2, buf1, sizeof(buf1));
  printf("rv: %d\n", test1("no hook"));

  return 0;
}

void _hook_init(char *buf, int n)
{
  buf[0] = 0xff;
  buf[1] = 0x25;
  *(int *)(buf + 2) = (int)&t2_ptr;
}

void _hook(char *ptr, char *hook, char *bak, int n)
{
  memcpy(bak, ptr, n);
  memcpy(ptr, hook, n);
}

void _jmp(void)
{
  __asm__ __volatile__ ("jmp *t2_ptr;");
  __asm__ __volatile__ ("nop; nop; nop; nop;");
}