Copy a function in memory and execute it

Question

I would like to know how in C in can copy the content of a function into memory and the execute it?

I\'m trying to do something like this:

typedef vo         


        

Answer 1

Hacky solution and simple proof of concept that works for me (and compiles without warning on Mac OS X/GCC 4.2.1):

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include 

int function1(int x){
   return x-5;
}

int function2(int x){
  return x+5;
}


int main(){
  int diff = (&function2 - &function1);
  printf("pagesize: %d, diff: %d\n",getpagesize(),diff);

  int (*fptr)(int);

  void *memfun = malloc(4096);

  if (mprotect(memfun, 4096, PROT_READ|PROT_EXEC|PROT_WRITE) == -1) {
      perror ("mprotect");
  }

  memcpy(memfun, (const void*)&function2, diff);

  fptr = &function1;
  printf("native: %d\n",(*fptr)(6));
  fptr = memfun;
  printf("memory: %d\n",(*fptr)(6) );
  fptr = &function1;
  printf("native: %d\n",(*fptr)(6));

  free(memfun);
  return 0;
}