redirect.c

// Let's not mangle these names 0x0819ec3c
extern "C" {

#include <lua5.2/lua.h>
#include <lua5.2/lauxlib.h>
#include <sys/mman.h> 
#include <stdio.h>
#include <limits.h>
#ifndef PAGESIZE
#define PAGESIZE 4096
#endif


int redirect(void* from, void* to) {
  void* page_start = (void*) ((unsigned long) from & (~(PAGESIZE - 1)));
  
  if (mprotect(
        page_start, PAGESIZE, PROT_WRITE | PROT_READ | PROT_EXEC)) {
    perror("Couldn’t mprotect");
    return -1;
  }
  
  char* bb = (char*) from;
  int i = 0;
  unsigned long long target = (unsigned long long) to;
#define w bb[i++] = 
#define W(x) bb[i++] = (x) & 0xff; bb[i++] = ((x) & 0xff00)>>8; \
  bb[i++] = ((x) & 0xff0000)>>16; bb[i++] = ((x) & 0xff000000)>>24
  w 0x48; w 0xb8; 
  W(target & 0xffffffff);
  W(target >> 32); // movabs $target, %rax
  w 0xff; w 0xe0; // jmp *%rax
  return 0;
}

int main() {
  // redirect((void*) lol, (void*) lua_pushboolean);
  // lol(0,0);
  // lua_pushboolean(0, 0);
  return 0;
}

int LUA_API luaopen_patch(lua_State *L) {
  return 0;
}

}