Replace (aka «hook» or «override» or «route») implementation of any C function in runtime. Works on OS X with Mach–O binaries.

Do not use this code. It can destroy everthing. But if you do, I wish you a luck.

NOTE: rd_route won't work on iOS. You should take a look at libevil instead.
Aaand it won't work for you too if you're targeting ARM64. Unfortunately I don't have a modern iOS device and thus unable to look into it, but maybe you do?

#include <assert.h>
#include "rd_route.h"


static char* my_strerror(int err)
{
  return "It's OK";
}

int main (void)
{

    void *(*original)(int) = NULL;
    int err = 2;

    printf("Error(%d): %s", err, strerror(err));
    // >> No such file or directory

    rd_route(strerror, my_strerror, (void **)&original);
    
    // See if the patch works
    assert(0 == strcmp("It's OK", strerror(err)));
    // See if an original implementation is still available
    assert(0 == strcmp("No such file or directory", original(err)));

    return 0;
}

$ cd /your/project/path
$ git submodule add https://github.com/rodionovd/rd_route

Just copy rd_route.h and rd_route.c files into your project's directory.

I've created this library because mach_override requires an external disassembler in order to work properly. For those of us who don't want another few thousands of lines of foreign code in their projects, the only option is to hard-code every function prologue they know in order to patch it correctly — which isn't a great alternative to have, to be honest.

• The source code is based on Landon Fuller's (@landonf) gorgeous libevil library.

• I'm also glade we have Jonathan 'Wolf' Rentzsch out there with his classy mach_override 👍

If you found any bug(s) or something, please open an issue or a pull request — I'd appreciate your help! (^,,^)

Dmitry Rodionov, 2014-2015
i.am.rodionovd@gmail.com