What is the exact equivalent to LD_PRELOAD on OSX?

Question

I am using LD_PRELOAD to hook a library function, and in Linux it works perfectly. But I cannot figure out how to do the equivalent in OSX.

The setup I have on Linux is as follows:

The code is:

#include <stdio.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <unistd.h>
#include <ruby.h>

void
rb_raise(unsigned long exc, const char *fmt, ...)
{
  static void (*libruby_rb_raise)
    (unsigned long exc, const char *fmt, ...) = NULL;

  void * handle;
  char * error;

  if (!libruby_rb_raise) {
    handle = dlopen("/path/to/libruby.so",
                    RTLD_LAZY);
    if (!handle) {
      fputs(dlerror(), stderr);
      exit(1);
    }
    libruby_rb_raise = dlsym(handle, "rb_raise");
    if ((error = dlerror()) != NULL) {
      fprintf(stderr, "%s\n", error);
      exit(1);
    }
  }

  // ...code... 

  return Qnil;
}

Which I then compile with:

gcc -Wall -O2 -fpic -shared -ldl -g -I/path/to/includes/ -o raise_shim.so raise_shim.c

I then execute with:

LD_PRELOAD=./raise_shim.so ruby

All of the above works well on Linux, what is the equivalent for each step to get this working on OSX? I have googled this and have not been able to get it to work with the information provided as the info for some of the steps are missing.

Thanks in advance!

Solution

Take a look at DYLD_INSERT_LIBRARIES. That's the variable you're looking for.

See also this answer.

Comments

[horseyguy]

Thanks, I knew this much :) But it's not just as simple as setting that i found, i have to make major modifications to my source, and the compilation step is different, too. It is the execution of these steps i cannot figure out how to do :(

[Dan Fego]

Are you sure? I'm pretty sure I've used this before (but not 100% -- I just know I've looked at it. :P) What exactly isn't working?

[horseyguy]

What line exactly should i use to build the library, the one (shown in the question above) no longer works. do i have to modify my source code in any way? What is this i hear about needing to set another FLAT_NAMESPACES macro, and something about DYLD_INTERPOSEI know it's not simply a matter of substituting DYLD_INSERT_LIBRARIES for LD_PRELOAD.

[Dan Fego]

Hmm, I'm not sure without a Mac in front of me. Are you saying that the line to build it no longer works, i.e. it won't build, or that the library's symbol isn't taking precedence when using DYLD_INTERPOSE? Perhaps ruby on OSX is different? These are just possibilities, but I'll have to check later. Though I'm sure someone else will come to the rescue in the meantime. :)

[horseyguy]

Hi, i changed the gcc line when building on osx to gcc -Wall -ldl -I/path/to/includes -o lib_overrides.dylib -dynamiclib ./raise_shim.c and i get a bunch of symbol lookup errors, any idea?