How to set the runtime path (-rpath) of an executable with gcc under Mac OSX?

Question

I want to set under Mac OSX the runtime path of an executable (for the linker) at compile time, such that shared libraries at non-standard locations are found by the dynamic linker at program start.

Under Linux this is possible with -Xlinker -rpath -Xlinker /path/to (or using -Wl,-rpath,/path/to) and under Solaris you can add -R/path/to to the compiler command line.

I found some information that Mac OS X gcc has -rpath support since 10.5, i.e. since ~ 2008.

I tried to get it working with a minimal example - without success:

$ cat blah.c 
int blah(int b)
{
  return b+1;
}

And:

$ cat main.c 

#include <stdio.h>

int blah(int);

int main ()
{
  printf("%d\n", blah(22));
  return 0;
}

Compiled it like this:

$ gcc -c  blah.c
$ gcc -dynamiclib blah.o -o libblah.dylib
$ gcc main.c -lblah -L`pwd`  -Xlinker -rpath -Xlinker `pwd`/t

Now the test:

$ mkdir t
$ mv libblah.dylib t
$ ./a.out
dyld: Library not loaded: libblah.dylib
  Referenced from: /Users/max/test/./a.out
  Reason: image not found
Trace/BPT trap

Thus the question: How to I set the runtime path for the linker under Mac OSX?

Btw, setting DYLD_LIBRARY_PATH works - but I don't want to use this hack.

Edit: Regarding otool -L:

$ otool -L a.out 
a.out:
        libblah.dylib (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 125.2.1)

It seems that otool -L only prints the library names (and probable the locations at link time) the executable was linked against and no runtime path information.

Kinescope

I don't have an OS X system but searching around, install_name_tool can add rpaths to your binary. Not sure why yours isn't working — what does otool -L say? – Descent

Use otool -l <file> and search for the LC_RPATH sections to see the paths that a binary (library or exe) is setup to search for dependent libs. – Irruption

This page is helpful to understand rpath on Mac: https://blog.krzyzanowskim.com/2018/12/05/rpath-what/ – Irruption

Answer 1

Found by experimentation, and inspecting the command lines generated by Xcode for a reference rpath demo project by Dave Driblin:

otool -L shows you the install name of the linked libraries. To get @rpath to work, you need to change the install name of the library:

$ gcc -dynamiclib blah.o -install_name @rpath/t/libblah.dylib -o libblah.dylib
$ mkdir t ; mv libblah.dylib t/
$ gcc main.c -lblah -L`pwd`/t -Xlinker -rpath -Xlinker `pwd`

Padishah

Yes, this works. Given that there are existing semantics of -rpath on other Unix-like OS, Apples deviating implementation seems a bit awkward. At least they should document it in their version of the gcc man-page. – Kinescope

@Karel is correct, but this might be helpful as well, if you want a more complete list of alternatives. – Novella

Use otool -l <file> and search for the LC_RPATH sections to see the paths that a binary (library or exe) is setup to search for dependent libs. – Irruption

@Novella Your link appears to be dead. – Venezuela

@dstromberg, You're right. But this links the same dead link with more elucidation and explains how to use install_name_tool, which is what I use to set the rpath. – Novella