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.

Solution

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`

Comments

[ephemient]

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?

[codesniffer]

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.

[codesniffer]

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

[maxschlepzig]

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.

[cdunn2001]

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

[codesniffer]

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.

[dstromberg]

@cdunn2001 Your link appears to be dead.

[cdunn2001]

@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.