How to properly set run paths, search paths, and install names?

Question

I have a collection of projects that I'm compiling as dynamic libraries. Each of these .dylibs depend on other various .dylibs that I would like to place in various other directories (i.e. some at the executable path, some at the loader path, some at a fixed path).

When I run otool -L on the compiled libraries, I get a list of paths to those dependencies but I have know idea how those paths are being set/determined. They almost appear pseudo random. I've spent hours messing with the "Build Settings" in Xcode to try and change these paths (w/ @rpath, @executable_path, @loader_path, etc.) but I can't seem to change anything (as checked by running otool -L). I'm not even entirely sure where to add these flags and don't really understand the difference between the following or how to properly use them:

Linking - "Dynamic Library Install Name"
Linking - "Runpath Search Paths"
Linking - "Other Linking Flags"
Search Paths - "Library Search Paths"

When I run install_name_tool -change on the various libraries, I am able to successfully change the run path search paths (again as verified by running otool -L to confirm).

I'm running Xcode 4.2 and I'm very close to giving up and just using a post-build script that runs install_tool_name to make the changes. But its a kludge hack fix and I'd prefer not to do it.

Where can I see how the search/run paths for the dylib dependencies are being set?
Anyone have any ideas on what I might be doing wrong?

Answer 1

Typically, in my dylib's target, I set INSTALL_PATH aka "Installation Directory" to the prefix I want (e.g. @executable_path/../Frameworks).

I leave LD_DYLIB_INSTALL_NAME aka "Dynamic Library Install Name" set to its default value, which is $(DYLIB_INSTALL_NAME_BASE:standardizepath)/$(EXECUTABLE_PATH).

Xcode expands that based on your target's name, so it might end up being @executable_path/../Frameworks/MyFramework.framework/Versions/A/MyFramework, for instance.

The important thing to realize is that the install path is built into the dylib, as part of its build process. Later on, when you link B.dylib that refers to A.dylib, A.dylib's install path is copied into B.dylib. (That's what otool is showing you -- those copied install paths.) So it's best to get the correct install path built into the dylib in the first place.

Before trying to get all the dylibs working together, check each one individually. Build it, then otool -L on the built dylib. The first line for each architecture should be what LD_DYLIB_INSTALL_NAME was showing you.

Once you have that organized, try to get the dylibs linking against each other. It should be much more straightforward.

Answer 2

install_name_tool is very useful for setting the names and paths. Its especially useful if the program runs its self-tests in the build directory, and then things change during a make install. In this case, you can use install_name_tool without the need for a separate build.

install_name_tool is also useful because Apple's LD does not honor rpath linker options like Linux/GCC does. That is, you need to use a different set of commands to set them.

Here's the man page for it. Its included in its entirety because it discusses other options, like -headerpad_max_install_names.

INSTALL_NAME_TOOL(1)                                      INSTALL_NAME_TOOL(1)

NAME
       install_name_tool - change dynamic shared library install names

SYNOPSIS
       install_name_tool  [-change  old  new  ]  ...  [-rpath  old  new  ] ...
       [-add_rpath new ] ... [-delete_rpath new ] ... [-id name] file

DESCRIPTION
       Install_name_tool changes the dynamic shared library install names  and
       or  adds,  changes  or  deletes the rpaths recorded in a Mach-O binary.
       For this tool to work when the install names or rpaths are  larger  the
       binary  should  be  built  with  the ld(1) -headerpad_max_install_names
       option.

       -change old new
              Changes the dependent shared library install name old to new  in
              the specified Mach-O binary.  More than one of these options can
              be specified.  If the Mach-O binary does  not  contain  the  old
              install  name  in  a  specified  -change  option  the  option is
              ignored.

       -id name
              Changes the shared library  identification  name  of  a  dynamic
              shared  library  to name.  If the Mach-O binary is not a dynamic
              shared library and the -id option is specified it is ignored.

       -rpath old new
              Changes the rpath path name old to new in the  specified  Mach-O
              binary.   More  than  one of these options can be specified.  If
              the Mach-O binary does not contain the old rpath path name in  a
              specified -rpath it is an error.

       -add_rpath new
              Adds  the  rpath  path  name new in the specified Mach-O binary.
              More than one of these options can be specified.  If the  Mach-O
              binary  already  contains  the  new rpath path name specified in
              -add_rpath it is an error.

       -delete_rpath old
              deletes the rpath path name old in the specified Mach-O  binary.
              More  than one of these options can be specified.  If the Mach-O
              binary does not contains the old rpath path  name  specified  in
              -delete_rpath it is an error.

SEE ALSO
       ld(1)