[cmake-developers] rpaths on Mac

[Clinton Stimpson]

On Thursday, November 17, 2011 02:03:15 pm Brad King wrote:
> On 11/17/2011 11:49 AM, Clinton Stimpson wrote:
> > I'm experimenting with using @rpath instead of @executable_path and
> > @loader_path, because @rpath is useful in some situations where the
> > others don't work as well.  For example, I want to avoid setting
> > DYLD_LIBRARY_PATH when using a relocatable SDK.  Using @rpath allows a
> > user to embed a path in their executable/library that gives the location
> > of the SDK libraries that they linked with.  Public SDK libraries would
> > also know how to find private SDK libraries with an rpath of
> > @loader_path and dependencies starting with @rpath.
> > 
> > What needs to be considered if the following is added to
> > Platforms/Darwin.cmake?
> > 
> >    set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")
> >    set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")
> 
> Is that all that is necessary to get the standard RPATH behavior on OS X?
> Nice!

Basically, yes, along with:
  set(CMAKE_INSTALL_NAME_DIR "@rpath")
  set(CMAKE_INSTALL_RPATH ...)

To get the desired behavior, we can automate
  set(CMAKE_INSTALL_NAME_DIR "@rpath")
I think it would be nice to have it be @rpath even in the build tree, but I 
don't see that as a requirement.  It could help avoid install name changes at 
install time, or allow people to copy the libraries.

> 
> > Would that have undesirable side effects?
> 
> Since the original RPATH support in CMake pre-dated the feature on OS X
> we implemented INSTALL_NAME_DIR instead.  We need to investigate how the
> two features would/should interact.

We still need a separate INSTALL_NAME_DIR setting and RPATH setting.
But from what I can tell, INSTALL_NAME_DIR can be fixed to @rpath.

> 
> > One possibility is adding -rpath link flags to those who currently don't
> > have/want it.
> 
> We may need a switch to choose between RPATH and INSTALL_NAME_DIR.  The
> default of the switch can be chosen based on the minimum required version
> of CMake.  Over time everyone will start using RPATH instead.

It does look like we need a switch.  But overall, it looks like CMake is quite 
close to having this feature.
Any idea what the switch can be called?

As a side note, I had been using BundleUtilities and that falls apart with 
@rpath so that is something to fix before having everyone use this.

-- 
Clinton Stimpson
Elemental Technologies, Inc
Computational Simulation Software, LLC
www.csimsoft.com