cmake and RPATH

[Brad King]

Alexander Neundorf wrote:
> Ok, how about these options for KDE:
> 
> 1) Build without RPATH at all:
> 
> set(CMAKE_SKIP_RPATH ON)

This is correct.

> 2) Build with RPATH to the builddir:
> 
> # nothing required, no relinking will happen

This is the default, but relinking WILL happen on install to remove the 
rpath or setup the rpath specified by the INSTALL_RPATH target property.

> 3) Build with RPATH only to the install dir:
> 
> set(CMAKE_BUILD_WITH_INSTALL_RPATH ON)
> 
> With this option executables will not run if the libs have not yet been 
> installed.

This option will avoid the relinking for installation.

> 4) Build with RPATH to both install and build dir
> 
> set_target_properties( kde-config PROPERTIES INSTALL_RPATH 
> "${LIBRARY_OUTPUT_DIR};${LIBRARY_INSTALL_PATH}" )
> 
> Is this possible ?
> If yes, will this have the effect that the linker will first look in the 
> builddir and after that in the install dir ? If so, is this the desired 
> order ?

This is not a good idea.  First, the INSTALL_RPATH is not used in the 
build tree unless option #3 above is set.  Second, this will go back to 
installing binaries that have an rpath pointing back at the build tree.

> For 1) and 3): The executables will not run without the libs already 
> installed. For this case simple shell scripts could be created which set 
> (DY)LD_LIBRARY_PATH accordingly, so that these executables can be run by 
> running the small wrapper shell scripts.
> 
> Do we need all these four options ? Or is our preferred option actually still 
> missing ? Personally I'd like to have option 1) available.

If we go with this:

option(KDE4_BUILD_FOR_DEVELOPER "Enable running from build tree." OFF)
if(NOT KDE4_BUILD_FOR_DEVELOPER)
    set(CMAKE_BUILD_WITH_INSTALL_RPATH 1)
endif(NOT KDE4_BUILD_FOR_DEVELOPER)

then users who build and install KDE will not have to do anything 
special and the installed binaries will have the proper install-tree 
rpath.  Developers who wish to have the option of running from the build 
tree may enable this option at the expense of requiring the automatic 
relinking before installation.

Option #1 is always available because CMake always creates 
CMAKE_SKIP_RPATH as an advanced cache option.  Developers may simply 
enable that and then no rpath will be used no matter what the project does.

-Brad