[CMake] RPATH and $ORIGIN

[Iker Arizmendi]

I've run into some trouble with how CMake 2.4.2 (and perhaps
later) handles the string "$ORIGIN" when it appears as part of
an RPATH. I've gotten around the trouble (see below), but would
appreciate any pointers on the correct way to use "$ORIGIN".

Regards,
Iker

Briefly, the problem seems to be that CMake inconsistently
carries out the expansion of the "$ORIGIN" string. If one
extends the install rpath like so:

    SET(CMAKE_INSTALL_RPATH
        "${CMAKE_INSTALL_RPATH}:$ORIGIN/../xxx")

the rpath for an installed executable or shared library ends up
like this (using readelf -d):

    0x0000000f (RPATH)
    Library rpath: [/home/iker/tmp/rpath_test/xxx]
    0x0000001d (RUNPATH)
    Library runpath: [/home/iker/tmp/rpath_test/xxx]

where "/home/iker/tmp/rpath_test" is the path to my build tree.
The "$ORIGIN" token disappears.

If the above test is changed so that the ".." is removed:

    SET(CMAKE_INSTALL_RPATH
        "${CMAKE_INSTALL_RPATH}:$ORIGIN/xxx")

the rpath handling differs. The rpath for an installed
executable now looks like this:

    0x0000000f (RPATH)
    Library rpath: [/home/iker/tmp/rpath_test/:RIGIN/xxx]
    0x0000001d (RUNPATH)
    Library runpath: [/home/iker/tmp/rpath_test/:RIGIN/xxx]

Note that "$ORIGIN" has been truncated to "RIGIN". The rpath
for an installed shared library seems to do the right thing:

    0x0000000f (RPATH)
    Library rpath: [/home/iker/tmp/rpath_test/:$ORIGIN/xxx]
    0x0000001d (RUNPATH)
    Library runpath: [/home/iker/tmp/rpath_test/:$ORIGIN/xxx]

To get around the two problems above I tried setting the linker
flag variables directly:

    SET (CMAKE_EXE_LINKER_FLAGS
    "${CMAKE_EXE_LINKER_FLAGS} -Wl,-rpath,'$ORIGIN/../xxx/'" )

    SET (CMAKE_SHARED_LINKER_FLAGS
    "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-rpath,'$ORIGIN/../xxx'" )

For installed shared libraries we get the right behavior:

    0x0000000f (RPATH)
    Library rpath: [$ORIGIN/../xxx]
    0x0000001d (RUNPATH)
    Library runpath: [$ORIGIN/../xxx]

But not for installed executables:

    0x0000000f (RPATH)
    Library rpath: [RIGIN/../xxx/]
    0x0000001d (RUNPATH)
    Library runpath: [RIGIN/../xxx/]

To fix the problem with executables I tried adding an extra "$"
character like this:

    SET (CMAKE_EXE_LINKER_FLAGS
    "${CMAKE_EXE_LINKER_FLAGS} -Wl,-rpath,'$$ORIGIN/../xxx/'" )

And, on my system (Gentoo 1.2, Intel x86), this solves the
problem for exes:

    0x0000000f (RPATH)
    Library rpath: [$ORIGIN/../xxx/]
    0x0000001d (RUNPATH)
    Library runpath: [$ORIGIN/../xxx/]

Unfortunately, on CentOS 4.6 systems using the same CMake
release (2.4.2) the behavior with respect to shared libs
and exes is the opposite of what it is on my system. That is,
the shared library flags require the special "$$ORIGIN" string
and exes work fine with "$ORIGIN".

To get the right behavior and ensure that my CMake files work
across all of our machines I resorted to using both forms:

    $ORIGIN/../xxx/:$$ORIGIN/../

which clutters the resulting rpaths but gets the job done.


-- 
Iker Arizmendi
AT&T Labs - Research
Speech and Image Processing Lab
e: iker at research.att.com
w: http://research.att.com
p: 973-360-8516