How to link a shared library with CMake with relative path - c++

Question

I want to link a third-party libLibrary.so and distribute it with my program. If user unzips my archive, he will get this folder structure:
game
libLibrary.so
game_executable
game_executable depends on ./libLibrary.so.
My project structure:
game
bin
libLibrary.so
lib
Library.h
src
game_executable.cpp
CMakeLists.txt
My CMakeLists.txt:
cmake_minimum_required(VERSION 3.7)
project(game)
set(CMAKE_CXX_STANDARD 14)
set(CMAKE_BINARY_DIR ${CMAKE_SOURCE_DIR}/bin)
set(EXECUTABLE_OUTPUT_PATH ${CMAKE_BINARY_DIR})
set(LIBRARY_OUTPUT_PATH ${CMAKE_BINARY_DIR})
set(SOURCE_FILES src/game_executable.cpp)
include_directories(${CMAKE_SOURCE_DIR}/lib)
add_executable(game ${SOURCE_FILES})
target_link_libraries(${PROJECT_NAME} ${CMAKE_BINARY_DIR}/libLibrary.so)
However, what I get is my game_executable depends on the .../game/bin/libLibrary.so, not on the ./libLibrary.so that is in the folder with game_executable, making this totally unportable!
How can I make linking path relative instead of absolute?

Answer 1

From the documentation:
By default if you don't change any RPATH related settings, CMake will link the executables and shared libraries with full RPATH to all used libraries in the build tree.
This is the behaviour you are seeing.
However, there are a number of ways to change this to match the behaviour you require.
Some examples from the above linked docs:
# use, i.e. don't skip the full RPATH for the build tree
SET(CMAKE_SKIP_BUILD_RPATH FALSE)
# when building, don't use the install RPATH already
# (but later on when installing)
SET(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)
# the RPATH to be used when installing
SET(CMAKE_INSTALL_RPATH "")
# don't add the automatically determined parts of the RPATH
# which point to directories outside the build tree to the install RPATH
SET(CMAKE_INSTALL_RPATH_USE_LINK_PATH FALSE)
Using the above you'll likely want to set CMAKE_INSTALL_RPATH and then distribute the installed binary.
If you want to distribute from the binary in your build tree, it is also possible to bypass CMake's rpath handling and modify the rpath directly using linker flags:
set_target_properties(game PROPERTIES LINK_FLAGS "-Wl,-rpath,./")

Answer 2

Most of the time you want to set the RPATH to $ORIGIN instead of ., because it refers to the executable's path instead while . refers to the current directory at runtime (which can be anything else).
I find it simple to edit LINK_FLAGS instead of INSTALL_RPATH target property, because CMakes already has a variable named ORIGIN (see CMake's documentation).
So that boils down to the following:
# Find shared libraries next to the executable
set_target_properties(target_name PROPERTIES
BUILD_WITH_INSTALL_RPATH FALSE
LINK_FLAGS "-Wl,-rpath,$ORIGIN/")

Answer 3

Talking about distribution the executable or shared library with dynamically linked libraries and CMake build system:
SET(CMAKE_BUILD_RPATH_USE_ORIGIN TRUE)
This var forces linking with relative path within the build tree, so in result the build directory can be movable.
If you use this command on linux machine
find <YOUR_TARGET_NAME> -type f -perm /a+x -exec ldd {} \; | grep so | sed -e '/^[^\t]/ d' | sed -e 's/\t//' | sed -e 's/.*=..//' | sed -e 's/ (0.*)//' | sort | uniq -c | sort -n
you will see the dot in the path, which indicates the relativity, example:
~/project/build/./lib/my_shared_lib.so
See more in CMake docs.

Answer 4

If you use target_link_directories then cmake will add it to the linker command as a manual rpath