[CMake] Creating relocatable packages

Tue Oct 20 09:58:58 EDT 2015

Yes, that was exactly what I needed.

Now my installed targets file has IMPORTED_LINK_INTERFACE_LIBRARIES "PCAP"
instead of an absolute path, and the FindPCAP.cmake module kicks in and
does what I would expect.

Thanks again for your time - much appreciated.

Zac

On Tue, Oct 20, 2015 at 9:25 AM, Guillaume Dumont <
dumont.guillaume at gmail.com> wrote:

> Hi Zac,
>
> target_link_libraries will work with either full library paths or target
> names including imported targets.
>
> You need to use target_link_libraries in your CMakeLists.txt and
> find_dependency in your PackageConfig.cmake. Like so:
>
> in CMakeLists.txt:
>
> target_link_libraries(mylib ${PCAP_LIBRARIES})
>
> in PackageConfig.cmake
>
> include(CMakeFindDependencyMacro)
> find_depdency(PCAP)
>
> this way your exported targets will carry a link dependency to an imported
> target called PCAP and your PackageConfig.cmake will resolve that
> dependency for consuming projects. (Provided you install your
> FindPCAP.cmake and add the path to this file to CMAKE_MODULE_PATH)
>
> Clearer now?
>
>
>
>
> On Tue, Oct 20, 2015 at 8:24 AM, Zac Bergquist <zbergquist99 at gmail.com>
> wrote:
>
>> I think I'm on the right track now.  I was definitely missing the
>> add_library(PCAP IMPORTED) section.
>>
>> Could you elaborate on the last part?  I thought target_link_libraries()
>> is the reason I'm getting absolute paths.  Should I be using the
>> FindDependency macro instead of target_link_libraries()?
>>
>>
>> On Mon, Oct 19, 2015 at 9:54 PM, Guillaume Dumont <
>> dumont.guillaume at gmail.com> wrote:
>>
>>> Hi Zac,
>>>
>>> Sorry I read your post very quickly the first time... If your library
>>> uses its own FindPCAP.cmake then you can define an imported target for the
>>> PCAP libraries like so:
>>>
>>> # FindPCAP.cmake
>>>
>>> find_path(PCAP_INCLUDE_DIR pcap.h ... )
>>> find_library(PCAP_LIBRARY pcap ... )
>>>
>>> include(FindPackageHandleStandardArgs)
>>> find_package_handle_standard_args(PCAP  DEFAULT_MSG PCAP_LIBRARY
>>> PCAP_INCLUDE_DIR)
>>>
>>> if(PCAP_FOUND AND NOT TARGET PCAP)
>>>   add_library(PCAP IMPORTED) # you can(or should) also specify if it's a
>>> shared or static library
>>>   set_target_properties(PCAP PROPERTIES IMPORTED_LOCATION
>>> ${PCAP_LIBRARY})
>>>   # also add the interface include directories here via
>>> set_target_properties
>>>   set(PCAP_LIBRARIES PCAP)
>>> endif()
>>>
>>> then in your CMakeLists.txt:
>>>
>>> find_package(PCAP)
>>>
>>> target_link_libraries(mylib ${PCAP_LIBRARIES})
>>>
>>> Install your FindPCAP.cmake with your exported targets so that you can
>>> use the FindDependencyMacro to resolve the dependency when a consuming
>>> project finds your  library.
>>>
>>> Would that work for you?
>>>
>>> HTH
>>>
>>> Guillaume
>>>
>>>
>>>
>>> On Mon, Oct 19, 2015 at 7:06 PM, Pau Garcia i Quiles <
>>> pgquiles at elpauer.org> wrote:
>>>
>>>> Hello,
>>>>
>>>> In your case, what you need to do is to modify the config file
>>>> generation in the library (i. e. you will need to patch the third-party
>>>> library) so that the generated config file is relative.
>>>>
>>>> As an alternative, if you do not want to patch the third-party library,
>>>> try modifying the generated config file by replacing absolute prefixes with
>>>> a variable (to the cross-compilation sysroot) or relative paths.
>>>>
>>>> On Tue, Oct 20, 2015 at 1:02 AM, Zac Bergquist <zbergquist99 at gmail.com>
>>>> wrote:
>>>>
>>>>> Yes, Pau, this is exactly my problem. Or more specifically, as the
>>>>> author of a library that uses CMake and depends on libpcap, how can I best
>>>>> structure and distribute the library to make it easy to use (and cross
>>>>> compile)?  I would say using the system libpcap is strongly preferred over
>>>>> distributing a copy of it.
>>>>>
>>>>> That tutorial is very interesting.  I'll have to take a closer look at
>>>>> it because the solution isn't jumping out at me.  The tutorial shows a
>>>>> project that contains both a library and a program that links to that
>>>>> library in the same list file.  In my case that would not be possible.
>>>>> Also, the library in the example has no dependencies so it wouldn't suffer
>>>>> from the absolute path issue I'm encountering.
>>>>> On Oct 19, 2015 5:36 PM, "Pau Garcia i Quiles" <pgquiles at elpauer.org>
>>>>> wrote:
>>>>>
>>>>>> Hi Dan,
>>>>>>
>>>>>> On a second read, it seems Zac's problem was actually finding the
>>>>>> dependency (libpcap) of a dependency. Or rather, making if findable,
>>>>>> because the second depenency contains an absolute path which is broken due
>>>>>> to cross-compilation.
>>>>>>
>>>>>> I have never used it but this page contains information on how to fix
>>>>>> the paths in the config file to be relative instead of absolute. That
>>>>>> should fix the problem:
>>>>>>
>>>>>>
>>>>>> https://cmake.org/Wiki/CMake/Tutorials/How_to_create_a_ProjectConfig.cmake_file
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Mon, Oct 19, 2015 at 11:15 PM, Dan Kegel <dank at kegel.com> wrote:
>>>>>>
>>>>>>> Well, that's one answer.  But if you want to use system libpcap,
>>>>>>> it's not a very satisfying one.
>>>>>>>
>>>>>>> It's odd that pcap doesn't ship with a .pc file.
>>>>>>> I guess the pcap folks are hostile to pkgconfig because it's LGPL;
>>>>>>> see
>>>>>>> https://github.com/the-tcpdump-group/libpcap/issues/374
>>>>>>> - Dan
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Oct 19, 2015 at 2:04 PM, Pau Garcia i Quiles <
>>>>>>> pgquiles at elpauer.org> wrote:
>>>>>>>
>>>>>>>> Hello,
>>>>>>>>
>>>>>>>> Use ExternalProject to build libpcap as part of your project. Make
>>>>>>>> sure you use $ORIGIN in rpath everywhere. Install your application (and
>>>>>>>> your bundled libpcap) to /opt to avoid polluting the system.
>>>>>>>>
>>>>>>>> On Mon, Oct 19, 2015 at 10:37 PM, Zac Bergquist <
>>>>>>>> zbergquist99 at gmail.com> wrote:
>>>>>>>>
>>>>>>>>> Thank you for your reply, Guillaume.
>>>>>>>>>
>>>>>>>>> I understand that this is the expected behavior.  I even linked to
>>>>>>>>> the documentation that says this is the expected behavior.  What I don't
>>>>>>>>> understand is how to resolve it.  Are you saying it is not possible to
>>>>>>>>> create a relocatable package unless all dependencies are also using CMake?
>>>>>>>>> That doesn't seem right.
>>>>>>>>>
>>>>>>>>> Should I be trying to write a package config file for libpcap, or
>>>>>>>>> is there a better way to approach this?
>>>>>>>>>
>>>>>>>>> On Sat, Oct 17, 2015 at 8:19 AM, Guillaume Dumont <
>>>>>>>>> dumont.guillaume at gmail.com> wrote:
>>>>>>>>>
>>>>>>>>>> What you are seeing is the expected behavior. You can get a
>>>>>>>>>> relocatable package if all your dependencies (in your case libcap) have
>>>>>>>>>> themselves relocatable package config files with exported targets. Then you
>>>>>>>>>> package should make use of find_dependency macro.
>>>>>>>>>>
>>>>>>>>>> On Fri, Oct 16, 2015 at 4:56 PM, Zac Bergquist <
>>>>>>>>>> zbergquist99 at gmail.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> I've created a sample project to replicate my issue in hopes
>>>>>>>>>>> that it would make it easier to troubleshoot.
>>>>>>>>>>>
>>>>>>>>>>> Thanks for any help,
>>>>>>>>>>> Zac
>>>>>>>>>>>
>>>>>>>>>>> https://github.com/zmb3/cmaketest
>>>>>>>>>>>
>>>>>>>>>>> On Mon, Oct 12, 2015 at 8:53 AM, Zac Bergquist <
>>>>>>>>>>> zbergquist99 at gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Hello,
>>>>>>>>>>>>
>>>>>>>>>>>> I'm trying to fix a project so that its output is relocatable.
>>>>>>>>>>>> The project is a library that itself depends on libpcap.  My goal is to be
>>>>>>>>>>>> able to import the library into my CMake application and have CMake
>>>>>>>>>>>> automatically link libpcap with it.
>>>>>>>>>>>>
>>>>>>>>>>>> I'm using a toolchain file that invokes an ARM cross compiler,
>>>>>>>>>>>> sets CMAKE_INSTALL_PREFIX and appends it to CMAKE_FIND_ROOT_PATH.  This all
>>>>>>>>>>>> seems to work well.
>>>>>>>>>>>>
>>>>>>>>>>>> What I'm seeing is that the exported files that get installed
>>>>>>>>>>>> to CMAKE_INSTALL_PREFIX contain absolute paths to libpcap on my machine,
>>>>>>>>>>>> which make them useless to other team members.
>>>>>>>>>>>>
>>>>>>>>>>>> The first thing I changed was to use
>>>>>>>>>>>> CONFIGURE_PACKAGE_CONFIG_FILE instead of CONFIGURE_FILE.  This got rid of
>>>>>>>>>>>> absolute paths in the generated CMake config file.
>>>>>>>>>>>>
>>>>>>>>>>>> However, I still have absolute paths in the CMake target import
>>>>>>>>>>>> file that gets generated.  The IMPORTED_LINK_INTERFACE_LIBRARIES target
>>>>>>>>>>>> property has an absolute path instead of one relative to
>>>>>>>>>>>> CMAKE_INSTALL_PREFIX.
>>>>>>>>>>>>
>>>>>>>>>>>> I've read the "Creating Relocatable Packages" [1] section of
>>>>>>>>>>>> the CMake packages documentation. I'm pretty sure this is what I'm running
>>>>>>>>>>>> into, but I don't quite understand how to solve it.  The documentation says
>>>>>>>>>>>> that I should be using imported targets, but I'm not sure how to do so.
>>>>>>>>>>>> The library is just using its own FindPCAP.cmake file to locate libpcap.
>>>>>>>>>>>>
>>>>>>>>>>>> Does anyone know of an example of a CMake package that imports
>>>>>>>>>>>> other libraries?  I could also try to create a minimal example project with
>>>>>>>>>>>> this setup if it would be helpful.
>>>>>>>>>>>>
>>>>>>>>>>>> Thanks,
>>>>>>>>>>>> Zac
>>>>>>>>>>>>
>>>>>>>>>>>> [1]:
>>>>>>>>>>>> https://cmake.org/cmake/help/v3.3/manual/cmake-packages.7.html#creating-relocatable-packages
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>>
>>>>>>>>>>> Powered by www.kitware.com
>>>>>>>>>>>
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>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> Guillaume Dumont
>>>>>>>>>> =========================
>>>>>>>>>> dumont.guillaume at gmail.com
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>>
>>>>>>>>> Powered by www.kitware.com
>>>>>>>>>
>>>>>>>>> Please keep messages on-topic and check the CMake FAQ at:
>>>>>>>>> http://www.cmake.org/Wiki/CMake_FAQ
>>>>>>>>>
>>>>>>>>> Kitware offers various services to support the CMake community.
>>>>>>>>> For more information on each offering, please visit:
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>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Pau Garcia i Quiles
>>>>>>>> http://www.elpauer.org
>>>>>>>> (Due to my workload, I may need 10 days to answer)
>>>>>>>>
>>>>>>>> --
>>>>>>>>
>>>>>>>> Powered by www.kitware.com
>>>>>>>>
>>>>>>>> Please keep messages on-topic and check the CMake FAQ at:
>>>>>>>> http://www.cmake.org/Wiki/CMake_FAQ
>>>>>>>>
>>>>>>>> Kitware offers various services to support the CMake community. For
>>>>>>>> more information on each offering, please visit:
>>>>>>>>
>>>>>>>> CMake Support: http://cmake.org/cmake/help/support.html
>>>>>>>> CMake Consulting: http://cmake.org/cmake/help/consulting.html
>>>>>>>> CMake Training Courses: http://cmake.org/cmake/help/training.html
>>>>>>>>
>>>>>>>> Visit other Kitware open-source projects at
>>>>>>>> http://www.kitware.com/opensource/opensource.html
>>>>>>>>
>>>>>>>> Follow this link to subscribe/unsubscribe:
>>>>>>>> http://public.kitware.com/mailman/listinfo/cmake
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Pau Garcia i Quiles
>>>>>> http://www.elpauer.org
>>>>>> (Due to my workload, I may need 10 days to answer)
>>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Pau Garcia i Quiles
>>>> http://www.elpauer.org
>>>> (Due to my workload, I may need 10 days to answer)
>>>>
>>>> --
>>>>
>>>> Powered by www.kitware.com
>>>>
>>>> Please keep messages on-topic and check the CMake FAQ at:
>>>> http://www.cmake.org/Wiki/CMake_FAQ
>>>>
>>>> Kitware offers various services to support the CMake community. For
>>>> more information on each offering, please visit:
>>>>
>>>> CMake Support: http://cmake.org/cmake/help/support.html
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>>>>
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>>>>
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>>>>
>>>
>>>
>>>
>>> --
>>> Guillaume Dumont
>>> =========================
>>> dumont.guillaume at gmail.com
>>>
>>
>>
>
>
> --
> Guillaume Dumont
> =========================
> dumont.guillaume at gmail.com
>
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