[CMake] Creating relocatable packages

Mon Oct 19 21:54:23 EDT 2015

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
>>>>>>>>
>>>>>>>> Please keep messages on-topic and check the CMake FAQ at:
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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:
>>>>>>
>>>>>> CMake Support: http://cmake.org/cmake/help/support.html
>>>>>> CMake Consulting: http://cmake.org/cmake/help/consulting.html
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>>>>>>
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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
> CMake Consulting: http://cmake.org/cmake/help/consulting.html
> CMake Training Courses: http://cmake.org/cmake/help/training.html
>
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-- 
Guillaume Dumont
=========================
dumont.guillaume at gmail.com
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