[CMake] Handling library interdependencies

[Michael Wild]

On 17. Jun, 2009, at 1:22, Mark Lohry wrote:

> Thanks for the reply.
>
> I added "add_dependencies( lib1 lib2 )", "add_dependencies( lib2  
> lib1 )",
> and "add_dependencies( execthing lib1 lib2 )" in their appropriate  
> places,
> and changed the libraries to STATIC, but no change.

First off, you're creating a cyclic dependency between lib1 and lib2.  
Never a good thing. Second, how do your libraries relate to each  
other? Does lib2 use symbols from lib1? Or is it the other way round?  
If lib1 uses symbols from lib2 and lib2 from lib1, you have a design  
issue.

For the moment, assume that lib2 uses symbols from lib2, in that case  
in lib/lib2/CMakeLists.txt you would do:

include_directories( ${proj_SOURCE_DIR}/lib )
set( lib2_SRCS
  ..... bunch of c++ sources )
add_library( lib2 SHARED ${lib2_SRCS} )
# THIS ONE IS IMPORTANT!
target_link_libraries( lib2 lib1 )


The target_link_libraries command automatically adds a dependency of  
lib2 on lib1.

>
> Yes, everything compiles when i build the libraries and executables
> separately; it fails on the link step after this, with "undefined  
> reference"
> to every library function used.

Is this Windows or some kind of Unix system? If the former, have you  
exported your symbols in the library using __declspec(dllexport)? You  
can get started here: http://msdn.microsoft.com/en-us/library/9h658af8.aspx 
  and http://msdn.microsoft.com/en-us/library/9h658af8.aspx

>
> I'm unfamiliar with 'nm', can you be more specific as to what I  
> should be
> looking for?


Again, are you using Windows? In that case the tool you're looking for  
is dumpbin.exe (http://msdn.microsoft.com/en-us/library/c1h23y6c(VS.80).aspx 
), especially the options /SYMOBOLS and /EXPORTS should be of interest.


HTH

Michael

>
>
> On Tue, Jun 16, 2009 at 4:55 PM, Tyler Roscoe <tyler at cryptio.net>  
> wrote:
>
>> On Tue, Jun 16, 2009 at 03:41:51PM -0500, Mark Lohry wrote:
>>> I have a number of subdirectories, each containing source to be  
>>> built
>> into
>>> their own libraries, which contain many interdependencies. I'm  
>>> trying to
>>> build an executable to link against these libraries, and I'm  
>>> getting a
>>> console full of "undefined reference to..." errors on linking  
>>> step. The
>>> libraries and executable source all compile individually without  
>>> issue.
>>>
>>> Structure is like so:
>>>
>>> # top-level CMakeLists.txt
>>> project( proj )
>>> ADD_SUBDIRECTORY( lib )
>>> ADD_SUBDIRECTORY( src )
>>>
>>>
>>> # /lib/CMakeLists.txt
>>> ADD_SUBDIRECTORY( lib1 )
>>> ADD_SUBDIRECTORY( lib2 )
>>>
>>>
>>> # /lib/lib1/CMakeLists.txt
>>> include_directories( ${proj_SOURCE_DIR}/lib )
>>> set( lib1_SRCS
>>>  ..... bunch of c++ sources )
>>> add_library( lib1 SHARED ${lib1_SRCS} )
>>>
>>>
>>> # /lib/lib2/CMakeLists.txt
>>> include_directories( ${proj_SOURCE_DIR}/lib )
>>> set( lib2_SRCS
>>>  ..... bunch of c++ sources )
>>> add_library( lib2 SHARED ${lib2_SRCS} )
>>>
>>>
>>> # src/CMakeLists.txt
>>> include_directories( ${proj_SOURCE_DIR}/lib )
>>> set( execthing_SRCS
>>> .... bunch of C++ sources )
>>> add_executable( execthing ${execthing_SRCS} )
>>> target_link_libraries( execthing lib1 lib2 )
>>
>> This all looks reasonable to me, so the devil is probably in the
>> details. Are you sure all your paths make sense? Can you use nm or
>> dumpbin or whatever to see the "undefined" symbols in the libraries
>> where you expect to find them?
>>
>> So if you build the libraries individually and then build the  
>> executable
>> individually, everything works? You might try playing with some  
>> explicit
>> add_dependencies() to see if there's some kind of build order  
>> problem.
>> CMake should be smart enough to figure this out from your
>> target_link_libraries, but maybe you have something strange going on
>> under the covers?
>>
>> tyler
>>
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