[CMake] How to specify -fpic ?

[David Aldrich]

Hi Michael

> So, the options are:
> 
> - use -whole-archive as you do now
> - make the Kernel library shared
> - link the dlopen'ed libraries against Kernel

Thanks very much - I understand. I think I will keep the -whole-archive method.

However, now I'm worried about how I link in the Python library:

/usr/bin/c++ -O3 -DNDEBUG -Wall -m64 -o myProj -rdynamic -Wl,-whole-archive Kernel/libKernel.a -Wl,-no-whole-archive -ldl -lpython2.4

The dlopen'ed libraries may use the Python library. I guess I could include it in the -whole-archive part, but perhaps it would be better to link each shared library against Python. Would you agree?

Sorry that I am now off topic w.r.t cmake.

By the way, I think I am pretty much there with changing our build system from manually coded makefiles to cmake. I like cmake!  Thanks for all your help in getting there.  The support on this list is excellent.

Best regards 

David 

> -----Original Message-----
> From: Michael Wild [mailto:themiwi at gmail.com]
> Sent: 30 September 2010 12:20
> To: David Aldrich
> Cc: cmake at cmake.org
> Subject: Re: [CMake] How to specify -fpic ?
> 
> 
> On 30. Sep, 2010, at 13:05 , David Aldrich wrote:
> 
> > Hi
> >
> > Ok, by following the link to the wiki suggested by Michael Loose, I used:
> >
> > target_link_libraries( myProj -Wl,-whole-archive Kernel
> > -Wl,-no-whole-archive)
> >
> > This has fixed my problem. The executable links and runs correctly.
> >
> > My link command is now:
> >
> > /usr/bin/c++   -O3 -DNDEBUG -Wall -m64  -Wl,--export-dynamic   -o myProj -
> Wl,-whole-archive Kernel/libKernel.a -Wl,-no-whole-archive -ldl -lpython2.4
> >
> > I don't need portability so I think this is ok.
> >
> > Michael Wild wrote:
> >
> >> The -whole-archive flag is pretty useless with executables (unless,
> >> you plan to use it as a library too, but that is outlandish).
> >> --export-dynamic may be also necessary, if your dlopen'ed libraries
> >> use symbols in your executable.
> >
> > So my concern is now: am I being 'outlandish' ?  The dlopen'ed libraries do
> use functions in libKernel.a that is linked to the executable. Is this
> outlandish? Is there a better way?
> 
> The "outlandish" referred to using an executable also as a library, so you're
> fine :-) But I think I found the reason for why you need this -whole-archive
> flag: Since your executable doesn't use all of the functions in the Kernel
> library, the linker throws them away. This results in your dlopen'ed
> functions to fail.
> 
> So, the options are:
> 
> - use -whole-archive as you do now
> - make the Kernel library shared
> - link the dlopen'ed libraries against Kernel
> 
> Michael
>