[vtkusers] compilation with -fPIC necessary?

[Sebastiaan]

Hi,

On Fri, 17 Mar 2006, Obada Mahdi wrote:

> Hi Sebastiaan!
>
> Actually, you (almost) always need "-fPIC" when creating shared
> libraries.  Do I understand you correctly that the "-fPIC" flag is
> present when compiling VTK for shared libraries on AMD64, but not on the
> EMT64?  That could be a problem.
>
I made a mistake here: on the amd64 I did not compile VTK with MPI or 
PARALLEL, so it does not need the mpich library. So I do not know if amd64 
breaks, but I guess it will, which makes sense.

I have also read about -fPIC is almost always needed on 64 bit (don't know 
why it is not needed on 32 bit). I also read that -fPIC can break 
packages. Since most of VTK compiles clean without -fPIC, it seems 
overkill to compile all of VTK with this flag.

Why isn't this flag automatically added to the compiler for those shared 
libraries, if it is compiled on a 32 bit system?

Greetz,
Sebastiaan


> However, that "libmpich.a" issue is not related to VTK:
>
> On Thu, 16 Mar 2006, Sebastiaan wrote:
>> Linking CXX shared library ../bin/libvtkParallel.so
>> /usr/lib/gcc/x86_64-pc-linux-gnu/4.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: 
>> /usr/X11R6/lib64/libmpich.a(isend.o): relocation R_X86_64_32 against `a 
>> local symbol'
>> can not be used when making a shared object; recompile with -fPIC
>
> Linking static libraries when creating a shared library just does not
> work generally.  Any chance there is a dynamic version like
> "libmpich.so" or so a available?  If not, you really need to recompile
> the "mpich" library in order to create shared VTK libraries.
>
>
> HTH,
>
> Obada
>


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