Re: Fwd: .so interdependencies

On Fri, Apr 16, 2010 at 4:45 AM, Anderson Lizardo
<[email protected]> wrote:
> [forgot to CC the mailing list]
>
>
> ---------- Forwarded message ----------
> From: Anderson Lizardo <[email protected]>
> Date: Fri, Apr 16, 2010 at 7:44 AM
> Subject: Re: [ctypes-users] .so interdependencies
> To: Paul Northug <[email protected]>
>
>
> On Fri, Apr 16, 2010 at 3:44 AM, Paul Northug <[email protected]> wrote:
>> I get an error:
>>
>> libmytest.so: undefined symbol: slamch_
>>
>> which is a function in a different library .so that is used by a
>> function in my library.
>>
>> They are both in LD_LIBRARY_PATH. Is there a way to resolve this? I
>> have the freedom of creating the library, if that helps, but I don't
>> know much about shared libraries and how the dependencies between
>> libraries get resolved. Did I build my .so correctly given that it
>> works fine in other C programs that use it?
>>
>> I have read one other post describing a similar problem but it didn't
>> seem to have gotten resolved.
>
> On that thread (?) I posted this example:
>
> libx11 = ctypes.CDLL("libX11.so.6", mode=ctypes.RTLD_GLOBAL)
>
> Does it work for you ? (replace libx11 with the library that contains
> the "slamch_" symbol, and put the line above your libmytest.so
> library.

Your suggestion worked, but before I loaded my .so with LoadLibrary, I
had to load in all the libraries that this particular .so depended on
one by one with RTLD_GLOBAL, which made me realize I had not built it
the correct way in the first place. So using something similar to
Michelle's suggestion, I did:

g++ -shared -o libmytest.so -L. -L(other lib paths) -lacml -lacml_mv
-l(a bunch of other libs) src/*.o

and I was able to load the library correctly. I am guessing that this
type of error would not occur if the original .so is properly linked
with all its dependencies and that they are all in LD_LIBRARY_PATH
(checking with 'ldd'). I think I need to better understand what a
shared library is before I use ctypes more.

Thanks,
Pål

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