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Subject: Re: [OMPI devel] libtool issue with crs/self
From: Josh Hursey (jjhursey_at_[hidden])
Date: 2009-08-05 10:51:59

As an update on this thread. I had a bit of time this morning to look
into this.

I noticed that the "-fvisibility=hidden" option when passed to libltdl
will cause it to fail in its configure test for:
  "checking whether a program can dlopen itself"
This is because the symbol they are trying to look for with dlsym() is
not postfixed with:
   __attribute__ ((visibility("default")))
If I do that, then the test passes correctly.

I am not sure if this is a configure bug in Libtool or not. But what
it means is that even with the wrapper around the OPAL libltdl
routines, it is not useful to me since I need to open the executable
to examine it for the necessary symbols.

So I might try to go down the track of using dlopen/dlsym/dlclose
directly instead of through the libtool interfaces. However I just
wanted to mention that this is happening in case there are other
places in the codebase that ever want to look into the executable for
symbols, and find that lt_dlopen() fails in non-obvious ways.

-- Josh

On Jul 29, 2009, at 11:01 AM, Brian W. Barrett wrote:

> Never mind, I'm an idiot. I still don't like the wrappers around
> lt_dlopen in util, but it might be your best option. Are you
> looking for symbols in components or the executable? I assumed the
> executable, in which case you might be better off just using dlsym()
> directly. If you're looking for a symbol first place it's found,
> then you can just do:
> dlsym(RTLD_DEFAULT, symbol);
> The lt_dlsym only really helps if you're running on really obscure
> platforms which don't support dlsym and loading "preloaded"
> components.
> Brian
> On Wed, 29 Jul 2009, Brian W. Barrett wrote:
>> What are you trying to do with lt_dlopen? It seems like you should
>> always go through the MCA base utilities. If one's missing, adding
>> it there seems like the right mechanism.
>> Brian
>> On Wed, 29 Jul 2009, Josh Hursey wrote:
>>> George suggested that to me as well yesterday after the meeting.
>>> So we would create opal interfaces to libtool (similar to what we
>>> do with the event engine). That might be the best way to approach
>>> this.
>>> I'll start to take a look at implementing this. Since opal/libltdl
>>> is not part of the repository, is there a 'right' place to put
>>> this header? maybe in opal/util/?
>>> Thanks,
>>> Josh
>>> On Jul 28, 2009, at 6:57 PM, Jeff Squyres (jsquyres) wrote:
>>>> Josh - this is almost certainly what happened. Yoibks.
>>>> Unfortunately, there's good reasons for it. :(
>>>> What about if we proxy calls to lt_dlopen through an opal
>>>> function call?
>>>> -jms
>>>> Sent from my PDA. No type good.
>>>> ----- Original Message -----
>>>> From: devel-bounces_at_[hidden] <devel-bounces_at_[hidden]>
>>>> To: Open MPI Developers <devel_at_[hidden]>
>>>> Sent: Tue Jul 28 16:39:42 2009
>>>> Subject: Re: [OMPI devel] libtool issue with crs/self
>>>> It was mentioned to me that r21731 might have caused this problem
>>>> by
>>>> restricting the visibility of the libltdl library.
>>>> Brian,
>>>> Do you have any thoughts on how we might extend the visibility so
>>>> that
>>>> MCA components could also use the libtool in opal?
>>>> I can try to initialize libtool in the Self CRS component and use
>>>> it
>>>> directly, but since it is already opened by OPAL, I think it
>>>> might be
>>>> better to use the instantiation in OPAL.
>>>> Cheers,
>>>> Josh
>>>> On Jul 28, 2009, at 3:06 PM, Josh Hursey wrote:
>>>>> Once upon a time, the Self CRS module worked correctly, but I
>>>>> admit
>>>>> that I have not tested it in a long time.
>>>>> The Self CRS component uses dl_open and friends to inspect the
>>>>> running process for a particular set of functions. When I try to
>>>>> run
>>>>> an MPI program that contains these signatures I get the following
>>>>> error when it tries to resolve lt_dlopen() in
>>>>> opal_crs_self_component_query():
>>>>> ------------------
>>>>> my-app: symbol lookup error: /path/to/install/lib/openmpi/
>>>>> undefined symbol: lt_dlopen
>>>>> ------------------
>>>>> I am configuring with the following:
>>>>> ------------------
>>>>> ./configure --prefix=/path/to/install \
>>>>> --enable-binaries \
>>>>> --with-devel-headers \
>>>>> --enable-debug \
>>>>> --enable-mpi-threads \
>>>>> --with-ft=cr \
>>>>> --without-memory-manager \
>>>>> --enable-ft-thread \
>>>>> CC=gcc CXX=g++ \
>>>>> F77=gfortran FC=gfortran
>>>>> ------------------
>>>>> The source code is at the link below:
>>>>> Does anyone have any thoughts on what might be going wrong here?
>>>>> Thanks,
>>>>> Josh
>>>>> _______________________________________________
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