[petsc-dev] PetscDLSym called on an empty handle

[Lisandro Dalcin]

On 5 August 2010 18:07, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>
>
> On Thu, Aug 5, 2010 at 4:00 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
>>
>> On 5 August 2010 13:40, Dmitry Karpeev <karpeev at mcs.anl.gov> wrote:
>> > What is the intended behavior of PetscDLSym when called on an empty
>> > handle:
>> > PetscDLSym(handle=PETSC_NULL, symbol, &value)
>> > My understanding was that this should look for symbol in the symbol
>> > table of
>> > the main executable.
>> > This is based on what happens in the Windows case (#ifdef
>> > PETSC_HAVE_WINDOWS_H),
>> > but when using dlopen (#ifdef PETSC_HAVE_DLFCN_H), this probably won't
>> > behave correctly,as currently implemented.
>> > This is because the above call will boil down to
>> >    value = dlsym((dlhandle_t)0, symbol),
>> > which on many systems returns NULL (e.g., on Ubuntu 9.10).
>>
>> Look at your dlfch.h header file.. Does it have the line below?:
>>
>> # define RTLD_DEFAULT   ((void *) 0)
>
> Yes.  Ah, I see: my problem was that the symbol wasn't being exported, not
> that the null handle wasn't referring to the executable.

Yep

> I guess I can
> change it to use RTLD_DEFAULT, but that would require changes to configure.

Using RTLD_DEFAULT is the right way to do it.

> Also, this may be less portable: OSX uses a different define for the default
> handle, so configure would have to
> test for that too.  I wonder what OSX does for dlopen(0,flags)?
>

It likely fails with "invalid handle passed to dlsym()"
(http://www.opensource.apple.com/source/dyld/dyld-132.13/src/dyldAPIs.cpp)

-- 
Lisandro Dalcin
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