[petsc-dev] PetscDLSym called on an empty handle

[Dmitry Karpeev]

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

Dmitry.

>
>
>
> --
> Lisandro Dalcin
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