Fix building system: correct libltdl check for advise capability.

[artpol84]

ompi commit: open-mpi/ompi@3ff16e7
ompi pull request: open-mpi/ompi#240

[jsquyres]

Artem --

I'm struggling to remember why the initial -I. was there. In my comment on your master PR (open-mpi/ompi#240 (comment)), I was only referring to your new second -I, not the first/original -I..

Can you check to see exactly which gcc -E ... command is emitted, and see if changing -I. to -I$srcdir is necessary?

FWIW: the libltdl.h file should be in the source tree (vs. the build tree), so -I$srcdir might actually be correct. But I'm not remembering exactly what that -I. was for -- i.e., was it actually for libltdl.h, or was it for something else? And if it was actually for libltdl.h, is it just plain wrong, and your now -I$srcdir/... is the correct one? I.e., should the original -I. (now -I$srcdir) just be deleted?

[artpol84]

That is a good point, Jeff.

Looking closely to the configuration system I can see that we deal with following conftest.c template:

CPPFLAGS="-I$srcdir/ -I$srcdir/opal/libltdl/"
# Must specifically mention $srcdir here for VPATH builds
# (this file is in the src tree).
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h.  */
#include <$srcdir/opal/libltdl/ltdl.h>

_ACEOF

That will turn into

//... < lots of defines > ....
#define OMPI_MPI_CONTRIBS "libompitrace, vt"
#define OPAL_C_HAVE_VISIBILITY 1
#define HAVE_DLFCN_H 1
#define LT_OBJDIR ".libs/"
/* end confdefs.h.  */

#include < ./opal/libltdl/ltdl.h > 

For local config and to

...
#include < /some/vpath/path/opal/libltdl/ltdl.h >

for VPATH.

So we don't actually need "-I." or "-I$srcdir" at all because conftest.c always contains correct path relative to the current configuration directory.
I updated my pull branch by changing the commit of interest.

[artpol84]

I guess I need to go back to ompi and apply this patch there? Additionall pull request?

[jsquyres]

Wait, let's figure this out before doing anything...

If we don't need the -I, then why did adding it fix your problem?

[artpol84]

Sure,
I didn't add -I. I proposed to add -I$srcdir/opal/libltdl/. And now I think that we can also remove "-I."

[jsquyres]

I know you didn't add -I. -- I just said -I, meaning the -I$srcdir... one. :-)

I was responding to your prior comment:

So we don't actually need "-I." or "-I$srcdir" at all ...

So if we need neither -I, then why did your adding -I$srcdir... fix the problem for you?

[artpol84]

Because in conftest.c we include ltdl.h using its full path. And ltdl.h includes few others:

#include <libltdl/lt_system.h>
#include <libltdl/lt_error.h>

They are located in opal/libltdl/libltdl and are reffered by relative paths and inaccessible for gcc without corresponding -I$srcdir/opal/libltdl/.

P.S. Check the latest patch to clarify my current version.

[jsquyres]

Ok, got it -- we do need the -I$srcdir.... Got it.

Yes, please push the final change back to master (i.e., delete the -I.), put the master hash here (per the requirement that we have to have all the relevant commits/functionality on master before bringing to v1.8, and then we'll be good to go.

[artpol84]

Done: open-mpi/ompi@ce7102c