Re: Status of GDB support for debugging of Fortran programs?

[Tobias Burnus <burnus at net-b dot de>]

On 09/04/2012 09:16 PM, Harald Anlauf wrote:
> does anybody know whether there has been any progress in GDB
> that supports debugging of Fortran programs on Linux/x86?

Yes, but only slowly: Support for modules is in GDB 7.2 (use: print 
'mod1::myvar') as is support for UCS-4 strings (character(kind=4)).

> Are there some secret patches that are needed to get it working?

Yes - but they don't help with your problem.

The unpatched GDB from Sourceware.org doesn't support Fortran 90 style 
arrays which use an array descriptor (assumed-shape, deferred-shape, 
assumed-rank) - nor does it support the similar but rarely used C99 
varying length arrays (VLA). Jan Kratochvil of Red Hat has some patches 
(the initial version is from 2007/2008) which add support for those 
arrays, but they do not work in all cases - such as yours.

Jan believes that the current approach is not the best one and, thus, he 
doesn't want to spend time on the current approach. He does intent to 
work on a new implementation, but so far he hadn't the time to do so. At 
the GNU Tools Cauldron in Prague he said that he shifted some projects 
to someone else and hopes to have more time to work on this in the 
(near) future. For details, see also 
http://sourceware.org/ml/gdb/2011-03/msg00021.html and 
http://sourceware.org/gdb/wiki/ArcherBranchManagement

See also page 11 at 
http://gcc.gnu.org/wiki/cauldron2012?action=AttachFile&do=get&target=jkratoch.pdf 
(-> http://gcc.gnu.org/wiki/cauldron2012 ).

To a certain extend the problem seems to be that some big customers (of 
Red Hat, SUSE, etc.) don't put strong pressure/large financial incentive 
to their vendors to implement Fortran features. I think many bigger 
customers are using gfortran/gdb, but either they are happy with the 
current support or the issues don't escalate high enough in the 
hierarchy to reach the management. To a certain extent that's also 
because several most sites also have commercial compilers. [You also 
seem to use idb.] Given the complexity/size of, e.g., VLA, it simply 
takes a while to get it implemented, unless those project get rated with 
a very high priority.

> I tried gdb-7.3 that comes with OpenSuse 12.1, as well as a
> self-compiled gdb-7.5.

As the Red Hat/Fedora version contains at least some VLA/F90 array 
support, I recommend to avoid using the unpatched sourceware.org 
version. Note that (open)SUSE's gdb includes the VLA patches.

If you want to have a newer gdb (or GCC) on you openSUSE 12.1, you could 
use the builds from 
http://download.opensuse.org/repositories/devel:/gcc/openSUSE_12.1/

You find gdb 7.4.50 of July there. That version should match 7.5 
(released 2012-08-17) minus a few later patches.

Tobias