[Dune-devel] Building dune-common with gcc-4.8 fails

[Carsten Gräser]

Hi Christian,

Am 07.07.2015 um 08:21 schrieb Christian Engwer:
> Hi Carsten,
> 
> Am 7. Juli 2015 07:24:03 MESZ, schrieb "Carsten Gräser" <graeser at mi.fu-berlin.de>:
>> Hi Christian,
>>
>> Am 03.07.2015 um 16:39 schrieb Christian Engwer:
>>> Hi Carsten,
>>>
>>> I can confirm this behaviour for debian testing.
>> that's a little sad, because it means that none of our
>> debian-using dev's has lately tested the release branch
>> with any but the newest compilers.
> 
> that is not actually true.
I hope so ;-).

>>> The problem seems to be inherent to mpich, as the mpicc.mpich always
>>> uses these flags, regardless of the chosen compiler, this
>>>
>>> mpicc -cc=/usr/bin/gcc-4.8 ...
>>>
>>> will results in the same problem.
>>>
>>> I think we have to work around this. How about just removing all
>>> "-f..." options from MPI flags?
> 
> the problem does not occurre with openmpi, which many people are using (isn't it even the default?).
That's good news. As far as I remember, I never installed mpich
explicitly but it came as a dependency of another package.

>> I don't know if this is viable. Maybe some of them are necessary
>> to compile with mpi?
> 
> Not in this case.
> 
>> Unfortunately cmake does not allow to overwrite these flags
>> properly. For the moment I use the attached patch and pass
>> the corresponding flag via CMAKE_FLAGS.
> 
> Not a good option. In particular as we encourage people to use the packages.
I know, it's a pretty dirty hack and I'd never propose to push
it to master. I just wanted to give a hint, how to trick around
this with minimal effort, because neither passing the flag to
cmake via -D... nor putting it in the cache via -c... works here.

Best,
Carsten


> 
> I think it is a Debian bug, because also when I change the compiler via the mpicc switch it includes these wrong options.
> 
> Christian
> 
>>
>> Carsten
>>
>>
>>
>>>
>>> Christian
>>>
>>> On Wed, Jul 01, 2015 at 10:20:57PM +0200, Carsten Gräser wrote:
>>>> Am 01.07.2015 um 15:50 schrieb Carsten Gräser:
>>>>> Am 01.07.2015 um 15:40 schrieb Jö Fahlke:
>>>>>> Am Wed,  1. Jul 2015, 15:35:12 +0200 schrieb Carsten Gräser:
>>>>>>> Date: Wed, 01 Jul 2015 15:35:12 +0200
>>>>>>> From: Carsten Gräser <graeser at mi.fu-berlin.de>
>>>>>>> To: "dune-devel at dune-project.org" <dune-devel at dune-project.org>
>>>>>>> Subject: Re: [Dune-devel] Building dune-common with gcc-4.8 fails
>>>>>>>
>>>>>>> Hi Jö,
>>>>>>
>>>>>>> CMakeCache shows that this flag is also present in
>> MPI_CXX_COMPILE_FLAGS
>>>>>>> and MPI_C_COMPILE_FLAGS.
>>>>>>
>>>>>> In your other Mail you bisected the problem to the patch that
>> enabled mpi by
>>>>>> default in cmake.  So this sounds very mpi-related.  Maybe that
>> flag is
>>>>>> extracted from mpicc?  And you don't have a problem before the
>> patch because
>>>>>> dune-common did not look for mpi then, but is doing it now?
>>>>>>
>>>>>> Which MPI are you using?
>>>>> It's mpich-3.1.
>>>>>
>>>>> I also noticed that passing the compiler to mpic++ via -cxx
>> preserves
>>>>> this -fstack-protector-strong option which seems to be the ubuntu
>> default.
>>>>
>>>> I guess I've found the origin of the problem, but I don't now
>>>> who's to blame and how to fix this: Recent Ubuntu decided to enable
>>>>
>>>>   -D_FORTIFY_SOURCE=2  -fstack-protector-strong
>>>>
>>>> by default for security reasons. This also seems to imply that these
>>>> flags are by default used with the mpi compiler wrappers, at least
>>>> according to
>>>>
>>>>   mpicxx -show
>>>>
>>>> Not surprisingly the cmake module FindMPI detects these flags and
>>>> stores them in MPI_C_COMPILER_FLAGS which we forwarded to
>>>> MPI_DUNE_COMPILE_FLAGS and thus use when building dune
>>>> applications with mpi. The problem is that the second flag is
>>>> not supported with gcc versions < 4.9, but the flag is always
>> passed.
>>>> It's a little unclear, who is to blame for this problem:
>>>>
>>>> a)Dune is blindly passing the mpi compile flags regardless of the
>>>>   selected compiler.
>>>>
>>>> b)FindMPI does not allow to pass a compiler in order to detect
>>>>   suitable flags.
>>>>
>>>> c)Even "mpicc -cc=/usr/bin/gcc-4.8" does not provide suitable flags.
>>>>
>>>> d)Is it a ubuntu bug to always provide these flags with mpi,
>>>>   regardless of the compiler?
>>>>
>>>> I'd like to at least circumvent the problem to be able to test
>>>> with all my compilers, but it seems that one cannot overwrite
>>>> the MPI_C_COMPILER_FLAGS with a command line argument.
>>>> For now I have to manually remove the flag in the cache
>>>> if I want to test with a packaged but older compiler. Does
>>>> anybody more familiar with mpi and cmake now a better way
>>>> to get around this?
>>>>
>>>> Best,
>>>> Carsten

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