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

[Dominic Kempf]

Hey Carsten,

that sounds much like an Ubuntu bug to me.

It might not be very nice, but you could write a cmake macro, that
restricts a given set of compiler flags to the set of flags accepted by the
compiler:

Untested scetch:
macro(discarded_unsupported_flags flaglist)
  set(SUPPORTED_FLAGS)
  foreach(flag ${flaglist})
    execute_command(COMMAND ${CMAKE_CXX_COMPILER} ${flag} dummy.cc
RESULT_VARIABLE return_value)
    if(return_value STREQUAL "0")
      list(APPEND SUPPORTED_FLAGS ${flag})
    endif()
  endforeach()
endmacro()

Unfortunately, I have no better idea.

Dominic

On Wed, Jul 1, 2015 at 10:20 PM, Carsten Gräser <graeser at mi.fu-berlin.de>
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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>
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