[Bug fortran/47571] [4.7 Regression] undefined reference to clock_gettime in Linux build of 02/01/2011

[ro at CeBiTec dot Uni-Bielefeld.DE]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47571

--- Comment #45 from ro at CeBiTec dot Uni-Bielefeld.DE <ro at CeBiTec dot Uni-Bielefeld.DE> 2011-03-21 14:47:20 UTC ---
> --- Comment #38 from Janne Blomqvist <jb at gcc dot gnu.org> 2011-03-15 17:04:41 UTC ---
> Created attachment 23669
>   --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23669
> Updated patch
>
> This patch takes into account the comments by Jakub, and unconditionally sets
> GF_CLOCK_MONOTONIC if clock_gettime is available; this should fix a bug if
> CLOCK_* are not preprocessor macros.

This patch doesn't work:

SUPPORTS_WEAK is 1, GTHREAD_USE_WEAK is 1 since acinclude.m4
(LIBGFOR_GTHREAD_WEAK) doesn't set it to 0, and HAVE_CLOCK_GETTIME_LIBRT
is 1, too, so we still have an undefined reference to clock_gettime ;-(

Could we please avoid this mess with SUPPORTS_WEAK and GTHREAD_USE_WEAK
and make configure define SUPPORTS_WEAKREF or something like this, since
this is what we are actually looking for?

If we include alpha*-dec-osf* in the list of targets that don't support
weakrefs, things should start working again, but I'd prefer a patch where
you can actually read *and understand* what's going on here.

Apart from that, has anyone actually *measured* the overhead of simply
linking libgfortran with librt on Linux, rather than claiming that there
might be some?  It the overhead were acceptable or even neglegible, we
could avoid all this mess in the first place, link with -lrt if need be,
and be done with it.

Additionally, the usage model for the weakref seems questionable to
me: while the technique is well-known and common on ELF targets to
produce code that can work with or without libpthread linked into the
application (which is what users will actually do!), which user is
supposed to link his Fortran code with librt to get improved system
clock resolution?  I dare say that close to nobody will even think about
this.

    Rainer