Dear libtoolers,
my project uses C, C++, Fortran 77. One library consists of mixed CC and
F77 sources. I intend to switch to more modern Fortran (FC) for this
library.
Linking this library with F77LINK worked well. Switching to FCLINK
causes errors for some compilers due to broken postedeps_FC.
- For HPE Cray PrgEnv-cray's ftn, postedeps_FC contains '... -L -L ...'.
- For HPE Cray PrgEnv-gnu's ftn, OpenMPI's and MPICH's mpifort
(delegating to gfortran), postedeps_FC contains '... -l -l ...'.
During investigating the cause of the broken postdeps_FC, several
questions arose.
1. Why do we have postdeps for CXX and FC, but not for CC and F77?
_LT_SYS_HIDDEN_LIBDEPS is expanded in _LT_LANG_CXX_CONFIG and
_LT_LANG_FC_CONFIG only.
2. Why do we need postdeps at all? Isn't the compiler supposed to do
just the right thing?
3. Without a C++ compiler (AC_PROG_CXX), postedeps_FC is always empty,
as output_verbose_link_cmd, the command producing the input to determine
the postdeps, is set in _LT_LANG_CXX_CONFIG only. If this is coupling
intended, can you please explain why?
Now, where do the bogus `... -L -L ...` and `... -l -l ...` come from?
The output_verbose_link_cmd used for CXX and FC postdeps is
'$CC -shared $CFLAGS -v conftest.$objext 2>&1 | $GREP -v
"^Configured with:" | $GREP " [[-]]L"'
For the compilers mentioned above, the output of this command contains a
line starting with 'Driving:', e.g.,
Driving: /p/software/jedi/stages/2025/software/GCCcore/13.3.0/bin/
gfortran -shared -g -O2 -v conftest.o -I/p/software/default/stages/2025/
software/OpenMPI/5.0.5-GCC-13.3.0/include -I/p/software/default/
stages/2025/software/OpenMPI/5.0.5-GCC-13.3.0/lib -L/p/software/default/
stages/2025/software/OpenMPI/5.0.5-GCC-13.3.0/lib -Wl,-rpath -Wl,/p/
software/default/stages/2025/software/OpenMPI/5.0.5-GCC-13.3.0/lib -
Wl,--enable-new-dtags -lmpi_usempif08 -lmpi_usempi_ignore_tkr -
lmpi_mpifh -lmpi -l gfortran -l m -shared-libgcc
The part '-l gfortran -l m' results in '... -l -l ...'
Lines starting with 'Configured with:' are already omitted in
output_verbose_link_cmd. Omitting lines starting with 'Driving:' as
well would fix the invalid postdeps_FC. Note that autoconf's
_AC_PROG_FC_V_OUTPUT also omits both, '^Driving:' and '^Configured
with:', see [1].
A patch omitting lines '^Driving:' is attached. But do we need to
expand _LT_SYS_HIDDEN_LIBDEPS for FC at all?
Thanks,
Christian
[1] https://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=blob;f=lib/
autoconf/
fortran.m4;h=cdc197bd67f4abab036cfe6a3a59d16aa712a386;hb=6199cff2909e0ac84c9391aa49ed097d6a33268d#l514
smime.p7s