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oshfort -- Open SHMEM Fortran wrapper compiler
oshfort [-showme|-showme:compile|-showme:link]
...
- --showme
- This option comes in several different variants (see below).
None of the variants invokes the underlying compiler; they all provide
information on how the underlying compiler would have been invoked had
--showme not been used. The basic --showme option outputs the command line that
would be executed to compile the program. NOTE: If a non-filename argument
is passed on the command line, the -showme option will not display any additional
flags. For example, both "oshfort --showme" and "oshfort --showme my_source.c"
will show all the wrapper-supplied flags. But "oshfort --showme -v" will only
show the underlying compiler name and "-v".
- --showme:compile
- Output the compiler
flags that would have been supplied to the Fortran compiler.
- --showme:link
- Output the linker flags that would have been supplied to the Fortran compiler.
- --showme:command
- Outputs the underlying Fortran compiler command (which may
be one or more tokens).
- --showme:incdirs
- Outputs a space-delimited (but otherwise
undecorated) list of directories that the wrapper compiler would have provided
to the underlying Fortran compiler to indicate where relevant header files
are located.
- --showme:libdirs
- Outputs a space-delimited (but otherwise undecorated)
list of directories that the wrapper compiler would have provided to the
underlying linker to indicate where relevant libraries are located.
- --showme:libs
- Outputs a space-delimited (but otherwise undecorated) list of library names
that the wrapper compiler would have used to link an application. For example:
"mpi open-rte open-pal util".
- --showme:version
- Outputs the version number of
Open MPI.
- --showme:help
- Output a brief usage help message.
See the man page
for your underlying Fortran compiler for other options that can be passed
through oshfort.
Conceptually, the role of these commands is
quite simple: transparently add relevant compiler and linker flags to the
user’s command line that are necessary to compile / link Open SHMEM programs,
and then invoke the underlying compiler to actually perform the command.
As such, these commands are frequently referred to as "wrapper" compilers
because they do not actually compile or link applications themselves; they
only add in command line flags and invoke the back-end compiler.
Open
MPI is comprised of three software layers: OPAL (Open Portable Access Layer),
ORTE (Open Run-Time Environment), and OMPI (Open MPI). There are wrapper
compilers for each layer; each layer’s wrapper only links in the libraries
relevant for that layer. Specifically, each layer provides the following
wrapper compilers:
- OPAL
- opalcc and opalc++
- ORTE
- ortecc and ortec++
- OMPI
- mpicc, mpic++, mpicxx, mpiCC (only on systems with case-senstive file systems),
and mpifort (and its legacy/deprecated names mpif77 and mpif90). Note that
mpic++, mpicxx, and mpiCC all invoke the same underlying C++ compiler with
the same options. All are provided as compatibility with other MPI implementations.
The Fortran wrapper compiler for MPI (mpifort, and its legacy/deprecated
names mpif77 and mpif90) can compile and link MPI applications that use
any/all of the MPI Fortran bindings: mpif.h, the mpi module, and the mpi_f08
module (assuming Open MPI was installed with support for each of these
Fortran bindings). Specifically: it is no longer necessary to use different
wrapper compilers for applications that use mpif.h vs. applications that
use the mpi module -- just use mpifort for all Fortran MPI applications.
Note, however, that the Fortran compiler may require additional command-line
options to enforce a specific Fortran dialect. For example, in some versions
of the IBM XLF compiler, if xlf90 is the underlying Fortran compiler, -qfixed
may be necessary to compile fixed-format Fortran source files.
Finally,
note that mpifort will be inoperative and will return an error on use if
Fortran support was not built into the MP Ilayer.
oshfort is a
convenience wrappers for the underlying Fortran compiler. Translation of
an Open SHMEM program requires the linkage of the Open SHMEM-specific libraries
which may not reside in one of the standard search directories of ld(1).
It also often requires the inclusion of header files what may also not
be found in a standard location.
oshfort passes its arguments to the underlying
Fortran compiler along with the -I, -L and -l options required by Open SHMEM
programs.
The Open SHMEM Team strongly encourages using the wrapper compilers
instead of attempting to link to the Open SHMEM libraries manually. This
allows the specific implementation of Open SHMEM to change without forcing
changes to linker directives in users’ Makefiles. Indeed, the specific set
of flags and libraries used by the wrapper compilers depends on how Open
SHMEM was configured and built; the values can change between different
installations of the same version of Open SHMEM.
Indeed, since the wrappers
are simply thin shells on top of an underlying compiler, there are very,
very few compelling reasons not to use oshfort. When it is not possible
to use the wrappers directly, the -showme:compile and -showme:link options
should be used to determine what flags the wrappers would have used. For
example:
shell$ cc -c file1.c ‘mpicc -showme:compile‘
shell$ cc -c file2.c ‘mpicc
-showme:compile‘
shell$ cc file1.o file2.o ‘mpicc -showme:link‘ -o my_mpi_program
It is possible to make the wrapper compilers multi-lib aware. That
is, the libraries and includes specified may differ based on the compiler
flags specified (for example, with the GNU compilers on Linux, a different
library path may be used if -m32 is seen versus -m64 being seen). This is
not the default behavior in a standard build, but can be activated (for
example, in a binary package providing both 32 and 64 bit support). More
information can be found at:
https://github.com/open-mpi/ompi/wiki/compilerwrapper3264
The string that the wrapper compilers insert into the command line
before invoking the underlying compiler are stored in a text file created
by Open SHMEM and installed to $pkgdata/oshfort-wrapper-data.txt, where $pkgdata
is typically $prefix/share/openmpi, and $prefix is the top installation
directory of Open SHMEM.
It is rarely necessary to edit this file, but
it can be examined to gain insight into what flags the wrappers are placing
on the command line.
By default, the wrappers use
the compilers that were selected when Open SHMEM was configured. These
compilers were either found automatically by Open MPI’s "configure" script,
or were selected by the user in the CC, CXX, F77, and/or FC environment
variables before "configure" was invoked. Additionally, other arguments
specific to the compiler may have been selected by configure.
These values
can be selectively overridden by either editing the text files containing
this configuration information (see the FILES section), or by setting selected
environment variables of the form "OSHMEM_value".
Valid value names are:
- CPPFLAGS
- Flags added when invoking the preprocessor (C or C++)
- LDFLAGS
- Flags added when invoking the linker (C, C++, or Fortran)
- LIBS
- Libraries
added when invoking the linker (C, C++, or Fortran)
- CC
- C compiler
- CFLAGS
- C compiler flags
- CXX
- C++ compiler
- CXXFLAGS
- C++ compiler flags
- FC
- Fortran
compiler
- FCFLAGS
- Fortran compiler flags
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