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mpif77 -- Open MPI Fortran 77 wrapper compiler
mpif77 [-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 "mpif77 --showme" and "mpif77 --showme my_source.c"
will show all the wrapper-supplied flags. But "mpif77 --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 77 compiler.
- --showme:link
- Output the linker flags that would have been supplied to the Fortran 77
compiler.
- --showme:command
- Outputs the underlying Fortran 77 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 77 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.
See the man page for your underlying
Fortran 77 compiler for other options that can be passed through mpif77.
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 MPI 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),
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 compilers
for MPI (mpif77 and mpif90) will be inoperative and will return an error
on use if Fortran 77 / Fortran 90 support was not built into the MPI layer.
mpif77 is a convenience wrappers for the underlying Fortran 77
compiler. Translation of an Open MPI program requires the linkage of the
Open MPI-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.
mpif77 passes
its arguments to the underlying Fortran 77 compiler along with the -I, -L
and -l options required by Open MPI programs.
The Open MPI Team strongly
encourages using the wrapper compilers instead of attempting to link to
the Open MPI libraries manually. This allows the specific implementation
of Open MPI 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 MPI was configured and built; the
values can change between different installations of the same version of
Open MPI.
Indeed, since the wrappers are simply thin shells on top of an
underlying compiler, there are very, very few compelling reasons not to
use mpif77. 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://svn.open-mpi.org/trac/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 MPI and installed to $pkgdata/mpif77-wrapper-data.txt, where $pkgdata
is typically $prefix/share/openmpi, and $prefix is the top installation
directory of Open MPI.
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 MPI 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 "OMPI_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
- F77
- Fortran
77 compiler
- FFLAGS
- Fortran 77 compiler flags
- FC
- Fortran 90 compiler
- FCFLAGS
- Fortran 90 compiler flags
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