mpicc(1) Open MPI mpicc(1)
NAME
mpicc -- Open MPI C wrapper compiler
SYNTAX
mpicc [-showme|-showme:compile|-showme:link] ...
OPTIONS
-showme
Do not invoke the underlying compiler. Instead, show 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 "mpicc --showme" and
"mpicc --showme my_source.c" will show all the wrapper-supplied flags. But "mpicc -showme -v"
will only show the underlying compiler name and "-v".
-showme:compile
Do not invoke the underlying C compiler. Instead, show the compiler flags that would be sup-plied supplied
plied to the C compiler.
-showme:link
Do not invoke the underlying C compiler. Instead, show the linker flags that would be sup-plied supplied
plied to the C compiler.
See the man page for your underlying compiler for other options that can be passed through mpicc
DESCRIPTION
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 actu-ally actually
ally compile or link applications themselves; they only add in command line flags and invoke the
back-end compiler.
Background
Open MPI is comprised of three software layers: OPAL (Open Portable Access Layer), ORTE (Open Run-Time RunTime
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.
Overview
mpicc is a convenience wrappers for the underlying C 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.
mpicc passes its arguments to the underlying C 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 with-out without
out 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 mpicc. 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
NOTES
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 provid-ing providing
ing both 32 and 64 bit support). More information can be found at:
https://svn.open-mpi.org/trac/ompi/wiki/compilerwrapper3264
FILES
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/mpicc-wrapper-data.txt, $pkgdata/mpicc-wrapperdata.txt,
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.
ENVIRONMENT VARIABLES
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. Addition-ally, Additionally,
ally, 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 configu-ration configuration
ration 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
OMPI Open MPI mpicc(1)
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