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 supplied to the C compiler.
-showme:link
Do not invoke the underlying C compiler. Instead, show the
linker flags that would be supplied 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 actually 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 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 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 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 providing 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,
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. 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