|
« Return to documentation listing
Table of Contents
mpicc -- Open MPI C wrapper compiler
mpicc [-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 "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
- Output the compiler
flags that would have been supplied to the C compiler.
- --showme:link
- Output
the linker flags that would have been supplied to the C compiler.
- --showme:command
- Outputs the underlying C 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
C 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 C compiler for other options that
can be passed through mpicc.
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.
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
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/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.
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
Table of Contents
« Return to documentation listing
|
