NAME

       opalcc -- Open PAL C wrapper compiler

SYNTAX

       opalcc [-showme|-showme:compile|-showme:link] ...

OPTIONS

       --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 "opalcc
              --showme" and "opalcc --showme my_source.c" will show all the wrapper-supplied flags.  But "opalcc
              --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.

       --showme:help
              Output a brief usage help message.

       See the man page for your underlying C compiler for other options that can be passed through opalcc.

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 PAL 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), 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.

   Fortran Notes
       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.

   Overview
       opalcc  is  a  convenience  wrappers  for  the underlying C compiler.  Translation of an Open PAL program
       requires the linkage of the Open PAL-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.

       opalcc passes its arguments to the underlying C compiler along with the -I, -L and -l options required by
       Open PAL programs.

       The  Open  PAL  Team strongly encourages using the wrapper compilers instead of attempting to link to the
       Open PAL libraries manually.  This allows the specific implementation  of  Open  PAL  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 PAL was configured and built; the values  can
       change between different installations of the same version of Open PAL.

       Indeed,  since the wrappers are simply thin shells on top of an underlying compiler, there are very, very
       few compelling reasons not to use opalcc.  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://github.com/open-mpi/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 PAL and installed to $pkgdata/opalcc-wrapper-data.txt,
       where $pkgdata is typically $prefix/share/openmpi, and $prefix is the top installation directory of  Open
       PAL.

       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  PAL  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
       "OPAL_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