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NAME

       opalcc -- Open PAL C wrapper compiler

SYNTAX

       opalcc [-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   "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
              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 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), 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
       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://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 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

       F77    Fortran 77 compiler

       FFLAGS Fortran 77 compiler flags

       FC     Fortran 90 compiler

       FCFLAGS
              Fortran 90 compiler flags