opalcc(1)							     Open MPI								 opalcc(1)

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 them-
       selves; 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 implementa-
	   tions.

       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  com-
       piler 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 cre-
       ated 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  automati-
       cally  by  Open MPI's "configure" script, or were selected by the user in the CC, CXX, F77, and/or FC environment variables before "config-
       ure" 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  sec-
       tion), 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

1.4.5								   Feb 10, 2012 							 opalcc(1)