opalc++(1) Open MPI opalc++(1)
NAME
opalc++ -- Open PAL C++ wrapper compiler
SYNTAX
opalc++ [-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 op-
tion 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 "opalc++ --showme" and "opalc++
--showme my_source.c" will show all the wrapper-supplied flags.
But "opalc++ --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 lo-
cated.
--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 opalc++.
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" compil-
ers 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 Ac-
cess 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 pro-
vided as compatibility with other MPI implementations.
Fortran Notes
The Fortran wrapper compiler for MPI (mpifort, and its legacy/depre-
cated 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 com-
mand-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 For-
tran 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
opalc++ 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.
opalc++ 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 in-
stead of attempting to link to the Open PAL libraries manually. This
allows the specific implementation of Open PAL to change without forc-
ing changes to linker directives in users' Makefiles. Indeed, the spe-
cific 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 underly-
ing compiler, there are very, very few compelling reasons not to use
opalc++. 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 dif-
ferent 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 be-
fore invoking the underlying compiler are stored in a text file created
by Open PAL and installed to $pkgdata/opalc++-wrapper-data.txt, where
$pkgdata is typically $prefix/share/openmpi, and $prefix is the top in-
stallation 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 in-
voked. 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
FC Fortran compiler
FCFLAGS
Fortran compiler flags
4.1.4 May 26, 2022 opalc++(1)
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