18.1.1. OpenSHMEM Wrapper Compilers — Open MPI 5.0.10 documentation

# 18.1.1. OpenSHMEM Wrapper Compilers

oshcc, oshcxx, oshc++, oshfort, shmemcc, shmemcxx, shmemc++, shmemfort — OpenSHMEM wrapper compilers

## 18.1.1.1. SYNTAX

`oshcc [--showme | --showme:compile | --showme:link] ...`

`oshcxx [--showme | --showme:compile | --showme:link] ...`

`oshc++ [--showme | --showme:compile | --showme:link] ...`

`oshfort [--showme | --showme:compile | --showme:link] ...`

`shmemcc [--showme | --showme:compile | --showme:link] ...`

`shmemcxx [--showme | --showme:compile | --showme:link] ...`

`shmemc++ [--showme | --showme:compile | --showme:link] ...`

`shmemfort [--showme | --showme:compile | --showme:link] ...`

## 18.1.1.2. OPTIONS

The options below apply to all of the wrapper compilers:

- `--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 `"oshcc --showme` and `oshcc --showme my_source.c` will show all the wrapper-supplied flags. But `oshcc --showme -v` will only show the underlying compiler name and `-v`.

- `--showme:compile`: Output the compiler flags that would have been supplied to the underlying compiler.

- `--showme:link`: Output the linker flags that would have been supplied to the underlying compiler.

- `--showme:command`: Outputs the underlying 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 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-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 compiler for other options that can be passed through oshcc.

## 18.1.1.3. 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 OpenSHMEM 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.

## 18.1.1.4. Background

Open MPI provides wrapper compilers for several languages:

- `oshcc`, `shmemcc`: C

- `oshc++`, `oshcxx`, `shmemc++`, shmemcxx`:: C++

- `oshfort`, `shmemfort`: Fortran

The wrapper compilers for each of the languages are identical; they can be used interchangeably. The different names are provided solely for backwards compatibility.

## 18.1.1.5. Fortran Notes

The Fortran wrapper compiler for OpenSHMEM (`oshfort` and `shmemfort`) can compile and link OpenSHMEM applications that use any/all of the OpenSHMEM Fortran bindings.

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 `oshfort` will be inoperative and will return an error on use if Fortran support was not built into the OpenSHMEM layer.

## 18.1.1.6. Overview

`oshcc` and `shmemcc` are convenience wrappers for the underlying C compiler. Translation of an OpenSHMEM program requires the linkage of the OpenSHMEM-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.

`oshcc` and `shmemcc` pass their arguments to the underlying C compiler along with the `-I`, `-L` and `-l` options required by OpenSHMEM programs.

The same is true for all the other language wrapper compilers.

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

Indeed, since the wrappers are simply thin shells on top of an underlying compiler, there are very, very few compelling reasons not to use `oshcc`. 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 `shmemcc --showme:compile`

    shell$ cc -c file2.c `shmemcc --showme:compile`

    shell$ cc file1.o file2.o `shmemcc --showme:link` -o my_oshmem_program

## 18.1.1.7. 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 here.

## 18.1.1.8. FILES

The strings that the wrapper compilers insert into the command line before invoking the underlying compiler are stored in a text file created by OpenSHMEM and installed to `$pkgdata/NAME-wrapper-data.txt`, where:

- `$pkgdata` is typically `$prefix/share/openmpi`

- `$prefix` is the top installation directory of OpenSHMEM

- `NAME` is the name of the wrapper compiler (e.g., `$pkgdata/shmemcc-wrapper-data.txt`)

It is rarely necessary to edit these files, but they can be examined to gain insight into what flags the wrappers are placing on the command line.

## 18.1.1.9. ENVIRONMENT VARIABLES

By default, the wrappers use the compilers that were selected when OpenSHMEM was configured. These compilers were either found automatically by Open MPI’s “configure” script, or were selected by the user in the `CC`, `CXX`, 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 `oshmem_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