oshfort(1)

oshfort(1) 💖

okay bestie, sit down, hydrate, because this is the Open MPI manual page for oshfort — the Open SHMEM Fortran wrapper compiler — and we're gonna get you fluent in it. no cap. ✨

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NAME 🎀

oshfort — the Open SHMEM Fortran wrapper compiler. that's it, that's the name, she's iconic and she knows it 💅

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SYNTAX 🦋

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

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OPTIONS ✨

• --showme — okay so this one comes in several different variants (scroll down, they're all here). here's the tea: none of the variants actually invoke the underlying compiler. they just tell you how that compiler would have been invoked if you hadn't used --showme. the basic --showme spits out the command line that would've been executed to compile your program. NOTE: if a non-filename argument gets passed on the command line, -showme won't display any additional flags. for example, both oshfort --showme and oshfort --showme my_source.c will show all the wrapper-supplied flags. but oshfort --showme -v will only show the underlying compiler name and -v. iykyk 😭
• --showme:compile — outputs the compiler flags that would've been handed to the Fortran compiler.
• --showme:link — outputs the linker flags that would've been handed to the Fortran compiler.
• --showme:command — outputs the underlying Fortran compiler command (which may be one or more tokens, so don't be shocked).
• --showme:incdirs — outputs a space-delimited (but otherwise undecorated, she's bare-faced) list of directories that the wrapper compiler would've given to the underlying Fortran compiler to say where the relevant header files live.
• --showme:libdirs — outputs a space-delimited (again, otherwise undecorated) list of directories that the wrapper compiler would've given to the underlying linker to say where the relevant libraries live.
• --showme:libs — outputs a space-delimited (you guessed it, otherwise undecorated) list of library names that the wrapper compiler would've used to link an application. for example: "mpi open-rte open-pal util".
• --showme:version — outputs the version number of Open MPI.
• --showme:help — outputs a brief usage help message. short king 👑

also, go peek at the man page for your underlying Fortran compiler for other options that can be passed through oshfort. she's a conduit, not a gatekeeper.

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DESCRIPTION 🌸

conceptually? the role of these commands is genuinely so simple: transparently add the relevant compiler and linker flags to your command line — the ones you need to compile / link Open SHMEM programs — and then invoke the underlying compiler to actually do the thing.

so yeah, that's why these commands get called "wrapper" compilers: they don't actually compile or link applications themselves. they just add in command line flags and invoke the back-end compiler. middle-management, but make it useful. 💅

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, and 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. one compiler, all the vibes. ✨

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 MPI layer. she will simply not show up to the function. 💀

Overview 🦋

oshfort is a convenience wrapper for the underlying Fortran compiler. translating an Open SHMEM program requires linking the Open SHMEM-specific libraries, which may not live in one of the standard search directories of ld(1). it also often requires including header files that may also not be found in a standard location.

oshfort passes its arguments to the underlying Fortran compiler along with the -I, -L and -l options required by Open SHMEM programs.

the Open SHMEM Team strongly encourages using the wrapper compilers instead of attempting to link to the Open SHMEM libraries manually. this lets the specific implementation of Open SHMEM 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 SHMEM was configured and built; the values can change between different installations of the same version of Open SHMEM. (yes, same version, different flags. she contains multitudes.) 🌈

indeed, since the wrappers are simply thin shells on top of an underlying compiler, there are very, very few compelling reasons not to use oshfort. when it's 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

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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

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FILES 🎀

the string that the wrapper compilers insert into the command line before invoking the underlying compiler is stored in a text file created by Open SHMEM and installed to $pkgdata/oshfort-wrapper-data.txt, where $pkgdata is typically $prefix/share/openmpi, and $prefix is the top installation directory of Open SHMEM.

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. peek, don't touch, bestie. 🙈

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ENVIRONMENT VARIABLES 🌱

by default, the wrappers use the compilers that were selected when Open SHMEM 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 "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

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and that's the whole page, bestie!! 💖✨🦋 this was Open MPI oshfort(1), version 4.1.6, dated Sep 30, 2023. go forth and link your Open SHMEM Fortran programs, you absolute main character 👑💅 periodt.