ABI: multiple fixes

git ignore additions

ABI library: don't include functions in 19.3.4/5

in the library as they are not part of the ABI.

fixes to handle count/offset/aint in abi.h

fix req converter abi to ompi

fix problem with request_get_status_some

bindings: fix up REQUEST_CONST for abi

tools: first steps to add support for ABI

Turns out that the ABI standard impacts MPI_T related constants, etc.
and we don't want to switch to this for our OMPI standard, so we need
to add support for MPI_T_ ABI compliant functions.

Additions to the binding infrastructure to support generation of ABI
bindings will be introduced in a subsequent commit.

fix problem with undefined symbols in libmpi_abi

hack on abi json file

The MPI_T source order and MPI_T cb named enum types
and their enum constants need special treatment.

Ultimately the tool used to generate this json file -

https://github.com/Joe-Downs/mpi-standard/blob/pr/handle-constant-tool/const-tool/test.py

needs to find a home either in the MPI standard or in the pympistandard repo or elsewhere.

abi.h template - add MPI_T related structs

binding framework: fixes for MPI T stuff

Add various MPI_T related structs to the manglizer.
Also more workarounds for pympistandard not knowing about
MPI 5.1 chapter sections 19.3.4 and 19.3.5 not being part
of the ABI standard.

binding framework: add a TS_LEVEL type

more hacks on the mpi-standard-5.0-abi.json

json file

fix for enable-mca-dso

makefile changes to add symbols to libmpi_abi

abi: fix problems with error handler converters

Fix problem with the abi -> ompi and ompi -> abi
converters for errhandler handles.

Also fix the bindings code where the original problem
was.  We aren't using the bindings framework now to
generate the converters but we may possibly return
to that approach at some point so fix that code in
this commit.

fix problems with makefiles and some symbols

being doubly defined in the profile/non-profile abi mpi libs.

abi: move mpi_type_get_envelope etc. into templates

MPI_Type_get_envelop and MPI_Type_get_contents are a big
mess as the MPI Forum decided not just to add big variants
but also add additional arguments for the big count variants.

So this necessitated enhancements to the binding infrastructure
to support optional suppressing of bc and non-bc variants of
prototype files.

rebase fixup

add abi variantes of mpi_aint_diff and add

add abi_set/get_fortran_info

implementation of abi_set_fortran_info is not
complete.

abi_fortran_stuff: fix up the imp of these

abi_converters: add fortran datatypes to

the converters.

fix for mac-os CI

pr feedback on add/diff for aints

configury: discover fortran logical false

rather than assuming its '0'/

configury fix

for case of configure with fortran

abi_fortran: add support for LOGICAL16

logical16 patch

missed something

add comm_from/toint

simpler to hard code abi/ompi variants.
For ABI version add an offset to the values normally
used for original "f2c/c2f" ops to push the values normally
returned by "c2f" functions to be greater than any ABI
defined constants.

complete toint/fromint interfaces

basic implementation checks if constant is <= 16384
(the largest value reserved for mpi abi constants)
and returns the constant back or looks up the value
in the relevant array of pointers and offsets by 16385.

fix error return values for ABI routines

somehow was using the wrong converter to translate
ompi intern error values with abi ones.
Many are actually the same but that's just by chance.

minor fixup for toint/fromint

rebase fix

handle TAG more correctly

even though currently MPI_ANY_TAG is the same in ABI and OMPI

squash compiler warning

add hooks for TAG_OUT type

add better support for MPI_ROOT and source

since MPI_ROOT for ABI is not equal to ompi.
MPI_ANY_SOURCE is but still generate conversion code
rather than just beining lucky.

squash a compiler warning

this fix kind of messes up the indenter so the resulting line
in the generated code isn't nicely indented but that can be fixed later.

some fixes to comm attributes wrappers

also see about fixing an issue with some of the ompi
mca components when using --enable-mca-dso.

fix bug in comm attr copy code

some fixes for attributes and more

to start using the ompi-tests/ibm had to complete adding
MPI_T_ to the abi.

Also some other fixes.

Attributes still need more work.

checkpoint

many changes.  go back to generating abi_converters.h
fix up tools for abi case, etc.

fix for datatype converters

distcheck fix

EVENT_INSTANCE: arg type cast fix

and add in a file that wasn't in the makefile!

MPI_ROOT: capture proc null type too

needed to get a lot of intercommunicator collectives to pass.

requests: fixes to some multirequest test functions

weights and source out support/fixes

fixes problems with dist graph constructors
and cart_shift output.

some fixes for message related functions

also add better support for the 'some' test/wait functions.

fix testall and startall

fix mpi4py break

fix a few problems with datatype bindings

add replacements to code bodies for various string lengths

We now scan the generated internal 'c' body of each
function for replaceable variants of

MPI_MAX_DATAREP_STRING
MPI_MAX_ERROR_STRING
MPI_MAX_INFO_KEY
MPI_MAX_INFO_VAL
MPI_MAX_LIBRARY_VERSION_STRING
MPI_MAX_OBJECT_NAME
MPI_MAX_PORT_NAME
MPI_MAX_PROCESSOR_NAME
MPI_MAX_STRINGTAG_LEN
MPI_MAX_PSET_NAME_LEN

This way the code body sees the same constant values as the
app sees using either the OMPI or ABI variants of the mpi.h

add support for distrib array and order

for subarray type datatype constructors

add support for mode bits - in only

add support for amode out

add support for whence

used by some MPI I/O functions

add support for some win attributes

handle special case of MPI_DISPLACEMENT_CURRENT

add support for combiner, typeclass, win lock assert

types

c_header: comment out deprecated functions

The ABI doesn't support any of the functions deprecated in MPI 3.1
or earlier.  See section 20.2.1 of the MPI 5.0 standard.

fix problem with special attrs for windows

fix for win_shared_query

fixes to rget/rget_accumulate

fix problem with code gen for win create keyval

fix rank problem in rput/raccumulate

add MPI_GROUP_EMPTY to predefined group handles

handle user error classes and codes

temporary WAR for non-blocking alltoallw

variants.

We'll need to append the temporary arrays holding
translated datatype handles to the nbc request for
cleanup after the non-blocking op is completed or
the persistent request has been freed.

add support for comm topos

support INOUT attribute for all handles

thanks to dalcinl for help here

fix problem with attribute callback handling

need to convert the ompi internal keyval to abi one
before invoking user supplied callbacks for win, type, comm

catch use of special buffer consts

like MPI_BUFFER_AUTOMATIC

remove some debug statements

swat nit

patch get_address

add new type to handle out void stars

from buffer detach operations.

fixes for datatypes for neighbor collectives

add inouts for op, errhandler, info

cleanup datatype tmps for ialltoallw and friends

leverage nbc infrastructure

a logical16 fix

Thanks to dalcinl for finding.

abi_get_version/get_info add to ompi abi lib

and correction major/minor versoin returned from the ABI
build.

toint fixes

thanks to dalcinl !

fix issue with ASYNC data arrays cleanup

various fixes from dalcinl

ompi-codegen.patch from dalcinl
ompi-abiinfo.patch from dalcinl
ompi-status.patch from dalcinl
fixes to setting/getting status fields and some more
move some deprecated funcs out of libmpi-abi
add support for typeclass
ops: convert data from internal to abi
for user ops
split rdma modes out from modes for files

the ompi internal rdma and file mode bits overlap,
so we need to treat them that way in the bindings
generation code too.

add SOURCE_ARRAY type

to help out MPI_Group_translate_ranks

fixes to abi_get_fortran_info

for logicals

apply patch omp-op-inout.patch

from dalcinl

apply patch ompi-abi-fortran.patch

from dalcinl

fix for FD_INOUT

fix for isend dst arg

needs to go through translation

apply patch ompi-query-thread.patch

from dalcinl

various pt2pt fixes to handle proc_null etc.

eventually we'll use separate SOURCE and DEST (or something like that)
types.

rma: updates to args to handle proc_null etc

adjustments for improbe and iprobe

fix for status array for MPI_Request_testsome

switch to using a malloc wrapper

per dalcinl suggestion

plug memory leak handling REQUEST_INOUT type

patch status out to handle copy in

there are many functions where a status is conditionally
returned.  Trying to treat each of these would be too
complex so instead copy contents of the status supplied as
input into any temporary status variables then copy back
out.

handle dargs for darray_create correctly

fixes for spawn multiple - array of info args

and array of errorcodes

disable async NBC-based cleanup for now
turn back on async array cleanup stuff
and add a check that the returned request isn't
complete.

mpi_info_toint/fromint prior to MPI_Init or MPI_Session_init
first pass at errhandler support
simplify python support for user-defined err handlers
VERSION - add support for versioning libmpi_abi
add a blurb about how current and age and revision
should work for this library.
add man pages for new MPI_Abi and fromint/toint functions
attributes - clean up extra helper data
using the bindings_extra_state arg to ompi_attr_create_keyval
add a readme about the MPI ABI support
fortran: add the MPI_Abi entry points
python framework: improve debugging
also import util module

Signed-off-by: Howard Pritchard <[email protected]>
Co-authored-by: Lisandro Dalcin <[email protected]>

Author: hppritcha

.gitignore

@@ -537,7 +537,11 @@ docs/man
 ompi/mpi/c/*_generated*.c
 ompi/mpi/c/standard_*.c
 ompi/mpi/c/abi.h
+ompi/mpi/c/abi_get_info.c
+ompi/mpi/c/abi_converters.h
+ompi/mpi/c/abi_converters.c
 ompi/mpi/c/standard_abi
+ompi/mpi/tool/*_generated*.c
 
 # Generated Fortran Bindings
 ompi/mpi/fortran/use-mpi-f08/*_generated.F90

VERSION

@@ -20,7 +20,7 @@ minor=1
 release=0
 
 # MPI Standard Compliance Level
-mpi_standard_version=3
+mpi_standard_version=5
 mpi_standard_subversion=1
 
 # OMPI required dependency versions.
@@ -92,6 +92,14 @@ date="Unreleased developer copy"
 # but they are "public" within the OMPI code base and select 3rd party
 # software packages.
 
+# The current and age values of the libmpi_abi shared library are
+# implicitly determined by the MPI ABI definition of the
+# version of the MPI specification supported by this Open MPI release.
+# The MPI ABI is intended not to break backward compatibility,
+# so presumably the current and age values will move in lock step.
+# We assume we have flexibility with the revision number as
+# bugs are fixed, etc.
+
 # Version numbers are described in the Libtool current:revision:age
 # format.
 
@@ -100,6 +108,7 @@ libmpi_mpifh_so_version=0:0:0
 libmpi_usempi_tkr_so_version=0:0:0
 libmpi_usempi_ignore_tkr_so_version=0:0:0
 libmpi_usempif08_so_version=0:0:0
+libmpi_abi_so_version=0:0:0
 libopen_pal_so_version=0:0:0
 libmpi_java_so_version=0:0:0
 liboshmem_so_version=0:0:0

config/ompi_fortran_check_logical_array.m4

@@ -11,6 +11,8 @@ dnl                         All rights reserved.
 dnl Copyright (c) 2011-2012 Cisco Systems, Inc.  All rights reserved.
 dnl Copyright (c) 2015      Research Organization for Information Science
 dnl                         and Technology (RIST). All rights reserved.
+dnl Copyright (c) 2025      Triad National Security, LLC. All rights
+dnl                         reserved.
 dnl $COPYRIGHT$
 dnl
 dnl Additional copyrights may follow
@@ -64,7 +66,7 @@ void ompi_check_f(ompi_fortran_logical_t * logical)
     FILE *f=fopen("conftestval", "w");
     if (!f) exit(1);
 
-    if (logical[[0]] == 0 &&
+    if (logical[[0]] == $ompi_cv_fortran_false_value &&
         logical[[1]] == $ompi_cv_fortran_true_value)
       result = 1;
     fprintf(f, "%d\n", result);

config/ompi_fortran_get_value_true.m4

@@ -11,6 +11,8 @@ dnl                         All rights reserved.
 dnl Copyright (c) 2011-2012 Cisco Systems, Inc.  All rights reserved.
 dnl Copyright (c) 2015      Research Organization for Information Science
 dnl                         and Technology (RIST). All rights reserved.
+dnl Copyright (c) 2025      Triad National Security, LLC. All rights
+dnl                         reserved.
 dnl $COPYRIGHT$
 dnl
 dnl Additional copyrights may follow
@@ -27,16 +29,22 @@ AC_DEFUN([OMPI_FORTRAN_GET_VALUE_TRUE],[
     if test "$ompi_cv_fortran_true_value" = "0" ; then
         unset ompi_cv_fortran_true_value
     fi
+    if test "$ompi_cv_fortran_false_value" = "0" ; then
+        unset ompi_cv_fortran_false_value
+    fi
 
     AS_VAR_PUSHDEF([fortran_true_var],
                    [ompi_cv_fortran_true_value])
+    AS_VAR_PUSHDEF([fortran_false_var],
+                   [ompi_cv_fortran_false_value])
 
     AC_CACHE_CHECK([Fortran value for .TRUE. logical type],
         fortran_true_var,
         [if test "$1" = "none" || \
             test $OMPI_TRY_FORTRAN_BINDINGS -eq $OMPI_FORTRAN_NO_BINDINGS || \
             test $ompi_fortran_happy -eq 0 ; then
-             value=77
+             tvalue=77
+             fvalue=77
          else
              #
              # C module
@@ -98,6 +106,14 @@ EOF
       CALL ompi_print(value)
       end
 EOF
+             cat > conftestf2.f <<EOF
+      program main
+      logical value
+      value=.FALSE.
+      CALL ompi_print(value)
+      end
+EOF
+
 
              #
              # Try the compilation and run.
@@ -114,11 +130,40 @@ EOF
              AS_IF([test "$cross_compiling" = "yes"],
                  [AC_MSG_ERROR([Can not determine value of .TRUE. when cross-compiling])],
                  [OPAL_LOG_COMMAND([./conftest],
-                     [value=`sed 's/  *//' conftestval`],
+                     [tvalue=`sed 's/  *//' conftestval`],
                      [AC_MSG_ERROR([Could not determine value of Fotran .TRUE..  Aborting.])])])
+
+             cat > conftestf.f <<EOF
+      program main
+      logical value
+      value=.FALSE.
+      CALL ompi_print(value)
+      end
+EOF
+
+             #
+             # Try the compilation and run.
+             #
+             OPAL_LOG_COMMAND([$CC $CFLAGS -I. -c conftest.c],
+                 [OPAL_LOG_COMMAND([$FC $FCFLAGS -o conftest conftest.o conftestf.f $LDFLAGS $LIBS],
+                      [happy=1], [happy=0])],
+                 [happy=0])
+
+             AS_IF([test $happy -eq 0 && test $ompi_fortran_happy -eq 1],
+                          [AC_MSG_ERROR([Could not compile Fortran .FALSE. test.  Aborting.])
+                          ])
+
+             AS_IF([test "$cross_compiling" = "yes"],
+                 [AC_MSG_ERROR([Can not determine value of .FALSE. when cross-compiling])],
+                 [OPAL_LOG_COMMAND([./conftest],
+                     [fvalue=`sed 's/  *//' conftestval`],
+                     [AC_MSG_ERROR([Could not determine value of Fotran .FALSE..  Aborting.])])])
          fi
-         AS_VAR_SET(fortran_true_var, [$value])
-         unset value
+         AS_VAR_SET(fortran_true_var, [$tvalue])
+         unset tvalue
+         AS_VAR_SET(fortran_false_var, [$fvalue])
+         unset fvalue
+
         ])
 
     AS_VAR_COPY([ompi_fortran_true_value], [fortran_true_var])
@@ -127,6 +172,13 @@ EOF
         [Fortran value for LOGICAL .TRUE. value])
     AS_VAR_POPDEF([fortran_true_var])
 
+   AS_VAR_COPY([ompi_fortran_false_value], [fortran_false_var])
+    AC_DEFINE_UNQUOTED([OMPI_FORTRAN_VALUE_FALSE],
+        [$ompi_fortran_false_value],
+        [Fortran value for LOGICAL .FALSE. value])
+    AS_VAR_POPDEF([fortran_false_var])
+
+
     unset happy ompi_print_logical_fn
     rm -rf conftest*
 ])dnl

configure.ac

@@ -147,6 +147,7 @@ OPAL_SAVE_VERSION([OPAL], [Open Portable Access Layer], [$srcdir/VERSION],
 
 m4_ifdef([project_ompi],
          [AC_SUBST(libmpi_so_version)
+          AC_SUBST(libmpi_abi_so_version)
           AC_SUBST(libmpi_mpifh_so_version)
           AC_SUBST(libmpi_usempi_tkr_so_version)
           AC_SUBST(libmpi_usempi_ignore_tkr_so_version)

docs/Makefile.am

@@ -87,6 +87,12 @@ OMPI_MAN1 = \
         opal_wrapper.1
 
 OMPI_MAN3 = \
+        MPI_Abi_get_fortran_booleans.3 \
+        MPI_Abi_get_fortran_info.3 \
+        MPI_Abi_get_info.3 \
+        MPI_Abi_get_version.3 \
+        MPI_Abi_set_fortran_booleans.3 \
+        MPI_Abi_set_fortran_info.3 \
         MPI_Abort.3 \
         MPI_Accumulate.3 \
         MPI_Add_error_class.3 \
@@ -151,6 +157,7 @@ OMPI_MAN3 = \
         MPI_Comm_flush_buffer.3 \
         MPI_Comm_free.3 \
         MPI_Comm_free_keyval.3 \
+        MPI_Comm_fromint.3 \
         MPI_Comm_get_attr.3 \
         MPI_Comm_get_errhandler.3 \
         MPI_Comm_get_info.3 \
@@ -174,6 +181,7 @@ OMPI_MAN3 = \
         MPI_Comm_split.3 \
         MPI_Comm_split_type.3 \
         MPI_Comm_test_inter.3 \
+        MPI_Comm_toint.3 \
         MPI_Compare_and_swap.3 \
         MPI_Dims_create.3 \
         MPI_Dist_graph_create.3 \
@@ -182,8 +190,10 @@ OMPI_MAN3 = \
         MPI_Dist_graph_neighbors_count.3 \
         MPI_Errhandler_create.3 \
         MPI_Errhandler_free.3 \
+        MPI_Errhandler_fromint.3 \
         MPI_Errhandler_get.3 \
         MPI_Errhandler_set.3 \
+        MPI_Errhandler_toint.3 \
         MPI_Error_class.3 \
         MPI_Error_string.3 \
         MPI_Errors.3 \
@@ -196,6 +206,7 @@ OMPI_MAN3 = \
         MPI_File_create_errhandler.3 \
         MPI_File_delete.3 \
         MPI_File_f2c.3 \
+        MPI_File_fromint.3 \
         MPI_File_get_amode.3 \
         MPI_File_get_atomicity.3 \
         MPI_File_get_byte_offset.3 \
@@ -239,6 +250,7 @@ OMPI_MAN3 = \
         MPI_File_set_size.3 \
         MPI_File_set_view.3 \
         MPI_File_sync.3 \
+        MPI_File_toint.3 \
         MPI_File_write.3 \
         MPI_File_write_all.3 \
         MPI_File_write_all_begin.3 \
@@ -282,13 +294,15 @@ OMPI_MAN3 = \
         MPI_Group_excl.3 \
         MPI_Group_f2c.3 \
         MPI_Group_free.3 \
+        MPI_Group_fromint.3 \
         MPI_Group_from_session_pset.3 \
         MPI_Group_incl.3 \
         MPI_Group_intersection.3 \
         MPI_Group_range_excl.3 \
         MPI_Group_range_incl.3 \
         MPI_Group_rank.3 \
         MPI_Group_size.3 \
+        MPI_Group_toint.3 \
         MPI_Group_translate_ranks.3 \
         MPI_Group_union.3 \
         MPI_Iallgather.3 \
@@ -317,12 +331,14 @@ OMPI_MAN3 = \
         MPI_Info_env.3 \
         MPI_Info_f2c.3 \
         MPI_Info_free.3 \
+        MPI_Info_fromint.3 \
         MPI_Info_get.3 \
         MPI_Info_get_nkeys.3 \
         MPI_Info_get_nthkey.3 \
         MPI_Info_get_string.3 \
         MPI_Info_get_valuelen.3 \
         MPI_Info_set.3 \
+        MPI_Info_toint.3 \
         MPI_Init.3 \
         MPI_Initialized.3 \
         MPI_Init_thread.3 \
@@ -348,6 +364,8 @@ OMPI_MAN3 = \
         MPI_Lookup_name.3 \
         MPI_Message_c2f.3 \
         MPI_Message_f2c.3 \
+        MPI_Message_fromint.3 \
+        MPI_Message_toint.3 \
         MPI_Mprobe.3 \
         MPI_Mrecv.3 \
         MPI_Neighbor_allgather.3 \
@@ -366,6 +384,8 @@ OMPI_MAN3 = \
         MPI_Open_port.3 \
         MPI_Op_f2c.3 \
         MPI_Op_free.3 \
+        MPI_Op_fromint.3 \
+        MPI_Op_toint.3 \
         MPI_Pack.3 \
         MPI_Pack_external.3 \
         MPI_Pack_external_size.3 \
@@ -398,10 +418,12 @@ OMPI_MAN3 = \
         MPI_Request_c2f.3 \
         MPI_Request_f2c.3 \
         MPI_Request_free.3 \
+        MPI_Request_fromint.3 \
         MPI_Request_get_status.3 \
         MPI_Request_get_status_all.3 \
         MPI_Request_get_status_any.3 \
         MPI_Request_get_status_some.3 \
+        MPI_Request_toint.3 \
         MPI_Rget.3 \
         MPI_Rget_accumulate.3 \
         MPI_Rput.3 \
@@ -423,12 +445,14 @@ OMPI_MAN3 = \
         MPI_Session_f2c.3 \
         MPI_Session_finalize.3 \
         MPI_Session_flush_buffer.3 \
+        MPI_Session_fromint.3 \
         MPI_Session_get_info.3 \
         MPI_Session_get_nth_pset.3 \
         MPI_Session_get_num_psets.3 \
         MPI_Session_get_pset_info.3 \
         MPI_Session_iflush_buffer.3 \
         MPI_Session_init.3 \
+        MPI_Session_toint.3 \
         MPI_Sizeof.3 \
         MPI_Ssend.3 \
         MPI_Ssend_init.3 \
@@ -440,6 +464,7 @@ OMPI_MAN3 = \
         MPI_Status_f082f.3 \
         MPI_Status_f2c.3 \
         MPI_Status_f2f08.3 \
+        MPI_Status_fromint.3 \
         MPI_Status_get_error.3 \
         MPI_Status_get_source.3 \
         MPI_Status_get_tag.3 \
@@ -449,6 +474,7 @@ OMPI_MAN3 = \
         MPI_Status_set_error.3 \
         MPI_Status_set_source.3 \
         MPI_Status_set_tag.3 \
+        MPI_Status_toint.3 \
         MPI_T.3 \
         MPI_T_category_changed.3 \
         MPI_T_category_get_categories.3 \
@@ -525,6 +551,7 @@ OMPI_MAN3 = \
         MPI_Type_f2c.3 \
         MPI_Type_free.3 \
         MPI_Type_free_keyval.3 \
+        MPI_Type_fromint.3 \
         MPI_Type_get_attr.3 \
         MPI_Type_get_contents.3 \
         MPI_Type_get_envelope.3 \
@@ -544,6 +571,7 @@ OMPI_MAN3 = \
         MPI_Type_size.3 \
         MPI_Type_size_x.3 \
         MPI_Type_struct.3 \
+        MPI_Type_toint.3 \
         MPI_Type_ub.3 \
         MPI_Type_vector.3 \
         MPI_Unpack.3 \
@@ -573,6 +601,7 @@ OMPI_MAN3 = \
         MPI_Win_flush_local_all.3 \
         MPI_Win_free.3 \
         MPI_Win_free_keyval.3 \
+        MPI_Win_fromint.3 \
         MPI_Win_get_attr.3 \
         MPI_Win_get_errhandler.3 \
         MPI_Win_get_group.3 \
@@ -589,6 +618,7 @@ OMPI_MAN3 = \
         MPI_Win_start.3 \
         MPI_Win_sync.3 \
         MPI_Win_test.3 \
+        MPI_Win_toint.3 \
         MPI_Win_unlock.3 \
         MPI_Win_unlock_all.3 \
         MPI_Win_wait.3 \

docs/building-apps/index.rst

@@ -14,6 +14,7 @@ Open MPI "wrapper" compilers.
    removed-mpi-constructs
    deprecation-warnings
    building-static-apps
+   mpi-abi
 
 .. warning:: Open MPI does not attempt to interoperate with other MPI
              implementations, nor executables that were compiled for

docs/building-apps/mpi-abi.rst

@@ -0,0 +1,33 @@
+.. _label-building-with-mpi-abi:
+
+Building MPI applications using the MPI ABI
+===========================================
+
+What is the MPI ABI
+-------------------
+
+Starting with MPI 5.0, the MPI standard specifies an ABI for the c and
+Fortran MPI interfaces.  In this release, Open MPI supports the c
+part of the MPI ABI.
+
+By using the MPI ABI, an MPI application can be built against one 
+implementation of MPI that supports the MPI ABI, and later run using
+the MPI ABI compliant MPI library generated using a different MPI
+implementation.  This assumes that the application is dynamically linked.
+
+The MPI 5.0 standard specifies the file name of the MPI ABI compliant
+library - libmpi_abi.  The major version of the library is 1 and minor
+version is 0.
+
+How to build an application using the MPI ABI
+---------------------------------------------
+
+To build an application against the MPI ABI compliant Open MPI library,
+the ``mpicc_abi`` compiler wrapper must be used for compiling and 
+linking the application or shared library.
+
+This release does not support the Fortran ABI so there is no ``mpifort_abi``
+compiler wrapper.  This mixed c/Fortran MPI apps cannot make use of the
+MPI ABI library with this release.
+
+