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ompi_setup_fc.m4: use -Wl,-ld_classic if supported
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Per #12427, on MacOS, add
-Wl,-ld_classic to the Fortran wrapper compiler if that flag is
needed.

Specifically, Open MPI has used -Wl,-commons,use_dylibs for decades to
support common symbols (e.g., MPI_BOTTOM) in the Fortran bindings.
There is a window of Xcode versions where this switch was effectively
disabled; it effectively required the additional -Wl,-ld_classic
switch to force the use of the "old" Apple linker (that still
supported -Wl,-commons,use_dylibs).  Update the configury to test
whether we need -Wl,-ld_classic or not.

Signed-off-by: Jeff Squyres <[email protected]>
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jsquyres committed Jul 9, 2024
1 parent b4bf0f8 commit 84555f0
Showing 1 changed file with 177 additions and 14 deletions.
191 changes: 177 additions & 14 deletions config/ompi_setup_fc.m4
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Original file line number Diff line number Diff line change
Expand Up @@ -50,9 +50,183 @@ AC_DEFUN_ONCE([_OMPI_SETUP_FC_COMPILER],[

#############################################################################

dnl On macOS with Xcode, test whether -Wl,-commons,use_dylibs works
dnl by itself or whether it also needs -Wl,-ld_classic.
dnl
dnl Backstory
dnl
dnl The history is that for a long time (decades),
dnl -Wl,-commons,use_dylibs worked by itself.
dnl
dnl XCode 15 introduced a a new linker (either "the new linker" or
dnl "ld_prime", according to
dnl https://developer.apple.com/forums/thread/715385). The new linker
dnl originally did not support "-commons use_dylibs", but Apple recently
dnl added support for that feature to the new linker in the XCode 16
dnl beta. "-ld_classic" forces using the old linker (which doesn't support
dnl some other features that customers might like, but Open MPI doesn't
dnl use for its Fortran bindings, like mergable libraries).
dnl
dnl Sidenode: Open MPI needs this "-commons use_dylibs" functionality
dnl because Fortran sentinel values (e.g., MPI_BOTTOM) are implemented
dnl with Fortran common blocks.
dnl
dnl So there's three cases:
dnl
dnl 1. Customer's default linker is the classic linker, which always
dnl supported "-commons use_dylibs".
dnl 2. Customer's default linker is the new linker, but not new enough
dnl to support "-commons use_dylibs", so we need to force using the old
dnl linker via "-ld_classic".
dnl 3. Customer's default linker is the new linker, new enough to support
dnl "-commons use_dylibs", so we do not want to force using the old
dnl linker.
dnl
dnl We have to use a slightly complex test code that will actually
dnl fail if the version of Xcode being used requires "-ld_classic"
dnl with "-commons,use_dylibs".
dnl
dnl 1. Build a shared library (with C source code) with a public
dnl symbol that can be used as a Fortran common block symbol.
dnl 2. Compile a Fortran program that calls a function in the shared
dnl library, and link it against the shared library.
dnl
dnl Note: This is a linker test; we are checking to see if this all
dnl compiles and links properly. The logic in the C / Fortran code
dnl below specifically does not test for correctness because we do not
dnl actually run the code.
AC_DEFUN([_OMPI_SETUP_FC_XCODE_COMMONS_LDFLAGS],[
OPAL_VAR_SCOPE_PUSH([xcode_flags])

# This variable is used by the invoking macro to display the
# results via AC RESULT (just to keep the symmetry of
# MSG_CHECKING / RESULT in the same upper-level macro).
OMPI_FORTRAN_WRAPPER_FLAGS=

xcode_flags="-Wl,-commons,use_dylibs"
_OMPI_SETUP_FC_XCODE_COMMONS_LDFLAGS_BACKEND(
[$xcode_flags],
[OMPI_FORTRAN_WRAPPER_FLAGS=$xcode_flags], [])
AS_IF([test -z "$OMPI_FORTRAN_WRAPPER_FLAGS"],
[xcode_flags="-Wl,-commons,use_dylibs -Wl,-ld_classic"
_OMPI_SETUP_FC_XCODE_COMMONS_LDFLAGS_BACKEND(
[$xcode_flags],
[OMPI_FORTRAN_WRAPPER_FLAGS=$xcode_flags], [])])
AS_IF([test -z "$OMPI_FORTRAN_WRAPPER_FLAGS"],
[OMPI_FORTRAN_WRAPPER_FLAGS="none"])

OPAL_VAR_SCOPE_POP
])

dnl Companion to _OMPI SETUP_FC_XCODE_COMMONS_LDFLAGS;
dnl see that macro for an explanation of this macro.
dnl
dnl $1: LDFLAGS to test
dnl $2: action to perform upon success
dnl $3: action to perform upon failure
AC_DEFUN([_OMPI_SETUP_FC_XCODE_COMMONS_LDFLAGS_BACKEND],[
OPAL_VAR_SCOPE_PUSH([xcode_happy xcode_dir LDFLAGS_save_xcode LIBS_save_xcode])

xcode_dir=conftest.$$
rm -rf $xcode_dir
mkdir -p $xcode_dir
cd $xcode_dir

LIBS_save_xcode=$LIBS
LDFLAGS_save_xcode=$LDFLAGS
LDFLAGS="$LDFLAGS -L. $1"

# Note: we use COMPILE_IFELSE and LANG_SOURCE below, which assume
# that confdefs.h exists. This is being invoked extremely early
# in the configure sequence, so we haven't AC DEFINE'ed anything
# yet, and therefore confdefs.h won't be automatically created
# yet. So we'll make an empty confdefs.h to avoid some error
# messages (it'll be removed with the whole tempdir, later).
touch confdefs.h

# Step 1: make a C library with some public symbols
xcode_happy=0
AC_LANG_PUSH([C])
AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
/* Must end the symbol in _ (remember: we are specifically targeting
the MacOS compilation environment, so it is ok to target a specific
Fortran symbol convention), otherwise the Fortran linker will not
find it, and will just create a new Fortran symbol for it */
int ompi_mpi_bottom_ = 42;

void ompi_init_f(int *bogus);

/* Empty / useless function that still ensures that this compilation
unit will not be optimized out */
void ompi_init_f(int *bogus)
{
*bogus = ompi_mpi_bottom_;
}
]])],
[ # If the above compiled successfully, Then use
# conftest.OBJEXT to make the library. Note that
# conftest.OBJEXT will automatically be deleted upon exit of
# COMPILE_IFELSE.
#
# NOTE: this is pretty gross -- we're manually making a
# shared library. But the libtool binary doesn't exist yet,
# so this is the best that we can do.
OPAL_LOG_COMMAND([$CC -dynamiclib -Wl,-undefined -Wl,dynamic_lookup $LDFLAGS conftest.$OBJEXT -o libconftest.dylib],
[xcode_happy=1])])
AC_LANG_POP

# Now compile and link a Fortran program against this shared
# library.
AC_LANG_PUSH([Fortran])
AS_IF([test $xcode_happy -eq 1],
[LIBS="$LIBS -lconftest"
AC_LINK_IFELSE([AC_LANG_SOURCE([
program test
integer :: mpi_bottom
common/ompi_mpi_bottom/mpi_bottom

interface
subroutine ompi_init(bogus) BIND(C, name="ompi_init_f")
implicit none
integer bogus
end subroutine ompi_init
end interface

integer bogus
call ompi_init(bogus)
end program
])],

[],
[xcode_happy=0])])
AC_LANG_POP

# Exit the temp dir
cd ..
rm -rf $xcode_dir

# LIBS was set specifically for the artificial conditions of this
# test, so reset it
LIBS=$LIBS_save_xcode

AS_IF([test $xcode_happy -eq 1],
[ # Restore LDFLAFGS + the new flags (i.e., get rid of the
# "-L." we added for this test)
LDFLAGS="$LDFLAGS_xcode_save $1"
$2],
[ # If we failed the test, reset LDFLAGS back to its
# original value.
LDFLAGS=$LDFLAGS_xcode_save
$3])

OPAL_VAR_SCOPE_POP
])

#############################################################################

# General Fortran compiler setup
AC_DEFUN([OMPI_SETUP_FC],[
OPAL_VAR_SCOPE_PUSH([ompi_fc_happy LDFLAGS_save fc_version])
OPAL_VAR_SCOPE_PUSH([ompi_fc_happy LDFLAGS_save fc_version OMPI_FORTRAN_WRAPPER_FLAGS])

# Force the intro banner to be displayed first
AC_REQUIRE([_OMPI_SETUP_FC_BANNER])
Expand Down Expand Up @@ -226,23 +400,12 @@ I = 3]])],
])
])

# Per #1982, on OS X, we may need some esoteric linker flags in the
# Per Trac #1982, on OS X, we may need some esoteric linker flags in the
# Fortran wrapper compiler.
AC_MSG_CHECKING([to see if mpifort compiler needs additional linker flags])
case "$host" in
*apple-darwin*)
# Test whether -Wl,-commons,use_dylibs works; if it does, use it.
LDFLAGS_save=$LDFLAGS
LDFLAGS="$LDFLAGS -Wl,-commons,use_dylibs"
AC_LANG_PUSH([Fortran])
AC_LINK_IFELSE([AC_LANG_SOURCE([[program test
integer :: i
end program]])],
[OMPI_FORTRAN_WRAPPER_FLAGS="-Wl,-commons,use_dylibs"
OPAL_WRAPPER_FLAGS_ADD([FCFLAGS], [$OMPI_FORTRAN_WRAPPER_FLAGS])],
[OMPI_FORTRAN_WRAPPER_FLAGS=none])
AC_LANG_POP([Fortran])
LDFLAGS=$LDFLAGS_save
_OMPI_SETUP_FC_XCODE_COMMONS_LDFLAGS
AC_MSG_RESULT([$OMPI_FORTRAN_WRAPPER_FLAGS])
;;
*)
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