Build failure of v. 2.1.1 with gcc-14: `Error: Ambiguous interfaces in generic interface 'verify' for 'verify_logical' at (1) and 'verify_c_bool' at (2)`

[barracuda156]

Describe the bug

[ 88%] Building Fortran object fortran/test/CMakeFiles/hdf5_test_fortran-shared.dir/shared/tf_gen.F90.o
cd /opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/test && /opt/local/bin/gfortran-mp-14 -DH5_BUILT_AS_DYNAMIC_LIB -Dhdf5_test_fortran_shared_EXPORTS -I/opt/local/var/macports/build/hdf5-122b9169/work/build/mod/shared -I/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran -I/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/shared -I/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/test -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/fortran/test -I/opt/local/var/macports/build/hdf5-122b9169/work/build/test -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/test -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/src/H5FDsubfiling -I/opt/local/var/macports/build/hdf5-122b9169/work/build/src -I/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/fortran/src -pipe -Os -m32 -fdiagnostics-urls=never -fno-diagnostics-color -O3 -mmacosx-version-min=10.6 -J../../mod/shared -fPIC -Waliasing -Wall -Wcharacter-truncation -Wextra -Wimplicit-interface -Wsurprising -Wunderflow -pedantic -Wno-unused-dummy-argument -ffree-form -fimplicit-none -std=f2008 -Wintrinsics-std -Wimplicit-procedure -Wreal-q-constant -Wfunction-elimination -Wrealloc-lhs -Wrealloc-lhs-all -Wno-c-binding-type -Wno-array-temporaries -Winteger-division -Wfrontend-loop-interchange -c /opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/test/shared/tf_gen.F90 -o CMakeFiles/hdf5_test_fortran-shared.dir/shared/tf_gen.F90.o
[ 88%] Building Fortran object hl/fortran/src/CMakeFiles/hdf5_hl_fortran-shared.dir/H5DOff.F90.o
cd /opt/local/var/macports/build/hdf5-122b9169/work/build/hl/fortran/src && /opt/local/bin/gfortran-mp-14 -DH5_BUILT_AS_DYNAMIC_LIB -Dhdf5_hl_fortran_shared_EXPORTS -I/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran -I/opt/local/var/macports/build/hdf5-122b9169/work/build/mod/shared -I/opt/local/var/macports/build/hdf5-122b9169/work/build/hl/fortran/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/hl/fortran/src -I/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/fortran/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/src/H5FDsubfiling -I/opt/local/var/macports/build/hdf5-122b9169/work/build/src -I/opt/local/var/macports/build/hdf5-122b9169/work/build/hl/src -I/opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/hl/src -pipe -Os -m32 -O3 -mmacosx-version-min=10.6 -J../../../mod/shared -fPIC -c /opt/local/var/macports/build/hdf5-122b9169/work/hdf5-2.1.1/hl/fortran/src/H5DOff.F90 -o CMakeFiles/hdf5_hl_fortran-shared.dir/H5DOff.F90.o
/opt/local/var/macports/build/hdf5-122b9169/work/build/fortran/test/shared/tf_gen.F90:279:27:

  279 |   SUBROUTINE verify_logical(string,value,correct_value,total_error,chck_eq)
      |                           1
......
  303 |   SUBROUTINE verify_c_bool(string,value,correct_value,total_error,chck_eq)
      |                          2 
Error: Ambiguous interfaces in generic interface 'verify' for 'verify_logical' at (1) and 'verify_c_bool' at (2)
make[2]: *** [fortran/test/CMakeFiles/hdf5_test_fortran-shared.dir/shared/tf_gen.F90.o] Error 1
make[2]: Leaving directory `/opt/local/var/macports/build/hdf5-122b9169/work/build'
make[1]: *** [fortran/test/CMakeFiles/hdf5_test_fortran-shared.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

Expected behavior
Build should succeed.

Platform (please complete the following information)

• HDF5 version: 2.1.1
• OS and version: macOS 10.6.8
• Compiler and version: gcc 14.3.0
• Build system: CMake
• MPI library and version: disabled

Additional context
MacPorts build env

[brtnfld]

check_fortran_source_compiles only sees CMAKE_Fortran_FLAGS. Anything that bypasses that variable is invisible to the configure checks, so could that be the case, and the test program is getting compiled without -m32?

However, gfortran-14 should not be reporting ambiguity for LOGICAL(C_BOOL) vs LOGICAL in the first place; that seems like a GCC bug. HDF5's code and configure checks are correct.

At least for gfortran 15.2.1 / Linux. No issue with this test program.

---

#!/bin/sh
# Test whether the system gfortran can compile a generic interface that
# distinguishes LOGICAL(C_BOOL) from default LOGICAL.
#
# This reproduces the pattern used in the generated tf_gen.F90 and the
# PROG_FC_C_BOOL_EQ_LOGICAL configure check, and tries both variants:
#
#   Case A - WITH call sites (what the configure check currently does)
#   Case B - WITHOUT call sites (what tf_gen.F90 compilation looks like)
#
# Each case is compiled with and without -m32 if the compiler supports it.
#
# Usage:
#   ./test_cbool_generic.sh [gfortran]

FC=${1:-gfortran}
TMPDIR=$(mktemp -d)
trap 'rm -rf "$TMPDIR"' EXIT

echo "Compiler: $($FC --version | head -1)"
echo ""

# --------------------------------------------------------------------------
# Write the two test sources
# --------------------------------------------------------------------------

# Case A: generic interface WITH call sites (current configure check pattern)
cat > "$TMPDIR/test_with_calls.f90" << 'FORTRAN'
MODULE l_type_mod
  USE ISO_C_BINDING
  INTERFACE h5t
     MODULE PROCEDURE h5t_c_bool
     MODULE PROCEDURE h5t_logical
  END INTERFACE
CONTAINS
  SUBROUTINE h5t_c_bool(lcb)
    LOGICAL(KIND=C_BOOL) :: lcb
  END SUBROUTINE h5t_c_bool
  SUBROUTINE h5t_logical(l)
    LOGICAL :: l
  END SUBROUTINE h5t_logical
END MODULE l_type_mod
PROGRAM test_with_calls
  USE ISO_C_BINDING
  USE l_type_mod
  LOGICAL(KIND=C_BOOL) :: lcb
  LOGICAL              :: l
  lcb = .TRUE._C_BOOL
  l   = .TRUE.
  CALL h5t(lcb)
  CALL h5t(l)
END PROGRAM test_with_calls
FORTRAN

# Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90 compilation)
cat > "$TMPDIR/test_no_calls.f90" << 'FORTRAN'
MODULE l_type_mod
  USE ISO_C_BINDING
  INTERFACE h5t
     MODULE PROCEDURE h5t_c_bool
     MODULE PROCEDURE h5t_logical
  END INTERFACE
CONTAINS
  SUBROUTINE h5t_c_bool(lcb)
    LOGICAL(KIND=C_BOOL) :: lcb
  END SUBROUTINE h5t_c_bool
  SUBROUTINE h5t_logical(l)
    LOGICAL :: l
  END SUBROUTINE h5t_logical
END MODULE l_type_mod
PROGRAM test_no_calls
  USE l_type_mod
END PROGRAM test_no_calls
FORTRAN

# --------------------------------------------------------------------------
# Also report the actual kinds so we know if C_BOOL == default LOGICAL
# --------------------------------------------------------------------------
cat > "$TMPDIR/report_kinds.f90" << 'FORTRAN'
PROGRAM report_kinds
  USE ISO_C_BINDING
  IMPLICIT NONE
  INTEGER :: cbool_kind, logical_kind
  cbool_kind  = C_BOOL
  logical_kind = KIND(.TRUE.)
  WRITE(*,'(A,I0)') "  KIND(C_BOOL)    = ", cbool_kind
  WRITE(*,'(A,I0)') "  KIND(.TRUE.)    = ", logical_kind
  IF (cbool_kind == logical_kind) THEN
    WRITE(*,'(A)') "  => SAME kind: C_BOOL and default LOGICAL are identical"
  ELSE
    WRITE(*,'(A)') "  => DIFFERENT kinds: C_BOOL and default LOGICAL are distinct"
  END IF
END PROGRAM report_kinds
FORTRAN

# --------------------------------------------------------------------------
# Helper: compile and report result
# --------------------------------------------------------------------------
try_compile() {
    label="$1"
    src="$2"
    shift 2
    flags="$*"
    out=$(cd "$TMPDIR" && $FC $flags -c "$src" 2>&1)
    if [ $? -eq 0 ]; then
        echo "  PASS  $label"
    else
        echo "  FAIL  $label"
        echo "$out" | sed 's/^/        /'
    fi
}

try_run() {
    label="$1"
    src="$2"
    shift 2
    flags="$*"
    out=$(cd "$TMPDIR" && $FC $flags "$src" -o kinds_prog 2>&1 && ./kinds_prog 2>&1)
    echo "$out" | sed "s/^/  $label: /"
}

# --------------------------------------------------------------------------
# Run tests
# --------------------------------------------------------------------------
echo "=== Kind information (default flags) ==="
try_run "" report_kinds.f90
echo ""

echo "=== Case A: generic interface WITH call sites ==="
try_compile "default flags          " test_with_calls.f90
try_compile "-std=f2008             " test_with_calls.f90 -std=f2008
try_compile "-std=f2008 -pedantic   " test_with_calls.f90 -std=f2008 -pedantic

# Only try -m32 if the compiler accepts it
if $FC -m32 -c "$TMPDIR/test_with_calls.f90" -o /dev/null 2>/dev/null; then
    try_compile "-m32                   " test_with_calls.f90 -m32
    try_compile "-m32 -std=f2008        " test_with_calls.f90 -m32 -std=f2008
    try_compile "-m32 -std=f2008 -pedantic" test_with_calls.f90 -m32 -std=f2008 -pedantic
else
    echo "  SKIP  -m32 (not supported by this compiler/platform)"
fi
echo ""

echo "=== Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90) ==="
try_compile "default flags          " test_no_calls.f90
try_compile "-std=f2008             " test_no_calls.f90 -std=f2008
try_compile "-std=f2008 -pedantic   " test_no_calls.f90 -std=f2008 -pedantic

if $FC -m32 -c "$TMPDIR/test_no_calls.f90" -o /dev/null 2>/dev/null; then
    try_compile "-m32                   " test_no_calls.f90 -m32
    try_compile "-m32 -std=f2008        " test_no_calls.f90 -m32 -std=f2008
    try_compile "-m32 -std=f2008 -pedantic" test_no_calls.f90 -m32 -std=f2008 -pedantic
else
    echo "  SKIP  -m32 (not supported by this compiler/platform)"
fi
echo ""

echo "=== Summary ==="
echo "If Case A passes but Case B fails: the compiler suppresses the ambiguity"
echo "  error when call sites are present -- and the configure check is masking"
echo "  a real compiler bug."
echo "If both A and B fail: C_BOOL and LOGICAL are the same kind, or the"
echo "  compiler cannot disambiguate them (genuine compiler bug)."
echo "If both pass: no issue on this platform/flags."


 

Can you give it a try?

[barracuda156]

@brtnfld Bool is 4 bytes on powerpc-darwin, does that matter in this context?

[brtnfld]

We are more interested in the KIND of the logicals. If you run the script, it will tell us what KIND is C_BOOL and the default logical.

[barracuda156]

@brtnfld I had to explicitly define FC and use gmktemp (mktemp does not support GNU syntax), but then I get the following:

$ /Users/svacchanda/Desktop/hdf5_test.sh Compiler: GNU Fortran (MacOS PowerPC gcc14 14.3.0_0+G5+stdlib_flag) 14.3.0

=== Kind information (default flags) ===
  :   KIND(C_BOOL)    = 4
  :   KIND(.TRUE.)    = 4
  :   => SAME kind: C_BOOL and default LOGICAL are identical

=== Case A: generic interface WITH call sites ===
  FAIL  default flags          
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008             
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008 -pedantic   
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  SKIP  -m32 (not supported by this compiler/platform)

=== Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90) ===
  FAIL  default flags          
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008             
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008 -pedantic   
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  SKIP  -m32 (not supported by this compiler/platform)

=== Summary ===
If Case A passes but Case B fails: the compiler suppresses the ambiguity
  error when call sites are present -- and the configure check is masking
  a real compiler bug.
If both A and B fail: C_BOOL and LOGICAL are the same kind, or the
  compiler cannot disambiguate them (genuine compiler bug).
If both pass: no issue on this platform/flags.

Suspicious that the test claims -m32 (not supported by this compiler/platform) because it must work as expected.

Also, where does l_type_mod.mod come from? Do I need to include something from HDF5? I do not have HDF5 installed now (because I cannot compile it). If needed, I can install 1.x version.

[brtnfld]

We can see that the KINDS are the same, and gfortran correctly rejects the generic interface (which is why it does not generate the .mod files). This is a standalone script, so it does not need HDF5.

However, the script had an error testing the -m32 flag. Can you try it again?

What I don't understand is why H5_FORTRAN_C_BOOL_IS_UNIQUE is being set to 1 in the build. The configure check in aclocal_fc.f90 uses the identical interface test, so check_fortran_source_compiles should fail and then set the flag to 0, which should exclude verify_c_bool

You should make sure this is from a clean HDF5 build, so we are not getting any stale CMake cache artifacts.

#!/bin/sh
# Test whether the system gfortran can compile a generic interface that
# distinguishes LOGICAL(C_BOOL) from default LOGICAL.
#
# This reproduces the pattern used in the generated tf_gen.F90 and the
# PROG_FC_C_BOOL_EQ_LOGICAL configure check, and tries both variants:
#
#   Case A - WITH call sites (what the configure check currently does)
#   Case B - WITHOUT call sites (what tf_gen.F90 compilation looks like)
#
# Each case is compiled with and without -m32 if the compiler supports it.
#
# Usage:
#   ./test_cbool_generic.sh [gfortran]

FC=${1:-gfortran}
TMPDIR=$(mktemp -d)
trap 'rm -rf "$TMPDIR"' EXIT

echo "Compiler: $($FC --version | head -1)"
echo ""

# --------------------------------------------------------------------------
# Write the two test sources
# --------------------------------------------------------------------------

# Case A: generic interface WITH call sites (current configure check pattern)
cat > "$TMPDIR/test_with_calls.f90" << 'FORTRAN'
MODULE l_type_mod
  USE ISO_C_BINDING
  INTERFACE h5t
     MODULE PROCEDURE h5t_c_bool
     MODULE PROCEDURE h5t_logical
  END INTERFACE
CONTAINS
  SUBROUTINE h5t_c_bool(lcb)
    LOGICAL(KIND=C_BOOL) :: lcb
  END SUBROUTINE h5t_c_bool
  SUBROUTINE h5t_logical(l)
    LOGICAL :: l
  END SUBROUTINE h5t_logical
END MODULE l_type_mod
PROGRAM test_with_calls
  USE ISO_C_BINDING
  USE l_type_mod
  LOGICAL(KIND=C_BOOL) :: lcb
  LOGICAL              :: l
  lcb = .TRUE._C_BOOL
  l   = .TRUE.
  CALL h5t(lcb)
  CALL h5t(l)
END PROGRAM test_with_calls
FORTRAN

# Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90 compilation)
cat > "$TMPDIR/test_no_calls.f90" << 'FORTRAN'
MODULE l_type_mod
  USE ISO_C_BINDING
  INTERFACE h5t
     MODULE PROCEDURE h5t_c_bool
     MODULE PROCEDURE h5t_logical
  END INTERFACE
CONTAINS
  SUBROUTINE h5t_c_bool(lcb)
    LOGICAL(KIND=C_BOOL) :: lcb
  END SUBROUTINE h5t_c_bool
  SUBROUTINE h5t_logical(l)
    LOGICAL :: l
  END SUBROUTINE h5t_logical
END MODULE l_type_mod
PROGRAM test_no_calls
  USE l_type_mod
END PROGRAM test_no_calls
FORTRAN

# --------------------------------------------------------------------------
# Also report the actual kinds so we know if C_BOOL == default LOGICAL
# --------------------------------------------------------------------------
cat > "$TMPDIR/report_kinds.f90" << 'FORTRAN'
PROGRAM report_kinds
  USE ISO_C_BINDING
  IMPLICIT NONE
  INTEGER :: cbool_kind, logical_kind
  cbool_kind  = C_BOOL
  logical_kind = KIND(.TRUE.)
  WRITE(*,'(A,I0)') "  KIND(C_BOOL)    = ", cbool_kind
  WRITE(*,'(A,I0)') "  KIND(.TRUE.)    = ", logical_kind
  IF (cbool_kind == logical_kind) THEN
    WRITE(*,'(A)') "  => SAME kind: C_BOOL and default LOGICAL are identical"
  ELSE
    WRITE(*,'(A)') "  => DIFFERENT kinds: C_BOOL and default LOGICAL are distinct"
  END IF
END PROGRAM report_kinds
FORTRAN

# --------------------------------------------------------------------------
# Helper: compile and report result
# --------------------------------------------------------------------------
try_compile() {
    label="$1"
    src="$2"
    shift 2
    flags="$*"
    out=$(cd "$TMPDIR" && $FC $flags -c "$src" 2>&1)
    if [ $? -eq 0 ]; then
        echo "  PASS  $label"
    else
        echo "  FAIL  $label"
        echo "$out" | sed 's/^/        /'
    fi
}

try_run() {
    label="$1"
    src="$2"
    shift 2
    flags="$*"
    out=$(cd "$TMPDIR" && $FC $flags "$src" -o kinds_prog 2>&1 && ./kinds_prog 2>&1)
    echo "$out" | sed "s/^/  $label: /"
}

# --------------------------------------------------------------------------
# Detect -m32 support by compiling AND linking a trivial program.
# Using compile-only (-c) is not sufficient — a real build needs to link.
# --------------------------------------------------------------------------
cat > "$TMPDIR/probe_m32.f90" << 'FORTRAN'
PROGRAM probe
END PROGRAM probe
FORTRAN

M32_SUPPORTED=0
if $FC -m32 "$TMPDIR/probe_m32.f90" -o "$TMPDIR/probe_m32" 2>/dev/null; then
    M32_SUPPORTED=1
fi

# --------------------------------------------------------------------------
# Run tests
# --------------------------------------------------------------------------
echo "=== Kind information (default flags) ==="
try_run "" report_kinds.f90
if [ "$M32_SUPPORTED" = "1" ]; then
    echo "=== Kind information (-m32) ==="
    try_run "-m32" report_kinds.f90 -m32
fi
echo ""

echo "=== Case A: generic interface WITH call sites ==="
try_compile "default flags          " test_with_calls.f90
try_compile "-std=f2008             " test_with_calls.f90 -std=f2008
try_compile "-std=f2008 -pedantic   " test_with_calls.f90 -std=f2008 -pedantic

if [ "$M32_SUPPORTED" = "1" ]; then
    try_compile "-m32                   " test_with_calls.f90 -m32
    try_compile "-m32 -std=f2008        " test_with_calls.f90 -m32 -std=f2008
    try_compile "-m32 -std=f2008 -pedantic" test_with_calls.f90 -m32 -std=f2008 -pedantic
else
    echo "  SKIP  -m32 (not supported by this compiler/platform)"
fi
echo ""

echo "=== Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90) ==="
try_compile "default flags          " test_no_calls.f90
try_compile "-std=f2008             " test_no_calls.f90 -std=f2008
try_compile "-std=f2008 -pedantic   " test_no_calls.f90 -std=f2008 -pedantic

if [ "$M32_SUPPORTED" = "1" ]; then
    try_compile "-m32                   " test_no_calls.f90 -m32
    try_compile "-m32 -std=f2008        " test_no_calls.f90 -m32 -std=f2008
    try_compile "-m32 -std=f2008 -pedantic" test_no_calls.f90 -m32 -std=f2008 -pedantic
else
    echo "  SKIP  -m32 (not supported by this compiler/platform)"
fi
echo ""

echo "=== Summary ==="
echo "If Case A passes but Case B fails: the compiler suppresses the ambiguity"
echo "  error when call sites are present -- and the configure check is masking"
echo "  a real compiler bug."
echo "If both A and B fail: C_BOOL and LOGICAL are the same kind on this platform"
echo "  (correct behavior -- H5_FORTRAN_C_BOOL_IS_UNIQUE should be 0)."
echo "If A/B fail without -m32 but pass with -m32 (or vice versa): the flag"
echo "  changes the C_BOOL kind mapping, pointing to a flag-mismatch between"
echo "  the CMake configure check and the actual build."
echo "If both pass: no issue on this platform/flags."

After installing 32-bit multilib libraries. this is what I get:

Compiler: GNU Fortran (SUSE Linux) 15.2.1 20260202

=== Kind information (default flags) ===
: KIND(C_BOOL) = 1
: KIND(.TRUE.) = 4
: => DIFFERENT kinds: C_BOOL and default LOGICAL are distinct
=== Kind information (-m32) ===
-m32: KIND(C_BOOL) = 1
-m32: KIND(.TRUE.) = 4
-m32: => DIFFERENT kinds: C_BOOL and default LOGICAL are distinct

=== Case A: generic interface WITH call sites ===
PASS default flags
PASS -std=f2008
PASS -std=f2008 -pedantic
PASS -m32
PASS -m32 -std=f2008
PASS -m32 -std=f2008 -pedantic

=== Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90) ===
PASS default flags
PASS -std=f2008
PASS -std=f2008 -pedantic
PASS -m32
PASS -m32 -std=f2008
PASS -m32 -std=f2008 -pedantic

[barracuda156]

$ ./hdf5_test.sh
Compiler: GNU Fortran (MacOS PowerPC gcc14 14.3.0_0+G5+stdlib_flag) 14.3.0

=== Kind information (default flags) ===
  :   KIND(C_BOOL)    = 4
  :   KIND(.TRUE.)    = 4
  :   => SAME kind: C_BOOL and default LOGICAL are identical
=== Kind information (-m32) ===
  -m32:   KIND(C_BOOL)    = 4
  -m32:   KIND(.TRUE.)    = 4
  -m32:   => SAME kind: C_BOOL and default LOGICAL are identical

=== Case A: generic interface WITH call sites ===
  FAIL  default flags          
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008             
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008 -pedantic   
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -m32                   
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -m32 -std=f2008        
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -m32 -std=f2008 -pedantic
        test_with_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_with_calls.f90:17:7:
        
           17 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.

=== Case B: generic interface WITHOUT call sites (mirrors tf_gen.F90) ===
  FAIL  default flags          
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008             
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -std=f2008 -pedantic   
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -m32                   
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -m32 -std=f2008        
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.
  FAIL  -m32 -std=f2008 -pedantic
        test_no_calls.f90:8:23:
        
            8 |   SUBROUTINE h5t_c_bool(lcb)
              |                       1
        ......
           11 |   SUBROUTINE h5t_logical(l)
              |                        2
        Error: Ambiguous interfaces in generic interface 'h5t' for 'h5t_c_bool' at (1) and 'h5t_logical' at (2)
        test_no_calls.f90:16:7:
        
           16 |   USE l_type_mod
              |       1
        Fatal Error: Cannot open module file 'l_type_mod.mod' for reading at (1): No such file or directory
        compilation terminated.

=== Summary ===
If Case A passes but Case B fails: the compiler suppresses the ambiguity
  error when call sites are present -- and the configure check is masking
  a real compiler bug.
If both A and B fail: C_BOOL and LOGICAL are the same kind on this platform
  (correct behavior -- H5_FORTRAN_C_BOOL_IS_UNIQUE should be 0).
If A/B fail without -m32 but pass with -m32 (or vice versa): the flag
  changes the C_BOOL kind mapping, pointing to a flag-mismatch between
  the CMake configure check and the actual build.
If both pass: no issue on this platform/flags.