Hi,
I'm getting a build failure when building Open MPI 5.0.9 with LLVM
compilers on macOS (Apple Silicon). Configure succeeds, but make fails when
linking:
```
flang-21: error: unknown argument: '-compatibility_version'
flang-21: error: unknown argument: '-current_version'
flang-21: error: no such file or directory: '81'
flang-21: error: no such file or directory: '81.3'
make[3]: *** [libmpi_usempif08.la] Error 1
```
I believe this error comes from config/ltmain_flang_darwin.diff. The patch
has three hunks that add flang-specific handling for Darwin linker flags.
Hunks 1 and 3 match against $CC directly using `case $CC in flang*)`, which
fails when the Fortran compiler is specified as a full path (e.g.,
/opt/homebrew/opt/flang/bin/flang). Hunk 2 correctly uses `func_cc_basename
$CC` before matching, so it doesn't have this problem.
*Environment:*
- macOS 26.2 (Darwin 25.2.0), aarch64 (Apple M1 Pro)
- Homebrew clang/clang++/flang 21.1.8
- Open MPI 5.0.9
*Configure command:*
*```*
$ ./configure \
CC=/opt/homebrew/opt/llvm/bin/clang \
CPPFLAGS=-I/opt/homebrew/opt/llvm/include \
CXX=/opt/homebrew/opt/llvm/bin/clang++ \
CXXCPPFLAGS=-I/opt/homebrew/opt/llvm/include \
FC=flang \
LDFLAGS="-L/opt/homebrew/opt/llvm/lib
-L/opt/homebrew/opt/llvm/lib/c++ -L/opt/homebrew/opt/llvm/lib/unwind
-lunwind" \
--with-hwloc=/opt/homebrew/opt/hwloc \
--with-libevent=/opt/homebrew/opt/libevent \
--with-pmix=/opt/homebrew/opt/pmix
*```*
*Build output:*
https://www.icloud.com/iclouddrive/00dSkBghSZdP0-MRsCPN7M7pw#ompi-output (let
me know if you cannot access this, and I'll resubmit using a different
service)
*Workaround:* Use `FC=flang` (bare name) instead of the full path, with
/opt/homebrew/opt/flang/bin in $PATH.
*Suggested fix:* Update hunks 1 and 3 in config/ltmain_flang_darwin.diff to
use `func_cc_basename $CC` and `$func_cc_basename_result` instead of
matching $CC directly, consistent with hunk 2.
If this is indeed a bug and not intentional, I'd be happy to submit an
issue/PR on GitHub if you can advise on the preferred approach. I wasn't
sure whether to regenerate the diff against a specific libtool version or
patch it directly.
Thanks,
Matthew Mehrtens
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