Apple builds for MPICH broke in recent toolchain update

[eschnett]

See #7736.

I saw some recent messages about downgrading elfutils in the RootFS. Is this expected to correct this problem?

@gbaraldi

[benlorenz]

I recently encountered this as well, one workaround is to set LDFLAGS=-fuse-ld=ld on macos to undo the linker change.

But I did look into this a bit further and this might be caused by a broken linker-flag detection in libtool:
https://savannah.gnu.org/support/?110937

libtool checks whether -single_module is supported, but in the gfortran 4 and 5 builds lld gives a warning that this is the default anyway and deprecated. This confuses libtool and it assumes the flag is unsupported:

[17:49:34] checking for -single_module linker flag... ld64.lld: warning: Option `-single_module' is deprecated in ld64:
[17:49:34] no

The fallback flags -r -keep_private_extern are not supported by lld.

Patching libtool is a bit annoying since we would need to regenerate all the configure scripts.
But we could pass lt_cv_apple_cc_single_mod=yes to configure instead, then the flag will always be assumed to work but that should be fine since it is the default anyway.

In my local experiments this seems to work for the MPICH macos builds and for Singular as well.

[eschnett]

I am now seeing a similar (related?) build error on Apple #7762 . This time it's with cmake (not configure) and the option is -commons (possibly Fortran-related):

[23:05:06] ld64.lld: warning: Option `-commons' is not yet implemented. Stay tuned...
[23:05:06] ld64.lld: error: No LC_DYLD_INFO_ONLY or LC_DYLD_EXPORTS_TRIE found in /opt/x86_64-apple-darwin14/x86_64-apple-darwin14/lib/libgcc_s.1.dylib
[23:05:06] ld64.lld: error: No LC_DYLD_INFO_ONLY or LC_DYLD_EXPORTS_TRIE found in /opt/x86_64-apple-darwin14/x86_64-apple-darwin14/lib/libgcc_ext.10.5.dylib

@gbaraldi Do you have some insight here as well?

[eschnett]

This approach also seems to work – deleting the new linkers:

if [[ "${target}" == x86_64-apple-darwin* ]]; then
    # See <https://github.com/JuliaPackaging/Yggdrasil/issues/7745>:
    # Remove the new linkers which don't work yet
    rm /opt/bin/${bb_full_target}/ld64.lld
    rm /opt/bin/${bb_full_target}/ld64.${target}
    rm /opt/bin/${bb_full_target}/${target}-ld64.lld
    rm /opt/${MACHTYPE}/bin/ld64.lld
fi

[ViralBShah]

Is this still an issue?

[MaximeBouton]

I encountered the same issue here: #8707 and fixed it using the keyword from #7876