ld -m elf_x86_64 recognizes semantics of OS-specific STT_GNU_IFUNC/STB_GNU_UNIQUE in ELFOSABI_NONE object files.
LLVM integrated assembler as of 12.0.0 does not set ELFOSABI_GNU if you use @gnu_indirect_function/@gnu_unique_object.
Question: how do GNU as set OSABI for STT_GNU_IFUNC/STB_GNU_UNIQUE on FreeBSD? Is the behavior host platform dependent?
However, ld -m elf_x86_64 does not recognize SHF_GNU_RETAIN in ELFOSABI_NONE object files.
So these section/symbol properties have some inconsistency.
I can see two choices.
1. (Current behavior)
Ignore semantics of SHF_GNU_RETAIN in ELFOSABI_NONE object files.
If we want to make rules consistent, we should do this for STT_GNU_IFUNC/STB_GNU_UNIQUE,
but it would break all the object files produced by LLVM integrated assembler.
Recognize the semantics of SHF_GNU_RETAIN if the ld configuration & options indicate Linux target (e.g. ld -m elf_x86_64 on Linux),
regardless of EI_OSABI in object files.
This choice gives discretion to the linker.
I think the only downside is that readelf -S does not display 'R' for SHF_GNU_RETAIN,
like readelf -s doesn't show IFUNC for LLVM integrated assembler assembled object files today.
You can close this one.
For SHF_GNU_RETAIN, I've changed clang 13 to set ELFOSABI_GNU.
I am happy with the current GNU ld behavior.
For STT_GNU_IFUNC, clang has always been using ELFOSABI_NONE.
So please don't drop support.