Does the LLD support linking of XCOFF format object files?

I’m thinking about re-implementing an old cross-toolchain with LLVM.

My old compiler and linker used XCOFF as the object file format. I’ve been scrutinizing the LLVM code base for a while, and I think the support for XCOFF format is not as extensible as that of ELF. I also heard that LLD only support linking of ELF, COFF, and MachO. Is that true?

That is true. The in-tree linkers support ELF, COFF, and MachO. IBM uses there own linker for XCOFF.