[clang] [llvm] [X86] Extend kCFI with a 3-bit arity indicator (PR #121070)

[Sami Tolvanen via llvm-commits]

samitolvanen wrote:

> And AFAIK there's no other users of kCFI besides the Linux kernel (but please correct me if I'm wrong).

There are firmware projects that use KCFI, but AFAIK none of them run on x86. I'm also fairly certain that only Linux performs runtime patching based on the code sequence we emit, so I'm not particularly concerned about breaking other KCFI users with this change.

https://github.com/llvm/llvm-project/pull/121070