Naked EII impl functions are currently not working

[boozook]

Naked functions as eii-impl are not work.

• without default impl — error: impl not found
• with default impl — used default impl instead of external impl, without errors by rustc or linker

Reproducible examples

Without default impl:

#[eii(requires_impl)]
unsafe extern "C" fn entry_eh(_: usize);


#[crate::requires_impl]
#[unsafe(naked)]
unsafe extern "C" fn eh(_: usize) { core::arch::naked_asm!("nop"); }

With default impl:

#[eii(opt_impl)]
unsafe extern "C" fn entry_eh(_: usize) { println!("called default") }


#[crate::opt_impl]
#[unsafe(naked)]
unsafe extern "C" fn eh(_: usize) { core::arch::naked_asm!("nop"); }

Expected

I hope it's possible to have naked impls, but as explained there (comment) — may not be possible, so I expecting proper errors.

I'd expect error with some explanation in case of default impl;
and error with explanation better then "just not found" in case without default impl.

Meta

rustc --version --verbose:

rustc 1.98.0-nightly (8b6558a02 2026-06-20)
binary: rustc
commit-hash: 8b6558a02b2774acfb25cf15e199467c37ba7490
commit-date: 2026-06-20
host: aarch64-apple-darwin
release: 1.98.0-nightly
LLVM version: 22.1.7

---

Related

• Tracking issue: Tracking Issue for externally implementable items #125418
• PR adding EII functions: Externally implementable items #146348

[bjorn3]

Copying my comment from #125418 (comment):

Naked functions as EII may not be possible. It is possible that we will have to introduce a wrapper function that forwards to the right EII impl. But naked functions can't have wrapper functions. If you only need ELF and Mach-O platforms, you could directly define weak functions in your inline asm. EII also has to work with PE/COFF and other object file formats that have bad weak symbol support.

We should give an error, at least until we know if we can or can not support naked functions as EII.