Re: [PATCH] objtool/rust: add one more `noreturn` Rust function

On Wed, Aug 5, 2026 at 4:45 PM Miguel Ojeda <[email protected]> wrote:
>
> When the pointer formatting series [1] is applied and KUnit tests
> are enabled, `objtool` would report an error with any of our
> supported Rust versions. For instance, with Rust 1.97.1:
>
>     rust/kernel.o: error: objtool: _R..._4core3fmt7Pointer3fmtB7_()
>     falls through to next function _R..._4core7convert5AsRefNtB5_4BStrE6as_ref()
>
> Or, with Rust 1.85.0:
>
>     rust/kernel.o: error: objtool: _R..._4core3fmt7Pointer3fmtB7_()
>     falls through to next function _R..._4core3ffi5c_str4CStrENtNtBS_3fmt7Display3fmtB7_()
>
> This happens due to calls to the `noreturn` symbol:
>
>     core::str::slice_error_fail
>
> Thus add the mangled one to the list so that `objtool` knows it is
> actually `noreturn`.
>
> See commit 56d680dd23c3 ("objtool/rust: list `noreturn` Rust functions")
> for more details.
>
> Cc: Josh Poimboeuf <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Reported-by: Alice Ryhl <[email protected]>
> Link: https://lore.kernel.org/rust-for-linux/[email protected]/
> Link: https://lore.kernel.org/rust-for-linux/[email protected]/ [1]
> Signed-off-by: Miguel Ojeda <[email protected]>

Applied to `rust-fixes` -- thanks!

    [ While the series [1] mentioned above was not applied in a way
      that triggered this, Gary found another case [2]:

        I am seeing this function causing issue on my 1.85.1 -Os
build, although the
        error message is different this time:

            rust/kernel.o: warning: objtool:
_R..._5range9RangeFromjEE5indexCsldbe0TGTmNx_6kernel+0x1d:
            stack state mismatch: cfa1=4+8 cfa2=4+16

        Disassembly shows that the function call before the warning location
        is a call to _4core3str16slice_error_fail, and objtool thought it can
        return (which will end up with a unbalanced stack if it does return).

      Thus apply it. - Miguel ]

    Cc: [email protected] # Needed in 6.12.y and later (Rust is
pinned in older LTSs).

Cheers,
Miguel