Re: Re: [PATCH v2 0/3] Inline helpers into Rust without full LTO

[Miguel Ojeda <ojeda@kernel.org>]

On Sun, 22 Mar 2026 20:21:59 +0100 Miguel Ojeda <ojeda@kernel.org> wrote:
>
> I will reply to a couple other bindings in separate emails to avoid
> spamming people too much.

In a series of tests, in some cases, I noticed an `objtool` warning for
x86_64:

    rust/kernel.o: warning: objtool: _R..._9RegulatorNtB5_8DisabledE3get() is missing an ELF size annotation
    rust/kernel.o: warning: objtool: _R..._9RegulatorNtB5_7EnabledE3get() is missing an ELF size annotation

I noticed that it only happened when `CONFIG_REGULATOR` was disabled. It
seems that we have undefined behavior in `regulator.rs`...

We have `Regulator<Enabled/Disabled>::get()` which calls
`get_internal()` which calls the `regulator_get()` helper, which returns
`NULL` when `CONFIG_REGULATOR` is not set. Then the return value is
passed to `from_err_ptr` which checks `IS_ERR`, which returns false
(unlike `IS_ERR_OR_NULL`), and thus we return an `Ok(NULL)`, which we
then pass to `NonNull::new_unchecked`:

    // SAFETY: We can safely trust `inner` to be a pointer to a valid
    // regulator if `ERR_PTR` was not returned.
    let inner = unsafe { NonNull::new_unchecked(inner) };

So we should fix that -- it is there since its introduction in commit
9b614ceada7c ("rust: regulator: add a bare minimum regulator
abstraction"). How to fix that depends on whether the Rust abstraction
supposed to work transparently like the C API, I assume.

Now, two improvements I think we should independently do too:

  - The docs on `regulator_get()` don't say it may return `NULL`. It
    originally that case, but commit be1a50d4eba4 ("regulator: Let
    drivers know when they use the stub API") changed that without
    changing the docs.

    I mean, the "docs" are on the real function, but still, one may look
    into those and not realize the stub does something different.

    The implementation comment on the stub is also a bit contradictory.
    The original sentence (which still is there) says that nothing
    should look at the value, but then it goes onto say that drivers may
    actually look at the value.

  - On the Rust general infrastructure side, we should document more
    prominently that `from_err_ptr` may return `Ok(NULL)` just fine,
    since it calls `IS_ERR`. It may be obvious, since `NULL` is not an
    error value, but still, it could have perhaps prevented this issue.

    We should also include an example to the doctest showing and testing
    that particular case to drive the point home.

    I can add that as a "good first issue".

Cc'ing Liam, Mark, Daniel, Jean.

I hope that helps.

Cheers,
Miguel