linux-kernel - Re: [PATCH 2/2] rust: enable `no_mangle_with_rust

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Message-ID: <CALNs47sn5GT9_VKn-SGb+STFwpbUipoNyU_+ZbpDwzLXUknUUQ@mail.gmail.com>
Date:   Wed, 2 Aug 2023 03:49:43 -0400
From:   Trevor Gross <tmgross@...ch.edu>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH 2/2] rust: enable `no_mangle_with_rust_abi` Clippy lint

On Sat, Jul 29, 2023 at 6:05 PM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> Introduced in Rust 1.69.0 [1], this lint prevents forgetting to set
> the C ABI when using `#[no_mangle]` (or thinking it is implied).
>
> For instance, it would have prevented the issue [2] fixed by commit
> c682e4c37d2b ("rust: kernel: Mark rust_fmt_argument as extern "C"").
>
>     error: `#[no_mangle]` set on a function with the default (`Rust`) ABI
>       --> rust/kernel/print.rs:21:1
>        |
>     21 | / unsafe fn rust_fmt_argument(
>     22 | |     buf: *mut c_char,
>     23 | |     end: *mut c_char,
>     24 | |     ptr: *const c_void,
>     25 | | ) -> *mut c_char {
>        | |________________^
>        |
>        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#no_mangle_with_rust_abi
>        = note: requested on the command line with `-D clippy::no-mangle-with-rust-abi`
>     help: set an ABI
>        |
>     21 | unsafe extern "C" fn rust_fmt_argument(
>        |        ++++++++++
>     help: or explicitly set the default
>        |
>     21 | unsafe extern "Rust" fn rust_fmt_argument(
>        |        +++++++++++++
>
> Thus enable it.
>
> In rare cases, we may need to use the Rust ABI even with `#[no_mangle]`
> (e.g. one case, before 1.71.0, would have been the `__rust_*`
> functions). In those cases, we would need to `#[allow(...)]` the lint,
> since using `extern "Rust"` explicitly (as the compiler suggests)
> currently gets overwritten by `rustfmt` [3].
>
> Link: https://github.com/rust-lang/rust-clippy/issues/10347 [1]
> Link: https://github.com/Rust-for-Linux/linux/pull/967 [2]
> Link: https://github.com/rust-lang/rustfmt/issues/5701 [3]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
> [...]

Reviewed-by: Trevor Gross <tmgross@...ch.edu>