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

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Message-ID: <de0f5630-a0ad-92c4-a11c-0824b334cd84@gmail.com>
Date:   Sun, 30 Jul 2023 12:04:55 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>
Cc:     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 7/29/23 19:03, Miguel Ojeda 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: Martin Rodriguez Reboredo <yakoyoku@...il.com>