linux-kernel - Re: [PATCH] rust: kernel: Mark rust_fmt

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Date:   Wed, 15 Feb 2023 07:28:39 +0000
From:   Gary Guo <gary@...yguo.net>
To:     David Gow <davidgow@...gle.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Björn Roy Baron" <bjorn3_gh@...tonmail.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] rust: kernel: Mark rust_fmt_argument as extern "C"

On Wed, 15 Feb 2023 06:47:35 +0800
David Gow <davidgow@...gle.com> wrote:

> The rust_fmt_argument function is called from printk() to handle the %pA
> format specifier.
> 
> Since it's called from C, we should mark it extern "C" to make sure it's
> ABI compatible.
> 
> Cc: stable@...r.kernel.org
> Fixes: 247b365dc8dc ("rust: add `kernel` crate")
> Signed-off-by: David Gow <davidgow@...gle.com>

Reviewed-by: Gary Guo <gary@...yguo.net>

> ---
> 
> See discussion in:
> https://github.com/Rust-for-Linux/linux/pull/967
> and
> https://github.com/Rust-for-Linux/linux/pull/966
> 
> ---
>  rust/kernel/print.rs | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
> index 30103325696d..ec457f0952fe 100644
> --- a/rust/kernel/print.rs
> +++ b/rust/kernel/print.rs
> @@ -18,7 +18,7 @@ use crate::bindings;
>  
>  // Called from `vsprintf` with format specifier `%pA`.
>  #[no_mangle]
> -unsafe fn rust_fmt_argument(buf: *mut c_char, end: *mut c_char, ptr: *const c_void) -> *mut c_char {
> +unsafe extern "C" fn rust_fmt_argument(buf: *mut c_char, end: *mut c_char, ptr: *const c_void) -> *mut c_char {
>      use fmt::Write;
>      // SAFETY: The C contract guarantees that `buf` is valid if it's less than `end`.
>      let mut w = unsafe { RawFormatter::from_ptrs(buf.cast(), end.cast()) };