linux-kernel - Re: [PATCH v2 1/5] rust: fix signature of rust_fmt

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Message-ID: <CAJ-ks9nmFDqsBrmxC0nCPQB=OTeKKUucs4AqJSRN4hsGkSPwEg@mail.gmail.com>
Date: Fri, 28 Feb 2025 10:13:44 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	Rasmus Villemoes <linux@...musvillemoes.dk>, Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 1/5] rust: fix signature of rust_fmt_argument

On Fri, Feb 28, 2025 at 7:41 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> Without this change, the rest of this series will emit the following
> error message:
>
> error[E0308]: `if` and `else` have incompatible types
>   --> <linux>/rust/kernel/print.rs:22:22
>    |
> 21 | #[export]
>    | --------- expected because of this
> 22 | unsafe extern "C" fn rust_fmt_argument(
>    |                      ^^^^^^^^^^^^^^^^^ expected `u8`, found `i8`
>    |
>    = note: expected fn item `unsafe extern "C" fn(*mut u8, *mut u8, *mut c_void) -> *mut u8 {bindings::rust_fmt_argument}`
>               found fn item `unsafe extern "C" fn(*mut i8, *mut i8, *const c_void) -> *mut i8 {print::rust_fmt_argument}`
>
> The error may be different depending on the architecture.
>
> To fix this, change the void pointer argument to use a const pointer,
> and change the imports to use crate::ffi instead of core::ffi for
> integer types.
>
> Fixes: 787983da7718 ("vsprintf: add new `%pA` format specifier")
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
>  lib/vsprintf.c       | 2 +-
>  rust/kernel/print.rs | 7 +++----
>  2 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 56fe96319292..a8ac4c4fffcf 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2285,7 +2285,7 @@ int __init no_hash_pointers_enable(char *str)
>  early_param("no_hash_pointers", no_hash_pointers_enable);
>
>  /* Used for Rust formatting ('%pA'). */
> -char *rust_fmt_argument(char *buf, char *end, void *ptr);
> +char *rust_fmt_argument(char *buf, char *end, const void *ptr);
>
>  /*
>   * Show a '%p' thing.  A kernel extension is that the '%p' is followed
> diff --git a/rust/kernel/print.rs b/rust/kernel/print.rs
> index b19ee490be58..61ee36c5e5f5 100644
> --- a/rust/kernel/print.rs
> +++ b/rust/kernel/print.rs
> @@ -6,12 +6,11 @@
>  //!
>  //! Reference: <https://docs.kernel.org/core-api/printk-basics.html>
>
> -use core::{
> +use crate::{
>      ffi::{c_char, c_void},
> -    fmt,
> +    str::RawFormatter,
>  };
> -
> -use crate::str::RawFormatter;
> +use core::fmt;
>
>  // Called from `vsprintf` with format specifier `%pA`.
>  #[expect(clippy::missing_safety_doc)]
>
> --
> 2.48.1.711.g2feabab25a-goog

Reviewed-by: Tamir Duberstein <tamird@...il.com>