linux-kernel - Re: [PATCH 1/4] rust: fix signature of rust_fmt

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Message-ID: <CAH5fLgjKoHpGS9ugxawwJJbb68trHEVvBCCNWFcNSbScGKpuDA@mail.gmail.com>
Date: Fri, 28 Feb 2025 09:44:21 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
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>, 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 1/4] rust: fix signature of rust_fmt_argument

On Fri, Feb 28, 2025 at 9:20 AM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>
> "Alice Ryhl" <aliceryhl@...gle.com> writes:
>
> > 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.
> >
> > Fixes: 787983da7718 ("vsprintf: add new `%pA` format specifier")
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> > ---
> >  lib/vsprintf.c       | 2 +-
> >  rust/kernel/print.rs | 8 ++++----
> >  2 files changed, 5 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..8551631dedf1 100644
> > --- a/rust/kernel/print.rs
> > +++ b/rust/kernel/print.rs
> > @@ -6,13 +6,13 @@
> >  //!
> >  //! Reference: <https://docs.kernel.org/core-api/printk-basics.html>
> >
> > -use core::{
> > +use core::fmt;
> > +
> > +use crate::{
> >      ffi::{c_char, c_void},
> > -    fmt,
> > +    str::RawFormatter,
> >  };
> >
> > -use crate::str::RawFormatter;
> > -
> >  // Called from `vsprintf` with format specifier `%pA`.
> >  #[expect(clippy::missing_safety_doc)]
> >  #[no_mangle]
>
> The changes in this last hunk is not mentioned in the commit message.

The diff is rendered pretty poorly, but this is just importing
integers from crate::ffi instead of core::ffi, and I do believe that
the commit message makes it clear that this is needed.

Alice