Re: [PATCH] rust: allow `suspicious_runtime_symbol_definitions` lint for Rust >= 1.98

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Jun 15, 2026 at 04:32:25PM +0200, Miguel Ojeda wrote:
> Starting with Rust 1.98.0 (expected 2026-08-20), Rust is introducing a
> couple new lints, `invalid_runtime_symbol_definitions` (deny-by-default)
> and `suspicious_runtime_symbol_definitions` (warn-by-default), which check
> the signature of items whose symbol name is a runtime symbol expected by
> `core`.
> 
> Our build hits the second one, i.e. the warning:
> 
>     error: suspicious definition of the runtime `strlen` symbol used by the standard library
>          --> rust/bindings/bindings_generated.rs:20018:5
>           |
>     20018 |     pub fn strlen(s: *const ffi::c_char) -> usize;
>           |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>           |
>           = note: expected `unsafe extern "C" fn(*const i8) -> usize`
>                   found    `unsafe extern "C" fn(*const u8) -> usize`
>           = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "strlen")]`, or `#[link_name = "strlen"]`
>           = help: allow this lint if the signature is compatible
>           = note: `-D suspicious-runtime-symbol-definitions` implied by `-D warnings`
>           = help: to override `-D warnings` add `#[allow(suspicious_runtime_symbol_definitions)]`
> 
>     error: suspicious definition of the runtime `strlen` symbol used by the standard library
>          --> rust/uapi/uapi_generated.rs:14236:5
>           |
>     14236 |     pub fn strlen(s: *const ffi::c_char) -> usize;
>           |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>           |
>           = note: expected `unsafe extern "C" fn(*const i8) -> usize`
>                   found    `unsafe extern "C" fn(*const u8) -> usize`
>           = help: either fix the signature or remove any attributes like `#[unsafe(no_mangle)]`, `#[unsafe(export_name = "strlen")]`, or `#[link_name = "strlen"]`
>           = help: allow this lint if the signature is compatible
>           = note: `-D suspicious-runtime-symbol-definitions` implied by `-D warnings`
>           = help: to override `-D warnings` add `#[allow(suspicious_runtime_symbol_definitions)]`
> 
> Thus `allow` the lint in `bindings` and `uapi`.
> 
> A more targeted alternative to avoid `allow`ing it would be to pass
> `--blocklist-function strlen` to `bindgen`, but we would perhaps need
> to adjust if other C headers end up adding more (or Rust checking more).
> Since it is just the less critical one that we hit, and since eventually
> this should be properly fixed by getting upstream Rust to provide a flag
> like GCC/Clang's `-funsigned-char` [2][3], just `allow` it for now.
> 
> Cc: Urgau <urgau@numericable.fr>
> Link: https://github.com/rust-lang/rust/pull/155521 [1]
> Link: https://github.com/rust-lang/rust/issues/138446 [2]
> Link: https://github.com/Rust-for-Linux/linux/issues/355 [3]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

The change itself LGTM. With below question answered:
Reviewed-by: Alice Ryhl <aliceryhl@google.com>

>  #![cfg_attr(CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES, allow(unnecessary_transmutes))]
> +#![cfg_attr(
> +    CONFIG_RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS,
> +    allow(suspicious_runtime_symbol_definitions)
> +)]

I'm wondering whether the cfg_attr is required? Is there a warning from
specifying an unknown warning otherwise?

Alice