rust: allow suspicious_runtime_symbol_definitions lint for Rust >= 1.98

commit 608045a upstream.

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>
Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Link: rust-lang/rust#155521 [1]
Link: rust-lang/rust#138446 [2]
Link: Rust-for-Linux/linux#355 [3]
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Tamir Duberstein <tamird@kernel.org>
Link: https://patch.msgid.link/20260615143225.471756-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ojeda

init/Kconfig

@@ -140,6 +140,9 @@ config LD_CAN_USE_KEEP_IN_OVERLAY
 config RUSTC_HAS_UNNECESSARY_TRANSMUTES
 	def_bool RUSTC_VERSION >= 108800
 
+config RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS
+	def_bool RUSTC_VERSION >= 109800
+
 config PAHOLE_VERSION
 	int
 	default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))

rust/bindings/lib.rs

@@ -27,6 +27,10 @@
 #[allow(dead_code)]
 #[allow(clippy::undocumented_unsafe_blocks)]
 #[cfg_attr(CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES, allow(unnecessary_transmutes))]
+#[cfg_attr(
+    CONFIG_RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS,
+    allow(suspicious_runtime_symbol_definitions)
+)]
 mod bindings_raw {
     // Manual definition for blocklisted types.
     type __kernel_size_t = usize;

rust/uapi/lib.rs

@@ -25,6 +25,10 @@
     unsafe_op_in_unsafe_fn
 )]
 #![cfg_attr(CONFIG_RUSTC_HAS_UNNECESSARY_TRANSMUTES, allow(unnecessary_transmutes))]
+#![cfg_attr(
+    CONFIG_RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS,
+    allow(suspicious_runtime_symbol_definitions)
+)]
 
 // Manual definition of blocklisted types.
 type __kernel_size_t = usize;