kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/net/rfkill/rfkill.h b/net/rfkill/rfkill.h
new file mode 100644
index 000000000..001c40caa
--- /dev/null
+++ b/net/rfkill/rfkill.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2007 Ivo van Doorn
+ * Copyright 2009 Johannes Berg <johannes@sipsolutions.net>
+ */
+
+
+#ifndef __RFKILL_INPUT_H
+#define __RFKILL_INPUT_H
+
+/* core code */
+void rfkill_switch_all(const enum rfkill_type type, bool blocked);
+void rfkill_epo(void);
+void rfkill_restore_states(void);
+void rfkill_remove_epo_lock(void);
+bool rfkill_is_epo_lock_active(void);
+bool rfkill_get_global_sw_state(const enum rfkill_type type);
+
+/* input handler */
+int rfkill_handler_init(void);
+void rfkill_handler_exit(void);
+
+#endif /* __RFKILL_INPUT_H */