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/io_uring/timeout.h b/io_uring/timeout.h
new file mode 100644
index 000000000..1620f94dd
--- /dev/null
+++ b/io_uring/timeout.h
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+struct io_timeout_data {
+	struct io_kiocb			*req;
+	struct hrtimer			timer;
+	ktime_t				time;
+	enum hrtimer_mode		mode;
+	u32				flags;
+};
+
+__cold void io_flush_timeouts(struct io_ring_ctx *ctx);
+struct io_cancel_data;
+int io_timeout_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd);
+__cold bool io_kill_timeouts(struct io_ring_ctx *ctx, struct io_uring_task *tctx,
+			     bool cancel_all);
+void io_queue_linked_timeout(struct io_kiocb *req);
+void io_disarm_next(struct io_kiocb *req);
+
+int io_timeout_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_link_timeout_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_timeout(struct io_kiocb *req, unsigned int issue_flags);
+int io_timeout_remove_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_timeout_remove(struct io_kiocb *req, unsigned int issue_flags);