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, 49 insertions, 0 deletions

diff --git a/io_uring/cancel.h b/io_uring/cancel.h
new file mode 100644
index 000000000..1b201a094
--- /dev/null
+++ b/io_uring/cancel.h
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef IORING_CANCEL_H
+#define IORING_CANCEL_H
+
+#include <linux/io_uring_types.h>
+
+struct io_cancel_data {
+	struct io_ring_ctx *ctx;
+	u64 data;
+	struct file *file;
+	u8 opcode;
+	u32 flags;
+	int seq;
+};
+
+int io_async_cancel_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_async_cancel(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_try_cancel(struct io_uring_task *tctx, struct io_cancel_data *cd,
+		  unsigned int issue_flags);
+
+int io_sync_cancel(struct io_ring_ctx *ctx, void __user *arg);
+bool io_cancel_req_match(struct io_kiocb *req, struct io_cancel_data *cd);
+bool io_match_task_safe(struct io_kiocb *head, struct io_uring_task *tctx,
+			bool cancel_all);
+
+bool io_cancel_remove_all(struct io_ring_ctx *ctx, struct io_uring_task *tctx,
+			  struct hlist_head *list, bool cancel_all,
+			  bool (*cancel)(struct io_kiocb *));
+int io_cancel_remove(struct io_ring_ctx *ctx, struct io_cancel_data *cd,
+		     unsigned int issue_flags, struct hlist_head *list,
+		     bool (*cancel)(struct io_kiocb *));
+__cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
+					 struct io_uring_task *tctx,
+					 bool cancel_all, bool is_sqpoll_thread);
+__cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd);
+__cold bool io_cancel_ctx_cb(struct io_wq_work *work, void *data);
+
+static inline bool io_cancel_match_sequence(struct io_kiocb *req, int sequence)
+{
+	if (req->cancel_seq_set && sequence == req->work.cancel_seq)
+		return true;
+
+	req->cancel_seq_set = true;
+	req->work.cancel_seq = sequence;
+	return false;
+}
+
+#endif