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, 79 insertions, 0 deletions

diff --git a/io_uring/net.h b/io_uring/net.h
new file mode 100644
index 000000000..51fda715d
--- /dev/null
+++ b/io_uring/net.h
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/net.h>
+#include <linux/uio.h>
+#include <linux/io_uring_types.h>
+#include <uapi/linux/io_uring/bpf_filter.h>
+
+struct io_async_msghdr {
+#if defined(CONFIG_NET)
+	struct iou_vec				vec;
+
+	struct_group(clear,
+		int				namelen;
+		struct iovec			fast_iov;
+		__kernel_size_t			controllen;
+		__kernel_size_t			payloadlen;
+		struct sockaddr __user		*uaddr;
+		struct msghdr			msg;
+		struct sockaddr_storage		addr;
+	);
+#else
+	struct_group(clear);
+#endif
+};
+
+#if defined(CONFIG_NET)
+
+int io_shutdown_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_shutdown(struct io_kiocb *req, unsigned int issue_flags);
+
+void io_sendmsg_recvmsg_cleanup(struct io_kiocb *req);
+int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_send(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags);
+int io_recv(struct io_kiocb *req, unsigned int issue_flags);
+
+void io_sendrecv_fail(struct io_kiocb *req);
+
+int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_accept(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_socket_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_socket(struct io_kiocb *req, unsigned int issue_flags);
+void io_socket_bpf_populate(struct io_uring_bpf_ctx *bctx, struct io_kiocb *req);
+void io_connect_bpf_populate(struct io_uring_bpf_ctx *bctx, struct io_kiocb *req);
+
+int io_connect_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_connect(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_sendmsg_zc(struct io_kiocb *req, unsigned int issue_flags);
+int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+void io_send_zc_cleanup(struct io_kiocb *req);
+
+int io_bind_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_bind(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_listen_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_listen(struct io_kiocb *req, unsigned int issue_flags);
+
+void io_netmsg_cache_free(const void *entry);
+#else
+static inline void io_netmsg_cache_free(const void *entry)
+{
+}
+static inline void io_socket_bpf_populate(struct io_uring_bpf_ctx *bctx,
+					  struct io_kiocb *req)
+{
+}
+
+static inline void io_connect_bpf_populate(struct io_uring_bpf_ctx *bctx,
+					   struct io_kiocb *req)
+{
+}
+
+#endif