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, 226 insertions, 0 deletions

diff --git a/net/rds/tcp_send.c b/net/rds/tcp_send.c
new file mode 100644
index 000000000..7c52acc74
--- /dev/null
+++ b/net/rds/tcp_send.c
@@ -0,0 +1,226 @@
+/*
+ * Copyright (c) 2006, 2017 Oracle and/or its affiliates. All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/in.h>
+#include <net/tcp.h>
+
+#include "rds_single_path.h"
+#include "rds.h"
+#include "tcp.h"
+
+void rds_tcp_xmit_path_prepare(struct rds_conn_path *cp)
+{
+	struct rds_tcp_connection *tc = cp->cp_transport_data;
+
+	tcp_sock_set_cork(tc->t_sock->sk, true);
+}
+
+void rds_tcp_xmit_path_complete(struct rds_conn_path *cp)
+{
+	struct rds_tcp_connection *tc = cp->cp_transport_data;
+
+	tcp_sock_set_cork(tc->t_sock->sk, false);
+}
+
+/* the core send_sem serializes this with other xmit and shutdown */
+static int rds_tcp_sendmsg(struct socket *sock, void *data, unsigned int len)
+{
+	struct kvec vec = {
+		.iov_base = data,
+		.iov_len = len,
+	};
+	struct msghdr msg = {
+		.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL,
+	};
+
+	return kernel_sendmsg(sock, &msg, &vec, 1, vec.iov_len);
+}
+
+/* the core send_sem serializes this with other xmit and shutdown */
+int rds_tcp_xmit(struct rds_connection *conn, struct rds_message *rm,
+		 unsigned int hdr_off, unsigned int sg, unsigned int off)
+{
+	struct rds_conn_path *cp = rm->m_inc.i_conn_path;
+	struct rds_tcp_connection *tc = cp->cp_transport_data;
+	struct msghdr msg = {};
+	struct bio_vec bvec;
+	int done = 0;
+	int ret = 0;
+
+	if (hdr_off == 0) {
+		/*
+		 * m_ack_seq is set to the sequence number of the last byte of
+		 * header and data.  see rds_tcp_is_acked().
+		 */
+		tc->t_last_sent_nxt = rds_tcp_write_seq(tc);
+		rm->m_ack_seq = tc->t_last_sent_nxt +
+				sizeof(struct rds_header) +
+				be32_to_cpu(rm->m_inc.i_hdr.h_len) - 1;
+		smp_mb__before_atomic();
+		set_bit(RDS_MSG_HAS_ACK_SEQ, &rm->m_flags);
+		tc->t_last_expected_una = rm->m_ack_seq + 1;
+
+		if (test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags))
+			rm->m_inc.i_hdr.h_flags |= RDS_FLAG_RETRANSMITTED;
+
+		rdsdebug("rm %p tcp nxt %u ack_seq %llu\n",
+			 rm, rds_tcp_write_seq(tc),
+			 (unsigned long long)rm->m_ack_seq);
+	}
+
+	if (hdr_off < sizeof(struct rds_header)) {
+		/* see rds_tcp_write_space() */
+		set_bit(SOCK_NOSPACE, &tc->t_sock->sk->sk_socket->flags);
+
+		ret = rds_tcp_sendmsg(tc->t_sock,
+				      (void *)&rm->m_inc.i_hdr + hdr_off,
+				      sizeof(rm->m_inc.i_hdr) - hdr_off);
+		if (ret < 0)
+			goto out;
+		done += ret;
+		if (hdr_off + done != sizeof(struct rds_header))
+			goto out;
+	}
+
+	while (sg < rm->data.op_nents) {
+		msg.msg_flags = MSG_SPLICE_PAGES | MSG_DONTWAIT | MSG_NOSIGNAL;
+		if (sg + 1 < rm->data.op_nents)
+			msg.msg_flags |= MSG_MORE;
+
+		bvec_set_page(&bvec, sg_page(&rm->data.op_sg[sg]),
+			      rm->data.op_sg[sg].length - off,
+			      rm->data.op_sg[sg].offset + off);
+		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1,
+			      rm->data.op_sg[sg].length - off);
+		ret = sock_sendmsg(tc->t_sock, &msg);
+		rdsdebug("tcp sendpage %p:%u:%u ret %d\n", (void *)sg_page(&rm->data.op_sg[sg]),
+			 rm->data.op_sg[sg].offset + off, rm->data.op_sg[sg].length - off,
+			 ret);
+		if (ret <= 0)
+			break;
+
+		off += ret;
+		done += ret;
+		if (off == rm->data.op_sg[sg].length) {
+			off = 0;
+			sg++;
+		}
+	}
+
+out:
+	if (ret <= 0) {
+		/* write_space will hit after EAGAIN, all else fatal */
+		if (ret == -EAGAIN) {
+			rds_tcp_stats_inc(s_tcp_sndbuf_full);
+			ret = 0;
+		} else {
+			/* No need to disconnect/reconnect if path_drop
+			 * has already been triggered, because, e.g., of
+			 * an incoming RST.
+			 */
+			if (rds_conn_path_up(cp)) {
+				pr_warn("RDS/tcp: send to %pI6c on cp [%d]"
+					"returned %d, "
+					"disconnecting and reconnecting\n",
+					&conn->c_faddr, cp->cp_index, ret);
+				rds_conn_path_drop(cp, false);
+			}
+		}
+	}
+	if (done == 0)
+		done = ret;
+	return done;
+}
+
+/*
+ * rm->m_ack_seq is set to the tcp sequence number that corresponds to the
+ * last byte of the message, including the header.  This means that the
+ * entire message has been received if rm->m_ack_seq is "before" the next
+ * unacked byte of the TCP sequence space.  We have to do very careful
+ * wrapping 32bit comparisons here.
+ */
+int rds_tcp_is_acked(struct rds_message *rm, uint64_t ack)
+{
+	if (!test_bit(RDS_MSG_HAS_ACK_SEQ, &rm->m_flags))
+		return 0;
+	return (__s32)((u32)rm->m_ack_seq - (u32)ack) < 0;
+}
+
+void rds_tcp_write_space(struct sock *sk)
+{
+	void (*write_space)(struct sock *sk);
+	struct rds_conn_path *cp;
+	struct rds_tcp_connection *tc;
+
+	read_lock_bh(&sk->sk_callback_lock);
+	cp = sk->sk_user_data;
+	if (!cp) {
+		write_space = sk->sk_write_space;
+		goto out;
+	}
+
+	tc = cp->cp_transport_data;
+	rdsdebug("write_space for tc %p\n", tc);
+	write_space = tc->t_orig_write_space;
+	rds_tcp_stats_inc(s_tcp_write_space_calls);
+
+	rdsdebug("tcp una %u\n", rds_tcp_snd_una(tc));
+	tc->t_last_seen_una = rds_tcp_snd_una(tc);
+	rds_send_path_drop_acked(cp, rds_tcp_snd_una(tc), rds_tcp_is_acked);
+
+	rcu_read_lock();
+	if ((refcount_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf &&
+	    !rds_destroy_pending(cp->cp_conn))
+		queue_delayed_work(cp->cp_wq, &cp->cp_send_w, 0);
+	rcu_read_unlock();
+
+out:
+	read_unlock_bh(&sk->sk_callback_lock);
+
+	/*
+	 * write_space is only called when data leaves tcp's send queue if
+	 * SOCK_NOSPACE is set.  We set SOCK_NOSPACE every time we put
+	 * data in tcp's send queue because we use write_space to parse the
+	 * sequence numbers and notice that rds messages have been fully
+	 * received.
+	 *
+	 * tcp's write_space clears SOCK_NOSPACE if the send queue has more
+	 * than a certain amount of space. So we need to set it again *after*
+	 * we call tcp's write_space or else we might only get called on the
+	 * first of a series of incoming tcp acks.
+	 */
+	write_space(sk);
+
+	if (sk->sk_socket)
+		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+}