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, 458 insertions, 0 deletions

diff --git a/net/rxrpc/peer_event.c b/net/rxrpc/peer_event.c
new file mode 100644
index 000000000..9d02448ac
--- /dev/null
+++ b/net/rxrpc/peer_event.c
@@ -0,0 +1,458 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Peer event handling, typically ICMP messages.
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/module.h>
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/errqueue.h>
+#include <linux/udp.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <linux/icmp.h>
+#include <net/sock.h>
+#include <net/af_rxrpc.h>
+#include <net/ip.h>
+#include "ar-internal.h"
+
+static void rxrpc_store_error(struct rxrpc_peer *, struct sk_buff *);
+static void rxrpc_distribute_error(struct rxrpc_peer *, struct sk_buff *,
+				   enum rxrpc_call_completion, int);
+
+/*
+ * Find the peer associated with a local error.
+ */
+static struct rxrpc_peer *rxrpc_lookup_peer_local_rcu(struct rxrpc_local *local,
+						      const struct sk_buff *skb,
+						      struct sockaddr_rxrpc *srx)
+{
+	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
+
+	_enter("");
+
+	memset(srx, 0, sizeof(*srx));
+	srx->transport_type = local->srx.transport_type;
+	srx->transport_len = local->srx.transport_len;
+	srx->transport.family = local->srx.transport.family;
+
+	/* Can we see an ICMP4 packet on an ICMP6 listening socket?  and vice
+	 * versa?
+	 */
+	switch (srx->transport.family) {
+	case AF_INET:
+		srx->transport_len = sizeof(srx->transport.sin);
+		srx->transport.family = AF_INET;
+		srx->transport.sin.sin_port = serr->port;
+		switch (serr->ee.ee_origin) {
+		case SO_EE_ORIGIN_ICMP:
+			memcpy(&srx->transport.sin.sin_addr,
+			       skb_network_header(skb) + serr->addr_offset,
+			       sizeof(struct in_addr));
+			break;
+		case SO_EE_ORIGIN_ICMP6:
+			memcpy(&srx->transport.sin.sin_addr,
+			       skb_network_header(skb) + serr->addr_offset + 12,
+			       sizeof(struct in_addr));
+			break;
+		default:
+			memcpy(&srx->transport.sin.sin_addr, &ip_hdr(skb)->saddr,
+			       sizeof(struct in_addr));
+			break;
+		}
+		break;
+
+#ifdef CONFIG_AF_RXRPC_IPV6
+	case AF_INET6:
+		switch (serr->ee.ee_origin) {
+		case SO_EE_ORIGIN_ICMP6:
+			srx->transport.sin6.sin6_port = serr->port;
+			memcpy(&srx->transport.sin6.sin6_addr,
+			       skb_network_header(skb) + serr->addr_offset,
+			       sizeof(struct in6_addr));
+			break;
+		case SO_EE_ORIGIN_ICMP:
+			srx->transport_len = sizeof(srx->transport.sin);
+			srx->transport.family = AF_INET;
+			srx->transport.sin.sin_port = serr->port;
+			memcpy(&srx->transport.sin.sin_addr,
+			       skb_network_header(skb) + serr->addr_offset,
+			       sizeof(struct in_addr));
+			break;
+		default:
+			memcpy(&srx->transport.sin6.sin6_addr,
+			       &ipv6_hdr(skb)->saddr,
+			       sizeof(struct in6_addr));
+			break;
+		}
+		break;
+#endif
+
+	default:
+		BUG();
+	}
+
+	return rxrpc_lookup_peer_rcu(local, srx);
+}
+
+/*
+ * Handle an MTU/fragmentation problem.
+ */
+static void rxrpc_adjust_mtu(struct rxrpc_peer *peer, unsigned int mtu)
+{
+	unsigned int max_data;
+
+	/* wind down the local interface MTU */
+	if (mtu > 0 && peer->if_mtu == 65535 && mtu < peer->if_mtu)
+		peer->if_mtu = mtu;
+
+	if (mtu == 0) {
+		/* they didn't give us a size, estimate one */
+		mtu = peer->if_mtu;
+		if (mtu > 1500) {
+			mtu >>= 1;
+			if (mtu < 1500)
+				mtu = 1500;
+		} else {
+			mtu -= 100;
+			if (mtu < peer->hdrsize)
+				mtu = peer->hdrsize + 4;
+		}
+	}
+
+	max_data = max_t(int, mtu - peer->hdrsize, 500);
+	if (max_data < peer->max_data) {
+		if (peer->pmtud_good > max_data)
+			peer->pmtud_good = max_data;
+		if (peer->pmtud_bad > max_data + 1)
+			peer->pmtud_bad = max_data + 1;
+
+		trace_rxrpc_pmtud_reduce(peer, 0, max_data, rxrpc_pmtud_reduce_icmp);
+		peer->max_data = max_data;
+	}
+}
+
+/*
+ * Handle an error received on the local endpoint.
+ */
+void rxrpc_input_error(struct rxrpc_local *local, struct sk_buff *skb)
+{
+	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
+	struct sockaddr_rxrpc srx;
+	struct rxrpc_peer *peer = NULL;
+
+	_enter("L=%x", local->debug_id);
+
+	if (!skb->len && serr->ee.ee_origin == SO_EE_ORIGIN_TIMESTAMPING) {
+		_leave("UDP empty message");
+		return;
+	}
+
+	rcu_read_lock();
+	peer = rxrpc_lookup_peer_local_rcu(local, skb, &srx);
+	if (peer && !rxrpc_get_peer_maybe(peer, rxrpc_peer_get_input_error))
+		peer = NULL;
+	rcu_read_unlock();
+	if (!peer)
+		return;
+
+	trace_rxrpc_rx_icmp(peer, &serr->ee, &srx);
+
+	if ((serr->ee.ee_origin == SO_EE_ORIGIN_ICMP &&
+	     serr->ee.ee_type == ICMP_DEST_UNREACH &&
+	     serr->ee.ee_code == ICMP_FRAG_NEEDED)) {
+		rxrpc_adjust_mtu(peer, serr->ee.ee_info);
+		goto out;
+	}
+
+	if ((serr->ee.ee_origin == SO_EE_ORIGIN_ICMP6 &&
+	     serr->ee.ee_type == ICMPV6_PKT_TOOBIG &&
+	     serr->ee.ee_code == 0)) {
+		rxrpc_adjust_mtu(peer, serr->ee.ee_info);
+		goto out;
+	}
+
+	rxrpc_store_error(peer, skb);
+out:
+	rxrpc_put_peer(peer, rxrpc_peer_put_input_error);
+}
+
+/*
+ * Map an error report to error codes on the peer record.
+ */
+static void rxrpc_store_error(struct rxrpc_peer *peer, struct sk_buff *skb)
+{
+	enum rxrpc_call_completion compl = RXRPC_CALL_NETWORK_ERROR;
+	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
+	struct sock_extended_err *ee = &serr->ee;
+	int err = ee->ee_errno;
+
+	_enter("");
+
+	switch (ee->ee_origin) {
+	case SO_EE_ORIGIN_NONE:
+	case SO_EE_ORIGIN_LOCAL:
+		compl = RXRPC_CALL_LOCAL_ERROR;
+		break;
+
+	case SO_EE_ORIGIN_ICMP6:
+		if (err == EACCES)
+			err = EHOSTUNREACH;
+		fallthrough;
+	case SO_EE_ORIGIN_ICMP:
+	default:
+		break;
+	}
+
+	rxrpc_distribute_error(peer, skb, compl, err);
+}
+
+/*
+ * Distribute an error that occurred on a peer.
+ */
+static void rxrpc_distribute_error(struct rxrpc_peer *peer, struct sk_buff *skb,
+				   enum rxrpc_call_completion compl, int err)
+{
+	struct rxrpc_call *call;
+	HLIST_HEAD(error_targets);
+
+	spin_lock_irq(&peer->lock);
+	hlist_move_list(&peer->error_targets, &error_targets);
+
+	while (!hlist_empty(&error_targets)) {
+		call = hlist_entry(error_targets.first,
+				   struct rxrpc_call, error_link);
+		hlist_del_init(&call->error_link);
+		spin_unlock_irq(&peer->lock);
+
+		rxrpc_see_call(call, rxrpc_call_see_distribute_error);
+		rxrpc_set_call_completion(call, compl, 0, -err);
+		rxrpc_input_call_event(call);
+
+		spin_lock_irq(&peer->lock);
+	}
+
+	spin_unlock_irq(&peer->lock);
+}
+
+/*
+ * Reconstruct the last transmission time.  The difference calculated should be
+ * valid provided no more than ~68 years elapsed since the last transmission.
+ */
+static time64_t rxrpc_peer_get_tx_mark(const struct rxrpc_peer *peer, time64_t base)
+{
+	s32 last_tx_at = READ_ONCE(peer->last_tx_at);
+	s32 base_lsw = base;
+	s32 diff = last_tx_at - base_lsw;
+
+	diff = clamp(diff, -RXRPC_KEEPALIVE_TIME, RXRPC_KEEPALIVE_TIME);
+
+	return diff + base;
+}
+
+/*
+ * Perform keep-alive pings.
+ */
+static void rxrpc_peer_keepalive_dispatch(struct rxrpc_net *rxnet,
+					  struct list_head *collector,
+					  time64_t base,
+					  u8 cursor)
+{
+	struct rxrpc_peer *peer;
+	const u8 mask = ARRAY_SIZE(rxnet->peer_keepalive) - 1;
+	time64_t keepalive_at;
+	bool use;
+	int slot;
+
+	spin_lock_bh(&rxnet->peer_hash_lock);
+
+	while (!list_empty(collector)) {
+		peer = list_entry(collector->next,
+				  struct rxrpc_peer, keepalive_link);
+
+		list_del_init(&peer->keepalive_link);
+		if (!rxrpc_get_peer_maybe(peer, rxrpc_peer_get_keepalive))
+			continue;
+
+		use = __rxrpc_use_local(peer->local, rxrpc_local_use_peer_keepalive);
+		spin_unlock_bh(&rxnet->peer_hash_lock);
+
+		if (use) {
+			keepalive_at = rxrpc_peer_get_tx_mark(peer, base) + RXRPC_KEEPALIVE_TIME;
+			slot = keepalive_at - base;
+			_debug("%02x peer %u t=%d {%pISp}",
+			       cursor, peer->debug_id, slot, &peer->srx.transport);
+
+			if (keepalive_at <= base ||
+			    keepalive_at > base + RXRPC_KEEPALIVE_TIME) {
+				rxrpc_send_keepalive(peer);
+				slot = RXRPC_KEEPALIVE_TIME;
+			}
+
+			/* A transmission to this peer occurred since last we
+			 * examined it so put it into the appropriate future
+			 * bucket.
+			 */
+			slot += cursor;
+			slot &= mask;
+			spin_lock_bh(&rxnet->peer_hash_lock);
+			list_add_tail(&peer->keepalive_link,
+				      &rxnet->peer_keepalive[slot & mask]);
+			spin_unlock_bh(&rxnet->peer_hash_lock);
+			rxrpc_unuse_local(peer->local, rxrpc_local_unuse_peer_keepalive);
+		}
+		rxrpc_put_peer(peer, rxrpc_peer_put_keepalive);
+		spin_lock_bh(&rxnet->peer_hash_lock);
+	}
+
+	spin_unlock_bh(&rxnet->peer_hash_lock);
+}
+
+/*
+ * Perform keep-alive pings with VERSION packets to keep any NAT alive.
+ */
+void rxrpc_peer_keepalive_worker(struct work_struct *work)
+{
+	struct rxrpc_net *rxnet =
+		container_of(work, struct rxrpc_net, peer_keepalive_work);
+	const u8 mask = ARRAY_SIZE(rxnet->peer_keepalive) - 1;
+	time64_t base, now, delay;
+	u8 cursor, stop;
+	LIST_HEAD(collector);
+
+	now = ktime_get_seconds();
+	base = rxnet->peer_keepalive_base;
+	cursor = rxnet->peer_keepalive_cursor;
+	_enter("%lld,%u", base - now, cursor);
+
+	if (!rxnet->live)
+		return;
+
+	/* Remove to a temporary list all the peers that are currently lodged
+	 * in expired buckets plus all new peers.
+	 *
+	 * Everything in the bucket at the cursor is processed this
+	 * second; the bucket at cursor + 1 goes at now + 1s and so
+	 * on...
+	 */
+	spin_lock_bh(&rxnet->peer_hash_lock);
+	list_splice_init(&rxnet->peer_keepalive_new, &collector);
+
+	stop = cursor + ARRAY_SIZE(rxnet->peer_keepalive);
+	while (base <= now && (s8)(cursor - stop) < 0) {
+		list_splice_tail_init(&rxnet->peer_keepalive[cursor & mask],
+				      &collector);
+		base++;
+		cursor++;
+	}
+
+	base = now;
+	spin_unlock_bh(&rxnet->peer_hash_lock);
+
+	rxnet->peer_keepalive_base = base;
+	rxnet->peer_keepalive_cursor = cursor;
+	rxrpc_peer_keepalive_dispatch(rxnet, &collector, base, cursor);
+	ASSERT(list_empty(&collector));
+
+	/* Schedule the timer for the next occupied timeslot. */
+	cursor = rxnet->peer_keepalive_cursor;
+	stop = cursor + RXRPC_KEEPALIVE_TIME - 1;
+	for (; (s8)(cursor - stop) < 0; cursor++) {
+		if (!list_empty(&rxnet->peer_keepalive[cursor & mask]))
+			break;
+		base++;
+	}
+
+	now = ktime_get_seconds();
+	delay = base - now;
+	if (delay < 1)
+		delay = 1;
+	delay *= HZ;
+	if (rxnet->live)
+		timer_reduce(&rxnet->peer_keepalive_timer, jiffies + delay);
+
+	_leave("");
+}
+
+/*
+ * Do path MTU probing.
+ */
+void rxrpc_input_probe_for_pmtud(struct rxrpc_connection *conn, rxrpc_serial_t acked_serial,
+				 bool sendmsg_fail)
+{
+	struct rxrpc_peer *peer = conn->peer;
+	unsigned int max_data = peer->max_data;
+	int good, trial, bad, jumbo;
+
+	good  = peer->pmtud_good;
+	trial = peer->pmtud_trial;
+	bad   = peer->pmtud_bad;
+	if (good >= bad - 1) {
+		conn->pmtud_probe = 0;
+		peer->pmtud_lost = false;
+		return;
+	}
+
+	if (!peer->pmtud_probing)
+		goto send_probe;
+
+	if (sendmsg_fail || after(acked_serial, conn->pmtud_probe)) {
+		/* Retry a lost probe. */
+		if (!peer->pmtud_lost) {
+			trace_rxrpc_pmtud_lost(conn, acked_serial);
+			conn->pmtud_probe = 0;
+			peer->pmtud_lost = true;
+			goto send_probe;
+		}
+
+		/* The probed size didn't seem to get through. */
+		bad = trial;
+		peer->pmtud_bad = bad;
+		if (bad <= max_data)
+			max_data = bad - 1;
+	} else {
+		/* It did get through. */
+		good = trial;
+		peer->pmtud_good = good;
+		if (good > max_data)
+			max_data = good;
+	}
+
+	max_data = umin(max_data, peer->ackr_max_data);
+	if (max_data != peer->max_data)
+		peer->max_data = max_data;
+
+	jumbo = max_data + sizeof(struct rxrpc_jumbo_header);
+	jumbo /= RXRPC_JUMBO_SUBPKTLEN;
+	peer->pmtud_jumbo = jumbo;
+
+	trace_rxrpc_pmtud_rx(conn, acked_serial);
+	conn->pmtud_probe = 0;
+	peer->pmtud_lost = false;
+
+	if (good < RXRPC_JUMBO(2) && bad > RXRPC_JUMBO(2))
+		trial = RXRPC_JUMBO(2);
+	else if (good < RXRPC_JUMBO(4) && bad > RXRPC_JUMBO(4))
+		trial = RXRPC_JUMBO(4);
+	else if (good < RXRPC_JUMBO(3) && bad > RXRPC_JUMBO(3))
+		trial = RXRPC_JUMBO(3);
+	else if (good < RXRPC_JUMBO(6) && bad > RXRPC_JUMBO(6))
+		trial = RXRPC_JUMBO(6);
+	else if (good < RXRPC_JUMBO(5) && bad > RXRPC_JUMBO(5))
+		trial = RXRPC_JUMBO(5);
+	else if (good < RXRPC_JUMBO(8) && bad > RXRPC_JUMBO(8))
+		trial = RXRPC_JUMBO(8);
+	else if (good < RXRPC_JUMBO(7) && bad > RXRPC_JUMBO(7))
+		trial = RXRPC_JUMBO(7);
+	else
+		trial = (good + bad) / 2;
+	peer->pmtud_trial = trial;
+
+	if (good >= bad)
+		return;
+
+send_probe:
+	peer->pmtud_pending = true;
+}