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, 227 insertions, 0 deletions

diff --git a/net/bluetooth/bnep/netdev.c b/net/bluetooth/bnep/netdev.c
new file mode 100644
index 000000000..ee1e39a3d
--- /dev/null
+++ b/net/bluetooth/bnep/netdev.c
@@ -0,0 +1,227 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+   BNEP implementation for Linux Bluetooth stack (BlueZ).
+   Copyright (C) 2001-2002 Inventel Systemes
+   Written 2001-2002 by
+	Clément Moreau <clement.moreau@inventel.fr>
+	David Libault  <david.libault@inventel.fr>
+
+   Copyright (C) 2002 Maxim Krasnyansky <maxk@qualcomm.com>
+
+   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 OF THIRD PARTY RIGHTS.
+   IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) AND AUTHOR(S) BE LIABLE FOR ANY
+   CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES
+   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+   ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+   ALL LIABILITY, INCLUDING LIABILITY FOR INFRINGEMENT OF ANY PATENTS,
+   COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS, RELATING TO USE OF THIS
+   SOFTWARE IS DISCLAIMED.
+*/
+
+#include <linux/etherdevice.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+#include <net/bluetooth/l2cap.h>
+
+#include "bnep.h"
+
+#define BNEP_TX_QUEUE_LEN 20
+
+static int bnep_net_open(struct net_device *dev)
+{
+	netif_start_queue(dev);
+	return 0;
+}
+
+static int bnep_net_close(struct net_device *dev)
+{
+	netif_stop_queue(dev);
+	return 0;
+}
+
+static void bnep_net_set_mc_list(struct net_device *dev)
+{
+#ifdef CONFIG_BT_BNEP_MC_FILTER
+	struct bnep_session *s = netdev_priv(dev);
+	struct sock *sk = s->sock->sk;
+	struct bnep_set_filter_req *r;
+	struct sk_buff *skb;
+	int size;
+
+	BT_DBG("%s mc_count %d", dev->name, netdev_mc_count(dev));
+
+	size = sizeof(*r) + (BNEP_MAX_MULTICAST_FILTERS + 1) * ETH_ALEN * 2;
+	skb  = alloc_skb(size, GFP_ATOMIC);
+	if (!skb) {
+		BT_ERR("%s Multicast list allocation failed", dev->name);
+		return;
+	}
+
+	r = (void *) skb->data;
+	__skb_put(skb, sizeof(*r));
+
+	r->type = BNEP_CONTROL;
+	r->ctrl = BNEP_FILTER_MULTI_ADDR_SET;
+
+	if (dev->flags & (IFF_PROMISC | IFF_ALLMULTI)) {
+		u8 start[ETH_ALEN] = { 0x01 };
+
+		/* Request all addresses */
+		__skb_put_data(skb, start, ETH_ALEN);
+		__skb_put_data(skb, dev->broadcast, ETH_ALEN);
+		r->len = htons(ETH_ALEN * 2);
+	} else {
+		struct netdev_hw_addr *ha;
+		int i, len = skb->len;
+
+		if (dev->flags & IFF_BROADCAST) {
+			__skb_put_data(skb, dev->broadcast, ETH_ALEN);
+			__skb_put_data(skb, dev->broadcast, ETH_ALEN);
+		}
+
+		/* FIXME: We should group addresses here. */
+
+		i = 0;
+		netdev_for_each_mc_addr(ha, dev) {
+			if (i == BNEP_MAX_MULTICAST_FILTERS)
+				break;
+			__skb_put_data(skb, ha->addr, ETH_ALEN);
+			__skb_put_data(skb, ha->addr, ETH_ALEN);
+
+			i++;
+		}
+		r->len = htons(skb->len - len);
+	}
+
+	skb_queue_tail(&sk->sk_write_queue, skb);
+	wake_up_interruptible(sk_sleep(sk));
+#endif
+}
+
+static int bnep_net_set_mac_addr(struct net_device *dev, void *arg)
+{
+	BT_DBG("%s", dev->name);
+	return 0;
+}
+
+static void bnep_net_timeout(struct net_device *dev, unsigned int txqueue)
+{
+	BT_DBG("net_timeout");
+	netif_wake_queue(dev);
+}
+
+#ifdef CONFIG_BT_BNEP_MC_FILTER
+static int bnep_net_mc_filter(struct sk_buff *skb, struct bnep_session *s)
+{
+	struct ethhdr *eh = (void *) skb->data;
+
+	if ((eh->h_dest[0] & 1) && !test_bit(bnep_mc_hash(eh->h_dest), (ulong *) &s->mc_filter))
+		return 1;
+	return 0;
+}
+#endif
+
+#ifdef CONFIG_BT_BNEP_PROTO_FILTER
+/* Determine ether protocol. Based on eth_type_trans. */
+static u16 bnep_net_eth_proto(struct sk_buff *skb)
+{
+	struct ethhdr *eh = (void *) skb->data;
+	u16 proto = ntohs(eh->h_proto);
+
+	if (proto >= ETH_P_802_3_MIN)
+		return proto;
+
+	if (get_unaligned((__be16 *) skb->data) == htons(0xFFFF))
+		return ETH_P_802_3;
+
+	return ETH_P_802_2;
+}
+
+static int bnep_net_proto_filter(struct sk_buff *skb, struct bnep_session *s)
+{
+	u16 proto = bnep_net_eth_proto(skb);
+	struct bnep_proto_filter *f = s->proto_filter;
+	int i;
+
+	for (i = 0; i < BNEP_MAX_PROTO_FILTERS && f[i].end; i++) {
+		if (proto >= f[i].start && proto <= f[i].end)
+			return 0;
+	}
+
+	BT_DBG("BNEP: filtered skb %p, proto 0x%.4x", skb, proto);
+	return 1;
+}
+#endif
+
+static netdev_tx_t bnep_net_xmit(struct sk_buff *skb,
+				 struct net_device *dev)
+{
+	struct bnep_session *s = netdev_priv(dev);
+	struct sock *sk = s->sock->sk;
+
+	BT_DBG("skb %p, dev %p", skb, dev);
+
+#ifdef CONFIG_BT_BNEP_MC_FILTER
+	if (bnep_net_mc_filter(skb, s)) {
+		kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+#endif
+
+#ifdef CONFIG_BT_BNEP_PROTO_FILTER
+	if (bnep_net_proto_filter(skb, s)) {
+		kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+#endif
+
+	/*
+	 * We cannot send L2CAP packets from here as we are potentially in a bh.
+	 * So we have to queue them and wake up session thread which is sleeping
+	 * on the sk_sleep(sk).
+	 */
+	netif_trans_update(dev);
+	skb_queue_tail(&sk->sk_write_queue, skb);
+	wake_up_interruptible(sk_sleep(sk));
+
+	if (skb_queue_len(&sk->sk_write_queue) >= BNEP_TX_QUEUE_LEN) {
+		BT_DBG("tx queue is full");
+
+		/* Stop queuing.
+		 * Session thread will do netif_wake_queue() */
+		netif_stop_queue(dev);
+	}
+
+	return NETDEV_TX_OK;
+}
+
+static const struct net_device_ops bnep_netdev_ops = {
+	.ndo_open            = bnep_net_open,
+	.ndo_stop            = bnep_net_close,
+	.ndo_start_xmit	     = bnep_net_xmit,
+	.ndo_validate_addr   = eth_validate_addr,
+	.ndo_set_rx_mode     = bnep_net_set_mc_list,
+	.ndo_set_mac_address = bnep_net_set_mac_addr,
+	.ndo_tx_timeout      = bnep_net_timeout,
+
+};
+
+void bnep_net_setup(struct net_device *dev)
+{
+
+	eth_broadcast_addr(dev->broadcast);
+	dev->addr_len = ETH_ALEN;
+
+	ether_setup(dev);
+	dev->min_mtu = 0;
+	dev->max_mtu = ETH_MAX_MTU;
+	dev->priv_flags &= ~IFF_TX_SKB_SHARING;
+	dev->netdev_ops = &bnep_netdev_ops;
+
+	dev->watchdog_timeo  = HZ * 2;
+}