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, 254 insertions, 0 deletions

diff --git a/net/openvswitch/vport-netdev.c b/net/openvswitch/vport-netdev.c
new file mode 100644
index 000000000..e7e8490a5
--- /dev/null
+++ b/net/openvswitch/vport-netdev.c
@@ -0,0 +1,254 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2007-2012 Nicira, Inc.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/if_arp.h>
+#include <linux/if_bridge.h>
+#include <linux/if_vlan.h>
+#include <linux/kernel.h>
+#include <linux/llc.h>
+#include <linux/rtnetlink.h>
+#include <linux/skbuff.h>
+#include <linux/openvswitch.h>
+#include <linux/export.h>
+
+#include <net/ip_tunnels.h>
+#include <net/rtnetlink.h>
+
+#include "datapath.h"
+#include "vport.h"
+#include "vport-internal_dev.h"
+#include "vport-netdev.h"
+
+static struct vport_ops ovs_netdev_vport_ops;
+
+/* Must be called with rcu_read_lock. */
+static void netdev_port_receive(struct sk_buff *skb)
+{
+	struct vport *vport;
+
+	vport = ovs_netdev_get_vport(skb->dev);
+	if (unlikely(!vport))
+		goto error;
+
+	if (unlikely(skb_warn_if_lro(skb)))
+		goto error;
+
+	/* Make our own copy of the packet.  Otherwise we will mangle the
+	 * packet for anyone who came before us (e.g. tcpdump via AF_PACKET).
+	 */
+	skb = skb_share_check(skb, GFP_ATOMIC);
+	if (unlikely(!skb))
+		return;
+
+	if (skb->dev->type == ARPHRD_ETHER)
+		skb_push_rcsum(skb, ETH_HLEN);
+
+	ovs_vport_receive(vport, skb, skb_tunnel_info(skb));
+	return;
+error:
+	kfree_skb(skb);
+}
+
+/* Called with rcu_read_lock and bottom-halves disabled. */
+static rx_handler_result_t netdev_frame_hook(struct sk_buff **pskb)
+{
+	struct sk_buff *skb = *pskb;
+
+	if (unlikely(skb->pkt_type == PACKET_LOOPBACK))
+		return RX_HANDLER_PASS;
+
+	netdev_port_receive(skb);
+	return RX_HANDLER_CONSUMED;
+}
+
+static struct net_device *get_dpdev(const struct datapath *dp)
+{
+	struct vport *local;
+
+	local = ovs_vport_ovsl(dp, OVSP_LOCAL);
+	return local->dev;
+}
+
+struct vport *ovs_netdev_link(struct vport *vport, bool tunnel)
+{
+	int err;
+
+	if (WARN_ON_ONCE(!vport->dev)) {
+		err = -ENODEV;
+		goto error_free_vport;
+	}
+
+	rtnl_lock();
+	/* Do not link devices that are not registered to avoid a potential
+	 * race with the NETDEV_UNREGISTER notification in dp_device_event().
+	 */
+	if (vport->dev->reg_state != NETREG_REGISTERED) {
+		err = -ENODEV;
+		goto error_put_unlock;
+	}
+
+	err = netdev_master_upper_dev_link(vport->dev,
+					   get_dpdev(vport->dp),
+					   NULL, NULL, NULL);
+	if (err)
+		goto error_put_unlock;
+
+	err = netdev_rx_handler_register(vport->dev, netdev_frame_hook,
+					 vport);
+	if (err)
+		goto error_master_upper_dev_unlink;
+
+	dev_disable_lro(vport->dev);
+	dev_set_promiscuity(vport->dev, 1);
+	vport->dev->priv_flags |= IFF_OVS_DATAPATH;
+	rtnl_unlock();
+
+	return vport;
+
+error_master_upper_dev_unlink:
+	netdev_upper_dev_unlink(vport->dev, get_dpdev(vport->dp));
+error_put_unlock:
+	if (tunnel && vport->dev->reg_state == NETREG_REGISTERED)
+		rtnl_delete_link(vport->dev, 0, NULL);
+	netdev_put(vport->dev, &vport->dev_tracker);
+	rtnl_unlock();
+error_free_vport:
+	ovs_vport_free(vport);
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL_GPL(ovs_netdev_link);
+
+static struct vport *netdev_create(const struct vport_parms *parms)
+{
+	struct vport *vport;
+	int err;
+
+	vport = ovs_vport_alloc(0, &ovs_netdev_vport_ops, parms);
+	if (IS_ERR(vport))
+		return vport;
+
+	vport->dev = dev_get_by_name(ovs_dp_get_net(vport->dp), parms->name);
+	if (!vport->dev) {
+		err = -ENODEV;
+		goto error_free_vport;
+	}
+	netdev_tracker_alloc(vport->dev, &vport->dev_tracker, GFP_KERNEL);
+
+	/* Ensure that the provided name is not an alias. */
+	if (strcmp(parms->name, ovs_vport_name(vport))) {
+		err = -ENODEV;
+		goto error_put;
+	}
+
+	if (vport->dev->flags & IFF_LOOPBACK ||
+	    (vport->dev->type != ARPHRD_ETHER &&
+	     vport->dev->type != ARPHRD_NONE) ||
+	    ovs_is_internal_dev(vport->dev)) {
+		err = -EINVAL;
+		goto error_put;
+	}
+
+	return ovs_netdev_link(vport, false);
+error_put:
+	netdev_put(vport->dev, &vport->dev_tracker);
+error_free_vport:
+	ovs_vport_free(vport);
+	return ERR_PTR(err);
+}
+
+static void vport_netdev_free(struct rcu_head *rcu)
+{
+	struct vport *vport = container_of(rcu, struct vport, rcu);
+
+	netdev_put(vport->dev, &vport->dev_tracker);
+	ovs_vport_free(vport);
+}
+
+void ovs_netdev_detach_dev(struct vport *vport)
+{
+	ASSERT_RTNL();
+	netdev_rx_handler_unregister(vport->dev);
+	netdev_upper_dev_unlink(vport->dev,
+				netdev_master_upper_dev_get(vport->dev));
+	dev_set_promiscuity(vport->dev, -1);
+
+	/* paired with smp_mb() in netdev_destroy() */
+	smp_wmb();
+
+	vport->dev->priv_flags &= ~IFF_OVS_DATAPATH;
+}
+
+static void netdev_destroy(struct vport *vport)
+{
+	/* When called from ovs_db_notify_wq() after a dp_device_event(), the
+	 * port has already been detached, so we can avoid taking the RTNL by
+	 * checking this first.
+	 */
+	if (netif_is_ovs_port(vport->dev)) {
+		rtnl_lock();
+		/* Check again while holding the lock to ensure we don't race
+		 * with the netdev notifier and detach twice.
+		 */
+		if (netif_is_ovs_port(vport->dev))
+			ovs_netdev_detach_dev(vport);
+		rtnl_unlock();
+	}
+
+	/* paired with smp_wmb() in ovs_netdev_detach_dev() */
+	smp_mb();
+
+	call_rcu(&vport->rcu, vport_netdev_free);
+}
+
+void ovs_netdev_tunnel_destroy(struct vport *vport)
+{
+	rtnl_lock();
+	if (netif_is_ovs_port(vport->dev))
+		ovs_netdev_detach_dev(vport);
+
+	/* We can be invoked by both explicit vport deletion and
+	 * underlying netdev deregistration; delete the link only
+	 * if it's not already shutting down.
+	 */
+	if (vport->dev->reg_state == NETREG_REGISTERED)
+		rtnl_delete_link(vport->dev, 0, NULL);
+
+	/* We can't put the device reference yet, since it can still be in
+	 * use, but rtnl_unlock()->netdev_run_todo() will block until all
+	 * the references are released, so the RCU call must be before it.
+	 */
+	call_rcu(&vport->rcu, vport_netdev_free);
+	rtnl_unlock();
+}
+EXPORT_SYMBOL_GPL(ovs_netdev_tunnel_destroy);
+
+/* Returns null if this device is not attached to a datapath. */
+struct vport *ovs_netdev_get_vport(struct net_device *dev)
+{
+	if (likely(netif_is_ovs_port(dev)))
+		return (struct vport *)
+			rcu_dereference_rtnl(dev->rx_handler_data);
+	else
+		return NULL;
+}
+
+static struct vport_ops ovs_netdev_vport_ops = {
+	.type		= OVS_VPORT_TYPE_NETDEV,
+	.create		= netdev_create,
+	.destroy	= netdev_destroy,
+	.send		= dev_queue_xmit,
+};
+
+int __init ovs_netdev_init(void)
+{
+	return ovs_vport_ops_register(&ovs_netdev_vport_ops);
+}
+
+void ovs_netdev_exit(void)
+{
+	ovs_vport_ops_unregister(&ovs_netdev_vport_ops);
+}