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, 459 insertions, 0 deletions

diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
new file mode 100644
index 000000000..1272d49cd
--- /dev/null
+++ b/net/phonet/pn_dev.c
@@ -0,0 +1,459 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * File: pn_dev.c
+ *
+ * Phonet network device
+ *
+ * Copyright (C) 2008 Nokia Corporation.
+ *
+ * Authors: Sakari Ailus <sakari.ailus@nokia.com>
+ *          Rémi Denis-Courmont
+ */
+
+#include <linux/kernel.h>
+#include <linux/net.h>
+#include <linux/slab.h>
+#include <linux/netdevice.h>
+#include <linux/phonet.h>
+#include <linux/proc_fs.h>
+#include <linux/if_arp.h>
+#include <net/sock.h>
+#include <net/netns/generic.h>
+#include <net/phonet/pn_dev.h>
+
+struct phonet_routes {
+	spinlock_t		lock;
+	struct net_device __rcu	*table[64];
+};
+
+struct phonet_net {
+	struct phonet_device_list pndevs;
+	struct phonet_routes routes;
+};
+
+static unsigned int phonet_net_id __read_mostly;
+
+static struct phonet_net *phonet_pernet(struct net *net)
+{
+	return net_generic(net, phonet_net_id);
+}
+
+struct phonet_device_list *phonet_device_list(struct net *net)
+{
+	struct phonet_net *pnn = phonet_pernet(net);
+	return &pnn->pndevs;
+}
+
+/* Allocate new Phonet device. */
+static struct phonet_device *__phonet_device_alloc(struct net_device *dev)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
+	struct phonet_device *pnd = kmalloc_obj(*pnd, GFP_ATOMIC);
+	if (pnd == NULL)
+		return NULL;
+	pnd->netdev = dev;
+	bitmap_zero(pnd->addrs, 64);
+
+	lockdep_assert_held(&pndevs->lock);
+	list_add_rcu(&pnd->list, &pndevs->list);
+	return pnd;
+}
+
+static struct phonet_device *__phonet_get(struct net_device *dev)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
+	struct phonet_device *pnd;
+
+	lockdep_assert_held(&pndevs->lock);
+
+	list_for_each_entry(pnd, &pndevs->list, list) {
+		if (pnd->netdev == dev)
+			return pnd;
+	}
+	return NULL;
+}
+
+static struct phonet_device *__phonet_get_rcu(struct net_device *dev)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
+	struct phonet_device *pnd;
+
+	list_for_each_entry_rcu(pnd, &pndevs->list, list) {
+		if (pnd->netdev == dev)
+			return pnd;
+	}
+	return NULL;
+}
+
+static void phonet_device_destroy(struct net_device *dev)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
+	struct phonet_device *pnd;
+
+	ASSERT_RTNL();
+
+	spin_lock(&pndevs->lock);
+
+	pnd = __phonet_get(dev);
+	if (pnd)
+		list_del_rcu(&pnd->list);
+
+	spin_unlock(&pndevs->lock);
+
+	if (pnd) {
+		struct net *net = dev_net(dev);
+		u32 ifindex = dev->ifindex;
+		u8 addr;
+
+		for_each_set_bit(addr, pnd->addrs, 64)
+			phonet_address_notify(net, RTM_DELADDR, ifindex, addr);
+
+		kfree_rcu(pnd, rcu);
+	}
+}
+
+struct net_device *phonet_device_get(struct net *net)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(net);
+	struct phonet_device *pnd;
+	struct net_device *dev = NULL;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(pnd, &pndevs->list, list) {
+		dev = pnd->netdev;
+		BUG_ON(!dev);
+
+		if ((dev->reg_state == NETREG_REGISTERED) &&
+			((pnd->netdev->flags & IFF_UP)) == IFF_UP)
+			break;
+		dev = NULL;
+	}
+	dev_hold(dev);
+	rcu_read_unlock();
+	return dev;
+}
+
+int phonet_address_add(struct net_device *dev, u8 addr)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
+	struct phonet_device *pnd;
+	int err = 0;
+
+	spin_lock(&pndevs->lock);
+
+	/* Find or create Phonet-specific device data */
+	pnd = __phonet_get(dev);
+	if (pnd == NULL)
+		pnd = __phonet_device_alloc(dev);
+	if (unlikely(pnd == NULL))
+		err = -ENOMEM;
+	else if (test_and_set_bit(addr >> 2, pnd->addrs))
+		err = -EEXIST;
+
+	spin_unlock(&pndevs->lock);
+
+	return err;
+}
+
+int phonet_address_del(struct net_device *dev, u8 addr)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
+	struct phonet_device *pnd;
+	int err = 0;
+
+	spin_lock(&pndevs->lock);
+
+	pnd = __phonet_get(dev);
+	if (!pnd || !test_and_clear_bit(addr >> 2, pnd->addrs)) {
+		err = -EADDRNOTAVAIL;
+		pnd = NULL;
+	} else if (bitmap_empty(pnd->addrs, 64))
+		list_del_rcu(&pnd->list);
+	else
+		pnd = NULL;
+
+	spin_unlock(&pndevs->lock);
+
+	if (pnd)
+		kfree_rcu(pnd, rcu);
+
+	return err;
+}
+
+/* Gets a source address toward a destination, through a interface. */
+u8 phonet_address_get(struct net_device *dev, u8 daddr)
+{
+	struct phonet_device *pnd;
+	u8 saddr;
+
+	rcu_read_lock();
+	pnd = __phonet_get_rcu(dev);
+	if (pnd) {
+		BUG_ON(bitmap_empty(pnd->addrs, 64));
+
+		/* Use same source address as destination, if possible */
+		if (test_bit(daddr >> 2, pnd->addrs))
+			saddr = daddr;
+		else
+			saddr = find_first_bit(pnd->addrs, 64) << 2;
+	} else
+		saddr = PN_NO_ADDR;
+	rcu_read_unlock();
+
+	if (saddr == PN_NO_ADDR) {
+		/* Fallback to another device */
+		struct net_device *def_dev;
+
+		def_dev = phonet_device_get(dev_net(dev));
+		if (def_dev) {
+			if (def_dev != dev)
+				saddr = phonet_address_get(def_dev, daddr);
+			dev_put(def_dev);
+		}
+	}
+	return saddr;
+}
+
+int phonet_address_lookup(struct net *net, u8 addr)
+{
+	struct phonet_device_list *pndevs = phonet_device_list(net);
+	struct phonet_device *pnd;
+	int err = -EADDRNOTAVAIL;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(pnd, &pndevs->list, list) {
+		/* Don't allow unregistering devices! */
+		if ((pnd->netdev->reg_state != NETREG_REGISTERED) ||
+				((pnd->netdev->flags & IFF_UP)) != IFF_UP)
+			continue;
+
+		if (test_bit(addr >> 2, pnd->addrs)) {
+			err = 0;
+			goto found;
+		}
+	}
+found:
+	rcu_read_unlock();
+	return err;
+}
+
+/* automatically configure a Phonet device, if supported */
+static int phonet_device_autoconf(struct net_device *dev)
+{
+	struct if_phonet_req req;
+	int ret;
+
+	if (!dev->netdev_ops->ndo_siocdevprivate)
+		return -EOPNOTSUPP;
+
+	ret = dev->netdev_ops->ndo_siocdevprivate(dev, (struct ifreq *)&req,
+						  NULL, SIOCPNGAUTOCONF);
+	if (ret < 0)
+		return ret;
+
+	ASSERT_RTNL();
+	ret = phonet_address_add(dev, req.ifr_phonet_autoconf.device);
+	if (ret)
+		return ret;
+
+	phonet_address_notify(dev_net(dev), RTM_NEWADDR, dev->ifindex,
+			      req.ifr_phonet_autoconf.device);
+	return 0;
+}
+
+static void phonet_route_autodel(struct net_device *dev)
+{
+	struct net *net = dev_net(dev);
+	DECLARE_BITMAP(deleted, 64);
+	u32 ifindex = dev->ifindex;
+	struct phonet_net *pnn;
+	unsigned int i;
+
+	pnn = phonet_pernet(net);
+
+	/* Remove left-over Phonet routes */
+	bitmap_zero(deleted, 64);
+
+	spin_lock(&pnn->routes.lock);
+	for (i = 0; i < 64; i++) {
+		if (rcu_access_pointer(pnn->routes.table[i]) == dev) {
+			RCU_INIT_POINTER(pnn->routes.table[i], NULL);
+			set_bit(i, deleted);
+		}
+	}
+	spin_unlock(&pnn->routes.lock);
+
+	if (bitmap_empty(deleted, 64))
+		return; /* short-circuit RCU */
+	synchronize_rcu();
+	for_each_set_bit(i, deleted, 64) {
+		rtm_phonet_notify(net, RTM_DELROUTE, ifindex, i);
+		dev_put(dev);
+	}
+}
+
+/* notify Phonet of device events */
+static int phonet_device_notify(struct notifier_block *me, unsigned long what,
+				void *ptr)
+{
+	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
+
+	switch (what) {
+	case NETDEV_REGISTER:
+		if (dev->type == ARPHRD_PHONET)
+			phonet_device_autoconf(dev);
+		break;
+	case NETDEV_UNREGISTER:
+		phonet_device_destroy(dev);
+		phonet_route_autodel(dev);
+		break;
+	}
+	return 0;
+
+}
+
+static struct notifier_block phonet_device_notifier = {
+	.notifier_call = phonet_device_notify,
+	.priority = 0,
+};
+
+/* Per-namespace Phonet devices handling */
+static int __net_init phonet_init_net(struct net *net)
+{
+	struct phonet_net *pnn = phonet_pernet(net);
+
+	if (!proc_create_net("phonet", 0, net->proc_net, &pn_sock_seq_ops,
+			sizeof(struct seq_net_private)))
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&pnn->pndevs.list);
+	spin_lock_init(&pnn->pndevs.lock);
+	spin_lock_init(&pnn->routes.lock);
+	return 0;
+}
+
+static void __net_exit phonet_exit_net(struct net *net)
+{
+	struct phonet_net *pnn = phonet_pernet(net);
+
+	remove_proc_entry("phonet", net->proc_net);
+	WARN_ON_ONCE(!list_empty(&pnn->pndevs.list));
+}
+
+static struct pernet_operations phonet_net_ops = {
+	.init = phonet_init_net,
+	.exit = phonet_exit_net,
+	.id   = &phonet_net_id,
+	.size = sizeof(struct phonet_net),
+};
+
+/* Initialize Phonet devices list */
+int __init phonet_device_init(void)
+{
+	int err;
+
+	err = register_pernet_subsys(&phonet_net_ops);
+	if (err)
+		return err;
+
+	if (!proc_create_net("pnresource", 0, init_net.proc_net,
+			     &pn_res_seq_ops, sizeof(struct seq_net_private))) {
+		err = -ENOMEM;
+		goto err_pernet;
+	}
+
+	err = register_netdevice_notifier(&phonet_device_notifier);
+	if (err)
+		goto err_proc;
+
+	err = phonet_netlink_register();
+	if (err)
+		goto err_notifier;
+
+	return 0;
+
+err_notifier:
+	unregister_netdevice_notifier(&phonet_device_notifier);
+err_proc:
+	remove_proc_entry("pnresource", init_net.proc_net);
+err_pernet:
+	unregister_pernet_subsys(&phonet_net_ops);
+	return err;
+}
+
+void phonet_device_exit(void)
+{
+	rtnl_unregister_all(PF_PHONET);
+	unregister_netdevice_notifier(&phonet_device_notifier);
+	remove_proc_entry("pnresource", init_net.proc_net);
+	unregister_pernet_subsys(&phonet_net_ops);
+}
+
+int phonet_route_add(struct net_device *dev, u8 daddr)
+{
+	struct phonet_net *pnn = phonet_pernet(dev_net(dev));
+	struct phonet_routes *routes = &pnn->routes;
+	int err = -EEXIST;
+
+	daddr = daddr >> 2;
+
+	spin_lock(&routes->lock);
+	if (routes->table[daddr] == NULL) {
+		rcu_assign_pointer(routes->table[daddr], dev);
+		dev_hold(dev);
+		err = 0;
+	}
+	spin_unlock(&routes->lock);
+
+	return err;
+}
+
+int phonet_route_del(struct net_device *dev, u8 daddr)
+{
+	struct phonet_net *pnn = phonet_pernet(dev_net(dev));
+	struct phonet_routes *routes = &pnn->routes;
+
+	daddr = daddr >> 2;
+
+	spin_lock(&routes->lock);
+	if (rcu_access_pointer(routes->table[daddr]) == dev)
+		RCU_INIT_POINTER(routes->table[daddr], NULL);
+	else
+		dev = NULL;
+	spin_unlock(&routes->lock);
+
+	if (!dev)
+		return -ENOENT;
+
+	/* Note : our caller must call synchronize_rcu() and dev_put(dev) */
+
+	return 0;
+}
+
+struct net_device *phonet_route_get_rcu(struct net *net, u8 daddr)
+{
+	struct phonet_net *pnn = phonet_pernet(net);
+	struct phonet_routes *routes = &pnn->routes;
+	struct net_device *dev;
+
+	daddr >>= 2;
+	dev = rcu_dereference(routes->table[daddr]);
+	return dev;
+}
+
+struct net_device *phonet_route_output(struct net *net, u8 daddr)
+{
+	struct phonet_net *pnn = phonet_pernet(net);
+	struct phonet_routes *routes = &pnn->routes;
+	struct net_device *dev;
+
+	daddr >>= 2;
+	rcu_read_lock();
+	dev = rcu_dereference(routes->table[daddr]);
+	dev_hold(dev);
+	rcu_read_unlock();
+
+	if (!dev)
+		dev = phonet_device_get(net); /* Default route */
+	return dev;
+}