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, 367 insertions, 0 deletions

diff --git a/net/sched/act_sample.c b/net/sched/act_sample.c
new file mode 100644
index 000000000..2ceb4d141
--- /dev/null
+++ b/net/sched/act_sample.c
@@ -0,0 +1,367 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * net/sched/act_sample.c - Packet sampling tc action
+ * Copyright (c) 2017 Yotam Gigi <yotamg@mellanox.com>
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/skbuff.h>
+#include <linux/rtnetlink.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/gfp.h>
+#include <net/net_namespace.h>
+#include <net/netlink.h>
+#include <net/pkt_sched.h>
+#include <linux/tc_act/tc_sample.h>
+#include <net/tc_act/tc_sample.h>
+#include <net/psample.h>
+#include <net/pkt_cls.h>
+#include <net/tc_wrapper.h>
+
+#include <linux/if_arp.h>
+
+static struct tc_action_ops act_sample_ops;
+
+static const struct nla_policy sample_policy[TCA_SAMPLE_MAX + 1] = {
+	[TCA_SAMPLE_PARMS]		= { .len = sizeof(struct tc_sample) },
+	[TCA_SAMPLE_RATE]		= { .type = NLA_U32 },
+	[TCA_SAMPLE_TRUNC_SIZE]		= { .type = NLA_U32 },
+	[TCA_SAMPLE_PSAMPLE_GROUP]	= { .type = NLA_U32 },
+};
+
+static int tcf_sample_init(struct net *net, struct nlattr *nla,
+			   struct nlattr *est, struct tc_action **a,
+			   struct tcf_proto *tp,
+			   u32 flags, struct netlink_ext_ack *extack)
+{
+	struct tc_action_net *tn = net_generic(net, act_sample_ops.net_id);
+	bool bind = flags & TCA_ACT_FLAGS_BIND;
+	struct nlattr *tb[TCA_SAMPLE_MAX + 1];
+	struct psample_group *psample_group;
+	u32 psample_group_num, rate, index;
+	struct tcf_chain *goto_ch = NULL;
+	struct tc_sample *parm;
+	struct tcf_sample *s;
+	bool exists = false;
+	int ret, err;
+
+	if (!nla)
+		return -EINVAL;
+	ret = nla_parse_nested_deprecated(tb, TCA_SAMPLE_MAX, nla,
+					  sample_policy, NULL);
+	if (ret < 0)
+		return ret;
+
+	if (!tb[TCA_SAMPLE_PARMS])
+		return -EINVAL;
+
+	parm = nla_data(tb[TCA_SAMPLE_PARMS]);
+	index = parm->index;
+	err = tcf_idr_check_alloc(tn, &index, a, bind);
+	if (err < 0)
+		return err;
+	exists = err;
+	if (exists && bind)
+		return ACT_P_BOUND;
+
+	if (!exists) {
+		ret = tcf_idr_create(tn, index, est, a,
+				     &act_sample_ops, bind, true, flags);
+		if (ret) {
+			tcf_idr_cleanup(tn, index);
+			return ret;
+		}
+		ret = ACT_P_CREATED;
+	} else if (!(flags & TCA_ACT_FLAGS_REPLACE)) {
+		tcf_idr_release(*a, bind);
+		return -EEXIST;
+	}
+
+	if (!tb[TCA_SAMPLE_RATE] || !tb[TCA_SAMPLE_PSAMPLE_GROUP]) {
+		NL_SET_ERR_MSG(extack, "sample rate and group are required");
+		err = -EINVAL;
+		goto release_idr;
+	}
+
+	err = tcf_action_check_ctrlact(parm->action, tp, &goto_ch, extack);
+	if (err < 0)
+		goto release_idr;
+
+	rate = nla_get_u32(tb[TCA_SAMPLE_RATE]);
+	if (!rate) {
+		NL_SET_ERR_MSG(extack, "invalid sample rate");
+		err = -EINVAL;
+		goto put_chain;
+	}
+	psample_group_num = nla_get_u32(tb[TCA_SAMPLE_PSAMPLE_GROUP]);
+	psample_group = psample_group_get(net, psample_group_num);
+	if (!psample_group) {
+		err = -ENOMEM;
+		goto put_chain;
+	}
+
+	s = to_sample(*a);
+
+	spin_lock_bh(&s->tcf_lock);
+	goto_ch = tcf_action_set_ctrlact(*a, parm->action, goto_ch);
+	s->rate = rate;
+	s->psample_group_num = psample_group_num;
+	psample_group = rcu_replace_pointer(s->psample_group, psample_group,
+					    lockdep_is_held(&s->tcf_lock));
+
+	if (tb[TCA_SAMPLE_TRUNC_SIZE]) {
+		s->truncate = true;
+		s->trunc_size = nla_get_u32(tb[TCA_SAMPLE_TRUNC_SIZE]);
+	}
+	spin_unlock_bh(&s->tcf_lock);
+
+	if (psample_group)
+		psample_group_put(psample_group);
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+
+	return ret;
+put_chain:
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+release_idr:
+	tcf_idr_release(*a, bind);
+	return err;
+}
+
+static void tcf_sample_cleanup(struct tc_action *a)
+{
+	struct tcf_sample *s = to_sample(a);
+	struct psample_group *psample_group;
+
+	/* last reference to action, no need to lock */
+	psample_group = rcu_dereference_protected(s->psample_group, 1);
+	RCU_INIT_POINTER(s->psample_group, NULL);
+	if (psample_group)
+		psample_group_put(psample_group);
+}
+
+static bool tcf_sample_dev_ok_push(struct net_device *dev)
+{
+	switch (dev->type) {
+	case ARPHRD_TUNNEL:
+	case ARPHRD_TUNNEL6:
+	case ARPHRD_SIT:
+	case ARPHRD_IPGRE:
+	case ARPHRD_IP6GRE:
+	case ARPHRD_VOID:
+	case ARPHRD_NONE:
+		return false;
+	default:
+		return true;
+	}
+}
+
+TC_INDIRECT_SCOPE int tcf_sample_act(struct sk_buff *skb,
+				     const struct tc_action *a,
+				     struct tcf_result *res)
+{
+	struct tcf_sample *s = to_sample(a);
+	struct psample_group *psample_group;
+	u8 cookie_data[TC_COOKIE_MAX_SIZE];
+	struct psample_metadata md = {};
+	struct tc_cookie *user_cookie;
+	int retval;
+
+	tcf_lastuse_update(&s->tcf_tm);
+	bstats_update(this_cpu_ptr(s->common.cpu_bstats), skb);
+	retval = READ_ONCE(s->tcf_action);
+
+	psample_group = rcu_dereference_bh(s->psample_group);
+
+	/* randomly sample packets according to rate */
+	if (psample_group && (get_random_u32_below(s->rate) == 0)) {
+		if (!skb_at_tc_ingress(skb)) {
+			md.in_ifindex = skb->skb_iif;
+			md.out_ifindex = skb->dev->ifindex;
+		} else {
+			md.in_ifindex = skb->dev->ifindex;
+		}
+
+		/* on ingress, the mac header gets popped, so push it back */
+		if (skb_at_tc_ingress(skb) && tcf_sample_dev_ok_push(skb->dev))
+			skb_push(skb, skb->mac_len);
+
+		rcu_read_lock();
+		user_cookie = rcu_dereference(a->user_cookie);
+		if (user_cookie) {
+			memcpy(cookie_data, user_cookie->data,
+			       user_cookie->len);
+			md.user_cookie = cookie_data;
+			md.user_cookie_len = user_cookie->len;
+		}
+		rcu_read_unlock();
+
+		md.trunc_size = s->truncate ? s->trunc_size : skb->len;
+		psample_sample_packet(psample_group, skb, s->rate, &md);
+
+		if (skb_at_tc_ingress(skb) && tcf_sample_dev_ok_push(skb->dev))
+			skb_pull(skb, skb->mac_len);
+	}
+
+	return retval;
+}
+
+static void tcf_sample_stats_update(struct tc_action *a, u64 bytes, u64 packets,
+				    u64 drops, u64 lastuse, bool hw)
+{
+	struct tcf_sample *s = to_sample(a);
+	struct tcf_t *tm = &s->tcf_tm;
+
+	tcf_action_update_stats(a, bytes, packets, drops, hw);
+	tm->lastuse = max_t(u64, tm->lastuse, lastuse);
+}
+
+static int tcf_sample_dump(struct sk_buff *skb, struct tc_action *a,
+			   int bind, int ref)
+{
+	unsigned char *b = skb_tail_pointer(skb);
+	struct tcf_sample *s = to_sample(a);
+	struct tc_sample opt = {
+		.index      = s->tcf_index,
+		.refcnt     = refcount_read(&s->tcf_refcnt) - ref,
+		.bindcnt    = atomic_read(&s->tcf_bindcnt) - bind,
+	};
+	struct tcf_t t;
+
+	spin_lock_bh(&s->tcf_lock);
+	opt.action = s->tcf_action;
+	if (nla_put(skb, TCA_SAMPLE_PARMS, sizeof(opt), &opt))
+		goto nla_put_failure;
+
+	tcf_tm_dump(&t, &s->tcf_tm);
+	if (nla_put_64bit(skb, TCA_SAMPLE_TM, sizeof(t), &t, TCA_SAMPLE_PAD))
+		goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_SAMPLE_RATE, s->rate))
+		goto nla_put_failure;
+
+	if (s->truncate)
+		if (nla_put_u32(skb, TCA_SAMPLE_TRUNC_SIZE, s->trunc_size))
+			goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_SAMPLE_PSAMPLE_GROUP, s->psample_group_num))
+		goto nla_put_failure;
+	spin_unlock_bh(&s->tcf_lock);
+
+	return skb->len;
+
+nla_put_failure:
+	spin_unlock_bh(&s->tcf_lock);
+	nlmsg_trim(skb, b);
+	return -1;
+}
+
+static void tcf_psample_group_put(void *priv)
+{
+	struct psample_group *group = priv;
+
+	psample_group_put(group);
+}
+
+static struct psample_group *
+tcf_sample_get_group(const struct tc_action *a,
+		     tc_action_priv_destructor *destructor)
+{
+	struct tcf_sample *s = to_sample(a);
+	struct psample_group *group;
+
+	group = rcu_dereference_protected(s->psample_group,
+					  lockdep_is_held(&s->tcf_lock));
+	if (group) {
+		psample_group_take(group);
+		*destructor = tcf_psample_group_put;
+	}
+
+	return group;
+}
+
+static void tcf_offload_sample_get_group(struct flow_action_entry *entry,
+					 const struct tc_action *act)
+{
+	entry->sample.psample_group =
+		act->ops->get_psample_group(act, &entry->destructor);
+	entry->destructor_priv = entry->sample.psample_group;
+}
+
+static int tcf_sample_offload_act_setup(struct tc_action *act, void *entry_data,
+					u32 *index_inc, bool bind,
+					struct netlink_ext_ack *extack)
+{
+	if (bind) {
+		struct flow_action_entry *entry = entry_data;
+
+		entry->id = FLOW_ACTION_SAMPLE;
+		entry->sample.trunc_size = tcf_sample_trunc_size(act);
+		entry->sample.truncate = tcf_sample_truncate(act);
+		entry->sample.rate = tcf_sample_rate(act);
+		tcf_offload_sample_get_group(entry, act);
+		*index_inc = 1;
+	} else {
+		struct flow_offload_action *fl_action = entry_data;
+
+		fl_action->id = FLOW_ACTION_SAMPLE;
+	}
+
+	return 0;
+}
+
+static struct tc_action_ops act_sample_ops = {
+	.kind	  = "sample",
+	.id	  = TCA_ID_SAMPLE,
+	.owner	  = THIS_MODULE,
+	.act	  = tcf_sample_act,
+	.stats_update = tcf_sample_stats_update,
+	.dump	  = tcf_sample_dump,
+	.init	  = tcf_sample_init,
+	.cleanup  = tcf_sample_cleanup,
+	.get_psample_group = tcf_sample_get_group,
+	.offload_act_setup    = tcf_sample_offload_act_setup,
+	.size	  = sizeof(struct tcf_sample),
+};
+MODULE_ALIAS_NET_ACT("sample");
+
+static __net_init int sample_init_net(struct net *net)
+{
+	struct tc_action_net *tn = net_generic(net, act_sample_ops.net_id);
+
+	return tc_action_net_init(net, tn, &act_sample_ops);
+}
+
+static void __net_exit sample_exit_net(struct list_head *net_list)
+{
+	tc_action_net_exit(net_list, act_sample_ops.net_id);
+}
+
+static struct pernet_operations sample_net_ops = {
+	.init = sample_init_net,
+	.exit_batch = sample_exit_net,
+	.id   = &act_sample_ops.net_id,
+	.size = sizeof(struct tc_action_net),
+};
+
+static int __init sample_init_module(void)
+{
+	return tcf_register_action(&act_sample_ops, &sample_net_ops);
+}
+
+static void __exit sample_cleanup_module(void)
+{
+	tcf_unregister_action(&act_sample_ops, &sample_net_ops);
+}
+
+module_init(sample_init_module);
+module_exit(sample_cleanup_module);
+
+MODULE_AUTHOR("Yotam Gigi <yotam.gi@gmail.com>");
+MODULE_DESCRIPTION("Packet sampling action");
+MODULE_LICENSE("GPL v2");