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, 346 insertions, 0 deletions

diff --git a/net/sched/cls_basic.c b/net/sched/cls_basic.c
new file mode 100644
index 000000000..492cd9ce8
--- /dev/null
+++ b/net/sched/cls_basic.c
@@ -0,0 +1,346 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * net/sched/cls_basic.c	Basic Packet Classifier.
+ *
+ * Authors:	Thomas Graf <tgraf@suug.ch>
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/rtnetlink.h>
+#include <linux/skbuff.h>
+#include <linux/idr.h>
+#include <linux/percpu.h>
+#include <net/netlink.h>
+#include <net/act_api.h>
+#include <net/pkt_cls.h>
+#include <net/tc_wrapper.h>
+
+struct basic_head {
+	struct list_head	flist;
+	struct idr		handle_idr;
+	struct rcu_head		rcu;
+};
+
+struct basic_filter {
+	u32			handle;
+	struct tcf_exts		exts;
+	struct tcf_ematch_tree	ematches;
+	struct tcf_result	res;
+	struct tcf_proto	*tp;
+	struct list_head	link;
+	struct tc_basic_pcnt __percpu *pf;
+	struct rcu_work		rwork;
+};
+
+TC_INDIRECT_SCOPE int basic_classify(struct sk_buff *skb,
+				     const struct tcf_proto *tp,
+				     struct tcf_result *res)
+{
+	int r;
+	struct basic_head *head = rcu_dereference_bh(tp->root);
+	struct basic_filter *f;
+
+	list_for_each_entry_rcu(f, &head->flist, link) {
+		__this_cpu_inc(f->pf->rcnt);
+		if (!tcf_em_tree_match(skb, &f->ematches, NULL))
+			continue;
+		__this_cpu_inc(f->pf->rhit);
+		*res = f->res;
+		r = tcf_exts_exec(skb, &f->exts, res);
+		if (r < 0)
+			continue;
+		return r;
+	}
+	return -1;
+}
+
+static void *basic_get(struct tcf_proto *tp, u32 handle)
+{
+	struct basic_head *head = rtnl_dereference(tp->root);
+	struct basic_filter *f;
+
+	list_for_each_entry(f, &head->flist, link) {
+		if (f->handle == handle) {
+			return f;
+		}
+	}
+
+	return NULL;
+}
+
+static int basic_init(struct tcf_proto *tp)
+{
+	struct basic_head *head;
+
+	head = kzalloc_obj(*head);
+	if (head == NULL)
+		return -ENOBUFS;
+	INIT_LIST_HEAD(&head->flist);
+	idr_init(&head->handle_idr);
+	rcu_assign_pointer(tp->root, head);
+	return 0;
+}
+
+static void __basic_delete_filter(struct basic_filter *f)
+{
+	tcf_exts_destroy(&f->exts);
+	tcf_em_tree_destroy(&f->ematches);
+	tcf_exts_put_net(&f->exts);
+	free_percpu(f->pf);
+	kfree(f);
+}
+
+static void basic_delete_filter_work(struct work_struct *work)
+{
+	struct basic_filter *f = container_of(to_rcu_work(work),
+					      struct basic_filter,
+					      rwork);
+	rtnl_lock();
+	__basic_delete_filter(f);
+	rtnl_unlock();
+}
+
+static void basic_destroy(struct tcf_proto *tp, bool rtnl_held,
+			  struct netlink_ext_ack *extack)
+{
+	struct basic_head *head = rtnl_dereference(tp->root);
+	struct basic_filter *f, *n;
+
+	list_for_each_entry_safe(f, n, &head->flist, link) {
+		list_del_rcu(&f->link);
+		tcf_unbind_filter(tp, &f->res);
+		idr_remove(&head->handle_idr, f->handle);
+		if (tcf_exts_get_net(&f->exts))
+			tcf_queue_work(&f->rwork, basic_delete_filter_work);
+		else
+			__basic_delete_filter(f);
+	}
+	idr_destroy(&head->handle_idr);
+	kfree_rcu(head, rcu);
+}
+
+static int basic_delete(struct tcf_proto *tp, void *arg, bool *last,
+			bool rtnl_held, struct netlink_ext_ack *extack)
+{
+	struct basic_head *head = rtnl_dereference(tp->root);
+	struct basic_filter *f = arg;
+
+	list_del_rcu(&f->link);
+	tcf_unbind_filter(tp, &f->res);
+	idr_remove(&head->handle_idr, f->handle);
+	tcf_exts_get_net(&f->exts);
+	tcf_queue_work(&f->rwork, basic_delete_filter_work);
+	*last = list_empty(&head->flist);
+	return 0;
+}
+
+static const struct nla_policy basic_policy[TCA_BASIC_MAX + 1] = {
+	[TCA_BASIC_CLASSID]	= { .type = NLA_U32 },
+	[TCA_BASIC_EMATCHES]	= { .type = NLA_NESTED },
+};
+
+static int basic_set_parms(struct net *net, struct tcf_proto *tp,
+			   struct basic_filter *f, unsigned long base,
+			   struct nlattr **tb,
+			   struct nlattr *est, u32 flags,
+			   struct netlink_ext_ack *extack)
+{
+	int err;
+
+	err = tcf_exts_validate(net, tp, tb, est, &f->exts, flags, extack);
+	if (err < 0)
+		return err;
+
+	err = tcf_em_tree_validate(tp, tb[TCA_BASIC_EMATCHES], &f->ematches);
+	if (err < 0)
+		return err;
+
+	if (tb[TCA_BASIC_CLASSID]) {
+		f->res.classid = nla_get_u32(tb[TCA_BASIC_CLASSID]);
+		tcf_bind_filter(tp, &f->res, base);
+	}
+
+	f->tp = tp;
+	return 0;
+}
+
+static int basic_change(struct net *net, struct sk_buff *in_skb,
+			struct tcf_proto *tp, unsigned long base, u32 handle,
+			struct nlattr **tca, void **arg,
+			u32 flags, struct netlink_ext_ack *extack)
+{
+	int err;
+	struct basic_head *head = rtnl_dereference(tp->root);
+	struct nlattr *tb[TCA_BASIC_MAX + 1];
+	struct basic_filter *fold = (struct basic_filter *) *arg;
+	struct basic_filter *fnew;
+
+	if (tca[TCA_OPTIONS] == NULL)
+		return -EINVAL;
+
+	err = nla_parse_nested_deprecated(tb, TCA_BASIC_MAX, tca[TCA_OPTIONS],
+					  basic_policy, NULL);
+	if (err < 0)
+		return err;
+
+	if (fold != NULL) {
+		if (handle && fold->handle != handle)
+			return -EINVAL;
+	}
+
+	fnew = kzalloc_obj(*fnew);
+	if (!fnew)
+		return -ENOBUFS;
+
+	err = tcf_exts_init(&fnew->exts, net, TCA_BASIC_ACT, TCA_BASIC_POLICE);
+	if (err < 0)
+		goto errout;
+
+	if (!handle) {
+		handle = 1;
+		err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
+				    INT_MAX, GFP_KERNEL);
+	} else if (!fold) {
+		err = idr_alloc_u32(&head->handle_idr, fnew, &handle,
+				    handle, GFP_KERNEL);
+	}
+	if (err)
+		goto errout;
+	fnew->handle = handle;
+	fnew->pf = alloc_percpu(struct tc_basic_pcnt);
+	if (!fnew->pf) {
+		err = -ENOMEM;
+		goto errout;
+	}
+
+	err = basic_set_parms(net, tp, fnew, base, tb, tca[TCA_RATE], flags,
+			      extack);
+	if (err < 0) {
+		if (!fold)
+			idr_remove(&head->handle_idr, fnew->handle);
+		goto errout;
+	}
+
+	*arg = fnew;
+
+	if (fold) {
+		idr_replace(&head->handle_idr, fnew, fnew->handle);
+		list_replace_rcu(&fold->link, &fnew->link);
+		tcf_unbind_filter(tp, &fold->res);
+		tcf_exts_get_net(&fold->exts);
+		tcf_queue_work(&fold->rwork, basic_delete_filter_work);
+	} else {
+		list_add_rcu(&fnew->link, &head->flist);
+	}
+
+	return 0;
+errout:
+	free_percpu(fnew->pf);
+	tcf_exts_destroy(&fnew->exts);
+	kfree(fnew);
+	return err;
+}
+
+static void basic_walk(struct tcf_proto *tp, struct tcf_walker *arg,
+		       bool rtnl_held)
+{
+	struct basic_head *head = rtnl_dereference(tp->root);
+	struct basic_filter *f;
+
+	list_for_each_entry(f, &head->flist, link) {
+		if (!tc_cls_stats_dump(tp, arg, f))
+			break;
+	}
+}
+
+static void basic_bind_class(void *fh, u32 classid, unsigned long cl, void *q,
+			     unsigned long base)
+{
+	struct basic_filter *f = fh;
+
+	tc_cls_bind_class(classid, cl, q, &f->res, base);
+}
+
+static int basic_dump(struct net *net, struct tcf_proto *tp, void *fh,
+		      struct sk_buff *skb, struct tcmsg *t, bool rtnl_held)
+{
+	struct tc_basic_pcnt gpf = {};
+	struct basic_filter *f = fh;
+	struct nlattr *nest;
+	int cpu;
+
+	if (f == NULL)
+		return skb->len;
+
+	t->tcm_handle = f->handle;
+
+	nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
+	if (nest == NULL)
+		goto nla_put_failure;
+
+	if (f->res.classid &&
+	    nla_put_u32(skb, TCA_BASIC_CLASSID, f->res.classid))
+		goto nla_put_failure;
+
+	for_each_possible_cpu(cpu) {
+		struct tc_basic_pcnt *pf = per_cpu_ptr(f->pf, cpu);
+
+		gpf.rcnt += pf->rcnt;
+		gpf.rhit += pf->rhit;
+	}
+
+	if (nla_put_64bit(skb, TCA_BASIC_PCNT,
+			  sizeof(struct tc_basic_pcnt),
+			  &gpf, TCA_BASIC_PAD))
+		goto nla_put_failure;
+
+	if (tcf_exts_dump(skb, &f->exts) < 0 ||
+	    tcf_em_tree_dump(skb, &f->ematches, TCA_BASIC_EMATCHES) < 0)
+		goto nla_put_failure;
+
+	nla_nest_end(skb, nest);
+
+	if (tcf_exts_dump_stats(skb, &f->exts) < 0)
+		goto nla_put_failure;
+
+	return skb->len;
+
+nla_put_failure:
+	nla_nest_cancel(skb, nest);
+	return -1;
+}
+
+static struct tcf_proto_ops cls_basic_ops __read_mostly = {
+	.kind		=	"basic",
+	.classify	=	basic_classify,
+	.init		=	basic_init,
+	.destroy	=	basic_destroy,
+	.get		=	basic_get,
+	.change		=	basic_change,
+	.delete		=	basic_delete,
+	.walk		=	basic_walk,
+	.dump		=	basic_dump,
+	.bind_class	=	basic_bind_class,
+	.owner		=	THIS_MODULE,
+};
+MODULE_ALIAS_NET_CLS("basic");
+
+static int __init init_basic(void)
+{
+	return register_tcf_proto_ops(&cls_basic_ops);
+}
+
+static void __exit exit_basic(void)
+{
+	unregister_tcf_proto_ops(&cls_basic_ops);
+}
+
+module_init(init_basic)
+module_exit(exit_basic)
+MODULE_DESCRIPTION("TC basic classifier");
+MODULE_LICENSE("GPL");