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, 106 insertions, 0 deletions

diff --git a/net/openvswitch/conntrack.h b/net/openvswitch/conntrack.h
new file mode 100644
index 000000000..317e525c8
--- /dev/null
+++ b/net/openvswitch/conntrack.h
@@ -0,0 +1,106 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2015 Nicira, Inc.
+ */
+
+#ifndef OVS_CONNTRACK_H
+#define OVS_CONNTRACK_H 1
+
+#include "flow.h"
+
+struct ovs_conntrack_info;
+struct ovs_ct_limit_info;
+enum ovs_key_attr;
+
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+int ovs_ct_init(struct net *);
+void ovs_ct_exit(struct net *);
+bool ovs_ct_verify(struct net *, enum ovs_key_attr attr);
+int ovs_ct_copy_action(struct net *, const struct nlattr *,
+		       const struct sw_flow_key *, struct sw_flow_actions **,
+		       bool log);
+int ovs_ct_action_to_attr(const struct ovs_conntrack_info *, struct sk_buff *);
+
+int ovs_ct_execute(struct net *, struct sk_buff *, struct sw_flow_key *,
+		   const struct ovs_conntrack_info *);
+int ovs_ct_clear(struct sk_buff *skb, struct sw_flow_key *key);
+
+void ovs_ct_fill_key(const struct sk_buff *skb, struct sw_flow_key *key,
+		     bool post_ct);
+int ovs_ct_put_key(const struct sw_flow_key *swkey,
+		   const struct sw_flow_key *output, struct sk_buff *skb);
+void ovs_ct_free_action(const struct nlattr *a);
+
+#define CT_SUPPORTED_MASK (OVS_CS_F_NEW | OVS_CS_F_ESTABLISHED | \
+			   OVS_CS_F_RELATED | OVS_CS_F_REPLY_DIR | \
+			   OVS_CS_F_INVALID | OVS_CS_F_TRACKED | \
+			   OVS_CS_F_SRC_NAT | OVS_CS_F_DST_NAT)
+#else
+#include <linux/errno.h>
+
+static inline int ovs_ct_init(struct net *net) { return 0; }
+
+static inline void ovs_ct_exit(struct net *net) { }
+
+static inline bool ovs_ct_verify(struct net *net, int attr)
+{
+	return false;
+}
+
+static inline int ovs_ct_copy_action(struct net *net, const struct nlattr *nla,
+				     const struct sw_flow_key *key,
+				     struct sw_flow_actions **acts, bool log)
+{
+	return -ENOTSUPP;
+}
+
+static inline int ovs_ct_action_to_attr(const struct ovs_conntrack_info *info,
+					struct sk_buff *skb)
+{
+	return -ENOTSUPP;
+}
+
+static inline int ovs_ct_execute(struct net *net, struct sk_buff *skb,
+				 struct sw_flow_key *key,
+				 const struct ovs_conntrack_info *info)
+{
+	kfree_skb(skb);
+	return -ENOTSUPP;
+}
+
+static inline int ovs_ct_clear(struct sk_buff *skb,
+			       struct sw_flow_key *key)
+{
+	return -ENOTSUPP;
+}
+
+static inline void ovs_ct_fill_key(const struct sk_buff *skb,
+				   struct sw_flow_key *key,
+				   bool post_ct)
+{
+	key->ct_state = 0;
+	key->ct_zone = 0;
+	key->ct.mark = 0;
+	memset(&key->ct.labels, 0, sizeof(key->ct.labels));
+	/* Clear 'ct_orig_proto' to mark the non-existence of original
+	 * direction key fields.
+	 */
+	key->ct_orig_proto = 0;
+}
+
+static inline int ovs_ct_put_key(const struct sw_flow_key *swkey,
+				 const struct sw_flow_key *output,
+				 struct sk_buff *skb)
+{
+	return 0;
+}
+
+static inline void ovs_ct_free_action(const struct nlattr *a) { }
+
+#define CT_SUPPORTED_MASK 0
+#endif /* CONFIG_NF_CONNTRACK */
+
+#if IS_ENABLED(CONFIG_NETFILTER_CONNCOUNT)
+extern struct genl_family dp_ct_limit_genl_family;
+#endif
+#endif /* ovs_conntrack.h */