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, 43 insertions, 0 deletions

diff --git a/net/batman-adv/mesh-interface.h b/net/batman-adv/mesh-interface.h
new file mode 100644
index 000000000..5e1e83e04
--- /dev/null
+++ b/net/batman-adv/mesh-interface.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Marek Lindner
+ */
+
+#ifndef _NET_BATMAN_ADV_MESH_INTERFACE_H_
+#define _NET_BATMAN_ADV_MESH_INTERFACE_H_
+
+#include "main.h"
+
+#include <linux/kref.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/types.h>
+
+int batadv_skb_head_push(struct sk_buff *skb, unsigned int len);
+void batadv_interface_rx(struct net_device *mesh_iface,
+			 struct sk_buff *skb, int hdr_size,
+			 struct batadv_orig_node *orig_node);
+bool batadv_meshif_is_valid(const struct net_device *net_dev);
+extern struct rtnl_link_ops batadv_link_ops;
+int batadv_meshif_create_vlan(struct batadv_priv *bat_priv, unsigned short vid);
+void batadv_meshif_destroy_vlan(struct batadv_priv *bat_priv,
+				struct batadv_meshif_vlan *vlan);
+void batadv_meshif_vlan_release(struct kref *ref);
+struct batadv_meshif_vlan *batadv_meshif_vlan_get(struct batadv_priv *bat_priv,
+						  unsigned short vid);
+
+/**
+ * batadv_meshif_vlan_put() - decrease the vlan object refcounter and
+ *  possibly release it
+ * @vlan: the vlan object to release
+ */
+static inline void batadv_meshif_vlan_put(struct batadv_meshif_vlan *vlan)
+{
+	if (!vlan)
+		return;
+
+	kref_put(&vlan->refcount, batadv_meshif_vlan_release);
+}
+
+#endif /* _NET_BATMAN_ADV_MESH_INTERFACE_H_ */