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, 155 insertions, 0 deletions

diff --git a/net/batman-adv/hard-interface.h b/net/batman-adv/hard-interface.h
new file mode 100644
index 000000000..af31696c3
--- /dev/null
+++ b/net/batman-adv/hard-interface.h
@@ -0,0 +1,155 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Marek Lindner, Simon Wunderlich
+ */
+
+#ifndef _NET_BATMAN_ADV_HARD_INTERFACE_H_
+#define _NET_BATMAN_ADV_HARD_INTERFACE_H_
+
+#include "main.h"
+
+#include <linux/compiler.h>
+#include <linux/init.h>
+#include <linux/kref.h>
+#include <linux/netdevice.h>
+#include <linux/rcupdate.h>
+#include <linux/stddef.h>
+#include <linux/types.h>
+
+/**
+ * enum batadv_hard_if_state - State of a hard interface
+ */
+enum batadv_hard_if_state {
+	/**
+	 * @BATADV_IF_NOT_IN_USE: interface is not used as slave interface of a
+	 * batman-adv mesh interface
+	 */
+	BATADV_IF_NOT_IN_USE,
+
+	/**
+	 * @BATADV_IF_TO_BE_REMOVED: interface will be removed from mesh
+	 * interface
+	 */
+	BATADV_IF_TO_BE_REMOVED,
+
+	/** @BATADV_IF_INACTIVE: interface is deactivated */
+	BATADV_IF_INACTIVE,
+
+	/** @BATADV_IF_ACTIVE: interface is used */
+	BATADV_IF_ACTIVE,
+
+	/** @BATADV_IF_TO_BE_ACTIVATED: interface is getting activated */
+	BATADV_IF_TO_BE_ACTIVATED,
+};
+
+/**
+ * enum batadv_hard_if_bcast - broadcast avoidance options
+ */
+enum batadv_hard_if_bcast {
+	/** @BATADV_HARDIF_BCAST_OK: Do broadcast on according hard interface */
+	BATADV_HARDIF_BCAST_OK = 0,
+
+	/**
+	 * @BATADV_HARDIF_BCAST_NORECIPIENT: Broadcast not needed, there is no
+	 *  recipient
+	 */
+	BATADV_HARDIF_BCAST_NORECIPIENT,
+
+	/**
+	 * @BATADV_HARDIF_BCAST_DUPFWD: There is just the neighbor we got it
+	 *  from
+	 */
+	BATADV_HARDIF_BCAST_DUPFWD,
+
+	/** @BATADV_HARDIF_BCAST_DUPORIG: There is just the originator */
+	BATADV_HARDIF_BCAST_DUPORIG,
+};
+
+extern struct notifier_block batadv_hard_if_notifier;
+
+struct net_device *__batadv_get_real_netdev(struct net_device *net_device);
+struct net_device *batadv_get_real_netdev(struct net_device *net_device);
+u32 batadv_netdev_get_wifi_flags(struct net_device *net_dev);
+u32 batadv_hardif_get_wifi_flags(struct batadv_hard_iface *hard_iface);
+bool batadv_is_wifi_hardif(struct batadv_hard_iface *hard_iface);
+struct batadv_hard_iface*
+batadv_hardif_get_by_netdev(const struct net_device *net_dev);
+int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
+				   struct net_device *mesh_iface);
+void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface);
+int batadv_hardif_min_mtu(struct net_device *mesh_iface);
+void batadv_update_min_mtu(struct net_device *mesh_iface);
+void batadv_hardif_release(struct kref *ref);
+int batadv_hardif_no_broadcast(struct batadv_hard_iface *if_outgoing,
+			       u8 *orig_addr, u8 *orig_neigh);
+int __init batadv_wifi_net_devices_init(void);
+void batadv_wifi_net_devices_deinit(void);
+
+/**
+ * batadv_hardif_put() - decrement the hard interface refcounter and possibly
+ *  release it
+ * @hard_iface: the hard interface to free
+ */
+static inline void batadv_hardif_put(struct batadv_hard_iface *hard_iface)
+{
+	if (!hard_iface)
+		return;
+
+	kref_put(&hard_iface->refcount, batadv_hardif_release);
+}
+
+/**
+ * batadv_primary_if_get_selected() - Get reference to primary interface
+ * @bat_priv: the bat priv with all the mesh interface information
+ *
+ * Return: primary interface (with increased refcnt), otherwise NULL
+ */
+static inline struct batadv_hard_iface *
+batadv_primary_if_get_selected(struct batadv_priv *bat_priv)
+{
+	struct batadv_hard_iface *hard_iface;
+
+	rcu_read_lock();
+	hard_iface = rcu_dereference(bat_priv->primary_if);
+	if (!hard_iface)
+		goto out;
+
+	if (!kref_get_unless_zero(&hard_iface->refcount))
+		hard_iface = NULL;
+
+out:
+	rcu_read_unlock();
+	return hard_iface;
+}
+
+/**
+ * batadv_is_cfg80211() - check if the given hardif is a cfg80211
+ *  wifi interface
+ * @wifi_flags: extracted batadv_hard_iface_wifi_flags of a net_device
+ *
+ * Return: true if the net device is a cfg80211 wireless device, false
+ *  otherwise.
+ */
+static inline bool batadv_is_cfg80211(u32 wifi_flags)
+{
+	u32 allowed_flags = 0;
+
+	allowed_flags |= BATADV_HARDIF_WIFI_CFG80211_DIRECT;
+	allowed_flags |= BATADV_HARDIF_WIFI_CFG80211_INDIRECT;
+
+	return !!(wifi_flags & allowed_flags);
+}
+
+/**
+ * batadv_is_wifi() - check if flags belong to wifi interface
+ * @wifi_flags: extracted batadv_hard_iface_wifi_flags of a net_device
+ *
+ * Return: true if the net device is a 802.11 wireless device, false otherwise.
+ */
+static inline bool batadv_is_wifi(u32 wifi_flags)
+{
+	return wifi_flags != 0;
+}
+
+#endif /* _NET_BATMAN_ADV_HARD_INTERFACE_H_ */