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, 71 insertions, 0 deletions

diff --git a/net/dsa/user.h b/net/dsa/user.h
new file mode 100644
index 000000000..016884bea
--- /dev/null
+++ b/net/dsa/user.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef __DSA_USER_H
+#define __DSA_USER_H
+
+#include <linux/if_bridge.h>
+#include <linux/if_vlan.h>
+#include <linux/list.h>
+#include <linux/netpoll.h>
+#include <linux/types.h>
+#include <net/dsa.h>
+#include <net/gro_cells.h>
+
+struct net_device;
+struct netlink_ext_ack;
+
+extern struct notifier_block dsa_user_switchdev_notifier;
+extern struct notifier_block dsa_user_switchdev_blocking_notifier;
+
+struct dsa_user_priv {
+	/* Copy of CPU port xmit for faster access in user transmit hot path */
+	struct sk_buff *	(*xmit)(struct sk_buff *skb,
+					struct net_device *dev);
+
+	struct gro_cells	gcells;
+
+	/* DSA port data, such as switch, port index, etc. */
+	struct dsa_port		*dp;
+
+#ifdef CONFIG_NET_POLL_CONTROLLER
+	struct netpoll		*netpoll;
+#endif
+
+	/* TC context */
+	struct list_head	mall_tc_list;
+};
+
+void dsa_user_mii_bus_init(struct dsa_switch *ds);
+int dsa_user_create(struct dsa_port *dp);
+void dsa_user_destroy(struct net_device *user_dev);
+int dsa_user_suspend(struct net_device *user_dev);
+int dsa_user_resume(struct net_device *user_dev);
+int dsa_user_register_notifier(void);
+void dsa_user_unregister_notifier(void);
+int dsa_user_host_uc_install(struct net_device *dev, const u8 *addr);
+void dsa_user_host_uc_uninstall(struct net_device *dev);
+void dsa_user_sync_ha(struct net_device *dev);
+void dsa_user_unsync_ha(struct net_device *dev);
+void dsa_user_setup_tagger(struct net_device *user);
+int dsa_user_change_mtu(struct net_device *dev, int new_mtu);
+int dsa_user_change_conduit(struct net_device *dev, struct net_device *conduit,
+			    struct netlink_ext_ack *extack);
+int dsa_user_manage_vlan_filtering(struct net_device *dev,
+				   bool vlan_filtering);
+
+static inline struct dsa_port *dsa_user_to_port(const struct net_device *dev)
+{
+	struct dsa_user_priv *p = netdev_priv(dev);
+
+	return p->dp;
+}
+
+static inline struct net_device *
+dsa_user_to_conduit(const struct net_device *dev)
+{
+	struct dsa_port *dp = dsa_user_to_port(dev);
+
+	return dsa_port_to_conduit(dp);
+}
+
+#endif