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, 148 insertions, 0 deletions

diff --git a/include/net/mrp.h b/include/net/mrp.h
new file mode 100644
index 000000000..b28915ffe
--- /dev/null
+++ b/include/net/mrp.h
@@ -0,0 +1,148 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_MRP_H
+#define _NET_MRP_H
+
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/types.h>
+
+#define MRP_END_MARK		0x0
+
+struct mrp_pdu_hdr {
+	u8	version;
+};
+
+struct mrp_msg_hdr {
+	u8	attrtype;
+	u8	attrlen;
+};
+
+struct mrp_vecattr_hdr {
+	__be16	lenflags;
+	unsigned char	firstattrvalue[];
+#define MRP_VECATTR_HDR_LEN_MASK cpu_to_be16(0x1FFF)
+#define MRP_VECATTR_HDR_FLAG_LA cpu_to_be16(0x2000)
+};
+
+enum mrp_vecattr_event {
+	MRP_VECATTR_EVENT_NEW,
+	MRP_VECATTR_EVENT_JOIN_IN,
+	MRP_VECATTR_EVENT_IN,
+	MRP_VECATTR_EVENT_JOIN_MT,
+	MRP_VECATTR_EVENT_MT,
+	MRP_VECATTR_EVENT_LV,
+	__MRP_VECATTR_EVENT_MAX
+};
+
+struct mrp_skb_cb {
+	struct mrp_msg_hdr	*mh;
+	struct mrp_vecattr_hdr	*vah;
+	unsigned char		attrvalue[];
+};
+
+static inline struct mrp_skb_cb *mrp_cb(struct sk_buff *skb)
+{
+	BUILD_BUG_ON(sizeof(struct mrp_skb_cb) >
+		     sizeof_field(struct sk_buff, cb));
+	return (struct mrp_skb_cb *)skb->cb;
+}
+
+enum mrp_applicant_state {
+	MRP_APPLICANT_INVALID,
+	MRP_APPLICANT_VO,
+	MRP_APPLICANT_VP,
+	MRP_APPLICANT_VN,
+	MRP_APPLICANT_AN,
+	MRP_APPLICANT_AA,
+	MRP_APPLICANT_QA,
+	MRP_APPLICANT_LA,
+	MRP_APPLICANT_AO,
+	MRP_APPLICANT_QO,
+	MRP_APPLICANT_AP,
+	MRP_APPLICANT_QP,
+	__MRP_APPLICANT_MAX
+};
+#define MRP_APPLICANT_MAX	(__MRP_APPLICANT_MAX - 1)
+
+enum mrp_event {
+	MRP_EVENT_NEW,
+	MRP_EVENT_JOIN,
+	MRP_EVENT_LV,
+	MRP_EVENT_TX,
+	MRP_EVENT_R_NEW,
+	MRP_EVENT_R_JOIN_IN,
+	MRP_EVENT_R_IN,
+	MRP_EVENT_R_JOIN_MT,
+	MRP_EVENT_R_MT,
+	MRP_EVENT_R_LV,
+	MRP_EVENT_R_LA,
+	MRP_EVENT_REDECLARE,
+	MRP_EVENT_PERIODIC,
+	__MRP_EVENT_MAX
+};
+#define MRP_EVENT_MAX		(__MRP_EVENT_MAX - 1)
+
+enum mrp_tx_action {
+	MRP_TX_ACTION_NONE,
+	MRP_TX_ACTION_S_NEW,
+	MRP_TX_ACTION_S_JOIN_IN,
+	MRP_TX_ACTION_S_JOIN_IN_OPTIONAL,
+	MRP_TX_ACTION_S_IN_OPTIONAL,
+	MRP_TX_ACTION_S_LV,
+};
+
+struct mrp_attr {
+	struct rb_node			node;
+	enum mrp_applicant_state	state;
+	u8				type;
+	u8				len;
+	unsigned char			value[];
+};
+
+enum mrp_applications {
+	MRP_APPLICATION_MVRP,
+	__MRP_APPLICATION_MAX
+};
+#define MRP_APPLICATION_MAX	(__MRP_APPLICATION_MAX - 1)
+
+struct mrp_application {
+	enum mrp_applications	type;
+	unsigned int		maxattr;
+	struct packet_type	pkttype;
+	unsigned char		group_address[ETH_ALEN];
+	u8			version;
+};
+
+struct mrp_applicant {
+	struct mrp_application	*app;
+	struct net_device	*dev;
+	struct timer_list	join_timer;
+	struct timer_list	periodic_timer;
+
+	spinlock_t		lock;
+	struct sk_buff_head	queue;
+	struct sk_buff		*pdu;
+	struct rb_root		mad;
+	struct rcu_head		rcu;
+	bool			active;
+};
+
+struct mrp_port {
+	struct mrp_applicant __rcu	*applicants[MRP_APPLICATION_MAX + 1];
+	struct rcu_head			rcu;
+};
+
+int mrp_register_application(struct mrp_application *app);
+void mrp_unregister_application(struct mrp_application *app);
+
+int mrp_init_applicant(struct net_device *dev, struct mrp_application *app);
+void mrp_uninit_applicant(struct net_device *dev, struct mrp_application *app);
+
+int mrp_request_join(const struct net_device *dev,
+		     const struct mrp_application *app,
+		     const void *value, u8 len, u8 type);
+void mrp_request_leave(const struct net_device *dev,
+		       const struct mrp_application *app,
+		       const void *value, u8 len, u8 type);
+
+#endif /* _NET_MRP_H */