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, 159 insertions, 0 deletions

diff --git a/net/packet/internal.h b/net/packet/internal.h
new file mode 100644
index 000000000..b76e645cd
--- /dev/null
+++ b/net/packet/internal.h
@@ -0,0 +1,159 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PACKET_INTERNAL_H__
+#define __PACKET_INTERNAL_H__
+
+#include <linux/refcount.h>
+
+struct packet_mclist {
+	struct packet_mclist	*next;
+	int			ifindex;
+	int			count;
+	unsigned short		type;
+	unsigned short		alen;
+	unsigned char		addr[MAX_ADDR_LEN];
+	struct list_head	remove_list;
+};
+
+/* kbdq - kernel block descriptor queue */
+struct tpacket_kbdq_core {
+	struct pgv	*pkbdq;
+	unsigned int	feature_req_word;
+	unsigned int	hdrlen;
+	unsigned char	reset_pending_on_curr_blk;
+	unsigned short	kactive_blk_num;
+	unsigned short	blk_sizeof_priv;
+
+	unsigned short  version;
+
+	char		*pkblk_start;
+	char		*pkblk_end;
+	int		kblk_size;
+	unsigned int	max_frame_len;
+	unsigned int	knum_blocks;
+	uint64_t	knxt_seq_num;
+	char		*prev;
+	char		*nxt_offset;
+
+	struct sk_buff	*skb;
+
+	rwlock_t	blk_fill_in_prog_lock;
+
+	/* Default is set to 8ms */
+#define DEFAULT_PRB_RETIRE_TOV	(8)
+
+	ktime_t		interval_ktime;
+
+	/* timer to retire an outstanding block */
+	struct hrtimer  retire_blk_timer;
+};
+
+struct pgv {
+	char *buffer;
+};
+
+struct packet_ring_buffer {
+	struct pgv		*pg_vec;
+
+	unsigned int		head;
+	unsigned int		frames_per_block;
+	unsigned int		frame_size;
+	unsigned int		frame_max;
+
+	unsigned int		pg_vec_order;
+	unsigned int		pg_vec_pages;
+	unsigned int		pg_vec_len;
+
+	unsigned int __percpu	*pending_refcnt;
+
+	union {
+		unsigned long			*rx_owner_map;
+		struct tpacket_kbdq_core	prb_bdqc;
+	};
+};
+
+extern struct mutex fanout_mutex;
+#define PACKET_FANOUT_MAX	(1 << 16)
+
+struct packet_fanout {
+	possible_net_t		net;
+	unsigned int		num_members;
+	u32			max_num_members;
+	u16			id;
+	u8			type;
+	u8			flags;
+	union {
+		atomic_t		rr_cur;
+		struct bpf_prog __rcu	*bpf_prog;
+	};
+	struct list_head	list;
+	spinlock_t		lock;
+	refcount_t		sk_ref;
+	struct packet_type	prot_hook ____cacheline_aligned_in_smp;
+	struct sock	__rcu	*arr[] __counted_by(max_num_members);
+};
+
+struct packet_rollover {
+	int			sock;
+	atomic_long_t		num;
+	atomic_long_t		num_huge;
+	atomic_long_t		num_failed;
+#define ROLLOVER_HLEN	(L1_CACHE_BYTES / sizeof(u32))
+	u32			history[ROLLOVER_HLEN] ____cacheline_aligned;
+} ____cacheline_aligned_in_smp;
+
+struct packet_sock {
+	/* struct sock has to be the first member of packet_sock */
+	struct sock		sk;
+	struct packet_fanout	*fanout;
+	union  tpacket_stats_u	stats;
+	struct packet_ring_buffer	rx_ring;
+	struct packet_ring_buffer	tx_ring;
+	int			copy_thresh;
+	spinlock_t		bind_lock;
+	struct mutex		pg_vec_lock;
+	unsigned long		flags;
+	int			ifindex;	/* bound device		*/
+	u8			vnet_hdr_sz;
+	__be16			num;
+	struct packet_rollover	*rollover;
+	struct packet_mclist	*mclist;
+	atomic_long_t		mapped;
+	enum tpacket_versions	tp_version;
+	unsigned int		tp_hdrlen;
+	unsigned int		tp_reserve;
+	unsigned int		tp_tstamp;
+	struct completion	skb_completion;
+	struct net_device __rcu	*cached_dev;
+	struct packet_type	prot_hook ____cacheline_aligned_in_smp;
+	atomic_t		tp_drops ____cacheline_aligned_in_smp;
+};
+
+#define pkt_sk(ptr) container_of_const(ptr, struct packet_sock, sk)
+
+enum packet_sock_flags {
+	PACKET_SOCK_ORIGDEV,
+	PACKET_SOCK_AUXDATA,
+	PACKET_SOCK_TX_HAS_OFF,
+	PACKET_SOCK_TP_LOSS,
+	PACKET_SOCK_RUNNING,
+	PACKET_SOCK_PRESSURE,
+	PACKET_SOCK_QDISC_BYPASS,
+};
+
+static inline void packet_sock_flag_set(struct packet_sock *po,
+					enum packet_sock_flags flag,
+					bool val)
+{
+	if (val)
+		set_bit(flag, &po->flags);
+	else
+		clear_bit(flag, &po->flags);
+}
+
+static inline bool packet_sock_flag(const struct packet_sock *po,
+				    enum packet_sock_flags flag)
+{
+	return test_bit(flag, &po->flags);
+}
+
+#endif