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, 182 insertions, 0 deletions

diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
new file mode 100644
index 000000000..365925c9d
--- /dev/null
+++ b/include/net/inet_frag.h
@@ -0,0 +1,182 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_FRAG_H__
+#define __NET_FRAG_H__
+
+#include <linux/rhashtable-types.h>
+#include <linux/completion.h>
+#include <linux/in6.h>
+#include <linux/rbtree_types.h>
+#include <linux/refcount.h>
+#include <net/dropreason-core.h>
+
+/* Per netns frag queues directory */
+struct fqdir {
+	/* sysctls */
+	long			high_thresh;
+	long			low_thresh;
+	int			timeout;
+	int			max_dist;
+	struct inet_frags	*f;
+	struct net		*net;
+	bool			dead;
+
+	struct rhashtable       rhashtable ____cacheline_aligned_in_smp;
+
+	/* Keep atomic mem on separate cachelines in structs that include it */
+	atomic_long_t		mem ____cacheline_aligned_in_smp;
+	struct work_struct	destroy_work;
+	struct llist_node	free_list;
+};
+
+/**
+ * enum: fragment queue flags
+ *
+ * @INET_FRAG_FIRST_IN: first fragment has arrived
+ * @INET_FRAG_LAST_IN: final fragment has arrived
+ * @INET_FRAG_COMPLETE: frag queue has been processed and is due for destruction
+ * @INET_FRAG_HASH_DEAD: inet_frag_kill() has not removed fq from rhashtable
+ * @INET_FRAG_DROP: if skbs must be dropped (instead of being consumed)
+ */
+enum {
+	INET_FRAG_FIRST_IN	= BIT(0),
+	INET_FRAG_LAST_IN	= BIT(1),
+	INET_FRAG_COMPLETE	= BIT(2),
+	INET_FRAG_HASH_DEAD	= BIT(3),
+	INET_FRAG_DROP		= BIT(4),
+};
+
+struct frag_v4_compare_key {
+	__be32		saddr;
+	__be32		daddr;
+	u32		user;
+	u32		vif;
+	__be16		id;
+	u16		protocol;
+};
+
+struct frag_v6_compare_key {
+	struct in6_addr	saddr;
+	struct in6_addr	daddr;
+	u32		user;
+	__be32		id;
+	u32		iif;
+};
+
+/**
+ * struct inet_frag_queue - fragment queue
+ *
+ * @node: rhash node
+ * @key: keys identifying this frag.
+ * @timer: queue expiration timer
+ * @lock: spinlock protecting this frag
+ * @refcnt: reference count of the queue
+ * @rb_fragments: received fragments rb-tree root
+ * @fragments_tail: received fragments tail
+ * @last_run_head: the head of the last "run". see ip_fragment.c
+ * @stamp: timestamp of the last received fragment
+ * @len: total length of the original datagram
+ * @meat: length of received fragments so far
+ * @tstamp_type: stamp has a mono delivery time (EDT)
+ * @flags: fragment queue flags
+ * @max_size: maximum received fragment size
+ * @fqdir: pointer to struct fqdir
+ * @rcu: rcu head for freeing deferall
+ */
+struct inet_frag_queue {
+	struct rhash_head	node;
+	union {
+		struct frag_v4_compare_key v4;
+		struct frag_v6_compare_key v6;
+	} key;
+	struct timer_list	timer;
+	spinlock_t		lock;
+	refcount_t		refcnt;
+	struct rb_root		rb_fragments;
+	struct sk_buff		*fragments_tail;
+	struct sk_buff		*last_run_head;
+	ktime_t			stamp;
+	int			len;
+	int			meat;
+	u8			tstamp_type;
+	__u8			flags;
+	u16			max_size;
+	struct fqdir		*fqdir;
+	struct rcu_head		rcu;
+};
+
+struct inet_frags {
+	unsigned int		qsize;
+
+	void			(*constructor)(struct inet_frag_queue *q,
+					       const void *arg);
+	void			(*destructor)(struct inet_frag_queue *);
+	void			(*frag_expire)(struct timer_list *t);
+	struct kmem_cache	*frags_cachep;
+	const char		*frags_cache_name;
+	struct rhashtable_params rhash_params;
+	refcount_t		refcnt;
+	struct completion	completion;
+};
+
+int inet_frags_init(struct inet_frags *);
+void inet_frags_fini(struct inet_frags *);
+
+int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net);
+
+void fqdir_pre_exit(struct fqdir *fqdir);
+void fqdir_exit(struct fqdir *fqdir);
+
+void inet_frag_kill(struct inet_frag_queue *q, int *refs);
+void inet_frag_destroy(struct inet_frag_queue *q);
+struct inet_frag_queue *inet_frag_find(struct fqdir *fqdir, void *key);
+
+void inet_frag_queue_flush(struct inet_frag_queue *q,
+			   enum skb_drop_reason reason);
+
+static inline void inet_frag_putn(struct inet_frag_queue *q, int refs)
+{
+	if (refs && refcount_sub_and_test(refs, &q->refcnt))
+		inet_frag_destroy(q);
+}
+
+/* Memory Tracking Functions. */
+
+static inline long frag_mem_limit(const struct fqdir *fqdir)
+{
+	return atomic_long_read(&fqdir->mem);
+}
+
+static inline void sub_frag_mem_limit(struct fqdir *fqdir, long val)
+{
+	atomic_long_sub(val, &fqdir->mem);
+}
+
+static inline void add_frag_mem_limit(struct fqdir *fqdir, long val)
+{
+	atomic_long_add(val, &fqdir->mem);
+}
+
+/* RFC 3168 support :
+ * We want to check ECN values of all fragments, do detect invalid combinations.
+ * In ipq->ecn, we store the OR value of each ip4_frag_ecn() fragment value.
+ */
+#define	IPFRAG_ECN_NOT_ECT	0x01 /* one frag had ECN_NOT_ECT */
+#define	IPFRAG_ECN_ECT_1	0x02 /* one frag had ECN_ECT_1 */
+#define	IPFRAG_ECN_ECT_0	0x04 /* one frag had ECN_ECT_0 */
+#define	IPFRAG_ECN_CE		0x08 /* one frag had ECN_CE */
+
+extern const u8 ip_frag_ecn_table[16];
+
+/* Return values of inet_frag_queue_insert() */
+#define IPFRAG_OK	0
+#define IPFRAG_DUP	1
+#define IPFRAG_OVERLAP	2
+int inet_frag_queue_insert(struct inet_frag_queue *q, struct sk_buff *skb,
+			   int offset, int end);
+void *inet_frag_reasm_prepare(struct inet_frag_queue *q, struct sk_buff *skb,
+			      struct sk_buff *parent);
+void inet_frag_reasm_finish(struct inet_frag_queue *q, struct sk_buff *head,
+			    void *reasm_data, bool try_coalesce);
+struct sk_buff *inet_frag_pull_head(struct inet_frag_queue *q);
+
+#endif