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, 189 insertions, 0 deletions

diff --git a/include/net/sctp/ulpevent.h b/include/net/sctp/ulpevent.h
new file mode 100644
index 000000000..994e984ee
--- /dev/null
+++ b/include/net/sctp/ulpevent.h
@@ -0,0 +1,189 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* SCTP kernel implementation
+ * (C) Copyright IBM Corp. 2001, 2004
+ * Copyright (c) 1999-2000 Cisco, Inc.
+ * Copyright (c) 1999-2001 Motorola, Inc.
+ * Copyright (c) 2001 Intel Corp.
+ * Copyright (c) 2001 Nokia, Inc.
+ * Copyright (c) 2001 La Monte H.P. Yarroll
+ *
+ * These are the definitions needed for the sctp_ulpevent type.  The
+ * sctp_ulpevent type is used to carry information from the state machine
+ * upwards to the ULP.
+ *
+ * This file is part of the SCTP kernel implementation
+ *
+ * Please send any bug reports or fixes you make to the
+ * email address(es):
+ *    lksctp developers <linux-sctp@vger.kernel.org>
+ *
+ * Written or modified by:
+ *   Jon Grimm             <jgrimm@us.ibm.com>
+ *   La Monte H.P. Yarroll <piggy@acm.org>
+ *   Karl Knutson          <karl@athena.chicago.il.us>
+ *   Sridhar Samudrala     <sri@us.ibm.com>
+ */
+
+#ifndef __sctp_ulpevent_h__
+#define __sctp_ulpevent_h__
+
+/* A structure to carry information to the ULP (e.g. Sockets API) */
+/* Warning: This sits inside an skb.cb[] area.  Be very careful of
+ * growing this structure as it is at the maximum limit now.
+ *
+ * sctp_ulpevent is saved in sk->cb(48 bytes), whose last 4 bytes
+ * have been taken by sock_skb_cb, So here it has to use 'packed'
+ * to make sctp_ulpevent fit into the rest 44 bytes.
+ */
+struct sctp_ulpevent {
+	struct sctp_association *asoc;
+	struct sctp_chunk *chunk;
+	unsigned int rmem_len;
+	union {
+		__u32 mid;
+		__u16 ssn;
+	};
+	union {
+		__u32 ppid;
+		__u32 fsn;
+	};
+	__u32 tsn;
+	__u32 cumtsn;
+	__u16 stream;
+	__u16 flags;
+	__u16 msg_flags;
+} __packed;
+
+/* Retrieve the skb this event sits inside of. */
+static inline struct sk_buff *sctp_event2skb(const struct sctp_ulpevent *ev)
+{
+	return container_of((void *)ev, struct sk_buff, cb);
+}
+
+/* Retrieve & cast the event sitting inside the skb. */
+static inline struct sctp_ulpevent *sctp_skb2event(struct sk_buff *skb)
+{
+	return (struct sctp_ulpevent *)skb->cb;
+}
+
+void sctp_ulpevent_free(struct sctp_ulpevent *);
+int sctp_ulpevent_is_notification(const struct sctp_ulpevent *);
+unsigned int sctp_queue_purge_ulpevents(struct sk_buff_head *list);
+
+struct sctp_ulpevent *sctp_ulpevent_make_assoc_change(
+	const struct sctp_association *asoc,
+	__u16 flags,
+	__u16 state,
+	__u16 error,
+	__u16 outbound,
+	__u16 inbound,
+	struct sctp_chunk *chunk,
+	gfp_t gfp);
+
+void sctp_ulpevent_notify_peer_addr_change(struct sctp_transport *transport,
+					   int state, int error);
+
+struct sctp_ulpevent *sctp_ulpevent_make_remote_error(
+	const struct sctp_association *asoc,
+	struct sctp_chunk *chunk,
+	__u16 flags,
+	gfp_t gfp);
+struct sctp_ulpevent *sctp_ulpevent_make_send_failed(
+	const struct sctp_association *asoc,
+	struct sctp_chunk *chunk,
+	__u16 flags,
+	__u32 error,
+	gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_send_failed_event(
+	const struct sctp_association *asoc,
+	struct sctp_chunk *chunk,
+	__u16 flags,
+	__u32 error,
+	gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_shutdown_event(
+	const struct sctp_association *asoc,
+	__u16 flags,
+	gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_pdapi(
+	const struct sctp_association *asoc,
+	__u32 indication, __u32 sid, __u32 seq,
+	__u32 flags, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_adaptation_indication(
+	const struct sctp_association *asoc, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
+	struct sctp_chunk *chunk,
+	gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_authkey(
+	const struct sctp_association *asoc, __u16 key_id,
+	__u32 indication, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_sender_dry_event(
+	const struct sctp_association *asoc, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_stream_reset_event(
+	const struct sctp_association *asoc, __u16 flags,
+	__u16 stream_num, __be16 *stream_list, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_assoc_reset_event(
+	const struct sctp_association *asoc, __u16 flags,
+	 __u32 local_tsn, __u32 remote_tsn, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_ulpevent_make_stream_change_event(
+	const struct sctp_association *asoc, __u16 flags,
+	__u32 strchange_instrms, __u32 strchange_outstrms, gfp_t gfp);
+
+struct sctp_ulpevent *sctp_make_reassembled_event(
+	struct net *net, struct sk_buff_head *queue,
+	struct sk_buff *f_frag, struct sk_buff *l_frag);
+
+void sctp_ulpevent_read_sndrcvinfo(const struct sctp_ulpevent *event,
+				   struct msghdr *);
+void sctp_ulpevent_read_rcvinfo(const struct sctp_ulpevent *event,
+				struct msghdr *);
+void sctp_ulpevent_read_nxtinfo(const struct sctp_ulpevent *event,
+				struct msghdr *, struct sock *sk);
+
+__u16 sctp_ulpevent_get_notification_type(const struct sctp_ulpevent *event);
+
+static inline void sctp_ulpevent_type_set(__u16 *subscribe,
+					  __u16 sn_type, __u8 on)
+{
+	if (sn_type > SCTP_SN_TYPE_MAX)
+		return;
+
+	if (on)
+		*subscribe |=  (1 << (sn_type - SCTP_SN_TYPE_BASE));
+	else
+		*subscribe &= ~(1 << (sn_type - SCTP_SN_TYPE_BASE));
+}
+
+/* Is this event type enabled? */
+static inline bool sctp_ulpevent_type_enabled(__u16 subscribe, __u16 sn_type)
+{
+	if (sn_type > SCTP_SN_TYPE_MAX)
+		return false;
+
+	return subscribe & (1 << (sn_type - SCTP_SN_TYPE_BASE));
+}
+
+/* Given an event subscription, is this event enabled? */
+static inline bool sctp_ulpevent_is_enabled(const struct sctp_ulpevent *event,
+					    __u16 subscribe)
+{
+	__u16 sn_type;
+
+	if (!sctp_ulpevent_is_notification(event))
+		return true;
+
+	sn_type = sctp_ulpevent_get_notification_type(event);
+
+	return sctp_ulpevent_type_enabled(subscribe, sn_type);
+}
+
+#endif /* __sctp_ulpevent_h__ */