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, 151 insertions, 0 deletions

diff --git a/net/llc/llc_if.c b/net/llc/llc_if.c
new file mode 100644
index 000000000..1514362e6
--- /dev/null
+++ b/net/llc/llc_if.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * llc_if.c - Defines LLC interface to upper layer
+ *
+ * Copyright (c) 1997 by Procom Technology, Inc.
+ * 		 2001-2003 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+#include <linux/gfp.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/netdevice.h>
+#include <linux/errno.h>
+#include <net/llc_if.h>
+#include <net/llc_sap.h>
+#include <net/llc_s_ev.h>
+#include <net/llc_conn.h>
+#include <net/sock.h>
+#include <net/llc_c_ev.h>
+#include <net/llc_c_ac.h>
+#include <net/llc_c_st.h>
+#include <net/tcp_states.h>
+
+/**
+ *	llc_build_and_send_pkt - Connection data sending for upper layers.
+ *	@sk: connection
+ *	@skb: packet to send
+ *
+ *	This function is called when upper layer wants to send data using
+ *	connection oriented communication mode. During sending data, connection
+ *	will be locked and received frames and expired timers will be queued.
+ *	Returns 0 for success, -ECONNABORTED when the connection already
+ *	closed and -EBUSY when sending data is not permitted in this state or
+ *	LLC has send an I pdu with p bit set to 1 and is waiting for it's
+ *	response.
+ *
+ *	This function always consumes a reference to the skb.
+ */
+int llc_build_and_send_pkt(struct sock *sk, struct sk_buff *skb)
+{
+	struct llc_conn_state_ev *ev;
+	int rc = -ECONNABORTED;
+	struct llc_sock *llc = llc_sk(sk);
+
+	if (unlikely(llc->state == LLC_CONN_STATE_ADM))
+		goto out_free;
+	rc = -EBUSY;
+	if (unlikely(llc_data_accept_state(llc->state) || /* data_conn_refuse */
+		     llc->p_flag)) {
+		llc->failed_data_req = 1;
+		goto out_free;
+	}
+	ev = llc_conn_ev(skb);
+	ev->type      = LLC_CONN_EV_TYPE_PRIM;
+	ev->prim      = LLC_DATA_PRIM;
+	ev->prim_type = LLC_PRIM_TYPE_REQ;
+	skb->dev      = llc->dev;
+	return llc_conn_state_process(sk, skb);
+
+out_free:
+	kfree_skb(skb);
+	return rc;
+}
+
+/**
+ *	llc_establish_connection - Called by upper layer to establish a conn
+ *	@sk: connection
+ *	@lmac: local mac address
+ *	@dmac: destination mac address
+ *	@dsap: destination sap
+ *
+ *	Upper layer calls this to establish an LLC connection with a remote
+ *	machine. This function packages a proper event and sends it connection
+ *	component state machine. Success or failure of connection
+ *	establishment will inform to upper layer via calling it's confirm
+ *	function and passing proper information.
+ */
+int llc_establish_connection(struct sock *sk, const u8 *lmac, u8 *dmac, u8 dsap)
+{
+	int rc = -EISCONN;
+	struct llc_addr laddr, daddr;
+	struct sk_buff *skb;
+	struct llc_sock *llc = llc_sk(sk);
+	struct sock *existing;
+
+	laddr.lsap = llc->sap->laddr.lsap;
+	daddr.lsap = dsap;
+	memcpy(daddr.mac, dmac, sizeof(daddr.mac));
+	memcpy(laddr.mac, lmac, sizeof(laddr.mac));
+	existing = llc_lookup_established(llc->sap, &daddr, &laddr, sock_net(sk));
+	if (existing) {
+		if (existing->sk_state == TCP_ESTABLISHED) {
+			sk = existing;
+			goto out_put;
+		} else
+			sock_put(existing);
+	}
+	sock_hold(sk);
+	rc = -ENOMEM;
+	skb = alloc_skb(0, GFP_ATOMIC);
+	if (skb) {
+		struct llc_conn_state_ev *ev = llc_conn_ev(skb);
+
+		ev->type      = LLC_CONN_EV_TYPE_PRIM;
+		ev->prim      = LLC_CONN_PRIM;
+		ev->prim_type = LLC_PRIM_TYPE_REQ;
+		skb_set_owner_w(skb, sk);
+		rc = llc_conn_state_process(sk, skb);
+	}
+out_put:
+	sock_put(sk);
+	return rc;
+}
+
+/**
+ *	llc_send_disc - Called by upper layer to close a connection
+ *	@sk: connection to be closed
+ *
+ *	Upper layer calls this when it wants to close an established LLC
+ *	connection with a remote machine. This function packages a proper event
+ *	and sends it to connection component state machine. Returns 0 for
+ *	success, 1 otherwise.
+ */
+int llc_send_disc(struct sock *sk)
+{
+	u16 rc = 1;
+	struct llc_conn_state_ev *ev;
+	struct sk_buff *skb;
+
+	sock_hold(sk);
+	if (sk->sk_type != SOCK_STREAM || sk->sk_state != TCP_ESTABLISHED ||
+	    llc_sk(sk)->state == LLC_CONN_STATE_ADM ||
+	    llc_sk(sk)->state == LLC_CONN_OUT_OF_SVC)
+		goto out;
+	/*
+	 * Postpone unassigning the connection from its SAP and returning the
+	 * connection until all ACTIONs have been completely executed
+	 */
+	skb = alloc_skb(0, GFP_ATOMIC);
+	if (!skb)
+		goto out;
+	skb_set_owner_w(skb, sk);
+	sk->sk_state  = TCP_CLOSING;
+	ev	      = llc_conn_ev(skb);
+	ev->type      = LLC_CONN_EV_TYPE_PRIM;
+	ev->prim      = LLC_DISC_PRIM;
+	ev->prim_type = LLC_PRIM_TYPE_REQ;
+	rc = llc_conn_state_process(sk, skb);
+out:
+	sock_put(sk);
+	return rc;
+}