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, 63 insertions, 0 deletions

diff --git a/include/net/llc_if.h b/include/net/llc_if.h
new file mode 100644
index 000000000..a33325961
--- /dev/null
+++ b/include/net/llc_if.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef LLC_IF_H
+#define LLC_IF_H
+/*
+ * Copyright (c) 1997 by Procom Technology,Inc.
+ * 		 2001 by Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+/* Defines LLC interface to network layer */
+/* Available primitives */
+#include <linux/if.h>
+#include <linux/if_arp.h>
+#include <linux/llc.h>
+#include <linux/etherdevice.h>
+#include <net/llc.h>
+
+#define LLC_DATAUNIT_PRIM	1
+#define LLC_CONN_PRIM		2
+#define LLC_DATA_PRIM		3
+#define LLC_DISC_PRIM		4
+#define LLC_RESET_PRIM		5
+#define LLC_FLOWCONTROL_PRIM	6 /* Not supported at this time */
+#define LLC_DISABLE_PRIM	7
+#define LLC_XID_PRIM		8
+#define LLC_TEST_PRIM		9
+#define LLC_SAP_ACTIVATION     10
+#define LLC_SAP_DEACTIVATION   11
+
+#define LLC_NBR_PRIMITIVES     11
+
+#define LLC_IND			1
+#define LLC_CONFIRM		2
+
+/* Primitive type */
+#define LLC_PRIM_TYPE_REQ	1
+#define LLC_PRIM_TYPE_IND	2
+#define LLC_PRIM_TYPE_RESP	3
+#define LLC_PRIM_TYPE_CONFIRM	4
+
+/* Reset reasons, remote entity or local LLC */
+#define LLC_RESET_REASON_REMOTE	1
+#define LLC_RESET_REASON_LOCAL	2
+
+/* Disconnect reasons */
+#define LLC_DISC_REASON_RX_DM_RSP_PDU	0
+#define LLC_DISC_REASON_RX_DISC_CMD_PDU	1
+#define LLC_DISC_REASON_ACK_TMR_EXP	2
+
+/* Confirm reasons */
+#define LLC_STATUS_CONN		0 /* connect confirm & reset confirm */
+#define LLC_STATUS_DISC		1 /* connect confirm & reset confirm */
+#define LLC_STATUS_FAILED	2 /* connect confirm & reset confirm */
+#define LLC_STATUS_IMPOSSIBLE	3 /* connect confirm */
+#define LLC_STATUS_RECEIVED	4 /* data conn */
+#define LLC_STATUS_REMOTE_BUSY	5 /* data conn */
+#define LLC_STATUS_REFUSE	6 /* data conn */
+#define LLC_STATUS_CONFLICT	7 /* disconnect conn */
+#define LLC_STATUS_RESET_DONE	8 /*  */
+
+int llc_establish_connection(struct sock *sk, const u8 *lmac, u8 *dmac,
+			     u8 dsap);
+int llc_build_and_send_pkt(struct sock *sk, struct sk_buff *skb);
+int llc_send_disc(struct sock *sk);
+#endif /* LLC_IF_H */