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, 86 insertions, 0 deletions

diff --git a/include/net/gtp.h b/include/net/gtp.h
new file mode 100644
index 000000000..c0253c870
--- /dev/null
+++ b/include/net/gtp.h
@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _GTP_H_
+#define _GTP_H_
+
+#include <linux/netdevice.h>
+#include <linux/types.h>
+#include <net/rtnetlink.h>
+
+/* General GTP protocol related definitions. */
+
+#define GTP0_PORT	3386
+#define GTP1U_PORT	2152
+
+/* GTP messages types */
+#define GTP_ECHO_REQ	1	/* Echo Request */
+#define GTP_ECHO_RSP	2	/* Echo Response */
+#define GTP_TPDU	255
+
+#define GTPIE_RECOVERY	14
+
+struct gtp0_header {	/* According to GSM TS 09.60. */
+	__u8	flags;
+	__u8	type;
+	__be16	length;
+	__be16	seq;
+	__be16	flow;
+	__u8	number;
+	__u8	spare[3];
+	__be64	tid;
+} __attribute__ ((packed));
+
+struct gtp1_header {	/* According to 3GPP TS 29.060. */
+	__u8	flags;
+	__u8	type;
+	__be16	length;
+	__be32	tid;
+} __attribute__ ((packed));
+
+struct gtp1_header_long {	/* According to 3GPP TS 29.060. */
+	__u8	flags;
+	__u8	type;
+	__be16	length;
+	__be32	tid;
+	__be16	seq;
+	__u8	npdu;
+	__u8	next;
+} __packed;
+
+/* GTP Information Element */
+struct gtp_ie {
+	__u8	tag;
+	__u8	val;
+} __packed;
+
+struct gtp0_packet {
+	struct gtp0_header gtp0_h;
+	struct gtp_ie ie;
+} __packed;
+
+struct gtp1u_packet {
+	struct gtp1_header_long gtp1u_h;
+	struct gtp_ie ie;
+} __packed;
+
+struct gtp_pdu_session_info {	/* According to 3GPP TS 38.415. */
+	u8	pdu_type;
+	u8	qfi;
+};
+
+static inline bool netif_is_gtp(const struct net_device *dev)
+{
+	return dev->rtnl_link_ops &&
+		!strcmp(dev->rtnl_link_ops->kind, "gtp");
+}
+
+#define GTP1_F_NPDU	0x01
+#define GTP1_F_SEQ	0x02
+#define GTP1_F_EXTHDR	0x04
+#define GTP1_F_MASK	0x07
+
+struct gtp_ext_hdr {
+	__u8	len;
+	__u8	data[];
+};
+
+#endif