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, 90 insertions, 0 deletions

diff --git a/include/net/pfcp.h b/include/net/pfcp.h
new file mode 100644
index 000000000..639553797
--- /dev/null
+++ b/include/net/pfcp.h
@@ -0,0 +1,90 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _PFCP_H_
+#define _PFCP_H_
+
+#include <uapi/linux/if_ether.h>
+#include <net/dst_metadata.h>
+#include <linux/netdevice.h>
+#include <uapi/linux/ipv6.h>
+#include <net/udp_tunnel.h>
+#include <uapi/linux/udp.h>
+#include <uapi/linux/ip.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/bits.h>
+
+#define PFCP_PORT 8805
+
+/* PFCP protocol header */
+struct pfcphdr {
+	u8	flags;
+	u8	message_type;
+	__be16	message_length;
+};
+
+/* PFCP header flags */
+#define PFCP_SEID_FLAG		BIT(0)
+#define PFCP_MP_FLAG		BIT(1)
+
+#define PFCP_VERSION_MASK	GENMASK(4, 0)
+
+#define PFCP_HLEN (sizeof(struct udphdr) + sizeof(struct pfcphdr))
+
+/* PFCP node related messages */
+struct pfcphdr_node {
+	u8	seq_number[3];
+	u8	reserved;
+};
+
+/* PFCP session related messages */
+struct pfcphdr_session {
+	__be64	seid;
+	u8	seq_number[3];
+#ifdef __LITTLE_ENDIAN_BITFIELD
+	u8	message_priority:4,
+		reserved:4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	u8	reserved:4,
+		message_priority:4;
+#else
+#error "Please fix <asm/byteorder>"
+#endif
+};
+
+struct pfcp_metadata {
+	u8 type;
+	__be64 seid;
+} __packed;
+
+enum {
+	PFCP_TYPE_NODE		= 0,
+	PFCP_TYPE_SESSION	= 1,
+};
+
+#define PFCP_HEADROOM (sizeof(struct iphdr) + sizeof(struct udphdr) + \
+		       sizeof(struct pfcphdr) + sizeof(struct ethhdr))
+#define PFCP6_HEADROOM (sizeof(struct ipv6hdr) + sizeof(struct udphdr) + \
+			sizeof(struct pfcphdr) + sizeof(struct ethhdr))
+
+static inline struct pfcphdr *pfcp_hdr(struct sk_buff *skb)
+{
+	return (struct pfcphdr *)(udp_hdr(skb) + 1);
+}
+
+static inline struct pfcphdr_node *pfcp_hdr_node(struct sk_buff *skb)
+{
+	return (struct pfcphdr_node *)(pfcp_hdr(skb) + 1);
+}
+
+static inline struct pfcphdr_session *pfcp_hdr_session(struct sk_buff *skb)
+{
+	return (struct pfcphdr_session *)(pfcp_hdr(skb) + 1);
+}
+
+static inline bool netif_is_pfcp(const struct net_device *dev)
+{
+	return dev->rtnl_link_ops &&
+	       !strcmp(dev->rtnl_link_ops->kind, "pfcp");
+}
+
+#endif