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, 44 insertions, 0 deletions

diff --git a/drivers/net/wireguard/socket.h b/drivers/net/wireguard/socket.h
new file mode 100644
index 000000000..bab5848ef
--- /dev/null
+++ b/drivers/net/wireguard/socket.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#ifndef _WG_SOCKET_H
+#define _WG_SOCKET_H
+
+#include <linux/netdevice.h>
+#include <linux/udp.h>
+#include <linux/if_vlan.h>
+#include <linux/if_ether.h>
+
+int wg_socket_init(struct wg_device *wg, u16 port);
+void wg_socket_reinit(struct wg_device *wg, struct sock *new4,
+		      struct sock *new6);
+int wg_socket_send_buffer_to_peer(struct wg_peer *peer, void *data,
+				  size_t len, u8 ds);
+int wg_socket_send_skb_to_peer(struct wg_peer *peer, struct sk_buff *skb,
+			       u8 ds);
+int wg_socket_send_buffer_as_reply_to_skb(struct wg_device *wg,
+					  struct sk_buff *in_skb,
+					  void *out_buffer, size_t len);
+
+int wg_socket_endpoint_from_skb(struct endpoint *endpoint,
+				const struct sk_buff *skb);
+void wg_socket_set_peer_endpoint(struct wg_peer *peer,
+				 const struct endpoint *endpoint);
+void wg_socket_set_peer_endpoint_from_skb(struct wg_peer *peer,
+					  const struct sk_buff *skb);
+void wg_socket_clear_peer_endpoint_src(struct wg_peer *peer);
+
+#if defined(CONFIG_DYNAMIC_DEBUG) || defined(DEBUG)
+#define net_dbg_skb_ratelimited(fmt, dev, skb, ...) do {                       \
+		struct endpoint __endpoint;                                    \
+		wg_socket_endpoint_from_skb(&__endpoint, skb);                 \
+		net_dbg_ratelimited(fmt, dev, &__endpoint.addr,                \
+				    ##__VA_ARGS__);                            \
+	} while (0)
+#else
+#define net_dbg_skb_ratelimited(fmt, skb, ...)
+#endif
+
+#endif /* _WG_SOCKET_H */