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, 28 insertions, 0 deletions

diff --git a/include/net/rawv6.h b/include/net/rawv6.h
new file mode 100644
index 000000000..82810cbe3
--- /dev/null
+++ b/include/net/rawv6.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _NET_RAWV6_H
+#define _NET_RAWV6_H
+
+#include <net/protocol.h>
+#include <net/raw.h>
+
+extern struct raw_hashinfo raw_v6_hashinfo;
+bool raw_v6_match(struct net *net, const struct sock *sk, unsigned short num,
+		  const struct in6_addr *loc_addr,
+		  const struct in6_addr *rmt_addr, int dif, int sdif);
+
+int raw_abort(struct sock *sk, int err);
+
+void raw6_icmp_error(struct sk_buff *, int nexthdr,
+		u8 type, u8 code, int inner_offset, __be32);
+bool raw6_local_deliver(struct sk_buff *, int);
+
+int rawv6_rcv(struct sock *sk, struct sk_buff *skb);
+
+#if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE)
+int rawv6_mh_filter_register(int (*filter)(struct sock *sock,
+					   struct sk_buff *skb));
+int rawv6_mh_filter_unregister(int (*filter)(struct sock *sock,
+					     struct sk_buff *skb));
+#endif
+
+#endif