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/af_unix.h b/include/net/af_unix.h
new file mode 100644
index 000000000..34f53dde6
--- /dev/null
+++ b/include/net/af_unix.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_NET_AFUNIX_H
+#define __LINUX_NET_AFUNIX_H
+
+#include <linux/atomic.h>
+#include <linux/mutex.h>
+#include <linux/net.h>
+#include <linux/path.h>
+#include <linux/refcount.h>
+#include <linux/spinlock.h>
+#include <linux/wait.h>
+#include <net/sock.h>
+#include <uapi/linux/un.h>
+
+#if IS_ENABLED(CONFIG_UNIX)
+struct unix_sock *unix_get_socket(struct file *filp);
+#else
+static inline struct unix_sock *unix_get_socket(struct file *filp)
+{
+	return NULL;
+}
+#endif
+
+struct unix_address {
+	refcount_t	refcnt;
+	int		len;
+	struct sockaddr_un name[];
+};
+
+struct scm_stat {
+	atomic_t nr_fds;
+	unsigned long nr_unix_fds;
+};
+
+/* The AF_UNIX socket */
+struct unix_sock {
+	/* WARNING: sk has to be the first member */
+	struct sock		sk;
+	struct unix_address	*addr;
+	struct path		path;
+	struct mutex		iolock, bindlock;
+	struct sock		*peer;
+	struct sock		*listener;
+	struct unix_vertex	*vertex;
+	spinlock_t		lock;
+	struct socket_wq	peer_wq;
+#define peer_wait		peer_wq.wait
+	wait_queue_entry_t	peer_wake;
+	struct scm_stat		scm_stat;
+	int			inq_len;
+	bool			recvmsg_inq;
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+	struct sk_buff		*oob_skb;
+#endif
+};
+
+#define unix_sk(ptr) container_of_const(ptr, struct unix_sock, sk)
+#define unix_peer(sk) (unix_sk(sk)->peer)
+
+#define unix_state_lock(s)	spin_lock(&unix_sk(s)->lock)
+#define unix_state_unlock(s)	spin_unlock(&unix_sk(s)->lock)
+
+#endif