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, 49 insertions, 0 deletions

diff --git a/include/net/netns/mctp.h b/include/net/netns/mctp.h
new file mode 100644
index 000000000..89555f90b
--- /dev/null
+++ b/include/net/netns/mctp.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * MCTP per-net structures
+ */
+
+#ifndef __NETNS_MCTP_H__
+#define __NETNS_MCTP_H__
+
+#include <linux/hash.h>
+#include <linux/hashtable.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+
+#define MCTP_BINDS_BITS 7
+
+struct netns_mctp {
+	/* Only updated under RTNL, entries freed via RCU */
+	struct list_head routes;
+
+	/* Bound sockets: hash table of sockets, keyed by
+	 * (type, src_eid, dest_eid).
+	 * Specific src_eid/dest_eid entries also have an entry for
+	 * MCTP_ADDR_ANY. This list is updated from non-atomic contexts
+	 * (under bind_lock), and read (under rcu) in packet rx.
+	 */
+	struct mutex bind_lock;
+	DECLARE_HASHTABLE(binds, MCTP_BINDS_BITS);
+
+	/* tag allocations. This list is read and updated from atomic contexts,
+	 * but elements are free()ed after a RCU grace-period
+	 */
+	spinlock_t keys_lock;
+	struct hlist_head keys;
+
+	/* MCTP network */
+	unsigned int default_net;
+
+	/* neighbour table */
+	struct mutex neigh_lock;
+	struct list_head neighbours;
+};
+
+static inline u32 mctp_bind_hash(u8 type, u8 local_addr, u8 peer_addr)
+{
+	return hash_32(type | (u32)local_addr << 8 | (u32)peer_addr << 16,
+		       MCTP_BINDS_BITS);
+}
+
+#endif /* __NETNS_MCTP_H__ */