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, 40 insertions, 0 deletions

diff --git a/net/dsa/dsa.h b/net/dsa/dsa.h
new file mode 100644
index 000000000..3cc7823e9
--- /dev/null
+++ b/net/dsa/dsa.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef __DSA_H
+#define __DSA_H
+
+#include <linux/list.h>
+#include <linux/types.h>
+
+struct dsa_db;
+struct dsa_device_ops;
+struct dsa_lag;
+struct dsa_switch_tree;
+struct net_device;
+struct work_struct;
+
+extern struct list_head dsa_tree_list;
+
+bool dsa_db_equal(const struct dsa_db *a, const struct dsa_db *b);
+bool dsa_schedule_work(struct work_struct *work);
+void dsa_lag_map(struct dsa_switch_tree *dst, struct dsa_lag *lag);
+void dsa_lag_unmap(struct dsa_switch_tree *dst, struct dsa_lag *lag);
+struct dsa_lag *dsa_tree_lag_find(struct dsa_switch_tree *dst,
+				  const struct net_device *lag_dev);
+struct net_device *dsa_tree_find_first_conduit(struct dsa_switch_tree *dst);
+int dsa_tree_change_tag_proto(struct dsa_switch_tree *dst,
+			      const struct dsa_device_ops *tag_ops,
+			      const struct dsa_device_ops *old_tag_ops);
+void dsa_tree_conduit_admin_state_change(struct dsa_switch_tree *dst,
+					 struct net_device *conduit,
+					 bool up);
+void dsa_tree_conduit_oper_state_change(struct dsa_switch_tree *dst,
+					struct net_device *conduit,
+					bool up);
+unsigned int dsa_bridge_num_get(const struct net_device *bridge_dev, int max);
+void dsa_bridge_num_put(const struct net_device *bridge_dev,
+			unsigned int bridge_num);
+struct dsa_bridge *dsa_tree_bridge_find(struct dsa_switch_tree *dst,
+					const struct net_device *br);
+
+#endif