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, 27 insertions, 0 deletions

diff --git a/include/net/sch_priv.h b/include/net/sch_priv.h
new file mode 100644
index 000000000..4789f668a
--- /dev/null
+++ b/include/net/sch_priv.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_SCHED_PRIV_H
+#define __NET_SCHED_PRIV_H
+
+#include <net/sch_generic.h>
+
+struct mq_sched {
+	struct Qdisc		**qdiscs;
+};
+
+int mq_init_common(struct Qdisc *sch, struct nlattr *opt,
+		   struct netlink_ext_ack *extack,
+		   const struct Qdisc_ops *qdisc_ops);
+void mq_destroy_common(struct Qdisc *sch);
+void mq_attach(struct Qdisc *sch);
+void mq_dump_common(struct Qdisc *sch, struct sk_buff *skb);
+struct netdev_queue *mq_select_queue(struct Qdisc *sch,
+				     struct tcmsg *tcm);
+struct Qdisc *mq_leaf(struct Qdisc *sch, unsigned long cl);
+unsigned long mq_find(struct Qdisc *sch, u32 classid);
+int mq_dump_class(struct Qdisc *sch, unsigned long cl,
+		  struct sk_buff *skb, struct tcmsg *tcm);
+int mq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
+			struct gnet_dump *d);
+void mq_walk(struct Qdisc *sch, struct qdisc_walker *arg);
+
+#endif