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, 51 insertions, 0 deletions

diff --git a/drivers/dpll/dpll_nl.h b/drivers/dpll/dpll_nl.h
new file mode 100644
index 000000000..fa8280e3d
--- /dev/null
+++ b/drivers/dpll/dpll_nl.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
+/* Do not edit directly, auto-generated from: */
+/*	Documentation/netlink/specs/dpll.yaml */
+/* YNL-GEN kernel header */
+/* To regenerate run: tools/net/ynl/ynl-regen.sh */
+
+#ifndef _LINUX_DPLL_GEN_H
+#define _LINUX_DPLL_GEN_H
+
+#include <net/netlink.h>
+#include <net/genetlink.h>
+
+#include <uapi/linux/dpll.h>
+
+/* Common nested types */
+extern const struct nla_policy dpll_pin_parent_device_nl_policy[DPLL_A_PIN_OPERSTATE + 1];
+extern const struct nla_policy dpll_pin_parent_pin_nl_policy[DPLL_A_PIN_STATE + 1];
+extern const struct nla_policy dpll_reference_sync_nl_policy[DPLL_A_PIN_STATE + 1];
+
+int dpll_lock_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
+		   struct genl_info *info);
+int dpll_pre_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
+		  struct genl_info *info);
+int dpll_pin_pre_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
+		      struct genl_info *info);
+void
+dpll_unlock_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
+		 struct genl_info *info);
+void
+dpll_post_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
+	       struct genl_info *info);
+void
+dpll_pin_post_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
+		   struct genl_info *info);
+
+int dpll_nl_device_id_get_doit(struct sk_buff *skb, struct genl_info *info);
+int dpll_nl_device_get_doit(struct sk_buff *skb, struct genl_info *info);
+int dpll_nl_device_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb);
+int dpll_nl_device_set_doit(struct sk_buff *skb, struct genl_info *info);
+int dpll_nl_pin_id_get_doit(struct sk_buff *skb, struct genl_info *info);
+int dpll_nl_pin_get_doit(struct sk_buff *skb, struct genl_info *info);
+int dpll_nl_pin_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb);
+int dpll_nl_pin_set_doit(struct sk_buff *skb, struct genl_info *info);
+
+enum {
+	DPLL_NLGRP_MONITOR,
+};
+
+extern struct genl_family dpll_nl_family;
+
+#endif /* _LINUX_DPLL_GEN_H */