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, 78 insertions, 0 deletions

diff --git a/net/bluetooth/msft.h b/net/bluetooth/msft.h
new file mode 100644
index 000000000..fe538e9c9
--- /dev/null
+++ b/net/bluetooth/msft.h
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Google Corporation
+ */
+
+#define MSFT_FEATURE_MASK_BREDR_RSSI_MONITOR		BIT(0)
+#define MSFT_FEATURE_MASK_LE_CONN_RSSI_MONITOR		BIT(1)
+#define MSFT_FEATURE_MASK_LE_ADV_RSSI_MONITOR		BIT(2)
+#define MSFT_FEATURE_MASK_LE_ADV_MONITOR		BIT(3)
+#define MSFT_FEATURE_MASK_CURVE_VALIDITY		BIT(4)
+#define MSFT_FEATURE_MASK_CONCURRENT_ADV_MONITOR	BIT(5)
+
+#if IS_ENABLED(CONFIG_BT_MSFTEXT)
+
+bool msft_monitor_supported(struct hci_dev *hdev);
+void msft_register(struct hci_dev *hdev);
+void msft_release(struct hci_dev *hdev);
+void msft_do_open(struct hci_dev *hdev);
+void msft_do_close(struct hci_dev *hdev);
+void msft_vendor_evt(struct hci_dev *hdev, void *data, struct sk_buff *skb);
+__u64 msft_get_features(struct hci_dev *hdev);
+int msft_add_monitor_pattern(struct hci_dev *hdev, struct adv_monitor *monitor);
+int msft_remove_monitor(struct hci_dev *hdev, struct adv_monitor *monitor);
+void msft_req_add_set_filter_enable(struct hci_request *req, bool enable);
+int msft_set_filter_enable(struct hci_dev *hdev, bool enable);
+int msft_suspend_sync(struct hci_dev *hdev);
+int msft_resume_sync(struct hci_dev *hdev);
+bool msft_curve_validity(struct hci_dev *hdev);
+
+#else
+
+static inline bool msft_monitor_supported(struct hci_dev *hdev)
+{
+	return false;
+}
+
+static inline void msft_register(struct hci_dev *hdev) {}
+static inline void msft_release(struct hci_dev *hdev) {}
+static inline void msft_do_open(struct hci_dev *hdev) {}
+static inline void msft_do_close(struct hci_dev *hdev) {}
+static inline void msft_vendor_evt(struct hci_dev *hdev, void *data,
+				   struct sk_buff *skb) {}
+static inline __u64 msft_get_features(struct hci_dev *hdev) { return 0; }
+static inline int msft_add_monitor_pattern(struct hci_dev *hdev,
+					   struct adv_monitor *monitor)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int msft_remove_monitor(struct hci_dev *hdev,
+				      struct adv_monitor *monitor)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void msft_req_add_set_filter_enable(struct hci_request *req,
+						  bool enable) {}
+static inline int msft_set_filter_enable(struct hci_dev *hdev, bool enable)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int msft_suspend_sync(struct hci_dev *hdev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int msft_resume_sync(struct hci_dev *hdev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline bool msft_curve_validity(struct hci_dev *hdev)
+{
+	return false;
+}
+
+#endif