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, 198 insertions, 0 deletions

diff --git a/drivers/bluetooth/btrtl.h b/drivers/bluetooth/btrtl.h
new file mode 100644
index 000000000..a2d9d34f9
--- /dev/null
+++ b/drivers/bluetooth/btrtl.h
@@ -0,0 +1,198 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  Bluetooth support for Realtek devices
+ *
+ *  Copyright (C) 2015 Endless Mobile, Inc.
+ */
+
+#define RTL_FRAG_LEN 252
+
+#define rtl_dev_err(dev, fmt, ...) bt_dev_err(dev, "RTL: " fmt, ##__VA_ARGS__)
+#define rtl_dev_warn(dev, fmt, ...) bt_dev_warn(dev, "RTL: " fmt, ##__VA_ARGS__)
+#define rtl_dev_info(dev, fmt, ...) bt_dev_info(dev, "RTL: " fmt, ##__VA_ARGS__)
+#define rtl_dev_dbg(dev, fmt, ...) bt_dev_dbg(dev, "RTL: " fmt, ##__VA_ARGS__)
+
+struct btrtl_device_info;
+
+struct rtl_chip_type_evt {
+	__u8 status;
+	__u8 type;
+} __packed;
+
+struct rtl_download_cmd {
+	__u8 index;
+	__u8 data[RTL_FRAG_LEN];
+} __packed;
+
+struct rtl_download_response {
+	__u8 status;
+	__u8 index;
+} __packed;
+
+struct rtl_rom_version_evt {
+	__u8 status;
+	__u8 version;
+} __packed;
+
+struct rtl_epatch_header {
+	__u8 signature[8];
+	__le32 fw_version;
+	__le16 num_patches;
+} __packed;
+
+struct rtl_vendor_config_entry {
+	__le16 offset;
+	__u8 len;
+	__u8 data[];
+} __packed;
+
+struct rtl_vendor_config {
+	__le32 signature;
+	__le16 total_len;
+	__u8 entry[];
+} __packed;
+
+struct rtl_epatch_header_v2 {
+	__u8   signature[8];
+	__u8   fw_version[8];
+	__le32 num_sections;
+} __packed;
+
+struct rtl_section {
+	__le32 opcode;
+	__le32 len;
+	u8     data[];
+} __packed;
+
+struct rtl_section_hdr {
+	__le16 num;
+	__le16 reserved;
+} __packed;
+
+struct rtl_common_subsec {
+	__u8   eco;
+	__u8   prio;
+	__u8   cb[2];
+	__le32 len;
+	__u8   data[];
+};
+
+struct rtl_sec_hdr {
+	__u8   eco;
+	__u8   prio;
+	__u8   key_id;
+	__u8   reserved;
+	__le32 len;
+	__u8   data[];
+} __packed;
+
+struct rtl_subsection {
+	struct list_head list;
+	u32 opcode;
+	u32 len;
+	u8 prio;
+	u8 *data;
+};
+
+struct rtl_iovec {
+	u8  *data;
+	u32 len;
+};
+
+struct rtl_vendor_cmd {
+	__u8 param[5];
+} __packed;
+
+enum {
+	REALTEK_ALT6_CONTINUOUS_TX_CHIP,
+
+	__REALTEK_NUM_FLAGS,
+};
+
+struct rtl_dump_info {
+	const char *driver_name;
+	char *controller;
+	u32  fw_version;
+};
+
+struct btrealtek_data {
+	DECLARE_BITMAP(flags, __REALTEK_NUM_FLAGS);
+
+	struct rtl_dump_info rtl_dump;
+};
+
+#define btrealtek_set_flag(hdev, nr)					\
+	do {								\
+		struct btrealtek_data *realtek = hci_get_priv((hdev));	\
+		set_bit((nr), realtek->flags);				\
+	} while (0)
+
+#define btrealtek_get_flag(hdev)					\
+	(((struct btrealtek_data *)hci_get_priv(hdev))->flags)
+
+#define btrealtek_test_flag(hdev, nr)	test_bit((nr), btrealtek_get_flag(hdev))
+
+#if IS_ENABLED(CONFIG_BT_RTL)
+
+struct btrtl_device_info *btrtl_initialize(struct hci_dev *hdev,
+					   const char *postfix);
+void btrtl_free(struct btrtl_device_info *btrtl_dev);
+int btrtl_download_firmware(struct hci_dev *hdev,
+			    struct btrtl_device_info *btrtl_dev);
+void btrtl_set_quirks(struct hci_dev *hdev,
+		      struct btrtl_device_info *btrtl_dev);
+int btrtl_setup_realtek(struct hci_dev *hdev);
+int btrtl_shutdown_realtek(struct hci_dev *hdev);
+int btrtl_get_uart_settings(struct hci_dev *hdev,
+			    struct btrtl_device_info *btrtl_dev,
+			    unsigned int *controller_baudrate,
+			    u32 *device_baudrate, bool *flow_control);
+void btrtl_set_driver_name(struct hci_dev *hdev, const char *driver_name);
+
+#else
+
+static inline struct btrtl_device_info *btrtl_initialize(struct hci_dev *hdev,
+							 const char *postfix)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void btrtl_free(struct btrtl_device_info *btrtl_dev)
+{
+}
+
+static inline int btrtl_download_firmware(struct hci_dev *hdev,
+					  struct btrtl_device_info *btrtl_dev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void btrtl_set_quirks(struct hci_dev *hdev,
+				    struct btrtl_device_info *btrtl_dev)
+{
+}
+
+static inline int btrtl_setup_realtek(struct hci_dev *hdev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int btrtl_shutdown_realtek(struct hci_dev *hdev)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int btrtl_get_uart_settings(struct hci_dev *hdev,
+					  struct btrtl_device_info *btrtl_dev,
+					  unsigned int *controller_baudrate,
+					  u32 *device_baudrate,
+					  bool *flow_control)
+{
+	return -ENOENT;
+}
+
+static inline void btrtl_set_driver_name(struct hci_dev *hdev, const char *driver_name)
+{
+}
+
+#endif