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, 138 insertions, 0 deletions

diff --git a/net/bluetooth/hci_sysfs.c b/net/bluetooth/hci_sysfs.c
new file mode 100644
index 000000000..8957ce7c2
--- /dev/null
+++ b/net/bluetooth/hci_sysfs.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Bluetooth HCI driver model support. */
+
+#include <linux/module.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+static const struct class bt_class = {
+	.name = "bluetooth",
+};
+
+static void bt_link_release(struct device *dev)
+{
+	struct hci_conn *conn = to_hci_conn(dev);
+	kfree(conn);
+}
+
+static const struct device_type bt_link = {
+	.name    = "link",
+	.release = bt_link_release,
+};
+
+void hci_conn_init_sysfs(struct hci_conn *conn)
+{
+	struct hci_dev *hdev = conn->hdev;
+
+	bt_dev_dbg(hdev, "conn %p", conn);
+
+	conn->dev.type = &bt_link;
+	conn->dev.class = &bt_class;
+	conn->dev.parent = &hdev->dev;
+
+	device_initialize(&conn->dev);
+}
+
+void hci_conn_add_sysfs(struct hci_conn *conn)
+{
+	struct hci_dev *hdev = conn->hdev;
+
+	bt_dev_dbg(hdev, "conn %p", conn);
+
+	if (device_is_registered(&conn->dev))
+		return;
+
+	dev_set_name(&conn->dev, "%s:%d", hdev->name, conn->handle);
+
+	if (device_add(&conn->dev) < 0)
+		bt_dev_err(hdev, "failed to register connection device");
+}
+
+void hci_conn_del_sysfs(struct hci_conn *conn)
+{
+	struct hci_dev *hdev = conn->hdev;
+
+	bt_dev_dbg(hdev, "conn %p", conn);
+
+	if (!device_is_registered(&conn->dev)) {
+		/* If device_add() has *not* succeeded, use *only* put_device()
+		 * to drop the reference count.
+		 */
+		put_device(&conn->dev);
+		return;
+	}
+
+	/* If there are devices using the connection as parent reset it to NULL
+	 * before unregistering the device.
+	 */
+	while (1) {
+		struct device *dev;
+
+		dev = device_find_any_child(&conn->dev);
+		if (!dev)
+			break;
+		device_move(dev, NULL, DPM_ORDER_DEV_LAST);
+		put_device(dev);
+	}
+
+	device_unregister(&conn->dev);
+}
+
+static void bt_host_release(struct device *dev)
+{
+	struct hci_dev *hdev = to_hci_dev(dev);
+
+	if (hci_dev_test_flag(hdev, HCI_UNREGISTER)) {
+		hci_release_dev(hdev);
+	} else {
+		cleanup_srcu_struct(&hdev->srcu);
+		kfree(hdev);
+	}
+	module_put(THIS_MODULE);
+}
+
+static ssize_t reset_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t count)
+{
+	struct hci_dev *hdev = to_hci_dev(dev);
+
+	if (hdev->reset)
+		hdev->reset(hdev);
+
+	return count;
+}
+static DEVICE_ATTR_WO(reset);
+
+static struct attribute *bt_host_attrs[] = {
+	&dev_attr_reset.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(bt_host);
+
+static const struct device_type bt_host = {
+	.name    = "host",
+	.release = bt_host_release,
+	.groups = bt_host_groups,
+};
+
+void hci_init_sysfs(struct hci_dev *hdev)
+{
+	struct device *dev = &hdev->dev;
+
+	dev->type = &bt_host;
+	dev->class = &bt_class;
+
+	__module_get(THIS_MODULE);
+	device_initialize(dev);
+}
+
+int __init bt_sysfs_init(void)
+{
+	return class_register(&bt_class);
+}
+
+void bt_sysfs_cleanup(void)
+{
+	class_unregister(&bt_class);
+}