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, 100 insertions, 0 deletions

diff --git a/net/bluetooth/leds.c b/net/bluetooth/leds.c
new file mode 100644
index 000000000..6e349704e
--- /dev/null
+++ b/net/bluetooth/leds.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2015, Heiner Kallweit <hkallweit1@gmail.com>
+ */
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+#include "leds.h"
+
+DEFINE_LED_TRIGGER(bt_power_led_trigger);
+
+struct hci_basic_led_trigger {
+	struct led_trigger	led_trigger;
+	struct hci_dev		*hdev;
+};
+
+#define to_hci_basic_led_trigger(arg) container_of(arg, \
+			struct hci_basic_led_trigger, led_trigger)
+
+void hci_leds_update_powered(struct hci_dev *hdev, bool enabled)
+{
+	if (hdev->power_led)
+		led_trigger_event(hdev->power_led,
+				  enabled ? LED_FULL : LED_OFF);
+
+	if (!enabled) {
+		struct hci_dev *d;
+
+		read_lock(&hci_dev_list_lock);
+
+		list_for_each_entry(d, &hci_dev_list, list) {
+			if (test_bit(HCI_UP, &d->flags))
+				enabled = true;
+		}
+
+		read_unlock(&hci_dev_list_lock);
+	}
+
+	led_trigger_event(bt_power_led_trigger, enabled ? LED_FULL : LED_OFF);
+}
+
+static int power_activate(struct led_classdev *led_cdev)
+{
+	struct hci_basic_led_trigger *htrig;
+	bool powered;
+
+	htrig = to_hci_basic_led_trigger(led_cdev->trigger);
+	powered = test_bit(HCI_UP, &htrig->hdev->flags);
+
+	led_set_brightness(led_cdev, powered ? LED_FULL : LED_OFF);
+
+	return 0;
+}
+
+static struct led_trigger *led_allocate_basic(struct hci_dev *hdev,
+			int (*activate)(struct led_classdev *led_cdev),
+			const char *name)
+{
+	struct hci_basic_led_trigger *htrig;
+
+	htrig =	devm_kzalloc(&hdev->dev, sizeof(*htrig), GFP_KERNEL);
+	if (!htrig)
+		return NULL;
+
+	htrig->hdev = hdev;
+	htrig->led_trigger.activate = activate;
+	htrig->led_trigger.name = devm_kasprintf(&hdev->dev, GFP_KERNEL,
+						 "%s-%s", hdev->name,
+						 name);
+	if (!htrig->led_trigger.name)
+		goto err_alloc;
+
+	if (devm_led_trigger_register(&hdev->dev, &htrig->led_trigger))
+		goto err_register;
+
+	return &htrig->led_trigger;
+
+err_register:
+	devm_kfree(&hdev->dev, (void *)htrig->led_trigger.name);
+err_alloc:
+	devm_kfree(&hdev->dev, htrig);
+	return NULL;
+}
+
+void hci_leds_init(struct hci_dev *hdev)
+{
+	/* initialize power_led */
+	hdev->power_led = led_allocate_basic(hdev, power_activate, "power");
+}
+
+void bt_leds_init(void)
+{
+	led_trigger_register_simple("bluetooth-power", &bt_power_led_trigger);
+}
+
+void bt_leds_cleanup(void)
+{
+	led_trigger_unregister_simple(bt_power_led_trigger);
+}