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, 165 insertions, 0 deletions

diff --git a/drivers/leds/trigger/ledtrig-input-events.c b/drivers/leds/trigger/ledtrig-input-events.c
new file mode 100644
index 000000000..d057b2a23
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-input-events.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Input Events LED trigger
+ *
+ * Copyright (C) 2024 Hans de Goede <hansg@kernel.org>
+ */
+
+#include <linux/input.h>
+#include <linux/jiffies.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+#include "../leds.h"
+
+static unsigned long led_off_delay_ms = 5000;
+module_param(led_off_delay_ms, ulong, 0644);
+MODULE_PARM_DESC(led_off_delay_ms,
+	"Specify delay in ms for turning LEDs off after last input event");
+
+static struct input_events_data {
+	struct delayed_work work;
+	spinlock_t lock;
+	/* To avoid repeatedly setting the brightness while there are events */
+	bool led_on;
+	unsigned long led_off_time;
+} input_events_data;
+
+static struct led_trigger *input_events_led_trigger;
+
+static void led_input_events_work(struct work_struct *work)
+{
+	struct input_events_data *data =
+		container_of(work, struct input_events_data, work.work);
+
+	spin_lock_irq(&data->lock);
+
+	/*
+	 * This time_after_eq() check avoids a race where this work starts
+	 * running before a new event pushed led_off_time back.
+	 */
+	if (time_after_eq(jiffies, data->led_off_time)) {
+		led_trigger_event(input_events_led_trigger, LED_OFF);
+		data->led_on = false;
+	}
+
+	spin_unlock_irq(&data->lock);
+}
+
+static void input_events_event(struct input_handle *handle, unsigned int type,
+			       unsigned int code, int val)
+{
+	struct input_events_data *data = &input_events_data;
+	unsigned long led_off_delay = msecs_to_jiffies(led_off_delay_ms);
+	unsigned long flags;
+
+	spin_lock_irqsave(&data->lock, flags);
+
+	if (!data->led_on) {
+		led_trigger_event(input_events_led_trigger, LED_FULL);
+		data->led_on = true;
+	}
+	data->led_off_time = jiffies + led_off_delay;
+
+	spin_unlock_irqrestore(&data->lock, flags);
+
+	mod_delayed_work(system_percpu_wq, &data->work, led_off_delay);
+}
+
+static int input_events_connect(struct input_handler *handler, struct input_dev *dev,
+				const struct input_device_id *id)
+{
+	struct input_handle *handle;
+	int ret;
+
+	handle = kzalloc_obj(*handle);
+	if (!handle)
+		return -ENOMEM;
+
+	handle->dev = dev;
+	handle->handler = handler;
+	handle->name = KBUILD_MODNAME;
+
+	ret = input_register_handle(handle);
+	if (ret)
+		goto err_free_handle;
+
+	ret = input_open_device(handle);
+	if (ret)
+		goto err_unregister_handle;
+
+	return 0;
+
+err_unregister_handle:
+	input_unregister_handle(handle);
+err_free_handle:
+	kfree(handle);
+	return ret;
+}
+
+static void input_events_disconnect(struct input_handle *handle)
+{
+	input_close_device(handle);
+	input_unregister_handle(handle);
+	kfree(handle);
+}
+
+static const struct input_device_id input_events_ids[] = {
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_REL) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT,
+		.evbit = { BIT_MASK(EV_ABS) },
+	},
+	{ }
+};
+
+static struct input_handler input_events_handler = {
+	.name = KBUILD_MODNAME,
+	.event = input_events_event,
+	.connect = input_events_connect,
+	.disconnect = input_events_disconnect,
+	.id_table = input_events_ids,
+};
+
+static int __init input_events_init(void)
+{
+	int ret;
+
+	INIT_DELAYED_WORK(&input_events_data.work, led_input_events_work);
+	spin_lock_init(&input_events_data.lock);
+
+	led_trigger_register_simple("input-events", &input_events_led_trigger);
+
+	ret = input_register_handler(&input_events_handler);
+	if (ret) {
+		led_trigger_unregister_simple(input_events_led_trigger);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void __exit input_events_exit(void)
+{
+	input_unregister_handler(&input_events_handler);
+	cancel_delayed_work_sync(&input_events_data.work);
+	led_trigger_unregister_simple(input_events_led_trigger);
+}
+
+module_init(input_events_init);
+module_exit(input_events_exit);
+
+MODULE_AUTHOR("Hans de Goede <hansg@kernel.org>");
+MODULE_DESCRIPTION("Input Events LED trigger");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ledtrig:input-events");