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, 142 insertions, 0 deletions

diff --git a/drivers/leds/trigger/ledtrig-gpio.c b/drivers/leds/trigger/ledtrig-gpio.c
new file mode 100644
index 000000000..3b3e6869e
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-gpio.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ledtrig-gio.c - LED Trigger Based on GPIO events
+ *
+ * Copyright 2009 Felipe Balbi <me@felipebalbi.com>
+ * Copyright 2023 Linus Walleij <linus.walleij@linaro.org>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/gpio/consumer.h>
+#include <linux/interrupt.h>
+#include <linux/leds.h>
+#include <linux/slab.h>
+#include "../leds.h"
+
+struct gpio_trig_data {
+	struct led_classdev *led;
+	unsigned desired_brightness;	/* desired brightness when led is on */
+	struct gpio_desc *gpiod;	/* gpio that triggers the led */
+};
+
+static irqreturn_t gpio_trig_irq(int irq, void *_led)
+{
+	struct led_classdev *led = _led;
+	struct gpio_trig_data *gpio_data = led_get_trigger_data(led);
+	int tmp;
+
+	tmp = gpiod_get_value_cansleep(gpio_data->gpiod);
+	if (tmp) {
+		if (gpio_data->desired_brightness)
+			led_set_brightness_nosleep(gpio_data->led,
+					   gpio_data->desired_brightness);
+		else
+			led_set_brightness_nosleep(gpio_data->led, LED_FULL);
+	} else {
+		led_set_brightness_nosleep(gpio_data->led, LED_OFF);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static ssize_t desired_brightness_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpio_trig_data *gpio_data = led_trigger_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%u\n", gpio_data->desired_brightness);
+}
+
+static ssize_t desired_brightness_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t n)
+{
+	struct gpio_trig_data *gpio_data = led_trigger_get_drvdata(dev);
+	u8 desired_brightness;
+	int ret;
+
+	ret = kstrtou8(buf, 10, &desired_brightness);
+	if (ret)
+		return ret;
+
+	gpio_data->desired_brightness = desired_brightness;
+
+	return n;
+}
+static DEVICE_ATTR_RW(desired_brightness);
+
+static struct attribute *gpio_trig_attrs[] = {
+	&dev_attr_desired_brightness.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(gpio_trig);
+
+static int gpio_trig_activate(struct led_classdev *led)
+{
+	struct gpio_trig_data *gpio_data;
+	struct device *dev = led->dev;
+	int ret;
+
+	gpio_data = kzalloc_obj(*gpio_data);
+	if (!gpio_data)
+		return -ENOMEM;
+
+	/*
+	 * The generic property "trigger-sources" is followed,
+	 * and we hope that this is a GPIO.
+	 */
+	gpio_data->gpiod = gpiod_get_optional(dev, "trigger-sources",
+					      GPIOD_IN | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
+	if (IS_ERR(gpio_data->gpiod)) {
+		ret = PTR_ERR(gpio_data->gpiod);
+		kfree(gpio_data);
+		return ret;
+	}
+	if (!gpio_data->gpiod) {
+		dev_err(dev, "no valid GPIO for the trigger\n");
+		kfree(gpio_data);
+		return -EINVAL;
+	}
+
+	gpiod_set_consumer_name(gpio_data->gpiod, "led-trigger");
+
+	gpio_data->led = led;
+	led_set_trigger_data(led, gpio_data);
+
+	ret = request_threaded_irq(gpiod_to_irq(gpio_data->gpiod), NULL, gpio_trig_irq,
+			IRQF_ONESHOT | IRQF_SHARED | IRQF_TRIGGER_RISING
+			| IRQF_TRIGGER_FALLING, "ledtrig-gpio", led);
+	if (ret) {
+		dev_err(dev, "request_irq failed with error %d\n", ret);
+		gpiod_put(gpio_data->gpiod);
+		kfree(gpio_data);
+		return ret;
+	}
+
+	/* Finally update the LED to initial status */
+	gpio_trig_irq(0, led);
+
+	return 0;
+}
+
+static void gpio_trig_deactivate(struct led_classdev *led)
+{
+	struct gpio_trig_data *gpio_data = led_get_trigger_data(led);
+
+	free_irq(gpiod_to_irq(gpio_data->gpiod), led);
+	gpiod_put(gpio_data->gpiod);
+	kfree(gpio_data);
+}
+
+static struct led_trigger gpio_led_trigger = {
+	.name		= "gpio",
+	.activate	= gpio_trig_activate,
+	.deactivate	= gpio_trig_deactivate,
+	.groups		= gpio_trig_groups,
+};
+module_led_trigger(gpio_led_trigger);
+
+MODULE_AUTHOR("Felipe Balbi <me@felipebalbi.com>");
+MODULE_DESCRIPTION("GPIO LED trigger");
+MODULE_LICENSE("GPL v2");