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, 199 insertions, 0 deletions

diff --git a/drivers/input/misc/gpio-vibra.c b/drivers/input/misc/gpio-vibra.c
new file mode 100644
index 000000000..ad44b4d18
--- /dev/null
+++ b/drivers/input/misc/gpio-vibra.c
@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ *  GPIO vibrator driver
+ *
+ *  Copyright (C) 2019 Luca Weiss <luca@z3ntu.xyz>
+ *
+ *  Based on PWM vibrator driver:
+ *  Copyright (C) 2017 Collabora Ltd.
+ *
+ *  Based on previous work from:
+ *  Copyright (C) 2012 Dmitry Torokhov <dmitry.torokhov@gmail.com>
+ *
+ *  Based on PWM beeper driver:
+ *  Copyright (C) 2010, Lars-Peter Clausen <lars@metafoo.de>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/input.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+
+struct gpio_vibrator {
+	struct input_dev *input;
+	struct gpio_desc *gpio;
+	struct regulator *vcc;
+
+	struct work_struct play_work;
+	bool running;
+	bool vcc_on;
+};
+
+static int gpio_vibrator_start(struct gpio_vibrator *vibrator)
+{
+	struct device *pdev = vibrator->input->dev.parent;
+	int err;
+
+	if (!vibrator->vcc_on) {
+		err = regulator_enable(vibrator->vcc);
+		if (err) {
+			dev_err(pdev, "failed to enable regulator: %d\n", err);
+			return err;
+		}
+		vibrator->vcc_on = true;
+	}
+
+	gpiod_set_value_cansleep(vibrator->gpio, 1);
+
+	return 0;
+}
+
+static void gpio_vibrator_stop(struct gpio_vibrator *vibrator)
+{
+	gpiod_set_value_cansleep(vibrator->gpio, 0);
+
+	if (vibrator->vcc_on) {
+		regulator_disable(vibrator->vcc);
+		vibrator->vcc_on = false;
+	}
+}
+
+static void gpio_vibrator_play_work(struct work_struct *work)
+{
+	struct gpio_vibrator *vibrator =
+		container_of(work, struct gpio_vibrator, play_work);
+
+	if (vibrator->running)
+		gpio_vibrator_start(vibrator);
+	else
+		gpio_vibrator_stop(vibrator);
+}
+
+static int gpio_vibrator_play_effect(struct input_dev *dev, void *data,
+				     struct ff_effect *effect)
+{
+	struct gpio_vibrator *vibrator = input_get_drvdata(dev);
+	int level;
+
+	level = effect->u.rumble.strong_magnitude;
+	if (!level)
+		level = effect->u.rumble.weak_magnitude;
+
+	vibrator->running = level;
+	schedule_work(&vibrator->play_work);
+
+	return 0;
+}
+
+static void gpio_vibrator_close(struct input_dev *input)
+{
+	struct gpio_vibrator *vibrator = input_get_drvdata(input);
+
+	cancel_work_sync(&vibrator->play_work);
+	gpio_vibrator_stop(vibrator);
+	vibrator->running = false;
+}
+
+static int gpio_vibrator_probe(struct platform_device *pdev)
+{
+	struct gpio_vibrator *vibrator;
+	int err;
+
+	vibrator = devm_kzalloc(&pdev->dev, sizeof(*vibrator), GFP_KERNEL);
+	if (!vibrator)
+		return -ENOMEM;
+
+	vibrator->input = devm_input_allocate_device(&pdev->dev);
+	if (!vibrator->input)
+		return -ENOMEM;
+
+	vibrator->vcc = devm_regulator_get(&pdev->dev, "vcc");
+	if (IS_ERR(vibrator->vcc))
+		return dev_err_probe(&pdev->dev, PTR_ERR(vibrator->vcc),
+				     "Failed to request regulator\n");
+
+	vibrator->gpio = devm_gpiod_get(&pdev->dev, "enable", GPIOD_OUT_LOW);
+	if (IS_ERR(vibrator->gpio))
+		return dev_err_probe(&pdev->dev, PTR_ERR(vibrator->gpio),
+				     "Failed to request main gpio\n");
+
+	INIT_WORK(&vibrator->play_work, gpio_vibrator_play_work);
+
+	vibrator->input->name = "gpio-vibrator";
+	vibrator->input->id.bustype = BUS_HOST;
+	vibrator->input->close = gpio_vibrator_close;
+
+	input_set_drvdata(vibrator->input, vibrator);
+	input_set_capability(vibrator->input, EV_FF, FF_RUMBLE);
+
+	err = input_ff_create_memless(vibrator->input, NULL,
+				      gpio_vibrator_play_effect);
+	if (err) {
+		dev_err(&pdev->dev, "Couldn't create FF dev: %d\n", err);
+		return err;
+	}
+
+	err = input_register_device(vibrator->input);
+	if (err) {
+		dev_err(&pdev->dev, "Couldn't register input dev: %d\n", err);
+		return err;
+	}
+
+	platform_set_drvdata(pdev, vibrator);
+
+	return 0;
+}
+
+static int gpio_vibrator_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct gpio_vibrator *vibrator = platform_get_drvdata(pdev);
+
+	cancel_work_sync(&vibrator->play_work);
+	if (vibrator->running)
+		gpio_vibrator_stop(vibrator);
+
+	return 0;
+}
+
+static int gpio_vibrator_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct gpio_vibrator *vibrator = platform_get_drvdata(pdev);
+
+	if (vibrator->running)
+		gpio_vibrator_start(vibrator);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(gpio_vibrator_pm_ops,
+				gpio_vibrator_suspend, gpio_vibrator_resume);
+
+#ifdef CONFIG_OF
+static const struct of_device_id gpio_vibra_dt_match_table[] = {
+	{ .compatible = "gpio-vibrator" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, gpio_vibra_dt_match_table);
+#endif
+
+static struct platform_driver gpio_vibrator_driver = {
+	.probe	= gpio_vibrator_probe,
+	.driver	= {
+		.name	= "gpio-vibrator",
+		.pm	= pm_sleep_ptr(&gpio_vibrator_pm_ops),
+		.of_match_table = of_match_ptr(gpio_vibra_dt_match_table),
+	},
+};
+module_platform_driver(gpio_vibrator_driver);
+
+MODULE_AUTHOR("Luca Weiss <luca@z3ntu.xy>");
+MODULE_DESCRIPTION("GPIO vibrator driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:gpio-vibrator");