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, 217 insertions, 0 deletions

diff --git a/drivers/extcon/extcon-intel-int3496.c b/drivers/extcon/extcon-intel-int3496.c
new file mode 100644
index 000000000..7d16d5b7d
--- /dev/null
+++ b/drivers/extcon/extcon-intel-int3496.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Intel INT3496 ACPI device extcon driver
+ *
+ * Copyright (c) 2016 Hans de Goede <hdegoede@redhat.com>
+ *
+ * Based on android x86 kernel code which is:
+ *
+ * Copyright (c) 2014, Intel Corporation.
+ * Author: David Cohen <david.a.cohen@linux.intel.com>
+ */
+
+#include <linux/acpi.h>
+#include <linux/devm-helpers.h>
+#include <linux/extcon-provider.h>
+#include <linux/gpio/consumer.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+
+#define INT3496_GPIO_USB_ID	0
+#define INT3496_GPIO_VBUS_EN	1
+#define INT3496_GPIO_USB_MUX	2
+#define DEBOUNCE_TIME		msecs_to_jiffies(50)
+
+struct int3496_data {
+	struct device *dev;
+	struct extcon_dev *edev;
+	struct delayed_work work;
+	struct gpio_desc *gpio_usb_id;
+	struct gpio_desc *gpio_vbus_en;
+	struct gpio_desc *gpio_usb_mux;
+	struct regulator *vbus_boost;
+	int usb_id_irq;
+	bool vbus_boost_enabled;
+};
+
+static const unsigned int int3496_cable[] = {
+	EXTCON_USB_HOST,
+	EXTCON_NONE,
+};
+
+static const struct acpi_gpio_params id_gpios = { INT3496_GPIO_USB_ID, 0, false };
+static const struct acpi_gpio_params vbus_gpios = { INT3496_GPIO_VBUS_EN, 0, false };
+static const struct acpi_gpio_params mux_gpios = { INT3496_GPIO_USB_MUX, 0, false };
+
+static const struct acpi_gpio_mapping acpi_int3496_default_gpios[] = {
+	/*
+	 * Some platforms have a bug in ACPI GPIO description making IRQ
+	 * GPIO to be output only. Ask the GPIO core to ignore this limit.
+	 */
+	{ "id-gpios", &id_gpios, 1, ACPI_GPIO_QUIRK_NO_IO_RESTRICTION },
+	{ "vbus-gpios", &vbus_gpios, 1 },
+	{ "mux-gpios", &mux_gpios, 1 },
+	{ },
+};
+
+static void int3496_set_vbus_boost(struct int3496_data *data, bool enable)
+{
+	int ret;
+
+	if (IS_ERR_OR_NULL(data->vbus_boost))
+		return;
+
+	if (data->vbus_boost_enabled == enable)
+		return;
+
+	if (enable)
+		ret = regulator_enable(data->vbus_boost);
+	else
+		ret = regulator_disable(data->vbus_boost);
+
+	if (ret == 0)
+		data->vbus_boost_enabled = enable;
+	else
+		dev_err(data->dev, "Error updating Vbus boost regulator: %d\n", ret);
+}
+
+static void int3496_do_usb_id(struct work_struct *work)
+{
+	struct int3496_data *data =
+		container_of(work, struct int3496_data, work.work);
+	int id = gpiod_get_value_cansleep(data->gpio_usb_id);
+
+	/* id == 1: PERIPHERAL, id == 0: HOST */
+	dev_dbg(data->dev, "Connected %s cable\n", id ? "PERIPHERAL" : "HOST");
+
+	/*
+	 * Peripheral: set USB mux to peripheral and disable VBUS
+	 * Host: set USB mux to host and enable VBUS
+	 */
+	if (!IS_ERR(data->gpio_usb_mux))
+		gpiod_direction_output(data->gpio_usb_mux, id);
+
+	if (!IS_ERR(data->gpio_vbus_en))
+		gpiod_direction_output(data->gpio_vbus_en, !id);
+	else
+		int3496_set_vbus_boost(data, !id);
+
+	extcon_set_state_sync(data->edev, EXTCON_USB_HOST, !id);
+}
+
+static irqreturn_t int3496_thread_isr(int irq, void *priv)
+{
+	struct int3496_data *data = priv;
+
+	/* Let the pin settle before processing it */
+	mod_delayed_work(system_percpu_wq, &data->work, DEBOUNCE_TIME);
+
+	return IRQ_HANDLED;
+}
+
+static int int3496_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct int3496_data *data;
+	int ret;
+
+	if (has_acpi_companion(dev)) {
+		ret = devm_acpi_dev_add_driver_gpios(dev, acpi_int3496_default_gpios);
+		if (ret) {
+			dev_err(dev, "can't add GPIO ACPI mapping\n");
+			return ret;
+		}
+	}
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->dev = dev;
+	ret = devm_delayed_work_autocancel(dev, &data->work, int3496_do_usb_id);
+	if (ret)
+		return ret;
+
+	data->gpio_usb_id =
+		devm_gpiod_get(dev, "id", GPIOD_IN | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
+	if (IS_ERR(data->gpio_usb_id)) {
+		ret = PTR_ERR(data->gpio_usb_id);
+		dev_err(dev, "can't request USB ID GPIO: %d\n", ret);
+		return ret;
+	}
+
+	data->usb_id_irq = gpiod_to_irq(data->gpio_usb_id);
+	if (data->usb_id_irq < 0) {
+		dev_err(dev, "can't get USB ID IRQ: %d\n", data->usb_id_irq);
+		return data->usb_id_irq;
+	}
+
+	data->gpio_vbus_en = devm_gpiod_get(dev, "vbus", GPIOD_ASIS);
+	if (IS_ERR(data->gpio_vbus_en)) {
+		dev_dbg(dev, "can't request VBUS EN GPIO\n");
+		data->vbus_boost = devm_regulator_get_optional(dev, "vbus");
+	}
+
+	data->gpio_usb_mux = devm_gpiod_get(dev, "mux", GPIOD_ASIS);
+	if (IS_ERR(data->gpio_usb_mux))
+		dev_dbg(dev, "can't request USB MUX GPIO\n");
+
+	/* register extcon device */
+	data->edev = devm_extcon_dev_allocate(dev, int3496_cable);
+	if (IS_ERR(data->edev))
+		return -ENOMEM;
+
+	ret = devm_extcon_dev_register(dev, data->edev);
+	if (ret < 0) {
+		dev_err(dev, "can't register extcon device: %d\n", ret);
+		return ret;
+	}
+
+	ret = devm_request_threaded_irq(dev, data->usb_id_irq,
+					NULL, int3496_thread_isr,
+					IRQF_SHARED | IRQF_ONESHOT |
+					IRQF_TRIGGER_RISING |
+					IRQF_TRIGGER_FALLING,
+					dev_name(dev), data);
+	if (ret < 0) {
+		dev_err(dev, "can't request IRQ for USB ID GPIO: %d\n", ret);
+		return ret;
+	}
+
+	/* process id-pin so that we start with the right status */
+	queue_delayed_work(system_percpu_wq, &data->work, 0);
+	flush_delayed_work(&data->work);
+
+	platform_set_drvdata(pdev, data);
+
+	return 0;
+}
+
+static const struct acpi_device_id int3496_acpi_match[] = {
+	{ "INT3496" },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, int3496_acpi_match);
+
+static const struct platform_device_id int3496_ids[] = {
+	{ .name = "intel-int3496" },
+	{},
+};
+MODULE_DEVICE_TABLE(platform, int3496_ids);
+
+static struct platform_driver int3496_driver = {
+	.driver = {
+		.name = "intel-int3496",
+		.acpi_match_table = int3496_acpi_match,
+	},
+	.probe = int3496_probe,
+	.id_table = int3496_ids,
+};
+
+module_platform_driver(int3496_driver);
+
+MODULE_AUTHOR("Hans de Goede <hdegoede@redhat.com>");
+MODULE_DESCRIPTION("Intel INT3496 ACPI device extcon driver");
+MODULE_LICENSE("GPL v2");