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, 373 insertions, 0 deletions

diff --git a/drivers/regulator/virtual.c b/drivers/regulator/virtual.c
new file mode 100644
index 000000000..218a0d66a
--- /dev/null
+++ b/drivers/regulator/virtual.c
@@ -0,0 +1,373 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * reg-virtual-consumer.c
+ *
+ * Copyright 2008 Wolfson Microelectronics PLC.
+ *
+ * Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
+ */
+
+#include <linux/err.h>
+#include <linux/mutex.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/of.h>
+
+struct virtual_consumer_data {
+	struct mutex lock;
+	struct regulator *regulator;
+	bool enabled;
+	int min_uV;
+	int max_uV;
+	int min_uA;
+	int max_uA;
+	unsigned int mode;
+};
+
+static void update_voltage_constraints(struct device *dev,
+				       struct virtual_consumer_data *data)
+{
+	int ret;
+
+	if (data->min_uV && data->max_uV
+	    && data->min_uV <= data->max_uV) {
+		dev_dbg(dev, "Requesting %d-%duV\n",
+			data->min_uV, data->max_uV);
+		ret = regulator_set_voltage(data->regulator,
+					data->min_uV, data->max_uV);
+		if (ret != 0) {
+			dev_err(dev,
+				"regulator_set_voltage() failed: %d\n", ret);
+			return;
+		}
+	}
+
+	if (data->min_uV && data->max_uV && !data->enabled) {
+		dev_dbg(dev, "Enabling regulator\n");
+		ret = regulator_enable(data->regulator);
+		if (ret == 0)
+			data->enabled = true;
+		else
+			dev_err(dev, "regulator_enable() failed: %d\n",
+				ret);
+	}
+
+	if (!(data->min_uV && data->max_uV) && data->enabled) {
+		dev_dbg(dev, "Disabling regulator\n");
+		ret = regulator_disable(data->regulator);
+		if (ret == 0)
+			data->enabled = false;
+		else
+			dev_err(dev, "regulator_disable() failed: %d\n",
+				ret);
+	}
+}
+
+static void update_current_limit_constraints(struct device *dev,
+					  struct virtual_consumer_data *data)
+{
+	int ret;
+
+	if (data->max_uA
+	    && data->min_uA <= data->max_uA) {
+		dev_dbg(dev, "Requesting %d-%duA\n",
+			data->min_uA, data->max_uA);
+		ret = regulator_set_current_limit(data->regulator,
+					data->min_uA, data->max_uA);
+		if (ret != 0) {
+			dev_err(dev,
+				"regulator_set_current_limit() failed: %d\n",
+				ret);
+			return;
+		}
+	}
+
+	if (data->max_uA && !data->enabled) {
+		dev_dbg(dev, "Enabling regulator\n");
+		ret = regulator_enable(data->regulator);
+		if (ret == 0)
+			data->enabled = true;
+		else
+			dev_err(dev, "regulator_enable() failed: %d\n",
+				ret);
+	}
+
+	if (!(data->min_uA && data->max_uA) && data->enabled) {
+		dev_dbg(dev, "Disabling regulator\n");
+		ret = regulator_disable(data->regulator);
+		if (ret == 0)
+			data->enabled = false;
+		else
+			dev_err(dev, "regulator_disable() failed: %d\n",
+				ret);
+	}
+}
+
+static ssize_t show_min_uV(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	return sprintf(buf, "%d\n", data->min_uV);
+}
+
+static ssize_t set_min_uV(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	long val;
+
+	if (kstrtol(buf, 10, &val) != 0)
+		return count;
+
+	mutex_lock(&data->lock);
+
+	data->min_uV = val;
+	update_voltage_constraints(dev, data);
+
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+static ssize_t show_max_uV(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	return sprintf(buf, "%d\n", data->max_uV);
+}
+
+static ssize_t set_max_uV(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	long val;
+
+	if (kstrtol(buf, 10, &val) != 0)
+		return count;
+
+	mutex_lock(&data->lock);
+
+	data->max_uV = val;
+	update_voltage_constraints(dev, data);
+
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+static ssize_t show_min_uA(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	return sprintf(buf, "%d\n", data->min_uA);
+}
+
+static ssize_t set_min_uA(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	long val;
+
+	if (kstrtol(buf, 10, &val) != 0)
+		return count;
+
+	mutex_lock(&data->lock);
+
+	data->min_uA = val;
+	update_current_limit_constraints(dev, data);
+
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+static ssize_t show_max_uA(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	return sprintf(buf, "%d\n", data->max_uA);
+}
+
+static ssize_t set_max_uA(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	long val;
+
+	if (kstrtol(buf, 10, &val) != 0)
+		return count;
+
+	mutex_lock(&data->lock);
+
+	data->max_uA = val;
+	update_current_limit_constraints(dev, data);
+
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+static ssize_t show_mode(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+
+	switch (data->mode) {
+	case REGULATOR_MODE_FAST:
+		return sprintf(buf, "fast\n");
+	case REGULATOR_MODE_NORMAL:
+		return sprintf(buf, "normal\n");
+	case REGULATOR_MODE_IDLE:
+		return sprintf(buf, "idle\n");
+	case REGULATOR_MODE_STANDBY:
+		return sprintf(buf, "standby\n");
+	default:
+		return sprintf(buf, "unknown\n");
+	}
+}
+
+static ssize_t set_mode(struct device *dev, struct device_attribute *attr,
+			const char *buf, size_t count)
+{
+	struct virtual_consumer_data *data = dev_get_drvdata(dev);
+	unsigned int mode;
+	int ret;
+
+	/*
+	 * sysfs_streq() doesn't need the \n's, but we add them so the strings
+	 * will be shared with show_mode(), above.
+	 */
+	if (sysfs_streq(buf, "fast\n"))
+		mode = REGULATOR_MODE_FAST;
+	else if (sysfs_streq(buf, "normal\n"))
+		mode = REGULATOR_MODE_NORMAL;
+	else if (sysfs_streq(buf, "idle\n"))
+		mode = REGULATOR_MODE_IDLE;
+	else if (sysfs_streq(buf, "standby\n"))
+		mode = REGULATOR_MODE_STANDBY;
+	else {
+		dev_err(dev, "Configuring invalid mode\n");
+		return count;
+	}
+
+	mutex_lock(&data->lock);
+	ret = regulator_set_mode(data->regulator, mode);
+	if (ret == 0)
+		data->mode = mode;
+	else
+		dev_err(dev, "Failed to configure mode: %d\n", ret);
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+static DEVICE_ATTR(min_microvolts, 0664, show_min_uV, set_min_uV);
+static DEVICE_ATTR(max_microvolts, 0664, show_max_uV, set_max_uV);
+static DEVICE_ATTR(min_microamps, 0664, show_min_uA, set_min_uA);
+static DEVICE_ATTR(max_microamps, 0664, show_max_uA, set_max_uA);
+static DEVICE_ATTR(mode, 0664, show_mode, set_mode);
+
+static struct attribute *regulator_virtual_attributes[] = {
+	&dev_attr_min_microvolts.attr,
+	&dev_attr_max_microvolts.attr,
+	&dev_attr_min_microamps.attr,
+	&dev_attr_max_microamps.attr,
+	&dev_attr_mode.attr,
+	NULL
+};
+
+static const struct attribute_group regulator_virtual_attr_group = {
+	.attrs	= regulator_virtual_attributes,
+};
+
+#ifdef CONFIG_OF
+static const struct of_device_id regulator_virtual_consumer_of_match[] = {
+	{ .compatible = "regulator-virtual-consumer" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, regulator_virtual_consumer_of_match);
+#endif
+
+static int regulator_virtual_probe(struct platform_device *pdev)
+{
+	char *reg_id = dev_get_platdata(&pdev->dev);
+	struct virtual_consumer_data *drvdata;
+	static bool warned;
+	int ret;
+
+	if (!warned) {
+		warned = true;
+		pr_warn("**********************************************************\n");
+		pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
+		pr_warn("**                                                      **\n");
+		pr_warn("** regulator-virtual-consumer is only for testing and   **\n");
+		pr_warn("** debugging.  Do not use it in a production kernel.    **\n");
+		pr_warn("**                                                      **\n");
+		pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
+		pr_warn("**********************************************************\n");
+	}
+
+	drvdata = devm_kzalloc(&pdev->dev, sizeof(struct virtual_consumer_data),
+			       GFP_KERNEL);
+	if (drvdata == NULL)
+		return -ENOMEM;
+
+	/*
+	 * This virtual consumer does not have any hardware-defined supply
+	 * name, so just allow the regulator to be specified in a property
+	 * named "default-supply" when we're being probed from devicetree.
+	 */
+	if (!reg_id && pdev->dev.of_node)
+		reg_id = "default";
+
+	mutex_init(&drvdata->lock);
+
+	drvdata->regulator = devm_regulator_get(&pdev->dev, reg_id);
+	if (IS_ERR(drvdata->regulator))
+		return dev_err_probe(&pdev->dev, PTR_ERR(drvdata->regulator),
+				     "Failed to obtain supply '%s'\n",
+				     reg_id);
+
+	ret = sysfs_create_group(&pdev->dev.kobj,
+				 &regulator_virtual_attr_group);
+	if (ret != 0) {
+		dev_err(&pdev->dev,
+			"Failed to create attribute group: %d\n", ret);
+		return ret;
+	}
+
+	drvdata->mode = regulator_get_mode(drvdata->regulator);
+
+	platform_set_drvdata(pdev, drvdata);
+
+	return 0;
+}
+
+static void regulator_virtual_remove(struct platform_device *pdev)
+{
+	struct virtual_consumer_data *drvdata = platform_get_drvdata(pdev);
+
+	sysfs_remove_group(&pdev->dev.kobj, &regulator_virtual_attr_group);
+
+	if (drvdata->enabled)
+		regulator_disable(drvdata->regulator);
+}
+
+static struct platform_driver regulator_virtual_consumer_driver = {
+	.probe		= regulator_virtual_probe,
+	.remove		= regulator_virtual_remove,
+	.driver		= {
+		.name		= "reg-virt-consumer",
+		.probe_type	= PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = of_match_ptr(regulator_virtual_consumer_of_match),
+	},
+};
+
+module_platform_driver(regulator_virtual_consumer_driver);
+
+MODULE_AUTHOR("Mark Brown <broonie@opensource.wolfsonmicro.com>");
+MODULE_DESCRIPTION("Virtual regulator consumer");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:reg-virt-consumer");