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, 225 insertions, 0 deletions

diff --git a/drivers/regulator/userspace-consumer.c b/drivers/regulator/userspace-consumer.c
new file mode 100644
index 000000000..72bb5ffb4
--- /dev/null
+++ b/drivers/regulator/userspace-consumer.c
@@ -0,0 +1,225 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * userspace-consumer.c
+ *
+ * Copyright 2009 CompuLab, Ltd.
+ *
+ * Author: Mike Rapoport <mike@compulab.co.il>
+ *
+ * Based of virtual consumer driver:
+ *   Copyright 2008 Wolfson Microelectronics PLC.
+ *   Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
+ */
+
+#include <linux/err.h>
+#include <linux/mutex.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+#include <linux/regulator/userspace-consumer.h>
+#include <linux/slab.h>
+
+struct userspace_consumer_data {
+	const char *name;
+
+	struct mutex lock;
+	bool enabled;
+	bool no_autoswitch;
+
+	int num_supplies;
+	struct regulator_bulk_data *supplies;
+};
+
+static ssize_t name_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	struct userspace_consumer_data *data = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%s\n", data->name);
+}
+
+static ssize_t state_show(struct device *dev,
+			  struct device_attribute *attr, char *buf)
+{
+	struct userspace_consumer_data *data = dev_get_drvdata(dev);
+
+	if (data->enabled)
+		return sprintf(buf, "enabled\n");
+
+	return sprintf(buf, "disabled\n");
+}
+
+static ssize_t state_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t count)
+{
+	struct userspace_consumer_data *data = dev_get_drvdata(dev);
+	bool enabled;
+	int ret;
+
+	/*
+	 * sysfs_streq() doesn't need the \n's, but we add them so the strings
+	 * will be shared with show_state(), above.
+	 */
+	if (sysfs_streq(buf, "enabled\n") || sysfs_streq(buf, "1"))
+		enabled = true;
+	else if (sysfs_streq(buf, "disabled\n") || sysfs_streq(buf, "0"))
+		enabled = false;
+	else {
+		dev_err(dev, "Configuring invalid mode\n");
+		return count;
+	}
+
+	mutex_lock(&data->lock);
+	if (enabled != data->enabled) {
+		if (enabled)
+			ret = regulator_bulk_enable(data->num_supplies,
+						    data->supplies);
+		else
+			ret = regulator_bulk_disable(data->num_supplies,
+						     data->supplies);
+
+		if (ret == 0)
+			data->enabled = enabled;
+		else
+			dev_err(dev, "Failed to configure state: %d\n", ret);
+	}
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+static DEVICE_ATTR_RO(name);
+static DEVICE_ATTR_RW(state);
+
+static struct attribute *attributes[] = {
+	&dev_attr_name.attr,
+	&dev_attr_state.attr,
+	NULL,
+};
+
+static umode_t attr_visible(struct kobject *kobj, struct attribute *attr, int idx)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct userspace_consumer_data *data = dev_get_drvdata(dev);
+
+	/* If a name hasn't been set, don't bother with the attribute */
+	if (attr == &dev_attr_name.attr && !data->name)
+		return 0;
+
+	return attr->mode;
+}
+
+static const struct attribute_group attr_group = {
+	.attrs	= attributes,
+	.is_visible =  attr_visible,
+};
+
+static int regulator_userspace_consumer_probe(struct platform_device *pdev)
+{
+	struct regulator_userspace_consumer_data tmpdata;
+	struct regulator_userspace_consumer_data *pdata;
+	struct userspace_consumer_data *drvdata;
+	int ret;
+
+	pdata = dev_get_platdata(&pdev->dev);
+	if (!pdata) {
+		if (!pdev->dev.of_node)
+			return -EINVAL;
+
+		pdata = &tmpdata;
+		memset(pdata, 0, sizeof(*pdata));
+
+		pdata->no_autoswitch = true;
+		pdata->num_supplies = 1;
+		pdata->supplies = devm_kzalloc(&pdev->dev, sizeof(*pdata->supplies), GFP_KERNEL);
+		if (!pdata->supplies)
+			return -ENOMEM;
+		pdata->supplies[0].supply = "vout";
+	}
+
+	if (pdata->num_supplies < 1) {
+		dev_err(&pdev->dev, "At least one supply required\n");
+		return -EINVAL;
+	}
+
+	drvdata = devm_kzalloc(&pdev->dev,
+			       sizeof(struct userspace_consumer_data),
+			       GFP_KERNEL);
+	if (drvdata == NULL)
+		return -ENOMEM;
+
+	drvdata->name = pdata->name;
+	drvdata->num_supplies = pdata->num_supplies;
+	drvdata->supplies = pdata->supplies;
+	drvdata->no_autoswitch = pdata->no_autoswitch;
+
+	mutex_init(&drvdata->lock);
+
+	ret = devm_regulator_bulk_get_exclusive(&pdev->dev, drvdata->num_supplies,
+						drvdata->supplies);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "Failed to get supplies\n");
+
+	platform_set_drvdata(pdev, drvdata);
+
+	ret = sysfs_create_group(&pdev->dev.kobj, &attr_group);
+	if (ret != 0)
+		return ret;
+
+	if (pdata->init_on && !pdata->no_autoswitch) {
+		ret = regulator_bulk_enable(drvdata->num_supplies,
+					    drvdata->supplies);
+		if (ret) {
+			dev_err(&pdev->dev,
+				"Failed to set initial state: %d\n", ret);
+			goto err_enable;
+		}
+	}
+
+	ret = regulator_is_enabled(pdata->supplies[0].consumer);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to get regulator status\n");
+		goto err_enable;
+	}
+	drvdata->enabled = !!ret;
+
+	return 0;
+
+err_enable:
+	sysfs_remove_group(&pdev->dev.kobj, &attr_group);
+
+	return ret;
+}
+
+static void regulator_userspace_consumer_remove(struct platform_device *pdev)
+{
+	struct userspace_consumer_data *data = platform_get_drvdata(pdev);
+
+	sysfs_remove_group(&pdev->dev.kobj, &attr_group);
+
+	if (data->enabled && !data->no_autoswitch)
+		regulator_bulk_disable(data->num_supplies, data->supplies);
+}
+
+static const struct of_device_id regulator_userspace_consumer_of_match[] = {
+	{ .compatible = "regulator-output", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, regulator_userspace_consumer_of_match);
+
+static struct platform_driver regulator_userspace_consumer_driver = {
+	.probe		= regulator_userspace_consumer_probe,
+	.remove		= regulator_userspace_consumer_remove,
+	.driver		= {
+		.name		= "reg-userspace-consumer",
+		.probe_type	= PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table	= regulator_userspace_consumer_of_match,
+	},
+};
+
+module_platform_driver(regulator_userspace_consumer_driver);
+
+MODULE_AUTHOR("Mike Rapoport <mike@compulab.co.il>");
+MODULE_DESCRIPTION("Userspace consumer for voltage and current regulators");
+MODULE_LICENSE("GPL");