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, 285 insertions, 0 deletions

diff --git a/drivers/regulator/ad5398.c b/drivers/regulator/ad5398.c
new file mode 100644
index 000000000..eb2a666a4
--- /dev/null
+++ b/drivers/regulator/ad5398.c
@@ -0,0 +1,285 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Voltage and current regulation for AD5398 and AD5821
+ *
+ * Copyright 2010 Analog Devices Inc.
+ *
+ * Enter bugs at http://blackfin.uclinux.org/
+ */
+
+#include <linux/module.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/driver.h>
+#include <linux/regulator/machine.h>
+#include <linux/regulator/of_regulator.h>
+
+#define AD5398_SW_POWER_DOWN	BIT(15)
+
+struct ad5398_chip_info {
+	struct i2c_client *client;
+	int min_uA;
+	int max_uA;
+	unsigned int current_level;
+	unsigned int current_mask;
+	unsigned int current_offset;
+	struct regulator_dev *rdev;
+};
+
+static int ad5398_calc_current(struct ad5398_chip_info *chip,
+	unsigned selector)
+{
+	unsigned range_uA = chip->max_uA - chip->min_uA;
+
+	return chip->min_uA + (selector * range_uA / chip->current_level);
+}
+
+static int ad5398_read_reg(struct i2c_client *client, unsigned short *data)
+{
+	unsigned short val;
+	int ret;
+
+	ret = i2c_master_recv(client, (char *)&val, 2);
+	if (ret < 0) {
+		dev_err(&client->dev, "I2C read error\n");
+		return ret;
+	}
+	*data = be16_to_cpu(val);
+
+	return ret;
+}
+
+static int ad5398_write_reg(struct i2c_client *client, const unsigned short data)
+{
+	unsigned short val;
+	int ret;
+
+	val = cpu_to_be16(data);
+	ret = i2c_master_send(client, (char *)&val, 2);
+	if (ret != 2) {
+		dev_err(&client->dev, "I2C write error\n");
+		return ret < 0 ? ret : -EIO;
+	}
+
+	return 0;
+}
+
+static int ad5398_get_current_limit(struct regulator_dev *rdev)
+{
+	struct ad5398_chip_info *chip = rdev_get_drvdata(rdev);
+	struct i2c_client *client = chip->client;
+	unsigned short data;
+	int ret;
+
+	ret = ad5398_read_reg(client, &data);
+	if (ret < 0)
+		return ret;
+
+	ret = (data & chip->current_mask) >> chip->current_offset;
+
+	return ad5398_calc_current(chip, ret);
+}
+
+static int ad5398_set_current_limit(struct regulator_dev *rdev, int min_uA, int max_uA)
+{
+	struct ad5398_chip_info *chip = rdev_get_drvdata(rdev);
+	struct i2c_client *client = chip->client;
+	unsigned range_uA = chip->max_uA - chip->min_uA;
+	unsigned selector;
+	unsigned short data;
+	int ret;
+
+	if (min_uA < chip->min_uA)
+		min_uA = chip->min_uA;
+	if (max_uA > chip->max_uA)
+		max_uA = chip->max_uA;
+
+	if (min_uA > chip->max_uA || max_uA < chip->min_uA)
+		return -EINVAL;
+
+	selector = DIV_ROUND_UP((min_uA - chip->min_uA) * chip->current_level,
+				range_uA);
+	if (ad5398_calc_current(chip, selector) > max_uA)
+		return -EINVAL;
+
+	dev_dbg(&client->dev, "changing current %duA\n",
+		ad5398_calc_current(chip, selector));
+
+	/* read chip enable bit */
+	ret = ad5398_read_reg(client, &data);
+	if (ret < 0)
+		return ret;
+
+	/* prepare register data */
+	selector = (selector << chip->current_offset) & chip->current_mask;
+	data = (unsigned short)selector | (data & AD5398_SW_POWER_DOWN);
+
+	/* write the new current value back as well as enable bit */
+	ret = ad5398_write_reg(client, data);
+
+	return ret;
+}
+
+static int ad5398_is_enabled(struct regulator_dev *rdev)
+{
+	struct ad5398_chip_info *chip = rdev_get_drvdata(rdev);
+	struct i2c_client *client = chip->client;
+	unsigned short data;
+	int ret;
+
+	ret = ad5398_read_reg(client, &data);
+	if (ret < 0)
+		return ret;
+
+	if (data & AD5398_SW_POWER_DOWN)
+		return 0;
+	else
+		return 1;
+}
+
+static int ad5398_enable(struct regulator_dev *rdev)
+{
+	struct ad5398_chip_info *chip = rdev_get_drvdata(rdev);
+	struct i2c_client *client = chip->client;
+	unsigned short data;
+	int ret;
+
+	ret = ad5398_read_reg(client, &data);
+	if (ret < 0)
+		return ret;
+
+	if (!(data & AD5398_SW_POWER_DOWN))
+		return 0;
+
+	data &= ~AD5398_SW_POWER_DOWN;
+
+	ret = ad5398_write_reg(client, data);
+
+	return ret;
+}
+
+static int ad5398_disable(struct regulator_dev *rdev)
+{
+	struct ad5398_chip_info *chip = rdev_get_drvdata(rdev);
+	struct i2c_client *client = chip->client;
+	unsigned short data;
+	int ret;
+
+	ret = ad5398_read_reg(client, &data);
+	if (ret < 0)
+		return ret;
+
+	if (data & AD5398_SW_POWER_DOWN)
+		return 0;
+
+	data |= AD5398_SW_POWER_DOWN;
+
+	ret = ad5398_write_reg(client, data);
+
+	return ret;
+}
+
+static const struct regulator_ops ad5398_ops = {
+	.get_current_limit = ad5398_get_current_limit,
+	.set_current_limit = ad5398_set_current_limit,
+	.enable = ad5398_enable,
+	.disable = ad5398_disable,
+	.is_enabled = ad5398_is_enabled,
+};
+
+static const struct regulator_desc ad5398_reg = {
+	.name = "isink",
+	.id = 0,
+	.ops = &ad5398_ops,
+	.type = REGULATOR_CURRENT,
+	.owner = THIS_MODULE,
+};
+
+struct ad5398_current_data_format {
+	int current_bits;
+	int current_offset;
+	int min_uA;
+	int max_uA;
+};
+
+static const struct ad5398_current_data_format df_10_4_120 = {10, 4, 0, 120000};
+
+static const struct i2c_device_id ad5398_id[] = {
+	{ "ad5398", (kernel_ulong_t)&df_10_4_120 },
+	{ "ad5821", (kernel_ulong_t)&df_10_4_120 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ad5398_id);
+
+static int ad5398_probe(struct i2c_client *client)
+{
+	const struct i2c_device_id *id = i2c_client_get_device_id(client);
+	struct regulator_init_data *init_data = dev_get_platdata(&client->dev);
+	struct regulator_config config = { };
+	struct ad5398_chip_info *chip;
+	const struct ad5398_current_data_format *df =
+			(struct ad5398_current_data_format *)id->driver_data;
+
+	chip = devm_kzalloc(&client->dev, sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
+
+	config.dev = &client->dev;
+	if (client->dev.of_node)
+		init_data = of_get_regulator_init_data(&client->dev,
+						       client->dev.of_node,
+						       &ad5398_reg);
+	if (!init_data)
+		return -EINVAL;
+
+	config.init_data = init_data;
+	config.of_node = client->dev.of_node;
+	config.driver_data = chip;
+
+	chip->client = client;
+
+	chip->min_uA = df->min_uA;
+	chip->max_uA = df->max_uA;
+	chip->current_level = 1 << df->current_bits;
+	chip->current_offset = df->current_offset;
+	chip->current_mask = (chip->current_level - 1) << chip->current_offset;
+
+	chip->rdev = devm_regulator_register(&client->dev, &ad5398_reg,
+					     &config);
+	if (IS_ERR(chip->rdev)) {
+		dev_err(&client->dev, "failed to register %s %s\n",
+			id->name, ad5398_reg.name);
+		return PTR_ERR(chip->rdev);
+	}
+
+	i2c_set_clientdata(client, chip);
+	dev_dbg(&client->dev, "%s regulator driver is registered.\n", id->name);
+	return 0;
+}
+
+static struct i2c_driver ad5398_driver = {
+	.probe = ad5398_probe,
+	.driver		= {
+		.name	= "ad5398",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+	.id_table	= ad5398_id,
+};
+
+static int __init ad5398_init(void)
+{
+	return i2c_add_driver(&ad5398_driver);
+}
+subsys_initcall(ad5398_init);
+
+static void __exit ad5398_exit(void)
+{
+	i2c_del_driver(&ad5398_driver);
+}
+module_exit(ad5398_exit);
+
+MODULE_DESCRIPTION("AD5398 and AD5821 current regulator driver");
+MODULE_AUTHOR("Sonic Zhang");
+MODULE_LICENSE("GPL");