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, 226 insertions, 0 deletions

diff --git a/drivers/misc/isl29020.c b/drivers/misc/isl29020.c
new file mode 100644
index 000000000..c288aeec1
--- /dev/null
+++ b/drivers/misc/isl29020.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * isl29020.c - Intersil  ALS Driver
+ *
+ * Copyright (C) 2008 Intel Corp
+ *
+ *  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Data sheet at: http://www.intersil.com/data/fn/fn6505.pdf
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/i2c.h>
+#include <linux/err.h>
+#include <linux/delay.h>
+#include <linux/sysfs.h>
+#include <linux/pm_runtime.h>
+
+static DEFINE_MUTEX(mutex);
+
+static ssize_t als_sensing_range_show(struct device *dev,
+			struct device_attribute *attr,  char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int  val;
+
+	val = i2c_smbus_read_byte_data(client, 0x00);
+
+	if (val < 0)
+		return val;
+	return sprintf(buf, "%d000\n", 1 << (2 * (val & 3)));
+
+}
+
+static ssize_t als_lux_input_data_show(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int ret_val, val;
+	unsigned long int lux;
+	int temp;
+
+	pm_runtime_get_sync(dev);
+	msleep(100);
+
+	mutex_lock(&mutex);
+	temp = i2c_smbus_read_byte_data(client, 0x02); /* MSB data */
+	if (temp < 0) {
+		pm_runtime_put_sync(dev);
+		mutex_unlock(&mutex);
+		return temp;
+	}
+
+	ret_val = i2c_smbus_read_byte_data(client, 0x01); /* LSB data */
+	mutex_unlock(&mutex);
+
+	if (ret_val < 0) {
+		pm_runtime_put_sync(dev);
+		return ret_val;
+	}
+
+	ret_val |= temp << 8;
+	val = i2c_smbus_read_byte_data(client, 0x00);
+	pm_runtime_put_sync(dev);
+	if (val < 0)
+		return val;
+	lux = ((((1 << (2 * (val & 3))))*1000) * ret_val) / 65536;
+	return sprintf(buf, "%lu\n", lux);
+}
+
+static ssize_t als_sensing_range_store(struct device *dev,
+		struct device_attribute *attr, const  char *buf, size_t count)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int ret_val;
+	unsigned long val;
+
+	ret_val = kstrtoul(buf, 10, &val);
+	if (ret_val)
+		return ret_val;
+
+	if (val < 1 || val > 64000)
+		return -EINVAL;
+
+	/* Pick the smallest sensor range that will meet our requirements */
+	if (val <= 1000)
+		val = 1;
+	else if (val <= 4000)
+		val = 2;
+	else if (val <= 16000)
+		val = 3;
+	else
+		val = 4;
+
+	ret_val = i2c_smbus_read_byte_data(client, 0x00);
+	if (ret_val < 0)
+		return ret_val;
+
+	ret_val &= 0xFC; /*reset the bit before setting them */
+	ret_val |= val - 1;
+	ret_val = i2c_smbus_write_byte_data(client, 0x00, ret_val);
+
+	if (ret_val < 0)
+		return ret_val;
+	return count;
+}
+
+static void als_set_power_state(struct i2c_client *client, int enable)
+{
+	int ret_val;
+
+	ret_val = i2c_smbus_read_byte_data(client, 0x00);
+	if (ret_val < 0)
+		return;
+
+	if (enable)
+		ret_val |= 0x80;
+	else
+		ret_val &= 0x7F;
+
+	i2c_smbus_write_byte_data(client, 0x00, ret_val);
+}
+
+static DEVICE_ATTR(lux0_sensor_range, S_IRUGO | S_IWUSR,
+	als_sensing_range_show, als_sensing_range_store);
+static DEVICE_ATTR(lux0_input, S_IRUGO, als_lux_input_data_show, NULL);
+
+static struct attribute *mid_att_als[] = {
+	&dev_attr_lux0_sensor_range.attr,
+	&dev_attr_lux0_input.attr,
+	NULL
+};
+
+static const struct attribute_group m_als_gr = {
+	.name = "isl29020",
+	.attrs = mid_att_als
+};
+
+static int als_set_default_config(struct i2c_client *client)
+{
+	int retval;
+
+	retval = i2c_smbus_write_byte_data(client, 0x00, 0xc0);
+	if (retval < 0) {
+		dev_err(&client->dev, "default write failed.");
+		return retval;
+	}
+	return 0;
+}
+
+static int  isl29020_probe(struct i2c_client *client)
+{
+	int res;
+
+	res = als_set_default_config(client);
+	if (res <  0)
+		return res;
+
+	res = sysfs_create_group(&client->dev.kobj, &m_als_gr);
+	if (res) {
+		dev_err(&client->dev, "isl29020: device create file failed\n");
+		return res;
+	}
+	dev_info(&client->dev, "%s isl29020: ALS chip found\n", client->name);
+	als_set_power_state(client, 0);
+	pm_runtime_enable(&client->dev);
+	return res;
+}
+
+static void isl29020_remove(struct i2c_client *client)
+{
+	pm_runtime_disable(&client->dev);
+	sysfs_remove_group(&client->dev.kobj, &m_als_gr);
+}
+
+static const struct i2c_device_id isl29020_id[] = {
+	{ "isl29020" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(i2c, isl29020_id);
+
+#ifdef CONFIG_PM
+
+static int isl29020_runtime_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	als_set_power_state(client, 0);
+	return 0;
+}
+
+static int isl29020_runtime_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	als_set_power_state(client, 1);
+	return 0;
+}
+
+static const struct dev_pm_ops isl29020_pm_ops = {
+	.runtime_suspend = isl29020_runtime_suspend,
+	.runtime_resume = isl29020_runtime_resume,
+};
+
+#define ISL29020_PM_OPS (&isl29020_pm_ops)
+#else	/* CONFIG_PM */
+#define ISL29020_PM_OPS NULL
+#endif	/* CONFIG_PM */
+
+static struct i2c_driver isl29020_driver = {
+	.driver = {
+		.name = "isl29020",
+		.pm = ISL29020_PM_OPS,
+	},
+	.probe = isl29020_probe,
+	.remove = isl29020_remove,
+	.id_table = isl29020_id,
+};
+
+module_i2c_driver(isl29020_driver);
+
+MODULE_AUTHOR("Kalhan Trisal <kalhan.trisal@intel.com>");
+MODULE_DESCRIPTION("Intersil isl29020 ALS Driver");
+MODULE_LICENSE("GPL v2");