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, 349 insertions, 0 deletions

diff --git a/drivers/mfd/max8998.c b/drivers/mfd/max8998.c
new file mode 100644
index 000000000..eb13bbaed
--- /dev/null
+++ b/drivers/mfd/max8998.c
@@ -0,0 +1,349 @@
+// SPDX-License-Identifier: GPL-2.0+
+//
+// max8998.c - mfd core driver for the Maxim 8998
+//
+//  Copyright (C) 2009-2010 Samsung Electronics
+//  Kyungmin Park <kyungmin.park@samsung.com>
+//  Marek Szyprowski <m.szyprowski@samsung.com>
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/pm_runtime.h>
+#include <linux/mutex.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/max8998.h>
+#include <linux/mfd/max8998-private.h>
+
+#define RTC_I2C_ADDR		(0x0c >> 1)
+
+static const struct mfd_cell max8998_devs[] = {
+	{
+		.name = "max8998-pmic",
+	}, {
+		.name = "max8998-rtc",
+	}, {
+		.name = "max8998-battery",
+	},
+};
+
+static const struct mfd_cell lp3974_devs[] = {
+	{
+		.name = "lp3974-pmic",
+	}, {
+		.name = "lp3974-rtc",
+	},
+};
+
+int max8998_read_reg(struct i2c_client *i2c, u8 reg, u8 *dest)
+{
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+	int ret;
+
+	mutex_lock(&max8998->iolock);
+	ret = i2c_smbus_read_byte_data(i2c, reg);
+	mutex_unlock(&max8998->iolock);
+	if (ret < 0)
+		return ret;
+
+	ret &= 0xff;
+	*dest = ret;
+	return 0;
+}
+EXPORT_SYMBOL(max8998_read_reg);
+
+int max8998_bulk_read(struct i2c_client *i2c, u8 reg, int count, u8 *buf)
+{
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+	int ret;
+
+	mutex_lock(&max8998->iolock);
+	ret = i2c_smbus_read_i2c_block_data(i2c, reg, count, buf);
+	mutex_unlock(&max8998->iolock);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(max8998_bulk_read);
+
+int max8998_write_reg(struct i2c_client *i2c, u8 reg, u8 value)
+{
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+	int ret;
+
+	mutex_lock(&max8998->iolock);
+	ret = i2c_smbus_write_byte_data(i2c, reg, value);
+	mutex_unlock(&max8998->iolock);
+	return ret;
+}
+EXPORT_SYMBOL(max8998_write_reg);
+
+int max8998_bulk_write(struct i2c_client *i2c, u8 reg, int count, u8 *buf)
+{
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+	int ret;
+
+	mutex_lock(&max8998->iolock);
+	ret = i2c_smbus_write_i2c_block_data(i2c, reg, count, buf);
+	mutex_unlock(&max8998->iolock);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(max8998_bulk_write);
+
+int max8998_update_reg(struct i2c_client *i2c, u8 reg, u8 val, u8 mask)
+{
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+	int ret;
+
+	mutex_lock(&max8998->iolock);
+	ret = i2c_smbus_read_byte_data(i2c, reg);
+	if (ret >= 0) {
+		u8 old_val = ret & 0xff;
+		u8 new_val = (val & mask) | (old_val & (~mask));
+		ret = i2c_smbus_write_byte_data(i2c, reg, new_val);
+	}
+	mutex_unlock(&max8998->iolock);
+	return ret;
+}
+EXPORT_SYMBOL(max8998_update_reg);
+
+#ifdef CONFIG_OF
+static const struct of_device_id max8998_dt_match[] = {
+	{ .compatible = "maxim,max8998", .data = (void *)TYPE_MAX8998 },
+	{ .compatible = "national,lp3974", .data = (void *)TYPE_LP3974 },
+	{ .compatible = "ti,lp3974", .data = (void *)TYPE_LP3974 },
+	{},
+};
+#endif
+
+/*
+ * Only the common platform data elements for max8998 are parsed here from the
+ * device tree. Other sub-modules of max8998 such as pmic, rtc and others have
+ * to parse their own platform data elements from device tree.
+ *
+ * The max8998 platform data structure is instantiated here and the drivers for
+ * the sub-modules need not instantiate another instance while parsing their
+ * platform data.
+ */
+static struct max8998_platform_data *max8998_i2c_parse_dt_pdata(
+							struct device *dev)
+{
+	struct max8998_platform_data *pd;
+
+	pd = devm_kzalloc(dev, sizeof(*pd), GFP_KERNEL);
+	if (!pd)
+		return ERR_PTR(-ENOMEM);
+
+	pd->ono = irq_of_parse_and_map(dev->of_node, 1);
+
+	/*
+	 * ToDo: the 'wakeup' member in the platform data is more of a linux
+	 * specfic information. Hence, there is no binding for that yet and
+	 * not parsed here.
+	 */
+	return pd;
+}
+
+static int max8998_i2c_probe(struct i2c_client *i2c)
+{
+	struct max8998_platform_data *pdata = dev_get_platdata(&i2c->dev);
+	struct max8998_dev *max8998;
+	int ret = 0;
+
+	max8998 = devm_kzalloc(&i2c->dev, sizeof(struct max8998_dev),
+				GFP_KERNEL);
+	if (max8998 == NULL)
+		return -ENOMEM;
+
+	if (IS_ENABLED(CONFIG_OF) && i2c->dev.of_node) {
+		pdata = max8998_i2c_parse_dt_pdata(&i2c->dev);
+		if (IS_ERR(pdata))
+			return PTR_ERR(pdata);
+	}
+
+	i2c_set_clientdata(i2c, max8998);
+	max8998->dev = &i2c->dev;
+	max8998->i2c = i2c;
+	max8998->irq = i2c->irq;
+	max8998->type = (uintptr_t)i2c_get_match_data(i2c);
+	max8998->pdata = pdata;
+	if (pdata) {
+		max8998->ono = pdata->ono;
+		max8998->irq_base = pdata->irq_base;
+		max8998->wakeup = pdata->wakeup;
+	}
+	mutex_init(&max8998->iolock);
+
+	max8998->rtc = i2c_new_dummy_device(i2c->adapter, RTC_I2C_ADDR);
+	if (IS_ERR(max8998->rtc)) {
+		dev_err(&i2c->dev, "Failed to allocate I2C device for RTC\n");
+		return PTR_ERR(max8998->rtc);
+	}
+	i2c_set_clientdata(max8998->rtc, max8998);
+
+	max8998_irq_init(max8998);
+
+	pm_runtime_set_active(max8998->dev);
+
+	switch (max8998->type) {
+	case TYPE_LP3974:
+		ret = mfd_add_devices(max8998->dev, -1,
+				      lp3974_devs, ARRAY_SIZE(lp3974_devs),
+				      NULL, 0, NULL);
+		break;
+	case TYPE_MAX8998:
+		ret = mfd_add_devices(max8998->dev, -1,
+				      max8998_devs, ARRAY_SIZE(max8998_devs),
+				      NULL, 0, NULL);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	if (ret < 0)
+		goto err;
+
+	device_init_wakeup(max8998->dev, max8998->wakeup);
+
+	return ret;
+
+err:
+	mfd_remove_devices(max8998->dev);
+	max8998_irq_exit(max8998);
+	i2c_unregister_device(max8998->rtc);
+	return ret;
+}
+
+static const struct i2c_device_id max8998_i2c_id[] = {
+	{ "max8998", TYPE_MAX8998 },
+	{ "lp3974", TYPE_LP3974},
+	{ }
+};
+
+static int max8998_suspend(struct device *dev)
+{
+	struct i2c_client *i2c = to_i2c_client(dev);
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(max8998->irq);
+	return 0;
+}
+
+static int max8998_resume(struct device *dev)
+{
+	struct i2c_client *i2c = to_i2c_client(dev);
+	struct max8998_dev *max8998 = i2c_get_clientdata(i2c);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(max8998->irq);
+	/*
+	 * In LP3974, if IRQ registers are not "read & clear"
+	 * when it's set during sleep, the interrupt becomes
+	 * disabled.
+	 */
+	return max8998_irq_resume(i2c_get_clientdata(i2c));
+}
+
+struct max8998_reg_dump {
+	u8	addr;
+	u8	val;
+};
+#define SAVE_ITEM(x)	{ .addr = (x), .val = 0x0, }
+static struct max8998_reg_dump max8998_dump[] = {
+	SAVE_ITEM(MAX8998_REG_IRQM1),
+	SAVE_ITEM(MAX8998_REG_IRQM2),
+	SAVE_ITEM(MAX8998_REG_IRQM3),
+	SAVE_ITEM(MAX8998_REG_IRQM4),
+	SAVE_ITEM(MAX8998_REG_STATUSM1),
+	SAVE_ITEM(MAX8998_REG_STATUSM2),
+	SAVE_ITEM(MAX8998_REG_CHGR1),
+	SAVE_ITEM(MAX8998_REG_CHGR2),
+	SAVE_ITEM(MAX8998_REG_LDO_ACTIVE_DISCHARGE1),
+	SAVE_ITEM(MAX8998_REG_LDO_ACTIVE_DISCHARGE1),
+	SAVE_ITEM(MAX8998_REG_BUCK_ACTIVE_DISCHARGE3),
+	SAVE_ITEM(MAX8998_REG_ONOFF1),
+	SAVE_ITEM(MAX8998_REG_ONOFF2),
+	SAVE_ITEM(MAX8998_REG_ONOFF3),
+	SAVE_ITEM(MAX8998_REG_ONOFF4),
+	SAVE_ITEM(MAX8998_REG_BUCK1_VOLTAGE1),
+	SAVE_ITEM(MAX8998_REG_BUCK1_VOLTAGE2),
+	SAVE_ITEM(MAX8998_REG_BUCK1_VOLTAGE3),
+	SAVE_ITEM(MAX8998_REG_BUCK1_VOLTAGE4),
+	SAVE_ITEM(MAX8998_REG_BUCK2_VOLTAGE1),
+	SAVE_ITEM(MAX8998_REG_BUCK2_VOLTAGE2),
+	SAVE_ITEM(MAX8998_REG_LDO2_LDO3),
+	SAVE_ITEM(MAX8998_REG_LDO4),
+	SAVE_ITEM(MAX8998_REG_LDO5),
+	SAVE_ITEM(MAX8998_REG_LDO6),
+	SAVE_ITEM(MAX8998_REG_LDO7),
+	SAVE_ITEM(MAX8998_REG_LDO8_LDO9),
+	SAVE_ITEM(MAX8998_REG_LDO10_LDO11),
+	SAVE_ITEM(MAX8998_REG_LDO12),
+	SAVE_ITEM(MAX8998_REG_LDO13),
+	SAVE_ITEM(MAX8998_REG_LDO14),
+	SAVE_ITEM(MAX8998_REG_LDO15),
+	SAVE_ITEM(MAX8998_REG_LDO16),
+	SAVE_ITEM(MAX8998_REG_LDO17),
+	SAVE_ITEM(MAX8998_REG_BKCHR),
+	SAVE_ITEM(MAX8998_REG_LBCNFG1),
+	SAVE_ITEM(MAX8998_REG_LBCNFG2),
+};
+/* Save registers before hibernation */
+static int max8998_freeze(struct device *dev)
+{
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(max8998_dump); i++)
+		max8998_read_reg(i2c, max8998_dump[i].addr,
+				&max8998_dump[i].val);
+
+	return 0;
+}
+
+/* Restore registers after hibernation */
+static int max8998_restore(struct device *dev)
+{
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(max8998_dump); i++)
+		max8998_write_reg(i2c, max8998_dump[i].addr,
+				max8998_dump[i].val);
+
+	return 0;
+}
+
+static const struct dev_pm_ops max8998_pm = {
+	.suspend = max8998_suspend,
+	.resume = max8998_resume,
+	.freeze = max8998_freeze,
+	.restore = max8998_restore,
+};
+
+static struct i2c_driver max8998_i2c_driver = {
+	.driver = {
+		   .name = "max8998",
+		   .pm = &max8998_pm,
+		   .suppress_bind_attrs = true,
+		   .of_match_table = of_match_ptr(max8998_dt_match),
+	},
+	.probe = max8998_i2c_probe,
+	.id_table = max8998_i2c_id,
+};
+
+static int __init max8998_i2c_init(void)
+{
+	return i2c_add_driver(&max8998_i2c_driver);
+}
+/* init early so consumer devices can complete system boot */
+subsys_initcall(max8998_i2c_init);