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, 338 insertions, 0 deletions

diff --git a/drivers/mfd/max8907.c b/drivers/mfd/max8907.c
new file mode 100644
index 000000000..7bac1d651
--- /dev/null
+++ b/drivers/mfd/max8907.c
@@ -0,0 +1,338 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * max8907.c - mfd driver for MAX8907
+ *
+ * Copyright (C) 2010 Gyungoh Yoo <jack.yoo@maxim-ic.com>
+ * Copyright (C) 2010-2012, NVIDIA CORPORATION. All rights reserved.
+ */
+
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/max8907.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+static const struct mfd_cell max8907_cells[] = {
+	{ .name = "max8907-regulator", },
+	{ .name = "max8907-rtc", },
+};
+
+static bool max8907_gen_is_volatile_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case MAX8907_REG_ON_OFF_IRQ1:
+	case MAX8907_REG_ON_OFF_STAT:
+	case MAX8907_REG_ON_OFF_IRQ2:
+	case MAX8907_REG_CHG_IRQ1:
+	case MAX8907_REG_CHG_IRQ2:
+	case MAX8907_REG_CHG_STAT:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool max8907_gen_is_precious_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case MAX8907_REG_ON_OFF_IRQ1:
+	case MAX8907_REG_ON_OFF_IRQ2:
+	case MAX8907_REG_CHG_IRQ1:
+	case MAX8907_REG_CHG_IRQ2:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool max8907_gen_is_writeable_reg(struct device *dev, unsigned int reg)
+{
+	return !max8907_gen_is_volatile_reg(dev, reg);
+}
+
+static const struct regmap_config max8907_regmap_gen_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.volatile_reg = max8907_gen_is_volatile_reg,
+	.precious_reg = max8907_gen_is_precious_reg,
+	.writeable_reg = max8907_gen_is_writeable_reg,
+	.max_register = MAX8907_REG_LDO20VOUT,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static bool max8907_rtc_is_volatile_reg(struct device *dev, unsigned int reg)
+{
+	if (reg <= MAX8907_REG_RTC_YEAR2)
+		return true;
+
+	switch (reg) {
+	case MAX8907_REG_RTC_STATUS:
+	case MAX8907_REG_RTC_IRQ:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool max8907_rtc_is_precious_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case MAX8907_REG_RTC_IRQ:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool max8907_rtc_is_writeable_reg(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case MAX8907_REG_RTC_STATUS:
+	case MAX8907_REG_RTC_IRQ:
+		return false;
+	default:
+		return true;
+	}
+}
+
+static const struct regmap_config max8907_regmap_rtc_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.volatile_reg = max8907_rtc_is_volatile_reg,
+	.precious_reg = max8907_rtc_is_precious_reg,
+	.writeable_reg = max8907_rtc_is_writeable_reg,
+	.max_register = MAX8907_REG_MPL_CNTL,
+	.cache_type = REGCACHE_MAPLE,
+};
+
+static const struct regmap_irq max8907_chg_irqs[] = {
+	{ .reg_offset = 0, .mask = 1 << 0, },
+	{ .reg_offset = 0, .mask = 1 << 1, },
+	{ .reg_offset = 0, .mask = 1 << 2, },
+	{ .reg_offset = 1, .mask = 1 << 0, },
+	{ .reg_offset = 1, .mask = 1 << 1, },
+	{ .reg_offset = 1, .mask = 1 << 2, },
+	{ .reg_offset = 1, .mask = 1 << 3, },
+	{ .reg_offset = 1, .mask = 1 << 4, },
+	{ .reg_offset = 1, .mask = 1 << 5, },
+	{ .reg_offset = 1, .mask = 1 << 6, },
+	{ .reg_offset = 1, .mask = 1 << 7, },
+};
+
+static const struct regmap_irq_chip max8907_chg_irq_chip = {
+	.name = "max8907 chg",
+	.status_base = MAX8907_REG_CHG_IRQ1,
+	.mask_base = MAX8907_REG_CHG_IRQ1_MASK,
+	.wake_base = MAX8907_REG_CHG_IRQ1_MASK,
+	.irq_reg_stride = MAX8907_REG_CHG_IRQ2 - MAX8907_REG_CHG_IRQ1,
+	.num_regs = 2,
+	.irqs = max8907_chg_irqs,
+	.num_irqs = ARRAY_SIZE(max8907_chg_irqs),
+};
+
+static const struct regmap_irq max8907_on_off_irqs[] = {
+	{ .reg_offset = 0, .mask = 1 << 0, },
+	{ .reg_offset = 0, .mask = 1 << 1, },
+	{ .reg_offset = 0, .mask = 1 << 2, },
+	{ .reg_offset = 0, .mask = 1 << 3, },
+	{ .reg_offset = 0, .mask = 1 << 4, },
+	{ .reg_offset = 0, .mask = 1 << 5, },
+	{ .reg_offset = 0, .mask = 1 << 6, },
+	{ .reg_offset = 0, .mask = 1 << 7, },
+	{ .reg_offset = 1, .mask = 1 << 0, },
+	{ .reg_offset = 1, .mask = 1 << 1, },
+};
+
+static const struct regmap_irq_chip max8907_on_off_irq_chip = {
+	.name = "max8907 on_off",
+	.status_base = MAX8907_REG_ON_OFF_IRQ1,
+	.mask_base = MAX8907_REG_ON_OFF_IRQ1_MASK,
+	.irq_reg_stride = MAX8907_REG_ON_OFF_IRQ2 - MAX8907_REG_ON_OFF_IRQ1,
+	.num_regs = 2,
+	.irqs = max8907_on_off_irqs,
+	.num_irqs = ARRAY_SIZE(max8907_on_off_irqs),
+};
+
+static const struct regmap_irq max8907_rtc_irqs[] = {
+	{ .reg_offset = 0, .mask = 1 << 2, },
+	{ .reg_offset = 0, .mask = 1 << 3, },
+};
+
+static const struct regmap_irq_chip max8907_rtc_irq_chip = {
+	.name = "max8907 rtc",
+	.status_base = MAX8907_REG_RTC_IRQ,
+	.mask_base = MAX8907_REG_RTC_IRQ_MASK,
+	.num_regs = 1,
+	.irqs = max8907_rtc_irqs,
+	.num_irqs = ARRAY_SIZE(max8907_rtc_irqs),
+};
+
+static struct max8907 *max8907_pm_off;
+static void max8907_power_off(void)
+{
+	regmap_update_bits(max8907_pm_off->regmap_gen, MAX8907_REG_RESET_CNFG,
+			MAX8907_MASK_POWER_OFF, MAX8907_MASK_POWER_OFF);
+}
+
+static int max8907_i2c_probe(struct i2c_client *i2c)
+{
+	struct max8907 *max8907;
+	int ret;
+	struct max8907_platform_data *pdata = dev_get_platdata(&i2c->dev);
+	bool pm_off = false;
+
+	if (pdata)
+		pm_off = pdata->pm_off;
+	else if (i2c->dev.of_node)
+		pm_off = of_property_read_bool(i2c->dev.of_node,
+					"maxim,system-power-controller");
+
+	max8907 = devm_kzalloc(&i2c->dev, sizeof(struct max8907), GFP_KERNEL);
+	if (!max8907) {
+		ret = -ENOMEM;
+		goto err_alloc_drvdata;
+	}
+
+	max8907->dev = &i2c->dev;
+	max8907->i2c_gen = i2c;
+	i2c_set_clientdata(i2c, max8907);
+	max8907->regmap_gen = devm_regmap_init_i2c(i2c,
+						&max8907_regmap_gen_config);
+	if (IS_ERR(max8907->regmap_gen)) {
+		ret = PTR_ERR(max8907->regmap_gen);
+		dev_err(&i2c->dev, "gen regmap init failed: %d\n", ret);
+		goto err_regmap_gen;
+	}
+
+	max8907->i2c_rtc = i2c_new_dummy_device(i2c->adapter, MAX8907_RTC_I2C_ADDR);
+	if (IS_ERR(max8907->i2c_rtc)) {
+		ret = PTR_ERR(max8907->i2c_rtc);
+		goto err_dummy_rtc;
+	}
+	i2c_set_clientdata(max8907->i2c_rtc, max8907);
+	max8907->regmap_rtc = devm_regmap_init_i2c(max8907->i2c_rtc,
+						&max8907_regmap_rtc_config);
+	if (IS_ERR(max8907->regmap_rtc)) {
+		ret = PTR_ERR(max8907->regmap_rtc);
+		dev_err(&i2c->dev, "rtc regmap init failed: %d\n", ret);
+		goto err_regmap_rtc;
+	}
+
+	ret = regmap_add_irq_chip(max8907->regmap_gen, max8907->i2c_gen->irq,
+				  IRQF_ONESHOT | IRQF_SHARED,
+				  -1, &max8907_chg_irq_chip,
+				  &max8907->irqc_chg);
+	if (ret != 0) {
+		dev_err(&i2c->dev, "failed to add chg irq chip: %d\n", ret);
+		goto err_irqc_chg;
+	}
+	ret = regmap_add_irq_chip(max8907->regmap_gen, max8907->i2c_gen->irq,
+				  IRQF_ONESHOT | IRQF_SHARED, -1,
+				  &max8907_on_off_irq_chip,
+				  &max8907->irqc_on_off);
+	if (ret != 0) {
+		dev_err(&i2c->dev, "failed to add on off irq chip: %d\n", ret);
+		goto err_irqc_on_off;
+	}
+	ret = regmap_add_irq_chip(max8907->regmap_rtc, max8907->i2c_gen->irq,
+				  IRQF_ONESHOT | IRQF_SHARED, -1,
+				  &max8907_rtc_irq_chip,
+				  &max8907->irqc_rtc);
+	if (ret != 0) {
+		dev_err(&i2c->dev, "failed to add rtc irq chip: %d\n", ret);
+		goto err_irqc_rtc;
+	}
+
+	ret = mfd_add_devices(max8907->dev, -1, max8907_cells,
+			      ARRAY_SIZE(max8907_cells), NULL, 0, NULL);
+	if (ret != 0) {
+		dev_err(&i2c->dev, "failed to add MFD devices %d\n", ret);
+		goto err_add_devices;
+	}
+
+	if (pm_off && !pm_power_off) {
+		max8907_pm_off = max8907;
+		pm_power_off = max8907_power_off;
+	}
+
+	return 0;
+
+err_add_devices:
+	regmap_del_irq_chip(max8907->i2c_gen->irq, max8907->irqc_rtc);
+err_irqc_rtc:
+	regmap_del_irq_chip(max8907->i2c_gen->irq, max8907->irqc_on_off);
+err_irqc_on_off:
+	regmap_del_irq_chip(max8907->i2c_gen->irq, max8907->irqc_chg);
+err_irqc_chg:
+err_regmap_rtc:
+	i2c_unregister_device(max8907->i2c_rtc);
+err_dummy_rtc:
+err_regmap_gen:
+err_alloc_drvdata:
+	return ret;
+}
+
+static void max8907_i2c_remove(struct i2c_client *i2c)
+{
+	struct max8907 *max8907 = i2c_get_clientdata(i2c);
+
+	mfd_remove_devices(max8907->dev);
+
+	regmap_del_irq_chip(max8907->i2c_gen->irq, max8907->irqc_rtc);
+	regmap_del_irq_chip(max8907->i2c_gen->irq, max8907->irqc_on_off);
+	regmap_del_irq_chip(max8907->i2c_gen->irq, max8907->irqc_chg);
+
+	i2c_unregister_device(max8907->i2c_rtc);
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id max8907_of_match[] = {
+	{ .compatible = "maxim,max8907" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, max8907_of_match);
+#endif
+
+static const struct i2c_device_id max8907_i2c_id[] = {
+	{ "max8907" },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, max8907_i2c_id);
+
+static struct i2c_driver max8907_i2c_driver = {
+	.driver = {
+		.name = "max8907",
+		.of_match_table = of_match_ptr(max8907_of_match),
+	},
+	.probe = max8907_i2c_probe,
+	.remove = max8907_i2c_remove,
+	.id_table = max8907_i2c_id,
+};
+
+static int __init max8907_i2c_init(void)
+{
+	int ret = -ENODEV;
+
+	ret = i2c_add_driver(&max8907_i2c_driver);
+	if (ret != 0)
+		pr_err("Failed to register I2C driver: %d\n", ret);
+
+	return ret;
+}
+subsys_initcall(max8907_i2c_init);
+
+static void __exit max8907_i2c_exit(void)
+{
+	i2c_del_driver(&max8907_i2c_driver);
+}
+module_exit(max8907_i2c_exit);
+
+MODULE_DESCRIPTION("MAX8907 multi-function core driver");
+MODULE_AUTHOR("Gyungoh Yoo <jack.yoo@maxim-ic.com>");
+MODULE_LICENSE("GPL v2");