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, 267 insertions, 0 deletions

diff --git a/drivers/mfd/sec-i2c.c b/drivers/mfd/sec-i2c.c
new file mode 100644
index 000000000..4eec8f7ce
--- /dev/null
+++ b/drivers/mfd/sec-i2c.c
@@ -0,0 +1,267 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2012 Samsung Electronics Co., Ltd
+ *                http://www.samsung.com
+ * Copyright 2025 Linaro Ltd.
+ *
+ * Samsung SxM I2C driver
+ */
+
+#include <linux/dev_printk.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/mfd/samsung/core.h>
+#include <linux/mfd/samsung/s2mpa01.h>
+#include <linux/mfd/samsung/s2mps11.h>
+#include <linux/mfd/samsung/s2mps13.h>
+#include <linux/mfd/samsung/s2mps14.h>
+#include <linux/mfd/samsung/s2mps15.h>
+#include <linux/mfd/samsung/s2mpu02.h>
+#include <linux/mfd/samsung/s2mu005.h>
+#include <linux/mfd/samsung/s5m8767.h>
+#include <linux/module.h>
+#include <linux/pm.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+#include "sec-core.h"
+
+struct sec_pmic_i2c_platform_data {
+	const struct regmap_config *regmap_cfg;
+	int device_type;
+};
+
+static bool s2mpa01_volatile(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case S2MPA01_REG_INT1M:
+	case S2MPA01_REG_INT2M:
+	case S2MPA01_REG_INT3M:
+		return false;
+	default:
+		return true;
+	}
+}
+
+static bool s2mps11_volatile(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case S2MPS11_REG_INT1M:
+	case S2MPS11_REG_INT2M:
+	case S2MPS11_REG_INT3M:
+		return false;
+	default:
+		return true;
+	}
+}
+
+static bool s2mpu02_volatile(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case S2MPU02_REG_INT1M:
+	case S2MPU02_REG_INT2M:
+	case S2MPU02_REG_INT3M:
+		return false;
+	default:
+		return true;
+	}
+}
+
+static bool s2mu005_volatile(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case S2MU005_REG_CHGR_INT1M:
+	case S2MU005_REG_FLED_INT1M:
+	case S2MU005_REG_MUIC_INT1M:
+	case S2MU005_REG_MUIC_INT2M:
+		return false;
+	default:
+		return true;
+	}
+}
+
+static const struct regmap_config s2dos05_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static const struct regmap_config s2mpa01_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MPA01_REG_LDO_OVCB4,
+	.volatile_reg = s2mpa01_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static const struct regmap_config s2mps11_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MPS11_REG_L38CTRL,
+	.volatile_reg = s2mps11_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static const struct regmap_config s2mps13_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MPS13_REG_LDODSCH5,
+	.volatile_reg = s2mps11_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static const struct regmap_config s2mps14_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MPS14_REG_LDODSCH3,
+	.volatile_reg = s2mps11_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static const struct regmap_config s2mps15_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MPS15_REG_LDODSCH4,
+	.volatile_reg = s2mps11_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static const struct regmap_config s2mpu02_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MPU02_REG_DVSDATA,
+	.volatile_reg = s2mpu02_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static const struct regmap_config s2mpu05_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static const struct regmap_config s2mu005_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S2MU005_REG_MUIC_LDOADC_H,
+	.volatile_reg = s2mu005_volatile,
+	.cache_type = REGCACHE_FLAT_S,
+};
+
+static const struct regmap_config s5m8767_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+
+	.max_register = S5M8767_REG_LDO28CTRL,
+	.volatile_reg = s2mps11_volatile,
+	.cache_type = REGCACHE_FLAT,
+};
+
+static int sec_pmic_i2c_probe(struct i2c_client *client)
+{
+	const struct sec_pmic_i2c_platform_data *pdata;
+	struct regmap *regmap_pmic;
+
+	pdata = device_get_match_data(&client->dev);
+	if (!pdata)
+		return dev_err_probe(&client->dev, -ENODEV,
+				     "Unsupported device type\n");
+
+	regmap_pmic = devm_regmap_init_i2c(client, pdata->regmap_cfg);
+	if (IS_ERR(regmap_pmic))
+		return dev_err_probe(&client->dev, PTR_ERR(regmap_pmic),
+				     "regmap init failed\n");
+
+	return sec_pmic_probe(&client->dev, pdata->device_type, client->irq,
+			      regmap_pmic, client);
+}
+
+static void sec_pmic_i2c_shutdown(struct i2c_client *i2c)
+{
+	sec_pmic_shutdown(&i2c->dev);
+}
+
+static const struct sec_pmic_i2c_platform_data s2dos05_data = {
+	.regmap_cfg = &s2dos05_regmap_config,
+	.device_type = S2DOS05
+};
+
+static const struct sec_pmic_i2c_platform_data s2mpa01_data = {
+	.regmap_cfg = &s2mpa01_regmap_config,
+	.device_type = S2MPA01,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mps11_data = {
+	.regmap_cfg = &s2mps11_regmap_config,
+	.device_type = S2MPS11X,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mps13_data = {
+	.regmap_cfg = &s2mps13_regmap_config,
+	.device_type = S2MPS13X,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mps14_data = {
+	.regmap_cfg = &s2mps14_regmap_config,
+	.device_type = S2MPS14X,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mps15_data = {
+	.regmap_cfg = &s2mps15_regmap_config,
+	.device_type = S2MPS15X,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mpu02_data = {
+	.regmap_cfg = &s2mpu02_regmap_config,
+	.device_type = S2MPU02,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mpu05_data = {
+	.regmap_cfg = &s2mpu05_regmap_config,
+	.device_type = S2MPU05,
+};
+
+static const struct sec_pmic_i2c_platform_data s2mu005_data = {
+	.regmap_cfg = &s2mu005_regmap_config,
+	.device_type = S2MU005,
+};
+
+static const struct sec_pmic_i2c_platform_data s5m8767_data = {
+	.regmap_cfg = &s5m8767_regmap_config,
+	.device_type = S5M8767X,
+};
+
+static const struct of_device_id sec_pmic_i2c_of_match[] = {
+	{ .compatible = "samsung,s2dos05", .data = &s2dos05_data, },
+	{ .compatible = "samsung,s2mpa01-pmic", .data = &s2mpa01_data, },
+	{ .compatible = "samsung,s2mps11-pmic", .data = &s2mps11_data, },
+	{ .compatible = "samsung,s2mps13-pmic", .data = &s2mps13_data, },
+	{ .compatible = "samsung,s2mps14-pmic", .data = &s2mps14_data, },
+	{ .compatible = "samsung,s2mps15-pmic", .data = &s2mps15_data, },
+	{ .compatible = "samsung,s2mpu02-pmic", .data = &s2mpu02_data, },
+	{ .compatible = "samsung,s2mpu05-pmic", .data = &s2mpu05_data, },
+	{ .compatible = "samsung,s2mu005-pmic", .data = &s2mu005_data, },
+	{ .compatible = "samsung,s5m8767-pmic", .data = &s5m8767_data, },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, sec_pmic_i2c_of_match);
+
+static struct i2c_driver sec_pmic_i2c_driver = {
+	.driver = {
+		.name = "sec-pmic-i2c",
+		.pm = pm_sleep_ptr(&sec_pmic_pm_ops),
+		.of_match_table = sec_pmic_i2c_of_match,
+	},
+	.probe = sec_pmic_i2c_probe,
+	.shutdown = sec_pmic_i2c_shutdown,
+};
+module_i2c_driver(sec_pmic_i2c_driver);
+
+MODULE_AUTHOR("Sangbeom Kim <sbkim73@samsung.com>");
+MODULE_AUTHOR("André Draszik <andre.draszik@linaro.org>");
+MODULE_DESCRIPTION("I2C driver for the Samsung S5M");
+MODULE_LICENSE("GPL");