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, 133 insertions, 0 deletions

diff --git a/drivers/mfd/rt5033.c b/drivers/mfd/rt5033.c
new file mode 100644
index 000000000..072fd4447
--- /dev/null
+++ b/drivers/mfd/rt5033.c
@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * MFD core driver for the Richtek RT5033.
+ *
+ * RT5033 comprises multiple sub-devices switcing charger, fuel gauge,
+ * flash LED, current source, LDO and BUCK regulators.
+ *
+ * Copyright (C) 2014 Samsung Electronics, Co., Ltd.
+ * Author: Beomho Seo <beomho.seo@samsung.com>
+ */
+
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/rt5033.h>
+#include <linux/mfd/rt5033-private.h>
+
+static const struct regmap_irq rt5033_irqs[] = {
+	{ .mask = RT5033_PMIC_IRQ_BUCKOCP, },
+	{ .mask = RT5033_PMIC_IRQ_BUCKLV, },
+	{ .mask = RT5033_PMIC_IRQ_SAFELDOLV, },
+	{ .mask = RT5033_PMIC_IRQ_LDOLV, },
+	{ .mask = RT5033_PMIC_IRQ_OT, },
+	{ .mask = RT5033_PMIC_IRQ_VDDA_UV, },
+};
+
+static const struct regmap_irq_chip rt5033_irq_chip = {
+	.name		= "rt5033",
+	.status_base	= RT5033_REG_PMIC_IRQ_STAT,
+	.unmask_base	= RT5033_REG_PMIC_IRQ_CTRL,
+	.num_regs	= 1,
+	.irqs		= rt5033_irqs,
+	.num_irqs	= ARRAY_SIZE(rt5033_irqs),
+};
+
+static const struct mfd_cell rt5033_devs[] = {
+	{ .name = "rt5033-regulator", },
+	{
+		.name = "rt5033-charger",
+		.of_compatible = "richtek,rt5033-charger",
+	}, {
+		.name = "rt5033-led",
+		.of_compatible = "richtek,rt5033-led",
+	},
+};
+
+static const struct regmap_config rt5033_regmap_config = {
+	.reg_bits	= 8,
+	.val_bits	= 8,
+	.max_register	= RT5033_REG_END,
+};
+
+static int rt5033_i2c_probe(struct i2c_client *i2c)
+{
+	struct rt5033_dev *rt5033;
+	unsigned int dev_id, chip_rev;
+	int ret;
+
+	rt5033 = devm_kzalloc(&i2c->dev, sizeof(*rt5033), GFP_KERNEL);
+	if (!rt5033)
+		return -ENOMEM;
+
+	i2c_set_clientdata(i2c, rt5033);
+	rt5033->dev = &i2c->dev;
+	rt5033->irq = i2c->irq;
+	rt5033->wakeup = true;
+
+	rt5033->regmap = devm_regmap_init_i2c(i2c, &rt5033_regmap_config);
+	if (IS_ERR(rt5033->regmap)) {
+		dev_err(&i2c->dev, "Failed to allocate register map.\n");
+		return PTR_ERR(rt5033->regmap);
+	}
+
+	ret = regmap_read(rt5033->regmap, RT5033_REG_DEVICE_ID, &dev_id);
+	if (ret) {
+		dev_err(&i2c->dev, "Device not found\n");
+		return -ENODEV;
+	}
+	chip_rev = dev_id & RT5033_CHIP_REV_MASK;
+	dev_info(&i2c->dev, "Device found (rev. %d)\n", chip_rev);
+
+	ret = devm_regmap_add_irq_chip(rt5033->dev, rt5033->regmap,
+			rt5033->irq, IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
+			0, &rt5033_irq_chip, &rt5033->irq_data);
+	if (ret) {
+		dev_err(&i2c->dev, "Failed to request IRQ %d: %d\n",
+							rt5033->irq, ret);
+		return ret;
+	}
+
+	ret = devm_mfd_add_devices(rt5033->dev, -1, rt5033_devs,
+				   ARRAY_SIZE(rt5033_devs), NULL, 0,
+				   regmap_irq_get_domain(rt5033->irq_data));
+	if (ret < 0) {
+		dev_err(&i2c->dev, "Failed to add RT5033 child devices.\n");
+		return ret;
+	}
+
+	if (rt5033->wakeup) {
+		ret = devm_device_init_wakeup(rt5033->dev);
+		if (ret)
+			return dev_err_probe(rt5033->dev, ret, "Failed to init wakeup\n");
+	}
+
+	return 0;
+}
+
+static const struct i2c_device_id rt5033_i2c_id[] = {
+	{ "rt5033", },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, rt5033_i2c_id);
+
+static const struct of_device_id rt5033_dt_match[] = {
+	{ .compatible = "richtek,rt5033", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, rt5033_dt_match);
+
+static struct i2c_driver rt5033_driver = {
+	.driver = {
+		.name = "rt5033",
+		.of_match_table = rt5033_dt_match,
+	},
+	.probe = rt5033_i2c_probe,
+	.id_table = rt5033_i2c_id,
+};
+module_i2c_driver(rt5033_driver);
+
+MODULE_DESCRIPTION("Richtek RT5033 multi-function core driver");
+MODULE_AUTHOR("Beomho Seo <beomho.seo@samsung.com>");
+MODULE_LICENSE("GPL");