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, 246 insertions, 0 deletions

diff --git a/drivers/mfd/tps65090.c b/drivers/mfd/tps65090.c
new file mode 100644
index 000000000..24f42175a
--- /dev/null
+++ b/drivers/mfd/tps65090.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Core driver for TI TPS65090 PMIC family
+ *
+ * Copyright (c) 2012, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * Author: Venu Byravarasu <vbyravarasu@nvidia.com>
+ */
+
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/tps65090.h>
+#include <linux/of.h>
+#include <linux/err.h>
+
+#define NUM_INT_REG 2
+
+#define TPS65090_INT1_MASK_VAC_STATUS_CHANGE		1
+#define TPS65090_INT1_MASK_VSYS_STATUS_CHANGE		2
+#define TPS65090_INT1_MASK_BAT_STATUS_CHANGE		3
+#define TPS65090_INT1_MASK_CHARGING_STATUS_CHANGE	4
+#define TPS65090_INT1_MASK_CHARGING_COMPLETE		5
+#define TPS65090_INT1_MASK_OVERLOAD_DCDC1		6
+#define TPS65090_INT1_MASK_OVERLOAD_DCDC2		7
+#define TPS65090_INT2_MASK_OVERLOAD_DCDC3		0
+#define TPS65090_INT2_MASK_OVERLOAD_FET1		1
+#define TPS65090_INT2_MASK_OVERLOAD_FET2		2
+#define TPS65090_INT2_MASK_OVERLOAD_FET3		3
+#define TPS65090_INT2_MASK_OVERLOAD_FET4		4
+#define TPS65090_INT2_MASK_OVERLOAD_FET5		5
+#define TPS65090_INT2_MASK_OVERLOAD_FET6		6
+#define TPS65090_INT2_MASK_OVERLOAD_FET7		7
+
+static const struct resource charger_resources[] = {
+	{
+		.start  = TPS65090_IRQ_VAC_STATUS_CHANGE,
+		.end    = TPS65090_IRQ_VAC_STATUS_CHANGE,
+		.flags  = IORESOURCE_IRQ,
+	}
+};
+
+enum tps65090_cells {
+	PMIC = 0,
+	CHARGER = 1,
+};
+
+static struct mfd_cell tps65090s[] = {
+	[PMIC] = {
+		.name = "tps65090-pmic",
+	},
+	[CHARGER] = {
+		.name = "tps65090-charger",
+		.num_resources = ARRAY_SIZE(charger_resources),
+		.resources = &charger_resources[0],
+		.of_compatible = "ti,tps65090-charger",
+	},
+};
+
+static const struct regmap_irq tps65090_irqs[] = {
+	/* INT1 IRQs*/
+	[TPS65090_IRQ_VAC_STATUS_CHANGE] = {
+		.mask = TPS65090_INT1_MASK_VAC_STATUS_CHANGE,
+	},
+	[TPS65090_IRQ_VSYS_STATUS_CHANGE] = {
+		.mask = TPS65090_INT1_MASK_VSYS_STATUS_CHANGE,
+	},
+	[TPS65090_IRQ_BAT_STATUS_CHANGE] = {
+		.mask = TPS65090_INT1_MASK_BAT_STATUS_CHANGE,
+	},
+	[TPS65090_IRQ_CHARGING_STATUS_CHANGE] = {
+		.mask = TPS65090_INT1_MASK_CHARGING_STATUS_CHANGE,
+	},
+	[TPS65090_IRQ_CHARGING_COMPLETE] = {
+		.mask = TPS65090_INT1_MASK_CHARGING_COMPLETE,
+	},
+	[TPS65090_IRQ_OVERLOAD_DCDC1] = {
+		.mask = TPS65090_INT1_MASK_OVERLOAD_DCDC1,
+	},
+	[TPS65090_IRQ_OVERLOAD_DCDC2] = {
+		.mask = TPS65090_INT1_MASK_OVERLOAD_DCDC2,
+	},
+	/* INT2 IRQs*/
+	[TPS65090_IRQ_OVERLOAD_DCDC3] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_DCDC3,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET1] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET1,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET2] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET2,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET3] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET3,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET4] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET4,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET5] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET5,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET6] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET6,
+	},
+	[TPS65090_IRQ_OVERLOAD_FET7] = {
+		.reg_offset = 1,
+		.mask = TPS65090_INT2_MASK_OVERLOAD_FET7,
+	},
+};
+
+static const struct regmap_irq_chip tps65090_irq_chip = {
+	.name = "tps65090",
+	.irqs = tps65090_irqs,
+	.num_irqs = ARRAY_SIZE(tps65090_irqs),
+	.num_regs = NUM_INT_REG,
+	.status_base = TPS65090_REG_INTR_STS,
+	.unmask_base = TPS65090_REG_INTR_MASK,
+};
+
+static bool is_volatile_reg(struct device *dev, unsigned int reg)
+{
+	/* Nearly all registers have status bits mixed in, except a few */
+	switch (reg) {
+	case TPS65090_REG_INTR_MASK:
+	case TPS65090_REG_INTR_MASK2:
+	case TPS65090_REG_CG_CTRL0:
+	case TPS65090_REG_CG_CTRL1:
+	case TPS65090_REG_CG_CTRL2:
+	case TPS65090_REG_CG_CTRL3:
+	case TPS65090_REG_CG_CTRL4:
+	case TPS65090_REG_CG_CTRL5:
+		return false;
+	}
+	return true;
+}
+
+static const struct regmap_config tps65090_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = TPS65090_MAX_REG,
+	.num_reg_defaults_raw = TPS65090_NUM_REGS,
+	.cache_type = REGCACHE_MAPLE,
+	.volatile_reg = is_volatile_reg,
+};
+
+#ifdef CONFIG_OF
+static const struct of_device_id tps65090_of_match[] = {
+	{ .compatible = "ti,tps65090",},
+	{},
+};
+#endif
+
+static int tps65090_i2c_probe(struct i2c_client *client)
+{
+	struct tps65090_platform_data *pdata = dev_get_platdata(&client->dev);
+	int irq_base = 0;
+	struct tps65090 *tps65090;
+	int ret;
+
+	if (!pdata && !client->dev.of_node) {
+		dev_err(&client->dev,
+			"tps65090 requires platform data or of_node\n");
+		return -EINVAL;
+	}
+
+	if (pdata)
+		irq_base = pdata->irq_base;
+
+	tps65090 = devm_kzalloc(&client->dev, sizeof(*tps65090), GFP_KERNEL);
+	if (!tps65090)
+		return -ENOMEM;
+
+	tps65090->dev = &client->dev;
+	i2c_set_clientdata(client, tps65090);
+
+	tps65090->rmap = devm_regmap_init_i2c(client, &tps65090_regmap_config);
+	if (IS_ERR(tps65090->rmap)) {
+		ret = PTR_ERR(tps65090->rmap);
+		dev_err(&client->dev, "regmap_init failed with err: %d\n", ret);
+		return ret;
+	}
+
+	if (client->irq) {
+		ret = regmap_add_irq_chip(tps65090->rmap, client->irq,
+					  IRQF_ONESHOT | IRQF_TRIGGER_LOW, irq_base,
+					  &tps65090_irq_chip, &tps65090->irq_data);
+		if (ret) {
+			dev_err(&client->dev,
+				"IRQ init failed with err: %d\n", ret);
+			return ret;
+		}
+	} else {
+		/* Don't tell children they have an IRQ that'll never fire */
+		tps65090s[CHARGER].num_resources = 0;
+	}
+
+	ret = mfd_add_devices(tps65090->dev, -1, tps65090s,
+			      ARRAY_SIZE(tps65090s), NULL,
+			      0, regmap_irq_get_domain(tps65090->irq_data));
+	if (ret) {
+		dev_err(&client->dev, "add mfd devices failed with err: %d\n",
+			ret);
+		goto err_irq_exit;
+	}
+
+	return 0;
+
+err_irq_exit:
+	if (client->irq)
+		regmap_del_irq_chip(client->irq, tps65090->irq_data);
+	return ret;
+}
+
+
+static const struct i2c_device_id tps65090_id_table[] = {
+	{ "tps65090" },
+	{ }
+};
+
+static struct i2c_driver tps65090_driver = {
+	.driver	= {
+		.name	= "tps65090",
+		.suppress_bind_attrs = true,
+		.of_match_table = of_match_ptr(tps65090_of_match),
+	},
+	.probe		= tps65090_i2c_probe,
+	.id_table	= tps65090_id_table,
+};
+
+static int __init tps65090_init(void)
+{
+	return i2c_add_driver(&tps65090_driver);
+}
+subsys_initcall(tps65090_init);