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, 160 insertions, 0 deletions

diff --git a/drivers/input/misc/tps65218-pwrbutton.c b/drivers/input/misc/tps65218-pwrbutton.c
new file mode 100644
index 000000000..fc450fce0
--- /dev/null
+++ b/drivers/input/misc/tps65218-pwrbutton.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Texas Instruments' TPS65217 and TPS65218 Power Button Input Driver
+ *
+ * Copyright (C) 2014 Texas Instruments Incorporated - http://www.ti.com/
+ * Author: Felipe Balbi <balbi@ti.com>
+ * Author: Marcin Niestroj <m.niestroj@grinn-global.com>
+ */
+
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/mfd/tps65217.h>
+#include <linux/mfd/tps65218.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+struct tps6521x_data {
+	unsigned int reg_status;
+	unsigned int pb_mask;
+	const char *name;
+};
+
+static const struct tps6521x_data tps65217_data = {
+	.reg_status = TPS65217_REG_STATUS,
+	.pb_mask = TPS65217_STATUS_PB,
+	.name = "tps65217_pwrbutton",
+};
+
+static const struct tps6521x_data tps65218_data = {
+	.reg_status = TPS65218_REG_STATUS,
+	.pb_mask = TPS65218_STATUS_PB_STATE,
+	.name = "tps65218_pwrbutton",
+};
+
+struct tps6521x_pwrbutton {
+	struct device *dev;
+	struct regmap *regmap;
+	struct input_dev *idev;
+	const struct tps6521x_data *data;
+	char phys[32];
+};
+
+static const struct of_device_id of_tps6521x_pb_match[] = {
+	{ .compatible = "ti,tps65217-pwrbutton", .data = &tps65217_data },
+	{ .compatible = "ti,tps65218-pwrbutton", .data = &tps65218_data },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, of_tps6521x_pb_match);
+
+static irqreturn_t tps6521x_pb_irq(int irq, void *_pwr)
+{
+	struct tps6521x_pwrbutton *pwr = _pwr;
+	const struct tps6521x_data *tps_data = pwr->data;
+	unsigned int reg;
+	int error;
+
+	error = regmap_read(pwr->regmap, tps_data->reg_status, &reg);
+	if (error) {
+		dev_err(pwr->dev, "can't read register: %d\n", error);
+		goto out;
+	}
+
+	if (reg & tps_data->pb_mask) {
+		input_report_key(pwr->idev, KEY_POWER, 1);
+		pm_wakeup_event(pwr->dev, 0);
+	} else {
+		input_report_key(pwr->idev, KEY_POWER, 0);
+	}
+
+	input_sync(pwr->idev);
+
+out:
+	return IRQ_HANDLED;
+}
+
+static int tps6521x_pb_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct tps6521x_pwrbutton *pwr;
+	struct input_dev *idev;
+	const struct of_device_id *match;
+	int error;
+	int irq;
+
+	match = of_match_node(of_tps6521x_pb_match, dev->of_node);
+	if (!match)
+		return -ENXIO;
+
+	pwr = devm_kzalloc(dev, sizeof(*pwr), GFP_KERNEL);
+	if (!pwr)
+		return -ENOMEM;
+
+	pwr->data = match->data;
+
+	idev = devm_input_allocate_device(dev);
+	if (!idev)
+		return -ENOMEM;
+
+	idev->name = pwr->data->name;
+	snprintf(pwr->phys, sizeof(pwr->phys), "%s/input0",
+		pwr->data->name);
+	idev->phys = pwr->phys;
+	idev->dev.parent = dev;
+	idev->id.bustype = BUS_I2C;
+
+	input_set_capability(idev, EV_KEY, KEY_POWER);
+
+	pwr->regmap = dev_get_regmap(dev->parent, NULL);
+	pwr->dev = dev;
+	pwr->idev = idev;
+	device_init_wakeup(dev, true);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return -EINVAL;
+
+	error = devm_request_threaded_irq(dev, irq, NULL, tps6521x_pb_irq,
+					  IRQF_TRIGGER_RISING |
+						IRQF_TRIGGER_FALLING |
+						IRQF_ONESHOT,
+					  pwr->data->name, pwr);
+	if (error) {
+		dev_err(dev, "failed to request IRQ #%d: %d\n", irq, error);
+		return error;
+	}
+
+	error= input_register_device(idev);
+	if (error) {
+		dev_err(dev, "Can't register power button: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+static const struct platform_device_id tps6521x_pwrbtn_id_table[] = {
+	{ "tps65218-pwrbutton", },
+	{ "tps65217-pwrbutton", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(platform, tps6521x_pwrbtn_id_table);
+
+static struct platform_driver tps6521x_pb_driver = {
+	.probe	= tps6521x_pb_probe,
+	.driver	= {
+		.name	= "tps6521x_pwrbutton",
+		.of_match_table = of_tps6521x_pb_match,
+	},
+	.id_table = tps6521x_pwrbtn_id_table,
+};
+module_platform_driver(tps6521x_pb_driver);
+
+MODULE_DESCRIPTION("TPS6521X Power Button");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Felipe Balbi <balbi@ti.com>");