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, 150 insertions, 0 deletions

diff --git a/drivers/input/misc/tps65219-pwrbutton.c b/drivers/input/misc/tps65219-pwrbutton.c
new file mode 100644
index 000000000..7a58bae4f
--- /dev/null
+++ b/drivers/input/misc/tps65219-pwrbutton.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Driver for TPS65219 Push Button
+//
+// Copyright (C) 2022 BayLibre Incorporated - https://www.baylibre.com/
+
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/mfd/tps65219.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+struct tps65219_pwrbutton {
+	struct device *dev;
+	struct input_dev *idev;
+	char phys[32];
+};
+
+static irqreturn_t tps65219_pb_push_irq(int irq, void *_pwr)
+{
+	struct tps65219_pwrbutton *pwr = _pwr;
+
+	input_report_key(pwr->idev, KEY_POWER, 1);
+	pm_wakeup_event(pwr->dev, 0);
+	input_sync(pwr->idev);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t tps65219_pb_release_irq(int irq, void *_pwr)
+{
+	struct tps65219_pwrbutton *pwr = _pwr;
+
+	input_report_key(pwr->idev, KEY_POWER, 0);
+	input_sync(pwr->idev);
+
+	return IRQ_HANDLED;
+}
+
+static int tps65219_pb_probe(struct platform_device *pdev)
+{
+	struct tps65219 *tps = dev_get_drvdata(pdev->dev.parent);
+	struct device *dev = &pdev->dev;
+	struct tps65219_pwrbutton *pwr;
+	struct input_dev *idev;
+	int error;
+	int push_irq;
+	int release_irq;
+
+	pwr = devm_kzalloc(dev, sizeof(*pwr), GFP_KERNEL);
+	if (!pwr)
+		return -ENOMEM;
+
+	idev = devm_input_allocate_device(dev);
+	if (!idev)
+		return -ENOMEM;
+
+	idev->name = pdev->name;
+	snprintf(pwr->phys, sizeof(pwr->phys), "%s/input0",
+		 pdev->name);
+	idev->phys = pwr->phys;
+	idev->id.bustype = BUS_I2C;
+
+	input_set_capability(idev, EV_KEY, KEY_POWER);
+
+	pwr->dev = dev;
+	pwr->idev = idev;
+	device_init_wakeup(dev, true);
+
+	push_irq = platform_get_irq(pdev, 0);
+	if (push_irq < 0)
+		return -EINVAL;
+
+	release_irq = platform_get_irq(pdev, 1);
+	if (release_irq < 0)
+		return -EINVAL;
+
+	error = devm_request_threaded_irq(dev, push_irq, NULL,
+					  tps65219_pb_push_irq,
+					  IRQF_ONESHOT,
+					  dev->init_name, pwr);
+	if (error) {
+		dev_err(dev, "failed to request push IRQ #%d: %d\n", push_irq,
+			error);
+		return error;
+	}
+
+	error = devm_request_threaded_irq(dev, release_irq, NULL,
+					  tps65219_pb_release_irq,
+					  IRQF_ONESHOT,
+					  dev->init_name, pwr);
+	if (error) {
+		dev_err(dev, "failed to request release IRQ #%d: %d\n",
+			release_irq, error);
+		return error;
+	}
+
+	error = input_register_device(idev);
+	if (error) {
+		dev_err(dev, "Can't register power button: %d\n", error);
+		return error;
+	}
+
+	/* Enable interrupts for the pushbutton */
+	regmap_clear_bits(tps->regmap, TPS65219_REG_MASK_CONFIG,
+			  TPS65219_REG_MASK_INT_FOR_PB_MASK);
+
+	/* Set PB/EN/VSENSE pin to be a pushbutton */
+	regmap_update_bits(tps->regmap, TPS65219_REG_MFP_2_CONFIG,
+			   TPS65219_MFP_2_EN_PB_VSENSE_MASK, TPS65219_MFP_2_PB);
+
+	return 0;
+}
+
+static void tps65219_pb_remove(struct platform_device *pdev)
+{
+	struct tps65219 *tps = dev_get_drvdata(pdev->dev.parent);
+	int ret;
+
+	/* Disable interrupt for the pushbutton */
+	ret = regmap_set_bits(tps->regmap, TPS65219_REG_MASK_CONFIG,
+			      TPS65219_REG_MASK_INT_FOR_PB_MASK);
+	if (ret)
+		dev_warn(&pdev->dev, "Failed to disable irq (%pe)\n", ERR_PTR(ret));
+}
+
+static const struct platform_device_id tps65219_pwrbtn_id_table[] = {
+	{ "tps65219-pwrbutton", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(platform, tps65219_pwrbtn_id_table);
+
+static struct platform_driver tps65219_pb_driver = {
+	.probe = tps65219_pb_probe,
+	.remove = tps65219_pb_remove,
+	.driver = {
+		.name = "tps65219_pwrbutton",
+	},
+	.id_table = tps65219_pwrbtn_id_table,
+};
+module_platform_driver(tps65219_pb_driver);
+
+MODULE_DESCRIPTION("TPS65219 Power Button");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Markus Schneider-Pargmann <msp@baylibre.com");