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, 129 insertions, 0 deletions

diff --git a/drivers/input/misc/max77650-onkey.c b/drivers/input/misc/max77650-onkey.c
new file mode 100644
index 000000000..ee55f22db
--- /dev/null
+++ b/drivers/input/misc/max77650-onkey.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Copyright (C) 2018 BayLibre SAS
+// Author: Bartosz Golaszewski <bgolaszewski@baylibre.com>
+//
+// ONKEY driver for MAXIM 77650/77651 charger/power-supply.
+
+#include <linux/i2c.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/max77650.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define MAX77650_ONKEY_MODE_MASK	BIT(3)
+#define MAX77650_ONKEY_MODE_PUSH	0x00
+#define MAX77650_ONKEY_MODE_SLIDE	BIT(3)
+
+struct max77650_onkey {
+	struct input_dev *input;
+	unsigned int code;
+};
+
+static irqreturn_t max77650_onkey_falling(int irq, void *data)
+{
+	struct max77650_onkey *onkey = data;
+
+	input_report_key(onkey->input, onkey->code, 0);
+	input_sync(onkey->input);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t max77650_onkey_rising(int irq, void *data)
+{
+	struct max77650_onkey *onkey = data;
+
+	input_report_key(onkey->input, onkey->code, 1);
+	input_sync(onkey->input);
+
+	return IRQ_HANDLED;
+}
+
+static int max77650_onkey_probe(struct platform_device *pdev)
+{
+	int irq_r, irq_f, error, mode;
+	struct max77650_onkey *onkey;
+	struct device *dev, *parent;
+	struct regmap *map;
+	unsigned int type;
+
+	dev = &pdev->dev;
+	parent = dev->parent;
+
+	map = dev_get_regmap(parent, NULL);
+	if (!map)
+		return -ENODEV;
+
+	onkey = devm_kzalloc(dev, sizeof(*onkey), GFP_KERNEL);
+	if (!onkey)
+		return -ENOMEM;
+
+	error = device_property_read_u32(dev, "linux,code", &onkey->code);
+	if (error)
+		onkey->code = KEY_POWER;
+
+	if (device_property_read_bool(dev, "maxim,onkey-slide")) {
+		mode = MAX77650_ONKEY_MODE_SLIDE;
+		type = EV_SW;
+	} else {
+		mode = MAX77650_ONKEY_MODE_PUSH;
+		type = EV_KEY;
+	}
+
+	error = regmap_update_bits(map, MAX77650_REG_CNFG_GLBL,
+				   MAX77650_ONKEY_MODE_MASK, mode);
+	if (error)
+		return error;
+
+	irq_f = platform_get_irq_byname(pdev, "nEN_F");
+	if (irq_f < 0)
+		return irq_f;
+
+	irq_r = platform_get_irq_byname(pdev, "nEN_R");
+	if (irq_r < 0)
+		return irq_r;
+
+	onkey->input = devm_input_allocate_device(dev);
+	if (!onkey->input)
+		return -ENOMEM;
+
+	onkey->input->name = "max77650_onkey";
+	onkey->input->phys = "max77650_onkey/input0";
+	onkey->input->id.bustype = BUS_I2C;
+	input_set_capability(onkey->input, type, onkey->code);
+
+	error = devm_request_any_context_irq(dev, irq_f, max77650_onkey_falling,
+					     IRQF_ONESHOT, "onkey-down", onkey);
+	if (error < 0)
+		return error;
+
+	error = devm_request_any_context_irq(dev, irq_r, max77650_onkey_rising,
+					     IRQF_ONESHOT, "onkey-up", onkey);
+	if (error < 0)
+		return error;
+
+	return input_register_device(onkey->input);
+}
+
+static const struct of_device_id max77650_onkey_of_match[] = {
+	{ .compatible = "maxim,max77650-onkey" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max77650_onkey_of_match);
+
+static struct platform_driver max77650_onkey_driver = {
+	.driver = {
+		.name = "max77650-onkey",
+		.of_match_table = max77650_onkey_of_match,
+	},
+	.probe = max77650_onkey_probe,
+};
+module_platform_driver(max77650_onkey_driver);
+
+MODULE_DESCRIPTION("MAXIM 77650/77651 ONKEY driver");
+MODULE_AUTHOR("Bartosz Golaszewski <bgolaszewski@baylibre.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:max77650-onkey");