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, 204 insertions, 0 deletions

diff --git a/drivers/input/keyboard/adc-keys.c b/drivers/input/keyboard/adc-keys.c
new file mode 100644
index 000000000..f17532074
--- /dev/null
+++ b/drivers/input/keyboard/adc-keys.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Input driver for resistor ladder connected on ADC
+ *
+ * Copyright (c) 2016 Alexandre Belloni
+ */
+
+#include <linux/err.h>
+#include <linux/iio/consumer.h>
+#include <linux/iio/types.h>
+#include <linux/input.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+struct adc_keys_button {
+	u32 voltage;
+	u32 keycode;
+};
+
+struct adc_keys_state {
+	struct iio_channel *channel;
+	u32 num_keys;
+	u32 last_key;
+	u32 keyup_voltage;
+	const struct adc_keys_button *map;
+};
+
+static void adc_keys_poll(struct input_dev *input)
+{
+	struct adc_keys_state *st = input_get_drvdata(input);
+	int i, value, ret;
+	u32 diff, closest = 0xffffffff;
+	int keycode = 0;
+
+	ret = iio_read_channel_processed(st->channel, &value);
+	if (unlikely(ret < 0)) {
+		/* Forcibly release key if any was pressed */
+		value = st->keyup_voltage;
+	} else {
+		for (i = 0; i < st->num_keys; i++) {
+			diff = abs(st->map[i].voltage - value);
+			if (diff < closest) {
+				closest = diff;
+				keycode = st->map[i].keycode;
+			}
+		}
+	}
+
+	if (abs(st->keyup_voltage - value) < closest)
+		keycode = 0;
+
+	if (st->last_key && st->last_key != keycode)
+		input_report_key(input, st->last_key, 0);
+
+	if (keycode)
+		input_report_key(input, keycode, 1);
+
+	input_sync(input);
+	st->last_key = keycode;
+}
+
+static int adc_keys_load_keymap(struct device *dev, struct adc_keys_state *st)
+{
+	struct adc_keys_button *map;
+	int i;
+
+	st->num_keys = device_get_child_node_count(dev);
+	if (st->num_keys == 0) {
+		dev_err(dev, "keymap is missing\n");
+		return -EINVAL;
+	}
+
+	map = devm_kmalloc_array(dev, st->num_keys, sizeof(*map), GFP_KERNEL);
+	if (!map)
+		return -ENOMEM;
+
+	i = 0;
+	device_for_each_child_node_scoped(dev, child) {
+		if (fwnode_property_read_u32(child, "press-threshold-microvolt",
+					     &map[i].voltage)) {
+			dev_err(dev, "Key with invalid or missing voltage\n");
+			return -EINVAL;
+		}
+		map[i].voltage /= 1000;
+
+		if (fwnode_property_read_u32(child, "linux,code",
+					     &map[i].keycode)) {
+			dev_err(dev, "Key with invalid or missing linux,code\n");
+			return -EINVAL;
+		}
+
+		i++;
+	}
+
+	st->map = map;
+	return 0;
+}
+
+static int adc_keys_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct adc_keys_state *st;
+	struct input_dev *input;
+	enum iio_chan_type type;
+	int i, value;
+	int error;
+
+	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
+	if (!st)
+		return -ENOMEM;
+
+	st->channel = devm_iio_channel_get(dev, "buttons");
+	if (IS_ERR(st->channel))
+		return PTR_ERR(st->channel);
+
+	if (!st->channel->indio_dev)
+		return -ENXIO;
+
+	error = iio_get_channel_type(st->channel, &type);
+	if (error < 0)
+		return error;
+
+	if (type != IIO_VOLTAGE) {
+		dev_err(dev, "Incompatible channel type %d\n", type);
+		return -EINVAL;
+	}
+
+	if (device_property_read_u32(dev, "keyup-threshold-microvolt",
+				     &st->keyup_voltage)) {
+		dev_err(dev, "Invalid or missing keyup voltage\n");
+		return -EINVAL;
+	}
+	st->keyup_voltage /= 1000;
+
+	error = adc_keys_load_keymap(dev, st);
+	if (error)
+		return error;
+
+	input = devm_input_allocate_device(dev);
+	if (!input) {
+		dev_err(dev, "failed to allocate input device\n");
+		return -ENOMEM;
+	}
+
+	input_set_drvdata(input, st);
+
+	input->name = pdev->name;
+	input->phys = "adc-keys/input0";
+
+	input->id.bustype = BUS_HOST;
+	input->id.vendor = 0x0001;
+	input->id.product = 0x0001;
+	input->id.version = 0x0100;
+
+	__set_bit(EV_KEY, input->evbit);
+	for (i = 0; i < st->num_keys; i++)
+		__set_bit(st->map[i].keycode, input->keybit);
+
+	if (device_property_read_bool(dev, "autorepeat"))
+		__set_bit(EV_REP, input->evbit);
+
+
+	error = input_setup_polling(input, adc_keys_poll);
+	if (error) {
+		dev_err(dev, "Unable to set up polling: %d\n", error);
+		return error;
+	}
+
+	if (!device_property_read_u32(dev, "poll-interval", &value))
+		input_set_poll_interval(input, value);
+
+	error = input_register_device(input);
+	if (error) {
+		dev_err(dev, "Unable to register input device: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id adc_keys_of_match[] = {
+	{ .compatible = "adc-keys", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, adc_keys_of_match);
+#endif
+
+static struct platform_driver adc_keys_driver = {
+	.driver = {
+		.name = "adc_keys",
+		.of_match_table = of_match_ptr(adc_keys_of_match),
+	},
+	.probe = adc_keys_probe,
+};
+module_platform_driver(adc_keys_driver);
+
+MODULE_AUTHOR("Alexandre Belloni <alexandre.belloni@free-electrons.com>");
+MODULE_DESCRIPTION("Input driver for resistor ladder connected on ADC");
+MODULE_LICENSE("GPL v2");