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, 256 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/zet6223.c b/drivers/input/touchscreen/zet6223.c
new file mode 100644
index 000000000..a341142f3
--- /dev/null
+++ b/drivers/input/touchscreen/zet6223.c
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2016, Jelle van der Waa <jelle@vdwaa.nl>
+ */
+
+#include <linux/delay.h>
+#include <linux/i2c.h>
+#include <linux/input.h>
+#include <linux/input/mt.h>
+#include <linux/input/touchscreen.h>
+#include <linux/interrupt.h>
+#include <linux/module.h>
+#include <linux/regulator/consumer.h>
+#include <linux/unaligned.h>
+
+#define ZET6223_MAX_FINGERS		16
+#define ZET6223_MAX_PKT_SIZE		(3 + 4 * ZET6223_MAX_FINGERS)
+
+#define ZET6223_CMD_INFO		0xB2
+#define ZET6223_CMD_INFO_LENGTH		17
+#define ZET6223_VALID_PACKET		0x3c
+
+#define ZET6223_POWER_ON_DELAY_MSEC	30
+
+struct zet6223_ts {
+	struct i2c_client *client;
+	struct input_dev *input;
+	struct touchscreen_properties prop;
+	struct regulator_bulk_data supplies[2];
+	u16 max_x;
+	u16 max_y;
+	u8 fingernum;
+};
+
+static int zet6223_start(struct input_dev *dev)
+{
+	struct zet6223_ts *ts = input_get_drvdata(dev);
+
+	enable_irq(ts->client->irq);
+
+	return 0;
+}
+
+static void zet6223_stop(struct input_dev *dev)
+{
+	struct zet6223_ts *ts = input_get_drvdata(dev);
+
+	disable_irq(ts->client->irq);
+}
+
+static irqreturn_t zet6223_irq(int irq, void *dev_id)
+{
+	struct zet6223_ts *ts = dev_id;
+	u16 finger_bits;
+
+	/*
+	 * First 3 bytes are an identifier, two bytes of finger data.
+	 * X, Y data per finger is 4 bytes.
+	 */
+	u8 bufsize = 3 + 4 * ts->fingernum;
+	u8 buf[ZET6223_MAX_PKT_SIZE];
+	int i;
+	int ret;
+	int error;
+
+	ret = i2c_master_recv(ts->client, buf, bufsize);
+	if (ret != bufsize) {
+		error = ret < 0 ? ret : -EIO;
+		dev_err_ratelimited(&ts->client->dev,
+				    "Error reading input data: %d\n", error);
+		return IRQ_HANDLED;
+	}
+
+	if (buf[0] != ZET6223_VALID_PACKET)
+		return IRQ_HANDLED;
+
+	finger_bits = get_unaligned_be16(buf + 1);
+	for (i = 0; i < ts->fingernum; i++) {
+		if (!(finger_bits & BIT(15 - i)))
+			continue;
+
+		input_mt_slot(ts->input, i);
+		input_mt_report_slot_state(ts->input, MT_TOOL_FINGER, true);
+		input_event(ts->input, EV_ABS, ABS_MT_POSITION_X,
+				((buf[i + 3] >> 4) << 8) + buf[i + 4]);
+		input_event(ts->input, EV_ABS, ABS_MT_POSITION_Y,
+				((buf[i + 3] & 0xF) << 8) + buf[i + 5]);
+	}
+
+	input_mt_sync_frame(ts->input);
+	input_sync(ts->input);
+
+	return IRQ_HANDLED;
+}
+
+static void zet6223_power_off(void *_ts)
+{
+	struct zet6223_ts *ts = _ts;
+
+	regulator_bulk_disable(ARRAY_SIZE(ts->supplies), ts->supplies);
+}
+
+static int zet6223_power_on(struct zet6223_ts *ts)
+{
+	struct device *dev = &ts->client->dev;
+	int error;
+
+	ts->supplies[0].supply = "vio";
+	ts->supplies[1].supply = "vcc";
+
+	error = devm_regulator_bulk_get(dev, ARRAY_SIZE(ts->supplies),
+					ts->supplies);
+	if (error)
+		return error;
+
+	error = regulator_bulk_enable(ARRAY_SIZE(ts->supplies), ts->supplies);
+	if (error)
+		return error;
+
+	msleep(ZET6223_POWER_ON_DELAY_MSEC);
+
+	error = devm_add_action_or_reset(dev, zet6223_power_off, ts);
+	if (error) {
+		dev_err(dev, "failed to install poweroff action: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+static int zet6223_query_device(struct zet6223_ts *ts)
+{
+	u8 buf[ZET6223_CMD_INFO_LENGTH];
+	u8 cmd = ZET6223_CMD_INFO;
+	int ret;
+	int error;
+
+	ret = i2c_master_send(ts->client, &cmd, sizeof(cmd));
+	if (ret != sizeof(cmd)) {
+		error = ret < 0 ? ret : -EIO;
+		dev_err(&ts->client->dev,
+			"touchpanel info cmd failed: %d\n", error);
+		return error;
+	}
+
+	ret = i2c_master_recv(ts->client, buf, sizeof(buf));
+	if (ret != sizeof(buf)) {
+		error = ret < 0 ? ret : -EIO;
+		dev_err(&ts->client->dev,
+			"failed to retrieve touchpanel info: %d\n", error);
+		return error;
+	}
+
+	ts->fingernum = buf[15] & 0x7F;
+	if (ts->fingernum > ZET6223_MAX_FINGERS) {
+		dev_warn(&ts->client->dev,
+			 "touchpanel reports %d fingers, limiting to %d\n",
+			 ts->fingernum, ZET6223_MAX_FINGERS);
+		ts->fingernum = ZET6223_MAX_FINGERS;
+	}
+
+	ts->max_x = get_unaligned_le16(&buf[8]);
+	ts->max_y = get_unaligned_le16(&buf[10]);
+
+	return 0;
+}
+
+static int zet6223_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct zet6223_ts *ts;
+	struct input_dev *input;
+	int error;
+
+	if (!client->irq) {
+		dev_err(dev, "no irq specified\n");
+		return -EINVAL;
+	}
+
+	ts = devm_kzalloc(dev, sizeof(*ts), GFP_KERNEL);
+	if (!ts)
+		return -ENOMEM;
+
+	ts->client = client;
+
+	error = zet6223_power_on(ts);
+	if (error)
+		return error;
+
+	error = zet6223_query_device(ts);
+	if (error)
+		return error;
+
+	ts->input = input = devm_input_allocate_device(dev);
+	if (!input)
+		return -ENOMEM;
+
+	input_set_drvdata(input, ts);
+
+	input->name = client->name;
+	input->id.bustype = BUS_I2C;
+	input->open = zet6223_start;
+	input->close = zet6223_stop;
+
+	input_set_abs_params(input, ABS_MT_POSITION_X, 0, ts->max_x, 0, 0);
+	input_set_abs_params(input, ABS_MT_POSITION_Y, 0, ts->max_y, 0, 0);
+
+	touchscreen_parse_properties(input, true, &ts->prop);
+
+	error = input_mt_init_slots(input, ts->fingernum,
+				    INPUT_MT_DIRECT | INPUT_MT_DROP_UNUSED);
+	if (error)
+		return error;
+
+	error = devm_request_threaded_irq(dev, client->irq, NULL, zet6223_irq,
+					  IRQF_ONESHOT, client->name, ts);
+	if (error) {
+		dev_err(dev, "failed to request irq %d: %d\n",
+			client->irq, error);
+		return error;
+	}
+
+	zet6223_stop(input);
+
+	error = input_register_device(input);
+	if (error)
+		return error;
+
+	return 0;
+}
+
+static const struct of_device_id zet6223_of_match[] = {
+	{ .compatible = "zeitec,zet6223" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, zet6223_of_match);
+
+static const struct i2c_device_id zet6223_id[] = {
+	{ .name = "zet6223" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, zet6223_id);
+
+static struct i2c_driver zet6223_driver = {
+	.driver = {
+		.name = "zet6223",
+		.of_match_table = zet6223_of_match,
+	},
+	.probe = zet6223_probe,
+	.id_table = zet6223_id
+};
+module_i2c_driver(zet6223_driver);
+
+MODULE_AUTHOR("Jelle van der Waa <jelle@vdwaa.nl>");
+MODULE_DESCRIPTION("ZEITEC zet622x I2C touchscreen driver");
+MODULE_LICENSE("GPL");