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, 97 insertions, 0 deletions

diff --git a/drivers/input/misc/ad714x-i2c.c b/drivers/input/misc/ad714x-i2c.c
new file mode 100644
index 000000000..c3cb56151
--- /dev/null
+++ b/drivers/input/misc/ad714x-i2c.c
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * AD714X CapTouch Programmable Controller driver (I2C bus)
+ *
+ * Copyright 2009-2011 Analog Devices Inc.
+ */
+
+#include <linux/input.h>	/* BUS_I2C */
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/pm.h>
+#include "ad714x.h"
+
+static int ad714x_i2c_write(struct ad714x_chip *chip,
+			    unsigned short reg, unsigned short data)
+{
+	struct i2c_client *client = to_i2c_client(chip->dev);
+	int error;
+
+	chip->xfer_buf[0] = cpu_to_be16(reg);
+	chip->xfer_buf[1] = cpu_to_be16(data);
+
+	error = i2c_master_send(client, (u8 *)chip->xfer_buf,
+				2 * sizeof(*chip->xfer_buf));
+	if (unlikely(error < 0)) {
+		dev_err(&client->dev, "I2C write error: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+static int ad714x_i2c_read(struct ad714x_chip *chip,
+			   unsigned short reg, unsigned short *data, size_t len)
+{
+	struct i2c_client *client = to_i2c_client(chip->dev);
+	int i;
+	int error;
+
+	chip->xfer_buf[0] = cpu_to_be16(reg);
+
+	error = i2c_master_send(client, (u8 *)chip->xfer_buf,
+				sizeof(*chip->xfer_buf));
+	if (error >= 0)
+		error = i2c_master_recv(client, (u8 *)chip->xfer_buf,
+					len * sizeof(*chip->xfer_buf));
+
+	if (unlikely(error < 0)) {
+		dev_err(&client->dev, "I2C read error: %d\n", error);
+		return error;
+	}
+
+	for (i = 0; i < len; i++)
+		data[i] = be16_to_cpu(chip->xfer_buf[i]);
+
+	return 0;
+}
+
+static int ad714x_i2c_probe(struct i2c_client *client)
+{
+	struct ad714x_chip *chip;
+
+	chip = ad714x_probe(&client->dev, BUS_I2C, client->irq,
+			    ad714x_i2c_read, ad714x_i2c_write);
+	if (IS_ERR(chip))
+		return PTR_ERR(chip);
+
+	i2c_set_clientdata(client, chip);
+
+	return 0;
+}
+
+static const struct i2c_device_id ad714x_id[] = {
+	{ .name = "ad7142_captouch" },
+	{ .name = "ad7143_captouch" },
+	{ .name = "ad7147_captouch" },
+	{ .name = "ad7147a_captouch" },
+	{ .name = "ad7148_captouch" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ad714x_id);
+
+static struct i2c_driver ad714x_i2c_driver = {
+	.driver = {
+		.name = "ad714x_captouch",
+		.pm   = pm_sleep_ptr(&ad714x_pm),
+	},
+	.probe = ad714x_i2c_probe,
+	.id_table = ad714x_id,
+};
+
+module_i2c_driver(ad714x_i2c_driver);
+
+MODULE_DESCRIPTION("Analog Devices AD714X Capacitance Touch Sensor I2C Bus Driver");
+MODULE_AUTHOR("Barry Song <21cnbao@gmail.com>");
+MODULE_LICENSE("GPL");