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, 186 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/inexio.c b/drivers/input/touchscreen/inexio.c
new file mode 100644
index 000000000..ac3836ff2
--- /dev/null
+++ b/drivers/input/touchscreen/inexio.c
@@ -0,0 +1,186 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * iNexio serial touchscreen driver
+ *
+ * Copyright (c) 2008 Richard Lemon
+ * Based on the mtouch driver (c) Vojtech Pavlik and Dan Streetman
+ */
+
+
+/*
+ * 2008/06/19 Richard Lemon <richard@codelemon.com>
+ *   Copied mtouch.c and edited for iNexio protocol
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"iNexio serial touchscreen driver"
+
+MODULE_AUTHOR("Richard Lemon <richard@codelemon.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define INEXIO_FORMAT_TOUCH_BIT 0x01
+#define INEXIO_FORMAT_LENGTH 5
+#define INEXIO_RESPONSE_BEGIN_BYTE 0x80
+
+/* todo: check specs for max length of all responses */
+#define INEXIO_MAX_LENGTH 16
+
+#define INEXIO_MIN_XC 0
+#define INEXIO_MAX_XC 0x3fff
+#define INEXIO_MIN_YC 0
+#define INEXIO_MAX_YC 0x3fff
+
+#define INEXIO_GET_XC(data) (((data[1])<<7) | data[2])
+#define INEXIO_GET_YC(data) (((data[3])<<7) | data[4])
+#define INEXIO_GET_TOUCHED(data) (INEXIO_FORMAT_TOUCH_BIT & data[0])
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct inexio {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[INEXIO_MAX_LENGTH];
+	char phys[32];
+};
+
+static void inexio_process_data(struct inexio *pinexio)
+{
+	struct input_dev *dev = pinexio->dev;
+
+	if (INEXIO_FORMAT_LENGTH == ++pinexio->idx) {
+		input_report_abs(dev, ABS_X, INEXIO_GET_XC(pinexio->data));
+		input_report_abs(dev, ABS_Y, INEXIO_GET_YC(pinexio->data));
+		input_report_key(dev, BTN_TOUCH, INEXIO_GET_TOUCHED(pinexio->data));
+		input_sync(dev);
+
+		pinexio->idx = 0;
+	}
+}
+
+static irqreturn_t inexio_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct inexio *pinexio = serio_get_drvdata(serio);
+
+	pinexio->data[pinexio->idx] = data;
+
+	if (INEXIO_RESPONSE_BEGIN_BYTE&pinexio->data[0])
+		inexio_process_data(pinexio);
+	else
+		printk(KERN_DEBUG "inexio.c: unknown/unsynchronized data from device, byte %x\n",pinexio->data[0]);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * inexio_disconnect() is the opposite of inexio_connect()
+ */
+
+static void inexio_disconnect(struct serio *serio)
+{
+	struct inexio *pinexio = serio_get_drvdata(serio);
+
+	input_get_device(pinexio->dev);
+	input_unregister_device(pinexio->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(pinexio->dev);
+	kfree(pinexio);
+}
+
+/*
+ * inexio_connect() is the routine that is called when someone adds a
+ * new serio device that supports iNexio protocol and registers it as
+ * an input device. This is usually accomplished using inputattach.
+ */
+
+static int inexio_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct inexio *pinexio;
+	struct input_dev *input_dev;
+	int err;
+
+	pinexio = kzalloc_obj(*pinexio);
+	input_dev = input_allocate_device();
+	if (!pinexio || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	pinexio->serio = serio;
+	pinexio->dev = input_dev;
+	scnprintf(pinexio->phys, sizeof(pinexio->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "iNexio Serial TouchScreen";
+	input_dev->phys = pinexio->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_INEXIO;
+	input_dev->id.product = 0;
+	input_dev->id.version = 0x0001;
+	input_dev->dev.parent = &serio->dev;
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(pinexio->dev, ABS_X, INEXIO_MIN_XC, INEXIO_MAX_XC, 0, 0);
+	input_set_abs_params(pinexio->dev, ABS_Y, INEXIO_MIN_YC, INEXIO_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, pinexio);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(pinexio->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(pinexio);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id inexio_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_INEXIO,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, inexio_serio_ids);
+
+static struct serio_driver inexio_drv = {
+	.driver		= {
+		.name	= "inexio",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= inexio_serio_ids,
+	.interrupt	= inexio_interrupt,
+	.connect	= inexio_connect,
+	.disconnect	= inexio_disconnect,
+};
+
+module_serio_driver(inexio_drv);