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, 174 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/touchright.c b/drivers/input/touchscreen/touchright.c
new file mode 100644
index 000000000..d7fdf201e
--- /dev/null
+++ b/drivers/input/touchscreen/touchright.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Touchright serial touchscreen driver
+ *
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ *
+ * Based on MicroTouch driver (drivers/input/touchscreen/mtouch.c)
+ * Copyright (c) 2004 Vojtech Pavlik
+ * and Dan Streetman <ddstreet@ieee.org>
+ */
+
+
+#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	"Touchright serial touchscreen driver"
+
+MODULE_AUTHOR("Rick Koch <n1gp@hotmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define TR_FORMAT_TOUCH_BIT	0x01
+#define TR_FORMAT_STATUS_BYTE	0x40
+#define TR_FORMAT_STATUS_MASK	~TR_FORMAT_TOUCH_BIT
+
+#define TR_LENGTH 5
+
+#define TR_MIN_XC 0
+#define TR_MAX_XC 0x1ff
+#define TR_MIN_YC 0
+#define TR_MAX_YC 0x1ff
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct tr {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[TR_LENGTH];
+	char phys[32];
+};
+
+static irqreturn_t tr_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct tr *tr = serio_get_drvdata(serio);
+	struct input_dev *dev = tr->dev;
+
+	tr->data[tr->idx] = data;
+
+	if ((tr->data[0] & TR_FORMAT_STATUS_MASK) == TR_FORMAT_STATUS_BYTE) {
+		if (++tr->idx == TR_LENGTH) {
+			input_report_abs(dev, ABS_X,
+				(tr->data[1] << 5) | (tr->data[2] >> 1));
+			input_report_abs(dev, ABS_Y,
+				(tr->data[3] << 5) | (tr->data[4] >> 1));
+			input_report_key(dev, BTN_TOUCH,
+				tr->data[0] & TR_FORMAT_TOUCH_BIT);
+			input_sync(dev);
+			tr->idx = 0;
+		}
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * tr_disconnect() is the opposite of tr_connect()
+ */
+
+static void tr_disconnect(struct serio *serio)
+{
+	struct tr *tr = serio_get_drvdata(serio);
+
+	input_get_device(tr->dev);
+	input_unregister_device(tr->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(tr->dev);
+	kfree(tr);
+}
+
+/*
+ * tr_connect() is the routine that is called when someone adds a
+ * new serio device that supports the Touchright protocol and registers it as
+ * an input device.
+ */
+
+static int tr_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct tr *tr;
+	struct input_dev *input_dev;
+	int err;
+
+	tr = kzalloc_obj(*tr);
+	input_dev = input_allocate_device();
+	if (!tr || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	tr->serio = serio;
+	tr->dev = input_dev;
+	scnprintf(tr->phys, sizeof(tr->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Touchright Serial TouchScreen";
+	input_dev->phys = tr->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TOUCHRIGHT;
+	input_dev->id.product = 0;
+	input_dev->id.version = 0x0100;
+	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(tr->dev, ABS_X, TR_MIN_XC, TR_MAX_XC, 0, 0);
+	input_set_abs_params(tr->dev, ABS_Y, TR_MIN_YC, TR_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, tr);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(tr->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(tr);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id tr_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TOUCHRIGHT,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, tr_serio_ids);
+
+static struct serio_driver tr_drv = {
+	.driver		= {
+		.name	= "touchright",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= tr_serio_ids,
+	.interrupt	= tr_interrupt,
+	.connect	= tr_connect,
+	.disconnect	= tr_disconnect,
+};
+
+module_serio_driver(tr_drv);