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, 340 insertions, 0 deletions

diff --git a/drivers/input/mouse/sermouse.c b/drivers/input/mouse/sermouse.c
new file mode 100644
index 000000000..c334a4887
--- /dev/null
+++ b/drivers/input/mouse/sermouse.c
@@ -0,0 +1,340 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 1999-2001 Vojtech Pavlik
+ */
+
+/*
+ *  Serial mouse driver for Linux
+ */
+
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/interrupt.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Serial mouse driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+static const char *sermouse_protocols[] = { "None", "Mouse Systems Mouse", "Sun Mouse", "Microsoft Mouse",
+					"Logitech M+ Mouse", "Microsoft MZ Mouse", "Logitech MZ+ Mouse",
+					"Logitech MZ++ Mouse"};
+
+struct sermouse {
+	struct input_dev *dev;
+	signed char buf[8];
+	unsigned char count;
+	unsigned char type;
+	unsigned long last;
+	char phys[32];
+};
+
+/*
+ * sermouse_process_msc() analyzes the incoming MSC/Sun bytestream and
+ * applies some prediction to the data, resulting in 96 updates per
+ * second, which is as good as a PS/2 or USB mouse.
+ */
+
+static void sermouse_process_msc(struct sermouse *sermouse, signed char data)
+{
+	struct input_dev *dev = sermouse->dev;
+	signed char *buf = sermouse->buf;
+
+	switch (sermouse->count) {
+
+		case 0:
+			if ((data & 0xf8) != 0x80)
+				return;
+			input_report_key(dev, BTN_LEFT,   !(data & 4));
+			input_report_key(dev, BTN_RIGHT,  !(data & 1));
+			input_report_key(dev, BTN_MIDDLE, !(data & 2));
+			break;
+
+		case 1:
+		case 3:
+			input_report_rel(dev, REL_X, data / 2);
+			input_report_rel(dev, REL_Y, -buf[1]);
+			buf[0] = data - data / 2;
+			break;
+
+		case 2:
+		case 4:
+			input_report_rel(dev, REL_X, buf[0]);
+			input_report_rel(dev, REL_Y, buf[1] - data);
+			buf[1] = data / 2;
+			break;
+	}
+
+	input_sync(dev);
+
+	if (++sermouse->count == 5)
+		sermouse->count = 0;
+}
+
+/*
+ * sermouse_process_ms() anlyzes the incoming MS(Z/+/++) bytestream and
+ * generates events. With prediction it gets 80 updates/sec, assuming
+ * standard 3-byte packets and 1200 bps.
+ */
+
+static void sermouse_process_ms(struct sermouse *sermouse, signed char data)
+{
+	struct input_dev *dev = sermouse->dev;
+	signed char *buf = sermouse->buf;
+
+	if (data & 0x40)
+		sermouse->count = 0;
+	else if (sermouse->count == 0)
+		return;
+
+	switch (sermouse->count) {
+
+		case 0:
+			buf[1] = data;
+			input_report_key(dev, BTN_LEFT,   (data >> 5) & 1);
+			input_report_key(dev, BTN_RIGHT,  (data >> 4) & 1);
+			break;
+
+		case 1:
+			buf[2] = data;
+			data = (signed char) (((buf[1] << 6) & 0xc0) | (data & 0x3f));
+			input_report_rel(dev, REL_X, data / 2);
+			input_report_rel(dev, REL_Y, buf[4]);
+			buf[3] = data - data / 2;
+			break;
+
+		case 2:
+			/* Guessing the state of the middle button on 3-button MS-protocol mice - ugly. */
+			if ((sermouse->type == SERIO_MS) && !data && !buf[2] && !((buf[0] & 0xf0) ^ buf[1]))
+				input_report_key(dev, BTN_MIDDLE, !test_bit(BTN_MIDDLE, dev->key));
+			buf[0] = buf[1];
+
+			data = (signed char) (((buf[1] << 4) & 0xc0) | (data & 0x3f));
+			input_report_rel(dev, REL_X, buf[3]);
+			input_report_rel(dev, REL_Y, data - buf[4]);
+			buf[4] = data / 2;
+			break;
+
+		case 3:
+
+			switch (sermouse->type) {
+
+				case SERIO_MS:
+					sermouse->type = SERIO_MP;
+					fallthrough;
+
+				case SERIO_MP:
+					if ((data >> 2) & 3) break;	/* M++ Wireless Extension packet. */
+					input_report_key(dev, BTN_MIDDLE, (data >> 5) & 1);
+					input_report_key(dev, BTN_SIDE,   (data >> 4) & 1);
+					break;
+
+				case SERIO_MZP:
+				case SERIO_MZPP:
+					input_report_key(dev, BTN_SIDE,   (data >> 5) & 1);
+					fallthrough;
+
+				case SERIO_MZ:
+					input_report_key(dev, BTN_MIDDLE, (data >> 4) & 1);
+					input_report_rel(dev, REL_WHEEL,  (data & 8) - (data & 7));
+					break;
+			}
+
+			break;
+
+		case 4:
+		case 6:	/* MZ++ packet type. We can get these bytes for M++ too but we ignore them later. */
+			buf[1] = (data >> 2) & 0x0f;
+			break;
+
+		case 5:
+		case 7: /* Ignore anything besides MZ++ */
+			if (sermouse->type != SERIO_MZPP)
+				break;
+
+			switch (buf[1]) {
+
+				case 1: /* Extra mouse info */
+
+					input_report_key(dev, BTN_SIDE, (data >> 4) & 1);
+					input_report_key(dev, BTN_EXTRA, (data >> 5) & 1);
+					input_report_rel(dev, data & 0x80 ? REL_HWHEEL : REL_WHEEL, (data & 7) - (data & 8));
+
+					break;
+
+				default: /* We don't decode anything else yet. */
+
+					printk(KERN_WARNING
+						"sermouse.c: Received MZ++ packet %x, don't know how to handle.\n", buf[1]);
+					break;
+			}
+
+			break;
+	}
+
+	input_sync(dev);
+
+	sermouse->count++;
+}
+
+/*
+ * sermouse_interrupt() handles incoming characters, either gathering them into
+ * packets or passing them to the command routine as command output.
+ */
+
+static irqreturn_t sermouse_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct sermouse *sermouse = serio_get_drvdata(serio);
+
+	if (time_after(jiffies, sermouse->last + HZ/10))
+		sermouse->count = 0;
+
+	sermouse->last = jiffies;
+
+	if (sermouse->type > SERIO_SUN)
+		sermouse_process_ms(sermouse, data);
+	else
+		sermouse_process_msc(sermouse, data);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * sermouse_disconnect() cleans up after we don't want talk
+ * to the mouse anymore.
+ */
+
+static void sermouse_disconnect(struct serio *serio)
+{
+	struct sermouse *sermouse = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(sermouse->dev);
+	kfree(sermouse);
+}
+
+/*
+ * sermouse_connect() is a callback form the serio module when
+ * an unhandled serio port is found.
+ */
+
+static int sermouse_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct sermouse *sermouse;
+	struct input_dev *input_dev;
+	unsigned char c = serio->id.extra;
+	int err = -ENOMEM;
+
+	sermouse = kzalloc_obj(*sermouse);
+	input_dev = input_allocate_device();
+	if (!sermouse || !input_dev)
+		goto fail1;
+
+	sermouse->dev = input_dev;
+	snprintf(sermouse->phys, sizeof(sermouse->phys), "%s/input0", serio->phys);
+	sermouse->type = serio->id.proto;
+
+	input_dev->name = sermouse_protocols[sermouse->type];
+	input_dev->phys = sermouse->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor  = sermouse->type;
+	input_dev->id.product = c;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);
+	input_dev->keybit[BIT_WORD(BTN_MOUSE)] = BIT_MASK(BTN_LEFT) |
+		BIT_MASK(BTN_RIGHT);
+	input_dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y);
+
+	if (c & 0x01) set_bit(BTN_MIDDLE, input_dev->keybit);
+	if (c & 0x02) set_bit(BTN_SIDE, input_dev->keybit);
+	if (c & 0x04) set_bit(BTN_EXTRA, input_dev->keybit);
+	if (c & 0x10) set_bit(REL_WHEEL, input_dev->relbit);
+	if (c & 0x20) set_bit(REL_HWHEEL, input_dev->relbit);
+
+	serio_set_drvdata(serio, sermouse);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(sermouse->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(sermouse);
+	return err;
+}
+
+static struct serio_device_id sermouse_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_MSC,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_SUN,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_MS,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_MP,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_MZ,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_MZP,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_MZPP,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, sermouse_serio_ids);
+
+static struct serio_driver sermouse_drv = {
+	.driver		= {
+		.name	= "sermouse",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= sermouse_serio_ids,
+	.interrupt	= sermouse_interrupt,
+	.connect	= sermouse_connect,
+	.disconnect	= sermouse_disconnect,
+};
+
+module_serio_driver(sermouse_drv);