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, 290 insertions, 0 deletions

diff --git a/drivers/input/joystick/spaceball.c b/drivers/input/joystick/spaceball.c
new file mode 100644
index 000000000..1af299a41
--- /dev/null
+++ b/drivers/input/joystick/spaceball.c
@@ -0,0 +1,290 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 1999-2001 Vojtech Pavlik
+ *
+ *  Based on the work of:
+ *	David Thompson
+ *	Joseph Krahn
+ */
+
+/*
+ * SpaceTec SpaceBall 2003/3003/4000 FLX driver for Linux
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+#include <linux/unaligned.h>
+
+#define DRIVER_DESC	"SpaceTec SpaceBall 2003/3003/4000 FLX driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Constants.
+ */
+
+#define SPACEBALL_MAX_LENGTH	128
+#define SPACEBALL_MAX_ID	9
+
+#define SPACEBALL_1003      1
+#define SPACEBALL_2003B     3
+#define SPACEBALL_2003C     4
+#define SPACEBALL_3003C     7
+#define SPACEBALL_4000FLX   8
+#define SPACEBALL_4000FLX_L 9
+
+static int spaceball_axes[] = { ABS_X, ABS_Z, ABS_Y, ABS_RX, ABS_RZ, ABS_RY };
+static char *spaceball_names[] = {
+	"?", "SpaceTec SpaceBall 1003", "SpaceTec SpaceBall 2003", "SpaceTec SpaceBall 2003B",
+	"SpaceTec SpaceBall 2003C", "SpaceTec SpaceBall 3003", "SpaceTec SpaceBall SpaceController",
+	"SpaceTec SpaceBall 3003C", "SpaceTec SpaceBall 4000FLX", "SpaceTec SpaceBall 4000FLX Lefty" };
+
+/*
+ * Per-Ball data.
+ */
+
+struct spaceball {
+	struct input_dev *dev;
+	int idx;
+	int escape;
+	unsigned char data[SPACEBALL_MAX_LENGTH];
+	char phys[32];
+};
+
+/*
+ * spaceball_process_packet() decodes packets the driver receives from the
+ * SpaceBall.
+ */
+
+static void spaceball_process_packet(struct spaceball* spaceball)
+{
+	struct input_dev *dev = spaceball->dev;
+	unsigned char *data = spaceball->data;
+	int i;
+
+	if (spaceball->idx < 2) return;
+
+	switch (spaceball->data[0]) {
+
+		case 'D':					/* Ball data */
+			if (spaceball->idx != 15) return;
+			/*
+			 * Skip first three bytes; read six axes worth of data.
+			 * Axis values are signed 16-bit big-endian.
+			 */
+			data += 3;
+			for (i = 0; i < ARRAY_SIZE(spaceball_axes); i++) {
+				input_report_abs(dev, spaceball_axes[i],
+					(__s16)get_unaligned_be16(&data[i * 2]));
+			}
+			break;
+
+		case 'K':					/* Button data */
+			if (spaceball->idx != 3) return;
+			input_report_key(dev, BTN_1, (data[2] & 0x01) || (data[2] & 0x20));
+			input_report_key(dev, BTN_2, data[2] & 0x02);
+			input_report_key(dev, BTN_3, data[2] & 0x04);
+			input_report_key(dev, BTN_4, data[2] & 0x08);
+			input_report_key(dev, BTN_5, data[1] & 0x01);
+			input_report_key(dev, BTN_6, data[1] & 0x02);
+			input_report_key(dev, BTN_7, data[1] & 0x04);
+			input_report_key(dev, BTN_8, data[1] & 0x10);
+			break;
+
+		case '.':					/* Advanced button data */
+			if (spaceball->idx != 3) return;
+			input_report_key(dev, BTN_1, data[2] & 0x01);
+			input_report_key(dev, BTN_2, data[2] & 0x02);
+			input_report_key(dev, BTN_3, data[2] & 0x04);
+			input_report_key(dev, BTN_4, data[2] & 0x08);
+			input_report_key(dev, BTN_5, data[2] & 0x10);
+			input_report_key(dev, BTN_6, data[2] & 0x20);
+			input_report_key(dev, BTN_7, data[2] & 0x80);
+			input_report_key(dev, BTN_8, data[1] & 0x01);
+			input_report_key(dev, BTN_9, data[1] & 0x02);
+			input_report_key(dev, BTN_A, data[1] & 0x04);
+			input_report_key(dev, BTN_B, data[1] & 0x08);
+			input_report_key(dev, BTN_C, data[1] & 0x10);
+			input_report_key(dev, BTN_MODE, data[1] & 0x20);
+			break;
+
+		case 'E':					/* Device error */
+			spaceball->data[spaceball->idx - 1] = 0;
+			printk(KERN_ERR "spaceball: Device error. [%s]\n", spaceball->data + 1);
+			break;
+
+		case '?':					/* Bad command packet */
+			spaceball->data[spaceball->idx - 1] = 0;
+			printk(KERN_ERR "spaceball: Bad command. [%s]\n", spaceball->data + 1);
+			break;
+	}
+
+	input_sync(dev);
+}
+
+/*
+ * Spaceball 4000 FLX packets all start with a one letter packet-type decriptor,
+ * and end in 0x0d. It uses '^' as an escape for CR, XOFF and XON characters which
+ * can occur in the axis values.
+ */
+
+static irqreturn_t spaceball_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct spaceball *spaceball = serio_get_drvdata(serio);
+
+	switch (data) {
+		case 0xd:
+			spaceball_process_packet(spaceball);
+			spaceball->idx = 0;
+			spaceball->escape = 0;
+			break;
+		case '^':
+			if (!spaceball->escape) {
+				spaceball->escape = 1;
+				break;
+			}
+			spaceball->escape = 0;
+			fallthrough;
+		case 'M':
+		case 'Q':
+		case 'S':
+			if (spaceball->escape) {
+				spaceball->escape = 0;
+				data &= 0x1f;
+			}
+			fallthrough;
+		default:
+			if (spaceball->escape)
+				spaceball->escape = 0;
+			if (spaceball->idx < SPACEBALL_MAX_LENGTH)
+				spaceball->data[spaceball->idx++] = data;
+			break;
+	}
+	return IRQ_HANDLED;
+}
+
+/*
+ * spaceball_disconnect() is the opposite of spaceball_connect()
+ */
+
+static void spaceball_disconnect(struct serio *serio)
+{
+	struct spaceball* spaceball = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(spaceball->dev);
+	kfree(spaceball);
+}
+
+/*
+ * spaceball_connect() is the routine that is called when someone adds a
+ * new serio device that supports Spaceball protocol and registers it as
+ * an input device.
+ */
+
+static int spaceball_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct spaceball *spaceball;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+	int i, id;
+
+	if ((id = serio->id.id) > SPACEBALL_MAX_ID)
+		return -ENODEV;
+
+	spaceball = kmalloc_obj(*spaceball);
+	input_dev = input_allocate_device();
+	if (!spaceball || !input_dev)
+		goto fail1;
+
+	spaceball->dev = input_dev;
+	snprintf(spaceball->phys, sizeof(spaceball->phys), "%s/input0", serio->phys);
+
+	input_dev->name = spaceball_names[id];
+	input_dev->phys = spaceball->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_SPACEBALL;
+	input_dev->id.product = id;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+
+	switch (id) {
+		case SPACEBALL_4000FLX:
+		case SPACEBALL_4000FLX_L:
+			input_dev->keybit[BIT_WORD(BTN_0)] |= BIT_MASK(BTN_9);
+			input_dev->keybit[BIT_WORD(BTN_A)] |= BIT_MASK(BTN_A) |
+				BIT_MASK(BTN_B) | BIT_MASK(BTN_C) |
+				BIT_MASK(BTN_MODE);
+			fallthrough;
+		default:
+			input_dev->keybit[BIT_WORD(BTN_0)] |= BIT_MASK(BTN_2) |
+				BIT_MASK(BTN_3) | BIT_MASK(BTN_4) |
+				BIT_MASK(BTN_5) | BIT_MASK(BTN_6) |
+				BIT_MASK(BTN_7) | BIT_MASK(BTN_8);
+			fallthrough;
+		case SPACEBALL_3003C:
+			input_dev->keybit[BIT_WORD(BTN_0)] |= BIT_MASK(BTN_1) |
+				BIT_MASK(BTN_8);
+	}
+
+	for (i = 0; i < 3; i++) {
+		input_set_abs_params(input_dev, ABS_X + i, -8000, 8000, 8, 40);
+		input_set_abs_params(input_dev, ABS_RX + i, -1600, 1600, 2, 8);
+	}
+
+	serio_set_drvdata(serio, spaceball);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(spaceball->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(spaceball);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id spaceball_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_SPACEBALL,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, spaceball_serio_ids);
+
+static struct serio_driver spaceball_drv = {
+	.driver		= {
+		.name	= "spaceball",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= spaceball_serio_ids,
+	.interrupt	= spaceball_interrupt,
+	.connect	= spaceball_connect,
+	.disconnect	= spaceball_disconnect,
+};
+
+module_serio_driver(spaceball_drv);