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, 315 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/penmount.c b/drivers/input/touchscreen/penmount.c
new file mode 100644
index 000000000..4b57b6664
--- /dev/null
+++ b/drivers/input/touchscreen/penmount.c
@@ -0,0 +1,315 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Penmount serial touchscreen driver
+ *
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ * Copyright (c) 2011 John Sung <penmount.touch@gmail.com>
+ *
+ * Based on ELO driver (drivers/input/touchscreen/elo.c)
+ * Copyright (c) 2004 Vojtech Pavlik
+ */
+
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/input/mt.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"PenMount serial touchscreen driver"
+
+MODULE_AUTHOR("Rick Koch <n1gp@hotmail.com>");
+MODULE_AUTHOR("John Sung <penmount.touch@gmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define	PM_MAX_LENGTH	6
+#define	PM_MAX_MTSLOT	16
+#define	PM_3000_MTSLOT	2
+#define	PM_6250_MTSLOT	12
+
+/*
+ * Multi-touch slot
+ */
+
+struct mt_slot {
+	unsigned short x, y;
+	bool active; /* is the touch valid? */
+};
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct pm {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[PM_MAX_LENGTH];
+	char phys[32];
+	unsigned char packetsize;
+	unsigned char maxcontacts;
+	struct mt_slot slots[PM_MAX_MTSLOT];
+	void (*parse_packet)(struct pm *);
+};
+
+/*
+ * pm_mtevent() sends mt events and also emulates pointer movement
+ */
+
+static void pm_mtevent(struct pm *pm, struct input_dev *input)
+{
+	int i;
+
+	for (i = 0; i < pm->maxcontacts; ++i) {
+		input_mt_slot(input, i);
+		input_mt_report_slot_state(input, MT_TOOL_FINGER,
+				pm->slots[i].active);
+		if (pm->slots[i].active) {
+			input_event(input, EV_ABS, ABS_MT_POSITION_X, pm->slots[i].x);
+			input_event(input, EV_ABS, ABS_MT_POSITION_Y, pm->slots[i].y);
+		}
+	}
+
+	input_mt_report_pointer_emulation(input, true);
+	input_sync(input);
+}
+
+/*
+ * pm_checkpacket() checks if data packet is valid
+ */
+
+static bool pm_checkpacket(unsigned char *packet)
+{
+	int total = 0;
+	int i;
+
+	for (i = 0; i < 5; i++)
+		total += packet[i];
+
+	return packet[5] == (unsigned char)~(total & 0xff);
+}
+
+static void pm_parse_9000(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0x80) && pm->packetsize == ++pm->idx) {
+		input_report_abs(dev, ABS_X, pm->data[1] * 128 + pm->data[2]);
+		input_report_abs(dev, ABS_Y, pm->data[3] * 128 + pm->data[4]);
+		input_report_key(dev, BTN_TOUCH, !!(pm->data[0] & 0x40));
+		input_sync(dev);
+		pm->idx = 0;
+	}
+}
+
+static void pm_parse_6000(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0xbf) == 0x30 && pm->packetsize == ++pm->idx) {
+		if (pm_checkpacket(pm->data)) {
+			input_report_abs(dev, ABS_X,
+					pm->data[2] * 256 + pm->data[1]);
+			input_report_abs(dev, ABS_Y,
+					pm->data[4] * 256 + pm->data[3]);
+			input_report_key(dev, BTN_TOUCH, pm->data[0] & 0x40);
+			input_sync(dev);
+		}
+		pm->idx = 0;
+	}
+}
+
+static void pm_parse_3000(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0xce) == 0x40 && pm->packetsize == ++pm->idx) {
+		if (pm_checkpacket(pm->data)) {
+			int slotnum = pm->data[0] & 0x0f;
+			pm->slots[slotnum].active = pm->data[0] & 0x30;
+			pm->slots[slotnum].x = pm->data[2] * 256 + pm->data[1];
+			pm->slots[slotnum].y = pm->data[4] * 256 + pm->data[3];
+			pm_mtevent(pm, dev);
+		}
+		pm->idx = 0;
+	}
+}
+
+static void pm_parse_6250(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0xb0) == 0x30 && pm->packetsize == ++pm->idx) {
+		if (pm_checkpacket(pm->data)) {
+			int slotnum = pm->data[0] & 0x0f;
+			pm->slots[slotnum].active = pm->data[0] & 0x40;
+			pm->slots[slotnum].x = pm->data[2] * 256 + pm->data[1];
+			pm->slots[slotnum].y = pm->data[4] * 256 + pm->data[3];
+			pm_mtevent(pm, dev);
+		}
+		pm->idx = 0;
+	}
+}
+
+static irqreturn_t pm_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct pm *pm = serio_get_drvdata(serio);
+
+	pm->data[pm->idx] = data;
+
+	pm->parse_packet(pm);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * pm_disconnect() is the opposite of pm_connect()
+ */
+
+static void pm_disconnect(struct serio *serio)
+{
+	struct pm *pm = serio_get_drvdata(serio);
+
+	serio_close(serio);
+
+	input_unregister_device(pm->dev);
+	kfree(pm);
+
+	serio_set_drvdata(serio, NULL);
+}
+
+/*
+ * pm_connect() is the routine that is called when someone adds a
+ * new serio device that supports PenMount protocol and registers it as
+ * an input device.
+ */
+
+static int pm_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct pm *pm;
+	struct input_dev *input_dev;
+	int max_x, max_y;
+	int err;
+
+	pm = kzalloc_obj(*pm);
+	input_dev = input_allocate_device();
+	if (!pm || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	pm->serio = serio;
+	pm->dev = input_dev;
+	scnprintf(pm->phys, sizeof(pm->phys), "%s/input0", serio->phys);
+	pm->maxcontacts = 1;
+
+	input_dev->name = "PenMount Serial TouchScreen";
+	input_dev->phys = pm->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_PENMOUNT;
+	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);
+
+	switch (serio->id.id) {
+	default:
+	case 0:
+		pm->packetsize = 5;
+		pm->parse_packet = pm_parse_9000;
+		input_dev->id.product = 0x9000;
+		max_x = max_y = 0x3ff;
+		break;
+
+	case 1:
+		pm->packetsize = 6;
+		pm->parse_packet = pm_parse_6000;
+		input_dev->id.product = 0x6000;
+		max_x = max_y = 0x3ff;
+		break;
+
+	case 2:
+		pm->packetsize = 6;
+		pm->parse_packet = pm_parse_3000;
+		input_dev->id.product = 0x3000;
+		max_x = max_y = 0x7ff;
+		pm->maxcontacts = PM_3000_MTSLOT;
+		break;
+
+	case 3:
+		pm->packetsize = 6;
+		pm->parse_packet = pm_parse_6250;
+		input_dev->id.product = 0x6250;
+		max_x = max_y = 0x3ff;
+		pm->maxcontacts = PM_6250_MTSLOT;
+		break;
+	}
+
+	input_set_abs_params(pm->dev, ABS_X, 0, max_x, 0, 0);
+	input_set_abs_params(pm->dev, ABS_Y, 0, max_y, 0, 0);
+
+	if (pm->maxcontacts > 1) {
+		input_mt_init_slots(pm->dev, pm->maxcontacts, 0);
+		input_set_abs_params(pm->dev,
+				     ABS_MT_POSITION_X, 0, max_x, 0, 0);
+		input_set_abs_params(pm->dev,
+				     ABS_MT_POSITION_Y, 0, max_y, 0, 0);
+	}
+
+	serio_set_drvdata(serio, pm);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(pm->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(pm);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id pm_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_PENMOUNT,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, pm_serio_ids);
+
+static struct serio_driver pm_drv = {
+	.driver		= {
+		.name	= "serio-penmount",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= pm_serio_ids,
+	.interrupt	= pm_interrupt,
+	.connect	= pm_connect,
+	.disconnect	= pm_disconnect,
+};
+
+module_serio_driver(pm_drv);