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, 294 insertions, 0 deletions

diff --git a/drivers/input/joystick/interact.c b/drivers/input/joystick/interact.c
new file mode 100644
index 000000000..507cec36b
--- /dev/null
+++ b/drivers/input/joystick/interact.c
@@ -0,0 +1,294 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2001 Vojtech Pavlik
+ *
+ *  Based on the work of:
+ *	Toby Deshane
+ */
+
+/*
+ * InterAct digital gamepad/joystick driver for Linux
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/delay.h>
+#include <linux/gameport.h>
+#include <linux/input.h>
+#include <linux/jiffies.h>
+
+#define DRIVER_DESC	"InterAct digital joystick driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define INTERACT_MAX_START	600	/* 400 us */
+#define INTERACT_MAX_STROBE	60	/* 40 us */
+#define INTERACT_MAX_LENGTH	32	/* 32 bits */
+
+#define INTERACT_TYPE_HHFX	0	/* HammerHead/FX */
+#define INTERACT_TYPE_PP8D	1	/* ProPad 8 */
+
+struct interact {
+	struct gameport *gameport;
+	struct input_dev *dev;
+	int bads;
+	int reads;
+	unsigned char type;
+	unsigned char length;
+	char phys[32];
+};
+
+static short interact_abs_hhfx[] =
+	{ ABS_RX, ABS_RY, ABS_X, ABS_Y, ABS_HAT0X, ABS_HAT0Y, -1 };
+static short interact_abs_pp8d[] =
+	{ ABS_X, ABS_Y, -1 };
+
+static short interact_btn_hhfx[] =
+	{ BTN_TR, BTN_X, BTN_Y, BTN_Z, BTN_A, BTN_B, BTN_C, BTN_TL, BTN_TL2, BTN_TR2, BTN_MODE, BTN_SELECT, -1 };
+static short interact_btn_pp8d[] =
+	{ BTN_C, BTN_TL, BTN_TR, BTN_A, BTN_B, BTN_Y, BTN_Z, BTN_X, -1 };
+
+struct interact_type {
+	int id;
+	short *abs;
+	short *btn;
+	char *name;
+	unsigned char length;
+	unsigned char b8;
+};
+
+static struct interact_type interact_type[] = {
+	{ 0x6202, interact_abs_hhfx, interact_btn_hhfx, "InterAct HammerHead/FX",    32, 4 },
+	{ 0x53f8, interact_abs_pp8d, interact_btn_pp8d, "InterAct ProPad 8 Digital", 16, 0 },
+	{ 0 }};
+
+/*
+ * interact_read_packet() reads and InterAct joystick data.
+ */
+
+static int interact_read_packet(struct gameport *gameport, int length, u32 *data)
+{
+	unsigned long flags;
+	unsigned char u, v;
+	unsigned int t, s;
+	int i;
+
+	i = 0;
+	data[0] = data[1] = data[2] = 0;
+	t = gameport_time(gameport, INTERACT_MAX_START);
+	s = gameport_time(gameport, INTERACT_MAX_STROBE);
+
+	local_irq_save(flags);
+	gameport_trigger(gameport);
+	v = gameport_read(gameport);
+
+	while (t > 0 && i < length) {
+		t--;
+		u = v; v = gameport_read(gameport);
+		if (v & ~u & 0x40) {
+			data[0] = (data[0] << 1) | ((v >> 4) & 1);
+			data[1] = (data[1] << 1) | ((v >> 5) & 1);
+			data[2] = (data[2] << 1) | ((v >> 7) & 1);
+			i++;
+			t = s;
+		}
+	}
+
+	local_irq_restore(flags);
+
+	return i;
+}
+
+/*
+ * interact_poll() reads and analyzes InterAct joystick data.
+ */
+
+static void interact_poll(struct gameport *gameport)
+{
+	struct interact *interact = gameport_get_drvdata(gameport);
+	struct input_dev *dev = interact->dev;
+	u32 data[3];
+	int i;
+
+	interact->reads++;
+
+	if (interact_read_packet(interact->gameport, interact->length, data) < interact->length) {
+		interact->bads++;
+	} else {
+
+		for (i = 0; i < 3; i++)
+			data[i] <<= INTERACT_MAX_LENGTH - interact->length;
+
+		switch (interact->type) {
+
+			case INTERACT_TYPE_HHFX:
+
+				for (i = 0; i < 4; i++)
+					input_report_abs(dev, interact_abs_hhfx[i], (data[i & 1] >> ((i >> 1) << 3)) & 0xff);
+
+				for (i = 0; i < 2; i++)
+					input_report_abs(dev, ABS_HAT0Y - i,
+						((data[1] >> ((i << 1) + 17)) & 1)  - ((data[1] >> ((i << 1) + 16)) & 1));
+
+				for (i = 0; i < 8; i++)
+					input_report_key(dev, interact_btn_hhfx[i], (data[0] >> (i + 16)) & 1);
+
+				for (i = 0; i < 4; i++)
+					input_report_key(dev, interact_btn_hhfx[i + 8], (data[1] >> (i + 20)) & 1);
+
+				break;
+
+			case INTERACT_TYPE_PP8D:
+
+				for (i = 0; i < 2; i++)
+					input_report_abs(dev, interact_abs_pp8d[i],
+						((data[0] >> ((i << 1) + 20)) & 1)  - ((data[0] >> ((i << 1) + 21)) & 1));
+
+				for (i = 0; i < 8; i++)
+					input_report_key(dev, interact_btn_pp8d[i], (data[1] >> (i + 16)) & 1);
+
+				break;
+		}
+	}
+
+	input_sync(dev);
+}
+
+/*
+ * interact_open() is a callback from the input open routine.
+ */
+
+static int interact_open(struct input_dev *dev)
+{
+	struct interact *interact = input_get_drvdata(dev);
+
+	gameport_start_polling(interact->gameport);
+	return 0;
+}
+
+/*
+ * interact_close() is a callback from the input close routine.
+ */
+
+static void interact_close(struct input_dev *dev)
+{
+	struct interact *interact = input_get_drvdata(dev);
+
+	gameport_stop_polling(interact->gameport);
+}
+
+/*
+ * interact_connect() probes for InterAct joysticks.
+ */
+
+static int interact_connect(struct gameport *gameport, struct gameport_driver *drv)
+{
+	struct interact *interact;
+	struct input_dev *input_dev;
+	__u32 data[3];
+	int i, t;
+	int err;
+
+	interact = kzalloc_obj(*interact);
+	input_dev = input_allocate_device();
+	if (!interact || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	interact->gameport = gameport;
+	interact->dev = input_dev;
+
+	gameport_set_drvdata(gameport, interact);
+
+	err = gameport_open(gameport, drv, GAMEPORT_MODE_RAW);
+	if (err)
+		goto fail1;
+
+	i = interact_read_packet(gameport, INTERACT_MAX_LENGTH * 2, data);
+
+	if (i != 32 || (data[0] >> 24) != 0x0c || (data[1] >> 24) != 0x02) {
+		err = -ENODEV;
+		goto fail2;
+	}
+
+	for (i = 0; interact_type[i].length; i++)
+		if (interact_type[i].id == (data[2] >> 16))
+			break;
+
+	if (!interact_type[i].length) {
+		printk(KERN_WARNING "interact.c: Unknown joystick on %s. [len %d d0 %08x d1 %08x i2 %08x]\n",
+			gameport->phys, i, data[0], data[1], data[2]);
+		err = -ENODEV;
+		goto fail2;
+	}
+
+	gameport_set_poll_handler(gameport, interact_poll);
+	gameport_set_poll_interval(gameport, 20);
+
+	snprintf(interact->phys, sizeof(interact->phys), "%s/input0", gameport->phys);
+
+	interact->type = i;
+	interact->length = interact_type[i].length;
+
+	input_dev->name = interact_type[i].name;
+	input_dev->phys = interact->phys;
+	input_dev->id.bustype = BUS_GAMEPORT;
+	input_dev->id.vendor = GAMEPORT_ID_VENDOR_INTERACT;
+	input_dev->id.product = interact_type[i].id;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &gameport->dev;
+
+	input_set_drvdata(input_dev, interact);
+
+	input_dev->open = interact_open;
+	input_dev->close = interact_close;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+
+	for (i = 0; (t = interact_type[interact->type].abs[i]) >= 0; i++) {
+		if (i < interact_type[interact->type].b8)
+			input_set_abs_params(input_dev, t, 0, 255, 0, 0);
+		else
+			input_set_abs_params(input_dev, t, -1, 1, 0, 0);
+	}
+
+	for (i = 0; (t = interact_type[interact->type].btn[i]) >= 0; i++)
+		__set_bit(t, input_dev->keybit);
+
+	err = input_register_device(interact->dev);
+	if (err)
+		goto fail2;
+
+	return 0;
+
+fail2:	gameport_close(gameport);
+fail1:  gameport_set_drvdata(gameport, NULL);
+	input_free_device(input_dev);
+	kfree(interact);
+	return err;
+}
+
+static void interact_disconnect(struct gameport *gameport)
+{
+	struct interact *interact = gameport_get_drvdata(gameport);
+
+	input_unregister_device(interact->dev);
+	gameport_close(gameport);
+	gameport_set_drvdata(gameport, NULL);
+	kfree(interact);
+}
+
+static struct gameport_driver interact_drv = {
+	.driver		= {
+		.name	= "interact",
+	},
+	.description	= DRIVER_DESC,
+	.connect	= interact_connect,
+	.disconnect	= interact_disconnect,
+};
+
+module_gameport_driver(interact_drv);