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, 191 insertions, 0 deletions

diff --git a/drivers/input/joystick/stinger.c b/drivers/input/joystick/stinger.c
new file mode 100644
index 000000000..011f9b137
--- /dev/null
+++ b/drivers/input/joystick/stinger.c
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *  Copyright (c) 2000 Mark Fletcher
+ */
+
+/*
+ * Gravis Stinger gamepad driver for Linux
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Gravis Stinger gamepad driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Constants.
+ */
+
+#define STINGER_MAX_LENGTH 8
+
+/*
+ * Per-Stinger data.
+ */
+
+struct stinger {
+	struct input_dev *dev;
+	int idx;
+	unsigned char data[STINGER_MAX_LENGTH];
+	char phys[32];
+};
+
+/*
+ * stinger_process_packet() decodes packets the driver receives from the
+ * Stinger. It updates the data accordingly.
+ */
+
+static void stinger_process_packet(struct stinger *stinger)
+{
+	struct input_dev *dev = stinger->dev;
+	unsigned char *data = stinger->data;
+
+	if (!stinger->idx) return;
+
+	input_report_key(dev, BTN_A,	  ((data[0] & 0x20) >> 5));
+	input_report_key(dev, BTN_B,	  ((data[0] & 0x10) >> 4));
+	input_report_key(dev, BTN_C,	  ((data[0] & 0x08) >> 3));
+	input_report_key(dev, BTN_X,	  ((data[0] & 0x04) >> 2));
+	input_report_key(dev, BTN_Y,	  ((data[3] & 0x20) >> 5));
+	input_report_key(dev, BTN_Z,	  ((data[3] & 0x10) >> 4));
+	input_report_key(dev, BTN_TL,     ((data[3] & 0x08) >> 3));
+	input_report_key(dev, BTN_TR,     ((data[3] & 0x04) >> 2));
+	input_report_key(dev, BTN_SELECT, ((data[3] & 0x02) >> 1));
+	input_report_key(dev, BTN_START,   (data[3] & 0x01));
+
+	input_report_abs(dev, ABS_X, (data[1] & 0x3F) - ((data[0] & 0x01) << 6));
+	input_report_abs(dev, ABS_Y, ((data[0] & 0x02) << 5) - (data[2] & 0x3F));
+
+	input_sync(dev);
+
+	return;
+}
+
+/*
+ * stinger_interrupt() is called by the low level driver when characters
+ * are ready for us. We then buffer them for further processing, or call the
+ * packet processing routine.
+ */
+
+static irqreturn_t stinger_interrupt(struct serio *serio,
+	unsigned char data, unsigned int flags)
+{
+	struct stinger *stinger = serio_get_drvdata(serio);
+
+	/* All Stinger packets are 4 bytes */
+
+	if (stinger->idx < STINGER_MAX_LENGTH)
+		stinger->data[stinger->idx++] = data;
+
+	if (stinger->idx == 4) {
+		stinger_process_packet(stinger);
+		stinger->idx = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * stinger_disconnect() is the opposite of stinger_connect()
+ */
+
+static void stinger_disconnect(struct serio *serio)
+{
+	struct stinger *stinger = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(stinger->dev);
+	kfree(stinger);
+}
+
+/*
+ * stinger_connect() is the routine that is called when someone adds a
+ * new serio device that supports Stinger protocol and registers it as
+ * an input device.
+ */
+
+static int stinger_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct stinger *stinger;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+
+	stinger = kmalloc_obj(*stinger);
+	input_dev = input_allocate_device();
+	if (!stinger || !input_dev)
+		goto fail1;
+
+	stinger->dev = input_dev;
+	snprintf(stinger->phys, sizeof(stinger->phys), "%s/serio0", serio->phys);
+
+	input_dev->name = "Gravis Stinger";
+	input_dev->phys = stinger->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_STINGER;
+	input_dev->id.product = 0x0001;
+	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_A)] = BIT_MASK(BTN_A) | BIT_MASK(BTN_B) |
+		BIT_MASK(BTN_C) | BIT_MASK(BTN_X) | BIT_MASK(BTN_Y) |
+		BIT_MASK(BTN_Z) | BIT_MASK(BTN_TL) | BIT_MASK(BTN_TR) |
+		BIT_MASK(BTN_START) | BIT_MASK(BTN_SELECT);
+	input_set_abs_params(input_dev, ABS_X, -64, 64, 0, 4);
+	input_set_abs_params(input_dev, ABS_Y, -64, 64, 0, 4);
+
+	serio_set_drvdata(serio, stinger);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(stinger->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(stinger);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id stinger_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_STINGER,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, stinger_serio_ids);
+
+static struct serio_driver stinger_drv = {
+	.driver		= {
+		.name	= "stinger",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= stinger_serio_ids,
+	.interrupt	= stinger_interrupt,
+	.connect	= stinger_connect,
+	.disconnect	= stinger_disconnect,
+};
+
+module_serio_driver(stinger_drv);