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, 194 insertions, 0 deletions

diff --git a/drivers/input/joystick/maplecontrol.c b/drivers/input/joystick/maplecontrol.c
new file mode 100644
index 000000000..6293b6e81
--- /dev/null
+++ b/drivers/input/joystick/maplecontrol.c
@@ -0,0 +1,194 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *	SEGA Dreamcast controller driver
+ *	Based on drivers/usb/iforce.c
+ *
+ *	Copyright Yaegashi Takeshi, 2001
+ *	Adrian McMenamin, 2008 - 2009
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/timer.h>
+#include <linux/maple.h>
+
+MODULE_AUTHOR("Adrian McMenamin <adrian@mcmen.demon.co.uk>");
+MODULE_DESCRIPTION("SEGA Dreamcast controller driver");
+MODULE_LICENSE("GPL");
+
+struct dc_pad {
+	struct input_dev *dev;
+	struct maple_device *mdev;
+};
+
+static void dc_pad_callback(struct mapleq *mq)
+{
+	unsigned short buttons;
+	struct maple_device *mapledev = mq->dev;
+	struct dc_pad *pad = maple_get_drvdata(mapledev);
+	struct input_dev *dev = pad->dev;
+	unsigned char *res = mq->recvbuf->buf;
+
+	buttons = ~le16_to_cpup((__le16 *)(res + 8));
+
+	input_report_abs(dev, ABS_HAT0Y,
+		(buttons & 0x0010 ? -1 : 0) + (buttons & 0x0020 ? 1 : 0));
+	input_report_abs(dev, ABS_HAT0X,
+		(buttons & 0x0040 ? -1 : 0) + (buttons & 0x0080 ? 1 : 0));
+	input_report_abs(dev, ABS_HAT1Y,
+		(buttons & 0x1000 ? -1 : 0) + (buttons & 0x2000 ? 1 : 0));
+	input_report_abs(dev, ABS_HAT1X,
+		(buttons & 0x4000 ? -1 : 0) + (buttons & 0x8000 ? 1 : 0));
+
+	input_report_key(dev, BTN_C,      buttons & 0x0001);
+	input_report_key(dev, BTN_B,      buttons & 0x0002);
+	input_report_key(dev, BTN_A,      buttons & 0x0004);
+	input_report_key(dev, BTN_START,  buttons & 0x0008);
+	input_report_key(dev, BTN_Z,      buttons & 0x0100);
+	input_report_key(dev, BTN_Y,      buttons & 0x0200);
+	input_report_key(dev, BTN_X,      buttons & 0x0400);
+	input_report_key(dev, BTN_SELECT, buttons & 0x0800);
+
+	input_report_abs(dev, ABS_GAS,    res[10]);
+	input_report_abs(dev, ABS_BRAKE,  res[11]);
+	input_report_abs(dev, ABS_X,      res[12]);
+	input_report_abs(dev, ABS_Y,      res[13]);
+	input_report_abs(dev, ABS_RX,     res[14]);
+	input_report_abs(dev, ABS_RY,     res[15]);
+}
+
+static int dc_pad_open(struct input_dev *dev)
+{
+	struct dc_pad *pad = dev_get_platdata(&dev->dev);
+
+	maple_getcond_callback(pad->mdev, dc_pad_callback, HZ/20,
+		MAPLE_FUNC_CONTROLLER);
+
+	return 0;
+}
+
+static void dc_pad_close(struct input_dev *dev)
+{
+	struct dc_pad *pad = dev_get_platdata(&dev->dev);
+
+	maple_getcond_callback(pad->mdev, dc_pad_callback, 0,
+		MAPLE_FUNC_CONTROLLER);
+}
+
+/* allow the controller to be used */
+static int probe_maple_controller(struct device *dev)
+{
+	static const short btn_bit[32] = {
+		BTN_C, BTN_B, BTN_A, BTN_START, -1, -1, -1, -1,
+		BTN_Z, BTN_Y, BTN_X, BTN_SELECT, -1, -1, -1, -1,
+		-1, -1, -1, -1, -1, -1, -1, -1,
+		-1, -1, -1, -1, -1, -1, -1, -1,
+	};
+
+	static const short abs_bit[32] = {
+		-1, -1, -1, -1, ABS_HAT0Y, ABS_HAT0Y, ABS_HAT0X, ABS_HAT0X,
+		-1, -1, -1, -1, ABS_HAT1Y, ABS_HAT1Y, ABS_HAT1X, ABS_HAT1X,
+		ABS_GAS, ABS_BRAKE, ABS_X, ABS_Y, ABS_RX, ABS_RY, -1, -1,
+		-1, -1, -1, -1, -1, -1, -1, -1,
+	};
+
+	struct maple_device *mdev = to_maple_dev(dev);
+	struct maple_driver *mdrv = to_maple_driver(dev->driver);
+	int i, error;
+	struct dc_pad *pad;
+	struct input_dev *idev;
+	unsigned long data = be32_to_cpu(mdev->devinfo.function_data[0]);
+
+	pad = kzalloc_obj(*pad);
+	idev = input_allocate_device();
+	if (!pad || !idev) {
+		error = -ENOMEM;
+		goto fail;
+	}
+
+	pad->dev = idev;
+	pad->mdev = mdev;
+
+	maple_set_drvdata(mdev, pad);
+
+	idev->open = dc_pad_open;
+	idev->close = dc_pad_close;
+
+	for (i = 0; i < 32; i++) {
+		if (data & (1 << i)) {
+			if (btn_bit[i] >= 0)
+				__set_bit(btn_bit[i], idev->keybit);
+			else if (abs_bit[i] >= 0)
+				__set_bit(abs_bit[i], idev->absbit);
+		}
+	}
+
+	if (idev->keybit[BIT_WORD(BTN_JOYSTICK)])
+		idev->evbit[0] |= BIT_MASK(EV_KEY);
+
+	if (idev->absbit[0])
+		idev->evbit[0] |= BIT_MASK(EV_ABS);
+
+	for (i = ABS_X; i <= ABS_BRAKE; i++)
+		input_set_abs_params(idev, i, 0, 255, 0, 0);
+
+	for (i = ABS_HAT0X; i <= ABS_HAT3Y; i++)
+		input_set_abs_params(idev, i, 1, -1, 0, 0);
+
+	idev->dev.platform_data = pad;
+	idev->dev.parent = &mdev->dev;
+	idev->name = mdev->product_name;
+	idev->id.bustype = BUS_HOST;
+
+	error = input_register_device(idev);
+	if (error)
+		goto fail;
+
+	mdev->driver = mdrv;
+
+	return 0;
+
+fail:
+	input_free_device(idev);
+	kfree(pad);
+	maple_set_drvdata(mdev, NULL);
+	return error;
+}
+
+static int remove_maple_controller(struct device *dev)
+{
+	struct maple_device *mdev = to_maple_dev(dev);
+	struct dc_pad *pad = maple_get_drvdata(mdev);
+
+	mdev->callback = NULL;
+	input_unregister_device(pad->dev);
+	maple_set_drvdata(mdev, NULL);
+	kfree(pad);
+
+	return 0;
+}
+
+static struct maple_driver dc_pad_driver = {
+	.function =	MAPLE_FUNC_CONTROLLER,
+	.drv = {
+		.name	= "Dreamcast_controller",
+		.probe	= probe_maple_controller,
+		.remove	= remove_maple_controller,
+	},
+};
+
+static int __init dc_pad_init(void)
+{
+	return maple_driver_register(&dc_pad_driver);
+}
+
+static void __exit dc_pad_exit(void)
+{
+	maple_driver_unregister(&dc_pad_driver);
+}
+
+module_init(dc_pad_init);
+module_exit(dc_pad_exit);