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, 170 insertions, 0 deletions

diff --git a/drivers/hid/hid-mf.c b/drivers/hid/hid-mf.c
new file mode 100644
index 000000000..6ff54a1ec
--- /dev/null
+++ b/drivers/hid/hid-mf.c
@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Force feedback support for Mayflash game controller adapters.
+ *
+ * These devices are manufactured by Mayflash but identify themselves
+ * using the vendor ID of DragonRise Inc.
+ *
+ * Tested with:
+ * 0079:1801 "DragonRise Inc. Mayflash PS3 Game Controller Adapter"
+ * 0079:1803 "DragonRise Inc. Mayflash Wireless Sensor DolphinBar"
+ * 0079:1843 "DragonRise Inc. Mayflash GameCube Game Controller Adapter"
+ * 0079:1844 "DragonRise Inc. Mayflash GameCube Game Controller Adapter (v04)"
+ *
+ * The following adapters probably work too, but need to be tested:
+ * 0079:1800 "DragonRise Inc. Mayflash WIIU Game Controller Adapter"
+ *
+ * Copyright (c) 2016-2017 Marcel Hasler <mahasler@gmail.com>
+ */
+
+/*
+ */
+
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+struct mf_device {
+	struct hid_report *report;
+};
+
+static int mf_play(struct input_dev *dev, void *data, struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct mf_device *mf = data;
+	int strong, weak;
+
+	strong = effect->u.rumble.strong_magnitude;
+	weak = effect->u.rumble.weak_magnitude;
+
+	dbg_hid("Called with 0x%04x 0x%04x.\n", strong, weak);
+
+	strong = strong * 0xff / 0xffff;
+	weak = weak * 0xff / 0xffff;
+
+	dbg_hid("Running with 0x%02x 0x%02x.\n", strong, weak);
+
+	mf->report->field[0]->value[0] = weak;
+	mf->report->field[0]->value[1] = strong;
+	hid_hw_request(hid, mf->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int mf_init(struct hid_device *hid)
+{
+	struct mf_device *mf;
+
+	struct list_head *report_list =
+			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
+
+	struct list_head *report_ptr;
+	struct hid_report *report;
+
+	struct list_head *input_ptr = &hid->inputs;
+	struct hid_input *input;
+
+	struct input_dev *dev;
+
+	int error;
+
+	/* Setup each of the four inputs */
+	list_for_each(report_ptr, report_list) {
+		report = list_entry(report_ptr, struct hid_report, list);
+
+		if (report->maxfield < 1 || report->field[0]->report_count < 2) {
+			hid_err(hid, "Invalid report, this should never happen!\n");
+			return -ENODEV;
+		}
+
+		if (list_is_last(input_ptr, &hid->inputs)) {
+			hid_err(hid, "Missing input, this should never happen!\n");
+			return -ENODEV;
+		}
+
+		input_ptr = input_ptr->next;
+		input = list_entry(input_ptr, struct hid_input, list);
+
+		mf = kzalloc_obj(struct mf_device);
+		if (!mf)
+			return -ENOMEM;
+
+		dev = input->input;
+		set_bit(FF_RUMBLE, dev->ffbit);
+
+		error = input_ff_create_memless(dev, mf, mf_play);
+		if (error) {
+			kfree(mf);
+			return error;
+		}
+
+		mf->report = report;
+		mf->report->field[0]->value[0] = 0x00;
+		mf->report->field[0]->value[1] = 0x00;
+		hid_hw_request(hid, mf->report, HID_REQ_SET_REPORT);
+	}
+
+	hid_info(hid, "Force feedback for HJZ Mayflash game controller "
+		      "adapters by Marcel Hasler <mahasler@gmail.com>\n");
+
+	return 0;
+}
+
+static int mf_probe(struct hid_device *hid, const struct hid_device_id *id)
+{
+	int error;
+
+	dev_dbg(&hid->dev, "Mayflash HID hardware probe...\n");
+
+	/* Apply quirks as needed */
+	hid->quirks |= id->driver_data;
+
+	error = hid_parse(hid);
+	if (error) {
+		hid_err(hid, "HID parse failed.\n");
+		return error;
+	}
+
+	error = hid_hw_start(hid, HID_CONNECT_DEFAULT & ~HID_CONNECT_FF);
+	if (error) {
+		hid_err(hid, "HID hw start failed\n");
+		return error;
+	}
+
+	error = mf_init(hid);
+	if (error) {
+		hid_err(hid, "Force feedback init failed.\n");
+		hid_hw_stop(hid);
+		return error;
+	}
+
+	return 0;
+}
+
+static const struct hid_device_id mf_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE, USB_DEVICE_ID_DRAGONRISE_PS3),
+		.driver_data = HID_QUIRK_MULTI_INPUT },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE, USB_DEVICE_ID_DRAGONRISE_DOLPHINBAR),
+		.driver_data = HID_QUIRK_MULTI_INPUT },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE, USB_DEVICE_ID_DRAGONRISE_GAMECUBE1),
+		.driver_data = HID_QUIRK_MULTI_INPUT },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE, USB_DEVICE_ID_DRAGONRISE_GAMECUBE2),
+		.driver_data = 0 }, /* No quirk required */
+	{ HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE, USB_DEVICE_ID_DRAGONRISE_GAMECUBE3),
+		.driver_data = HID_QUIRK_MULTI_INPUT },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, mf_devices);
+
+static struct hid_driver mf_driver = {
+	.name = "hid_mf",
+	.id_table = mf_devices,
+	.probe = mf_probe,
+};
+module_hid_driver(mf_driver);
+
+MODULE_DESCRIPTION("Force feedback support for Mayflash game controller adapters.");
+MODULE_LICENSE("GPL");