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, 174 insertions, 0 deletions

diff --git a/drivers/hid/hid-sjoy.c b/drivers/hid/hid-sjoy.c
new file mode 100644
index 000000000..963c45113
--- /dev/null
+++ b/drivers/hid/hid-sjoy.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Force feedback support for SmartJoy PLUS PS2->USB adapter
+ *
+ *  Copyright (c) 2009 Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
+ *
+ *  Based of hid-pl.c and hid-gaff.c
+ *   Copyright (c) 2007, 2009 Anssi Hannula <anssi.hannula@gmail.com>
+ *   Copyright (c) 2008 Lukasz Lubojanski <lukasz@lubojanski.info>
+ */
+
+/*
+ */
+
+/* #define DEBUG */
+
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+#include "hid-ids.h"
+
+#ifdef CONFIG_SMARTJOYPLUS_FF
+
+struct sjoyff_device {
+	struct hid_report *report;
+};
+
+static int hid_sjoyff_play(struct input_dev *dev, void *data,
+			 struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct sjoyff_device *sjoyff = data;
+	u32 left, right;
+
+	left = effect->u.rumble.strong_magnitude;
+	right = effect->u.rumble.weak_magnitude;
+	dev_dbg(&dev->dev, "called with 0x%08x 0x%08x\n", left, right);
+
+	left = left * 0xff / 0xffff;
+	right = (right != 0); /* on/off only */
+
+	sjoyff->report->field[0]->value[1] = right;
+	sjoyff->report->field[0]->value[2] = left;
+	dev_dbg(&dev->dev, "running with 0x%02x 0x%02x\n", left, right);
+	hid_hw_request(hid, sjoyff->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int sjoyff_init(struct hid_device *hid)
+{
+	struct sjoyff_device *sjoyff;
+	struct hid_report *report;
+	struct hid_input *hidinput;
+	struct list_head *report_list =
+			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
+	struct list_head *report_ptr = report_list;
+	struct input_dev *dev;
+	int error;
+
+	if (list_empty(report_list)) {
+		hid_err(hid, "no output reports found\n");
+		return -ENODEV;
+	}
+
+	list_for_each_entry(hidinput, &hid->inputs, list) {
+		report_ptr = report_ptr->next;
+
+		if (report_ptr == report_list) {
+			hid_err(hid, "required output report is missing\n");
+			return -ENODEV;
+		}
+
+		report = list_entry(report_ptr, struct hid_report, list);
+		if (report->maxfield < 1) {
+			hid_err(hid, "no fields in the report\n");
+			return -ENODEV;
+		}
+
+		if (report->field[0]->report_count < 3) {
+			hid_err(hid, "not enough values in the field\n");
+			return -ENODEV;
+		}
+
+		sjoyff = kzalloc_obj(struct sjoyff_device);
+		if (!sjoyff)
+			return -ENOMEM;
+
+		dev = hidinput->input;
+
+		set_bit(FF_RUMBLE, dev->ffbit);
+
+		sjoyff->report = report;
+		sjoyff->report->field[0]->value[0] = 0x01;
+		sjoyff->report->field[0]->value[1] = 0x00;
+		sjoyff->report->field[0]->value[2] = 0x00;
+		hid_hw_request(hid, sjoyff->report, HID_REQ_SET_REPORT);
+
+		error = input_ff_create_memless(dev, sjoyff, hid_sjoyff_play);
+		if (error) {
+			kfree(sjoyff);
+			return error;
+		}
+	}
+
+	hid_info(hid, "Force feedback for SmartJoy PLUS PS2/USB adapter\n");
+
+	return 0;
+}
+#else
+static inline int sjoyff_init(struct hid_device *hid)
+{
+	return 0;
+}
+#endif
+
+static int sjoy_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int ret;
+
+	hdev->quirks |= id->driver_data;
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "parse failed\n");
+		goto err;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT & ~HID_CONNECT_FF);
+	if (ret) {
+		hid_err(hdev, "hw start failed\n");
+		goto err;
+	}
+
+	sjoyff_init(hdev);
+
+	return 0;
+err:
+	return ret;
+}
+
+static const struct hid_device_id sjoy_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP_LTD, USB_DEVICE_ID_SUPER_JOY_BOX_3_PRO),
+		.driver_data = HID_QUIRK_NOGET },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP_LTD, USB_DEVICE_ID_SUPER_DUAL_BOX_PRO),
+		.driver_data = HID_QUIRK_MULTI_INPUT | HID_QUIRK_NOGET |
+			       HID_QUIRK_SKIP_OUTPUT_REPORTS },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP_LTD, USB_DEVICE_ID_SUPER_JOY_BOX_5_PRO),
+		.driver_data = HID_QUIRK_MULTI_INPUT | HID_QUIRK_NOGET |
+			       HID_QUIRK_SKIP_OUTPUT_REPORTS },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP, USB_DEVICE_ID_SMARTJOY_PLUS) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP, USB_DEVICE_ID_SUPER_JOY_BOX_3) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP, USB_DEVICE_ID_DUAL_USB_JOYPAD),
+		.driver_data = HID_QUIRK_MULTI_INPUT |
+			       HID_QUIRK_SKIP_OUTPUT_REPORTS },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_PLAYDOTCOM, USB_DEVICE_ID_PLAYDOTCOM_EMS_USBII),
+		.driver_data = HID_QUIRK_MULTI_INPUT |
+			       HID_QUIRK_SKIP_OUTPUT_REPORTS },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, sjoy_devices);
+
+static struct hid_driver sjoy_driver = {
+	.name = "smartjoyplus",
+	.id_table = sjoy_devices,
+	.probe = sjoy_probe,
+};
+module_hid_driver(sjoy_driver);
+
+MODULE_DESCRIPTION("Force feedback support for SmartJoy PLUS PS2->USB adapter");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jussi Kivilinna");
+