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, 193 insertions, 0 deletions

diff --git a/drivers/hid/hid-axff.c b/drivers/hid/hid-axff.c
new file mode 100644
index 000000000..3c5c2bf02
--- /dev/null
+++ b/drivers/hid/hid-axff.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Force feedback support for ACRUX game controllers
+ *
+ * From what I have gathered, these devices are mass produced in China
+ * by several vendors. They often share the same design as the original
+ * Xbox 360 controller.
+ *
+ * 1a34:0802 "ACRUX USB GAMEPAD 8116"
+ *  - tested with an EXEQ EQ-PCU-02090 game controller.
+ *
+ * Copyright (c) 2010 Sergei Kolzun <x0r@dv-life.ru>
+ */
+
+/*
+ */
+
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+#ifdef CONFIG_HID_ACRUX_FF
+
+struct axff_device {
+	struct hid_report *report;
+};
+
+static int axff_play(struct input_dev *dev, void *data, struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct axff_device *axff = data;
+	struct hid_report *report = axff->report;
+	int field_count = 0;
+	int left, right;
+	int i, j;
+
+	left = effect->u.rumble.strong_magnitude;
+	right = effect->u.rumble.weak_magnitude;
+
+	dbg_hid("called with 0x%04x 0x%04x", left, right);
+
+	left = left * 0xff / 0xffff;
+	right = right * 0xff / 0xffff;
+
+	for (i = 0; i < report->maxfield; i++) {
+		for (j = 0; j < report->field[i]->report_count; j++) {
+			report->field[i]->value[j] =
+				field_count % 2 ? right : left;
+			field_count++;
+		}
+	}
+
+	dbg_hid("running with 0x%02x 0x%02x", left, right);
+	hid_hw_request(hid, axff->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int axff_init(struct hid_device *hid)
+{
+	struct axff_device *axff;
+	struct hid_report *report;
+	struct hid_input *hidinput;
+	struct list_head *report_list =&hid->report_enum[HID_OUTPUT_REPORT].report_list;
+	struct input_dev *dev;
+	int field_count = 0;
+	int i, j;
+	int error;
+
+	if (list_empty(&hid->inputs)) {
+		hid_err(hid, "no inputs found\n");
+		return -ENODEV;
+	}
+	hidinput = list_first_entry(&hid->inputs, struct hid_input, list);
+	dev = hidinput->input;
+
+	if (list_empty(report_list)) {
+		hid_err(hid, "no output reports found\n");
+		return -ENODEV;
+	}
+
+	report = list_first_entry(report_list, struct hid_report, list);
+	for (i = 0; i < report->maxfield; i++) {
+		for (j = 0; j < report->field[i]->report_count; j++) {
+			report->field[i]->value[j] = 0x00;
+			field_count++;
+		}
+	}
+
+	if (field_count < 4 && hid->product != 0xf705) {
+		hid_err(hid, "not enough fields in the report: %d\n",
+			field_count);
+		return -ENODEV;
+	}
+
+	axff = kzalloc_obj(struct axff_device);
+	if (!axff)
+		return -ENOMEM;
+
+	set_bit(FF_RUMBLE, dev->ffbit);
+
+	error = input_ff_create_memless(dev, axff, axff_play);
+	if (error)
+		goto err_free_mem;
+
+	axff->report = report;
+	hid_hw_request(hid, axff->report, HID_REQ_SET_REPORT);
+
+	hid_info(hid, "Force Feedback for ACRUX game controllers by Sergei Kolzun <x0r@dv-life.ru>\n");
+
+	return 0;
+
+err_free_mem:
+	kfree(axff);
+	return error;
+}
+#else
+static inline int axff_init(struct hid_device *hid)
+{
+	return 0;
+}
+#endif
+
+static int ax_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int error;
+
+	dev_dbg(&hdev->dev, "ACRUX HID hardware probe...\n");
+
+	error = hid_parse(hdev);
+	if (error) {
+		hid_err(hdev, "parse failed\n");
+		return error;
+	}
+
+	error = hid_hw_start(hdev, HID_CONNECT_DEFAULT & ~HID_CONNECT_FF);
+	if (error) {
+		hid_err(hdev, "hw start failed\n");
+		return error;
+	}
+
+	error = axff_init(hdev);
+	if (error) {
+		/*
+		 * Do not fail device initialization completely as device
+		 * may still be partially operable, just warn.
+		 */
+		hid_warn(hdev,
+			 "Failed to enable force feedback support, error: %d\n",
+			 error);
+	}
+
+	/*
+	 * We need to start polling device right away, otherwise
+	 * it will go into a coma.
+	 */
+	error = hid_hw_open(hdev);
+	if (error) {
+		dev_err(&hdev->dev, "hw open failed\n");
+		hid_hw_stop(hdev);
+		return error;
+	}
+
+	return 0;
+}
+
+static void ax_remove(struct hid_device *hdev)
+{
+	hid_hw_close(hdev);
+	hid_hw_stop(hdev);
+}
+
+static const struct hid_device_id ax_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ACRUX, 0x0802), },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ACRUX, 0xf705), },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, ax_devices);
+
+static struct hid_driver ax_driver = {
+	.name		= "acrux",
+	.id_table	= ax_devices,
+	.probe		= ax_probe,
+	.remove		= ax_remove,
+};
+module_hid_driver(ax_driver);
+
+MODULE_AUTHOR("Sergei Kolzun");
+MODULE_DESCRIPTION("Force feedback support for ACRUX game controllers");
+MODULE_LICENSE("GPL");