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, 219 insertions, 0 deletions

diff --git a/drivers/hid/hid-holtekff.c b/drivers/hid/hid-holtekff.c
new file mode 100644
index 000000000..32d08f7a6
--- /dev/null
+++ b/drivers/hid/hid-holtekff.c
@@ -0,0 +1,219 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Force feedback support for Holtek On Line Grip based gamepads
+ *
+ *  These include at least a Brazilian "Clone Joypad Super Power Fire"
+ *  which uses vendor ID 0x1241 and identifies as "HOLTEK On Line Grip".
+ *
+ *  Copyright (c) 2011 Anssi Hannula <anssi.hannula@iki.fi>
+ */
+
+/*
+ */
+
+#include <linux/hid.h>
+#include <linux/input.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+
+#include "hid-ids.h"
+
+#ifdef CONFIG_HOLTEK_FF
+
+/*
+ * These commands and parameters are currently known:
+ *
+ * byte 0: command id:
+ * 	01  set effect parameters
+ * 	02  play specified effect
+ * 	03  stop specified effect
+ * 	04  stop all effects
+ * 	06  stop all effects
+ * 	(the difference between 04 and 06 isn't known; win driver
+ * 	 sends 06,04 on application init, and 06 otherwise)
+ * 
+ * Commands 01 and 02 need to be sent as pairs, i.e. you need to send 01
+ * before each 02.
+ *
+ * The rest of the bytes are parameters. Command 01 takes all of them, and
+ * commands 02,03 take only the effect id.
+ *
+ * byte 1:
+ *	bits 0-3: effect id:
+ * 		1: very strong rumble
+ * 		2: periodic rumble, short intervals
+ * 		3: very strong rumble
+ * 		4: periodic rumble, long intervals
+ * 		5: weak periodic rumble, long intervals
+ * 		6: weak periodic rumble, short intervals
+ * 		7: periodic rumble, short intervals
+ * 		8: strong periodic rumble, short intervals
+ * 		9: very strong rumble
+ * 		a: causes an error
+ * 		b: very strong periodic rumble, very short intervals
+ * 		c-f: nothing
+ *	bit 6: right (weak) motor enabled
+ *	bit 7: left (strong) motor enabled
+ *
+ * bytes 2-3:  time in milliseconds, big-endian
+ * bytes 5-6:  unknown (win driver seems to use at least 10e0 with effect 1
+ * 		       and 0014 with effect 6)
+ * byte 7:
+ *	bits 0-3: effect magnitude
+ */
+
+#define HOLTEKFF_MSG_LENGTH     7
+
+static const u8 start_effect_1[] = { 0x02, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00 };
+static const u8 stop_all4[] =	   { 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
+static const u8 stop_all6[] =	   { 0x06, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
+
+struct holtekff_device {
+	struct hid_field *field;
+};
+
+static void holtekff_send(struct holtekff_device *holtekff,
+			  struct hid_device *hid,
+			  const u8 data[HOLTEKFF_MSG_LENGTH])
+{
+	int i;
+
+	for (i = 0; i < HOLTEKFF_MSG_LENGTH; i++) {
+		holtekff->field->value[i] = data[i];
+	}
+
+	dbg_hid("sending %7ph\n", data);
+
+	hid_hw_request(hid, holtekff->field->report, HID_REQ_SET_REPORT);
+}
+
+static int holtekff_play(struct input_dev *dev, void *data,
+			 struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct holtekff_device *holtekff = data;
+	int left, right;
+	/* effect type 1, length 65535 msec */
+	u8 buf[HOLTEKFF_MSG_LENGTH] =
+		{ 0x01, 0x01, 0xff, 0xff, 0x10, 0xe0, 0x00 };
+
+	left = effect->u.rumble.strong_magnitude;
+	right = effect->u.rumble.weak_magnitude;
+	dbg_hid("called with 0x%04x 0x%04x\n", left, right);
+
+	if (!left && !right) {
+		holtekff_send(holtekff, hid, stop_all6);
+		return 0;
+	}
+
+	if (left)
+		buf[1] |= 0x80;
+	if (right)
+		buf[1] |= 0x40;
+
+	/* The device takes a single magnitude, so we just sum them up. */
+	buf[6] = min(0xf, (left >> 12) + (right >> 12));
+
+	holtekff_send(holtekff, hid, buf);
+	holtekff_send(holtekff, hid, start_effect_1);
+
+	return 0;
+}
+
+static int holtekff_init(struct hid_device *hid)
+{
+	struct holtekff_device *holtekff;
+	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 error;
+
+	if (list_empty(&hid->inputs)) {
+		hid_err(hid, "no inputs found\n");
+		return -ENODEV;
+	}
+	hidinput = list_entry(hid->inputs.next, struct hid_input, list);
+	dev = hidinput->input;
+
+	if (list_empty(report_list)) {
+		hid_err(hid, "no output report found\n");
+		return -ENODEV;
+	}
+
+	report = list_entry(report_list->next, struct hid_report, list);
+
+	if (report->maxfield < 1 || report->field[0]->report_count != 7) {
+		hid_err(hid, "unexpected output report layout\n");
+		return -ENODEV;
+	}
+
+	holtekff = kzalloc_obj(*holtekff);
+	if (!holtekff)
+		return -ENOMEM;
+
+	set_bit(FF_RUMBLE, dev->ffbit);
+
+	holtekff->field = report->field[0];
+
+	/* initialize the same way as win driver does */
+	holtekff_send(holtekff, hid, stop_all4);
+	holtekff_send(holtekff, hid, stop_all6);
+
+	error = input_ff_create_memless(dev, holtekff, holtekff_play);
+	if (error) {
+		kfree(holtekff);
+		return error;
+	}
+
+	hid_info(hid, "Force feedback for Holtek On Line Grip based devices by Anssi Hannula <anssi.hannula@iki.fi>\n");
+
+	return 0;
+}
+#else
+static inline int holtekff_init(struct hid_device *hid)
+{
+	return 0;
+}
+#endif
+
+static int holtek_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int ret;
+
+	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;
+	}
+
+	holtekff_init(hdev);
+
+	return 0;
+err:
+	return ret;
+}
+
+static const struct hid_device_id holtek_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_HOLTEK, USB_DEVICE_ID_HOLTEK_ON_LINE_GRIP) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, holtek_devices);
+
+static struct hid_driver holtek_driver = {
+	.name = "holtek",
+	.id_table = holtek_devices,
+	.probe = holtek_probe,
+};
+module_hid_driver(holtek_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Anssi Hannula <anssi.hannula@iki.fi>");
+MODULE_DESCRIPTION("Force feedback support for Holtek On Line Grip based devices");