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, 398 insertions, 0 deletions

diff --git a/drivers/hid/hid-thrustmaster.c b/drivers/hid/hid-thrustmaster.c
new file mode 100644
index 000000000..48a79c97b
--- /dev/null
+++ b/drivers/hid/hid-thrustmaster.c
@@ -0,0 +1,398 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * When connected to the machine, the Thrustmaster wheels appear as
+ * a «generic» hid gamepad called "Thrustmaster FFB Wheel".
+ *
+ * When in this mode not every functionality of the wheel, like the force feedback,
+ * are available. To enable all functionalities of a Thrustmaster wheel we have to send
+ * to it a specific USB CONTROL request with a code different for each wheel.
+ *
+ * This driver tries to understand which model of Thrustmaster wheel the generic
+ * "Thrustmaster FFB Wheel" really is and then sends the appropriate control code.
+ *
+ * Copyright (c) 2020-2021 Dario Pagani <dario.pagani.146+linuxk@gmail.com>
+ * Copyright (c) 2020-2021 Kim Kuparinen <kimi.h.kuparinen@gmail.com>
+ */
+#include <linux/hid.h>
+#include <linux/usb.h>
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+/*
+ * These interrupts are used to prevent a nasty crash when initializing the
+ * T300RS. Used in thrustmaster_interrupts().
+ */
+static const u8 setup_0[] = { 0x42, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
+static const u8 setup_1[] = { 0x0a, 0x04, 0x90, 0x03, 0x00, 0x00, 0x00, 0x00 };
+static const u8 setup_2[] = { 0x0a, 0x04, 0x00, 0x0c, 0x00, 0x00, 0x00, 0x00 };
+static const u8 setup_3[] = { 0x0a, 0x04, 0x12, 0x10, 0x00, 0x00, 0x00, 0x00 };
+static const u8 setup_4[] = { 0x0a, 0x04, 0x00, 0x06, 0x00, 0x00, 0x00, 0x00 };
+static const u8 *const setup_arr[] = { setup_0, setup_1, setup_2, setup_3, setup_4 };
+static const unsigned int setup_arr_sizes[] = {
+	ARRAY_SIZE(setup_0),
+	ARRAY_SIZE(setup_1),
+	ARRAY_SIZE(setup_2),
+	ARRAY_SIZE(setup_3),
+	ARRAY_SIZE(setup_4)
+};
+/*
+ * This struct contains for each type of
+ * Thrustmaster wheel
+ *
+ * Note: The values are stored in the CPU
+ * endianness, the USB protocols always use
+ * little endian; the macro cpu_to_le[BIT]()
+ * must be used when preparing USB packets
+ * and vice-versa
+ */
+struct tm_wheel_info {
+	uint16_t wheel_type;
+
+	/*
+	 * See when the USB control out packet is prepared...
+	 * @TODO The TMX seems to require multiple control codes to switch.
+	 */
+	uint16_t switch_value;
+
+	char const *const wheel_name;
+};
+
+/*
+ * Known wheels.
+ * Note: TMX does not work as it requires 2 control packets
+ */
+static const struct tm_wheel_info tm_wheels_infos[] = {
+	{0x0306, 0x0006, "Thrustmaster T150RS"},
+	{0x0200, 0x0005, "Thrustmaster T300RS (Missing Attachment)"},
+	{0x0206, 0x0005, "Thrustmaster T300RS"},
+	{0x0209, 0x0005, "Thrustmaster T300RS (Open Wheel Attachment)"},
+	{0x020a, 0x0005, "Thrustmaster T300RS (Sparco R383 Mod)"},
+	{0x0204, 0x0005, "Thrustmaster T300 Ferrari Alcantara Edition"},
+	{0x0002, 0x0002, "Thrustmaster T500RS"}
+	//{0x0407, 0x0001, "Thrustmaster TMX"}
+};
+
+static const uint8_t tm_wheels_infos_length = 7;
+
+/*
+ * This structs contains (in little endian) the response data
+ * of the wheel to the request 73
+ *
+ * A sufficient research to understand what each field does is not
+ * beign conducted yet. The position and meaning of fields are a
+ * just a very optimistic guess based on instinct....
+ */
+struct __packed tm_wheel_response
+{
+	/*
+	 * Seems to be the type of packet
+	 * - 0x0049 if is data.a (15 bytes)
+	 * - 0x0047 if is data.b (7 bytes)
+	 */
+	uint16_t type;
+
+	union {
+		struct __packed {
+			uint16_t field0;
+			uint16_t field1;
+			/*
+			 * Seems to be the model code of the wheel
+			 * Read table thrustmaster_wheels to values
+			 */
+			uint16_t model;
+
+			uint16_t field2;
+			uint16_t field3;
+			uint16_t field4;
+			uint16_t field5;
+		} a;
+		struct __packed {
+			uint16_t field0;
+			uint16_t field1;
+			uint16_t model;
+		} b;
+	} data;
+};
+
+struct tm_wheel {
+	struct usb_device *usb_dev;
+	struct urb *urb;
+
+	struct usb_ctrlrequest *model_request;
+	struct tm_wheel_response *response;
+
+	struct usb_ctrlrequest *change_request;
+};
+
+/* The control packet to send to wheel */
+static const struct usb_ctrlrequest model_request = {
+	.bRequestType = 0xc1,
+	.bRequest = 73,
+	.wValue = 0,
+	.wIndex = 0,
+	.wLength = cpu_to_le16(0x0010)
+};
+
+static const struct usb_ctrlrequest change_request = {
+	.bRequestType = 0x41,
+	.bRequest = 83,
+	.wValue = 0, // Will be filled by the driver
+	.wIndex = 0,
+	.wLength = 0
+};
+
+/*
+ * On some setups initializing the T300RS crashes the kernel,
+ * these interrupts fix that particular issue. So far they haven't caused any
+ * adverse effects in other wheels.
+ */
+static void thrustmaster_interrupts(struct hid_device *hdev)
+{
+	int ret, trans, i, b_ep;
+	u8 *send_buf = kmalloc(256, GFP_KERNEL);
+	struct usb_host_endpoint *ep;
+	struct device *dev = &hdev->dev;
+	struct usb_interface *usbif = to_usb_interface(dev->parent);
+	struct usb_device *usbdev = interface_to_usbdev(usbif);
+
+	if (!send_buf) {
+		hid_err(hdev, "failed allocating send buffer\n");
+		return;
+	}
+
+	if (usbif->cur_altsetting->desc.bNumEndpoints < 2) {
+		kfree(send_buf);
+		hid_err(hdev, "Wrong number of endpoints?\n");
+		return;
+	}
+
+	ep = &usbif->cur_altsetting->endpoint[1];
+	b_ep = ep->desc.bEndpointAddress;
+
+	/* Are the expected endpoints present? */
+	u8 ep_addr[2] = {b_ep, 0};
+
+	if (!usb_check_int_endpoints(usbif, ep_addr)) {
+		kfree(send_buf);
+		hid_err(hdev, "Unexpected non-int endpoint\n");
+		return;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(setup_arr); ++i) {
+		memcpy(send_buf, setup_arr[i], setup_arr_sizes[i]);
+
+		ret = usb_interrupt_msg(usbdev,
+			usb_sndintpipe(usbdev, b_ep),
+			send_buf,
+			setup_arr_sizes[i],
+			&trans,
+			USB_CTRL_SET_TIMEOUT);
+
+		if (ret) {
+			hid_err(hdev, "setup data couldn't be sent\n");
+			kfree(send_buf);
+			return;
+		}
+	}
+
+	kfree(send_buf);
+}
+
+static void thrustmaster_change_handler(struct urb *urb)
+{
+	struct hid_device *hdev = urb->context;
+
+	// The wheel seems to kill himself before answering the host and therefore is violating the USB protocol...
+	if (urb->status == 0 || urb->status == -EPROTO || urb->status == -EPIPE)
+		hid_info(hdev, "Success?! The wheel should have been initialized!\n");
+	else
+		hid_warn(hdev, "URB to change wheel mode seems to have failed with error %d\n", urb->status);
+}
+
+/*
+ * Called by the USB subsystem when the wheel responses to our request
+ * to get [what it seems to be] the wheel's model.
+ *
+ * If the model id is recognized then we send an opportune USB CONTROL REQUEST
+ * to switch the wheel to its full capabilities
+ */
+static void thrustmaster_model_handler(struct urb *urb)
+{
+	struct hid_device *hdev = urb->context;
+	struct tm_wheel *tm_wheel = hid_get_drvdata(hdev);
+	uint16_t model = 0;
+	int i, ret;
+	const struct tm_wheel_info *twi = NULL;
+
+	if (urb->status) {
+		hid_err(hdev, "URB to get model id failed with error %d\n", urb->status);
+		return;
+	}
+
+	if (tm_wheel->response->type == cpu_to_le16(0x49))
+		model = le16_to_cpu(tm_wheel->response->data.a.model);
+	else if (tm_wheel->response->type == cpu_to_le16(0x47))
+		model = le16_to_cpu(tm_wheel->response->data.b.model);
+	else {
+		hid_err(hdev, "Unknown packet type 0x%x, unable to proceed further with wheel init\n", tm_wheel->response->type);
+		return;
+	}
+
+	for (i = 0; i < tm_wheels_infos_length && !twi; i++)
+		if (tm_wheels_infos[i].wheel_type == model)
+			twi = tm_wheels_infos + i;
+
+	if (twi)
+		hid_info(hdev, "Wheel with model id 0x%x is a %s\n", model, twi->wheel_name);
+	else {
+		hid_err(hdev, "Unknown wheel's model id 0x%x, unable to proceed further with wheel init\n", model);
+		return;
+	}
+
+	tm_wheel->change_request->wValue = cpu_to_le16(twi->switch_value);
+	usb_fill_control_urb(
+		tm_wheel->urb,
+		tm_wheel->usb_dev,
+		usb_sndctrlpipe(tm_wheel->usb_dev, 0),
+		(char *)tm_wheel->change_request,
+		NULL, 0, // We do not expect any response from the wheel
+		thrustmaster_change_handler,
+		hdev
+	);
+
+	ret = usb_submit_urb(tm_wheel->urb, GFP_ATOMIC);
+	if (ret)
+		hid_err(hdev, "Error %d while submitting the change URB. I am unable to initialize this wheel...\n", ret);
+}
+
+static void thrustmaster_remove(struct hid_device *hdev)
+{
+	struct tm_wheel *tm_wheel = hid_get_drvdata(hdev);
+
+	usb_kill_urb(tm_wheel->urb);
+
+	kfree(tm_wheel->change_request);
+	kfree(tm_wheel->response);
+	kfree(tm_wheel->model_request);
+	usb_free_urb(tm_wheel->urb);
+	kfree(tm_wheel);
+
+	hid_hw_stop(hdev);
+}
+
+/*
+ * Function called by HID when a hid Thrustmaster FFB wheel is connected to the host.
+ * This function starts the hid dev, tries to allocate the tm_wheel data structure and
+ * finally send an USB CONTROL REQUEST to the wheel to get [what it seems to be] its
+ * model type.
+ */
+static int thrustmaster_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int ret = 0;
+	struct tm_wheel *tm_wheel = NULL;
+
+	if (!hid_is_usb(hdev))
+		return -EINVAL;
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "parse failed with error %d\n", ret);
+		goto error0;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT & ~HID_CONNECT_FF);
+	if (ret) {
+		hid_err(hdev, "hw start failed with error %d\n", ret);
+		goto error0;
+	}
+
+	// Now we allocate the tm_wheel
+	tm_wheel = kzalloc_obj(struct tm_wheel);
+	if (!tm_wheel) {
+		ret = -ENOMEM;
+		goto error1;
+	}
+
+	tm_wheel->urb = usb_alloc_urb(0, GFP_ATOMIC);
+	if (!tm_wheel->urb) {
+		ret = -ENOMEM;
+		goto error2;
+	}
+
+	tm_wheel->model_request = kmemdup(&model_request,
+					  sizeof(struct usb_ctrlrequest),
+					  GFP_KERNEL);
+	if (!tm_wheel->model_request) {
+		ret = -ENOMEM;
+		goto error3;
+	}
+
+	tm_wheel->response = kzalloc_obj(struct tm_wheel_response);
+	if (!tm_wheel->response) {
+		ret = -ENOMEM;
+		goto error4;
+	}
+
+	tm_wheel->change_request = kmemdup(&change_request,
+					   sizeof(struct usb_ctrlrequest),
+					   GFP_KERNEL);
+	if (!tm_wheel->change_request) {
+		ret = -ENOMEM;
+		goto error5;
+	}
+
+	tm_wheel->usb_dev = interface_to_usbdev(to_usb_interface(hdev->dev.parent));
+	hid_set_drvdata(hdev, tm_wheel);
+
+	thrustmaster_interrupts(hdev);
+
+	usb_fill_control_urb(
+		tm_wheel->urb,
+		tm_wheel->usb_dev,
+		usb_rcvctrlpipe(tm_wheel->usb_dev, 0),
+		(char *)tm_wheel->model_request,
+		tm_wheel->response,
+		sizeof(struct tm_wheel_response),
+		thrustmaster_model_handler,
+		hdev
+	);
+
+	ret = usb_submit_urb(tm_wheel->urb, GFP_ATOMIC);
+	if (ret) {
+		hid_err(hdev, "Error %d while submitting the URB. I am unable to initialize this wheel...\n", ret);
+		goto error6;
+	}
+
+	return ret;
+
+error6: kfree(tm_wheel->change_request);
+error5: kfree(tm_wheel->response);
+error4: kfree(tm_wheel->model_request);
+error3: usb_free_urb(tm_wheel->urb);
+error2: kfree(tm_wheel);
+error1: hid_hw_stop(hdev);
+error0:
+	return ret;
+}
+
+static const struct hid_device_id thrustmaster_devices[] = {
+	{ HID_USB_DEVICE(0x044f, 0xb65d)},
+	{}
+};
+
+MODULE_DEVICE_TABLE(hid, thrustmaster_devices);
+
+static struct hid_driver thrustmaster_driver = {
+	.name = "hid-thrustmaster",
+	.id_table = thrustmaster_devices,
+	.probe = thrustmaster_probe,
+	.remove = thrustmaster_remove,
+};
+
+module_hid_driver(thrustmaster_driver);
+
+MODULE_AUTHOR("Dario Pagani <dario.pagani.146+linuxk@gmail.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Driver to initialize some steering wheel joysticks from Thrustmaster");
+