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, 354 insertions, 0 deletions

diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c
new file mode 100644
index 000000000..16883592f
--- /dev/null
+++ b/drivers/usb/misc/appledisplay.c
@@ -0,0 +1,354 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Apple Cinema Display driver
+ *
+ * Copyright (C) 2006  Michael Hanselmann (linux-kernel@hansmi.ch)
+ *
+ * Thanks to Caskey L. Dickson for his work with acdctl.
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/hid.h>
+#include <linux/usb.h>
+#include <linux/backlight.h>
+#include <linux/timer.h>
+#include <linux/workqueue.h>
+#include <linux/atomic.h>
+
+#define APPLE_VENDOR_ID		0x05AC
+
+#define ACD_USB_TIMEOUT		250
+
+#define ACD_USB_EDID		0x0302
+#define ACD_USB_BRIGHTNESS	0x0310
+
+#define ACD_BTN_NONE		0
+#define ACD_BTN_BRIGHT_UP	3
+#define ACD_BTN_BRIGHT_DOWN	4
+
+#define ACD_URB_BUFFER_LEN	2
+#define ACD_MSG_BUFFER_LEN	2
+
+#define APPLEDISPLAY_DEVICE(prod)				\
+	.match_flags = USB_DEVICE_ID_MATCH_DEVICE |		\
+		       USB_DEVICE_ID_MATCH_INT_CLASS |		\
+		       USB_DEVICE_ID_MATCH_INT_PROTOCOL,	\
+	.idVendor = APPLE_VENDOR_ID,				\
+	.idProduct = (prod),					\
+	.bInterfaceClass = USB_CLASS_HID,			\
+	.bInterfaceProtocol = 0x00
+
+/* table of devices that work with this driver */
+static const struct usb_device_id appledisplay_table[] = {
+	{ APPLEDISPLAY_DEVICE(0x9218) },
+	{ APPLEDISPLAY_DEVICE(0x9219) },
+	{ APPLEDISPLAY_DEVICE(0x921c) },
+	{ APPLEDISPLAY_DEVICE(0x921d) },
+	{ APPLEDISPLAY_DEVICE(0x9222) },
+	{ APPLEDISPLAY_DEVICE(0x9226) },
+	{ APPLEDISPLAY_DEVICE(0x9236) },
+
+	/* Terminating entry */
+	{ }
+};
+MODULE_DEVICE_TABLE(usb, appledisplay_table);
+
+/* Structure to hold all of our device specific stuff */
+struct appledisplay {
+	struct usb_device *udev;	/* usb device */
+	struct urb *urb;		/* usb request block */
+	struct backlight_device *bd;	/* backlight device */
+	u8 *urbdata;			/* interrupt URB data buffer */
+	u8 *msgdata;			/* control message data buffer */
+
+	struct delayed_work work;
+	int button_pressed;
+	struct mutex sysfslock;		/* concurrent read and write */
+};
+
+static atomic_t count_displays = ATOMIC_INIT(0);
+
+static void appledisplay_complete(struct urb *urb)
+{
+	struct appledisplay *pdata = urb->context;
+	struct device *dev = &pdata->udev->dev;
+	int status = urb->status;
+	int retval;
+
+	switch (status) {
+	case 0:
+		/* success */
+		break;
+	case -EOVERFLOW:
+		dev_err(dev,
+			"OVERFLOW with data length %d, actual length is %d\n",
+			ACD_URB_BUFFER_LEN, pdata->urb->actual_length);
+		fallthrough;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* This urb is terminated, clean up */
+		dev_dbg(dev, "%s - urb shuttingdown with status: %d\n",
+			__func__, status);
+		return;
+	default:
+		dev_dbg(dev, "%s - nonzero urb status received: %d\n",
+			__func__, status);
+		goto exit;
+	}
+
+	switch(pdata->urbdata[1]) {
+	case ACD_BTN_BRIGHT_UP:
+	case ACD_BTN_BRIGHT_DOWN:
+		pdata->button_pressed = 1;
+		/*
+		 * there is a window during which no device
+		 * is registered
+		 */
+		if (pdata->bd )
+			schedule_delayed_work(&pdata->work, 0);
+		break;
+	case ACD_BTN_NONE:
+	default:
+		pdata->button_pressed = 0;
+		break;
+	}
+
+exit:
+	retval = usb_submit_urb(pdata->urb, GFP_ATOMIC);
+	if (retval) {
+		dev_err(dev, "%s - usb_submit_urb failed with result %d\n",
+			__func__, retval);
+	}
+}
+
+static int appledisplay_bl_update_status(struct backlight_device *bd)
+{
+	struct appledisplay *pdata = bl_get_data(bd);
+	int retval;
+
+	mutex_lock(&pdata->sysfslock);
+	pdata->msgdata[0] = 0x10;
+	pdata->msgdata[1] = bd->props.brightness;
+
+	retval = usb_control_msg(
+		pdata->udev,
+		usb_sndctrlpipe(pdata->udev, 0),
+		HID_REQ_SET_REPORT,
+		USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+		ACD_USB_BRIGHTNESS,
+		0,
+		pdata->msgdata, 2,
+		ACD_USB_TIMEOUT);
+	mutex_unlock(&pdata->sysfslock);
+
+	if (retval < 0)
+		return retval;
+	else
+		return 0;
+}
+
+static int appledisplay_bl_get_brightness(struct backlight_device *bd)
+{
+	struct appledisplay *pdata = bl_get_data(bd);
+	int retval, brightness;
+
+	mutex_lock(&pdata->sysfslock);
+	retval = usb_control_msg(
+		pdata->udev,
+		usb_rcvctrlpipe(pdata->udev, 0),
+		HID_REQ_GET_REPORT,
+		USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+		ACD_USB_BRIGHTNESS,
+		0,
+		pdata->msgdata, 2,
+		ACD_USB_TIMEOUT);
+	if (retval < 2) {
+		if (retval >= 0)
+			retval = -EMSGSIZE;
+	} else {
+		brightness = pdata->msgdata[1];
+	}
+	mutex_unlock(&pdata->sysfslock);
+
+	if (retval < 0)
+		return retval;
+	else
+		return brightness;
+}
+
+static const struct backlight_ops appledisplay_bl_data = {
+	.get_brightness	= appledisplay_bl_get_brightness,
+	.update_status	= appledisplay_bl_update_status,
+};
+
+static void appledisplay_work(struct work_struct *work)
+{
+	struct appledisplay *pdata =
+		container_of(work, struct appledisplay, work.work);
+	int retval;
+
+	retval = appledisplay_bl_get_brightness(pdata->bd);
+	if (retval >= 0)
+		pdata->bd->props.brightness = retval;
+
+	/* Poll again in about 125ms if there's still a button pressed */
+	if (pdata->button_pressed)
+		schedule_delayed_work(&pdata->work, HZ / 8);
+}
+
+static int appledisplay_probe(struct usb_interface *iface,
+	const struct usb_device_id *id)
+{
+	struct backlight_properties props;
+	struct backlight_device *backlight;
+	struct appledisplay *pdata;
+	struct usb_device *udev = interface_to_usbdev(iface);
+	struct usb_endpoint_descriptor *endpoint;
+	int int_in_endpointAddr = 0;
+	int retval, brightness;
+	char bl_name[20];
+
+	/* set up the endpoint information */
+	/* use only the first interrupt-in endpoint */
+	retval = usb_find_int_in_endpoint(iface->cur_altsetting, &endpoint);
+	if (retval) {
+		dev_err(&iface->dev, "Could not find int-in endpoint\n");
+		return retval;
+	}
+
+	int_in_endpointAddr = endpoint->bEndpointAddress;
+
+	/* allocate memory for our device state and initialize it */
+	pdata = kzalloc_obj(struct appledisplay);
+	if (!pdata) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	pdata->udev = udev;
+
+	INIT_DELAYED_WORK(&pdata->work, appledisplay_work);
+	mutex_init(&pdata->sysfslock);
+
+	/* Allocate buffer for control messages */
+	pdata->msgdata = kmalloc(ACD_MSG_BUFFER_LEN, GFP_KERNEL);
+	if (!pdata->msgdata) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	/* Allocate interrupt URB */
+	pdata->urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!pdata->urb) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	/* Allocate buffer for interrupt data */
+	pdata->urbdata = usb_alloc_coherent(pdata->udev, ACD_URB_BUFFER_LEN,
+		GFP_KERNEL, &pdata->urb->transfer_dma);
+	if (!pdata->urbdata) {
+		retval = -ENOMEM;
+		dev_err(&iface->dev, "Allocating URB buffer failed\n");
+		goto error;
+	}
+
+	/* Configure interrupt URB */
+	usb_fill_int_urb(pdata->urb, udev,
+		usb_rcvintpipe(udev, int_in_endpointAddr),
+		pdata->urbdata, ACD_URB_BUFFER_LEN, appledisplay_complete,
+		pdata, 1);
+	pdata->urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
+	if (usb_submit_urb(pdata->urb, GFP_KERNEL)) {
+		retval = -EIO;
+		dev_err(&iface->dev, "Submitting URB failed\n");
+		goto error;
+	}
+
+	/* Register backlight device */
+	snprintf(bl_name, sizeof(bl_name), "appledisplay%d",
+		atomic_inc_return(&count_displays) - 1);
+	memset(&props, 0, sizeof(struct backlight_properties));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = 0xff;
+	backlight = backlight_device_register(bl_name, NULL, pdata,
+					      &appledisplay_bl_data, &props);
+	if (IS_ERR(backlight)) {
+		dev_err(&iface->dev, "Backlight registration failed\n");
+		retval = PTR_ERR(backlight);
+		goto error;
+	}
+	pdata->bd = backlight;
+
+	/* Try to get brightness */
+	brightness = appledisplay_bl_get_brightness(pdata->bd);
+
+	if (brightness < 0) {
+		retval = brightness;
+		dev_err(&iface->dev,
+			"Error while getting initial brightness: %d\n", retval);
+		goto error;
+	}
+
+	/* Set brightness in backlight device */
+	pdata->bd->props.brightness = brightness;
+
+	/* save our data pointer in the interface device */
+	usb_set_intfdata(iface, pdata);
+
+	printk(KERN_INFO "appledisplay: Apple Cinema Display connected\n");
+
+	return 0;
+
+error:
+	if (pdata) {
+		if (pdata->urb) {
+			usb_kill_urb(pdata->urb);
+			cancel_delayed_work_sync(&pdata->work);
+			usb_free_coherent(pdata->udev, ACD_URB_BUFFER_LEN,
+					pdata->urbdata, pdata->urb->transfer_dma);
+			usb_free_urb(pdata->urb);
+		}
+		if (!IS_ERR(pdata->bd))
+			backlight_device_unregister(pdata->bd);
+		kfree(pdata->msgdata);
+	}
+	usb_set_intfdata(iface, NULL);
+	kfree(pdata);
+	return retval;
+}
+
+static void appledisplay_disconnect(struct usb_interface *iface)
+{
+	struct appledisplay *pdata = usb_get_intfdata(iface);
+
+	if (pdata) {
+		usb_kill_urb(pdata->urb);
+		cancel_delayed_work_sync(&pdata->work);
+		backlight_device_unregister(pdata->bd);
+		usb_free_coherent(pdata->udev, ACD_URB_BUFFER_LEN,
+			pdata->urbdata, pdata->urb->transfer_dma);
+		usb_free_urb(pdata->urb);
+		kfree(pdata->msgdata);
+		kfree(pdata);
+	}
+
+	printk(KERN_INFO "appledisplay: Apple Cinema Display disconnected\n");
+}
+
+static struct usb_driver appledisplay_driver = {
+	.name		= "appledisplay",
+	.probe		= appledisplay_probe,
+	.disconnect	= appledisplay_disconnect,
+	.id_table	= appledisplay_table,
+};
+module_usb_driver(appledisplay_driver);
+
+MODULE_AUTHOR("Michael Hanselmann");
+MODULE_DESCRIPTION("Apple Cinema Display driver");
+MODULE_LICENSE("GPL");