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, 450 insertions, 0 deletions

diff --git a/drivers/usb/misc/usblcd.c b/drivers/usb/misc/usblcd.c
new file mode 100644
index 000000000..f794695de
--- /dev/null
+++ b/drivers/usb/misc/usblcd.c
@@ -0,0 +1,450 @@
+// SPDX-License-Identifier: GPL-2.0
+/*****************************************************************************
+ *                          USBLCD Kernel Driver                             *
+ *                            Version 1.05                                   *
+ *             (C) 2005 Georges Toth <g.toth@e-biz.lu>                       *
+ *                                                                           *
+ *     This file is licensed under the GPL. See COPYING in the package.      *
+ * Based on usb-skeleton.c 2.0 by Greg Kroah-Hartman (greg@kroah.com)        *
+ *                                                                           *
+ *                                                                           *
+ * 28.02.05 Complete rewrite of the original usblcd.c driver,                *
+ *          based on usb_skeleton.c.                                         *
+ *          This new driver allows more than one USB-LCD to be connected     *
+ *          and controlled, at once                                          *
+ *****************************************************************************/
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/mutex.h>
+#include <linux/rwsem.h>
+#include <linux/uaccess.h>
+#include <linux/usb.h>
+
+#define DRIVER_VERSION "USBLCD Driver Version 1.05"
+
+#define USBLCD_MINOR		144
+
+#define IOCTL_GET_HARD_VERSION	1
+#define IOCTL_GET_DRV_VERSION	2
+
+
+static const struct usb_device_id id_table[] = {
+	{ .idVendor = 0x10D2, .match_flags = USB_DEVICE_ID_MATCH_VENDOR, },
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+struct usb_lcd {
+	struct usb_device	*udev;			/* init: probe_lcd */
+	struct usb_interface	*interface;		/* the interface for
+							   this device */
+	unsigned char		*bulk_in_buffer;	/* the buffer to receive
+							   data */
+	size_t			bulk_in_size;		/* the size of the
+							   receive buffer */
+	__u8			bulk_in_endpointAddr;	/* the address of the
+							   bulk in endpoint */
+	__u8			bulk_out_endpointAddr;	/* the address of the
+							   bulk out endpoint */
+	struct kref		kref;
+	struct semaphore	limit_sem;		/* to stop writes at
+							   full throttle from
+							   using up all RAM */
+	struct usb_anchor	submitted;		/* URBs to wait for
+							   before suspend */
+	struct rw_semaphore	io_rwsem;
+	unsigned long		disconnected:1;
+};
+#define to_lcd_dev(d) container_of(d, struct usb_lcd, kref)
+
+#define USB_LCD_CONCURRENT_WRITES	5
+
+static struct usb_driver lcd_driver;
+
+
+static void lcd_delete(struct kref *kref)
+{
+	struct usb_lcd *dev = to_lcd_dev(kref);
+
+	usb_put_dev(dev->udev);
+	kfree(dev->bulk_in_buffer);
+	kfree(dev);
+}
+
+
+static int lcd_open(struct inode *inode, struct file *file)
+{
+	struct usb_lcd *dev;
+	struct usb_interface *interface;
+	int subminor, r;
+
+	subminor = iminor(inode);
+
+	interface = usb_find_interface(&lcd_driver, subminor);
+	if (!interface) {
+		pr_err("USBLCD: %s - error, can't find device for minor %d\n",
+		       __func__, subminor);
+		return -ENODEV;
+	}
+
+	dev = usb_get_intfdata(interface);
+
+	/* increment our usage count for the device */
+	kref_get(&dev->kref);
+
+	/* grab a power reference */
+	r = usb_autopm_get_interface(interface);
+	if (r < 0) {
+		kref_put(&dev->kref, lcd_delete);
+		return r;
+	}
+
+	/* save our object in the file's private structure */
+	file->private_data = dev;
+
+	return 0;
+}
+
+static int lcd_release(struct inode *inode, struct file *file)
+{
+	struct usb_lcd *dev;
+
+	dev = file->private_data;
+	if (dev == NULL)
+		return -ENODEV;
+
+	/* decrement the count on our device */
+	usb_autopm_put_interface(dev->interface);
+	kref_put(&dev->kref, lcd_delete);
+	return 0;
+}
+
+static ssize_t lcd_read(struct file *file, char __user * buffer,
+			size_t count, loff_t *ppos)
+{
+	struct usb_lcd *dev;
+	int retval = 0;
+	int bytes_read;
+
+	dev = file->private_data;
+
+	down_read(&dev->io_rwsem);
+
+	if (dev->disconnected) {
+		retval = -ENODEV;
+		goto out_up_io;
+	}
+
+	/* do a blocking bulk read to get data from the device */
+	retval = usb_bulk_msg(dev->udev,
+			      usb_rcvbulkpipe(dev->udev,
+					      dev->bulk_in_endpointAddr),
+			      dev->bulk_in_buffer,
+			      min(dev->bulk_in_size, count),
+			      &bytes_read, 10000);
+
+	/* if the read was successful, copy the data to userspace */
+	if (!retval) {
+		if (copy_to_user(buffer, dev->bulk_in_buffer, bytes_read))
+			retval = -EFAULT;
+		else
+			retval = bytes_read;
+	}
+
+out_up_io:
+	up_read(&dev->io_rwsem);
+
+	return retval;
+}
+
+static long lcd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct usb_lcd *dev;
+	u16 bcdDevice;
+	char buf[30];
+
+	dev = file->private_data;
+	if (dev == NULL)
+		return -ENODEV;
+
+	switch (cmd) {
+	case IOCTL_GET_HARD_VERSION:
+		bcdDevice = le16_to_cpu((dev->udev)->descriptor.bcdDevice);
+		sprintf(buf, "%1d%1d.%1d%1d",
+			(bcdDevice & 0xF000)>>12,
+			(bcdDevice & 0xF00)>>8,
+			(bcdDevice & 0xF0)>>4,
+			(bcdDevice & 0xF));
+		if (copy_to_user((void __user *)arg, buf, strlen(buf)) != 0)
+			return -EFAULT;
+		break;
+	case IOCTL_GET_DRV_VERSION:
+		sprintf(buf, DRIVER_VERSION);
+		if (copy_to_user((void __user *)arg, buf, strlen(buf)) != 0)
+			return -EFAULT;
+		break;
+	default:
+		return -ENOTTY;
+	}
+
+	return 0;
+}
+
+static void lcd_write_bulk_callback(struct urb *urb)
+{
+	struct usb_lcd *dev;
+	int status = urb->status;
+
+	dev = urb->context;
+
+	/* sync/async unlink faults aren't errors */
+	if (status &&
+	    !(status == -ENOENT ||
+	      status == -ECONNRESET ||
+	      status == -ESHUTDOWN)) {
+		dev_dbg(&dev->interface->dev,
+			"nonzero write bulk status received: %d\n", status);
+	}
+
+	/* free up our allocated buffer */
+	usb_free_coherent(urb->dev, urb->transfer_buffer_length,
+			  urb->transfer_buffer, urb->transfer_dma);
+	up(&dev->limit_sem);
+}
+
+static ssize_t lcd_write(struct file *file, const char __user * user_buffer,
+			 size_t count, loff_t *ppos)
+{
+	struct usb_lcd *dev;
+	int retval = 0, r;
+	struct urb *urb = NULL;
+	char *buf = NULL;
+
+	dev = file->private_data;
+
+	/* verify that we actually have some data to write */
+	if (count == 0)
+		goto exit;
+
+	r = down_interruptible(&dev->limit_sem);
+	if (r < 0)
+		return -EINTR;
+
+	down_read(&dev->io_rwsem);
+
+	if (dev->disconnected) {
+		retval = -ENODEV;
+		goto err_up_io;
+	}
+
+	/* create a urb, and a buffer for it, and copy the data to the urb */
+	urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!urb) {
+		retval = -ENOMEM;
+		goto err_up_io;
+	}
+
+	buf = usb_alloc_coherent(dev->udev, count, GFP_KERNEL,
+				 &urb->transfer_dma);
+	if (!buf) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	if (copy_from_user(buf, user_buffer, count)) {
+		retval = -EFAULT;
+		goto error;
+	}
+
+	/* initialize the urb properly */
+	usb_fill_bulk_urb(urb, dev->udev,
+			  usb_sndbulkpipe(dev->udev,
+			  dev->bulk_out_endpointAddr),
+			  buf, count, lcd_write_bulk_callback, dev);
+	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+	usb_anchor_urb(urb, &dev->submitted);
+
+	/* send the data out the bulk port */
+	retval = usb_submit_urb(urb, GFP_KERNEL);
+	if (retval) {
+		dev_err(&dev->udev->dev,
+			"%s - failed submitting write urb, error %d\n",
+			__func__, retval);
+		goto error_unanchor;
+	}
+
+	/* release our reference to this urb,
+	   the USB core will eventually free it entirely */
+	usb_free_urb(urb);
+
+	up_read(&dev->io_rwsem);
+exit:
+	return count;
+error_unanchor:
+	usb_unanchor_urb(urb);
+error:
+	usb_free_coherent(dev->udev, count, buf, urb->transfer_dma);
+	usb_free_urb(urb);
+err_up_io:
+	up_read(&dev->io_rwsem);
+	up(&dev->limit_sem);
+	return retval;
+}
+
+static const struct file_operations lcd_fops = {
+	.owner =        THIS_MODULE,
+	.read =         lcd_read,
+	.write =        lcd_write,
+	.open =         lcd_open,
+	.unlocked_ioctl = lcd_ioctl,
+	.release =      lcd_release,
+	.llseek =	 noop_llseek,
+};
+
+/*
+ * usb class driver info in order to get a minor number from the usb core,
+ * and to have the device registered with the driver core
+ */
+static struct usb_class_driver lcd_class = {
+	.name =         "lcd%d",
+	.fops =         &lcd_fops,
+	.minor_base =   USBLCD_MINOR,
+};
+
+static int lcd_probe(struct usb_interface *interface,
+		     const struct usb_device_id *id)
+{
+	struct usb_lcd *dev = NULL;
+	struct usb_endpoint_descriptor *bulk_in, *bulk_out;
+	int i;
+	int retval;
+
+	/* allocate memory for our device state and initialize it */
+	dev = kzalloc_obj(*dev);
+	if (!dev)
+		return -ENOMEM;
+
+	kref_init(&dev->kref);
+	sema_init(&dev->limit_sem, USB_LCD_CONCURRENT_WRITES);
+	init_rwsem(&dev->io_rwsem);
+	init_usb_anchor(&dev->submitted);
+
+	dev->udev = usb_get_dev(interface_to_usbdev(interface));
+	dev->interface = interface;
+
+	if (le16_to_cpu(dev->udev->descriptor.idProduct) != 0x0001) {
+		dev_warn(&interface->dev, "USBLCD model not supported.\n");
+		retval = -ENODEV;
+		goto error;
+	}
+
+	/* set up the endpoint information */
+	/* use only the first bulk-in and bulk-out endpoints */
+	retval = usb_find_common_endpoints(interface->cur_altsetting,
+			&bulk_in, &bulk_out, NULL, NULL);
+	if (retval) {
+		dev_err(&interface->dev,
+			"Could not find both bulk-in and bulk-out endpoints\n");
+		goto error;
+	}
+
+	dev->bulk_in_size = usb_endpoint_maxp(bulk_in);
+	dev->bulk_in_endpointAddr = bulk_in->bEndpointAddress;
+	dev->bulk_in_buffer = kmalloc(dev->bulk_in_size, GFP_KERNEL);
+	if (!dev->bulk_in_buffer) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	dev->bulk_out_endpointAddr = bulk_out->bEndpointAddress;
+
+	/* save our data pointer in this interface device */
+	usb_set_intfdata(interface, dev);
+
+	/* we can register the device now, as it is ready */
+	retval = usb_register_dev(interface, &lcd_class);
+	if (retval) {
+		/* something prevented us from registering this driver */
+		dev_err(&interface->dev,
+			"Not able to get a minor for this device.\n");
+		goto error;
+	}
+
+	i = le16_to_cpu(dev->udev->descriptor.bcdDevice);
+
+	dev_info(&interface->dev, "USBLCD Version %1d%1d.%1d%1d found "
+		 "at address %d\n", (i & 0xF000)>>12, (i & 0xF00)>>8,
+		 (i & 0xF0)>>4, (i & 0xF), dev->udev->devnum);
+
+	/* let the user know what node this device is now attached to */
+	dev_info(&interface->dev, "USB LCD device now attached to USBLCD-%d\n",
+		 interface->minor);
+	return 0;
+
+error:
+	kref_put(&dev->kref, lcd_delete);
+	return retval;
+}
+
+static void lcd_draw_down(struct usb_lcd *dev)
+{
+	int time;
+
+	time = usb_wait_anchor_empty_timeout(&dev->submitted, 1000);
+	if (!time)
+		usb_kill_anchored_urbs(&dev->submitted);
+}
+
+static int lcd_suspend(struct usb_interface *intf, pm_message_t message)
+{
+	struct usb_lcd *dev = usb_get_intfdata(intf);
+
+	if (!dev)
+		return 0;
+	lcd_draw_down(dev);
+	return 0;
+}
+
+static int lcd_resume(struct usb_interface *intf)
+{
+	return 0;
+}
+
+static void lcd_disconnect(struct usb_interface *interface)
+{
+	struct usb_lcd *dev = usb_get_intfdata(interface);
+	int minor = interface->minor;
+
+	/* give back our minor */
+	usb_deregister_dev(interface, &lcd_class);
+
+	down_write(&dev->io_rwsem);
+	dev->disconnected = 1;
+	up_write(&dev->io_rwsem);
+
+	usb_kill_anchored_urbs(&dev->submitted);
+
+	/* decrement our usage count */
+	kref_put(&dev->kref, lcd_delete);
+
+	dev_info(&interface->dev, "USB LCD #%d now disconnected\n", minor);
+}
+
+static struct usb_driver lcd_driver = {
+	.name =		"usblcd",
+	.probe =	lcd_probe,
+	.disconnect =	lcd_disconnect,
+	.suspend =	lcd_suspend,
+	.resume =	lcd_resume,
+	.id_table =	id_table,
+	.supports_autosuspend = 1,
+};
+
+module_usb_driver(lcd_driver);
+
+MODULE_AUTHOR("Georges Toth <g.toth@e-biz.lu>");
+MODULE_DESCRIPTION(DRIVER_VERSION);
+MODULE_LICENSE("GPL");