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, 403 insertions, 0 deletions

diff --git a/drivers/usb/serial/opticon.c b/drivers/usb/serial/opticon.c
new file mode 100644
index 000000000..152dfc901
--- /dev/null
+++ b/drivers/usb/serial/opticon.c
@@ -0,0 +1,403 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Opticon USB barcode to serial driver
+ *
+ * Copyright (C) 2011 - 2012 Johan Hovold <jhovold@gmail.com>
+ * Copyright (C) 2011 Martin Jansen <martin.jansen@opticon.com>
+ * Copyright (C) 2008 - 2009 Greg Kroah-Hartman <gregkh@suse.de>
+ * Copyright (C) 2008 - 2009 Novell Inc.
+ */
+
+#include <linux/kernel.h>
+#include <linux/tty.h>
+#include <linux/slab.h>
+#include <linux/tty_flip.h>
+#include <linux/serial.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+#define CONTROL_RTS			0x02
+#define RESEND_CTS_STATE	0x03
+
+/* max number of write urbs in flight */
+#define URB_UPPER_LIMIT	8
+
+/* This driver works for the Opticon 1D barcode reader
+ * an examples of 1D barcode types are EAN, UPC, Code39, IATA etc.. */
+#define DRIVER_DESC	"Opticon USB barcode to serial driver (1D)"
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE(0x065a, 0x0009) },
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+/* This structure holds all of the individual device information */
+struct opticon_private {
+	spinlock_t lock;	/* protects the following flags */
+	bool rts;
+	bool cts;
+	int outstanding_urbs;
+	int outstanding_bytes;
+
+	struct usb_anchor anchor;
+};
+
+
+static void opticon_process_data_packet(struct usb_serial_port *port,
+					const unsigned char *buf, size_t len)
+{
+	tty_insert_flip_string(&port->port, buf, len);
+	tty_flip_buffer_push(&port->port);
+}
+
+static void opticon_process_status_packet(struct usb_serial_port *port,
+					const unsigned char *buf, size_t len)
+{
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+
+	spin_lock_irqsave(&priv->lock, flags);
+	if (buf[0] == 0x00)
+		priv->cts = false;
+	else
+		priv->cts = true;
+	spin_unlock_irqrestore(&priv->lock, flags);
+}
+
+static void opticon_process_read_urb(struct urb *urb)
+{
+	struct usb_serial_port *port = urb->context;
+	const unsigned char *hdr = urb->transfer_buffer;
+	const unsigned char *data = hdr + 2;
+	size_t data_len = urb->actual_length - 2;
+
+	if (urb->actual_length <= 2) {
+		dev_dbg(&port->dev, "malformed packet received: %d bytes\n",
+							urb->actual_length);
+		return;
+	}
+	/*
+	 * Data from the device comes with a 2 byte header:
+	 *
+	 * <0x00><0x00>data...
+	 *      This is real data to be sent to the tty layer
+	 * <0x00><0x01>level
+	 *      This is a CTS level change, the third byte is the CTS
+	 *      value (0 for low, 1 for high).
+	 */
+	if ((hdr[0] == 0x00) && (hdr[1] == 0x00)) {
+		opticon_process_data_packet(port, data, data_len);
+	} else if ((hdr[0] == 0x00) && (hdr[1] == 0x01)) {
+		opticon_process_status_packet(port, data, data_len);
+	} else {
+		dev_dbg(&port->dev, "unknown packet received: %02x %02x\n",
+							hdr[0], hdr[1]);
+	}
+}
+
+static int send_control_msg(struct usb_serial_port *port, u8 requesttype,
+				u8 val)
+{
+	struct usb_serial *serial = port->serial;
+	int retval;
+	u8 *buffer;
+
+	buffer = kzalloc(1, GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	buffer[0] = val;
+	/* Send the message to the vendor control endpoint
+	 * of the connected device */
+	retval = usb_control_msg(serial->dev, usb_sndctrlpipe(serial->dev, 0),
+				requesttype,
+				USB_DIR_OUT|USB_TYPE_VENDOR|USB_RECIP_INTERFACE,
+				0, 0, buffer, 1, USB_CTRL_SET_TIMEOUT);
+	kfree(buffer);
+
+	if (retval < 0)
+		return retval;
+
+	return 0;
+}
+
+static int opticon_open(struct tty_struct *tty, struct usb_serial_port *port)
+{
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+	int res;
+
+	spin_lock_irqsave(&priv->lock, flags);
+	priv->rts = false;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	/* Clear RTS line */
+	send_control_msg(port, CONTROL_RTS, 0);
+
+	/* clear the halt status of the endpoint */
+	usb_clear_halt(port->serial->dev, port->read_urb->pipe);
+
+	res = usb_serial_generic_open(tty, port);
+	if (res)
+		return res;
+
+	/* Request CTS line state, sometimes during opening the current
+	 * CTS state can be missed. */
+	send_control_msg(port, RESEND_CTS_STATE, 1);
+
+	return res;
+}
+
+static void opticon_close(struct usb_serial_port *port)
+{
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+
+	usb_kill_anchored_urbs(&priv->anchor);
+
+	usb_serial_generic_close(port);
+}
+
+static void opticon_write_control_callback(struct urb *urb)
+{
+	struct usb_serial_port *port = urb->context;
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	int status = urb->status;
+	unsigned long flags;
+
+	/* free up the transfer buffer, as usb_free_urb() does not do this */
+	kfree(urb->transfer_buffer);
+
+	/* setup packet may be set if we're using it for writing */
+	kfree(urb->setup_packet);
+
+	if (status)
+		dev_dbg(&port->dev,
+			"%s - non-zero urb status received: %d\n",
+			__func__, status);
+
+	spin_lock_irqsave(&priv->lock, flags);
+	--priv->outstanding_urbs;
+	priv->outstanding_bytes -= urb->transfer_buffer_length;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	usb_serial_port_softint(port);
+}
+
+static int opticon_write(struct tty_struct *tty, struct usb_serial_port *port,
+			 const unsigned char *buf, int count)
+{
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	struct urb *urb;
+	unsigned char *buffer;
+	unsigned long flags;
+	struct usb_ctrlrequest *dr;
+	int ret = -ENOMEM;
+
+	spin_lock_irqsave(&priv->lock, flags);
+	if (priv->outstanding_urbs > URB_UPPER_LIMIT) {
+		spin_unlock_irqrestore(&priv->lock, flags);
+		dev_dbg(&port->dev, "%s - write limit hit\n", __func__);
+		return 0;
+	}
+	priv->outstanding_urbs++;
+	priv->outstanding_bytes += count;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	buffer = kmemdup(buf, count, GFP_ATOMIC);
+	if (!buffer)
+		goto error_no_buffer;
+
+	urb = usb_alloc_urb(0, GFP_ATOMIC);
+	if (!urb)
+		goto error_no_urb;
+
+	usb_serial_debug_data(&port->dev, __func__, count, buffer);
+
+	/* The connected devices do not have a bulk write endpoint,
+	 * to transmit data to de barcode device the control endpoint is used */
+	dr = kmalloc_obj(struct usb_ctrlrequest, GFP_ATOMIC);
+	if (!dr)
+		goto error_no_dr;
+
+	dr->bRequestType = USB_TYPE_VENDOR | USB_RECIP_INTERFACE | USB_DIR_OUT;
+	dr->bRequest = 0x01;
+	dr->wValue = 0;
+	dr->wIndex = 0;
+	dr->wLength = cpu_to_le16(count);
+
+	usb_fill_control_urb(urb, serial->dev,
+		usb_sndctrlpipe(serial->dev, 0),
+		(unsigned char *)dr, buffer, count,
+		opticon_write_control_callback, port);
+
+	usb_anchor_urb(urb, &priv->anchor);
+
+	/* send it down the pipe */
+	ret = usb_submit_urb(urb, GFP_ATOMIC);
+	if (ret) {
+		dev_err(&port->dev, "failed to submit write urb: %d\n", ret);
+		usb_unanchor_urb(urb);
+		goto error;
+	}
+
+	/* we are done with this urb, so let the host driver
+	 * really free it when it is finished with it */
+	usb_free_urb(urb);
+
+	return count;
+error:
+	kfree(dr);
+error_no_dr:
+	usb_free_urb(urb);
+error_no_urb:
+	kfree(buffer);
+error_no_buffer:
+	spin_lock_irqsave(&priv->lock, flags);
+	--priv->outstanding_urbs;
+	priv->outstanding_bytes -= count;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return ret;
+}
+
+static unsigned int opticon_write_room(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+
+	/*
+	 * We really can take almost anything the user throws at us
+	 * but let's pick a nice big number to tell the tty
+	 * layer that we have lots of free space, unless we don't.
+	 */
+	spin_lock_irqsave(&priv->lock, flags);
+	if (priv->outstanding_urbs > URB_UPPER_LIMIT * 2 / 3) {
+		spin_unlock_irqrestore(&priv->lock, flags);
+		dev_dbg(&port->dev, "%s - write limit hit\n", __func__);
+		return 0;
+	}
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 2048;
+}
+
+static unsigned int opticon_chars_in_buffer(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+	unsigned int count;
+
+	spin_lock_irqsave(&priv->lock, flags);
+	count = priv->outstanding_bytes;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return count;
+}
+
+static int opticon_tiocmget(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+	int result = 0;
+
+	spin_lock_irqsave(&priv->lock, flags);
+	if (priv->rts)
+		result |= TIOCM_RTS;
+	if (priv->cts)
+		result |= TIOCM_CTS;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	dev_dbg(&port->dev, "%s - %x\n", __func__, result);
+	return result;
+}
+
+static int opticon_tiocmset(struct tty_struct *tty,
+			   unsigned int set, unsigned int clear)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+	bool rts;
+	bool changed = false;
+	int ret;
+
+	/* We only support RTS so we only handle that */
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rts = priv->rts;
+	if (set & TIOCM_RTS)
+		priv->rts = true;
+	if (clear & TIOCM_RTS)
+		priv->rts = false;
+	changed = rts ^ priv->rts;
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	if (!changed)
+		return 0;
+
+	ret = send_control_msg(port, CONTROL_RTS, !rts);
+	if (ret)
+		return usb_translate_errors(ret);
+
+	return 0;
+}
+
+static int opticon_port_probe(struct usb_serial_port *port)
+{
+	struct opticon_private *priv;
+
+	priv = kzalloc_obj(*priv);
+	if (!priv)
+		return -ENOMEM;
+
+	spin_lock_init(&priv->lock);
+	init_usb_anchor(&priv->anchor);
+
+	usb_set_serial_port_data(port, priv);
+
+	return 0;
+}
+
+static void opticon_port_remove(struct usb_serial_port *port)
+{
+	struct opticon_private *priv = usb_get_serial_port_data(port);
+
+	kfree(priv);
+}
+
+static struct usb_serial_driver opticon_device = {
+	.driver = {
+		.name =		"opticon",
+	},
+	.id_table =		id_table,
+	.num_ports =		1,
+	.num_bulk_in =		1,
+	.bulk_in_size =		256,
+	.port_probe =		opticon_port_probe,
+	.port_remove =		opticon_port_remove,
+	.open =			opticon_open,
+	.close =		opticon_close,
+	.write =		opticon_write,
+	.write_room = 		opticon_write_room,
+	.chars_in_buffer =	opticon_chars_in_buffer,
+	.throttle =		usb_serial_generic_throttle,
+	.unthrottle =		usb_serial_generic_unthrottle,
+	.tiocmget =		opticon_tiocmget,
+	.tiocmset =		opticon_tiocmset,
+	.process_read_urb =	opticon_process_read_urb,
+};
+
+static struct usb_serial_driver * const serial_drivers[] = {
+	&opticon_device, NULL
+};
+
+module_usb_serial_driver(serial_drivers, id_table);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL v2");