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, 454 insertions, 0 deletions

diff --git a/net/nfc/nci/uart.c b/net/nfc/nci/uart.c
new file mode 100644
index 000000000..aa20e8603
--- /dev/null
+++ b/net/nfc/nci/uart.c
@@ -0,0 +1,454 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2015, Marvell International Ltd.
+ *
+ * Inspired (hugely) by HCI LDISC implementation in Bluetooth.
+ *
+ *  Copyright (C) 2000-2001  Qualcomm Incorporated
+ *  Copyright (C) 2002-2003  Maxim Krasnyansky <maxk@qualcomm.com>
+ *  Copyright (C) 2004-2005  Marcel Holtmann <marcel@holtmann.org>
+ */
+
+#include <linux/module.h>
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/interrupt.h>
+#include <linux/ptrace.h>
+#include <linux/poll.h>
+
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/signal.h>
+#include <linux/ioctl.h>
+#include <linux/skbuff.h>
+
+#include <net/nfc/nci.h>
+#include <net/nfc/nci_core.h>
+
+/* TX states  */
+#define NCI_UART_SENDING	1
+#define NCI_UART_TX_WAKEUP	2
+
+static struct nci_uart *nci_uart_drivers[NCI_UART_DRIVER_MAX];
+
+static inline struct sk_buff *nci_uart_dequeue(struct nci_uart *nu)
+{
+	struct sk_buff *skb = nu->tx_skb;
+
+	if (!skb)
+		skb = skb_dequeue(&nu->tx_q);
+	else
+		nu->tx_skb = NULL;
+
+	return skb;
+}
+
+static inline int nci_uart_queue_empty(struct nci_uart *nu)
+{
+	if (nu->tx_skb)
+		return 0;
+
+	return skb_queue_empty(&nu->tx_q);
+}
+
+static int nci_uart_tx_wakeup(struct nci_uart *nu)
+{
+	if (test_and_set_bit(NCI_UART_SENDING, &nu->tx_state)) {
+		set_bit(NCI_UART_TX_WAKEUP, &nu->tx_state);
+		return 0;
+	}
+
+	schedule_work(&nu->write_work);
+
+	return 0;
+}
+
+static void nci_uart_write_work(struct work_struct *work)
+{
+	struct nci_uart *nu = container_of(work, struct nci_uart, write_work);
+	struct tty_struct *tty = nu->tty;
+	struct sk_buff *skb;
+
+restart:
+	clear_bit(NCI_UART_TX_WAKEUP, &nu->tx_state);
+
+	if (nu->ops.tx_start)
+		nu->ops.tx_start(nu);
+
+	while ((skb = nci_uart_dequeue(nu))) {
+		int len;
+
+		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+		len = tty->ops->write(tty, skb->data, skb->len);
+		skb_pull(skb, len);
+		if (skb->len) {
+			nu->tx_skb = skb;
+			break;
+		}
+		kfree_skb(skb);
+	}
+
+	if (test_bit(NCI_UART_TX_WAKEUP, &nu->tx_state))
+		goto restart;
+
+	if (nu->ops.tx_done && nci_uart_queue_empty(nu))
+		nu->ops.tx_done(nu);
+
+	clear_bit(NCI_UART_SENDING, &nu->tx_state);
+}
+
+static int nci_uart_set_driver(struct tty_struct *tty, unsigned int driver)
+{
+	struct nci_uart *nu = NULL;
+	int ret;
+
+	if (driver >= NCI_UART_DRIVER_MAX)
+		return -EINVAL;
+
+	if (!nci_uart_drivers[driver])
+		return -ENOENT;
+
+	nu = kzalloc_obj(*nu);
+	if (!nu)
+		return -ENOMEM;
+
+	memcpy(nu, nci_uart_drivers[driver], sizeof(struct nci_uart));
+	nu->tty = tty;
+	skb_queue_head_init(&nu->tx_q);
+	INIT_WORK(&nu->write_work, nci_uart_write_work);
+	spin_lock_init(&nu->rx_lock);
+
+	ret = nu->ops.open(nu);
+	if (ret) {
+		kfree(nu);
+		return ret;
+	} else if (!try_module_get(nu->owner)) {
+		nu->ops.close(nu);
+		kfree(nu);
+		return -ENOENT;
+	}
+	tty->disc_data = nu;
+
+	return 0;
+}
+
+/* ------ LDISC part ------ */
+
+/* nci_uart_tty_open
+ *
+ *     Called when line discipline changed to NCI_UART.
+ *
+ * Arguments:
+ *     tty    pointer to tty info structure
+ * Return Value:
+ *     0 if success, otherwise error code
+ */
+static int nci_uart_tty_open(struct tty_struct *tty)
+{
+	/* Error if the tty has no write op instead of leaving an exploitable
+	 * hole
+	 */
+	if (!tty->ops->write)
+		return -EOPNOTSUPP;
+
+	tty->disc_data = NULL;
+	tty->receive_room = 65536;
+
+	/* Flush any pending characters in the driver */
+	tty_driver_flush_buffer(tty);
+
+	return 0;
+}
+
+/* nci_uart_tty_close()
+ *
+ *    Called when the line discipline is changed to something
+ *    else, the tty is closed, or the tty detects a hangup.
+ */
+static void nci_uart_tty_close(struct tty_struct *tty)
+{
+	struct nci_uart *nu = tty->disc_data;
+
+	/* Detach from the tty */
+	tty->disc_data = NULL;
+
+	if (!nu)
+		return;
+
+	kfree_skb(nu->tx_skb);
+	kfree_skb(nu->rx_skb);
+
+	skb_queue_purge(&nu->tx_q);
+
+	nu->ops.close(nu);
+	nu->tty = NULL;
+	module_put(nu->owner);
+
+	cancel_work_sync(&nu->write_work);
+
+	kfree(nu);
+}
+
+/* nci_uart_tty_wakeup()
+ *
+ *    Callback for transmit wakeup. Called when low level
+ *    device driver can accept more send data.
+ *
+ * Arguments:        tty    pointer to associated tty instance data
+ * Return Value:    None
+ */
+static void nci_uart_tty_wakeup(struct tty_struct *tty)
+{
+	struct nci_uart *nu = tty->disc_data;
+
+	if (!nu)
+		return;
+
+	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+
+	if (tty != nu->tty)
+		return;
+
+	nci_uart_tx_wakeup(nu);
+}
+
+/* -- Default recv_buf handler --
+ *
+ * This handler supposes that NCI frames are sent over UART link without any
+ * framing. It reads NCI header, retrieve the packet size and once all packet
+ * bytes are received it passes it to nci_uart driver for processing.
+ */
+static int nci_uart_default_recv_buf(struct nci_uart *nu, const u8 *data,
+				     int count)
+{
+	int chunk_len;
+
+	if (!nu->ndev) {
+		nfc_err(nu->tty->dev,
+			"receive data from tty but no NCI dev is attached yet, drop buffer\n");
+		return 0;
+	}
+
+	/* Decode all incoming data in packets
+	 * and enqueue then for processing.
+	 */
+	while (count > 0) {
+		/* If this is the first data of a packet, allocate a buffer */
+		if (!nu->rx_skb) {
+			nu->rx_packet_len = -1;
+			nu->rx_skb = nci_skb_alloc(nu->ndev,
+						   NCI_MAX_PACKET_SIZE,
+						   GFP_ATOMIC);
+			if (!nu->rx_skb)
+				return -ENOMEM;
+		}
+
+		/* Eat byte after byte till full packet header is received */
+		if (nu->rx_skb->len < NCI_CTRL_HDR_SIZE) {
+			skb_put_u8(nu->rx_skb, *data++);
+			--count;
+			continue;
+		}
+
+		/* Header was received but packet len was not read */
+		if (nu->rx_packet_len < 0)
+			nu->rx_packet_len = NCI_CTRL_HDR_SIZE +
+				nci_plen(nu->rx_skb->data);
+
+		/* Compute how many bytes are missing and how many bytes can
+		 * be consumed.
+		 */
+		chunk_len = nu->rx_packet_len - nu->rx_skb->len;
+		if (count < chunk_len)
+			chunk_len = count;
+		skb_put_data(nu->rx_skb, data, chunk_len);
+		data += chunk_len;
+		count -= chunk_len;
+
+		/* Check if packet is fully received */
+		if (nu->rx_packet_len == nu->rx_skb->len) {
+			/* Pass RX packet to driver */
+			if (nu->ops.recv(nu, nu->rx_skb) != 0)
+				nfc_err(nu->tty->dev, "corrupted RX packet\n");
+			/* Next packet will be a new one */
+			nu->rx_skb = NULL;
+		}
+	}
+
+	return 0;
+}
+
+/* nci_uart_tty_receive()
+ *
+ *     Called by tty low level driver when receive data is
+ *     available.
+ *
+ * Arguments:  tty          pointer to tty instance data
+ *             data         pointer to received data
+ *             flags        pointer to flags for data
+ *             count        count of received data in bytes
+ *
+ * Return Value:    None
+ */
+static void nci_uart_tty_receive(struct tty_struct *tty, const u8 *data,
+				 const u8 *flags, size_t count)
+{
+	struct nci_uart *nu = tty->disc_data;
+
+	if (!nu || tty != nu->tty)
+		return;
+
+	spin_lock(&nu->rx_lock);
+	nci_uart_default_recv_buf(nu, data, count);
+	spin_unlock(&nu->rx_lock);
+
+	tty_unthrottle(tty);
+}
+
+/* nci_uart_tty_ioctl()
+ *
+ *    Process IOCTL system call for the tty device.
+ *
+ * Arguments:
+ *
+ *    tty        pointer to tty instance data
+ *    cmd        IOCTL command code
+ *    arg        argument for IOCTL call (cmd dependent)
+ *
+ * Return Value:    Command dependent
+ */
+static int nci_uart_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
+			      unsigned long arg)
+{
+	struct nci_uart *nu = tty->disc_data;
+	int err = 0;
+
+	switch (cmd) {
+	case NCIUARTSETDRIVER:
+		if (!nu)
+			return nci_uart_set_driver(tty, (unsigned int)arg);
+		else
+			return -EBUSY;
+		break;
+	default:
+		err = n_tty_ioctl_helper(tty, cmd, arg);
+		break;
+	}
+
+	return err;
+}
+
+/* We don't provide read/write/poll interface for user space. */
+static ssize_t nci_uart_tty_read(struct tty_struct *tty, struct file *file,
+				 u8 *buf, size_t nr, void **cookie,
+				 unsigned long offset)
+{
+	return 0;
+}
+
+static ssize_t nci_uart_tty_write(struct tty_struct *tty, struct file *file,
+				  const u8 *data, size_t count)
+{
+	return 0;
+}
+
+static int nci_uart_send(struct nci_uart *nu, struct sk_buff *skb)
+{
+	/* Queue TX packet */
+	skb_queue_tail(&nu->tx_q, skb);
+
+	/* Try to start TX (if possible) */
+	nci_uart_tx_wakeup(nu);
+
+	return 0;
+}
+
+int nci_uart_register(struct nci_uart *nu)
+{
+	if (!nu || !nu->ops.open ||
+	    !nu->ops.recv || !nu->ops.close)
+		return -EINVAL;
+
+	/* Set the send callback */
+	nu->ops.send = nci_uart_send;
+
+	/* Add this driver in the driver list */
+	if (nci_uart_drivers[nu->driver]) {
+		pr_err("driver %d is already registered\n", nu->driver);
+		return -EBUSY;
+	}
+	nci_uart_drivers[nu->driver] = nu;
+
+	pr_info("NCI uart driver '%s [%d]' registered\n", nu->name, nu->driver);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nci_uart_register);
+
+void nci_uart_unregister(struct nci_uart *nu)
+{
+	pr_info("NCI uart driver '%s [%d]' unregistered\n", nu->name,
+		nu->driver);
+
+	/* Remove this driver from the driver list */
+	nci_uart_drivers[nu->driver] = NULL;
+}
+EXPORT_SYMBOL_GPL(nci_uart_unregister);
+
+void nci_uart_set_config(struct nci_uart *nu, int baudrate, int flow_ctrl)
+{
+	struct ktermios new_termios;
+
+	if (!nu->tty)
+		return;
+
+	down_read(&nu->tty->termios_rwsem);
+	new_termios = nu->tty->termios;
+	up_read(&nu->tty->termios_rwsem);
+	tty_termios_encode_baud_rate(&new_termios, baudrate, baudrate);
+
+	if (flow_ctrl)
+		new_termios.c_cflag |= CRTSCTS;
+	else
+		new_termios.c_cflag &= ~CRTSCTS;
+
+	tty_set_termios(nu->tty, &new_termios);
+}
+EXPORT_SYMBOL_GPL(nci_uart_set_config);
+
+static const struct tty_ldisc_ops nci_uart_ldisc = {
+	.owner		= THIS_MODULE,
+	.num		= N_NCI,
+	.name		= "n_nci",
+	.open		= nci_uart_tty_open,
+	.close		= nci_uart_tty_close,
+	.read		= nci_uart_tty_read,
+	.write		= nci_uart_tty_write,
+	.receive_buf	= nci_uart_tty_receive,
+	.write_wakeup	= nci_uart_tty_wakeup,
+	.ioctl		= nci_uart_tty_ioctl,
+	.compat_ioctl	= nci_uart_tty_ioctl,
+};
+
+static int __init nci_uart_init(void)
+{
+	return tty_register_ldisc(&nci_uart_ldisc);
+}
+
+static void __exit nci_uart_exit(void)
+{
+	tty_unregister_ldisc(&nci_uart_ldisc);
+}
+
+module_init(nci_uart_init);
+module_exit(nci_uart_exit);
+
+MODULE_AUTHOR("Marvell International Ltd.");
+MODULE_DESCRIPTION("NFC NCI UART driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_LDISC(N_NCI);