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, 271 insertions, 0 deletions

diff --git a/drivers/bluetooth/hci_ath.c b/drivers/bluetooth/hci_ath.c
new file mode 100644
index 000000000..8201fa7f6
--- /dev/null
+++ b/drivers/bluetooth/hci_ath.c
@@ -0,0 +1,271 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Atheros Communication Bluetooth HCIATH3K UART protocol
+ *
+ *  HCIATH3K (HCI Atheros AR300x Protocol) is a Atheros Communication's
+ *  power management protocol extension to H4 to support AR300x Bluetooth Chip.
+ *
+ *  Copyright (c) 2009-2010 Atheros Communications Inc.
+ *
+ *  Acknowledgements:
+ *  This file is based on hci_h4.c, which was written
+ *  by Maxim Krasnyansky and Marcel Holtmann.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/errno.h>
+#include <linux/ioctl.h>
+#include <linux/skbuff.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+#include "hci_uart.h"
+
+struct ath_struct {
+	struct hci_uart *hu;
+	unsigned int cur_sleep;
+
+	struct sk_buff *rx_skb;
+	struct sk_buff_head txq;
+	struct work_struct ctxtsw;
+};
+
+#define OP_WRITE_TAG	0x01
+
+#define INDEX_BDADDR	0x01
+
+struct ath_vendor_cmd {
+	__u8 opcode;
+	__le16 index;
+	__u8 len;
+	__u8 data[251];
+} __packed;
+
+static int ath_wakeup_ar3k(struct tty_struct *tty)
+{
+	int status = tty->driver->ops->tiocmget(tty);
+
+	if (status & TIOCM_CTS)
+		return status;
+
+	/* Clear RTS first */
+	tty->driver->ops->tiocmget(tty);
+	tty->driver->ops->tiocmset(tty, 0x00, TIOCM_RTS);
+	msleep(20);
+
+	/* Set RTS, wake up board */
+	tty->driver->ops->tiocmget(tty);
+	tty->driver->ops->tiocmset(tty, TIOCM_RTS, 0x00);
+	msleep(20);
+
+	status = tty->driver->ops->tiocmget(tty);
+	return status;
+}
+
+static void ath_hci_uart_work(struct work_struct *work)
+{
+	int status;
+	struct ath_struct *ath;
+	struct hci_uart *hu;
+	struct tty_struct *tty;
+
+	ath = container_of(work, struct ath_struct, ctxtsw);
+
+	hu = ath->hu;
+	tty = hu->tty;
+
+	/* verify and wake up controller */
+	if (ath->cur_sleep) {
+		status = ath_wakeup_ar3k(tty);
+		if (!(status & TIOCM_CTS))
+			return;
+	}
+
+	/* Ready to send Data */
+	clear_bit(HCI_UART_SENDING, &hu->tx_state);
+	hci_uart_tx_wakeup(hu);
+}
+
+static int ath_open(struct hci_uart *hu)
+{
+	struct ath_struct *ath;
+
+	BT_DBG("hu %p", hu);
+
+	if (!hci_uart_has_flow_control(hu))
+		return -EOPNOTSUPP;
+
+	ath = kzalloc_obj(*ath);
+	if (!ath)
+		return -ENOMEM;
+
+	skb_queue_head_init(&ath->txq);
+
+	hu->priv = ath;
+	ath->hu = hu;
+
+	INIT_WORK(&ath->ctxtsw, ath_hci_uart_work);
+
+	return 0;
+}
+
+static int ath_close(struct hci_uart *hu)
+{
+	struct ath_struct *ath = hu->priv;
+
+	BT_DBG("hu %p", hu);
+
+	skb_queue_purge(&ath->txq);
+
+	kfree_skb(ath->rx_skb);
+
+	cancel_work_sync(&ath->ctxtsw);
+
+	hu->priv = NULL;
+	kfree(ath);
+
+	return 0;
+}
+
+static int ath_flush(struct hci_uart *hu)
+{
+	struct ath_struct *ath = hu->priv;
+
+	BT_DBG("hu %p", hu);
+
+	skb_queue_purge(&ath->txq);
+
+	return 0;
+}
+
+static int ath_vendor_cmd(struct hci_dev *hdev, uint8_t opcode, uint16_t index,
+			  const void *data, size_t dlen)
+{
+	struct sk_buff *skb;
+	struct ath_vendor_cmd cmd;
+
+	if (dlen > sizeof(cmd.data))
+		return -EINVAL;
+
+	cmd.opcode = opcode;
+	cmd.index = cpu_to_le16(index);
+	cmd.len = dlen;
+	memcpy(cmd.data, data, dlen);
+
+	skb = __hci_cmd_sync(hdev, 0xfc0b, dlen + 4, &cmd, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+	kfree_skb(skb);
+
+	return 0;
+}
+
+static int ath_set_bdaddr(struct hci_dev *hdev, const bdaddr_t *bdaddr)
+{
+	return ath_vendor_cmd(hdev, OP_WRITE_TAG, INDEX_BDADDR, bdaddr,
+			      sizeof(*bdaddr));
+}
+
+static int ath_setup(struct hci_uart *hu)
+{
+	BT_DBG("hu %p", hu);
+
+	hu->hdev->set_bdaddr = ath_set_bdaddr;
+
+	return 0;
+}
+
+static const struct h4_recv_pkt ath_recv_pkts[] = {
+	{ H4_RECV_ACL,   .recv = hci_recv_frame },
+	{ H4_RECV_SCO,   .recv = hci_recv_frame },
+	{ H4_RECV_EVENT, .recv = hci_recv_frame },
+};
+
+static int ath_recv(struct hci_uart *hu, const void *data, int count)
+{
+	struct ath_struct *ath = hu->priv;
+
+	if (!ath)
+		return -ENODEV;
+
+	ath->rx_skb = h4_recv_buf(hu, ath->rx_skb, data, count,
+				  ath_recv_pkts, ARRAY_SIZE(ath_recv_pkts));
+	if (IS_ERR(ath->rx_skb)) {
+		int err = PTR_ERR(ath->rx_skb);
+		bt_dev_err(hu->hdev, "Frame reassembly failed (%d)", err);
+		ath->rx_skb = NULL;
+		return err;
+	}
+
+	return count;
+}
+
+#define HCI_OP_ATH_SLEEP 0xFC04
+
+static int ath_enqueue(struct hci_uart *hu, struct sk_buff *skb)
+{
+	struct ath_struct *ath = hu->priv;
+
+	if (hci_skb_pkt_type(skb) == HCI_SCODATA_PKT) {
+		kfree_skb(skb);
+		return 0;
+	}
+
+	/* Update power management enable flag with parameters of
+	 * HCI sleep enable vendor specific HCI command.
+	 */
+	if (hci_skb_pkt_type(skb) == HCI_COMMAND_PKT) {
+		struct hci_command_hdr *hdr = (void *)skb->data;
+
+		if (__le16_to_cpu(hdr->opcode) == HCI_OP_ATH_SLEEP)
+			ath->cur_sleep = skb->data[HCI_COMMAND_HDR_SIZE];
+	}
+
+	BT_DBG("hu %p skb %p", hu, skb);
+
+	/* Prepend skb with frame type */
+	memcpy(skb_push(skb, 1), &hci_skb_pkt_type(skb), 1);
+
+	skb_queue_tail(&ath->txq, skb);
+	set_bit(HCI_UART_SENDING, &hu->tx_state);
+
+	schedule_work(&ath->ctxtsw);
+
+	return 0;
+}
+
+static struct sk_buff *ath_dequeue(struct hci_uart *hu)
+{
+	struct ath_struct *ath = hu->priv;
+
+	return skb_dequeue(&ath->txq);
+}
+
+static const struct hci_uart_proto athp = {
+	.id		= HCI_UART_ATH3K,
+	.name		= "ATH3K",
+	.manufacturer	= 69,
+	.open		= ath_open,
+	.close		= ath_close,
+	.flush		= ath_flush,
+	.setup		= ath_setup,
+	.recv		= ath_recv,
+	.enqueue	= ath_enqueue,
+	.dequeue	= ath_dequeue,
+};
+
+int __init ath_init(void)
+{
+	return hci_uart_register_proto(&athp);
+}
+
+int __exit ath_deinit(void)
+{
+	return hci_uart_unregister_proto(&athp);
+}