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/bluetooth/virtio_bt.c b/drivers/bluetooth/virtio_bt.c
new file mode 100644
index 000000000..140ab55c9
--- /dev/null
+++ b/drivers/bluetooth/virtio_bt.c
@@ -0,0 +1,450 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/module.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/skbuff.h>
+
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_bt.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+#define VERSION "0.1"
+#define VIRTBT_RX_BUF_SIZE 1000
+
+enum {
+	VIRTBT_VQ_TX,
+	VIRTBT_VQ_RX,
+	VIRTBT_NUM_VQS,
+};
+
+struct virtio_bluetooth {
+	struct virtio_device *vdev;
+	struct virtqueue *vqs[VIRTBT_NUM_VQS];
+	struct work_struct rx;
+	struct hci_dev *hdev;
+};
+
+static int virtbt_add_inbuf(struct virtio_bluetooth *vbt)
+{
+	struct virtqueue *vq = vbt->vqs[VIRTBT_VQ_RX];
+	struct scatterlist sg[1];
+	struct sk_buff *skb;
+	int err;
+
+	skb = alloc_skb(VIRTBT_RX_BUF_SIZE, GFP_KERNEL);
+	if (!skb)
+		return -ENOMEM;
+
+	sg_init_one(sg, skb->data, VIRTBT_RX_BUF_SIZE);
+
+	err = virtqueue_add_inbuf(vq, sg, 1, skb, GFP_KERNEL);
+	if (err < 0) {
+		kfree_skb(skb);
+		return err;
+	}
+
+	return 0;
+}
+
+static int virtbt_open(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int virtbt_open_vdev(struct virtio_bluetooth *vbt)
+{
+	if (virtbt_add_inbuf(vbt) < 0)
+		return -EIO;
+
+	virtqueue_kick(vbt->vqs[VIRTBT_VQ_RX]);
+	return 0;
+}
+
+static int virtbt_close(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int virtbt_close_vdev(struct virtio_bluetooth *vbt)
+{
+	int i;
+
+	cancel_work_sync(&vbt->rx);
+
+	for (i = 0; i < ARRAY_SIZE(vbt->vqs); i++) {
+		struct virtqueue *vq = vbt->vqs[i];
+		struct sk_buff *skb;
+
+		while ((skb = virtqueue_detach_unused_buf(vq)))
+			kfree_skb(skb);
+		cond_resched();
+	}
+
+	return 0;
+}
+
+static int virtbt_flush(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int virtbt_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	struct virtio_bluetooth *vbt = hci_get_drvdata(hdev);
+	struct scatterlist sg[1];
+	int err;
+
+	memcpy(skb_push(skb, 1), &hci_skb_pkt_type(skb), 1);
+
+	sg_init_one(sg, skb->data, skb->len);
+	err = virtqueue_add_outbuf(vbt->vqs[VIRTBT_VQ_TX], sg, 1, skb,
+				   GFP_KERNEL);
+	if (err) {
+		kfree_skb(skb);
+		return err;
+	}
+
+	virtqueue_kick(vbt->vqs[VIRTBT_VQ_TX]);
+	return 0;
+}
+
+static int virtbt_setup_zephyr(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Read Build Information */
+	skb = __hci_cmd_sync(hdev, 0xfc08, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	bt_dev_info(hdev, "%s", (char *)(skb->data + 1));
+
+	hci_set_fw_info(hdev, "%s", skb->data + 1);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_set_bdaddr_zephyr(struct hci_dev *hdev,
+				    const bdaddr_t *bdaddr)
+{
+	struct sk_buff *skb;
+
+	/* Write BD_ADDR */
+	skb = __hci_cmd_sync(hdev, 0xfc06, 6, bdaddr, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_setup_intel(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Intel Read Version */
+	skb = __hci_cmd_sync(hdev, 0xfc05, 0, NULL, HCI_CMD_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_set_bdaddr_intel(struct hci_dev *hdev, const bdaddr_t *bdaddr)
+{
+	struct sk_buff *skb;
+
+	/* Intel Write BD Address */
+	skb = __hci_cmd_sync(hdev, 0xfc31, 6, bdaddr, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_setup_realtek(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Read ROM Version */
+	skb = __hci_cmd_sync(hdev, 0xfc6d, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	bt_dev_info(hdev, "ROM version %u", *((__u8 *) (skb->data + 1)));
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static int virtbt_shutdown_generic(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	/* Reset */
+	skb = __hci_cmd_sync(hdev, HCI_OP_RESET, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
+	kfree_skb(skb);
+	return 0;
+}
+
+static void virtbt_rx_handle(struct virtio_bluetooth *vbt, struct sk_buff *skb)
+{
+	size_t min_hdr;
+	__u8 pkt_type;
+
+	pkt_type = *((__u8 *) skb->data);
+	skb_pull(skb, 1);
+
+	switch (pkt_type) {
+	case HCI_EVENT_PKT:
+		min_hdr = sizeof(struct hci_event_hdr);
+		break;
+	case HCI_ACLDATA_PKT:
+		min_hdr = sizeof(struct hci_acl_hdr);
+		break;
+	case HCI_SCODATA_PKT:
+		min_hdr = sizeof(struct hci_sco_hdr);
+		break;
+	case HCI_ISODATA_PKT:
+		min_hdr = sizeof(struct hci_iso_hdr);
+		break;
+	default:
+		kfree_skb(skb);
+		return;
+	}
+
+	if (skb->len < min_hdr) {
+		bt_dev_err_ratelimited(vbt->hdev,
+				       "rx pkt_type 0x%02x payload %u < hdr %zu\n",
+				       pkt_type, skb->len, min_hdr);
+		kfree_skb(skb);
+		return;
+	}
+
+	hci_skb_pkt_type(skb) = pkt_type;
+	hci_recv_frame(vbt->hdev, skb);
+}
+
+static void virtbt_rx_work(struct work_struct *work)
+{
+	struct virtio_bluetooth *vbt = container_of(work,
+						    struct virtio_bluetooth, rx);
+	struct sk_buff *skb;
+	unsigned int len;
+
+	skb = virtqueue_get_buf(vbt->vqs[VIRTBT_VQ_RX], &len);
+	if (!skb)
+		return;
+
+	if (!len || len > VIRTBT_RX_BUF_SIZE) {
+		bt_dev_err_ratelimited(vbt->hdev,
+				       "rx reply len %u outside [1, %u]\n",
+				       len, VIRTBT_RX_BUF_SIZE);
+		kfree_skb(skb);
+	} else {
+		skb_put(skb, len);
+		virtbt_rx_handle(vbt, skb);
+	}
+
+	if (virtbt_add_inbuf(vbt) < 0)
+		return;
+
+	virtqueue_kick(vbt->vqs[VIRTBT_VQ_RX]);
+}
+
+static void virtbt_tx_done(struct virtqueue *vq)
+{
+	struct sk_buff *skb;
+	unsigned int len;
+
+	while ((skb = virtqueue_get_buf(vq, &len)))
+		kfree_skb(skb);
+}
+
+static void virtbt_rx_done(struct virtqueue *vq)
+{
+	struct virtio_bluetooth *vbt = vq->vdev->priv;
+
+	schedule_work(&vbt->rx);
+}
+
+static int virtbt_probe(struct virtio_device *vdev)
+{
+	struct virtqueue_info vqs_info[VIRTBT_NUM_VQS] = {
+		[VIRTBT_VQ_TX] = { "tx", virtbt_tx_done },
+		[VIRTBT_VQ_RX] = { "rx", virtbt_rx_done },
+	};
+	struct virtio_bluetooth *vbt;
+	struct hci_dev *hdev;
+	int err;
+	__u8 type;
+
+	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
+		return -ENODEV;
+
+	type = virtio_cread8(vdev, offsetof(struct virtio_bt_config, type));
+
+	switch (type) {
+	case VIRTIO_BT_CONFIG_TYPE_PRIMARY:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	vbt = kzalloc_obj(*vbt);
+	if (!vbt)
+		return -ENOMEM;
+
+	vdev->priv = vbt;
+	vbt->vdev = vdev;
+
+	INIT_WORK(&vbt->rx, virtbt_rx_work);
+
+	err = virtio_find_vqs(vdev, VIRTBT_NUM_VQS, vbt->vqs, vqs_info, NULL);
+	if (err)
+		return err;
+
+	hdev = hci_alloc_dev();
+	if (!hdev) {
+		err = -ENOMEM;
+		goto failed;
+	}
+
+	vbt->hdev = hdev;
+
+	hdev->bus = HCI_VIRTIO;
+	hci_set_drvdata(hdev, vbt);
+
+	hdev->open  = virtbt_open;
+	hdev->close = virtbt_close;
+	hdev->flush = virtbt_flush;
+	hdev->send  = virtbt_send_frame;
+
+	if (virtio_has_feature(vdev, VIRTIO_BT_F_VND_HCI)) {
+		__u16 vendor;
+
+		if (virtio_has_feature(vdev, VIRTIO_BT_F_CONFIG_V2))
+			virtio_cread(vdev, struct virtio_bt_config_v2,
+				     vendor, &vendor);
+		else
+			virtio_cread(vdev, struct virtio_bt_config,
+				     vendor, &vendor);
+
+		switch (vendor) {
+		case VIRTIO_BT_CONFIG_VENDOR_ZEPHYR:
+			hdev->manufacturer = 1521;
+			hdev->setup = virtbt_setup_zephyr;
+			hdev->shutdown = virtbt_shutdown_generic;
+			hdev->set_bdaddr = virtbt_set_bdaddr_zephyr;
+			break;
+
+		case VIRTIO_BT_CONFIG_VENDOR_INTEL:
+			hdev->manufacturer = 2;
+			hdev->setup = virtbt_setup_intel;
+			hdev->shutdown = virtbt_shutdown_generic;
+			hdev->set_bdaddr = virtbt_set_bdaddr_intel;
+			hci_set_quirk(hdev, HCI_QUIRK_STRICT_DUPLICATE_FILTER);
+			hci_set_quirk(hdev, HCI_QUIRK_SIMULTANEOUS_DISCOVERY);
+			hci_set_quirk(hdev, HCI_QUIRK_WIDEBAND_SPEECH_SUPPORTED);
+			break;
+
+		case VIRTIO_BT_CONFIG_VENDOR_REALTEK:
+			hdev->manufacturer = 93;
+			hdev->setup = virtbt_setup_realtek;
+			hdev->shutdown = virtbt_shutdown_generic;
+			hci_set_quirk(hdev, HCI_QUIRK_SIMULTANEOUS_DISCOVERY);
+			hci_set_quirk(hdev, HCI_QUIRK_WIDEBAND_SPEECH_SUPPORTED);
+			break;
+		}
+	}
+
+	if (virtio_has_feature(vdev, VIRTIO_BT_F_MSFT_EXT)) {
+		__u16 msft_opcode;
+
+		if (virtio_has_feature(vdev, VIRTIO_BT_F_CONFIG_V2))
+			virtio_cread(vdev, struct virtio_bt_config_v2,
+				     msft_opcode, &msft_opcode);
+		else
+			virtio_cread(vdev, struct virtio_bt_config,
+				     msft_opcode, &msft_opcode);
+
+		hci_set_msft_opcode(hdev, msft_opcode);
+	}
+
+	if (virtio_has_feature(vdev, VIRTIO_BT_F_AOSP_EXT))
+		hci_set_aosp_capable(hdev);
+
+	if (hci_register_dev(hdev) < 0) {
+		hci_free_dev(hdev);
+		err = -EBUSY;
+		goto failed;
+	}
+
+	virtio_device_ready(vdev);
+	err = virtbt_open_vdev(vbt);
+	if (err)
+		goto open_failed;
+
+	return 0;
+
+open_failed:
+	hci_free_dev(hdev);
+failed:
+	vdev->config->del_vqs(vdev);
+	return err;
+}
+
+static void virtbt_remove(struct virtio_device *vdev)
+{
+	struct virtio_bluetooth *vbt = vdev->priv;
+	struct hci_dev *hdev = vbt->hdev;
+
+	hci_unregister_dev(hdev);
+	virtio_reset_device(vdev);
+	virtbt_close_vdev(vbt);
+
+	hci_free_dev(hdev);
+	vbt->hdev = NULL;
+
+	vdev->config->del_vqs(vdev);
+	kfree(vbt);
+}
+
+static struct virtio_device_id virtbt_table[] = {
+	{ VIRTIO_ID_BT, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+
+MODULE_DEVICE_TABLE(virtio, virtbt_table);
+
+static const unsigned int virtbt_features[] = {
+	VIRTIO_BT_F_VND_HCI,
+	VIRTIO_BT_F_MSFT_EXT,
+	VIRTIO_BT_F_AOSP_EXT,
+	VIRTIO_BT_F_CONFIG_V2,
+};
+
+static struct virtio_driver virtbt_driver = {
+	.driver.name         = KBUILD_MODNAME,
+	.feature_table       = virtbt_features,
+	.feature_table_size  = ARRAY_SIZE(virtbt_features),
+	.id_table            = virtbt_table,
+	.probe               = virtbt_probe,
+	.remove              = virtbt_remove,
+};
+
+module_virtio_driver(virtbt_driver);
+
+MODULE_AUTHOR("Marcel Holtmann <marcel@holtmann.org>");
+MODULE_DESCRIPTION("Generic Bluetooth VIRTIO driver ver " VERSION);
+MODULE_VERSION(VERSION);
+MODULE_LICENSE("GPL");