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, 266 insertions, 0 deletions

diff --git a/drivers/bluetooth/bcm203x.c b/drivers/bluetooth/bcm203x.c
new file mode 100644
index 000000000..c738ad040
--- /dev/null
+++ b/drivers/bluetooth/bcm203x.c
@@ -0,0 +1,266 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *
+ *  Broadcom Blutonium firmware driver
+ *
+ *  Copyright (C) 2003  Maxim Krasnyansky <maxk@qualcomm.com>
+ *  Copyright (C) 2003  Marcel Holtmann <marcel@holtmann.org>
+ */
+
+#include <linux/module.h>
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+
+#include <linux/device.h>
+#include <linux/firmware.h>
+
+#include <linux/usb.h>
+
+#include <net/bluetooth/bluetooth.h>
+
+#define VERSION "1.2"
+
+static const struct usb_device_id bcm203x_table[] = {
+	/* Broadcom Blutonium (BCM2033) */
+	{ USB_DEVICE(0x0a5c, 0x2033) },
+
+	{ }	/* Terminating entry */
+};
+
+MODULE_DEVICE_TABLE(usb, bcm203x_table);
+
+#define BCM203X_ERROR		0
+#define BCM203X_RESET		1
+#define BCM203X_LOAD_MINIDRV	2
+#define BCM203X_SELECT_MEMORY	3
+#define BCM203X_CHECK_MEMORY	4
+#define BCM203X_LOAD_FIRMWARE	5
+#define BCM203X_CHECK_FIRMWARE	6
+
+#define BCM203X_IN_EP		0x81
+#define BCM203X_OUT_EP		0x02
+
+struct bcm203x_data {
+	struct usb_device	*udev;
+
+	unsigned long		state;
+
+	struct work_struct	work;
+	atomic_t		shutdown;
+
+	struct urb		*urb;
+	unsigned char		*buffer;
+
+	unsigned char		*fw_data;
+	unsigned int		fw_size;
+	unsigned int		fw_sent;
+};
+
+static void bcm203x_complete(struct urb *urb)
+{
+	struct bcm203x_data *data = urb->context;
+	struct usb_device *udev = urb->dev;
+	int len;
+
+	BT_DBG("udev %p urb %p", udev, urb);
+
+	if (urb->status) {
+		BT_ERR("URB failed with status %d", urb->status);
+		data->state = BCM203X_ERROR;
+		return;
+	}
+
+	switch (data->state) {
+	case BCM203X_LOAD_MINIDRV:
+		memcpy(data->buffer, "#", 1);
+
+		usb_fill_bulk_urb(urb, udev, usb_sndbulkpipe(udev, BCM203X_OUT_EP),
+				data->buffer, 1, bcm203x_complete, data);
+
+		data->state = BCM203X_SELECT_MEMORY;
+
+		/* use workqueue to have a small delay */
+		schedule_work(&data->work);
+		break;
+
+	case BCM203X_SELECT_MEMORY:
+		usb_fill_int_urb(urb, udev, usb_rcvintpipe(udev, BCM203X_IN_EP),
+				data->buffer, 32, bcm203x_complete, data, 1);
+
+		data->state = BCM203X_CHECK_MEMORY;
+
+		if (usb_submit_urb(data->urb, GFP_ATOMIC) < 0)
+			BT_ERR("Can't submit URB");
+		break;
+
+	case BCM203X_CHECK_MEMORY:
+		if (data->buffer[0] != '#') {
+			BT_ERR("Memory select failed");
+			data->state = BCM203X_ERROR;
+			break;
+		}
+
+		data->state = BCM203X_LOAD_FIRMWARE;
+		fallthrough;
+	case BCM203X_LOAD_FIRMWARE:
+		if (data->fw_sent == data->fw_size) {
+			usb_fill_int_urb(urb, udev, usb_rcvintpipe(udev, BCM203X_IN_EP),
+				data->buffer, 32, bcm203x_complete, data, 1);
+
+			data->state = BCM203X_CHECK_FIRMWARE;
+		} else {
+			len = min_t(uint, data->fw_size - data->fw_sent, 4096);
+
+			usb_fill_bulk_urb(urb, udev, usb_sndbulkpipe(udev, BCM203X_OUT_EP),
+				data->fw_data + data->fw_sent, len, bcm203x_complete, data);
+
+			data->fw_sent += len;
+		}
+
+		if (usb_submit_urb(data->urb, GFP_ATOMIC) < 0)
+			BT_ERR("Can't submit URB");
+		break;
+
+	case BCM203X_CHECK_FIRMWARE:
+		if (data->buffer[0] != '.') {
+			BT_ERR("Firmware loading failed");
+			data->state = BCM203X_ERROR;
+			break;
+		}
+
+		data->state = BCM203X_RESET;
+		break;
+	}
+}
+
+static void bcm203x_work(struct work_struct *work)
+{
+	struct bcm203x_data *data =
+		container_of(work, struct bcm203x_data, work);
+
+	if (atomic_read(&data->shutdown))
+		return;
+
+	if (usb_submit_urb(data->urb, GFP_KERNEL) < 0)
+		BT_ERR("Can't submit URB");
+}
+
+static int bcm203x_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	const struct firmware *firmware;
+	struct usb_device *udev = interface_to_usbdev(intf);
+	struct bcm203x_data *data;
+	int size;
+
+	BT_DBG("intf %p id %p", intf, id);
+
+	if (intf->cur_altsetting->desc.bInterfaceNumber != 0)
+		return -ENODEV;
+
+	data = devm_kzalloc(&intf->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->udev  = udev;
+	data->state = BCM203X_LOAD_MINIDRV;
+
+	data->urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!data->urb)
+		return -ENOMEM;
+
+	if (request_firmware(&firmware, "BCM2033-MD.hex", &udev->dev) < 0) {
+		BT_ERR("Mini driver request failed");
+		usb_free_urb(data->urb);
+		return -EIO;
+	}
+
+	BT_DBG("minidrv data %p size %zu", firmware->data, firmware->size);
+
+	size = max_t(uint, firmware->size, 4096);
+
+	data->buffer = kmalloc(size, GFP_KERNEL);
+	if (!data->buffer) {
+		BT_ERR("Can't allocate memory for mini driver");
+		release_firmware(firmware);
+		usb_free_urb(data->urb);
+		return -ENOMEM;
+	}
+
+	memcpy(data->buffer, firmware->data, firmware->size);
+
+	usb_fill_bulk_urb(data->urb, udev, usb_sndbulkpipe(udev, BCM203X_OUT_EP),
+			data->buffer, firmware->size, bcm203x_complete, data);
+
+	release_firmware(firmware);
+
+	if (request_firmware(&firmware, "BCM2033-FW.bin", &udev->dev) < 0) {
+		BT_ERR("Firmware request failed");
+		usb_free_urb(data->urb);
+		kfree(data->buffer);
+		return -EIO;
+	}
+
+	BT_DBG("firmware data %p size %zu", firmware->data, firmware->size);
+
+	data->fw_data = kmemdup(firmware->data, firmware->size, GFP_KERNEL);
+	if (!data->fw_data) {
+		BT_ERR("Can't allocate memory for firmware image");
+		release_firmware(firmware);
+		usb_free_urb(data->urb);
+		kfree(data->buffer);
+		return -ENOMEM;
+	}
+
+	data->fw_size = firmware->size;
+	data->fw_sent = 0;
+
+	release_firmware(firmware);
+
+	INIT_WORK(&data->work, bcm203x_work);
+
+	usb_set_intfdata(intf, data);
+
+	/* use workqueue to have a small delay */
+	schedule_work(&data->work);
+
+	return 0;
+}
+
+static void bcm203x_disconnect(struct usb_interface *intf)
+{
+	struct bcm203x_data *data = usb_get_intfdata(intf);
+
+	BT_DBG("intf %p", intf);
+
+	atomic_inc(&data->shutdown);
+	cancel_work_sync(&data->work);
+
+	usb_kill_urb(data->urb);
+
+	usb_set_intfdata(intf, NULL);
+
+	usb_free_urb(data->urb);
+	kfree(data->fw_data);
+	kfree(data->buffer);
+}
+
+static struct usb_driver bcm203x_driver = {
+	.name		= "bcm203x",
+	.probe		= bcm203x_probe,
+	.disconnect	= bcm203x_disconnect,
+	.id_table	= bcm203x_table,
+	.disable_hub_initiated_lpm = 1,
+};
+
+module_usb_driver(bcm203x_driver);
+
+MODULE_AUTHOR("Marcel Holtmann <marcel@holtmann.org>");
+MODULE_DESCRIPTION("Broadcom Blutonium firmware driver ver " VERSION);
+MODULE_VERSION(VERSION);
+MODULE_LICENSE("GPL");
+MODULE_FIRMWARE("BCM2033-MD.hex");
+MODULE_FIRMWARE("BCM2033-FW.bin");