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, 476 insertions, 0 deletions

diff --git a/drivers/usb/misc/lvstest.c b/drivers/usb/misc/lvstest.c
new file mode 100644
index 000000000..9b6e10177
--- /dev/null
+++ b/drivers/usb/misc/lvstest.c
@@ -0,0 +1,476 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * drivers/usb/misc/lvstest.c
+ *
+ * Test pattern generation for Link Layer Validation System Tests
+ *
+ * Copyright (C) 2014 ST Microelectronics
+ * Pratyush Anand <pratyush.anand@gmail.com>
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/usb.h>
+#include <linux/usb/ch11.h>
+#include <linux/usb/hcd.h>
+#include <linux/usb/phy.h>
+
+struct lvs_rh {
+	/* root hub interface */
+	struct usb_interface *intf;
+	/* if lvs device connected */
+	bool present;
+	/* port no at which lvs device is present */
+	int portnum;
+	/* urb buffer */
+	u8 buffer[8];
+	/* class descriptor */
+	struct usb_hub_descriptor descriptor;
+	/* urb for polling interrupt pipe */
+	struct urb *urb;
+	/* LVH RH work */
+	struct work_struct	rh_work;
+	/* RH port status */
+	struct usb_port_status port_status;
+};
+
+static struct usb_device *create_lvs_device(struct usb_interface *intf)
+{
+	struct usb_device *udev, *hdev;
+	struct usb_hcd *hcd;
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+
+	if (!lvs->present) {
+		dev_err(&intf->dev, "No LVS device is present\n");
+		return NULL;
+	}
+
+	hdev = interface_to_usbdev(intf);
+	hcd = bus_to_hcd(hdev->bus);
+
+	udev = usb_alloc_dev(hdev, hdev->bus, lvs->portnum);
+	if (!udev) {
+		dev_err(&intf->dev, "Could not allocate lvs udev\n");
+		return NULL;
+	}
+	udev->speed = USB_SPEED_SUPER;
+	udev->ep0.desc.wMaxPacketSize = cpu_to_le16(512);
+	usb_set_device_state(udev, USB_STATE_DEFAULT);
+
+	if (hcd->driver->enable_device) {
+		if (hcd->driver->enable_device(hcd, udev) < 0) {
+			dev_err(&intf->dev, "Failed to enable\n");
+			usb_put_dev(udev);
+			return NULL;
+		}
+	}
+
+	return udev;
+}
+
+static void destroy_lvs_device(struct usb_device *udev)
+{
+	struct usb_device *hdev = udev->parent;
+	struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
+
+	if (hcd->driver->free_dev)
+		hcd->driver->free_dev(hcd, udev);
+
+	usb_put_dev(udev);
+}
+
+static int lvs_rh_clear_port_feature(struct usb_device *hdev,
+		int port1, int feature)
+{
+	return usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
+		USB_REQ_CLEAR_FEATURE, USB_RT_PORT, feature, port1,
+		NULL, 0, 1000);
+}
+
+static int lvs_rh_set_port_feature(struct usb_device *hdev,
+		int port1, int feature)
+{
+	return usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
+		USB_REQ_SET_FEATURE, USB_RT_PORT, feature, port1,
+		NULL, 0, 1000);
+}
+
+static ssize_t u3_entry_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	struct usb_device *udev;
+	int ret;
+
+	udev = create_lvs_device(intf);
+	if (!udev) {
+		dev_err(dev, "failed to create lvs device\n");
+		return -ENOMEM;
+	}
+
+	ret = lvs_rh_set_port_feature(hdev, lvs->portnum,
+			USB_PORT_FEAT_SUSPEND);
+	if (ret < 0)
+		dev_err(dev, "can't issue U3 entry %d\n", ret);
+
+	destroy_lvs_device(udev);
+
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+static DEVICE_ATTR_WO(u3_entry);
+
+static ssize_t u3_exit_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	struct usb_device *udev;
+	int ret;
+
+	udev = create_lvs_device(intf);
+	if (!udev) {
+		dev_err(dev, "failed to create lvs device\n");
+		return -ENOMEM;
+	}
+
+	ret = lvs_rh_clear_port_feature(hdev, lvs->portnum,
+			USB_PORT_FEAT_SUSPEND);
+	if (ret < 0)
+		dev_err(dev, "can't issue U3 exit %d\n", ret);
+
+	destroy_lvs_device(udev);
+
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+static DEVICE_ATTR_WO(u3_exit);
+
+static ssize_t hot_reset_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	int ret;
+
+	ret = lvs_rh_set_port_feature(hdev, lvs->portnum,
+			USB_PORT_FEAT_RESET);
+	if (ret < 0) {
+		dev_err(dev, "can't issue hot reset %d\n", ret);
+		return ret;
+	}
+
+	return count;
+}
+static DEVICE_ATTR_WO(hot_reset);
+
+static ssize_t warm_reset_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	int ret;
+
+	ret = lvs_rh_set_port_feature(hdev, lvs->portnum,
+			USB_PORT_FEAT_BH_PORT_RESET);
+	if (ret < 0) {
+		dev_err(dev, "can't issue warm reset %d\n", ret);
+		return ret;
+	}
+
+	return count;
+}
+static DEVICE_ATTR_WO(warm_reset);
+
+static ssize_t u2_timeout_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul(buf, 10, &val);
+	if (ret < 0) {
+		dev_err(dev, "couldn't parse string %d\n", ret);
+		return ret;
+	}
+
+	if (val > 127)
+		return -EINVAL;
+
+	ret = lvs_rh_set_port_feature(hdev, lvs->portnum | (val << 8),
+			USB_PORT_FEAT_U2_TIMEOUT);
+	if (ret < 0) {
+		dev_err(dev, "Error %d while setting U2 timeout %ld\n", ret, val);
+		return ret;
+	}
+
+	return count;
+}
+static DEVICE_ATTR_WO(u2_timeout);
+
+static ssize_t u1_timeout_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	unsigned long val;
+	int ret;
+
+	ret = kstrtoul(buf, 10, &val);
+	if (ret < 0) {
+		dev_err(dev, "couldn't parse string %d\n", ret);
+		return ret;
+	}
+
+	if (val > 127)
+		return -EINVAL;
+
+	ret = lvs_rh_set_port_feature(hdev, lvs->portnum | (val << 8),
+			USB_PORT_FEAT_U1_TIMEOUT);
+	if (ret < 0) {
+		dev_err(dev, "Error %d while setting U1 timeout %ld\n", ret, val);
+		return ret;
+	}
+
+	return count;
+}
+static DEVICE_ATTR_WO(u1_timeout);
+
+static ssize_t get_dev_desc_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *udev;
+	struct usb_device_descriptor *descriptor;
+	int ret;
+
+	descriptor = kmalloc_obj(*descriptor);
+	if (!descriptor)
+		return -ENOMEM;
+
+	udev = create_lvs_device(intf);
+	if (!udev) {
+		dev_err(dev, "failed to create lvs device\n");
+		ret = -ENOMEM;
+		goto free_desc;
+	}
+
+	ret = usb_control_msg(udev, (PIPE_CONTROL << 30) | USB_DIR_IN,
+			USB_REQ_GET_DESCRIPTOR, USB_DIR_IN, USB_DT_DEVICE << 8,
+			0, descriptor, sizeof(*descriptor),
+			USB_CTRL_GET_TIMEOUT);
+	if (ret < 0)
+		dev_err(dev, "can't read device descriptor %d\n", ret);
+
+	destroy_lvs_device(udev);
+
+free_desc:
+	kfree(descriptor);
+
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+static DEVICE_ATTR_WO(get_dev_desc);
+
+static ssize_t enable_compliance_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	struct usb_interface *intf = to_usb_interface(dev);
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+	int ret;
+
+	ret = lvs_rh_set_port_feature(hdev,
+			lvs->portnum | USB_SS_PORT_LS_COMP_MOD << 3,
+			USB_PORT_FEAT_LINK_STATE);
+	if (ret < 0) {
+		dev_err(dev, "can't enable compliance mode %d\n", ret);
+		return ret;
+	}
+
+	return count;
+}
+static DEVICE_ATTR_WO(enable_compliance);
+
+static struct attribute *lvs_attrs[] = {
+	&dev_attr_get_dev_desc.attr,
+	&dev_attr_u1_timeout.attr,
+	&dev_attr_u2_timeout.attr,
+	&dev_attr_hot_reset.attr,
+	&dev_attr_warm_reset.attr,
+	&dev_attr_u3_entry.attr,
+	&dev_attr_u3_exit.attr,
+	&dev_attr_enable_compliance.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(lvs);
+
+static void lvs_rh_work(struct work_struct *work)
+{
+	struct lvs_rh *lvs = container_of(work, struct lvs_rh, rh_work);
+	struct usb_interface *intf = lvs->intf;
+	struct usb_device *hdev = interface_to_usbdev(intf);
+	struct usb_hcd *hcd = bus_to_hcd(hdev->bus);
+	struct usb_hub_descriptor *descriptor = &lvs->descriptor;
+	struct usb_port_status *port_status = &lvs->port_status;
+	int i, ret = 0;
+	u16 portchange;
+
+	/* Examine each root port */
+	for (i = 1; i <= descriptor->bNbrPorts; i++) {
+		ret = usb_control_msg(hdev, usb_rcvctrlpipe(hdev, 0),
+			USB_REQ_GET_STATUS, USB_DIR_IN | USB_RT_PORT, 0, i,
+			port_status, sizeof(*port_status), 1000);
+		if (ret < 4)
+			continue;
+
+		portchange = le16_to_cpu(port_status->wPortChange);
+
+		if (portchange & USB_PORT_STAT_C_LINK_STATE)
+			lvs_rh_clear_port_feature(hdev, i,
+					USB_PORT_FEAT_C_PORT_LINK_STATE);
+		if (portchange & USB_PORT_STAT_C_ENABLE)
+			lvs_rh_clear_port_feature(hdev, i,
+					USB_PORT_FEAT_C_ENABLE);
+		if (portchange & USB_PORT_STAT_C_RESET)
+			lvs_rh_clear_port_feature(hdev, i,
+					USB_PORT_FEAT_C_RESET);
+		if (portchange & USB_PORT_STAT_C_BH_RESET)
+			lvs_rh_clear_port_feature(hdev, i,
+					USB_PORT_FEAT_C_BH_PORT_RESET);
+		if (portchange & USB_PORT_STAT_C_CONNECTION) {
+			lvs_rh_clear_port_feature(hdev, i,
+					USB_PORT_FEAT_C_CONNECTION);
+
+			if (le16_to_cpu(port_status->wPortStatus) &
+					USB_PORT_STAT_CONNECTION) {
+				lvs->present = true;
+				lvs->portnum = i;
+				if (hcd->usb_phy)
+					usb_phy_notify_connect(hcd->usb_phy,
+							USB_SPEED_SUPER);
+			} else {
+				lvs->present = false;
+				if (hcd->usb_phy)
+					usb_phy_notify_disconnect(hcd->usb_phy,
+							USB_SPEED_SUPER);
+			}
+			break;
+		}
+	}
+
+	ret = usb_submit_urb(lvs->urb, GFP_KERNEL);
+	if (ret != 0 && ret != -ENODEV && ret != -EPERM)
+		dev_err(&intf->dev, "urb resubmit error %d\n", ret);
+}
+
+static void lvs_rh_irq(struct urb *urb)
+{
+	struct lvs_rh *lvs = urb->context;
+
+	schedule_work(&lvs->rh_work);
+}
+
+static int lvs_rh_probe(struct usb_interface *intf,
+		const struct usb_device_id *id)
+{
+	struct usb_device *hdev;
+	struct usb_host_interface *desc;
+	struct usb_endpoint_descriptor *endpoint;
+	struct lvs_rh *lvs;
+	unsigned int pipe;
+	int ret, maxp;
+
+	hdev = interface_to_usbdev(intf);
+	desc = intf->cur_altsetting;
+
+	ret = usb_find_int_in_endpoint(desc, &endpoint);
+	if (ret)
+		return ret;
+
+	/* valid only for SS root hub */
+	if (hdev->descriptor.bDeviceProtocol != USB_HUB_PR_SS || hdev->parent) {
+		dev_err(&intf->dev, "Bind LVS driver with SS root Hub only\n");
+		return -EINVAL;
+	}
+
+	lvs = devm_kzalloc(&intf->dev, sizeof(*lvs), GFP_KERNEL);
+	if (!lvs)
+		return -ENOMEM;
+
+	lvs->intf = intf;
+	usb_set_intfdata(intf, lvs);
+
+	/* how many number of ports this root hub has */
+	ret = usb_control_msg(hdev, usb_rcvctrlpipe(hdev, 0),
+			USB_REQ_GET_DESCRIPTOR, USB_DIR_IN | USB_RT_HUB,
+			USB_DT_SS_HUB << 8, 0, &lvs->descriptor,
+			USB_DT_SS_HUB_SIZE, USB_CTRL_GET_TIMEOUT);
+	if (ret < (USB_DT_HUB_NONVAR_SIZE + 2)) {
+		dev_err(&hdev->dev, "wrong root hub descriptor read %d\n", ret);
+		return ret < 0 ? ret : -EINVAL;
+	}
+
+	/* submit urb to poll interrupt endpoint */
+	lvs->urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!lvs->urb)
+		return -ENOMEM;
+
+	INIT_WORK(&lvs->rh_work, lvs_rh_work);
+
+	pipe = usb_rcvintpipe(hdev, endpoint->bEndpointAddress);
+	maxp = usb_maxpacket(hdev, pipe);
+	usb_fill_int_urb(lvs->urb, hdev, pipe, &lvs->buffer[0], maxp,
+			lvs_rh_irq, lvs, endpoint->bInterval);
+
+	ret = usb_submit_urb(lvs->urb, GFP_KERNEL);
+	if (ret < 0) {
+		dev_err(&intf->dev, "couldn't submit lvs urb %d\n", ret);
+		goto free_urb;
+	}
+
+	return ret;
+
+free_urb:
+	usb_free_urb(lvs->urb);
+	return ret;
+}
+
+static void lvs_rh_disconnect(struct usb_interface *intf)
+{
+	struct lvs_rh *lvs = usb_get_intfdata(intf);
+
+	usb_poison_urb(lvs->urb); /* used in scheduled work */
+	flush_work(&lvs->rh_work);
+	usb_free_urb(lvs->urb);
+}
+
+static struct usb_driver lvs_driver = {
+	.name =		"lvs",
+	.probe =	lvs_rh_probe,
+	.disconnect =	lvs_rh_disconnect,
+	.dev_groups =	lvs_groups,
+};
+
+module_usb_driver(lvs_driver);
+
+MODULE_DESCRIPTION("Link Layer Validation System Driver");
+MODULE_LICENSE("GPL");