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, 254 insertions, 0 deletions

diff --git a/drivers/input/tablet/acecad.c b/drivers/input/tablet/acecad.c
new file mode 100644
index 000000000..ba79dff21
--- /dev/null
+++ b/drivers/input/tablet/acecad.c
@@ -0,0 +1,254 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2001-2005 Edouard TISSERANT   <edouard.tisserant@wanadoo.fr>
+ *  Copyright (c) 2004-2005 Stephane VOLTZ      <svoltz@numericable.fr>
+ *
+ *  USB Acecad "Acecad Flair" tablet support
+ *
+ *  Changelog:
+ *      v3.2 - Added sysfs support
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb/input.h>
+
+MODULE_AUTHOR("Edouard TISSERANT <edouard.tisserant@wanadoo.fr>");
+MODULE_DESCRIPTION("USB Acecad Flair tablet driver");
+MODULE_LICENSE("GPL");
+
+#define USB_VENDOR_ID_ACECAD	0x0460
+#define USB_DEVICE_ID_FLAIR	0x0004
+#define USB_DEVICE_ID_302	0x0008
+
+struct usb_acecad {
+	char name[128];
+	char phys[64];
+	struct usb_interface *intf;
+	struct input_dev *input;
+	struct urb *irq;
+
+	unsigned char *data;
+	dma_addr_t data_dma;
+};
+
+static void usb_acecad_irq(struct urb *urb)
+{
+	struct usb_acecad *acecad = urb->context;
+	unsigned char *data = acecad->data;
+	struct input_dev *dev = acecad->input;
+	struct usb_interface *intf = acecad->intf;
+	struct usb_device *udev = interface_to_usbdev(intf);
+	int prox, status;
+
+	switch (urb->status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&intf->dev, "%s - urb shutting down with status: %d\n",
+			__func__, urb->status);
+		return;
+	default:
+		dev_dbg(&intf->dev, "%s - nonzero urb status received: %d\n",
+			__func__, urb->status);
+		goto resubmit;
+	}
+
+	prox = (data[0] & 0x04) >> 2;
+	input_report_key(dev, BTN_TOOL_PEN, prox);
+
+	if (prox) {
+		int x = data[1] | (data[2] << 8);
+		int y = data[3] | (data[4] << 8);
+		/* Pressure should compute the same way for flair and 302 */
+		int pressure = data[5] | (data[6] << 8);
+		int touch = data[0] & 0x01;
+		int stylus = (data[0] & 0x10) >> 4;
+		int stylus2 = (data[0] & 0x20) >> 5;
+		input_report_abs(dev, ABS_X, x);
+		input_report_abs(dev, ABS_Y, y);
+		input_report_abs(dev, ABS_PRESSURE, pressure);
+		input_report_key(dev, BTN_TOUCH, touch);
+		input_report_key(dev, BTN_STYLUS, stylus);
+		input_report_key(dev, BTN_STYLUS2, stylus2);
+	}
+
+	/* event termination */
+	input_sync(dev);
+
+resubmit:
+	status = usb_submit_urb(urb, GFP_ATOMIC);
+	if (status)
+		dev_err(&intf->dev,
+			"can't resubmit intr, %s-%s/input0, status %d\n",
+			udev->bus->bus_name,
+			udev->devpath, status);
+}
+
+static int usb_acecad_open(struct input_dev *dev)
+{
+	struct usb_acecad *acecad = input_get_drvdata(dev);
+
+	acecad->irq->dev = interface_to_usbdev(acecad->intf);
+	if (usb_submit_urb(acecad->irq, GFP_KERNEL))
+		return -EIO;
+
+	return 0;
+}
+
+static void usb_acecad_close(struct input_dev *dev)
+{
+	struct usb_acecad *acecad = input_get_drvdata(dev);
+
+	usb_kill_urb(acecad->irq);
+}
+
+static int usb_acecad_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_host_interface *interface = intf->cur_altsetting;
+	struct usb_endpoint_descriptor *endpoint;
+	struct usb_acecad *acecad;
+	struct input_dev *input_dev;
+	int pipe, maxp;
+	int err;
+
+	if (interface->desc.bNumEndpoints != 1)
+		return -ENODEV;
+
+	endpoint = &interface->endpoint[0].desc;
+
+	if (!usb_endpoint_is_int_in(endpoint))
+		return -ENODEV;
+
+	pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);
+	maxp = usb_maxpacket(dev, pipe);
+
+	acecad = kzalloc_obj(*acecad);
+	input_dev = input_allocate_device();
+	if (!acecad || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	acecad->data = usb_alloc_coherent(dev, 8, GFP_KERNEL, &acecad->data_dma);
+	if (!acecad->data) {
+		err= -ENOMEM;
+		goto fail1;
+	}
+
+	acecad->irq = usb_alloc_urb(0, GFP_KERNEL);
+	if (!acecad->irq) {
+		err = -ENOMEM;
+		goto fail2;
+	}
+
+	acecad->intf = intf;
+	acecad->input = input_dev;
+
+	if (dev->manufacturer)
+		strscpy(acecad->name, dev->manufacturer, sizeof(acecad->name));
+
+	if (dev->product) {
+		if (dev->manufacturer)
+			strlcat(acecad->name, " ", sizeof(acecad->name));
+		strlcat(acecad->name, dev->product, sizeof(acecad->name));
+	}
+
+	usb_make_path(dev, acecad->phys, sizeof(acecad->phys));
+	strlcat(acecad->phys, "/input0", sizeof(acecad->phys));
+
+	input_dev->name = acecad->name;
+	input_dev->phys = acecad->phys;
+	usb_to_input_id(dev, &input_dev->id);
+	input_dev->dev.parent = &intf->dev;
+
+	input_set_drvdata(input_dev, acecad);
+
+	input_dev->open = usb_acecad_open;
+	input_dev->close = usb_acecad_close;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_DIGI)] = BIT_MASK(BTN_TOOL_PEN) |
+		BIT_MASK(BTN_TOUCH) | BIT_MASK(BTN_STYLUS) |
+		BIT_MASK(BTN_STYLUS2);
+
+	switch (id->driver_info) {
+	case 0:
+		input_set_abs_params(input_dev, ABS_X, 0, 5000, 4, 0);
+		input_set_abs_params(input_dev, ABS_Y, 0, 3750, 4, 0);
+		input_set_abs_params(input_dev, ABS_PRESSURE, 0, 512, 0, 0);
+		if (!strlen(acecad->name))
+			snprintf(acecad->name, sizeof(acecad->name),
+				"USB Acecad Flair Tablet %04x:%04x",
+				le16_to_cpu(dev->descriptor.idVendor),
+				le16_to_cpu(dev->descriptor.idProduct));
+		break;
+
+	case 1:
+		input_set_abs_params(input_dev, ABS_X, 0, 53000, 4, 0);
+		input_set_abs_params(input_dev, ABS_Y, 0, 2250, 4, 0);
+		input_set_abs_params(input_dev, ABS_PRESSURE, 0, 1024, 0, 0);
+		if (!strlen(acecad->name))
+			snprintf(acecad->name, sizeof(acecad->name),
+				"USB Acecad 302 Tablet %04x:%04x",
+				le16_to_cpu(dev->descriptor.idVendor),
+				le16_to_cpu(dev->descriptor.idProduct));
+		break;
+	}
+
+	usb_fill_int_urb(acecad->irq, dev, pipe,
+			acecad->data, maxp > 8 ? 8 : maxp,
+			usb_acecad_irq, acecad, endpoint->bInterval);
+	acecad->irq->transfer_dma = acecad->data_dma;
+	acecad->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+	err = input_register_device(acecad->input);
+	if (err)
+		goto fail3;
+
+	usb_set_intfdata(intf, acecad);
+
+	return 0;
+
+ fail3:	usb_free_urb(acecad->irq);
+ fail2:	usb_free_coherent(dev, 8, acecad->data, acecad->data_dma);
+ fail1: input_free_device(input_dev);
+	kfree(acecad);
+	return err;
+}
+
+static void usb_acecad_disconnect(struct usb_interface *intf)
+{
+	struct usb_acecad *acecad = usb_get_intfdata(intf);
+	struct usb_device *udev = interface_to_usbdev(intf);
+
+	usb_set_intfdata(intf, NULL);
+
+	input_unregister_device(acecad->input);
+	usb_free_urb(acecad->irq);
+	usb_free_coherent(udev, 8, acecad->data, acecad->data_dma);
+	kfree(acecad);
+}
+
+static const struct usb_device_id usb_acecad_id_table[] = {
+	{ USB_DEVICE(USB_VENDOR_ID_ACECAD, USB_DEVICE_ID_FLAIR), .driver_info = 0 },
+	{ USB_DEVICE(USB_VENDOR_ID_ACECAD, USB_DEVICE_ID_302),	 .driver_info = 1 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(usb, usb_acecad_id_table);
+
+static struct usb_driver usb_acecad_driver = {
+	.name =		"usb_acecad",
+	.probe =	usb_acecad_probe,
+	.disconnect =	usb_acecad_disconnect,
+	.id_table =	usb_acecad_id_table,
+};
+
+module_usb_driver(usb_acecad_driver);