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, 259 insertions, 0 deletions

diff --git a/drivers/usb/misc/emi26.c b/drivers/usb/misc/emi26.c
new file mode 100644
index 000000000..24d841850
--- /dev/null
+++ b/drivers/usb/misc/emi26.c
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Emagic EMI 2|6 usb audio interface firmware loader.
+ * Copyright (C) 2002
+ * 	Tapio Laxström (tapio.laxstrom@iptime.fi)
+ *
+ * emi26.c,v 1.13 2002/03/08 13:10:26 tapio Exp
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/delay.h>
+#include <linux/firmware.h>
+#include <linux/ihex.h>
+
+#define EMI26_VENDOR_ID 		0x086a  /* Emagic Soft-und Hardware GmBH */
+#define EMI26_PRODUCT_ID		0x0100	/* EMI 2|6 without firmware */
+#define EMI26B_PRODUCT_ID		0x0102	/* EMI 2|6 without firmware */
+
+#define ANCHOR_LOAD_INTERNAL	0xA0	/* Vendor specific request code for Anchor Upload/Download (This one is implemented in the core) */
+#define ANCHOR_LOAD_EXTERNAL	0xA3	/* This command is not implemented in the core. Requires firmware */
+#define ANCHOR_LOAD_FPGA	0xA5	/* This command is not implemented in the core. Requires firmware. Emagic extension */
+#define MAX_INTERNAL_ADDRESS	0x1B3F	/* This is the highest internal RAM address for the AN2131Q */
+#define CPUCS_REG		0x7F92  /* EZ-USB Control and Status Register.  Bit 0 controls 8051 reset */ 
+#define INTERNAL_RAM(address)   (address <= MAX_INTERNAL_ADDRESS)
+
+static int emi26_writememory( struct usb_device *dev, int address,
+			      const unsigned char *data, int length,
+			      __u8 bRequest);
+static int emi26_set_reset(struct usb_device *dev, unsigned char reset_bit);
+static int emi26_load_firmware (struct usb_device *dev);
+static int emi26_probe(struct usb_interface *intf, const struct usb_device_id *id);
+static void emi26_disconnect(struct usb_interface *intf);
+
+/* thanks to drivers/usb/serial/keyspan_pda.c code */
+static int emi26_writememory (struct usb_device *dev, int address,
+			      const unsigned char *data, int length,
+			      __u8 request)
+{
+	int result;
+	unsigned char *buffer =  kmemdup(data, length, GFP_KERNEL);
+
+	if (!buffer) {
+		dev_err(&dev->dev, "kmalloc(%d) failed.\n", length);
+		return -ENOMEM;
+	}
+	/* Note: usb_control_msg returns negative value on error or length of the
+	 * 		 data that was written! */
+	result = usb_control_msg (dev, usb_sndctrlpipe(dev, 0), request, 0x40, address, 0, buffer, length, 300);
+	kfree (buffer);
+	return result;
+}
+
+/* thanks to drivers/usb/serial/keyspan_pda.c code */
+static int emi26_set_reset (struct usb_device *dev, unsigned char reset_bit)
+{
+	int response;
+	dev_info(&dev->dev, "%s - %d\n", __func__, reset_bit);
+	/* printk(KERN_DEBUG "%s - %d", __func__, reset_bit); */
+	response = emi26_writememory (dev, CPUCS_REG, &reset_bit, 1, 0xa0);
+	if (response < 0) {
+		dev_err(&dev->dev, "set_reset (%d) failed\n", reset_bit);
+	}
+	return response;
+}
+
+#define FW_LOAD_SIZE		1023
+
+static int emi26_load_firmware (struct usb_device *dev)
+{
+	const struct firmware *loader_fw = NULL;
+	const struct firmware *bitstream_fw = NULL;
+	const struct firmware *firmware_fw = NULL;
+	const struct ihex_binrec *rec;
+	int err = -ENOMEM;
+	int i;
+	__u32 addr;	/* Address to write */
+	__u8 *buf;
+
+	buf = kmalloc(FW_LOAD_SIZE, GFP_KERNEL);
+	if (!buf)
+		goto wraperr;
+
+	err = request_ihex_firmware(&loader_fw, "emi26/loader.fw", &dev->dev);
+	if (err)
+		goto nofw;
+
+	err = request_ihex_firmware(&bitstream_fw, "emi26/bitstream.fw",
+				    &dev->dev);
+	if (err)
+		goto nofw;
+
+	err = request_ihex_firmware(&firmware_fw, "emi26/firmware.fw",
+				    &dev->dev);
+	if (err) {
+	nofw:
+		dev_err(&dev->dev, "%s - request_firmware() failed\n",
+			__func__);
+		goto wraperr;
+	}
+
+	/* Assert reset (stop the CPU in the EMI) */
+	err = emi26_set_reset(dev,1);
+	if (err < 0)
+		goto wraperr;
+
+	rec = (const struct ihex_binrec *)loader_fw->data;
+	/* 1. We need to put the loader for the FPGA into the EZ-USB */
+	while (rec) {
+		err = emi26_writememory(dev, be32_to_cpu(rec->addr),
+					rec->data, be16_to_cpu(rec->len),
+					ANCHOR_LOAD_INTERNAL);
+		if (err < 0)
+			goto wraperr;
+		rec = ihex_next_binrec(rec);
+	}
+
+	/* De-assert reset (let the CPU run) */
+	err = emi26_set_reset(dev,0);
+	if (err < 0)
+		goto wraperr;
+	msleep(250);	/* let device settle */
+
+	/* 2. We upload the FPGA firmware into the EMI
+	 * Note: collect up to 1023 (yes!) bytes and send them with
+	 * a single request. This is _much_ faster! */
+	rec = (const struct ihex_binrec *)bitstream_fw->data;
+	do {
+		i = 0;
+		addr = be32_to_cpu(rec->addr);
+
+		/* intel hex records are terminated with type 0 element */
+		while (rec && (i + be16_to_cpu(rec->len) < FW_LOAD_SIZE)) {
+			memcpy(buf + i, rec->data, be16_to_cpu(rec->len));
+			i += be16_to_cpu(rec->len);
+			rec = ihex_next_binrec(rec);
+		}
+		err = emi26_writememory(dev, addr, buf, i, ANCHOR_LOAD_FPGA);
+		if (err < 0)
+			goto wraperr;
+	} while (rec);
+
+	/* Assert reset (stop the CPU in the EMI) */
+	err = emi26_set_reset(dev,1);
+	if (err < 0)
+		goto wraperr;
+
+	/* 3. We need to put the loader for the firmware into the EZ-USB (again...) */
+	for (rec = (const struct ihex_binrec *)loader_fw->data;
+	     rec; rec = ihex_next_binrec(rec)) {
+		err = emi26_writememory(dev, be32_to_cpu(rec->addr),
+					rec->data, be16_to_cpu(rec->len),
+					ANCHOR_LOAD_INTERNAL);
+		if (err < 0)
+			goto wraperr;
+	}
+	msleep(250);	/* let device settle */
+
+	/* De-assert reset (let the CPU run) */
+	err = emi26_set_reset(dev,0);
+	if (err < 0)
+		goto wraperr;
+
+	/* 4. We put the part of the firmware that lies in the external RAM into the EZ-USB */
+
+	for (rec = (const struct ihex_binrec *)firmware_fw->data;
+	     rec; rec = ihex_next_binrec(rec)) {
+		if (!INTERNAL_RAM(be32_to_cpu(rec->addr))) {
+			err = emi26_writememory(dev, be32_to_cpu(rec->addr),
+						rec->data, be16_to_cpu(rec->len),
+						ANCHOR_LOAD_EXTERNAL);
+			if (err < 0)
+				goto wraperr;
+		}
+	}
+
+	/* Assert reset (stop the CPU in the EMI) */
+	err = emi26_set_reset(dev,1);
+	if (err < 0)
+		goto wraperr;
+
+	for (rec = (const struct ihex_binrec *)firmware_fw->data;
+	     rec; rec = ihex_next_binrec(rec)) {
+		if (INTERNAL_RAM(be32_to_cpu(rec->addr))) {
+			err = emi26_writememory(dev, be32_to_cpu(rec->addr),
+						rec->data, be16_to_cpu(rec->len),
+						ANCHOR_LOAD_INTERNAL);
+			if (err < 0)
+				goto wraperr;
+		}
+	}
+
+	/* De-assert reset (let the CPU run) */
+	err = emi26_set_reset(dev,0);
+	if (err < 0)
+		goto wraperr;
+	msleep(250);	/* let device settle */
+
+	/* return 1 to fail the driver inialization
+	 * and give real driver change to load */
+	err = 1;
+
+wraperr:
+	if (err < 0)
+		dev_err(&dev->dev,"%s - error loading firmware: error = %d\n",
+			__func__, err);
+
+	release_firmware(loader_fw);
+	release_firmware(bitstream_fw);
+	release_firmware(firmware_fw);
+
+	kfree(buf);
+	return err;
+}
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE(EMI26_VENDOR_ID, EMI26_PRODUCT_ID) },
+	{ USB_DEVICE(EMI26_VENDOR_ID, EMI26B_PRODUCT_ID) },
+	{ }                                             /* Terminating entry */
+};
+
+MODULE_DEVICE_TABLE (usb, id_table);
+
+static int emi26_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+
+	dev_info(&intf->dev, "%s start\n", __func__);
+
+	emi26_load_firmware(dev);
+
+	/* do not return the driver context, let real audio driver do that */
+	return -EIO;
+}
+
+static void emi26_disconnect(struct usb_interface *intf)
+{
+}
+
+static struct usb_driver emi26_driver = {
+	.name		= "emi26 - firmware loader",
+	.probe		= emi26_probe,
+	.disconnect	= emi26_disconnect,
+	.id_table	= id_table,
+};
+
+module_usb_driver(emi26_driver);
+
+MODULE_AUTHOR("Tapio Laxström");
+MODULE_DESCRIPTION("Emagic EMI 2|6 firmware loader.");
+MODULE_LICENSE("GPL");
+
+MODULE_FIRMWARE("emi26/loader.fw");
+MODULE_FIRMWARE("emi26/bitstream.fw");
+MODULE_FIRMWARE("emi26/firmware.fw");
+/* vi:ai:syntax=c:sw=8:ts=8:tw=80
+ */